Patent Application
20060090968
This invention generally relates to a brake assembly, and more specifically to a brake assembly including a sensor for monitoring brake pad wear and clearance between a brake pad and a rotating brake member.
Conventional brake assemblies include an adjustable member known in the art as a tappet assembly driven by a rotatable operating shaft. The operating shaft includes eccentrically positioned pockets that transmit rotational forces through rollers to the tappet assembly. Typically, the tappet assembly includes a threaded nut and screw that are adjusted to change length and thereby a clearance between a brake pad and a rotating brake member such as a rotor. An electric motor is employed to drive either the screw or nut to change the overall length of the tappet assembly and adjust the clearance between the brake pad and the rotor.
The clearance between the brake pad and rotor is monitored by measuring displacement of specific brake components, such as the operating shaft, with sensors such as linear or rotary encoders, which are driven by a brake component during operation. Signals from the linear or rotary encoder are stored in a memory for use by a controller during adjustment of the clearance. Displacement of the brake components combined with known mechanical relationships between brake components is then used to determine the clearance between the brake pad and the rotor. A brake pad wear condition is monitored by measuring the position of specific brake components such as a brake housing, pad back plates, tappet screws or nuts or any other mechanically connected components.
Disadvantageously, modifications to specific brake components, such as the operating shaft, may be required to provide mounting and drive features for the encoders. The mounting and drive features within the brake assembly may wear with use, possibly causing inaccurate position information. Encoders provide limited accuracy and dependability, due to the high temperatures and vibrations to which the brake assemblies are subjected. The encoders also consume much of the limited space within the brake assembly. Further, the encoder may require modification of many brake components to incorporate specific mounting and drive features.
Accordingly, it is desirable to design an accurate, adaptable, compact and reliable method and device for determining a wear condition and clearance between a brake pad and a rotor.
The present invention is a brake assembly including a sensor mounted to a movable brake component. The sensor is in communication with a transceiver that provides information indicative of a current position of a brake component.
The brake assembly of this invention includes a caliper housing mounted over a rotor, which is mounted to an axle of a vehicle. The brake assembly is actuated by movement of an actuator that drives an operating shaft for rotation about an axis. The operating shaft includes eccentrically positioned pockets engaged to rollers. Rotation of the operating shaft about the axis drives the rollers linearly against a pair of tappet assemblies. The tappet assemblies in turn move brake pads into contact with the rotor.
A controller receives information concerning the current position of the tappet assemblies and operating shaft from a transceiver. The transceiver communicates with a sensor positioned to relay information indicative of a brake component position. The position of the brake component is combined with known mechanical relationships between various brake components to determine a clearance between the brake pads and the rotor. Adjustment is then made to the length of the tappet assemblies to maintain the clearance within desired limits. Additionally, the length of the tappet assemblies is measured by a further transceiver and sensor. This measurement is compared to a start or datum length of the tappet assemblies to determine the amount of wear of the brake pads.
Accordingly, the present invention provides an accurate and adaptable method and device for determining clearance between a brake pad and rotor, and the wear conditions of the brake pads.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:
Referring to
The brake assembly 10 is actuated by movement of an actuator such as an air cylinder and pushrod schematically shown at 15. The actuator 15 may be of any known configuration including, for example, a pneumatically or hydraulically actuated piston or an electric motor. The actuator 15 rotationally drives an operating shaft 22 about an axis 26. A load sensor 21 is provided for detecting a load on the actuator 15.
The operating shaft 22 is supported on bearings 27 mounted within the inner housing 20 and includes pockets 24 engaged with rollers 28 that are positioned eccentric to axis 26. Rotation of the operating shaft 22 perpendicular to the axis 26 transmits a force to the rollers 28. The pockets 24 of the operating shaft 22 provide a magnification of the force exerted by the actuator 15 on the operating shaft 22. The rollers 28 translate movement of the operating shaft 22 into linear movement against tappet assemblies 29. The tappet assemblies 29 in turn drive against a rear surface 13 of a first brake pad 12A. The first brake pad 12A traverses a clearance 17 to engage the rotor 14. Contact between the rotor 14 and the first brake pad 12A pulls the caliper housing 18 and a second brake pad 12B on an opposite side of the rotor 14 into clamping engagement. Clamping engagement of the rotor 14 between the first and second brake pads 12A, 12B produces the desired braking force to control rotation of the rotor 14.
The brake pads 12A, 12B wear and therefore a length of the tappet assemblies 29 is adjustable to maintain the clearance 17 within desired parameters. Each tappet assembly 29 includes a tappet screw 30 threaded within a stationary tappet nut 32. Rotation of the tappet screw 30 changes the overall length of the tappet assembly 29 to adjust the clearance 17 between the rotor 14 and the brake pads 12A, 12B.
An electric motor 38 is disposed within the brake assembly 10 and drives a gear assembly 36. The gear assembly 36 is engaged to tappet gears 34 disposed on the tappet screws 30. The electric motor 38 rotates the tappet screws 30 to change the overall length of the tappet assemblies 29. A controller 19 controls actuation of the electric motor 38 to adjust the length of the tappet assemblies 29 and maintain the clearance 17 within desired limits.
