GB2185945A - Off-road vehicle - Google Patents

Abstract

In an off-road vehicle which comprises a chassis (12) in which an internal combustion engine drives a plurality of hydraulic motors of road wherein the road wheels (32) are wheels (32) via a hydraulic pump, mounted in pairs on pivot beams (34) extending longitudinally of the chassis (12) and each pivot beam (34) is pivotally mounted centrally of its length, a plurality of hydraulic ram arrangements (48) Figure 3A which are hydraulically powered by the hydraulic pump are mechanically interconnected between the pivot beams and the vehicle chassis, so as to impose a torque on the pertaining beams to prevent unwanted pivotal movement of the longitudinal beams arising due to torque reaction and weight transfer when the vehicle is inclined to the horizontal. <IMAGE>

Description

SPECIFICATION Off-road vehicle This invention relates to off-road vehicles.

Off-road vehicles are well known and comprise a chassis on which is mounted an internal combustion engine coupled to drive a plurality of road wheels.

The road wheels are mounted in pairs on pivot beams extending longitudinally of the chassis with a plurality of pivot beams at each side of the chassis.

Typically there are eight road wheels, four at each side of the chassis and therefore there are two pivot beams at each side of the chassis. Each pivot beam is pivotally mounted centrally of its length and a road wheel is mounted at each end of each pivot beam so that a relatively large range of vertical wheel movement is possible due to pivotal movement of the beams thereby enabling the wheels to groundengage despite large bumps and deep ditches such asarecommonlyencountered in off-road con- ditions.

In a known off-road vehicle the internal combustion engine is a diesel engine which mechanically drives a variable output hydraulic pump which in turn is hydraulically coupled to drive a plurality of hydraulic motors, one located in the hub of each road wheel, the hydraulic motors being coupled to deliver mechanical drive to the respective road wheels.

With such known arrangementthere is a tendency arising during negotiation of sloping terrain forthe torque applied by one hydraulic motor to liftthe other road wheel on the same pivot beam due to unwanted pivotal movementofthe beam, thereby sub stantially reducing the power available to propel the vehicle.

It is an object of the present invention to provide an improved form of off-road vehicle in which the foregoing disadvantage is obviated or mitigated.

According to the present invention there is provided an off-road vehicle comprising a chassis on which is adapted to be mounted an internal combustion engine for driving a plurality of road wheels, the road wheels being mounted in pairs on pivot beams extending longitudinally of the chassis, each pivot beam being pivotally mounted centrally of its length and carrying a road wheel at each end of the beam, wherein said engine mechanically drives a variable output hydraulic pump which is hydraulically coupled to drive a plurality of hydraulic motors, said motors being respectively coupled to deliver mechanical drivetothe plurality of road wheels characterised in that a plurality of hydraulic ram arrangements hydraulically powered by said pump mechanically interconnectthe pivot beams and a generally non-horizontally pivotable structure to impose a torque on the pertaining beams preventing unwanted pivotal movement of the beams arising due to torque reaction and weight transfer when the vehicle is inclined to the horizontal.

Each hydraulic ram arrangement may be in the form of a double-acting hydraulic cylinder or a pair of single-acting hydraulic cylinders.

Embodiments of the present invention will now be described, byway of example, with reference to the accompanying drawings.

Figure lisa perspective and part exploded view of an off-road vehicle with a prior art road wheel mounting system; Figure 2 is a diagrammatic view of forceps acting on a pivoted double wheel system; Figure 3a is a side view of a wheel mounting arrangementwith hydraulic biasing means in accordance with an embodiment of the present invention; Figure 3b is a view similar to Figure 1 with hydraulic biasing means for biasing each wheel of a pair of road wheels; Figure 4 of the drawings depicts an off-road vehicle similarto Figure 1 in accordance with an embodiment of the invention, and Figure5is a viewsimilarto Figure 3a, 3b butofan alternative embodiment.

