GB2246844A

GB2246844A - Vehicle with auxiliary drive system

Info

Publication number: GB2246844A
Application number: GB9015478A
Authority: GB
Inventors: Eric Dean Horsfield; David Roderick Lloyd
Original assignee: GLOWREACH Ltd
Current assignee: GLOWREACH Ltd
Priority date: 1990-07-13
Filing date: 1990-07-13
Publication date: 1992-02-12
Also published as: GB9015478D0

Abstract

A vehicle having wheels arranged in pairs has a hydraulic auxiliary drive system for driving one of the pairs of wheels, the system comprising a fixed displacement motor 12 for driving each one of the pair of wheels 6, a variable displacement pressure compensated tandem pump 10 for supplying pressure from each section thereof to each one of the motors 12 and means for controlling the pump to regulate the supply to each motor. The motors 12 are carried on the outer side of the wheels which they drive. The vehicle may be a conventional two-wheel drive vehicle and the auxiliary system may be employed to drive the front wheels thereof. The auxiliary system is preferably automatically activated, in particular, in response to movement of the gear shift lever into first or reverse gear. A signal from a solenoid valve 16 causes isolating valves 14 to move into the drive mode and pass oil from the pumps to the motors. The motors then turn at a rate dependent upon the swash-plate angles of the pumps set by controllers (22) and potentiometers (23) (Fig 3). <IMAGE>

Description

Title: Improvements in and relating to a vehicle auxiliary drive system This invention relates to hydraulic auxiliary drive systems for use particularly, but not only, with large vehicles, for example farm tractors and dump trucks.

Many large vehicles today are of the conventional two-wheel drive type and have two mechanically-driven rear wheels and two steerable front wheels which are not driven. The vehicles are provided with conventional drives which serve to power the rear wheels. Under most conditions the drive wheels provide sufficient tractive effort to propel the vehicle as required. However, under certain conditions, particularly in wet conditions, the main drive wheels may begin to spin and will not provide sufficient tractive effort to move the vehicle from the wet ground. One particular example of this is in the use of tipper trucks to remove earth from a site.

The tipper trucks are brought into the works area adjacent to the earth-moving machines and filled up.

If the works area is wet then due to slip on the main drive wheels, the trucks become stuck. It is then necessary to employ another vehicle to push the truck out or to leave it until the area becomes sufficiently dry for it to move again under its own power. Thus one is faced with either providing additional vehicles in order to push trucks out of the works area or one has to leave the trucks in the area for a period of time. The second option is often followed and it is estimated that, as a result of this, dump trucks spend a third of their time idle. This is obviously undesirable.

A solution to this problem is to provide an add-on auxiliary drive system for the vehicle which powers the front steerable wheels. The additional tractive effort provided by the front wheels is normally sufficient to enable the vehicle to be removed from the works area.

Various types of auxiliary drive system have been suggested, the majority of which are powered from the main drive system of the vehicle since, as the additional tractive effort is required when the main drive wheels are spinning, so that the full power capacity of the vehicle is not being utilised, the unutilised capacity can be converted to hydraulic energy to drive the front wheels. In one known system variable displacement motors are employed to drive the front wheels. These are supplied with hydraulic power by way of a single pump, the flow from the pump being divided between the two motors. This arrangement has several disadvantages.

Firstly, the use of variable displacement motors means that the torque available at the wheels varies, with the result that at high speed the torque availability is reduced. Secondly, it is difficult to ensure that the speed of the front wheels is evenly matched. This is because, as noted above, a single pump is employed with a flow divider to supply oil to each motor. Given the fact that flow dividers are known to be generally inefficient and the fact that the motors will have different volumatric efficiencies, it would be difficult, if not impossible, to achieve equal wheel speeds since firstly the flow to the motors would probably not be the same and secondly, even if it is, a given flow would not produce the same motor speed to each motor.

