BACKGROUND With all trailers there are inherent problems, which are relevant for present purposes. When trailing forward and negotiating a bend, the trailer describes a path, which is inside the path of the towing vehicle, tractor or horse. The sharper the bend the more this effect is accentuated. When trailing in reverse direction, jack-knifing is hard to prevent, skilled drivers can overcome the tendency to jack-knife but manoeuvring is much more difficult and is restricted, compared to the towing vehicle. Finally, multiple wheeled trailers having wheels in separate axle sets have a scuff effect on the wheel sets when turning, the sharper the bend, the more severe this effect is.

Steering trailers have been proposed to address one or more of these problems. Examples may be seen, for example, in South African patents 88/8257 (a steering agricultural trailer), 85/0323 (a flat bed trailer with a steering axle or axles), 83/1059 (a tractor-trailer combination with a steering front axle on the trailer) and 93/0489 (a truck and trailer combination).

U. S. patent 4 042 255 discloses a trailer with an actuator for selectively conditioning the steering of the trailer to be locked straight ahead for forward drive and a system of levers for steering into a bend for reverse drive, by means of an electrical connection from the gear selector of the towing vehicle to the actuator. U. S. patent 4 208 063 discloses an actuator for straight ahead steering in forward drive not unlike that of the preceding patent, and a system of levers for steering the wheels into the bend, only in the reverse direction.

U. S. patent 5 244 226 discloses a two wheeled trailer with wheels that can be actuated by complex hydraulic circuits to steer both in the forward direction and the reverse.

THE INVENTION The present invention provides a steering mechanism, which can give an advantageous steering effect for trailers both when going forward and when reversing. The mechanism reverses the steering action on a trailer when the tractor-trailer rig is being reversed, necessary in order to give the advantageous steering effect. The mechanism can also provide for the steering effect to be neutralised when going forward but brought into action when reversing. The steering mechanism is for a wheel, several wheels, a wheel axle or axles or wheel set or sets for a trailer.

A steering mechanism for a trailer in accordance with this invention, comprises a rotation means for sensing a rotation and the direction of rotation of a wheel or wheels of a trailer and/or a thrust means for sensing a forward or reverse direction of thrust applied to the trailer at a connection with a towing vehicle, a reaction means which reacts to the rotation direction and/or the thrust direction, a yaw means for sensing the yaw angle between the towing vehicle and the trailer, the yaw means connected with steering wheels of the trailer to cause a steering action responsive to the yaw and the rotation means and/or thrust means responsive to the rotation and/or thrust direction to reverse the sense in which the steering action is caused to occur or to neutralise the steering action in forward direction.

This mechanism and steering linkages may be entirely mechanical, as will be described further below, or partially hydraulic or pneumatic and/or electrical.

In accordance with an embodiment of the invention, the yaw means comprises a yaw link on the trailer connected to the towing vehicle at a horizontally offset position to a towing hitch and the rotation means a swivel plate which is acted on by a wheel to swivel to a forward steer position when the wheel rotates for forward movement and a reverse steer position when the wheel rotates for reverse movement. The swivel plate forms an intermediate connection between the yaw link and steering linkages on the trailer, to reverse the sense (i. e. clockwise or counter-clockwise) of steering caused by a yaw between trailer and tow vehicle dependant on whether the movement is forward or reverse.

In accordance with another embodiment, a tow hitch is provided on the towing vehicle or on the trailer, which can be pivoted on a horizontal axis according to whether the towing thrust is forward or reverse. This pivoting action is connected by suitable linkages to a swivel plate, which again can reverse the sense in which the steering is caused by the yaw between trailer and towing vehicle. This means can be combined with the rotation sensing means.

Hydraulic and/or pneumatic circuits can substitute for linkages and sensing means partially or wholly, in these embodiments of the invention.

THE DRAWINGS The invention will be more fully described by way of example of a car and small trailer, with reference to the drawings.

