GB2142291A

GB2142291A - Apparatus for controlling the direction of a towed vehicle

Info

Publication number: GB2142291A
Application number: GB08315546A
Authority: GB
Inventors: Raymond John Vincent; Colin David Hughes
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-06-07
Filing date: 1983-06-07
Publication date: 1985-01-16
Also published as: GB2142291B; GB8315546D0

Abstract

An arrangement is provided for controlling the direction of a towed vehicle having an angularly displaceable wheel, in response to the direction of a towing vehicle which is connected to the towed vehicle. A trailing (2) carries steerable wheels operatively connected to a reversible motor (6). The motor (6) is controlled by power relays in response to signals from a linearly variable potentiometer or an optical linear displacement transducer (11) which senses the portion of the steerable wheels, and from a rotary variable potentiometer or an optical angular displacement transducer (12) which senses turning of the trailer relative to the towing vehicle 3. The combination of towed and towing vehicle then exhibits, when reversing, the steering characteristics of a single vehicle having a wheel base comparable to that of the combination. In another embodiment the transducers sense turning of the steerable wheels on the trailer and on the towing vehicle respectively. <IMAGE>

Description

SPECIFICATION Apparatus for controlling the direction of a towed vehicle This invention relates to apparatus for controlling the direction of a towed vehicle.

It is presently very difficult to control the direction of a towed vehicle satisfactorily, especially when reversing around corners, or when manoeuvring into small spaces.

One arrangement which has been developed decreases the radius of a circle around which a towed vehicle or trailer can move by means of a rigid bar, linking turntables carrying wheels at the back and the front of the towed vehicle. This bar ensures that movement of the front turntable in one sense imparts an equal movement to the back turntable in the opposite sense. However, such an arrangement is limited to use on a trailer having two sets of wheels on respective turntables, and does not allow any control of the trailer wheels in response to the direction of the trailer with respect to a towing vehicle.

In accordance with one aspect of the present invention there is provided apparatus, for controlling the direction of a towed vehicle having an angularly displaceable wheel, in response to the direction of a towing vehicle which is connected to the towed vehicle, the apparatus comprising first sensing means for sensing the angular position of the towed vehicle with respect to the towing vehicle; second sensing means for sensing the angular displacement of a wheel of the towed vehicle; and control means for controlling said angular displacement of the wheel of the towed vehicle in response to both (a) said angular position of the towed vehicle with respect to the towing vehicle and (b) said angular displacement of the wheel of the towed vehicle; whereby the combination of towing and towed vehicles exhibits the steering characteristics of a single vehicle having a wheel base comparable to that of the combination.

In accordance with another aspect of the present invention there is provided apparatus, for controlling the direction of a towed vehicle having an angularly displaceable wheel, in response to the direction of a towing vehicle which is connected to the towed vehicle, the apparatus comprising first sensing means for sensing the angular displacement of an angularly displaceable wheel of the towing vehicle; second sensing means for sensing the angular displacement of a wheel of the towed vehicle; and control means for controlling said angular displacement of the wheel of the towed vehicle in response to both (a) said angular displacement of the wheel of the towing vehicle and (b) said angular displacement of the wheel of the towed vehicle; whereby the combination of towing and towed vehicles exhibits the steering characteristics of a single vehicle having a wheel base comparable to that of the combination.

Throughout the present description and claims the terms "towed vehicle" and "towing vehicle" refer to the respective vehicles in the positions which they would normally be in, with the combination moving forward; i.e.

with the towing vehicle preceding the towed vehicle, regardless of whether they are in fact in those positions; and the term "angular displacement" referring to a wheel of a vehicle, means the angular displacement of a plane containing the wheel, with respect to the plane which contains the wheel when the latter is aligned for rectilinear movement of the vehicle.

Although the present invention will be described with reference to a towed vehicle having an axle with a wheel at each end, angularly displaceable with respect to the axle in response to the control means, it will be appreciated that the present invention is equally applicable to a towed vehicle having one or more angularly displaceable turntables, each carrying two wheels; or to a towed vehicle having two or more axles carrying a wheel at each end, with a suitable gearing arrangement between the sets of wheels.

