Abstract:
The invention relates to a brake system for motor vehicle. A piston-cylinder arrangement can be actuated by means of a brake pedal, a controllable pressure source and brake pressure modulation valves. In order to provide a piston-cylinder arrangement which is easy to implement and axially short, the invention proposes that the piston of the piston-cylinder arrangement is directly guided in a housing that accommodates further components of the brake system according to the invention.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to German Patent Application Nos. 10 2010 062 010.6, filed Nov. 26, 2010; 10 2011 086 258.7, filed Nov. 14, 2011; and PCT/EP2011/070338, filed Nov. 17, 2011. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a brake system for motor vehicles which, in a brake-by-wire operating mode, can be activated both by the vehicle driver and also independently of the vehicle driver, is preferably operated in the brake-by-wire operating mode and can be operated in at least one fall-back operating mode in which only operation by the vehicle driver is possible, comprising: 
         [0003]    a brake pedal for actuating a hydraulic piston-cylinder arrangement having a hydraulic piston on which an actuating force (pedal force) is exerted when the brake system is actuated by the vehicle driver and which is guided displaceably in a housing along an actuation axis, 
         [0004]    a hydraulically actuable pedal travel simulator which is releasable and blockable by means of a simulator release valve, 
         [0005]    a travel detection device which detects the actuation travel of the piston, 
         [0006]    a pressure medium reservoir, 
         [0007]    an electrically controllable pressure source which delivers a brake system pressure, 
         [0008]    a pressure modulation unit having electrically controllable pressure regulating valves for adjusting wheel-individual brake pressures which are derived from the brake system pressure, the brake system pressure being supplied via a brake system pressure line to the inlet connections of the pressure regulating valves which deliver or transmit the brake system pressure in the unactivated state, 
         [0009]    dividing piston devices which are associated with the motor vehicle wheel brakes and are subjected on a first dividing piston surface to the pressure set or transmitted by the pressure regulating valves and which transmit the pressure exerted by a second dividing piston surface to the motor vehicle wheel brakes, 
         [0010]    activating elements for exerting the actuating force or for mechanically activating the dividing piston devices, which activating elements can be brought into force-transmitting connection with the piston, and 
         [0011]    an electronic control and regulation unit. 
       BACKGROUND OF THE INVENTION 
       [0012]    A brake system of the general type mentioned above is known from DE 10 2009 024 034 A1. In the known brake system, the piston coupled to the brake pedal is guided in a further hydraulic piston of larger diameter which is referred to as the retaining piston. Rod-shaped force transmitting elements associated with the dividing piston devices bear against the retaining piston, which delimits a hydraulic retaining chamber which radially encompasses the retaining piston in a housing. The complex structure of the actuating arrangement described, and the considerable axial space requirement associated therewith, are regarded as disadvantageous. 
         [0013]    It is therefore the object of the present invention to propose a simplification of the actuating arrangement which makes possible a shortening of the axial space requirement thereof. 
         [0014]    This object is achieved according to the invention by a brake system as described herein. 
