GB2176616A

GB2176616A - Magnetic field responsive device for measuring rotation

Info

Publication number: GB2176616A
Application number: GB08614206A
Authority: GB
Inventors: Heinz Loreck
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1985-06-20
Filing date: 1986-06-11
Publication date: 1986-12-31
Also published as: FR2583886A1; JPS61294313A; DE3521966A1; GB8614206D0

Abstract

To provide a pulsed output signal with a frequency indicative of rotational speed of a toothed wheel 2 spaced from a fixed magnet 1, there is provided on the face 6 of the magnet a field responsive semiconductor chip 3 comprising an integrated circuit with two Hall generators 9, 10 arranged one after the other in the direction of rotation and associated electrical energy supply, measuring, and evaluation circuits, including a differential amplifier with hysteresis for receiving the Hall signals in order to reduce spurious signal due to vibration. The distance between the two Hall generators (9, 10) should equal or be less than one tooth width B. The electric energy supply and the measured signals are conducted via one sole double line. <IMAGE>

Description

SPECIFICATION Device for measuring a magnetic field andl or magnetic field changes in an air gap This invention relates to a device for measuring a magnetic field and/or magnetic field changes in an air gap between a stationary transducer and a rotating transmitter which is mounted on a shaft, a wheel, or the like or which is a component of such a revolving body, said device comprising a Hall generator integrated on a semiconductor chip and fastened in the air gap on a face of the transducer facing the transmitter.

In order to measure the rotational speed of a shaft it is already known to mount a transmitter wheel designed as an annular magnet or a toothed wheel rim on said shaft and to provide a stationary transducer at an edge zone of the transmitter wheel. In the air gap between transmitter and transducer a magnetic field is formed by means of the magnets in the transmitter wheel or by means of a magnet within the transducer, the changes of said magnetic field being detected by means of a Hall IC and by means of an evaluation circuit connected via a capacitor (DE OS-West German Printed Patent Application No. 32 31 391).

Such an arrangement is disadvantageous particularly since vibrations between the transmitter wheel and the transducer, and air gap changes caused thereby, cause spurious signals which are indistinguishable from the useful signals, namely, the speed-dependent signals, or which, at least, considerably deteriorate the signal resolution. A further disadvantage of such a circit consists in that the Hall IC needs separate lines for electric energy supply and for picking up the measured signals.

To measure rotary motions, further, it is already known to arrange two inductive transducers at the circumference of a toothed disk, which serves as a transmitter, in a staggered manner such as to ensure that the useful signals depending on the speed will occur 180 out of phase in the two transducers. Spurious signals, on the contrary, will lead to equidirectional signals in the two transducers. It is expected to thus be able to tell useful signals from spurious signals (DE-OS-West German Printed Patent Application No. 22 39 926).

Arrangements with exclusively inductive transducers in principle have the disadvantage that the amplitude of the output signal depends on the velocity of rotation, therefore -at least in the case of small velocities- differentiation between useful and spurious signals is hardly possible.

It is thus an object of the present invention to overcome the described disadvantages and to develop a sensor, i.e. a measuring device, which, on the one hand, will deliver an output signal with a sufficient amplitude even in the case of slow rotary motions and which, on the other hand, will largely be insensitive to spurious signals such as the unavoidable air gap vibrations.

According to the present invention there is provided a device for measuring a magnetic field and/or magnetic field changes in an air gap between a stationary transducer and a rotating transmitter which is mounted on a shaft, a wheel, or the like or which is a component of such a revolving body, said device comprising a Hall generator integrated on a semiconductor chip and fastened in the air gap on a face of the transducer facing the transmitter, characterised in that the semiconductor chip comprises two similar Hall generators arranged one after the other in respect of the direction of rotation of the transmitter, electrical energy supply circuit, measuring circuitry and evaluation circuitry (IC).

It has been found out that the above object can be solved in a surprisingly simple, technically advanced manner by means of a device of the present invention.

According to an advantageous embodiment of the invention, which requires a transmitter in the form of a toothed disk, the distance between the two Hall generators approximately corresponds to one tooth width, that is the extent of a tooth in the circumferential direction of the disk. In other examples of embodiments it is advantageous to select the distance between the two Hall elements to be less than the tooth width.