Preferably the first sensing means is located at the connection point of the towing vehicle and the towed vehicle; and may comprise a rotary variable potentiometer or an angular displacement transducer.

Preferably the second sensing means senses the linear displacement of linking means operatively connected to the wheel of the towed vehicle; and may comprise a linear variable potentiometer or as linear displacement transducer.

The said transducers may be optical transducers.

Preferably said control means includes switching means, responsive to said first and second sensing means, for switching power to drive a motor, which motor is operatively connected to the wheel of the towed vehicle, in a sense dependent on said angular position of the towed vehicle and said angular displacement of the wheel of the towed vehicle.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figures 1 to 3 show a trailer and towing vehicle, with their respective positions, in operation of the system; Figure 4 shows means by which the wheels of the trailer can be steered; Figure 5 is a plan view of an optical angular displacement transducer with the top cover removed; Figure 6 is a section through line Vl-Vl of Figure 5; Figure 7 is an underside view of the trans ducer of Figure 5; Figures 8 and 9 show respectively a plan view and a cross-section of a steering system which may be fitted to a wheel axle; Figure 10 shows a standard wheel axle assembly; Figure 11 is a circuit diagram of an electronic control system using potentiometers;; Figure 1 2 is a block diagram of an electronic control system using transducers and encoders; and Figure 1 3 is a more detailed circuit diagram of Figure 12.

Figure 1 shows a towing vehicle 1 and a towed vehicle or trailer 2.

Wheels 3 of the trailer 2 are controlled in such a manner that the combination of the trailer 2 and towing vehicle 1 behaves, as regards steering, as if it were a single vehicle having a rigid chassis with an effective wheel base, b, being the distance between the steered wheels 4 of the towing vehicle 1 and the steered wheels 3 of the towed vehicle, for example a trailer 2. There would be similar behaviour whether the unit was travelling forwards or backwards.

There may be circumstances where the trailer 2 is towed forward with the trailer wheels 3 locked in a central steering position as a conventional fixed axle unit. When the control system is switched on, for example by selecting reverse gear, the trailer wheels 3 will automatically turn in such a direction as to rectify the discrepancy of angular displacement (the angular displacement between the towing vehicle 1 and the trailer 2) angle X, as shown in Figure 2, the angle X being measured by a transducer/encoder system, to be described in more detail hereinafter, fitted to the towing connection.

The angular displacement of the steered wheels 3 on the trailer 2, angle Y in Figure 3, is controlled by measuring the direction and angular displacement of the trailer 2 relative to the towing vehicle 1, angle X in Figure 2, at the point of connection between the towing vehicle 1 and the trailer 2, causing the steered wheels 3, having an angular displacement denoted by angle Y, to move in a direction necessary to reduce angle X to zero.

According to Figure 4, the wheels 3 of the trailer 2 are steered by means of a 1 2 volt motor 6. The motor 6 drives a screw thread 7 via a reduction gear box 8, making a nut move linearly along the thread 7. The linear motion of the nut is transferred to a track rod 9, fitted with ball joints 10 as necessary, thereby causing the two wheels 3 to effect an angular motion, as shown in Figure 3. The 1 2 volt motor 6 can be made stationary, or switched to rotate in either direction by means of relays or power transistors controlling the polarity of power supplied to the motor brushes. Reference numerals 11 and 12 denote optical linear and angular displacement transducers respectively.

The optical angular displacement transducer 1 2 is shown more clearly in Figures 5 to 7.

The transducer 1 2 comprises an encoded disc 13, for producing Gray code, four OFF LED and phototransistors 14, and a drive pin 15, which moves in a guide track 16, and passes through a drive socket 1 7. A protective guide cover 18 and a spring 1 9 are provided for the drive pin and socket arrangement. Figure 6 also illustrates the ball socket fitted to the trailer 2.

