GB2398047A

GB2398047A - Tow bar length calculation

Info

Publication number: GB2398047A
Application number: GB0302827A
Authority: GB
Inventors: David Neil Carter
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2003-02-07
Filing date: 2003-02-07
Publication date: 2004-08-11
Anticipated expiration: 2023-02-07
Also published as: GB2398047B; GB0302827D0

Abstract

A tow bar length calculation system, used to aid the determination of a proposed path for a vehicle-trailer guidance system, comprises a control unit and vehicle movement sensors. The vehicle movement sensors are a steering angle sensor 38, a trailer angle sensor 47, a gear sensor 46 and a distance sensor 42. The distance sensor is a propshaft mounted rotation sensor. Using measurements from the sensors, values of tow bar length are calculated at regular intervals of distance travelled and an average value is calculated.

Description

TOW BAR LENGTH CALCULATION

The present invention relates to a system for calculating the length of a tow bar which may, for example, provide a coupling between a vehicle and trailer combination.

It is advantageous to know the tow bar length of a vehicle and trailer combination, for example to determining the response of the trailer to movements of the vehicle provided by a steering aid or parking aid system.

According to a first aspect of the invention there is provided a tow bar length calculation system for measuring the tow bar length of a vehicletrailer combination, comprising trailer angle measurement means for measuring the angle of the trailer relative to the vehicle, steering angle measurement means for measuring a steering angle of the vehicle, distance measurement means for measuring the distance moved by the vehicle and processor means for calculating the tow bar length from the steering angle and the trailer angle as the vehicle moves.

Preferably the system is arranged to measure the change in the angle of the trailer relative to the vehicle produced in response to the distance travelled by the vehicle and the steering angle of the vehicle to deduce therefrom a value for the tow bar length.

The trailer angle and steering angle measurement means may be adapted to make measurements when the combination is moving forwards or perhaps when the combination is moving backwards.

The trailer angle and steering angle measurement means are preferably adapted to make measurements when the vehicle has moved a predetermined distance as measured by the distance measurement means. The trailer angle and steering angle measurement means are preferably adapted to make measurements at regular intervals of the predetermined distance moved by the vehicle. The trailer angle and steering measurement means may be adapted to make measurements at regular intervals of time. The trailer angle and steering angle measurement means may be adapted to make measurements at regular intervals of change in angle. The predetermined distance may be of the order of 0.05 metres.

The trailer angle measurement means preferably comprises a trailer angle sensor mounted on the vehicle. The steering angle measurement means preferably comprises a steering angle sensor mounted on the vehicle. The distance measurement means preferably comprises a rear propshaft rotation sensor mounted on the vehicle.

The processor means is preferably adapted to calculate a plurality of values for the tow bar length from the measurements and obtain a average value of the tow bar length. The processor means may be adapted to calculate separate values for the tow bar length as the combination moves towards the left and towards the right.

According to a second aspect of the invention there is provided a method of calculating the tow bar length of a vehicle trailer combination comprising the steps of measuring the steering angle and the trailer angle whilst the combination is moving and calculating the tow bar length from the measured values.

Measurements may be made when the combination is moving forwards or backwards. Measurements are preferably made when the combination has moved a predetermined distance. Measurements may be made when the combination has moved for predetermined time intervals. Measurements may be made when the combination has moved through a predetermined angle.

Preferably a plurality of values of the tow bar length are calculated and an average value obtained for the tow bar length.

Preferably separate values for the tow bar length are calculated as the combination moves towards the left and towards the right.

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure I is as diagram of a vehicle and trailer combination including a tow bar length calculation system according to the invention; and Figure 2 is a diagram of the combination of Figure 1 showing details of a trailer reversing aid system.

Referring to Figure 1, a vehicle 10 is shown towing a trailer 12. The trailer 12 is connected to the vehicle 10 via a towball 14 about which the trailer can pivot relative to the vehicle. The vehicle 10 has front wheels 2 which are rotatable for steering and rear wheels 4, which remain aligned with a longitudinal axis of the vehicle 10.

For the purposes of this specification, "tow bar length" is the distance between a tow ball 14 of a vehicle 10 towing a trailer 12 and the centre of rotation of the trailer 12 i.e. the point about which the trailer will rotate if the tow bar is moved in a direction transverse to the trailer. This is shown in Figure I as the length T. The tow bar length may be used to determine a proposed path for the vehicle and trailer combination for pre-determined steering inputs by a driver. This may be as part of a steering aid system in which the driver is prompted to steer the vehicle at a specified angle in order to move the trailer into a desired position, such as a parking space or driveway.

