GB2249289A

GB2249289A - Vehicle, eg mower, with skid steering and articulated steering

Info

Publication number: GB2249289A
Application number: GB9016065A
Authority: GB
Inventors: David Auty
Original assignee: AUTOSTEER CONTROLS Ltd; Itochu Corp
Current assignee: AUTOSTEER CONTROLS Ltd; Itochu Corp
Priority date: 1990-07-21
Filing date: 1990-07-21
Publication date: 1992-05-06
Also published as: GB9016065D0

Abstract

A skid steered all terrain vehicle, eg a remotely controlled mower, has skid steering provided by a hydraulic circuit which supplies fluid to wheel motors at respective sides of the vehicle through independently controlled valves 34, 36. The vehicle may also have articulated steering such that the control valves operate together such that the wheels rotate in the same direction and vary in speed together. The vehicle can operate at slopes of up to 45 DEG and can carry an implement such as a grass cutter (44) to be lowered to work and raised for transport. Means for sensing the load demand at each wheel may control the operation of the valves so that speed of the vehicle is adjusted automatically to the terrain. The hydraulic grass cutter motor (42) may be supplied independently of the speed of the wheels. The cutter may fold away above the vehicle, a height detector stopping the cutter drive above a certain height. <IMAGE>

Description

Improvements Relating to Hydraulic Vehicles The present invention relates to hydraulically operated vehicles and to the hydraulic systems for such vehicles.

There are many types of hydraulically operated vehicle which are currently in use and such vehicles have the advantage that they are often suited to off road and all terrain use.

Many of these vehicles are equipped with all wheel skid steering which makes them highly manoeuvrable and in some cases the wheels on either side of the vehicle can be contra rotated which further increases the manoeuvrablilty of the vehicle.

Such hydraulically operated vehicles do however have a number of disadvantages. In the first place it is not always ideal for a vehicle to be equipped with skid steering as the vehicle may become difficult to control, particularly at high speeds. In addiction, as described in our co-pending PCT patent application which claims priority from British patent application No. 8916254.9, the vehicle may be connected to an implement. This implement may be run from the same hydraulic circuit as the drive for the vehicle but in the past there has arisen the disadvantage that the implement cannot be controlled independently of the vehicle so that for example, in the case when the implement is a grass cutter, the speed of rotation of the cutter blades would be dependent on the speed at which the vehicle wheels are rotating.

It is therefore the object of the present invention to provide a hydraulic system for a vehicle which can increase the versatility of a vehicle and of a vehicle-implement combination.

In a first aspect of the present invention therefore there is provided a hydraulic system for a vehicle characterised in that the system includes means for sensing changes in pressure demand at hydraulic motors for driving the wheels, control valves which adjust to an extent which is directly proportional to the pressure demand at the wheel motors and a pump which pumps hydraulic fluid at a rate dependent upon the degree of adjustment of the valves, so that the speed of the vehicle wheels will automatically vary in response to variations in the terrain over which the vehicle is operating.

There may be provided in the circuit a flow divider so that half of the hydraulic fluid is available to each of two drive trains to allow skid steering of the vehicle.

There may additionally be a bypass valve for the flow divider so that each of the wheel motors is supplied independently of the other wheels thus allowing each wheel motor to be supplied whith hydraulic fluid according to its own pressure demand. The bypass valve may be a solenoid valve which can be remotely operated.

There may be included in the circuit an additional hydraulic motor which controls an agricultural or other implement.

The implement motor may be provided with a load sensing control connected to a variable pump which supplies fluid in proportion to the required implement load and independently of the speed of the wheels.

In a second aspect of the invention there is provided a steerable vehicle wherein the steering control may be either by articulated steering or by skid steering at the option of an operator.

The vehicle may be in two sections and may be provided with an actuator which holds the vehicle rigid with its wheels aligned when skid steering is used and will allow the two sections to pivot relative to one another when articulated steering is used.

The actuator may be electrically operated.

The vehicle may be operated by remote control.

