GB2125969A - Rotary Wiegand effect pulse generator - Google Patents

Abstract

A rotary pulse generator for use in ignition or fuel injection control of an i.c. engine, has a driven hollow rotor 2 on the internal surface of which are disposed a closely spaced series 9 of equidistant Wiegand wires 10 and also reference indicia (such as gaps in said series 9 or an axially separate series of Wiegand wires), which are scanned by a stationary magnetic reading head 4 within the rotor and in which Wiegand pulses are induced. <IMAGE>

Description

SPECIFICATION Rotary pulser The invention relates to a rotary pulser suitable for use in the ignition system of an internal combustion engine.

A rotary pulser is known in the form of an ignition transmitter for a four-stroke i.c. engine from the prior publication "A Wiegand Effect Crankshaft Position Sensor", SAE Technical Paper Series, Feb., 1980, by J. David Marks and Michael J. Sinko. In this known device the teeth of a gear wheel rim secured to the crankshaft are scanned by a Wiegand reading head comprising a Wiegand wire carrying a sensor winding and two permanent magnets in the field of which the Wiegand wire lies. The two permanent magnets are partly magnetically short-circuited by the teeth of the gear moving past them, whereby a magnetic field of alternating polarity is produced at the Wiegand wire which field creates Wiegand pulses in the sensor winding.

This ignition transmitter has the disadvantage though that since it is built into the crankcase, it is not convenient for installation in existing motor vehicles, and further that, in order to obtain satisfactory angular resolution of the ignition transmitter, a relatively large diameter rotor is required.

The abovementioned prior publication also discloses ignition transmitters employing the Wiegand effect which are more suitable for use in, conversion work (conversion of existing engines with conventional ignition systems) and possess the same reading head but which due to the small rotor diameter used are suitable only for ignition pulse production without an accurate determination of the top-dead-centre and without determination of the rotational speed of the engine.

Wiegand wires as used in the present invention are homogeneous ferromagnetic wires (e.g. of an iron-nickel alloy, preferably 48% iron and 52% nickel, or of an iron and cobalt alloy, or of an iron, cobalt and nickel alloy, or of a cobalt, iron and vanadium alloy, preferably 52% cobalt, 38% iron and 10% vanadium), which, as a result of special mechanical and thermal treatment, possess a soft magnetic core and a hard magnetic shell, i.e. the shell possesses a higher coercive force than the core. Wiegand wires normally have a length of 10 mm-50 mm, preferably 20 mm-30 mm.If a Wiegand wire, in which the magnetisation direction of the soft magnetic core is the same as that of the hard shell, is introduced into an external magnetic field the direction of which corresponds to that of the axis of the wire but is disposed opposite to the magnetisation direction of the Wiegand wire, on exceeding a field strength of appx. 1 6A/cm, the magnetisation direction of the soft core of the Wiegand wire is reverse the resulting state is conveniently referred to as non-parallel magnetisation. This reversal is also referred to as resetting.On further directionreversal of the outer magnetic field, on exceeding a critical field strength of the external magnetic field (which is referred to as ignition field strength) the magnetisation direction of the core is again reversed whereby the core and shell are once again magnetised in the same direction this state is conveniently referred to as parallel magnetisation. This reversal of the direction of magnetisation occurs very quickly and proceeds with a correspondingly sharp change in magnetisation flow per unit of time (Wiegand effect). This change in magnetic flow can induce in an induction winding (referred to as a sensor winding) a short, very high voltage pulse (according to the number of turns and load resistance of the induction coil, up to appx. 1 2 volts) known as a Wiegand pulse.

Also, when the core is reset, a pulse is triggered in the sensor winding, in this case however of a much lower amplitude and with reverse sign to that in the case of the reversal from anti-parallel to parallel magnetisation direction. If the Wiegand wire lies in an external magnetic field whose direction reverses from time to time and which is so strong that it can reverse the magnetisation firstly of the core and then also of the shell and in each case bring these to magnetic saturation, as a result of the reversal of magnetisation direction of the soft magnetic core Wiegand pulses are produced alternately of positive and negative polarity and this is referred to as symmetrical excitation of the Wiegand wire.

