Patent Publication Number: US-2023159012-A1

Title: Device and method for estimating parameters for a vehicle brake system equipped with a motorized piston-cylinder device

Description:
FIELD 
     The present invention relates to a device for parameter estimation for a vehicle brake system equipped with a motorized piston-cylinder device, and to a vehicle brake system for a vehicle. The present invention also relates to a method for parameter estimation for a vehicle brake system equipped with a motorized piston-cylinder device. In addition, the present invention relates to a method for operating a vehicle brake system equipped with a motorized piston-cylinder device. 
     BACKGROUND INFORMATION 
     German Patent Δpplication No. DE 10 2017 212 360 A1 describes equipping a brake system with a motorized piston-cylinder device, which can also be referred to as a motorized plunger device, and with a device or control device for controlling an electric motor of the motorized piston-cylinder device. 
     SUMMARY 
     The present invention provides, among other things, a device for parameter estimation for a vehicle brake system equipped with a motorized piston-cylinder device, a vehicle brake system, a method for parameter estimation for a vehicle brake system equipped with a motorized piston-cylinder device, and a method for operating a vehicle brake system equipped with a motorized piston-cylinder device. 
     The present invention provides advantageous possibilities for defining/determining at least one elasticity or rigidity as necessary parameters of an inverse system model for a vehicle brake system equipped with a motorized piston-cylinder device. In particular, the present invention provides “robust” possibilities for determining the elasticity and/or the rigidity of the respective brake system, in which a quantity impairing the elasticity and/or rigidity can also be taken into account. Here, even under extreme boundary conditions, a reliable defining of the elasticity and/or of the rigidity of the respective brake system is ensured by the present invention. In particular, the elasticity and/or the rigidity of the respective brake system can be adapted to production-related deviation of the respective brake system from its standard brake system type, changes due to aging in the respective brake system, and/or changing environmental influences acting on the respective brake system. In all the cases listed here, the elasticity and/or rigidity of the respective brake system can be reliably determined. The present invention thus also supports a low-cost mass production of brake systems each equipped with a motorized piston-cylinder device, because even when there is a deviation in one of the brake systems from its typical series product, its elasticity and/or rigidity can still be reliably determined using the present invention. 
     An advantageous specific embodiment of the device of the present invention has a first low-pass filter device and/or a second low-pass filter device, the computing device being designed and/or programmed to determine the elasticity of the brake system and/or the rigidity of the brake system at least taking into account the displaced brake fluid volume, unfiltered or filtered by the first low-pass filter device, and to determine the change in pressure, unfiltered or filtered by the second low-pass filter device. Through a low-pass filtering carried out by the first low-pass filter device and/or by the second low-pass filter device, a signal noise occurring in the respectively filtered signal can be limited/reduced. 
     Preferably, according to an example embodiment of the present invention, the computing device is in addition designed and/or programmed to estimate a displacement path of the at least one piston, displaced by the controlled electric motor, of the motorized piston-cylinder device from its respective initial position, or to read it out from a displacement path sensor signal provided to the computing device, the computing device being designed and/or programmed to estimate the brake fluid volume displaced by the at least one movable piston between the motorized piston-cylinder device and at least the part of the brake system adjoining the motorized piston-cylinder device on the basis of the estimated or read-out displacement path of the at least one displaced piston. Because in most cases a motorized piston-cylinder device is standardly equipped with at least one displacement path sensor, such as an angle of rotation sensor of its electric motor, a reliable estimated value can easily be determined for the displaced brake fluid volume using the specific embodiment described here of the device, so that further sensor equipment for measuring the displaced brake fluid volume is no longer required. 
     In a further advantageous specific embodiment of the device of the present invention, the computing device is in addition designed and/or programmed to estimate a storage volume temporarily stored in at least one storage chamber of the brake system, or to read the storage volume out from a storage volume sensor signal provided to the computing device, the computing device also being designed and/or programmed to determine the elasticity of the brake system and/or the rigidity of the brake system at least taking into account the estimated or read-out displaced brake fluid volume, the estimated or read-out change in pressure, and the storage volume temporarily stored in the at least one storage chamber. The specific embodiment of the device described here thus enables a more accurate and more reliable determination of the elasticity and/or rigidity of the respective brake system. 
     Likewise, according to an example embodiment of the present invention, the motor control device can in addition be designed and/or programmed to control an electric motor of a motorized brake pressure buildup device of the brake system in such a way that a differential volume can be displaced by the motorized brake pressure buildup device into or out of at least the part of the brake system adjoining the motorized piston-cylinder device, the computing device in addition being designed and/or programmed to estimate the differential volume or to read the differential volume out from at least one additional volume sensor signal provided to the computing device, and to determine the elasticity of the brake system and/or the rigidity of the brake system at least taking into account the estimated or read-out displaced brake fluid volume, the estimated or read-out change in pressure, and the differential volume displaced into or out of at least the part of the brake system adjoining the motorized piston-cylinder device. In this way as well, the elasticity and/or rigidity of the respective brake system can be determined more accurately and more reliably. 
     Alternatively or in addition, according to an example embodiment of the present invention, the computing device can also be designed and/or programmed to estimate a dead volume of the brake system at least taking into account the estimated or read-out displaced brake fluid volume and the estimated or read-out change in pressure, and to determine the elasticity of the brake system and/or the rigidity of the brake system at least taking into account the estimated or read-out displaced brake fluid volume, the estimated or read-out change in pressure, and the estimated dead volume. The estimation and taking into account of the dead volume of the brake system can also contribute to improving the accuracy and reliability of the determined elasticity or rigidity of the respective brake system. 
