Abstract:
Systems and methods for reducing transient brake caliper drag in a motor vehicle are provided. The motor vehicle, for example, may include, but is not limited to, an axle, a rotor coupled to the axle, a brake caliper comprising a brake pad configured to engage the rotor, a brake pedal assembly communicatively coupled to the brake caliper, the brake pedal assembly configured to receive user input directing the brake pad to apply a force to the rotor and user input directing the brake pad to disengage the rotor, and a processor coupled to the brake caliper, wherein the processor is configured to determine, after the brake pedal assembly receives user input directing the brake pad to disengage the rotor, the force applied to the rotor, and command the brake caliper to retract the brake pad away from the rotor when the determined force exceeds a predetermined threshold.

Description:
TECHNICAL FIELD 
     The technical field generally relates to braking systems in motor vehicles, and more particularly relates to systems and methods for reducing transient brake caliper drag. 
     BACKGROUND 
     Fuel economy is becoming an increasingly important aspect of motor vehicles for a variety of reasons. Accordingly, systems and methods which can improve fuel economy are desirable. 
     SUMMARY 
     In one embodiment, for example, a vehicle is provided. The vehicle may include, but is not limited to, an axle, a rotor coupled to the axle, a brake caliper comprising a brake pad configured to engage the rotor, a brake pedal assembly communicatively coupled to the brake caliper, the brake pedal assembly configured to receive user input directing the brake pad to apply a force the rotor and user input directing the brake pad to disengage the rotor, and a processor coupled to the brake caliper, wherein the processor is configured to determine, after the brake pedal assembly receives user input directing the brake pad to disengage the rotor, the force applied to the rotor, and command the brake caliper to retract the brake pad away from the rotor when the determined force exceeds a predetermined threshold. 
     In another embodiment, for example, a method is provided for controlling a braking system of a motor vehicle, the braking system comprising a rotor and a brake caliper comprising a brake pad. The method may include, but is not limited to determining, by a processor communicatively coupled to the brake caliper, a force at which the brake pad was applied to the rotor, and commanding, by the processor, the brake caliper to retract the brake pad from the rotor when the force was greater than a predetermined threshold. 
     In yet another embodiment, for example, a brake system is provided. The brake system may include, but is not limited to, a rotor, a brake caliper comprising a brake pad configured to engage the rotor, a brake pedal assembly communicatively coupled to the brake caliper, the brake pedal assembly configured to receive user input directing the brake pad to engage the rotor and user input directing the brake pad to disengage the rotor, a processor coupled to the brake caliper, wherein the processor is configured to determine, after the brake pedal assembly receives user input directing the brake pad to disengage the rotor, a force applied to the rotor, and command the brake caliper to retract the brake pad away from the rotor when the determined force exceeds a predetermined threshold. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The exemplary embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
         FIG. 1  is a chart illustrating the amount of drag experienced by a vehicle relative to the speed of a vehicle after six different applications of the brakes, in accordance with an embodiment; 
         FIG. 2  is a block diagram of a vehicle including a system for reducing transient brake caliper drag, in accordance with an embodiment; and 
         FIG. 3  is a flow chart illustrating a method for mitigating transient brake caliper drag in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the application and uses. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
     The amount of drag experienced by a rotor (otherwise known as a brake disc) of a vehicle by a brake pad after the application of the brakes (i.e., after a user releases the brake pedal) is proportional to the force with which the brakes were applied. In other words, after the vehicle experiences a hard brake event, the amount of drag on the rotors by the brake pads is greater than after an average brake event. This can sometimes be caused by a slight repositioning of the brake pads in the direction of the rotors even after the driver of the motor vehicle completely releases the brake pedal. The drag on the rotor generally reduces over time since the rotor will push the brake pads back to a steady state position once the vehicle begins moving again. In other words, the brake pads eventually return to a nominal position where a nominal amount of drag is imparted on the rotor of the vehicle. However, the increased drag immediately following a brake negatively affects the fuel economy of the vehicle and can decrease the life cycle of the brake pads. 
       FIG. 1  is a chart  100  illustrating the amount of drag (the vertical axis  110 ) experienced by a vehicle in units of Newton-meters (Nm) relative to the speed (the horizontal axis  120 ) of a vehicle time in seconds (s) after six different applications of the brakes in units of kilopascals (kPa). As seen in  FIG. 1 , a brake application with a force of ten thousand kPa causes roughly seven times more drag on the rotors than an application with a force of five hundred kPa. Furthermore, as seen in  FIG. 1 , the drag on the rotors, and thus the position of the brake pad within the brake caliper, takes longer to return to a nominal value and position when the brake force is higher. 
       FIG. 2  is a block diagram of a vehicle  200  including a braking system  210  for reducing transient brake caliper drag, in accordance with an embodiment. The vehicle  200  includes an axle  220  coupled to at least one tire  230 . The vehicle further includes at least one rotor  240  coupled to the axle  220 . While the braking system  210  is illustrated as being configured around tire  230  on one axle  220 , the braking system  210  may be coupled to any number of axles in the vehicle  200  and around any number of tires  230   
     The vehicle further includes a brake caliper  250 . The brake caliper  250  includes a brake pad  252  and a system  254  for actuating the brake pad. The system  254  of actuating the brake pad  252  may be hydraulic, electronic, pneumatic, or electro-mechanic. A hydraulic system  254 , for example, generally includes a hydraulic piston coupled to a pump or a linear actuator via a hydraulic line. The hydraulic piston is coupled to the brake pad  252 . When the brakes need to be applied, the pump or linear actuator increases the pressure in the hydraulic line to move the piston and thus apply the brake pad  252  to the rotor  240 . An electronic system  254 , for example, generally includes an electronic motor coupled a piston. When the brakes need to be applied, the electronic motor advances the position of the piston. 