For this purpose field strengths of approximately -(80-120A/cm) to +(80--120A/cm) are required. Reverse magnetisation of the shell also occurs at high speed and also produces a pulse in the sensor winding but this pulse is much smaller than that produced by magnetisation direction reversal of the core.

If however the external magnetic field chosen is one which is capable of reversing the magnetisation direction of only the soft core and not the hard shell, the high amplitude Wiegand pulses maintain constant polarity which is termed unsymmetrical excitation of the Wiegand wire.

For this purpose a field strength is required in one direction of at least 1 6A/cm (for resetting the Wiegand wire? and in the opposite direction a field strength of approximately 80-1 20A/cm.

It is characteristic of the Wiegand effect that the pulses produced thereby are largely independent in amplitude and width of the speed of alteration of the outer magnetic field and show a high signal-to-noise ratio.

Bistable magnetic elements of different construction are also suited to the invention provided that these have two zones of differing 'hardness' (coercive force) which are magnetically coupled together and which can be employed in a manner similar to Wiegand wires for producing pulses by induced rapidly occurring reversal of the soft magnetic zone. Thus, in DE-PS 2514131, for example, a bistable magnetic switch core is described, in the form of a wire comprising a hard magnetic core (e.g. of nickel-cobalt), an electrically conductive intermediate layer (for example of copper) deposited thereon, and a soft magnetic layer (e.g. of nickel-iron) deposited thereon.Another variant employs in addition a core of a magnetically non-conductive metal inner conductor (e.g. of beryllium-copper) whereon are successively deposited the hard magnetic layer, the intermediate layer, and then the soft magnetic layer. This known bistable magnetic switch core does however produce weaker switch pulses than does a Wiegand wire.

It is an object of the present invention to provide a rotary pulser of simple, robust construction and high angular resolution, which is also suitable for use in controlling internal combustion engines, in particular as an ignition transmitter for adapting to four-stroke i.c.

engines.

The present invention provides a rotary pulser suitable for use with a four-stroke internal combustion engine, said pulser having a driven rotor provided with a series of Wiegand wires angularly spaced at predetermined intervals, and a stationary scanning device for magnetically scanning said Wiegand wires in a contactless manner, said scanning device comprising magnet means formed and arranged relative to said rotor so that at each revolution of said rotor, each Wiegand wire is conveyed through a spatially alternating magnetic field generated by said magnet means, said magnetic field being alternately in one direction until magnetic saturation is reached with the hard magnetic and soft magnetic zones of the Wiegand wire being magnetised, in the same direction and magnetically reset in the other direction with the hard magnetic and the soft magnetic zones of the Wiegand wire being magnetised in opposite directions, and a sensor winding for receiving Wiegand pulses generated by the relative movement between the rotor and scanning device.

Although the rotor pulser of the invention is particularly suitable for the control of i.c. engines, it is also suitable for the control of machine tools, packaging machines and other apparatus in which information concerning the rotary speed of a rotating shaft and its instantaneous angular position are required for the proper operation of various parts thereof.

Since the rotor need carry only the Wiegand wires, which in the normal case are themselves only approximately 0.2 mm thick and does not carry the magnets for the Wiegand wires or ferromagnetic forward conductance elements (shields) for influencing stationary magnets, or the sensor winding(s) the rotor may be provided with extremely closely spaced indices via these Wiegand wires. The minimum spacing between these Wiegand wires is defined by one half-width of the Wiegand pulses (normally 20 ,us) in conjunction with the maximum rotary speed of the rotor, and also by the magnetic mutual interaction of adjacent Wiegand wires when these are too close.In any case, the serial arrangement of Wiegand wires on the rotor can be arranged to be so close that, even with a rotor such as is accommodated in a conventional distributor casing, the resolution of the azimuth angle position of the rotor, and consequently also of the position of the crankshaft (and hence the position of the pistons of an i.c. engine) is so high that, from the rotor position and motion, the injection timings for a diesei engine or the ignition timings for a petrol engine taking into account the rotary speed-dependent degree of ignition advance or retardation, can be defined, without the need for additional aids such as a centrifugal governor or vacuum chamber, simply by means of an electronic ignition computer of known type.Since the ignition pulser can be housed in a distributor casing of conventional size, it is convenient for the conversion of motor vehicles with conventional ignition systems. The ignition computer evaluates the sequence of Wiegand pulses conveyed to it in an arrangement whereby, starting from a reference signal which denotes a given piston position and which may be provided by a gap in an otherwise equidistant series of Wiegand wires, it continues to count a calculated number of Wiegand pulses before triggering an ignition pulse, this number of Wiegand pulses being determined in relation to the sequence frequency of the Wiegand pulses at a given moment which frequency is proportional to the rotary speed of the rotor and consequently to that of the engine.

