Patent Application
20100082213
This application claims priority to Great Britain Patent Application No. GB 0817229.8 filed Sep. 19, 2008.
The present invention relates to a control system and a method for a parking brake mechanism. More particularly, the present invention relates to a control system and method for an electrically actuated parking brake mechanism for disc brakes or drum brakes having an air actuated service brake.
Various proposals have been put forward for utilizing an electric motor to apply parking brakes, both on light passenger vehicles utilizing hydraulic brake systems and heavy commercial vehicles that use air actuated service brakes.
Electric parking brakes have gone into commercial production for certain models of passenger cars, in which they essentially replace a cable linkage between a handbrake lever located in the passenger compartment and a disc or drum brake mounted in proximity to rear wheels of a vehicle.
By contrast, despite various proposals being put forward for heavy vehicle brakes that are intended to replace a conventional spring brake on commercial vehicles, to the knowledge of the applicants, no electric parking brake has yet entered volume production for commercial vehicles. Conventional parking brake cylinders include a spring acting in a brake-on direction connected to a piston and a push rod that is normally held in a parking brake-off position by pressurized air, but in which the air is vented to apply the parking brake. One disadvantage of spring parking brakes is their size. A second disadvantage is their inability to finely control a parking brake clamp force that they apply. Additionally, a failure in an air supply may cause the parking brake cylinders to become applied with no way for this to be controlled by the driver.
A number of hurdles need to be overcome to provide a practical electric parking brake that is specific to commercial vehicles. It is believed these have prevented adoption of this technology to date. One problem is that disc brakes used on commercial vehicles have significantly thicker discs and pads compared to light passenger vehicles to enable the brakes to have a suitably long service life despite the increased energy that is dissipated during braking due to their increased vehicle weight. As a result, when a heavy commercial vehicle is parked when the brakes are hot, an appreciable shrinkage of those brake components, in particular the brake disc and the brake pads, will occur. If this is not accounted for in some way by a parking brake mechanism, the clamp load applied by the parking brake will reduce as the brake components cool and contract, and there is a reduced clamp load exerted by the brake pads on the brake disc that may cause the vehicle to roll away.
If used in conjunction with a drum brake on the other hand, the drum brake may contract as it cools and the reduction of the drum diameter may damage components within the brake due to a lack of the compliance of such mechanisms
Such a problem does not arise with conventional spring parking brake cylinders because the spring can extend by a certain amount with only a slight drop in clamp load.
However, parking brakes such as those disclosed in U.S. Pat. No. 6,851,761 (Knorr-Bremse) that are electrically powered are not provided with a similar resilient, extensible component, and it is therefore necessary either to apply an initial excess parking brake force to account for this shrinkage or to re-apply the parking brake once a certain amount of time has lapsed to bring the clamp load back up to the amount required. A control sequence for the latter approach is discussed in U.S. Pat. No. 6,851,761. Neither of these solutions is particularly satisfactory, since in the former case an excess stress is placed on the brake components that may shorten their life and in the latter scenario, there is a danger that if electrical power is not available to drive the parking brake motor once the vehicle has been parked, a re-application of the parking brake will not be achieved and there is a risk that the vehicle will roll away.
A further problem with known electric parking brakes relates to their speed of application. In order to produce a parking brake having a sufficiently compact size, it is usual to propose the use of a relatively small electric motor and a reduction gear arrangement that results in a relatively low speed of application for the parking brake. In U.S. Pat. No. 6,851,761, a two-speed application arrangement is proposed, in order to attempt to overcome this problem. However, such arrangements are relatively complex.
The present invention seeks to overcome, or at least mitigate, the problems of the prior art.
A first aspect of the present invention relates to a method of applying a parking brake mechanism for a foundation brake. The parking brake mechanism incorporates an electric actuator, an extensible device drivably connected to the electric actuator, and a resilient device arranged to act on the extensible device and maintain a desired level of force to be applied by the parking brake mechanism in the event of contraction of components of the foundation brake.
The method includes the steps of signaling application of a service brake actuator to apply a brake, signaling driving of a first electric actuator to cause the extensible device to be able to retain the foundation brake in the brake applied position achieved by the service brake actuator, signaling the release of the service brake actuator, signaling driving of a second electric actuator to compress the resilient element, monitoring a characteristic of brake mechanism to determine if a desired force has been applied by the parking brake mechanism, and signaling driving of the electric motor to stop once the desired force has been reached.
