GB2275662A

GB2275662A - Vehicle steering systems

Info

Publication number: GB2275662A
Application number: GB9304215A
Authority: GB
Inventors: David Lewis John Dunbar
Original assignee: Gloster Saro Ltd
Current assignee: Gloster Saro Ltd
Priority date: 1993-03-02
Filing date: 1993-03-02
Publication date: 1994-09-07
Also published as: GB9304215D0; IE940179A1

Abstract

The steering system comprises a pivotable steering lever 98, 100 connected to the wheel 106, 108 so as to control the direction of the wheel, an outboard steering link 94, 96 connected to the steering lever for controlling the position of the steering lever, and a linear hydraulic ram 80, 86. The piston 80 (or alternatively the cylinder 86) is rigidly fixed to the vehicle chassis 20 and the outboard steering link 94, 96 is connected to the cylinder 86 (or the piston 80). The system is lightweight and saves space so that the chassis may be lower eg. to allow more space to carry fire-fighting liquids in an airport fire-fighting vehicle. <IMAGE>

Description

"Vehicle Steering Systems" The invention relates to steering systems for vehicles, and particularly, although not exclusively, for heavy off-road vehicles having independent suspension.

A known vehicle steering system comprises a steering box controlled by a rotatable shaft driven by the steering wheel of the vehicle, a drop arm pivotally mounted on the steering box, a relay arm pivotally mounted on the underside of the vehicle chassis and controlled by movement of the drop arm, and a pivotable steering lever for controlling the direction of a wheel, the steering lever being connected to the relay arm by means of an outboard steering link. A hydraulic assistor ram may be pivotally connected to the underside of the chassis and also to the relay lever in order to provide steering assistance. Such an assistor ram is controlled by valves in the steering box. This known steering system is complex, heavy, and space consuming, particularly in view of the fact that each of the steerable wheels must be provided with its own relay bar, and the separate relay bars are mechanically connected to one another by means of connecting links. If more than one pair of steerable wheels is present, adjacent pairs of steerable wheels may be connected by means of a central balance beam, which again is heavy, complex and space consuming.

In many off-road vehicles there is a need to mount-the chassis of the vehicle as low as possible to the ground while maintaining adequate ground clearance. This is because a lower chassis results in more storage space being available above the chassis. The present invention has arisen out of the need to lower the chassis of a heavy off-road airport fire fighting vehicle in order to provide more space above the chassis for the storage of fire fighting liquids.

The invention seeks to provide a vehicle steering system for steering at least one wheel of a vehicle, which overcomes some of the disadvantages of the prior art.

According to the invention there is provided a vehicle steering system for steering a wheel of a vehicle, the steering system comprising a pivotable steering lever connected to the wheel so as to control the direction of the wheel, an outboard steering link connected to the steering lever for controlling the position of the steering lever, and a hydraulic ram comprising first and second parts linearly slidably connected together, the relative positions of said first and second parts being controlled, at least in part, by hydraulic fluid, wherein one of said first and second parts is rigidly fixed to the vehicle chassis, and the outboard steering link is connected to the other of said first and second parts so as to be linearly guided and controlled by movement of said other part along said one part.

It will be appreciated that such a system is relatively simple, and can be made to be lightweight and space saving.

Preferably, said one of said first and second parts is fixed to the vehicle chassis at at least two positions spaced along the length of said one part, so as to ensure that said one part is securely rigidly fixed to the vehicle chassis.

It will be appreciated that said one part is prevented from pivoting by virtue of the fact that it is connected at two positions.

Conveniently, said second part comprises a cylinder for containing hydraulic fluid, and said first part comprises an elongate member extending within and along the cylinder, and extending beyond the ends of the cylinder, the elongate member being sealed to the cylinder so as to prevent loss of the hydraulic fluid.

In this case, the or each part of the elongate member extending beyond an end of the cylinder may be connected to the vehicle chassis, or to an outboard steering link.

