GB1582264A - Hydraulic apparatus - Google Patents

Description

(54) HYDRAULIC APPARATUS (71) We, SMITHS INDUSTRIES LIMITED, a British Company of Cricklewood, London NW2 6JN, 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 hydraulic apparatus.

This invention particularly, though not exclusively, relates to hydraulic apparatus for use in lifting such as, for example, demountable bodies on commercial vehicles. In such a case, it is usual for the hydraulic apparatus to include four hydraulically-operable lifting mechanisms, for example, jacks disposed adjacent to respective corners of the demountable body. Various forms of hydraulic apparatus have been proposed for controlling the operation of the lifting mechanisms.

In one form of such hydraulic apparatus individual multi-piston pumps are provided to deliver hydraulic fluid to the lifting mechanisms. The pumps may be arranged in pairs and controlled by a common motor. While this hydraulic apparatus functions satisfactorily when the load in the demountable body is distributed fairly evenly, it has been found that when there is a substantially uneven distribution of the load, the corners of the demountable body will be lifted at different rates. The reason for this would appear to be that the rate at which fluid is delivered by the pump varies to a considerable extent in dependence upon the fluid pressure in the collection galleries of the pumps and hence in dependence upon the load being lifted by the respective lifting mechanisms.It is clearly desirable from the safety point of view that the demountable body should be maintained substantially level otherwise there is a danger that it will slide off the lifting mechanisms.

In an alternative proposed form of the hydraulic apparatus a single pump, for example, a multi-piston pump or a gear pump, is provided and the pumped fluid is delivered to the lifting mechanisms by flow divider valves. Although such a hydraulic apparatus is generally speaking capable of maintaining the demountable body level while it is being lifted and also lowered, this form of hydraulic apparatus has the disadvantage that in order to provide more than two fluid outlets it is necessary to connect a plurality of flow divider valves in series with the result that errors in the valves are compounded.

Also, it is not possible to provide an odd number of outlets and only possible to provide a limited even number of outlets 2, 4, 8 etc.

It is an object of the present invention to provide an hydraulic apparatus which is capable of being used in lifting loads and which substantially overcomes the aforementioned disadvantages.

According to a first aspect of the present invention there is provided hydraulic apparatus comprising a plurality of hydraulic fluid supply means having respective fluid paths for supplying pressurised fluid to respective hydraulicallyoperable displacement mechanisms, wherein each hydraulic fluid supply means includes pressure-responsive, flow regulator means for controlling the rate of fluid flow through its fluid path, and control means for applying a predetermined pressure to the flow regulator means to control the rate of fluid flow permitted therethrough, the control means being adjustable to vary the pressure applied to the respective flow regulator means so as to provide a predetermined relationship between the rates of fluid flow through the fluid paths permitted by the flow regulator means.

It has been found that with such an hydraulic apparatus it is possible to control hydraulicallyoperable displacement mechanisms in such a manner that the displacement of the mechanisms in such a manner that the displacement of the mechanisms is substantially independent of the loads being displaced by the mechanisms. Thus, for example, when the displacement mechanisms are being used to lift loads, the loads may be maintained substantially level while they are being lifted irrespective of the distribution of the loads on the displacement mechanisms. The said control means permit individual adjustment of the fluid flow rates through the flow regulator means to equalise the flow rates and thereby correct for any differences in the operative dimensions of the flow regulator means.Furthermore, the hydraulic apparatus is relatively inexpensive and may readily be arranged to control the operation of any number of displacement mechanisms.

The flow regulator means may comprise spool valves.

Each flow regulator means may comprise an elongate member slidably mounted in a housing and defining therewith an orifice through which the fluid is to flow, the respective said control means being arranged to control the position of-the elongate member within the housing and thereby the dimensions of the said orifice.

The flow regulator means may include resilient means for urging the said elongate members to a predetermined position in the housings.

Each housing may include first and second apertures communicating with respective surfaces of the elongate member, the respective control means being arranged to control the position of the elongate member within the housing by controlling the fluid pressures in the said apertures. In such a case the said surfaces may be end surfaces of the elongate members.

The control means may comprise valve means which are connected in the respective said fluid paths and which are adjustable to vary the fluid pressure difference between their inlets and outlets. In such a case the inlets and outlets of the said adjustable valve means may be coupled to respective ones of the said first and second apertures.