In the drawings:- figure 1 is a plan view of a trailer with steering provided on its wheels in accordance with a preferred embodiment of the invention, figure 2 is a plan view of the trailer showing wheels turned while moving in reverse, figure 2A schematically shows the car and trailer moving along a curve in reverse, figure 3 is a plan view of the trailer showing wheels turned while moving forward, figure 3A schematically shows the car and trailer moving forward along a curve, figure 4 is a plan view of a swivel plate arrangement to change the steering from forward to reverse operation, figure 5 is a front elevation of the swivel plate arrangement, figure 6 is a side elevation of the swivel plate arrangement, figure 7 is a plan view of the swivel plate component, figure 8 is an elevation of a gear which meshes with the swivel plate, figure 9 is a plan view of another component of the swivel plate arrangement, figure 10 is a plan view of a connection to the towing vehicle, figure 11 is an elevation of the connection. and figure 12 is a plan view of a simplified linkage according to the invention, for reversing movement.

THE PREFERRED EMBODIMENTS Figures 1 to 3 show the geometry of the mechanical arrangements for steering and conveniently allow an explanation of the mechanical principles.

The trailer 1 is a small trailer (in this example) to be hitched to a motorcar at hitch 2. The trailer has a chassis 3 with two wheels 4 and 5, which can be steered according to this invention. An axle 6 is sprung on leaf springs 7 and 8 and the wheels are mounted on king pins 9 and 10 for steering. Steering cranks 11 and 12 are connected by a tie rod 13 in conventional way.

The invention provides a connection 14 on the rear of the towing vehicle, displaced to one side of the hitch, this provides for the means sensing the yaw angle between the towing vehicle and the trailer. A yaw link 15 is pivotally connected to the connection 14 and leads to a connection 16 on an intermediate or transfer arm 17, which is pivotally mounted, on the chassis, which keeps the link 15 parallel to the longitudinal axis of the trailer. A transfer link 18 is also pivotally connected at the connection 16 and leads to a pivotal connection 19 on an arm 20, which is fixed to the king pin 10 of the steering. The arm 20 is shown in the position it is caused automatically to adopt while the trailer moves forward.

Figures 2 and 2A show that when a yaw angle develops between the car and trailer, due to a turn being negotiated in reverse travel, this causes the wheels to be steered, so as to turn along the curve of the path followed by the car.

By correct selection of the degree of steering of the wheels, this avoids jack- knifing and the car and trailer reverse around curves as a co-ordinated unit. and more closely follow the curve being negotiated by the car.

Figures 3 and 3A show that when the trailer is drawn forward the arm 20 is automatically moved to a position shown in figure 3 as 20'. A mechanism by which this is done is described with reference to figures 4 to 9 below, comprising a plate with a slotted hole, but the principle is the same as the movable arm here referred to. The effect of the arm moving to the position shown in figure 3 is that the same yaw angle developed between the car and trailer while reversing causes the wheels to be steered opposite to the case when moving forward, as shown.

Referring to figures 4 to 9, the way in which the forward or reverse movement of the trailer is sensed is by sensing the rotation direction of the trailer wheel 5. A spur gear 21 is fixed on the hub of the wheel and so rotates with the wheel at all times. The teeth of the spur gear can mesh with the teeth of a gear quadrant 22 which is pivotally mounted on the same shaft as the king pin but can freely rotate independently of the king pin. At each end of the gear teeth of the quadrant is a nylon buffer 23 and 24. The quadrant has a slotted hole 25 in which the end of the link18 is able to slide and pivot in that slotted hole.

The link 18 has its pivotal connection 19 to the arm 20 (figure 1) but the"arm" 20 is a plate as can be seen in figures 4 and 9 with a slotted hole 26, the connection 19 can slide and pivot in this slotted hole. The plate 20 is fixed to the bush 27 (figure 5), which turns on the king pin 10. The wheel is journalled on a stub axle extending from the bush. So the plate functions as the steering arm. The link 18 is shown in figure 4 in the position, which it adopts when the trailer is reversed and in which it will remain until the trailer is moved forward.

This position is also shown in figures 1 and 2. The quadrant 22 holds the connection 19 of the link 18 to the arm 20 in this position.