Another problem with known systems is the motors are mounted between the wheels which generally requires the provision of a special design of steering axle and prohibits, or at least complicates, the retrofitting of a vehicle with the add-on auxiliary drive system. Secondly, the motors have to be connected to the wheels by a hub-reduction gear and, with the motor in free-wheel mode, the motor shaft, cylinder block, etc. and hub-reduction unit have to rotate causing considerable resistance to turn. Thus, in the free-wheel position, power dissipation is relatively high.

In accordance with one aspect of the present invention, a vehicle has a number of wheels arranged in pairs and a hydraulic auxiliary -drive system for driving one of the pairs of wheels, comprising a fixed displacement motor for driving each one of said pair of wheels, a variable displacement pressurecompensated pump for supplying pressure to each one of said motors, and, means for controlling the pumps to regulate the supply to each one of said motors.

The use of fixed displacement motors for driving the pair of wheels ensures that maximum torque is available to the wheels at all times no matter what the speed is. Thus, the maximum tractive power will always be available for the wheels driven by the auxiliary system. Furthermore, a pump is provided for each motor and thus the speed of each motor can be directly controlled by control of the relevant pump.

This improves considerably the ability to match the motor speeds of the two wheels over that possible with known arrangements since the error introduced by employing a flow divider is avoided. Furthermore, also as a result of the ability to individually control the speed of each motor, automatic variation of wheel speed during steering is possible to ensure that the speed of the wheels on cornering is correct.

In accordance with another aspect of the present invention, a vehicle has a number of wheels arranged in pairs and a hydraulic auxiliary drive system for driving one of said pairs of wheels, comprising a motor for driving each one of said pair of wheels and at least one pump for supplying pressure to said motors, wherein the motors are carried on the outsides of the wheels.

The advantage of this is that by positioning the motors on the outer sides of the wheels there is no need to provide a specially designed axle for the vehicle and the auxiliary system can be both readily provided with new vehicles and fitted to existing vehicles with the minimum of modification. In addition, the motors can be readily removed from a vehicle to convert it, or reconvert it, to a conventional arrangement.

Preferably the motors are fixed displacement motors and a variable displacement pressure compensated pump is provided for each motor together with means for controlling the pumps to regulate flow to each one of the motors.

The vehicle may be a conventional two-wheel drive vehicle, that is a vehicle with two rear wheels which are driven by the main vehicle drive and two front non-driven wheels, the auxiliary system being employed to drive the front wheels. However, the auxiliary system can be employed with other types of vehicles, for example, large earth-moving vehicles or lorries with six or eight wheels.

Suitably the means for controlling the pumps is coupled to the throttle pedal of the vehicle, the arrangement being such that the speed of the wheels driven by the auxiliary system is controlled in proportion to the speed of the wheels driven by the main vehicle drive, very preferably, this control is automatic and depends on the position of the vehicle throttle pedal. The control means may comprise a potentiometer for each pump connected between the throttle and the pump. The synchronisation of the speeds of the two systems in the vehicle, that is, the known drive system and the auxiliary system ensures that the conventionally driven wheels work in unison with the hydraulic driven wheels for maximum efficiency.

Very suitably, a variable flow closed-loop pressure compensated tandem pump is employed. The pumps may have pressure over-ride systems which automatically reduces the swash-plate angle therein if the pressure rises to a pre-set maximum level, due for example to spinning of the wheels driven by the main vehicle drive, to reduce the speed of the wheels driven by the auxiliary drive system.

If the vehicle in question has other hydraulic components, then the hydraulic fluid tank for these may be employed for the auxiliary system.

Furthermore, power for the auxiliary system pumps can be provided by the main drive of the vehicle, that is the main engine. Thus, the auxiliary system requires no additional supply sources which makes it particularly suitable for retro-fitting to existing vehicles. Of course, if desirable for some reason, an auxiliary hydraulic fluid tank or tanks and an auxiliary engine could be employed for the auxiliary system.

