The present invention relates to a brake control apparatus adapted to control braking force, and specifically to a brake control apparatus capable of executing brake-by-wire (BBW) control.
Japanese Patent Application Publication No. 2002-187537 discloses a previously-proposed brake control apparatus. In this technique, target wheel-cylinder pressures are calculated based on the detected values of stroke sensor and master-cylinder pressure sensor, under the situation where the hydraulic communication between a brake pedal and wheel cylinders is shut off. By driving electromagnetic valves and a motor connected with pump on the basis of this target wheel-cylinder pressures, desired wheel-cylinder pressures are obtained. The brake control apparatus in this disclosure includes a first microcomputer that calculates target braking forces by receiving input signals of various sensors, and a second microcomputer provided separately from the first microcomputer as a backup. First and second microcomputers are connected respectively to different two of a drive circuit for electromagnetic valves for one pair of road wheels of vehicle in X-split layout, and a drive circuit for electromagnetic valves for another pair of road wheels in the X-split layout.
However, in the above-described technique, the first microcomputer calculates the target braking force by receiving all the input signals of various sensors. Accordingly, there has been a possibility that the brake control becomes incapable of continuing when the first microcomputer becomes failed.
It is therefore an object of the present invention to provide brake control apparatus and method, devised to continuously execute a brake control even if a means of calculating a target braking controlled variable becomes failed.
According to one aspect of the present invention, there is provided a brake control apparatus comprising: an actuator configured to generate a braking force of road wheel; a first control unit configured to calculate a target braking controlled variable in accordance with an amount of brake manipulation of a driver; and a second control unit comprising a backup calculation section configured to calculate a backup target braking controlled variable, by receiving the amount of brake manipulation separately from the first control unit, the second control unit being configured to select one of the target braking controlled variable and the backup target braking controlled variable in accordance with operating conditions of the first control unit and the second control unit, the second control unit being configured to output a drive signal to the actuator so as to bring the braking force of road wheel closer to the selected one of the target braking controlled variable and the backup target braking controlled variable.
According to another aspect of the present invention, there is provided a brake control apparatus comprising: a master cylinder provided as a first fluid-pressure source; a first fluid passage adapted to allow a fluid pressure of the master cylinder to be applied via a first changeover valve to front-left and front-right wheel cylinders of a plurality of wheel cylinders; a second fluid passage connected with a second fluid-pressure source provided independently of the master cylinder, and adapted to apply a fluid pressure produced from the second fluid-pressure source via a second changeover valve directly to at least one of the plurality of wheel cylinders; and a control unit configured to switch between the fluid-pressure application from the master cylinder to the front-left and front-right wheel cylinders, and the fluid-pressure application from the second fluid-pressure source to the at least one of the plurality of wheel cylinders, by opening/closing the first changeover valve and the second changeover valve, the control unit comprising a first control unit configured to calculate a target braking controlled variable for obtaining a desired braking force, in accordance with an amount of brake manipulation of a driver; and a second control unit configured to calculate a backup target braking controlled variable separately from the first control unit, in accordance with the amount of brake manipulation, the second control unit being configured to select one of the target braking controlled variable and the backup target braking controlled variable in accordance with operating conditions of the first control unit and the second control unit, the second control unit being configured to output drive signals to the second fluid-pressure source and the first and second changeover valves, so as to bring a fluid pressure of the at least one of the plurality of wheel cylinders closer to a target fluid pressure based on the selected one of the target braking controlled variable and the backup target braking controlled variable.
According to still another aspect of the present invention, there is provided a brake control apparatus comprising: an electrical caliper provided at a road wheel and configured to be driven by a motor to generate a braking force of the road wheel; a first control unit configured to calculate a target braking controlled variable in accordance with an amount of brake manipulation of a driver; and a second control unit configured to calculate a backup target braking controlled variable, by receiving the amount of brake manipulation separately from the first control unit, the second control unit being configured to select one of the target braking controlled variable and the backup target braking controlled variable in accordance with operating conditions of the first control unit and the second control unit, the second control unit being configured to output a drive signal to the motor so as to bring the braking force of the road wheel closer to the selected one of the target braking controlled variable and the backup target braking controlled variable.
According to still another aspect of the present invention, there is provided a brake control method comprising the steps of: calculating a first target braking controlled variable in accordance with an amount of brake manipulation of a driver; calculating a second target braking controlled variable, by receiving the amount of brake manipulation separately from the calculation of the first target braking controlled variable; selecting one of the first target braking controlled variable and the second target braking controlled variable, in accordance with properness in the calculations of the first and second target braking controlled variables; and outputting a drive signal to an actuator that generates a braking force of road wheel, so as to bring the braking force of road wheel closer to the selected one of the first target braking controlled variable and the second target braking controlled variable.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.
FIG. 1 is a schematic system configuration view of a brake control apparatus in a first embodiment according to the present invention.
FIG. 2 is a schematic hydraulic circuit diagram of first hydraulic unit.
FIG. 3 is a schematic hydraulic circuit diagram of second hydraulic unit.
FIG. 4 is a schematic sectional view showing a structure of first hydraulic unit and first sub-ECU in the first embodiment.
FIG. 5 is a schematic block diagram showing a control configuration of brake-by-wire system in the first embodiment.
FIG. 6 is a flowchart showing a command-value calculating processing which is executed in main ECU in the first embodiment.
FIG. 7 is a flowchart showing a communication processing which is executed in main ECU in the first embodiment.
FIG. 8 is a flowchart showing a fluid-pressure control processing which is executed in first and second sub-ECUs in the first embodiment.
FIG. 9 is a flowchart showing a communication processing which is executed in first and second sub-ECUs in the first embodiment.
FIG. 10 is a flowchart showing a command-value judging processing which is executed in first and second sub-ECUs in the first embodiment.
FIG. 11 is a schematic system configuration view showing a brake-by-wire control system in a second embodiment according to the present invention.
FIG. 12 is a schematic block diagram showing a control configuration of brake-by-wire system in the second embodiment.
Reference will hereinafter be made to the drawings in order to facilitate a better understanding of the present invention. Embodiments according to the present invention will be explained in detail referring to the drawings.
[System Configuration]
A system configuration according to a first embodiment of the present invention will now be explained referring to FIGS. 1 to 5. FIG. 1 is a schematic system configuration view of a brake control apparatus according to the first embodiment. The brake control apparatus according to the first embodiment is exemplified as a four-wheel brake-by-wire (BBM) system, and includes two of a first hydraulic unit HU 1 and a second hydraulic unit HU 2 capable of controlling or adjusting brake fluid pressures (wheel-brake cylinder pressures) independently of the manipulation of a brake pedal BP by a driver.
As shown in FIG. 1, a control unit 1 includes a main electronic control unit (main ECU) 300 and first and second sub-electronic control units (sub-ECUs) 100 and 200 . Main ECU 300 (hereinafter also called “first control unit”) serves to calculate respective target wheel cylinder pressures P*fl, P*fr, P*rl, and P*rr for road wheels FL, FR, RL, and RR. First sub-ECU 100 serves to drive first hydraulic unit HU 1 , and second sub-ECU 200 serves to drive second hydraulic unit HU 2 (each of first and second sub-ECUs 100 and 200 is hereinafter also called “second control unit”).
First and second hydraulic units HU 1 and HU 2 are respectively driven by first and second sub-ECUs 100 and 200 on the basis of commands derived from main ECU 300 . A stroke simulator S/Sim connected with a master cylinder M/C applies reaction force to brake pedal BP.
First and second hydraulic units HU 1 and HU 2 are connected to master cylinder M/C respectively through fluid passages (oil lines) A 1 and A 2 , and are connected to a reservoir RSV respectively through fluid passages B 1 and B 2 . A first master-cylinder pressure sensor MC/Sen 1 is provided in or screwed into fluid passage A 1 , and a second master-cylinder pressure sensor MC/Sen 2 is provided in or screwed into fluid passage A 2 . First master-cylinder pressure sensor MC/Sen 1 is mounted integrally in first hydraulic unit HU 1 , and similarly second master-cylinder pressure sensor MC/Sen 2 is mounted integrally in second hydraulic unit HU 2 . The detailed explanations thereof will be mentioned below.
Moreover, as shown in FIG. 2, first hydraulic unit HU 1 includes a gear-type pump P 1 , a motor M 1 , and solenoid (electromagnetic) valves. Similarly as shown in FIG. 3, second hydraulic unit HU 2 includes a gear-type pump P 2 , a motor M 2 , and solenoid (electromagnetic) valves. Each of first and second hydraulic units HU 1 and HU 2 functions as a hydraulic actuator capable of generating fluid pressure (hydraulic pressure) independently. First hydraulic unit HU 1 is adapted to perform the brake-fluid-pressure control for wheels FL and RR, and second hydraulic unit HU 2 is adapted to perform the brake-fluid-pressure control for wheels FR and RL.
Namely, the fluid pressures of wheel cylinders W/C (FL˜RR) are increased or built up directly by gear-type pumps P 1 and P 2 serving as two fluid-pressure sources. Since each fluid pressure of wheel cylinder W/C is increased directly by first or second pump P 1 or P 2 without using any accumulator, there is no possibility that gas maintained inside the accumulator leaks into the fluid passages at the time of failed condition. As discussed above, first pump P 1 functions to increase the cylinder pressures of a first pair of diagonally-opposed road wheels, namely, front-left and rear-right wheels FL and RR; and second pump P 2 functions to increase the cylinder pressures of a second pair of diagonally-opposed road wheels, namely, front-right and rear-left wheels FR and RL. That is, pumps P 1 and P 2 are provided to construct a so-called diagonal split layout of brake circuits, sometimes termed “X-split layout”.
