GB2328524A

GB2328524A - An electro hydraulic proportional control valve assembly

Info

Publication number: GB2328524A
Application number: GB9818200A
Authority: GB
Inventors: David Franz Lakin; Stephen Brian Turner
Original assignee: Ultronics Ltd
Current assignee: Ultronics Ltd
Priority date: 1997-08-22
Filing date: 1998-08-21
Publication date: 1999-02-24
Anticipated expiration: 2018-08-21
Also published as: GB9717713D0; GB2328524B; GB9818200D0

Abstract

An electro hydraulic proportional control valve assembly comprises first valve member 12, of second valve member 13, position sensing means 23,24 for supplying electrical position signals indicative of the actual positions of the first and second valve members 12,13, pressure sensing means 26,27,28 for supplying electrical pressure signals indicative of the fluid pressures in the first and second actuating ports 4,5 and the pump port, and servo control means for controlling the positions of the first and second valve members in dependence on the electrical position and pressure signals and in response to an electrical demand signal provided in response to operator actuation, and, if the pressure difference between the first and second actuating ports or the pressure at the actuating port connected to the pump port reaches a predetermined value, for alerting an operator or for controlling the pressure difference between the first and second actuating ports or the pressure at the actuating port connected to the pump port at or below said predetermined value, unless overridden by an operator, in order to protect an object with which a machine, operated in use by the bidirectional fluid actuated device, makes contact.

Description

AN ELECTRO HYDRAULIC PROPORTIONAL CONTROL VALVE ASSEMBLY This invention relates to electro hydraulic proportional control valve assemblies for controlling fluid actuated devices.

It is known from GB-A-2298291 to provide an electro hydraulic proportional control valve assembly for controlling a fluid actuated device. This known control valve assembly is said to be able to sense a pressure overload so as to rapidly open one of the main spools of the control valve assembly to tank in order to protect a machine operated by the fluid actuated device when movement of the machine is blocked.

According to the present invention there is provided an electro hydraulic proportional control valve assembly for controlling a bidirectional fluid actuated device having first and second ports, the valve assembly having a first actuating port for bidirectional fluid flow between the valve assembly and the first port of the fluid actuated device, a second actuating port for bidirectional fluid flow between the valve assembly and the second port of the fluid actuated device, a pump port for input fluid flow to the valve assembly from a hydraulic pump, and a tank port for output fluid flow from the valve assembly to a hydraulic tank, the valve assembly comprising first valve means connected to the first actuating port, the pump port and the tank port for controlling the direction and rate of fluid flow between the first actuating port and the pump port and between the first actuating port and the tank port, and second valve means connected to the second actuating port, the pump port and the tank port for controlling the direction and rate of fluid flow between the second actuating port and the pump port and between the second actuating port and the tank port, the first valve means having a first valve member which is movable to vary the throughflow crosssection for fluid flow between the first actuating port and the pump or tank port, and the second valve means having a second valve member which is movable, independently of movement of the first valve member, to vary the throughflow crosssection for fluid flow between the second actuating port and the pump or tank port, position sensing means for supplying electrical position signals indicative of the actual positions of the first and second valve members, pressure sensing means for supplying electrical pressure signals indicative of the fluid pressures in the first and second actuating ports and the pump port, and servo control means for controlling the positions of the first and second valve members in dependence on the electrical position and pressure signals and in response to an electrical demand signal provided in response to operator actuation, in order to set the throughflow cross-sections for fluid flow through the first and second valve means between the first actuating port and the pump or tank port and between the second actuating port and the pump or tank port to effect the required control of the fluid actuated device, and for sensing the pressure difference between the first and second actuating ports of the fluid actuated device or the pressure at the actuating port connected to the pump port and, if the pressure difference between the first and second actuating ports or the pressure at the actuating port connected to the pump port reaches a predetermined value, for alerting an operator or for controlling the pressure difference between the first and second actuating ports or the pressure at the actuating port connected to the pump port at or below said predetermined value, unless overridden by an operator, in order to protect an object with which a machine, operated in use by the bidirectional fluid actuated device, makes contact.