The semiconductor chip of the inventive device advantageously accommodates the two Hall generators as well as the supply, measuring, and evaluation circuitry in a single integrated circuit. In doing so, in one embodiment, in the integrated circuit there are provided a constant current source and a voltage amplifier for each Hall generator-the voltage amplifiers each being feedable with the output signal for the respective Hall generator, namely with the Hall voltage, a differential amplifier comparing the output voltages of the two Hall voltage amplifiers, a transistor stage whose output signal represents the measured result detected by means of the two Hall generators, as well as finally a voltage regulator for the stabilisation of the supply voltage for the various amplifier stages.

The differential amplifier expediently has a hysterisis characteristic so that for the switching-over of the output signals of the two Hall voltage amplifiers it is required that a predetermined threshold value of the input voltage difference of the differential amplifier be exceeded.

Further, in one embodiment of this invention, it is provided to rate the transistor stage acted upon by the differential amplifier as a switching stage whose position represents the measured result. In one example said switch ing stage is designed in the form of a transistor operated as an emitter follower whose collector-emitter path connects connection lines of the measuring device.

Further, one embodiment of this invention consists in that the same is connectible via a double line through which both the energy supply to the circuit, i.e. to the amplifiers and the two Hall generators, and the output of signals are effected.

If the inventive device is connected via a Graetz rectifier circuit likewise integrated in the semiconductor chip, the polarity of the connection lines will be of no importance.

A substantial advantage of this invention thus consists in that the described way of solution can be realised by one sole integrated circuit. This implies low manufacturing cost and a high degree of reliability. The confinement to one double line serving both for the energy supply and for the picking-up of the measured values likewise simplifies assembly, reduces sources of troubles, and leads to a reduction in the manufacturing expenses.

The amplitude of the output signal of the inventive measuring device is independent of the rotary motion to be measured. Thus, even in case of low speeds, a usable signal will be available.

Spurious signals, in particular air gap vibrations, practically will have no influence on the output signal, thereby faulty interpretations of the measured signals are avoided even in case of unfavourable conditions.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is the partial and schematic illustration of the arrangement of a transducer in relation to a transmitter; Figure 2 shows schematically the arrangement of Hall generators in a semiconductor chip when looking in the direction towards the face of the transducer facing the transmitter according to Fig. 1; Figure 3 is a circuit configuration of an integrated circuit according to one embodiment of the present invention; Figure 4 is the diagram of the variation of the output signals of the Hall voltage amplifiers of the circuit of Fig. 3 and of the output signal measured according to the one embodiment of this invention, and Figure 5 shows the same variations as Fig.

4 but for a second embodiment of this invention.

Fig. 1 shows the basic arrangement of a transducer 1 at the edge of a toothed disc 2, which is rotatable in either of the directions indicated by the double headed arrow, serving as a transmitter and of a semiconductor chip 3 or rather of a measuring device of the inventive type. In this instance, the magnetic field is generated by a rod-shaped permanent magnet 4 which generates the magnetic field 5 represented in an idealised manner by dashed lines. Said magnetic field 5 fills the air gap L between the front face 6 of the rod magnet 4 (the face of the transducer facing the transmitter) and the toothed disk 2. Thus, the effective air gap L is either determined by the distance L1 +L2 or by the distance L1+L2+L3.

The magnetic field is illustrated in an idealised manner in Fig. 1. The magnetic flux density in the air gap depends on the relative position of the tooth 7 or rather of the corresponding tooth gap 8 in respect of the magnet 4 of width M. The greater flux density 01 in the area of the tooth 7 as compared to the flux 02 in the tooth gap 8 is symbolised by the mutual distances between the lines of flux or rather by the number or density of the lines of flux in the area 7, 8.

Referring to Fig. 1, on its underneath side, as viewed in the drawing, the semiconductor chip 3 carries two similar Hall generators 9 and 10. The distance L1 of the Hall generators 9, 10 in respect of the front face 6 of the magnet 4 in reality is defined by the substrate's thickness or rather by the thickness of the semiconductor chip 3. It is advisable to glue the chip 3 directly onto the front face 6.

