GB2041659A

GB2041659A - Sensing position of armature in an electromagnetic device

Info

Publication number: GB2041659A
Application number: GB7940110A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1979-02-09
Filing date: 1979-11-20
Publication date: 1980-09-10

Abstract

An electromagnetic linear actuator including an armature, a core member and an energising winding (31) which, when supplied with electric current from an energising circuit (38), creates magnetic flux to move the armature and core member relative to each other, has associated with it an electrical circuit (39) to provide a signal indicative of the inductance of the winding (31) and hence the relative positions of the armature and core member. The circuit (39) may include a frequency determining section to determine the frequency of an oscillator which includes the winding (31) as one of the following determining components: change in the inductance will result in a change in frequency. Other methods are disclosed for sensing changes in the inductance. A protection circuit (40) may be included to protect the circuit (39) from high voltage surges. The actuator may be used in a fuel pump/injector for an internal combustion engine. <IMAGE>

Description

SPECIFICATION Electromagnetic devices This invention relates to electromagnetic devices of the kind comprising a magnetisable armature, a magnetisable yoke structure and a winding associated with the yoke structure and which when supplied in use, with electric current from an energising circuit magnetises the yoke structure, thereby resulting in movement of the armature to cause a reduction in the reluctance of the flux path or paths defined by the yoke structure and the armature.

It is frequently necessary with such a device to provide an indication of the amount of movement of the armature and such an indication can be provided by a transducer responsive to the movement of the armature. It is not always easy to accommodate a transducer within the structure of the device and even if such accommodation is possible electrical connections must be provided on the device for the transducer.

The object of the present invention is to provide for use with a device of the kind specified, means whereby an indication of the movement of the armature can be obtained without the need for a separate transducer.

According to the invention for use with a device of the kind specified an electrical circuit for connection in use to said winding, said circuit providing an output signal depending upon the inductanceofthe winding.

One example of an electromagnetic device to which the invention may be applied will now be described with reference to the accompanying drawings in which: Figure 1 shows the electromagnetic device in assembly with a fuel pump/injector for an internal combustion engine, Figures 2 and 3 illustrate ways of connecting the electrical circuit to the winding and Figure 4 illustrates an alternative form of connection.

With reference to Figure 1 of the drawings a pump/injector 10 comprises a hollow cylindrical stepped body 11 the narrower end of which mounts an injection valve assembly 12. This comprises a nozzle body 13 which is stepped at one end for location within the body lithe bodies 11 and 13 being secured by electron beam welding. A bore is formed in the body 13 and located and slidable within the bore is a valve member 14 having a head 15 engageable with a seating defined at the outer end of the body 13. The valve member 14 is fluted or otherwise recessed to enable fuel when the head 15 is lifted from the seating, to flow through the bore into the associated combustion chamber.The valve member extends from the end of the bore remote kom the seating and it carries an abutment 16 for cne end of a coiled compression spring 17 the other end of which engages the body 13. The head therefore is biased into engagement with the seating and the head is lifted from the seating by the pressure of fuel developed in a pumping chamber 18 within the narrower portion of the body 11.

The volume of the pumping chamber 18 is varied by means of a pumping plunger 19 which is slidable within a flanged sleeve 20 secured against a step defined in the internal surface of the narrower portion of the body 11. The plunger 19 is resiliently loaded in the outward direction i.e. in a direction to increase the volume of the pumping chamber 18, by means of a coiled compression spring 21 extending between the sleeve 20 and a head 22 defined on the plunger. The sleeve is retained in position by rolling the body 11.

The plunger 19 is provided with passages incorporating a non-return valve 23 and by way of this valve fuel can flow into the pumping chamber as the plunger is moved outwardly by the spring 21.

For effecting inward movement of the plunger 19 an elecaromagnetic device 24 is provided and this is housed within the wider portion of the body 11. The electromagnetic device comprises a hollow cylindrical armature 25 which is positioned adjacent the inner surface of the wider portion of the body 1 T and which is formed from magnetisable material. The end portion of the armature which is nearer to the narrower portion of the body 11 is mounted upon a member 26 which is slidably carried on a central support member 27. The member 26 also has a hollow slotted extension 28 which is positioned for engagement with the head 22 of the plunger. The support member 27 at its lower end also mounts a support 28A which locates the support member in the body 11.

The interior surface of the armature is provided with a two start helical thread which defines a pair of helical ribs 29. Moreover, the aforesaid central support member 27 forms a yoke and is also provided with a pair of helical ribs 30. The presented surfaces of the ribs 29 and 30 are inclined to the longitudinal axis of the pump/injector and are spaced from each other in the de-energised condition (as shown) of the electromagnetic device. The central support member carries in the two helical troughs defined between the ribs 30, an electrical winding 31 and conveniently the winding is formed by winding a length of wire along one trough from one end of the support member and returning from the other end of the support member along the other trough. The winding can have a number of turns as required.When the winding is energised the two ribs 30 will assume opposite magnetic polarity and flux paths will be set up which include the air gaps between the ribs 29, and 30. As a result, she armature will be moved by the magnetic forces in a direction to reduce the reluctance of the air gaps and in so doing will effect inward movement of the plunger 19 causing an increase in the pressure of the fuel in the pumping chamber. When the pressure rise is sufficient to lift the head 15 of the valve member from its seat, fuel is delivered to the associated combustion chamber until the ribs 29 and 30 engage with each other. When the winding is de-energised, the plunger and armature are returned to the position shown at a rate determined by the rate at which fuel can flow into the chamber 18.