     As an advantageous development of the present invention, the motor control device can in addition be designed and/or programmed to determine at least one target quantity relating to a target operating mode of the electric motor of the motorized piston-cylinder device, taking into account at least one specified quantity relating to a vehicle speed and/or vehicle deceleration requested by a driver or an automatic speed control system of the vehicle, and additionally taking into account the elasticity and/or rigidity of the brake system determined by the computing device, and, taking into account at least the determined target quantity, to output at least one motor control signal to the electric motor. The development described here of the device can bring about both a brake force boosting and also an autonomous braking of the respective vehicle, it being ensured in both cases, through the taking into account of the determined elasticity and/or rigidity of the respective brake system, that the requested vehicle speed and/or vehicle deceleration is reliably maintained. 
     The advantages described above may also be ensured in a vehicle brake system having such a device for parameter estimation and in the motorized piston-cylinder device having the electric motor controllable by the device. 
     The carrying out of a corresponding method for parameter estimation for a vehicle brake system equipped with a motorized piston-cylinder device also brings about the advantages described above. The method for parameter estimation can be developed according to the specific embodiments explained above of the device. 
     In addition, the carrying out of a corresponding method for operating a vehicle brake system equipped with a motorized piston-cylinder device also achieves the advantages described above; in this case as well, the method can be developed according to the specific embodiments of the device explained above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the present invention are explained in the following on the basis of the Figures. 
         FIG.  1    shows a flow diagram for the explanation of a specific embodiment of the method for parameter estimation for a vehicle brake system equipped with a motorized piston-cylinder device, according to the present invention. 
         FIG.  2    shows a flow diagram for the explanation of a specific embodiment of the method for operating a vehicle brake system equipped with a motorized piston-cylinder device, according to the present invention. 
         FIGS.  3 A and  3 B  show a schematic partial representation of a specific embodiment of the brake system and a coordinate system for the explanation of its pressure-volume characteristic curve, according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
       FIG.  1    shows a flow diagram for the explanation of a specific embodiment of the method for parameter estimation for a vehicle brake system equipped with a motorized piston-cylinder device. 
     The method described below can be carried out with (almost) any brake system that is at least equipped with a motorized piston-cylinder device, which can also be referred to as a motorized plunger device. The motorized piston-cylinder device is to be understood as a device having at least one piston situated inside a cylindrical volume, in which the at least one piston is capable of being displaced/is displaced linearly by operation of an electric motor of the motorized piston-cylinder device, in such a way that brake fluid is displaceable between the at least one cylindrical volume of the motorized piston-cylinder device and a connected brake system volume. The practicability of the method is likewise not limited to a specific type of vehicle or motor vehicle equipped with the respective brake system. 
     In a method step S 1 , the electric motor of the motorized piston-cylinder device is controlled in such a way that the at least one piston, displaceable by the operated electric motor, of the motorized piston-cylinder device is displaced from its respective initial position. In addition, when the method described here is carried out, a brake fluid volume ΔV displaced by the at least one displaceable piston of the motorized piston-cylinder device between the motorized piston-cylinder device and at least a part of the brake system adjoining the motorized piston-cylinder device is estimated or ascertained. 
     For example, a displacement path of the at least one piston, displaced by the controlled electric motor, of the motorized piston-cylinder device is estimated from its respective initial position or is read out from at least one displacement path sensor signal, and subsequently the brake fluid volume ΔV displaced by the at least one displaceable piston between the motorized piston-cylinder device and at least of the part of the brake system adjoining the motorized piston-cylinder device is estimated on the basis of the estimated displacement path of the at least one volume. The displacement path of the at least one displaceable piston can for example be estimated with a high degree of accuracy and good reliability on the basis of the controlling of the electric motor carried out as method step Sl, for example by correspondingly evaluating a current outputted to the electric motor in order to control it. Alternatively or in addition, the displacement path of the at least one displaceable piston can also be read out from a signal, evaluated as a displacement path sensor signal, of an angle of rotation sensor of the electric motor of the motorized piston-cylinder device. Optionally, at least one separate sensor can also be installed on the motorized piston-cylinder device to determine a current position of the at least one piston, whose signal is then evaluated as a displacement path sensor signal for reading out the displacement path of the at least one piston. If at least one volume sensor, designed to determine the brake fluid volume ΔV displaced by the at least one displaceable piston, is installed in the brake system, the displaced brake fluid volume ΔV can also be read out from at least one volume sensor signal of the at least one volume sensor. 
     Only as an example, in the method described here, as method step S 2 , in order to determine the brake fluid volume ΔV displaced by the at least one displaceable piston, an overall brake fluid volume V(t) of the brake system is continuously estimated or ascertained. The estimation or ascertaining of the overall brake fluid volume V(t) of the brake system can take place taking into account the respective displacement path of the at least one piston displaced by the controlled electric motor, the at least one displacement path sensor signal, and/or the at least one volume sensor signal. 
     In addition, when carrying out the method described here, a change in pressure Δp occurring at least in the part of the brake system adjoining the motorized piston-cylinder device due to the displaced brake fluid volume ΔV is ascertained or estimated. As the respective change in pressure Δp, for example a change in a system pressure can be estimated or measured by at least one system pressure sensor. As an example, in the specific embodiment described here a pressure p(t) prevailing in at least the part of the brake system adjoining the motorized piston-cylinder device is continuously ascertained or estimated as method step S 3 . Preferably, when carrying out method steps S 2  and S 3 , care is taken that there are no large time delays between the ascertained or estimated values for the overall brake fluid volume V(t) and the pressure p(t). 
     In the specific embodiment of  FIG.  1   , in an (optional) method step S 4  the ascertained or estimated overall brake fluid volume V(t) is subsequently filtered with a further variable low-pass filter. Likewise, in an optional method step S 5  the ascertained or estimated pressure p(t) is filtered with a further variable low-pass filter. Using the low-pass filtering, carried out as method steps S 4  and S 5 , a signal noise in the volume values V(t) and pressure values p(t), or the values derived later therefrom for the displaced brake fluid volume ΔV and the change in pressure Δp, can be limited. 
     In a method step S 6 , the displaced brake fluid volume ΔV is then determined according to equation (Eq. 1): 
     
