WO1995008751A1

WO1995008751A1 - Steering angle transducer

Info

Publication number: WO1995008751A1
Application number: PCT/SE1994/000884
Authority: WO
Inventors: Mats Hugo Rolf Dahlgren
Original assignee: Nira Automotive Ab
Priority date: 1993-09-24
Filing date: 1994-09-26
Publication date: 1995-03-30
Also published as: JPH09503293A; SE9303127D0; SE9303127L; SE502358C2

Abstract

A steering angle transducer (10) for a motor vehicle is arranged to generate an electric signal having a parameter u(α) varying in dependence upon the steering angle α of the vehicle, said parameter having an extreme value U for a steering angle of 0° and varying in dependence upon the steering angle α according to a curve of its value as a function of the steering angle having a considerable inclination within portions thereof located adjacent to and on opposite sides of the steering angle value 0°.

Description

Steering angle transducer

The present invention relates to a steering angle transducer for a motor vehicle.

Previously, such steering angle transducers have usually been designed so as to make it possible to determine the steering angle of a vehicle with a sub¬ stantially constant accuracy within a very wide range of variation of said angle. For this reason, steering angle transducers for vehicles hitherto known have been comparatively complicated and expensive. However, there exist several application fields for steering angle transducers within which it is of interest to determine the magnitude of the steering angle with a comparatively high accuracy only within a very narrow angle range extending only a few degrees on each side of the steering angle value 0°. By way of example, it could be mentioned that one such applica¬ tion field is the determination of the lateral inclina¬ tion of a motorcycle in relation to the roadway on the basis of the speed and the steering angle of the motor- cycle. Another application field is the detection of the steering angle 0° in an automobile in order to per¬ mit an adjustment and/or calibration of a brake control system during periods of time when the steering angle has said value. The invention has for its purpose to provide a steering angle transducer which is well suited for such application fields and which is considerably more simple and inexpensive than the steering ngle transducers previously known. The steering angle transducer, in accordance with the invention proposed for said purpose, is primarily characterized in that it is arranged to generate an electric signal having a parameter varying in dependence upon the steering angle of the vehicle, said parameter having an extreme value for a steering angle of 0° and varying in dependence upon the steering angle according to a curve of its value as a function of the steering angle having a considerable inclination within portions thereof located adjacent to and on opposite sides of the steering angle value 0°.

As a consequence of the fact that said parameter of the signal generated by the steering angle transducer varying in dependence upon the steering angle has an extreme value, i.e. a maximum value or a minimum value, for the steering angle 0°, the transducer cannot be utilized for determining the true value of the steering angle but only to determine the absolute value of said angle, i.e. its magnitude without sign. However, within the application fields above mentioned by way of example as well as within several other possible application fields, this is quite sufficient.

Said parameter may suitably consist of the magni¬ tude of the electric signal generated by the steering angle transducer which signal may consist of a D.C. voltage signal or an A.C. voltage signal. Alternatively, said parameter may however instead consist of the fre¬ quency of an A.C. voltage signal generated by the steering angle transducer. The steering angle transducer may suitably be constructed so as to cause said parameter to vary in dependence upon the steering angle according to a curve of its value as a function of the steering angle which is symmetrical with respect to the steering angle value 0°. In this case, said parameter will assume the same value for both angles of each pair of steering angles of mutually equal magnitude but of opposite sign.

However, in some special cases, it may be desirable to detect when the steering angle passes any of two steering angle values of opposite sign deviating from the steering angle value 0° and having mutually different magnitudes. In order to facilitate such a detection in an easy manner, the transducer may be constructed so as to cause said parameter to vary in dependence upon the steering angle according to a curve of its value as a function of the steering angle which is asym¬ metrical with respect to the steering angle value 0°. In order to avoid false measurement results as a consequence of temperature variations and drift in electric circuits, the steering angle transducer may be connected to an evaluation unit serving to evaluate the generated electric signal and arranged to calibrate the transducer by repeatedly determining the extreme value of said parameter. Said calibration is rendered possible due to the fact that during the use of the vehicle, the parameter assumes its extreme value as soon as the vehicle is driven in a straight forward direction which necessarily happens very often.

