Patent Application
20130291527
This patent disclosure relates generally to hydraulic power control systems and methods and, more particularly to systems and methods of controlling hydraulic power systems using non-productive flow control.
Machines may include one or more hydraulic power systems to drive one or more loads. The load may be a work implement on the machine or it may be a drive component that provides propulsion for the machine itself For example, in a machine drive train, a hydraulic power system, also known as a hydrostatic transmission, may be used in lieu of a mechanical transmission.
A hydraulic power system may include a variable displacement hydraulic pump and a hydraulic motor, which may also have variable displacement, that are connected together in a closed loop configuration. Fluid pumping through the hydraulic motor can cause it to spin an output shaft to thereby move a load such as a drive mechanism, such as a wheel or track, or a work implement. By varying the displacement of the pump, the amount of fluid pumped to the hydraulic motor may be controlled. This can be in response to a received operator input. For example, when an operator depresses an accelerator pedal to indicate a desire for more speed or torque of a drive mechanism, a discharge of the pump (flow and/or pressure) is proportionally increased.
To protect components of the transmission from damage, operation of the pump and/or motor is commonly limited according to pressure. Pressure may build in a hydraulic power system that functions to power the drive mechanism of a machine when the machine encounters an external resistance such as when pushing on something that is heavy or substantially immovable, like a large pile of earth. When the machine meets the resistance of the large pile of earth, the forward travel of the machine may be slowed or stopped, which, in turn, slows or stops the hydraulic motor that drives the drive mechanism. This substantially inhibits the flow of fluid through the motor. However, the variable displacement pump may continue to pump fluid to the hydraulic motor resulting in a build-up of pressure in the system.
One way to relieve this kind of pressure build up is with a cross-over relief (COR) valve, which may permit hydraulic fluid to flow (i.e., cross over) from the high pressure side of the circuit over to the low pressure side. While a COR valve can prevent spikes in pressure, continued flow across a COR valve can cause significant heating of the hydraulic fluid due to the pressure drop of the fluid as it passes from the high pressure side to the low pressure side of the system. Moreover, flow across a COR can be an inefficient use of energy since the flow through the valve is not productive, that is, not being used in a productive manner, such as, for example to turn the hydraulic motor.
Another common way to provide pressure relief is with an electronic pressure override (EPOR) system. An EPOR system senses system pressure and acts to reduce the displacement of the variable displacement pump, and thus reduce the amount of fluid being pumped to the hydraulic motor (or implement actuator), when the pressure exceeds a certain amount. Many hydraulic systems include EPOR systems in addition to COR valves.
An example of an EPOR system with COR is disclosed in U.S. Pat. No. 6,202,411 (the '411 patent). The '411 patent discloses a system that adjusts the discharge flow rate of a hydraulic pump when the system is held at a predetermined pressure for a predetermined period of time and when a specific operational condition of the system is sensed. Some of the disclosed operational conditions include use of a specific type of work implement, a high revolution condition of the engine and an operator selected work mode.
While effective to reduce pressure in the system, EPOR systems that are based on pressure control can be difficult to tune in a way that yields a consistent, intuitive feel to an operator of the machine. In particular, since the pressure control can be quite sensitive, when the EPOR system activates to reduce the pressure in a system, it can overshoot and to an operator it can feel as though the machine has suddenly stopped pushing. Moreover, an EPOR system based on pressure control can be relatively stiff to control and must be set to a pressure that is less than the upper limit of the system meaning that the machine may produce less than its maximum capable performance.
The disclosure describes, in one aspect, a hydraulic power control system for a machine. The system includes a hydraulic motor and a hydraulic pump configured to supply hydraulic fluid to the hydraulic motor. A relief valve is provided that is configured to release hydraulic fluid from a location between the hydraulic pump and the hydraulic motor when a pressure of the hydraulic fluid exceeds a predetermined pressure. A controller is in communication with the hydraulic motor and the hydraulic pump. The controller is configured to determine a first hydraulic fluid flow across the relief valve and determine a desired maximum flow across the relief valve. The controller also can regulate one or both of the hydraulic pump and the hydraulic motor to control the first hydraulic fluid flow based on the desired maximum flow.
In another aspect, the disclosure describes a method of controlling a hydraulic power system for a machine. The method includes the step of releasing hydraulic fluid from a location between a hydraulic pump and a hydraulic motor when the pressure of the hydraulic fluid exceeds a predetermined threshold pressure. A first flow of released hydraulic fluid is monitored. A desired maximum flow of released hydraulic fluid is determined and one or both of the hydraulic pump and the hydraulic motor is regulated to control the first flow based on the desired maximum flow.
