GB1594451A - Electro-hydraulic valve systems - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO ELECTRO HYDRAULIC VALVE SYSTEMS (71) We, HAWKER SIDDELEY DYNAMICS ENGINEERING LIMITED, a British Company of Manor Road, Hatfield, Hertfordshire AL10 9LL, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to the control of fluid flow in a hydraulic control system and in particular the invention is ooncerned with providing means enabling reliable control of the movement of a valve to be achieved in a contaminated environment.

The invention further seeks to provide a reliable interface between an electric/electronic controller and a hydraulic system. In the following discussion and description emphasis is placed upon the application d the invention to mining equipment. It is to be understood, however, that the invention is not so limited in application and could be applied to other uses.

With the increasing emphasis on automation in the mining industry and the increasing usage of computers and micro-processors to provide proportional and remote control of mining machines and equipment, a requirement exists for a reliable interface between the electric/electronic controllers and the machine hydraulic systems.

In electro-hydraulic systems where a high standard of component and fluid cleanliness can be achieved and maintained, the interface requirement can be met by a standard electro-hydraulic servo valve. Such valves, however, employ spools moving in sleeves with very small diametrical clearance and movement of the spool to direct the fluid flow is dependent on very small differential pressures acting on the spool. Because of the low forces available contaminant particles between the spool and sleeve may cause the spool to lock.

If reliable operation is to be achieved in systems using these valves the level od contamination that can be tolerated is very low.

Filtration of 10 microns or better is essential and particular care has to be taken in toppingup fluid and monitoring its contamination level. In a mining environment 10 micron filter elements would require replacing too frequently to be practical and in any event do not protect the systems downstream of the valve. Even the process of changing the element could introduce contamination, as could topping up the system, unless done with special equipment.

With coal mining equipment the ffuid con tamination problem is further aggravated by the fact that to get the machinery to its working location it almost invariably has to be dismantled on the surface and re-assembled underground. Since the initial build, cleaning and flushing of hydraulic servo systems, even in good workshop conditions, has to be done with great care if contamination of the fluid is to be avoided, then re-assembly underground would present major problems.

Further problems can arise from contamina- tion generated within the system, particularly from flexible hoses between the servo valve and the hydraulic cylinders or motors. Not only do the hoses and prime movers generate contaminant partioles but the fact that the flow is bi-directional makes filtration difficult.

The most comrnon cause of failure of electro-hydraulic servo valves used with contaminated fluid results from the entry of contaminant particles between the valve spool and sleeve preventing the movement of the spool in response to the small differential forces typically available in this type of valve.

According to the present invention, there is provided an electro-hydraulic servo valve assembly for regulating the amount or pressure of hydraulic fluid supplied to a hydraulicallyoperated machine system, comprising a progressively movable valve spool sliding rectilinearly in a ported valve sleeve, a motive power unit, means coupling the drive of the motive power unit to the valve spool, feedback signal generating means supplying a feedback signal representative of the instantaneous position of the valve spool, and electrical control means controlling the energisation of the motive power unit in accordance with input command signals and the feedback signal and wherein the coupling means includes disengageable elements, and a manual over-ride lever is provided for moving the valve spool when the power drive is disengaged.

Thus, in the event of movement of the valve spool being hindered or prevented by ccntaminant particles, valve spool lock can be overcome by use of the manual over-ride lever.

Figure 1 shows a schematic arrangement of a valve spool to control the direction of fluid flow in a machine system, but which is actuated by a mechanical drive other than that according to the invention, and Figure 2 shows a worm drive mechanism with a manual over-ride lever for driving a valve spool as shown in Figure 1 in an arrangement according to the invention.

In Fig. 1, the valve spool 11 sliding in a ported valve sleeve 10 is moved rectilinearly by an eccentric 12 acting through a coupling link 13. The eccentric 12 is mounted on a shaft 14 driven by an electric motor 15 through a speed-reduction gearbox 16. A spool position feedback transducer 17 is also driven by the shaft 14 to provide feedback signals to electrical control means which controls the energisation of the motor 15 in response to input command signals and the feedback signals. This permits a very high effective gear ratio, providing a high spool driving force from a small motor, but does not provide the manual over-ride feature of the present invention.

