DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

[0022] A control device 1 has a proportional valve 2 as control valve, which is merely shown schematically in FIG. 1 . The proportional valve 2 has two adjustable throttles A, B, which can be adjusted by means of an operating handle 3 , which is also only shown schematically. The proportional valve 2 is connected with a high-pressure connection P and a low-pressure connection T. In the connection to the high-pressure connection P is arranged a compensation valve 4 , which has a return spring 5 prestressing the compensation valve 4 in the opening direction. For this purpose, the compensation valve 4 can, for example, have a slide, which is loaded by the return spring 5 in the opening direction. In the closing direction, the slide can be acted upon via the line 6 by a pressure at a point 7 between the compensation valve 4 and the throttle A. When the throttle A is closed, the pressure at the point 7 increases to a level, which closes the compensation valve 4 . When the throttle A is opened, the pressure at the point 7 is reduced, and the return spring 5 can open the compensation valve 4 further. For this reason, the compensation valve 4 can also be called pressure control valve or pressure balance valve.

[0023] The proportional valve 2 is connected with a motor 10 via working lines 8 , 9 . In the present case, the motor 10 consists of two part drives, both acting upon the wheels of a vehicle. The motor 10 is provided with a brake 11 , which can be released via a control line 12 . In the control line, the pressure rules behind the throttle A. As, in a manner not shown in detail, the proportional valve 2 can also lead the pressure from the high-pressure connection P via the throttle B to the motor 10 , a shuttle valve 13 is provided, which uses the highest pressure between the throttles A, B for releasing the brake 11 .

[0024] Additionally, the compensation valve 4 is acted upon by a load sensing pressure LS in the opening direction, that is, the load sensing pressure LS acts in the same direction as the return spring 5 . The return spring 5 produces a force, which, for example, corresponds to a pressure of 7 bars.

[0025] In the working line 8 is arranged a return compensation valve 14 , and in the working line 9 is arranged a return compensation valve 15 . Both return compensation valves 14 , 15 are acted upon in the opening direction by return springs 16 , 17 . Both return springs 16 , 17 produce a force, which corresponds to, for example, 8 bars. In the same direction acts a pressure in a load sensing connection LSA for the return compensation valve 14 and LSB for the return compensation valve 15 .

[0026] In the closing direction, the return compensation valve 14 is acted upon by a pressure at a point 18 between the proportional valve 2 and the return compensation valve 14 . In the same way, the return compensation valve 15 is acted upon in the closing direction by a pressure at a point 19 between the proportional valve 2 and the return compensation valve 15 .

[0027] An anti-cavitation valve arrangement 20 with an anti-cavitation valve 21 for the working line 8 and an anti-cavitation valve 22 for the working line 9 is connected with the low-pressure connection T via an anti-cavitation line 23 . However, between the low-pressure connection T and the anti-cavitation line 23 is arranged an additional parallel connection of a non-return valve 24 , which is prestressed by a spring 25 , and a non-return valve 26 . The non-return valve 26 has a magnetic drive 27 , which can switch the non-return valve from the open position shown to a closed position. In the closed position of the non-return valve 26 a refilling from the low-pressure connection T is not possible.

[0028] The control device 1 works as follows:

[0029] As long as the two throttles A, B of the proportional valve 2 are closed, the pressure 0 rules also in the load sensing connection LS, so that the brake 11 retains the motor 10 . As soon as the proportional valve 2 is activated, that is, the throttles A, B are opened, the pressure in the load sensing line LS increases, so that the brake 11 is released.

[0030] When the two throttles A, B of the proportional valve 2 are opened, the pressure at the point 7 decreases and the compensation valve 4 opens, so that hydraulic fluid can flow to the motor 10 through the return compensation valve 14 . The return compensation valve 14 is acted upon in the one direction by the pressure at point 18 , that is, by the pressure in the working line 8 . In the other direction, the return compensation valve 14 is, however, acted upon by the pressure at the load sensing connection LSA, which corresponds to the pressure after the throttle A (that is, also the pressure in the working line 8 ), so that the return compensation valve 14 is completely opened. In the same way, the return compensation valve 15 is completely opened. The return compensation valve 15 is acted upon in the closing direction by the pressure at point 19 , that is, by the pressure in the working line 9 . In the opening direction, the force of the return spring 17 and the pressure in the load-sensing connection LSB, which is at least as large as the pressure in the point 19 , act upon the return compensation valve 15 . Thus, the hydraulic fluid more or less unpreventedly reaches through the return compensation valve 15 and through the throttle B to the low-pressure connection T, flowing off through the non-return valve 26 , which is open. If the non-return valve 26 is closed, the hydraulic fluid can pass through the return valve 24 , when it can overcome the force of the spring 25 . This force, for example, corresponds to a pressure of 5 bars.

