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Pump control system for variable displacement pumpRelated Patent Categories: Pumps, ProcessesPump control system for variable displacement pump description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060198736, Pump control system for variable displacement pump. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] 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 [0002] 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. [0003] 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. [0004] 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. [0005] 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. [0006] The drive system of the present disclosure solves one or more of the problems set forth above. SUMMARY OF THE INVENTION [0007] 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. [0008] 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 [0009] FIG. 1 is a diagrammatic illustration of a work machine with which the pump control system consistent with one disclosed embodiment may be utilized; [0010] FIG. 2 is a schematic illustration of a variable-displacement pump and a pump control system according to one disclosed embodiment; and [0011] 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 [0012] 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. [0013] 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. [0014] 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. [0015] 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. [0016] 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. [0017] 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. [0018] 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. [0019] 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. Continue reading about Pump control system for variable displacement pump... Full patent description for Pump control system for variable displacement pump Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Pump control system for variable displacement pump patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Pump control system for variable displacement pump or other areas of interest. ### Previous Patent Application: Vacuum pump and method of starting the same Next Patent Application: Actuator control apparatus Industry Class: Pumps ### FreshPatents.com Support Thank you for viewing the Pump control system for variable displacement pump patent info. 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