Reference is first made to Figure 1 of the drawings and depicts an off-road vehicle, generally indicated by reference numeral 10, which has a generally rectangular chassis 12, having front and rear crossbeams 14, 16. The front cross-beam 14 has a central bush 18 for receiving rotatably a shaft 20 of a front wheel mount assembly, generally indicated by reference numeral 22, for permitting the assembly to steer the vehicle. The shaft is mounted on a bracket on which is pivotally slung a cross-member 24 for permitting the wheels to rock about axis 26. Along- itudinal beam 28 is mounted at its centre 30 to each end of the cross-membervia rubber bushes. A pair of wheels 32, shown in broken outline, are mounted at each end ofthe beam.Each wheel 32 has a hydraulic motor (not shown) mounted in the hub connected to a common variable output hydraulic pump.

The rear cross-beam 16 is adapted to pivotally receive a rear wheel mount assembly 34, which also have longitudinal beams 36, of which is shown, which are fitted with a pair of wheels 32 in the same manner as the front assembly.

Each hydraulic wheel motor is fixed to one end of the respective beam and the beam takesthetorque reaction of the motor under load. As outlined in the introduction, when negotiating an incline as shown in Figure 2, the rear wheel 38 is more heavily loaded because ofweighttransfer, so thatW1 > W2 and therefore the front wheel, having less load applied to it has a tendency to slip.

Also, because the rear wheel has a drive torque applied to it by its drive motor any equal and opposite reaction to the beams may liftthe frontwheel off the ground, increasing the tendency to slip and reducing the power to propel the vehicle forwards. It will be appreciated that slip of the rear wheel may also occur travelling downhill for similar reasons set forth above because the weight of the vehicle is shifted onto the front wheels.

The aforesaid problems are overcome using the arrangement depicted in Figure 3 and Figure 3b of the drawings. Reference is first made to Figure 3a which illustrates the rear part of a chassis with the wheel mountassembly 34 with the wheels removed in the interest of clarity. Mounted on the chassis 12 is a plate 44to which is coupled one end 46 of a hydraulic double acting ram 48. The ram piston has a rod 50 coupled to a plate 52 with a plurality of mount- ing points 53 mounted at one end of the beam 36.

Hydraulic lines 54,56 are connected between the hydraulic pump and motor (not shown) and to the ram 48. In operation, as the vehicle moves forwards line S4contains high pressurefluidand return line56 contains low pressure fluid. As the vehicle begins to negotiate a slope pressure on the line 54 increases and so torque output of the motors increases, torque reaction on the beam 36 increases, and weig htwill betransferred to the rearwheel. However, via the double acting ram 48, pressure on the front of the beam increases in proportion to the pressure, cancelling outtorque reaction and weight transfer, and retainsthe frontwheel in ground contactto prevent slippage.

Similarly, when going downhill,the ram 48 acts to provide pressure on the rearwheel to minimise the liklihood ofslippage. The position and diameter of the rams are selected to balance the forces involved and the length is such thatthe beam fulfils its intended range of movementforterrain covering purposes.

Reference is now madeto Figure3bofthe drawings which also illustrates the rear part of the chassis 12 with a single acting hydraulic pistons 60, 62 coupled between the chassis and the frontand rear ends of the longitudinal member 36.

The operation is similarto the double acting ram; when the vehicle is moving forward up a slope, ram 60 applies downward pressure on the front of the beam to maintain ground contact ofthe front wheel and when moving down a slope ram 62 applies pressuretothe rearandto cancel outtorque reaction and weighttransfer and maintain ground contact ofthe rearwheels.

The same principle applies when reversing the vehicle with the rams acting on appropriate beam ends to prevent slippage. In the case ofthefront wheels the rams are mounted on the cross-beam 14.

Reference is now made to Figures 4 and 5 ofthe drawings which depict an off-road vehicle in accordance with a second embodiment of the invention in which like numerals denote like parts but with the suffix 'a' added. In this embodiment the frontwheel mount assembly 22a is, in fact rotably coupled to the floor 60 ofthe chassis 1 2a by shaft 20a. The shaft 20a is mounted on plate 62 which is mounted on the underside of the chassisfloorto provide lateral movement. The plate 62 is, in turn, mounted to aturntable plate 64 being on plate 62 to permit steering ofthe assembly 22a. The cross-beam 24a has plates 62,64 mounted thereon which is of inverted U-shaped cross-section with a tube 66 disposed underneath.

