Title:
CONTROL SYSTEM FOR HYDRAULIC MOTORS
United States Patent 3576104


Abstract:
A hydraulic control system for selectively operating a hydraulic motor in at least two operating speeds. The system including first and second pumps and a pilot valve having a fluid passage in communication with the first pump and the motor. First restrictive valve means provide restricted flow from the fluid passage to a first pilot flow passage and selectively communicate the fluid passage with a drain passage. Second restrictive valve means provide restricted flow from the second pump into a second pilot flow passage and selectively communicate the second pump with the fluid passage in the pilot valve and with the drain passage. The restrictive valve means are responsive to a main control valve effective to selectively communicate the first and second pilot flow passages to drain, thus providing for variable speed operation of the motor.



Inventors:
Kokaly, Joseph (Phoenix, AZ)
Schexnayder, Lawrence F. (Joliet, IL)
Application Number:
04/861627
Publication Date:
04/27/1971
Filing Date:
09/29/1969
Assignee:
CATERPILLAR TRACTOR CO.
Primary Class:
Other Classes:
91/6
International Classes:
F15B11/17; F16H61/40; F16H61/444; (IPC1-7): F15B15/18
Field of Search:
60/52 (HE)
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US Patent References:



Primary Examiner:
Geoghegan, Edgar W.
Claims:
We claim

1. A hydraulic control system for selectively driving a hydraulic motor in at least two operating speeds, comprising:

2. The invention of claim 1 wherein the first restrictive means comprises a spring loaded piston defining a restrictive orifice communicating the fluid passage with the first pilot flow passage and means for selectively communicating the fluid passage with the drain passage, the second restrictive means including a spring loaded piston defining a restrictive orifice for communicating outlet fluid from the second source with the second pilot flow passage and means for selectively communicating outlet fluid from the second source with the fluid passage and the drain passage respectively.

3. The invention of claim 2 wherein the main control valve is operable into a neutral position wherein both of the pilot flow passages are in communication with drain, a low-speed operating position wherein the first pilot flow passage is blocked and a high-speed operating position wherein both pilot flow passages are blocked from drain.

4. The invention of claim 3 further comprising relief valve means in effective communication with the fluid passage to relieve excessive hydraulic fluid pressure therein.

5. The invention of claim 1 wherein the main control valve is operable into a neutral position wherein both of the pilot flow passages are in communication with drain, a low-speed operating position wherein the first pilot flow passage is blocked and a high-speed operating position wherein both pilot flow passages are blocked from drain.

6. The invention of claim 5 further comprising relief valve means in effective communication with the fluid passage to relieve excessive hydraulic fluid pressures therein.

7. The invention of claim 1 further comprising a common drain reservoir for the two fluid sources and the motor, a single conduit communicating the fluid passage with the motor and a separate single conduit communicating the motor with the drain reservoir.

8. The invention of claim 7 wherein the main control valve is operable into a neutral position wherein both of the pilot flow passages are in communication with drain, a low-speed operating position wherein the first pilot flow passage is blocked and a high-speed operating position wherein both pilot flow passages are blocked from drain.

9. The invention of claim 8 further comprising an additional inlet conduit in communication with the conduit from the fluid passage to the motor for introducing additional fluid under pressure and providing for additional variation in operation of the motor.

10. The invention of claim 1 further comprising an additional inlet conduit in effective communication with the fluid passage for selectively introducing additional fluid under pressure and providing for additional variation in operation of the motor.

Description:
The present invention relates to a control system for selectively driving a hydraulic motor in at least two operating speeds. More particularly, the invention provides restrictive valve means which are responsive to a main control valve and are respectively associated with two sources of fluid under pressure for selectively delivering fluid under pressure from the two sources to a motor while preferably delivering excess fluid directly to drain.

Control systems of this type are commonly employed, for example, to operate various hydraulic motors and implements on machinery such as earth moving equipment. The hydraulic motors for such equipment are often in a relatively remote location from pumps which provide fluid under pressure to the control system. It is particularly desirable to minimize the number and size of fluid conduits communicating the pumps in the control system with the relatively remote motor. This is particularly important in articulated machinery where the pumps are located on one articulated section of the machine and the motor or motors are located on another articulated section with swivel joints commonly provided at the articulated intersection of the machine for each of the fluid conduits.

