Patent Publication Number: US-2013228402-A1

Title: Parking brake in a vehicle

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a parking brake in a vehicle. 
     2. Description of the Related Art 
     Electromechanical parking brakes are known for generating a clamping force which holds the vehicle at a standstill with the aid of an electric brake motor. When the brake motor is activated, a brake piston, which is the carrier of a brake lining, presses against a brake disk. Such a parking brake is known from German patent document DE 103 61 042 B3, for example. 
     The parking brake usually acts upon the wheel brake units of both wheels of the rear axle, each wheel brake unit being assigned an electric brake motor for generating the desirable clamping force. During the engagement process for building up the clamping force, the electric brake motors are controlled via an assigned control electronics in one direction, and for releasing the clamping force, the brake motors are controlled in the opposite direction. The control unit typically includes one H-bridge circuit and one associated driver unit per brake motor for controlling the electromechanical relays or transistors in the H-bridges. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to control, using simple measures, a parking brake in a vehicle which has wheel brake units, each having one brake motor on two vehicle wheels, in a simple and space-saving manner. 
     The parking brake according to the present invention may be used in vehicles to generate a clamping force which holds the vehicle at a standstill. The parking brake has an electromechanical braking device which includes an electric DC brake motor. The parking brake is assigned two wheel brake units, each having one electric brake motor. The wheel brake units having the electric brake motor are preferably located on the opposite wheels of a common axle, in particular of the rear axle of the vehicle. 
     During a rotational movement of the electric brake motor, a final control element executes an actuating motion via which a brake piston, which is the carrier of a brake lining, is pressed axially against a brake disk of the wheel brake unit for generating the desirable clamping force. This engagement process is carried out until the desirable setpoint clamping force is reached. To disengage the parking brake, the brake motor is activated in the opposite direction so that the brake piston and the brake lining are removed from the brake disk. 
     If necessary, the hydraulic pressure of the regular vehicle brake may act upon the brake piston to decelerate the vehicle while driving. Basically, the hydraulic pressure of the vehicle brake may also be active when the vehicle is at a standstill and may result in an additional clamping force which adds to the electromechanically generated clamping force of the brake motor. 
     The engagement and the disengagement processes of the two electric brake motors take place simultaneously at the different wheels. The control is carried out with the aid of a control electronics which is designed as an H-bridge in the embodiment of the parking brake according to the present invention. Each brake motor is assigned one H-bridge, the H-bridges being interconnected in such a way that the two H-bridges have a shared half-bridge branch having two switches, in particular transistors, and the shared half-bridge branch is used to control both brake motors. Thus, there is a shared control electronics for both brake motors, the design including the double H-bridge having one shared half-bridge branch allowing for an independent switching of the two brake motors, while the motors, however, rotate in the same direction of rotation during the engagement and the disengagement processes. 
     This design has the advantage that one half-bridge branch having two switches may be omitted compared to a design having two separate H-bridges. In the embodiment according to the present invention, the control electronics comprises a total of three half-bridge branches, the middle half-bridge branch being assigned to both DC brake motors. By omitting one half-bridge branch having two switches or transistors, it is also possible to save printed-board space so that the control unit may have a smaller design. 
     Advantageously, fully electronic H-bridges having transistors as switches, e.g., MOSFETs, are used. Basically, other H-bridges having electromechanical relays are, however, also possible. 
     According to one advantageous embodiment, the control unit has one shared driver unit for controlling the switches in the H-bridges. All six switches in the three individual half-bridge branches may be controlled via the shared driver unit for the H-bridges of the two brake motors in such a way that the current flows in the one or the other direction through the two electric motors in order to carry out the engagement and the disengagement processes. The driver unit may be a so-called B6 or three-phase bridge circuit, for example, which is available as a standard circuit and is usually used for three-phase motors. When used in the parking brake according to the present invention which has two DC brake motors, the six switches of the H-bridges may be controlled and switched via the B6 bridge circuit. 
     According to another advantageous embodiment, measuring devices are provided for measuring the motor currents through the two brake motors. The instantaneous clamping force may be inferred from the motor current so that during the engagement process, the electric brake motors are activated until the desirable setpoint clamping force is reached. 
     In particular, when using a B6 bridge circuit as the driver unit, it may have a total of three measuring devices, of which two measuring devices are used to measure the current of the brake motors and the third measuring device may be used to redundantly measure the current, in particular to check the current measurements of the two brake motors for plausibility. 
     The brake motors are advantageously designed as DC motors. According to one advantageous embodiment, the control of the brake motors may take place without pulse width modulation (PWM), in that the current flow is maintained until the desirable setpoint clamping force is reached. However, a control and regulation via a PWM is basically also possible. 
     To prevent a false polarity, a polarity reversal protection is advantageously integrated into the voltage supply line of the electric brake motors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a section through an electromechanical parking brake for a vehicle having an electric brake motor for generating a clamping force which holds the vehicle. 
         FIG. 2  shows a wiring diagram for controlling electric brake motors in a vehicle. 
