GB2178476A

GB2178476A - Lock with controllable clutch

Info

Publication number: GB2178476A
Application number: GB08621452A
Authority: GB
Inventors: Leslie Victor Herriott
Original assignee: Lowe and Fletcher Ltd
Current assignee: Lowe and Fletcher Ltd
Priority date: 1984-10-06
Filing date: 1986-09-05
Publication date: 1987-02-11
Also published as: GB8621452D0

Abstract

A lock includes a clutch (140, 141) for transmitting drive between a key-receiving barrel 115 and a driven element 118. Setting of the clutch is controlled by a device 124 which compares with stored information information read from a key, when the key is introduced into the barrel. <IMAGE>

Description

SPECIFICATION Improvements relating to reading information from a key From one aspect, the present invention relates to a key-reading device. Such devices are used to control access to equipment or to an area and are used to prevent unauthorised persons operating equipment.

It is known to use for these purposes a device capable of reading information from a card which identifies the user or person requiring access. Typically, the card incorporates a strip of magnetisable material which has been magnetised in a manner to present in an encoded form information identifying the user.

The card-reading device has one or more sensor elements capable of sensing the magnetic field of the card to read the information therefrom. The or each sensor element is mounted in a fixed position in the card-reader. The function of the card-reader is simply to read information from the card and pass that information to control means. The door lock or other controlled structure can then be operated directly by the user.

It is also known to operate a lock by means of a key which has two functions. The key presents to the lock information which identifies the user and also transmits mechanical drive from the user to the lock. The information may be presented in a mechanical manner, in which case the key incorporates a bit which engages tumblers of the lock to displace those tumblers to releasing positions. In other known examples, the key presents the information in the form of a magnetic field which acts on movable magnetic iocking elements of the lock to displace these elements to releasing positions.

According to the present invention, there is provided a key reading device comprising a key-receiving member defining a key slot, a housing containing the key-receiving member, reading means for reading information from a key when the key is present in the key slot, a driven member arranged for movement relative to the housing and coupling means for transmitting drive from the key-receiving member to the driven member, wherein the coupling means is settable upon reading of a predetermined set of information from the key from an inoperative condition in which the coupling means cannot transmit drive from the key receiving member to the driven member into an operative condition in which the coupling means is capable of transmitting drive from the key-receiving member to the driven member.

The coupling means may be adapted to transmit a limited force only from the keyreceiving member to the driven member, when the coupling means is in the operative condition, and be adapted to restrain movement of the driven member when the coupling means is in the inoperative condition, so that, when the coupling means is in the inoperative condition, insufficient force can be transmitted from the key-receiving member to the driven member to move the latter.

The arrangement may be such that the coupling means remains in one of its conditions only whilst electrical energy is supplied to the coupling means. Alternatively, the arrangement may be such that the coupling means can be set from a first condition to a second condition by a brief pulse of energy and will remain in the second condition until a further brief pulse of energy changes the condition of the coupling means once more.

The key-receiving member may be freely rotatable relative to the housing when the key is absent.

Examples of embodiments of the present invention will now be described, with reference, to the accompanying drawings, wherein: Figure 1 shows a diagrammatic representation of a lock and of a key, certain parts of the lock being separated from one another for clarity of illustration; Figure 2 is a diagrammatic representation of a modification of the lock of Fig. 1; Figure 3 is a similar representation of a further modification of the lock of Fig. 1; Figure 4 shows a perspective view of a second lock, a body of the lock and certain parts associated therewith being omitted; Figure 5 shows components of the lock of Fig. 4 separated from one another; and Figure 6 shows a key for use with the lock of Fig. 4.

The particular reading device illustrated in Fig. 1 of the accompanying drawing is a lock suitable for locking a door or other closure member in a closed position. The key 10 intended for operating the lock includes a handle 11 and a shank 12 integral with the handle or rigidly connected therewith. At least the shank is formed of a substantially rigid material. The handle and the shank have sufficient strength for transmitting from a user to the lock torque which will operate the lock to release the door.

The key is adapted to present to the lock information which identifies the key. The key may be unique or may be one of a plurality of identical keys. In the example illustrated, the information is presented by the key in a form which can be read by means of radiation. The shank 12 defines a window containing a sheet of material which is transparent to radiation, for example infra-red radiation, and which bears marks 13 of a material which is opaque to the radiation. The marks are arranged in two rows extending along the key shank sideby-side.

