US20060198736A1

US20060198736A1 - Pump control system for variable displacement pump

Info

Publication number: US20060198736A1
Application number: US11/067,689
Authority: US
Inventors: Paul Rousseau
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2005-03-01
Filing date: 2005-03-01
Publication date: 2006-09-07

Abstract

A pump control system has pump-displacement controls configured to selectively activate and deactivate a predetermined pump-displacement limit between physical displacement limits of a variable-displacement pump. The pump-displacement controls may be configured to adjust an operating displacement of the variable-displacement pump within a range bounded by the predetermined pump-displacement limit when the predetermined pump-displacement limit has been activated. Further, the pump-displacement controls may be configured to adjust the operating displacement of the variable-displacement pump without restriction from the predetermined pump-displacement limit when the predetermined pump-displacement limit has been deactivated.

Description

TECHNICAL FIELD

The present disclosure relates to variable-displacement pump for a work machine and, more particularly, to a pump control system for the variable-displacement pump.

BACKGROUND

Work machines, such as hydraulic excavators, wheel loaders, off-highway trucks and other heavy construction and mining machines, are used to perform many tasks. To effectively perform these tasks, a work machine requires a power source such as a diesel engine, a gasoline engine, a natural gas engine, a turbine engine or any other type of power source that provides the power required to complete these tasks. Such work machines often include various hydraulically-powered implements or hydraulic drive motors for performing the tasks of the work machine.
Generally, work machines include a pump operatively coupled to the power source for producing a flow of pressurized hydraulic fluid to power implements or drive motors of the machine. In many work machines, the pump is a variable-displacement pump. Control systems of these machines adjust the fluid volume displaced by the pump each cycle based on various operating conditions of the work machine. For example, the control systems may increase the displacement of the hydraulic pump in response to increased power needs of various work machine implements. Increasing the displacement of the pump also increases the load the pump places on the power source, which may adversely affect operation of the power source. In some circumstances, if a variable-displacement pump is operated at a relatively high displacement, the power requirements of the pump may exceed the power capacity of the power source.
At least one pump control system has been constructed with provisions for controlling a variable-displacement pump to avoid placing undesirably high power loads on its power source. For example, U.S. Pat. No. 6,010,309 (“the '309 patent”) by Fujitoshi Takamura, issued on Jan. 4, 2000, shows a pump control system that controls the absorption torque of a variable-displacement pump dependant upon the speed of the engine powering the pump. The pump control system of the '309 patent includes a number of interconnected control valves that control the swash plate angle of the variable-displacement pump by controlling the flow of hydraulic fluid to a servo piston connected to the swash plate. A controller of the pump control system delivers a control current to one of the control valves, and the control valves collectively control the angle of the swash plate to maintain a constant absorption torque. According to the '309 patent, the magnitude of the torque depends on the value of the control current. Thus, the control current and the resulting absorption torque of the variable displacement pump are a continuous function of the speed of the engine powering the pump. This accommodates the engine's different torque capacity at different operating speeds.
Although the pump control system of the '309 patent prevents the variable-displacement pump from overwhelming the engine at low engine speeds, the design includes disadvantages. For instance, the pump control system requires a great deal of tuning to make it function as intended. Determining the appropriate operating characteristics of each valve, spring, and plumbing connection to provide continuously-variable control of the absorption torque of the variable-displacement pump would be labor-intensive and costly. A designer would further have to expend significant resources in calibrating the appropriate control current that the controller should provide for each engine speed to produce the desired absorption torque for that engine speed. The complexity of the design also increases the probability that minor changes in operating conditions will cause aberrant performance.
The drive system of the present disclosure solves one or more of the problems set forth above.

