Patent Publication Number: US-2006009901-A1

Title: Braking device for a motor vehicle

Description:
BACKGROUND OF THE INVENTION  
      More precisely, the invention relates to a motor vehicle braking device of the type comprising a parking brake.  
      It is known practice to fit motor vehicles with electronic driving aid devices to improve road holding or the effectiveness of the braking of the vehicles.  
      Amongst these electronic aid devices, mention can be made of ABS (Antilock Braking System), which is a device preventing the wheels from locking up during braking, or ESP (Electronic Stability Program) which is a device ensuring the stability of the vehicle particularly in turns or on a slippery pavement.  
      These electronic aid devices usually use a computer which processes data originating from sensors situated close to the wheels, and which automatically acts on the motor vehicle&#39;s braking device. The data are normally transferred between the sensors and the computer via electric cables.  
      The function of a vehicle parking brake is to immobilize the vehicle&#39;s wheels when the latter is parked. The parking brake may be actuated by mechanical or electric means whose correct operation it is desirable to monitor.  
      However, the addition of means of monitoring the parking brake requires a priori the management of monitoring data that must be transferred via electric cables as is the case with the aforementioned aid devices.  
      Now, the cost of installing electric cables in a vehicle increases with the number of these cables.  
      The main aim of the invention is to monitor the correct operation of a parking brake with the aid of simple and effective means, while minimizing the number of additional electric cables necessary for the operation of the means of monitoring the parking brake.  
     SUMMARY OF THE INVENTION  
      As a result, the subject of the invention is a motor vehicle braking device, of the type comprising a parking brake, characterized in that it comprises means for detecting the state of a member of the parking brake, these state detection means providing an item of information to a computer via an electric cable connecting this computer to a device placed close to the state detection means, called the adjacent device.  
      Thanks to this braking device, the motor vehicle comprises means detecting the state of a member of the parking brake, providing an item of information to the motor vehicle&#39;s computer. In addition, since the state detection means use an electric cable shared with the adjacent device, the number of additional cables necessary for the operation of the state detection means is limited.  
      A braking device according to the invention may also comprise one or more of the following features: 
          the adjacent device is capable of providing a signal, called the adjacent signal, transmitted via the electric cable, this adjacent signal being able to change between a first value s v   1  and a second value s v   2  to within a noise level, these two values corresponding respectively to a first and a second state of the adjacent device;     the state detection means provide a signal carrying the item of information on the state of the parking brake, called the state detection signal, intended to be added to the adjacent signal, this state detection signal being capable of taking a first value s p   1  and a second value s p   2 , corresponding respectively to a state in which the parking brake is deactivated and to a state in which the parking brake is activated;     the four values s v   1 +s p   1 , s v   2 +s p   1 , s v   1 +s p   2  and s v   2 +s p   2  of the signal equal to the sum of the adjacent signal and the detection signal are different by twos to within the noise level;     the parking brake member is a key intended to immobilize a brake in a position of immobilization of a vehicle wheel;     the adjacent device comprises a member chosen from a wheel rotation detection device and a brake actuator;     the adjacent device comprises a brake actuator supported by a caliper of the braking device;     the two values of the adjacent signal correspond respectively to a state E p   1  in which the brake actuator is activated and a state E p   2  in which the brake actuator is deactivated;     the adjacent device comprises a wheel rotation detection device supported by a hub carrier;     the two values of the adjacent signal are provided by the wheel rotation detection device, these two values corresponding respectively to a state E v   1  in which the wheel is immobile, and a state E v   2  in which the wheel is rotating;     the wheel rotation detection device comprises magnetic or optical means supported by a hub carrier of the wheel;     the wheel rotation detection device comprises a Hall effect probe;     the adjacent device is capable of providing a signal characteristic of at least three states of the adjacent device;     the signal provided by the adjacent device is a pulse whose duration is a function of the state of the adjacent device.        