In a particuarly preferred embodiment, the auxiliary system is activated by an automatic activation means. The automatic activation means may be coupled to one or more of the following items generally included in vehicles: the gear shift lever; the accelerator pedal or lever; or the conventionally-powered traction system by way of either the wheels, the transmission or the differential. In one particularly suitable case, the automatic activation means is coupled to the gear shift lever and the arrangement is such that when the vehicle is put into first or reverse gears the auxiliary system will be activated and when the vehicle is put into any other gear it is automatically de-activated.It is in first and reverse gear that the auxiliary system will normally be required and this arrangement means that it will be automatically put into operation in these gears without any action on the part of the driver. Suitably however a manual over-ride is provided for the auxiliary system so that it can be de-activated by the driver if necessary.

The automatic activation means may comprise a solonoid valve connected to the system and capable of presenting fluid flow to the motors.

In a second particularly preferred embodiment the motor casings are attached to the wheels and it is these which rotate. With this arrangement and the motors in the free-wheel mode, there is little resistance to turn since it is only the motor casing which is rotated, not the shaft etc.

Thus there is little loss of power in the free-wheel mode. The shafts of the motors which will remain stationery may be attached to the axle of the vehicle.

The feed to the motors may be via external hoses. However, very preferably the hydraulic power supply to the motors is via ducts extending through the stub-axles of the wheels and the motor spindles.

This method of feeding is particularly advantageous, since it reduces, the length of feed hoses and the possibility of their becoming tangled and damaged.

To provide the auxiliary system for an existent vehicle the hub cap and stub axle of the vehicle at the appropriate wheel has to be modified to provide at least one oil passage through the stub-axle and further to allow the motor spindle to be connected to the stub-axle.

With a new vehicle the wheels thereof should be designed so that they include a single casting which acts both as a stub-axle and as the spindle for the motor attached to the wheel, the casting being formed with at least one oil supply passage.

Thus, as noted above the auxiliary system can be readily employed with either existent vehicles by retro-fitting it thereto or with new vehicles by forming the vehicle with the auxiliary system incorporated therein.

The motors are very suitably such that the pistons thereof are sprung-loaded, pressure supply to the motors causing the pistons to move into the casing with consequent rotation of the casing and cessation of the pressure supply resulting in the piston moving back under the action of the spring. Thus the casing rotates totally freely in the free-wheel mode and there is very little resistance to turn. Furthermore if there is any failure of the electrical control system which will cause cut-off of the pressure supply to the motor, the springs will cause the pistons to move back so automatically bringing the motors into free-wheel mode.

The invention will now be further described by way of reference to the accompanying drawings in which: Fig.l is a schematic side view of a vehicle in accordance with the invention; Fig.2 is a schematic plan view of the vehicle of Figure 1; Fig.3 is a system diagram showing the salient features of the auxiliary system of the vehicle of Figures 1 and 2; Fig.4 is an enlarged view of the left-hand portion of the diagram of Figure 3; Fig.5 is an enlarged view of the right-hand portion of the diagram of Figure 3; Fig.6 is a side view, partly cut away, of part of one wheel, and an attached motor of the vehicle of Figures 1 and 2; Fig.7 is an end view of the wheel of Figure 6; Fig.8 is the side view of a section of the stub axle of the wheel of Figure 6; Fig.9 is an end view of the stub axle section shown in Figure 8.

The vehicle (2) shown in Figures 1 and 2 is a conventional two-wheel drive dump truck, that is, its two rear wheels (4) are driven whilst its two front steerable wheels (6) are non-driven. The vehicle (2) is fitted with an auxiliary system for driving the front wheels (6), shown generally at (8).

The auxiliary system (8) serves to drive the front wheels (6) to provide additional tractive power as and when required, particularly when the vehicle (2) is employed in wet conditions and the rear wheels (4) begin to spin.

The main components of the auxiliary system (8) are shown in Figure 2 and comprise a pump (10), a motor (12) attached to each front wheel (4), an isolating valve (14) for each motor, a solonoid valve (16) for controlling the isolating valves (14) and a hydraulic fluid supply tank (18). All of the components of the auxiliary system (8) are connected by fluid pipes and electrical connectors, generally indicated in Figure 2 by the reference numeral (20).

