The present invention relates to a device in an arrangement for steering wheels, for example the rear wheel pair on a trailer and/or towed wagon, in which a front reference element, for example a potentiometer, is mounted to the coupling device of the tractor vehicle, for example the king pin, and a rear real value element, for example a potentiometer, is mounted on a steering rod for the steered wheels, the elements being interconnected in a regulator circuit for a number of hydraulic cylinders between the steering rod and the chassis.

In order to facilitate the manoeuvring of vehicles or truck combinations with towed trailers, the rear wheel pair can be steerable. This applies particularly to long truck combinations that are provided with a plurality of wheel pairs. In the occurrence of three wheel pairs on a trailer, it is desirable that at least the wheel pair located furthest to the rear can be steered. Known devices for steering a wheel pair on a trailer in proportion to the angular displacement, or truck swing, of the tractor vehicle in relation to the longitudinal axis of the combination comprise steering arms between the steerable wheels and a steering rod and hydraulically powered steering arms between the steering rod and the frame or chassis of the trailer. These steering arms are connected into a regulator circuit with one forward reference element potentiometer and a rear real value potentiometer. The drawbacks inherent in such prior art devices substantially reside in difficulties in achieving the desired angular displacement between the tractor vehicle and the reference element potentiometer as well as the real value potentiometer and the steerable rear wheels.

The task forming the basis of the present invention is to eliminate or at least reduce the drawbacks inherent in prior devices of the type disclosed by way of introduction.

This task is solved according to the present invention in that the device disclosed by way of introduction is characterized in that the front reference element is connected to the coupling device on the tractor vehicle for positive

rotation thereof by means of the coupling device on the trailer whose wheels are to be steered; and that the rear real value element is coupled to the rear steering rod via coupling means which permit rotation thereof during simultaneous longitudinal displacement of the point of engagement between the steering rod and a coupling device in the real value element. The rear real value element is mounted for displacement movements to and from the steering rod along the longitudinal axis of the trailer. In that case when the elements consist of potentiometers, the rear real value potentiometer is provided with a rotary arm whose length is variable and which is pivotally connected with the steering rod. The stub shaft is mounted on an arm departing from the steering rod. The arm and/or the stub shaft are disposed for adjustment of the position of the stub shaft in relation to the pivot centre of the steering rod. The rear real value potentiometer is coupled to the steering rod via an arm whose one end is pivotal about the potentiometer and whose other end is pivotally interconnected with the steering rod. The point of interconnection between the arm and the steering rod is adjustable. The rear real value potentiometer is mounted on a number of rails that extend parallel to the longitudinal axis of the trailer. The point of interconnection between the arm and the steering rod is located more proximal the centre of the steering rod than the point of interconnection between the rotary arm of the real value potentiometer and the steering rod.

As a result of the device according to the present invention, the contemplated objects will be attained, and the task addressed by the present invention will thereby be solved in a relatively simple and operationally reliable manner. In one prototype of a device according to the present invention, it has been possible to ascertain that the sought-for angular displacement or truck swing is achieved with very great accuracy. A major advantage afforded by the device according to the present invention further resides in the fact that it moreover makes possible greater angular displacement, or truck swing, than do prior art devices. The greater the angular displacement that is made possible, the easier will be manoeuvring of the vehicle or the combination, and, thereby, accessibility with the vehicle will be greatly improved.

The present invention will now be described in greater detail herein below, with particular reference to the accompanying Drawings. Fig. 1A is a schematic top plan view of a forward portion of a vehicle carrying a device according to one embodiment of the present invention. Fig. 1B shows a view similar to that of Fig. 1 A of a rear portion of the vehicle. Fig. 2 is a schematic top plan view of the angular displacement or truck swing for wheels steerable according to the present invention. Fig. 3 is a schematic front elevation of parts of a steerable wheel pair according to one embodiment of the present invention. Fig. 4 is a side elevation of parts of the wheel pair of Fig. 3. Fig. 5 is a top plan view of parts of the wheel pair of Figs. 3 and 4. Fig. 6 is a side elevation, partly in section, of a front portion of the device according to the present invention. Fig. 7 is a top plan view of the portion shown in Fig. 6. Fig. 8 is a view from beneath of the portion shown in Figs. 6 and 7. Fig. 9 shows a view similar to that of Fig. 6 with additional parts. Fig. 10 is a top plan view of Fig. 9. Fig. 11 is a perspective view of parts included in a rear portion of the device according to the present invention. Fig. 12 is a side elevation of the parts illustrated in Fig. 11. Fig. 13 is a top plan view of the parts illustrated in Fig. 11 and Fig. 12.