The more accurately the computer knows the rotary speed of the engine, the more exactly it can determine the required degree of pre- or postignition, and the more Wiegand wires there are provided at the periphery of the rotor, the more accurately can the rotary speed of the engine be determined.

Basically, the rotor may be in the form of a disc on which the Wiegand wires are located in radial fashion. On a cylindrical or bell-shaped rotor of equal diameter however, more Wiegand wires may be mounted in axially parallel disposition, which is a preferred arrangement, especially in the case where the Wiegand wires are arranged on the inside of the hollow-cylindrical or bellshaped rotor since in this case the scanner device can be located radially inwardly of the rotor. Thus, for a given size of distributor casing, the rotor may have a much greater diameter than in the case where the Wiegand wires are arranged on the outside since this would require the scanning device to be located on the outside as is customary in the conventional devices. A further advantage of such an arrangement, especialiy in the case of a bell-shaped rotor, is that the Wiegand wires and scanner device are protected from high voltage flash-over in the distributor casing.

As has already been stated, the ignition computer for a four-stroke i.c. engine requires at least one reference signal which gives the piston position and from which the next ignition timing is determined. Such a reference signal can be produced by a gap in an otherwise equidistant series of Wiegand wires. The ignition computer detects the absence of a Wiegand pulse in a series of Wiegand pulses and evaluates it accordingly. From this one reference signal all the ignition timings can be determined for a complete cycle of operation. Greater reliability and accuracy may be obtained, though, where each cylinder is allocated a separate reference signal e.g. via a separate gap in the series of closely spaced Wiegand wires.

Furthermore, this enables detection of the failure of any of the Wiegand wires which failure might misleadingly provide a "reference signal" at the wrong place because, where each cylinder has a separate "reference signal" gap, the position of these gaps relative to each other is known to correspond to predetermined numbers of Wiegand wires therebetween. If a Wiegand wire fails prematurely, the computer can recognise this as an accidental omission and compensate for this by calculation. Thus, the provision of a separate gap for each cylinder increases the degree of redundancy in the ignition pulser.

Instead of gaps in an otherwise equidistant series of Wiegand wires, a second series of Wiegand wires may be provided, arranged so as to be axially offset from the first series. This second series preferably contains for each cylinder of the i.c. engine exactly one Wiegand wire which represents a given piston position for the piston in this cylinder.

The evaluation of pulses of the Wiegand wires in this second series occurs in the same manner as that of the separate alternative gaps in the close-set series of Wiegand wires which is preferably an integral multiple of the number of cylinders.

Where two such series of Wiegand wires are provided, the type of structure of scanning device selected is preferably such that Wiegand pulses of different polarity are emitted from the Wiegand wires of the two series so that these pulses may be easily distinguished from one another.

In a very simple rotor construction, preferably made of aluminium or other such nonferromagnetic material, the rotor carries a flexible carrier foil, preferably of a thermoplastic plastics material, in which the Wiegand wires are embedded. The rotor is preferably provided with a groove in which this carrier strip can be inserted and fixed. The construction of a suitable scanning device will be familiar to those skilled in the art.

Further preferred features and advantages of the present invention will appear from the following detailed description given by way of example of two preferred embodiments with reference to the accompanying drawings in which: Fig. 1 is a vertial diametrical sectional elevation of a first ignition pulser of the invention: Fig. 2 is a panoramic vertical elevation of the carrier showing the series of Wiegand wires of the ignition pulser of Fig. 1; Figs. 3 and 4 show schematically two suitable reading heads for the ignition pulser of Fig. 1; and Figs. 5 to 8 are corresponding views of a second ignition pulser with two rows of Wiegand wires.

In the various figures like reference numerals are used to indicate like parts.