The auxiliary system is-best understood and is most clearly shown with reference to Figure 3 and the enlargements of the two halves thereof, Figures 4 and 5. The pump (10) is a variable flow, closed loop, pressure compensated tandem pump, each section of which, (l0a) and (lOb), in effect comprises a single "pump". Each of these pumps, (lOa) and (lOb), supply pressure to one of the motors (12) which are fixed displacement motors. The advantages of employing fixed displacement motors is that maximum torque is available at all times no matter what the speed of movement is, which is important in achieving one of the primary purposes of the provision of the auxiliary system, namely the extrication of vehicles from wet areas.

Each pump, (lOa) or (lOb), is provided with an electrical pump controller (22) for setting the angle of the swash-plate of the pump (lOa) or (lOb).

Signals to the electrical controllers (22) are passed via potentiometers (23) which control the value of the signal passed to the controllers (22) and thus the position of the swash-plate of the pumps (lOa) or (lOb). The potentiometers (23) therefore control the speeds at which the motors (12) rotate. The potentiometers are connected electrically to the throttle of the vehicle (2), the arrangement being that the control provided by the potentiometers (23) to the swash-plates of the pumps (lOa) and (lOb) is proportional to the throttle pedal angle. Thus, the speed of the motors (12) will automatically be set in proportion to the speed of the wheels (4) driven by the vehicle main drive. Furthermore, since the control of the pressure supply to each motor (12) is individual the flow to each wheel (6) is, on steering, automatically compensated.The gear shift lever of the vehicle (2) is also connected to the potentiometers (23) so that when the vehicle (2) is to be reversed, the potentiometers (23) cause the swashplates of the pumps (10a) and (lOb) to move over to cause the wheels (6) to be driven in reverse.

Oil from the pumps (lOa) and (lOb) flows through isolating valves (14a) and (14b) to the motors (12). The isolating valves (14a) and (14b) are pilot operated by solonoid valve (16) which is supplied with oil from a charge pump (24) built into the main tandem pump (10). Means are provided for energising or deenergising the solonoid valve (16). When the solonoid valve (16) is energised it passes a "pilot" signal to the isolating valves (14a) and (14b), that is, it allows the passage of oil from the charge pump (24) through the isolating valves (14a) and (14b). The solonoid valve (16) is shown in this position in the Figures. The "pilot" signal from the solonoid valve (16) causes the isolating valves (14a) and (14b) to move into the drive mode and act to pass oil from the pumps (lOa) and (lOb) to the motors (12).The motors (12) will then turn at a rate dependent on the angle at which the swash-plates of the pumps (lOa) and (lOb) have been set by the controllers (22) as signalled by the potentiometers (23).

When the solonoid valve (16) is deenergised, the pilot signal to the isolating valves (14a) and (14b) stops and these valves (14a) and (14b) move into a position in which they cut off the flow from the pumps (lOa) and (lOb) to the motors (12). In this position the isolating valves (14a) and (14b) also serve to drain off the oil in the motor pistons.

The motor pistons are sprung loaded towards the position in which they are withdrawn from the motor casing and the draining off achieved by the isolating valves (14a) and (14b) causes the pistons to retract and move out of the motor casing.

The solonoid valve (16) is preferably electrically connected to one or more of the following vehicle items: the gear shift lever; the accelerator pedal or one of the parts of the traction system, that is, the wheels, the transmission or differential so that the part to which it is connected serves in a pre-arranged way to energise or de-energise the valve (16). Very preferably the solonoid valve is connected electrically to the gear-shift lever. The arrangement is such that when the vehicle is put in first or reverse gear the solonoid valve (16) is energised and when it is put into neutral or a higher gear the solonoid valve (16) is de-energised. It is in first and reverse gear that the auxiliary system (8) is likely to be required and it will automatically be brought into operation without need for the driver to take any positive action.

