GB2069765A

GB2069765A - Electromagnetic switch

Info

Publication number: GB2069765A
Application number: GB8104543A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1980-02-14
Filing date: 1981-02-13
Publication date: 1981-08-26
Also published as: FR2476383B1; DE3005460A1; FR2476383A1; DE3005460C2; GB2069765B

Abstract

An electromagnetic switch suitable for controlling glow-plugs of an internal combustion engine, has an additional single-turn coil (22) for monitoring the current flowing through the fixed contacts (19, 20) on a contact carrier (21) of the relay. The coil (22), the connection (23) and the contact carrier (21) are together stamped from a metal sheet and are subsequently bent to the desired shape. Separate connections between the ends ofthe coil (22) and the connection (23) and the contact carrier (21) are thus avoided, thereby reducing the voltage drop between the connection and the contact carrier. The coil 22 may have a single turn and carry the current for four glow-plugs. A further coil 27, having four turns, may carry the current for a fifth glow-plug; any unbalance between the magnetic fields of the coils due to a fault actuating contacts disposed in coil 27. <IMAGE>

Description

SPECIFICATION Electromagnetic switch The invention relates to an electromagnetic switch.

A magnetic switch is already known from (published German Patent Specification (Offenlegungsschrift) No. 1904731) in which one end of a coil is electrically connected to a connection plate and the other end of the coil is electrically conductively connected to the contact carrier of a fixed switch contact, with which a moving contact actuated by an energising winding cooperates. The disadvantage of a solution of this kind is that the connection points at the ends of the coil constitute an electrical resistance which is subjected to considerable stress, particularly in the case of a power relay, and causes a voltage drop by the amount of which the voltage available to the load is decreased. This has a particularly great effect in motor vehicles whose internal combustion engines have to be made ready to start by preliminary heating by means of glow plugs.It is important, particularly during the cold season, that, as far as is possible, the full voltage of the battery should be applied to the glow plugs, since, at low temperature, the capacity of the vehicle battery is reduced and the preliminary heating time required is relatively long.

The invention consists in an electromagnetic switch in which a coil of at least 9 turn is located between a connection part and a contact-carrying part for a fixed switch contact with which a moving contact actuated by an energising winding cooperates, and in which said coil is manufactured from one piece together with at least one of said parts which is contiguous with the respective end of the coil.

This has the advantage that the voltage drop between the connection terminals of the switch is reduced and, moreover, working operations, hitherto required for separate electrical connection of the ends of the coil during manufacture of the switch, are saved.

It is particularly advantageous to manufacture the connection part, the coil and the contact carrier from a stamped part and subsequently to impart the desired shape to it. In the event of it being possible to construct the connection part in the form of a round plug, it is advantageous to manufacture the coil and the round plug from one piece by the impact extrusion method, the thinner end being coiled to form a coil (with a plurality of turns).

The invention is further described, by way of example, with reference to the drawings, in which Fig. 1 is a perspective view of a relay, without a housing, Fig. 2 is a perspective view of the connection part, the coil and the contact carrier to show its one-piece construction, and Fig. 3 shows a round plug constituting a connection part with an integrally formed coil.

The relay 10 shown in Fig. 1 is an electromagnetic switch in accordance with the invention and serves to determine the glow period of glow plugs of a diesel engine fitted to a motor vehicle. The glow period relay 10 comprises a base 11 on which are disposed a printed circuit board 12 having an electronic circuit (not shown) for determining the preliminary heating time, and a power relay 13 which has to switch the currentforfive glow plugs. The power relay 13 has an L-shaped magnetic angled bracket 14 to which is secured an energising winding 15 which is slipped onto an iron core. An armature 16 is pivotably mounted on the top end of the magnetic angled bracket 14. A leaf spring 30 is secured to the armature.The free end of the leaf spring 30 carries two contact 17 and 18 which cooperate with two fixed contacts 19 and 20 of a contactcarrying part (contact carrier) 21.The two pairs of contacts are electrically connected in parallel, one pair of contacts being designed for a high switching capacity and the other pair of contacts being designed for a small voltage drop.

As is shown in Fig. 2, the contact carrier 21 is connected to a connection part 23 by way of a currentmonitoring coil 22, these three parts being formed from one piece. The connection part 23, the coil 22 and the contact carrier 21 are stamped from a metal sheet of, for example, copper. The contact carrying part 21 has subsequently been bent into the shape which is shown, and has been provided with the switching contacts 19 and 20. The coil 22 comprises one turn which has also subsequently been bent, and the connection part 23 is of plate-shaped construction and is provided with a plurality of holes 24.

