Abstract:
A brake system for motor vehicles, with a brake pedal for operating a master brake cylinder with a piston and pressure chamber connected to a wheel brake, a displacement sensor that detects the brake pedal displacement, a pedal force detection device that detects the brake pedal force, a brake pressure modulation unit applying pressure to the wheel brakes and regulating the wheel brakes individually. A cylinder-piston device for hydraulically producing a force that acts on the master cylinder piston in addition to the pedal force. A pressure supply device to supply pressure medium into the cylinder-piston arrangement. A hydraulic device supplying pressure medium into the brake circuit. A cylinder-piston arrangement upstream of the master brake cylinder generates a force acting on the master cylinder piston. An electronic control and regulation unit, executes an algorithm for the regulation of the brake system pressure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to German Patent Application Nos. 10 2013 216 141.7, filed Aug. 14, 2013 and PCT/EP2014/066573, filed Aug. 1, 2014. 
     FIELD OF THE INVENTION 
     The present invention concerns a brake system for motor vehicles, with a brake pedal for operating a master brake cylinder with at least one hydraulic piston, at least one pressure chamber and at least one connected brake circuit that is placed under a brake system pressure when the brake pedal is operated and to which are connected hydraulically activated wheel brakes that are associated with wheels of the motor vehicle, a displacement detection device that detects the operating displacement of the brake pedal or of a piston connected to the brake pedal, a pedal force detection device that detects the force exerted by the brake pedal on the master brake cylinder, a brake pressure modulation unit that is designed to pass the brake system pressure to the wheel brakes and, if necessary, to regulate the wheel brakes individually, a cylinder-piston device connected upstream of the master brake cylinder for hydraulically producing a force that acts on the piston of the master brake cylinder in the operation direction in addition to the pedal force acting on the piston, a pressure supply device for feeding a pressure medium into the cylinder-piston arrangement, a hydraulic device for supplying a pressure medium into the brake circuit, a cylinder-piston arrangement connected upstream of the master brake cylinder for the hydraulic generation of a force acting on the master cylinder piston in the operating direction in addition to the pedal force, an electronic control and regulation unit, in which an algorithm for the regulation of the brake system pressure is implemented, and at least one pressure sensor for detecting the brake system pressure. 
     BACKGROUND 
     One brake system related to the above mentioned system is known from the older patent application DE 10 2011 086 916 A1 of the applicant. The special feature of the prior art brake system is that with braking processes assisted by boosting forces the volume of pressure medium delivered to the wheel brakes is composed of a first pressure medium volumetric component, which is output by the master brake cylinder, and a second pressure medium volumetric component, which is controlled by the device for producing the boosting force. However, the above-referenced application discloses no reference to a control engineering method for the simultaneous provision of an optimal brake pedal feel and a brake system pressure. 
     Starting from the previously described prior art, the object of the present invention is to propose a brake system with which an optimal brake pedal feel and a brake system pressure can be provided at the same time. 
     This object is achieved according to the invention by a brake system described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in detail in the following description in combination with the accompanying schematic figures for two exemplary embodiments. In the figures: 
         FIG. 1  shows a hydraulic circuit diagram of an exemplary embodiment of a brake system according to the invention, 
         FIG. 2  shows a predeterminable characteristic showing the relationship between brake pedal displacement and brake pedal force, 
         FIG. 3  shows the simplified structure of a control path of the electronic control and regulation unit according to the present invention containing an optimal regulator, and 
         FIG. 4  shows a modification of the control path shown in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The brake system that is shown in the figures essentially includes a hydraulic master brake cylinder  2  in a tandem implementation operated by an operating pedal or a brake pedal  1 , a cylinder-piston arrangement  13  connected upstream of the master brake cylinder  2 , a pressure medium reservoir container  3 , a brake pressure modulation unit  4 , to the output ports of which wheel brakes  9 ,  10 ,  11 ,  12  of a motor vehicle that is not shown are connected, with a motor-pump unit  5 , electrically controllable pressure modulation valves or inlet and outlet valves  6   a - 6   d ,  7   a - 7   d , as well as with low pressure storage devices  8   a ,  8   b , in addition an electrically controllable pressure supply device  19  for producing a boosting force, and an electronic control and regulation unit  14  that activates the electrically controllable components. The input ports of the inlet valves  6   a - 6   d  are supplied with brake medium at pressures that are referred to as brake system pressures conducted by system pressure lines  22   a ,  22   b , whilst return lines  23   a ,  23   b  connect the output ports of the outlet valves  7   a - 7   d  to the aforementioned low pressure storage devices  8   a ,  8   b.    