Referring to Figure 2, the vehicle 10 is equipped with a reversing aid system which is controlled by a control unit 16. Two front lateral distance sensors 18, are mounted on the vehicle, one on each side near the front of the vehicle, and pointing laterally so that they can measure the distance to objects to either side of the vehicle 10. Two rear distance sensors 22, 24 are mounted on the rear of the trailer, one on each side of the trailer and also pointing laterally so that they can measure the distance to objects to either side of the trailer 12. The vehicle also includes forwards looking distance sensors 26, 28 mounted on the front of the vehicle 10. Two side view video cameras 30, 32 are mounted one in each of the vehicle wing mirrors, and are angled so that each of them is pointing in a direction to the side of the vehicle and slightly to the rear. Two further rear view video cameras 34, 36 are mounted on the rear of the trailer, one on each side, pointing to the rear. The control unit 16 is also connected to a steering angle sensor 38 arranged to measure the steering angle SA of the front steered wheels 2 of the vehicle 10. The steering angle SA is the angle between the longitudinal axis of a vehicle 10 and the line along which the front wheels 2 of the vehicle point i.e. the direction in which the vehicle 10 is to be driven.

This is shown in Figure I as the angle SA. The control unit 16 is also connected to a distance sensor 42 in the form of a rotation sensor arranged to measure rotation of the rear propshaft to monitor indirectly the rotation of the rear wheels 4 and arranged to measure the distance the vehicle 10 moves. Mounting the sensor 42 on the propshaft is preferable to mounting a sensor on one of the rear wheels 44 since an indication of the average movement of the rear wheels is obtained and this is closer to the value of actual tow bar 14 displacement than measurements via the rotation of one rear wheel 44, which may be affected by the radius of turn. An alternative to this method of measuring distance moved could be an accelerometer based system to monitor the position of the vehicle and obtain a value for the distance moved indirectly. This alternative method may be particularly useful in conditions where wheels 44 of the vehicle are likely to slip e.g. muddy road conditions. This could be used as an alternative, or in combination with, the propshaft mounted sensor 42. A gear sensor 46 arranged to detect which gear the vehicle gearbox is in, and in particular whether it is in reverse or a forward gear, and a trailer angle sensor 47 arranged to measure the angle between the trailer and the vehicle are also connected to the control unit 16. The trailer angle TA is the angle between the longitudinal axis of the trailer 12 being towed and the longitudinal axis of the vehicle 10.

The trailer angle, TA, is therefore the difference between angles TO and CO, shown in Figure 1. RF transmitters 48, SO are arranged to transmit signals from the rear distance sensors 22, 24 and the rear video cameras 34, 36, and an RF receiver 52 is connected to the control unit 16 to enable it to receive signals from the rear distance sensors 22, 24 and the rear video cameras 34, 36. A user interface 54 is provided in the vehicle, connected to the control unit 16 to allow the driver to receive instructions from the system and provide inputs to it. The control unit 16 is also connected to a vehicle brake control unit 56 which in turn controls operation of the vehicle's brakes 58, only one of which is shown in Figure 2. An audible alarm 59 is also provided in the vehicle 10 connected to the control unit 16 and is able to provide warning signals and prompts at various stages of the vehicle positioning manoeuvres as required.

The reversing aid system is required to predict and recommend a path for a driver of the vehicle 10 and trailer 12 and in order to be able to do this, it is necessary to determine the tow bar length (as previously defined). The control unit 16 therefore comprises tow bar length calculation means to calculate the tow bar length from the measurements taken of the steering angle, trailer angle and distance travelled via the relevant sensors 28, 47, 42. Measurements are taken as the vehicle 10 and trailer 12 move both forwards and backwards.

Measurements taken when the vehicle 10 and trailer 12 move to the left are separated from measurements taken when the combination 10, 12 moves to the right. This is because there may be irregularities in the combination 10,12, for example a wheel imbalance or a relatively deflated lyre, which causes the movement toward the left to differ from the movement towards the right and hence the effective tow bar length as the vehicle turns to the left to differ from that as it turns to the right. Several values for tow bar length are obtained by taking measurements at regular intervals, for example, every O.O5m of towball 14 displacement. An average of these values is obtained by the control unit 16 to determine the tow bar length more accurately. In this way the motion of the combination 10, 12 moving to the left and to the right can be predicted taking account of any imbalances.

A matrix of values of steering angle - v- trailer angle - v- towball displacement is obtained by the control unit 16. The control unit 16 is able to relate these three measurements to the tow bar length using an algorithm based upon the reasoning detailed below.

The variables used in calculating the tow bar length are as follows: This is the orientation of the vehicle 10 relative to an

CO

arbitrary reference line.

This is the orientation of the trailer 12 relative to the

TO

same reference line.

This is the wheel base of the vehicle i.e. the distance WE between the axis of the front wheels 2 and the rear wheels 4 of the vehicle 10.

This is the radius of turn of the vehicle 10.

This is the distance from the axis of the rear wheels 4 d to the towball 14.

R This is the hypotenuse of the right angle triangle formed by R and d.

This is an increment of longitudinal towball AX displacement (as the vehicle is reversing) This is the distance moved laterally by the towball 14, AT i.e. in a direction perpendicular to its longitudinal axis l as a result of the incremental longitudinal displacement of the towball (AX).

l This is the tow bar length.

