Patent Application
20070052289
The present invention relates generally to vehicle disc brakes, and more specifically, to a system and method for electrically monitoring the status of one or more disc brakes and using such status information to control the one or more disc brakes.
Virtually all wheeled vehicles utilize braking systems to selectively inhibit wheel rotation and, therefore, reduce vehicle speed. Braking may be accomplished by the use of a disc braking system whereby a friction force is applied at one or more wheel assemblies to inhibit wheel rotation. Numerous disc brake systems are known in the art. Typically, the vehicle operator would generate a brake signal through a pedal thereby activating the disc brake system. The system generally includes a rotor or disc secured to the vehicle wheel, a caliper assembly mounted to the vehicle chassis, and a pair of friction pads (also called brake pads or brake linings) disposed on opposite sides of the rotor. Upon activation of the disc brake system, the friction pads are moved toward one another into frictional engagement with the rotor thereby actuating the braking force and slowing the vehicle.
Repeated braking actuation eventually leads to a wearing of the friction pads and an overall reduction in thickness. Disc brake systems are designed to accommodate certain levels of wear by compensating for reductions in pad thickness. Continued pad wear, however, may lead to mechanical problems such as reduced braking efficiency and damage to the rotor and/or caliper assemblies. To overcome this, strategies have been developed to monitor friction pad wear and to alert the vehicle operator of excessive pad wear and potential mechanical problems.
Early systems for monitoring brake pad wear relied upon some type of physical contact between system components once a portion of the wear monitoring system had been worn away and a predetermined brake pad distance had been traveled.
U.S. Pat. No. 4,850,454 to Korody is an example of such a disc brake lining wear system. In the Korody patent, a wear sensor comprises a plastic encapsulated sensor having a support bracket that is attached to the support member of the disc brake. As the inner and outer linings wear, a peripheral portion of the inner brake pad is displaced axially by the caliper piston. The peripheral portion wears away the sensor surface and engages a metal conductor to complete a circuit. In this manner, the inner brake pad wears away the sensor and completes the warning circuit.
U.S. Pat. No. 4,606,435 to Johnson is another example of a brake lining wear sensor and indicator circuit which relies upon physical contact of system components. In the Johnson patent, the brake lining wear sensor includes a metal contact secured to a grounded brake lining support plate. When the brake lining is not worn, a semiconductive ceramic bushing establishes an electrical resistance between the contact and the support plate. When the brake lining is worn, the contact touches a grounded brake rotor or drum thereby causing a short to ground. Furthermore, the sensor is coupled by a lead wire to an indicator circuit that tests for resistance values to determine whether the contact is electrically grounded to the rotor.
While these patents may disclose strategies for determining the brake lining wear status and relaying this information via an indicator apparatus, they suffer from a number of disadvantages. The systems disclosed in the above patents generally require that the sensor is either associated with or part of the friction pad(s), and/or has a portion worn away along with the friction pad. This may increase maintenance and manufacturing costs by increasing parts and installation time.
More recent wear indicator systems generally do not rely upon a sensor which is either associated with or part of the friction pad(s), and/or has a portion worn away along with the friction pad.
For example, U.S. Pat. No. 5,697,472 to Walker et al. discloses an indicating apparatus designed to determine the amount of wear that has occurred in the friction material of a brake assembly or other friction coupling. The apparatus utilizes a pin member that is positioned in a sealed bore in the housing of the friction coupling. A first end portion of the pin member is positioned for contact and movement of an actuating piston when the piston is in an engaged position. The distance between a second end portion of the pin member, housed within the bore, and an outer surface of the housing may be determined by a depth gage. Measurements may be taken to determine movement of the pin member within the bore and thereby establish the amount of wear of the friction material.
U.S. Pat. No. 5,632,359 to Camps et al. discloses a wear indicator for a disc brake having a caliper that slides in a carrier to apply friction pads against a disc. The wear indicator comprises a continuous variation sensor, such as a capacitive sensor, connected to a monitor. The capacitive sensor has first and second electrodes having a variable overlap area. A guide pin for the caliper forms the first electrode. As the guide pin moves during a brake application, the monitor periodically measures the overlap area to define a current operational output signal which is compared with a predetermined signal and when the comparison differs from a normal result a failure signal is provided to indicate that the disc brake in not properly operating.