A steering system 20 (Figure 4) is shown in detail in Figures 8 and 9. Figure 8 shows a part of an existing rubber suspension unit 21.

shown in full in Figure 4. The steering system 20 is attached to the unit 21 by way of a splined shaft 22 and clamp bolt 23. Figure 9 is a cross-section of the system shown in Figure 8, showing a king pin 24, Glacier type dry bearing drive unit 25, and thrust washer 26. A wheel hub assembly 27 fits onto the system. Figure 10 shows a standard rigid wheel axle assembly. The steering system 20 fits the existing unit 21 as shown, and results in an increase in length of the axle of about 3 3/8" (about 8.5 cm).This results in a 6 3/4" (about 17.1cm) track increase which gives a reasonable lock, but may be altered according to individual trailer requirements and designs.

The turning of the trailer wheels 3 in response to the orientation of the trailer 2 with respect to the towing vehicle 1 may be electronically controlled in a number of ways, including the use of a potentiometer system; or a transducer/encoder system.

A control system using potentiometers will now be described with reference to Figure 11.

The circuit of Figure 11 shows a linear variable potentiometer which is fixed to the track rod 9 of the trailer 2; and a rotary variable potentiometer, which is fixed at the centre of the towing fixture. To set up the system, both potentiometers are adjusted to their mid-way positions when the trailer wheels are set with angle Y = 90 (Figure 3) and angle X = 0 (Figure 2). The two cermet trimming potentiometers are then adjusted to give a dead band, i.e. a position when the output from both comparators is zero, resulting in both relays 28 (Figure 12), being deenergised, and hence the motor 8 being stationary. The width of the dead band is adjustable to prevent hunting.

If one of the rotary and linear potentiometer is unbalanced, a signal will cause the output from one of the comparators 29 to switch on one of the relays 28 and cause the motor 8 to rotate in one direction. Rotation of the motor 8 in that direction will continue until the other potentiometer becomes unbalanced in a sense which cancels out the original signal, making the outputs of both comparators 29 equal to zero and hence stopping the motor. The adjustment ratio of one potentiometer with re spect to the other may be adjusted so that the amount of turn of the trailer wheels 3 may be less than, or greater than, the amount of turn of the wheels 4 of the towing vehicle 1 to enable the sensitivity of the system to be controlled.

Although linear potentiometers are readily available in standard form, they are prone, in varying degrees depending on the quality, and consequently expense, thereof to variations in their operation due to changes in temperature and moisture. When in position on a vehicle, they may be subject to the effects of nature for long periods of time, for example around 6 to 1 2 months, and consequent degeneration of the operation of the potentiometers may occur. Also, any control unit, situated at the towing connection of a vehicle, may be subject to accidental and deliberate damage. An optical encoding system could be produced in a very robust housing resistant to the vagaries of heat, humidity, fools or vandals.

Such a system is shown in Figures 1 2 and 13.

Figure 12 shows the linear displacement transducer 11 and angular displacement transducer 1 2 each connected to a respective Gray to binary convertor 30, which is in turn connected to a digital to analogue converter 31 whose analogue output is connected to an amplifier and buffer 32. The outputs of the amplifiers 32 feed comparators 29 in a similar manner to that shown in Figure 11 to allow null adjustment. Power relays 29 than cause the motor 8 to rotate in a direction depending on which relay 29 is activated.

Figure 1 3 shows one half of the circuit of Figure 12 in more detail.

The encoders 1 3 (Figure 6) produce a Gray code to eliminate the possibility of a false code occurring for a couple of microseconds, which may occur with a binary code. A four input exclusive OR gate, e.g. 4070B, is used to convert Gray code to binary and a ZN425 converter 31 is used to convert the digital signal from the Gray code converter 30 to an analogue signal which is then fed to a 741 operational amplifier 32. The remainder of the circuit is as described with reference to Figure 1 2. Figure 1 3 shows a circuit using only a 4 bit code, which would result in a 5" motion of the steered wheels 3 on the trailer 2 for every code change, assuming that the wheels have a total angular displacement of 454 either side of their central position.The units 7815, 7915 allow voltage regulation.

