Patent Application
20080223026
The present invention relates to a hydraulic power management system that may be used, for example, in a compact construction vehicle such as a skid steer loader.
Skid steer loaders are typically equipped with a drive and steering system and a main implement, such as a lift arm with a bucket attachment. Hydraulic fluid is provided under pressure to the drive system and to the main implement by way of hydraulic pumps that are driven under the influence of an internal combustion engine.
In many skid steer loaders, the lift arm is raised and lowered under the influence of a lift cylinder, and the bucket is curled and dumped under the influence of a tilt cylinder. The bucket can be replaced or enhanced with various auxiliary implements, such as augers or jack hammers, which provide additional functionality to the skid steer loader. A main valve often controls the supply of hydraulic fluid to the lift cylinder, tilt cylinder, and auxiliary implement in response to actuation of a joystick or other control. In some skid steer loaders, hydraulic fluid from a first hydraulic pump is provided to the lift and tilt cylinders, while hydraulic fluid provided by a second hydraulic pump in addition to the first hydraulic pump is provided to the auxiliary device. In such systems, the pressure and flow of hydraulic fluid provided to the lift and tilt cylinders is often limited to avoid stalling the internal combustion engine. Such pressure and/or flow limitation may be achieved, for example, by using a variable displacement pump, a variable speed drive mechanism, a variable pressure relief valve, or a combination of such devices. However, such systems still may permit the pressure of fluid provided to the auxiliary device to reach levels that would stall the internal combustion engine, for instance, when the operator demands maximum work from the auxiliary implement.
The invention provides a machine comprising an internal combustion engine having an output threshold below which the internal combustion engine operates and at which the internal combustion engine stalls. First and second fixed displacement pumps are driven by operation of the internal combustion engine to produce a combined flow of pressurized fluid. Main and auxiliary implements are operable in response to a flow of pressurized fluid, and a control valve selectively directs the combined flow to the main and auxiliary implements. A power management system is operable to stop the flow of pressurized fluid to the main implement from the second pump when the pressure of the combined flow exceeds a pressure indicative of the engine reaching the output threshold. The invention also provides a means for providing the combined flow to the auxiliary implement without regard to the pressure of the combined flow.
In some embodiments, the means for providing the combined flow may include an override mechanism that disables operation of the power management system in response to the control valve directing the combined flow to the auxiliary implement. In other embodiments, the means for providing the combined flow may include a bypass valve for providing the flow of pressurized fluid from the second pump to the auxiliary implement without flowing through the control valve. The invention may be embodied in a compact construction vehicle, such as a skid steer loader. In such embodiments, the main implement may include a lift arm and a bucket, for example.
The invention also provides a method for operating a machine that includes an internal combustion engine, first and second fixed displacement pumps, a main implement, and an auxiliary implement. The method comprises (a) driving operation of the first and second fixed displacement pumps with the internal combustion engine; (b) producing a combined flow of pressurized fluid with the first and second pumps; (c) selectively operating the main and auxiliary implements with the combined flow of pressurized fluid; (d) sensing the pressure of the combined flow; (e) preventing the flow of pressurized fluid to the main implement from the second pump when the pressure of the combined flow exceeds a pressure indicative of potential engine stall; and (f) permitting the combined flow of pressurized fluid to the auxiliary implements without regard to the pressure of the combined flow.
The invention therefore permits a main implement (e.g., the lift and tilt functions of a skid steer loader), in addition to an auxiliary implement, to utilize the combined flow from two fixed displacement pumps.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.
The right side wheels 20 are driven independently of the left side wheels 25. When all four wheels 20, 25 turn at the same speed, the loader 10 moves forward and backward, depending on the direction of rotation of the wheels 20, 25. The loader 10 turns by rotating the right and left side wheels 20, 25 in the same direction but at different rates, and rotates about a substantially zero turn radius by rotating the right and left side wheels 20, 25 in opposite directions.
The lift arms 40 raise (i.e., rotate counterclockwise in
Turning now to
With reference to
In the illustrated embodiment, the first and second pumps 95, 100 are fixed displacement pumps, and are driven at constant speed under the influence of the internal combustion engine 30. In the illustrated embodiment, the first and second pumps 95, 100 provide hydraulic fluid at rates of sixteen and ten gallons per minute, respectively. In other embodiments, the first and second pumps 95, 100 may provide hydraulic fluid at other rates that are most suitable for the vehicle or machine in which they are incorporated. The first and second pumps 95, 100 are both in fluid communication with the MCV 90, and therefore both supply pressurized hydraulic fluid to the lift, tilt, and auxiliary spools 115, 120, 125. A return line 127 returns hydraulic fluid to the reservoir 70 after it passes through the MCV 90.
Should an operator wish to disable the second pump 100 (i.e., provide no hydraulic fluid from the second pump 100 to the MCV 90), an on/off valve 128 may be moved into the illustrated open position to place the second pump 100 in communication with the reservoir 70. Otherwise, when the operator wishes to use pressurized hydraulic fluid from both pumps 95, 100, the on/off valve 128 is shifted into a closed condition.
The first pump 95 is in direct communication with the MCV 90 while the second pump 100 communicates with the MCV 90 through the power management system 105. The illustrated power management system 105 includes a power management loop valve 130 that is biased into the illustrated closed position by a valve spring 135. The power management system 105 also includes a check valve 140 that permits one-way flow of hydraulic fluid out of the power management system 105 and into the MCV 90.
