Patent Publication Number: US-2021162968-A1

Title: Vehicle brake system and method for increasing brake pressure in a first wheel brake cylinder and limiting brake pressure in a second wheel brake cylinder of a vehicle brake system

Description:
FIELD 
     The present invention relates to a vehicle brake system. The present invention also relates to a method for increasing brake pressure in a first wheel brake cylinder and for limiting brake pressure in a second wheel brake cylinder of a vehicle brake system. 
     BACKGROUND INFORMATION 
       FIGS. 1 a  through 1 c    show a schematic partial representation of a vehicle brake system and coordinate systems for the explanation of a conventional procedure for increasing brake pressure with simultaneous brake pressure limiting. 
       FIG. 1 a    shows a schematic partial representation of a conventional brake system as described, for example, in German Patent Application No. DE 10 2012 222 974 A1. The conventional brake system has at least one brake circuit  10  having a first wheel brake cylinder  12 , a second wheel brake cylinder  14 , a first wheel inlet valve  16  assigned to first wheel brake cylinder  12 , a first wheel outlet valve  18  assigned to first wheel brake cylinder  12 , a second wheel inlet valve  20  assigned to second wheel brake cylinder  14 , and a second wheel outlet valve  22  assigned to second wheel brake cylinder  14 . Moreover, brake circuit  10  is realized having a high-pressure switching valve  24 , a changeover valve  26 , a storage chamber situated after wheel outlet valves  18  and  22 , a return pump  30 , a check valve  32  situated between storage chamber  28  and return pump  30 , and a pressure sensor/pre-pressure sensor  34 . Brake circuit  10  is connected (together with a further brake circuit (not shown)) to a master brake cylinder  36 . In addition, another brake actuating element/brake pedal  38 , a brake booster  40 , and a brake fluid reservoir  42  are connected to master brake cylinder  36 . An actuation of brake actuating element/brake pedal  38  by a driver with a schematically shown driver&#39;s braking force  44  is detectable by at least one brake actuating element sensor  46 .  FIG. 1 a    also shows a pump motor  48  on whose shaft the return pump  30  is situated (together with a further return pump of the further brake circuit (not shown)). 
     Using the coordinate systems of  FIGS. 1 b  and 1 c   , a conventional procedure for increasing brake pressure with simultaneous brake pressure limiting is shown that is internal existing art. Each of the abscissas of the coordinate systems of  FIGS. 1 b  and 1 c    is a time axis t. Using the ordinate of the coordinate system of  FIG. 1 b   , a current strength I- 30  of an operating current is shown that, for the operation of return pump  30 , is supplied to its pump motor  48 . The ordinate of the coordinate system of  FIG. 1 c    shows a current strength I- 22  of a control signal for controlling/switching second wheel outlet valve  22 . 
     Using the conventional procedure described below for increasing brake pressure with simultaneous brake pressure limiting, a first brake pressure in first wheel brake cylinder  12  (during an actuation of brake actuating element/brake pedal  38 ) is to be rapidly increased by, from a time t 1  until a time t 2 , transferring brake fluid into first wheel brake cylinder  12  by an operation of return pump  30 . During the transferring of brake fluid into first wheel brake cylinder  12 , first wheel inlet valve  16  is controlled into its open state, and first wheel outlet valve  18  is controlled into its closed state. 
     In order at the same time to counteract an undesired increase of a second brake pressure in second wheel brake cylinder  14 , second wheel inlet valve  20  is controlled into its closed state during the transfer of brake fluid into first wheel brake cylinder  12 . However, an undesired flow  50  of brake fluid into second wheel brake cylinder  14  often cannot be completely suppressed/prevented by closed second wheel inlet valve  20 . Therefore, during the transfer of brake fluid into first wheel brake cylinder  12 , second wheel outlet valve  22  is repeatedly (for example, every 0.8 seconds) briefly controlled, with a load of 100%, from its closed state into its open state in order to conduct brake fluid out of second wheel brake cylinder  14  into storage chamber  28  via the briefly (e.g., for approximately 0.2 seconds) opened second wheel outlet valve  22 . Thus, second wheel outlet valve  22  is periodically opened and closed. In order to switch the second wheel outlet valve into its open state with a load of 100%, as a rule a signal having a current strength value, constant over time, of 2 A (amperes) is required. 
     SUMMARY 
     The present invention provides a vehicle brake system and a method for increasing brake pressure in a first wheel brake cylinder and for limiting brake pressure in a second wheel brake cylinder of a vehicle brake system. 