Each hydraulic fluid supply means may include a second fluid path for delivering fluid from a respective said hydraulically-operable displacement mechanism, and the said second fluid path may include the respective said pressure-responsive flow regulator means and control means. In these circumstances, the first-mentioned and second fluid paths of the hydraulic fluid supply means may include respective valve means to permit fluid flow through one only of said paths at any one time.

Each hydraulic fluid supply means may include a second adjustable control means. In such a case, the second control means may be coupled in one only of the said fluid paths and connected in parallel with the first mentioned control means.

By this means it is possible to provide a rate of fluid flow through the second fluid paths which is different from the rate of fluid flow through the first mentioned fluid paths.

According to a second aspect of the present invention there is provided an hydraulic system comprising hydraulic apparatus in accordance with the first aspect of the present invention, and a source of pressurised fluid to be coupled to one end of the first-mentioned fluid paths.

The said pressurised fluid source may comprise fluid pumping means.

The pressurised fluid source may be arranged to deliver a quantity of fluid in excess of the total fluid capacity of the system.

The hydraulic system may include respective hydraulically-operable displacement mechanisms coupled to the other ends of the first-mentioned fluid paths.

The hydraulically operable displacement mechanisms may be lifting mechanisms.

A hydraulic fluid reservoir may be coupled to the hydraulic fluid supply means.

The hydraulic system may include an electrically-operable valve means through which the hydraulic fluid reservoir is to be coupled to the hydraulic fluid supply means.

The hydraulic fluid supply means may be mounted on the hydraulically-operable displacement mechanisms.

The hydraulically-operable displacement mechanisms may be double-acting mechanisms having first ports through which pressurised hydraulic fluid is to be delivered to the doubleacting mechanisms to actuate the mechanisms in one sense and second ports through which pressurised hydraulic fluid is to be delivered to the double-acting mechanisms to actuate the mechanisms in the other sense.

The first-mentioned and second fluid paths of the hydraulic fluid supply means may have common ends. In these circumstances, the first ports of the double-acting mechanisms may be coupled to one another, and the second ports of the double-acting mechanisms may be coupled to one of the common ends of the said firstmentioned and second fluid paths.

The hydraulic system may include electrically-operable valve means having a first port coupled to the first ports of the double-acting mechanisms, a second port coupled to the other common ends of the said first-mentioned and second fluid paths, a third port coupled to the pressurised fluid source, and a fourth port coupled to the hydraulic fluid reservoir, and in these circumstances electrically-operable valve means may have a first position in which the first and second ports of the electrically-operable valve means are coupled to the third and fourth ports thereof respectively, and a second position in which the first and second ports of the electrically-operable valve means are coupled to the fourth and third ports thereof respectively.

The second ports of the said double-acting mechanisms may be disposed immediately adjacent the said one common ends of the said one common ends of the said first-mentioned and second fluid paths.

Two forms of hydraulic system including hydraulic apparatus in accordance with the present invention and for lifting demountable bodies from a support platform of a commercial vehicle will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a block schematic diagram of one form of the hydraulic system for controlling the operation ofjacks to lift a demountable body; Figure 2 is a circuit diagram of a control unit of the hydraulic system of Figure 1 for controlling the operation of one of the jacks; Figure 3 is a sectional view of an assembly constituting the control unit of Figure 2; Figure 4 is a block schematic diagram of another form of the hydraulic system; and Figure 5 is a circuit diagram of a control unit of the hydraulic system of Figure 4 for controlling the operation of one of the jacks.

The hydraulic systems both include four jacks to be mounted on a commercial vehicle beneath a support platform thereof for demountable bodies to engage the demountable bodies adjacent respective ones of their corner. The jacks are of the single-acting or double-acting kind and hydraulic fluid is supplied to the jacks, to extend them, via respective flow regulator valves which deliver fluid to the jacks at a rate which is substantially independent of the loads being lifted by the jacks. The systems also permit fluid to be -delivered from the jacks to a fluid reservoir via the same flow regulator valves. The rate of such fluid delivery to and from the jacks is thus substantially independent of the loads being lifted by the jacks.The systems also include valve means for adjusting the rate at which fluid flows through the flow regulator means, these valve means being adjustable to equalise the rate at which fluid flows through the flow regulator means and thereby ensure that the demountable containers are maintained level while they are being lifted and lowered.