Conveniently, the cylinder is a right circular cylinder.

Preferably, the linear movement of said other part along said one part occurs in a direction which is perpendicular to the forward direction of motion of the vehicle.

Conveniently, the steering system further comprises a steering box operated by a shaft driven by the driver of the vehicle, and a drop arm pivotally mounted on the steering box and connected to said other part so as to control the position of said other part relative to said one part.

The invention also includes within its scope a steering arrangement comprising a plurality of steering systems as described above, each steering system being associated with, and controlling the direction of, a pair of wheels.

The invention is particularly suitable for use with wheels having independent suspension, but is also applicable to pairs of wheels connected by a common axle.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a first prior art steering system; Figure 2 shows a second prior art steering system; and Figure 3 shows a steering system according to the invention.

Figure 1 shows a steering system 1 for controlling the directions of four wheels 2 of a heavy off-road vehicle having independent suspension. A steering box 4 is controlled by a rotatable shaft 6 which is connected to the steering wheel (not shown) of the vehicle. A pair of drop arms 8 and 10 are pivotally mounted on the steering box 4, and are controlled by the position of the rotatable shaft 6. The two drop arms 8 and 10 are formed from an L-shaped member 12 which is pivoted to the steering box 4 at its corner.

The first drop arm 8 is connected to a first relay lever 14 via a first connecting link 16. The first connecting link 16 is connected at its ends by pivot joints 18 to the first drop arm 8 and the first relay lever 14. The first relay lever 14 is pivotally connected to the chassis 20 at its first end 22, and to a first outboard steering link 24 at its second end 26. The other end 28 of the first outboard steering link 24 is pivotally connected to a first steering lever 30 which controls the direction of the adjacent wheel 2.

A second connecting link 32 connects the first relay lever 14 to a second relay lever 34 which is also pivotally connected at one end to the chassis 20. The second relay lever 34 controls a second steering lever 36 via a second outboard steering link 38 in like manner to the first relay lever 14.

A hydraulic assistor ram 40 is pivotally connected at one end 42 to the second relay lever 34, and pivotally connected at its other end 44 to the chassis 20.

The assistor ram 40 is controlled by valves within the steering box 4, and provides steering assistance.

The second drop arm 10 is connected via a third connecting link 50 to a second L-shaped member 52 defining first and second drop arms 54 and 56. The first drop arm 54 controls third and fourth relay levers 58 and 60 in like manner to first drop arm 8. A further assistor ram 62 is connected between the chassis 20 and the fourth relay lever 60 in order to provide steering assistance.

The further assistor ram 62 is also controlled by valves in the steering box 4.

It will be appreciated that the presence of the four relay levers 14, 34, 58 and 60, together with the hydraulic assistor rams 40 and 62, render the steering system complex and bulky.

Figure 2 shows a further prior art steering arrangement, and similar parts are labelled using the same reference numerals as used in Figure 1. The steering system differs from that shown in Figure 1 in that the four drop arms 8, 10, 54 and 56 are replaced by a single drop arm 66 which is pivotally mounted on the steering box 4. The drop arm 66 drives a balance beam 68 via a connecting link 70. The balance beam 68 is pivotally connected to the chassis 20 at a mid point 72, and is connected via connecting links 74 and 76 at its ends to the first and third relay levers 14 and 58. Such an arrangement is even more bulky and space consuming than the arrangement shown in Figure 1.

Figure 3 shows an embodiment of the invention.

The steering box 4, rotatable shaft 6, and drop arms 8, 10, 54 and 56 are all identical to those shown in Figure 1. This is an advantage, since it allows the use of components which are already available.

An elongate member 80 is attached to the chassis at its ends 82 and 84. A cylinder 86 is mounted on the elongate member 80 so as to be slidable therealong. The elongate member 80 is arranged laterally across the vehicle, and is provided with a piston 88 fixed about halfway along its length. The piston 88 has a circular outer surface 90 of diameter equal to the diameter of the right circular cylindrical cavity 92 within the cylinder 86. It will be appreciated that the position of the cylinder 86 along the elongate member 80 can be controlled by hydraulic fluid within the cavity 92 on both sides of the piston 88.

