Patent Publication Number: US-2009230762-A1

Title: Brake System for Motor Vehicles

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a brake system for motor vehicles comprising 
     an actuating unit consisting of a brake booster operable by means of a brake pedal and actuatable independently of the driver&#39;s wish as well as of a master brake cylinder connected downstream of the brake booster, to which master brake cylinder wheel brakes of a motor vehicle are connected, a means to detect a deceleration request of the driver, a hydraulic control and regulation unit for performing driving-dynamics related control and regulation operations (ABS, ESP, TCS . . . ), which is connected between the master brake cylinder and the wheel brakes and includes at least one hydraulic pump, a first electronic control and regulation unit which is associated with the actuating unit and serves to actuate the brake booster, as well as a second control and regulation unit which is associated with the hydraulic control and regulation unit and serves to drive the components thereof. 
     A brake system of this type is disclosed in the applicant&#39;s international patent application WO 2004/005095 A1. The special feature of the prior art brake system resides in that means are provided for uncoupling a force-transmitting connection between the brake pedal and the brake booster. It is achieved by this provision that the brake system disclosed in the mentioned documents can be operated in the ‘brake-by-wire’ operating mode. In addition, a pedal travel simulator cooperating with the brake pedal is provided, which allows simulating a resetting force in the ‘brake-by-wire’ operating mode that acts on the brake pedal irrespective of an actuation of the brake booster, thereby imparting to the operator the customary pleasant brake pedal feeling. However, this mentioned publication does not give any hints to provisions which would permit carrying out a transfer of process-relevant data between the two electronic control and regulation units. 
     In view of the above, an object of the invention is to disclose appropriate measures that allow cross-linking the two electronic control and regulation units. 
     SUMMARY OF THE INVENTION 
     This object is achieved by the characterizing portion of the patent claim in that the first electronic control and regulation unit includes a means supplying the second electronic control and regulation unit with a nominal value of the hydraulic pressure that can be introduced into the brake system along with a request for activation of the hydraulic control and regulation unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       Further features and advantages of the invention will be explained in detail in the following description making reference to the accompanying drawings. 
       In the drawings: 
         FIG. 1  is a schematic representation of the brake system of the invention; and 
         FIG. 2  shows the type of communication between the electronic control and regulation units indicated in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The motor vehicle brake system as illustrated in  FIG. 1  of the drawing, which can preferably be operated in the ‘brake-by-wire’ operating mode, essentially consists of an actuating unit  1 , a brake pedal  1 , a hydraulic control and regulation unit (HCU)  17 , vehicle wheel brakes  13 ,  14 ,  15 ,  16  connected to the hydraulic control and regulation unit (HCU)  17 , a first electronic control and regulation unit  7  associated with the actuating unit  1 , and a second electronic control and regulation unit  12  that is associated with the hydraulic control and regulation unit (HCU)  17 . The actuating unit  1 , in turn, consists of a brake booster, preferably a vacuum brake booster  2 , a master brake cylinder connected downstream of the brake booster  2 , preferably a tandem master cylinder  3 , to the pressure chambers (not shown) of which the above-mentioned wheel brakes  13 ,  14 ,  15 ,  16  are connected by the intermediary of the hydraulic control and regulation unit  17 , and a pressure fluid tank  4  associated with the master brake cylinder  3 . A brake pedal  5  is used for actuation of the brake booster  2  by the driver, and a pedal travel simulator  6  is provided, which cooperates with the brake pedal  5  especially in the ‘brake-by-wire’ operating mode, the said simulator imparting the customary brake pedal feeling to the driver. At least one sensor device  21  is used to sense a driver&#39;s deceleration request and the actuating travel of the brake pedal  5 , respectively, and the signals of the sensor device are sent to the above-mentioned first electronic control unit  7 . The output signals of the first electronic control unit  7  enable, among others, actuation of an electromagnet  8  that is associated with the brake booster  2  and renders it possible to activate a pneumatic control valve  9  independently of the driver&#39;s wish, the said control valve controlling the supply of air to the brake booster  2 . As will be explained in detail in the following description, the first electronic control and regulation unit  7  comprises a control circuit for controlling a characteristic quantity of the brake booster  3 , preferably the travel covered by an output member  20  of the brake booster  2 , and/or for controlling the hydraulic pressure that prevails in the system. 
     An axial slot ‘a’ provided between the end of a piston rod  10  coupled to the brake pedal  1  and a valve piston  11  of the above-mentioned control valve  9  ensures uncoupling the force-transmitting connection between the brake pedal  5  and the brake booster  2  in the ‘brake-by-wire’ operating mode. A travel sensor  18  is used to sense the travel of a movable wall  19 , which generates the boosting force of the brake booster  2 , or the travel of the above-mentioned output member  20  of the brake booster  2 , which transmits its output force to a first piston (not shown) of the master brake cylinder  3 . Furthermore, a pressure sensor  34  is integrated in the hydraulic regulation unit  17 , sensing the hydraulic inlet pressure that prevails in the system. 