Advantageously, the proportional control valve assembly includes means whereby an operator can vary said predetermined value, typically but not necessarily, in steps.

Preferably, the first and second valve members are spools which are axially displaceable to vary the throughflow cross-section for fluid flow between each actuating port and the pump or tank port.

Preferably, the servo control means includes electrically operable pilot valve means for controlling the position of each of the valve members. In this case, preferably, the pilot valve means comprises a first pilot valve for effecting bidirectional axial movement of the first valve member1 and a second pilot valve for effecting bidirectional axial movement of the second valve member independently of movement of the first valve member. In this case, each pilot valve may comprise an actuating coil movable relative to a magnetic former by the application of an electrical actuating current to the coil, and a valve element movable by the coil to simultaneously control application of pilot fluid to said one part of the valve member and venting of pilot fluid from said other part of the valve member.

The electro hydraulic proportional control valve may be used to operate one or more of the axes of an earth moving vehicle and, in this case, the predetermined value of pressure difference between the first and second actuating ports or the pressure at the actuating port connected to the pump port can be set at a level which will prevent damage by the earth moving vehicle to pipes and/or cables buried in the ground.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a hydraulic circuit diagram of the assembly; Figure 2 is a diagrammatic sectional view through a part of the assembly; Figure 3 is a schematic view of an earth moving vehicle equipped with the assembly shown in figure 1.

Referring to Figure 1 the illustrated electro hydraulic proportional control valve assembly 1 comprises first and second spool valves 2 and 3 connected to first and second actuating ports 4 and 5 for controlling fluid flow to opposite sides of a movable piston 6 of a fluid actuated device 7 in the form of a hydraulic cylinder or motor. The first and second spool valves 2 and 3 have spools 12 and 13 which are axially movable by pilot fluid flows controlled by electrically operated pilot actuator valves 44 and 45 (described more fully below with reference to Figure 2) between end positions in which the spool 12 or 13 places the corresponding actuating port 4 or 5 in communication with either a pump port 15 or 16 connected to the output of a pump 17 or a tank port 18 or 19 connected to a tank 20. A pilot pressure regulator 14 regulates the pressure of fluid supplied to the pilot actuator valves 44 and 45 to hold this pressure substantially constant.

The spool 12 or 13 or each spool valve 2 or 3 is movable to effect opening of the spool valve 2 or 3 either to the pump port 15 or 16 or the tank port 18 or 19 over a throughflow cross-section which may be varied proportionately between a minimum opening value and a maximum opening value in dependence on the position of the spool 12 or 13. Furthermore both spools 12 and 13 are spring biased towards their neutral positions (in which they are shown in figure 1), and position sensors 23 and 24 are provided for supplying electrical position signals indicative of the positions of the spools 12 and 13. In addition a pressure relief valve 25 is provided for venting the output of the pump 17 to the tank 20 in a manner which will be described in more detail below. Four pressure sensors 26, 27, 28 and 29 are provided for supplying electrical pressure signals PAS PBX PSX and PT indicative of the fluid pressures in the first and second actuating ports 4 and 5, the pump port 15 or 16 and the tank port 18 or 19.

As shown diagrammatically on the right hand side of Figure 1, the pilot pressure regulator 14 may also serve to regulate pilot fluid supply to the pilot actuator valves of a further pair of spool valves, identical to the spool valves 2 and 3, for controlling supply of fluid to a further fluid actuated device 30. The two devices 7 and 30 may be two rams for controlling different linkage axes of an earth moving vehicle for example, and may be controlled by two valve slices in the assembly as described in more detail below.

