Abstract:
A brake system for motor vehicle having a system for reducing brake pedal travel. The system having an electronic control and regulating unit ( 11 ), a brake pedal ( 9 ) having an amplifier chamber ( 13 ), a travel detecting device ( 14 ), a main brake cylinder ( 3 ) with at least one pressure chamber, a brake circuit (I, II), an electrically controllable pressure supply device ( 18, 19 ), a pressure regulating valve ( 20 ), and a cylinder-piston arrangement ( 8 ) for reducing pedal travel. The cylinder-piston arrangement ( 8 ) is disposed separately from the brake force amplifier ( 18; 20; 13; 6 ) and from the main brake cylinder ( 3 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to German Patent Application Nos. 10 2009 028 551.2, filed Aug. 14, 2009, 10 2010 038 327.9, filed Jul. 23, 2010, and PCT/EP2010/061327, filed Aug. 4, 2010. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a brake system for motor vehicles, having a device for shortening pedal travel. 
       BACKGROUND OF THE INVENTION 
       [0003]    A brake system of the above-referenced type is known for example from the German patent DE 36 27 147 C2. A disadvantage of the known brake system is the considerable axial structural length of the combination of the hydraulic brake force booster with the master brake cylinder which is formed as a tandem master cylinder and in the housing of which the cylinder-piston arrangement is integrated coaxially. 
         [0004]    It is therefore an object of the present invention to provide for a reduction in the axial structural length of the abovementioned combination. 
         [0005]    The above object is achieved according to the invention in that the cylinder-piston arrangement is arranged separately from the brake force booster and the master brake cylinder. 
         [0006]    Advantageous refinements of the subject matter of the invention are further provided in accordance with this invention. 
         [0007]    A disablement or a modification of the pedal travel shortening obtained with the subject matter of the invention is may be provided for example during so-called recuperation braking operations in which a part of the braking action demanded via the depression of the brake pedal is generated by an electric traction drive operating in the generator mode, the friction brake system contributes only the remaining difference in deceleration, and the familiar dependency of the brake pedal position on the force exerted on the brake pedal is produced by means of an electronically controlled modification of the pedal travel. This feature is preferably realized by virtue of an electrically actuable 2/2 directional control valve being positioned in the hydraulic connection for charging the cylinder-piston arrangement with the boost pressure. 
         [0008]    According to another feature of the subject matter of the invention, a disablement of the pedal-controlled activation of the pressure regulating valve, which is expedient for example during so-called recuperation braking operations is achieved in that an electrically actuable 2/2 directional control valve which is open in the deenergized state is positioned in the activation line between a second control port and the pressure chamber and, in the actuated switching position, performs the function of a check valve which blocks in the direction of the pressure regulating valve. 
     
    
     
       BRIEF DESCRIPTION OF THE INVENTION 
         [0009]    The present invention will be explained in more detail below on the basis of two exemplary embodiments and with reference to the appended schematic drawing, wherein identical components are provided with the same reference symbols. In the drawing: 
           [0010]      FIG. 1  shows the design of a first embodiment of the brake system according to the invention, 
           [0011]      FIG. 2  shows an important part of the brake force booster used in the brake system according to  FIG. 1 , on an enlarged scale, and 
           [0012]      FIG. 3  shows the design of a second embodiment of the brake system according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    The electrohydraulic brake system illustrated by way of example in  FIG. 1  is composed substantially of an actuating unit  1 , of an electrically controllable pressure generating device  2 , wherein the actuating unit  1  and the pressure generating device  2  form a brake force booster, and of a master brake cylinder or tandem brake cylinder  3  which is positioned operatively downstream of the brake force booster and to the pressure chambers (not shown in any more detail) of which are connected wheel brake circuits I and II which supply hydraulic pressure medium to wheel brakes  5   a  to  5   d  of a motor vehicle via a known ABS/ESP hydraulic unit or a controllable wheel brake pressure modulation module  4 . Furthermore, the brake system has an electronic brake system control unit  11 . For the activation of the brake actuating unit  1 , a brake pedal  9  is provided to which is coupled a piston rod  10  which is connected in a force-transmitting manner via a booster piston  6  to a first piston or primary piston  7  of the master brake cylinder  1 . The booster piston  6  is guided in an axially movable manner in a booster housing  12  and, in the latter, delimits a hydraulic booster chamber provided with the reference numeral  13 . Signals from a travel sensor  14  which serves to detect a driver deceleration demand and which senses the actuating travel of the piston rod  10  are supplied to the electronic brake system control unit  11 . From said signals, in the electronic brake system control unit  11 , activation signals are prepared for electromagnetically actuable 2/2 directional control valves  15 ,  16 ,  17 , the task of which will be explained in the text below, and for hydraulic pressure regulating valves contained in the wheel brake pressure modulation module  4 . 