U.S. Pat. No. 6,481,539 to Shaw et al. discloses a system and method for monitoring brake pad wear which provides a vehicle disc brake caliper assembly including a boot assembly and at least one friction pad. The system further provides at least one caliper bolt including a caliper bolt switch point, the caliper bolt movably positioned within the boot assembly. A conductive element is positioned a predetermined distance from the caliper bolt switch point. An electrical circuit is switched when the conductive element contacts the switch point. The contact is established when the friction pad wears to a predetermined level corresponding to the predetermined distance. The method provides a caliper bolt including a caliper bolt switch point. A conductive element is positioned a predetermined distance from the caliper bolt switch point. The predetermined distance is progressively decreased as the brake pad wears. An electrical circuit is switched when the conductive element contacts the caliper bolt switch point.
While the systems disclosed in the Walker et al., Camps et al. and Shaw et al. patents may obviate some of the problems associated with the systems disclosed in the Korody and Johnson patents, they suffer from disadvantages of their own. One such disadvantage is that the systems are complex, and are therefore likely prone to failure and/or expensive to install and maintain. A further disadvantage of all of the systems discussed above is that they all require additional components which do not already form part of the braking system. It would be far more desirable from complexity, reliability and cost standpoints if the wear system relied upon components which were already part of the brake system. This is particularly true in the case of electrically actuated braking systems which are becoming more common, and which already include all components which are required for a pad wear monitoring system to function.
It is also desirable that the pad wear indicator system further includes brake adjustment functionality to compensate for brake pad wear. U.S. Pat. No. 6,276,494 to Ward et al. discloses such a system. More specifically, the Ward et al. patent discloses a vehicle brake assembly of the kind that comprises actuating means for applying the brake linings to a brake rotor, adjusting means adapted to be driven by the actuating means for the purpose of maintaining the brake linings in close proximity to the brake rotor, and wear sensing means responsive to actuation movement of the brake in a brake-applying direction. The wear sensing means comprises a sensor adapted to be operated by movement of an operating member in a linear direction, a rotatable follower member responsive to movement of the adjusting means, and a transmission mechanism for translating rotary movement of the follower member into linear movement of the operating member. The brake includes re-set means for resetting the relationship between a datum for the sensing means and the brake during servicing of the brake. The re-set means may comprise means for adjusting the effective length of the operating member.
Similarly, U.S. Pat. No. 6,390,244 to Sitter discloses a brake wear indicator to provide visual and tactile indication of unacceptable brake wear. The brake wear indicator has a hub drive attached to a cam shaft, a brake wear disc attached to the hub drive and a body attached to a slack adjuster lever. The brake wear disc has a wear detector lug. The body has two travel limit lugs which extend towards the centerline of the brake wear disc and are on the end of flexible fingers. When the brake linings are approaching unacceptable wear, the wear detector lug contacts one of the travel limit lugs and pushes the travel limit lug and the end of the corresponding finger away from the adjacent outer surface of the body. The rising of the end of the finger above the adjacent surface provides visual and tactile indication of unacceptable brake wear.
While both of the Ward et al. patent and the Sitter patent disclose pad wear indicator systems which further include brake adjustment functionality to compensate for brake pad wear, the systems suffer from a number of disadvantages similar to those described above in connection with the pad wear indicator systems. More specifically, the brake adjustment portions of the systems disclosed in the Ward et al. patent and the Sitter patent are complex, and are therefore likely prone to failure and/or expensive to install and maintain. A further disadvantage of the brake adjustment portions of the systems disclosed in the Ward et al. patent and the Sitter patent is that they require additional components which do not already form part of the braking system. It would be far more desirable from complexity, reliability and cost standpoints if the brake adjustment functionality relied upon components which were already part of the brake system. This is particularly true in the case of electrically actuated braking systems which are becoming more common, and which already include all components which are required for brake adjustment functionality.
What is desired, therefore, is a brake monitoring and control system which includes brake pad wear indicator functionality, which does not employ a brake pad wear sensor that is either associated with or part of the friction pad(s) and/or has a portion worn away along with the friction pad, which includes brake adjustment functionality to compensate for brake pad wear, which is not relatively complex and therefore not likely prone to failure and/or expensive to install and maintain, which does not require additional components that do not already form part of the braking system, and which is compatible with electrically actuated braking systems.
Accordingly, it is an object of the present invention to provide a brake monitoring and control system which includes brake pad wear indicator functionality.
Another object of the present invention is to provide a brake monitoring and control system having the above characteristics and which does not employ a brake pad wear sensor that is either associated with or part of the friction pad(s) and/or has a portion worn away along with the friction pad.
A further object of the present invention is to provide a brake monitoring and control system having the above characteristics and which includes brake adjustment functionality to compensate for brake pad wear.
Still another object of the present invention is to provide a brake monitoring and control system having the above characteristics and which is not relatively complex and therefore not likely prone to failure and/or expensive to install and maintain.
Yet a further object of the present invention is to provide a brake monitoring and control system having the above characteristics and which does not require additional components that do not already form part of the braking system.