Referring to Figure 1, the hydraulic system includes four single-acting jacks 10 to 13 which each comprise a cylinder 14, a piston 15 slidably mounted in the cylinder, a rod 16 carried by the piston and extending through an end of the cylinder, and a helical spring 17 which surrounds the portion of the rod within the cylinder 14 and which acts on the piston in a sense to effect retraction of the rod into the cylinder 14. Hydraulic fluid is supplied to the jacks 10 to 13 through the ends of the cylinders 14 remote from the springs 17.

The hydraulic circuit for the jacks 10 to 13 includes a hydraulic pump 18, for example, a multi-piston pump or a gear pump, which acts to draw hydraulic fluid from a reservoir 19 through a conduit 20 and to delivery the fluid through a conduit 21 coupled to ports 22 of four hydraulic control units 23.

These control units 23 each have ports 24 through which hydraulic fluid is delivered to and removed from, the respective jacks 10 via conduits 25 to effect operation of the jacks, the fluid removed from the jacks being delivered to outlets 26 of the control units 23 and returned to the reservoir 19 via a common circuit comprising conduits 27 and 28 and a solenoid-operated valve 29. In order to maintain the required operating pressures within the hydraulic system the quantity of fluid delivered by the pump 18 is arranged to be greater than the total quantity of fluid required by the system, excess fluid supplied by the pump 18 being returned to the reservoir 19 via a pressure relief circuit comprising a conduit 30 and a pressure relief valve 31.

The control units 23 are each of the form shown in Figure 2 wherein the inlet 22 is coupled to a spool valve 32 (constituting a flow regulator valve) through a check valve 33 coupled to the inlet 22 and serially connected with an adjustable metering valve 34. This valve 34 is manually adjustable to select the fluid pressure drop across that valve. The spool valve 32 comprises a spool 35 which is slidably mounted in a housing 36 and which has an intermediate portion 37 of reduced diameter, and a helical spring 38 acting between the housing 36 and the upper end (in the drawing) of the spool 35. The housing 36 is shaped to define an annular recess 39 coupled to the outlet of the metering valve 34 via a conduit 40, this recess 39 partially overlying the reduced-diameter portion 37 of the spool 35 to define therewith an orifice through which hydraulic fluid is delivered to the port 24.This fluid delivery is via a check valve 41 and conduits 42 and 43.

The junction between check valve 33 and the metering valve 34 is coupled via a conduit 44 to a space between the non-spring end of the spool 35 and the housing 36 while the space between the other end of the spool 35 and the housing 36 is coupled via a conduit 45 to the end of the metering valve 34 remote from the check valve 33.

The fluid pressure drop across the metering valve 34 is applied across the ends of the spool 35 to cause the spool to adopt a position in the housing 36 which is dependent on the pressure drop across the metering valve 34 and its setting. The characteristics of the spool valve 32 and especially its spring 38 are selected such that changes in the fluid pressure drop across the metering valve 34, due to change in the load applied to the respective jack 10, will cause an appropriate repositioning of the spool 35 in its housing to maintain a substantially constant rate of fluid flow through the spool valve 32.

Thus the cross-sectional dimensions of the orifice of the spool valve 32 are modified to provide a rate of fluid flow through the spool valve which is substantially independent on the load on the respective jack 10.

The control unit 23 is also arranged to deliver fluid from the port 24 to the outlet 26 via the metering valve 34 and the spool valve 32. The circuit for this purpose comprises a first part having a conduit 46 and check valves 47 and 48 coupling the port 24 to the junction of the check valve 33 and the metering valve 34, and a second part having a check valve 49 and a conduit 50 coupling the output of the spool valve 32 to the outlet 26. A further metering valve 51, that is adjustable to select the fluid pressure drop thereacross, is connected between the conduits 45 and 46 so that during operation of the check valve 48 the two metering valves 34 and 51 are connected in parallel.