The central support member 27 is carried by an end closure 32 which is retained relative to the body 11 by means of a retaining nut 33. The end closure has a fuel inlet 34 which communicates with the interior of the wider portion of the body through a passage 36. Also provided is an electrical terminal 35 which is connected to one end of the winding 31, the other end of the winding being connected to the end closure. The armature defines a tongue 37 located with an axial slot formed in the body 11, to prevent angular movement of the armature.

In order to control the quantity of fuel supplied through the nozzle assembly, the return motion of the pumping plunger under the action of the spring is carefully measured. The return motion of the plunger may be allowed to take place immediately prior to delivery of fuel to the engine or it may take place some time before the delivery of fuel in which case when the required amount of fuel has entered the pumping chamber, the plunger is held by partial energisation of the electromagnetic device.

As shown in Figures 2 and 3 the winding 31 is supplied with energising current by an energising circuit 38 and an electrical circuit 39 is provided which provides an output signal which depends upon the inductance of the winding 31. In order to provide protection for the components of the circuit 39 against high voltage surges which may occur when the winding is energised and de-energised, a protection circuit 40 is provided. This may take the form of a passive circuit responsive to the high voltages and operable to limit the voltage applied to the circuit 39 or as shown in Figure 3, it may have the form of an electronic switch shown as a pair of contacts 41, operable by synchronising pulses from the circuit 38, to disconnect the circuit 39 from the winding 31 when the high voltage pulses can be expected.

The circuit 39 of Figures 2 and 3 may include a frequency determining section which is utilised to determine the frequency of an oscillator which includes the winding 31 as one of the frequency determining components. As the inductance of the winding 31 changes so also will the frequency of oscillation of the oscillator.

ir another example the electronic circuit 39 may incorporate an AC source which acts to supply the winding 31 with a high frequency low level voltage.

The resulting alternating current in the winding can be sensed and as its amplitude will vary with the inductance of the winding 31 an indication can be obtained of the position of the armature.

In Figure 4 a low value non-inductive resistor 42 is connected in series with the winding 31 and the circuit 39 is responsive to the voltage developed across the resistor 42. Since there will be no voltage developed across the resistor when the winding 31 is de-energised it is necessary for the circuit 38 to provide low energy pulses to the winding 31 during th period when the plunger is partaking of its movement under the action of its spring. The pulses may be of low voltage and appreciable width or of a higher voltage but narrower. In either case the force znerated is insufficient to have any substantial influence on the rate of movement of the plunger.

The circuit 39 in this case may provide a measure of the rise or fall time of the current through the resistor and this time will depend upon the inductance of the winding which itself will vary with the position of the armature.

In each of the examples described above it will be necessary to check the calibration of the position indicating device even though once per cycle of operation the armature will assume by virtue of contact of the ribs 29 and 30 a predetermined position. It is envisaged that at regular intervais during the use of the pump/injector, the plunger is allowed to partake of its full movement under the action of its spring. Since the maximum movement of the plunger is determined mechanically and is fixed, the calibration of the circuit can then be checked.

Claims

1. An electromagnetic device comprising a mag netisable armature, a magnetisable yoke structure, a winding associated with the yoke structure and which when supplied in use with electric current from an energising circuit magnetises the yoke structure thereby resulting in movement of the armature to cause a reduction in the reluctance of the flux path or paths defined by the yoke structure and the armature and an electrical circuit for connection in use to said winding, said circuit providing an output signal depending upon the inductance of said winding.

2. An electromagnetic device according to claim 1 in which said electrical circuit includes an oscillator, the one of the frequency determining components of the oscillator being the winding and the circuit also including a frequency determining section which provides a signal representative of the frequency and hence the inductance of the winding.

3. An electromagnetic device according to claim 1 in which said circuit incorporates an AC source which acts to supply the winding with a high frequency low level voltage and means for sensing the alternating current in the winding.

4. An electromagnetic device according to claim 1 including a resistor in series with said winding and the energising circuit, said electrical circuit being responsive to the voltage developed across said resistor, said energising circuit being arranged to supply low energy pulses to the winding in the otherwise de-energised condition of the winding.

5. An electromagnetic device according to claim 2 or 3 including a protection circuit inter 7sed between the winding and said electrical circuit.

6. An electromagnetic device according to claim 5 in which the protection circuit comprises a passive network.

7. An electromagnetic device according to claim 5 in which the protection circuit comprises an electronic switch operable by pulses from the energising circuit to disconnect the electrical circuit from the winding when high voltage could exist at the ends of the winding.

8. An electromagnetic device comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.