POTTER LAURENCE JOHN (GB)
WO2002073058A1 | 2002-09-19 |
US3759147A | 1973-09-18 | |||
US3173726A | 1965-03-16 | |||
US3151525A | 1964-10-06 |
1. | A brake actuator comprising a actuating part movable between an operative position to apply a brake and an inoperative position, and a lock mechanism operable to hold the actuating part in the operative position, wherein the actuating part is of variable length. |
2. | A brake actuator according to claim 1 wherein the actuating part comprises a first part which is engagable by the lock mechanism and a second part which is carried by the first part, wherein a biasing element is disposed between the first part and the second part. |
3. | A brake actuator according to claim 2 wherein the second part is biased to an extended position relative to the first part and may be displaced from its extended position against the resistance of the biasing element. |
4. | A brake actuator according to claim 3 wherein the actuating part is movable to a service braking position, wherein the second part remains in its extended position when the brake actuator is in the service braking position, and is moved relative to the first part when the braking actuator is in the operative position. |
5. | A brake actuator according to any one of claims 2 to 4 wherein the lock mechanism comprises a latch member movable to engage the first part. |
6. | A brake actuator according to claim 5 wherein the latch member comprises a ratchet operable to engage a toothed section of the first part. |
7. | A brake actuator according to claim 5 wherein the lock mechanism comprises a plunger operable to engage an end part of the first part. |
8. | A brake actuator according to any one of claims 5 to 7 wherein the lock mechanism comprises a lock biasing element to urge the latch member out of engagement of the first part, and wherein a lock signal may be supplied to the lock mechanism to cause the latch member to engage the first part. |
9. | A brake actuator according to claim 8 wherein the lock signal comprises a pneumatic signal. |
10. | A brake actuator according to any one of claims 2 to 9 comprising a chamber having a pressure responsive element, wherein the actuating part is connected to the pressure responsive element and is movable between its operative position and inoperative position in response to the supply of fluid pressure to the chamber. |
11. | A brake actuator according to claim 10where dependent on claim 8 wherein a control valve is connected between the brake chamber and the lock mechanism, whereby a lock signal may be supplied from the brake chamber to the lock mechanism. |
12. | A brake actuator according to claim 11 wherein the control valve is operable to connect the lock mechanism either to the brake chamber or to an exhaust. |
13. | A brake actuator according to claim 12 further comprising a security valve, the valve being operable to permit or prevent fluid flow between the lock mechanism and the control valve. |
14. | A brake actuator substantially as described herein and/or with reference to the accompanying drawings. |
15. | A brake system for a vehicle, the brake system comprising a brake actuator according to any one of the preceding claims, a fluid pressure supply, and a parking brake demand control operable by a driver to cause the actuating part to move between its inoperative and operative position. |
16. | A brake system according to claim 15 where dependent directly or indirectly on claim 8 wherein operation of the parking brake demand control causes a lock signal to be transmitted to the lock mechanism. |
17. | A brake actuator according to claim 15 or claim 16 further comprising a service brake demand control operable to supply fluid pressure to the chamber of the brake actuator. |
18. | A brake actuator according to claim 17 wherein the service brake demand control is operable to supply fluid pressure at a first pressure to the chamber of the brake actuator, and wherein the parking brake demand control is operable to supply fluid pressure at a second, higher pressure to the chamber of brake actuator. |
19. | A brake system substantially as described herein and/or with reference to the accompanying drawings. |
20. | Any novel feature or novel combination of features described herein and/or in the accompanying drawings. |
For large or heavy vehicles, it is known to provide brake actuators which are operable both to provide service braking, for deceleration when a vehicle is in motion, and a parking braking, to hold the vehicle stationary.
Conventionally, such brake actuators have a chamber in which a pressure responsive member such as a diaphragm is located and in which an actuating part such as a brake rod is attached to the pressure responsive element. By supplying fluid pressure to the brake chamber, the brake rod is extended to act on the brake discs to provide braking operation. The brake rod is typically withdrawn when pressure is released from the brake chamber. For a brake actuator to operate as a parking brake, it is a requirement that the brake rod remain extended even when there is no fluid pressure in the brake chamber.
Conventionally, this is implemented by providing a gripper or other holding mechanism which is operable to grip or clamp the brake rod and hold it in its extended position even when fluid pressure is released from the brake chamber.
A problem with this system is referred to as"compliance". When a vehicle's brakes are used, the brake discs and pads typically heat up and expand. If the brake actuator is used to provide parking braking while the brake discs and pads are hot, then as the discs and pads cool and contract, the brake actuator may not be operable to hold the discs and pads in sufficiently close engagement to provide effective parking braking, with potentially undesirable results. It has been attempted to overcome this problem by applying a high force to the brake rod and hence to the brake, but this has disadvantages in terms of potential deformation of the brake and the brake
actuator. An aim of the present invention is to provide a new or improved brake actuator.