     The vehicle further includes a brake pedal assembly  260 . The brake pedal assembly  260  is coupled to a brake control unit  270 . In one embodiment, for example, the brake control unit  270  may be an anti-lock brake module. The brake control unit  270  controls the brake caliper  250  to control the application of the brakes based upon input from a user via the brake pedal assembly  260 . The brake control unit  270  also controls a retraction of the brake pads  252 , as discussed in further detail below. 
     The vehicle further includes a processor  280 . The processor  280  may be a central processing unit (CPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a microcontroller, a programmable logic controller (PLC) or any other type of logic device, or combination thereof. In one embodiment, for example, the processor  280  may be part of the brake control unit  270 , as illustrated in  FIG. 2 . However, the processor  280  may be a stand-alone processor or it may be a shared resource among one or more other systems in the vehicle  200 . In one embodiment, for example, each brake caliper  250  within the vehicle  200  may have its own processor  280 . In other embodiments, for example, a single processor  280  may control each brake caliper  250 . 
     The vehicle further includes one or more sensors  290 . The sensor(s)  290  are used to monitor a force and/or a rate at which the brakes were applied. In one embodiment, for example a sensor  290  may monitor a pressure in a hydraulic line. In another embodiment, for example, the sensor  290  may be an accelerometer capable of measuring a deceleration experienced by the vehicle. In yet another embodiment, for example, the sensor  290  may measure a distance the brake pedal in the brake pedal assembly  260  has traveled. In another embodiment, for example, a sensor  290  may monitor a decrease in the speed of the vehicle via one or more sensors  290  coupled to a transmission in the vehicle or to wheel bearings in the vehicle. In yet other embodiments a combination of sensors may be used to measure the force and/or a rate at which the brakes were applied. In another embodiment, for example, a sensor  290  may monitor a position of the brake caliper  250 , as discussed in further detail below. 
       FIG. 3  is a flow chart illustrating a method  300  for mitigating transient brake caliper drag, in accordance with an embodiment. The method begins when a processor, such as the processor  280  illustrated in  FIG. 2 , receives data from one or more sensors, such as the sensor(s)  290  illustrated in  FIG. 2 . (Step  310 ). As discussed above, the sensor data could include a pressure in a hydraulic or pneumatic system, a deceleration force experienced by the vehicle, a distance a brake pedal travelled, a rate at which the brake pedal was depressed, a decrease in speed experienced by the vehicle, or any combination thereof. 
     The processor then compares the sensor data against a predetermined threshold. (Step  320 ). As seen in  FIG. 1 , the amount of drag a brake caliper imparts on a rotor after the brakes are released is proportional to the force at which the brakes were applied. Accordingly, in one embodiment, for example, the predetermined threshold can be selected such that the brake calipers are refracted after only hard stops. By retracting the brake calipers after only hard stops, the resulting drag most affecting the fuel economy of the vehicle is reduced. In other embodiments, for example, the predetermined threshold can be set at a lower level to capture medium or low force brake applications. In yet another embodiment, for example, the predetermined threshold may be set such that every application of the brakes triggers the caliper retraction, as discussed in further detail below. When multiple sensors are on the vehicle, a threshold may be assigned to each sensor. In one embodiment, for example, the processor may determine to retract the brake calipers if any of the sensor data exceeds the predetermined threshold for a respective sensor. In another embodiment, for example, the processor may determine to retract the brake calipers if the sensor data for multiple or all of the sensors exceeds the predetermined threshold for a respective sensor. If the sensor data does not exceed the predetermined threshold, the method returns to step  310  to await the next brake application. 
     If the sensor data exceeds the predetermined threshold, the processor determines a position of the brake pad within the brake caliper. (Step  330 ). As discussed above, after the application of the brakes the brake pad does not immediately return to a nominal position. Further, as illustrated in  FIG. 1 , the position of the brake pads shift more after a hard brake event (imparting more drag on the rotors) than after a low force brake event. Accordingly, in one embodiment, for example, the processor may estimate the position of the brake pad based upon the sensor data indicating the force and/or rate of the brake application, wherein the position of the brake pad is estimated to be closer to the rotor after a hard stop relative to a medium or low force stop. In another embodiment, for example, a sensor can measure the actual position of the brake pad relative to the rotor. 
     The processor then commands the brake caliper to retract the brake pad based upon the determined position. (Step  340 ). As discussed above, the system  210  illustrated in  FIG. 2  can be implemented in any type of brake system. In a hydraulic brake system featuring a pump, for example, the processor would run the pump in reverse, relative to a pump direction which actuates the brakes, for a length of time based upon the determined position of the brake pads to return the brake pad to the nominal position. In a brake system featuring a linear actuator, the processor would determine a distance the linear actuator would have to move to return the brake pad to the nominal position. In an electronic braking system featuring a motor, the processor would determine the length of time to run the motor in reverse to return the brake pad to the nominal position. The method then returns to step  310  to await the next application of the brakes. Accordingly, by retracting the brake pads after brake application which exceed the predetermined threshold, the amount of drag on the rotor of the motor vehicle is reduced, thereby improving fuel economy. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the disclosure as set forth in the appended claims and the legal equivalents thereof.