The controller 19 receives information concerning the current length of the tappet assemblies 29 from a transceiver 44. The transceiver 44 communicates with a sensor 42, which in one example embodiment is positioned on an idler gear 40. The sensor 42 is preferably an inductive resonance device that receives and transmits signals in response to a prompt signal from the transceiver 44. The inductive resonance device does not require an external, or internal power source or any other wired connection with a transceiver, power source or controller. Power for the sensor 42 is provided by prompt signals emitted from the transceiver 44. The transceiver 44 and sensor 42 are easily packaged within the brake assembly 10. Moreover, the transceiver 44 and sensor 42 may be arranged in numerous configurations, as will be appreciated from the examples described below. The transceiver 44 coupled with information from the load sensor 21 provides for the determination of the clearance 17 and of brake pad wear.
The idler gear 40 is driven by one of the tappet gears 34 and rotates in proportion to rotation of the tappet gears 34. The sensor 42 transmits a signal indicative of an angular position 23 (
In addition to the angular position of the idler gear 40, the sensor 42 provides speed information. By sampling several different signals from the sensor 42 over a known period, a speed of rotation of the idler gear 40, and thereby the tappet assemblies 29 can be established. The controller 19 receives information indicative of the position of idler gear 40 over a known period and correlates the position and speed of the idler gear 40 with known relationships with the tappet assemblies 29, and the operating shaft 22. The gear ratio between the tappet gear 34 and the idler gear 40, and the speed of the idler gear 40 provide information used to determine the speed of rotation of the tappet assemblies 29.
In addition, knowledge of the thread pitch between the tappet screw 30 and the tappet nut 32, combined with the determined speed of rotation of the tappet screw 30 is used to determine a linear speed of the tappet assemblies 29 during adjustment of the clearance 17. The linear speed of the tappet assemblies 29 is the speed at which the length of the tappet assembly 29 changes.
The brake assembly 10 provides measurement of the clearance 17 between the brake pads 12A, 12B and the rotor 14, along with a measurement of the remaining amount of brake lining on each brake pad 12A, 12B. Once the brake pads 12A, 12B engage the rotor 14; a load is sensed by the load sensor 21 that indicates the engagement. The position of the tappet assembly 29 can be determined to provide a measure of the clearance 17. The tappet assemblies 29 can then be adjusted accordingly.
Additionally, once the load is released, the amount of movement from an engaged position to a released position is measured and is used to provide the measurement of the clearance 17. The load sensor 21 measures a force indicative of the brake pads 12A, 12B abutting the rotor 14. The tappet assembly position when the brake pads 12A, 12B are engaged is compared to the position of the tappet assemblies 29 when the brake pads 12A, 12B are in the released position. The difference between tappet assembly positions in the engaged and released positions provides the clearance 17.
In operation, the actuator 15 rotates the operating shaft 22. The rollers 28 are driven by the operating shaft 22 and move linearly in a direction perpendicular to the axis 26 against the tappet assemblies 29. Linear movement of the tappet assemblies 29 moves the brake pads 12A, 12B into engagement with the rotor 14. The load sensor 21 senses a load on the actuator 15 indicative of contact with the rotor 14. The load sensor 21 configuration is dependent on the actuator 15. For example, an electric actuator may measure current load, while a hydraulic or pneumatic actuator may sense a pressure to determine when contact is made between the brake pads 12A, 12B and the rotor 14. The sensed contact between the rotor 14 and the brake pads 12A, 12B provide a reference point for movement from a home position. The home position is the position of the operating shaft 22 and/or tappet assemblies 29 before movement toward the rotor 14.
Release of the actuator 15 rotates the operating shaft 22 to disengage brake pads 12A, 12B from the rotor 14. Rotational movement of the tappet assemblies 29, rotates the idler gear 40 and thereby the sensor 42, providing a signal indicative of the change in length of the tappet assemblies 29 and angular position 43 of the idler gear 40, relative to the transceiver 44. The rotational displacement of the sensor 42 mounted to the idler gear 40 along with the known mechanical relationship between movement of the idler gear 40 and tappet assemblies 29, provides information indicative of the total distance that the brake pads 12A, 12B have moved from the home position, and thereby the amount of wear of the friction material on each brake pad 12A, 12B.
Knowledge of the amount of clearance 17 provides information to the controller 19 that is used to determine the amount of adjustment necessary in the tappet assemblies 29 to maintain the clearance 17 within desired limits. Once the brake pads 12A, 12B are disengaged from the rotor 14, the electric motor 38 rotates in response to instructions from the controller 19 to drive the tappet screws 30 and adjust the clearance 17. The electric motor 38 preferably moves to adjust the length of the tappet assemblies 29 when the brake pads 12A, 12B are disengaged from the rotor 14. As appreciated, while the brake pads 12A, 12B are disengaged from the rotor 14 the electric motor 38 is not required to overcome the braking force applied to the rotor 14. Adjustment of the tappet assemblies 29 only occurs when the brake pads 12A, 12B are disengaged from the rotor 14, which provides for the use of a smaller, lighter and less power consuming electric motor 38.