      The invention will be better understood on reading the following description, given as an example only and made with reference to the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagram of a motor vehicle furnished with a braking device according to the invention;  
       FIG. 2  is a view of the braking device state detection means according to a first embodiment of the invention;  
       FIG. 3  is a diagram of an electric circuit comprising different elements of the state detection means according to the first embodiment of the invention;  
       FIG. 4  is a graph representing the values taken by a signal I T  transmitted on the electric cable between the state detection means shown in  FIG. 3  and the vehicle&#39;s computer, the signal I T  being characteristic of the state of the braking device;  
       FIG. 5  is a view of the braking device state detection means according to a second embodiment of the invention;  
       FIG. 6  is an electric circuit diagram of one of the elements of the state detection means, according to the second embodiment of the invention; and  
       FIGS. 7   a  to  7   e  are graphs representing over time signals transmitted in the form of pulses between the state detection means, according to a third embodiment, and the vehicle&#39;s computer. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      A motor vehicle  10  schematized by four wheels  11  is represented in  FIG. 1 . The motor vehicle  10  comprises a braking device designated by the general reference number  12 . The braking device  12  comprises in particular a parking brake of which only one member  14  placed close to the wheels  11  has been represented. The braking device  12  is furnished with means  16  for detecting the state of the parking brake member  14 . These state detection means  16 , which will be described later, are suitable for providing data relating to the state of the parking brake member  14 .  
      Close to these state detection means  16 , the braking device comprises a device  18  called the adjacent device. The adjacent device  18  interchanges data with a computer  20  of the braking device  12 .  
      The interchanged data are carried by a signal, called the adjacent signal S v , transmitted on at least one electric cable  22  connecting the computer  20  to the braking device  12 .  
      The adjacent device is, for example, a wheel rotation detection device or a valve of the braking device  12 , intended to control the inflow of brake fluid.  
      The computer  20  is for example the computer of an electronic aid device.  
      The state detection means  16  are connected to the electric cable  22 , in order to be able to transmit to the computer  20  a signal, called the state detection signal S p , carrying the data relating to the state of the parking brake member  14 . Thus, the number of additional cables necessary to the operation of the state detection means  16  is limited because the electric cable  22  is common to the transmission of the adjacent signal and of the state detection signal. It may be considered that the adjacent signal S v  and the state detection signal S p  are multiplexed on the electric cable  22 .  
      The braking device  12  comprises disk braking means equipping at least the front wheels of the vehicle.  
      Thus, with reference to  FIG. 2 , it can be seen that the device  12  comprises, associated with each front wheel of the vehicle, a brake disk  23 , represented in  
       FIG. 2 , integral in rotation with the wheel. The brake disk  23  is mobile relative to a hub carrier  24 . The braking device  12  comprises brake pads  26  intended to rub against the brake disk  23  to counter its rotation relative to the hub carrier  24 . The brake pads  26  are intended to be pressed against the brake disk  23  with the aid of conventional hydraulic means of which a caliper  28  supporting a conventional hydraulic cylinder (not shown) has been represented. These hydraulic means are supplied with brake fluid via a pipe  30 .  
      The state detection means  16  of the parking brake member  14  are supported by the caliper  28 . These means  16  detect for example the movement or force sustained by the parking brake member  14 . This member  14  may be a key intended to stop the stroke of the hydraulic cylinder in the position in which the wheel is immobilized.  
      The means  16  may detect two states of the parking brake member  14 : a first state in which this member  14  is activated and a second state in which this member  14  is deactivated, which have been designated respectively by E p   1  and E p   2 .  
      According to a first embodiment shown in  FIG. 2 , the adjacent device  18  comprises a wheel rotation detection device  32 , supported by the hub carrier  24 , used for example in an ABS system.  
      This wheel rotation detection device  32  comprises conventional means of the magnetic or optical type. In the example described, the detection device  32  comprises magnetic means such as a Hall effect probe H, supported by the hub carrier  24 , associated with a phonic wheel  33  connected in rotation to the disk  23 .  
      The wheel rotation detection device  32  can detect two states: a first state in which the wheel is immobile and a second state in which the wheel is rotating, which are designated respectively by E v   1  and E v   2 .  
      The four states E p   1 , E p   2 , E v   1  and E v   2  detected by the means  16  (the first two) and the device  32  (the last two) correspond respectively to the four signals s p   1 , s p   2 , s v   1  and s v   2  intended to be transmitted on the electric cable  22 .  
      The transmission to the computer  20 , on a single electric cable  22 , of the state data of the wheel rotation detection device  32  and of the state data of the state detection means  16  is carried out by means of a simple multiplexing consisting of summing the signals corresponding to the detected states. The various cases are assembled in the following table:  
                                                  Adjacent device                                     Parking brake   E v   1     E v   2                         E p   1     S v   1  + S p   1     S v   2  + S p   1             E p   2     S v   1  + S p   2     S v   2  + S p   2                        
 
      As will be specified in greater detail hereinafter, the values of the signals s p   1 , s p   2 , s v   1  and s v   2  must comply with certain relationships for the computer  20  to carry out an effective demultiplexing, that is to say for the computer  20  to differentiate between the summed signals.  
       FIG. 3  shows an electric circuit diagram comprising different elements of the state detection means  16  and of the wheel rotation detection device  32  according to the first embodiment of the invention.  
      The electric circuit comprises a first module  34  comprising the adjacent device  18 , and various electric elements associated with the Hall effect probe H, particularly the current generators I 1  and I 2 . On the electric cable  22 , these generators provide: 
          a signal s v   1 =I 1  when the probe detects the state E v   1 , that is to say when the wheel is immobile, and     a signal s v   2 =I 1 +I 2  when the probe detects the state E v   2 , that is to say when the wheel is moving.        