According to a first aspect of the invention, we provide a brake actuator comprising a actuating part movable between an operative position to apply a brake and an inoperative position, and a lock mechanism operable to hold the actuating part in the operative position, wherein the actuating part is of variable length.
The actuating part may comprise a first part which is engagable by the lock mechanism and a second part which is carried by the first part, wherein a biasing element is disposed between the first part and the second part.
The second part may be biased to an extended position relative to the first part and may be displaced from its extended position against the resistance of the biasing element.
The actuating part may be movable to a service braking position, wherein the second part remains in its extended position when the brake actuator is in the service braking position, and is moved relative to the first part when the braking actuator is in the operative position.
The lock mechanism may comprise a latch member movable to engage the first part.
The latch member may comprise a ratchet operable to engage a toothed section of the first part.
The lock mechanism comprises a plunger operable to engage an end part of the first part.
The latch mechanism may comprise a lock biasing element to urge the latch member out of engagement of the first part, and wherein a lock signal may be supplied to the lock mechanism to cause the latch member to engage the first part.
The lock signal may comprise a pneumatic signal.
The brake actuator may comprise a chamber having a pressure responsive element, wherein the actuating part may be connected to the pressure responsive element and is movable between its operative position and inoperative position in response to the supply of fluid pressure to the chamber.
A control valve may be connected between the brake chamber and the lock mechanism, whereby a lock signal may be supplied from the brake chamber to the lock mechanism.
The control valve may be operable to connect the lock mechanism either to the brake chamber or to an exhaust.
The brake actuator may comprise a security valve, the valve may be operable to permit or prevent fluid flow between the lock mechanism and the control valve.
According to a second aspect of the invention, we provide a brake system for a vehicle, the brake system comprising a brake actuator according to any one of the preceding claims, a fluid pressure supply, and a parking brake demand control operable by a driver to cause the actuating part to move between its inoperative and operative position.
-Operation of the parking brake demand control may cause a lock signal to be transmitted to the lock mechanism.
The brake actuator may further comprise a service brake demand control operable to supply fluid pressure to the chamber of the brake actuator.
The service brake demand control may be operable to supply fluid pressure at a first pressure to the chamber of the brake actuator, and wherein the parking brake demand control is operable to supply fluid pressure at a second, higher pressure to the chamber of brake actuator.
Some embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings wherein ; Figure 1 is a cutaway perspective view of a brake actuator embodying the present invention,
Figure 2 shows the brake actuator of Figure 1 during service braking at maximum-stroke, Figure 3 shows the brake actuator of Figure 1 during parking braking, Figure 4 shows the brake actuator of Figure 1 wherein parking braking is being released, Figure 5 is a cutaway perspective view of a further brake actuator embodying the present invention, Figure 6 shows the brake actuator of Figure 1 during service braking at maximum stroke, Figure 7a shows the brake actuator of Figure 5 when parking braking is being applied, Figure 7b shows the brake actuator of Figure 5 during parking braking with, a lock mechanism engaged, Figure 8a shows the brake actuator of Figure 5 wherein the parking braking is being released manually, Figure 8b shows the brake actuator of Figure 5 wherein the parking brake is being further released manually, Figure 9 is a diagrammatic illustration of the brake-actuator of Figure 5 provided with a control valve, Figure 10 is a diagrammatic illustration of a brake system embodying the present invention, Figure 11 is a diagrammatic illustration of the brake actuator of Figure 9 provided with a security valve, Figure 12 is a cut away perspective view of yet another brake actuator embodying the present invention, Figure 13 shows the brake actuator of Figure 12 during service braking, Figure 14 shows a brake actuator of Figure 12 during parking braking, Figure 15 shows the brake actuator of Figure 12 in a further parking braking position,
Figure 16 shows the brake actuator of Figure 12 wherein parking braking is being released manually, and Figure 17 shows a cut away perspective view of a modified brake actuator similar to that of Figure 12.
