FR2512208A3 - Speed sensor for stepped rotation of shaft - uses integrated hall effect sensor with Schmitt trigger circuit providing digital output - Google Patents

Abstract

A wheel (1) is fixed onto a shaft (2) whose rotational speed is to be measured. The wheel has several permanent magnetic pole elements around its periphery. These successive pole elements are of alternate magnetic pole polarity. A fixed detector (3) is positioned facing the peripheral surface of the wheel. This detector contains a linear Hall effect detector which is integrated on a common substrate with a Schmitt trigger circuit (5) to form a hybrid circuit of thick and thin film component technologies. Compensating components are mounted on these circuits. The Schmitt trigger provides a digital output signal each time the Hall effect detector senses a zero value.

Description

 The invention relates to a device for detecting the speed of rotation of a shaft, which carries a transmitting wheel constituted by an annular magnet, or else a toothed crown.

 The invention aims to create a device for detecting the speed of rotation in incremental or segmental systems, and which can be of universal application as much as possible, for example for fully electronic ignition with coils ( VSZ), for digital engine electronics (DNE), for coil and transistor ignition (Tsz), for contactless ignition or injection systems, for anti-lock protection (Â3s) .

 For the detection of fluctuations in induction as a result of changes in the magnetic flux on annular magnets (polar wheels) or else on starter crowns, a device can be provided which is fully effective, characterized in that, opposite -vis the edge zone of the transmitting wheel, is placed a linear integrated Hall circuit to which is connected a Schmitt trigger controlled by this integrated Hall circuit.

 The particular advantage here resides in that the rotational speed signals are obtained in digital form which, consequently, can be easily processed or deducted using microcomputers.

The invention will be explained in more detail with reference to two embodiments shown in the accompanying drawings in which t
FIG. I represents an exemplary embodiment of the invention in which a pole wheel is used,
- Figure 2 shows another embodiment of the invention in which a toothed transmitting wheel is used.

 In the case of the exemplary embodiment; tion according to Figure 1 there is provided a pole wheel 1 in the form of a disc, placed on a shaft 2 whose speed of rotation must be detected and restored in digital form. The polar wheel 1 comprises, on its border area, a plurality of permanent magnetic batteries which alternate in the peripheral direction of the polar wheel and which are indicated by pale south S and north poles N. To detect the changes in induction occurring during the rotation of the pole wheel 1 a fixed detector 3 is provided, carrying on its front face turned towards the peripheral surface of the pole wheel i, an integrated linear circuit of Hall 4, integrated on a semiconductor chip and mounted on a common substrate plate with a Schmitt 5 detector integrated on another chip. At output 6 you can take digital signals, not shown, which arise each time the induction opposite the Hall integrated circuit crosses the value zero or a value located near zero.

In the case of the exemplary embodiment according to FIG. 2, there is provided a transmitting wheel II which is fitted on its border zone with rectangular teeth 12 between the leagues which is each time provided with an interval of teeth 13. The transmitting wheel 11 is placed on a shaft indicated in section by 14, whose speed of rotation must 8trie detected by induction. To this end, vis-a-vis the peripheral surface of the emitting wheel 11, is placed a linear integrated circuit of Hall 15 against the face behind which is placed an aijiant 16 in the shape of a rod polarized in the longitudinal direction and generating a high magnetic flux which crosses the integrated circuit of Hall when this is opposite one of the teeth of the emitting wheel 11 in soft iron . When, instead of a tooth 12, an interval 13 is located in front of the Hall 15 integrated circuit, the magnetic flux passing through the integrated circuit
Hall is notably weaker. The output voltage of the Hall integrated circuit 15 is then notably lower than for one of the teeth 12.

 To convert the induction variations, there is provided, as in the first embodiment, a Schmitt trigger 17 which is mounted at the same time as the Hall integrated circuit 15 and that the permanent magnet 16 on a substrate plate 18. This substrate plate may bear on its front or back (not identifiable in the drawing) compensation resistors reported by the thin film or thick film technique, and which can be adjusted to the correct value for example by a laser ray.

 In the two exemplary embodiments, it is assumed that a semiconductor chip is provided for the integrated linear circuit of Hall 4 or else 15, while the Schmitt trigger 5 or else 17 is integrated on a second semi-chip conductive. According to an alternative embodiment of the invention, the Hall integrated circuit and the Schmitt trigger can both be integrated on a common single semiconductor chip.

Claims (4)

 1.- Device for detecting the speed of rotation of a shaft, which carries a transmitting wheel constituted by an annular magnet, or else a ring gear, device characterized in that, vis-à-vis the border area of the transmitting wheel, is placed an integrated linear circuit of Hall (4, 15) to which is connected a Schmitt trip device controlled by this integrated Hall circuit.  2.- Device according to claim 1, characterized in that the Hall integrated circuit and the Schmitt trigger are integrated on a common semiconductor chip.  3.- Device according to claim 1, characterized in that the Hall integrated circuit is disposed on a first conductive chip and the Schmitt trigger has a second conductive chip, these two conductive chips being arranged on a common hybrid.  4.- Device according to claim 3, characterized in that I'hypr, ide includes compensation possibilities in particular in the form of resistant bands reported by the technique of thin layers or thick layers.