     The present invention provides possibilities for bringing about a brake pressure increase in a first wheel brake cylinder of a vehicle brake system, in which a first brake pressure in the first wheel brake cylinder can be increased relatively quickly using at least one brake pressure buildup device, while at the same time an undesired increase is reliably prevented of a second brake pressure in a second wheel brake cylinder of the vehicle brake system, which can likewise be filled by the at least one brake pressure buildup device. In addition, when the present invention is used it is ensured that the undesired increase of the second brake pressure in the respective second wheel brake cylinder is prevented in (substantially) noiseless fashion. This is a significant advantage compared to the existing art described above, in which the (periodic/cyclical) opening and closing of the second wheel outlet valve causes comparatively loud noise. A further advantage of the present invention is that during its use the undesired increase of the second brake pressure is not only limitable, but is constantly preventable. As is explained more precisely in the following, overheating of the second wheel outlet valve also need not be feared during use of the present invention. 
     The present invention can be used to increase a first brake pressure in a first wheel brake cylinder of a brake circuit of a vehicle brake system, and at the same time to prevent an undesired increase of a second brake pressure in a second wheel brake cylinder of the same brake circuit (realized having the respective first wheel brake cylinder). Thus, the present invention provides possibilities for bringing about a brake pressure increase in at most one (first) wheel brake cylinder per brake circuit of a vehicle brake system, with simultaneous prevention of a brake pressure increase in at least one further (second) wheel brake cylinder of the vehicle brake system. Likewise, the present invention can be used to increase a first brake pressure in at least one first wheel brake cylinder of a first brake circuit of a vehicle brake system, and at the same time to prevent an undesired increase of a second brake pressure in at least one second wheel brake cylinder of a second brake circuit of the vehicle brake system. The present invention is thus versatile in its possible uses. 
     In an advantageous specific embodiment of the vehicle brake system in accordance with the present invention, the control device is designed to hold, during operation of the at least one brake pressure buildup device, a current strength maximum and a duty cycle of the pulse width-modulated signal low enough that the current strength maximum and the duty cycle are just sufficient for the second wheel outlet valve, controlled by the pulse width-modulated signal, to be permanently in its open state. A current strength, averaged over time, of the pulse width-modulated signal outputted to the second wheel outlet valve during the transferring of brake fluid into the first wheel brake cylinder is thus comparatively low, so that no overheating of the second wheel outlet valve (or of its electronics) need be feared. 
     For example, the control device can be designed to hold, during the operation of the at least one brake pressure buildup device, the current strength maximum and the duty cycle of the pulse width-modulated signal low enough that the pulse width-modulated signal has a current strength, averaged over time, of less than 0.5 A. Using the example procedure according to the present invention described here, a thermal load of the second wheel outlet valve (or its electronics) can thus reliably be minimized. Moreover, current consumption can be reduced using the procedure described here. 
     Preferably, the control device includes at least one flyback diode and is designed to output the pulse width-modulated signal to the second wheel outlet valve using the flyback diode. Thus, the flyback diode, frequently already in use, can also be used for the realization of the present invention. The present invention thus also contributes to increasing the multifunctionality of the flyback diode additionally used in this way. 
     For example, the vehicle brake system can include a master brake cylinder to which a brake actuating element is connectable or is connected and/or before which there is connected a brake booster, at least one pump, and/or at least one motorized plunger device as the at least one brake pressure buildup device. Thus, brake pressure buildup devices that are frequently already present in a vehicle brake system can additionally be used for the present invention. However, it is to be noted that the practicability of the present invention is not limited to the use of the examples listed here of the at least one brake pressure buildup device. 
     As mentioned above, the first wheel brake cylinder with its first wheel inlet valve and its first wheel outlet valve, and the second wheel brake cylinder with its second wheel inlet valve and its second wheel outlet valve, can be situated in a common brake circuit of the vehicle brake system. The present invention can thus be used to trigger different braking actions of two wheel brake cylinders of the same brake circuit. 
     The advantages described above are also brought about by a realization of a corresponding method for increasing brake pressure in a first wheel brake cylinder and for limiting brake pressure in a second wheel brake cylinder of a vehicle brake system. Here it is expressly noted that the method is capable of being further developed according to the above-explained specific embodiments of the vehicle brake system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the present invention are explained below on the basis of the Figures. 
         FIGS. 1 a  through 1 c    show a schematic partial representation of a vehicle brake system and coordinate systems for the explanation of a conventional procedure for increasing brake pressure with simultaneous brake pressure limiting. 
         FIGS. 2 a  through 2 d    show a schematic partial representation of a vehicle brake system and coordinate systems for the explanation of a first specific embodiment of a method in accordance with the present invention for increasing brake pressure in a first wheel brake cylinder and for limiting brake pressure in a second wheel brake cylinder of the vehicle brake system. 