Referring now to Figures 1 to 4, a brake actuator embodying the present invention is shown generally at 10. The brake actuator 10 has a casing generally illustrated at 11 and which has a first, frusto-conical end casing part 12 and a second, intermediate casing part 13 having a generally cylindrical chamber part, 13a, a generally cylindrical lock part 13b of smaller diameter than the chamber part 13a, and a transverse wall 13c of generally annular configuration connecting the chamber part 13 a and the wall part 13b. In the present example, the first casing part 12 and second casing part 13 comprise steel. The first casing part 12 and the second casing part 13 are connected by a ring clamp 14 and define a brake chamber 15a. Located in the chamber 15a is a pressure responsive member comprising a diaphragm 16, an edge part 16a of which is clamped in the ring clamp 14 between the edge parts of the first casing part 12 and the second casing part 13. A generally cylindrical third casing part 17, in the present example comprising a die casting is provided surrounding the lock part 13b of the second casing part 13. The third casing part 17 is provided with an end wall 18. The end wall 18 is further provided with an aperture 19, in this example at a central axis thereof.
The actuator 10 comprises an actuating part generally indicated at 20 which extends through the aperture 19. The aperture 19 is provided with a seal 19a which surrounds the actuating part 20 to prevent entry of dirt through the aperture 19. The actuating part 20 is connected to the diaphragm 16 and may be extended or retracted in response to supply of pressure to the brake chamber 15. The actuating part 20 comprises a first part 21 and a second part 22 which is carried by and movable relative to the first part 21. In this embodiment, the first part 21 comprises a generally cylindrical part 2 la having an end wall 23
provided with a central aperture 24 and connected to a generally circular base part 25 which engages the diaphragm 16. The second part 22 comprises a cylindrical rod partly received in the cylindrical part 21a and passing through the aperture 24. The second part 22 is provided with a flange 26 extending part way along its length. The flange 26 is operable to engage the end wall 23 to limit the range of movement of the second part 22 relative to the first part 21.
A biasing element 27 is disposed between the first part 21 and second part 22, acting between the base part 25 and the flange 26 to urge the second part 22 to the right as shown in Figure 1 so that the flange 26 is held in abutment with the end wall 23. The biasing element 27, in this example a helical spring, is pre-compressed during assembly of the actuator 10 such that during normal service braking, the biasing element 27 resists further compression, or is further compressed only minimally, such that the first part 21 and second part 22 in effect act as a single, solid, braking rod.
A return spring 28 is provided extending between the annular wall 13c and the base part 25 to urge the base part 25 and diaphragm 16 to the left as seen in the Figures.
The first part 21 comprises a toothed surface section 29 which is engagable by a locking mechanism as shown at 30. The tooth section 29 has a plurality of teeth shaped to permit movement of the actuating part 20 to the right when the tooted teeth engage with a ratchet of the locking mechanism, but to resist movement of the actuating part 20 to the left when the teeth are engaged with the ratchet.
The locking mechanism 30 comprises a plunger 31 movable in a channel 32 defined by an outwardly extending limb 33 attached to the lock part 13b of the second casing part 13. The plunger 31 comprises a ratchet surface 34 having a plurality of teeth 35. The ratchet surface 34 is curved in such a manner as to engage the toothed surface section 29 of the first part 21. The interior of the plunger 30 defines a chamber 36 in which is located a piston 37
fixed relative to the casing. A lock bias element 38 is located in the chamber 36 above the piston 37 and acts between the piston and an upper surface of the chamber 36. A stem 39 having an exit 40 is connected to the piston 37 such that the part of the chamber 36 below the piston 30 is in flow communication with a chamber 41 to which fluid pressure may be supplied. A seal 37a extends around the edge of the piston 37, and a similarly a seal 39a provides a slidable seal between the plunger 31 and the rod 39. In general, in this description, where a seal is referred to, although in the Figures each seal is shown as an 0 ring seal, in practise any appropriate type of seal such as a lip seal or otherwise may be used as appropriate.
When it is desired to use the brake actuator 10 to provide service braking, then as shown in Figure 2, fluid pressure up to a pressure necessary to provide the desired level of braking is supplied to the brake chamber 15. This urges the diaphragm 16 to the right, extending the actuating part 20. In this method of operation, the actuating part 20 acts as a standard rigid brake rod, to apply required service braking. The pre-compression of the biasing element is such that during service braking it undergoes relative little or no further deformation. In the present example, the maximum fluid pressure supply to the chamber 15 will be about 8 bar but in normal service braking the pressure supplied will be lower than this. The strength and pre-compression of the spring 27 is selected that it will not further deform at less than about 6 bar. In the example of Figure 2, pressure supply is maintained to the chamber 41 and hence to the part of the chamber-36 below the piston 37, thus acting to maintain the plunger 31 in its retracted position as shown.