A second aspect of the present invention provides a control system for a parking brake mechanism for a foundation brake. The parking brake mechanism incorporates an electric actuator, an extensible device drivably connected to the actuator, and a resilient device arranged to act on the extensible device and maintain a desired level of force to be applied by the parking brake mechanism in the event of contraction of components of an associated foundation brake. The control system is configured to signal the following sequence of operations to apply the brake:
a) application of an associated service brake actuator to apply the brake,
b) driving of a first electric actuator to bring the extensible device up to a point at which it retains the parking brake in the braked position achieved by the service brake actuator,
c) the release of the service brake actuator,
d) the driving of a second electric actuator to compress the resilient device,
e) monitoring a characteristic of the brake to determine if a desired force has been applied by the parking brake, and
f) driving of the electric actuator to stop once a desired force has been reached.
A third aspect of the present invention relates to a method of disengaging a parking brake mechanism for a foundation brake from a parking brake applied state. The parking brake mechanism incorporates an electric actuator, an extensible device drivably connected to the actuator, and a resilient device arranged to act on the extensible device and maintain a desired level of force to be applied by the parking brake mechanism in the event of contraction of components of the foundation brake. The method includes the steps of signaling application of a service brake actuator to at least partially remove the load on the parking brake mechanism, signaling drive of the electric actuator such that the extensible device is no longer able to retain the foundation brake in the brake applied position, and signaling release of the service brake actuator.
A fourth aspect of the present invention provides a control system for a parking brake mechanism configured to signal the disengaging of a parking brake mechanism in accordance with the method of the above paragraph.
A fifth aspect of the present invention provides a method of applying a parking brake mechanism for a foundation brake in the event of failure of an associated service brake actuator. The parking brake mechanism incorporates an electric actuator, an extensible device drivably connected to the actuator, and a resilient device arranged to act on the extensible device and maintain a desired level of force to be applied by the parking brake mechanism in the event of contraction of components of the foundation brake. The method includes the steps of detecting a failure of an associated service brake actuator, signaling driving of an electric actuator to cause the extensible device to be able to retain the foundation brake in the brake applied position and to compress the resilient element, monitoring a characteristic of the brake to determine if a desired force has been applied by the parking brake mechanism, and signaling driving of an electric motor to stop once the desired force has been reached.
A sixth aspect of the present invention provides a control system for a parking brake mechanism configured to signal application of a parking brake mechanism in accordance with the method of the preceding paragraph.
Embodiments of the present invention will be described, by way of example only, with reference to the accompanying drawings, in which:
With reference to
The term “inboard” as used below denotes a direction towards a centerline of a vehicle to which the brake is fitted, whereas “outboard” refers to a direction away from the centerline.
The first shell 12 and the second shell 16 are held together by a clamp band arrangement 20 that engages corresponding lips on the shells 12 and 16, as is well known. In this embodiment, the clamp band arrangement 20 also acts to sandwich a flexible diaphragm (not shown) between the lips and which is also connected to a service brake push rod 22 so as to split the service brake chamber 14 into a non-pressurized region at an outboard side of the chamber (a side incorporating a free end of the push rod) as illustrated in
The service brake push rod 22 terminates at its inboard end with a pressure distribution disc 30 and a central recess 32 to releasably accommodate a parking brake push rod 34 of the parking brake mechanism 18, as discussed in more detail below.
The parking brake mechanism 18 includes a stepped piston 36 that is sealed in relation to the second shell 16 at its axially outboard end and may slide axially relative thereto. At its inboard end, it is also sealed relative to a circular lip 38 that projects from an inboard end wall 40 of the second shell 16 in an outboard direction. The stepped piston 36 therefore also separates the parking brake mechanism 18 into a pressurized region 42 that is contiguous with the pressurized region 26 of the service brake chamber, and an unpressurized toroidal region 44. The stepped piston 36 is prevented from sliding outboard beyond a predetermined position by stops 37 (see
The unpressurized region 44 houses a resilient device in the form of a helical spring 46 that is supported at its inboard end by the inboard end wall 40 and its outboard end by the stepped piston 36. The helical spring 46 is designed such that it is preloaded by a predetermined amount when resting against the stops 37.
An electric motor 48 is provided in a separate housing 50 to the side of the second shell 16. The electric motor 48 is connected to a drive shaft that extends down the center of the parking brake mechanism 18 via reduction gears 54a, 54b and 54c. A cover plate 55 is provided on the inboard end of the second shell 16 and the electric motor housing 50 to protect the reduction gears 54a, 54b and 54c. The outboard end of the drive shaft 52 drives an extensible device and is splined such that it is rotationally fixed to an inner bayonet member 56 of the extensible device, but enables the inner bayonet member 56 to slide axially with respect to the drive shaft 52.
As can be seen more clearly from the exploded isometric view of
An outer bayonet sleeve 66 is provided with three axially extending channels 68 (only one visible in the cut-away of
Referring back to
The outboard threaded portion 64 of the inner bayonet member 56 locates within an internally threaded bore 76 of the parking brake push rod 34. Consequently, rotation of the drive shaft 52 and the inner bayonet member 56 results in the extension and retraction of the parking brake push rod 34 with respect to the remainder of the parking brake mechanism 18. A pair of axially extending slots 78 are provided at opposed locations on the outer face of the parking brake push rod 34 and are arranged to be engaged by a corresponding pair of prongs (not shown) on the circular leaf spring 74 such that the parking brake push rod 34 may move axially, but not rotate, with respect to the remainder of the brake actuator 10.