SUMMARY OF THE INVENTION

One disclosed embodiment includes a pump control system for a variable-displacement pump. The pump control system may include pump-displacement controls configured to selectively activate and deactivate a predetermined pump-displacement limit between physical displacement limits of the variable-displacement pump. The pump-displacement controls may also be configured to adjust an operating displacement of the variable-displacement pump within a range bounded by the predetermined pump-displacement limit when the predetermined pump-displacement limit has been activated. Further, the pump-displacement controls may be configured to adjust the operating displacement of the variable-displacement pump without restriction from the predetermined pump-displacement limit when the predetermined pump-displacement limit has been deactivated.
Another embodiment relates to a method of controlling a variable-displacement pump. The method may include selectively activating and deactivating a predetermined pump-displacement limit between the physical displacement limits of the variable-displacement pump. The method may also include adjusting an operating displacement of the variable-displacement pump within a range bounded by the predetermined pump-displacement limit when the predetermined pump-displacement limit has been activated. Further, the method may include adjusting the operating displacement of the variable-displacement pump without restriction from the predetermined pump-displacement limit when the predetermined pump-displacement limit has been deactivated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of a work machine with which the pump control system consistent with one disclosed embodiment may be utilized;
FIG. 2 is a schematic illustration of a variable-displacement pump and a pump control system according to one disclosed embodiment; and
FIG. 3 is a flow chart illustrating a method of operation of a pump control system according to one embodiment of the present disclosure.

