REFERENCE TO RELATED APPLICATIONS
This application claims priority to United Kingdom Patent Application 0410838.7 filed on May 14, 2004.
BACKGROUND OF THE INVENTION
The present invention relates generally to a parking brake assembly. More particularly, the present invention relates to a parking brake assembly for an air actuated disc brake.
Air actuated disc brakes are typically used in heavy vehicle applications, such as for braking trucks or buses. Such brakes typically operate as follows. Pressurized air is introduced behind a diaphragm of an air chamber, which generates a load in a push rod. The push rod in turn applies a force to a pivotably mounted operating shaft, causing it to rotate. By means of an eccentric action, an amplified force is applied to one or more adjustable tappet assemblies that advance a brake pad towards a brake rotor. This causes a clamping effect on the brake rotor, thereby retarding rotation of the brake rotor due to friction generated between the brake pad in contact with the tappet assembly and a further brake pad mounted on an opposite face of the brake rotor.
To comply with safety legislation, when a vehicle fitted with air actuated brakes is parked, the brakes must be applied mechanically without reliance on the pressurized air to overcome the risk of the brake force being removed due to accidental leakage of the air, with obvious consequences.
Conventionally, in air actuated brakes of the type described above, the parking brake function is achieved by the addition of a large spring to the rear of the air chamber that generates a load on the push rod when no pressurized air is present.
The addition of the spring, together with an additional air chamber required to release the parking brake that is mounted behind the air chamber for the application of service brakes, adds to the bulk, weight and expense of the vehicle braking system.
The present invention seeks to overcome, or at least mitigate, the problems of the prior art.
The present invention provides a parking brake assembly for an air actuated disc brake including a pneumatic actuator including a push rod for applying a brake force to brake pads. The push rod is generally translatable between a rest position at which the brake force is not applied and an actuated position at which a brake force is applied. The parking brake assembly includes a clamp assembly operable to retain the push rod in the actuated position and thereby apply the parking brake. The clamp assembly is configured for fitment within a caliper housing of the brake.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described, by way of example only, with reference to the accompanying drawings in which:
FIG. 1 shows a cross section of a vehicle brake according to the present invention in an unactuated, or brakes off, position;
FIG. 2 shows vehicle brake of FIG. 1 with the parking brake applied;
FIG. 3 shows an isometric view of certain parts of the vehicle brake of FIG. 1;
FIG. 4 shows a view of FIG. 3 taken in the direction of arrow A;
FIG. 5 shows an enlarged cross section view of a collet of FIG. 2 in isolation;
FIG. 6 shows an enlarged view of part of FIG. 1;
FIG. 7 shows a second embodiment of a clamp arrangement for a parking brake according to the present invention;
FIG. 8 shows a third embodiment of a clamp arrangement for a parking brake according to the present invention; and
FIG. 9 is a further isometric view of certain parts of the vehicle brake of FIG. 1; and
FIG. 10 is a further isometric view of certain parts of the vehicle brake of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIGS. 1 to 6 show parts of a brake 8 which is operable in a service mode, i.e., is operable to retard an associated vehicle when the vehicle is being used on public highways, etc. The brake 8 can also be operated as a parking brake, i.e., the parking brake can be applied, and the vehicle operator can then leave the vehicle.
Service operation of the brake 8 is conventional and well known. However, in summary, the brake 8 is of the type including a caliper housing that straddles a disc or rotor (not shown). The caliper is typically mounted on an axle of the vehicle to be braked (not shown) and is slideable longitudinally relative to the axle. The rotor is mounted for rotation together with a wheel of the vehicle. The brake 8 is actuated by the introduction of pressurized air (represented by arrows B1) behind a diaphragm 9 of an air chamber 15 (only shown in FIG. 2). The diaphragm 9 includes sealing features (not shown) sealing between the diaphragm 9 and the air chamber 15 and is connected to a push rod 11 that cooperates with a socket 17 at a radially outer end of an operating shaft or “op-shaft” 14 of the brake 8. The op-shaft 14 is generally “T” shaped. The lower end (when viewing FIG. 1) of the op-shaft 14 has at its opposite ends arcuate bearing surfaces 42 seated in bearing seats 43 arranged at the lower end of an inner housing part 16 of the caliper to permit the op-shaft 14 to rotate about an axis. The lower end of the op-shaft 14 is further provided with pockets (not shown) positioned eccentric to the op-shaft axis of rotation which, upon rotation, cause a force to be transmitted to a pair of spaced adjustable tappet assemblies. The tappet assemblies apply the input load from the actuator to a rear face of an inner brake pad (not shown), thus pressing the friction material of the brake pad into frictional engagement with the rotor.
A reaction force is generated through the frictional engagement between the rotor and the inner brake pad that is fed back through the tappet assemblies and the op-shaft 14 that is supported by the inner housing part 16. The inner housing part 16 is secured to an outer housing part (not shown). Thus, the applied force generated by movement of the op-shaft 14 is ultimately transmitted by reaction means to the outer housing part, which in turn presses an outer brake pad (not shown) into frictional engagement with the rotor. Therefore, upon movement of the op-shaft 14 in an application direction APP (see FIG. 1), the rotor is clamped between the inner and outer brake pads to generate a braking force for service braking the vehicle under control of the applied input movement from the push rod 11. Release of air pressure from the air chamber 15 causes the push rod 11 to move in a release direction RLS (see FIG. 1) under the action of a return spring (not shown).