The cylinder 88 is pivotally connected at its ends to first and second outboard steering links 94 and 96. The first and second outboard steering links 94 and 96 are connected at their other ends to first and second steering levers 98 and 100 respectively. The first and second steering levers 98 and 100 are pivotally mounted at their other ends 102 and 104 respectively, and control the direction of first and second wheels 106 and 108 respectively.

The cylinder 86 together with the elongate member 80 form a hydraulic ram which is controlled by valves within the steering box 4. It will be appreciated that this removes the need for the two hydraulic assistor rams 40 and 62 of the prior art.

A second pair of wheels 110 are controlled by an identical arrangement comprising a second hydraulic ram 112 which is also controlled by valves within the steering box 4. The second drop arm 56 is pivotally connected to the second drop arm 10 by means of a connecting link 114.

In view of the fact that the steering system shown in Figure 3 does not require a lot of space, it is possible to lower the chassis of the vehicle while maintaining adequate ground clearance. In the prior art arrangements, in order to provide a lower chassis, it would have been necessary to mount at least some of the parts of the steering system above the chassis in order to maintain adequate ground clearance. This is of course disadvantageous in view of the fact that the presence of components above the chassis reduces the amount of space above the chassis which is available for other purposes.

Claims

1. A vehicle steering system for steering a wheel of a vehicle, the steering system comprising a pivotable steering lever connected to the wheel so as to control the direction of the wheel, an outboard steering link connected to the steering lever for controlling the position of the steering lever, and a hydraulic ram comprising first and second parts linearly slidably connected together, the relative positions of said first and second parts being controlled, at least in part, by hydraulic fluid, wherein one of said first and second parts is rigidly fixed to the vehicle chassis, and the outboard steering link is connected to the other of said first and second parts so as to be guided and controlled by linear movement of said other part along said one part.

2. A vehicle steering system as claimed in claim 1, comprising two pivotable steering levers connected respectively to two steerable wheels of the vehicle, and two outboard steering links connected respectively to the two steering levers and to the other of said first and second parts of the hydraulic ram.

3. A vehicle steering system as claimed in claim 1 or claim 2, wherein said one of said first and second parts is fixed to the vehicle chassis at at least two positions spaced along the length of said one part, so as to ensure that said one part is securely rigidly fixed to the vehicle chassis.

4. A vehicle steering system as claimed in any one of the preceding claims, wherein said second part comprises a cylinder for containing hydraulic fluid, and said first part comprises an elongate member extending within and along the cylinder, and extending beyond the ends of the cylinder, the elongate member being sealed to the cylinder so as to prevent loss of the hydraulic fluid.

5. A vehicle steering system as claimed in claim 4, wherein the or each part of the elongate member extending beyond an end of the cylinder is connected to the vehicle chassis, or to an outboard steering link.

6. A vehicle steering system as claimed in any one of the preceding claims, wherein the linear movement of said other part along said one part occurs in a direction which is perpendicular to the in use forward direction of motion of the vehicle.

7. A vehicle steering system as claimed in any one of the preceding claims, further comprising a steering box operated by a shaft driven by the driver of the vehicle, and a drop arm pivotally mounted on the steering box and connected to said other part so as to control the position of said other part relative to said one part.

8. A vehicle steering system as claimed in any one of the preceding claims, further comprising one or more further hydraulic rams, each ram being associated with and arranged to control a pair of steerable wheels.

9. A vehicle steering system as claimed in claim 8, when dependent on claim 7, wherein the steering box has one or more further drop arms connected to said other part or respectively to said other parts of said one or more further rams.

10. A vehicle steering system substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

11. A vehicle equipped with a steering system according to any one of the preceding claims.

12. A vehicle as claimed in claim 11 having an independent suspension.