SA This is the steering angle.

TA This is the trailer angle Using these definitions it can be seen that the following relationships apply: tan SA = WB (1) Then defining a by: a = tan'(d) (2) and (p by: = TA-a (3) and trailer angle TA by: TA = TO-CO (4) then for any incremental movement of the vehicle increment in CO=- (5) where Rl = /(d2 + R2) (6) and the resulting increment in trailer orientation Increment in TO =- (7)

T

It can therefore be seen that Increment in CO = x 57.296 (8) :ó tan2 SA) and therefore AX x 57.296 x singly - tan '( S)) Increment in TO = WB (9) The number 57.296 is a conversion factor since calculations must be carried out in radians and measurements are in degrees.

In this way from equation 9 the tow bar length, T may be calculated from measurements of the steering angle SA, the trailer angle TA, and distance AX moved by the towball 14, which for small distances is equivalent to the distance moved by the rear wheels 4 of the vehicle 10.

Since this system continually monitors the steering angle, trailer angle and distance moved to provide updated values for tow bar length, the system is able to adapt to the use of different trailers or the changing performance of the same vehicle-trailer combination, for example due to a deflating lyre.

Various modifications may be made to the present invention without departing from its scope. For example, a different configuration of sensor may be used to measure the steering angle, trailer angle and distance moved by the vehicle. For example, the steering angle could be measured indirectly by considering the distance moved with a corresponding change in car orientation. A further alternative measurement method for the angles may utilise compass or satellite navigation means.

Claims

1. A tow bar length calculation system for measuring the tow bar length of a vehicle-trailer combination, comprising trailer angle measurement means for measuring the angle of the trailer relative to the vehicle, steering angle measurement means for measuring a steering angle of the vehicle, distance measurement means for measuring the distance moved by the vehicle and processor means for calculating the tow bar length from the steering angle and the trailer angle as the vehicle moves.

2. A system according to claim 1 which is arranged to measure the change in the angle of the trailer relative to the vehicle produced in response to the distance travelled by the vehicle and the steering angle of the vehicle, and to deduce therefrom a value for the tow bar length.

3. A system according to claim I or claim 2, in which the trailer angle and steering angle measurement means are adapted to make measurements when the combination is moving forwards.

4. A system according to any of claims I to 3, in which the trailer angle and steering angle measurement means are adapted to make measurements when the combination is moving backwards.

5. A system according to any preceding claim, in which the trailer angle and steering angle measurement means are adapted to make measurements when the vehicle has moved a predetermined distance as measured by the distance measurement means.

6. A system according to claim 5, in which the trailer angle and steering angle measurement means are adapted to make measurements at regular intervals of the predetermined distance moved by the vehicle.

7. A system according to any preceding claim, in which the trailer angle and steering angle measurement means are adapted to make measurements at regular intervals of time.

8. A system according to any preceding claims, in which the trailer angle and steering angle measurement means are adapted to make measurements at regular intervals of change in angle.

9. A system according to any of claims 5 to 8 in which the measured distance is of the order of 0.05m.

10. A system according to any preceding claim, in which the trailer angle measurement means comprises a trailer angle sensor mounted on the vehicle.

11. A system according to any preceding claim, in which the steering angle measurement means comprises a steering angle sensor mounted on the vehicle.

12. A system according to any preceding claim, in which the distance measurement means comprises a rear propshaft rotation sensor mounted on the vehicle.

13. A system according to any preceding claim, in which the processor means is adapted to calculate a plurality of values for the tow bar length from the measurements and obtain an average value of the tow bar length.

14. A system according to any preceding claim, in which the processor means is adapted to calculate separate values for the tow bar length as the combination moves towards the left and towards the right.

15. A method of calculating the tow bar length of a vehicle trailer combination comprising the steps of measuring the steering angle and the trailer angle whilst the combination is moving and calculating the tow bar length from the measured values.

16. A method according to claim 15, in which said measurements are made when the combination is moving forwards.

17. A method according to claim 15 or claim 16, in which said measurements are made when the combination is moving backwards.

18. A method according to any of claims 15 to 17 in which measurements are made when the combination has moved a predetermined distance.

19 A method according to any of claims 15 to 18, in which measurements are made when the combination has moved for a predetermined time interval.

20. A method according to any of claims 15 to 19, in which measurements are made when the combination has moved through a predetermined angle.

21. A method according to any of claims 15 to 2O, in which a plurality of values of the tow bar length are calculated made and an average value obtained for the tow bar length.

22. A method according to any of claims 15 to 21, in which separate values for the tow bar length are calculated as the combination moves towards the left and towards the right.

23. Tow bar length calculation system substantially as hereinbefore described with reference to the accompanying drawings.

24. A method of calculating the tow bar length of a vehicle combination substantially as hereinbefore described with reference to the accompanying drawings.