       
         
           
             
               
                 
                   
                     Δ 
                     ⁢ 
                     V 
                   
                   = 
                   
                     
                       
                         V 
                         ⁡ 
                         ( 
                         
                           t 
                           + 
                           
                             Δ 
                             ⁢ 
                             t 
                           
                         
                         ) 
                       
                       - 
                       
                         V 
                         ⁡ 
                         ( 
                         t 
                         ) 
                       
                     
                     ≈ 
                     
                       
                         d 
                         ⁢ 
                         
                           V 
                           ⁡ 
                           ( 
                           t 
                           ) 
                         
                       
                       
                         d 
                         ⁢ 
                         t 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Eq 
                     . 
                         
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
     Correspondingly, in a method step S 7  the change in pressure Δp is determined according to equation (Eq. 2): 
     
       
         
           
             
               
                 
                   
                     Δ 
                     ⁢ 
                     p 
                   
                   = 
                   
                     
                       
                         p 
                         ⁡ 
                         ( 
                         
                           t 
                           + 
                           
                             Δ 
                             ⁢ 
                             t 
                           
                         
                         ) 
                       
                       - 
                       
                         p 
                         ⁡ 
                         ( 
                         t 
                         ) 
                       
                     
                     ≈ 
                     
                       
                         d 
                         ⁢ 
                         
                           p 
                           ⁡ 
                           ( 
                           t 
                           ) 
                         
                       
                       
                         d 
                         ⁢ 
                         t 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Eq 
                     . 
                         