Referring to
The controller 19 communicates with the first and second sensors 52,54 through the first and second transceivers 56, 58 and controls actuation of the electric motor 38. The electric motor 38 provides for the adjustment of the clearance 17.
In operation, the brake pads 12A, 12B engage the rotor 14 in response to actuation of the actuator 15. After engagement, the brake pads 12A, 12B are released and movement of the tappet assemblies 29 and/or the operating shaft 22 away from the rotor 14 is measured. Upon determination that the brake pads 12A, 12B have been disengaged from the rotor 14; the controller 19 determines if an adjustment of the clearance 17 is required. The determination is made with information obtained from the first and second sensors 52, 54 and the known mechanical relationship between the tappet assemblies 29, operating shaft 22 and the brake pads 12A, 12B.
Referring to
The second sensor 54, mounted to operating shaft 22, communicates angular displacement information with the second transceiver 58. Angular displacement of the operating shaft 22 combined with knowledge of the known mechanical relationship provides information used by the controller 19 to determine the clearance 17.
Referring to
The wear sensors 76A, 76B communicate a position of the backing plates 74A, 74B to the wear transceivers 78A, 78B. The position of the backing plates 74A, 74B, when engaged to the rotor 14, provides an indication of a thickness of the friction material 72A, 72B. Further, even when not engaged to the rotor 14, the position of the backing plates 74A, 74B, along with known relationships between other brake components and the rotor 14 provides information indicative of displacement of the backing plates 74A, 74B and thereby the thickness of the friction material 72A, 72B. With the brake pads 12A, 12B engaged to the rotor 14, the distance between the backing plates 74A, 74B and the rotor 14 is the same as the remaining thickness of the friction material 72A, 72B. Further, even if not engaged to the rotor 14, the thickness of the friction material 72A, 72B can be determined with information on the position of the brake pad backing plates 74A, 74B. Therefore, the thickness of the friction material 72A, 72B during each engagement of the brake pads 12A, 12B is measured and this information forwarded to the controller 19.
A housing sensor 80 is attached to the inner housing 20 and a housing transceiver 82 is mounted to the caliper housing 18. The caliper housing 18 moves relative to the fixed caliper pad carrier 23 in response to engagement of the brake pad 12A with the rotor 14. The displacement of the caliper housing 18 relative to the fixed pad carrier 23 compared to the relative position between the two with the brake pads 12A, 12B in a new condition provides information indicative of wear on the brake pads 12A, 12B.
The brake assembly 70 also includes a tappet sensor 84 mounted to the tappet nut 32. The tappet sensor 84 communicates displacement of the tappet nut 32 with a tappet transceiver 86 mounted to inner housing 20. The measured displacement between the tappet sensor 84 and the tappet transceiver 86 is indicative of displacement of the tappet nut 32 from an engaged position with the rotor 14, and is forwarded to the controller 19. The displacement of the tappet nut 32 relative to the inner housing 20, combined with known mechanical relationships between the tappet nut 32 and the brake pads 12A, 12B, is used to determine the amount of pad wear.
An idler gear 41 is driven by one of the tappet nuts 32 and includes an idler gear sensor 88 in communication with an idler gear transceiver 90. The idler gear sensor 88 communicates information indicative of angular displacement of the idler gear 41. The idler gear sensor 88 is mounted on a threaded shaft 89. The idler gear sensor 88 moves linearly in response to rotation of the shaft 89. The number of rotations of the shaft 89 relative to linear movement of the idler gear sensor 88 is known. Accordingly, the linear distance traveled by the idler gear sensor 88 corresponds according to the known mechanical relationship between the threaded shaft 89, idler 41 and the tappet nut 32.
Multiple rotations of the idler gear 41, communicated by the idler gear sensor 88 to the idler gear transceiver 90, are used to determine the length of the tappet nut 32. Each rotation of the tappet screw 30 increases the length of the tappet assembly 29 by a known amount. Counting each rotation of the idler gear 41 to communicate angular displacement provides information indicative of the change of length of the tappet assemblies 29 to the controller 19. Counting rotations of the idler gear 41 provides information regarding the change in length of the tappet assemblies 29. The length of the tappet assemblies 29 can then be used to determine wear to the brake pads 12A, 12B.
A brake assembly designed with the advantage of this disclosure provides an accurate and reliable means of determining brake pad thickness and the clearance between a rotor and brake pads without modification to existing brake components. Further, because the sensors are powered by signals from the transceiver and because no additional wiring is required for the sensors, modifications to current brake configurations to include the sensors are minimized.
The foregoing description is exemplary and not just a material specification. The invention has been described in an illustrative manner, and should be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications are within the scope of this invention. It is understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.