In Figure 3, the brake actuator 10 is shown with the mechanism lock 30 engaged to provide parking braking. The pressure in the chamber 41 and hence in the volume 36 under the piston 37 is reduced, thus allowing the locking element 38 to act on the plunger 31 to urge it upwards to engage with the first part 21 of the actuating part 20. Fluid pressure at a relatively high pressure, for
example at or near the maximum pressure, is supplied to the brake chamber 15, urging the diaphragm 16 to its rightmost position as seen in Figure 3. The second part 22 of the actuating part 20 will engage a brake mechanically, but its range of movement will be such limited by the position of the brakes mechanism. The biasing element 27 will therefore be compressed between the flange 26 and the base 25. The ratchet surface 34 will engage the toothed surface panel 29 of the first part 21, and the spring 38 and the shape of the teeth will enable the first part 21 to move in a rightward direction as seen in the Figure but resist movement of the first part 21 to the left as a result of the engagement of the teeth, in ratchet fashion. The fluid pressure in the brake chamber 15 may then be released, and the actuating part 20 will be prevented moving leftward from its operative, parking position to its inoperative position by virtue of the locking mechanism 30. The stored energy in the biasing element 27 will be such that as the brakes cool and contract, the second part 22 actuating part 20 will be urged to extend further relative to the first part 21, to maintain the brakes in a firm braking condition. In the present example, the range of movement of the second part 22 relative to the first part 21 is in the range of about 10 to 15 millimetres, and the distance of movement-required to maintain brakes in the braking configuration is about 8 to 10 millimetres. Thus, the biasing element 27 and the range of movement of the second part 22 of the actuating part 20 are sufficient to provide the desired compliance to accommodate cooling and contraction of the brakes, whilst the lock mechanism 30 permits pressure to be release from the brake chamber 15 whilst retaining effective parking braking as required.
To release the parking brake, as shown in Figure 4, pressure is supplied to the chamber 41, thus urging the plunger in a generally downwards direction as seen in Figure 4. However, the frictional engagement between the tooth part 34 and the teeth part 29 will be such as to prevent withdrawal of the plunger 31.
To release the parking brake, it is therefore necessary to supply further pressure
to the brake chamber 15. This will urge the actuating part 20 to the right as seen in the Figure, thus disengaging the ratchet 34 and toothed surface section part 29 sufficiently for the plunger 31 to move out of engagement with the first part 21. The pressure in the brake chamber 15 is then reduced in a controlled manner, permitting the piston 16 and the actuating part 20 to move to the left as shown in the Figure. As the actuating part 20 is relatively moved to the left, the resilient biasing part 27 will urge the flange 26 to the right relative to the first part 21 until it abuts the end wall 23. The actuating part 20 will then move as a whole to the left until it reaches the inoperative position as shown in Figure 1.
A conventional measure of the response time of a brake actuator is the time taken for the pressure supplied to the brake actuator 10 to reach 75% of its maximum value. In the present example, the strength and pre-compression of the biasing element 27 is selected such that no further compression of the biasing element 27 occurs until pressure supplied to the brake actuator 10 has reached 75% of the maximum value, thus ensuring that for practical purposes, during service braking the brake actuator 10 behaves as if the actuating part 20 was a solid rod. For example, in the example where the maximum pressure is 8 bar, the strength and pre-compression of the biasing element 27 is selected such that further compression of the biasing element 27 only incurs over 6 bar. It will therefore be apparent, that, since no further compression on the biasing element occurs below 6 bar, below this pressure the biasing element 27 will act as a solid rod.
In some circumstances, it is desirable or obligatory to be able to release a brake from the parking position manually. Referring now to Figures 5 to 8b, a second embodiment of a brake actuator is shown which is operable in like manner to the first embodiment of the invention as shown in figures 1 to 4 but which permits manual retraction of the actuating part or"caging".
Referring now to Figures 5 to 8b, a brake actuator embodying the invention is generally shown at 60. The actuator 60 operates in like manner to
the actuator 10 of Figures 1 to 4, but wherein an actuating part 61 now extends through a brake chamber 65 to provide access to the rear of the actuator for caging purposes. The brake actuator 60 comprises an actuator part 61 comprising a first part 62 and a second part 63 carried on the first part 62. A resilient biasing element 64 extends between the first part 62 and the second part 63. The actuator 60, however has a brake chamber 65 in which a pressure responsive member comprising a diaphragm 66 is located attached to an annular plate 67 attached to a forward portion of the first part 61 rather than the base part 25 as shown in the previous embodiments of the present invention. A spring 69 extends between the annular plate 67 and an end wall 65a of the_ brake chamber 65. In this example, a different lock mechanism is shown at 70, comprising a plunger 71 slidable in a channel 72 and biased to a withdrawn position by a spring 73. The plunger 71 is movable to engage the first part 62 of the actuating part 61 in response to the supply of fluid pressure to a piston 74 located at its lower part.