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
     In an optional method step S 8 , in the specific embodiment described here the change in pressure Δp determined in method step S 7  is compared with a specified minimum change in pressure Δp min . If the change in pressure Δp is greater than the minimum change in pressure Δp min , the method can be continued with an optional method step S 9 . As method step S 9 , the displaced brake fluid volume ΔV determined in method step S 6  can be compared with a specified minimum change in volume ΔV min . If the determined displaced brake fluid volume ΔV is greater than the minimum change in volume ΔV min , the method can be continued with method step S 10 . 
     In method step S 10 , an elasticity E of the brake system and/or a rigidity of the brake system is determined at least taking into account the displaced brake fluid volume ΔV and the change in pressure Δp. In the specific embodiment of  FIG.  1    described here, in particular the elasticity of the brake system is determined according to equation (Eq. 3): 
     
       
         
           
             
               
                 
                   E 
                   = 
                   
                     
                       Δ 
                       ⁢ 
                       V 
                     
                     
                       Δ 
                       ⁢ 
                       p 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Eq 
                     . 
                         
                     3 
                   
                   ) 
                 
               
             
           
         
       
     
     Equation (Eq. 3) can therefore be reliably used in particular because method step S 8  ensures that the change in pressure Δp is sufficiently large. (In the case of a change in pressure Δp of almost 0, the elasticity E determined in this way would go towards infinity.) Moreover, method step S 9  ensures that the elasticity E determined according to equation (Eq. 3) differs significantly from zero. 
     Alternatively or in addition, the rigidity of the brake system can also be determined according to equation (Eq. 4): 
     
       
         
           
             
               
                 
                   Σ 
                   = 
                   
                     
                       Δ 
                       ⁢ 
                       p 
                     
                     
                       Δ 
                       ⁢ 
                       V 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Gl 
                     . 
                         
                     4 
                   
                   ) 
                 
               
             
           
         
       
     
     As an advantageous development, more complicated equations can also be used to determine the elasticity E of the brake system and/or the rigidity of the brake system in method step S 10 . For example, in at least one method step that is not shown, an intermediately stored storage volume V acc  temporarily stored in at least one storage chamber of the respective brake system can also be estimated or read out from at least one storage chamber sensor signal. The elasticity E of the brake system and/or the rigidity of the brake system may, if desired, then be determined at least taking into account the displaced brake fluid volume ΔV, the change in pressure Δp, and the storage volume V acc  temporarily stored in the at least one storage chamber. If the brake system also includes a further motorized brake pressure buildup device, then in addition a differential volume V diff  displaced by the motorized brake pressure buildup device into or out of at least the part of the brake system adjoining the motorized piston-cylinder device can also be estimated or determined, after which the elasticity E and/or the rigidity Σ of the respective brake system can be determined at least taking into account the displaced brake fluid volume ΔV, the change in pressure Δp, and the differential volume V diff  displaced into or out of at least the part of the brake system adjoining the motorized piston-cylinder device. In many brake systems, moreover, first a so-called dead volume V 0  has to be exceeded before a pressure buildup in the respective brake system begins through operation at least of the motorized piston-cylinder device. If this is true of the respective brake system, then the elasticity E of the brake system and/or the rigidity of the brake system can also be determined at least taking into account the displaced brake fluid volume ΔV, the change in pressure Δp, and the estimated dead volume V 0 . In this way, to determine the elasticity E or the rigidity of the brake system, the equations (Eq. 5) and/or (Eq. 6) can also be used: 
     
       
         
           
             
               
                 
                   E 
                   = 
                   
                     
                       
                         Δ 
                         ⁢ 
                         V 
                       
                       + 
                       
                         V 
                         + 
                       
                     
                     
                       Δ 
                       ⁢ 
                       p 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Gl 
                     . 
                         
                     5 
                   
                   ) 
                 
               
             
           
         
       
       
         
           
             
               
                 
                   Σ 
                   = 
                   
                     
                       Δ 
                       ⁢ 
                       p 
                     
                     
                       
                         Δ 
                         ⁢ 
                         V 
                       
                       + 
                       
                         V 
                         + 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Gl 
                     . 
                         