In many of the Drawing figures, the parts are shown in a plurality of different positions (angular displacement or truck swing). Angular values disclosed in the Drawing figures are by way of exemplification and the angular range may be 0 - 90° and above, although the examples cited in the Drawing figures are preferred values of the illustrated prototype or the embodiment according to the present invention. Moreover, all figure values that are disclosed in the Drawing figures should be considered as constituting a part of this description. It should here be observed that the figure values that are preceded by an "R" are radii, while the figure values that are ended by a degree symbol are angles. The figure values are given in millimetres and degrees. It should further be observed that the Drawing figures 1 A, 1 B and 2 may be placed together to form a large drawing sheet and that the borderlines between the different figures are clearly apparent by a certain overlapping.

The vehicle or combination shown on the Drawings consists of a tractor vehicle 1 with two rear wheel pairs 2 and 3 each of four wheels. The tractor

vehicle 1 is provided with a coupling device in the form of a king pin which is placed in a centre point 4. A trailer is coupled to the tractor vehicle 1 , the trailer having a chassis or frame 5 of substantially per se known type. The trailer has three rear wheel pairs 6, 7 and 8, of which the rearmost wheel pair 8 is steerable, as illustrated in Fig. 1 B.

In the embodiment illustrated in Figs. 1A and B, the front wheel pair 6 of the trailer is placed approximately 7,760 millimetres from the pivot centre or the king pin 4. The wheel pair 7 is placed 2,020 mm from the wheel pair 6, and the wheel pair 8 is placed 3,400 mm from the wheel pair 7. As has been mentioned above, the design and construction of the chassis 5 are per se known, like the design and construction of the wheel pairs 6 and 7, while the steerable wheel pair 8 is included in one embodiment of a device according to the present invention. With the values of angles disclosed on the Drawing or in Figs. 1A-1B and 2, the radii disclosed on the Drawings will be achieved. The outward swing of the tractor vehicle 1 in relation to the longitudinal axis of the trailer at an angle of 51.78° results in a turning radius of 13,401.84 mm, the inner wheel in the steerable rear wheel pair 8 achieving an angle of 38°, and the outer wheel an angle of 30.76°. With the device according to the present invention, the outward swinging of the wheels in the rear wheel pair 8 will be in accordance with that shown in Fig. 2.

Figs. 3 - 5 show one embodiment for steering the wheels of the rear wheel pair 8 in greater detail, although only those parts of requisite importance for the device according to the present invention are shown. A steering rod 9 is pivotally disposed in the chassis 5 between the wheels in the wheel pair 8. The steering rod 9 is pivotal with the aid of hydraulic cylinders 10 and 11 which are coupled for co-operation for wheel turning to the right or the left. The steering rod 9 displays a ball pin 12 for a steering arm and a ball pin 13 for a steering arm for the opposite wheel. A part of the steering arm 14 is shown to the left in Fig. 3 and the opposite steering arm 15 is shown to the right in Fig. 3. The steering arms 14 and 15 are shown in positions with the steering rod 9 swung outwards for placing of the ball pins 12 and 13, respectively, in the same position as the ball pins which are shown in the ends of the steering arms 14 and 15. The ball pins 12 and 13 are mounted on a lower plate on the steering rod 9, which is connected to an upper plate

via a stay 9A and a bracket for placing on a square axle A for the wheel pair 8. An axle A1 extends parallel with the stay 9A and constitutes an anchorage for the piston rod ends of the cylinders 10 and 11.

Fig. 4 shows one of the wheels in the steered wheel pair 8 with a pneumatic spring 16 between a mounting arm 17 and the chassis 5. As is apparent from Fig. 4, the arm 17 is pivotally mounted in the chassis 5 in a per se conventional manner.