Additionally, implements and hydraulic motors which may be operated by the present control system are often operated only intermittently. The control system returns output fluid from the pumps to a drain reservoir during intervals when the motor is not operated. In many prior art control systems of the type presently contemplated, this return flow of outlet fluid from the pumps is commonly delivered to a drain passage over a main control spool and provides an undesirable source of heat generation.

Accordingly, it is an object of the present invention to provide a hydraulic control system for eliminating or minimizing one or more of the problems discussed above.

It is another object of the invention to provide a hydraulic control system for selectively communicating one or more hydraulic pumps with a motor.

It is a further object to provide for substantially direct communication of any excess pump outlet fluid to a suitable drain passage.

It is a still further object in such a control system to employ restrictive valve means which are responsive to a main control valve for respectively communicating fluid pumps with the motor and with a suitable drain passage .

Additional objects and advantages of the present invention are made apparent in the following description having reference to the accompanying drawing.

The drawing is a schematic representation, with parts shown in section, of a control system for selectively operating a hydraulic motor.

Referring now to the drawing, operating communication of a pair of hydraulic pumps 11 and 12 with a hydraulic motor 13 is selectively controlled by a pilot valve assembly indicated at 14. The pumps 11 and 12 provide two sources of fluid under pressure which are selectively communicated with the motor 13 to provide for variable speed of the motor. Operation of the pilot valve assembly 14 for selectively communicating the pumps with the motor is in turn regulated by a main control valve indicated at 16.

The pilot valve assembly 14 includes restrictive valves 17 and 18 which are respectively associated with the pumps 11 and 12 in a manner more fully described below. The restrictive valves 17 and 18 provide restricted fluid flow into first and second pilot flow passages 19 and 21. The pilot flow passages are in selective communication with a drain passage 22 across the main control valve 16 so that the restrictive valves 17 and 18 are made responsive to positioning of the main control valve 16.

To briefly set forth operation of the components summarized above, outlet fluid from the first pump 11 in a conduit 23 is in communication with the motor 13 and with a fluid passage 24 formed by a housing 26 in the pilot valve assembly 14. The housing 26 also forms a drain passage 27 which is in communication with a common drain reservoir 28 by means of a conduit 29. The first restrictive valve 17 permits restricted fluid flow from the fluid passage 24 into the first pilot passage 19. The restrictive valve means 17 is responsive to the main control valve 16 for either communicating the fluid passage 24 with the drain passage 27 or for blocking communication between those two passages so that fluid under pressure in the passage 24 is caused to operate the motor 13.

The second restrictive valve 18 provides restricted fluid flow from the second pump 12 through a conduit 31 into the second pilot flow conduit 21. The second restrictive valve 18 is responsive to the control valve for either communicating the second pump outlet fluid to the drain passage 27 or alternatively to the fluid passage 24 where it is combined with fluid from the pump 11 to operate the motor 13 at a higher speed.

Additional fluid under pressure may also be delivered to the motor 13 through a conduit 32, from a source of fluid under pressure (not shown), to provide for still greater variation in the operating speed for the motor 13.

In many applications, the motor 13 is located in a relatively remote location from the pumps 11, 12 and the pilot valve assembly 14 of the drawing. It is particularly noted that the remote motor 13 is in communication with the pumps 11, 12 and pilot valve assembly 14 by a common conduit indicated at 33 and with the common drain reservoir 28 by another conduit indicated at 34. The conduits 32, 33 and the conduit 34 are shown in respective communication with the motor 13 across swivel joints indicated at 36 and 37 respectively as would be necessary on an articulated vehicle or machine (not shown) of the type discussed above. A bypass or check valve 38 is also associated with the motor 13 to conventionally prevent cavitation within the motor during overrunning conditions.

To describe various portions of the control system in greater detail, the main control valve 16 includes a spool 41 reciprocably mounted within a bore 42 formed by a valve body partially shown at 43. The valve body 43 also defines a manifold passage 44 which is in communication with the drain passage 27 in the valve assembly 14, and accordingly, the common reservoir 28 by means of a drain conduit 22. The manifold or drain passage 44 is also in communication with opposite ends of the bore 42 by means of annular recesses 47 and 48. The pilot flow passages 19 and 21 are in communication with the bore 42 by means of annular recesses 51 and 52 located respectively adjacent the annular recesses 47 and 48. The control valve spool 41 includes slots 53 and 54 which are selectively effective for respectively communicating with pilot flow passages 19 and 21 with the drain passage 44 through the annular recesses 47 and 48.

