GB2357374A

GB2357374A - Battery cut off switch

Info

Publication number: GB2357374A
Application number: GB9929680A
Authority: GB
Inventors: Brian Johnson; Matthew King; Adrian Thomas Campbe Patterson
Original assignee: Inertia Switch Ltd; First Inertia Switch Ltd
Current assignee: Sensata Technologies Ltd
Priority date: 1999-12-15
Filing date: 1999-12-15
Publication date: 2001-06-20
Anticipated expiration: 2019-12-15
Also published as: GB9929680D0; GB2357374B

Abstract

A cut off switch for a battery consisting of a pair of external contacts 8,9 protruding from a main body 6 with cover 1 which form a housing. The external contacts are connected together using a bridge contact 7 within the housing and is held in position by magnetic attraction. A permanent magnet 16 attracts a keeper plate 11 to hold the connection of the contacts against the action of spring 5. To trip the mechanism an opposing magnetic force is applied to the permanent magnet by solenoid coil 17, powered from trigger contacts 12, to counteract the magnetic field and release the bridging contact. Then under action of the spring the keeper plate is moved away from the permanent magnet breaking the connection between the external contacts. The gap between keeper plate and permanent magnet is set to a level where the force of the spring cannot be overcome by the magnet field from the permanent magnet once the opposing field is removed A manual input to button 13 is required to re-establish connection of the bridging contact. In an alternative embodiment a magnetisable element (23 see fig 3) is used to attract keeper plate (11a, fig 3) and retains magnetic charge until a cancelling charge is applied to the solenoid coil to release the bridging contact under action of a spring. In this embodiment re-magnetising the magnetic element will re-establish the connection between external contact thereby removing the need for a manual reset of the trip mechanism.

Description

2357374 BATTERY CUT-OFF DEVICE AND METHOD The invention relates to a

circuit-breaker device for cutting off a battery from its associated circuit, and will find special application in the automotive field, as well as diverse other applications.

US 5,917,162 discloses a circuit-breaker device for cutting off a battery. This device is based on a mechanical latching arrangement that is de-latched by actuation with a solenoid armature. In the primed or latched position in which electrical contact is made, a cylindrical member has an upwards force acting thereon from a compression spring. However, the cylindrical member is inhibited from responding to this force with an upwards movement by shoulders of an elongate plunger mounted within the member which engage with balls that are prevented from radially inwards movement by a head portion of the plunger. The circuit breaker action follows from independent upward actuation of the plunger by a solenoid armature, arranged below the plunger. Energisation of the solenoid urges the plunger upwards. When the plunger is urged upwards by the armature, the head of the plunger moves above the balls, allowing the balls to move radially inwards which, in turn, frees the cylindrical member for upwards movement. The cylindrical member then acts on a movable contact to move it upwards and separate it from fixed contacts with which it is normally positively engaged, thereby breaking the circuit. This electro- mechanical device has the advantage that it constitutes no electrical load in the normal, closed configuration of the device, so that no power is consumed in this configuration. By contrast, in older devices (see US 312,985 and US 1,643,415) in which actuation also takes place with solenoid and armature arrangements, the solenoid coils represent an ever-present electrical load in the normal, closed configuration of the device, so that power is continuously consumed. Despite the advantage of no power consumption when in its normal closed configuration, the device of US 5,917,162 has a considerable mechanical complexity. As a result, manufacturing costs are relatively high. It also has the disadvantage that it must be mounted vertically to allow the device to operate, since it relies on gravity to move the balls.

It is therefore an object of the invention to provide a simplified and less expensive battery cut-off device which does not consume power in its normal, closed configuration.

According to a first aspect of the invention there is provided a battery cut-off device comprising:

a pair of external contacts; a bridge contact positionable to form a contact between the pair of external contacts; a magnetic element arranged to hold the bridge contact in contact with the pair of external contacts by an attractive magnetic force in a closed configuration; and a contact separator actuatable to overcome or reduce the attractive magnetic force and move the bridge contact out of contact with the pair of external contacts into an open configuration.