Figure 2 shows a section through a valve slice part incorporating one of the first and second spool valves 2 and 3 and one of the associated pilot actuator valves 44 and 45, two such parts being provided in each valve slice. The pilot actuator valve 44 or 45 comprises a moving coil 35 fixed to a pilot spool 36 which is centred by two springs 37 and 38, the coil 35 being displaceable in an annular air gap 39 within a magnetic former 40 when a current is supplied to the coil 35 so as to provide magnetic interaction between the magnetic field associated with the current flow and the magnetic flux produced in the air gap 39 by the former 40. The pilot actuator valve 44 or 45 has two actuating ports 46 and 47 connected to the ends of the spool valve 2 or 3 by connecting conduits 48 and 49 respectively, as well as a tank port 70 connected to the tank and two pump ports 71 and 72 connected to pump either directly or by way of the pilot pressure regulator 14. The spool 12 or 13 of the spool valve 2 or 3 is centred by two springs 73 and 74 and has an extension 75 at one end enabling a position feedback signal dependant on the position of the spool 12 or 13 to be outputted by the position sensor 23 or 24.

With the spool 36 of the pilot actuator valve 44 or 45 in the neutral position as shown in figure 2, only slight fluid leakage will take place through the pilot actuator valve, and hence the spool 12 or 13 of the main spool valve 2 or 3 will be held in its neutral position by the springs 73 and 74, as also shown in the figure.

When a position control current is supplied to the coil 35, a force acts on the spool 36 so as to move it in one or other direction (dependant on the sense of the current) until an equilibrium position is reached in which the force is balanced by the forces exerted by the springs 37 and 38. If the spool 36 moves to the right as shown in the figure, this results in passages of a throughflow cross-section determined by the magnitude of the current being opened between the pump port 71 and the actuating port 46 and between the tank port 70 and the actuating port 47, with the result that a controlled displacement flow of pilot fluid is applied along the conduit 48 to the left hand end of the spool 12 or 13 of the main spool valve 2 or 3, and at the same time controlled venting of pilot fluid from the right hand end of the spool 12 or 13 takes place by way of the conduit 49 to tank. This causes the main spool 12 or 13 to be driven to the right as shown in the figure, with the speed of movement being determined by the degree of opening of the pilot actuator valve 44 or 45, until the position feedback signal outputted by the position sensor 23 or 24 indicates that the spool has been driven to the required position at which time the current to the coil 35 is cut off and the spool 36 of the pilot actuator valve 44 or 45 is returned to its neutral position by the springs 37 and 38. This results in movement of the main spool 12 or 13 being stopped so that the spool is held in the required position to which it has been driven by virtue of the fluid pressures acting on the two ends of the spool.

In practice the pilot actuator valve current is controlled in a complex way by the control circuitry in order to achieve optimum dynamic and position control characteristics, that is in order to rapidly drive the main spool 12 or 13 to the required position and in order to accurately retain the spool in that position for as long as necessary. This may in practice require energisation of the coil 35 by a small current under servo control even when movement of the main spool 12 or 13 is not required, so as to provide small fluid flows through the pilot actuator valve 44 or 45 to compensate for fluid leakage so as to retain the main spool 12 or 13 in the position to which it has been driven. However, any current required to maintain the main spool in position will be very low, and will not adversely affect the generally low current consumption of the control circuitry which accurately monitors the position of the main spool valve 12 or 13 by means of the position sensor 23 or 24 at all times and controls the current to the coil 35 continuously so as to provide the required feedback control of the main spool position.

The control valve assembly also includes a control computer (not shown) which monitors operator actuation of a joy stick (not shown) so as to supply pressure (P) or flow (Q) demand signals, and pressure-flow (P-Q) select signals. In addition, the control computer serves to supply initial set up data utilising a plug-in programmer.

The control computer controls the positions of the first and second valve members in dependence on the electrical position and pressure signals and in response to an electrical demand signal provided in response to operator actuation of the joy stick, in order to set the through flow cross sections for fluid flow through the first and second spool valves 2 and 3 between the first actuating port 4 and the pump or tank port and between the second actuating port 5 and the pump or tank port to effect the required control of the fluid actuated device 7.

However, the control computer also monitors the pressure difference between the first and second actuating ports 4 and 5 or the pressure at the actuating port 4 or 5 which is connected to the pump port 15 or 16. If the pressure difference between the first and second actuating ports 4 and 5 or the pressure at the actuating port which is connected to the pump port 15 or 16 reaches a predetermined value, the control computer then controls the pressure difference between the first and second actuating ports or the pressure at the actuating port which was, at the time the pressure reached said predetermined value, connected to the pump port 15 or 16 at or below said predetermined value, thereby over-riding the electrical demand signal provided in response to operator actuation of the joy stick, in order to protect an object with which a machine, operated by the fluid actuated device 7, makes contact.