The air gap L2 or L2+L3 is defined by the distance of the outer surface area of the tooth 7 or by the toothed disk's outer surface within the gap 8.

In the illustrated example the teeth 7 of the toothed disk 2 are tapering towards the outer surface. Thus, they have a trapezoidal profile.

The width of the teeth 7 at the foot of the trapezium is marked B. Fig. 2 illustrates the arrangement of the Hall generators 9 and 10, namely the mutual arrangement and their positions in respect of the magnet 4 and the toothed disk 2. In the direction of rotation, the teeth 7 and the tooth gaps 8 pass the Hall generators 9 and 10 one after the other.

The distance D between the Hall generators is of importance with regard to the time variation of the Hall voltages and of the signal at the output of the measuring devices as will be explained in more detail later on with reference to the diagrams of Fig. 4 and Fig. 5.

The two Hall generators 9, 10 are integrated in a largely symmetrical arrangement, together with associated measuring and evaluation circuits as well as with a supply circuit, in an integrated circuit IC on the semiconductor chip 3. The wiring diagram is illustrated in Fig. 3.

The inventive measuring device or rather the circuit according to Fig. 3 is connected via the connections Al and A2 or Al' and A2'. UB symbolises a voltage source, e.g. a vehicle's battery. Via external resistors R or R2, it is, for example, possible to pick up the output signal in the form of a voltage proportional to the current i.

Thus, for the electric energy supply and for picking up the measured signal one sole conductor pair will be sufficient which is connectible to the terminals Al, A2.

The two Hall generators 9 and 10 forming part of the integrated circuit IC are supplied by means of constant current sources 11 and 12.

Each Hall voltage UHI and UH2 is connected to the input terminals of a respective voltage amplifier 13 or 14. The output levels of said two amplifiers 13 and 14 are compared in a differential amplifier 15 which has a hysterisis characteristic and whose output signal, on its part, is supplied to a transistor switching stage 16.

In the illustrated example a transistor T will be sufficient for the generation of an output signal which can be evaluated. Said transistor T is operated as emitter follower. The output of the differential amplifier 15 is coupled to the base of said transistor T.

As soon as the difference of the voltages Uis, U14 at the outputs of the two amplifiers 13, 14 exceeds a predetermined threshold value the transistor stage 16 will be switched over. Of decisive importance for the operating condition of the transistor stage 16 and, hence, for the output signal is thus the sign of the voltage difference U13-U14 between the two Hall voltage amplifiers 13 and 14.

A voltage regulator 17, also forming part of the integrated circuit IC, generates a constant supply voltage Uc out of which the two constant current sources 11 and 12, on the one hand, and-as symbolised by the supply lines 18, 19, 20 shown by broken lines-the Hall voltage amplifiers 13 and 14 as well as the differential amplifier 15, on the other hand are supplied.

In the embodiment according to Fig. 3 a Graetz rectifier circuit is inserted between the input terminals Al and A2 and the connections Al' and A2'. Said Graetz rectifier circuit consists of four diodes D1 to D4 and, likewise, may form part of the integrated circuit IC. Thanks to such a simple measure it will become unimportant which input terminal Al or A2 the battery terminal or the ground, respectively, are connected to.

In Fig. 4, the curves U13 and U14 show the voltage curve at the output of the Hall voltage amplifiers 13 and 14 for a measuring device where the distance D between the two Hall generators 9 and 10 approximately corresponds to the width B of each tooth 7 of the transmitter 2 or rather of the toothed disk.

The rotational speed of the disk 2 is constant in the period under consideration.

Each time the teeth 7 and tooth gaps 8 pass the air gap the magnitude of the Hall voltage UHi and UH2 and, accordingly, the voltage level U13 and U14 with regard to reference potential URIC, vary in the manner illustrated in Fig. 4.

The switching position of the transistor T or rather of the switching stage 16 will determine the circuit flow i(t). The current level 1 will be defined by the (approximately) constant current flow via the Hall generators and the amplifiers of the integrated circuit IC whereas the difference between the current 12 and said current Ii will flow via the emitter resistor R3 as soon as the transistor T is switched on.

