Abstract:
A vehicle braking system and method of control is disclosed which includes electromagnetic and friction braking functionality. The electromagnetic braking system includes a generator which supplies power to eddy current devices. Accordingly, the eddy current devices apply a retarding torque on the wheels of the vehicle. In the event the generator produces an amount of power greater than that needed by the electromagnetic braking system, the generator will supply power to a supplemental power source such as a battery.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of provisional patent application Ser. No. 60/404,680 filed Aug. 20, 2002. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to a vehicle braking system and, more specifically, to a power management system for a vehicle braking system having electromagnetic and friction braking. 
     2. Description of the Related Art 
     Hybrid braking systems for vehicles are well known. These braking systems usually include electromagnetic and friction braking capabilities. The use of electromagnetic braking improves efficiency in vehicles by recovering kinetic energy produced by the vehicle with an electric machine. The electric machine generates electric energy that is applied to electromagnetic retarders (also referred to as eddy current devices) within the braking system. In some instances, the electric machine generates an amount of power in excess of the amount required by the eddy current devices. When this occurs, prior art braking systems have disclosed methods of recovering the excess energy to power other components or to charge the vehicle battery. However, these prior art systems have proved to be costly and largely inefficient. Further, the determination of whether a surplus of power is available from the generator requires additional hardware. 
     It would therefore be desirable to provide a hybrid braking system that reduces the amount of hardware and efficiently distributes the energy generated within the braking system thereby utilizing any excess energy generated by the generator to charge a supplemental power source such as a battery. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantages of the prior art approaches by providing a an apparatus and a method of controlling power for a braking system, which permits use of electromagnetic and friction braking. 
     A method of operation is included which comprises the step of determining a throttle position of a vehicle based on inputs from a throttle position sensor The step of comparing the throttle position to a predetermined throttle position threshold is included. The method generates a signal for the battery switch to decouple the battery from the generator thereby preventing charging of the battery when the throttle position is greater than the predetermined throttle position threshold. The method compares the brake pedal position signal to a predetermined brake pedal threshold when the throttle position is less than the predetermined throttle position threshold. The battery switch decouples the battery from the generator when the brake pedal position signal is greater than the predetermined brake pedal threshold and the throttle position is less than the predetermined throttle position threshold. The wheel speed sensor signal based on the wheel speed is compared to a predetermined wheel speed threshold when the brake pedal position signal is less than the predetermined brake pedal threshold and the throttle position is less than the predetermined throttle position threshold. The method generates a signal for the battery switch to decouple the battery from the generator when the wheel speed is less than the predetermined wheel speed threshold, the brake pedal position signal is less than the predetermined brake pedal threshold, and the throttle position is less than the predetermined throttle position threshold. When the wheel speed is greater than the predetermined wheel speed threshold, the method generates a signal for the battery switch to decouple the battery from the generator if the generator output voltage is less than battery voltage. A signal is generated to electrically couple the battery to the generator thereby enabling the generator to charge the battery when the generator output voltage is greater than the battery voltage, the wheel speed is greater than the predetermined wheel speed threshold, the throttle position is less than the predetermined throttle position threshold, and the brake pedal position signal is less than the predetermined brake pedal threshold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a hardware diagram of a motor vehicle having a electromagnetic and friction braking system according to the present invention. 
         FIG. 2  is an electrical schematic of a electromagnetic braking system according to the present invention. 
         FIG. 3  is a flow chart illustrating a regenerative braking mode of operation for an electromagnetic and friction braking system according to the present invention. 