                     6 
                   
                   ) 
                 
               
             
           
         
       
     
     The quantity V +  can optionally include the storage volume V acc  temporarily stored in the at least one storage chamber, the differential volume V diff  displaced by the motorized pressure buildup device, and/or the dead volume V 0 . 
     As a possible development, in the determination of the elasticity E and/or of the rigidity Σ the respective brake system, a damping D and/or an inertia T of the respective brake system can also be taken into account. This can be done using equations (Eq. 7) and/or (Eq. 8): 
     
       
         
           
             
               
                 
                   
                     p 
                     ⁡ 
                     ( 
                     t 
                     ) 
                   
                   = 
                   
                     
                       Σ 
                       * 
                       
                         ( 
                         
                           
                             Δ 
                             ⁢ 
                             V 
                           
                           + 
                           
                             V 
                             + 
                           
                         
                         ) 
                       
                     
                     + 
                     
                       D 
                       * 
                       
                         
                           dV 
                           ⁡ 
                           ( 
                           t 
                           ) 
                         
                         
                           d 
                           ⁢ 
                           t 
                         
                       
                     
                     + 
                     
                       T 
                       * 
                       
                         
                           
                             d 
                             2 
                           
                           ⁢ 
                           
                             V 
                             ⁡ 
                             ( 
                             t 
                             ) 
                           
                         
                         
                           d 
                           ⁢ 
                           
                             t 
                             2 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Eq 
                     . 
                         
                     7 
                   
                   ) 
                 
               
             
           
         
       
       
         
           
             
               
                 
                   E 
                   = 
                   
                     1 
                     Σ 
                   
                 
               
               
                 
                   ( 
                   
                     Eq 
                     . 
                         
                     8 
                   
                   ) 
                 
               
             
           
         
       
     
     However, here it is to be noted that the use of the six parameters elasticity E/rigidity Σ, storage volume V acc , differential volume V diff , dead volume V 0 , damping D, and inertia T is merely optional. Instead of a complex and computationally intensive use of the equations (Eq. 7) or an equation derived therefrom for the elasticity E, in many cases it is enough to use only the equations (Eq. 3) and (Eq. 4) to determine the elasticity E and/or rigidity Σ. In order to ensure that the storage volume V acc , differential volume V diff , dead volume V 0 , damping D, and inertia T of the respective brake system do not play a relevant role in the determination of the elasticity E and/or of the rigidity Σ of the respective brake system, corresponding test boundary conditions can moreover be maintained in the parameter determination. The maintaining of these test boundary conditions can be ensured for example by the signal filtering carried out by method steps S 4  and S 5 . 
     In addition, using the method steps described below, it can be ensured that the value E determined by equation (Eq. 3) is a reliable value for the elasticity E. For this purpose, in an optional method step S 11  the value E determined by equation (Eq. 3) is first compared with a maximum value E max  specified for the elasticity. If the value E determined by equation (Eq. 3) is smaller than the maximum value E max , then the method is continued with an optional method step S 12 , in which the value E determined by equation (Eq. 3) is compared with a minimum value E min  specified for the elasticity. Only if the value E determined by equation (Eq. 3) is greater than the minimum value E min  is the value E determined as the elasticity E, in a method step S 13 . 
     If the change in pressure Op determined in method step S 7  is less than or equal to the minimum change in pressure Δp min , the displaced brake fluid volume ΔV determined in method step S 6  is less than or equal to the minimum change in volume ΔV min , or the value E determined by equation (Eq. 3) is greater than or equal to the maximum value E max , then, in the specific embodiment of the method described here, an optional method step S 14  is carried out. In method step S 14 , it is queried whether there is a previous valid value for the elasticity E. If this is the case, then, as method step S 15 , the previous valid value is determined as value E, and the method ends with method step S 13 . Otherwise, in a method step S 16  the maximum value E max  is determined as the value E, and the method ends with method step S 13 . 
     Method step S 14  is also carried out when the value E determined by equation (Eq. 3) is less than or equal to the minimum value E min . If there is a previous valid value for the elasticity E, then method steps S 13  and S 15  are carried out. Otherwise, as method step S 17  the minimum value E min  is determined as the value E, and the method ends with method step S 13 . 
       FIG.  2    shows a flow diagram explaining a specific embodiment of the method for operating a vehicle brake system equipped with a motorized piston-cylinder device. 
     The method described here can also be realized with (almost) any brake system that is equipped with at least one motorized piston-cylinder device. The practicability of the method is likewise not limited to any specific type of vehicle or motor vehicle equipped with the respective brake system. 
     In the method described here, first an elasticity E of the brake system and/or a rigidity Σ of the brake system are determined. This can be done for example by carrying out at least one of the method steps S 1  through S 17  explained above. 
     Later, as method step S 18 , at least one target quantity is determined relating to a target operating mode of the electric motor of the motorized piston-cylinder device, taking into account at least one specified quantity relating to a vehicle speed and/or vehicle acceleration requested by a driver or automated speed control system of the vehicle, and additionally taking into account the determined elasticity E and/or rigidity Σ of the brake system. The automated speed control system can be understood for example as an adaptive cruise control system, an automated system for autonomous driving of the vehicle, and/or an emergency braking system. In particular, first, a brake pressure p target  that is to be brought about in at least one wheel brake cylinder of the brake system can be determined. Subsequently, as the at least one target quantity a volume flow q that is to be brought about by the motorized piston-cylinder device can be determined, by which the desired brake pressure p target  can be built up in at the at least one wheel brake cylinder, determined according to equation (Eq. 9): 
     