         [0014]    The abovementioned pressure generating device  2  is formed, in the example shown, by a hydraulic high-pressure accumulator  18  with a downstream pressure regulating valve  20 . A motor-pump unit  19  serves for charging the high-pressure accumulator  18 . The outlet of the pressure regulating valve  20  is connected via a hydraulic connection  21  to the booster chamber  13  positioned upstream of the master brake cylinder  3 . The pressure regulating valve  20  is assigned a pilot control stage  22 , the task of which will be explained in the text below. A further line  23  connects the suction side of the motor-pump unit  19  to a pressure medium storage tank  24  assigned to the master brake cylinder  3 . The motor-pump unit  19  can preferably be formed as an independent assembly and provided with fastenings and hydraulic connections which isolate body-borne vibration and sound. The hydraulic pressure stored in the high-pressure accumulator  18  is measured by a pressure sensor provided with the reference numeral  25 . 
         [0015]    It can also be seen from the drawing that a hydraulic cylinder-piston arrangement  8  is connected to one (II) of the wheel brake circuits I and II. The cylinder-piston arrangement  8  is formed by a first hydraulic chamber  26 , a second hydraulic chamber  27 , a third hydraulic chamber  28  and a stepped piston  29  which separates the chambers  26 ,  27  and  28  from one another. Here, the larger effective surface of the stepped piston  29  separates the first chamber  26  from the second chamber  27 , while the third chamber  28  is delimited by the smaller effective surface of the stepped piston  29 . Here, the first chamber  26  is connected to the abovementioned hydraulic line  21  which leads to the booster chamber  13 , the second chamber  27  is connected via a further hydraulic connection  32  to the pressure medium reservoir  24 , and the third chamber  28  is connected to the brake circuit provided with the reference symbol II. Arranged in the second chamber  27  there is a restoring spring  49  which holds the stepped piston  29  in an unpressurized state in the rest position shown. The pressure induced in the second brake circuit II is measured by means of a pressure sensor  33 . 
         [0016]    As can be seen in particular from  FIG. 2  of the drawing, the pressure regulating valve  20  is of two-stage design and preferably has, aside from the said electrically actuable pilot control stage  22 , a doubly hydraulically activatable valve main stage provided with the reference numeral  30 , and a hydraulic activation stage, the design of which will be explained in the description below. 
         [0017]    The pilot control stage  22  is composed of a series connection of the abovementioned 2/2 directional control valves  15  and  16  which are designed as analog-regulable 2/2 directional control valves. The former 2/2 directional control valve  15  is designed as a 2/2 directional control valve which is closed in the deenergized state, whereas the latter directional valve  16  is designed as a 2/2 directional control valve which is open in the deenergized state, wherein the hydraulic central tapping point  31  between the two valves  15  and  16  provides one of the activation pressures for the valve main stage  30  via a first control port C 1 . The hydraulic activation stage is formed by a first activation chamber  34 , a first activation piston or stepped piston  35 , an annular chamber  41  which is connected to the pressure medium storage tank  24 , and a second activation chamber  36  which is delimited by the stepped piston  35  and which is connected to the abovementioned central tapping point  31  of the pilot control stage  22 . The second activation chamber  36  is delimited at the other side by a second activation piston  37  which, together with a valve body  40 , delimits a tank port chamber  39  and which, in the embodiment shown, is formed in one piece with a valve body  40  which is designed as a slide which has control edges. The valve sleeve  38  forms, together with the valve body  40 , the abovementioned main stage  30  of the pressure regulating valve  20 . 