DETAILED DESCRIPTION

FIG. 1 provides a diagrammatic perspective view of a work machine 10. Work machine, as the term is used herein, refers to a fixed or mobile machine that performs some type of operation associated with a particular industry, such as mining, construction, farming, etc. and operates between or within work environments (e.g., construction site, mine site, power plants, etc.). Non-limiting examples of mobile machines include commercial machines, such as trucks, cranes, earth moving vehicles, mining vehicles, backhoes, material handling equipment, farming equipment, marine vessels, aircraft, and any type of movable machine that operates in a work environment. Work machine 10 may include a power source 12, a variable-displacement pump 14, a pump control system 16, and a hydraulic load 18.
The power source 12 may be an engine such as a diesel engine, a gasoline engine, or a natural gas engine operable to generate a power output. In one embodiment, variable-displacement pump 14 may be operatively connected to power source 12. Variable-displacement pump 14 may be any type of positive-displacement pump with provisions for controlling the amount of fluid displaced per cycle. For example, variable-displacement pump 14 may have a swash plate for adjusting the displacement per cycle. Alternatively, variable-displacement pump 14 may be a bent-axis piston type pump or a variable-vane type pump. Pump control system 16 is operatively connected to variable-displacement pump 14 and is configured to control the operating displacement of variable-displacement pump 14.
Hydraulic load 18 may be operatively connected to variable-displacement pump 14. Hydraulic load 18 may be a hydraulically-powered implement with hydraulic motors or actuators, as is shown in FIG. 1. Alternatively, hydraulic load 18 may be a drive system for work machine 10. Additionally, hydraulic load 18 may be an integral part of work machine 10, or it may be a detachable accessory.
FIG. 2 shows variable-displacement pump 14 and pump control system 16 consistent with one disclosed embodiment. As shown, pump control system 16 may include pump-displacement controls 20 with displacement-control actuators 22 operatively connected to variable-displacement pump 14 and movable to control the operating displacement of variable-displacement pump 14. Displacement-actuator controls 24 may be operatively connected to the displacement-control actuators 22. Pump-displacement controls 20 may also include a displacement stop 26 and displacement-stop controls 28 operatively connected thereto.
Displacement-control actuators 22 may include a displacement-actuator piston 30 disposed within a cylinder 32 and a connecting rod 34 operatively connecting displacement-actuator piston 30 to a swash plate 36 of variable-displacement pump 14. Displacement-control actuators 22 may be any type of controllable and moveable actuators that can adjust the operating displacement of variable-displacement pump 14. In one embodiment, displacement-control actuators 22 may include one or more rotary or linear electric motors, rotary hydraulic motors, or pneumatic actuators in place of, or in addition to, a hydraulic cylinder and piston.
Displacement-actuator controls 24 provide control for variable-displacement pump 14. Displacement-actuator controls 24 may include a first hydraulic line 38 that provides fluid to one side of displacement-actuator piston 30 and a second hydraulic line 40 that provides fluid to the other side of displacement-actuator piston 30. Displacement-actuator controls 24 may also include displacement-control valves 42 operatively connected to second hydraulic line 40. Displacement-actuator controls 24 may be any controls configured to automatically control the position of displacement-control actuators 22 or to provide manual control of the position of displacement-control actuators 22.
Displacement stop 26 may be a limit-activating piston disposed within cylinder 32. Displacement stop 26 and the portion of cylinder 32 that hosts stop 26 have a stepped diameter. In other words, displacement stop 26 has a small-diameter portion and a large-diameter portion and cylinder 32 has a small-bore portion and a large-bore portion. An annular shoulder 44 positioned between the small-bore and large-bore portions of cylinder 32 forms a first stop for displacement stop 26, and an end cap 46 of cylinder 32 forms a second stop for displacement stop 26. When displacement stop 26 is positioned against annular shoulder 44, it is disposed within the travel path of displacement-actuator piston 30. When displacement stop 26 is positioned against end cap 46, it may be disposed outside the travel range of displacement-actuator piston 30, as dictated by the travel limits of swash plate 36.
