Patent Application
20070130935
Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to a hydraulic system having valves that are operated to control the flow of fluid to hydraulic actuators that move components on a machine, and more particularly to distributed control systems in which the valves are located adjacent the associated hydraulic actuator being controlled.
2. Description of the Related Art
A wide variety of machines are operated by hydraulic systems. For example, a backhoe is a common type of earth moving equipment that has a bucket rotatably attached to the end of an arm that in turn is pivotally coupled by a boom to a tractor. A hydraulic boom cylinder raises and lowers the boom with respect to the tractor and a hydraulic arm cylinder pivots the arm about the end of the boom. The bucket is rotated at the remote end of the arm by a hydraulic bucket cylinder.
Traditionally, the boom assembly was controlled by valves located near the cab of the tractor and mechanically connected to levers which the operator manipulated to independently move the boom, arm and bucket. A separate valve assembly was provided for each cylinder on the boom assembly. Operating one of the valve assemblies permitted pressurized hydraulic fluid to flow from a pump on the tractor to the associated cylinder and other fluid to return from that cylinder back to the tank on the tractor. A separate pair of hydraulic conduits ran from each valve assembly adjacent the operator cab along the boom assembly to the associated cylinder.
There has been a recent trend away from mechanically operated valves to electrohydraulic valves that are operated by electrical signals. Initially, all of the electrohydraulic valves were mounted on a single manifold block, such as the one described in U.S. Pat. No. 6,505,645, that was centrally located on the machine. Pairs of hydraulic conduits ran from that common manifold block to each hydraulic actuator on the machine. The use of electrohydraulic valves eventually evolved to the development of a distributed hydraulic system in which the valve assembly is collocated with the associated hydraulic actuator, such as a cylinder. With this type of system, the operator in the tractor cab manipulates joysticks or other input devices to generate electrical control signals for operating the valve assemblies. Because each valve assembly is adjacent the respective hydraulic actuator, the amount of plumbing on the machine is reduced. Now only a pair of conduits, a supply conduit and a tank return conduit, extends along the boom assembly to power the cylinders for the boom, arm and bucket on a backhoe, for example. Electrical cables run from a central electronic controller for the machine to the valves on the assemblies near the hydraulic actuators.
Other types of equipment also incorporate such distributed hydraulic systems.
A distributed control assembly for operating a hydraulically powered actuator includes a manifold block on which a housing for an electronic controller is mounted. The manifold block has a first supply port for connection to a source of pressurized fluid such as a pump, a first return port for connection to a fluid reservoir, and first and second workports for connection to the hydraulically powered actuator. The manifold block also has a plurality of bores each for receiving a valve to control flow of fluid among the first and second workports, the first supply port and the first return port. A separate one of a plurality of electrohydraulic valves is received in one of the plurality of bores of the manifold block and is electrically controlled by the electronic controller.
One aspect of the distributed control assembly relates to providing one or more pressure ports at which to sense pressure at different locations within the manifold block. The controller housing, in addition to containing an electronic function controller, also contains a separate pressure sensor for each pressure port of the manifold block. The controller housing is mounted against the manifold block so that each pressure sensor is connected to one of the pressure ports.
Another aspect of the distributed control assembly relates to the manifold block including a pair of exterior walls that extend on opposites sides of the controller housing. The wall protect the controller housing and its contents from damage that could result from objects striking the machine on which the distributed control assembly is mounted.
A further aspect of the distributed control assembly relates to providing additional ports on the manifold block. In one embodiment, a second supply port is connected to the first supply port, and a second return port is connected to the first return port, thereby facilitating the connection of a plurality of distributed control assemblies in a daisy chain manner. Another embodiment provides ports for various pressure relief valves, an inlet check valve, and an optional manual emergency valve.
With initial reference to
A workhead 18, such a pair of pallet forks 20 or a platform for lifting items, is attached at pivot point 24 to the remote end of the first boom section 14. Other types of workheads may be attached to the first boom section 14. A third hydraulic cylinder 23 rotates the workhead 18 vertically at the end of the boom 13. Extension of a piston rod from the third, or workhead, hydraulic cylinder 23 tilts the tips of the pallet forks 20 upward, and retraction of that piston rod lowers the fork tips.
Referring to
The outlet pressure from the pump 32 is measured by a first sensor 35, which provides a signal indicating that pressure to a system controller 50. An unloader valve 36 is operated by the system controller 50 to regulate pressure in the supply conduit 34 by releasing some of the fluid into the tank 33. Other hydraulic systems utilize a variable displacement pump, which is be operated by the system controller 50. The system controller 50 also receives a signal from a second pressure sensor 38 that measures the pressure in the tank return conduit 40. In the preferred embodiment of the distributed hydraulic system, the system controller 50 is located in or near the operator cab 49 of the tractor 12 and receives control signals via a conventional communication network 56 from joysticks 54 that are manipulated by the telehandler operator.
