GB1576403A - Pulse generators - Google Patents

Description

(54) IMPROVEMENTS IN PULSE GENERATORS (71) We,, ROBERT BOSCH GMBH., a German Company, of Postfach 50, 7.

Stuttgart 1, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a contactless pulse generator, e.g. for producing pulses for an ingnition system of an internal combustion engine.

U.S. patent specification No. 3,875,920 describes a contactless pulse generator in which a Hall generator is included in a magnetic circuit. The magnetic flux through the Hall generator is changed in that a member, made from magnetically conductive material and rotating together with the rotor, periodically forms a magnetic shunt with the Hall generator, so that the Hall generator produces a signal whose value varies in dependence upon the flux permeating the Hall generator. This arranged ment has the disadvantage that the changes in the flux effected in the Hall generator by the shunt are only small and the changes in the signal produced by the Hall generator are correspondingly small. Thus, the arrangement is very sensitive to external interference of the type which can readily occur particularly in internal combustion engines.

A contactless pulse generator according to the present invention comprises a stator on which is mounted a Hall generator which is adapted to produce a signal upon a change in magnetic flux through the generator, and a rotor which is formed by a magnetically non-conductive body to which are secured a single annular magnet arranged co-axially to the rotor axis, polarized in an axial direction relative to that axis and connected thereto by the magnetically non-conductive body, and at least a pair of yoke members one extending from each of the magnet poles, at least one yoke member comprising a portion which extends in a radial direction relative to the rotor axis and a plurality of projections extending in an axial direction relative to the rotor axis, the projections directed in an axial direction being arranged to pass by the Hall generator upon rotation of the rotor to change the magnetic flux through the generator.

This has the advantage. that a large change in the magnetic flux through the field-dependent Hall generator can be obtained by the yoke member or members, since the magnetic flux can be virtually completely diverted from the generator. A further advantage is that the yoke members can be manufactured as simple stamped members and it is thus possible to massproduce a simple and inexpensive pulse generator.

For the purpose of triggering pulses, it is particularly advantageous to allow the same yoke members to flank the element first from one end and then from the other end.

The flux in the Hall generator is thus reversed, whereby the change in the magnetic flux is doubled with the same magnetic intensity.

The invention is further described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a cross section of a first embodiment of a contactless pulse generator in accordance with the invention; and Figs. 2, 3 and 4 are similar cross sections of second, third and fourth embodiments of a pulse generator in accordance with the invention.

Referring to Fig. 1, a single axially polarised annular magnet 10 provided with an upper yoke member 11 and a lower yoke member 12 is attached to a shaft 14 by means of a hub 13 made from magnetically non-conductive material. A magnetic field-dependent element in the form of a Hall generator 15 is mounted on a stator plate (not illustrated). The north and south poles of- the annular magnet 10 are located at the points at which or positions of the rotor 10 to 14 in which a magnetic flux is to be conducted through the field-dependent element 15, the upper yoke member 11 is directed radially away from the shaft in the angular range in which the upper and lower yoke members, respectively, are mounted. The yoke members 11 and 12, which are also of annular configuration, may be readily manufactured as stamped members.In the angular position the field-dependent element is located in the magnetic circuit (magnetic flux path), and the upper yoke member 11 is bent to form a plurality of axially-extending projections ila which pass the end of the element 15 remote from the shaft on rotation of the rotor. The magnetic circuit is then closed by way of the element 15 (see left hand side of Fig. 1). In the angular position or positions of the rotor 10 to 14 in which the element 15 is not located in the magnetic circuit, the upper yoke member 11 is bent to form projections 11 b extending axially in front of that end of the element 15 which faces the shaft (see right-hand side of Fig.

1). Preferably, the lower yoke member 12 terminates flush with the magnet opposite projections 1 lb, but has axiallyextending projections 12a opposite projections 1 la. A yoke member of opposite polarity is then located opposite the end of the element which is remote from the shaft, so that the magnetic flux through the element is zero or there may be a small stray flux in opposition to the normal flux.

In a second embodiment shown in Fig. 2, the element 15 is secured to the inside of the outer limb of a U-shaped stator 20.

The single annular magnet 10, the upper yoke member 11 and the lower yoke member 12 are again mounted on the shaft 14 by means of a hub 13.

The element is is enclosed in the magnetic circuit where the upper yoke member 11 is bent at an angle to form axially-extending projections, so that the upper yoke member projections pass the element 15 at a short distance from the end thereof facing the shaft (see left hand side of Fig. 2). The magnetic flux then flows back to the magnet by way of the yoke member 11, the magnetic element 15, the stator 20 and the yoke member 12. The lower yoke member 12 may, in this embodiment, be constructed in the form of a simple disc having a central bore whose diameter is equal to, or greater than, the diameter of the shaft.

The upper yoke member 11 is not bent where the field-dependent component is not to be permeated by a magnetic flux but extends radially (see right hand side of Fig. 2). A magnetic flux then does not flow through the element 15. In order to obtain a greater change in the flux, it is advantageous to extend the limb of the stator, to which the element 15 is secured, somewhat beyond the element. A stray flux then flows to the lower yoke member 12 by way of the end of the yoke member 11 and the tip of the stator limb carrying the element. By virtue of this measure, a slight magnetic flux in opposition to the normal flux can be obtained. Thus, the change in the magnetic flux is again increased.

Referring to Fig. 3, the annular magnet 10 having the two annular yoke members 11 and 12 is connected to the shaft 14 by means of the hub 13. The field-dependent element 15 secured to the stator (not illustrated) is located between the two angled yoke members. In this case, a signal is triggered by reversal of the direction of flux flowing through the field-dependent component (compare left and right hand sides of Fig. 3). In one case, the magnetic flux flows to the lower yoke member 12 by way of the upper yoke member 11 and the field-dependent element 15. For this purpose, the upper yoke member 11 is bent such as to provide axially-extending projections 1 1a located opposite to that end of the element 15 which is remote from the shaft.On the other hand, the lower yoke member 12 is bent such as to form axially-extending projections 12a in the vicinity of the element 15, parallel to the shaft 14 at that end of the element 15 which faces the shaft.