The number of optical sensors, and subsequently the number of bits of code, could be increased to give a more sensitive control, i.e.

a smaller angular displacement for each byte.

A standard pulse width modulated unit, for example a high torque position servo chip SG 1 731 could be used in place of the potentiometer system shown in Figure 11.

As an alternative to the apparatus hereinabove described, which enables the wheels 3 of the trailer 2 to be controlled in response to the angular position of the trailer 2 with respect to the towing vehicle 1, the 1 2 volt motor 8 driving the steering mechanism of the trailer wheels 3 could be controlled by an electronic bi-directional servo system, which has as its input signal the angular displacement Z (Figure 3) of the steering wheels 4 of the towing vehicle 1; and as a feedback signal the angular displacement Y of the trailer wheels 3. The object of the control system would be to control the displacement of the trailer wheels 3 and towing vehicle steering wheels 4 to be equal but opposite in direction.

It will be appreciated that control systems such as those hereinbefore described may also be used to control the direction of a towed vehicle which, while the combination is moving forward, is exhibiting instability; or to prevent a possible so-called "jack-knife" of a towed vehicle.

Claims

1. Apparatus, for controlling the direction of a towed vehicle having an angularly displaceable wheel, in response to the direction of a towing vehicle which is connected to the towed vehicle, the apparatus comprising first sensing means for sensing the angular position of the towed vehicle with respect to the towing vehicle; second sensing means for sensing the angular displacement of a wheel of the towed vehicle; and control means for controlling said angular displacement of the wheel of the towed vehicle in response to both (a) said angular position of the towed vehicle with respect to the towing vehicle and (b) said angular displacement of the wheel of the towed vehicle; whereby the combination of towing and towed vehicles exhibits the steering characteristics of a single vehicle having a wheel base comparable to that of the combination.

2. Apparatus as claimed in claim 1, wherein said first sensing means is located at the connection point of the towing vehicle and the towed vehicle.

3. Apparatus as claimed in claim 1 or 2, wherein said second sensing means senses the linear displacement of linking means operatively connected to the wheel of the towed vehicle.

4. Apparatus as claimed in claim 3, wherein the first sensing means is a rotary variable potentiometer, and the second sensing means is a linear variable potentiometer.

5. Apparatus as claimed in claim 3, wherein the first sensing means is an angular displacement transducer, and the second sensing means is a linear displacement transducer.

6. Apparatus as claimed in claim 5, wherein said transducers are optical transducers.

7. Apparatus as claimed in any preceding claim wherein said control means includes switching means, responsive to said first and second sensing means, for switching power to drive a motor, which motor is operatively connected to the wheel of the towed vehicle, in a sense dependent on said angular position of the towed vehicle and said angular displacement of the wheel of the towed vehicle.

8. Apparatus for controlling the direction of a towed vehicle having an angularly displaceable wheel, in response to the direction of a towing vehicle, which is connected to the towed vehicle, substantially as hereinbefore described with reference to, and as shown in, Figures 1 to 4, 8, 9 and 11 or Figures 1 to 9, 1 2 and 1 3 of the accompanying drawings.

9. Apparatus, for controlling the direction of a towed vehicle having an angularly displaceable wheel, in response to the direction of a towing vehicle which is connected to the towed vehicle, the apparatus comprising first sensing means for sensing the angular displacement of an angularly displaceable wheel of the towing vehicle; second sensing means for sensing the angular displacement of a wheel of the towed vehicle; and control means for controlling said angular displacement of the wheel of the towed vehicle in response to both (a) said angular displacement of the wheel of the towing vehiclewand (b) said angular displacement of the wheel of the towed vehicle; whereby the combination of towing and towed vehicles exhibits the steering characteristics of a single vehicle having a wheel base comparable to that of the combination.