IMPROVEMENTS IN FLUID PRESSURE-OPERATED BOOSTERS FOR VEHICLE BRAKING SYSTEMS

Abstract: A booster is disclosed in which a pair of contact members (43 and 45) constructed from electrically conductive material are adapted to contact each other when the booster is in an inoperative position. When the booster is operated the contact members (43, 45) move away from each other to operate a circuit for auxiliary equipment (52), for example brake lamps and/or an anti-lock (ABS) system.

Description: IMPROVEMENTS IN FLUID PRESSURE-OPERATED BOOSTERS FOR VEHICLE BRAKING SYSTEMS This invention relates to improvements in fluid pressure-operated boosters for vehicle braking systems of the kind in which a wall is movable in a housing when subjected to fluid pressure in order to augment a brake-applying force from a pedal which, in turn, is applied to a master cylinder. A pneumatically-operated booster is disclosed in our E.P.-A-O 327 276. In this construction a valve element incorporated in a pressure-controlling valve mechanism carries a laterally extending abutment member arranged in such a way that the abutment member is adapted to actuate switch means, in turn to operate an electrical circuit, when the booster is operated. The electrical circuit may be adapted to actuate brake lamps. According to our invention, in a fluid pressure-operated booster of the kind set forth a pair of contact members constructed from electrically conductive material are adapted to contact each other when the wall is in an inoperative retracted position, relative movement of the contact members away from each other when the booster is operated being adapted to operate a circuit. Thus when the booster is operated an instant signal is produced upon separation of the contact members. Such a signal can be utilised to operate a circuit, for example to control operation of auxiliary devices, such as brake lamps and/or provide a signal for an anti-lock (ABS) system. By the use of this construction no additional, external, switch is required and existing components of the booster may be adapted to define the contact members. For example the contact members may be constituted by existing components which contact each other when the wall is in the inoperative retracted position. When the booster is of a pneumatically-operated type in which the wall is subjected to a pressure differential in order to augment the brake-applying force, and the booster is provided with an inwardly directed projection with which an abutment of a valve mechanism is adapted to co-operate to define a balanced position for the valve mechanism when the wall is in its retracted position, the abutment and the projection define the two contact members. In such a construction the only modification required to the booster is to ensure that the abutment and the projection are both constructed from electrically conductive material, and there is an electrically conductive path through the booster. In one construction the abutment comprises a laterally extending key, and the inwardly directed projection comprises an annular member swaged into the housing. In such a construction an electrical connection to the key can be made through the input rod to the booster in order to complete a circuit in respect of the key earthing out on the housing of the booster, with the movable parts of the booster normally conductably isolated from the surrounding housing by an elastomeric diaphragm, which forms a part of the movable wall, and an elastomeric seal through which a component of the valve mechanism extends rearwardly from the housing in the direction of the input rod. When the booster is operated the electrical circuit is actuated from a switching device by disengagement of the key from the housing. Normally the circuit actuated by operation of the switching device comprises brake lamps. The switching device may comprise a solid state circuit, or it may comprise a relay-operated circuit. A booster in accordance with our invention and two different switching circuits are illustrated in the accompanying drawings in which:- Figure 1 is a longitudinal section through a booster of the vacuum-suspended type; Figure 2 is a view on the large scale showing the switch in a closed position; Figure 3 shows the switch in an open position; Figure 4 is a exploded perspective view of a ignition circuit connection; Figure 5 is a section through the connection of Figure 4; Figure 6 is a layout of a solid state circuit for use with the booster of Figures 1 to 3; Figure 7 is a layout of a relay operated circuit in one position; and Figure 8 shows the circuit of Figure 5 in another position. The vacuum-suspended tandem pneumatic booster illustrated in Figure 1 of the drawings comprises a housing 1 comprising a pair of complementary shells 2 and 3, each of dished outline. A movable wall 4 divides the housing 1 into a front chamber 10 of constant pressure and a rear variable pressure chamber 11. The movable wall 4 comprises a diaphragm assembly which includes a flexible rolling diaphragm 17 of elastomeric material and a relatively rigid support plate 15. The diaphragm 17 is sealingly secured at its inner peripheral edge to the external surface of a central hub member 16 by means of a bead 20 and at its outer peripheral edge forms a seal 18 between the shells 2 and 3 where they join. The hub member 16 projects rearwardly from the shell 2, through an annular seal 22 of elastomeric material, and defines a housing for a valve mechanism 