When it is required to deliver fluid to the ports 24, to extend the jacks 10, the pump 18 is operated to deliver fluid to the inlets 22 and the fluid flows through the spool valves 32 and hence to the jacks 10 at a rate determined by the settings of the respective metering valves 34. These valves 32 are pre-set to select the pressures applied to the spool valves to compensate for manufacturing tolerances in the spool valves and equalise the rates of fluid flow through the spool valves. Thus the jacks 10 are all extended at the same rate irrespective of the distribution of the loads on the jacks and the vehicle container is maintained level while it is being lifted.

During this operation of the control units 23 the check valves 48 remain closed and the fluid pressure in the conduit 46 is greater than the fluid pressure in the conduit 43 to prevent operation of the check valves 47. Also, the solenoid-operable valve 29 is maintained closed to prevent operation of the check valves 49.

Retraction of the jacks 10 is initiated by energising the solenoid-operable valve 29 to open that valve and thereby permit fluid flow through the check valves 49. This operation of the valves 49 permits fluid trapped in the fluid return paths between the check valves 47 and 49 to flow to the reservoir 19 via the valves 49 and thereby reduce the pressure in the conduits 46 to a level sufficient to permit opening of the check valves 47. Fluid now commences to flow from the jacks 10 to the reservoir 18 via the conduits 46 and 50, the metering valves 34 and 51, and the spool valves 32.In this operation of the control units 23 there is an increased rate of fluid flow through the spool valves 32 with the rate of fluid flow being controlled in accordance with the fluid pressure drop across the pairs of metering valves 34 and 51 rather than merely the pressure drops provided by the metering valves 34. The metering valves 51 are pre-set in the same way as the metering valves 34 to equalise the rates of fluid flow through the spool valves 32. Thus the jacks 10 are all retracted at the same rate with the rate of fluid flow being determined by the pressure drops across the metering valves 34 and 51, rather than the loads on the jacks 10 and hence the fluid pressures in the conduits 46.

In certain applications it may be required to extend and retract the jacks 10 at the same rate and in these circumstances the metering valves 51 and the check valves 48 may be dispensed with.

Referring to Figure 3, the assembly of each control unit 23 includes three flat metal plates 60, 61 and 62 which are clamped together by screws 63 extending through clearance holes in the plates 60 and 61 and engaging screwthreaded holes (not shown) in the plate 62.

The fluid inlet 22 and fluid outlet 26 are constituted by respective holes 64 and 65 in the plate 62 while the port 24 (which is to be coupled to the respective jack 10) comprises an externally-threaded metal connector 66 screwed into the plate 61 and an annular seal 67 clamped between an annular flange on the connector 66 and a surface of the plate 61. The conduits of the control unit 23 are provided by respective holes formed in the plates 60, 61 and 62 and, for simplicity, these holes have been given the same reference numbers as the corresponding conduits shown in Figure 2. As shown in Figure 3, each of the check valves 33, 41, 47, 48 and 49 comprises a ball 68 carried by a member 70, and a biassing helical spring 69 which extends over a spigot 71 of the ballcarrying member 70.

The spool valve 32 comprises a spool, generally referenced at 77 in Figure 3, which is slidably mounted in a bore in the plate 61.

The spool 77 has upper and lower end portions 74, which are provided with balancing grooves 75 spaced at intervals across their respective surfaces, and an intermediate portion of reduced diameter. The bore in which the spool 77 is slidably mounted is shaped to define a chamber 78, constituting the annular recess 39, which partially overlies the reduced-diameter portion of the spool 77. A helical spring 76 disposed in a bore 73 of the plate 60 extends into a recess 72 in the uppermost end portion 74 of the spool 77 and urges the spool 77 downwardly.

The metering valves 34 and 51 are disposed respectively in the plates 60 and 61, and each includes a body 79 which is screwed into a threaded hole 80 in the respective plate. The body 79 has a slot 81 formed in one end thereof to facilitate rotation of the body 79 and adjustment of its position in the hole 80 while the other end of the body 79 is of reduced diameter to provide a stem 82 extending towards a reduced-diameter portion 83 of the hole 80. The free end of the stem 82 is tapered and extends partially into the hole portion 83, the extent of this insertion determining the fluid pressure drop across the metering valve.

A nut 84 is provided to lock the body 79 in its selected position.

