EP0324262A1

EP0324262A1 - Electromagnetic actuator

Info

Publication number: EP0324262A1
Application number: EP88312165A
Authority: EP
Inventors: Christopher Peter Squires; Donald Allen Young
Original assignee: Magneti Marelli Electrical Ltd
Current assignee: Magneti Marelli Electrical Ltd
Priority date: 1988-01-13
Filing date: 1988-12-22
Publication date: 1989-07-19
Also published as: GB8800691D0

Abstract

An electromagnetic actuator for use in conjunction with an internal combustion engine starter motor, the actuator comprising an electromagnet winding (17), an armature (23) for connection to the pinion assembly of a starter motor in use, said armature (23) being movable by energization of said winding (17) and first and second spaced, fixed, electrical contacts (27, 28). A bridging contact (41) is movable against the action of a return spring (31) to bridge said fixed contacts (27, 28) in response to movement of said armature (23), and an electrically conductive, resilient, bridging element (46) is movable with said bridging contact (41). The element is so shaped that during the movement of the bridging contact (41) the element (46) engages said first and second fixed contacts (27, 28) before the bridging contact (41) and thereafter flexes during movement of the bridging contact (41) to permit the bridging contact (41) also to bridge the first and second fixed contacts (27, 28).

Description

This invention relates to electromagnetic actuators for use in conjunction with internal combustion engine starter motors, such actuators commonly being referred to in the art as "starter solenoids".
In a known form of elecrtromagnetic actuator energisation of the winding of the electromagnet of the actuator causes movement of an associated armature towards the pole of the electromagnet. The armature is coupled, through a lever mechanism, to the pinion assembly of the associated starter motor and thus energization of the actuator causes movement of the pinion assembly of the starter motor towards an operative position. Within the construction of the electromagnetic actuator there is provided an electrical switch of high current carrying capacity, the switch controlling current flow to the armature winding of the starter motor in use. The switch includes a pair of spaced fixed contacts, and a bridging contact moveable by the electromagnet armature, against the action of a light return spring, to bridge the fixed contacts and so complete an electrical circuit therebetween.
In actuators of the type set out above the bridging contact is relatively massive owing to the high electrical current which it is to carry, and the bridging contact is moved rapidly into engagement with the fixed contacts. A known problem is contact bounce. The bridging contact impacts against the fixed contacts, and inspite of being loaded towards the fixed contacts a bouncing action occurs in which the engagement of the bridging contact with one or both of the fixed contacts is made and broken a number of times in rapid succession. Contact bounce is accompanied by arcing which reduces the effective life of the bridging contact and the fixed contacts, and which can in some instances give rise to the bridging contact welding to the fixed contacts thereby resisting opening of the contacts which of course is necessary to effect de-energisation of the starter motor. It has previously been proposed to coat the fixed and bridging contacts with materials which minimise the risk of contact welding, but these prior proposals are unsatisfactory in that the coatings emit toxic products during arcing. It is an object of the present invention to provide an electromagnetic actuator for an internal combustion engine starter motor, wherein the problems of contact arcing are minimised.
In accordance with the present invention there is provided an electromagnetic actuator for use in conjunction with an internal combustion engine starter motor, the actuator comprising an electromagnet winding, an armature for connection to the pinion assembly of a starter motor in use, said armature being movable by energization of said winding, first and second spaced, fixed, electrical contacts, a bridging contact movable against the action of a return spring to bridge said fixed contacts in response to movement of said armature, and, an electrically conductive, resilient, bridging element movable with said bridging contact and so shaped that during the movement of the bridging contact the element engages said first and second fixed contacts before the bridging contact and thereafter flexes during movement of the bridging contact to permit the bridging contact also to bridge the first and second fixed contacts.
Preferably said bridging element is in the form of an arcuate strip which is anchored, adjacent its mid point, to the bridging contact so that by virtue of its arcuate nature the free ends of the strip project away from the bridging contact towards the first and second fixed contacts respectively.
Conveniently said bridging element is welded to said bridging contact.
Preferably said bridging contact is formed, in that face which is presented towards the fixed contacts, with a recess for receiving the bridging element as the bridging element flexes during movement of the bridging contact into engagement with said fixed contacts.
One example of the present invention is illustrated in the accompanying drawings wherein;

Figure 1 is a longitudinal sectional view of an electromagnetic actuator for use with an internal combustion engine starter motor, the actuator being shown in its rest position,
Figures 2 and 3 are views similar to Figure 1, but illustrating two stages in the engagement of the bridging contact with the fixed contacts,
Figure 4 is a plan view of the bridging contact seen in Figures 1 to 3,
Figure 5 is a sectional view on the line 5-5 in Figure 4,
Figure 6 is a plan view of a bridging element seen in Figures 1 to 3, and
Figure 7 is a side elevational view of the element of Figure 6.