[0031] The vehicle driven in this way can now get into a situation, in which the motor 10 does not drive, but is driven. This is, for example, the case, when the vehicle drives down a slope or is braked from a certain speed. In this case, the motor supplies more hydraulic fluid into the working line 9 as it receives through the working line 8 from the high-pressure connection P. Accordingly, the pressure in the point 18 decreases. The return compensation valve 14 remains completely open. At the point 19 , however, the pressure increases, as the hydraulic fluid flowing off must pass through the throttle B, which with a large fluid amount causes an accordingly larger pressure drop. At the same time, the pressure in the load sensing line LSB (pressure between the throttle B and the low-pressure connection) is the tank pressure, so that the return compensation valve 15 is displaced to a more heavily throttled position against the force of the return spring 17 . The flow through the control device 1 , that is, the control of the motor 10 , thus still occurs via the proportional valve 2 . However, the fluid amount supplied to the proportional valve 2 is exclusively determined via the return compensation valve 15 and no longer through the compensation valve 4 on the inlet side of the proportional valve 2 .

[0032] This is described on the basis of the nominal flow lines shown in FIG. 2 . Upward is shown the flow F and to the right a deflection X of the slide of the proportional valve 2 . In other words, the value X also corresponds to the counter pressure, which the return compensation valves 14 , 15 or the compensation valve 4 , respectively, “experience” at the points 18 , 19 or 7 , respectively.

[0033] A nominal line 28 shows the behaviour of the compensation valve 4 , that is, the fluid amount in dependence of the position of the proportional valve 2 for the case, when the vehicle is driven via the motor 10 . Thus, the nominal flow line 28 is the nominal flow line of the compensation valve 4 .

[0034] A nominal flow line 29 , however, is the nominal flow line of the return compensation valves 14 , 15 . This is the same for both return compensation valves 14 , 15 . It shows the flow in dependence of the position of the proportional valve 2 for the case, when the vehicle drives the motor 10 .

[0035] It is obvious that the two nominal flow lines 28 , 29 are not congruent and that they do not intersect each other. On the contrary, they extend in parallel with each other. Thus, it is ensured that the fluid control through the control device 1 occurs either through the compensation valve 4 , namely with positive loads, or exclusively through one of the two return compensation valves 14 , 15 with negative loads.

[0036] When a negative load occurs, the non-return valve 26 is closed. In this case, the anti-cavitation valve arrangement 20 can no longer suck fluid from the low-pressure connection T. However, it can suck the required fluid via the line 23 from the low-pressure end of the throttle B via the valve 21 into the working line 8 , so that cavitation will not occur here. As, for a small distance, the hydraulic fluid can be led in a circle, a small energy saving will occur with negative loads. Mainly, however, an efficient refilling is achieved.

[0037] With the different nominal flow lines 28 , 29 , it is thus ensured that with a given slide deflection of the proportional valve 2 the flow is different in dependence of whether positive or negative loads are concerned. Thus, it is ensured that the compensation valve 4 on the one side and the return compensation valves 14 , 15 on the other side do not “fight” to find out, who is responsible. On the contrary, it is clearly defined that with a positive load exclusively the compensation valve 4 is responsible, whereas with a negative load exclusively one of the two return compensation valves 14 , 15 is responsible. In the simplest case, this can be achieved by means of different prestressing of the return springs 5 on the one side and 16 , 17 on the other side. For example, the spring 5 can be prestressed so that it corresponds to a pressure of 7 bars, whereas the springs 16 , 17 are prestressed so that they correspond to a pressure of 8 bars.

[0038] The two return compensation valves 14 , 15 can be combined to one component 30 . The component 30 can, for example, be arranged directly at the belonging proportional valve 2 . The component 30 only requires little space. It can also be arranged immediately next to the motor 10 .