Various modifications may be made to the embodiment described within the scope of the invention. For example, although the hydraulic apparatus has been described with reference to the lifting of demountable bodies, it is visualised that the apparatus may be used for lifting other forms of load. Furthermore, the jacks may be of the double-acting kind. Alternatively, the jacks may be replaced by other forms of hydraulically-operable lifting mechanisms, for example, motors.

Also the hydraulic apparatus may be used to control any number of jacks 10 by providing an appropriate number of the control units 23.

The solenoid operated valve could be replaced by other forms of control valve, for example, lever or other manually-controlled valves.

In an alternative form ofjack, the rod 16 is hollow and the spring 17 extends through the rod 16 and acts between the free end of the rod 16 and the end of the cylinder 14 remote from the free end of the rod 16.

Although the hydraulic system has been described in relation to the lifting of loads, it is visualised that the hydraulic system has numerous other applications. For example, the jacks 10 or other hydraulically-operable mechanisms may be used for displacing loads in other than vertical plane. Also, the hydraulically-operable mechanism may be used for positioning individual loads in predetermined relation to one another.

The metering valves 34 may be adjusted to permit predetermined and different flow rates through the spool valves 32.

The alternative form of hydraulic system shown in Figures 4 and 5 is of similar form to the hydraulic system described with reference to Figures 1 and 2, and for simplicity components of the system of Figures 4 and 5 similar or identical to the components of the system of Figures 1 and 2 have been given the same references. The main differences between the two systems are that the jacks 10 to 13 are double-acting rather than single-acting, and that in order to improve the reliability of the system, the hydraulic control units for the jacks through which hydraulic fluid is delivered to and removed from the jacks, are mounted directly on the jacks rather than being coupled to the jacks through conduits.

Referring to Figure 4, the springs 17 are omitted from the jacks 10 to 13 to permit their double action, and the hydraulic system includes four hydraulic control units 100 to 103 for the jacks which are mounted on the ends of the jack cylinders 14 remote from the ends of the cylinders through which the ends of the piston rods 16 project. This direct mounting of the control units 100 to 103 permits the conduits 25 to be dispensed with and thereby reduces the likelihood of malfunction of the hydraulic system due to hydraulic fluid leakage through the conduits 25 or their connections to the jacks and the control units.

The units 100 to 103 are of identical form and each have two parts 104 and 105 with the parts 105 being mounted directly on the jacks 10 to 13. The control units 100 to 103 are each of the form shown in Figure 5, from which it will be seen that the parts 104 are of very similar form to the control units 23 of Figures 1 and 2, having a port 22 through which hydraulic fluid is delivered to and from the ends of the jack cylinders 14 remote from the rods 16 via port 24. The port 24 is coupled to the junction of a pilot-operated lock valve 106, coupled at its other end to a port 107, and to a surge valve 108, coupled at its other end to an inlet port 109.The surge valve 108 comprises a piston 110 slidably mounted in a cylinder 111 and having a rod 112 which projects from one end of the cylinder 111 towards the lock valve 106 to engage and release a ball 113 of the lock valve 106 from its seating and thereby permit hydraulic fluid to flow from the jacks 10 to 13 into the control units 100 to 103.

The portions of the jack cylinders 14 through which the rods 16 extend are provided with fluid ports 114 which are coupled to one another and to the inlets 109 of the control units 100 to 103 by conduits 115, the conduits 115 being coupled to one port of a solenoidcontrolled valve 116 by a common conduit 117.

The ports 22 of the control units 100 to 103 are coupled to one another by conduits 118 which are coupled to another port of the solenoid-controlled valve 116 by a common conduit 119.

Hydraulic fluid is delivered via a check valve 120 to an inlet 121 of the solenoid-controlled valve 116 by the pump 18, an outlet 122Ofthe solenoid-controlled valve 116 being coupled via the conduit 28 to the fluid reservoir 19.

The conduit 28 is coupled to the junction of the pump 18 and the check valve 120 via the pressure-relief valve 31. The solenoid-controlled valve 116 is a three position valve in which in a first position (the position shown in Figure 4) the valve 116 is open and the inlet 121 and the outlet and the outlet 122 are disconnected from both the conduit 117 and the conduit 119. In a second position of the valve 116 the inlet 121 and the outlet 122 are connected to respectively the conduit 117 and the conduit 119 while in a third position of the valve 116, the inlet 121 and the outlet 122 are connected respectively to the conduit 119 and the conduit 117.