Referring to the drawings, the actuator includes a hollow cylindrical metal housing 11 closed at one end by a moulded synthetic resin cap 12. At its end remote from the cap 12 the housing 11 is partially closed by an inwardly directed peripheral flange 13 and secured to the outer surface of the flange 13 is an angular bearing plate 14. The central aperture of the bearing plate 14 is extended to define a cylindrical boss 15 the internal diameter of which is equal to the internal diameter of the aperture in the flange 13. The housing 11 and bearing plate 14 are formed from ferromagnetic material, conveniently mild steel, and disposed within the housing 11 is an electromagnet winding assembly 16 comprising one or more electromagnetic windings 17 wound on a cylindrical synthetic resin spool 18. Extending within the central passage of the spool 18 is a cylindrical brass liner 19, the liner 19 extending beyond the end of the spool 18, and through the aperture in the flange 13, and the boss 15 of the bearing plate 14.
Anchored to the housing 11 at its end closed by the cap 12 is an annular, mild steel pole plate 21 carrying a hollow mild steel pole 22. The pole 22 extends from the plate 21 into the liner 19 and slidable within the liner 19 towards and away from the pole 22 is a mild steel armature 23. At its outermost end the armature 23 carries a coupling member 24 whereby in use the armature is coupled to the driving lever arrangement of the pinion assembly of a starter motor. The coupling member 24 projects radially outwardly beyond the periphery of the armature 23, and a helically wound spring 25 extends between the coupling member 24 and the bearing plate 14 to urge the armature 23 in a direction away from the pole 22.
A switch chamber 26 is defined within the end cap 12 between the inner surface of the cap 12 and the pole plate 21. The end cap 12 carrys first and second fixed electrical contacts 27, 28 each of which is defined by an integral head at one end of a screw threaded copper shank of substantial cross-section. The contacts 27, 28 are disposed on the inner face of the cap 12 diametrically opposite one another, and are presented towards the pole plate 21. The respective screw threaded shanks extend through the material of the cap 12 and project at the exterior thereof to define screw terminals 27ª, 28ª for the reception of electrical connectors. The contacts 27, 28 and their respective terminals are of course electrically insulated from one another by the material of the cap 12.
Between the terminals 27, 28 the inner face of the cap 12 is formed with an axially extending recess 29 within which is housed the return spring 31 of a bridging contact arrangement 32.
The bridging contact arrangement 32 includes a main supporting spindle 33 disposed with its longitudinal axis coextensive with the longitudinal axis of the actuator, the spindle being carried for sliding movement relative to the remainder of the actuator in the axial through-bore of the pole 22. Partway along its length the spindle 33 is formed with a step against which abuts a washer 34, the washer 34 constituting an end abutment for a helical spring 35 the opposite end of which abuts an electrically insulating carrier 36 slidable on the spindle 33. The carrier 36 includes a region 36ª which lies within a central aperture of a moving contact assembly 37 and so electrically insulates the contact asssembly 37 from the spindle 33. The face of the moving contact assembly 37 remote from the spring 35 is engaged by an electrically insulating washer 38 which abuts a circlip 39 secured to the spindle 33. Thus the spring 35 urges the carrier 36, the moving contact assembly 37, and the insulating washer 38 into abutment with the circlip 39. In addition, the circlip 39 constitutes a reaction point against which the return spring 31 abuts.
Figure 1 illustrates the parts in their rest position in which the electromagnet winding or windings 17 are de-energised, the plunger 23 has been moved outwardly (to the right in Figure 1) by the spring 25, and the bridging contact arrangement 32 has been moved away from the fixed contacts 27, 28 by the spring 31. Movement of the bridging contact arrangement 32 under the action of the spring 31 is limited by engagement of the moving contact assembly 37 with the pole plate 21.
The moving contact assembly 37 comprises a main bridging contact 41 which is formed from copper and is of substantial cross-section. The bridging contact 41 is elongate, having opposite end regions 42, 43 for engagement with the contacts 27, 28 respectively. Intermediate the regions 42, 43 the contact 41 is of part-circular form and has a centrally disposed aperture 44 within which the portion 36ª of the carrier 36 is received. The face of the bridging contact 41 is presented towards the end cap 12, is formed with a recess 45 for receiving a bridging element 46 in use.
The bridging element 46 is formed from nickel-chome alloy strip and is in the form of an annulus 47 having diametrically opposed, outwardly extending, integral arms 48, 49. Moreover the element 46 is arcuate such that if the annulus 47 rests on a plane surface then the arms 48 and 49 curve upwardly away from that surface.
The shape of the recess 45 in the bridging contact 41 matches the developed shape of the arcuate element 46 such that if the element 46 is flattened against its inherent resilience then it will fit within the recess 45. The annulus 47 of the element 46 is disposed within the recess 45 such that the element 46 engages the contact 41 generally along a diameter of the annulus 47 at right angles to the extent of the arms 48 and 49, and the element 46 is spot welded to the contact 41 along this line of engagement. Thus the element 46 is anchored to the contact 41 and in the rest condition of the element 46 the arms 48, 49 curve outwardly from the recessed face of the contact 41. In the rest position of the bridging contact arrangement 32 the end of the spindle 33 remote from the cap 12 projects from the pole 22 into the path of movement of the armature 23.
The operation of the actuator is as follows.
Upon energisation of the electromagnet windings 17 the armature 23 is drawn towards the pole 22 and during this movement engages the spindle 33 thus moving the bridging contact arrangement 32 against the action of the spring 31. As the bridging contact arrangement 32 is driven towards the cap 12 the arms 48 and 49 of the element 46 engage, and complete an electrical circuit between, the fixed contacts 27 and 28. The contacts 27, 28 constitute the fixed contacts of an electrical switch controlling current flow to the armature of the starter motor in use, and thus must carry currents of the order of several hundred amperes. The element 46 is not capable of sustaining such current flow other than momentarily, but of course immediately the arms 48, 49 engage the contacts 27, 28 current starts to flow through the element 46.
The speed of movement of the armature 23 is of course extremely rapid, and the movement of the contact arrangement 32 is thus equally rapid. It will be understood therefore that the arms 48, 49 of the element 46 bridge the contacts 27, 28 only momentarily before the end regions 42, 43 of the main bridging contact 41 respectively engage the contacts 27, 28. The spindle 31 may continue to move under the action of the armature 23 and during such movement the spindle 33 moves relative to the carrier 36, the contact assembly 37 and the washer 38 compressing the spring 35. Equally, the force with which the bridging contact 41 hits the fixed contacts 27, 28 can give rise to contact bounce as a result of which the engagement of the contact 41 with one or both of the fixed contacts 27, 28 may be momentarily broken (Figure 2). The arms 48, 49 of the element 46 will however to remain engaged with the contacts 27, 28 thereby sustaining a current flow between the contacts 27, and minimising the risk of, and the energy of, arcing between the bridging contact 41 and either or both of the fixed contacts. Naturally, the bounce condition lasts only momentarily, and thereafter, because the spindle 33 has moved through a stroke greater than that necessary to engage the bridging contact 41 with the fixed contacts 27, 28 the spring 35 is in a compressed condition and loads the contact 41 against the contacts 27, 28 (Figure 3). The element 46 is held in a flexed condition with the arms 48, 49 received within the corresponding regions of the recess 45 in the contact 41. It is of course desirable to provide a recess into which the arms 48, 49 seat in order that there should be no risk of the arms 48, 49 preventing clean contact between the bridging contact 41 and the fixed contacts 27, 28.
When the actuator is de-energised the armature 23 is returned to its rest position permitting the spring 31 to restore the bridging contact arrangement 32 towards its rest position. The resilience of the element 46 assists the spring 31 in moving the bridging contact 41 rapidly away from the contacts 27, 28 and thus both electrically and mechanically assists in minimising the risk of arcing as the bridging contact 41 breaks from the fixed contacts 27, 28. Alignment of the moving contact assembly 37 with the fixed contacts 27, 28 is maintained by the wall of the switch chamber 26 in the cap 12, which prevents rotation of the assembly 37 about the axis of the spindle 33.
It will be recognised that it is not intended that the element 46 should be capable of carrying, for any significant length of time, the high currents which pass through the contacts 27 and 28. Although the contact 41 may bounce five or six times before permanent contact is made the time period involved is very small and is probably insufficient for peak current flow to be achieved. Nevertheless, the presence of the element 46 remaining in contact with the fixed contacts during the bounce period maintains an electrical path during contact bounce thus substantially obviating the risk of the contact member 41 welding to one or both of the fixed contacts 27, 28.