To reduce the risk of unauthorised persons reading information from the key, the shank may also include screens of material which are transparent to the radiation used for reading the key but are opaque to visible light, these screens obscuring the marks 13 from view.

The lock shown in Fig. 1 comprises a hollow housing 14 which would normally be fixed to an adjacent structure, for example a door, in use. A key-receiving member 15 is mounted in the housing for rotation relative thereto. This member includes a generally cylindrical head 16 which is accessible to a user when the housing is mounted on or in a door or other structure. A body 17 of the member 15 is, in use of the device, disposed within the housing 14 and is inaccessible.

However, for purposes of illustration, the member 15 is shown partly withdrawn from the housing to expose the body 17 to view.

On an end portion of the member 15 remote from the head 16, there is carried an eccentric driven element 18 which is constrained to rotate with the member 15 and is drivingly engaged with a sliding bolt 19 in a known manner so that the bolt can be reciprocated by rotation of the member 15.

In the end portion of the member 15 remote from the head 16, there is provided a recess 20 in which there can engage a nose 21 of a solenoid 22 incorporated in the housing 14. The solenoid is restrained against rotation relative to the housing about an axis 23 defined by the housing so that, when the nose 21 is engaged in the recess of the member 15, movement of that member and of the bolt 19 are prevented.

There is also incorporated in the housing 14 control means 24 for controlling operation of the solenoid 22 and a cell or battery (not shown) for supplying electrical power to the device.

The member 15 is formed with a slot 25 for receiving the shank 12 of the key. The slot and the key shank have complementary non-circular cross-sections so that torque can be transmitted to the member 15 via the key shank, when the latter has been introduced into the slot 25.

Sensor elements 26 and 27 are mounted in the member 15 for reading information from the shank of the key when the latter is introduced into the slot 25. In the example illustrated, a single sensor element is provided for each row of marks 13. The information is read from each row serially. Alternative arrangements of sensor elements may be used.

There are also mounted in the member 15 diodes (not shown) for emitting infra-red radiation which can be transmitted through the transparent parts of the key shank 12 to the sensor elements 26 and 27. It will be understood that the diodes and the sensor elements are carried around the axis 23 when the member 15 is rotated.

For providing electrical connections between the battery and control means 24, on the one hand, and the diodes and sensor elements 26 and 27, on the other hand, there is incorporated in the device transmitting means which includes several pairs of transfer elements, each pair forming a part of an electrically conductive path. In the example illustrated, there are four electrically conductive paths between the control means 24 and the member 15, two of these paths being used to energise the diodes and the sensor elements and the two further paths being used to convey signals from respective ones of the sensor elements to the control means.

One transfer element 28 of each path is fixedly mounted on the member 15 for rotation therewith whilst the other transfer element 29 of that path is fixedly mounted on the housing 14. The transfer elements are formed of electrically conductive material and the arrangement is such that, when the member 15 is in a first position, the elements 28 and 29 included in a particular path are in mutual contact. When the member 15 is rotated by means of the key, the transfer elements of each path are moved apart and the path is interrupted.

There may also be incorporated in the member 15 a switch 30 which the key shank 12 is adapted to operate mechanically by the provision of recesses 31 and 32 in the key shank adjacent to opposite ends thereof. When the key is absent from the member 15, neither the sensor elements 26 and 27, nor the diodes, nor the solenoid 22 are energised. The nose 21 occupies the recess 20 so that movement of the bolt 19 is prevented. When the tip of the key shank is introduced into the slot 25, the switch 30 is operated to energise the diodes and the sensor elements. As the key shank moves further into the slot, information is read from the key shank by the sensor elements 26 and 27 and is transmitted along respective current paths to the control means 24. One of the rows of marks 13 may be a clock track which determines the times at which the other row is interrogated. When each row of marks has completely passed the sensor elements 26 and 27, the switch 30 is again operated to de-energise the diodes and the sensor elements. This provides to the control means 24 an instruction to energise the solenoid 22, provided the information read from the key agrees with information stored in the control means. When the solenoid is energised, the nose 21 is withdrawn from the recess 20 so that the member 15 is freed for rotation. The user can then move the bolt 19 by the application of torque to the handle 11 of the key. As rotation of the member 15 occurs, each electrically conductive path between that member and the control means is interrupted by separation of the corresponding pair of transfer elements. The paths are restored when the member 15 is returned to its initial position.