     As is also shown in  FIG. 1 , the hydraulic master brake cylinder  2  of the brake system according to the example includes two hydraulic pistons  15 ,  16  that are disposed one after the other in a housing  20  and that bound hydraulic chambers or pressure chambers  17 ,  18 . The pressure chambers  17 ,  18  are connected to the pressure medium reservoir container  3  on the one hand via bores formed in the pistons  15 ,  16  as well as by corresponding pressure equalization lines, wherein the same can be shut off by a relative displacement of the pistons  15 ,  16  in the housing  20 . The pressure chambers  17 ,  18  also contain restoring springs that are not referred to in detail and that position the pistons  15 ,  16  into an initial position with the master brake cylinder  2  not operated. Separate brake circuits I, II associated with the pairs of wheel brakes  9 ,  10  or  11 ,  12  are connected to the pressure chambers  16 ,  17  by circuit pressure lines  21   a ,  21   b , to which the aforementioned system pressure lines  22   a ,  22   b  are connected by pressure increasing valves  50   a ,  50   b . Moreover, the suction sides of the pumps of the motor-pump units  5  can also be connected to the circuit pressure lines  21   a ,  21   b  by pressure medium feed valves  51   a ,  51   b , whereby using the pumps pressure medium can be fed to the system pressure lines  22   a ,  22   b  by the circuit pressure lines  21   a ,  21   b  for the purpose of a pressure increase that is controllable with the pressure increasing valves  50   a ,  50   b . Pressure sensors  60 ,  61  are provided for detecting the pressures occurring in the circuit pressure lines  21   a ,  21   b . The output ports of each separating piston device  24   a ,  24   b  are connected to the circuit pressure lines  21   a ,  21   b  in the exemplary embodiment shown. The separating piston devices  24   a ,  24   b  are essentially formed by actuation chambers  26   a ,  26   b  bounded by separating pistons  25   a ,  25   b  and pressure output chambers  27   a ,  27   b , wherein the pressure output chambers  27   a ,  27   b  accommodate the restoring springs, which are not referred to in detail, that bias the separating pistons  25   a ,  25   b.    
     As is also shown in the figures, the upstream hydraulic piston-cylinder arrangement  13  connected upstream of the master brake cylinder  2  includes a booster piston  34  bounding a booster chamber  33  in a booster housing  31 , the booster piston  34  also being connected to the aforementioned first master cylinder piston  15  in a force-transfer manner. The booster chamber  33  is hydraulically connected, together with the actuation chambers  26   a ,  26   b , to the pressure chamber  30  of an electrically controllable pressure supply device  19 , wherein the actuator pressure that is present in the connected chambers is detected by a pressure sensor  39 . A piston rod  35  couples the pivotal displacement of the brake pedal  1  resulting from a pedal operation to the translational displacement of the booster piston  34 , the operating displacement s of which is detected by a preferably redundantly implemented displacement sensor  36 . As a result, the corresponding piston displacement signal is a measure of the brake pedal operation angle. Moreover, a force sensor  32  for detecting the pedal force F acting on the brake pedal  1  during the operation is provided, and is also preferably implemented redundantly. As an alternative to the use of a force sensor  32 , the pedal force signal F can be indirectly determined from detected hydraulic pressure values. The pedal travel or the pedal angle or the piston travel and the directly measured or indirectly determined pedal force represent a braking intention by a vehicle driver. 
     Moreover, it can be seen from the graphical representation of the brake system according to the invention that the aforementioned pressure supply device  19  is in the form of an electrically controllable hydraulic pressure source or an electrohydraulic actuator, the piston  29  of which can be operated by a schematically indicated electric motor  28  with the interposition of a rotation-translation gearbox that is not shown. A rotor position sensor that is used for the detection of the rotor position of the electric motor  28  is referred to with the reference character  37 . Optionally, further sensors that are not shown can detect additional motor parameters, such as the motor currents and the winding temperature. The piston  29  bounds a pressure chamber  30  that is connected on the one hand by means of a hydraulic line  38  to the aforementioned booster chamber  33 , so that the boosting force acting towards the master brake cylinder piston  15  in the operating direction is produced by the action of the hydraulic pressure regulated in the pressure chamber  30 . On the other hand, the aforementioned actuation chambers  26   a ,  26   b  of the separating piston devices  24   a ,  24   b  can be subjected to the pressure regulated in the pressure chamber  30 . A sensor connected to the pressure chamber  30  for indirectly detecting the boosting force is in the form of a pressure sensor  39  in this case. 
       FIG. 2  shows the brake pedal characteristic of the brake pedal  1  in the S Ped -F Ped  plane, i.e. the dependency of the pedal force F Ped  acting on the brake pedal  1  during operation by the vehicle driver on the operating travel or pedal travel s Ped  detected by the displacement sensor  36 . The brake pedal characteristic is described by a mathematical function of the dependency of the pedal force on the pedal travel F soll [s Ped ] or the inverse function thereof S soll [F Ped ], which represents the dependency of the pedal travel on the pedal force. 
     In order to produce the mentioned relationship according to the brake pedal characteristic, the electronic control and regulation unit  14  mentioned in connection with  FIG. 1  contains an electronic regulator  40  ( FIGS. 3, 4 ) that calculates a control variable, for example a target value for the electric current fed to the pressure supply device  19 . According to the invention, the regulator  40  is implemented as an optimal regulator that activates the pressure supply device  19  such that a pedal state s, F that has been discovered, and that is defined by the brake pedal displacement s and the brake pedal force F, is converted into a target state s′, F′ by a control method that is optimal in the mathematical sense, wherein the method minimizes a quality criterion. In this case the optimal regulator  40  uses as the quality criterion the distance δ of the brake pedal state from the predetermined brake pedal characteristic, i.e. the corresponding curve/characteristic line in the {s, F}-state plane. 
     The brake pedal travel s and the brake pedal force F are also referred to below with s Ped  and F Ped . 
     The optimal control method consists in this case of associating the state (s Ped , F Ped ) that has been discovered as a target state (s Ped′ , F Ped′ ) with the point lying on the brake pedal characteristic or characteristic line at the shortest distance from the state (s Ped , F Ped ) that has been discovered ( FIG. 2 ). The following is calculated as a practical approximation formula for the distance δ 
     
