ELECTRICAL STEERING ANGLE SENSOR FOR MOTOR VEHICLES

Abstract: The sensor comprises a structure (5) with a periodic distribution of references (6a), and first and second electrical detector means (A, B) for furnishing a pulse each time they detect a reference (6a) of this structure (5). The detector means (A, B) and the structure (5) are connected to the steer­ ing column (2) so that rotation of this column (2) in one sense, or in the opposite sense, causes a corresponding relative movement between the structure (5) and the detector means (A, B) in one direction or sense, or in the opposite direction or sense. The first and second detector means (A, B) are disposed at a relative distance different from the period of distribution of the references (6a) of the structure (5) (and from multiples thereof) in such a way that, when the steering is operated, the pulses (V a , V b ) emitted by these detector means (A, B) have a phase difference the sign of which is indicative of the direc­ tion of steering, and the number of pulses emitted between two instants is a measure of the angle through which the steering column (2) has rotated between these instants.

Description: Electrical steering angle sensor for motor vehicles The present invention relates to an electrical steering angle sensor for furnishing electrical signals indicative of the angle through which the steering column of a motor vehicle has passed and its sense of rotation. The object of the invention is to produce a simple, robust, reliable and economical electrical sensor. This object is achieved according to the invention by means of an electrical steering angle sensor, characterised in that it comprises: a structure having a periodic distribution of references, and first and second electrical detector means for furnishing a pulse each time they detect a reference of the structure; the first and second detector means and the structure being connectible to the steering column so that rotation of the column in one sense, or in the opposite sense, causes a corresponding relative movement between the structure and the detector means in one direction or sense, or in the opposite direction or sense; the first and second detector means being disposed at a relative distance different from the period of distribution of the references (and from multiples thereof) in such a way that, when the steering is operated, the pulses emitted thereby have a phase difference the sign of which is indicative of the direction of steering, and the number of pulses emitted between two instants is a measure of the angle through which the steering column has rotated between these instants. Further characteristics and advantages of the sensor according to the invention will appear from the detailed description that follows with reference to the appended drawings, provided purely by way of non-limiting example, in which: Figure 1 shows a perspective view of a sensor according to the invention applied to the steering of a motor vehicle; Figure 2 is a perspective view of the electrical steering sensor according to the invention, on an enlarged scale; Figure 3 is a plan view of an annular element forming part of the device illustrated in Figure 2, and Figure 4 is a series of diagrams showing the progression of the waveform of some signals generated during the operation of the sensor, as function of time. With reference to Figures 1 and 2, a sensor according to the invention, generally indicated 1, is connected to the steering column 2 of a motor vehicle, adjacent the steering box 3. As apparent from Figure 2 in particular, in the embodiment illustrated by way of example, the sensor comprises a substantially cylindrical casing 4 secured to the body of the motor vehicle and having apertures in its end walls, through which the steering column 2 passes. Figures 2 and 3 show a supporting disc 5 made of electrically-insulating material and having a central aperture 5a fixed coaxially about the steering column 2 within the casing 4. An annular conductive coating 6 with a plurality of outwardly-directed equiangularly-spaced radial extensions 6a is deposited on one side of the disc 5, coaxial with the aperture 5a. All the radial projections 6a have the same dimension in the circumferential sense of the disc 5. Moreover, with the sole exception of a radially longer projection 6b, all the projections 6a have the same radial dimension. The conductive coating 6 is connected to the earth of the electrical system of the motor vehicle in a manner not illustrated, for example through the steering column 2 itself. A further supporting element 7, which in the embodiment illustrated in Figure 2 is also in the form of a disc provided with a central aperture, is fixed within the casing 4. The supporting element 7 is fixed to the casing 4, and the steering column 2 is thus rotatable relative to this element. On its side facing the disc 5, the latter carries three sliding contact members A, B, C the ends of which are in contact with the surface of the disc 5 bearing the conductive coating 6. The relative disposition of these contact members will now be described with particular reference to Figure 3, in which the projections of the contact members onto the disc 5 are indicated A, B and C. The contact members A and B are located at a distance from the axis of rotation of the steering column 2 such that their projections onto the disc 5 lie on a circumference which intersects the projections 6a of the conductive coating 6. Moreover, the distance between them in the circumferential sense is different from the period of distribution of the projections 6a of the coating 6. In the disposition illustrated by way of example in Figure 3, the contacts A and B are arranged so that, when the first contact impinges centrally on one projection 6a (or 6b), the other impinges on a lateral edge of another of these projections. The contact member C is located at a distance from the axis of rotation of the steering column 2 such that its projection onto the disc 5 lies on a circumference which intersects only the longer radial projection 6b of the conductive layer 6 The contact members A, B and C are connected (in a manner not shown) to the battery of the motor vehicle through resistors Rl, R2 and R3. The sensor described above operates in the following manner. In use, when the steering column 2 is turned, the supporting disc 5 fixed thereto rotates relative to the contacts A, B and C which are fixed. Consequently, the voltages VA, VB and Vc detectable between each of these contacts and earth have progressions which are shown qualitatively by the waveform of Figure 4: VA and VB show a succession of pulses each of which corresponds to a projection 6a of the conductive coating 6 on the disc 5. Vc produces a pulse each time the projection 6b of the conductive coating passes the contact C. According to the relative disposition of the contacts A and B shown in Figure 3, if the steering column and the disc 5 fixed thereto rotate in the sense of the arrow F in Figure 3, the waveform VB becomes phase-shifted in advance of the waveform VA, as shown in Figure 4. It is immediately recognisable that, whenever the steering column 2 is turned in the opposite sense to the arrow F, the waveform VA would lead the waveform VB. It can therefore be concluded that the sign of the phase difference between the waveforms VA and VB is indicative of the sense of rotation of the steering column. Moreover, it is immediately notable that the number of the pulses of VB or VA between two instants represents a measure of the angle through which the steering column 2 has rotated between these instants. The larger projection 6b of the conductive coating 6 serves to provide a reference for the angular position of the steering column; this appendage and its associated contact C may be arranged in such a way that the signal Vc produces a pulse when the steering column is in the "neutral" position or in the straight-ahead condition. The sensor described above, with only three outputs, furnishes electrical signals containing information about the direction of steering and the size of the steering angle relative to an angular reference position. Clearly, it is possible to make the sensor in such a way that the disc carrying the references 6a, 6b is fixed relative to the steering column, while the contacts A-C are fixed torsionally to the latter.