As shown in Figure 6, during normal braking fluid pressure is supplied to the brake chamber 65 urging the diaphragm 66 to the right and so extending the actuating part 61. As in the previous embodiment, the pre-compression of the biasing element 64 is such that the actuating part 61 operates as a conventional solid brake rod.
As shown in Figures 7a and 7b, the brake actuator 60 may be operated to supply parking braking in like manner to the brake actuator 10 of Figures 1 to 4. As shown in Figure 7a, a fluid pressure at a second, higher, pressure is supplied to the brake chamber 65, urging the diaphragm 66 and hence the annular plate 67 to their rightmost position. By virtue of the engagement of the second part 63 of the actuating part 61 with a brake mechanism at a distant short of the maximum travel of the first part 62 the actuating part 61, the second part 63 is displaced to the left with reference to the first part 62 against the resistance of the biasing element 64. When the piston is in its rightmost
position, the plunger 71 may be extended as shown in Figure 7b such that it extends behind a rear part 75 of the first part 62. When the fluid pressure is released from the brake chamber 65, the actuating part 61 will attempt to move to the left but will be prevented from doing so by the presence of the plunger 71. Frictional engagement between the first part 62 and the plunger 71 will be such that even when a fluid pressure lock signal is removed from the plunger 71, the plunger 71 and actuating part 61 will remain locked in their braking position.
As in the previous embodiment, to release the brakes, it is necessary to supply additional pressure 60 to the brake chamber 65, urging the actuating part 61 to the right sufficiently to release frictional engagement between the first part 62 and the plunger 71. The plunger 71 will then return to a retracted position as a result of the force of the spring 73, and the actuating part 61 can then be allowed to return to an inoperative position as shown in Figure 5 by controlled release of the pressure from the brake chamber 65, Caging of the actuator 60 will now be described with reference to Figures 8a and 8b. The first part 62 of the actuating part 61 is shown slidable~ in a generally cylindrical channel 76. The channel 76 has an end formation 77 having a threaded aperture 78 which in use is closed by means of a threaded plug 79.
When it is required to manually release the brakes, as shown in Figure 8a the plug 79 is withdrawn and a caging bolt 80 inserted into the aperture 78 in engagement with its internal thread. As will be apparent, the caging bolt 80 has a threaded part 81 to engage the thread of the aperture 78 and a head part 82 which may be engaged by a spanner or other suitable tool.
To release the brake, it is first necessary to release the lock mechanism 70. To do so, the caging bolt 80 is threadedly engaged in the threaded hole 78 and rotated until it engages a notch 83 provided in the first part 62. The caging bolt 80 is then rotated further in the same sense, such that it acts to urge the
actuating part 61 to the right as shown in the Figures. As discussed hereinbefore with reference to Figures 7b, this will then permit the plunger 71 to move to a retracted position under the influence of the spring 73. The actuating part 61 may then be withdrawn by rotating the caging bolt 30 in the opposite sense as shown in Figure 8b thus gradually permitting the actuating part 61 to move to the left under the influence of the biasing element 64 and spring 69. The use of a threaded caging bolt 80 ensures that the actuating part 61 is retracted in a controlled manner.
Advantageously, the lock mechanism may not need its own direct fluid pressure supply, but may be supplied with fluid from the same source as the brake chamber 64 via a control valve generally illustrated at 90 in Figure 9. As shown in Figure 9, the control valve 90 comprises a solenoid valve having an inlet 91 connected to the fluid pressure source, an outlet 92 connected to the lock mechanism 70 and an exhaust outlet 93. When fluid pressure is supplied to the brake chamber 64, the control valve 70 can be operated to provide a fluid connection between the inlet 71 and the outlet 72, thus also supplying fluid pressure to the lock mechanism 70 to provide a lock signal. When the actuating part 60 is in its parking position, the control valve 90 may be activated-to connect the outlet 92 to the exhaust 93, thus releasing the fluid pressure from the lock mechanism 70. As discussed hereinbefore, the actuating part 60 will be held in a parking position without requirement of the supply of fluid pressure to any part of the system.
A brake system embodying the present invention is shown at-Figure 10.
Referring now to Figure 10, a diagrammatic illustration of part of a braking system provided with a brake actuator as described hereinbefore is shown at 100. Only one brake actuator 60 is shown for clarity. The braking system comprises two driver-operable controls, a parking brake demand control shown at 101 and a service brake demand control shown at 102. In this example, the parking brake demand control 101 comprises a manually operable control, and
the service brake demand control 102 comprises a foot pedal in conventional manner. A first fluid pressure source is shown at 103 connected to the parking brake demand control 101. The parking brake demand control 101 is further connected to the inlet 16 of the brake actuator 10 via a double check valve 104.