       
         
           
             
               δ 
               ≈ 
               
                 
                   ( 
                   
                     
                       
                         ( 
                         
                           
                             λ 
                             s 
                           
                           ⁢ 
                           
                             δ 
                             s 
                           
                         
                         ) 
                       
                       
                         - 
                         2 
                       
                     
                     + 
                     
                       
                         ( 
                         
                           
                             λ 
                             F 
                           
                           ⁢ 
                           
                             δ 
                             F 
                           
                         
                         ) 
                       
                       
                         - 
                         2 
                       
                     
                   
                   ) 
                 
                 
                   
                     - 
                     1 
                   
                   / 
                   2 
                 
               
             
             = 
             
               
                 1 
                 
                   
                     1 
                     
                       
                         ( 
                         
                           
                             λ 
                             s 
                           
                           ⁢ 
                           
                             δ 
                             s 
                           
                         
                         ) 
                       
                       2 
                     
                   
                   + 
                   
                     1 
                     
                       
                         ( 
                         
                           
                             λ 
                             F 
                           
                           ⁢ 
                           
                             δ 
                             F 
                           
                         
                         ) 
                       
                       2 
                     
                   
                 
               
             
           
         
       
     
     with the travel deviation
 
δ s   =S   Ped   −S   soll   [F   Ped ]
 
and the force deviation
 
δ F   =F   Ped   −F   soll   [S   Ped ],
 
wherein λs and λ F  are scaling factors and S soll [F Ped ] and F soll [s Ped ] are functional representations of the predetermined characteristic line that are triggered according to the pedal travel and according to the pedal force. The two functions are held ready in the electronic regulator  40 , for example in tabular form, so that the quality measure can be calculated directly.
 
     The control paths used to implement the above steps of the method are shown in  FIGS. 3 and 4 . With the control path shown in  FIG. 3 , the output signal of the displacement sensor  36  mentioned in connection with  FIG. 1  and the output signal of a force sensor that is not shown are fed to a first calculation module  41  as input signals. Following the calculation of the distance δ in the calculation module  41 , the distance is provided to the optimal regulator  40  with the control aim δ→0, which provides as its output variable the activation current I to act upon the pressure supply device  19 , which outputs the actuator pressure p Actuator , which is detected by the pressure sensor  39 . 
     With the version shown in  FIG. 4 , the use of the force sensor can be dispensed with, since the pedal force F is determined in a second calculation module  42  from the pressure p syst  of the first brake circuit and the actuator pressure P Act  using the force balance
 
 F=A   THZ   *P   syst   −A   RK   *p   Act ,
 
wherein the effective hydraulic areas of the first master cylinder piston  15  and booster piston  34  are designated by A THZ  and A RK .
 
     Otherwise, the operation of the brake system according to the invention is revealed to the expert person active within the relevant technical field by the disclosure contents of the present description and the claims, and therefore needs no more detailed description. 
     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.