Claims: CLAIMS 1. An electrical steering angle sensor, characterised in that it comprises: a structure (5) having a periodic distribution of references (6a), and first and second electrical detector means (A, B) for furnishing a pulse each time they detect a reference (6a) of the structure (5); said first and second detector means (A, B) and said structure (5) being connectible to the steering column (2) so that rotation of the column (2) in one sense, or in the opposite sense, causes a corresponding relative movement between the structure (5) and the detector means (A, B) in one direction or sense, or in the opposite direction or sense; said first and second detector means (A, B) being disposed at a relative distance different from the period of distribution of the references (6a) (and from multiples thereof) in such a way that, when the steering (2) is operated, the pulses (VA, VB) emitted thereby have a phase difference the sign of which is indicative of the direction of steering, and the number of pulses emitted between two instants is a measure of the angle through which the column (2) has rotated between these instants. 2. A sensor according to Claim 1, characterised in that the structure (5) has a supplementary reference (6) associated with an angular reference position of the steering column (2), and third electrical detector means (C) for furnishing a pulse each time they detect the passage of the supplementary reference (6b) close thereto. 3. A sensor according to Claim 1 or Claim 2, characterised in that the structure (5) is rotatable with the steering column (2). 4. A sensor according to any one of the preceding claims, characterised in that the references comprise electrically conductive surface portions (6a) of the structure (5). 5. A sensor according to Claim 4, characterised in that the detector means for the references comprise electrical contact members or brushes (A, B) in contact with the structure (5). 6. A sensor according to Claims 3 and 5, characterised in that the contact members or brushes (A, B) are disposed in respective fixed positions relative to the steering column (2). 7. A sensor according to Claim 6, characterised in that the structure comprises a supporting disc (5) of electrically insulating material, which is mountable coaxially on the steering column (2) and has an annular circumferential metallic coating (6) on one side, and in that the references are constituted by a plurality of outwardly-directed and equiangularlyspaced radial projections (6a) of the coating. 8. A sensor according to Claims 2 and 7, characterised in that the supplementary reference is constituted by one of the radial projections (6b) which is longer than the other projections (6a), and in that the third detector means comprise a further contact member or brush (C) fixed to and in contact with the structure (5) at a distance from the axis of rotation of the structure greater than the distance of the outer ends of the projections (6a) from this axis, and less than or equal to the distance between the axis and the outer end of the longer projection (6b).

Inventors: SCARTEZZINI, VITO
Applicants: FIAT AUTO S.P.A.
Application year: 1985
Main classification: B62D15
IPC codes: G01D5, B62D15