         FIG. 4  is a hardware diagram of a motor vehicle having an electromagnetic and friction braking system according to the present invention 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , an electromagnetic and friction braking system  10  for a vehicle is illustrated which includes left and right rear wheels  12  and left and right front wheels  14 . The front wheels  14  have respective hydraulic friction brakes  20  coupled thereto. An active brake pedal  22  is coupled to a brake pedal sensor wherein the brake pedal sensor generates a braking demand signal for a controller  28 . The electromagnetic and friction braking system  10  is actuated when the brake pedal  22  is placed in a predetermined brake pedal position by a vehicle operator. Preferably, the predetermined brake pedal position occurs when the brake pedal  22  is in a depressed position. The front and rear wheels  14  and  12  are coupled to front and rear eddy current devices  18  and  16 . In a preferred embodiment, there are four eddy current devices wherein each wheel has an eddy current device connected thereto. The front and rear eddy current devices  18  and  16  are electromagnetic retarders which produce a braking force in the form of a retarding torque on the front and rear wheels  14  and  12  when energized. The front eddy current devices  18  are mounted on a sprung mass with the chassis of the vehicle. The rear eddy current devices  16  are mounted on the rear wheel hubs. A power module  40  is electrically coupled to the front and rear eddy current devices  18  and  16  and a controller  28 . The power module  40  receives signals from the controller  28  and generates signals for the controller  28  and the front and rear eddy current devices  18  and  16 . A generator  24  is mounted on the end of a transmission  25  and coupled to a drive shaft  27 . The generator  24  is preferably a three-phase synchronous brush type having excitation and output windings. An alternate embodiment of the generator  24  is a three-phase brushless hompolar type. The generator  24  is electrically connected to the controller  28  and the front and rear eddy current devices  18  and  16 . The generator  24  supplies power to the front and rear eddy current devices  18  and  16 . The generator  24  is also capable of supplying power to a battery  26  when a brake pedal sensor  35  senses that the vehicle operator has placed the brake pedal  22  in the depressed position. The operating voltage of the generator  24  is about 42 volts. An alternator  29  is mounted directly on an engine  31  and also charges the battery  26 . The battery  26  is capable of supplying power to the front and rear eddy current devices  18  and  16  to enhance braking performance or when the generator  24  does not produce an adequate amount of power for the front and rear eddy current devices  18  and  16 . The battery  26  has a voltage of thirty-six volts and is chargeable up to forty-two volts. A wheel speed sensor  37  is coupled to the front and rear wheels  14  and  12  and generates a signal for the controller  28  that corresponds to the speed of the wheels. An alternate embodiment has only a single wheel speed sensor that is coupled to a vehicle differential or only one wheel of the vehicle. 
     The brake pedal sensor  35  inputs the position of the brake pedal  22  into the controller  28 . A throttle position sensor  33  generates a signal for the controller  28  that corresponds to the position of the throttle (not shown). The position of the throttle varies as the vehicle operator presses an accelerator pedal. The controller  28  stores an actual power output of the generator  24  based on the amount of voltage and current produced by the generator  24 . The controller  28  also stores in memory a predetermined throttle position based on the position of the throttle. Preferably, the predetermined throttle position ranges from five to ten degrees from a non-depressed position. It is recognized that the predetermined throttle position range is vehicle dependent and can vary accordingly. For instance, the range may be fifteen to twenty degrees from the non-depressed position. The controller  28  also stores in memory an elapsed energization time, a predetermined ramp time, and a power consumption requirement of the front and rear eddy current devices  18  and  16 . The elapsed energization time is the elapsed time since the vehicle operator has made a braking demand, i.e. pressed the brake pedal. The predetermined ramp time is the amount of time required for the generator  24  to respond to the pressing of the brake pedal  22 . During the predetermined ramp time, the battery  26  will supply power to the eddy current devices  16  and  18 . The power consumption requirement of the front and rear eddy current devices  18  and  16  is the amount of power required by the front and rear eddy current devices  18  and  16  as requested by the vehicle operator when the brake pedal  22  is pressed. In addition, when the friction brake  20  is activated, the controller  28  generates a signal for a driver module  19 . The driver module  19  controls the amount of hydraulic pressure within the friction brake system. In response to the signal from controller  28 , the driver module  19  activates valves within the friction brake system to either increase or decrease the level of hydraulic pressure. 