Suitably however, the driver is provided with a manual over-ride switch so that he can cut out the auxiliary system if he wishes. This might be necessary for example when going down hill in first gear when the driver's natural reaction would be to take his foot off the throttle pedal which would tend to bring the swash-plates in the pumps (lOa) and (lOb) into the neutral position and the front wheels would be sliding faster than they were being turned. In such a situation it would be desirable to be able to cut out the auxiliary hydraulic system (8) to prevent skidding. Furthermore, in dry conditions where wheel spin does not occur and the conventional transmission is sufficient to meet all requirements, the driver is able to override the auxiliary system.

The system (8) is arranged to cope with the spinning of either the wheels (4) powered by the main drive (6) or those powered by the auxiliary system (8). The primary effect is when the main drive wheels (4) spin in which case the auxiliary system drives the wheels (6) to pull the vehicle (2) into an area where spinning ceases. Furthermore the main drive wheels do spin and as a consequence of this the pressure in the auxiliary system (8) rises dramatically then an automatic cut out system operates in the pumps (lOa) and (lOb) to cause the swish-plates therein to move back towards the neutral position to reduce the speed of the wheels driven by the auxiliary system and to restore an equilibrum.The independent drive to each of the motors (12) means that wheel slip of one of the wheels (6) does not affect the power supply to the other so that a continued tractive action will be applied to the vehicle (2). When the auxiliary system (8) is operational.

The power to the hydraulic tandem pump (10) can be provided by the main engine of the vehicle (2) or alternatively auxiliary engines can be employed.

The vehicle (2) may have other hydraulic components and the hydraulic fluid tanks for these can be used for the pump (10). Once again a separate tank or tanks could be provided.

The motors (12) are connected to the outer sides of the wheels (6) by bolting them thereto by way of a mounting bracket (25). In the arrangement shown in the Figures the auxiliary system (8) has been retro-fitted to the vehicle (2), that is, the auxiliary system (8) has been added to an existent vehicle. Whilst. the oil supply to the motors (12) could be via pipe lines it is preferably passed along passages provided in the stub axles (26) of the wheels (6) and thence into the motors (12). To provide for the oil supply and to allow fitting of the auxiliary system the stub axles (26) of the wheel (6) have to be modified and extensions (28) connected to the stub axles (26) Holes (30) have to be drilled through both the stub axles (26) and extensions (28) to act as oil passages to motor (12).The oil passages (30) in the stub axles (26) are connected to the pumps (10) by the isolating valves (14a) and (14b). The hub caps (32) of the wheels (6) also have to be modified to provide an oil seal.

The Figures also show the steering joint (34), brake lever (36), brake shoe pivot (38) and brake drum (40) of the wheel (6). As noted above, the motors (12) are attached to the wheel (6) with the spindles of the motors (12) connected to the axle extensions (28) of the wheels (6). When pressure is supplied to the motors (12) it is the casing which rotates around the main motor shaft or spindle causing the wheels (6) to turn. As also noted above the motor pistons are automatically withdrawn from the motor casing when the pumps (lOa) and (lOb) are in their neutral position. In the neutral position thereof only the motor casings are rotating and these provide little resistance to turn so that there is little power loss.

The auxiliary system described above can be retro-fitted to an existent vehicle or formed as part of a new vehicle. It does not require the provision of a specially designed steering axle since the motors are attached to the outer sides of the wheels.

Maximum torque is available at the wheels at all times when the system is operational by virtue of the use of fixed displacement motors. A tandem pump is employed, each section of which is individually controlled by a potentiometer which allows for close matching of speed of the wheels driven by the auxiliary system with those driven by the main vehicle drive. The system is capable of being activated and deactivated automatically as and when required, in particular, it can be arranged to be activated only when the vehicle is in first and reverse gear. It thus provides an efficient economical way of allowing for continuous use of conventional two-wheel drive vehicles in wet conditions. It should be noted, however, that whilst it has been particularly described in relation to such vehicles it is applicable also to other types of vehicles.