23 for controlling operation of the booster. A tie-rod 24 extends axially through the housing and is connected adjacent to axially projecting opposite end portions to the two shells 2 and 3. The tie-rod 24 is adapted for mounting the booster in an engine compartment and for providing a mounting for a master cylinder so that it can be carried direct from a bulk head through the tie-rod 24. The movable wall 4 is sealed to the tie-rod 24 by means of a sealing boot 25 which is integral with and projects forwardly from the diaphragm 17 and through a complementary opening in the support plate 15. The valve mechanism 23 comprises a pedal-operated rod 30 coupled at its inner end to a valve member 31 comprising a piston which is guided to slide in a axial bore 33 in the hub member 16. The valve member 31 is formed at its outer most end with a valve seating 34 of part-spherical outline. An annular valve head 35 at the inner end of a flexible valve member 36 is urged by means of a spring 37 abutting against a shoulder 38 on the rod 30 towards the valve head 34 and an annular valve head 39 on the hub member 31. Air is admitted into the valve device 32 through a filter 40 in the outer end of the hub member 31. A conical helical spring 41 acts as a return spring for the rod 30 and holds the valve member 36 against an abutment in the hub member 31. The valve member 31 is provided with a radial slot 42, and a key 43 fitted into the slot 42 projects radially from the valve member 31. The key 43 is so positioned as to allow free displacement of the valve member 41 with respect to the hub member 31 during operation of the booster, but to abut against the shell 2 on release of the pedal to define a balanced position for the valve mechanism 23. An electrically conductive member 45 of annular outline is swaged into the shell 2 at a step 46 in its diameter to form a stop face for engagement by the key 43, which is also of electrically conductive material, to define the balanced position for the booster. The member 45 and the key 43 comprise contact members defining a switch 47. When the shell 2 is constructed from metal, a electrical conductive path is defined through the booster from a connector 50 on the input rod 30, and through the metal piston 33, the key 43, the contact member 45, and the shell 2 to an earth connector 51 on the tie-rod 24. As illustrated in Figures 4 and 5 of the accompanying drawings the connector 50 is clamped against a shoulder 52 at a step between portions 53 and 54 of smaller and greater diameter of the input rod 30 by means of an abutment washer 55 which is a press fit onto the smaller diameter portion 53 of the rod 30. In a modification, when the shell is of plastics material, the earth connector 51 is attached directly to the contact member 45 for example by tags or strips which pass through the wall of the shell 2. Alternatively, an internal connection may be provided within the shell 2, between the contact member 45 and the tie-rod 24 itself, with the earth connector 51 secured to the tie-rod 24 as illustrated. In a construction from which the tie-rod is omitted, the internal connection may be connected to a mounting stud for the booster. The booster may be connected to a solid state electrical circuit as shown in Figure 6 which comprises a switching device. In this circuit a lead from the ignition switch of a vehicle is connected to the connector 50 on the input rod 30. An auxiliary device 56 is connected to the circuit in parallel with the booster 1, and connections between the ignition switch and the auxiliary device 56, and between the ignition switch and the booster are controlled by transistors 57 and 58 respectively. When the booster is in the balanced, inoperative, position shown in Figures 1 and 2 with the switch 47 closed, an unbroken circuit is established between the circuit and the booster, negative earth, and the auxiliary device 56 is switched off. When the booster is operated and the switch opens as shown in Figure 3, the solid state circuit automatically switches the brake lamps on. Upon release of the pedal and return of the input rod 30 to its initial, retracted, position continuity through the booster 1 is re-established and the solid state control circuit switches off the auxiliary device 56. As shown in Figures 7 and 8 the control circuit is operated by an NC relay 57. In this circuit the relay is open to isolate the auxiliary device 56 from the ignition when the switch 47 in the booster is closed, but closes when the switch 47 opens, in order to place the ignition in connection with the auxiliary device. In the construction described above the selection of the key 43 to form a movable contact member has the advantage of operating the circuit the precise instant that the booster receives a force from the pedal. As stated above, this is because the key 43 defines a balanced position for the valve mechanism when the booster is in its operative position. In consequence the key 43 is the first component of the booster to move in response to a pedal force. In view of the instant movement of the key 43, the auxiliary device 56 may comprise means which indicate the mode of the braking system, or are adapted, themselves, to control operation of the braking system itself, or both. Specifically the auxiliary device 56 may comprise brake lamps adapted to indicate operation of the system and/or an anti-lock (ABS) system adapted to control excessive deceleration of a braked wheel to avoid wheel lock.