         [0018]    It can also be seen from  FIG. 2  that the first activation chamber  34  is connected by means of a second control port C 2  to the second brake circuit II via the electromagnetically actuable 2/2 directional control valve  17  which is open in the deenergized state, as mentioned in conjunction with  FIG. 1 . In its energized switching position, the 2/2 directional control valve  17 , which is positioned in an activation line  62 , performs the function of a check valve which closes in the direction of the control port C 2 , as indicated by the corresponding hydraulic symbol. 
         [0019]    Meanwhile, the valve body  40  forms, together with the valve sleeve  38 , a high-pressure port chamber  43  which is connected via a high-pressure port P to the high-pressure accumulator  18 . By means of a displacement of the valve body  40 , the high-pressure port chamber  43  is connected to a working pressure chamber  44  which forms the outlet, denoted by the letter A, of the pressure regulating valve  20  and which, in the illustrated starting position or rest position of the valve body  40 , is connected to the tank port chamber  39  by means of pressure medium ducts  45  and  46  formed in the valve body  40 . The boost pressure induced in the working pressure chamber  44  is measured by a third pressure sensor  42 . Here, it is advantageous for the diameter of the valve body  40  which is guided in the valve sleeve  38  to be greater than the diameter of the smaller stage of the stepped piston  35 . It also emerges from  FIG. 2  that the abovementioned connecting line  21  which leads to the booster chamber  13 , and the further line  47  which is connected to said connecting line and which leads to the pressure medium storage tank  24 , are connected to the working pressure chamber  44 . Here, a check valve  48  which closes in the direction of the pressure medium storage reservoir  24  is positioned in the line  47 . 
         [0020]    The design of the second exemplary embodiment of the brake system according to the invention substantially corresponds to that of the first exemplary embodiment illustrated in  FIG. 1 . Therefore, for better clarity, a detail of the second exemplary embodiment of the brake system according to the invention is shown in  FIG. 3 . The second exemplary embodiment of the present invention is suitable for motor vehicles in which so-called recuperation braking operations are carried out. Here, in the example, there is connected to the first brake circuit I a second cylinder-piston arrangement  80  which constitutes a device for producing an additional brake pedal travel. The second cylinder-piston arrangement  80  has a first hydraulic chamber  50 , a second hydraulic chamber  51 , a third hydraulic chamber  52  and a stepped piston  53 . Here, the larger effective surface of the stepped piston  53  separates the first  50  from the second chamber  51 , while the third chamber  52  is delimited by the smaller effective surface of the stepped piston  53 . The first hydraulic chamber  50  is connected to the central tapping point  60  of a valve pair  54  which is formed by a series connection of two analog-regulable 2/2 directional control valves  55  and  56 . The former 2/2 directional control valve  55  is designed as a valve which is open in the deenergized state and is preferably positioned between the first chamber  50  and the abovementioned high-pressure accumulator  18 . The latter 2/2 directional control valve  56  is designed as a valve which is closed in the deenergized state and is preferably positioned between the first chamber  50  and the line  23  which leads to the pressure medium storage resevoir  24  (see also  FIG. 1 ). The second hydraulic chamber  51  is connected via a line section  57  to the line  23  and therefore to the pressure medium storage tank  24 , while the third chamber  52  is connected to the first brake circuit I via a 2/2 directional control valve  58 . In the illustrated operating (rest) state, the 2/2 directional control valve  58  performs the function of a check valve which closes in the direction of the second cylinder-piston arrangement  80 , whereas when the 2/2 directional control valve  58  is switched, the third chamber  52  is connected to the brake circuit I. 
         [0021]    A disablement of the action of the first cylinder-piston arrangement  8  is made possible by an electromagnetically actuable 2/2 directional control switching valve  63  which is positioned between the first chamber  26  of the first cylinder-piston arrangement  8  and the hydraulic line  21 . In the illustrated operating (rest) state, the 2/2 directional control switching valve  63  performs the function of a check valve which closes in the direction of the cylinder-piston arrangement  8 . 
         [0022]    The functioning of the illustrated brake system in the preferred “brake by wire” operating mode emerges to a person skilled in the art from the content of disclosure of the present documentation, and need not be explained in any more detail.