Displacement stop 26 may have many different constructions than that shown in FIG. 2. For example, displacement stop 26 may be any component that can be moved from a first position to a second position in the travel path of displacement-control actuator 22. Displacement stop 26 may be moveable between a first position located outside the travel path of displacement-control actuator 22 to a second position located within the travel path of displacement-control actuator 22. Alternatively, displacement stop 26 may be movable between a first position at a first point in the travel path of displacement-control actuator 22 and a second position at a second point in the travel path of displacement-control actuator 22.
Displacement stop 26 is not limited to the configuration shown in FIG. 2. For example, displacement stop 26 may be supported separately from displacement-control actuators 22. Additionally, displacement stop 26 and displacement-control actuators 22 may be movable in the same direction or in different directions.
In certain embodiments, pump control system 16 may omit a physical displacement stop 26. In such embodiments, displacement-actuator controls 24 may be configured with control logic that includes a predetermined pump-displacement limit that may be selectively activated.
Displacement-stop controls 28 may also include a third hydraulic line 48, a fourth hydraulic line 50, a fifth hydraulic line 52, and a valve 54. Third hydraulic line 48 may be connected between the output of variable-displacement pump 14 and valve 54. Fourth hydraulic line 50 may be connected between valve 54 and an opening in end cap 46 of cylinder 32. Fifth hydraulic line 52 may be connected between valve 54 and a reservoir 56. Valve 54 may have two positions. In the first position, valve 54 blocks third hydraulic line 48 and connects fourth hydraulic line 50 to fifth hydraulic line 52. In the second position, valve 54 connects third hydraulic line 48 to fourth hydraulic line 50 and blocks fifth hydraulic line 52.
Displacement-stop controls 28 are not limited to the configuration shown in FIG. 2. For example, while FIG. 2 shows valve 54 in a remote position from variable-displacement pump 14, valve 54 may be an integral part of variable-displacement pump 14. In such embodiments, in place of one or more of third, fourth, and fifth hydraulic lines 48, 50, and 52, a housing of variable-displacement pump 14 may define one or more integral channels connecting valve 54 to the output of variable-displacement pump 14, the opening in end cap 46, and/or reservoir 56. Additionally, instead of the output of variable-displacement pump 14, valve 54 may connect to some other source of pressurized fluid.
Displacement-stop controls 28 may also include a computer 58 operatively connected to valve 54. Computer 58 may also be communicatively linked to power source 12 and configured to monitor the speed of power source 12 (e.g., engine speed). Computer 58 may include one or more processors and memory devices (not shown). Computer 58 may be a dedicated controller for pump control system 16, a dedicated controller for power source 12 (e.g., an ECU), or any other controller for monitoring and controlling one or more systems of work machine 10. The control logic of computer 58 may be configured to control the position of valve 54, dependent upon operating conditions of work machine 10.
Displacement-stop controls 28 may be any type of controls configured to selectively effect movement of displacement stop 26 from a first position to a second position in the travel path of a displacement-control actuator 22 and to selectively effect or allow movement back from the second position to the first. Depending on the configuration of displacement-control actuators 22 and displacement stop 26, displacement-stop controls 28 may implement different configurations. For example, a switch may replace valve 54 when displacement-stop controls 28 utilize electrical energy, instead of hydraulic energy, to move displacement stop 26. Similarly, displacement-stop controls 28 may include hardwired program logic in place of computer 58. Moreover, in addition to, or in place of, electric controls, displacement-stop controls 28 may include mechanical, hydraulic, and/or pneumatic logic systems for monitoring one or more parameters of work machine 10, such as the speed of power source 12, and control the position of valve 54. For example, displacement-stop controls 28 may include a mechanical actuator driven by centrifugal forces to open and close a valve to allow or prevent flow of pressurized fluid to a hydraulic actuator operable to move valve 54 between its first position and its second position. Additionally displacement-stop controls 28 may be configured to receive user-initiated inputs for manual control of displacement stop 26.

