EP0044744A2

EP0044744A2 - Method of and device for providing an electrical signal in an ignition system

Info

Publication number: EP0044744A2
Application number: EP81303345A
Authority: EP
Inventors: Bruce Stanley Gunton
Original assignee: EDA Sparkrite Ltd
Current assignee: EDA Sparkrite Ltd
Priority date: 1980-07-22
Filing date: 1981-07-22
Publication date: 1982-01-27
Also published as: EP0044744A3

Abstract

The firing of a spark plug of an internal combustion engine is triggered by a Hall effect device (11) mounted adjacent to an annular magnet (10) which is rotated by the engine. On a peripheral surface (15) of the magnet, are adjacent magnetic pole faces of opposite polarity.

Description

This invention relates to a method of providing an electrical signal in an ignition system. A second aspect of the invention relates to a device for use in the method and the invention also relates to a spark ignition internal combustion engine which includes the device.
A spark ignition internal combustion engine requires a triggering device for providing a signal at predetermined stages in the operating cycle of the engine. Generally, the signal is fed to a system of primary and secondary windings which act as an energy store and transformer. From there,energy is discharged to a spark plug or, via a distributor, to one of a plurality of spark plugs. A common form of ignition triggering device comprises a pair of pivoted contacts and a cam for opening the contacts. The cam is rotated by the engine.
An advance over this form of triggering device comprises an electromagnetic transducer adapted to respond to the movement of magnetic material forming part of a rotor which is mounted for rotation in association with the cam. However, known electromagnetic transducers fail to provide a sharp signal in response to an instantaneous position of the rotor. Transducers are not able to respond precisely to a small change in a magnetic field and there occur variations in the angular positions of the rotor at which a spark is produced at a spark plug of the engine. Magnetic "noise" can increase the problem and even cause the engine to mis-fire.
In a method according to a first aspect of the invention of providing an electrical signal dependent upon the relative rotational position of a body and a sensor, there being associated with the body a magnetic field, when one of the body and the sensor rotates relative to the other, the direction of a component of the magnetic field at the sensor undergoes reversal and the sensor responds to such reversal by providing the signal.
The sensor's response depends precisely on the angular position of the rotor. The sensor is not sensitive to moderate variations in the distance between the sensor and magnetic poles of the body or to magnetic noise.
According to a second aspect of the invention there is provided a device comprising first and second elements, the first element being mounted for rotation relative to the second, wherein one of the elements is a body with which there is associated a magnetic field and the other element is a sensor, the sensor being arranged in proximity to the body and adapted to respond to a reversal in direction of the magnetic field of the body at the sensor arising from said rotation of the first element by providing an output signal.
There is also provided according to the invention a spark ignition internal combustion engine having an ignition system which includes a spark plug, a control unit for controlling the discharge of electrical energy at the spark plug, a device according to the second aspect of the invention and means for rotating the first element at a speed dependent on the speed of operation of the engine.
Preferably the sensor is a Hall effect device, comprising a Hall effect element, a multi-vibrator and an amplifier element, which is connected with the control unit by a single lead along which there passes a signal which triggers the discharge of energy at the spark plug.
Preferably the multi-vibrator is a Schmitt trigger element.
An example of a device embodying the invention, which constitutes a part of the ignition system of an engine according to the third aspect and provides a signal in accordance with the first aspect of the invention will now be described, with reference to the accompanying drawings wherein:-

FIGURE 1 shows a spark ignition internal combustion engine having an ignition system;
FIGURE 2 shows certain components of the ignition system; and
FIGURE 3 represents diagrammatically the circuit of the ignition system, and
FIGURE 4 shows a circuit diagram of a part of the ignition system.