         FIG. 3  shows a schematic representation of a vehicle brake system for the explanation of a second specific embodiment of the method in accordance with the present invention for increasing brake pressure in a first wheel brake cylinder and for limiting brake pressure in a second wheel brake cylinder of the vehicle brake system. 
         FIGS. 4 a  and 4 b    show schematic representations of a specific embodiment of the vehicle brake system and of its control device, in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
       FIGS. 2 a  through 2 d    show a schematic partial representation of a vehicle brake system and coordinate systems for the explanation of a first specific embodiment of the method for increasing brake pressure in a first wheel brake cylinder and for limiting brake pressure in a second wheel brake cylinder of the vehicle brake system. 
     The vehicle brake system partly shown schematically in  FIG. 2 a    has at least one brake circuit  10  having a first wheel brake cylinder  12 , a second wheel brake cylinder  14 , a first wheel inlet valve  16  assigned to first wheel brake cylinder  12 , a first wheel outlet valve  18  assigned to first wheel brake cylinder  12 , a second wheel inlet valve  20  assigned to second wheel brake cylinder  14 , and a second wheel outlet valve  22  assigned to second wheel brake cylinder  14 . Merely as an optional development, brake circuit  10  additionally includes a high-pressure switching valve  14 , a changeover valve  26 , a storage chamber  28  (such as a low-pressure storage chamber) connected after wheel outlet valves  18  and  22 , at least one pump/return pump  30 , a check valve  32  situated between storage chamber  28  and return pump  30 , and at least one pressure sensor and/or pre-pressure sensor  34 . However, the realization shown in  FIG. 2 a    of brake circuit  10 , having components  24  to  34 , is to be interpreted only as an example. 
     The vehicle brake system also has at least one brake pressure buildup device  30  and  36  connected both to first wheel brake cylinder  12  and to second wheel brake cylinder  14 . For example, in the specific embodiment of  FIG. 2 a   , brake pressure buildup device  36  includes the at least one pump  30  (having a pump motor  48 ) and/or a master brake cylinder  36  having a pre-positioned brake actuating element  38  (such as a brake pedal  38 ) for actuation by a driver with a schematically shown (and possibly detected by a brake actuation element sensor  46 ) driver&#39;s braking force  44 , and/or a pre-positioned brake booster  40 , at least brake circuit  10  and a brake fluid reservoir  42  being connected to master brake cylinder  36 . (Brake booster  40  can also be interpreted as at least part of the at least one brake pressure buildup device  30  and  36 .) However, as an alternative to the at least one pump  30  and/or master brake cylinder  36 , at least one motorized plunger device can also be used as (part of) brake pressure buildup device  30  and  36 . 
     In addition to brake circuit  10  connected to master brake cylinder  36 , the vehicle brake system can also have at least one further brake circuit (not shown). The at least one further brake circuit can be realized identically to depicted brake circuit  10 . Alternatively, the at least one further brake circuit may also differ from brake circuit  10 . For example, the at least one further brake circuit may be decoupled from master brake cylinder  10 , or may be capable of being decoupled from master brake cylinder  10 . 
     It is expressly to be noted that the practicability of the method described below is limited neither to a particular brake system type of the vehicle brake system nor to a specific vehicle type/motor vehicle type of the vehicle/motor vehicle equipped with the vehicle brake system. 
     Using the method described below, an increase in brake pressure is to be brought about in first wheel brake cylinder  12  of brake circuit  10 , while at the same time a brake pressure increase in second wheel brake cylinder  14  of the same brake circuit  10  is prevented. The method can also be realized, in a vehicle brake system having at least two brake circuits  10  each having two wheel brake cylinders  12  and  14 , in such a way that an increase in brake pressure in a (first) wheel brake cylinder  12  of the respective brake circuit  10  is brought about in all brake circuits  10  of the vehicle brake system, and at the same time is prevented in a (second) wheel brake cylinder  14  of the same brake circuit  10 , so that a number of (first) wheel brake cylinders  12  in which an increase in brake pressure is brought about is equal to a number of brake circuits  10  of the vehicle brake system, and each brake circuit  10  has the respective (first) wheel brake cylinder  12  in which an increase in brake pressure is brought about and has the respective (second) wheel brake cylinder  14  in which the increase in brake pressure is prevented. The respective increase in brake pressure can be used for example for a TCS function (drive slippage regulation, or Traction Control System), a VDC function (electronic stability program, or Vehicle Dynamics Control), a VAF function (autonomous driving function), or for a masking of a generator braking torque. However, the examples listed here of the use of the respective increase in brake pressure are not to be interpreted as exhaustive. 