INDUSTRIAL APPLICABILITY

The disclosed embodiments have potential application in any type of work machine 10 including a variable-displacement pump 14 for providing power to a hydraulic load 18. The operation of a work machine 10 with a pump control system 16 according to the disclosed embodiments are described below.
In one embodiment, power source 12 drives variable-displacement pump 14. Pump control system 16 adjusts the operating displacement of variable-displacement pump 14 dependant upon operating conditions of work machine 10, such as the power requirements of hydraulic load 18. Hydraulic load 18 receives a flow of pressurized hydraulic fluid from variable-displacement pump 14 and performs tasks of work machine 10.
To better describe these embodiments, FIG. 3 shows a flow chart 60 of a pump control system operation method. At step 62, computer 58 may determine whether the speed of power source 12 is below a first predetermined level, such as a speed below which power source 12 is considered to be operating at idle speed. If the speed of the power source 12 is below the first predetermined level, at step 64, computer 58 activates a predetermined pump-displacement limit by controlling valve 54 to its second position. This process results in the connection of third hydraulic line 48 to fourth hydraulic line 50. Pressurized hydraulic fluid flows from the output of variable-displacement pump 14 and drives displacement-stop 26 against annular shoulder 44 of cylinder 32, where displacement stop 26 is within the travel path of displacement-actuator piston 30. This position of displacement stop 26 causes a predetermined limit on the range of motion of displacement-actuator piston 30. This, in turn, imposes a predetermined limit on the operating displacement of variable-displacement pump 14.
In response to changes in the power requirements of hydraulic load 18, displacement-actuator controls 24 may adjust the operating displacement of variable-displacement pump 14 within a range bounded by the predetermined pump-displacement limit (step 66). Displacement-actuator controls 24 adjust the operating displacement of variable-displacement pump 14 by controlling the difference in hydraulic pressure acting on opposite sides of displacement-actuator piston 30. This controls the position of displacement-actuator piston 30. Displacement stop 26, which is held against annular shoulder 44 by hydraulic pressure, limits movement of displacement-actuator piston 30 to a particular position. This limit on the position of displacement-actuator piston 30 limits the range within which displacement-actuator controls 24 can adjust the operating displacement of variable-displacement pump 14. For instance, in the embodiment shown in FIG. 2, rightward movement of displacement-actuator piston 30 increases the operating displacement of variable-displacement pump 14. Additionally, in the embodiment shown in FIG. 2, when hydaulic pressure holds displacement stop 26 against annular shoulder 44, displacement stop 26 may limit rightward movement of displacement-actuator piston 30. As a result, the predetermined pump-displacement limit imposed by displacement stop 26 is a maximum limit on the operating displacement of variable-displacement pump 14.
At step 68, computer 58 may determine whether the speed of power source 12 is above a second predetermined level. In one embodiment, the second predetermined level may be higher than the first predetermined level described above in connection with step 62. If the speed of power source 12 is above the second predetermined level, computer 58 deactivates the predetermined pump-displacement limit (step 70). To do so, computer 58 may direct valve 54 to return to its first position. This connects fourth hydraulic line 50 to fifth hydraulic line 52, which provides a path for hydraulic fluid to flow out end cap 46 to reservoir 56. In its first position, valve 54 also blocks pressurized hydraulic fluid from third hydraulic line 48. Thus, following step 70, displacement-actuator piston 30 may move displacement stop 26 because hydraulic fluid between displacement stop 26 and end cap 46 may escape to reservoir 56. Following step 70, control returns to step 62. If, however, computer 58 determines that the speed of power source 12 is not above the second predetermined level, control returns to step 66 (step 68; NO).
Returning to step 62, if computer 58 determines that the speed of power source 12 is not below the first predetermined level (step 62; NO), control proceeds to step 72. At step 72, displacement-actuator controls 24 adjust the operating displacement of variable-displacement pump 14 in a manner similar to that described above in connection with step 66, except displacement stop 26 does not impose a limit on the operating displacement. Following step 72, control returns to step 62.
Operating pump-displacement controls 20 according to the method of FIG. 3 accommodates the changing needs of hydraulic load 18 without imposing undesirably high loads on power source 12. Displacement-actuator controls 24 adjust the operating displacement of variable-displacement pump 14 to accommodate changing needs of hydraulic load 18. If allowed to adjust the operating displacement unchecked, however, displacement-actuator controls 24 may cause variable-displacement pump 14 to impose undesirably high power loads on power source 12. For example, power source 12 may have reduced power capacity at low speed and variable-displacement pump 14 may load power source 12 beyond this reduced power capacity if operated at its maximum displacement. Activating a predetermined pump-displacement limit in accordance with disclosed embodiments may prevent displacement-actuator controls 24 from unduly loading power source 12 at low speeds.
The disclosed embodiments of pump control system 16 and methods of its operation provide a particularly simple, cost-effective, and dependable way to avoid unduly loading power source 12 with variable-displacement pump 14. Operating pump control system 16 in accordance with the disclosed embodiments enables relatively simple tuning of displacement-stop controls 28. For instance, a user may determine a set of operating conditions that trigger the predetermined pump-displacement limit and the corresponding predetermined pump-displacement limit values. For example, when power source 12 operates at speeds below 1300 RPM it may only provide sufficient power to operate variable-displacement pump 14 at 75% of its displacement capacity. In such a case, displacement-stop controls 28 may be configured to activate a predetermined pump-displacement limit of 75% of maximum capacity whenever power source 12 operates at a speed below 1300 RPM. Because methods consistent with the disclosed embodiments require limited development efforts and are easily integrated with known pump control systems, configuring pump control system 16 to operate according to the disclosed methods is relatively inexpensive.
Operation of pump-displacement controls 20 is not limited to the embodiments described above in connection with FIG. 3. For example, in addition to, or in place of, activating a predetermined pump-displacement limit that is a maximum limit on the operating displacement of variable-displacement pump 14, pump-displacement controls 20 may activate a predetermined pump-displacement limit that is a minimum limit on the operating displacement of variable-displacement pump 14.
While the embodiments described above in connection with FIG. 3 activate and deactivate the predetermined pump-displacement limit based on the speed of power source 12, the triggering conditions may involve other parameters. For example, in addition to, or in place of the speed of power source 12, pump control system 16 may activate and deactivate the predetermined pump-displacement limit dependant upon other conditions related to operation of power source 12. Pump control system 16 may also be configured to activate and deactivate a predetermined pump-displacement limit dependant upon conditions unrelated to power source 12, such as operating conditions of other systems of work machine 10. For example, pump control system 16 may be configured to activate a predetermined pump-displacement limit when other systems of work machine 10 have operating states that impose elevated power loads on power source 12. Additionally, pump control system 16 may activate a predetermined pump-displacement limit when hydraulic load 18 has an operating state that requires precise control of the flow rate of pressurized fluid from variable-displacement pump 14.
Further, while the embodiments described above in connection with FIG. 3 include automatic activation of a predetermined pump-displacement limit by computer 58, other configurations may be implemented. For instance, the embodiments may include control components other than computer 58 that automatically activate or deactivate the predetermined pump-displacement limit. Moreover, the disclosed embodiments may allow a user to manually activate and deactivate a predetermined pump-displacement limit through manipulation of a switch, valve, or other user-controlled component. Additionally, embodiments may include activating a predetermined pump-displacement limit without a physical displacement stop 26. For example, a computer that directly controls displacement-control actuator 22 may activate a predetermined pump-displacement limit within the computer's control logic, negating the need for a physical displacement stop 26.
It will be apparent to those skilled in the art that various modifications and variations can be implemented with pump control system 16 without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the pump control system disclosed herein. It is intended that the disclosure of these embodiments be considered as exemplary only, with a true scope of the disclosed embodiments being indicated by the following claims and their equivalents.