The four stroke internal combustion engine shown in Figure 1 has an ignition system with four spark plugs 23, a control unit 20 and distributing means in a housing 22 for distributing an electrical pulse to the appropriate spark plug in the firing sequence of the engine. The distributing means is of known construction and includes a rotor arm (not shown) mounted at one end of a shaft 12. The engine includes means for rotating the shaft at a speed which is directly related to the speed of the engine.
There is associated with the distributing means a device for providing a signal to the control unit 20 at predetermined stages in the operating cycle of the engine. The device includes a sensor 11 and a body in the form of a ring 10 with which there is associated a magnetic field and which is mounted on the shaft 12. The sensor is a Hall effect device and is connected with the control unit 20 by a single lead 19.The sensor 11 is also earthed.
The magnetic ring 10 conveniently includes a metal annulus 14 which is symmetrical about a plane perpendicular to the axis of rotation of the ring. The outer surface 15 of the ring is composed of a magnetisable material wherein magnetic poles are induced upon the outer surface in a known manner. In the example illustrated, the outer surface of the ring 10 is presented by the metal annulus. Alternatively, the magnetic material at the outer surface of the ring may be composed of ferrite particles embedded in a plastics matrix. The outer surface is of smoothly extending cylindrical shape and is coaxial with the shaft 12.
The magnetic poles are induced with pole faces forming part of the outer surface of the magnetic ring and with at least one North pole face and at least one South pole face adjacent to each other. By this we mean that there is no unmagnetized region between them. The number of pairs of pole faces is selected according to the number of spark plugs.
The Hall effect device 11 is arranged in proximity to the magnetic ring 10. By "in proximity" we mean that the Hall effect device is spaced perpendicularly from a closest point on the outer surface 15 of the magnetic ring by a distance which is less than the radius of the ring. Preferably the device 11 is spaced from the ring 10 just sufficiently to avoid contact between them.
The Hall effect device 11, contains a Hall effect element 17, as shown in Figure 3, in which a potential difference is induced in response to the moving magnetic field of the rotating ring 10. The direction of the magnetic field across the element, that is to say the direction of the radial component of a magnetic field associated with the ring, determines the polarity of the potential difference in the Hall effect element. As the ring rotates, this component will reverse when the element is equidistant from a North pole face and an adjacent South pole face of the ring 10. Because there is no unmagnetised region between the pole faces, the reversal of voltage in the Hall effect element is abrupt and occurs reliably when the ring 10 occupies a predetermined angular position.
The Hall effect device 11 also comprises a Schmitt trigger multi-vibrator 18 and an amplifier element 24 in series with the Hall effect element 17. The Schmitt trigger has two stable states which are determined by the polarity of the input voltage applied to the Schmitt trigger, i.e. the voltage induced in the Hall effect element. The output from the Schmitt trigger is amplified by the amplifier element 24 to provide an output of approximately 35 mA along the single lead 19 when a positive voltage is induced in the Hall effect element and one of approximately 5 mA when a negative voltage is induced. The single lead also provides a supply voltage to the Schmitt trigger. The Hall effect element, Schmitt trigger and amplifier element form an integrated circuit. The resistor 25 is a current limiting resistor.
In each cycle of the engine, there may be provided a number of pulses which is dependent upon the number of pairs of pole faces upon the magnetic ring 10, at a frequency dependent upon the rate of rotation of the ring.
The control unit 20 includes known means, for example a capacitor and an ignition coil, for storing energy and known means for discharging the stored energy via a lead 26 and the distributing means in the housing 22 to the plugs 23 in accordance with the pulses fed to the control unit by the Hall effect device.
The control unit 20 includes a switching means TR4 which operates in accordance with the changes in current flow in the single lead 19. Attendant changes in the voltage in the single lead are substantially eliminated by the zener diode D1. The transistor TR1 provides a compensating means which ensures that the voltage drop between the positive terminal of a battery of the vehicle and the single lead is substantially constant. The circuit of the control unit, other than the ignition coil,is shown in Figure 4.
The magnetic ring 10 may be fitted as a modification to a cam on the shaft 12 of an internal combustion engine. Fixed and movable electrical switch contacts are removed and the magnetic ring is pushed onto the cam. The Hall effect device 11 is then fitted in proximity to the magnetic ring. Alternatively the magnetic ring may be fitted directly onto a shaft during manufacture. The Hall effect device is largely enclosed by a plastics cover when in use.
Whilst we prefer to form the ring 10 and subsequently induce magnetic poles on the ring, it is within the scope of the invention for the ring to comprise an assembly of several parts, each part being magnetised before the parts are assembled together to form the ring.

Claims

1. A method of providing an electrical signal dependent upon the relative rotational position of a body and a sensor,characterised in that there is asssociated with the body a magnetic field, when one of the body (10) and sensor (11) rotates relative to the other, the direction of a component of the magnetic field at the sensor undergoes reversal and the sensor responds to such reversal by providing the signal.

2. A method according to Claim 1 wherein, during manufacture, the body (10) is formed into an annular ring and then magnetised, magnetic poles being induced upon the surface of said annular ring.

3. A method according to any preceding claim wherein said signal comprises a change in a flow of current in the sensor (11).

4. A device comprising first and second elements, the first element being mounted for rotation relative to the second element,charaterised in that one of the elements is a body (10) with which there is associated a magnetic field and the other element is a sensor (11), the sensor being arranged in proximity to the body and adapted to respond to a reversal in direction of the magnetic field of the body at the sensor arising from said rotation of the first element by providing an output signal.

5. A device according to Claim 4 wherein said body (10) comprises at least one North pole face and at least one South pole face at or adjacent to the periphery of the body.

6. A device according to Claim 5 wherein there is no significant gap between the adjacent North and South pole faces.

7. A device according to any of Claims 4 to 6 wherein the sensor consists of a Hall effect device.

8. A spark ignition internal combustion engine having an ignition system which includes a spark plug (23), a control unit (20)for controlling the discharge of electrical energy at the spark plug, a device according to any one of Claims 4 to 7 and means for rotating the first element (10) at a speed dependent on the speed of operation of the engine.

9. An engine according to Claim 8 wherein the sensor is a Hall effect device, comprising a multi-vibrator (18) and a Hall effect element (17), wherein the multi-vibrator is connected with a control unit (20) by a single lead (19) along which there passes a signal which triggers the discharge of energy at the spark plug.

10. Any novel feature or novel combination of features disclosed herein or in the accompanying drawing.