When the trailer is moved forward, the bush 23 engages the gear 21 frictionally and initiates a movement of the quadrant so that its teeth engage the teeth of the gear 21. This rotates the quadrant clockwise in the view of figure 4, which moves the connection 19 of the link 18 to the opposite end of the slotted hole 26 of the arm 20. At this position the gear teeth of the quadrant run off the gear teeth of the spur gear due to the bush 24 engaging the spur gear frictionally initially. This brings the link to the position shown in figure 3, thus suitable for a steering action in the forward direction. Running at speed causes the bush to move out of frictional contact with the spur gear. If movement of the trailer is changed to the reverse direction, the bush again by frictional contact with the spur gear initiates movement of the quadrant so that the teeth of the quadrant engage teeth of the spur gear to rotate the quadrant back to the position shown in figure 4.

The invention can also be applied in a manner in which there is no steering action in forward motion and steering action only in reverse motion. Figures 10 and 11 show an adaptation for this purpose. The connection 14 of the link 15 is provided in a slotted hole, which allows it to be moved to a position in which it is not offset from the tow hitch but is located in line with it. This has the effect that the yaw angle between car and trailer has no effect on the link and the steering remains fixed with the wheels straight ahead. To cause this movement of the connection 14 a hydraulic, pneumatic or other actuator can be provided.

The movement can also be provided automatically by mounting the hitch 2 pivotally on a horizontal pivot, e. g. 28. The hitch will then respond to thrust forward or rearward by pivoting. This pivoting can be transferred to a horizontal pivoting by links (not shown) to cause the connection to be slid along the slotted hole from the position shown in figures 10 and 11 for reversing to the position directly underneath the hitch. The vertical distance between the hitch and the connection can be minimised so that pitching movement of the trailer relative to the car will not cause an unwanted steering effect.

The pivoting of the hitch can also be used to move the connection 14 of the link 15 from one side of the hitch to the opposite side, to provide for desirable forward and reverse steering. This would replace the mechanism described with reference to figures 4 to 9. In this arrangement the mechanism would sense or be responsive to towing thrust either forwardly or rearward, instead of sensing or being responsive to rotational direction of the trailer wheels.

Figure 12 shows a connection 30 on the towing vehicle, displaced to one side of the hitch 31 for the trailer. A link 32 is pivotally connected at the connection and leads to a pivotal connection 42 at its other end to one arm 33 of a bell crank, which is pivotally mounted, on the trailer at 34. The other arm 35 of the bell crank is pivotally connected at 36 to a tie rod 37 of the steering linkages of the steering arrangement of the trailer wheels. The ends of the tie rod are connected at pivotal connections 43 and 44 to the steering arms 38 and 39, which are fixed to the king pins 40 and 41.

As will be seen the wheels turn in a sense, which prevents jack-knifing when reversing, given suitable dimensioning of the components. Again the connection position 30, or any point or points on link 32, may be made movable so that in towing forward, it is moved into alignment with the hitch 31, or any such point or points as to give nil effect on the trailer wheels when turning.

Apart from hydraulic or pneumatic actions, electrical actions can be implemented to supplement or substitute mechanical mechanisms.

Reference numerals list :- 1 the trailer 2 trailer hitch 3 trailer chassis 4 right trailer wheel 5 left trailer wheel 6 trailer axle 7 right leaf spring 8 left leaf spring 9 right king pin 10 left king pin 11 right steering crank 12 left steering crank 13 steering tie rod 14 offset connection for link 15 yaw link 16 connection for links 17 transfer arm 18 transfer link 19 connection of link to steering arm 20 steering arm (or plate) 21 spur gear on wheel 22 gear quadrant 23 nylon bush on quadrant 24 nylon bush on quadrant 25 slotted hole in quadrant 26 slotted hole in steering arm 27 slotted hole for connection of link to car 28 alternative pivotal mounting for hitch.

29- 30 connection 31 trailer hitch 32 link 33 bell crank arm 34 bell crank pivot 35 bell crank arm 36 connection to tie rod 37 steering tie rod 38 steering arm 39 steering arm 40 king pin 41 king pin 42 bell crank connection 43 tie rod connection 44 tie rod connection