     When the example method described herein is carried out, brake fluid is transferred into first wheel brake cylinder  12  at least of brake circuit  10 , in order to bring about a (preferably rapid and/or significant) increase of a first brake pressure in first wheel brake cylinder  12 . The transfer of brake fluid into first wheel brake cylinder  12  is carried out for example using the at least one pump  30 , as is shown in the coordinate system of  FIG. 2 b   . In the coordinate system of  FIG. 2 b   , the abscissa is a time axis t, while the ordinate of  FIG. 1 b    is used to show a current strength I- 30  of an operating current that, for the operation of the at least one pump  30 , is supplied to its pump motor  48 . From a time t 1  to a time t 2 , brake fluid is pumped in the direction towards first wheel brake cylinder  12  by operation of the at least one pump  30 . As an alternative or in addition to the operation of the at least one pump  30 , however, the transfer of brake fluid into the first wheel brake cylinder can also/additionally be brought about by a driver&#39;s braking force  44  exerted on brake actuating element/brake pedal  38 , and/or by an operation of brake booster  40  (or by an operation of the at least one motorized plunger device). 
     During the transfer of brake fluid into first wheel brake cylinder  12 , first wheel outlet valve  16  assigned to first wheel brake cylinder  12  is controlled and/or held in its open state. At the same time, first wheel outlet valve  18  assigned to first wheel brake cylinder  12  is controlled and/or held in its closed state. Because first wheel outlet valve  16  is in its open state and first wheel outlet valve  18  is in its closed state, during the transfer of brake fluid into first wheel brake cylinder  12  (by the operation of the at least one pump  30 ) it is ensured that the first brake pressure in first wheel brake cylinder  12  is increased, preferably rapidly and/or significantly. 
     In order to at least limit an (undesired) increase of the second brake pressure in second wheel brake cylinder  14  of (the same) brake circuit  10  during the transfer of brake fluid into first wheel brake cylinder  12 , second wheel outlet valve  20  assigned to second wheel brake cylinder  14  is controlled and/or held in its closed state. However, an undesired flow  50  of brake fluid into second wheel brake cylinder  14  often cannot be completely suppressed/prevented by the closed second wheel inlet valve  20 . Therefore, it is desirable for second wheel outlet valve  22  assigned to second wheel brake cylinder  14  to be controlled into its open state at least at times. 
     In the method described herein, this is brought about by controlling second wheel outlet valve  22 , during the transfer of brake fluid into first wheel brake cylinder  12 , with a pulse width-modulated signal in such a way that the pulse width-modulated signal (during the transfer of brake fluid into first wheel brake cylinder  12 ) brings it about that second wheel outlet valve  22  is permanently in its open state. This is shown graphically in the coordinate systems of  FIGS. 2 c    and  2   d.    
     The abscissas of the coordinate systems of  FIGS. 2 c  and 2 d    are each a time axis t. Using the ordinate of the coordinate system of  FIG. 2 c   , a current switching state ϕ of second wheel outlet valve  22  is shown that can alternate between “0=zero,” i.e., second wheel outlet valve  22  is closed, and “1=one,” i.e., second wheel outlet valve  22  is open. The ordinate of the coordinate system of  FIG. 2 d    indicates a current strength I- 22  of a control signal for controlling/switching second wheel outlet valve  22 . 
     Between a time t 0  (before or almost equal to time t 1 ) and time t 2 , the pulse width-modulated signal is outputted as control signal for controlling/switching second wheel outlet valve  22 . As can be seen in the coordinate system of  FIG. 2 c   , for this reason second wheel outlet valve  22  is permanently in its open state during the entire operation of the at least one pump  30  between times t 1  and t 2 . The example method described herein therefore not only brings about a limitation of the (undesired) increase of the second brake pressure, but also brings about a reliable prevention of an increase of the second brake pressure in second wheel brake cylinder  14  (past a reaction pressure of storage chamber  28 ). 
     The example method described here brings about a “permanent holding open” of second wheel outlet valve  22  during the transfer of brake fluid into first wheel outlet valve  12  (instead of the periodic opening and closing of second wheel outlet valve  22  according to the conventional procedure described above). Because, using the example method described here, second wheel outlet valve  22  is permanently (i.e., temporally constantly) held in its open state between times t 0  and t 2 , no valve switching noise is produced by the opening and closing of second wheel outlet valve  22 . The driver is thus not irritated or burdened by valve switching noises. The method described here is therefore significantly more driver-friendly than the conventional procedure described above, which frequently causes valve switching noises that are perceptible by the driver. 