Claims

1. A pump control system for a variable-displacement pump powered by a power source, comprising:

pump-displacement controls configured to:

selectively activate and deactivate a predetermined pump-displacement limit between physical displacement limits of the variable-displacement pump;

adjust an operating displacement of the variable-displacement pump within a range bounded by the predetermined pump-displacement limit when the predetermined pump-displacement limit has been activated; and

adjust the operating displacement of the variable-displacement pump without restriction from the predetermined pump-displacement limit when the predetermined-pump displacement limit has been deactivated.

2. The pump control system of claim 1, wherein the pump-displacement controls automatically activate the predetermined pump-displacement limit in response to a predetermined condition.

3. The pump control system of claim 2, wherein the predetermined condition relates to operations of the power source.

4. The pump control system of claim 2, wherein the predetermined condition includes the power source operating outside a predetermined speed range.

5. The pump control system of claim 2, wherein the predetermined condition includes the power source operating at idle speed.

6. A method of controlling a variable-displacement pump that is powered by a power source, the method including:

selectively activating and deactivating a predetermined pump-displacement limit between physical displacement limits of the variable-displacement pump;

adjusting an operating displacement of the variable-displacement pump within a range bounded by the predetermined pump-displacement limit when the predetermined pump-displacement limit has been activated; and

adjusting the operating displacement of the variable-displacement pump without restriction from the predetermined pump-displacement limit when the predetermined-pump displacement limit has been deactivated.

7. The method of claim 6, wherein pump-displacement controls automatically activate the predetermined pump-displacement limit in response to a predetermined condition.

8. The method of claim 7, wherein the predetermined condition relates to operations of the power source.

9. The method of claim 7, wherein the predetermined condition includes the power source operating outside a predetermined speed range.

10. The method of claim 7, wherein the predetermined condition includes the power source operating at idle speed.

11. The method of claim 6, wherein selectively activating the predetermined pump-displacement limit includes activating a displacement stop to move from a first position to a second position that is in a travel path of a displacement-control actuator, wherein the displacement-control actuator is movable to adjust the operating displacement of the variable-displacement pump.

12. The method of claim 11, wherein the displacement stop includes a limit-activating piston, and selectively activating the predetermined pump-displacement limit includes moving the displacement stop from the first position to the second position by supplying pressurized fluid to the limit-activating piston.

13. The method of claim 12, wherein the displacement-control actuator is a displacement-actuator piston disposed within a cylinder, at least a portion of the limit-activating piston is also disposed within the cylinder, and selectively activating the predetermined pump-displacement limit includes moving the displacement stop from the first position to the second position by supplying pressurized fluid to the limit-activating piston and moving the limit-activating piston toward the displacement-actuator piston.

14. The method of claim 11, wherein selectively activating the predetermined pump-displacement limit includes pump-displacement controls moving the displacement stop from the first position to the second position in response to a predetermined condition.

15. A pump control system for a variable-displacement pump powered by a power source of a work machine, comprising:

a displacement-control actuator movable to adjust the operating displacement of the variable-displacement pump;

a displacement stop movable between a first position and a second position that is in a travel path of the displacement-control actuator; and

displacement-stop controls configured to:

activate a predetermined pump-displacement limit by moving the displacement stop from the first position to the second position in response to a predetermined condition of the work machine.

16. The pump control system of claim 15, wherein the displacement stop includes a limit-activating piston and the displacement-stop controls move the displacement stop from the first position to the second position by supplying pressurized fluid to the limit-activating piston.

17. The pump control system of claim 16, wherein the displacement-control actuator is a displacement-actuator piston disposed within a cylinder and at least a portion of the limit-activating piston is also disposed within the cylinder.

18. The pump control system of claim 17, further including:

a stop that limits travel of the limit-activating piston toward the displacement-actuator piston.

19. The pump control system of claim 15, wherein the predetermined condition of the work machine relates to operations of the power source.

20. The pump control system of claim 15, wherein the predetermined condition of the work machine includes the power source operating outside a predetermined speed range.