Claims: CLAIMS 1. A fluid pressure-operated boosters for vehicle braking systems in which a wall (4) is movable in a housing (1) when subjected to fluid pressure in order to augment a brake-applying force from a pedal which, in turn, is applied to a master cylinder, characterised in that a pair of contact members (43,45) constructed from electrically conductive material are adapted to contact each other when the wall is in an inoperative retracted position, relative movement of the contact members away from each other when the booster is operated being adapted to operate a circuit. 2. A booster according to claim 1, characterised in that the contact members (43,45) are constituted by existing components which contact each other when the wall is in the inoperative retracted position. 3. A booster according to claim 1, characterised in that the booster is of a pneumatically-operated type in which the wall (4) is subjected to a pressure differential in order to augment the brake-applying force, and the booster is provided with an inwardly directed projection (45) with which an abutment (43) of a valve mechanism (23) is adapted to co-operate to define a balanced position for the valve mechanism when the wall is in its retracted position, the abutment and the projection defining the two contact members. 4. A booster according to any preceding claim, characterised in that the abutment (43) and the projection (45) are both constructed from electrically conductive material, and there is an electrically conductive path through the booster. 5. A booster according to claim 3 or claim 4, characterised in that the abutment (43) comprises a laterally extending key, and the inwardly directed projection (45) comprises an annular member swaged into the housing (1) . 6. A booster according to claim 5, characterised in that an electrical connection to the key is made through an input rod (30) to the booster in order to complete a circuit in respect of the key (43) earthing out on the housing (1) of the booster, with the movable parts of the booster normally conductably isolated from the surrounding housing by an elastomeric diaphragm (17), which forms a part of the movable wall (4), and an elastomeric seal (22) through which a component (31) of the valve mechanism (23) extends rearwardly from the housing (1) in the direction of the input rod (30) . 7. A booster according to claim 5 or claim 6, characterised in that the electrical circuit is actuated from a switching device by disengagement of the key (43) from the housing (1) when the booster is operated. 8. A booster according to claim 7, characterised in that the switching device comprises a solid state circuit comprises a relay-operated circuit. 9. A booster according to claim 7, characterised in that the switching device comprises a relay-operated circuit. 10. A booster according to any preceding claim, characterised in that an input rod (30) is adapted to be connected to the ignition circuit, and the housing (1) is adapted to be connected to earth.

Inventors: BYRNES SEAN, PHILLIPS MARK IAN, BYRNES, SEAN, PHILLIPS, MARK, IAN
Applicants: BYRNES SEAN, LUCAS IND PLC, PHILLIPS MARK IAN, BYRNES, SEAN, LUCAS INDUSTRIES PUBLIC LIMITED COMPANY, PHILLIPS, MARK, IAN
Application year: 1995
Main classification: B60T13
IPC codes: B60T13