Use of a magnet to hold the movable bridge contact in place has the advantage that no external electrical power is required or consumed in maintaining the battery cut-off device in its normal closed configuration while simultaneously allowing a simple construction. The magnetic attraction is provided in one embodiment by a permanent magnet and, in another embodiment, by a magnetisable and demagnetisable magnet. The contact separator preferably comprises a solenoid coil which, when energised, generates a magnetic field that counteracts that of the per manent magnet, or acts to demagnetise the magnetic element, thereby to initiate separation of the movable bridge contact from the (fixed) external contacts. Separation may be assisted and maintained by a mechanical force generating element. -A compression spring is used for this purpose in a first embodiment of the invention described hereinbelow.

According to a second aspect of the invention there is provided a method of operating a battery cut-off device comprising:

holding a bridge contact in contact with a pair of external contacts by an attractive magnetic force; receiving an electrical trigger signal; and channelling the electrical trigger signal into an electrical element to generate a repulsive magnetic force, or reduce the attractive magnetic force, thereby to separate the bridge contact from the pair of external contacts.

Further aspects of the invention are exemplified by the attached claims.

For a better understanding of the invention and to show how the same may be carried into effect reference is now made by way of example to the accompanying drawings in which:

Figure 1 is an exploded view of a battery cut-off device according to a first embodiment of the invention; Figure 2 is a schematic section of the device of Figure 1; and Figure 3 is a schematic section of a battery cut-off device according to a second embodiment of the invention.

A first embodiment of the invention is now described with reference to Figures 1 and 2. Figure 1 is an exploded view of a battery cut-off device according to the embodiment.

A main body 6 of the device comprises a base portion, a downwardly depending shroud for an electrical socket 19 and sidewalls terminating in an upper rim surface. First and second fixed contacts 8 and 9 extend through oppositely disposed ones of the sidewalls, each fixed contact having an exterior lug, shown with a circular aperture, and an interior upwardly facing contact surface. The main body 6 may be of plastics material and formed by injection moulding.

A cover or cap 1 abuts the upper rim surface of the main body 6 to define an interior volume which is protected against the ingress of moisture and other undesirable environmental impact. In Figure 1, a snap-fitting cusp is shown extending down from one side of the cover 1. Arranged in an upper surface of the cover 1 is a flexible membrane portion forming a reset button 13. Arranged in a sidewall of the cover 1 is a further flexible membrane portion forming a trip button 14. The function of buttons 13 and 14 are described further below.

A solenoid 4 is securely received in a base portion of the main body 6 and performs a latching function as described finther below. The latching solenoid 4 has arranged therein a magnet, in the form of a permanent magnet 16, and a solenoid coil 17 (see Figure 2). A printed circuit board 3 is arranged adjacent to the solenoid 4. The printed circuit board (PCB) 3 has a switch in the form of a microswitch 10 arranged at one end thereof and a pair of external trigger contacts 12 extending from the other end.

The microswitch 10 is arranged to lie adjacent to the trip button 14 when the assembled device is in its normal closed configuration, this configuration being described further below. The external trigger contacts 12 are electrically connected to terminals of the socket 19 arranged in the socket shroud of the main body 6. The tracks of the PCB 3 are arranged so that the solenoid coil 17 is connected to power and earth through either the microswitch 10 or the pair of external trigger contacts 12. In an automobile, for example, the external trigger contacts 12 could be connected to a separate crash module. The contacts 12 may also be connected to any system that may demand that the battery should be disconnected, e.g. for short-circuit detection or in response to a transit signal. In the latter case, it is beneficial to disconnect the battery during shipment of a vehicle from the factory to the dealer.

A carrier assembly 2 is arranged in the interior of the battery cut-off device. The carder assembly 2 has a hollow interior which is sufficiently large to allow an upper portion of the latching solenoid 4 freely to move up and down therein. Sidewalls of the carrier assembly extend to define the interior and terminate in a lower rim surface 15.