         [0015]    Preferred embodiments of the invention are apparent from the following description with reference to a figure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURE 
         [0016]    In the following description the present invention is explained with reference to an exemplary embodiment and to the appended schematic drawing. In the drawing the single  FIG. 1  shows the structure of an embodiment of the brake system according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    The brake system represented only schematically in  FIG. 1  comprises essentially a hydraulic piston  3  which is actuable by means of a brake pedal  1  and forms a component of a piston-cylinder arrangement which is denoted by reference numeral  2 . The piston  3 , the actuation travel of which is monitored by means of a travel sensor  26 , delimits a hydraulic pressure chamber  36  accommodating a return spring  37  which preloads the piston  3  against a stop  38 . The pressure built up in the pressure chamber  36  by displacement of the piston  3  is detected by means of a pressure sensor  24 . The piston-cylinder arrangement  2  is formed in a housing  35  which accommodates further components of the brake system according to the invention which will be explained in the following part of the description. The brake system according to the invention further comprises dividing piston devices  5   a - 5   d  connected downstream of the piston  3  via a mechanical and hydraulic active chain, upstream of which dividing piston devices  5   a - 5   d  electrically controllable pressure regulating valves  6   a - 6   d  are connected in the hydraulic active chain and are connected to the vehicle brakes  8 - 11 , a pressure medium reservoir  12 , a pedal travel simulator  13 , an electrically controllable hydraulic pressure source  7  and an electronic control and regulation unit  33 . One dividing piston device  5   a - 5   d  is preferably associated with each wheel brake  8 - 11 . Force is transmitted between a radial collar  4  formed on the piston  3  and the dividing piston devices  5   a - 5   d  by means of mechanical activation elements  17   a - d  which are in the form of force transmitting rods and are spaced at an axial distance from the collar  4  in the unactuated state of the brake system. This distance preferably constitutes a free clearance which corresponds to the possible actuation travel of the brake pedal  1  in the brake-by-wire operating mode. Sealing rings denoted by reference numerals  39   a - 39   d ,  40   a - 40   d  are provided to seal the activation elements  17   a - d  in the housing  35 . Damping elements (not shown) may be arranged between the activation elements  17   a - 17   d  and the piston  3 . 
         [0018]    For greater clarity, only the first two dividing piston devices  5   a ,  5   b  are represented and described in detail, while the reference numerals  5   c ,  5   d  denote the other two dividing piston devices not shown in the drawing. The dividing piston devices  5   a ,  5   b  represented include in each case a dividing piston  15   a ,  15   b  which has a respective first dividing piston surface  41   a ,  41   b  and a second dividing piston surface  42   a ,  42   b  and which is preloaded against its actuation direction by a respective compression spring  16   a ,  16   b . With regard to pressure, the allocation of the dividing piston surfaces  41   a ,  41   b  and  42   a ,  42   b  is preferably such that the first dividing piston surface  41   a ,  41   b  can be subjected to the pressure (wheel-individual pressure) set by the pressure regulating valves  6   a ,  6   b , while the dividing piston surface  42   a ,  42   b  serves to build up a hydraulic pressure in the wheel brakes  8 ,  9 . Pressure chambers  43   a ,  43   b  delimited by the dividing pistons  15   a ,  15   b  are connected by means of blockable hydraulic connections to the pressure medium reservoir  12 , making possible an exchange of pressure medium between the otherwise separate hydraulic circuits and the pressure medium reservoir  12  in the unactuated state of the brake system. 
         [0019]    The aforementioned pedal travel simulator  13 , which communicates the usual brake pedal feel to the driver in brake-by-wire mode, consists in the preferred configuration shown—which, however, is not necessarily mandatory for the invention—of a hydraulic simulator chamber  30 , a simulator piston  31  and a simulator spring  32  which is compressed by hydraulic displacement of the simulator piston  31 . Actuation of the pedal travel simulator  13  is effected by actuation of the aforementioned piston-cylinder arrangement  2 , the pressure chamber  36  of which is connected by means of hydraulic connections  18 ,  44  to the simulator chamber  30 . A simulator release valve  14 , which is closed when unenergized and is connected in parallel to a non-return valve  14   r  which closes towards the simulator chamber  30 , is inserted in the connection  44 . The simulator release valve  14  is provided with a restrictor so that, upon rapid actuation of the pedal, a pressure which is detectable with the pressure sensor  24  is present, even with a short pedal stroke, as a result of the throttling of the simulator volume flow, causing rapid activation of the wheel brakes  8 - 11  by the electronic unit  33 . As a result of the non-return valve  14   r  connected in parallel, it is achieved that the return flow of pressure medium from the simulator  13  to the piston cylinder arrangement  2  is not throttled when the pedal  1  is released, so that unpleasant lifting of the driver&#39;s foot from the pedal is avoided. 