The control means 24 is arranged to re spond to interruption of the electrically conductive paths between the member 15 and the control means by terminating energisation of the solenoid 22. Once the member 15 has been turned from the-position in which the key is inserted, the recess 20 is no longer aligned with the nose 21 so that the nose cannot re-enter the recess until the member 15 has been returned to its initial position.

During normal use, there is no substantial delay between energisation of the solenoid and turning of the member 15, so that the solenoid is energised for a very brief period only and the consumption of electrical energy is low. Respective transfer elements may be mounted in the housing 14 and member 15 to provide a signal which causes de-energisation of the solenoid when the member 15 is turned. Alternatively, transfer elements which are also used for energising the diodes and sensor elements may be used to provide this signal. If the member 15 is not turned after the solenoid has been energised, then it is deenergised by the control means at the end of a predetermined period of a few seconds, typically 2 to 3 seconds.

A further recess 20 may be provided in the member 1 5 at a diametrically opposite position. In this case, the member 15 can be locked in an alternative position and additional transfer elements (not shown) may be provided in the housing 14 to establish alternative electrically conductive paths between the member 15 and the control means 24 when the member 15 is locked in the alternative position.

It will be noted that, because the electrically conductive paths are not maintained during rotation of the member 15, it. is not necessary to restrict the degree of rotation of that member. There may be provided in place of the driving element 18 and bolt 19 a mechanism which requires rotation of the member 15 through two complete revolutions.

It will also be noted that, with the arrangement hereinbefore described with reference to Fig. 1, the electrical circuit which includes each pair of transfer elements through which electrical power is supplied to the diodes and to the sensor elements are opened before the transfer elements of the pair are moved apart.

There may be mounted on the head 16 of the key-receiving member a shutter which normally closes the key slot 25 at its outer end.

In this case, there may be associated with the shutter a microswitch or other device for providing an electrical output signal when the key enters the slot 25. This switch or other device may be used in place of the switch 30, in which case the recesses 31 and 32 in the key shank would not be required. A reed switch operated by a magnetic field of the key may be used. Opening of the circuits through which power is supplied to the diodes and to the sensors may be effected automatically by the control means, when the predetermined set of information has been read from the key.

Whilst the several pairs of transfer elements have been shown in positions spaced from each other circumferentially of the axis 23, it will be understood that these pairs may be arranged in other positions, for example in a row extending along the axis.

The lock can have a particularly compact configuration. For example, the control means 24 could be positioned somewhat nearer to the axis 23 than is the periphery of the head 16. Alternatively, the control means could be incorporated in an escutcheon surrounding the head 16.

Whilst, in the example illustrated, the member 15 is arranged for rotation relative to the housing 14 and is constrained against movement relative to the housing along the axis 23, the key-receiving member may be arranged for movement in an alternative manner, for example reciprocation relative to the housing along the axis. It will be understood that the arrangement illustrated is well suited to operation of switch contacts (not shown) which would be provided in place of the driving element 18 and bolt 19.

Whilst the provision of an electrically conductive path between the sensors and the control means has been described, a path for transmitting non-electrical signals may be provided. For example, optical signals may be used. The transmitting means may be adapted to transmit optical signals and may include optical fibres for this purpose. In this case, the transfer elements would be arranged to pass between them an optical signal, when the keyreceiving member is in its initial position but not when the transfer elements had been separated from each other by movement of the key-receiving member. The sensing elements would be adapted to receive and pass to the transfer elements optical signals.

The lock illustrated in Fig. 1 includes coupling means for transmitting drive from the key-receiving member 15 to the driven element 18 and thence to the driven bolt 19.

This coupling means includes surfaces defining a square opening in the element 18 and a complementary projection on the key-receiving member. The coupling means is always in a condition in which it can transmit drive from the key receiving member to the bolt. The lock may be modified by the provision of coupling means which is settable in an operative condition, in which drive can be transmitted from the key-receiving member to a driven member and in an inoperative condition in which the coupling means is incapable of transmitting drive from the key-receiving member to a driven member. For example, the coupling means may comprise a dog clutch of known form.

