Patent Publication Number: US-2010117448-A1

Title: Braking system for motor vehicles

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national phase application of PCT International Application No. PCT/EP2008/052888, filed Mar. 11, 2008, which claims priority to German Patent Application No. 102007016954.1, filed Apr. 5, 2007 and German Patent Application No. 102007024785.2, filed May 26, 2007, the contents of such applications being incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an electrohydraulic brake system for motor vehicles of the brake-by-wire type, having: 
     a hydraulic brake pressure sensor which can be activated by means of a brake pedal, and a master brake cylinder having at least one pressure space which is bounded by a master cylinder piston and to which wheel brakes of the motor vehicle can be connected, 
     means for decoupling the brake pedal from the pressure sensor, a booster device which is effectively connected upstream of the brake pressure sensor and has the purpose of generating an activation force which acts on the pressure sensor, 
     means for sensing a vehicle deceleration request, the control signals of which can be fed to an electronic open-loop and closed-loop control unit, a pedal force simulator which interacts with the brake pressure sensor and by means of which a restoring force which acts on the brake pedal can be simulated in the brake-by-wire operating mode, and having pressure control valves which can be actuated by the electronic open-loop and closed-loop control unit and are assigned to the wheel brakes. 
     2. Description of the Related Art 
     Such a brake system is known from DE 10 2005 018 649 A1. An electric motor with a transmission stage which is connected downstream and which interacts directly with the master brake cylinder piston serves to perform the boosting of the activation force which is applied to the brake pedal by the driver. The decoupling of the brake pedal from the master brake cylinder is carried out mechanically by means of an axial distance between the brake pedal, or an activation rod coupled to the brake pedal, and the master cylinder piston. However, this type of decoupling results in a loss of pedal travel in the event of emergency braking. In the previously known brake system, the structurally required necessity to mount the previously known electric motor in the direct vicinity of the master brake cylinder, i.e. on the splash wall of the vehicle, which causes unfavorable noises and vibrations, is felt to be less advantageous. Furthermore, the electric motor constitutes a considerable mass which has an adverse effect, in particular in the event of a crash. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is therefore to eliminate the abovementioned disadvantages of a brake system of the generic type mentioned at the beginning. 
     This object is achieved according to aspects of the invention, in that the booster device for boosting the activation force which is transmitted to the pressure sensor by the brake pedal is composed of a booster module, which is connected upstream of the pressure sensor, and of a hydraulic pressure source, and in that the pressure sensor forms, with the booster module, a first functionally capable assembly which can be handled independently, and the pressure source, the electronic open-loop and closed-loop control unit and a valve block which accommodates the pressure control valves form a second functionally capable assembly which can be handled independently and which is arranged spatially separate from the first assembly. 
     These measures minimize the installation space to a considerable degree, with the described disintegrated design permitting adaptation to various vehicle models merely through corresponding configuration of the second assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the invention are explained in more detail in the following description of an exemplary embodiment with reference to the appended drawing. 
       In the drawing, 
         FIG. 1  shows a basic circuit diagram of the brake system according to aspects of the invention, and 
         FIG. 2  shows the first assembly on an enlarged scale. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The electrohydraulic brake system according to aspects of the invention illustrated in the drawing is composed essentially of a hydraulic brake pressure sensor  2  which can be activated by means of a brake pedal  1 , a booster module  3  which is connected upstream of the brake pressure sensor  2 , a hydraulic pressure source  4 , a valve block  5 , an electronic open-loop and closed-loop control unit  6  and wheel brakes  7 ,  8 ,  9  and  10  which are connected to the valve block  5  and are assigned to two vehicle axles. The brake pressure sensor  2  is embodied as a dual-circuit master brake cylinder or tandem master cylinder which is provided with a pressureless pressure medium reservoir vessel (not illustrated).  FIG. 1  shows that while the pressure sensor or tandem master cylinder  2  with the booster module  3  form a first assembly which can be handled independently, a second functionally capable assembly which can be handled independently is formed by the pressure source  4 , the valve block  5 , which is preferably arranged spatially separate from the first assembly  2 ,  3 . The valve block  5  accommodates pressure control valves  17 ,  18 ,  19 ,  20  which are assigned to the individual wheel brakes  7 ,  8 ,  9 ,  10  and the input ports of which are connected to the pressure spaces  23 ,  24  of the tandem master cylinder  2  by means of two hydraulic lines  21 ,  22 . The pressure control valves  17 - 20 , which are operated as 2/2-way valves which are open in the currentless state (OC) 2/2-way valves, operate in what is referred to as the multiplex mode, the functional principle of which is known to a person skilled in the art and therefore does not need to be explained in more detail. The abovementioned pressure source  4  is embodied as a cylinder-piston arrangement, the piston  41  of which is driven by an electric motor  42  and bounds, in the valve block  5 , a hydraulic pressure space  43  which is connected to the booster module  3  via a line  25 . In the example shown, an electrical energy accumulator, provided with the reference number  44 , is assigned to the electric motor  42 . 
     As is apparent in particular from  FIG. 2 , the booster module  3  has essentially a first piston  31 , coupled to the brake pedal  1 , and a second piston  32  in which the first piston  31  is displaceably guided with the intermediate connection of a compression spring  33 . The compression spring  33  forms, together with an elastomer block  34 , a pedal force simulator which generates, in accordance with the desired characteristic curve, an opposing force which can be felt at the brake pedal  1 , and the function of which pedal force simulator is also known to a person skilled in the art. The second piston  32  and a first master cylinder piston  26  bound, in the housing of the booster module  3 , a hydraulic space  35  to which, as already mentioned, the pressure source  4  is connected. The space  35  forms means for decoupling the brake pedal  1  from the tandem master cylinder  2 . A travel sensor  36  which operates in a contactless fashion and which senses the relative travel of the first piston  31  with respect to the second piston  32  serves to sense the driver&#39;s deceleration request. 
     The method of functioning of brake systems of the brake-by-wire type is known essentially to a person skilled in the art. When a buildup of pressure occurs in the brake-by-wire operating mode, the brake pedal  1  is activated by the driver, with the driver deceleration request being sensed by the travel sensor  36 . At the same time, the electric motor  42  is actuated with the effect of increasing pressure in the pressure space  43 , the pressure of which pressure space  43  both holds the second piston  32  against a stop and causes the master cylinder pistons  26  to be shifted, to the left in the drawing. It is to be noted that suitable configuration of the diameters of the piston  41  and of the first master cylinder piston  26  permit the boosting ratio to be set over a large range. In the event of failure of the pressure source  4 , force is transmitted from the brake pedal  1  to the first master cylinder piston  26  via the second piston  32  in a purely mechanical fashion.