The hysterisis area, characterised by broken lines, indicates the fact that the transistor T or rather the transistor stage 16 will not switch over until the voltage difference between U13 and U14 exceeds a predetermined threshold value at time t1, t2, and t3.

If the tooth width B is smaller than the distance D between the two Hall generators 9 and 10 the signal cannot be processed correctly. On the contrary, in case of a larger tooth width B in relation to the distance D a trouble-free signal processing will be possible-as explained below with reference to Fig.

5.

Fig. 5 relates to an embodiment of the inventive measuring device where the distance D between the Hall generators in the direction of rotation is smaller than the width B of a tooth 7. In this case, temporarily a Hall voltage UH1 UH2 of the same magnitude will be generated in both Hall generators 9, 10, namely when the two Hall generators are simultaneously above a tooth 7 or a tooth gap 8, respectively. In this instance the voltage differences U13-U14 will outgrow the hysterisis area or exceed the predetermined threshold values, respectively, only when the inventive measuring device is passing the tooth profile.

The current flow i(t) caused in such an arrangement is likewise represented in Fig. 5.

Claims

1. A device for measuring a magnetic field and/or magnetic field changes in an air gap between a stationary transducer and a rotating transmitter which is mounted on a shaft, a wheel, or the like or which is a component of such a revolving body, said device comprising a Hall generator integrated on a semiconductor chip and fastened in the air gap on a face of the transducer facing the transmitter, characterised in that the semiconductor chip (3) comprises two similar Hall generators (9, 10) arranged one after the other in respect of the direction of rotation of the transmitter (2), electrical energy supply circuitry, measuring circuitry and evaluation circuitry (IC).

2. A device as claimed in claim 1, characterised in that the transmitter (2) is in the form of a toothed disk and in that the distance (D) between the two Hall generators (9, 10) approximately corresponds to one tooth width (B), that is the extent of a tooth (7) in the circumferential direction of the toothed disk.

3. A device as claimed in claim 1, characterised in that the transmitter (2) is in the form of a toothed disk and in that the distance (D) between the two Hall generators (9, 10) is smaller than one tooth width (B), that is the extent of a tooth (7) in the circumferential direction of the toothed disc.

4. A device as claimed in any one of claims 1 to 3, characterised in that the two Hall generators (9, 10) as well as the supply, measuring, and evaluation circuitry are accommodated in a single integrated circuit (IC).

5. A device as claimed in claim 4, characterised in that in the integrated circuit (IC) a constant voltage source (11, 12) and a voltage amplifier (13, 14) are provided for each Hall generator (9, 10), the voltage amplifiers (13, 14) each being feedable with the output signal of the respective Hall generator (9, 10), namely with the Hall voltage (us1, Us2); and in that the integrated circuit further has a differential amplifier (15) for comparing the output voltages of the two Hall voltage amplifiers (13, 14), a transistor stage (16) whose output signal represents the measured result detected by means of the two Hall generators (9, 10), and a voltage regulator (17) for the stabilisation of the supply voltage for the amplifier stages (13-15).

6. A device as claimed in claim 5, characterised in that the differential amplifier (15) has a hysterisis characteristic so that for the switching-over of the output signal of this amplifier it is required that a predetermined threshold value of the input voltage difference (U13-U14) be exceeded.

7. A device as claimed in claim 5 or in claim 6, characterised in that the transistor stage (16) acted upon by the differential amplifier (15) is a switching stage whose position represents the measured result.

8. A device as claimed in claim 7, characterised in that the switching stage (16) is in the form of a transistor (T) operated as an emitter follower whose collector-emitter path connects connection lines (awl', A2') of the measuring device.

9. A device as claimed in any one of claims 1 to 8, characterised in that it is connectible via a double line (awl', A2') through which both electrical energy supply and the output of signals are effected.

10. A device as claimed in claim 9, characterised in that the integrated circuit (IC) includes a Graetz rectifier circuit (D1-D4) via which it is connectible.

11. A device for measuring a magnetic field and/or magneticc field charges in an air gap substantially as herein described with reference to Figs. 1 to 4 or Fig. 5 of the accompanying drawings.