AU1678402A - Steering apparatus - Google Patents

Description

1 STEERING APPARATUS This invention relates to steering apparatus. It has particular application to 8wheeled off-road bulk-haulage vehicles, and for illustrative purposes reference will be made to such application. However, it is to be understood that the steering apparatus may be used in other applications such as swamp buggies and the like.

Large 8-wheeled bulk-haulage vehicles are typically built with two pairs of 00. transversely-separated front wheels, with the pair on each side pivoting for steering purposes about a vertical pivot placed between them. In order to provide access to the inner wheels of each pair for tyre-changing, it is essential that the steering gear be able Sto pivot substantially more than an angle of ±45 degrees, which is normal on large offroad vehicles. This is because the inner wheels are only exposed for tyre-changing at high steering angles. The use of high steering angles is also advantageous for good manoeuverability. If the inner wheel pair can turn 90 degrees from the straight-ahead position and the outer wheels about 70 degrees, the vehicle can U-turn in little more than its own length.

Thus a steering linkage for such a vehicle should have the capability to turn each wheel pair through about 160 degrees. Normal steering linkages are based on the wellknown four-bar kinematic linkage. This linkage works effectively up to an angle of 120 degrees or so, but has two serious shortcomings if used for larger angles. Firstly, the line of action of the forces in the linkage passes very close to the steering pivots at the extremes of motion, resulting in poor mechanical advantage. The consequence of this is that the available steering forces at the wheels are low, even for high linkage forces.

Secondly, the steering angles assumed by the wheels at the extremes of their motion become greatly affected by free play in the steering mechanism. Even for a moderate 2 degree of wear in the linkage, the wheels can move freely through significant angles.

With the foregoing and other objects in mind, this invention is one aspect resides broadly in steering apparatus for a vehicle requiring large steering angles and having a pair of substantially-vertical steering pivots attached to either side of the vehicle frame for supporting steered road wheels, said steering apparatus including:- A pair of primary steering arms attached to said steering pivots, said primary steering arms including steering drive means remote from said steering pivots; A pair of secondary steering arms pivoting about substantially vertical arm pivots attached to said vehicle frame, said secondary steering arms being joined by a steering 0 link attached to said secondary steering arms remote from said arm pivots, and said secondary steering arms being engageable with said steering drive means for transmitting steering forces between said secondary and said primary steering arms.

Preferably, the distance from the arm pivots to the engagement between the secondary and the primary steering arms is significantly longer than the distance from the steering pivots to the engagement between the secondary and primary steering arms, whereby the primary steering arms may be moved via the steering means through significantly larger angles than the angles through which the secondary steering arms are required to swing.

Preferably, the steering drive means includes a drive pin mounted on each primary steering arm and engaging with a slot formed in the secondary steering arm.

Of course, if desired, the steering drive means may be in the form of a slot or slide which engages with a slot or depression formed in the secondary steering arm. A pivoted block may be interposed between the drive pin and the slot to provide larger contact surfaces between the pin and the slot such that wear is minimised.

3 The steering apparatus may be provided with steering actuation means, and this may include a rotary actuator applied to any one of the steering arm pivots. It is preferred, however, that the steering actuation means include a linear actuator, such as a hydraulic cylinder, connected between the vehicle frame and a portion of one the secondary steering arms remote from its arm pivot. A pair of actuators may be provided, each preferably connected between one of the secondary steering arms and the vehicle frame.

The primary and secondary steering arms may be set to align fore-and-aft with the wheels in the straight-ahead position. It is preferred however that, in the straightahead position, the steering pivot and the arm pivot on each side of the vehicle be contained substantially within a vertical plane which also encompasses the steering drive means and the centre of the rear axle, such that an approximation to "Ackerman Effect" is achieved. When turning, this effect swings the outer wheels through a greater S• angle than the inner wheels, so that the centres of rotation of both inner and outer sets of front wheels intersect on or near a projection of the axis line of the rear axle. Thus all wheels swivel about a common vertical axis, with minimal tyre-scrubbing.

In order to more fully explain the invention and put it to practical use, reference will now be made to a preferred embodiment of the invention, wherein:- Figure 1 is a plan view of a steering apparatus according to the invention; Figure 2 is a cross-sectional view showing details of the steering apparatus of Figure 1, and Figure 3 is a series of plan views showing diagrammatically the effect of the steering apparatus at different steering angles.