This disclosure relates to an apparatus and method for controlling a hydraulic power system for a machine that may be operable to transmit power to a load associated with the machine. With particular reference to
While the hydraulic power system 14 is illustrated in connection with a track type tractor, the arrangement disclosed herein has universal applicability in various other types of machines as well. In this regard, the term “machine” may refer to any machine that performs some type of operation associated with an industry such as mining, construction, fanning, transportation, or any other industry known in the art. For example, the machine 10 may be an earth-moving machine, such as a wheel loader, excavator, dump truck, backhoe, motor grader, material handler or the like. Moreover, the hydraulic power system 14 may be used to transmit power to other loads as well such as, for example, an implement that is connected to the machine. Such implements may be utilized for a variety of tasks, including, for example, loading, compacting, lifting, brushing, and include, for example, buckets, compactors, forked lifting devices, brushes, grapples, cutters, shears, blades, breakers/hammers, augers, and others.
The power source 12 may be configured to produce a power output and may include an internal combustion engine. For example, the power source 12 may include a diesel engine, a gasoline engine, a gaseous fuel-powered engine, or any other type of engine apparent to one skilled in the art. It is contemplated that the power source 12 may alternatively embody a non-combustion source of power such as a fuel cell, a battery, or an electric motor, if desired. The power source 12 may produce a rotational mechanical output received by the hydraulic power system 14.
The traction device 16 may embody a track located on a side of the machine 10. When two drive trains are included within the machine 10, the two associated traction devices 16 may be located on opposing sides of the machine 10 and simultaneously controlled to propel the machine 10 or independently controlled to steer the machine 10. Alternatively, the traction device 16 may embody a wheel, a belt, or any other driven traction device.
The operator input device 18 may be located within an operator station of the machine 10, for example, in close proximity to an operator's seat as shown in
With additional reference to
The pump 20 may be a swashplate-type pump and include multiple piston bores, and pistons held against a tiltable swashplate 28. The pistons may reciprocate within the piston bores to produce a pumping action as the swashplate 28 rotates relative to the pistons. The swashplate 28 may be selectively tilted relative to a longitudinal axis of the pistons to vary a displacement of the pistons within their respective bores. The angular setting of the swashplate 28 relative to the pistons may be carried out by any actuator known in the art, for example, by a servo motor. Although shown in
The motor 22 may be a fixed or variable displacement type motor fluidly coupled to the pump 20. The motor 22 may convert the pressurized fluid from pump 20 into a rotational output of traction device 16. As a variable displacement motor, the motor 22 may include multiple piston bores and pistons (not shown) held against a fixed or rotatable swashplate 30. The angle of the swashplate 30 may determine an effective displacement of the pistons relative to the bores of the motor 22. The angular setting of the swashplate 30 relative to the pistons may be carried out by any actuator known in the art, for example, by a servo motor.
The hydraulic power system 14 may include a boost circuit associated with the pump that can operate to boost the pressure of the hydraulic fluid that is directed to the input side of the pump 20. As shown in
In some situations, it may be possible for the pressure of the fluid discharged by the pump 20 to exceed an acceptable threshold value. If unaccounted for, these high pressures could result in damage to the hydraulic power system 14. As shown in
Although illustrated as pilot operated, spring biased, valve mechanisms, it is contemplated that the cross-over pressure relief valves 46, 50 could alternatively embody an electronic valve actuated in response to a measured pressure, if desired. Additionally, the pressure limit of the pressure relief valves may be variable, and may also be adjustable.
In the hydraulic power system 14, any fluid flow that discharges from the hydraulic pump 20, but does not end up being used to generate speed of the hydraulic motor 22 may be considered as non-productive hydraulic fluid flow. The non-productive hydraulic fluid flow includes any fluid flow through the first and second bypass passageways 48, 52 as a result of operation of either of the cross-over pressure relief valves 46, 50. The non-productive hydraulic fluid flow in the hydraulic power system 14 may also include losses in the system as a result of leakage. For example, leakage in the system may be generated by clearances between the pistons and bores of the pump 20 and motor 22, and of any associated valves.
A control system 53 including a controller 54 with associated sensors may be provided to facilitate operation of the hydraulic power system 14. As schematically shown in
The controller 54 may be further configured to generate control signals for regulating operation of the pump 20 and the motor 22. More particularly, the controller 54 may be configured to control displacement of the pump 20 and the motor 22 by, for example, controlling a pump actuator device 64 (e.g., a solenoid and spool valve) to vary the displacement of the pump 20. Additionally, the pump actuator device 64 may provide information to the controller about actual or commanded displacement of the pump 20. Similarly, the displacement of the motor 22 may also be controlled by a motor actuator device 66. The motor actuator device 66 may also provide information to the controller about actual or commanded displacement of the motor 22. The controller 54 may control displacement of the pump 20 and motor 22 based on information received from the operator input device 18 and the various sensors. The controller 54 may be in communication with the operator input device 18, pump 20, motor 22 and sensors via control lines, which may carry digital, analog, or mixed types of signals. Alternatively, communication with the various components may be implemented by mechanical or hydraulic lines.