       
         
           
             
               
                 
                   q 
                   = 
                   
                     E 
                     * 
                     
                       
                         dp 
                         
                           t 
                           ⁢ 
                           a 
                           ⁢ 
                           r 
                           ⁢ 
                           g 
                           ⁢ 
                           e 
                           ⁢ 
                           t 
                         
                       
                       
                         d 
                         ⁢ 
                         t 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Eq 
                     . 
                         
                     9 
                   
                   ) 
                 
               
             
           
         
       
     
     In a further method step S 19 , the electric motor of the motorized piston-cylinder device is controlled by outputting at least one motor control signal to the electric motor, taking into account at least the determined target quantity. For example, for this purpose, as the at least one motor control signal a current signal can be outputted to the electric motor, which signal brings it about that the electric motor supplied with current initiates the desired volume flow q by displacing the at least one piston of the motorized piston-cylinder device. 
       FIGS.  3 A and  3     b  show a schematic partial representation of a specific embodiment of the brake system and a coordinate system for explaining its pressure-volume characteristic curve. 
     The brake system partially shown schematically in  FIG.  3 A  has at least one device  10  for parameter estimation and a motorized piston-cylinder device  12  having an electric motor  14  controllable by device  10 . At least one piston of motorized piston-cylinder device  12  can be linearly displaced by operation of its electric motor  14  in such a way that brake fluid can be displaced between motorized piston-cylinder device  12  and a remaining volume of the brake system. 
     Shown merely as examples in  FIG.  3 A , as additional components of the brake system, are a master brake cylinder  16  having an upstream brake pedal  18 , a brake fluid reservoir  20 , a first separating valve  22   a  for connecting or decoupling a first chamber of master brake cylinder  16  to a first brake circuit (not shown) of the brake system, a second separating valve  22   b  for connecting or decoupling a second chamber of the master brake cylinder  16  to a second brake circuit (not shown) of the brake system, a third separating valve  24   a  for connecting or decoupling the motorized piston-cylinder device  12  to the first brake circuit, a fourth separating valve  24   b  for connecting or decoupling the motorized piston-cylinder device  12  to the second brake circuit, a fifth separating valve  26  for connecting the motorized piston-cylinder device  12  to brake fluid reservoir  20 , and a simulator separating valve  28  for connecting or decoupling a simulator  30  to the first chamber of master brake cylinder  16 . Each of the two brake circuits of the brake system has at least one wheel brake cylinder. For example, each of the two brake circuits can have two wheel brake cylinders each. Optionally, at least one of the two brake circuits can further be fashioned having at least one wheel inlet valve, at least one wheel outlet valve, a storage chamber situated downstream from its at least one wheel outlet valve, and/or a return pump. However, the individual components of the two brake circuits are not graphically shown in  FIG.  3 A . Moreover, it is expressly noted here that the components of the brake system described in the present paragraph are to be interpreted only as examples. The applicability of device  10  described below is not limited to such a brake system or to a specific type of vehicle or motor vehicle equipped with the respective brake system. 
     Device  10  has a motor control device  32  that is designed and/or programmed to control electric motor  14  of motorized piston-cylinder device  12  using at least one motor control signal  34 , in such a way that the at least one displaceable piston of motorized piston-cylinder device  12  can be displaced or is displaced from its respective initial position by the controlled electric motor  14 . In addition, device  10  includes a computing device  36  that is designed and/or programmed to estimate a brake fluid volume displaced by the at least one displaceable piston between motorized piston-cylinder device  12  and at least a part of the brake system adjoining motorized piston-cylinder device  12 , or to read it out from at least one volume sensor signal provided to computing device  36 , and to estimate a change in pressure occurring due to the displaced brake fluid volume at least in the part of the brake system adjoining motorized piston-cylinder