The steering apparatus 10 shown in Figures 1 and 2 comprises a pair of vertical 4 steering pivots 11 mounted on the vehicle chassis 12 and to which wheel assemblies 13 are attached. To the top of each steering pivot 11 is attached a lower steering arm 14, and a pair of upper steering arms 15 are attached to the vehicle chassis 12 via upper arm pivots 16, the latter being positioned in front of and slightly outboard of the steering pivots 11. The upper steering arms 15 extend rearwards over the lower steering arms 14. With the steering in the straight-ahead position, the longitudinal axes of both the lower steering arms 14 and the upper steering arms 15 intersect the rear axle 17 of the vehicle near its centreline. The outer end of each lower steering arm 14 supports an upwardly-projecting steering pin 20 with a spherical outer surface. A pivot block 21, formed from two halves, fits around the spherical surface of the steering pin and engages with a slot 22 formed in the underside of each upper steering arm A steering link 23 extends between link pins 24 attached to the outer ends of the upper steering arms 15, and a steering actuator 25 extend from each link pin 24 to the vehicle chassis 12. A plunger 26 may be included in the pivot block 21, forced outwards into engagement with the slot 22 by a disc spring 27 to take up any clearance between the pivot block 21 and the slot 22, thus acting as an anti-rattle device.

The spacing between the axes of a steering pivot 11 and the corresponding upper arm pivot 16 is approximately the same as the distance along the lower arm 14 between the axis of the steering pivot 11 and the steering pin 17.

Referring now to Figure 3, it will be seen that, when the steering is aligned in a straight-ahead position, the wheel assemblies 12 are aligned longitudinally. As one of the actuators 25 is extended and the other retracted, the wheel assemblies 12 rotate in a geometric relationship which allows the axes of rotation of the front wheels to intersect reasonably close together on the axis 30 of the rear axle 17. Since the rear wheels must always rotate about the axis 30, this geometrical relationship results in smooth turns with minimal sideways scrub of the tyres. In the extreme case, with the inner wheels turned at 90 degrees to the direction of travel, linkage results in the outer wheels being turned through about 70 degrees, so that the instantaneous centre of rotation for all of the wheels is within the rear axle 17. This allows the vehicle to turn very sharply relative to its size. For the linkage shown, the wheel assemblies 13 are able to swing through a total steering angle of 160 degrees while the four-bar chain eoe comprising the chassis 12, the upper arms 15 and the link 23 operates through an angle of only 80 degrees.

It will of course be realised that the above has been given only by way of illustrative example of the invention, and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention.

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Claims (6)

1. Steering apparatus for a vehicle requiring large steering angles and having a pair of substantially-vertical steering pivots attached to either side of the vehicle frame for supporting steered road wheels, said steering apparatus including:- A pair of primary steering arms attached to said steering pivots, said primary steering arms including steering drive means remote from said steering pivots; S* A pair of secondary steering arms pivoting about arm pivots attached to said vehicle frame, said secondary steering arms being joined by a steering link attached to said secondary steering arms remote from said arm pivots, and said secondary steering arms being engageable with said steering drive means for transmitting steering forces between said secondary and said primary steering arms.

2. Steering apparatus as defined in Claim 1, wherein the distance from said arm pivots to the engagement between said secondary and said primary steering arms is significantly longer than the distance from said steering pivots to the engagement between said secondary and said primary steering arms, whereby said primary steering arms may be moved via said steering means through significantly larger angles than the angles through which said secondary steering arms are required to swing.

3. Steering apparatus as defined in Claim 2, wherein said steering drive means includes a drive pin mounted on each said primary steering arm and engaging with a slot formed in the secondary steering arm.

4. Steering apparatus as defined in Claim 3, whereby a pivoted block is interposed 7 between said drive pin and said slot.

Steering apparatus as defined in Claim 4, and including a linear actuator connected between said vehicle frame and a portion of one said secondary steering arm remote from its said arm pivot.

6. Steering apparatus as defined in Claim 5, wherein, in the straight-ahead position, S. *said steering pivot and said arm pivot on each side of the vehicle are contained substantially within a vertical plane which also encompasses the steering drive means and the centre of the rear axle. Dated this Twentieth day of February, 2002 CHASELING McGIFFIN PTY LTD CHASELING McGIFFIN PTY LTD Joe* *oo*