Claims

1. An electromagnetic actuator for use in conjunction with an internal combustion engine starter motor, the actuator comprising an electromagnet winding (17), an armature (23) for connection to the pinion assembly of a starter motor in use, said armature (23) being movable by energization of said winding (17), first and second spaced, fixed, electrical contacts (27, 28), and a bridging contact (41) movable against the action of a return spring (31) to bridge said fixed contacts (27, 28) in response to movement of said armature (23), the actuator being characterized by the provision of an electrically conductive, resilient, bridging element (46) movable with said bridging contact (41) and so shaped that during the movement of the bridging contact (41) the element (46) engages said first and second fixed contacts (27, 28) before the bridging contact (41) and thereafter flexes during movement of the bridging contact (41) to permit the bridging contact (41) also to bridge the first and second fixed contacts (27, 28).

2. An actuator as claimed in claim 1 characterized in that said bridging element (46) is in the form of an arcuate strip which is anchored, adjacent its mid point, to the bridging contact (41) so that by virtue of its arcuate nature the free ends (48, 49) of the strip project away from the bridging contact (41) towards the first and second fixed contacts (27, 28) respectively.

3. An actuator as claimed in claim 2 wherein said bridging element (46) is welded to said bridging contact (41).

4. An actuator as claimed in any one of claims 1 to 3 characterized in that said bridging contact (41) is formed in that face which is presented towards the fixed contacts (27, 28) with a recess (45) for receiving the bridging element (46) as the bridging element (46) flexes during movement of the bridging contact (41) into engagement with said fixed contacts (27, 28).