The coupling means may be arranged to be operated by a solenoid which takes the place of the solenoid 22. It will be appreciated that, if the key-receiving member can be uncoupled from the bolt or other driven member, then it is not essential for the key-receiving member to be restrained against rotation when the key is absent. During use of the modified lock, the coupling means is in its inoperative condition when the key is inserted and information is read from the key. if the predetermined set of information is read from the key, then the control means provides to the solenoid a signal which sets the coupling means in its operative condition.

Certain parts of the modified lock shown in Fig. 2 correspond to parts hereinbefore described with reference to Fig. 1. Such corresponding parts are indicated in Fig. 2 by like reference numerals with the prefix "1" and the preceding description is deemed to apply, except for the differences hereinafter mentioned.

In the device of Fig. 2, releasable coupling means is provided for transmitting torque from the key-receiving member 115 to the driven element 118. The coupling means comprises a clutch, a first element 140 of which is formed on or is mounted on an end portion of the key-receiving member. A second element 141 of the clutch is mounted on a shaft 142 for limited sliding along the shaft towards and away from the key-receiving member. The shaft 142 is keyed to both the driven element 118 and the clutch element 141.

For moving the clutch element 141 from the inoperative position illustrated in Fig. 2, in which the clutch elements 140 and 141 are separated sufficiently to prevent the transmission of torque therebetween, there is provided a rocker 143 which can rock on an axis 144 and is provided with an over-centre spring 145 which opposes movement of the rocker from whichever of two extreme positions it occupies. The rocker may include a fork, each limb of which carries a respective roller 146 engaging in a circumferential track defined by the clutch element 141. The rollers may lie at approximately diametrically opposite positions with respect to the axis 123.

Electrically energisable means is provided for setting the rocker 143 in a selected position.

In the example illustrated, the electrically energisable means comprises two solenoids, 147 and 148 respectively, having respective armatures connected with opposite end portions of the rocker 143. When the coupling means is in the condition illustrated in Fig. 2, energisation of the solenoid 148 by a brief current pulse rocks the rocker 143 to move the clutch element 141 along the shaft 142 into engagement with the clutch element 140. The spring 145 will then maintain the coupling means in the condition to which it has been set, without continued energisation of either of the solenoids. If the solenoid 147 is then energised by a brief current pulse, the rocker will be returned to the position shown in Fig. 2.It will be understood that a single solenoid may be associated with the rocker, that solenoid being energised on successive occasions by current flowing in opposite directions to move the rocker in opposite directions. Furthermore, in a case where a single solenoid is provided, the spring 145 may be arranged always to biase the coupling means into the inoperative condition, energisation of the solenoid establishing the operative condition until energisation is discontinued.

Energisation of the or each solenoid is controlled by the control means 124 in dependence on the reading of information from the key.

The device ilustrated in Fig. 3 also comprises parts corresponding to those hereinbefore described with reference to Fig. 1. In Fig.

3, such corresponding parts are indicated by like reference numerals with the prefix "2" and the preceding description is deemed to apply to such corresponding parts, except for the differences hereinafter mentioned.

The device of Fig. 3 includes coupling means for transmitting torque from the keyreceiving member 215 to the driven element 218, which drives the bolt 219 in a known manner. The coupling means includes a friction clutch, a first element of which is constituted by or is mounted on the key-receiving member 215, and a second element 140 which is mounted on a shaft 141 and is urged along the shaft towards the key-receiving member by resilient elements 142. The shaft 141 is keyed to the driven element 218 and to the clutch element 140. The spring loading of the clutch is selected to ensure that the coupling means can transmit sufficient torque to operate the bolt 219 or other apparatus to be controlled by the key-reading device.

The coupling means further comprises a solenoid 243 having an armature 244 which can engage in an opening in the driven element 218, positively to restrain the latter against rotation about the axis 223. When the armature is so engaged, the driven element 218 cannot be turned by the key-receiving member 215, because the clutch will slip.

Energisation of the solenoid 243 is controlled by the control means 224 in accordance with information read from a key. The solenoid may be used to drive the armature in each direction, a brief pulse of current being applied to the solenoid to move the armature and the solenoid then being de-energised whilst the armature remains in the position to which it has been set. A spring-loaded detent 245 may be provided for releasably holding the armature in the position to which it has been set by the solenoid. Alternatively, the armature may be spring-loaded in one direction and moved in the opposite direction by energisation of the solenoid.