The carrier assembly 2 has a bridge contact 7 extending laterally therethrough. First and second ends of the bridge contact 7 are arranged physically and electrically to contact the interior upwardly facing contact surfaces of the first and second fixed contacts 8 and 9 respectively. The carrier assembly 2 further comprises a keeper plate or armature 11 arranged above the latching solenoid 4 and suspended by a strut 19 that extends through an aperture in the bridge contact 7 from a blade spring 18 arranged upstanding from the upper surface of the bridge contact 7. The function of the keeper plate 11 is to provide a magnetisable element of the carrier assembly 2 which is interactive with the magnetic fields, permanent and transient, generated by the latching solenoid 4. The blade spring

18, strut 19 are arranged so that the keeper plate 11 is suspended a small distance above the solenoid when the blade spring 18 is unbiased and the bridge contact 7 is in contact with the first and second fixed contacts 8 and 9. The small distance is 2 mm in the embodiment. The small distance is such that the keeper plate 11 experiences an attractive force from the permanent magnet 16 sufficient to cause the keeper plate 11 to be pulled down against the bias of the blade spring 18. This assists a positive contact between the bridge and fixed contacts.

In a modification (not shown), the strut 19 can extend through the top of the assembly housing 2 and terminate in an upper surface which is directly actuated during manual reset through the button 13.

A separate keeper plate is shown in the drawings, but it will be understood that a central portion of the bridge contact 7 could perform this function, in which case a separate keeper plate, and also the blade spring 18, could be dispensed with.

A spring, in the form of a helical compression spring 5, is arranged concentrically around the latching solenoid 4. One end of the compression spring 5 presses on the base portion of the main body 6 and the other end presses on the lower rim surface 15 of the carrier assembly 2. The compression spring 5 thus acts to urge the carrier assembly 2 upwards within the interior volume of the device, away from the base portion of the main body 6.

Operation of the device of the first embodiment is now described.

In its normally closed configuration, the bridge contact 7 incorporated within the carrier assembly 2 is held against those portions of the first and second fixed contacts 8 and 9 that extend into the interior of the body 6, allowing current to flow from the first fixed contact 8 to the second fixed contact 9. The normally closed configuration is maintained by the action of the permanent magnet 16 attracting the keeper plate 11 that is incorporated within the carrier assembly 2. In the normally closed configuration, the magnetic attraction force between the permanent magnet 16 and the keeper plate 11 exceeds the mechanical force generated by the compression spring 5 acting to urge the carrier assembly 2 upwards.

The device is tripped from its normal closed configuration, into a stable open configuration, by application of an electrical impulse through the printed circuit board 3. The impulse will generally be triggered by an external source energising the external trigger contacts 12, but may also be triggered manually by actuation of the microswitch 10 through depression of the trip button 14 disposed in the side of the cover 1. In either case, the electrical impulse passes to the coil 17 of the latching solenoid 4 and generates a magnetic field which counteracts that of the permanent magnet 16. The urging force of the compression spring 5 then exceeds the combined net magnetic force of the permanent and transient magnetic fields in the closed configuration, and the carrier assembly 2 is pushed upwards away from the latching 6- solenoid 4 into the stable open configuration in which the bridge contacts 7 are separated from the fixed contacts 8 and 9, thereby to open-circuit the device. The energising electrical impulse is only required for a short time, since the magnetic attraction force between the permanent magnet 16 and keeper plate 11 falls off rapidly as the mutual separation between these elements increases.

It will thus be apparent that no electrical power is consumed or required either when the device is in its normal closed configuration or in its tripped open configuration. Moreover, a short electrical impulse is all that is required to trip the device from its normal closed configuration to the open configuration.

Resetting from the open configuration is performed by manual depression of the reset button 1 ') which pushes the carrier assembly 2 downwards until the keeper plate 11 is sufficiently attracted by the permanent magnet 16 to overcome the urging force of the compression spring 5 and adopt the closed configuration.