The parking brake push rod 34 terminates at its outboard end in a spherical ball-shaped head 80 that is dimensioned to fit within the central recess 32 of the pressure distribution disc 30 of the service brake push rod 22. A spring loaded ball-bearing 82 is mounted within the spherical ball-shaped head 80 and sits within a circumferentially extending depression 84 within the recess 32. As a result, a pre-determined force is required to cause the ball-bearing 82 to retract and for the parking brake push rod 34 to separate from the service brake push rod 22.
With reference to
In normal service brake operations, the compressed air is allowed to vent, and a return spring (not shown) causes the service brake push rod 22 to return to the rest position of
Referring to
In this embodiment, a parking brake hand control 320 located in a vehicle cab or a passenger compartment incorporates an ECU 325 (typically a microprocessor controller) programmed to interpret the demand signal, along with other vehicle parameters, such as its weight, angle of slope and brake status and send appropriate control signals to EBS modules 330 provided for each brake or an EBS twin module 330 for two brakes on the same axle and directly to the parking brake mechanism(s) 18. In this embodiment, communication takes place via a controller area network (CAN) bus 324 (dotted lines), but any other suitable communication method may be used in other embodiments. Each EBS module 330 also receives a compressed air supply 326 via air lines 328 (solid lines) and includes appropriate electronics and solenoid valves to control the functioning of its associated service brake mechanism(s) 14.
The electric brake control system also includes an electric brake system electronic control unit (EBS-ECU) 322. This controls the service brake function of the braking system.
With reference to
It is then necessary for the ECU 325 to signal the electric motor 48 to drive at step 416 via the reduction gears 54a, 54b, and 54c for the next stage of parking brake application, as shown in
With reference to
It will thus be appreciated with reference to
As is often the case, the parking brake is applied when the brake disc 310 and other brake components are hot, due to energy dissipated as heat by previous service brake applications as the heavy vehicle is operated. As the brake disc and other brake components cool back to ambient temperature while the heavy vehicle is parked, it is inevitable that the brake disc and the brake pads contract. In order to prevent the heavy vehicle from rolling away if parked on a slope, it is necessary to maintain a certain level of clamp load despite this contraction.
Referring to
Alternatively, if the brake disc and other brake components are cold (i.e., at ambient temperature) when the parking brake is applied, then at step 428 the helical spring 46 remains compressed.
In
With reference to
In
Therefore, it will be appreciated that the use of the helical spring 46 means that contraction of the brake disc and other brake components may be compensated for while the vehicle is standing with the parking brake applied. As a result, on the one hand the risk of the vehicle rolling away due to a reduced clamp load is minimized, while at the same time excess loadings do not need to be applied to the brake to account for such contractions and therefore fatigue on components may be reduced. Additionally, the use of the bayonet components enables a rapid application and release of the parking brake in normal circumstances when compressed air is available while enabling a relatively small, low power parking brake motor to be used, and still having a back-up of solely electrical parking in the event of failure of the air supply. Finally, by locating the motor external the main body of the cylinder, it may be orientated at any desired angle with respect to the brake caliper to ensure that its packaging can be optimized for wide variety of vehicle configurations.
The actuator 110 of
The ball-shaped head 80 at the outboard end of the parking brake push rod 34 of the first embodiment is replaced by a load spreading plate 180 that is magnetized such that it is normally held in contact with the pressure distribution disc 130 of the service brake push rod. In this embodiment, a flexible diaphragm 131 is shown extending between the pressure distribution disc 130 and the clamp band arrangement 120.
The parking brake push rod 134 extends through the piston 136, and a sealing arrangement is provided between the piston 136 and the parking brake push rod 134. Furthermore, the outboard end of the parking brake push rod 134 is provided with a non-circular profile to prevent rotation of the push rod with respect to piston 136. In this embodiment, the profile is a tri-lobed profile. In other embodiments, alternative profiles such as ovals, etc. may be used.
A thrust bearing arrangement 167 is provided between the outer bayonet sleeve 166 and a spring seat 169 that connects the helical spring 146 to the piston 136, such that the outer bayonet sleeve 166 is able to rotate freely with respect to the piston 136 but, nevertheless, transmit axial loads to the spring.