The tappet assemblies are adjustable to compensate for wear of the friction material of the brake pads. For a further explanation of the service operation of the brake 8, the reader is referred to U.S. Pat. No. 6,435,319 which shows a similar brake and the service operation thereof.
As mentioned above, the brake 8 can also be used as a parking brake, and FIGS. 3 and 9 show the major components of the parking brake assembly. Except for the push rod 11 and the diaphragm 9, all other components shown in FIG. 3 are primarily aimed at providing a parking brake function. These components include a collet 20 (also known as a wedgeable element), a clamp housing 22, a clamp housing mount 24 and 26, a release lever 28, a release actuator 30, a release lever pivot mount 32 and a spring 34 (best seen in FIG. 1).
The collet 20 (best seen in FIG. 5) includes a generally cylindrical body portion 46. Projections 48 (in this case six in total) depend from the cylindrical body portion 46. The cylindrical body portion 46 and the projections 48 have a common internal diameter 47. Each projection 48 is separated from the adjacent projection by a slit 49. Each projection 48 includes a radially outer wedge surface 50 which is orientated at an angle B (in this case approximately 6 degrees) relative to an axis C of the cylindrical body portion 46. The slits 49 allow each projection 48 to move radially inwardly to frictionally engage the push rod 11, as will be further described below. A stepped flange 50A projects generally radially from an end of the cylindrical body portion 46 remote from the projections 48. The stepped flange 50A includes a recess 51 and a release surface 52. The collet 20 is slideably mounted on the push rod 11 such that the axis C is substantially coincident with an axis D of the push rod 11.
The clamp housing 22 includes a generally cylindrical body 54 having four “flats” 56, as shown in FIG. 4. Cylindrical bosses 58 project from two opposing flats 56, also known as lugs. An inner bore 59 of the generally cylindrical body 54 is machined with a profile that compliments the radially outer profile of the cylindrical body portion 46 and the wedge surface 50 of the collet 20. In particular, a region 60 of the inner bore 59 is conical and is, angled relative to an axis of the inner bore 59 at an angle equivalent to angle B. As is best seen in FIG. 6, when assembled, the region 60 faces the wedge surface 50.
A spring 34 is mounted in the recess 51 which acts on and biases the collet 20 to the left when viewing FIG. 6 and reacts against the clamp housing 22.
The spring force is sufficient to move the collet 20 to the left relative to the clamp housing 22, thereby wedging the projections 48 between the region 60 of the clamp housing 22 and the push rod 11 when the parking brake is applied, as will be further described below. Thus, it will be appreciated that the collet 20 and the clamp housing 22 together provide a clamp assembly.
The clamp housing mounts 24 and 26 are secured to the inner housing part 16 and each includes a slot 62 within which a corresponding cylindrical boss 58 sits. The slots 62 allow vertical movement (when considering FIG. 3 i.e., movement in a lateral direction of the push rod 11) of the cylindrical bosses 58, and hence the clamp housing 22, but prevent axial movement (when considering the axis of the push rod 11) of the clamp housing 22.
As is best seen in FIG. 4, two flats 56 sit snugly between the clamp housing mounts 24 and 26. The interaction between the flats 56 and the inner surfaces of the clamp housing mounts 24 and 26 prevent rotation of the clamp housing 22 in a clockwise or counter-clockwise direction when viewing FIG. 4. The cylindrical bosses 58 have an axis E, and thus the clamp housing 22 can rotate about the axis E during operation of the brake. As will be appreciated from FIGS. 1 and 2, a socket 17 moves in an arc as the op-shaft 14 rotates during brake operation. However, the diaphragm 9 moves substantially in a straight line. Thus, as the brake moves from the position shown in FIG. 1 to the position shown in FIG. 2, the collet 20 is initially raised and then lowered and furthermore is caused to tip about the axis E. This raising and lowering is accommodated by the slot 62 (as mentioned above), and the tipping is accommodated by the slight rotation of the clamp housing 22 about the external surface of the cylindrical bosses 58.
The release lever 28 is pivotally mounted via a pin 64 about a pivot axis F. Opposing ends of the pin 64 are secured in corresponding release lever pivot mounts 32. The upper end of the release lever 28 is forked and includes fork tines 66 (only one of which is shown in FIG. 3) on either side of the push rod 11. The ends of the fork tines 66 engage an adjacent region of the release surface 52. The lower portion of the release lever 28 is connected to the release actuator 30. In this case, the release actuator 30 is an air operable actuator in which air is supplied to power the actuator to an actuated condition. To return the air actuator to a rest condition, air is vented and an internal return spring (not shown) returns the actuator to the rest condition. Alternative actuators could be used, such as air motors, electric motors or linear electric actuators.