The ends of round plugs 25 are riveted in the holes, and the round plugs extend through the base 11 of the glow-period relay 10 and serve to connect the relay 10 to the leads for four of the glow plugs. The connection plate 23 is designed such that all the round plugs 25 are at the same electrical potential.

Fig. 3 shows a further connection part constituted of a round plug 26 which is impact-extruded from one piece together with a coil 27. The four turns of the coil 27 are coiled from the wire-like end of the impact-extruded part. A different number of turns may be necessary in order to compensate for effects, conditioned by construction, on the magnetic fields.

The internal diameter of the coil 22 having one turn between the connection part 23 and the contact carrier 21 (as shown in Fig. 2) is dimensioned such that the coil 27 (Fig. 3) is received therein in an insulated manner (Fig. 1). The round plug 26 is secured in the base 11 of the glow-period relay 10 and serves for connection of the fifth glow plug. The free end 28 of the coil 27 is inserted into a corresponding hole 29 in the contact carrier 21 and is soldered or welded therein. A gas-protected contact (not shown in Fig. 1) is disposed in the coil 27 having four turns and, when the relay contacts are closed, the gasprotected contact is influenced by the oppositely directed magnetic fields of the two coils 22 and 27 having current flowing therethrough.The glow plugs of the internal combustion engine which are connected to the glow-period relay 10 are monitored by the gas-protected contact by virtue of the fact that the current of one glow plug flows through the coil 27 having four turns and the entire current of the other four glow plugs flows through the coil 22 having only one turn. The number of turns of the coil 27 to be connected to one glow plug by way of the round plug 26 is equal to the number of the other glow plugs which are to be connected to the other coil 22 by way of the round plug 25. It is thereby ensured that, when the glows plugs are intact, the magnetic fields of the two coils 22 and 27 cancel one another and the gas-protected contact remains in its rest or normal position. In the event of failure of a flow plug, the two magnetic fields are no longer equal to one another and the gas-protected contact is switched on by the resultant magnetic field. The gas-protected contact can be used to indicate a defect and also to switch off the glow-period relay 10.

The invention is not limited to the illustrated embodiment, since it can also be realised in the same manner in the case of overload switches or other electromagnetic switches in which the current to be switched flows through a coil.

Claims

1. An electromagnetic switch in which a coil of at least Q turn is iocated between a connection part and a contact-carrying part for a fixed switch contact with which a moving contact actuated by an energising winding cooperates, and in which said coil is manufactured from one piece together with at least one of said parts which is contiguous with the respective end of the coil.

2. An electromagnetic switch as claimed in claim 1, in which the connection part, the coil and the contact-carrying part are formed from one piece.

3. An electromagnetic switch as claimed in claim 2, in which the connection part, the coil and the contact-carrying part are stamped and bent from a metal sheet.

4. An electromagnetic switch as claimed in claim 3, in which the connection part is of plate-shaped construction and is provided with a plurality of connection plugs.

5. An electromagnetic switch as claimed in claim 1, in which the connection part is a round plug which is impact-extruded from one piece together with the coil, the coil comprising a plurality of turns.

6. An electromagnetic switch as claimed in claim 5, in which a coil having one turn is connected between a further connection part and the contactcarrying part and its internal diameter is dimensioned such that the coil having a plurality of turns is received therein in an insulated manner.

7. An electromagnetic switch as claimed in any of claims 1 to 4, in which the said coil has one turn and a further coil having a plurality of turns is received therein and is connected between a further connection part and the contact-carrying part.

8. An electromagnetic switch as claimed in claim 6 or7, in which a gas-protected contact is disposed in the coil having a plurality of turns and, when the switch is closed, experiences the oppositely directed magnetic fields of the two coils having current flowing therethrough.

9. An electromagnetic switch as claimed in claim 6,7 or8, in which, in order to monitorthe glow plugs of an internal combustion engine which are to be connected to the switch, the current of one glow plug flows through the coil having a plurality of turns and the entire current of the other glow plugs flows through the coil having only one turn.

10. An electromagnetic switch as claimed in claim 9, in which the number of turns of the coil to be connected to one glow plug is equal to the number of the other glow plugs which are to be connected to the other coil having one turn.

11. An electromagnetic switch constructed and adapted to operate substantially as herein described with reference to and as illustrated in the drawings.