     The pedal travel simulator  6  by which, as has been mentioned above, a resetting force acting on the brake pedal  5  in the ‘brake-by-wire’ operating mode can be simulated irrespective of an actuation of the brake booster  2  is designed in such a fashion that it can be enabled in the ‘brake-by-wire’ operating mode when the force-transmitting connection between the brake pedal  5  and the brake booster  2  is uncoupled, and can be disabled outside the ‘brake-by-wire’ operating mode. The activation of the pedal travel simulator  6  is executed by means of an actuating member  35  articulated at the brake pedal  1 . 
     In addition, it can be taken from the drawing that the hydraulic control and regulation unit (HCU)  17  includes all hydraulic and electrohydraulic components which are required to perform brake pressure control operations such as ABS, TCS, ESP . . . Among the components are per brake circuit: one separating valve  22   a, b , one electric change-over valve  23   a, b , one hydraulic pump  24   a, b,  respectively two electrically drivable pressure control valves or inlet and outlet valves  25   a, b ,  26   a, b ,  27   a, b  and  28   a, b  for the selective adjustment of the brake pressure at the wheel brakes  13  to  16 , respectively one low-pressure accumulator  29   a, b,  and pressure sensors  30  to  33  associated with the wheel brakes  13  to  16 . 
     The operation of the brake booster  2  causes hydraulic pressure to build up in the master brake cylinder  3 , as becomes apparent from the description referred to hereinabove. It is known, however, that in the mentioned pressure buildup the attainable maximum pressure is limited by the so-called point of maximum boosting which depends on the vacuum level available. If pressures above this point of maximum boosting are demanded, pressure is increased in the vehicle wheel brakes  13  to  16  by means of the hydraulic control and regulation unit  17 , or in particular by activation of the pumps  24   a, b.  To safeguard a proper function of the brake system of the invention, an exchange of information and data must be permitted to take place between the first ( 7 ) and the second control and regulation unit  12 . For the purpose of cross-linking the two control and regulation units  7 ,  12  (see  FIG. 2  in particular) the first control and regulation unit  7  includes a signal transmitting device  71 , which sends to the second control and regulation unit  12  a nominal value p nominal  of the pressure that is to be introduced into the wheel brakes  13  to  16  along with an activation request (St) which corresponds to the activation of the hydraulic pumps  24   a, b.  Criteria for the transmission of the above-mentioned nominal value p nominal  are the value of the requested pressure, which is preferably close to the hydraulic pressure that corresponds to the point of maximum boosting of the brake booster  2 , or the gradient of the nominal pressure. The corresponding signal path is designated by reference numeral  72  in  FIG. 2 . In the event of partial failure of the actuating unit  1  or the first control and regulation unit  7 , the respective unit reports the available maximum value of the pressure in the master brake cylinder  3  to the second electronic control and regulation unit  12 . The second electronic control and regulation unit  12  makes use of this information in order to perform pressure increase in the wheel brakes  13  to  16  by an appropriate boosting operation. This operating mode is indicated by the first electronic control and regulation unit  7  by setting a defined value of the activation request information (St). The maximum pressure value is the pressure value around the point of maximum boosting in the embodiment shown. The production of nominal values for the pressure increase in the wheel brakes  13  to  16  is carried out in the second electronic control and regulation unit  12  based on an internally measured pressure in the master brake cylinder  3 . 
     The second control and regulation unit  12  includes a first signal transmitting device  121 , which reports to the first electronic control and regulation unit  7  the availability of the readiness for service of the hydraulic control and regulation unit  17  or the hydraulic pumps  24   a, b.  The report occurs via a signal path which is designated by reference numeral  122  in  FIG. 2 . In the event that the readiness for service of the mentioned subsystem is not available, the first electronic control and regulation unit  7  utilizes this information for fixing an appropriate fallback mode and, as the case may be, for providing a driver&#39;s alarm. In the embodiment described above, the fallback mode represents the operation of the actuating unit  1  by the muscular power of the driver assisted by vacuum, in which case only the active actuation or independent assist actuation of the brake booster  2  no longer takes place. 
     In addition, the second electronic control and regulation unit  12  uses a second signal transmitting device  123  to send a report about the activity and the failure of the hydraulic control and regulation unit  17  to the first electronic control and regulation unit  7  via a signal transmitting path  124 , in which case the activity or the failure of driving dynamics control functions such as ABS, ESP . . . is concerned. When the brake system described is fitted in a motor vehicle equipped with a hybrid drive, the first electronic control and regulation unit  7  will adapt its strategy for including generator brake torques produced by the hybrid drive. An interface allowing a communication between the two electronic control and regulation units  7 ,  12  and the driving control  36  of the hybrid drive carries the reference numeral  37  in  FIG. 2 . 
     Finally, the second electronic control and regulation unit  12  includes a third signal transmitting device  125 , which reports information about the current vehicle speed and the vehicle standstill to the first electronic control and regulation unit  7  by way of a signal transmitting path  126 . The first electronic control and regulation unit  7  makes use of this information to optimize the control of the pressure in the master brake cylinder  3 . Examples of such optimizations are represented by the limitation of the pressure and/or the pressure increase speed during standstill or at low speeds as well as an additional increase of pressure and/or the pressure increase speed at high vehicle speeds.