First and second hydraulic units HU 1 and HU 2 are configured to separate from each other. By use of the two separate hydraulic units HU 1 and HU 2 ; even if there is a leakage of working fluid from either one of first and second hydraulic units HU 1 and HU 2 , it is possible to certainly produce a braking force by another not-failed hydraulic unit. Although first and second hydraulic units HU 1 and HU 2 are configured as separate units in this example, these hydraulic units HU 1 and HU 2 may be provided integral with each other. In such case, electric circuit configurations can be gathered to one place, and this contributes to shortened harness lengths, simplified brake system layout, and the like.
Recently, as a general layout of brake fluid passages (brake circuits) of vehicle, the so-called diagonal split layout (X-split layout or X-pipeline) is used. In the usual “X-split layout”, the diagonally-opposed wheels FL and RR (or FR and RL) are connected with each other by fluid passage. Namely, one of two different fluid-pressure sources (e.g., one output of tandem master cylinder) is connected via a first brake circuit to front-left and rear-right wheel cylinders W/C (FL) and W/C (RR), and another fluid-pressure source (e.g., another output of the tandem master cylinder) is connected via a second brake circuit to front-right and rear-left wheel cylinders W/C (FR) and W/C (RL), so as to be able to independently build up the first and second brake systems by means of the respective fluid-pressure sources (e.g., two-port outputs of the tandem master cylinder). By virtue of the use of X-split layout; for instance, assuming that the brake circuit associated with front-left wheel cylinder W/C (FL) is failed, the brake circuit associated with rear-right wheel cylinder W/C (RR) becomes failed simultaneously, and however the not-failed brake circuit (the second brake circuit) permits simultaneous braking force application to both of the front-right and rear-left road wheels. Conversely assuming that the brake circuit associated with front-right wheel cylinder W/C (FR) is failed, the brake circuit associated with rear-left wheel cylinder W/C (RL) becomes failed simultaneously, and however the not-failed brake circuit (the first brake circuit) permits simultaneous braking force application to both of the front-left and rear-right road wheels. Therefore, such X-split layout is superior in braking-force balance of vehicle even when either one of the first brake circuit (the first fluid-pressure source P 1 ) associated with front-left and rear-right wheel cylinders W/C (FL) and W/C (RR) and the second brake circuit (the second fluid-pressure source P 2 ) associated with front-right and rear-left wheel cylinders W/C (FR) and W/C (RL) is failed. The use of X-split layout contributes to the enhanced braking-force balance of vehicle.
Therefore, the brake control apparatus according to this embodiment is configured or designed to construct a dual fluid-pressure source system by way of first and second hydraulic units HU 1 and HU 2 having respective pumps P 1 and P 2 serving as two separate fluid-pressure sources, in order to enhance a fail-safe performance without changing the widespread or widely-used “X-split layout”.
[Main ECU]
Main ECU 300 is a broader central processing unit (CPU) that calculates target front-left wheel-cylinder pressure P*fl and target rear-right wheel-cylinder pressure P*rr for first hydraulic unit HU 1 and also calculates target front-right wheel-cylinder pressure P*fr and target rear-left wheel-cylinder pressure P*rl for second hydraulic unit HU 2 . Main ECU 300 is connected to both of a first electric power source BATT 1 and a second electric power source BATT 2 . Main ECU 300 can operate or work when at least one of power sources BATT 1 and BATT 2 is operating normally. Main ECU 300 is started responsively to an ignition switch signal IGN derived from an ignition switch, or responsively to an ECU starting requirement from each of control units CU 1 to CU 6 . Each of control units CU 1 to CU 6 is connected through a controller area network (CAN) communications line CAN 3 to main ECU 300 .
Main ECU 300 receives a stroke signal S 1 derived from a first stroke sensor S/Sen 1 , a stroke signal S 2 derived from a second stroke sensor S/Sen 2 , a master-cylinder pressure signal derived from first master-cylinder pressure sensor MC/Sen 1 which is indicative of a first master-cylinder pressure Pm 1 , and a master-cylinder pressure signal derived from second master-cylinder pressure sensor MC/Sen 2 which is indicative of a second master-cylinder pressure Pm 2 . As used hereafter, first and second master-cylinder pressures Pm 1 and Pm 2 are collectively referred to as “master-cylinder pressure Pm”.
Main ECU 300 also receives a signal indicative of vehicle speed (wheel speed) VSP, a signal indicative of yaw rate Y, and a signal indicative of longitudinal acceleration G. Furthermore, main ECU 300 receives a sensor signal from a fluid quantity sensor L/Sen provided to reservoir RSV to detect a quantity of brake fluid of reservoir RSV. On the basis of the detected value of fluid quantity sensor L/Sen, it is determined whether or not brake-by-wire (BBW) control is executable by driving the pumps P 1 and P 2 . Main ECU 300 also receives a signal from a stop lamp switch STP.SW, so as to detect a manipulation (depression) of brake pedal BP by the driver without using stroke sensor signals S 1 and S 2 and master-cylinder pressures Pm 1 and Pm 2 .
Two central processing units (CPUs), namely first CPU 310 and second CPU 320 , are provided in main ECU 300 for arithmetic calculations. First CPU 310 is defined as a main microcomputer (main microprocessor), and second CPU 320 is defined as a sub-microcomputer (sub-microprocessor) to construct a dual system. Thereby, these first and second CPUs 310 and 320 have a function of monitoring each other, so that fail-safe performance and safety performance of arithmetic device (microprocessor) are enhanced.
First CPU 310 is connected to first sub-ECU 100 via a CAN communications line CAN 1 , and second CPU 320 is connected to second sub-ECU 200 via a CAN communications line CAN 2 . Signals, respectively indicating a pump discharge pressure Pp 1 discharged from first pump P 1 , and actual front-left and rear-right wheel-cylinder pressures Pfl and Prr, are inputted via first sub-ECU 100 into first CPU 310 . Signals, respectively indicating a pump discharge pressure Pp 2 discharged from second pump P 2 , and actual front-right and rear-left wheel-cylinder pressures Pfr and Prl, are inputted via second sub-ECU 200 into second CPU 320 . Each of communications lines CAN 1 and CAN 2 is provided as a dual system for the purpose of backup, and these communications lines CAN 1 and CAN 2 are connected to each other.
On the basis of the input information such as stroke signals S 1 and S 2 , master-cylinder pressures Pm 1 and Pm 2 , and actual wheel-cylinder pressures Pfl, Pfr, Prl, and Prr; first CPU 310 calculates target front-left wheel-cylinder pressure P*fl and target rear-right wheel-cylinder pressure P*rr and outputs the calculated target wheel-cylinder pressures P*fl and P*rr via first CAN communications line CAN 1 to first sub-ECU 100 , while second CPU 320 calculates target front-right wheel-cylinder pressure P*fr and target rear-left wheel-cylinder pressure P*rl and outputs the calculated target wheel-cylinder pressures P*fr and P*rl via second CAN communications lines CAN 2 to second sub-ECU 200 .
In lieu thereof, first CPU 310 may calculate all the four target wheel-cylinder pressures P*fl to P*rr for first and second hydraulic units HU 1 and HU 2 , whereas second CPU 320 may be used as a backup CPU for first CPU 310 .
Main ECU 300 functions to start up each of first and second sub-ECUs 100 and 200 via CAN communications lines CAN 1 and CAN 2 . In this embodiment, main ECU 300 generates two of a command signal for starting up sub-ECU 100 and a command signal for starting up sub-ECU 200 independently of each other. In lieu thereof, sub-ECUs 100 and 200 may be started up simultaneously in response to a single command signal from main ECU 300 . Alternatively, sub-ECUs 100 and 200 may be started up simultaneously in response to the ignition switch signal IGN.
During execution of vehicle dynamic-behavior control including anti-skid brake control (often abbreviated to “ABS”, which is executed for increasing or decreasing a braking force for wheel-lock prevention), vehicle dynamics control (often abbreviated to “VDC”, which is executed for increasing or decreasing a braking force to prevent side slip occurring due to instable vehicle behaviors), traction control (often abbreviated to “TCS”, which is executed for acceleration-slip suppression of drive wheels), and the like; input information such as vehicle speed VSP, yaw rate Y, and longitudinal acceleration G is further extracted for executing the fluid-pressure control concerning target wheel-cylinder pressures P*fl, P*fr, P*rl, and P*rr. During the vehicle dynamics control (VDC), a warning buzzer BUZZ emits a buzzing sound cyclically to warn the driver or vehicle occupants that the VDC system comes into operation. A VDC switch VDC.SW serving as a man-machine interface is also provided so as to manually engage or disengage the VDC function in accordance with the driver's wishes.
Main ECU 300 is also connected to the other control units CU 1 to CU 6 via the CAN communications line CAN 3 for cooperative control. For energy regeneration, the regenerative brake control unit CU 1 is provided to return a braking force to an electric supply system by way of conversion from kinetic energy into electric energy. The radar control unit CU 2 is provided for vehicle-to-vehicle distance control. The EPS control unit CU 3 serves as a control unit for an electrically-operated (motor-driven) power steering system.
The ECM control unit CU 4 is an engine control unit, the At control unit CU 5 is an control unit for automatic transmission, and the meter control unit CU 6 is provided to control each of meters. The information indicative of vehicle speed VSP inputted into main ECU 300 is outputted via the CAN communications line CAN 3 to each of ECM control unit CU 4 , AT control unit CU 5 , and meter control unit CU 6 .
