GB2062187A

GB2062187A - Hydrostatic transmission unit

Info

Publication number: GB2062187A
Application number: GB7938320A
Authority: GB
Original assignee: HAMMOND ENG Ltd
Current assignee: HAMMOND ENG Ltd
Priority date: 1979-11-06
Filing date: 1979-11-06
Publication date: 1981-05-20
Also published as: GB2062187B

Abstract

A hydraulic unit to be connected to a pump (2) and a motor (4), comprises a reservoir (1) for hydraulic liquid, an outlet pipe for the connection of the reservoir (1) to the inlet of the pump (2), a pipe system for the connection of the outlet of the pump (2) to the inlet of the motor and a cooling system (6, 10) for the connection of the outlet of the motor to the reservoir (1), the pipe system including control valve means (9, 9') to control the liquid supplied to the motor, the cooling system being a forced air cooling system including a fan (10) driven by auxiliary motor (3) which may be in series with motor (2), as shown, or in parallel, in which latter case separate speed control means for motor (3) may be provided. In other modifications, the unit is equipped with additional valves to provide for control of one or more additional external motors. Relief valve (7) may be responsive to working fluid temperature. <IMAGE>

Description

SPECIFICATION A hydraulic unit The invention relates to a hydraulic unit to be interposed between a driven hydraulic pump and a hydraulic drive to be driven by the pump.

Large amounts of heat are generated in hydraulic systems which are imparted to the hydraulic liquid, usually oil, through inefficiencies in the system. To compensate for the heat buildup in the system it has been standard practice to have large reservoirs in the system with the resultant disadvantage of large quantities of hydraulic liquid, which penalized the operator heavily with additional costs and poor utilization of space and excessive weight.

This is particularly disadvantageous when the hydraulic system is used in mobile application, such as in a road tanker, where the operation is carried out using the vehicle engine as the source of power.

The aim of the invention is to avoid or at least to mitigate the disadvantages of known systems.

The invention provides a hydraulic unit to be interposed between a driven hydraulic pump and a hydraulic drive to be driven by the pump, the unit comprising a reservoir for hydraulic liquid, an outlet pipe for connection of the reservoir to the inlet of the pump, a pipe system for connection of the outlet of the pump to the inlet of the hydraulic drive, and a cooling system for connection of the outlet of the hydraulic drive to the reservoir, the pipe system including control valve means to control the liquid supplied to the hydraulic drive, the cooling system being a forced air cooling system.

In a preferred embodiment the cooling system includes a cooler matrix cooled by an air fan. The air fan is preferably driven by a fan motor incorporated in the pipe system.

Preferably a relief valve is situated upstream of the cooler matrix. The relief valve may be a pressure-controlled valve and/or temperaturecontrolled valve.

The cooling system preferably includes a filter which may be situated upstream of the cooler matrix and either upstream or downstream of the relief valve of the cooling system.

Preferably also the pipe system includes a relief valve, which is preferably a pressure-controlled valve.

In one preferred embodiment the fan motor is so incorporated in the pipe system that in normal operation the whole flow through the system may be passed through the fan motor. If the hydraulic drive to be served by the hydraulic unit according to the invention comprises more than one hydraulic motor, the hydraulic unit includes valves for directing the liquid flowing through the unit only to the selected motor or motors. The valves may be so arranged that the liquid may flow through the selected hydraulic motor in the selected direction, so that the motor rotates either clockwise or anticlockwise.

A hydraulic unit according to the invention is a compact self-contained unit having ports for the connection to the hydraulic pump and to the hydraulic drive.

The advantage of a hydraulic unit according to the invention is that due to the cooking system the hydraulic reservoir may be much smaller and this considerably reduces the number of pipe joints and consequently the whole weight of the unit.

The unit according to the invention is suitable for mobile applications because in the field servicing is simplified as all the hydraulic components may be removed as one unit and a replacement fitted. This brings about considerable savings in time and better utilization of expensive heavy vehicles.

The proposed unit is not limited to vehicles; it may be used also in the agricultural, plant hire and general engineering field, and on any plant where oil or liquid temperatures have to be reduced or controlled.

It can also be used in a variety of boat applications such as for winch drives, steering systems, and power systems.