The device is illustrated in Figs. 2 and 3 may additionally comprise tumblers arranged in a known manner for restraining rotation of the key-receiving member relative to the housing and being movable by an appropriate key into respective releasing positions, where they no longer restrain rotation.

Figs. 4 and 5 illustrate an alternative device and Fig. 6 shows a key for use with the device of Figs. 4 and 5. In Figs. 4 to 6, parts corresponding to those hereinbefore described with reference to Fig. 1 are indicated by like reference numerals with the prefix "3".

The device of Figs. 4 and 5 comprises a hollow housing 314 containing a key-receiving member 315 which, when the key of Fig. 6 has been inserted into a key-slot defined by the member 315, can be turned relative to the housing about an axis 323. A number, five in the illustrated example, of pin tumblers 340 are mounted in the housing 314 in a known manner for preventing turning of the key-receiving member relative to the housing when the key is absent from the lock. The key-slot 325 has a substantially rectangular shape, in planes perpendicular to the axis 323, and extends through the entire length of the member 315.

The key 310 has at one end a handle 311 and an elongate shank 312 projecting from the handle. This shank has a generally rectangular cross-sectional shape corresponding to that of the key-slot 325. Along a minor face of the key-shank, are provided formations 341 for engaging the tumblers 340 and displacing same to respective releasing positions in a known manner.

In at least one of the major faces of the key-shank 312, there are formed openings which, in the example shown in Fig. 4, have the form of apertures 342 extending through the entire thickness of the key-shank. These openings represent information which distinguishes the key from other keys suitable for insertion into the member 315. There may be a number of keys which have the same arrangement of formations 341 but which differ from one another in respect of the information represented by openings in the major faces.

The device of Fig. 2 comprises reading means for reading information from the key 310, when the latter is inserted into the slot 325. The reading means comprises a first follower 344 which is mounted in the key-receiving member 315 adjacent to the key-slot for engaging the key and traversing a row of openings defined by the shank of the key.

The reading means further comprises signalling means 345 for providing an electrical signal representing the information which is represented by the apertures 342. There is further provided transmission means 346 for transmitting motion from the first follower 344 to the signalling means 345.

The signalling means 345 comprises a diode 347 for emitting radiation, a detector 348 for receiving that radiation and an obstructing element 349 which can move into a position between the diode and the detector where the element 349 obstructs the transmission of radiation from the diode to the detector and can be moved out of the path of radiation from the diode to the detector. In the example illustrated, the obstructing element 349 is an end portion of a lever which constitutes the transmitting means 346. This lever is mounted in a groove 350 formed in the key-receiving member 315 for pivoting relative thereto about a pivot axis 351 which is perpendicular to the lock axis 323. It will be noted that the pivot axis 351 is much nearer to the first follower 344 than to the obstructing element 349.Accordingly, the transmitting means magnifies motion transmitted from the follower to the obstructing element. The lever is biased by a spring into engagement with the follower.

The first follower 344 is guided by the keyreceiving member 315 for reciprocation along a path which is perpendicular to the axis 323 and to the length of the key-slot 325. The follower is adapted to roll on adjacent surfaces of the key-receiving member and/or on the key when the latter is inserted into and is removed from the key-slot. The preferred form of the first follower is a ball, the diameter of the ball is substantially greater than the width of each of the apertures 342. Accordingly, when one of these apertures is aligned with the ball, the ball rests on the perimeter of the aperture. The diameter of the ball is, however, sufficiently small to enable the ball to penetrate a significant distance into the aperture, for example at least one millimetre.

A second follower 352 is mounted in the member 315 in the same manner as is the follower 344. This second follower is positioned so as to be aligned with a further row of recesses (not shown) in the shank 312 of the key when the key is inserted into the slot 325. The recesses of this further row do not extend through the entire thickness of the key-shank and open at one only of the major faces of the key. With the second follower, there are associated transmitting means 353 and signalling means 354 arranged in the same manner as are the transmitting means 346 and signalling means 345.

In the example illustrated, the transmitting means 346 and 353 lie on opposite sides of the key-slot 325. However, both transmitting means could lie at the same side as the keyslot. Furthermore, additional followers, transmitting means and signalling means may be provided for reading additional information from the key. The signalling means are conveniently mounted in a separately formed holder 355 which is secured on the key-receiving member 315. This is achieved by a cap 356 which fits over the holder 355 and has resilient fingers which are a snap-fit in the keyreceiving member.