In a modification reset can also be performed automatically by provision of an electrical reset element in the form of an additional solenoid coil (not shown) housed within the solenoid 4 and connected to receive an electrical reset signal which has the effect of generating an attractive magnetic force between the keeper plate 11 and solenoid 4 that is sufficient to pull the carrier assembly 2 back into the normal closed configuration from the open configuration.

In a modified arrangement, a multiple number of contact sets may be provided in a single device to allow switching of several circuits. These may be alongside each other, or may be piggy backed with a non-conductive spacer arranged between ad acent bridge contacts.

J The PCB 3 may also be modified to include short circuit detection, i.e.

detection of abnormal loads, and to energise the solenoid coil accordingly to trip the device.

Moreover, it will be understood that some crash sensing may be provided integrally with the battery cut-off device, instead of, or in addition to, externally triggered actuation of the device. For example, an inertia switch may be incorporated 3 in the battery cut-off device.

Further, the PCB 3 may incorporate some battery condition monitoring. For example, the device can be selectively tripped and reset (where autoreset is provided) to load the battery in such a way that battery life is prolonged during long storage periods.

In another variant, instead of the compression spring 5, a tension spring attached to the cover I could be used as the means for retaining separation of the contacts in the open configuration. Moreover, the spring could be dispensed with altogether and the device held in the open configuration by provision of a mechanical latch acting as the separation means. In this case, the mechanical latch latches onto the carrier assembly 2 when the carrier assembly is moved under action of the solenoid coil 17.

Figure 3 illustrates in schematic cross-section a battery cut-off device according to a second embodiment. Much of the basic structure will be understood from the first embodiment. Namely, first and second fixed contacts 8 and 9 are encapsulated in a main body 6 on which is seated a cap 1, the cap and main body defining an interior region. The interior region accommodates a solenoid unit 4a broadly comparable in function to the solenoid of the first embodiment. A carrier assembly 2a has a lower depending skirt portion that fits over the solenoid unit 4a terminating in a lower rim 15 that provides an abutment surface for a helical spring 5 which is in compression between the abutment surface and a lower base of the main body 6. The carrier assembly 2a has an upper portion in which a bridge contact 7 is encapsulated. Beneath the bridge contact 7, a keeper plate or armature 11 a is also encapsulated in the carrier assembly so that it faces the upper side of the solenoid unit 4a across an air gap 2 1. The carrier assembly 2a on its upper side terminates in a generally flat surface which, in Figure 3, is in a position of abutment with an annular spacer 20 fixed to, or integral with, the underside of the cap 1.

In the second embodiment, the solenoid unit 4a has the function of both releasing and resetting the device and has the following internal structure for that purpose. A magnet 23 having residual magnetic properties is arranged radially inside solenoid coils 17a. A spacer 24 is arranged above the magnet 23 extending to form the upper side of the solenoid unit 4a in its radially inward part. Radially outside the spacer 24 on the upper side of the solenoid unit 4a there is arranged a magnetic pole 22. A further magnetic pole 25 is then arranged radially outside the pole 22, and the solenoid coils 17a, and extends the full length of the solenoid unit 4a in the manner of a cylindrical sleeve. The remainder of the solenoid unit 4a is taken up with a core 26.

Finally, a pair of external trigger contacts 12 are connected for energising the solenoid coils 17a. The external trigger contacts 12 are connected to a PC13, as described for the first embodiment and shown in Figure 1, with a microswitch for manual actuation.

In operation, energising the coils 17a shuttles the carrier assembly 2a between two positions. One position is as shown in Figure 3, with the contacts in an open configuration. In this position, the bridge contact 7 is lifted above the external contacts 8 and 9 with the upper surface of the carrier assembly 2a in abutment with the spacer 20. The other position (not illustrated) is a closed configuration with the bridge contact 7 held down on the external contacts 8 and 9.

When a voltage pulse of one polarity is applied to the trigger contacts 12, the solenoid coils 17a are energised and the magnetic field produced thereby magnetises the magnet 23. A magnetic force is then created which attracts the keeper plate 11 a, pulling it down into the closed configuration of the contacts 7, 8 and 9. Once magnetised in this way by the voltage pulse, the magnet 2,3) will retain its magnetisation after the pulse has terminated, thereby continuing to hold the bridge contact 7 down onto the external contacts 8 & 9. This provides the auto- reset capability of the device.