Each hydraulic function 41-43 includes one of the hydraulic cylinders, a valve assembly, and an electronic function controller adjacent each other at various locations on the telehandler 10. Specifically, the boom lift function 41 has a first valve assembly 44 that selectively applies the pressurized fluid from the supply conduit 34 to one of the chambers of the boom lift cylinder 21 and drains fluid from the other cylinder chamber to the return conduit 40. A second valve assembly 45 in the boom length hydraulic function 42 controls the flow of hydraulic fluid to and from the boom length cylinder 22 and the supply and return conduits 34 and 40. The workhead hydraulic function 43 has a third valve assembly 46 that couples the chambers of the workhead cylinder 23 to the supply and tank conduits 34 and 40. The valve assemblies 44, 45 and 46 are respectively operated by electrical signals from a function controller 51, 52 and 53 for the hydraulic function. The system controller 50, function controllers 51-53, and the joysticks 54 exchange operational commands, control signals and data over a communication network 56, such as the Controller Area Network serial bus that uses the communication protocol defined by ISO 11898 promulgated by the International Organization for Standardization in Geneva, Switzerland, for example. The communication network 56 also carries other messages between the engine, transmission, and other components and computers on the vehicle
Each of these electrohydraulic valves 61-64 has a pilot valve 70 that is controlled by solenoid operator 71 which is activated by a signal from the function controller 51. The pilot valve 70 controls the pressure in a control chamber 72 of the respective electrohydraulic valve which pressure in turn controls movement of the main valve element 73 that governs the fluid flow through the electrohydraulic valve.
A first pressure relief valve 74 responds to pressure at the first workport 66 exceeding a predefined level by opening a path from the control chamber 72 of the third electrohydraulic valve 63 to the tank return conduit 40. This action releases the pressure in that control chamber, thereby allowing the workport pressure acting on the third electrohydraulic valve's main valve element 73 to open that valve. This combined action of a pressure relief valve and a main valve element creates a path from the first workport 66 to the tank return conduit 40 while releasing the excessive workport pressure. Because the first pressure relief valve 74 handles only minimal fluid flow from the control chamber 72, it can be smaller that a conventional relief valve through which fluid from the workport would flow due to an excessive pressure condition.
A second pressure relief valve 78 responds to pressure at the second workport 68 exceeding a predefined level by opening a path from the control chamber 72 of the fourth electrohydraulic valve 64 to the tank return conduit 40. That action provides a path through the fourth electrohydraulic valve 64 that releases the pressure at the second workport 68 into the tank return conduit 40. Here too, the combination of a relatively small pressure relief valve and a main valve element provide the workport pressure relief function.
A manually operated emergency valve 75 provides a controllable path between the first workport 66 and the tank return conduit 40. The emergency valve 75 is operated by turning a screwdriver that engages a threaded valve element 76. In the event that power driving the pump 32 is lost, opening the emergency valve 75 releases fluid from the head chamber 67 of the boom lift cylinder 21 which lowers the boom 13.
Referring again to
The first distributed control assembly 81 has a manifold block 80 with a first end face 84 and an opposite second end face 86. The first end face 84 has a first supply port 87 and a first return port 88 therein, and the second end face 86 has a second supply port 90 and a second return port 91. A supply passage 92 directly connects the first and second supply ports 87 and 90. Similarly, a return passage 94 directly connects the first and second return ports 88 and 91 through the manifold block 80. The terms “directly connects” and “directly connected ”, as used herein, mean that the associated components are connected together by a conduit without any intervening element, such as a valve, an orifice or other device, which restricts or controls the flow of fluid beyond the inherent restriction of any conduit. As seen in
A first workport 66 also is located on the first end face 84, while the second workport 68 is on the second end face 86. The first end face 84 of the manifold block 80 has a first valve bore 95, within which the first electrohydraulic valve 61 is received. The manifold block 80 has internal passages that connect the first valve bore 95 with the supply passage 92 and the first workport 66 so that the first electrohydraulic valve 61 can control the fluid flow there between as depicted in
Similarly, the second end face 86, as shown in
Referring again to both
The first and second side faces 100 and 102 each include an upstanding wall 112 and 114, respectively, that are spaced apart forming a cavity 116 on the exterior of the manifold block 80. The cavity 116 has a flat bottom surface 118 through which a pair of pressure ports 120 and 122 extends. As shown in
The first and second function pressure sensors 124 and 126 and the function controller 51 are enclosed within a controller housing 128, thereby forming a controller assembly 55 that is illustrated in
A printed circuit board within the housing 128 contains the electronic circuitry of the function controller 51 and the two pressure sensors 124 and 126. With additional reference to
U.S. Pat. No. 6,718,759 describes a velocity based system for controlling a hydraulic system, such as that shown in
Each function controller 51, 52 and 53 converts a joystick signal intended for it in to a velocity command specifying the desired direction and speed that the associated hydrolic cylinder is to move. That velocity command and pressures sensed at the workport ports of the associated valve assembly 44-46 are used to determine which of the four electrohydraulic valves 61-64 to open in order to produce the desired motion of hydraulic cylinder. Then drive signals for operating the designated valves are generated and applied to the solenoid operators of those valves.
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.