Between the ball pins 12, 13, the steering rod 9 displays an angular catcher or locking angle 18 for a ball or roller 19 at the end of a piston rod 20 in a piston and cylinder assembly 21 whose opposite end is secured in the chassis 5. The catcher 18 extends between the upper plate and lower plate of the steering rod 9 and thereby forms a connection and reinforcement between them. Between the catcher 18 and the lower anchorage for the axle A1 , there is provided a reinforcement plate. The piston and cylinder assembly 21 is constructed such that the piston rod 20 is urged with the aid of a spring to the position illustrated in Fig. 5, in which movement of the steering rod 9 is counteracted or is quite simply blocked. This blocking function is activated as a rule when the vehicle or the combination is advanced at a speed of, for instance, 25 kph or above, whereby the risk of disturbance of stability in the vehicle is reduced. As soon as the speed of the vehicle falls below the predetermined level, for example 30 or 35 kph (which is often also designated C3 signal in technical circles), the piston and cylinder assembly 21 is activated so that the piston 21 is retracted into the cylinder and the ball or roller 19 is released from the catcher 18 on the steering rod 9. In this way, the steering rod 9 is released for swinging movement and thereby steering of the wheels in the rear wheel pair 8 via the steering cylinders 10 and 11 , as well as the steering arms 14 and 15 which are normally of predetermined, fixed length. On pressure loss, the piston rod 20 will automatically return to the position illustrated in Fig. 5 because of its mechanical spring bias.

Figs. 6 - 10 show in greater detail the coupling devices which are disposed in the pivot centre 4 and which are generally designated king pin or quite simply the pin 22 with which the coupling device from the trailer is to be united. In

the present case, it is naturally of importance that pivoting or turning movements of the coupling devices from the trailer about the pin 22 are converted into rotational or swinging movements of the pin proper via an arm 23 which, in its turn, is fixedly connected with a dog 24 in a housing 25 which may consist of a bearing housing for the dog 24. On the opposite side of the housing 25 relative to the pin 22, the dog extends out therefrom and is fixedly retained in the housing 25 by means of a nut 26 via a washer 27. The end of the dog 24 extending through the nut 26 displays an arm 28. Beside the housing 25, there is disposed an anchorage 29 for a reference element. This element is, in the present embodiment of the invention, a potentiometer P1 whose rotor arm or shaft is interconnected with a rotor arm 30 which extends substantially parallel with the arm 28 on the end of the dog 24. For transmitting movement between the arms 28 and 30, a rod 31 is provided which may consist of a gas spring. On the anchorage 29 for the potentiometer P1, and end arrest 32 is adjustably disposed. The signal from this reference element P1 is fed to the regulator circuit in question on the vehicle or the combination, and this regulator circuit requires a real value signal for comparison with the reference signal, this real value signal deriving from a real value element in the form of a potentiometer P2 which is disposed at the steering rod 9 for the rear wheel pair 8. As is illustrated in Figs. 11 , 12 and 13, the rear end of the steering rod 9 is provided with an arm 33 whose free end displays a ball and socket joint 34 for coupling engagement with an arm 35. This arm 35 is longitudinally shiftably connected to the rotor arm or shaft of the potentiometer P2. The potentiometer P2 proper or its housing is longitudinally shiftable on one or more guides or rails 36, 37, which extend parallel with the longitudinal axis of the chassis 5. A dog 38 is pivotally disposed on the potentiometer P2. The free end of the dog 38 is pivotally or revolvingly interconnected, by means of a ball and socket joint, to the arm 33 or direct to the steering rod 9 a distance closer to the pivot centre of the steering rod 9 than the ball and socket joint 34. Both the distance between the coupling point 39 on the arm 33 and the roller 34, as well as the distance between the coupling point 39 and the pivot centre of the steering rod 9 may be adjustable for achieving the desired setting and adjustment possibilities.

As a result of the above-described linkage arrangement, the potentiometer P2 will thus be longitudinally displaced reciprocally along the rails 36, at the same time as it is rotated (or more exactly its shaft or rotor arm 35 is rotated) by the end of the arm 33. Naturally, the arm 35 need not be a fork-shaped arm, but may consist of an arm with a closed slot. Similarly, the roller 34 may consist of a ball. The coupling between the free end of the arm 38 and the coupling point 39 on the arm 33 may also consist of a roller or ball with a suitable anchorage and suitable engagement in the end of the dog 38.

Many modifications of the above-described embodiment of the present invention are naturally possible without departing from the spirit and scope of the inventive concept as defined in the appended Claims.