The release or trip mechanism functions as follows. When a voltage pulse of opposite polarity is applied to the trigger contacts 12, the solenoid coils 17a are energised and a magnetic flux is generated that has a flux pattern of opposite polarity to that of the magnetised magnet 23, and thus acts to de-magnetise the magnet 23. The compression force from the spring 5 then overcomes the magnetic attraction between magnet 23 and keeper plate 11, and the carrier assembly 2a is moved upwards, thereby lifting the bridge contact 7 away from the external contacts 7 and 8 into the open configuration.

In this second embodiment, repeated manual actuation of the microswitch toggles the device between the open and closed configurations.

For further details of the design of the solenoid unit 4a using residual magnetism, reference is made to prior art designs of solenoid-actuated fluid-flow control valves for automotive fuel injection systems, such as described in US 5,718,264.

The device of the second embodiment can thus be positively actuated to shuttle between the open and closed configurations by application of voltage pulses of the desired polarity. As in the first embodiment, the device is held either in the open or closed configuration under the action of a magnet with no electrical power consumption. Electrical power is only needed to trip and reset the device.

_10

Claims

1. A battery cut-off device comprising:

a pair of external contacts; a bridge contact positionable to form a contact between the pair of external contacts; a magnetic element configured to generate a magnetic field that holds the bridge contact in contact with the pair of external contacts in a closed configuration; and a contact separator actuatable to counteract the magnetic field and move the bridge contact out of contact with the pair of external contacts into an open configuration.

2. A device according to claim 1, further comprising a carrier which houses the bridge contact and a keeper plate that is responsive to the magnetic field generated by the magnetic element.

3. A device according to claim I or 2, wherein the contact separator comprises an electrical element connected to receive an electrical signal and, in response thereto, to generate a further magnetic field to counteract that of the magnetic element, thereby to move the bridge contact out of contact with the pair of external contacts into the open configuration.

4. A device according to claim 3, wherein the magnetic element is a permanent magnet and actuation of the electrical element generates the further magnetic field so as to oppose the magnetic field of the permanent magnet while the electrical element if being actuated.

5. A device according to claim 3, wherein the magnetic element is magnetisable and de-magnetisable by first and second polarities of the further magnetic field _11 generated responsive to respective first and second polarities of the electrical signal, thereby to move into, and maintain, the closed and open configurations.

6. A device according to claim 3), 4 or 5, wherein the electrical element comprises a solenoid coil.

7. A device according to any one of claims 33 to 6, wherein the contact separator comprises an external trigger contact for receiving the electrical signal as an external trigger signal.

8. A device according to any one of claims 3) to 7, wherein the contact separator comprises a manually actuatable switch, actuation of which generates the electrical signal.

9. A device according to any one of the preceding claims, wherein the contact separator further comprises a spring acting to force the bridge contact away from the pair of external contacts.

10. A method of operating a battery cut-off device comprising:

holding a bridge contact in contact with a pair of external contacts by magnetic attraction; receiving an electrical trigger signal; and channelling the electrical trigger signal into an electrical element to reduce the magnetic attraction and cause the bridge contact to separate from the pair of external contacts.

11. A method according to claim 10, wherein the magnetic attraction is generated by a permanent magnet and reduced by generating an opposing magnetic field with a D solenoid coil.

12. A method according to claim 10, wherein the magnetic attraction is generated and reduced respectively by magnetisation and de-magnetisation of a magnetic element.

13. A method according to any one of claims 10 to 12, wherein the bridge contact is caused to separate from the pair of external contacts under action of a mechanical force.

14. A battery cut-off device substantially as hereinbefore described with reference to Figures 1 and 2, or Figure 3), of the accompanying drawings.

15, A method of operating a battery cut-off device substantially as hereinbefore described with reference to Figures 1 and 2, or Figure of the accompanying drawings.