Patent Application
20080034957
With initial reference to
With additional reference to
The supply line 38 furnishes hydraulic fluid to a first control valve assembly 50 comprising a Wheatstone bridge configuration of four electrohydraulic proportional (EHP) valves 51, 52, 53 and 54 which control the flow of fluid to and from a boom hydraulic cylinder 56 that raises and lowers the boom 20. Each of these EHP valves 51-54 and other electrohydraulic proportional valves in the system 30 have only two ports and preferably are bidirectional poppet valves, thereby controlling flow of hydraulic fluid flowing in either direction through the valve and may be the type described in U.S. Pat. No. 6,328,275, for example. However, other types of control valves can be used.
A first pair of the EHP valves 51 and 52 governs the fluid flow from the supply line 38 into a head chamber 57 on one side of the piston in the boom cylinder 56 and from a rod chamber 55 on the opposite side of the piston to the tank return line 40. This action extends the piston rod from the cylinder 56 and raises the boom 20. A second pair of EHP valves 53 and 54 controls the fluid flow from the supply line into the rod chamber 55 and from the head chamber 57 to the tank return line, which retracts the piston rod into the cylinder 56 thereby lowering the boom 20. By controlling the rate at which pressurized fluid is sent into one cylinder chamber and drained from the other chamber, the boom 20 can be raised and lowered in a controlled manner. A first pair of pressure sensors 58 and 59 provide electrical signals indicating the pressure in the two chambers of the boom cylinder 56.
A second control valve assembly 60 controls the flow of hydraulic fluid into and out of an arm hydraulic cylinder 66. This control valve assembly comprises another set of four EHP valves 61, 62, 63, and 64 connected in a Wheatstone bridge configuration between the supply and tank return lines 38 and 40 and the chambers of the arm cylinder 66. Operation of the second control valve assembly 60 extends and retracts the arm 22 with respect to the boom 20. A second pair of pressure sensors 68 and 69 provide electrical signals indicating the pressure in the two chambers of the arm hydraulic cylinder 66.
A third control valve assembly 70 controls fluid flow to and from a load carrier hydraulic cylinder 76 that tilts the load carrier 24 up and down with respect to the remote end of the arm 22. This valve assembly differs from the others in that it has only two EHP valves 71 and 72 that are combined with two pressure operated counterbalance valves 73 and 74. The first EHP valve 71 controls flow of fluid from the supply line 38 to a first workport 78 to which a first port for the head chamber 77 of the load carrier cylinder 76 connects, and the second EHP valve 72 controls fluid flow from the supply line to a second workport 79 coupled to a second port for the rod chamber 75. A first load check valve 80 is provided in the path between the first EHP valve 71 and the head chamber, and a second load check valve 81 is provided in the path between the second EHP valve 72 and the rod chamber.
The first counterbalance valve 73 couples the rod chamber 75 to the tank return line 40, while a second counterbalance valve 74 is connected between the head chamber 77 and the tank return line. The two counterbalance valves 73 and 74 are pressure operated pilot valves. The first counterbalance valve 73 is operated by pressure at a first node 82 between the first EHP valve 71 and a first load check valve 80 and thus is slaved non-electrically to operate in unison with that EHP valve. The second counterbalance valve 74 is operated by pressure at a second node 83 between the second EHP valve 72 and the second load check valve 81, thereby being slaved non-electrically to operate in unison with the second EHP valve. The internal checking function of the first or second EHP valve 71 or 72 in conjunction with the operation of the associated first or second load check valves 80 or 81 and the inherent return line leakage in the respective first or second counterbalance valve 73 or 74 ensure that the appropriate counterbalance valve opens with opening of whichever EHP valve is electrically activated to open. A first or second check valve 86 or 88 is an integrated part and function of the first or second counterbalance valve 73 or 74, respectively, and allows flow only from the tank return line to the associated workport 78 or 79 to prevent cavitation in the cylinder 76.
The greater of the pressures at the first and a second nodes 82 and 83 is selected by a shuttle valve 84 and applied to a load pressure sensor 85. When one of the first or second EHP valve 71 or 72 is open, the selected pressure corresponds to the pressure in the workport connected to that opened EHP valve. This occurs even if the other workport has a greater load pressure, because the first or second check valve 86 or 88 prevents that greater pressure from reaching the shuttle valve 84.
The three control valve assemblies 50, 60, and 70 are operated by electrical signals from an electronic controller 90. The controller 90 has a conventional hardware design that is based around a microcomputer and a memory in which programs and data used by the microcomputer are stored. The microcomputer is connected input and output circuits within the controller that interface to the operator input devices, sensors, and valves of the hydraulic system 30. Specifically, the controller 90 receives an operator input signal from a joystick 92 in the telehandler operator cab 14 (
To command the controller 90 to move the load carrier 24, the operator manipulates the joystick 92 in a manner that indicates the desired motion. That action sends a signal to the controller 90 that in response determines which one of the first and second EHP valves 71 and 72 should be opened to produce that motion in the desired direction. If the joystick signal designates that the ends of the forks 28 on the load carrier 24 are desired to be tilted downward, the piston rod 94 has to be extended from the load carrier cylinder 76. Therefore, the first EHP valve 71 must be opened to convey fluid from the supply line 38 to the head chamber 77. That fluid forces the first check valve 80 open allowing the fluid to enter the head chamber 77. This action results in a relatively high pressure occurring at the first node 82 between first EHP valve 71 and the first check valve 80. That pressure is applied to the first counterbalance valve 73 forcing that valve to open and provide a path between the rod chamber 75 of the load carrier cylinder 76 and the tank return line 40. Thus pressurized fluid is applied to the head chamber 77 and the fluid in the rod chamber 75 drains into the tank 32, thereby extending the piston rod 94 from the load carrier cylinder.
If the signal from the joystick 92 designates that the ends of the load carrier forks 28 are to be tilted upward, the piston rod 94 has to be retracted into the load carrier cylinder 76. To accomplish that movement, the second EHP valve 72 must be opened to convey fluid from the supply line 38 to the rod chamber 75. Now a relatively high pressure occurs at the second node 83 between second EHP valve 72 and the second check valve 81, which forces the second counterbalance valve 74 open providing a drain path between the head chamber 77 and the tank return line 40. As a result of this action, pressurized fluid is applied to the rod chamber 75 and the fluid in the head chamber 77 drains into the tank 32, thereby retracting the piston rod 94 into the load carrier cylinder.
Thus fluid flow that drives the load carrier cylinder 76 in opposite directions is controlled by a valve assembly 70 that has only two electrically operated valves. Thus the number of electrical actuators and the amount of electrical drive circuitry needed to operate the third valve assembly 70 is reduced from that required for the other valve assemblies 50 and 60 which each have four electrically operated valves. For the load carrier cylinder 76, the two EHP valves 71 and 72 control the application of pressurized fluid from the supply line 38 and the two counterbalance valves 73 and 74, slaved to operation of those EHP valves, control the fluid draining from the load carrier cylinder.
The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.