Still yet another object of the present invention is to provide a brake monitoring and control system having the above characteristics and which is compatible with electrically actuated braking systems
These and other objects of the present invention are achieved in accordance with one embodiment of the present invention by provision of a brake monitoring and control system comprising a brake pad adapted to frictionally engage a brake disc when the brake is applied, a motor operatively attached to the brake pad, the motor causing the brake pad to be located in an unapplied position in response to a compensation signal and causing the brake pad to move to an applied position in response to a control signal, and an electronic control unit in communication with the motor. The electronic control unit receives, from a motor position sensor, motor position indicative signals indicative of an angular position of the motor when the brake pad is in the applied position, and calculates the compensation signal based at least in part upon the angular position of the motor when the brake pad is in the applied position.
In some embodiments, the electronic control unit calculates the compensation signal further based at least in part upon an angular displacement of the motor relative to the angular position of the motor when the brake pad is in the applied position, which angular displacement is of an extent necessary to create a desired pad gap between the brake pad and the disc. In certain of these embodiments, the electronic control unit calculates the compensation signal further based at least in part upon an angular reference position of the motor. In certain of these embodiments, the electronic control unit calculates the compensation signal based at least in part upon a difference between the angular position of the motor when the brake pad is in the applied position and the angular reference position of the motor, less the angular displacement of the motor which creates the desired pad gap.
In some embodiments, a difference between the angular position of the motor when the brake pad is in the applied position and the angular position of the motor when the brake pad is in the unapplied position defines a desired pad gap. In some embodiments, a difference between the angular position of the motor when the brake pad is in the unapplied position and the angular reference position of the motor defines an excess pad gap. In certain of these embodiments, the compensation signal corresponds to the excess pad gap. In some embodiments, the motor position sensor is integral with the motor. In some embodiments, the applied position of the brake pad comprises a position of the brake pad when a calibration level of clamping force is exerted.
In some embodiments, the motor causes the brake pad to be located in the unapplied position in response to the compensation signal by selective engagement of a clutch disposed between the motor and an adjuster mechanism. In certain of these embodiments, the electronic control unit calculates the compensation signal further based at least in part upon a position of at least a portion of the adjuster mechanism. In certain of these embodiments, a sensor is provided for detecting the position of at least a portion of the adjuster mechanism.
In some embodiments, the system further comprises friction indicative signals indicative of a level of friction between the brake pad and the brake disc when the brake is applied, and wherein the electronic control unit evaluates a quality of the brake pad based at least in part upon the friction indicative signals. In some embodiments, the system further comprises a temperature sensor which generates temperature indicative signals indicative of a temperature of the brake pad, and wherein the electronic control unit evaluates a quality of the brake pad based at least in part upon the temperature indicative signals. In some embodiments, the motor causes the brake pad to move to a ready position when braking is anticipated. In some embodiments, the electronic control unit calculates or adjusts the compensation signal based at least in part upon a sensed temperature within the system.
In some embodiments, the system further comprises a motor current sensor which generates motor current indicative signals indicative of a level of current passing through the motor when the brake is applied, and wherein the electronic control unit evaluates a quality of the brake pad based at least in part upon the motor position indicative signals and the motor current indicative signals. In some embodiments, the electronic control unit compares the compensation signal with an expected compensation signal stored in a memory in order to evaluate whether a brake failure has occurred.
In some embodiments, the system further comprises a clamping force sensor which generates clamping force indicative signals indicative of a clamping force exerted by the brake pad on the brake disc, and wherein the electronic control unit receives the motor position indicative signals and the clamping force indicative signals when the brake is applied and determines an extent of wear of the brake pad based at least in part upon a relationship between the motor position indicative signals and the clamping force indicative signals.
In accordance with a further embodiment of the present invention, a brake monitoring and control system includes a brake pad adapted to frictionally engage a brake disc when the brake is applied, an adjusting motor operatively attached to the brake pad, the adjusting motor causing the brake pad to be located in an unapplied position in response to a compensation signal, a brake application motor operatively attached to the brake pad, the brake application motor and causing the brake pad to move to an applied position in response to a control signal, and an electronic control unit in communication with the adjusting motor and the brake application motor. The electronic control unit receives, from at least one of an adjusting motor position sensor and a brake application motor sensor, motor position indicative signals indicative of an angular position of at least one of the adjusting motor and the brake application motor when the brake pad is in the applied position, and calculates the compensation signal based at least in part upon the motor position indicative signals.
In some embodiments, the electronic control unit calculates the compensation signal further based at least in part upon an angular displacement of at least one of the adjusting motor and the brake application motor relative to the angular position of thereof when the brake pad is in the applied position, which angular displacement is of an extent necessary to create a desired pad gap between the brake pad and the disc. In certain of these embodiments, the electronic control unit calculates the compensation signal further based at least in part upon an angular reference position of the at least one of the adjusting motor and the brake application motor. In certain of these embodiments, the electronic control unit calculates the compensation signal based at least in part upon a difference between the angular position of at least one of the adjusting motor and the brake application motor when the brake pad is in the applied position and the angular reference position thereof, less the angular displacement of the at least one of the adjusting motor and the brake application motor which creates the desired pad gap.
In some embodiments, a difference between the angular position of at least one of the adjusting motor and the brake application motor when the brake pad is in the applied position and the angular position thereof when the brake pad is in the unapplied position defines a desired pad gap. In certain of these embodiments, a difference between the angular position of at least one of the adjusting motor and the brake application motor when the brake pad is in the unapplied position and the angular reference position thereof defines an excess pad gap. In certain of these embodiments, the compensation signal corresponds to the excess pad gap. In some embodiments, the adjusting motor position sensor is integral with the adjusting motor and the brake application motor sensor is integral with the brake application motor. In some embodiments, the applied position of the brake pad comprises a position of the brake pad when a calibration level of clamping force is exerted.
In some embodiments, the system further comprises friction indicative signals indicative of a level of friction between the brake pad and the brake disc when the brake is applied, and the electronic control unit evaluates a quality of the brake pad based at least in part upon the friction indicative signals. In some embodiments, the system further comprises a temperature sensor which generates temperature indicative signals indicative of a temperature of the brake pad, and the electronic control unit evaluates a quality of the brake pad based at least in part upon the temperature indicative signals. In some embodiments, the motor causes the brake pad to move to a ready position when braking is anticipated. In some embodiments, the electronic control unit calculates or adjusts the compensation signal based at least in part upon a sensed temperature within the system.
In some embodiments, the system further comprises a motor current sensor which generates motor current indicative signals indicative of a level of current passing through the brake application motor when the brake is applied, and the electronic control unit evaluates a quality of the brake pad based at least in part upon the motor position indicative signals and the motor current indicative signals. In some embodiments, the electronic control unit compares the compensation signal with an expected compensation signal stored in a memory in order to evaluate whether a brake failure has occurred. In some embodiments, the system further includes a clamping force sensor which generates clamping force indicative signals indicative of a clamping force exerted by the brake pad on the brake disc, and the electronic control unit receives the motor position indicative signals and the clamping force indicative signals when the brake is applied and determines an extent of wear of the brake pad based at least in part upon a relationship between the motor position indicative signals and the clamping force indicative signals.
In accordance with another embodiment of the present invention, a brake monitoring and control system comprises a brake pad adapted to frictionally engage a brake disc when the brake is applied, a position sensor which generates position indicative signals indicative of a position of the brake pad with respect to the brake disc, a clamping force sensor which generates clamping force indicative signals indicative of a clamping force exerted by the brake pad on the brake disc, and an electronic control unit. The electronic control unit receives the position indicative signals and the clamping force indicative signals when the brake is applied and determines an extent of wear of the brake pad based at least in part upon a relationship between the position indicative signals and the clamping force indicative signals.
In some embodiments, the electronic control unit compares the relationship between the received position indicative signals and the clamping force indicative signals with at least one relationship stored in a memory in order to determine an extent of wear of the brake pad. In some embodiments, the electronic control unit receives first position indicative signals and first clamping force indicative signals when the brake is applied to a first extent and determines a first relationship between the first position indicative signals and the first clamping force indicative signals, receives second position indicative signals and second clamping force indicative signals when the brake is applied to a second extent and determines a second relationship between the second position indicative signals and the second clamping force indicative signals, and determines an extent of wear of the brake pad based at least in part upon a relationship between the first relationship and the second relationship.
In some embodiments, the system further comprises a motor operatively attached to the brake pad, the motor causing the brake pad to be applied in response to a control signal, and wherein the position indicative signals indicative of a position of the brake pad with respect to the brake disc comprise motor position signals indicative of an angular position of the motor. In certain of these embodiments, the motor causes the brake pad to be located in an unapplied position in response to a compensation signal and causes the brake pad to move to an applied position in response to a control signal, and wherein the electronic control unit receives the motor position indicative signals indicative of an angular position of the motor when the brake pad is in the applied position from the motor position sensor, and calculates the compensation signal based at least in part upon the angular position of the motor when the brake pad is in the applied position.
In some embodiments, the system further includes an adjusting motor operatively attached to the brake pad, the adjusting motor causing the brake pad to be located in an unapplied position in response to a compensation signal and a brake application motor operatively attached to the brake pad, the brake application motor and causing the brake pad to move to an applied position in response to a control signal. In these embodiments, the electronic control unit is in communication with the adjusting motor and the brake application motor, the electronic control unit receiving, from at least one of an adjusting motor position sensor and a brake application motor sensor, motor position indicative signals indicative of an angular position of at least one of the adjusting motor and the brake application motor when the brake pad is in the applied position, and calculating the compensation signal based at least in part upon the motor position indicative signals.
In some embodiments, the system further comprises friction indicative signals indicative of a level of friction between the brake pad and the brake disc when the brake is applied, and wherein the electronic control unit evaluates a quality of the brake pad based at least in part upon the friction indicative signals. In certain of these embodiments, the electronic control unit evaluates the quality of the brake pad by comparing the friction indicative signals to at least one level of friction stored in a memory. In some embodiments, the system further comprises a temperature sensor which generates temperature indicative signals indicative of a temperature of the brake pad, and wherein the electronic control unit evaluates a quality of the brake pad based at least in part upon the temperature indicative signals. In certain of these embodiments, the electronic control unit evaluates the quality of the brake pad by comparing the temperature indicative signals to at least one temperature stored in a memory.
In some embodiments, the system further comprises a motor current sensor which generates motor current indicative signals indicative of a level of current passing through the motor when the brake is applied, and wherein the electronic control unit evaluates a quality of the brake pad based at least in part upon the motor position indicative signals and the motor current indicative signals. In some embodiments, the electronic control unit compares the extent of wear with an expected extent of wear stored in a memory in order to evaluate whether a brake failure has occurred.
In accordance with another embodiment of the present invention, a brake monitoring and control system comprises a brake pad adapted to frictionally engage a brake disc when the brake is applied, a motor operatively attached to the brake pad, the motor causing the brake pad to be located in an unapplied position in response to a compensation signal and causing the brake pad to move to an applied position in response to a control signal, a motor position sensor which generates motor position indicative signals indicative of an angular position of the motor, a clamping force sensor which generates clamping force indicative signals indicative of a clamping force exerted by the brake pad on the brake disc, and an electronic control unit in communication with the motor. The electronic control unit receives the motor position indicative signals and the clamping force indicative signals when the brake is in the applied position, calculates the compensation signal based at least in part upon the angular position of the motor when the brake pad is in the applied position, and determines an extent of wear of the brake pad based at least in part upon a relationship between the position indicative signals and the clamping force indicative signals.
In accordance with another aspect of the present invention, one embodiment of a method for brake monitoring and control comprises the steps of providing a brake pad adapted to frictionally engage a brake disc when the brake is applied, proving a motor operatively attached to the brake pad, the motor causing the brake pad to be located in an unapplied position in response to a compensation signal and causing the brake pad to move to an applied position in response to a control signal, receiving, from a motor position sensor, motor position indicative signals indicative of an angular position of the motor when the brake pad is in the applied position, and calculating the compensation signal based at least in part upon the angular position of the motor when the brake pad is in the applied position.
In some embodiments, the compensation signal is calculated further based at least in part upon an angular displacement of the motor relative to the angular position of the motor when the brake pad is in the applied position, which angular displacement is of an extent necessary to create a desired pad gap between the brake pad and the disc. In certain of these embodiments, the compensation signal is calculated further based at least in part upon an angular reference position of the motor. In certain of these embodiments, the compensation signal is calculated based at least in part upon a difference between the angular position of the motor when the brake pad is in the applied position and the angular reference position of the motor, less the angular displacement of the motor which creates the desired pad gap.
In some embodiments, a difference between the angular position of the motor when the brake pad is in the applied position and the angular position of the motor when the brake pad is in the unapplied position defines a desired pad gap. In certain of these embodiments, a difference between the angular position of the motor when the brake pad is in the unapplied position and the angular reference position of the motor defines an excess pad gap. In certain of these embodiments, the compensation signal corresponds to the excess pad gap. In some embodiments, the motor position sensor is integral with the motor. In some embodiments, the applied position of the brake pad comprises a position of the brake pad when a calibration level of clamping force is exerted.
In some embodiments, the motor causes the brake pad to be located in the unapplied position in response to the compensation signal by selective engagement of a clutch disposed between the motor and an adjuster mechanism. In certain of these embodiments, the electronic control unit calculates the compensation signal further based at least in part upon a position of at least a portion of the adjuster mechanism. In certain of these embodiments, a sensor is provided for detecting the position of at least a portion of the adjuster mechanism.
In some embodiments, the method further comprises the steps of generating friction indicative signals indicative of a level of friction between the brake pad and the brake disc when the brake is applied, and evaluating a quality of the brake pad based at least in part upon the friction indicative signals. In some embodiments, the method further comprises the steps of generating temperature indicative signals indicative of a temperature of the brake pad, and evaluating a quality of the brake pad based at least in part upon the temperature indicative signals. In some embodiments, the motor causes the brake pad to move to a ready position when braking is anticipated. In some embodiments, the electronic control unit calculates or adjusts the compensation signal based at least in part upon a sensed temperature within the system.
In some embodiments, the method further comprises the steps of generating motor current indicative signals indicative of a level of current passing through the motor when the brake is applied, and evaluating a quality of the brake pad based at least in part upon the motor position indicative signals and the motor current indicative signals. In some embodiments, the method further comprises the step of comparing the compensation signal with an expected compensation signal stored in a memory in order to evaluate whether a brake failure has occurred.
In some embodiments, the method further comprises the steps of generating clamping force indicative signals indicative of a clamping force exerted by the brake pad on the brake disc, and receiving the motor position indicative signals and the clamping force indicative signals when the brake is applied and determining an extent of wear of the brake pad based at least in part upon a relationship between the motor position indicative signals and the clamping force indicative signals.
In accordance with another embodiment of the present invention, a method for brake monitoring and control comprises the steps of providing a brake pad adapted to frictionally engage a brake disc when the brake is applied, generating, with a position sensor, position indicative signals indicative of a position of the brake pad with respect to the brake disc, generating, with a clamping force sensor, clamping force indicative signals indicative of a clamping force exerted by the brake pad on the brake disc, receiving the position indicative signals and the clamping force indicative signals when the brake is applied, and determining an extent of wear of the brake pad based at least in part upon a relationship between the position indicative signals and the clamping force indicative signals.
In some embodiments, the determining step comprises the step of comparing the relationship between the received position indicative signals and the clamping force indicative signals with at least one relationship stored in a memory. In some embodiments, the receiving step comprises the steps of receiving first position indicative signals and first clamping force indicative signals when the brake is applied to a first extent and determining a first relationship between the first position indicative signals and the first clamping force indicative signals, and receiving second position indicative signals and second clamping force indicative signals when the brake is applied to a second extent and determining a second relationship between the second position indicative signals and the second clamping force indicative signals, and wherein the determining step comprises the step of determining an extent of wear of the brake pad based at least in part upon a relationship between the first relationship and the second relationship.
In some embodiments, the method further comprises the steps of providing a motor operatively attached to the brake pad, the motor causing the brake pad to be applied in response to a control signal, and wherein the position indicative signals indicative of a position of the brake pad with respect to the brake disc comprise motor position signals indicative of an angular position of the motor. In certain of these embodiments, the motor causes the brake pad to be located in an unapplied position in response to a compensation signal and causes the brake pad to move to an applied position in response to a control signal, and the method further comprises the steps of receiving the motor position indicative signals indicative of an angular position of the motor when the brake pad is in the applied position from the motor position sensor, and calculating the compensation signal based at least in part upon the angular position of the motor when the brake pad is in the applied position.
In some embodiments, the method further comprises the steps of generating friction indicative signals indicative of a level of friction between the brake pad and the brake disc when the brake is applied, and evaluating a quality of the brake pad based at least in part upon the friction indicative signals. In certain of these embodiments, the evaluating step comprises the step of comparing the friction indicative signals to at least one level of friction stored in a memory. In some embodiments, the method further comprises the steps of generating temperature indicative signals indicative of a temperature of the brake pad, and evaluating a quality of the brake pad based at least in part upon the temperature indicative signals. In certain of these embodiments, the quality of the brake pad is evaluated by comparing the temperature indicative signals to at least one temperature stored in a memory.
In some embodiments, the method further comprises the steps of generating motor current indicative signals indicative of a level of current passing through the motor when the brake is applied, and evaluating a quality of the brake pad based at least in part upon the motor position indicative signals and the motor current indicative signals. In certain embodiments, the method further comprises the step of comparing the extent of wear with an expected extent of wear stored in a memory in order to evaluate whether a brake failure has occurred.
In accordance with another embodiment of the present invention, a method for brake monitoring and control comprises the steps of providing a brake pad adapted to frictionally engage a brake disc when the brake is applied, providing a motor operatively attached to the brake pad, the motor causing the brake pad to be located in an unapplied position in response to a compensation signal and causing the brake pad to move to an applied position in response to a control signal, generating, with a motor position sensor, motor position indicative signals indicative of an angular position of the motor, generating, with a clamping force sensor, clamping force indicative signals indicative of a clamping force exerted by the brake pad on the brake disc, receiving the motor position indicative signals and the clamping force indicative signals when the brake is in the applied position, calculating the compensation signal based at least in part upon the angular position of the motor when the brake pad is in the applied position, and determining an extent of wear of the brake pad based at least in part upon a relationship between the position indicative signals and the clamping force indicative signals.
The invention and its particular features and advantages will become more apparent from the following detailed description considered with reference to the accompanying drawings.
Referring first to
As graphically shown in
Generally, the unapplied position will be closer to the disc than the fully open position. Thus, even with a new pad, the unapplied position is at least slightly displaced from the reference position. As the pad wears, the unapplied position shifts in order to accommodate the brake pad wear, as shown in
Electronic control unit 20 thus has at least two main functions in system 10—electronic control unit 20 causes the brake pad 14 to be located in the unapplied position by generating a compensation signal 22, and electronic control unit 20 causes the brake pad 14 to move to an applied position by generating a control signal 24. More specifically, the electronic control unit 20 receives, from a motor position sensor 26, motor position indicative signals 28 indicative of an angular position of the motor 18 when the brake pad 14 is in the applied position, and calculates the compensation signal 22 based at least in part upon the angular position of the motor 18 when the brake pad 14 is in the applied position. In making this calculation, the electronic control unit 20 preferably also takes into account an angular displacement of the motor 18 relative to the angular position of the motor when the brake pad is in the applied position, which angular displacement is of an extent necessary to create the desired pad gap between the brake pad 14 and the disc 12, as well as the angular position of the motor corresponding to the reference position of the brake pad 14. Even more specifically, the electronic control unit 20 may calculate the compensation signal 22 based at least in part upon a difference between the angular position of the motor when the brake pad is in the applied position and the angular reference position of the motor, less the angular displacement of the motor which creates the desired pad gap.
Once the compensation signal 22 has been calculated, a clutch 44 (an electromagnetic clutch in some embodiments) may be engaged between the motor and an adjuster mechanism 46 in order to compensate for wear. Preferably, such compensation takes place during slack movement when no clamping force is applied. As many designs for such clutches 44 and adjuster mechanisms 46 are well known in the art, the configuration and operation thereof are not described in detail herein.
As mentioned above, and as best understood with reference to
The motor position sensor 26 may be integral with the motor 18. In some embodiments, the applied position of the brake pad 14 is determined as a position of the brake pad 14 when a calibration level of clamping force (see
When the system 10 includes the clamping force sensor 30 the electronic control unit 20 preferably receives the motor position indicative signals 28 and the clamping force indicative signals 32 when the brake is applied and determines an extent of wear of the brake pad 14 based at least in part upon a relationship between the motor position indicative signals 28 and the clamping force indicative signals 32. Such may be accomplished in a number of ways. For example, the electronic control unit 20 may compare the relationship between the received position indicative signals 28 and the clamping force indicative signals 32 with at least one relationship stored in a memory 34 in order to determine an extent of wear of the brake pad 14.
Another way for the level of wear to be determined is if the electronic control unit 20 receives first position indicative signals 28 and first clamping force indicative signals 32 when the brake is applied to a first extent and determines a first relationship between the first position indicative signals and the first clamping force indicative signals, receives second position indicative signals 28 and second clamping force indicative signals 32 when the brake is applied to a second extent and determines a second relationship between the second position indicative signals and the second clamping force indicative signals, and determines an extent of wear of the brake pad 14 based at least in part upon a relationship between the first relationship and the second relationship. More specifically, the electronic control unit 20 may, for example, determine a slope of the line (when the relationship is linear) representing the clamping force versus stroke of the brake pad. This slope may then be compared with a value for the slope corresponding to various wear conditions stored in the memory 34. For example, as shown in
In the system described thus far, it will be noted that the only fixed reference in the system is when the brake is fully opened (i.e., when installing new pads) and the motor is stopped going backwards by current limitation. It should also be noted that there are several techniques that may be employed in determining the position of the brake with respect to this fixed reference. One of such techniques involves the use of a “stroke position” technique. In this technique, a “position counter” is employed, with the position counter being set to zero when the brake is in the fixed reference (i.e., the fully open) position. Then the brake is in operation and the wear is compensated for, and the “position counter” incrementally counts up until the pads are fully worn. The only way of checking the signal during this condition is to fully open the brake unit once more (i.e., reset the counter).
In order to avoid this and to provide even better wear compensation, an “absolute position” technique may be employed. Using this technique, an additional sensor 48 (a magnetic sensor in some embodiments) is provided for sensing the rotation of the adjuster mechanism 46 (preferably while the electromagnetic clutch 44 is engaged). The output of sensor 48, which provides a feedback signal 50 indicative of the position of the adjuster mechanism 46 may be employed by electronic control unit 20 to provide an even more accurate calculation of the pad wear. The feedback signal 50 may optionally be improved upon if the information from sensor 48 is combined with information from the non-volatile memory 34 where the total length of pad adjustment operations since the pad was changed is stored. In addition, diagnostics of the sensor signal 50 and/or the pad adjuster mechanism or a simplified sensor 48 may optionally be achieved from the combination of the non-volatile memory 34 and sensor 48 information. Furthermore, the method to calculate the total length of pad adjustment could optionally employ the motor position signal 28.
The electronic control unit 20 may compare the extent of wear of the brake pad 14 with an expected extent of wear stored in the memory 34 in order to evaluate whether a brake failure has occurred and/or whether something is amiss with the brake pad 14.
System 10 may also include a friction sensor 36 which generates friction indicative signals 38 indicative of a level of friction between the brake pad 14 and the brake disc 16 when the brake is applied, and/or may include a temperature sensor 37 which generates temperature indicative signals 39 indicative of the temperature of the brake pad 14 and/or other components of system 10. The electronic control unit 20 may evaluate a quality of the brake pad 14 based at least in part upon the friction indicative signals 38 and/or the temperature indicative signals 39. More specifically, the electronic control unit 20 may evaluate the quality of the brake pad 14 by comparing the friction indicative signals 38 to at least one level of friction stored in the memory 34 and/or by comparing the temperature indicative signals 39 to at least one temperature stored in the memory 34. For example, if more or less friction than expected is occurring and/or the pad temperature is higher or lower than expected, it may be determined that something is amiss with the brake pad 14. In addition, by comparing the control position of the motor (calibrated at a specific force-level) and the compensated position, the effect of heat to pads and rotors or the temperature can be roughly estimated.
Alternately, friction indicative signals 38 may be calculated from motor current signal 42 (which is proportional to motor torque) and motor position signal 28 in a brake actuator having a known mechanical geometry. If such is the case, there friction sensor 36 may be dispensed with. Moreover, by monitoring the force/position relation, the “elasticity” of the brake assembly can be continuously checked and compared (e.g., indicating structural defects, excessive loss or fracture of pad material and the like).
Moreover, the electronic control unit 20 may calculate or adjust compensation signal 22 based at least in part upon the sensed temperature. More specifically, as is well known, the temperature of the pad and/or other parts of system 10 may cause those parts to change size and/or shape; in general, materials will expand when heated and contract when cooled. As such, the compensation signal may not be completely accurate if it does not take temperature into account. For example, when various system components are warmer (and therefore larger), the pad may be closer to the disc than expected, and therefore, the pad gap may be smaller than desired. Conversely, when various system components are cooler (and therefore smaller), the pad may be farther from the disc than expected, and therefore, the pad gap may be larger than desired. Electronic control unit 20 may account for such thermal expansion and contraction by calculating or adjusting compensation signal 22 based at least in part upon the sensed temperature. This will provide a consistent pedal feel and reduce brake fade no matter what the temperature of system components.
System 10 may also include a motor current sensor 40 which generates motor current indicative signals 42 indicative of a level of current passing through the motor 18 when the brake is applied. The electronic control unit 20 may evaluate a quality of the brake pad 14 based at least in part upon the motor position indicative signals 28 and the motor current indicative signals 42. For example, if the relationship between the motor position indicative signals 28 and the motor current indicative signals 42 is different than expected, it may be determined that something is amiss with the brake pad 14.
Referring again to
Referring now to
Similar to the way sensor 48 may be provided for sensing the rotation of the adjuster mechanism 46 in system 10 described above, a sensor 48′ (which may comprise an angular position sensor), the output of which provides a feedback signal 50′ indicative of the position of the adjusting motor 52. Signal 50′ may be employed by electronic control unit 20 to provide an even more accurate calculation of the pad wear.
The present invention, therefore, provides a brake monitoring and control system which includes brake pad wear indicator functionality, which does not employ a brake pad wear sensor that is either associated with or part of the friction pad(s) and/or has a portion worn away along with the friction pad, which includes brake adjustment functionality to compensate for brake pad wear, which is not relatively complex and therefore not likely prone to failure and/or expensive to install and maintain, which does not require additional components that do not already form part of the braking system, and which is compatible with electrically actuated braking systems.
Although the invention has been described with reference to a particular arrangement of parts, features and the like, these are not intended to exhaust all possible arrangements or features, and indeed many other modifications and variations will be ascertainable to those of skill in the art.