First and second power sources BATT 1 and BATT 2 correspond to electric power sources for ECUs 100 , 200 , and 300 . Concretely, first power source BATT 1 is connected to main ECU 300 and first sub-ECU 100 , and second power source BATT 2 is connected to main ECU 300 and second sub-ECU 200 .
[Sub-ECU]
In this embodiment, first sub-ECU 100 is formed integral with first hydraulic unit HU 1 , and similarly second sub-ECU 200 is formed integral with second hydraulic unit HU 2 . FIG. 4 is a schematic sectional view showing a structure of first hydraulic unit HU 1 and first sub-ECU 100 . First hydraulic unit HU 1 is composed of an aluminum housing block HB which is in the shape of substantially rectangular parallelepiped. Inside this aluminum housing block HB, there are provided a plurality of fluid passages formed to drill or pierce in housing block HB. Motor M 1 is mounted on a first side surface HB 1 of housing block HB. First master-cylinder pressure sensor MC/Sen 1 and a wheel-cylinder pressure sensor WC/Sen are fixed to be pressed in a second side surface HB 2 opposite to first side surface HB 1 . A plurality of solenoid (electromagnetic) valves IN/V, OUT/V, and S.OFF/V are also mounted in second side surface HB 2 .
On the side of this second side surface HB 2 , a circuit board K 1 of first sub-ECU 100 is attached to housing block HB at a position opposed to second side surface HB 2 . Namely, circuit board KS is mounted so as to face the second side surface HB 2 . (Connecting) Terminals of the respective pressure sensors and electromagnetic valves are connected with circuit board KS to attach together by means of melting (e.g., soldering or welding). At one end portion of circuit board K 1 (on a lower portion of circuit board K 1 as viewed in FIG. 4), first sub-ECU 100 includes a connector portion K 2 for connecting the circuit board K 1 with the CAN communications lines, power sources, and the like.
As mentioned above, since first sub-ECU 100 is provided integral with first hydraulic unit HU 1 (integral with the drive circuits for driving respective electromagnetic valves and motor M 1 ), it is unnecessary to use harnesses for communicating first sub-ECU 100 to first hydraulic unit HU 1 . Accordingly, a downsizing (miniaturization) in control system can improve a flexibility in layout.
Here, a basic structure of (second hydraulic unit HU 2 +second sub-ECU 200 ) is in common with the basic structure of (first hydraulic unit HU 1 +first sub-ECU 100 ), and therefore explanations about the structure of second hydraulic unit HU 2 and second sub-ECU 200 will be omitted.
First sub-ECU 100 receives input information signals indicating the target wheel-cylinder pressures P*fl to P*rr which are outputted or generated from main ECU 300 , and also receives input informational signals indicating the pump discharge pressure Pp 1 discharged from first pump P 1 , actual front-left and rear-right wheel-cylinder pressures Pfl and Prr, and the master-cylinder pressure derived from first master-cylinder pressure sensor MC/Sen 1 which are outputted or generated from first hydraulic unit HU 1 . In the similar manner, second sub-ECU 200 receives input information signals indicating target wheel-cylinder pressures P*fl to P*rr which are outputted or generated from main ECU 300 , and also receives input informational signals indicating pump discharge pressure Pp 2 discharged from second pump P 2 , actual front-right and rear-left wheel-cylinder pressures Pfr and Prl, and the master-cylinder pressure derived from second master-cylinder pressure sensor MC/Sen 2 which are outputted or generated from second hydraulic unit HU 2 .
Each of first and second sub-ECUs 100 and 200 includes a backup calculation section serving to briefly (simply) calculate backup target wheel-cylinder pressures on the basis of the master-cylinder pressure, separately from target wheel-cylinder pressures P*fl to P*rr calculated by main ECU 300 . A configuration of this backup calculation section will be explained below.
On the basis of the latest up-to-date informational data (more recent data) about pump discharge pressures Pp 1 and Pp 2 and actual wheel-cylinder pressures Pfl to Prr, the fluid-pressure control is performed to realize target wheel-cylinder pressures P*fl to P*rr (or backup target wheel-cylinder pressures, as target controlled variables) by driving the electromagnetic valves and motors M 1 and M 2 for pumps P 1 and P 2 incorporated in respective hydraulic units HU 1 and HU 2 .
The above-mentioned first sub-ECU 100 constructs a servo control system that continuously executes fluid-pressure control for front-left and rear-right wheels FL and RR, based on the inputted values concerning target wheel-cylinder pressure P*fl and P*rr in such a manner as to bring actual wheel-cylinder pressures Pfl and Prr closer to these inputted values (i.e., as to cause pressures Pfl and Prr to converge to these inputted values), until new target values are inputted. In the similar manner, the above-mentioned second sub-ECU 200 constructs a servo control system that continuously executes fluid-pressure control for front-right and rear-left wheels FR and RL, based on the inputted values concerning target wheel-cylinder pressure P*fr and P*rl in such a manner as to bring actual wheel-cylinder pressures Pfr and Prl closer to these inputted values, until new target values are inputted.
By means of first sub-ECU 100 , electric power from first power source BATT 1 is converted into a valve driving current I 1 and a motor driving voltage V 1 for first hydraulic unit HU 1 , and then the converted valve driving current I 1 and motor driving voltage V 1 are relayed or outputted through respective relays RY 11 and RY 12 to first hydraulic unit HU 1 . In the similar manner, by means of second sub-ECU 200 , electric power from second power source BATT 2 is converted into a valve driving current I 2 and a motor driving voltage V 2 for second hydraulic unit HU 2 , and then the converted valve driving current I 2 and motor driving voltage V 2 are relayed or outputted through respective relays RY 21 and RY 22 to second hydraulic unit HU 2 .
[Target Value Calculation for Hydraulic Unit and Driving Current/Voltage Control, separated from each other]
As discussed above, main ECU 300 is configured to execute arithmetic processing for target values P*fl to P*rr for first and second hydraulic units HU 1 and HU 2 , but not configured to execute the above-mentioned driving current/voltage control concerning the valve driving currents I 1 and I 2 and motor driving voltages V 1 and V 2 . Assuming that main ECU 300 is configured to execute the driving current/voltage control as well as the target wheel-cylinder pressure calculations, main ECU 300 must output driving commands to first and second hydraulic units HU 1 and HU 2 in accordance with cooperative control with the other control units CU 1 to CU 6 by way of controller area network (CAN) communications and the like.
In such a case, target wheel-cylinder pressures P*fl to P*rr are outputted after the arithmetic operations of CAN communications line CAN 3 and of the other control units CU 1 to CU 6 have terminated. On the assumption that a transmission speed of CAN communications line CAN 3 and operation speeds of the other control units CU 1 to CU 6 are slow, there is an undesirable response delay in fluid-pressure control (brake control).
One way to avoid such undesirable response delay is to increase the transmission speed of each of communications lines needed for connections with the other controllers installed inside the vehicle. However, this leads to another problem of increased costs. Additionally, a deterioration in fail-safe performance occurs owing to noise caused by the increased transmission speed.
For the reasons discussed above, in this embodiment, the role of main ECU 300 in fluid-pressure control is limited to the arithmetic operations of target wheel-cylinder pressures P*fl to P*rr. Namely, the driving control for first and second hydraulic unit HU 1 and HU 2 (hydraulic actuators) is performed by first and second sub-ECUs 100 and 200 each including servo control system.
With the above-mentioned arrangement, first and second sub-ECUs 100 and 200 specialize in the driving control for first and second hydraulic units HU 1 and HU 2 , while the cooperative control with the other control units CU 1 to CU 6 is performed by main ECU 300 . Thus, it becomes possible to execute the fluid-pressure control (brake control) without being affected by several factors, i.e., the transmission speed of CAN communications line CAN 3 and the operation speeds of control units CU 1 to CU 6 . The above-mentioned backup calculation which is executed in each of first and second sub-ECUs 100 and 200 does not include complex arithmetic, namely is executed relatively simply on the basis of master-cylinder pressure. Hence, this backup calculation does not increase a load in arithmetic processing that much.
Therefore, even when integrated controllers (units) for a regenerative cooperative brake system necessary for a hybrid vehicle (HV) or a fuel-cell vehicle (FCV), an integrated vehicle control system, and/or an intelligent transport system (ITS) are further added; it is possible to ensure or realize a high brake control responsiveness while smoothly planning a fusion with these additional units/systems, by independently controlling the brake control system separately from the other control systems.
The brake control apparatus equipped with BBW system as this embodiment, requires a precise fluid-pressure control suited to a manipulated variable (a depression stroke) of brake pedal BP, during normal braking operations which occur frequently. Thus, separating arithmetic operations of target wheel-cylinder pressures P*fl to P*rr for hydraulic units HU 1 and HU 2 from the driving control for hydraulic units HU 1 and HU 2 is more effective and advantageous.
However, from a view point of fail-safe performance, it is not favorable that the target wheel-cylinder pressures cannot be calculated in the case where main ECU 300 becomes in some failed condition. Therefore, the brake control apparatus in this embodiment is designed to ensure a normally-minimum-necessary (backup) braking force by means of first and second sub-ECUs 100 and 200 even when main ECU 300 is in failed condition, although the complex cooperative control or vehicle dynamic-behavior control is consistently performed by main ECU 300 . Concretely, first and second sub-ECUs 100 and 200 perform the backup calculation for target wheel-cylinder pressures. Thus, the braking-force control according to the master-cylinder pressure can be continued by first and second sub-ECUs 100 and 200 if main ECU 300 becomes failed.