In Figure 2, the driving means for the valve- spool is replaced by a mechanism that gives an overall electrozhydraulic assembly having manual over-ride according to the in vention. The valve spool (not shown) is moved by a shaft 32 operating a crank 33. A motordriven worm 34 meshes with a worm wheel 35 the hub of which is loose on the shaft 32. One end of the worm wheel 35 is pro vided with a ring of drive teeth 36 that surround another ring. of drive teeth 37 of a shoulder 38 on the shaft 32, and a sleeve 39 slidable along the shaft has a further ring of teeth 40 which can be brought into simultaneous engagement with the teeth 36 on the worm wheel and the teeth 37 on the shaft 32 thereby coupling the motor drive to the shaft. A spring 41 normally urges the sleeve 39 into the engaged position.

X manual over-ride lever 42 has an inoperative position, shown at 43, and an operative position, shown in full lines, in which latter it disengages the motor drive and engages with the shaft 32 so that the spool valve oan be operated manually. The lever 42 is pivotally mounted at 44 on a trunnion 45 attached to the sleeve 39 and surrounding the end of the shaft 32 to swing about an axis at right angles to the axis of the shaft 32.

When the lever 42 is swung about its pivot 44 from the inoperative position 43 to the operative position, a cam portion 46 on the lever engages in a slot 47 in the end of the shaft 32 and thereby couples the lever to the shaft, at the same time forcing the trunnion 45 and sleeve 39 to the left, as seen in the drawing, against the action of the spring 41 so that the drive teeth 36, 37, 40 are disengaged.

The lever 42 will only engage with the slot 47 in the spool drive shaft 32 in one relative angular position ob the shaft and lever, thereby ensuring that the manual lever posi tions will always provide the same system responses.

In all cases there will be feedback signal generating means to generate a feedback signal, indicative of valve spool instantaneous position, for supply to electrical control means controlling the energisation of the motive power unit in response to input command signals and the feedback signal.

The electro Ihydraulic servo valve may be used to control position or speed of movement, or both speed and position, of machines or parts ob machines, feedback transducers appropriate to the requirements being incorporated.

A system deslgned to control a valve driven by a stepper motor can be arranged so that when a command/feedback error exists- it will output a number of drive pulses which will be related to the magnitude of the error and switched so that the direction of rot an tion which results will cause movement of the valve spool such that it takes up Q predetermined position directly related to the error, e.g. at zero error the spool will take up a null position.

The spool position feedback information may then be derived either directly from a spool position feedback transducer as in Figure 1, or indirectly from a stepper drive output pulse count system.

WHAT WE CLAIM IS: 1. An electro-hydraulic servo valve assembly for regulating the amount or pressure of hydraulic fluid supplied to a hydraulicallyoperated machine system, comprising a progressively movable valve spool sliding rectilinearly in a ported valve sleeve, a motive power unit, means coupling the drive of the motive power unit to the valve spool, feedback signal generating means supplying a feed back signal representative of the instantaneous position of the valve spool and electrical control means controlling the energisation of the motive power unit in accordance with input command signals and the feedback signal, and wherein the coupling means includes disengageable elements, and a manual override lever is provided for moving the valve spool when the power drive is disengaged.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   with input command signals and the feedback signal and wherein the coupling means includes disengageable elements, and a manual over-ride lever is provided for moving the valve spool when the power drive is disengaged.

   Thus, in the event of movement of the valve spool being hindered or prevented by ccntaminant particles, valve spool lock can be overcome by use of the manual over-ride lever.

   Figure 1 shows a schematic arrangement of a valve spool to control the direction of fluid flow in a machine system, but which is actuated by a mechanical drive other than that according to the invention, and Figure 2 shows a worm drive mechanism with a manual over-ride lever for driving a valve spool as shown in Figure 1 in an arrangement according to the invention.

   In Fig. 1, the valve spool 11 sliding in a ported valve sleeve 10 is moved rectilinearly by an eccentric 12 acting through a coupling link 13. The eccentric 12 is mounted on a shaft 14 driven by an electric motor 15 through a speed-reduction gearbox 16. A spool position feedback transducer 17 is also driven by the shaft 14 to provide feedback signals to electrical control means which controls the energisation of the motor 15 in response to input command signals and the feedback signals. This permits a very high effective gear ratio, providing a high spool driving force from a small motor, but does not provide the manual over-ride feature of the present invention.