In order to reverse the flux, the upper yoke member 11 is bent such as to form projections 1 lb extending axially and located between the shaft 14 and the element 15, whilst lower yoke member 12 is bent such as to provide projections 12b that pass that end of the element 15 which is remote from the shaft 14.

A further embodiment in accordance with the invention is illustrated in Fig. 4. The magnet 10 together with its two yoke members 11 and 12, is again connected to a shaft 14 by way of the hub 13. The field-dependent element 15 is mounted on the inside of that limb of the U-shaped stator 20 which is at the further distance from the rotor axis. The limb facing the rotor shaft may be provided with a lug which is directed away from the rotor axis.

The two yoke members 11 and 12 first lead away from the magnet 10 at right angles to the axis and are then bent axially to form projections such that the outer limb of the stator 20 with the element 15 mounted thereon is externally flanked by the upper yoke member projections 1 1a and internally flanked by projections 12a of the lower yoke member 12 (see left hand side of Fig. 4). In order to reverse the flux, the yoke member 11 is bent downwardly a different angular region of the rotor to form axially-extending projections 1 lib while the yoke member 12 is bent to form axially-extending projections 12b. The lower yoke member projections 12b are located opposite that limb of the stator 20 which faces the rotor axis (see right hand side of Fig. 4).By way of example, when, in the first case described, a flux flows to the lower yoke member 12 by way of the upper yoke member 11 and the fielddependent element 15, the flux is reversed in the second case, since, in this instance, the flux flows in the opposite direction from the upper yoke member 11 to the lower yoke member 12 by way of the field-dependent element 15 and the stator 20.

It is considered essential to use a Hall generator as the field-dependent element 15, because such generators have the characteristic that they produce an electrical signal in dependence upon the intensity of the flux with respect to amount and also with respect to direction.

WHAT WE CLAIM IS:- 1. A contactless pulse generator, comprising a stator in which is mounted a Hall generator which is adapted to produce a signal upon a change in magnetic flux through the generator, and a rotor which is formed by a magnetically non-conductive body to which are secured a single annular magnet arranged co-axially to the rotor axis, polarised in an axial direction relative to that axis and connected thereto by the magnetically non-conductive body, and a pair of yoke members one extending from each of the magnet poles, at least one yoke member comprising a portion which extends in a radial direction relative to the rotor axis and a plurality of projections extending in an axial direction relative to the rotor axis, the projections directed in an axial direction being arranged to pass by said Hall generator upon rotation of the rotor to change the magnetic flux through said generator.

2. A pulse generator as claimed in claim 1, in which in order to trigger pulses, the axial projections of the at least one yoke member flank the Hall generator first at one end and then at the other end thereof as the rotor is rotated.

3. A pulse generator as claimed in claim 1, or 2 in which the two yoke members extending from opposite poles of the magnet are embedded in the body and in which the axial projections of each yoke member are such that the Hall generator is enclosed by the axial projections when a signal is to be produced by the generator and the Hall generator is not enclosed by the projections of the yoke members when a signal is not to be produced by the generator.

4. Contactless pulse generators constructed substantially as herein described with reference to and as illustrated in any of the Figures of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. lower yoke member 12 (see left hand side of Fig. 4). In order to reverse the flux, the yoke member 11 is bent downwardly a different angular region of the rotor to form axially-extending projections 1 lib while the yoke member 12 is bent to form axially-extending projections 12b. The lower yoke member projections 12b are located opposite that limb of the stator 20 which faces the rotor axis (see right hand side of Fig. 4).By way of example, when, in the first case described, a flux flows to the lower yoke member 12 by way of the upper yoke member 11 and the fielddependent element 15, the flux is reversed in the second case, since, in this instance, the flux flows in the opposite direction from the upper yoke member 11 to the lower yoke member 12 by way of the field-dependent element 15 and the stator 20. It is considered essential to use a Hall generator as the field-dependent element 15, because such generators have the characteristic that they produce an electrical signal in dependence upon the intensity of the flux with respect to amount and also with respect to direction. WHAT WE CLAIM IS:-

1. A contactless pulse generator, comprising a stator in which is mounted a Hall generator which is adapted to produce a signal upon a change in magnetic flux through the generator, and a rotor which is formed by a magnetically non-conductive body to which are secured a single annular magnet arranged co-axially to the rotor axis, polarised in an axial direction relative to that axis and connected thereto by the magnetically non-conductive body, and a pair of yoke members one extending from each of the magnet poles, at least one yoke member comprising a portion which extends in a radial direction relative to the rotor axis and a plurality of projections extending in an axial direction relative to the rotor axis, the projections directed in an axial direction being arranged to pass by said Hall generator upon rotation of the rotor to change the magnetic flux through said generator.

2. A pulse generator as claimed in claim 1, in which in order to trigger pulses, the axial projections of the at least one yoke member flank the Hall generator first at one end and then at the other end thereof as the rotor is rotated.

3. A pulse generator as claimed in claim 1, or 2 in which the two yoke members extending from opposite poles of the magnet are embedded in the body and in which the axial projections of each yoke member are such that the Hall generator is enclosed by the axial projections when a signal is to be produced by the generator and the Hall generator is not enclosed by the projections of the yoke members when a signal is not to be produced by the generator.

4. Contactless pulse generators constructed substantially as herein described with reference to and as illustrated in any of the Figures of the accompanying drawings.