The brake control apparatus in this first embodiment is equipped with a mechanical backup system (manual brake circuit) that connects master cylinder MC with wheel cylinders WC in the case where some trouble occurs in the brake-by-wire (BBW) control system. However, it is difficult to secure a sufficient braking force, since this mechanical backup system generates only wheel-cylinder pressures directly according to the depression force applied by the driver.
At this time, by means of the above-mentioned backup calculation of first and second sub-ECUs 100 and 200 , the simplified (backup) brake-by-wire control becomes executable. Thereby, it is possible to secure sufficient braking force even if the depression force of driver is weak.
[Master Cylinder and Stroke Simulator]
Stroke simulator S/Sim is built in master cylinder M/C and provided to generate a reaction force of brake pedal BP. Also in master cylinder M/C, there is provided a stroke-simulator cutoff valve Can/V for establishing or blocking fluid communication between master cylinder M/C and stroke simulator S/Sim.
Opening and closing operation of stroke-simulator cutoff valve Can/V is controlled by means of main ECU 300 , such that the rapid switching to a manual brake mode can occur upon the termination of brake-by-wire control or when sub-ECUs 100 and 200 become failed. As described above, first and second stroke sensors S/Sen 1 and S/Sen 2 are provided at master cylinder M/C. Two stroke signals S 1 and S 2 each indicating the stroke of brake pedal BP are generated from respective stroke sensors S/Sen 1 and S/Sen 2 to main ECU 300 .
[Hydraulic Unit]
FIG. 2 is a schematic hydraulic circuit diagram of first hydraulic unit HU 1 . Components incorporated in first hydraulic unit HU 1 are electromagnetic valves (directional control valves or changeover valves), pump P 1 , check valves C/V, and motor M 1 . The electromagnetic valves include a shutoff valve S.OFF/V, a front-left inflow valve IN/V(FL), a rear-right inflow valve IN/V(RR), a front-left outflow valve OUT/V(FL), and a rear-right outflow valve OUT/V(RR).
A discharge line (a pump outlet side) of pump P 1 is connected through a fluid passage C 1 (FL) to the front-left wheel cylinder W/C(FL), and is also connected through a fluid passage C 1 (RR) to the rear-right wheel cylinder W/C(RR). A suction line (a pump inlet side) of pump P 1 is connected through a fluid passage B 1 to reservoir RSV. Fluid passage C 1 (FL) is connected through a fluid passage E 1 (FL) to fluid passage B 1 , and similarly the fluid passage C 1 (RR) is connected through a fluid passage E 1 (RR) to fluid passage B 1 .
A joining point I 1 of fluid passage C 1 (FL) and fluid passage E 1 (FL) is connected through fluid passage A 1 to master cylinder M/C. Furthermore, a joining point J 1 of fluid passage C 1 (FL) and fluid passage C 1 (RR) is connected through a fluid passage G 1 to fluid passage B 1 .
Shutoff valve S.OFF/V is a normally-open electromagnetic valve, and fluidly disposed in fluid passage A 1 for establishing or blocking fluid communication between master cylinder M/C and joining point I 1 .
Front-left inflow valve IN/V(FL) is fluidly disposed in fluid passage C 1 (FL), and is a normally-open proportional control valve that regulates the discharge pressure produced by pump P 1 by way of proportional control action and then supplies the proportional-controlled fluid pressure to front-left wheel cylinder W/C(FL). Similarly, front-right inflow valve IN/V(RR) is disposed in fluid passage C 1 (RR), and is a normally-open proportional control valve that regulates the discharge pressure produced by pump P 1 by way of proportional control action and then supplies the proportional-controlled fluid pressure to rear-right wheel cylinder W/C(RR).
Moreover, backflow-prevention check valves C/V(FL) and C/V(RR) are fluidly disposed in respective fluid passages C 1 (FL) and C 1 (RR) to prevent working fluid from flowing back to the discharge port of pump P 1 . These backflow-prevention check valves serve to reduce an electric power consumption by always blocking or shutting off the fluid flow from the road-wheel cylinder side toward the discharge port of pump P 1 . Furthermore as a matter of course, these backflow-prevention check valves prevent master-cylinder pressure Pm from acting on the discharge side of pump P 1 at the time of above-mentioned failed condition.
Front-left and rear-right outflow valves OUT/V(FL) and OUT/V(RR) are fluidly disposed in respective fluid passages E 1 (FL) and E 1 (RR). Front-left outflow valve OUT/V(FL) is a normally-closed proportional control valve, whereas rear-right outflow valve OUT/V(RR) is a normally-open proportional control valve. A relief valve Ref/V is fluidly disposed in fluid passage G 1 .
First M/C pressure sensor MC/Sen 1 is provided in or screwed into fluid passage A 1 interconnecting first hydraulic unit HU 1 and master cylinder M/C, for detecting first master-cylinder pressure Pm 1 and for outputting a signal indicative of the detected first master-cylinder pressure to main ECU 300 . Front-left and rear-right wheel-cylinder pressure sensors WC/Sen(FL) and WC/Sen(RR) are incorporated into first hydraulic unit HU 1 and provided in or screwed into respective fluid passages C 1 (FL) and C 1 (RR), for detecting actual front-left and rear-right wheel-cylinder pressures Pfl and Prr. A first pump discharge pressure sensor P 1 /Sen is provided in or screwed into the discharge passage of pump P 1 , for detecting the discharge pressure Pp 1 discharged from first pump P 1 . Signals indicative of the detected values Pfl, Prr, and Pp 1 are outputted from the respective sensors WC/Sen(FL), WC/Sen(RR), and P 1 /Sen to first sub-ECU 100 .
Alternatively, first master-cylinder pressure Pm 1 may be outputted to first sub-ECU 100 , and then outputted from first sub-ECU 100 through one or both of lines CAN 1 and CAN 2 to main ECU 300 .
[Normal Braking]
(During Pressure Buildup)
During normal braking at a pressure buildup mode (increase mode); shutoff valve S.OFF/V is kept closed, inflow valves IN/V(FL) and IN/V(RR) are kept open, outflow valves OUT/V(FL) and OUT/V(RR) are kept closed, and motor M 1 is rotated or driven. Pump P 1 is driven by motor M 1 , and thus a discharge pressure from pump P 1 is supplied to fluid passages C 1 (FL) and C 1 (RR). Then, the regulated working fluid, proportional-controlled by front-left inflow valve IN/V(FL), is introduced from inflow valve IN/V(FL) via a fluid passage D 1 (FL) into front-left wheel cylinder W/C(FL). Likewise, the regulated working fluid, proportional-controlled by rear-right inflow valve IN/V(RR), is introduced from inflow valve IN/V(RR) via a fluid passage D 1 (RR) into rear-right wheel cylinder W/C(RR). In this manner, the pressure buildup of wheel cylinders can be achieved. Alternatively, the pressure buildup may be conducted directly by regulating the discharge pressure of pump by means of motor driving control.
(During Pressure Reduction)
During normal braking at a pressure reduction mode, inflow valves IN/V(FL) and IN/V(RR) are kept closed (may be kept open because of the function of check valves C/V), while outflow valves OUT/V(FL) and OUT/V(RR) are kept open. Thus, front-left and rear-right wheel-cylinder pressures Pfl and Prr, namely working fluids in front-left and rear-right wheel cylinders W/C(FL) and W/C(RR) are exhausted through outflow valves OUT/V(FL) and OUT/V(RR) via fluid passage B 1 into reservoir RSV. In this manner, the pressure reduction of wheel cylinders can be achieved.
(During Pressure Hold)
During normal braking at a pressure hold mode, inflow valves IN/V(FL) and IN/V(RR) and outflow valves OUT/V(FL) and OUT/V(RR) are all kept closed, so as to hold or retain front-left and rear-right wheel-cylinder pressures Pfl and Prr unchanged.
[Manual Brake]
When the operating mode of BBW-system-equipped brake control apparatus has been switched to the manual brake mode due to a system failure or the like; shutoff valve S.OFF/V becomes open, and inflow valves IN/V(FL) and IN/V(RR) become open (but in closed state as viewed from the side of master cylinder MC because of the function of check valve C/V). As a result of this, master-cylinder pressure Pm is not delivered to rear-right wheel-cylinder W/C(RR).
On the other hand, front-left outflow valve OUT/V(FL) is a normally-closed valve and therefore is kept closed during the manual brake mode. Accordingly, master-cylinder pressure Pm is being applied to front-left wheel cylinder W/C(FL) during the manual brake mode. Thus, master-cylinder pressure Pm built up by the driver's brake-pedal depression is applied to front-left wheel cylinder W/C(FL). In this manner, the manual brake operation can be achieved or ensured.
Suppose that master-cylinder pressure Pm is applied to rear-right wheel cylinder W/C(RR) as well as front-left wheel cylinder W/C(FL) during the manual brake mode. In such case, when building up rear-right wheel-cylinder pressure Prr as well as front-left wheel-cylinder pressure Pfl by leg-power by the driver's foot (pedal depression power), there is a problem of unnatural feeling that the driver experiences an excessive leg-power load. This is not realistic. For this reason, during the manual brake mode, the brake system in this embodiment is configured to apply master-cylinder pressure Pm (namely, manual braking) only to front-left road wheel FL which can generate a relatively great braking force in comparison with rear-right road wheel RR in first hydraulic unit HU 1 . Therefore, rear-right outflow valve OUT/V(RR) is constructed as a normally-open valve, for rapidly exhausting the residual pressure in rear-right wheel cylinder W/C(RR) into reservoir RSV to avoid undesirable rear-right wheel lockup at the time of system failure (such as BBW system failure or battery failure).