The iongitudinal beam 28a has a transversely extending tube 68 which fits within tube 66 to provide longitudinal freedom to the beam 28a which carries motors and wheel mounting boxes, generally indicated by reference numeral 70. The rear assembly 34a is the same as in the first embodiment. Alternatively the rear assembly 34a is the same as front assembly 22a. This vehicle may have a hydraulic arrangement as shown in Figures 3a, 3b and the operator is the same.Alternatively, the off-road vehicle shown in Figure4hasa hydraulicarrangementshownin Figure 5. Inthis case a bracket 72 secured to the end of cross-beam 24a and a hydraulic double acting ram 48a is coupled between the bracket 72 and the longitudinal member 36a and is not directly coupled to the chassis in contrast to the arrangement in Figures 3a, 3b. It will be seen that the ram 48a is almost horizontal to provide a clearer line and to assist in the run of hydraulic hoses, so that they are less vulnerableto damage. Operation of this ram 48a is as described before with reference to the other rams 48.double acting piston may be used as well in a similar mannerto Figure3b.

It will be appreciated that various modifications may be made to the apparatus as hereinbefore des cribed without departing from the scope of the invention. For example, the rams may be electrically or pneumatically controlled although hydraulic is the preferred arrangement and the number and arrangement of rams can be selected to suit particular vehicles. Also the off-road vehicle may have a steering bridge at each end with a hydraulic system as shown in the first or second embodiments, so that no rams are directly attached to the chassis.

Advantages of the invention are that slippage of wheels is minimised, the existing hydraulic pump is utilised and the vehicle is readily modified to accomodate such apparatus minimising cost. The range of mounting points provided for the bottom of the ram permits the system to be fine "tuned" for particular vehicles. The system is self-contained and is therefore automatically self adjusting to settorque applied by the wheels.

Claims (9)

1. According to the present invention there is provided an off road vehicle comprising a chassis on which is adapted to be mounted an internal combustion engine for driving a plurality of road wheels,the road wheels being mounted in pairs on pivot beams extending longitudinally of the chassis, each pivot beam being pivotally mounted centrally of its length and carrying a road wheel at each end of the beam, wherein said engine mechanically drives a variable output hydraulic pump which is hydraulically coupled to drive a plurality of hydraulic motors, said motors being respectively coupled to deliver mechanical drive to the plurality of road wheels char acterised in thata plurality of hydraulic ram arrange- ments hydraulically powered by said pump mechanically interconnect the pivot beams and a generally non-horizontally pivotable structure to impose a torque on the pertaining beams preventing unwanted pivotal movement of the beams arising due to torque reaction and weighttransferwhen the vehicle is inclined to the horizontal.

2. An off-road vehicle as claimed in Claim 1 wherein each pivot beam is coupled to a steering bogie at the front and at the rear of the off-road vehicle.

3. An off-road vehicle as claimed in Claim 1 or Claim 2 wherein each hydraulic ram arrangement is in the form of a double acting hydraulic cylinder.

4. An off-road vehicle as claimed in Claim 1 or Claim 2 wherein said hydraulic ram arrangement is intheform of a pairofsingleacting hydrauliccylinders.

5. An off-road vehicle as claimed in any preceding claim wherein each hydraulic ram arrangement is coupled between chassis and a respective pivot beam.

6. An off-road vehicle as claimed in any one of claims 1 to 4wherein each hydraulic ram arrangement is coupled between a pivot beam and along- itudinal beam disposed on said pivot beam.

7. An off-road vehicle as claimed in any preceding claim wherein the hydraulic ram arrangement is such that the hydraulic piston is substantially hori zontally disposed.

8. An off-road vehicle substantially as hereinbefore described with reference to Figures 1 to 3 of the drawings.

9. An off-r6ad vehicle substantially as herein before described with reference to Figures 4 and 5 ofthe drawings.