GB2065310A

GB2065310A - Rotational speed or angle sensor and evaluation circuit

Info

Publication number: GB2065310A
Application number: GB8037569A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-11-24
Filing date: 1980-11-24
Publication date: 1981-06-24
Also published as: FR2470386A1; JPS5687860A; DE2947412A1; IT1134376B; IT8026110A0

Abstract

The disc(s) of a sensor for detecting the rotational speed and/or instantaneous angular position of a shaft (W) has angular segments (s1, s2 etc) about its periphery. Congruent segments each comprise a tooth (1, 2 etc) and a tooth gap. A reference mark on the disc is constituted by a segment from which the tooth (10) is absent. The teeth are detected by an inductive scanner (E) and the trailing edge of each tooth produces a pulse in a coil (8) and in a micro-processor connected thereto. Each scanner pulse causes a backward counter to be reset. The counter counts pulses fed at constant frequency and the initial setting is such that the counter only counts back through zero when the toothless segment is reached. The output thereby produced by the counter is used, for example, to control the operation of an internal combustion engine ignition system. <IMAGE>

Description

SPECIFICATION Rotational speed or rotary angle sensor and an associated evaluation circuit The invention relates to a sensor for detecting the rotation speed and/or a marked angle of rotation of rotatable member, comprising a disc which is adapted to be rotated with said member and whose periphery has a plurality of teeth which are located one after the other in the direction of rotation.

An object of the invention is to provide, in a disc of this kind which is made preferably from ferromagnetic material, a mark in the rim region thereof which can be detected by simple means.

In accordance with the invention, a sensor for detecting the rotational speed and/or angular position of a rotatable member, comprises a disc which is adapted to be rotated with said rotating member and whose periphery has a plurality of angular segments which are located one after the other in the direction of rotation, said segments including congruent segments each of which comprises a tooth and a tooth gap contiguous therewith, and a sensor for scanning these segments and for supplying a pulse when each tooth moves past the scanner, a reference mark to be detected being constituted by a non-congruent reference mark segment which is contiguous with at least two congruent angular segments and which is distinguished by the absence of a tooth so that it is in the form of a gap between the tooth of a preceding segment and a segment following in the direction of rotation.

An evaluation circuit including a counter may be provided for detecting the reference mark, the counter counting pulses which are fed to it at constant frequency and being re-set and started by sensor pulses induced in a scanner by the teeth.

The invention will be further described, by way of example, with reference to the drawings, in which: Figure 1 is an axial plan view of an approximately 800 portion of a sensor disc in accordance with the invention, Figure 2 is an evaluation circuit for the sensor disc of Figure 1, Figure 3 is a time graph of the voltage pulses J which are generated by the scanner indicated at E in Figure 1, and Figure 4 is a pulse diagram showing the reading N of a backward counter which varies in dependence upon time and angle.

The sensor disc illustrated in Figure 1 is punched out of, for example, iron sheet and its circumference is sub-divided into thirty-six segments s each extending over an arc of 100. All but one of these segments s has a respective tooth, the teeth associated with congruent segments being designated 1 to 6 in Figure 1.

Furthermore, each segment has a tooth gap 7 whose bottom is defined by a radius r2, while the circumferential tip surfaces of the teeth have a larger radius rl.

The disc S is mounted on a shaft W of an internal combustion engine, such as the distributor shaft thereof, but preferably the crankshaft. When the sensor disc is rotated in the direction of the arrow, the teeth of the disc move past an inductive scanner E in succession, the output of the scanner being connected to a rectifier V and pulse shaper.

As soon as the rear flanks of the teeth 1, 2, 3, etc.

pass the scanner E, short pulses, of the kind indicated at J1, J2, J3, etc. in Figure 3, are induced in a coil 8 forming part of the scanner E and in an evaluation circuit.

In order that a predetermined angular position of the sensor disc S can be associated with an operation of the internal combustion engine, such as for the purpose of determining the instant of ignition for one of the cylinders of the engine, one of the segments is marked relative to the other mutually congruent segments by a departure from the congruence in the manner shown in Figure 1.

This mark is obtained by omitting the associated tooth 10, indicated by broken lines, in the marked segment. A tooth gap 11 which is three times as large as the tooth gaps 7 associated with the congruent segments sil, s2, s3... s6,... is thereby provided in front of the next tooth 4. This can be detected by simple means in an electronic evaluation circuit, so that it is possible to select the marked segment from the other segments by means of the widened tooth gap 11 and to associate it with the desired operation of the internal combustion engine.

Only a single sensor, that is to say, the inductive scanner E, is used to detect the angle or tooth pulses J 1, J2, J3, etc. and the reference mark EM or the gap 11 representing the latter.