In a third aspect of the invention there is provided a vehicle connected to an agricultural or other implement, the vehicle speed and the implement operation being controllable from the same hydraulic circuit and independently of one another.

The implement may be controlled by a motor which rotates at a constant speed.

The invention will now be further described with reference to the accompanying drawings wherein: Fig. 1 is a schematic representation of a hydraulic system according to the invention for the operation of a vehicle with an implement attached; Fig. 2 is a side view of a vehicle according to the invention; Fig. 3 is a rear view of the vehicle of Fig. 2; and Fig. 4 is a plan view of the vehicle of Fig. 2.

A hydraulically operated vehicle 11 is controlled by a hydraulic system as shown in Fig. 1. A diesel engine 10 drives a pump 12 which pumps oil from a reservoir 14 around a hydraulic circuit.

The vehicle 11 has four wheels 16, 18, 20, 22, each of which is associated with a hydraulic motor 24, 26, 28, 30. The flow of oil in the circuit is separated by a flow divider 32 so that a part of the oil flows to the motors 24, 28 associated with the wheels 16, 20 of one drive train whilst the remainder flows to the motors 26, 30 associated with the wheels 18, 22 of the other drive train. The oil flows to the motors via valves 34, 36.

There is provided in the circuit a means for sensing the load pressure required at each of the wheels 16, 18, 20, 22 and this sensor is connected to the valves 34, 36 which open in response to the load demand at each wheel. The degree to which the valves 34, 36 open is directly proportional to the load demand. The pump 12 also pumps oil at a rate which is proportional to the degree of opening of the valves 34, 36 and therefore the system is capable of automatically adjusting the speed of the vehicle 11 to compensate for variations in the terrain over which the vehicle 11 is travelling and for changes in direction of travel.

There may be a bypass valve 38 fitted around the flow divider 32 which, when it is brought into operation, provides that the oil is no longer divided between two drive trains but can be supplied to any of the four wheels according to the load pressure demand at that wheel. This bypass valve 38 enables each wheel to be driven at an appropriate speed when the vehicle 11 is travelling around a corner or up or down hill and which makes it possible for the vehicle to be steered by articulated steering.

There may also be connected to the system a second pump 40 which supplies oil to a motor 42 which drives an implement 44 (Figs. 2 and 4) such as a grass cutter which is connected to the vehicle 11. The grass cutter 44 is required to be driven at a fixed speed which is independent of the speed of the vehicle wheels. The grass cutter motor 42 is therefore provided with a load sensing device (not shown) which detects changes in the amount of oil being supplied as the requirements of the wheel motors 24, 26, 28, 30 vary and control the pump 40 so that it supplies more or less oil as necessary.

The vehicle 11 is indicated in Figs. 2-4 and comprises a body 46 which is divided into a front 48 and a rear 50 section.

The two sections 48, 50 are joined at the centre of the vehicle body 46 by a pivot 52. A rotary actuator on pivot 52 allows the pivot either to be held rigid so that the wheels of the two drive trains are aligned, or the two parts 48, 50 of the body can be hinged in relation to one another so that the front section 48 with its wheels 16, 18 might be disposed at an angle to the rear section 50 with its wheels 20, 22.

This is of use if an operator wishes to vary the type of directional control by which the vehicle is steered.

For steering the vehicle 11, either of two types of directional control may be chosen. If a high degree of manoeuvrability is desirable then skid steering may be chosen and in this case the flow divider 32 would be in operation so that the right hand wheels 16, 20 are rotating at the same speed and the left hand wheels 18, 22 are also rotating at the same speed which for steering will be different from the speed of the right hand wheels. The two sections 48, 50 of the body would be held rigid by the actuator which is operated electrically. The vehicle 11 can be steered by allowing the wheels of the right hand drive train to rotate at a different speed from the wheels of the left hand drive train. If a very tight turn should be needed, the wheels of the two drive trains can be arranged to contra rotate.