FIG. 3 is a schematic hydraulic circuit diagram of second hydraulic unit HU 2 . Components incorporated in second hydraulic unit HU 2 are electromagnetic valves, check valves C/V, pump P 2 , and motor M 2 . The electromagnetic valves include a shutoff valve S.OFF/V, a front-right inflow valve IN/V(FR), a rear-left inflow valve IN/V(RL), a front-right outflow valve OUT/V(FR), and a rear-left outflow valve OUT/V(RL). The hydraulic circuit configurations and control operations are same in both first and second hydraulic units Hu 1 and HU 2 . In explaining the second hydraulic unit HU 2 , for the purpose of simplification of the disclosure, detailed descriptions of the similar components will be omitted because the above description thereon seems to be self-explanatory. In the similar manner to first hydraulic unit HU 1 , regarding second hydraulic unit HU 2 , front-right outflow valve OUT/V(FR) is a normally-closed proportional control valve, whereas rear-left outflow valve OUT/V(RL) is a normally-open proportional control valve. For second hydraulic unit HU 2 during the manual brake mode, the brake system in this embodiment is configured to apply master-cylinder pressure Pm only to front-right road wheel FR which generates a relatively great braking force in comparison with rear-left road wheel RL. As mentioned above, rear-left outflow valve OUT/V(RL) is constructed as a normally-open valve, for rapidly exhausting the residual pressure inside rear-left wheel cylinder W/C(RL) into reservoir RSV and for avoiding undesirable rear-left wheel lockup.
FIG. 5 is a schematic block diagram showing the control configuration of brake-by-wire (BBW) system in the first embodiment. As shown in FIG. 5, main ECU 300 includes a brake-manipulated-variable calculation section 301 and a fluid-pressure command-value calculation section 302 . Brake-manipulated-variable calculation section 301 calculates the brake manipulated variable of driver (manipulation quantity, i.e., the depression stroke amount of brake pedal or an amount corresponding to the state of brake manipulation such as the master-cylinder pressure) from each sensor signal. Fluid-pressure command-value calculation section 302 calculates target wheel-cylinder pressures P*fl, P*fr, P*rl, and P*rr as fluid-pressure command values for respective wheels on the basis of the calculated brake manipulated variable. Target wheel-cylinder pressures P*fl to P*rr calculated by fluid-pressure command-value calculation section 302 are transmitted to first and second sub-ECUs 100 and 200 .
First sub-ECU 100 includes a communication processing section 100 a serving to carry out a communication processing for the communication with main ECU 300 .
First sub-ECU 100 further includes a command-value judging section 100 b and a valve-and-motor control section 100 c . Command-value judging section 100 b calculates the backup target wheel-cylinder pressures in accordance with first master-cylinder pressure sensor MC/Sen 1 , and determines final target wheel-cylinder pressures by judging or checking the calculated backup target wheel-cylinder pressures in comparison with target wheel-cylinder pressures P*fl to P*rr transmitted from main ECU 300 . Valve-and-motor control section 100 c controls the respective electromagnetic valves and motor M 1 to achieve the final target wheel-cylinder pressures, on the basis of signals of wheel-cylinder pressure sensors WC/Sen(FL) and WC/Sen(RR).
Second sub-ECU 200 includes a communication processing section 200 a , a command-value judging section 200 b , and a valve-and-motor control section 200 c , in the same manner as first sub-ECU 100 .
[Brake-By-Wire Control Processing]
FIGS. 6 to 10 are flowcharts showing routines of the brake-by-wire control processing which is executed within main ECU 300 and first and second sub-ECUs 100 and 200 .
(Command-value Calculating Processing in Main ECU)
FIG. 6 is a flowchart showing a command-value calculating processing executed in main ECU 300 .
At step S 1 , main ECU 300 detects a brake pedal manipulation by the driver, on the basis of sensed values of first and second stroke sensors S/Sen 1 and S/Sen 2 .
At step S 2 , main ECU 300 judges whether or not there is a proper output-relation between the sensed values of first and second stroke sensors S/Sen 1 and S/Sen 2 and the sensed values of first and second master-cylinder pressure sensors MC/Sen 1 and MC/Sen 2 . If there is the proper output-relation; main ECU 300 determines that the sensors have no trouble (are not failed), and the routine proceeds to step S 3 . If there is not the proper output-relation at step S 2 ; main ECU 300 determines that some trouble (failure) has occurred in the sensors, and the routine proceeds to step 54 .
The proper output-relation of step S 2 is determined by judging whether or not both of first and second stroke sensors S/Sen 1 and S/Sen 2 detect an identical stroke amount (stroke degree) and whether or not first and second master-cylinder pressure sensors MC/Sen 1 and MC/Sen 2 output respective values of first and second master-cylinder pressures according to this identical stroke amount. In stroke simulator S/Sim, a load according to stroke amount (namely, force reacting to the depression force of pedal) is preset and applied by means of the load setting using an elastic member or the like. Hence, under the operating state of stroke simulator S/Sim, it is possible to judge whether or not the proper relation between the stroke amount and the master-cylinder pressure is satisfied (established). Thus, main ECU 300 detects a trouble in respective sensors.
At step S 3 , main ECU 300 calculates the manipulated variable of brake. Concretely, main ECU 300 calculates a depression degree of brake pedal manipulated by the driver, from the stroke amount and the master-cylinder pressure from respective sensors.
At step S 4 , since the proper output-relation is not satisfied, main ECU 300 finds which sensor has failed, namely identifies the failed sensor among respective sensors. For example, main ECU 300 determines that second stroke sensor S/Sen 2 is failed; in the case where the proper output-relation between the sensed value of first stroke sensor S/Sen 1 and the sensed values of first and second master-cylinder pressure sensors MC/Sen 1 and MC/Sen 2 is satisfied, and further where the proper output-relation between the sensed value of second stroke sensor S/Sen 2 and the sensed values of first and second master-cylinder pressure sensors MC/Sen 1 and MC/Sen 2 is not satisfied. For example, main ECU 300 determines that second master-cylinder pressure sensor MC/Sen 2 is failed; in the case where the proper output-relation between the sensed values of first and second stroke sensors S/Sen 1 and S/Sen 2 and the sensed value of first master-cylinder pressure sensor MC/Sen 1 is satisfied, and further where the proper output-relation between the sensed values of first and second stroke sensors S/Sen 1 and S/Sen 2 and the sensed value of second master-cylinder pressure sensor MC/Sen 2 is not satisfied.
At step S 5 , main ECU 300 calculates the manipulated variable of brake, on the basis of remaining sensors except the failed sensor(s).
At step S 6 , main ECU 300 executes the processing for the communication with first and second sub-ECUs 100 and 200 . Detailed explanation of this communication processing will be described below.
At step S 7 , main ECU 300 calculates the fluid-pressure command values (target wheel-cylinder pressures) on the basis of the result of communication processing. These fluid-pressure command values are calculated according to a value of main communication flag Fm set in the communication processing as explained below (the setting of main communication flag Fm will be described in the following explanations about communication processing). When main communication flag Fm is equal to 1, main ECU 300 calculates target wheel-cylinder pressures P*fl to P*rr for respective four road wheels. When main communication flag Fm is equal to 2; main ECU 300 determines that first sub-ECU 100 has been failed, and calculates target wheel-cylinder pressures P*fr and P*rl for only two road wheels which are driven by second sub-ECU 200 . When main communication flag Fm is equal to 3; main ECU 300 determines that second sub-ECU 200 has been failed, and calculates target wheel-cylinder pressures P*fl and P*rr for only two road wheels which are driven by first sub-ECU 100 .
At step S 8 , main ECU 300 transmits the fluid-pressure command values calculated at step S 7 to first and second sub-ECUs 100 and 200 .
(Main ECU Communication Processing)
FIG. 7 is a flowchart showing the communication processing which is executed in main ECU 300 .
At step S 31 , main ECU 300 judges whether or not main ECU 300 can communicate with (transmit or receive data to or from) second sub-ECU 200 via CAN communications line CAN 1 . If YES, namely if main ECU 300 can communicate with second sub-ECU 200 via CAN communications line CAN 1 , the routine proceeds to step S 36 . If NO at step S 31 , the routine proceeds to step S 32 .
At step S 32 , main ECU 300 judges whether or not main ECU 300 can communicate with second sub-ECU 200 via CAN communications line CAN 2 . If YES, namely if main ECU 300 can communicate with second sub-ECU 200 via CAN communications line CAN 2 , the routine proceeds to step S 36 . If NO at step S 32 , the routine proceeds to step S 33 .
At step S 33 , main ECU 300 judges whether or not main ECU 300 can communicate with first sub-ECU 100 via CAN communications line CAN 1 . If YES, namely if main ECU 300 can communicate with first sub-ECU 100 via CAN communications line CAN 1 , the routine proceeds to step S 40 . If NO at step S 33 , the routine proceeds to step S 34 .
At step S 34 , main ECU 300 judges whether or not main ECU 300 can communicate with first sub-ECU 100 via CAN communications line CAN 2 . If YES, namely if main ECU 300 can communicate with first sub-ECU 100 via CAN communications line CAN 2 , the routine proceeds to step S 40 . If NO at step S 34 , the routine proceeds to step S 35 .
At step S 35 , main ECU 300 determines that some trouble has occurred in main ECU 300 , and executes a processing for failure or a troubleshooting processing for main ECU 300 . Accordingly at step S 35 , main ECU 300 does not generate the communication flag or the like.