         FIG. 3  shows another wiring diagram for controlling electric brake motors having measuring devices for measuring the current. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an electromechanical parking brake  1  in a vehicle, a clamping force which holds the vehicle at a standstill being generatable via the parking brake. Parking brake  1  has a brake caliper  2  having a caliper unit  9  which reaches over brake disk  10 . A brake motor  3  which is designed as an electric motor and which rotatingly drives a spindle  4 , on which a spindle component  5  is displaceably installed, is used as the final control element of parking brake  1 . Spindle component  5  is axially displaced when spindle  4  rotates. Spindle component  5  moves within a brake piston  6 , which is the carrier of a brake lining  7  which is pressed by brake piston  6  against brake disk  10 . Another brake lining  8 , which is held in a fixed position on caliper unit  9 , is situated on the opposite side of brake disk  10 . 
     Within brake piston  6 , spindle component  5  is able to move axially forward in the direction of the brake disk when spindle  4  rotates, and it is able to move axially rearward until a stop  11  is reached when spindle  4  rotates in the opposite direction. In order to generate a desirable setpoint clamping force, spindle component  5  acts upon the inner front side of brake piston  6 , so that brake piston  6 , which is supported axially displaceably in parking brake  1 , is pressed with brake lining  7  against the facing front side of brake disk  10 . 
     Furthermore, the hydraulic pressure of the regular hydraulic vehicle brake, using which the vehicle is braked during the travel, may act upon the brake piston. The hydraulic pressure may also actively support the parking brake when activated and when the vehicle is at a standstill so that the total clamping force is composed of the portion provided by the electric motor and the hydraulic portion. 
       FIG. 2  shows a wiring diagram for controlling electric DC brake motors  28  and  29  which are part of the parking brake and have the structure according to  FIG. 1 . The two brake motors are located on the left and the right wheels of the rear axle of a vehicle and are controlled via a control unit  20  to carry out the engagement and the disengagement processes. 
     Control unit  20  includes a control electronics  21  having two interconnected H-bridges  23  and  24  as well as a driver unit  22  via which transistors  30  through  35  of the two H-bridges  23 ,  24  are controlled. 
     Each brake motor  28 ,  29  is assigned one H-bridge  23  and  24 , respectively, which are, however, interconnected in such a way that the H-bridges have a shared middle half-bridge branch  26 . In this way, brake motor  28  is assigned first H-bridge  23  having the two half-bridge branches  25  and  26 , between which brake motor  28  is situated, and second brake motor  29  is assigned second H-bridge  24  having half-bridge branches  26  and  27 , between which brake motor  29  is situated. In each half-bridge branch  25 ,  26 ,  27 , two transistors  30  and  31 ,  32  and  33 ,  34  and  35 , respectively, are located. Each transistor is assigned one diode. 
     The two H-bridges  23 ,  24  are connected to a voltage supply line  36  into which a polarity reversal protection  37  is integrated. 
     Transistors  30  through  35  in H-bridges  23 ,  24  are controlled and switched via driver unit  22  which is designed as a B6 or three-phase current bridge circuit and enables the setting of all transistors. Due to shared half-bridge branch  26 , the two brake motors  28 ,  29  may each only be operated in the same direction of rotation despite the independent control. For example, transistor  30  in first half-bridge branch  25  and transistor  33  in second half-bridge branch  26  are activated for the engagement process via driver unit  22  for the forward direction of first brake motor  28 . Similarly, transistor  34  in third half-bridge branch  27  is also activated by driver unit  22  for the engagement process of second brake motor  29 . In first H-bridge  23 , the current thus flows via transistor  30 , first brake motor  28 , and transistor  33 ; in second H-bridge  24 , the current, however, flows via transistor  34 , second brake motor  29 , and transistor  33  during the engagement process. During the disengagement process, the direction of rotation of the brake motors is reversed; transistors  31 ,  32 , and  35  are activated so that the current flows via transistor  32 , first brake motor  28 , and transistor  31  in first H-bridge  23  and via transistor  32 , second brake motor  29 , and transistor  35  in second H-bridge  24 . 
     As is apparent from the wiring diagram according to  FIG. 3 , in which control unit  20  basically has the same structure as in the exemplary embodiment according to  FIG. 2 , the control unit may be equipped with measuring devices  38 ,  39 , and  40  for measuring the current. Measuring devices  38  through  40  are an integral part of driver unit  22 , i.e., the signals of the measuring devices are evaluated in driver unit  22 . Measuring devices  38  through  40  each include a measuring shunt at which the voltage drop is measured. First measuring device  38  is assigned to first brake motor  28 , and second measuring device  39  is assigned to second brake motor  29  to ascertain the respective motor currents. Third measuring device  40  is located in the shared current path of the two brake motors and is used to check the measuring devices assigned to the respective brake motors for plausibility, in that the current measured in third measuring device  40  must correspond to the sum of the individual currents which are measured in first and second measuring devices  38  and  39 .