Abstract:
The present invention relates to a device for controlling electromagnetically operable valves of an electrohydraulic brake system for motor vehicles of the ‘brake-by-wire’ type having an electronic control or regulation unit that comprises at least one valve driver stage.  
     In order to ensure maximum possible availability of the electronically controlled system functions, especially with a view to achieving a short stopping distance and a sufficient degree of vehicle stability regardless of the vehicle type or of whether the vehicle is loaded or unloaded, according to the present invention, the control and regulation unit ( 26 ) includes two additional valve driver stages ( 32, 33 ) associated with which is a first and a second group of valves ( 11,13,14, 17,18, 27,28,34,35,37,38 ), the said driver stages being used to disable the first or the second group when malfunction occurs.

Description:
TECHNICAL FIELD  
         [0001]    The present invention generally relates to a device for controlling valves and more particularly relates to a device for controlling electromagnetically operable valves of an electrohydraulic brake system for motor vehicles.  
         BACKGROUND OF THE INVENTION  
         [0002]    International patent application WO 00/68053 discloses a brake system of this general type. The mentioned publication, however, does not provide any the failure probability of the actuation of the electromagnetically operable valves employed.  
         SUMMARY OF THE INVENTION  
         [0003]    In view of the above, an object of the present invention is to disclose a device for actuating electromagnetically operable valves of an electrohydraulic brake system of the type mentioned hereinabove, said device ensuring maximum possible availability of the electronically controlled system functions, especially with a view to achieving a short stopping distance and a sufficient degree of vehicle stability regardless of the vehicle type or of whether the vehicle is loaded or unloaded.  
           [0004]    This object is achieved by the present invention because the control and regulation unit includes two additional valve driver stages associated with which is a first and a second group of valves, the said driver stages isolating said group in addition from the supply voltage or mass, with a view to ensuring thereby the disabling of the first or the second group also when malfunction occurs.  
           [0005]    The present invention includes, in a first embodiment, a first valve driver stage for driving the separating valves and for driving the pressure control valves respectively associated with a brake of a first or a second vehicle axle. The present invention also includes a second valve driver stage for driving pressure-compensating valves and pressure control valves associated with the other two wheel brakes of the first or the second vehicle axle. The mentioned variant permits an electronic brake pressure control on each of the four vehicle wheels.  
           [0006]    A second embodiment of the present invention is that the first valve driver stage is coupled to the separating valve of a first vehicle axle, the pressure-compensating valve of a second vehicle axle, and the pressure control valves being associated with respectively one brake of the first or the second vehicle axle, while the second valve driver stage is provided for the separating valve of the second vehicle axle, the pressure-compensating valve of the first vehicle axle, and the pressure control valves being associated with the other two brakes of the first or the second vehicle axle. This variant allows an electronic brake pressure control of three wheels, while the master brake cylinder furnishes the brake pressure for the wheel brake associated with the fourth wheel.  
           [0007]    Finally, a third embodiment of the present invention includes coupling the first valve driver stage to the separating valve and the pressure-compensating valve as well as the pressure control valves of wheel brakes associated with a first vehicle axle, while the second valve driver stage is provided for the separating valve and the pressure-compensating valve as well as the pressure control valves of wheel brakes associated with a second vehicle axle. This allocation allows an electronic brake pressure control of two wheels, while the pressure introduced by the driver into the master brake cylinder is applied to the wheel brakes of the other wheels. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a simplified circuit diagram of a design of the electrohydraulic brake system of the present invention.  
         [0009]    [0009]FIG. 2 is a second alternative of actuating the electromagnetic valves in an electrohydraulic brake system according to FIG. 1.  
         [0010]    [0010]FIG. 3 is a third alternative of actuating the electromagnetic valves in an electrohydraulic brake system according to FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0011]    The electrohydraulic brake system illustrated in the drawings essentially comprises a dual-circuit master brake cylinder or tandem master cylinder  2  that is operable by means of an actuating pedal  1 , cooperates with a pedal travel simulator  3  and includes two pressure chambers isolated from one another and being in communication with a non-pressurized pressure fluid supply reservoir  4 . Wheel brakes  7 ,  8  e.g. associated with the rear axle are connected to the first pressure chamber (primary pressure chamber) by means of a closable first hydraulic line  5 , with wheel brake  7  being associated with the left rear wheel and wheel brake  8  being associated with the right rear wheel. Line  5  is closed by means of a first separating valve  11 , while in a line portion  12  between the wheel brakes  7 ,  8  an electromagnetically operable, preferably normally open (NO) pressure-compensating valve  13  is inserted which enables brake pressure control on each individual wheel, if required.  