This may require the spool to connect the actuator port 4 or 5 to the tank port 18 or 19.

Referring to Figure 3 of the drawings, there is shown therein an earth moving machine in the form of an excavator 50. The excavator has a boom 51, a dipper arm 52 and a bucket 53 all of which are operated by fluid pressure actuating devices in the form of hydraulic rams 54, 55 and 56, respectively. The ram 55 between the boom 51 and the dipper arm 52 is controlled by the proportional control valve assembly 1.

By controlling the pressure difference between the actuating ports 4 and 5 or by controlling the pressure at the port 4 or 5 connected to the pump port 15 or 16, the load applied by the dipper arm 52 can be controlled at a predetermined maximum level. This level can be set so that the excavator does not damage pipes and/or cables buried in the ground. If the bucket 53 makes contact with a pipe or cable, the bucket 53 may continue to operate in accordance with operator actuation of the joy stick, but the ram 55 will cause the dipper arm 52 to yield.

The proportional control valve assembly may include means by which this predetermined value of pressure difference or pressure can be varied by the operator so that as the dipper arm 52 yields in response to the bucket 53 meeting an object, such as a pipe, the operator can raise the predetermined value preferably in small steps.

Such an arrangement will protect buried pipes and/or cables from damage by an excavator.

Also, instead of controlling the pressure difference between the first and second actuating ports 4 and 5 or the pressure at the actuating port 4 or 5 connected to the pump port 15 or 16, the control computer can alert the operator if the predetermined value is reached, such as by a warning light, so that the operator can take an informed decision as to how to proceed.

In practice, the bucket 53 is dragged through the earth at an excavation site and the pressure differential across the ram 55 (or the pressure at the actuating port 4 or 5 connected to the pump port 15 or 16) is sensed and this pressure difference (or pressure) is registered. A pressure value which is greater by a preselected margin than the sensed pressure difference (or pressure) is then stored as the predetermined value so that if the sensed pressure differential (or pressure) reaches this predetermined value the operator is alerted and/or the pressure difference (or pressure) is controlled.

The proportional control valve assembly described above is not limited in its application to use with an excavator. It can be used with other machines. Also, when used with an excavator, it could control any one or more of the axes of the excavator rather than controlling the ram 55 alone.

The proportional control valve assembly does not need to be operated in a flow control mode. It can be operated in other modes as described in GB-A-2298291.

Whilst the above described valve assembly utilises first and second spool valves 2 and 3 for controlling fluid flow to and from the fluid actuated device, an alternative, non-illustrated valve assembly in accordance with the invention utilises a pair of poppet valves in place of each such spool valve for controlling respectively the flow of fluid to the device from the pump by way of the associated actuating port and the flow of fluid from the device to the tank by way of the actuating port. In each case the pair of poppet valves associated with each actuating port is controlled by the pilot actuator valves to provide the required fluid flows in the various control modes.

Furthermore each of the pilot actuator valves may itself comprise a pair of poppet valves for controlling the fluid flows to and from the main valve or valves in response to current actuation of the moving coil.