To provide service braking, a second fluid pressure source 105 is connected to the foot pedal 102 and to a relay valve 106 which is also connected via a control line 107 to the foot pedal 102. The relay valve 106 is connected to the other side of the double check valve 104 and hence to the inlet 16 of the brake actuator 60.
The second fluid pressure source 105 is further connected via line 108 to a valve 109 which is connected to the double check valve 104.
The system is further provided with an electronic control 112 which is connected by line 113 to parking brake demand control 101 and on lines 114 and 115 to the valve 109 and the control valve 90.
When the vehicle is in motion and no braking is demanded, the parking brake demand control 101, valve 109 and the control valve 90 are in their positions as shown. No pressure is hence supplied from the first fluid pressure source 103 to the actuator-60. When the driver requires service braking, he actuates the brake pedal 102 in conventional manner which supplies pressure on line 107 to the relay valve 106, opening the relay valve 106 and supplying pressure from the second fluid pressure source 105 via the double check valve 104 to the actuator 60, applying the service brake of the brake actuator 60 as described hereinbefore.
When it is desired to provide parking braking, the parking brake demand control 101 is moved to a second position as shown where in line 110 and the inlet 16 are connected to the first fluid pressure source 103, the parking brake demand control in this example is a variable control, such that a selected amount of pressure may be supplied from the fluid pressure source 103 to the actuator 60, and further has an end position in which the driver selects parking
braking as required. when parking braking is selected, the movement of the parking brake and demand control 101 to the end position is detected by an electronic control unit 112. The electronic control unit 112 is then operable to operate the control valve 90 to connect the lock mechanism 70 to the source of fluid pressure supply. The electronic control unit is also operable to supply fluid pressure to the brake chamber 64, for example by operating the valve 109 to supply fluid pressure from the fluid pressure source 105 to the brake actuator 60. When the actuating part 61 has been moved to its parking position as described hereinbefore, the valve 109 and control valve 90 can be returned to their positions as shown in Figure 10 to remove all fluid pressure from the system but leaving the actuator 60 locked in its braking position.
When it is desired to release the parking brake, the electronic control unit 112 may detect movement of the parking brake demand control 101 from its end position and operate the valve 109 to supply sufficient pressure to the brake chamber 64 to release the plunger 71 on the locking mechanism as discussed hereinbefore. To provide a controlled release of the actuating part 61 to its inoperative position, the pressure in the brake chamber 64 may be controlled either by the electronic control unit 112 operating the valve 109, or by providing a suitably graduated parking brake demand control 101, so that the driver is able to gradually release pressure from the brake chamber 64 by operation of the parking park demand control 101.
Advantageously, the brake actuator 60 may be made theft resistant by adding a further solenoid as shown in Figure 11. When vehicles are stolen, it is often the case that the thieves manually release the brake by using the caging mechanism described hereinbefore. In the embodiment of Figure 7, in addition to the control valve 90 a security valve 120 is provided connected between the outlet 92 of the control solenoid and the lock mechanism 70. When it is desired to park the brake and the plunger 71 is in its extended position as shown in Figure 11, the solenoid valve 120 may be operated to prevent the release of
fluid pressure from the locking mechanism 70. By preventing the release of the fluid pressure from the locking mechanism 70, the plunger 71 will remain extended even if an attempt to manually uncage the actuator 60 is performed as described hereinbefore. To release the brakes, it is necessary to supply the appropriate signal to the security valve 120, for example by sending a release signal to an electronic control unit such as that shown at 112 in Figure 10.
Advantageously, the control valve 90 and security valve 120 may be located within the casing of the brake actuator 60, as may any appropriate control electronics such as the electronic control unit 112. As the casings of brake actuators are conventionally very robust, such a configuration will be resistant to be released by, for example, the case being drilled to release the pressure in the locking mechanism 70. The casing of the brake actuator 10,60 may, for example, comprise a die cast casing.
It will be apparent that the fluid pressure may comprise either hydraulic or pneumatic pressure as required, and the fluid pressure sources 103,105 may be a common reservoir or separate reservoirs or pumps or other sources of fluid pressure as appropriate.
A further brake actuator-embodying the present invention will now be described with reference to Figures 12 to 16. Referring now to Figure 12, a brake actuator is shown generally at 100. The brake actuator 100 comprises a casing generally shown at 101 having a cylindrical side wall 102 closed by an end wall 103. Disposed within the casing 100 is a generally cylindrical internal wall 104 generally concentric with the cylindrical wall 102 and connected thereto by a annular end wall 105a. The internal cylindrical wall 104 has an internal end wall 105b closing the inner end thereof. The casing 101 thus defines an internal volume 106.