   In Figure 2, the driving means for the valve- spool is replaced by a mechanism that gives an overall electrozhydraulic assembly having manual over-ride according to the in vention. The valve spool (not shown) is moved by a shaft 32 operating a crank 33. A motordriven worm 34 meshes with a worm wheel

   35 the hub of which is loose on the shaft 32. One end of the worm wheel 35 is pro vided with a ring of drive teeth 36 that surround another ring. of drive teeth 37 of a shoulder 38 on the shaft 32, and a sleeve 39 slidable along the shaft has a further ring of teeth 40 which can be brought into simultaneous engagement with the teeth 36 on the worm wheel and the teeth 37 on the shaft 32 thereby coupling the motor drive to the shaft. A spring 41 normally urges the sleeve 39 into the engaged position.

   X manual over-ride lever 42 has an inoperative position, shown at 43, and an operative position, shown in full lines, in which latter it disengages the motor drive and engages with the shaft 32 so that the spool valve oan be operated manually. The lever 42 is pivotally mounted at 44 on a trunnion 45 attached to the sleeve 39 and surrounding the end of the shaft 32 to swing about an axis at right angles to the axis of the shaft 32.

   When the lever 42 is swung about its pivot 44 from the inoperative position 43 to the operative position, a cam portion 46 on the lever engages in a slot 47 in the end of the shaft 32 and thereby couples the lever to the shaft, at the same time forcing the trunnion 45 and sleeve 39 to the left, as seen in the drawing, against the action of the spring 41 so that the drive teeth 36, 37, 40 are disengaged.

   The lever 42 will only engage with the slot 47 in the spool drive shaft 32 in one relative angular position ob the shaft and lever, thereby ensuring that the manual lever posi tions will always provide the same system responses.

   In all cases there will be feedback signal generating means to generate a feedback signal, indicative of valve spool instantaneous position, for supply to electrical control means controlling the energisation of the motive power unit in response to input command signals and the feedback signal.

   The electro Ihydraulic servo valve may be used to control position or speed of movement, or both speed and position, of machines or parts ob machines, feedback transducers appropriate to the requirements being incorporated.

   A system deslgned to control a valve driven by a stepper motor can be arranged so that when a command/feedback error exists- it will output a number of drive pulses which will be related to the magnitude of the error and switched so that the direction of rot an tion which results will cause movement of the valve spool such that it takes up Q predetermined position directly related to the error, e.g. at zero error the spool will take up a null position.

   The spool position feedback information may then be derived either directly from a spool position feedback transducer as in Figure 1, or indirectly from a stepper drive output pulse count system.

   WHAT WE CLAIM IS: 1. An electro-hydraulic servo valve assembly for regulating the amount or pressure of hydraulic fluid supplied to a hydraulicallyoperated machine system, comprising a progressively movable valve spool sliding rectilinearly in a ported valve sleeve, a motive power unit, means coupling the drive of the motive power unit to the valve spool, feedback signal generating means supplying a feed back signal representative of the instantaneous position of the valve spool and electrical control means controlling the energisation of the motive power unit in accordance with input command signals and the feedback signal, and wherein the coupling means includes disengageable elements, and a manual override lever is provided for moving the valve spool when the power drive is disengaged.
2. 2. A valve assembly according to claim 1,

   wherein the motive power unit is a rotary electric motor and the coupling means ccmprise mechanical drive elements converting the rotary motor drive to rectilinear motion.
3. 3. A valve assembly according to claim 2, wherein the coupling means inolude a speedreducing worm and worm wheel.
4. 4. A valve assembly according to claim 1 or claim 2 or claim 3, wherein the coupling means comprises a shaft operatively connected to the valve spool and a sleeve around the shaft which is movable axially relatively to the shaft to engage and disengage said disengageable elements, and the manual lever is swangable about an axis at right angles to the shaft axis between an inoperative position and a position in which the sleeve is cammed axially into a position of. disengagement and the lever is engaged with the shaft.
5. 5. A valve assembly according to claim 4, in which the manual lever can only be engaged with the shaft in one relative angular position of the lever and shaft about the shaft axis.
6. 6. An eleotro-hydraullic servo valve assembly according to claim 1 and substantially as described with reference to the accompanying drawings.