Claims

CLAIMS:

1. A vehicle having a number of wheels arranged in pairs and a hydraulic auxiliary drive system for driving one of the pairs of wheels, comprising a fixed displacement motor for driving each one of said pairs of wheels, a variable displacement pressurecompensated pump for supplying pressure to each one of said motors, and, means for controlling the pumps to regulate the supply to each one of said motors.

2. A vehicle having a number of wheels arranged in pairs and a hydraulic auxiliary drive system for driving one of said pairs of wheels, comprising a motor for driving each one of said pair of wheels and at least one pump for supplying pressure to said motors, wherein the motors are carried on the outside of the wheels.

3. A vehicle as claimed in Claim 1 wherein the motors are carried on the outside of the wheels driven by the hydraulic auxiliary drive systems.

4. A vehicle as claimed in Claim 2 or Claim 3 wherein the casings of the motors are attached to the wheels driven by the hydraulic auxiliary drive system, rotation of the casing relative to the motor shaft serving to drive the wheels.

5. A vehicle as claimed in any one of Claims 2 to 4 wherein the hydraulic power supply to the motors is via a duct which extends through the stub axles of the wheels and the motors spindles.

6. A vehicle as claimed on either Claim 4 or Claim 5 wherein the pistons of the motors are biased by springs towards a position in which they are withdrawn from the casings, pressure supply to the motors causing the pistons to move into the casings against the spring bias with consequence rotation of the casings.

7. A vehicle as claimed in any one of Claims 2 or 4 to 6 wherein the hydraulic auxiliary drive system comprises a fixed displacement motor for driving each one of the pair of wheels, a variable displacement pressure compensated pump for supplying pressure to each one of the motors and means for controlling the pumps to regulate the supply to each one of motors.

8. A vehicle as claimed in Claim 1 or Claim 8 wherein the pumps are provided in the form of a variable flow closed-loop pressure compensated tandem pump.

9. A vehicle as claimed in any one of Claims 1, 7 or 8 wherein the pumps include pressure over-ride systems which automatically reduces the supply from the pumps to the motors when the pressure in the pumps rises to a pre-set maximum level.

10. A vehicle as claimed in any one of Claims 1 or 7 to 9 wherein the means for controlling the pumps is coupled to the throttle pedal of the vehicle, the arrangement being such that the speed of the wheels driven by the auxiliary system is controlled to be proportional to the speed of wheels driven by the main vehicle drive.

11. A vehicle as claimed in Claim 10 wherein the control means set the speed of the wheels driven by the auxiliary system in response to the position of the vehicle throttle pedal.

12. A vehicle as claimed in Claim 10 or 11 wherein the control means comprises a potentiometer connected between the throttle of the vehicle and each pump.

13. A vehicle as claimed in any preceding claim wherein the vehicle has two rear wheels which are driven by the main vehicle drive and two front wheels, the hydraulic auxiliary drive system being employed to drive the front wheels.

14. A vehicle as claimed in any preceding claim wherein power for the hydraulic auxiliary drive system pump(s) is provided by the main drive of the vehicle.

15. A vehicle as claimed in any preceding claim wherein automatic activation means is provided for activating the hydraulic auxiliary drive system.

16. A vehicle as claimed in Claim 15 wherein the automatic activation means is coupled to the vehicle gear shift lever and/or the vehicle accelerator pedal or lever and/or the vehicle transmission and/or the vehicle differential and/or the wheels of the vehicle which are driven by its main drive.

17. A vehicle as claimed in Claim 16 wherein the automatic activation means is coupled to the gear shift lever, the arrangement being such that whenever the vehicle is put into first or reverse gear the auxiliary system is activated and when the vehicle is put into any other gear it is automatically deactivated.

18. A vehicle as claimed in any one of Claims 15 to 17 wherein a manually operated over-ride switch is provided for deactivating the hydraulic auxiliary drive system.

19. A vehicle substantially as hereinbefore described and as shown in the accompanying figures.