The other method of steering the vehicle 11 is by means of articulated steering. In this case the two sections 48, 50 of the vehicle 11 can be hinged relative to each other and the bypass valve 38 is brought into operation so that each of the wheels 16, 19, 20, 22 can rotate at a different speed if necessary. Thus, if the vehicle turns to the right, the right hand wheels 16, 20 will be required to rotate at a slower speed than the left hand wheels 18, 22. This type of steering is particularly suitable for controlling the vehicle 11 when it is travelling at relatively high speeds.

The grass cutter 44 which is attached to the vehicle 11 is aranged so that it can be folded above the vehicle 11 when not in use. In addition there is a height detector associated with the grass cutter 44 which ensures that it cannot be folded away whilst in operation. This height detector is connected to a cut out switch which stops the cutter should it rise more than a certain height above the ground.

The vehicle can be operated remotely by means of an infra red control unit.

The invention therefore provides an all terrain vehicle which is extremely versatile and which can use either skid steering or articulated steering and can thus benefit from the advantages of both systems.

Claims

1. A skid steer wheeled vehicle which is also capable of articulated steering.

2. A vehicle as in claim 1 wherein the speed of the vehicle wheels will automatically vary in response to variations in the terrain over which the vehicle is travelling.

3. A vehicle according to claim 2, wherein the vehicle includes means for sensing changes in the pressure demand at hydraulic motors for driving the wheels, control valves which adjust to an extent which is directly proportional to the pressure demand at the wheel motors and a pump which pumps hydraulic fluid at a rate dependent upon the degree of adjustment of the valves.

4. A vehicle according to claim 3 wherein there is provided in the hydraulic circuit a flow divider so that half of the hydraulic fluid is available to each of two drive trains to allow skid steering of the vehicle.

5. A vehicle as in claim 4 wherein there is provided a bypass valve for the flow divider so that each of the wheel motors is supplied independently of the other wheels such that each wheel motor is allowed to be supplied with hydraulic fluid according to its own pressure demand.

6. A vehicle as in Figure 5 wherein the bypass valve may be a solenoid valve which can be remotely operated.

7.A vehicle according to any preceding claim wherein there is provided an additional hydraulic motor which controls an agricultural or other implement.

8. A vehicle as in Claim 7 wherein the implement motor is provided with a load sensing control connected to a variable pump which supplies fluid in proportion to the required implement load and independently of the speed of the wheels.

9. A vehicle according to claim 7 or 8 wherein the implement comprises a rotary grass cutter having a horizontal axis of rotation.

10. A vehicle according to claim 9 wherein the grass cutter can be raised from a lowered working position to a raised transport position.

11. A vehicle according to claim 10 wherein the implement in the raised position is within the plan area of the vehicle.

12. A vehicle according to claim 10 or 11 wherein the implement is carried on arms which are pivotably carried on the front wheel axle of the vehicle.

13. A steerable vehicle according to any preceding claim wherein the steering control may be either by articulated steering or by skid steering at the option of an operator.

14. A vehicle as in any of the preceding claims wherein the vehicle chassis is in two sections.

15. A vehicle as in Claim 14 wherein there is provided an actuator which holds the vehicle rigid with its wheels aligned when skid steering is used and will allow the two sections to pivot relative to one another when articulated steering is used.

16. A vehicle as in Claim 15 wherein the actuator is electrically operated.

17. A vehicle connected to an agricultural or other implement wherein the vehicle speed and the implement operation are controllable from the same hydraulic circuit and independently of one another.

18. A vehicle which is designed to traverse ground to be worked upon by a powered implement, said vehicle including such an implement mounted thereon so as to be movable between a lowered working position and a raised transport position, the implement lies within the plan area of the vehicle.

19. A vehicle according to claim 18, wherein the vehicle has front wheels and the implement is carried by the vehicle so as to be pivotable about the front wheel axle in being raised between the lowered and raised position.

20. A vehicle as in any of the preceding claims wherein at least one of the operating functions of the vehicle is controlled by means of remote control.

20. A vehicle as in claim 19 wherein said remote control means is provided by infra red signal detected by a receiver mounted on the vehicle.

21. A vehicle substantially as hereinbefore described with reference to the accompanying drawings.