The ignition pulser shown in Figs. 1 to 4 is housed in a distributor housing 1 into which the driven distributor shaft 3 of a four-stroke engine extends in conventional manner from below. An aluminium bell-shaped rotor 2 with a rotor shaft 7, which for purposes of adjustment extends through the distributor cover 6, is mounted on the free end of said distributor shaft 3 and secured thereto. On its inner, essentially cylindrical, peripheral wall surface the rotor 2 is provided with a flat annular groove 1 2 in which a foil substrate 13 is inserted and secured. A series 9 of Wiegand wires 10 is embedded in said foil substrate parallel to the rotor axis 14.On the underside of the cover 6 a reading head 4 and a mounting 8 with a bar magnet 8a of cobalt/samarium magnetised parallel to the rotor axis 14 are arranged diametrically opposite each other and extend into the interior of the rotor 2 at only a small radial spacing from the carrier foil 13.

For use with a four cylinder engine, the series 9 of Wiegand wires 10 has four equidistant gaps 11 between which the Wiegand wires are arranged at closely equidistant intervals-see Fig. 2 in which it will be appreciated that for convenience not all the wires in each sequence between the gaps 11 have been shown.

The reading head 4 comprises a generally U- or C-shaped iron core 1 5 which has two outer layers separated by an intermediate non-ferromagnetic layer 1 6 disposed radially and parallel to the rotor axis 14. Above and below the core 1 5 a cobalt/samarium magnet 17, 18 is mounted whose directions of magnetisation are tangential to the rotor 2 and forms with the rotor axis 14 an angle of approximately 70 . The magnets 17 and 1 8 form between them a magnetic field which essentially covers one layer 1 5a of the iron core 1 5 in one direction and the other zone 1 Sb of the iron core 1 5 in the opposite direction, whilst possessing in the region of the intermediate layer 1 6 a steep gradient of field strength with a zero field strength transition.

The direction of rotation of the rotor 2 is arranged so that the Wiegand wires approach the reading head 4 from the side at which the field lines span the greater distance between the magnets 17 and 18. The direction of movement of the Wiegand wires 10 is indicated in Fig. 4 by the arrow 1 9 which also corresponds to the direction of viewing of the elevation of Fig. 3.

Each Wiegand wire 10 has traverses firstly in front of the magnet 8a on the mounting 8 and is magnetically saturated. It then comes in the vicinity of the core region 1 sub, under the influence of a magnetic field disposed opposite to that of the saturation magnet 8a and is thereby returned to its anti-parallel magnetisation condition, whereupon it passes in the vicinity of the intermediate layer 16 through the zero magnetic field strength transition and immediately thereafter reverses its direction of magnetisation in the soft magnetic core of the Wiegand wire 10 whereby, in the sensor winding around the C-shaped iron core 15, a Wiegand pulse is produced which can be further processed in an electronic ignition computer. Thus, the ignition pulser operates with asymmetrical excitation of the Wiegand wires.

The ignition computer recognises the gaps 11 by the absence of a Wiegand pulse thereat.

Starting from each such reference position the ignition computer calculates the number of Wiegand pulses still awaited prior to the optimum release point for an ignition pulse. This number of Wiegand pulses is determined with the aid of the rotary speed of the rotor which the ignition computer can determine from the particular sequence frequency of the Wiegand pulses.

The embodiment of Figs. 5 to 8 differs from that of Figs. 1 to 4 in that the rotor has two series 9 and 29 of Wiegand wires 10, the first one 9 of which comprises a series of very closely spaced Wiegand wires 10 with a gap 11 for each cylinder, whereas the second series 29, which is axially spaced from the first series 9 in direction of the rotor axis 14, has a Wiegand wire 10 opposite each one of the gaps 11 in the first series 9.

The reading head 4 is of similar construction to that shown in Figs. 3 and 4 but has an E-shaped core 1 5 instead of a C-shaped one. The Wiegand wires 10 of the first series 9 move past the upper and middle E-limbs 15', 15', whilst the Wiegand wires 10 of the other series 29 pass the middle and lower E-limbs 1 5" and 15"'.

The sensor winding 20 is wound around the central E-limb 15". Therefore the magnetic flux which permeates the sensor winding 20 upon the reversal of a Wiegand wire 10 from the upper, first series 9 (Fig. 7a) is opposite to the magnetic flux produced by a reversal of a Wiegand wire 10 from the lower, second series 29 (Fig. 7b), so that the Wiegand pulses in the sensor winding 20 vary in polarity and can be distinguished from each other.