Practically any hydraulic system in which the main pump and drive units are remote from the oil reservoir has a potential use for a unit according to the invention.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a diagram of a first embodiment of a hydraulic circuit, Figure 2 is a diagram of a second embodiment of a hydraulic circuit, Figure 3 is a diagram of a third embodiment of a hydraulic circuit, Figure 4 is a diagram of a fourth embodiment of a hydraulic circuit, Figure 5 is a diagram of a fifth embodiment of a hydraulic circuit, Figure 6 is a front elevation, partly in section, of an air-cooled tank unit, and Figure 7 is a side elevation to Figure 6.

In all the Figures the same references indicate the same elements.

The hydraulic circuit shown in Figure 1 comprises a tank 1 for a hydraulic liquid (hereinafter: oil), a pump 2 for pumping the oil to the circuit, a hydraulic fan motor 3 arranged in series with a hydraulic drive motor 4, a filter 5 and a cooler matrix 6 through which air is blown by a fan 10 driven by the fan motor 3. The fan 10 is for simplicity shown as an axial fan, although it is preferably a centrifugal blower.

The circuit includes two relief valves, namely a relief valve 7, protecting the cooler matrix 6, and a relief valve 8 which protects the whole circuit, and particularly the motors 3 and 4. The relief valve 7 is a pressure-controlled valve, e.g. a ball and spring valve, or a temperature-controlled valve, e.g. a thermostatic valve controlled by a wax capsule, although preferably it is both a pressurecontrolled and a temperature-controlled valve. If the valve 7 is to be controlled by temperature it is preferably situated to be submerged in the oil in the tank 1, as shown in Figure 6. The relief valve 8 is also a pressure-controlled valve which is held closed by a spring if the pressure in the circuit immediately upstream of the valve 8 is below a preset value.

The circuit has also a manually operable control valve 9, in the illustrated example a needle valve, positioned downstream of the fan motor 3, as shown in solid lines. Instead of the valve 9, or in addition thereto, a manually operable control valve 9t may be positioned upstream of the fan motor 3, as shown in dashed lines.

The operation of the hydraulic circuit shown in Figure 1 will now be described, starting with normal operation. In the specification the term "normal operation" is intended to mean operation when the relief valves 7 and 8 are both closed.

In normal operation of the variant having only the control valve 9, and not the control valve 9', the oil is drawn from the tank 1 through a suction pipe by the pump 2 and supplied to the fan motor 3 from which, when the control valve 9 is closed, the oil is supplied to the drive motor 4, from which it flows through the filter 5 and cooler matrix 6 back to the tank 1. If the control valve 9 is fully open the oil does not flow through the drive motor 4 but flows through the control valve 9 and through the filter 5 and cooler matrix 6 back to the tank 1. If the control valve 9 is only partly open then the oil flows partly through the drive motor 4 and partly through the valve 9 and in this way the driving of the motor 4 may be controlled between maximum and zero output of the drive motor 4.

As can be seen from Figure 1 in normal operation of the variant without the valve 9' the oil always flows through the fan motor 3, filter 5 and cooler matrix 6, so that the oil returned to the tank 1 is always clean and cool.

If overpressure builds up between the filter 5 and the matrix 6, the relief valve 7, which could be a non-return valve, opens and the oil flows through the valve 7 into the tank 1 so that the cooler matrix 6 cannot be damaged by that overpressure which is thus relieved by the relief valve 7.

If the valve 7 is controlled by the temperature of the oil then, if the oil is at a temperature below a preset temperature, i.e. if it is too cold, such as on starting, the valve 7 is open so that the oil returns to the tank 1 directly through the valve 7 without passing through the cooler matrix 6 and consequently without being cooled.

In any mode of operation the oil flows to and through the filter 5 and from there through the cooler matrix 6 or, in the circumstances explained above, through the relief valve 7, to the tank 1.

Consequently flow past the filter 5 will no longer be mentioned.

If overpressure builds up between the pump 2 and the fan motor 3 and rises above the preset value, the relief valve 8 opens and the oil flows through the valve 8 directly to the filter 5.

In the variant having only the control valve 9', and not the valve 9, the operation is similar except that if the valve 9' is fully open no oil flows through the fan motor 3, so that the fan 10 is not driven and no air is blown through the cooler matrix 6.

The hydraulic circuit shown in Figure 2 is similar to that shown in Figure 1. The circuit includes in addition a selector valve 11, a directional control valve 12, and a supplementary driven motor 13.

The selector valve 11, in the illustrated example a spool valve, is situated downstream of the fan motor 3 and upstream of the drive motor 4 and the valve 12, the valve 12, the valve 12 being connected both downstream and upstream of the motor 13 as will be explained hereinafter.