The device also includes means for providing an entry signal upon entry of a key or other instrument into the key-slot 325 and for providing a signal when the key has been fully inserted. This means comprises a further lever 357 mounted in a groove formed in the member 315 and having an end portion 358 adjacent to an end face 359 of the key-receiving member which protrudes into the key-slot 325 and is urged towards such a position by a spring. As shown, a ball is preferably interposed between the end portion 358 and the key present in the key-slot. A pair of resilient switch contacts 360, 361 is provided inside the cap 156 and an end portion of the lever 357 remote from the portion 358 is arranged for engagement with the contact 360 to move same into engagement with the contact 361, when the key is introduced into the key-slot 325.When the key is fully inserted, it engages the contact 361 and moves this into engagement with a fixed contact 367. It will be noted that the holder 355 defines a passage through which the key can pass to the contacts 360, 361.

When the device is prepared for use, the housing 314 is mounted in a body 362 in which there are provided several electrical contact shoes 363 through which electrical connection is established with the diode 347, detector 348, diode and detector of the signalling means 354 and with the contacts 360, 361 and 367. The contact shoes 363 mounted in the body engage respective resilient conductors 364 mounted on the holder 355. As shown in Fig. 3, the holder is conveniently an assembly of two separately moulded parts, one of which supports the diodes and detectors and the other of which bears electrical conductors for facilitating connection of these components with the resilient conductors 364.

There is provided a micro-processor 365 which may be mounted in the body 362 or separately therefrom. The micro-processor is connected with the contacts 363 in the body by additional (not shown). There is further provided an electrical power source 366, for example a battery of cells. This power source also may be mounted in the body 362 of separately therefrom. The micro-processor is arranged to provide an electrical output signal to an associated device (not shown) which is to be controlled by the lock. Such associated device -may be data processing apparatus or an electrically energisable release mechanism for a door latch or bolt.

The device of Fig. 2 may further comprise electrically energisable means similar to that hereinbefore described with reference to Fig. 1 and controlled by the micro-processor 365 for preventing rotation of the key-receiving member 315 relative to the housing 314 unless a predetermined set of information has been read from the key during insertion of the latter into the key-slot 325. In the example illustrated in Figs. 2 and 3, rotation of the keyreceiving member relative to the housing is restrained only by the tumblers 340, when the key is absent. When the key has been fully inserted, the key-receiving member 315 is released for rotation relative to the housing and can be turned by means of the key. As the key-receiving member is turned from its initial position, the resilient conductors 364 move away from the corresponding conductors 363 in the body 362 so that electrically conductive paths between the micro-processor 365 and the signalling means are interrupted. These paths are reinstated when the key-receiving member is turned back to its initial position.

Claims

1. A key reading device comprising a keyreceiving member defining a key slot, a housing containing the key-receiving member, reading means for reading information from a key when the key is present in the key slot, a driven member arranged for movement relative to the housing and coupling means for transmitting drive from the key-receiving member to the driven member, wherein the coupling means is settable upon reading of a predetermined set of information from the key from an inoperative condition in which the coupling means cannot transmit drive from the key-receiving member to the driven member into an operative condition in which the coupling means is capable of transmitting drive from the key-receiving member to the driven member.

2. A device according to Claim 1 wherein the coupling means is adapted to remain in one of its conditions only whilst electrical energy is supplied to the coupling means.

3. A device according to Claim 1 wherein the coupling means is settable by a brief pulse of electrical energy from a first condition to a second condition and remains in that second condition without continuous dissipation of electrical energy until the condition of the coupling means is changed once more by the application of a further pulse of electrical energy.

4. A device according to any one of Claims 1 to 3 wherein the key-receiving member is freely rotatable relative to the housing, when the key is absent.

5. A device according to any one of Claims 1 to 3 wherein the reading means is adapted to provide an electrical signal representing information read from the key and wherein the device further comprises an electronic processor for comparing said information with information stored by the device, setting of the coupling means from one of said conditions to the other condition being dependent on the result of the comparison.

6. A device according to Claim 1 wherein the coupling means is an electrically energisable coupling means which is settable from a first of its conditions to a second of its conditions upon energisation of the coupling means by a brief pulse of electrical energy and which remains in said second condition when electrical energisation of the coupling means is discontinued.