At step S 36 , main ECU 300 judges whether or not main ECU 300 can communicate with first sub-ECU 100 via CAN communications line CAN 1 . If YES, namely if main ECU 300 can communicate with first sub-ECU 100 via CAN communications line CAN 1 , the routine proceeds to step S 38 . If NO at step S 36 , the routine proceeds to step S 37 .
At step S 37 , main ECU 300 judges whether or not main ECU 300 can communicate with first sub-ECU 100 via CAN communications line CAN 2 . If YES, namely if main ECU 300 can communicate with first sub-ECU 100 via CAN communications line CAN 2 , the routine proceeds to step S 38 . If NO at step S 37 , the routine proceeds to step S 39 .
At step S 38 , main ECU 300 determines that all the communication conditions are proper (under normal operating conditions), and sets main communication flag Fm at equal to 1 (Fm=1).
At step S 39 , main ECU 300 determines that first sub-ECU 100 has failed and second sub-ECU 200 is fine (under normal operating condition). Then, main ECU 300 sets main communication flag Fm at equal to 2 (Fm=2).
At step S 40 , main ECU 300 determines that second sub-ECU 200 has failed and first sub-ECU 100 is fine. Then, main ECU 300 sets main communication flag Fm at equal to 3 (Fm=3).
(Fluid-pressure Control Processing in Sub-ECU)
FIG. 8 is a flowchart showing a fluid-pressure control processing which is executed in first and second sub-ECUs 100 and 200 . Since both of first and second sub-ECUs 100 and 200 execute the similar fluid-pressure control processing, explanations only about the processing executed in first sub-ECU 100 will be described for the purpose of simplification of the disclosure.
At step S 10 , first sub-ECU 100 carries out a communication processing regarding first sub-ECU 100 . This communication processing is executed so as to judge whether or not the communication between first sub-ECU 100 and main ECU 300 is possible and whether or not the communication between first sub-ECU 100 and second sub-ECU 200 (the other sub-ECU) is possible. At step S 10 , first sub-ECU 100 determines that the communication processing has ended at “normal” in the case where the communications with all the ECUs (main ECU 300 and second sub-ECU 200 ) are possible. On the other hand, first sub-ECU 100 determines that the communication processing has ended at “abnormal” in the other cases. This communication processing regarding first sub-ECU 100 will be explained below.
At step S 11 , first sub-ECU 100 judges whether or not the communication processing has ended at “normal”, namely whether or not a sub-communication flag Fs set by the communication processing is equal to 1 (Fs=1). If YES, namely if the result of communication processing is “normal”; the routine proceeds to step S 12 . If NO at step S 11 ; the routine proceeds to step S 13 . The setting of sub-communication flag Fs will be described in the following explanations about sub-ECU communication processing.
At step S 12 , first sub-ECU 100 executes a command-value judging (checking) processing. This command-value judging processing is executed so as to judge whether or not the backup target wheel-cylinder pressures calculated in first sub-ECU 100 match or have a proper relation with target wheel-cylinder pressures P*fl to P*rr calculated in main ECU 300 , in the case where the result of communication processing is “normal” at step S 11 . Detailed explanations about the command-value judging processing will be described below.
At step S 13 , first sub-ECU 100 judges whether or not sub-communication flag Fs set in the communication processing is equal to 3, and whether or not a check flag Fc set in the command-value judging (checking) processing is equal to 2. The setting of check flag Fc will be described in the following explanations about the command-value judging processing. If at least either one of the above setting criteria of sub-communication flag Fs and check flag Fc is satisfied, namely if sub-communication flag Fs is equal to 3 or check flag Fc is equal to 2 at step S 13 ; the routine proceeds to step S 14 . If sub-communication flag Fs is not equal to 3 and check flag Fc is not equal to 2 at step S 13 ; the routine proceeds to step S 15 . If it has been determined that a self-control line (sub-ECU 100 ) is failed in the communication processing so that the control of sub-ECU 100 has been suspended; this routine of fluid-pressure control processing in sub-ECU 100 is terminated.
At step S 14 , first sub-ECU 100 sets the backup target wheel-cylinder pressures calculated by first sub-ECU 100 in accordance with actual master-cylinder pressure (first master-cylinder pressure Pm 1 ), as the final target wheel-cylinder pressures.
At step S 15 , first sub-ECU 100 sets the target wheel-cylinder pressures P*fl and P*rr transmitted from main ECU 300 , as the final target wheel-cylinder pressures.
At step S 16 , first sub-ECU 100 judges whether or not actual wheel-cylinder pressures Pfl and Prr are low relative to the final target wheel-cylinder pressures. If YES at step S 16 , the routine proceeds to step S 17 . If NO at step S 16 , the routine proceeds to step S 18 . At step S 17 , first sub-ECU 100 carries out a pressure-buildup control. At step S 18 , first sub-ECU 100 carries out a pressure-reduction control.
At step S 19 , first sub-ECU 100 judges whether or not actual wheel-cylinder pressures Pfl and Prr have become equal to (or have already accorded with) the final target wheel-cylinder pressures. If YES, namely if actual wheel-cylinder pressures Pfl and Prr have become equal to the final target wheel-cylinder pressures; this routine of fluid-pressure control processing in sub-ECU 100 is terminated. If NO, namely if actual wheel-cylinder pressures Pfl and Prr have not yet become equal to (or have not yet accorded with) the final target wheel-cylinder pressures; the steps between step S 16 and step S 19 are repeatedly executed (as corresponds to so-called servo control).
(Sub-ECU Communication Processing)
FIG. 9 is a flowchart showing the communication processing which is executed in first and second sub-ECUs 100 and 200 . Since both of first and second sub-ECUs 100 and 200 execute the similar communication processing, explanations only about the processing executed in first sub-ECU 100 will be described for the purpose of simplification of the disclosure.
At step S 51 , first sub-ECU 100 judges whether or not first sub-ECU 100 can communicate with (transmit or receive data to or from) main ECU 300 via CAN communications line CAN 1 . If YES, namely if first sub-ECU 100 can communicate with main ECU 300 via CAN communications line CAN 1 , the routine proceeds to step S 56 . If NO at step S 51 , the routine proceeds to step S 52 .
At step S 52 , first sub-ECU 100 judges whether or not first sub-ECU 100 can communicate with main ECU 300 via CAN communications line CAN 2 . If YES, namely if first sub-ECU 100 can communicate with main ECU 300 via CAN communications line CAN 2 , the routine proceeds to step S 56 . If NO at step S 52 , the routine proceeds to step S 53 .
At step S 53 , first sub-ECU 100 judges whether or not first sub-ECU 100 can communicate with second sub-ECU 200 via CAN communications line CAN 1 . If YES, namely if first sub-ECU 100 can communicate with second sub-ECU 200 via CAN communications line CAN 1 , the routine proceeds to step S 60 . If NO at step S 53 , the routine proceeds to step S 54 .
At step S 54 , first sub-ECU 100 judges whether or not first sub-ECU 100 can communicate with second sub-ECU 200 via CAN communications line CAN 2 . If YES, namely if first sub-ECU 100 can communicate with second sub-ECU 200 via CAN communications line CAN 2 , the routine proceeds to step S 60 . If NO at step S 54 , the routine proceeds to step S 55 .
At step S 55 , first sub-ECU 100 determines that some trouble has occurred in self-control line (first sub-ECU 100 ). Hence first sub-ECU 100 suspends or stops the control which is conducted by first sub-ECU 100 .
At step S 56 , first sub-ECU 100 judges whether or not first sub-ECU 100 can communicate with sub-ECU 200 via CAN communications line CAN 1 . If YES, namely if first sub-ECU 100 can communicate with second sub-ECU 200 via CAN communications line CAN 1 , the routine proceeds to step S 62 . If NO at step S 56 , the routine proceeds to step S 57 .
At step S 57 , first sub-ECU 100 judges whether or not first sub-ECU 100 can communicate with second sub-ECU 200 via CAN communications line CAN 2 . If YES, namely if first sub-ECU 100 can communicate with second sub-ECU 200 via CAN communications line CAN 2 , the routine proceeds to step S 62 . If NO at step S 57 , the routine proceeds to step S 58 .
At step S 58 , first sub-ECU 100 determines that second sub-ECU 200 is failed (or has some trouble) and the self-control line (first sub-ECU 100 ) is fine (under normal operating condition). Then, the routine proceeds to step S 59 , and first sub-ECU 100 sets sub-communication flag Fs at 2 (Fs=2) for the purpose of the control only using first sub-ECU 100 (i.e., control without second sub-ECU 200 ).
At step S 60 , first sub-ECU 100 determines that main ECU 300 has some trouble and both of first and second sub-ECUs 100 and 200 are under normal operating condition. Then, the routine proceeds to step S 61 , and first sub-ECU 100 sets sub-communication flag Fs at 3 (Fs=3) for the purpose of the control only using first and second sub-ECUs 100 and 200 .
At step S 62 , first sub-ECU 100 determines that all the communication conditions are proper (under normal operating conditions), and sets sub-communication flag Fs at 1 (Fs=1).
(Command-value Judging Processing in Sub-ECU)
FIG. 10 is a flowchart showing the command-value judging processing (i.e., check processing for command values) which is executed in first and second sub-ECUs 100 and 200 . Since both of first and second sub-ECUs 100 and 200 execute the similar check processing, explanations only about first sub-ECU 100 will be described for the purpose of simplification of the disclosure. This command-value judging processing is executed, only in the case where it has been determined that the communication conditions are proper (under normal operating conditions) in the above-mentioned sub-ECU communication processing. Namely, the command-value judging processing is not executed, in the case where it has been determined that any ECU has some trouble (some failure).