[0039] In a manner of speaking, the anti-cavitation valve arrangement 20 fills the area between the two nominal flow lines 28 , 29 . Thus, it ensured that cavitation does not occur in the control device 1 .

[0040] FIG. 3 shows an embodiment of a control device, in which the same and corresponding parts have the same reference numbers.

[0041] The control device in FIG. 3 has an inlet module 31 , which is provided with a number of known valves (not shown), such as, pressure control valves and pressure relief valves. Via this inlet module 31 , the proportional valve 2 is connected with the high-pressure connection P, the compensation valve 4 being arranged in said connection.

[0042] The proportional valve 2 has three working positions a, b, c. In the shown position b, the proportional valve 2 is in the neutral position. In this case, the load sensing line LS is acted upon by the pressure in the low-pressure connection T. Accordingly, the brakes 11 are activated and the vehicle is braked.

[0043] When the slide of the proportional valve 2 is displaced to the position a, the high-pressure connection P is connected with the working line 9 and the low-pressure connection T with the working line 8 . At the same time, the load sensing line LSB is acted upon by the pressure at the point 19 and the load sensing line LSA is acted upon by the pressure at the low-pressure connection T. When in this case, in the position a of the proportional valve 2 , the motor is driving, hydraulic fluid under pressure from a pump 32 reaches the motor 10 via the high-pressure connection P, the compensation valve 4 , the proportional valve 2 , the working line 9 and the return compensation valve 15 . In this connection, the compensation valve 4 is controlled along the nominal flow line 28 ( FIG. 2 ), in dependence of how much the throttles of the proportional valve 2 are opened. The pressure at the point 19 also reaches the load sensing line LSB, whereas the load sensing line LSA is supplied with the pressure at the low-pressure connection T. Accordingly, under the influence of the pressure in the load sensing line LSB and the return spring 17 , the return compensation valve 15 is opened against the pressure at the point 19 . The “net” effect of this is that merely the force of the return spring 17 is effective. The return compensation valve 14 is completely opened, as the pressure at the point 18 substantially corresponds to the tank pressure, so that practically no force is effective in the closing direction.

[0044] When now the motor 10 is exposed to a negative load, for example, when the vehicle is to be braked from a certain speed, the vehicle thus driving the motor 10 , the amount of hydraulic fluid supplied through the motor 10 is larger than that supplied through the proportional valve 2 . Accordingly, the pressure at the point 18 increases, and the return compensation valve 14 controls the flow in accordance with the nominal flow line 29 ( FIG. 2 ). As the pressure at the point 7 decreases—the hydraulic fluid is practically sucked off through the motor 10 —the compensation valve 4 opens completely, so that the amount of fluid supplied to the proportional valve 2 is merely determined by the return compensation valve 14 . The compensation valve supplies the amount, it has always supplied. As, however, the return compensation valve 14 is now in charge, some oil will be missing, and this oil will be resupplied.

[0045] The non-return valve 26 is acted upon on the one side by the pressure at the low-pressure connection T and on the other side by the higher of the two pressures in the load sensing lines LSA, LSB. As stated above, the pressure in the load sensing line LSA is practically 0, that is, it corresponds to the pressure at the low-pressure connection T. Also the pressure in the load sensing line LSB drops, so that, when a negative load occurs, the non-return valve 26 is automatically moved to the closed position shown in FIG. 3 . The refilling via the anti-cavitation valve 22 is thus made with hydraulic fluid, which is taken from the low-pressure connection of the proportional valve 2 . The non-return valve is stressed by a return spring 34 , which, with correspondingly low pressures at the low-pressure connection T and in the load sensing lines LSA, LSB, displaces the non-return valve 26 to the shown position.

[0046] As mentioned above, the various nominal flow lines 28 , 29 can be realised in that the return compensation valves 14 , 15 are provided with stronger return springs 16 , 17 than the compensation valve 4 , which has a correspondingly weaker return spring 5 . However, it can also be ensured that the throttles in the proportional valve 2 , which lead from the high-pressure connection P to the motor 10 , have a larger flow resistance than the throttles, which carry hydraulic fluid from the motor 10 to the low-pressure connection P.

[0047] It is thus seen that this invention will accomplish at least all of its stated objectives.