When the spool of the main control valve 16 is in a neutral position, N, to the left of its position shown in the drawing, the slots 53 and 54 respectively communicate the annular recesses 51 and 52 with the drain passage 44 through the annular recesses 47 and 48. As the spool is shifted rightwardly toward the position shown in the drawing, as indicated at L, it provides for low speed operation of the motor 13 as the slot 53 passes out of communication with the annular recess 51 and the slot 54 remains in communication with both of the annular recesses 48 and 52. As the spool 41 is shifted into its high-speed operating position shown in the drawing and indicated at H, the slot 54 also passes out of communication with the annular recess 48 to block the second pilot flow passage 21. As will be discussed in greater detail below, fluid from the first pump 11 is delivered to the motor 13 when the spool 41 is in its low-speed position while fluid from both pumps 11 and 12 is delivered to the motor 13 when the spool 41 is in its high-speed position.

The restrictive valve 17 includes a spring loaded piston 61 reciprocably mounted within a bore 62. The position 61 forms a restrictive orifice 63 which communicates the fluid passage 24 with the first pilot flow passage 19. Differential pressure caused by flow of fluid from the passage 24 through the orifice 63 produces a resultant upward force upon the piston 61 so that the piston shifted upwardly from its position shown in the drawing. With the piston 61 in its upward position, a plurality of ports 64, defined by the piston 61, communicates fluid from the passage 24 into the drain passage 27. This condition occurs when the control valve spool 41 is in its neutral position and the slot 53 is disposed to communicate fluid from the first pilot flow passage to drain.

As the control valve spool 41 is shifted into its low-speed position, the first pilot flow passage 19 is blocked, thus eliminating the pressure differential across the orifice 63 so that the piston is shifted downwardly into the position shown in the drawing by its spring. In that condition, the fluid passage 24 is isolated from the drain passage 27 and outlet fluid from the pump 11 is directed through the conduit 33 for operation of the motor 13.

The second restrictive valve 18 also includes a spring loaded piston 71 reciprocably arranged within a bore 72 and forming a restrictive orifice 73 which communicates fluid from the second pump outlet conduit 31 into the second pilot flow passage 21. When the second pilot flow passage is in communication with drain across the control valve 16, the piston 71 is similarly shifted upwardly from its position shown in the drawing by a differential pressure caused by the orifice 73. With the piston 71 in its upwardly shifted position, it communicates a substantial portion of fluid flow from the conduit 31 into the drain passage 27 through a plurality of ports 74 formed in the piston 71.

When the control valve spool 41 is shifted into its high-speed operating position shown in the drawing, the second pilot flow passage 21 is isolated from drain and eliminates the pressure differential across the orifice 73. Accordingly, the spool 71 is shifted downwardly by its spring to the position shown in the drawing. In that position, fluid from the conduit 31 is delivered into the fluid passage 24 by a plurality of ports 76 also formed in the piston 71. Fluid from the second pump 12 is then combined in the fluid passage 24 with fluid from the pump 11. Outlet fluid from both pumps is accordingly delivered to the motor 13 through the conduit 33 to achieve high speed operation of the motor 13.

The axial distance between the sets of ports 74 and 76 is selected such that they are momentarily in simultaneous communication with the fluid passage 24 and the drain passage 27. Loss of fluid from the passage 24 into the drain passage 27 during shifting of the piston 71 is substantially eliminated by the arrangement of the ports 74 and 76 in the piston 71, thus permitting efficient combination of the output from both pumps through the valve arrangement of the present invention.

A poppet valve 81 is also arranged within the housing 26 in communication with the first pilot flow passage 19 to provide for communication between the fluid passage 24 and the drain passage 27 across the restrictive valve 17 in the event that excessive pressures develop within the fluid passage 24. The poppet valve 81 thus protects the pilot valve assembly 14 as well as the pumps 11, 12 and the motor 13 from damage due to hydraulic overpressures.

A hydraulic control system is accordingly disclosed for providing variable speed operation of the motor 13. It is noted that the pilot valve assembly 14 and the pumps 11, 12 are in communication with the motor 13 through a single conduit 33. The only other conduit providing communication with the motor 13 is the conduit 34 which carries low pressure fluid to the drain reservoir 28. Further, the pilot valve assembly 14, is in communication with the main control valve 16 only by the low pressured drain conduit 22 and the first and second pilot flow passages 19, 21 which are designed to carry a minimum rate of fluid flow. Additionally, substantially excess fluid from the pumps 11 and 12 which is not employed to operate the motor 13 is delivered directly to drain through the respective valves 17 and 18.