At step S 21 , first sub-ECU 100 judges whether or not some failure has occurred in first and second stroke sensors S/Sen 1 and S/Sen 2 and first and second master-cylinder pressure sensors MC/Sen 1 and MC/Sen 2 , with reference to the above-mentioned command-value calculating processing in main ECU 300 (see FIG. 6). If some trouble has occurred in first and second stroke sensors S/Sen 1 and S/Sen 2 and first and second master-cylinder pressure sensors MC/Sen 1 and MC/Sen 2 ; the routine proceeds to step S 29 since the command-value check based on the signals of respective sensors is impossible. If the respective sensors are under normal operating conditions, the routine proceeds to step S 22 in order to carry out the command-value judgment (check) using the signals of respective sensors.
At step S 22 , first sub-ECU 100 detects the actual master-cylinder pressure (first master-cylinder pressure Pm 1 ) from the sensor which has been determined to have no trouble. Then, (the backup calculation section of) first sub-ECU 100 calculates the backup target wheel-cylinder pressures for four wheels on the basis of this actual master-cylinder pressure.
At step S 23 , first sub-ECU 100 judges whether or not target wheel-cylinder pressures P*fl, P*fr, P*rl, and P*rr derived from main ECU 300 are substantially equal to the backup target wheel-cylinder pressures calculated from the actual master-cylinder pressure. Concretely, first sub-ECU 100 judges whether or not each value of target wheel-cylinder pressures P*fl to P*rr ranges within a predetermined tolerance of corresponding value of backup target wheel-cylinder pressures calculated from the actual master-cylinder pressure. Namely, first sub-ECU 100 judges whether or not each value of target wheel-cylinder pressures P*fl to P*rr is lower than an upper limit set by adding a predetermined value (the tolerance) to the corresponding value of backup target wheel-cylinder pressures, and also judges whether or not each value of target wheel-cylinder pressures P*fl to P*rr is higher than a lower limit set by subtracting the predetermined value (tolerance) from the corresponding value of backup target wheel-cylinder pressures. If it is determined that target wheel-cylinder pressures P*fl to P*rr are substantially equal to the backup target wheel-cylinder pressures, namely, if each value of target wheel-cylinder pressures P*fl to P*rr is lower than the corresponding upper limit and also higher than the corresponding lower limit; the routine proceeds to step S 29 . If NO at step S 23 , the routine proceeds to step S 24 .
At step S 24 , first sub-ECU 100 judges whether or not target wheel-cylinder pressures P*fl to P*rr have been generated mainly based on the depression force applied by the driver. Namely, first sub-ECU 100 judges whether or not a current condition of brake control is being carried out due to the depression force applied by the driver. If the current condition of brake control is not based on the depression force, namely for example, if the current condition of brake control is based on vehicle dynamic-behavior control, vehicle-to-vehicle distance control, or the like; the routine proceeds to step S 29 . If YES at step S 24 , the routine proceeds to step S 25 . This is because it is inappropriate that the backup target wheel-cylinder pressures are calculated from the stroke sensor or master-cylinder pressure sensor in the case where the current condition of brake control is based on any braking command other than the pedal depression applied by the driver.
At step S 25 , first sub-ECU 100 judges whether or not the backup target wheel-cylinder pressures calculated in second sub-ECU 200 are equal to (or accord with) the backup target wheel-cylinder pressures calculated in first sub-ECU 100 . If YES at step S 25 , the routine proceeds to step S 27 . At step S 27 , first sub-ECU 100 determines that the command values from main ECU 300 (target wheel-cylinder pressures P*fl to P*rr) are not correct. Then, the routine proceeds to step S 28 . On the other hand, if NO at step S 25 , the routine proceeds to step S 26 . At step S 26 , first sub-ECU 100 determines that the backup target wheel-cylinder pressures calculated from the actual master-cylinder pressure are not correct, or determines that first and second master-cylinder pressure sensors MC/Sen 1 and MC/Sen 2 are failed. Then, the routine proceeds to step S 29 .
At step S 28 , first sub-ECU 100 sets check flag Fc at 2 (Fc=2). At step S 29 , first sub-ECU 100 sets check flag Fc at 1 (Fc=1).
Next, operations according to the above-mentioned control processing in the brake control apparatus of first embodiment will now be explained.
[Control Processing in Main ECU]
Main ECU 300 carries out the brake-manipulated-variable calculating processing when the brake-pedal manipulation is detected, and carries out the communication processing based on this brake manipulated variable. Moreover if the other control unit(s) (regenerative brake control unit CU 1 , radar control unit CU 2 , and the like) outputs a required braking force; main ECU 300 calculates target wheel-cylinder pressures for respective road wheels on the basis of this required braking force, as the command values.
In the brake-manipulated-variable calculating processing, main ECU 300 calculates or detects the brake manipulated variable (degree of manipulation) based on the brake pedal manipulation by driver, while executing the failure detection for the plurality of sensors at the same time. If main ECU 300 detects some kind of failure in respective sensors, the main ECU 300 outputs the information about this sensor failure to sub-ECUs 100 and 200 via communications.
In the communication processing, main ECU 300 judges whether or not main ECU 300 can communicate with first and second sub-ECUs 100 and 200 through CAN communications line CAN 1 or CAN communications line CAN 2 . Then, main ECU 300 calculates the target wheel-cylinder pressures P*fl to P*rr in accordance with the communication states with first and second sub-ECUs 100 and 200 .
{circle around (1)} The case where the communications with all the sub-ECUs are possible. (Fm=1)
In this case, main ECU 300 calculates target wheel-cylinder pressures P*fl to P*rr for four road wheels, and transmits these target wheel-cylinder pressures P*fl to P*rr to each sub-ECU 100 , 200 as the command values of main ECU 300 by way of command-value transmitting process.
{circle around (2)} The case where the communication with only either one of first and second sub-ECUs 100 and 200 is impossible. (Fm=2 or Fm=3)
In this case, there is a fear that the control by communication-impossible sub-ECU does not function properly. Hence, main ECU 300 calculates the target wheel-cylinder pressures that are most suitable when only the communication-possible sub-ECU is made to be operated or activated. Then, main ECU 300 transmits these target wheel-cylinder pressures to the communication-possible sub-ECU (i.e., the sub-ECU under normal operating condition) as the command values of main ECU 300 by way of command-value transmitting process.
{circle around (3)} The case where all the communications with respective sub-ECUs are impossible.
In this case, it is determined that main ECU 300 itself is failed (has some trouble) since the possibility that the other two sub-ECUs are failed concurrently is low. Accordingly, main ECU 300 executes the processing for the failure of main ECU 300 . Concretely, main ECU 300 switches the ongoing brake control to a control using only first and second sub-ECUs 100 and 200 (without using the command-values of main ECU 300 ).
[Control Processing in Sub-ECU]
Next, operations in sub-ECUs will now be explained. Sub-ECU 100 or 200 carries out the communication processing in which it is judged whether or not the communications with main ECU 300 and another sub-ECU are under normal operating condition. When it is determined that the communications are under normal operating condition in the communication processing, sub-ECU 100 or 200 executes the command-value judging (checking) processing. Further, sub-ECU 100 or 200 executes the servo control processing in which wheel-cylinder pressures Pfl to Prr are adjusted so as to be increased and reduced in accordance with the set (final) target wheel-cylinder pressures.
{circle around (1)} The case where both of the communication between first sub-ECU 100 and second sub-ECU 200 and the communication between first and second sub-ECUs 100 and 200 and main ECU 300 are possible. (Fs=1)
In this case, sub-ECU 100 or 200 determines that the communications are in normal operating condition (not failed), and sets the command values received from main ECU 300 as the target wheel-cylinder pressures. Then in this case, sub-ECU 100 or 200 executes the command-value judging processing in order to check a properness of these command values.
{circle around (2)} The case where only the communication between first sub-ECU 100 and second sub-ECU 200 is impossible. (Fs=2)
In this case, it is determined that the sub-ECU capable of communicating with main ECU 300 is normal (not failed) and the other sub-ECU incapable of communicating with main ECU 300 is abnormal (failed). At this time, as mentioned above, main ECU 300 has calculated the target wheel-cylinder pressures suitable when using only one not-failed sub-ECU, since either of first and second sub-ECUs 100 and 200 is abnormal (Fm=2 or Fm=3). Accordingly, sub-ECU 100 or 200 sets the command values received from main ECU 300 as the target wheel-cylinder pressures.
{circle around (3)} The case where both of first sub-ECU 100 and second sub-ECU 200 cannot communicate with main ECU 300 . (Fs=3)
In this case, sub-ECU 100 or 200 determines that main ECU 300 is abnormal. At this time, main ECU 300 has recognized that main ECU 300 itself is abnormal (has some failure) and has executed the processing for failure. Accordingly, sub-ECU 100 or 200 sets the backup target wheel-cylinder pressures calculated from the actual master-cylinder pressure by first and second sub-ECUs 100 and 200 , as the final target wheel-cylinder pressures. By virtue of this configuration, even if some trouble occurs in main ECU 300 , a normally-minimum-necessary braking force control based on the brake-pedal manipulation of driver can be maintained.
According to the brake control apparatus in the first embodiment, the following effects listed with configurations of the first embodiment can be obtained.