Located in the internal volume 106 is an actuating part generally indicated at 120. The actuating part 120 comprises a rod 121 which extends through an aperture 12a in the end wall 103. The actuating part 120 further
comprises a first part 122 comprising a piston 123 connected to the piston rod 121. A spring 124 extends between the end wall 103 and the piston 123 to urge the piston 123 to the left as shown in Figure 12, in which position the piston rod 121 is withdrawn to an inoperative position.
The actuating part 120 further comprises a second part 125. The second part 125 comprises an annular piston 126 movable in an annular chamber defined by the side wall 102 and the internal cylindrical wall 104. The second part 125 further comprises a generally cylindrical element 127 connected to the annular piston 126 and extending to the right as seen in Figure 12. An outer face of the cylindrical element 127 is provided with an annular groove 128, while an inwardly directed face of the cylindrical element 127 is provided with a ratchet surface 129.
To connect the first part 122 and second part 125, the first part 122 is provided with an annular connector 130 extending leftwards as shown in Figure 12, an end part of which is provided with a lip 131 which is received in the annular channel 128 of the cylindrical element 127. Extending between the first part 122 and the second part 125 is a biasing element 132, in this example comprising a pre-compressed helical spring. As shown in Figure 12 the spring 132 acts on the piston 123 and annular piston 126 to urge the first part 122 to the right relative to the second part 125, but relative movement of the first part 123 and second part 122 is limited by the engagement of the lip 131 in the annular channel 128. Seals are provided to provide a sliding seal between the annular piston 126 and the internal face of the cylindrical 102, shown at 133 and between the cylindrical part 127 and the extension part 130 as shown at 134.
The actuator 100 further has a lock mechanism shown at 140. The lock mechanism 140 comprises two plungers 141 each having a toothed end part 142 to engage the ratchet surface 129 of the cylindrical element 127. Each plunger 141 further comprises a piston 143 movable in a common chamber 144.
Retraction springs 145 located in the chamber 144 act on the pistons 143 to urge the plungers 141 to a withdrawn position. The lock mechanism 140 is shown purely by way of example, and it will be clear that any appropriate lock mechanism may be used, for example similar to those shown in Figures 1 to 4 or 5 to 9 or otherwise as desired.
A fluid pressure inlet 146 is provided to permit fluid pressure to be supplied to the common chamber 144 to extend the respective plungers 141 such that the toothed end parts 142 engages the ratchet surface 129.
To permit caging of the actuator 100, an aperture 150 is provided in the annular end wall 105a. The aperture 150 has an internal thread 151, and in normal use in closed by a caging plug 152.
The internal cylindrical wall 104 and end wall 105b define a volume 153 which may be used for any appropriate function, most particularly for including a modulator and control electronics where appropriate.
With reference to Figure 13, to apply service braking fluid pressure is introduced into a volume 106a, that is the annular volume defined by the outer wall 102, the inner cylindrical wall 104 and the annular end wall 105a.
Because no seal is provided between the cylindrical element 127 and the cylindrical and internal wall 104, fluid pressure passes from the volume 106a to a volume 106b defined by the piston 122, annular connector 130 and end wall 105b. Fluid pressure thus acts on both the annular piston 126 and the piston 123 of the first part 122, thus urging the piston rod 121 to the right as shown in Figure 13. The spring 132 does not deform further significantly or at all in this process and thus the first part 122 and second part 125 act as if they were solidly connected.
When it is desired to apply a parking brake force, then as shown in Figure 14 the pressure in the volume 106a is increased. Because the piston rod 121 is extended to the maximum that the brake will permit, the second part 125 moves to the right relative to the first part 122, thus compressing the spring
132. The second part 125 will move to the right relative to the first part 122 until the lip 131 of the annular connector 130 abuts the left hand edge of the annular channel 128. Fluid pressure is supplied to the inlet 146 to the common chamber 144 to urge the plungers 141 to extend such that the toothed surfaces 142 engage the ratchet surface 129 of the cylindrical element 127. The pressure in the volume 106au may then be released and the teeth of the toothed surfaces 142 and ratchet surface 129, are shaped such that they will frictionally engage and prevent movement of the actuating part 120 to the left as shown. As illustrated in Figure 15, as the brake cited on by the piston rod 121 cools, the piston rod 121 will be urged to the right by the spring 132, thus-maintaining the vehicle brake in a braked condition. The maximum travel of the piston rod 121 is shown in Figure 15, where the piston 123 abuts the inner face of the end wall 103 and/or the lip 131 of the annular connector 130 abuts the right hand edge of the annular channel 128.