         [0012]    The second pressure chamber of the master brake cylinder  2 , to which a pressure sensor  15  can be connected, is connectable to the other pair of wheel brakes  9 ,  10  associated with the front axle by way of a second hydraulic line  6  closable by means of a second separating valve  14 , with wheel brake  9  being associated with the left front wheel and wheel brake  10  being associated with the right front wheel. Again, an electromagnetically operable, preferably normally open (NO) pressure-compensating valve  19  is inserted into a line portion  16  disposed between the wheel brakes  9 ,  10 . Because the design of the hydraulic circuit connected to the second pressure chamber of the master brake cylinder  2  is identical with the brake circuit  11  that is explained in the preceding description, it need not be discussed in the following text.  
         [0013]    A high-pressure accumulator  21  is used as the above-mentioned auxiliary pressure source, said accumulator being filled with pressure fluid under high pressure by a motor-and-pump assembly  20 . The motor-and-pump assembly  20  comprises a pump  23  driven by means of an electric motor  22  as well as a pressure limiting valve  24  connected in parallel to said pump  23 . The suction side of the pump  23  is connected to the above-mentioned pressure fluid supply reservoir  4  by way of a non-return valve. A pressure sensor  25  monitors the hydraulic filling pressure of the high-pressure accumulator  21  generated by the pump  23 .  
         [0014]    As can further be taken from the drawings, two electromagnetic, normally closed two-way/two-position directional control valves  17 ,  18  of analog operation are associated with the wheel brakes  7 ,  8  of the vehicle rear axle, said valves fulfilling the function of inlet valves that are required for electrohydraulically controlled braking operations and the inlet ports of which are connected to the above-mentioned high-pressure accumulator  21 . Further, the wheel brakes  7 ,  8  are connected to a third hydraulic line  39  by way of each one electromagnetic, normally closed two-way/two-position directional control valve or outlet valve  27 ,  28  of analog operation, said line  39  being in communication with the non-pressurized pressure fluid supply reservoir  4 , on the other hand. The hydraulic pressure prevailing in the wheel brakes  7 ,  8  is determined by means of each one pressure sensor  30 ,  31 . The wheel brakes  9 ,  10  associated with the vehicle front axle cooperate similarly with valve pairs  34 ,  37  and  35 ,  38 , respectively, with pressure control valves  34 ,  35  fulfilling the function of the inlet valves and pressure control valves  37 ,  38  fulfilling the function of the outlet valves.  
         [0015]    An electronic control unit  26  is used for the joint actuation of the motor-and-pump assembly  20  as well as the electromagnetic valves  11 ,  13 ,  14 ,  17 ,  18 ,  19 ,  27 ,  28 ,  34 ,  35 ,  37 ,  38 . The output signals of an actuating travel sensor  36 , preferably of redundant design and cooperating with the actuating pedal  1 , and of the above-mentioned pressure sensor  15  are sent as input signals to said control unit  26 , thereby permitting a detection of the driver&#39;s deceleration demand. However, other means such as a force sensor sensing the actuating force at the actuating pedal  1  may also be used for the detection of the driver&#39;s deceleration demand. As further input quantities, the output signals of the pressure sensors  25 ,  30 ,  31  as well as the output signals of wheel sensors (only represented) representative of the speed of the vehicle are sent to the electronic control unit  26 .  
         [0016]    As is indicated in FIG. 1 only schematically, the electronic control unit  26  among others comprises a valve driver stage  29  and two additional valve driver stages  32 ,  33 , the purpose of which is explained in the following text.  
         [0017]    To ensure maximum possible availability of the electronically controlled system functions of the illustrated electrohydraulic brake system, the above-mentioned electromagnetically operable valves are subdivided into two groups and associated with the two additional valve driver stages  32 ,  33 . Thus, the group associated with the first additional valve driver stage  32  is composed of the two separating valves  11 ,  14 , the pressure control valves  34 ,  37  of the wheel brake  9  associated with the left front wheel, and the pressure control valves  18 ,  28  of the wheel brake  8  associated with the right rear wheel. In contrast thereto, the group associated with the second additional valve driver stage  33  is composed of the two pressure-compensating valves  13 ,  19 , the pressure control valves  35 ,  38  of the wheel brake  10  associated with the right front wheel as well as the pressure control valves  17 ,  27  of the wheel brake  7  associated with the left rear wheels.  