In said third position of the solenoidcontrolled valve 116, the hydraulic system is coupled to extend the jacks 10 to 13, pressurised fluid being delivered to the ports 22 of the control units 100 to 103 and thence via the metering valves 34 and the spool valves 32 in the manner previously decribed to provide the equalised rates of fluid flow at the ports 24.

These equalised fluid flows are then fed to the jack cylinders 14 via the check valves 106.

During this extension of the jacks 10 to 13 fluid expelled from the portions of the jack cylinders 14 through which the piston rods 16 extend is returned to the fluid reservoir 19 via the conduits 115, the conduit 117, the solenoid-controlled valve 116 and the conduit 28.

When the solenoid-controlled valve 116 is in its said second position, the hydraulic system is coupled to retract the jacks 10 to 13, and the pressurised fluid is delivered to the ports 114 of the jack cylinders 14. The resultant increased fluid pressure in the conduits 115 actuates the surge valves 108 to effect said opening of the lock valve 106 and permit fluid to be expelled from the jack cylinder 14 through the ports 107. This expelled fluid flows into the parts 104 of the respective control units 100 to 103 and thence flows into the spool valves 32 via the check valves 48 and the metering valves 34 to equalise the rates at which the fluid is expelled from the jack cylinders 14 and thus equalise the rates at which the jacks 10 to 13 are retracted.The fluid leaving the spool valves 32 flows to the ports 22 of the control units 100 to 103 via respective check valves 123, and is then returned to the fluid reservoir 19 via the conduits 118 and 119, the solenoidcontrolled valve 116 and the conduit 28.

In this form of the hydraulic system the metering valves 51 have been dispensed with so that the jacks 10 to 13 are extended and retracted at the same rate. However, it is visualised that in certain circumstances it may be required to extend and retract the jacks 10 to 13 at different rates and in these circumstances the metering valves 51 may be included in the control unit 100 to 103.

WHAT WE CLAIM IS: 1. Hydraulic apparatus comprising a plurality of hydraulic fluid supply means having respective fluid paths for supplying pressurised fluid to respective hydraulically-operable displacement mechanisms, wherein each hydraulic fluid supply means includes pressure-responsive, flow regulator means for controlling the rate of fluid flow through its fluid path, and control means for applying a predetermined pressure to the flow regulator means to control the rate of fluid flow permitted therethrough, the control means being adjustable to vary the pressure applied to the respective flow regulator means so as to provide a predetermined relationship between the rates of fluid flow through the fluid paths permitted by the flow regulator means.

2. Hydraulic apparatus according to Claim 1, wherein the control means are adjusted to equalise the rates of fluid flow permitted by the flow regulator means.

3. Hydraulic apparatus according to Claims 1 or Claim 2, wherein the flow regulator means comprise spool valves.

4. Hydraulic apparatus according to any one of Claims 1 to 3, wherein each flow regulator means comprises an elongate member slidably mounted in a housing and defining therewith an orifice through which the fluid is to flow, the respective said control means being arranged to control the position of the elongate member within the housing and thereby the dimensions of the said orifice.

5. Hydraulic apparatus according to Claim 4, wherein the flow regulator means includes resilient means for urging the said elongate members to a predetermined position in the housing.

6. Hydraulic apparatus according to Claim 4 or Claim 5, wherein each housing includes first and second apertures communicating with respective surfaces of the elongate member, the respective control means being arranged to control the position of the elongate member within the housing by controlling the fluid pressures in the said apertures.

7. Hydraulic apparatus according to Claim 6, wherein the said surfaces are end surfaces of the elongate members.

8. Hydraulic apparatus according to any one of the preceding claims, wherein the control means comprise valve means which are connected in the respective said fluid paths and which are adjustable to vary the fluid pressure difference between their inlets and outlets.

9. Hydraulic apparatus according to Claim 8 and Claim 6 or Claim 7, wherein the inlets and outlets of the said adjustable valve means are coupled to respective ones of the said first and second apertures.