      The electric circuit in  FIG. 3  also comprises a second module  38  corresponding to the state detection means  16 . To carry out the multiplexing, the second module  38  is connected in parallel with the first module  34 . The second module  38  comprises a current generator I 3  controlled by a dry or intelligent contactor  40 .  
      The contactor  40  is open when the parking brake member is in the state E p   1 , that is to say when it is deactivated, and is closed when the parking brake member is in the state E p   2 , that is to say when it is activated.  
      The signal resulting from the multiplexing of the two signals is a current marked I T , transmitted on the electric cable  22 . This current is equal to the sum of the currents created by the first two modules  34  and  38 . The possible values of the current I T  are assembled in the following table:  
                                                  Adjacent device                                     Parking brake   E v   1     E v   2                         E p   1     I 1     I 1  + I 2             E p   2     I 1  + I 3     I 1  + I 2  + I 3                        
 
       FIG. 4  is a graph representing the values taken by the multiplexed signal I T  transmitted on the electric cable  22  as a function of the states E p   1 , E p   2 , E v   1  and E v   2  of the wheel rotation detection device  32  and of the state detection device  14 .  
      δI v  designates the amplitude of the noise of the adjacent signal provided by the wheel rotation detection device  32 . The four states are distinguishable from one another provided that the values of the current I T  corresponding to these four states are different by twos to within 2δI v .  
      If in addition δI p  designates the amplitude of the state detection signal noise, then the four states are distinguishable from one another provided that the current values I T  corresponding to these four states are different by twos to within 2δI v +2δI p .  
      The electric circuit in  FIG. 3  also comprises a voltage limiter module  42  whose role is to prevent the signal transmitted on the electric cable from overloading and a stabilization module  44  intended to remove any signal fluctuations.  
      According to a second embodiment shown in  FIG. 5 , the adjacent device  18  comprises a brake actuator  46 , for example a valve  46  controlling the inflow of brake fluid. This valve  46 , which is supported by the caliper  28  of the braking device may have two states: a state E v   1  in which the caliper  28  is open and a state E v   2  in which the caliper  28  is clamped. The information relating to the state of the valve  46  is transmitted to the computer  20  via the electric cable  22 .  
      As in the first embodiment, the parking brake may have two states E p   1  and E p   2 : a first state in which it is activated and a second state in which it is deactivated.  
      The items of information relating to the state of the parking brake member  14  and the items of information relating to the state of the valve  46  are multiplexed on the electric cable  22 . The electric circuit corresponding to the second embodiment is identical to that of the first embodiment shown in  FIG. 3 , except for the first module  34  which is replaced by that shown in  FIG. 6 .  
      The first module  34  shown in  FIG. 6  comprises a current generator controlled by the valve  46 . The current generator is intended to provide a current I 2  when the valve is activated and a zero current otherwise.  
      The possible values of the current I T  are then assembled in the following table:  
                                                  Adjacent device                                     Parking brake   E v   1     E v   2                         E p   1     0   I 2             E p   2     I 3     I 2  + I 3                        
 
      The remarks concerning the prescribed relations between the values of the currents I 1 , I 2  and I 3  are identical to those formulated in the description of the first embodiment.  
      According to a third embodiment not shown, the adjacent device  18  comprises a sensor capable of detecting more than two states. The adjacent device  18  may, for example, be a wheel rotation detection device, also providing an item of information relating to the direction of rotation of the wheel.  
      The data provided by the adjacent device  18  are carried by the adjacent signal S v  transmitted to the computer  20  on the electric cable  22 . The  FIGS. 7   a  to  7   d  show four representations of the adjacent signal s v   1 , s v   2 m, S v   3  S v   4  each corresponding respectively to a state E v   1 , E v   2 , E v   3 , E v   4  that can be detected by the adjacent device  18 . Each state is coded in the form of a pulse of specific duration such that the pulses can be differentiated from one another.  
      The signal S p , carrying the data provided by the state detection means  16  of the parking brake member  14 , is shown in  FIG. 7   e.  This signal is represented by a pulse s v   1  with a different duration from those of the pulses provided by the adjacent device  18  if the parking brake is activated, and by a signal s v   2  that is zero if the parking brake is deactivated.  
      The signals S p  and S v  are multiplexed by summing them. The pulses are of different durations, so it is possible to distinguish them and demultiplex the signals.  
      The number of states that can be transmitted on the electric cable  22  increases as the transmission noise reduces.