The evaluation unit may preferably be arranged to determine the instantaneous magnitude of the steering angle. However, as an alternative, said unit may instead be arranged to determine whether the steering angle lies within a predetermined angle range containing the steering angle value 0° and extending a limited angle on each side of said value. Below the invention is further described with reference to the accompanying drawings, in which:-

Figure 1 shows a diagrammatic perspective view of a steering angle transducer according to a first embodiment of the invention, selected by way of example only,

Figure 2 shows a diagrammatic perspective view of a steering angle transducer according to a second embodiment of the invention, also selected by way of example only, Figure 3 is a diagram, illustrating an electric signal generated by the transducer according to Figure 1 by means of a curve of said signal as a function of the steering angle,

Figures 4 and 5 are diagrams, illustrating output signals from modified steering angle transducers by means of curves of said signals as functions of the steering angle, and

Figure 6 shows a flow chart, illustrating the manner of operation of an evaluation circuit, connected to the transducer according to Figure 1. The steering angle transducer shown in Figure 1 and generally designated 10 comprises a Hall effect member 11 and a permanent magnet 12, both mounted in stationary positions adjacent to each other in a motor vehicle, for instance an automobile or a motorcycle, and a movable cam 13 which consists of a magnetic mate¬ rial. As indicated by double arrow A, cam 13 may be arranged for rotation around a rotary axis 14 and con¬ nected to the steering system of the vehicle in such a manner that it will be rotated around said axis when the steering system is operated. Alternatively, cam 13 may instead be connected to the steering system of the vehicle in such a manner that, when the steering system is operated, it will be subjected to a rectilinear dis¬ placement as indicated by means of double arrow B. Furthermore, the steering angle transducer 10 also comprises an electric circuit unit 15 connected to Hall effect member 11. This unit forms a combined power supply unit and output signal amplifier for Hall effect member 11 and has an output 16 over which it may deliver an output signal proportional to a voltage generated by Hall effect member 11.

Cam 13 has the shape of a circular disc which is provided with a projecting ridge portion 13' . When the steering system is in a state corresponding to the steering angle 0°, i.e. when the vehicle is driven in a straight forward direction, ridge portion 13' is loca- ted centrally in front of Hall effect member 11 and permanent magnet 12. The magnetic flux from permanent magnet 12 flowing through Hall effect member 11 will assume a maximum value when cam 13 is located in this position and it will decrease successively when cam 13 is rotated in one or the other direction from said posi¬ tion. This means that the output signal

) from trans¬ ducer 10, which is delivered over output 16 and which may consist of a D.C. voltage, will vary in dependence upon the steering anglec^**^ according to a curve of the kind shown in Figure 3. Thus, the output signal f ^) has a maximum value U for the steering angle 0° and decreases successively when the steering angle is changed in one or the other direction from the value 0°. Hereby, transducer 10 is well suited to be utilized for deter¬ mining the magnitude of steering angle ^ within a limited angle range extending a few degrees on both sides of steering angle value 0°.

In order to make it possible to determine the magnitude of steering angleσ^ with an increased accuracy, ridge portion 13' of cam 13 may be given a substantially more narrow and pointed shape than the one shown in Figure 1 so that the output signal u (c£) will vary in dependence upon steering angled according to a curve of the kind shown in Figure 4, where portions of the curve located adjacent to and on opposite sides of steering angle value 0° have a steep inclination.

Steering angle transducer 10 may also be used to detect when the steering angle passes any of two predetermined steering angles of mutually opposite direc¬ tions deviating from the steering angle value 0°. Such a detection may be effected by detecting occasions when the output signal u lp£) assumes a certain predetermined value which is lower than the peak value. When the trans- ducer is intended to be utilized for such a detection, in some cases it may be desirable to give ridge portion 13' of cam 13 such a shape that, as shown in Figure 5, the curve of the output signal lp^) as a function of steering angleO^will become asymmetrical instead of symmetrical with respect to the steering angle value 0°. In order to facilitate an evaluation of the output signal ufc" -) delivered by transducer 10 at output 16, an evaluation unit 20, shown in dash-dotted lines in Figure 1, may be connected to output 16. This evaluation unit 20 may also be arranged to calibrate transducer 10 by repeatedly determining the peak value of output signal ufe^β.