10. Hydraulic apparatus according to any one of preceding claims, wherein each hydraulic fluid supply means includes a second fluid path for delivering fluid from a respective said hydraulically-operable displacement mechanism, the second fluid path including the respective said pressure-responsive, flow regulator means and control means, and wherein firstmentioned and second fluid paths of the hydraulic fluid supply means include respective valve means to permit fluid flow through one only of said paths at any one time.

11. Hydraulic apparatus according to any one of the preceding claims, wherein each hydraulic fluid supply means includes a second adjustable control means.

12. Hydraulic apparatus according to Claims 10 and Claim 11, wherein the second control means are coupled in one only of the said fluid paths and connected in parallel with the firstmentioned control means.

13. An hydraulic system comprising hydraulic apparatus as claimed in any one of the preceding claims, and a source of pressurised fluid to be coupled to one end of the first-mentioned fluid paths.

14. An hydraulic system according to Claim 13, wherein said pressurised fluid source comprises fluid pumping means.

15. An hydraulic system according to Claim 13 or Claim 14, wherein the pressurised fluid source is arranged to deliver a quantity of fluid in excess of the total fluid capacity of the system.

16. An hydraulic system according to any one of Claims 13 to 15, including respective hydraulically-operable displacement mechanisms coupled to the other ends of the firstmentioned fluid paths.

17. An hydraulic system according to Claim 16, wherein the hydraulically-operable displacement mechanisms are lifting mechanisms.

18. An hydraulic system according to any one of Claims 13 to 17, including an hydraulic fluid reservoir to be coupled to the hydraulic fluid supply means.

19. An hydraulic system according to Claim 18, including an electrically-operable valve

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

Claims (30)

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

   104 of the respective control units 100 to 103 and thence flows into the spool valves 32 via the check valves 48 and the metering valves 34 to equalise the rates at which the fluid is expelled from the jack cylinders 14 and thus equalise the rates at which the jacks 10 to 13 are retracted. The fluid leaving the spool valves 32 flows to the ports 22 of the control units 100 to 103 via respective check valves 123, and is then returned to the fluid reservoir 19 via the conduits 118 and 119, the solenoidcontrolled valve 116 and the conduit 28.

   In this form of the hydraulic system the metering valves 51 have been dispensed with so that the jacks 10 to 13 are extended and retracted at the same rate. However, it is visualised that in certain circumstances it may be required to extend and retract the jacks 10 to 13 at different rates and in these circumstances the metering valves 51 may be included in the control unit 100 to 103.