Operation of the release actuator 30 causes the lower end of the release lever 28 to move in the direction of arrow G (see FIGS. 1, 3 and 9), thereby causing the fork tines 66 to move the collet 20 to the right when viewing FIG. 1.
As can be seen from FIGS. 1, 2, 9 and 10, the release actuator 30 is located near a rear face 70 and base walls 72 of the inner housing part 16 substantially in alignment with a vertical centerline of the caliper and directly beneath push rod 11. To accommodate the release actuator 30 within the inner housing part 16, a projection 74 is provided in a lower portion of the rear face 70 where it does not interfere with the positioning of the air chamber 15 above the projection on the rear face 70.
Furthermore, as is most apparent from FIGS. 1, 2 and 9, the positioning of the release actuator 30 enables it to extend under the op-shaft 14 in a recess 76 between arcuate bearing surfaces 42, thereby optimizing the packaging of the release actuator 30 within the brake 8.
As previously mentioned, the brake 8 can be operated in a service mode or in a parking brake mode. When operated in a service mode, clearly the parking brake is not applied. Under these circumstances, the release actuator 30 is powered to an actuated condition to move the lower end of the release lever 28 to the left when viewing FIG. 1. This in turn causes the fork tines 66 to move the collet 20 to the right when viewing FIG. 1, thereby ensuring that there is no wedging action between the collet 20, the push rod 11 and the clamp housing 22. As such, the push rod 11 is free to slide within the collet 20. Thus, when it is required to apply the service brake, air is admitted into the air chamber 15, thereby forcing the diaphragm 9 and the push rod 11 to the right in an application direction APP, causing the op-shaft 14 to rotate and apply the brake. When the air is released from the air chamber 15, the brake 8 is free to return to the position shown in FIG. 1. In particular, the clamp arrangement does not restrict movement of the push rod 11 in the release direction RLS.
The release actuator 30 is deactivated when required to apply the parking brake, i.e., air is vented from the actuator, thereby allowing the lower portion of the release lever 28 to move to the right when viewing FIG. 2 and hence the fork tines 66 will move to the left when viewing FIG. 2. This in turn allows the spring 34 to force the collet 20 to the left when viewing FIG. 2. However, such leftward movement of the collet 20 is limited as the projections 48 are progressively wedged between the region 60 and the push rod 11, thereby clamping the push rod 11.
The wedging action prevents the push rod 11 from moving to the left when viewing FIG. 2. Thus, one method of applying the parking brake is to initially apply the service brake to pressurize the air chamber 15 such that the op-shaft 14 rotates and the brake 8 is applied. The release actuator can then be deactivated, causing the collet 20 to wedge between the clamp housing 22 and the push rod 11. Upon subsequent release of the service brake, air pressure B1 will be released, but the push rod 11 will remain in the position shown in FIG. 2 by virtue of it being clamped by the collet 20 and clamp housing 22.
The wedging action of the collet 20 prevents the push rod 11 moving to the left (in the release direction RLS) as shown in FIG. 2, but does not prevent the push rod 11 from moving to the right (in the application direction APP) as shown in FIG. 2.
Thus, starting from a position shown in FIG. 1, an alternative way of applying the parking brake is to initially deactivate the release actuator 30, thereby causing the collet 20 to wedge onto the push rod 11 with the brakes in the off condition. Subsequent application of the service brake causes the push rod 11 to move to the right (in the application direction APP) since the wedging action will be ineffective when the push rod 11 moves in this direction. However, once the service brake has been applied to apply the brakes 8, the push rod 11 will not move to the left (in the release direction RLS) when the service brake is released since it will be held in position by the clamp arrangement because the wedging action is effective when the push rod 11 attempts to move to the left. Once the release actuator 30 has been deactivated, the clamp arrangement is self engaging and self clamps the push rod 11 to apply the parking brake.
As mentioned above, the collet 20 has a radially outer wedge surface 50 (a wedgeable element wedge surface) which engages with a region 60 (a clamp housing wedge surface) of the clamp housing 22. In further embodiments, it is possible to provide a wedging action by providing a wedge surface on just the collet 20 and without having a wedge surface on the clamp housing 22.
FIG. 7 shows a part cross section view of a clamp arrangement including a wedgeable element 120 with a wedge surface 150 similar to the wedge surface 50. The clamp housing 122 does not include a wedge surface equivalent to the region 60 of the clamp housing 22. In a yet further alternative embodiment, it is also possible to apply a wedging action by having a wedging surface on just the clamp housing without having a wedging surface on the collet 20. See in particular FIG. 8, which is a part cross section view of a clamp arrangement having a clamp housing 222 with a wedged surface 260 equivalent to the region 60, but which has a wedgeable element 220 which does not include a wedge surface equivalent to wedge surface 50 of the collet 20. For this reason, the term wedgeable element as used in the present application is not restricted to an element having a wedge surface, but rather it refers to the ability of the element to be wedged. Therefore, the wedgeable element 220 does not have to include a wedge shaped surface.
The foregoing description is only exemplary of the principles of the invention. Many modifications and variations are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than using the example embodiments which have been specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.
Patent Application
20050252737