The power management system 105 further includes first and second pilot or reference signal lines 145, 150 acting on (i.e., providing a pilot or reference signal to) opposite ends of the valve 130. The first pilot signal line 145 taps into the hydraulic circuit on the MCV side of the check valve 140 to provide a force against the bias of the spring 135 in proportion to the hydraulic pressure being provided to the MCV 90 (i.e., the combined hydraulic pressure from the first and second pumps 95, 100). The spring 135 is calibrated to deflect when the hydraulic pressure approaches or reaches a level at which the engine 30 may stall, such hydraulic pressure level referred to herein as “stall pressure.” The engine 30 reaches its output threshold when the stall pressure is attained, and the engine stalls.
When the pressure of hydraulic fluid being provided to the MCV 90 reaches the stall pressure, the spring 135 deflects and the valve 130 opens. When the valve 130 is open, hydraulic fluid from the second pump 100 follows the path of least resistance to the reservoir 70 and the check valve 140 closes. In this regard, the valve 130 may be called a redirecting mechanism. When the hydraulic pressure to the MCV 90 again drops below the stall pressure, the spring 135 shifts the valve 130 to the closed position and the check valve 140 opens so that hydraulic fluid from both pumps 95, 100 is again provided to the MCV 90.
The second pilot line 150 taps into the hydraulic circuit at the auxiliary spool 125, and acts in the same direction as the spring 135 bias. The second pilot line 150 provides this signal to the valve 130 only when the auxiliary spool 125 is opened. Because of hydraulic pressure drop through the MCV 90, the pressure in the second pilot line 150 is slightly lower than the pressure in the first pilot line 145. The bias of the spring 135 more than compensates for the pressure difference in the first and second pilot lines 145, 150 such that the combined forces of the spring 135 and second pilot line 150 are equal to or greater than the force of the first pilot line 145. Consequently, the spring 135 will not deflect when the auxiliary spool 125 is out of its neutral or center position, and the operator of the skid steer loader 10 may provide maximum power to the auxiliary implement 57, even up to the stall pressure. The operator may also provide maximum power to the lift and tilt cylinders 50, 55 when the auxiliary spool 125 is off center, since the valve 130 is locked closed.
To further maximize power to the auxiliary implement 57, the optional bypass valve 110 may be used. The optional bypass valve 110 is opened by the operator when the auxiliary implement 57 is activated (i.e., upon shifting the auxiliary spool 125 off center). When open, the bypass valve 110 provides a direct line from the second pump 100 to the auxiliary implement 57, which avoids the pressure drop that arises when all hydraulic fluid flows through the MCV 90. Hydraulic fluid will follow the path of least resistance from the second pump 100 to the auxiliary implement 57 through the open bypass valve 110, and not go through the power management system 105 and MCV 90. As a result, the check valve 140 closes and hydraulic fluid pressurized only by the first pump 95 flows to the auxiliary implement 57 through the MCV 90. The first and second pilot lines 145, 150 keep the valve 130 closed under such circumstances.
The second pilot line 150 and the optional bypass valve 110 may be considered part of an auxiliary high flow mechanism that permits the auxiliary implement 57 to receive the combined flow of hydraulic fluid from the pumps 95, 100 without regard to the pressure of hydraulic fluid flowing into the MCV 90.
The second pilot line 150 enables the combined flow to enter the MCV 90 (i.e., to each of the lift, tilt, and auxiliary spools 115, 120, 125) and disables the relief valve 130 as long as the auxiliary spool 125 is shifted from its center position, and therefore acts as a power management system override mechanism. In other embodiments, the power management system override mechanism may include sensors and electric or electromechanical actuators to lock the valve 130 closed, instead of using pressure in the pilot or reference lines 145, 150.
The optional bypass valve 110 permits the combined flow to be provided to the auxiliary implement 57 with only the hydraulic fluid from the first pump 95 having passed through the MCV 90, and therefore acts as a power management system bypass mechanism.
An optional feature to further maximize or control auxiliary device operation is a solenoid or other suitable override disabling valve 155 in the second pilot line 150. The disabling valve 155 is operable to close off communication between the auxiliary spool 125 and the valve 130, thereby effectively disabling the functionality of the second pilot line 150 (i.e., disabling the power management override) to permit operation of the power management system 105 during operation of auxiliary devices 57. One example of a situation in which it may be desirable to enable the power management system 105 during auxiliary device operation is when the auxiliary device 57 is intended to operate in a high-torque mode rather than a high-speed mode. With the power management system 105 enabled, only hydraulic fluid from the first pump 95 is provided to the auxiliary device 57 once the valve 130 is opened. This results in the provision of hydraulic fluid to the auxiliary device 57 at a higher pressure, albeit at a lower flow rate, which is conducive to a higher torque mode of operation for the auxiliary device 57.
Another example of a situation in which it may be desirable to enable the power management system 105 during auxiliary device operation is when the auxiliary device 57 is intended to operate in a high-speed mode of operation, but the internal combustion engine 30 is approaching stall. Assuming that the stall pressure has been achieved in this situation, enabling the power management system 105 will take the second pump 100 off line. This would result in the provision of hydraulic fluid to the auxiliary device 57 only from the first pump 95, but also permits the engine 30 to recover from stalling. As the engine speed increases under the reduced load, it is able to drive the first pump 95 faster and provide a higher flow rate to the auxiliary device than would be possible with the first and second pumps 95, 100 when the engine was approaching stall. To enable the power management system 105 under such circumstances, the override disabling valve 155 may operate in response to engine speed, with a control system enabling the power management system 105 through the disabling valve 155 when engine speed (e.g., as measured in revolutions per minute or “rpm”) drops below a threshold speed at which it is assumed that a higher flow rate would be achieved by the first pump 95 alone.
The disabling valve 155 operates in both examples above as a means for selectively disabling the second pilot line 150 to permit the power management system 105 to operate under circumstances in which operation of the auxiliary device 57 is optimized (whether in high-torque or high-speed mode) by the supply of hydraulic fluid from only one of the first and second pumps 95, 100.
Various features and advantages of the invention are set forth in the following claims.