Claims

1. An electro hydraulic proportional control valve assembly having a first actuating port for bidirectional fluid flow between the valve assembly and the first port of the fluid actuated device, a second actuating port for bidirectional fluid flow between the valve assembly and the second port of the fluid actuated device, a pump port for input fluid flow to the valve assembly from a hydraulic pump, and a tank port for output fluid flow from the valve assembly to a hydraulic tank, the valve assembly comprising first valve means connected to the first actuating port, the pump port and the tank port for controlling the direction and rate of fluid flow between the first actuating port and the pump port and between the first actuating port and the tank port, and second valve means connected to the second actuating port, the pump port and the tank port for controlling the direction and rate of fluid flow between the second actuating port and the pump port and between the second actuating port and the tank port, the first valve means having a first valve member which is movable to vary the throughflow cross-section for fluid flow between the first actuating port and the pump or tank port, and the second valve means having a second valve member which is movable, independently of movement of the first valve member, to vary the throughflow cross-section for fluid flow between the second actuating port and the pump or tank port, position sensing means for supplying electrical position signals indicative of the actual positions of the first and second valve members, pressure sensing means for supplying electrical pressure signals indicative of the fluid pressures in the first and second actuating ports and the pump port, and servo control means for controlling the positions of the first and second valve members in dependence on the electrical position and pressure signals and in response to an electrical demand signal provided in response to operator actuation, in order to set the throughflow crosssections for fluid flow through the first and second valve means between the first actuating port and the pump or tank port and between the second actuating port and the pump or tank port to effect the required control of the fluid actuated device, and for sensing the pressure difference between the first and second actuating ports of the fluid actuated device or the pressure at the actuating port connected to the pump port and, if the pressure difference between the first and second actuating ports or the pressure at the actuating port connected to the pump port reaches a predetermined value, for alerting an operator or for controlling the pressure difference between the first and second actuating ports or the pressure at the actuating port connected to the pump port at or below said predetermined value, unless overridden by an operator, in order to protect an object with which a machine, operated in use by the bidirectional fluid actuated device, makes contact.

2. An electro hydraulic proportional control valve as claimed in claim 1, including means whereby an operator can vary said predetermined value.

3. An electro hydraulic proportional control valve assembly as claimed in claim 2, wherein the predetermined value can be varied in steps.

4. An electro hydraulic proportional control valve as claimed in any one of the preceding claims, wherein the first and second valve members are spools which are axially displaceable to vary the throughflow cross-section for fluid flow between each actuating port and the pump or tank port.

5. An electro hydraulic proportional control valve assembly as claimed in any one of the preceding claims, wherein the servo control means includes electrically operable pilot valve means for controlling the position of each of the valve members.

6. An electro hydraulic proportional control valve assembly as claimed in claim 5, wherein the pilot valve means comprises a first pilot valve for effecting bidirectional axial movement of the first valve member, and a second pilot valve for effecting bi-directional axial movement of the second valve member independently of movement of the first valve member.

7. An electro hydraulic proportional control valve assembly as claimed in claim 5 or claim 6, wherein each pilot valve comprises an actuating coil movable relative to a magnetic former by the application of an electrical actuating current to the coil, and a valve element movable by the coil to simultaneously control application of pilot fluid to one part of the valve member and venting of pilot fluid from another part of the valve member.

8. An electro hydraulic proportional control valve assembly as claimed in any one of claims 5 to 7, wherein a pilot pressure regulator regulates the pressure of fluid supplied to said pilot valve means to hold the last-named pressure substantially constant.

9. An electro hydraulic proportional control valve assembly as claimed in any one of the preceding claims, further comprising pressure sensing means for supplying electrical pressure signals indicative of the fluid pressure in the tank port.

10. An electro hydraulic proportional control valve assembly substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

11. An earth moving vehicle equipped with an electro hydraulic proportional control valve assembly as claimed in any one of the preceding claims, the predetermined value of pressure difference between the first and the second actuating ports or the pressure at the actuating port connected to the pump port being set at a level which will prevent damage by the earth moving vehicle to pipes and/or cables buried in the ground.

12. A method of controlling an earth digging machine having at least one bidirectional fluid activated device for operating the earth digging machine, the method comprising the steps of: (a) controlling the bi-directional fluid actuated device with an electrohydraulic proportional control valve assembly as claimed in any one of Claims 1 to 10, (b) sensing the pressure differential across the bidirectional fluid actuated device or the pressure on the side of the bi-directional fluid actuated device supplied with pressurised fluid during a digging operation, (c) commencing a digging operation, (d) registering said sensed pressure or pressure differential, (e) storing a pressure value which is greater than said sensed pressure or sensed pressure differential by a preselected margin, as said predetermined value.