The Wiegand pulses originating from the lower, second series 29 are the reference signals from which the ignition computer determines in each case the next ignition timing, whilst the upper, first series 9 of Wiegand wires serves only to determine the rotary speed of the rotor 2, i.e.

that of the four-stroke engine.

Rotary pu Isers corresponding to the ignition pulsers illustrated can be employed directly for purposes other than the control of the ignition systems of four-stroke engines. One such possibility is in the control of the timing of fuel injection in i.c. engines, in particular diesel engines. The rotary pulser may be of similar construction to that described above for use with four-stroke engines. In place of the ignition pulser, however, a control circuit would be employed which would be adapted to this particular use e.g.

a suitable computer circuit.

It is also possible to adapt the present invention directly for use with other machines in which operations require to be accurately controlled in accordance with the rotary speed and momentary angular disposition of a rotating shaft. The necessary adaptation may involve variation in the rotor diameter, the number of Wiegand wires used, the particular kind of connection with the shaft, and the final control circuit which receives and processes the Wiegand pulses. Such adaptation does not however alter the basic mode of operation of the rotary pulser.

Claims (10)

Claims

1. A rotary pulser suitable for use with a fourstroke internal combustion engine, said pulser having a driven rotor provided with a series of Wiegand wires angularly spaced at predetermined intervals and a stationary scanning device for magnetically scanning said Wiegand wires in a contactless manner, said scanning device comprising magnet means formed and arranged relative to said rotor so that at each revolution of said rotor, each Wiegand wire is conveyed through a spatially alternating magnetic field generated by said magnet means, said magnetic field being alternately in one direction until magnetic saturation is reached with the hard magnetic and soft magnetic zones of the Wiegand wire being magnetised in the same direction and magnetically reset in the other direction with the hard magnetic and the soft magnetic zones of the Wiegand wire being magnetised in opposite directions, and a sensor winding for receiving Wiegand pulses generated by the relative movement between the rotor and scanning device.

2. A rotary pulser according to claim 1, wherein the Wiegand wires are located on the inside of a hollow cylindrical or bell-shaped rotor and the scanner device is located within the rotor.

3. A rotary pulser according to claim 1 or claim 2 wherein the rotor contains a number of gaps in a closely spaced series of otherwise equidistant Wiegand wires for determining the rotary speed of the rotor.

4. A rotary pulser according to claim 3, for use as an ignition pulser or for controlling the fuel injection timing in an internal combustion engine, wherein the number of gaps in the otherwise equidistant series of Wiegand wires coincides with the number of cylinders in the engine, and wherein the positions of the gaps in the series of Wiegand wires correspond to predetermined piston positions.

5. A rotary pulser according to any one of claims 1 to 4, wherein the rotor contains one closely spaced series of equidistant Wiegand wires for the purpose of determining the rotary speed of the rotor and a second series of Wiegand wires axially offset from the first series of Wiegand wires and in predetermined positions.

6. A rotary pulser according to claim 5, wherein the azimuth position of the Wiegand wires in the second series coincides with the azimuth position of the gaps in the first series of the otherwise equidistant Wiegand wires.

7. A rotary pulser according to claim 5 or claim 6 for use as an ignition pulser or for controlling fuel injection timing in an internal combustion engine wherein the number of Wiegand wires in the second series corresponds to the number of cylinders in the i.c. engine, and wherein the positions of the Wiegand wires in this second series corresponds to predetermined piston positions.

8. A rotary pulser according to any one of claims 5 to 7 wherein the scanning means is formed and arranged so that the two series of Wiegand wires produce Wiegand pulses of opposite polarity.

9. A rotary pulser according to any one of the preceding claims, wherein the Wiegand wires are disposed on the rotor parallel to the rotor axis at a predetermined radial separation from the rotor axis and said Wiegand wires are sealed in a flexible carrier foil and are secured by means of this carrier foil to the periphery of said rotor.

10. A rotary pulser according to claim 1 substantially as described hereinbefore with particular reference to Figs. 1 to 4 or Figs. 5 to 8 of the accompanying drawings.