   WHAT WE CLAIM IS: 1. Hydraulic apparatus comprising a plurality of hydraulic fluid supply means having respective fluid paths for supplying pressurised fluid to respective hydraulically-operable displacement mechanisms, wherein each hydraulic fluid supply means includes pressure-responsive, flow regulator means for controlling the rate of fluid flow through its fluid path, and control means for applying a predetermined pressure to the flow regulator means to control the rate of fluid flow permitted therethrough, the control means being adjustable to vary the pressure applied to the respective flow regulator means so as to provide a predetermined relationship between the rates of fluid flow through the fluid paths permitted by the flow regulator means.
2. 2. Hydraulic apparatus according to Claim 1, wherein the control means are adjusted to equalise the rates of fluid flow permitted by the flow regulator means.
3. 3. Hydraulic apparatus according to Claims 1 or Claim 2, wherein the flow regulator means comprise spool valves.
4. 4. Hydraulic apparatus according to any one of Claims 1 to 3, wherein each flow regulator means comprises an elongate member slidably mounted in a housing and defining therewith an orifice through which the fluid is to flow, the respective said control means being arranged to control the position of the elongate member within the housing and thereby the dimensions of the said orifice.
5. 5. Hydraulic apparatus according to Claim 4, wherein the flow regulator means includes resilient means for urging the said elongate members to a predetermined position in the housing.
6. 6. Hydraulic apparatus according to Claim 4 or Claim 5, wherein each housing includes first and second apertures communicating with respective surfaces of the elongate member, the respective control means being arranged to control the position of the elongate member within the housing by controlling the fluid pressures in the said apertures.
7. 7. Hydraulic apparatus according to Claim 6, wherein the said surfaces are end surfaces of the elongate members.
8. 8. Hydraulic apparatus according to any one of the preceding claims, wherein the control means comprise valve means which are connected in the respective said fluid paths and which are adjustable to vary the fluid pressure difference between their inlets and outlets.
9. 9. Hydraulic apparatus according to Claim 8 and Claim 6 or Claim 7, wherein the inlets and outlets of the said adjustable valve means are coupled to respective ones of the said first and second apertures.
10. 10. Hydraulic apparatus according to any one of preceding claims, wherein each hydraulic fluid supply means includes a second fluid path for delivering fluid from a respective said hydraulically-operable displacement mechanism, the second fluid path including the respective said pressure-responsive, flow regulator means and control means, and wherein firstmentioned and second fluid paths of the hydraulic fluid supply means include respective valve means to permit fluid flow through one only of said paths at any one time.
11. 11. Hydraulic apparatus according to any one of the preceding claims, wherein each hydraulic fluid supply means includes a second adjustable control means.
12. 12. Hydraulic apparatus according to Claims 10 and Claim 11, wherein the second control means are coupled in one only of the said fluid paths and connected in parallel with the firstmentioned control means.
13. 13. An hydraulic system comprising hydraulic apparatus as claimed in any one of the preceding claims, and a source of pressurised fluid to be coupled to one end of the first-mentioned fluid paths.
14. 14. An hydraulic system according to Claim 13, wherein said pressurised fluid source comprises fluid pumping means.
15. 15. An hydraulic system according to Claim 13 or Claim 14, wherein the pressurised fluid source is arranged to deliver a quantity of fluid in excess of the total fluid capacity of the system.
16. 16. An hydraulic system according to any one of Claims 13 to 15, including respective hydraulically-operable displacement mechanisms coupled to the other ends of the firstmentioned fluid paths.
17. 17. An hydraulic system according to Claim 16, wherein the hydraulically-operable displacement mechanisms are lifting mechanisms.
18. 18. An hydraulic system according to any one of Claims 13 to 17, including an hydraulic fluid reservoir to be coupled to the hydraulic fluid supply means.
19. 19. An hydraulic system according to Claim 18, including an electrically-operable valve

    means through which the hydraulic fluid reservoir is to be coupled to the hydraulic fluid supply means.
20. 20. An hydraulic system according to any one of Claims 13 to 18, wherein the hydraulic fluid supply means are mounted on the hydraulically-operable displacement mechanisms.
21. 21. An hydraulic system according to any one of Claims 13 to 18, or Claim 20, wherein the hydraulically-operable displacement mechanisms are double-acting mechanisms having first ports through which pressurised hydraulic fluid is to be delivered to the doubleacting mechanisms to actuate the mechanisms in one sense and second ports through which pressurised hydraulic fluid is to be delivered to the double-acting mechanisms to actuate the mechanisms in the other sense.
22. 22. An hydraulic system according to Claim 21, wherein the first mentioned and second fluid paths of the hydraulic fluid supply means have common ends, and wherein the first ports of the double-acting mechanisms are coupled to one another, and the second ports of the double-acting mechanisms are coupled to one of the common ends of the said firstmentioned and second fluid paths.
23. 23. An hydraulic system according to Claim 22, including electrically-operable valve means having a first port coupled to the first ports of the double-acting mechanisms, a second port coupled to the other common ends of the said first-mentioned and second fluid paths, a third port coupled to the pressurised fluid source, and a fourth port coupled to the hydraulic fluid reservoir, and wherein the electrically-operable valve means has a first position in which the first and second ports of the electricallyoperable valve means are coupled to the third and fourth ports thereof respectively, and a second position in which the first and second ports of the electrically-operable valve means are coupled to the fourth and third ports thereof respectively.
24. 24. An hydraulic system according to Claim 22 or Claim 23, wherein the second ports of the said double-acting mechanisms are disposed immediately adjacent the said one common ends of the said first-mentioned and second fluid paths.
25. 25. Hydraulic apparatus substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.
26. 26. Hydraulic apparatus substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings.
27. 27. An hydraulic system substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

    28. An hydraulic system substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.
28. 28. An hydraulic system substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.
29. 29. Hydraulic apparatus substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.
30. 30. An hydraulic system substantially as hereinbefore described with reference to Figures 4 and 5 of the accompanying drawings.