GB2294977A

GB2294977A - Hydraulic drive system

Info

Publication number: GB2294977A
Application number: GB9522854A
Authority: GB
Inventors: Nicholas John Funnell
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-11-09
Filing date: 1995-11-08
Publication date: 1996-05-15
Anticipated expiration: 2015-11-08
Also published as: GB9422561D0; GB2294977B; GB9522854D0

Abstract

A drive system for a hydraulic actuator includes a variable speed/reversible electric motor (14) driving the pump (12) which transfers fluid between the reservoir (11) and the hydraulic actuator (10). Thus, the speed and/or direction of operation of the actuator (10) can be controlled without the need for additional valve arrangements. A second pump (15) may return fluid from the actuator to the reservoir. The activator (10) may drive an animal exerciser. <IMAGE>

Description

HYDRAULIC DRIVE SYSTEM The present invention relates to a drive system for a hydraulic actuator. More particularly, the present invention relates to a drive system of the general type which includes a fluid reservoir and a pump for pumping fluid between the reservoir and a hydraulic actuator.

The present invention has been developed for use in connection with a hydraulic motor driving a rotary exerciser for animals. However, the invention is suitable for use with all kinds of hydraulic motors and indeed other hydraulic actuators such as hydraulic rams.

United Kingdom Patent 2249012 describes an animal exerciser which is driven by a hydraulic motor. The speed of operation of the motor is controlled by manual alteration of the flow of oil to the hydraulic motor. This is achieved by using a flow valve which returns excess flow of oil to an oil container. The oil is pumped to the valve at a single flow rate by a pump driven by a single speed electric motor. The hydraulic system associated with the motor incorporates a pressure release valve so that if the oil pressure exceeds preset limits, oil will be returned to the oil container. The pressure release valve ensures that damage cannot be caused to the drive system, exerciser or animals within the preset limits. The electric motor and supply can be housed at a distance from the animal exerciser, preventing any chance of electrocution.The disadvantage of this system is that any alteration to the rate of flow from the flow valve to the hydraulic motor can only be achieved by manual or mechanical intervention.

Animal exercisers are available having a variable speed electric motor mounted at the centre of the annular walk-way.

These exercisers have no hydraulic system and therefore no pressure release valve to protect the system. Such systems have to be protected by overload cutouts. If such systems fail, damage to the system, exerciser or animals may occur.

The proximity of the electric motor to the animals presents a risk of electrocution of the animals.

The present invention provides a drive system for a hydraulic actuator including a fluid reservoir, a pump for pumping fluid between the reservoir and the hydraulic actuator and a variable speed or reversible electric motor arranged to drive the pump. Preferably the speed of the electric motor is variable as well as the electric motor being reversible.

Thus, in contrast to the available hydraulic drive systems for animal exercisers, the single speed uni-directional electric motor is replaced with a variable speed or reversible electric motor to drive the oil pump, allowing the pump to be driven at variable speeds in either direction giving a variable output.

As a result of the speed of the motor being variable, a manually operated flow control valve is no longer necessary.

The speed of the electric motor can be controlled manually and can be infinitely variable. However, a particular advantage of using a variable speed electric motor is that it can be preset to a variety of differing speeds, for example under the control of a microprocessor or other logic control system. An animal exerciser having a drive system according to the invention may be pre-programmed with an exercise programme including set time periods trotting, set time periods running and changes of direction. The drive system according to the invention retains the benefits of both electric and hydraulic controls.

Preferably the drive system according to the invention includes two pumps, arranged such that one returns fluid from the hydraulic actuator to the fluid reservoir while the other supplies fluid from the reservoir to the hydraulic actuator.

Preferably those pumps are controlled by the same electric motor. The pumps may be connected to the electric motor by a common drive shaft. Thus, in the case of a complete system including the hydraulic actuator itself, at any one time the output of one pump will be connected to the input of the hydraulic actuator and the output of the hydraulic actuator will be connected to the input of the other pump.

Two embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which: FIGURE 1 is a schematic diagram of a first hydraulic drive system according to the invention; and FIGURE 2 is a schematic diagram of a second drive system according to the invention.