The controller 54 may embody a single microprocessor or multiple microprocessors . Numerous commercially available microprocessors may be configured to perform the functions of the controller 54. It should be appreciated that the controller 54 may readily embody a general machine microprocessor capable of controlling numerous machine functions. Various other circuits may be associated with the controller 54, such as power supply circuitry, signal conditioning circuitry, data acquisition circuitry, signal output circuitry, signal amplification circuitry, and other types of circuitry known in the art.
The hydraulic power system 14 may be able to tolerate at least some flow through the cross-over relief valves 46, 50 under at least some operating conditions and for at least some period of time. In such circumstances, it may be possible to regulate operation of the pump 20 and the motor 22, and thereby control the power delivered to, in this case, the traction device 16 of the machine 10, via the controller 54 based on the flow across the cross-over pressure relief valve 46, 50 in the system, which may be referred to as non-productive flow. The control based on flow across the cross-over pressure relief valve 46, 50 may be in addition to or instead of a conventional EPOR system based on system hydraulic fluid pressure.
Referring to
In a further step shown in
A further step of the method shown
Another method by which the desired maximum level of flow across the cross-over pressure relief valve 46, 50 may be determined is based on a measured temperature of the hydraulic fluid in the sump 40, in this case, via temperature sensor 60. For example, a control map may be provided in the software of the controller 54 based on measurements in a test environment of the sump temperature for a given level of flow across the cross-over pressure relief valve 46, 50. The control map may provide a maximum flow across the cross-over pressure relief valve for a measured sump temperature and from that the controller 54 may select a lower flow across the cross-over relief valve for other reasons such as fuel savings. An example of a plot for such a control map is shown in
Another method by which the desired maximum level of flow across the cross-over pressure relief valve 46, 50 may be determined is based on an operating mode of the machine 10 that is, for example, selected by an operator and input to the controller 54. The operating modes may, for example, include a high efficiency mode and a high performance mode. In the high efficiency mode, the controller 54 would set the desired maximum flow across the cross-over pressure relief valve 46, 50 at a low level or in the most extreme condition at zero. In the high performance mode, the controller 54 would set the desired maximum flow across the cross-over pressure relief valve at a high level or in the most extreme condition at the maximum flow that can be produced by the power source 12. In order to avoid over-heating of the system in the high performance mode, the controller 54 may be configured such that the operator can only select the high performance mode when the temperature of the hydraulic fluid is low to intermediate.
Once the actual flow across the cross-over pressure relief valve 46, 50 is monitored and the desired maximum flow across the cross-over pressure relief valve 46, 50 is determined, the controller 54 can then compare the desired maximum flow with the actual flow in block 78 and then regulate one or both of the pump 20 and the motor 22 to control the flow across the cross-over pressure relief valve 46, 50 based on the desired maximum flow in block 80. In the embodiment disclosed in
While the embodiments of
The rotation of the vibratory mechanisms for the two drums can be driven by a single or respective hydraulic power system 14 such as shown in
The hydraulic power control system and method described herein may be implemented in a variety of different machines that utilize hydrostatic transmissions to power movement of the machine or operation of an implement that is connected to the machine. The disclosed control system and method may be particularly suitable to applications in which, under at least some operating conditions ,some amount of flow over a cross-over relief valve can be maintained without excessive heating of the hydraulic fluid in the system.
As compared to control systems that operate based on pressure of the hydraulic fluid in the system, the disclosed control system and method based on flow across the cross-over relief valve or non-productive flow may provide a more consistent, intuitive feel to an operator of the machine because it is easier to tune and will not be subject to the overshooting issues associated with pressure based control systems that may make an operator feel as if the machine has suddenly stopped pushing. Moreover, as compared to pressure based control systems, a control scheme based on flow across the cross-over pressure relief valve may allow the hydraulic power system to operate more closely to its maximum capable performance, at least under certain operating conditions. For instance, with respect to the start-up of the vibratory mechanism of a compactor, the disclosed control system and method may enable the vibratory mechanism to achieve a higher maximum acceleration while conserving fuel. In particular, the amount of energy required to start the vibratory system can vary depending upon whether the operator selects a single drum, both drums or different amplitude settings of the drums. Using the disclosed system or method will enable the system to provide the energy required regardless of the drum settings.
It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated.
Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.
Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.