     Preferably, during the transfer of brake fluid into first wheel brake cylinder  12 , a current strength maximum and a duty cycle of the pulse width-modulated signal are kept low enough that the current strength maximum and the duty cycle are just sufficient to bring it about that second wheel outlet valve  22  is permanently in its open state during the transfer of brake fluid into first wheel brake cylinder  12 . For example, during the transfer of brake fluid into first wheel brake cylinder  12 , the current strength maximum and the duty cycle of the pulse width-modulated signal can be kept low enough that the pulse width-modulated signal has a current strength, averaged over time, of less than 0.5 A (amperes). A thermal loading of second wheel outlet valve  22  (or of its electronics) can be reliably minimized in this way. Moreover, a current consumption can be reduced in this way. The pulse width-modulated signal can for example have a current strength, averaged over time, of less than 0.4 A, preferably less than 0.3 A, specifically less than 0.25 A. The duty cycle of the pulse width-modulated signal can be less than 0.25, specifically less than 0.2, in particular less than 0.15, and even less than 0.1. A pulse frequency of the pulse width-modulated signal is preferably less than 10 Hz (hertz), for example between 1 Hz and 9 Hz. (A period of the pulse width-modulated signal can thus have a duration of, e.g., between 50 ms and 1000 ms.) 
     The pulse width-modulated signal can be produced by a flyback diode and outputted to second wheel outlet valve  22 . In this way, the method described here increases a multifunctionality of the flyback diode, which in many cases is already being used. 
       FIG. 3  shows a schematic representation of a vehicle brake system for the explanation of a second specific embodiment of the method in accordance with the present invention for increasing the brake pressure in a first wheel brake cylinder and for limiting the brake pressure in a second wheel brake cylinder of the vehicle brake system. 
     The wheel brake system schematically shown in  FIG. 3  includes a first brake circuit  10  having at least one first wheel brake cylinder  12 , a respective first wheel inlet valve  16  assigned to the at least one first wheel brake cylinder  12 , and a respective first wheel outlet valve  18  assigned to the at least one first wheel brake cylinder  12 , and a second brake circuit  52  having at least one second wheel brake cylinder  14 , a respective second wheel inlet valve  20  assigned to the at least one second wheel brake cylinder  14 , and a respective second wheel outlet valve  22  assigned to the at least one second wheel brake cylinder  14 . Only as an example, each of the two brake circuits has exactly two wheel brake cylinders  12  and  14 . Moreover, second brake circuit  52  can be decoupled from a master brake cylinder  36  by closing a separating valve  54 . At least one pump  56  of second brake circuit  52  is connected to a brake fluid reservoir  42  via a suction line  58 . Second brake circuit  52  additionally has another continuously adjustable valve  59  also connected to suction line  58 . With regard to the further components of the vehicle brake system, reference is made to the earlier description above. 
     In the method shown graphically in  FIG. 3  as well, a first brake pressure in at least one first wheel brake cylinder  12  is increased by, during an operation brought about by driver&#39;s force and/or motorically of at least one brake pressure buildup device  56 , controlling and/or holding at least one first wheel inlet valve  16  in its open state and controlling and/or holding the at least one first wheel outlet valve  18  in its closed state, so that by the operation of the at least one brake pressure buildup device  56 , brake fluid is transferred through at least the at least one open first wheel inlet valve  16  into the at least one first wheel brake cylinder  12 . As the at least one brake pressure buildup device  56 , the at least one pump  56  of second brake circuit  52  is operated in such a way that brake fluid is pumped from brake fluid reservoir  42  into master brake cylinder  36  by the at least one pump  56  of second brake circuit  52 . (Due to the closed high-pressure switching valve  24 , concomitant operation of the at least one pump  30  of first brake circuit  10  has no/hardly any effect.) 
     At the same time, an increase of a second brake pressure in the at least one second wheel brake cylinder  14  during the transfer of brake fluid into the at least one first wheel brake cylinder  12  is limited/prevented by controlling and/or holding the at least one second wheel inlet valve  20  in its closed state and controlling the at least one second wheel outlet valve  22  into its open state at least at times. In the specific embodiment described here as well, this is done by controlling the at least one second wheel outlet valve  22 , during the transfer of brake fluid into the at least one first wheel brake cylinder  12 , using a pulse width-modulated signal that brings it about that the at least one second wheel outlet valve  22  is permanently in its open state during the transfer of brake fluid into the at least one first wheel brake cylinder  12 . 
     In this way, a brake pressure increase in the at least one first wheel brake cylinder  12  of first brake circuit  10  can be brought about by a pumping of brake fluid out of brake fluid reservoir  42 , even though first brake circuit  10  is not connected to brake fluid reservoir  42 . