Abstract:
An adjustment mechanism for a vehicle brake uses an electric motor to adjust brake clearance based on brake temperature and wheel speed. A temperature sensor transmits brake temperature data to a controller. If a brake is dragging during non-braking events, the controller identifies an increase in brake temperature and actuates the electric motor to increase brake clearance. The controller also adjusts brake clearance to accommodate for brake wear. When wheel speed is above a predetermined speed value, the controller actuates the electric motor to move a non-rotating brake component toward a rotating brake component until a predetermined temperature increase is sensed. Once the predetermined temperature increase is identified, the electric motor moves the non-rotating brake component away from the rotating brake component to provide an optimized brake clearance.

Description:
TECHNICAL FIELD  
       [0001]     An adjustment mechanism for a vehicle brake utilizes an electric motor and controller to optimize brake clearance based on brake temperature and wheel speed.  
       BACKGROUND OF THE INVENTION  
       [0002]     Vehicle brakes include adjustment mechanisms that adjust brake clearance, which comprises a distance between a brake pad and a rotating brake rotor when the vehicle brake is not applied. A minimum brake clearance is required such that brake pads do not drag against the brake rotor. As brake pads wear, the brake clearance increases, which can adversely affect the capability of the vehicle brake to achieve maximum brake torque. To compensate for this an adjustment mechanism is used to move the brake pads toward the brake rotor as the pad wears.  
         [0003]     One type of known adjustment mechanism utilizes a mechanical adjustment system that operates in a manner similar to that of a clutch with a known amount of backlash. One disadvantage with this type of system is that if over-adjustment occurs, then the brakes drag. This decreases the overall life of the brake pads.  
         [0004]     Another type of adjustment mechanism utilizes electric adjusters to adjust brake clearance. Typically these systems mimic the existing mechanical adjustment mechanism. These types of systems are often complex, expensive, and time consuming to install. Thus, there is a need for a simplified and cost-effective adjustment system that optimizes brake clearance, and which can adjust for brake wear as well as brake drag.  
       SUMMARY OF THE INVENETION  
       [0005]     An adjustment mechanism for a vehicle brake uses an electric motor to optimize brake clearance. A controller controls the electric motor to adjust brake clearance based on brake temperature and wheel speed. An increase in brake temperature during non-braking events signifies brake drag, and once brake drag is identified, the controller actuates the electric motor to increase brake clearance. The controller also adjusts brake clearance to accommodate for brake wear. During a specified adjustment cycle, when wheel speed is above a predetermined speed value, the controller actuates the electric motor to optimize brake clearance.  
         [0006]     In one example, the vehicle brake assembly includes a set of pads that are engaged against a rotating brake rotor during a braking event. If drag is identified, the controller actuates the electric motor to move the set of pads away from the rotating brake rotor. To accommodate for pad wear, if wheel speed is greater than the predetermined speed value, the controller actuates the electric motor to move the set of brake pads toward the rotating brake rotor until a predetermined temperature increase is sensed. Once the predetermined temperature increase is identified, the electric motor moves the non-rotating brake component away from the rotating brake component by a certain amount to provide an optimized brake clearance.  
         [0007]     The subject invention provides a simple, effective, and reduced cost method and apparatus for optimizing brake clearance. These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a schematic representation of a vehicle brake assembly and associated adjustment mechanism incorporating the subject invention.  
         [0009]      FIG. 2  is a flow chart describing a method of brake adjustment incorporating the subject invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0010]     As shown in  FIG. 1 , a vehicle brake  10  includes a rotor  12  that rotates about an axis  14 . Brake pads  16  are mounted to a non-rotating vehicle structure (not shown), and are spaced by a clearance shown generally at  18  from the rotor  12  when the vehicle brake  10  is not applied.  
         [0011]     An adjustment mechanism  20  that operates according to the subject invention is used to optimize the clearance  18  to accommodate both pad wear and brake drag. While the vehicle brake  10  shown in  FIG. 1  comprises a disc brake, it should be understood that the adjustment mechanism  20  and method of operating the adjustment mechanism  20  could also be used with other types of vehicle brakes.  
         [0012]     The adjustment mechanism  20  includes an electric motor  22  that is operated by a control unit or controller  24 . The controller  24  includes a power/ground connection interface and a vehicle data link, as indicated in  FIG. 1 . The electric motor includes a position sensor  26  that monitors motor position as known. Motor position data is communicated to the controller  24  via a motor signal  28 . The controller  24  compiles and tracks motor rotation data from the motor signal  28  to estimate the amount of clearance and to provide pad wear information to an operator.  
         [0013]     A temperature sensor  30  measures and monitors the temperature of at least one brake component. Preferably, the temperature sensor  30  measures the temperature of the rotor  12  and/or brake pad  16 . The temperature sensor  30  generates a temperature signal  32  that communicates brake temperature data to the controller  24 . A single brake temperature sensor can be used to measure the temperature of either the rotor  12  or brake pad  16 , or separate temperature sensors could be used for each of the brake pad  16  and rotor  12 . The sensor is shown schematically and would be positioned in an appropriate location to sense the temperature.  
         [0014]     A wheel speed sensor  34  measures and monitors wheel speed. The wheel speed sensor  34  generates a wheel speed signal  36  that communicates wheel speed data to the controller  24 .  
         [0015]     The electric motor  22  includes a motor output shaft  40  that drives a gear reduction  42 . The gear reduction  42  drives a set of tappets  44  that are associated with the brake pads  16 . Under predetermined/specified conditions, the controller  24  generates a control signal  46  to actuate the electric motor  22  to adjust clearance  18  by driving the gear reduction  42  and tappets  44 . The electric motor  22  can be used to increase or decrease the clearance  18  between the rotor  12  and pads  16 . A connection between pads  16  and tappets  44  may be as known, and is not shown here for purposes of clarity. Further, any type of known gear reduction can be used to drive the tappets  44 . The controller  24  determines which type of adjustment is needed based on various factors, such as brake temperature and/or wheel speed, for example. This will be discussed in greater detail below.  
         [0016]      FIG. 2  depicts a flowchart that sets forth the steps for adjusting clearance with the adjustment mechanism  20 . A closed-loop process is initiated at a start  100 . The controller  24  then determines if a measured brake temperature is excessive at step  110 . An excessive temperature level is typically a temperature at which a significant brake problem potentially exists. If an excessive brake temperature does exist, the controller  24  issues a warning and records the event at step  120 .  
         [0017]     After such a warning is issued, the controller  24  then determines if a deceleration that would be indicative of a recent braking event has occurred at step  130 . This can be accomplished by looking at the derivative of the wheel speed. If a recent deceleration event is identified, the controller  24  waits for the brakes to cool as indicated at  140  and finishes a loop cycle as indicated at  200 . Thus, if an excessive temperature is identified in combination with a recent deceleration, the adjustment mechanism  20  is not used to adjust clearance. The controller  24  waits until the brakes have cooled before determining whether adjustment of clearance is needed in a subsequent loop cycle.  
         [0018]     If during step  110 , the controller  24  determines that there is not an excessive brake temperature, the controller then compares a measured brake temperature to a predetermined temperature level as indicated at  115 . In one example, the predetermined temperature level is ambient temperature, however, other temperature levels could also be used.  
         [0019]     A separate sensor could be used to measure ambient temperature. Or, ambient temperature could be defined as a temperature point where it is known that the brakes have not been applied, e.g. vehicle start-up, and/or after a long period of time has passed without a deceleration. It is also known that ambient temperature lies within a relatively narrow range, which is well below typical brake operating temperatures. Thus, it would be possible to consider any temperature above thirty-five degrees Celsius, for example, to be above ambient. Finally, it is also possible to look at the absolute temperature and the derivative of the temperature, i.e. is the temperature increasing or decreasing, to make a determination as to whether the brake temperature is above ambient. For diagnostic purposes it is also useful to compare temperatures from one side of a vehicle to an opposite side of the vehicle. However, a data link is required for this type of information comparison.  
         [0020]     If, during step  115 , it is determined that the measured brake temperature is greater than the predetermined temperature level, the controller determines whether a recent deceleration has occurred as described above with regard to step  130 . If a recent deceleration is identified, the controller  24  performs steps  140  and  200  as described above.  
         [0021]     If the measured brake temperature is greater than the predetermined temperature level and there has not been a recent deceleration, the controller then determines whether or not it is time to perform an adjustment as indicated at  135 . Adjustment times can be determined/defined in many different ways. For example, the time to adjust could be once per a certain predetermined number of vehicle stops. Or, the time to adjust could be once per a predetermined time interval, such as once per day, for example. Or, the time to adjust could be made dependent on deceleration level, i.e. time of deceleration and temperature reached during deceleration. It should be understood that these are just examples and that other methods could be used to determine whether or not it is time to perform a brake adjustment.  
         [0022]     If the controller  24  determines that it is not time to perform an adjustment, then the loop cycle is completed as indicated at  200 . If the controller  24  determines that it is time to perform an adjustment, then the controller determines whether measured wheel speed is greater than a predetermined speed value as indicated at  145 . Preferably, the predetermined speed level is approximately thirty miles per hour, however, other speeds could also be used. A higher speed will result in more rapid and higher brake temperature increase making determination of brake pad contact easier. However the speed chosen must not be so high that the vehicle operates below the chosen speed for long periods of time. If the measured wheel speed is not greater than the predetermined speed value, then the loop cycle is completed as indicated at  200 .  
         [0023]     If the measured wheel speed is greater than the predetermined speed value and the measured brake temperature is less than the predetermined temperature level, then the controller  24  activates the electric motor  22  to move the brake pad  16  toward the rotor  12 , i.e. clearance  18  is tightened. Preferably, clearance is tightened by one increment as indicated at  150 . One increment comprises a discrete, predetermined distance value. After clearance  18  has been tightened by one increment, the controller  24  waits to see if there is an increase in brake temperature as indicated at  155 .  
         [0024]     After a predetermined time interval, the controller  24  compares the current measured brake temperature to the predetermined temperature level, which in the example discussed, is ambient temperature. This step is indicated at  160 . If the measured brake temperature is not greater than the predetermined temperature level, then the controller  24  returns to step  145  to determine whether wheel speed is above the predetermined speed value. If it is, the controller activates the motor to tighten clearance  18  by one more increment. The controller repeats steps  145  through  160  until the current measured brake temperature is greater than the predetermined temperature level.  
         [0025]     Once the current measured brake temperature is greater than the predetermined temperature level, then the controller  24  sets an adjustment flag—adjustment complete, as indicated at  165 . Then the controller  24  opens clearance  18 , i.e. increases clearance  18  by one increment as indicated at  170 . This provides an optimized, minimum clearance between the brake pads  16  and rotor  12 , which keeps braking response fast and provides optimum, high brake torque.  
         [0026]     Once the clearance  18  has been opened, the controller  24  waits for measured brake temperature to stabilize as indicated at  175 . Then the loop cycle is completed as indicated at  200 . The subject method is a closed loop system, thus, once a loop cycle is completed  200 , the controller returns to the start  100  and performs a subsequent loop cycle.  
         [0027]     The adjustment mechanism  20  also avoids the problem of over adjustment. Over adjustment causes brake drag. When the brakes are subjected to brake drag, the brakes run hot and have increased wear rates, which results in reduced fuel economy. To identify and eliminate brake drag, the controller performs steps  100 - 130  as described above. If during step  130 , the controller  24  determines that there has not been a recent deceleration, but the current measured brake temperature is above the predetermined temperature level, the controller proceeds to step  170 . As described above, during step  170  clearance  18  is opened by one increment. The controller  24  then proceeds with steps  175 - 200  as described above.  
         [0028]     The subject invention provides a method and apparatus for optimizing brake clearance in response to brake drag and brake wear. The subject invention is simpler than existing mechanical and electrical systems with better performance. The subject invention provides a simple closed loop approach that assures minimum clearance without risking the possibility of dragging brakes. Further, if brake temperature is being monitored for diagnostic purposes, only one additional component is needed, i.e. an electronic actuator. Either current feedback from the motor, or alternatively, a position/speed sensor on the motor output shaft  40  may be desirable to optimize control and enhance diagnostics.  
         [0029]     Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.