     In  FIG. 2 , there is illustrated an electrical schematic for the electromagnetic and friction braking system  10 . As the generator  24  generates power, the output is rectified and applied to a capacitor  42 . The capacitor  42  stabilizes the rectified output of the generator  24 . When the battery switch  32  is closed the battery  26  supplies power to a power rail  41 . The power rail  41  is a voltage summing junction for the generator  24  and the battery  26 . The power rail  41  provides the electrical connection between the battery switch  32  and the front and rear eddy current devices  18  and  16 . After the power module  40  receives signals from the controller  28 , either the generator  24  or the battery  26  energizes the front and rear eddy current devices  18  and  16 . The power module  40  includes front eddy current switches  34  and rear eddy current switches  36 . The controller  28  generates signals for the power module  40 . Preferably, the signals generated for the power module  40  are pulse-width-modulated. Thereafter, either the generator  24  or the battery  26  according to the method below energizes the front and rear eddy current devices  18  and  16 . The controller  28  monitors the current draw of the front and rear eddy current devices  18  and  16  The controller  28  monitors the current draw of the front and rear eddy current devices  18  and  16  by receiving a current feed back signal over a power line  17  A voltmeter enables the controller  28  to monitor the rectified output voltage of the generator  24 .  FIG. 4  illustrates an alternate configuration of the electromagnetic and friction braking system  10 . Duplicate reference numerals are used for components common with  FIG. 1 . The embodiment in  FIG. 4  differs from  FIG. 1  in that the generator  24  mechanically engages the driveshaft  27  at an opposite end of the driveshaft  27  from the transmission  25 . 
       FIG. 3  illustrates a regenerative braking method  44  for the electromagnetic and friction braking system  10  according to the present invention. A step  46  is the entrance into the regenerative braking method  44 . At a step  48 , the controller  28  receives a signal from the throttle position sensor  33 . The controller  28  compares the throttle position signal (TP) to the predetermined throttle position threshold (Tol TP ). If the throttle position is greater than the predetermined throttle position threshold, a step  50  occurs. One skilled in the art will recognize that sensing the throttle position enhances braking performance and may be excluded without departing from the scope of the invention. At the step  50 , the output of the generator  24  is applied to the front and rear eddy current devices  18  and  16 . At the step  50 , the generator is isolated from the battery. When the throttle position is less than the predetermined throttle position threshold, a step  52  occurs. At the step  52 , the controller  28  receives signals from the braked pedal sensor referred to herein as the braking demand. The controller  28  compares the braking demand to the predetermined brake demand threshold (Tol BRK ) which corresponds to a predetermined brake pedal position. Preferably, the predetermined brake demand threshold is about 1 in/s 2 . When the braking demand is greater than the predetermined brake demand threshold, a step  54  occurs. At the step  54 , the generator  24  supplies power to the front and rear eddy current devices  18  and  16  without charging the battery  26 . If the braking demand is less than the predetermined brake demand Threshold, a step  56  occurs. At the step  56 , the controller receives a wheel speed sensor signal from the wheel speed sensor  37  that correspond to the speed of the front and rear wheels  14  and  12 . The wheel speed (WhlSpd) is compared to a predetermined wheel speed threshold (Tol W ). Preferably, the predetermined wheel speed threshold is at least 50 revolutions per minute. When the wheel speed is less than the predetermined wheel speed threshold, a step  60  occurs. At the step  60 , the output of the generator  24  is a plied to the front and rear eddy current devices  18  and  16 . During the step  60 , the battery  26  is isolated from the generator  24 . If the wheel speed is greater than the predetermined wheel speed threshold, a step  57  occurs. In the step  57 , the voltage of the generator  24  (V GEN ) is compared with the voltage of the battery  26  (V BATT ). The method isolates the battery from the generator to prevent battery charging when the generator voltage is less than the battery voltage in step  59 . When the generator voltage is greater than the battery voltage, the generator charges the battery in step  58 . In the step  58 , the generator  24  produces an amount of power in excess of that required to power the front and rear eddy current devices  18  and  16 . The controller  28  generates signals for the battery switch  32  thereby allowing the generator  24  to charge the battery  26 . A step  62  completes each loop through the regenerative braking method  44 . 
     Various other modifications to the present invention may occur to those skilled in the art to which the present invention pertains. Other modifications not explicitly mentioned herein are also possible and within the scope of the present invention.