Each of the shown spool valves 11 and 12 is a three-position valve, the spool of which has at one end (in the drawings the top end) two parallel channels, at the other (bottom) end two channels which cross but do not communicate with each other, and in the centre two parallel channels communicating with each other through a small interconnecting channel. The said channels will herein be called parallel channels, X-channels and H-channels, respectively. The valves 11 and 12 are preferably identical for easy maintenance. In Figure 2 both the valves 11 and 12 are shown in the central position, i.e. the position in which the oil flows through the H-channels.

When the valve 11 is in the illustrated central position the oil flows through the H-channels which have only one inlet, connected to the outlet of the motor 3, and three outlets, one connected to the motor 4, one to the valve 12 and one to a pipe leading to the filter 5. In that position, assuming the valve 9 and/or 9' are closed, oil flows through the motor 3, which is thereby driven, and from there through the valve 11 directly to the filter 5, and also through the valve 11 and the valve 12 to the filter 5.

If the valve 11 is lowered from the illustrated position, oil flows from the fan motor 3 through one of the parallel channels and through the drive motor 4 to the filter 5.

If the valve 11 is raised from the illustrated position, oil flows from the fan motor 3 through one of the X-channels to the valve 12.

As is apparent from the preceding description if the valve 11 is in the lowered position no oil flows to the valve 12, while in the other two positions of the valve 11 the valve 12 is supplied with oil.

The function of the valve 12, when supplied with oil from the valve 11, will now be described.

If the valve 12 is in the illustrated central position oil simply flows through the H-channels of the valve 12 to the filter 5.

If the valve 12 is lowered from the illustrated position oil flows through the top one of the parallel channels, then from top to bottom (in Figure 2) through the motor 13, whereby the motor 1 3 is caused to rotate in one direction, e.g.

clockwise, and from the motor 1 3 the oil flows through the other parallel channel to the filter 5.

If the valve 12 is raised from the illustrated position, oil flows through one of the X-channels from the bottom to the top (in Figure 2) through the motor 13, causing the motor 13 to rotate in the opposite direction, e.g. anticlockwise, and from the motor 13 the oil flows through the other of the X-channels to the filter 5.

The remaining parts of the circuit shown in Figure 2 operate in a manner described in connection with Figure 1.

The embodiments illustrated in Figures 3 to 5 differ from those illustrated in Figures 1 and 2 in that the fan motor 3 and the drive motor 4 are not connected in series, so that the motor 4 receives oil directly from the pump 2 without the interposition of the fan motor 3.

In all the circuits shown in Figures 3 to 5 a flow controlling device 14 for controlling the speed of the fan motor 3 is incorporated. The device 14 may have either a constant orifice, or a variable orifice which is manually controlled, or an orifice automatically compensated to provide constant flow therethrough. In all these three embodiments the elements 5 to 10 operate as described in connection with Figure 1, while the elements 11, 1 2 and 1 3 in Figure 4 operate as described in connection with Figure 2.

Apart from the connection of the motors 3 and 4 and the provision of the controlling device 14, the circuit in Figure 3 is the same as that in Figure 1, and the circuit in Figure 4 the same as that in Figure 2, so that no detailed description of Figure 3 and 4 is needed.

Alternatively design circumstances can prevail which make the inclusion of the device 14 unnecessary.

The circuit illustrated in Figure 5 differs from the circuit illustrated in Figure 4 in that it has a further supplementary driven motor 1 5. Both the supplementary driven motors 13 and 1 5 are connected to the directional control valve 12 which is of the same design as described earlier in connection with Figure 2, but due to its different connection within the circuit according to Figure 5 the valve 12 operates with different results. As in the circuit described in connection with Figure 2 if the valve 11 is in the lowered position no oil flows through the valve 12, while in the other two positions of the valve 11 the valve 12 is supplied with oil.

If the valve 12 is in the illustrated central position oil flows through the H-channels of the valve 12 which have only one inlet, connected to one of the outlets of the valve 11, and three outlets, one connected to the motor 13, one connected to the motor 1 5 and one to a pipe leading to the filter 5. In that position oil flows directly through said pipe to the filter 5.

If the valve 12 is lowered from the illustrated position oil flows through the top one of the parallel channels and through the motor 15, which is thereby driven, to the filter 5. No oil flows through the motor 13.

If the valve 1 2 is raised from the illustrated position, oil flows through one of the X-channels through the motor 13, which is thereby driven, and from there to the filter 5. No oil flows through the motor 1 5.