         [0020]    In brake-by-wire mode the piston-cylinder arrangement  2  communicates hydraulically with the pedal travel simulator  13  via a hydraulic path consisting of the connections  18  and  44  and defined by energization of the solenoid valves  14 ,  19  and  21 . In the fall-back operating mode, by contrast, all the valves are unenergized, so that the hydraulic connection  44  to the pedal travel simulator  13  is blocked. In this operating mode the hydraulic connection  18  is a constituent of the hydraulic active chain from the pedal to the wheel brakes. In the event of possible leakage in this region, the brake pedal moves under no load over a distance corresponding to the aforementioned axial free clearance between collar  4  and activation elements  17   a - 17   d . When this clearance distance is covered the wheel brakes can be actuated by means of the activation elements. Another possible fault in the active chain in the region of the hydraulic connection  18  is undesired closure of this connection. This fault is more critical than the first-mentioned possibility of leakage because the piston-cylinder arrangement  2 , and therefore the brake pedal  1 , would be blocked thereby. For this reason, to provide a secure connection of the piston-cylinder arrangement  2  to a brake system pressure line  60 , the hydraulic connections  18  has, according to the invention, a section of dual-circuit configuration in which one of the two circuits  18   a  can be blocked separately with a first shut-off valve  19  and the other circuit  18   b  with a second shut-off valve  21 . 
         [0021]    The pressure regulating valves  6   a - 6   d  which, when operating at the fall-back level, continue to transmit the brake system pressure unchanged to the motor vehicle wheel brakes  8 - 11 , are connected to the brake system pressure line  60 . 
         [0022]    It is further apparent in the drawing that the aforementioned electrically controllable pressure source  7  is in the form of an electrohydraulic actuator, the piston  28  of which is actuable by means of a schematically indicated electric motor  27  via a rotation-translation gear. The distance traveled by the piston  28  is monitored by a sensor denoted by reference numeral  34 , the signal of which represents the discharge volume of the pressure source  7 . The piston  28  delimits a pressure chamber  29 , the hydraulic outlet of which is connected to the brake system pressure line  60  in which an electromagnetically actuable valve  23 , blockable in the flow direction to the pressure source  7 , is inserted. As already mentioned, on the one hand the inlet connections of the pressure modulating valves  6   a - 6   d  are connected to the brake system pressure line  60  and, on the other, the aforementioned circuits are connected to the hydraulic connection  18 . In addition, the brake system pressure line  60  is connectable via an electromagnetically actuable 2/2-way valve  22 , which is closed when unenergized (normally closed), to the pressure medium reservoir  12 . In this way pressure medium which was possibly drawn from the pressure medium reservoir via the sleeve sealing rings in the actuator and in the dividing piston devices upon rapid retraction of the electrohydraulic actuator can be discharged back into the pressure medium reservoir. The hydraulic connection from the line section  18  to the line section  44  leading to the pedal travel simulator  13  can be blocked by means of a further 2/2-way valve  20  which is open when unenergized (normally open). This valve makes it possible to test the simulator release valve  14  and the non-return valve  14   r  connected in parallel thereto for their leakage-free blocking function with the valve  14  unenergized, by energizing the solenoid valves  19 ,  20 ,  6   a ,  6   b ,  6   c ,  6   d  while the valve  21  remains unenergized and the electrically controllable pressure source  7  builds up a test pressure. A second pressure sensor  25  serves to detect the pressure produced by the pressure source  7  and present in the brake system pressure line  60 , and the volume discharged by the pressure source  7  is detected by the sensor  34 . It can therefore be determined by the aforedescribed test whether pressure medium is escaping into the simulator  13  when the test pressure is applied to the valves  14 ,  14   r.    
         [0023]    The operation of the brake system according to the invention is apparent to the specialist active in the relevant technical field from the disclosed content of the present patent application and therefore does not need to be explained further. 
         [0024]    While the above-description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.