The sensor in accordance with the invention is particularly suitable for the use in conjunction with a microprocessor (not illustrated in the drawings).

In order to relieve the load on the microprocessor, the reference mark BM is measured over only a small range. For this purpose, this range is selected in an initial phase, such that the reference mark reliably falls in this range. A backward counter shown as a counter/timer ZT in Figure 2 is used to detect the gap 11 or the reference mark BM. The course of the measuring phase described hereinafter is determined by a computing program. The measuring phase commences a few teeth before the probable arrival of the gap 11.

The measuring phase is determined in an initial phase which commences upon starting and which is described further below.

At the commencement of the measuring phase, the period which is indicated at T in Figure 3, and which extends from one tooth to the next tooth, is counted out by means of the counter/timer ZT to which counting pulses Ir are fed at a fixed frequency fr. The counter reading N resulting during such a period is increased by the microprocessor by half the counter reading attained and is used to charge the timer ZT to the initial value 1.5 T. The counting operation commences in each case upon the arrival of the next tooth pulse Jn which sets the counter to the initial value 1.5 T from which the counter is successively reset to the value 0.5 T by the counting pulses Ir up to the arrival of the next tooth staggered by the period T.

However, when the gap 11 has been scanned, the counter/timer ZT runs through zero, as indicated at B0 in Figure 4, and then produces a signal which, in the arrangement illustrated in Figure 2 for example, initiates an ignition operation in the ignition coil ZS. The ignition operation is not triggered directly by the reference mark (that is to say, the next tooth). The reference mark serves as a reference for calculating the opening and closing angles, i.e. the instants at which a semi-conductor switch in the primary circuit of an ignition coil is switched on and off.

The reference mark BM can be associated with the next tooth by the zero signal B,.

The above-mentioned initial phase takes place in the following manner: Upon starting, the period T extending from tooth to tooth must first be continuously monitored over one or two revolutions of the disc S. The period is doubled where the tooth 10 is absent. This is readily detected by the microprocessor which can thus determine the gap itself.

To improve comprehension, and in contrast to the thirty-six tooth disc S illustrated in Figure 1, it will be assumed that the disc is far more finely sub-divided and has a gap serving as a reference mark after each hundredth tooth. A counter is set to zero upon detecting this gap and is counted upwardly with the tooth pulses Jn. The reference mark is set internally as soon as the value 100 is reached. Consequently, the computer can itself count the gap as soon as the gap has once been detected.

For the purpose of monitoring and synchronization, the above-described measuring phase can be initiated for a short time once per revolution of the disc or, alternatively, only during each second or third revolution, such as at the counter reading 96 in each case.

If a gap does not arrive during the measuring phase as the result of a fault or if a gap is not detectable, the computer has to switch to the above-described initial phase and seek the next gap.

The special advantage resides in the fact that the computer automatically finds the reference mark.

Of course there may be more than one reference mark over the circumference of the disc.

For example, there may be one reference mark associated with each cylinder of a multi-cylinder internal combustion engine.

Claims

1. A sensor for detecting the rotational speed and/or an angular position of a rotating member comprising a disc which is adapted to be rotated with said rotating member and whose periphery has a plurality of angular segments which are located one after the other in the direction of rotation, said segments including congruent segments each of which comprises a tooth and a tooth gap contiguous therewith, and a sensor for scanning these segments and for supplying a pulse when each tooth moves past the scanner, a reference mark to be detected being constituted by a non-congruent reference mark segment which is contiguous with at least two congruent angular segments and which is distinguished by the absence of a tooth so that it is in the form of a gap between the tooth of a preceding segment and a segment following in the direction of rotation.

2. A sensor as claimed in claim 1, in which the toothless reference mark segment extends over at least half the angle associated with the congruent segments.

3. A sensor as claimed in claim 2, in which the toothless reference mark segment extends over an angle of rotation which is twice that of the congruent segments.

4. A sensor as claimed in claim 2 or 3, in which a counter is provided for detecting the reference mark.

5. A sensor as claimed in claim 4, in which the counter comprises a counter/timer.

6. A sensor as claimed in claim 4 or 5, in which the counter is a backward counter in which each angle pulse is preadjusted to a counter reading corresponding to approximately one and a half times the number of pulses being counted, and which are associated with a congruent segment, the frequency of the counted pulses being freely selectable, and in which the backward counter is reset from this reading with the passage of time or with a progressive angle of rotation and, upon passing through the zero position, indicates the passage of the toothless reference mark segment.

7. A sensor for detecting a rotational speed and/or angular position constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the drawings.