Figures 6 and 7 show an air-cooled tank unit according to the invention. Any such unit will include only the part of any one of the circuits according to Figures 1 to 5 which is delimited by the dashed line. That means that the pump 2, the drive motor 4 and also the supplementary drive motors 13 and 1 5, when used, are not part of the air-cooled tank unit. The reason for this is that the tank unit is intended to be used in connection with a hydraulic arrangement which already has its own pump, such as pump 2, and its own driving motor or motors, such as motors 4, 13 and 15.For this reason ports A and B for the connection of the pump 2, and ports C and D for the connection of the motor 4 are indicated in all the Figures 1 to 5, and also ports E and Fforthe connection of the motor 13 are shown in Figures 2 and 4, and ports E and F (and D) for the connection of the two motors 13 and 1 5 are shown in Figure 5.

The partial section in Figure 6 shows the filter 5 and valve 7 situated within the tank 1.

The three pipes or hoses are interconnections forming part of the tank unit. The fan motor 3 which drives the fan 10 (not shown) forcing a stream of air through the cooler matrix 6, is supported by three legs and carries a block including the control valve 9, the selector valve 11 and the directional control valve 12, all three of which are operated manually by the shown handles, or remotely, and it also carries the relief valve 8. From this is apparent that the air-cooled tank unit shown in Figures 6 and 7 incorporates a circuit such as that illustrated within the area delimited by a dashed line in Fgures 2, 4 or 5. An air-cooled tank unit incorporating the circuits in the area delimited by the dashed line in Figures 1 or 2 would be simpler because it would not contain the valves 11 and 12.

In alternative embodiments (not shown) it is also possible to dispose with the motor 3 and drive the fan 10 by an electric motor or some other means. Also the filter 5 may be situated between the relief valve 7 and the cooler matrix 6.

Claims

1. A hydraulic unit to be interposed between a driven hydraulic pump and a hydraulic drive to be driven by the pump, the unit comprising a reservoir for hydraulic liquid, an outlet pipe for connection of the reservoir to the inlet of the pump, a pipe system for connection of the outlet of the pump to the inlet of the hydraulic drive, and a cooling system for connection of the outlet of the hydraulic drive to the reservoir, the pipe system including control valve means to control the liquid supplied to the hydraulic drive, the cooling system being a forced air cooling system.

2. A unit according to Claim 1 wherein the cooling system includes a cooler matrix cooled by an air fan.

3. A unit according to Claim 2 wherein the air fan is driven by a fan motor incorporated in the pipe system.

4. A unit according to Claim 2 or 3 wherein a relief valve is situated upstream of the cooler matrix.

5. A unit according to Claim 4 wherein the relief valve is a pressure-controlled valve and/or temperature-controlled valve.

6. A unit according to Claim 4 or 5 wherein the cooling system includes a filter situated upstream of the cooler matrix and either upstream or downstream of the relief valve of the cooling system.

7. A unit according to any one of the preceding claims wherein the pipe system includes a further relief valve.

8. A unit according to Claim 7 wherein said further relief valve is a pressure-controlled valve.

9. A unit according to any one of Claims 3 to 8 wherein the fan motor is so incorporated in the pipe system that in normal operation either a part or the whole flow through the system may be passed through the fan motor.

10. A unit according to any one of the preceding claims to be interposed between a driven hydraulic pump and a hydraulic drive which comprises more than one hydraulic motor, wherein the unit includes valves for directing the liquid flowing through the unit only to the selected one or ones of said motors.

11. A unit according to Claim 10 wherein the valves are so arranged that the liquid may flow through each said selected hydraulic motor in the selected direction, so that the motor rotates either clockwise or anticlockwise.

12. A unit according to any one of the preceding claims which is a compact selfcontained unit having ports for the connection to the hydraulic pump and to the hydraulic drive.

13. A hydraulic unit to be interposed between a driven hydraulic pump and a hydraulic drive to be driven by the pump constructed, arranged and adapted to operate substantially as herein described with reference to, and as shown in Figure 1, or Figure 2, or Figure 3, or Figure 4 or Figure 5 of the accompanying drawings.

14. A hydraulic unit according to Claim 13 constructed, arranged and adapted to operate substantially as herein described with reference to, and as shown in, Figure 6 and Figure 7 of the accompanying drawings.

1 5. A vehicle comprising a hydraulic unit according to any one of Claims 1 to 14.