{circle around (1)} In the first embodiment, main ECU 300 calculates the target wheel-cylinder pressure(s) which is a target braking controlled variable, in accordance with the amount of brake manipulation of driver (stroke amount, master-cylinder pressure). Each of first and second sub-ECUs 100 and 200 includes the backup calculation section configured to calculate the backup target wheel-cylinder pressure(s) which is a backup target braking controlled variable (step S 22 ), by receiving the amount of brake manipulation separately from main ECU 300 . Further, each of first and second sub-ECUs 100 and 200 is configured to properly select one from the target wheel-cylinder pressure and the backup target wheel-cylinder pressure in accordance with operating conditions of main ECU 300 and/or first and second sub-ECUs 100 and 200 . Further, each of first and second sub-ECUs 100 and 200 is configured to output drive signals to the actuator(s) (or loads, e.g., motor M 1 and respective electromagnetic valves of shutoff valve S.OFF/V, valves IN/V(FL) and IN/V(RR) for front-left and rear-right wheels, and valves OUT/V(FL) and OUT/V(RR) for front-left and rear-right wheels) provided for generating or giving braking force of each road wheel, so as to bring the wheel-cylinder pressure of each road wheel closer to the selected one of the target wheel-cylinder pressure and the backup target wheel-cylinder pressure.
Namely, while the normal calculation based on the state (such as pedal stroke) of driver's brake manipulation is conducted by main ECU 300 (broader control unit), each of first and second sub-ECUs 100 and 200 conducts the backup calculation. Therefore, even if one of main ECU 300 and sub-ECU 100 , 200 becomes failed, another of main ECU 300 and sub-ECU 100 , 200 continues to calculate the target wheel-cylinder pressure. Hence, the automatic brake control can be continued to improve the safety-performance.
{circle around (2)} In the first embodiment, when main ECU 300 becomes failed, first and second sub-ECUs 100 and 200 are configured to output drive signals to motors M 1 and M 2 and the like, to bring the wheel-cylinder pressure of each road wheel closer to the backup target wheel-cylinder pressure calculated by the backup calculation section. Therefore, the target braking controlled variable can be attained by means of only first and second sub-ECUs 100 and 200 , and hence the brake-by-wire control can be continued while ensuring the minimum-necessary braking force.
{circle around (3)} In the first embodiment, main ECU 300 and/or sub-ECU 100 , 200 includes the main microcomputer and the sub-microcomputer to construct a dual system. Therefore, these two microcomputers have a function of monitoring each other, so that the fail-safe performance of arithmetic device (microprocessor) is enhanced.
{circle around (4)} In the first embodiment, main ECU 300 and/or sub-ECU 100 , 200 is configured to determine that one of main ECU 300 and sub-ECU 100 , 200 is failed when the difference between the target wheel-cylinder pressure calculated by main ECU 300 and the backup target wheel-cylinder pressure calculated by sub-ECU 100 , 200 is greater than a predetermined value. Therefore, the mutual monitoring between these main ECU and sub-ECU can be realized so that the fail-safe performance is further enhanced.
{circle around (5)} In the first embodiment, each of first and second sub-ECUs 100 and 200 is formed integral with the drive circuits for driving respective electromagnetic valves and/or motor M 1 , M 2 . Namely, the circuit board integrally including the sub-ECU and the drive circuits can be used. Therefore, it is unnecessary to use harnesses for connecting the sub-ECU with the drive circuits (in hydraulic unit HU). Thereby, a downsizing in control system is realized to improve a flexibility in layout.
{circle around (6)} In the first embodiment, gear-type pump P 1 , P 2 is used as a fluid-pressure source provided independently of master cylinder M/C, and is adapted to supply fluid pressure directly to each wheel cylinder WC. By using gear-type pump P 1 , P 2 driven by motor M 1 , M 2 as a fluid-pressure source; fluid pressure can be introduced to each wheel cylinder WC without any intervening accumulator. Thereby, it is necessary to secure a space for mounting the accumulator inside the housing of hydraulic unit HU. Hence, the downsizing in control system can be further enhanced.
{circle around (7)} In the first embodiment, the amount of brake manipulation of a driver is determined from at least one of the sensed value of fluid pressure inside master cylinder M/C and the sensed value of pedal stroke. Main ECU 300 is configured to calculate the target wheel-cylinder pressure(s) on the basis of two of the sensed value of fluid pressure inside master cylinder M/C and the sensed value of the pedal stroke, and each sub-ECU is configured to calculate the backup target wheel-cylinder pressure(s) on the basis of only one of the sensed value of fluid pressure inside master cylinder M/C and the sensed value of pedal stroke. Thereby, the broader control unit calculates the normal target braking controlled variable(s) on the basis of the amount of brake manipulation obtained from two of the sensed value of fluid pressure inside master cylinder M/C and the sensed value of pedal stroke, while each of the subordinate control units calculates the backup target braking controlled variable(s) on the basis of the amount of brake manipulation obtained from only one of the sensed value of fluid pressure inside master cylinder M/C and the sensed value of pedal stroke. Therefore, the computing load in each subordinate control unit can be lightened to secure a reliable backup.
Next, a second embodiment according to the present invention will now be explained. FIG. 11 is a schematic system configuration view showing a brake-by-wire control system in a brake control apparatus according to the second embodiment. Components having the same reference marks as the first embodiment have same features as the first embodiment, and detailed explanations thereof will be omitted for the purpose of simplification of the disclosure.
[System Configuration]
The brake control apparatus according to the second embodiment is exemplified as a four-wheel brake-by-wire system, and includes four electrical calipers (electrical units) EU
As a control unit, the brake control apparatus includes a main control unit MCU (hereinafter also called “first control unit”) and sub-control units SCU
Sub-control units SCU
Each of four electrical units EU
Respective sub-control units SCU
[Main Control Unit]
Main control unit MCU is a broader central processing unit (CPU) that calculates target front-left braking force F*fl, target rear-right braking force F*rr, target front-right braking force F*fr, and target rear-left braking force F*rl for electrical calipers EU
Main control unit MCU receives a stroke signal S 1 derived from a first stroke sensor S/Sen 1 , a stroke signal S 2 derived from a second stroke sensor S/Sen 2 , and a pressing force (tread force) signal F of brake-pedal derived from a thrust sensor F/Sen.
Main control unit MCU also receives a signal indicative of vehicle speed (wheel speed) VSP, a signal indicative of yaw rate Y, and a signal indicative of longitudinal acceleration G. Main control unit MCU also receives a signal from a stop lamp switch STP.SW, so as to detect the manipulation (depression) of brake pedal BP by the driver without using stroke sensor signals S 1 and S 2 and brake-pedal pressing force signal F.
Two central processing units (CPUs), namely a first CPU MCU 1 and a second CPU MCU 2 , are provided in main control unit MCU for arithmetic calculations. First CPU MCU 1 is defined as a main main microcomputer (microprocessor), and second CPU MCU 2 is defined as a sub-microcomputer (sub-microprocessor) to construct a dual system. Thereby, these first and second CPUs MCU 1 and MCU 2 have a function of monitoring each other, so that fail-safe performance and safety performance of arithmetic device are enhanced.
Respective first and second CPUs MCU 1 and MCU 2 are connected to sub-control units SCU
As mentioned above, these CAN communications lines CAN 1 and CAN 2 are arranged respectively to cause two sub-control units (SCU
On the basis of the input information such as stroke signals S 1 and S 2 , tread force signal F, and signals of actual braking forces Ffl, Ffr, Frl, and Frr; first and second CPUs MCU 1 and MCU 2 calculate target braking forces F*fl, F*fr, F*rl, and F*rr, and output the calculated target braking forces F*fl to F*rr via CAN communications lines CAN 1 and CAN 2 to respective sub-control units SCU
Main control unit MCU functions to start up each of sub-control units SCU
During execution of vehicle dynamic-behavior control including anti-skid brake control (often abbreviated to “ABS”, which is executed for increasing or decreasing a braking force for wheel-lock prevention), vehicle dynamics control (often abbreviated to “VDC”, which is executed for increasing or decreasing a braking force to prevent side slip occurring due to instable vehicle behaviors), traction control (often abbreviated to “TCS”, which is executed for acceleration-slip suppression of drive wheels), and the like; input information such as vehicle speed (vehicle wheel speed) VSP, yaw rate Y, and longitudinal acceleration G is further extracted for executing the braking control concerning target braking forces F*fl, F*fr, F*rl, and F*rr. During the vehicle dynamics control (VDC), a warning buzzer BUZZ emits a buzzing sound cyclically to warn the driver or vehicle occupants that the VDC system comes into operation. A VDC switch VDC.SW serving as a man-machine interface is also provided so as to manually engage or disengage the VDC function in accordance with the driver's wishes.
[Sub-Control Unit]
Sub-control units SCU
As mentioned above, these first and second stroke sensors S/Sen 1 and S/Sen 2 are provided to enable to calculate the target braking forces (target controlled variables for brake control) for diagonally-positioned two road-wheels. Namely, the brake control apparatus according to this embodiment is configured to construct a dual sensor-signal system so that first and second stroke sensors S/Sen 1 and S/Sen 2 electrically construct a so-called diagonal split layout of sensor-signal system, sometimes termed “X-split layout”. By virtue of such layout, even when carrying out a fail-safe control by brake-by-wire control using only two road-wheels, the braking control securing stable vehicle behavior can be performed.
Each of sub-control units SCU
On the basis of the latest up-to-date informational data (more recent data) about driving amounts of motors and actual braking forces Ffl, Ffr, Frl, and Frr, the braking force control is performed to realize target braking forces F*fl, F*fr, F*rl, and F*rr (or backup target braking forces) by driving motors M