Referring firstly to Figure 1, a hydraulic drive system includes a hydraulic motor 10 connected to a fluid reservoir, in this case an oil container 11, via pump 12 and direction/pressure relief valve 13. The pump 12 pumps oil from the container 11 to the motor 10 via the valve 13. The rate of flow of oil, i.e. the speed of the pump, is controlled by a variable speed electric motor 14. Under normal circumstances, oil is transferred to the hydraulic motor 10 via the oil pump 12 and returned to the container 11 after circulating and thus driving the motor 10. If excessive pressure is exerted from an external source, e.g. a stopped animal in the case of an animal exerciser, the pressure relief valve 13 will operate to divert oil back directly to the oil container and interrupt the operation of the motor until pressure from the external source is removed.Normal circulation of oil then continues to drive the hydraulic motor.

It will be noted that the arrangement does not include a flow rate control valve, the speed of the motor being controllable by varying the speed of the electric motor.

The arrangement shown in Figure 2 is similar to that shown in Figure 1 in many respects and like parts have been indicated by like reference numerals. In the arrangement of Figure 2, the variable speed electric motor has been replaced by a variable speed reversible electric motor 24. Two pumps 12 and 15 are connected between the hydraulic oil container 11 and the motor 10 via a pressure relief valve 23. The pumps 12 and 15 are mounted on a common shaft 30. The pumps 12 and 15 are reversible but at any one time one pump operates to supply fluid to the motor 10 and the other pump operates to supply fluid from the hydraulic motor to the oil container 11. In other words, one pump acts as the pressure pump and the other pump acts as the return pump.This can be achieved by having one rotate clockwise while the other rotates anticlockwise (through suitable gearing arrangements) and by connecting the flow lines between the pumps, the oil container and the hydraulic motor such that one pump supplies and the other pump returns. However, the presently preferred arrangement is to use two oppositely configured pumps mounted on the same shaft. One will be designed to pump when driven clockwise and simply act as a return (idle) when driven anticlockwise. The other will be designed to pump when driven anti-clockwise and act as a return when driven clockwise. The pump in "idle" or "return" mode at any time will act as a brake or speed limiter since it can only accommodate a certain maximum flow rate of fluid in its reverse direction.It will be noted that valve 23 is no longer controlling direction and is simply provided for the purpose of pressure relief.

The advantage of this second embodiment of the invention is that in addition to the speed of the hydraulic motor being variable by varying the speed of the electric motor, its direction can be reversed by reversing the operation of the electric motor so that the pumps reverse their action.

It will be appreciated that it is not essential to use two pumps in connection with a reversible electric motor, one will suffice for certain applications. In other applications it may not be necessary to use a pressure relief valve.

With both of the systems described above, the operating speed of the motor can be preset or varied manually. The arrangement of Figure 2 has the advantage that direction changes can also be preset. Thus, using a suitable control unit, the actuator can be arranged to operate according to a preset progamme including different time periods operating at different speeds in varying directions.

Claims

CLAIMS:

1. A drive system for a hydraulic actuator including a fluid reservoir, a pump for pumping the fluid between the reservoir and the hydraulic actuator and a variable speed electric motor arranged to drive the pump.

2. A drive system as claimed in claim 1 in which the electric motor is reversible.

3. A drive system for a hydraulic actuator including a fluid reservoir, a pump for pumping fluid between the reservoir and the hydraulic actuator and a reversible electric motor arranged to drive the pump.

4. A drive system as claimed in claim 3 in which the speed of the electric motor is variable.

5. A drive system as claimed in any preceding claim including a second pump arranged such that while one pump returns fluid from the hydraulic actuator to the fluid reservoir, the other supplies fluid from the reservoir to the hydraulic actuator.

6. A drive system as claimed in claim 5 in which both pumps are controlled by the same electric motor.

7. A drive system as claimed in claim 6 in which the pumps are connected to the electric motor by a common drive shaft.

8. A drive system as claimed in any preceding claim including the hydraulic actuator.

9. A drive system as claimed in claims 7 and 8 in which, at any time, the output of one pump is connected to the input of the hydraulic actuator and the output of the hydraulic actuator is connected to the input of the other pump.

10. A drive system as claimed in claim 8 or 9 in which the hydraulic actuator is a hydraulic motor.

11. A drive system as claimed in claim 8 or 9 in which the hydraulic actuator is a ram.

12. A exerciser for animals including a drive system as claimed in any preceding claim.

13. A drive system substantially as hereinbefore described with reference to the accompanying drawings.