In Figure 6 there is shown a flow chart, illustra¬ ting one possible manner of operation of evaluation unit 20 which preferably may consist of a microprocessor.

In block 21, the operation of unit 20 is started. In block 22, a value U, of the maximum value ϋ of voltage u (cP) previously stored in a memory is read. In block 23, there is calculated and stored a reduced value U_? of U according to the equation U = U, • (1-a), where a_ is a constant less than 1 and for instance amounting to 0.1. In block 24, u(θ--), i.e. the instantaneous value of the voltage at output 16, is read.

In block 25, it is asked whether u(o^) is larger than the value of U presently stored. If the answer is NO, the operation proceeds directly to block 26. If, instead, the answer is YES, the operation proceeds to block 27, where a new value U, of U, where U-, = u Ip^) , is stored instead of the value previously stored. From block 27, the operation proceeds to block 26. In said block, the quotient x = —ufc—> ) is calculated. Moreover, the magnitude of angleσ*^ is determined from a function

C^= f(x, U) stored in a matrix shape. Alternatively, in block 26, one may instead determine whether x >_^ b, where b is a constant less than 1 and corresponding to a threshold level U_φ inserted in the diagram according to Figures 3, 4 or 5. By way of example, such a thres¬ hold value has been indicated by a dashed line in Figure 4.

In block 28, it is asked whether the lapsed time t exceeds a predetermined value T which for instance may amount to one or a few minutes. If the answer to this question is NO, the operation returns directly to block 24 where fp ) is read again. If, instead, the answer is YES, the operation proceeds to block 29. In this block there is calculated and stored a new reduced value U. of U according to the equation U. = U • (1-c), where c is a constant much lower than 1 and for instance amounting to 0.05. Moreover, t is set to 0, i.e. the time counting is restarted. From block 29, the operation then returns to block 24.

Figure 2 shows a steering angle transducer according to a second embodiment of the invention where Hall effect member 11 and permanent magnet 12 h^ve been replaced by a coil 18 provided with an iron core. This coil 18 may be connected into an oscillation circuit, the resonance frequency of which will vary in dependence upon the position of cam 13. Hereby, it is possible, from the electric circuit unit 19 connected to the coil, to obtain an output signal consisting of an A.C. voltage having a frequency varying in dependence upon the steering angle.

Claims

1. Steering angle transducer for a motor vehicle, characterized in that it is arranged to generate an electric signal having a parameter varying in dependence upon the steering angle of the vehicle, said parameter having an extreme value for a steering angle of 0° and varying in dependence upon the steering angle according to a curve of its value as a function of the steering angle having a considerable inclination within portions thereof located adjacent to and on opposite sides of the steering angle value 0°.

2. Steering angle transducer according to claim 1, characterized in that said parameter consists of the magnitude of the electric signal generated by the steering angle transducer.

3. Steering angle transducer according to claim 1, characterized in that said parameter consists of the frequency of an A.C. voltage signal generated by the transducer.

4. Steering angle transducer according to any of claims 1 to 3, characterized in that said parameter varies in dependence upon the steering angle according to a curve of its value as a function of the steering angle which is symmetrical with respect to the steering angle value 0°.

5. Steering angle transducer according to any of claims 1 to 3, characterized in that said parameter varies in dependence upon the steering angle according to a curve of its value as a function of the steering angle which is asymmetrical with respect to the steering angle value 0°.

6. Steering angle transducer according to any of the preceding claims, characterized in that it is con¬ nected to an evaluation unit serving to evaluate the generated electric signal and arranged to calibrate the transducer by repeatedly determining the extreme value of said parameter.

7. Steering angle transducer according to claim 6, characterized in that the evaluation unit is arranged to determine the instantaneous magnitude of the steering angle.

8. Steering angle transducer according to claim 6, characterized in that the evaluation unit is arranged to determine whether the steering angle lies within a predetermined angle range containing the steering angle value 0° and extending a limited angle on each side of said value.