device  12 , or to read it out from at least one pressure sensor signal  38  provided to computing device  36 . The at least one pressure sensor signal  38  can be outputted to computing device  36  for example by a system pressure sensor  40 . In the specific embodiment described here, computing device  36  is moreover designed and/or programmed to read out a displacement path of the at least one piston, displaced by the controlled electric motor  14 , of motorized piston-cylinder device  12  from its respective initial position from a displacement path sensor signal  42  provided to computing device  36 , and subsequently to estimate the brake fluid volume displaced by the at least one displaceable piston between motorized piston-cylinder device  12  and at least the part of the brake system adjoining motorized piston-cylinder device  12 , on the basis of the estimated or read-out displacement path of the at least one displaced piston. The at least one displacement path sensor signal  42  can be outputted to computing device  36  in particular by an angle of rotation sensor  44  of electric motor  14 . 
     In addition, computing device  36  is designed and/or programmed to determine an elasticity E of the brake system and/or a rigidity Σ of the brake system at least taking into account the estimated or read-out displaced brake fluid volume and the estimated or read-out change in pressure. This can take place in particular using at least one of the equations indicated above. Even if the brake system has an “unusual” elasticity E or rigidity Σ due to its large-scale production, aging, or change due to environmental conditions, the respective values can be reliably determined by device  10 . In the coordinate system of  FIG.  3 B , an example is shown of a characteristic curve k that can be determined by computing device  36  for the elasticity E of the brake system, where an abscissa of the coordinate system indicates a pressure p in the brake system and an ordinate of the coordinate system indicates an overall brake fluid volume V of the brake system. In addition, a dead volume V 0  of the brake system is shown in the coordinate system of  FIG.  3 B . 
     In a development not shown graphically, device  10  can also have a first low-pass filter device and/or a second low-pass filter device, and computing device  36  can be designed and/or programmed to determine the elasticity E of the brake system and/or the rigidity Σ of the brake system at least taking into account the displaced brake fluid volume, unfiltered or filtered by the first low-pass filter device, and the change in pressure, unfiltered or filtered by the second low-pass filter device. Likewise, computing device  36  can also be designed and/or programmed to estimate a storage volume temporarily stored in at least one storage chamber (not shown) of the brake system, or to read it out from at least one storage chamber sensor signal provided to the computing device, and/or to estimate a dead volume V 0  of the brake system. In this case, the computing device  36  is preferably also designed and/or programmed to determine the elasticity E of the brake system and/or the rigidity Σ of the brake system, also taking into account the storage volume temporarily stored in the at least one storage chamber and/or the estimated dead volume V 0 . If motor control device  32  controls an electric motor of a motorized rate pressure buildup device (not shown) of the brake system in such a way that a differential volume can be displaced by the motorized brake pressure buildup device into or out of at least the part of the brake system adjoining the motorized piston-cylinder device, then computing device  36  can in addition be designed and/or programmed to estimate the differential volume or to read it out from at least one further volume sensor signal provided to the computing device, and to determine the elasticity E and/or the rigidity Σ of the brake system additionally taking into account the differential volume displaced into or out of at least the part of the brake system adjoining the motorized piston-cylinder device. As an advantageous development, motor control device  32 , in the specific embodiment of device  10  described here, is also designed and/or programmed to determine at least one target quantity relating to a target operating mode of electric motor  14  of the motorized piston-cylinder device, taking into account at least one specified quantity  46  relating to a vehicle speed and/or vehicle deceleration requested by a driver or by an automated speed control system of the vehicle, and additionally taking into account the elasticity E and/or rigidity Σ of the brake system determined by computing device  36 . The at least one specified quantity  46  can for example also be provided to motor control device  32  by a rod path sensor  48  and/or a differential path sensor. Motor control device  32  then outputs the at least one motor control signal  34  to electric motor  14  taking into account at least the determined target quantity. Device  10  can thus also be used for active or autonomous pressure modulations.