This embodiment is advantageous for applications where the maximum force required to be applied by the brake actuator 100 when applying parking braking is less than the maximum force available during service braking. For example, the maximum force available during service braking might be about 13 kN and it might be desirable only to apply a parking brake force of 6 kN.
This would be appropriate where, for example, a parking brake is supplied on more than 2 wheels of a vehicle and is advantageous in that any deformation of the brake and brake actuator 100 as a result of a high parking brake force is reduced. The brake actuator 100 of Figure 12 achieves this in that supply of fluid pressure to provide service braking acts not only on the annular piston 126 but also on the piston 123 of the first part 122. Fluid pressure to provide service braking is thus at least in part applied directly through the first part 123 to the piston rod 121, rather than all of the force being applied through the spring 132 in contrast with the embodiments described hereinbefore where all braking force is applied through the respective biasing element. Thus, the
strength and pre-compression of the spring 132 may be selected to provide the desired braking force whilst undergoing little or no additional compression during most normal service braking.
To release the brake actuator 100 from its pOsitioIl providing parlçing braking as shown in Figure 14 or 15, in like manner to previous embodiments fluid pressure is supplied to the volume 106a. This will urge the second part 125 slightly to the right as shown the Figures, this releasing the frictional engagement between the toothed surface parts 142 and the ratchet surface 129 and allowing the plungers 141 to retract under the influence of springs 145.
The pressure in the chamber 106a may then be reduced allowing the actuating part 120 to move to the left as shown in the Figures to return to the inoperative position as shown in Figure 12.
To permit caging, that is to release the brake actuator 100 from its parking braking position as shown in the Figures 14 and 15 when no fluid pressure supply is present, a caging bolt 153 may be used as shown in Figure 16. The caging plug 52 is removed from the aperture 150 and a caging bolt 153 is introduced in the aperture 150. The caging bolt 153 has a threaded shank 154 which engages the internal thread 151-of the aperture 150., The bolt 153 additionally has a head 155 which may be engaged by an appropriate tool. To release the brake actuator 100, the caging bolt 153 is rotated such that by virtue of engagement of the threads 151,154 the bolt moves to the right and acts on the annular piston 126. The caging bolt 153 will urge the piston 126 to the right sufficiently to reduce the friction between the toothed surfaces 142, and the ratchet surface 129, allowing the pistons 141 to retract under the influence of the springs 145. The caging bolt 153 can then be rotated in the opposite sense, such that the bolt 153 moves to the left as shown in Figure 16, permitting the actuating part 120 to move to the left as shown in Figure 16 and returning it to its inoperative position as shown in Figure 12.
It might be envisaged that under some circumstances it would be desirable to apply different pressures to the first part 122 and second part 125, and a modification to permit this is shown in Figure 17. As shown in Figure 17, a braking actuator 100'is shown which is the same as that shown in Figure 12 except that a further seal 160 is provided to provide a sliding seal between the annular piston 126 and the inner cylindrical wall 104. The provision of this seal thus separates the volume 106a from the volume 106b which acts on the piston 1 of the first part 123. Thus, the pressure supplied to volumes 106a, 106b may be varied independently to supply braking characteristics as desired.
The braking actuator 100'as shown in Figure 7b, permits the pressure supply to the brake actuator 100'and the braking force generated to be varied as desired. For example, in the example where the parking brake force is being applied, in the embodiment of Figures 12 to 16 pressure is supplied to both volumes 106a and 106b and thus the pressure supplied to the brake actuator 100 and thus the force applied by the brake actuator 100 is higher than that necessary to apply the parking brake. When the lock mechanism 140 is operated to hold the brake actuator 100 in its parked position, the force applied by the brake actuator 100 will fall to that supplied by compression of the spring 132. Thus, when parking braking is applied by the brake actuator 100, a relatively high transient force is applied during application of the parking brake.
Under some circumstances, this high force may be undesirable, and may be avoided in the brake actuator 100'by only supplying pressure to volume 106a to apply the parking brake. This further has the advantage that when parking braking is being supplied, a smaller volume of air is required to be supplied to the brake actuator 100'. A further potential advantage of the brake actuator 100'is that during braking, it is possible to select which volume 106a 106b to supply pressure to to provide finer control over the braking force applied. For example, where pressure is supplied to one chamber, a larger pressure over a
smaller area may be supplied to permit fmer control over the braking force generated.
Although the brake system of Figure 10 has been shown with a brake actuator 60 having a control valve 90 as shown in Figure 9, it will be apparent that a brake system may similarly be used with the actuator 10 or the actuator 100 as described hereinbefore as appropriate and as desired.
In the present specification"comprises"means"includes or consists of' and"comprising"means"including or consisting of'.
The features disclosed in the foregoing description, or the following claims or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.