         [0018]    Upon failure of the first additional valve driver stage  32  or one of the drivers of the associated valve group, said failure requiring subsequent closure of the pressure-compensating valves  13 ,  19 , it is still possible to electronically control the brake pressures in the wheel brake  10  associated with the right front wheel and the wheel brake  7  associated with the left rear wheel. A hydraulic through grip effected by the driver by way of his/her actuating or pedal force acting upon the master brake cylinder  2  can produce the brake pressures in the wheel brake  9  associated with the left front wheel and in the wheel brake  8  associated with the right rear wheel.  
         [0019]    Upon failure of the second additional valve driver stage  33  or one of the drivers of the associated valve group, the two separating valves  11 ,  14  can become closed. Since both pressure-compensating valves  13 ,  19  remain open, the brake pressures in all four wheel brakes  7 - 10  can be controlled electronically because the front axle is controlled by way of the valve pair  34 ,  37  and the rear axle by way of the valve pair  18 ,  28 .  
         [0020]    In the second example being shown in a greatly simplified view in FIG. 2, the group associated with the first additional valve driver stage  32  is composed of the separating valve  14  associated with the vehicle front axle, the pressure control valves  34 ,  37  of the wheel brake  9  associated with the left front wheel, the pressure-compensating valve  13  associated with the vehicle rear axle, as well as the pressure control valves  17 ,  27  of the wheel brake  7  associated with the left rear wheel. In contrast thereto, the group associated with the second additional valve driver stage  33  is composed of the separating valves  11  associated with the vehicle rear axle, the pressure control valves  18 ,  28  of the wheel brake  8  associated with the right rear wheel, the pressure-compensating valve  19  associated with the vehicle front axle as well as the pressure control valves  35 ,  38  of the wheel brake  10  associated with the right front wheel.  
         [0021]    Upon failure of the first additional valve driver stage  32  or one of the drivers of the associated valve group, said failure requiring subsequent closure of the pressure-compensating valve  19  associated with the vehicle front axle and the separating valve  11  associated with the vehicle rear axle, it is still possible to electronically control the brake pressures in the wheel brake  10  associated with the right front wheel and the wheel brakes  7 ,  8  associated with the rear vehicle axle. A hydraulic through grip effected by the driver by way of his/her actuating or pedal force acting upon the master brake cylinder  2  can produce the brake pressure in the wheel brake  9  associated with the left front wheel.  
         [0022]    Upon failure of the second additional valve driver stage  33  or one of the drivers of the associated valve group, said failure requiring subsequent closure of the pressure-compensating valve  13  associated with the vehicle rear axle and the separating valve  14  associated with the vehicle front axle, it is still possible to electronically control the brake pressures in the wheel brake  7  associated with the left rear wheel and the wheel brakes  9 ,  10  associated with the vehicle front axle. A hydraulic through grip effected by the driver by way of his/her actuating or pedal force acting upon the master brake cylinder  2  can produce the brake pressure in the wheel brake  8  associated with the right rear wheel.  
         [0023]    In the third example being shown in a greatly simplified view in FIG. 3, the group associated with the first additional valve driver stage  32  is composed of the separating valve  14  associated with the vehicle front axle, the pressure-compensating valve  19  associated with the vehicle front axle as well as the pressure control valves  34 ,  37 ,  35 ,  38  of the wheel brakes  9 ,  10  associated with the vehicle front axle. In contrast thereto, the group associated with the second additional valve driver stage  33  is composed of the separating valve  11  associated with the vehicle rear axle, the pressure-compensating valve  13  associated with the vehicle rear axle as well as the pressure control valves  17 ,  27 ,  18 ,  28  associated with the wheel brakes  7 ,  8  of the vehicle rear axle.  
         [0024]    Upon failure of the first additional valve driver stage  32  or one of the drivers of the associated valve group, it is possible to electronically control the brake pressures in the wheel brakes  7 ,  8  associated with the vehicle rear axle without restrictions. A hydraulic through grip effected by the driver by way of his/her actuating or pedal force acting upon the master brake cylinder  2  can produce the brake pressure in the wheel brakes  9 ,  10  associated with the vehicle front axle.  
         [0025]    Upon failure of the second additional valve driver stage  33  or one of the drivers of the associated valve group, it is possible to electronically control the brake pressures in the wheel brakes  9 ,  10  associated with the vehicle front axle without restrictions. A hydraulic through grip effected by the driver by way of his/her actuating or pedal force acting upon the master brake cylinder  2  can produce the brake pressure in the wheel brakes  7 ,  8  associated with the vehicle rear axle.  
         [0026]    As can be taken from FIGS. 2 and 3, in particular, the additional valve driver stages  32 ,  33  are connected in each case between the corresponding valve group and the positive pole of a vehicle battery (only represented). It is, however, also feasible to interconnect the additional valve driver stages  32 ,  33  between the corresponding valve group and the vehicle mass.