In operation, the parking brake mechanism 118 functions in a similar manner to that of the first embodiment. Compressed air is introduced via air inlet port 186 to shift the service brake push rod 122 outboard to apply the brake, and simultaneously, the parking brake push rod 134 is shifted outboard under the influence of the magnetic connection between the pressure distribution disc 130 and load spreading head 180. The electric motor 148 is then driven so as to engage the bayonet lugs 162 between appropriate projections 170 of the outer bayonet sleeve 166 so as to latch the two components together. Further driving of the motor causes the additional loading of the spring since the inner bayonet member 156 rotates relative to the parking brake push rod 134 and the two components are threaded together.
Once the required parking brake load has been achieved, the air can be released via an inlet port 186, and the parking brake load from the helical spring 146 is transmitted via the piston 136, the outer bayonet sleeve 166, the inner bayonet sleeve 156, the parking brake push rod 134, and the load spreading head 180 to the service brake push rod 122 to thereby maintain the parking brake clamp load and also account for any contraction of the brake disc by enabling this to be accommodated by relaxation of the helical spring 146 as required.
Furthermore, in the event of failure of the air supply, the parking brake can be applied by the electric motor 148 alone, via the rotation of the inner bayonet member 156 relative to the parking brake push rod 134, albeit more slowly than if air is available.
The brake actuator 210 is shown connected to a caliper housing 208 having an operating shaft 206 located therein, which is pivoted by movement of the service brake push rod 222.
In addition, in this embodiment, the electric motor 248 is mounted within the helical spring 246, but is off-set from the parking brake push rod 234, rather than being arranged concentrically around it. The electric motor 248 drives the parking brake push rod via an epicyclic reduction gear arrangement 254 that outputs its drive to an internally threaded sleeve portion 266 of a lead screw assembly, which additionally includes a parking brake push rod 234 having a complementary external thread and a splined central shaft 258 that is rotationally fixed such that drive from the outer sleeve causes the push rod to extend or retract.
A fixed wall 288 is provided between the service brake chamber and the parking brake mechanism 218, and a guide bore 290 extends inboard from the fixed wall 288 to support the parking brake push rod 234. A seal 292 is provided in the bore guide 290 such that the entire parking brake mechanism is in an unpressurized portion of the brake actuator 210.
The electric motor 248, the reduction gear arrangement 254 and the splined central shaft 258 are all mounted with respect to a moving casing 294, with a thrust bearing 296 supporting the reduction gear arrangement 254. The helical spring 246 is mounted between the second shell 216 and the moving casing 294 such that the extension of the parking brake push rod 234 may not only cause the brake to be applied by shifting the service brake push rod 222 outboard, but may also cause the moving casing to move inboard with respect to the second shell 216, and the helical spring 246 to thereby be compressed. Thus, when the parking brake is applied while the brake is in a hot condition, the spring may relax and enable a suitably high brake force to be applied to the op-shaft, despite the contraction of the hot brake components
As in the previous embodiment, a pre-determined amount of pre-load is applied to the helical spring 246 when in the rest position shown in
The shell 298 illustrates the usual position of a conventional spring parking braking shell so the overall reduction in size of the parking brake of the present invention can be seen by comparison.
The release sequence for the parking brake of
It should be appreciated that terms such as inner and outer, inboard and outboard, upper and lower should not be regarded as limiting and that the position of components may be adjusted as required. In particular, the actuator may be angled with respect to the caliper housing such that it is not strictly positioned in the inboard-outboard direction of a vehicle to which it is fitted.
It should be appreciated that numerous changes may be made within the scope of the present invention, the control system and method of the present invention may be used in conjunction with other parking brake mechanisms that include a resilient/compliant device in the transmission path to account for contraction of brake components due to cooling. For example, the system and method may be adapted for parking brakes in which the reduction gear arrangement may be replaced by suitable alternative types of reduction gearing, the helical spring may be replaced by other resilient components such as a stack of Belville washers, and the bayonet arrangement may be replaced by alternative latching mechanisms, such as clamping devices or collet arrangements similar to those of our earlier patent application, EP1596090. A magnetic parking brake push rod to service brake push rod connection may be used in the first embodiment and the spring loaded connection of the first embodiment used in the second embodiment. The control system may be adapted for use with an electrically actuated service brake. The control system may also be used in conjunction with drum brakes as well as disc brakes. Operation of the parking brake may be controlled by any other suitable control unit, such as the central EBS-ECU, the EBS modules or a microprocessor within each parking brake mechanism itself rather than the dedicated ECU module for the parking brake. Control may also be distributed between these components. The EBS module may be connected to load sensors to directly measure loads applied by the parking brake rather than deriving loads from motor current and the like. The deflection of the spring or components connected thereto such as the piston may alternatively be measured to determine the load. In alternative embodiments, the entire parking brake mechanism may be within the pressurized area, or the mechanism of the first embodiment may be entirely within the unpressurized area. The bayonet arrangement may have lugs and projections with a curved or helical form to assist with engagement thereof during latching.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| GB 0817229.8 | Sep 2008 | GB | national |
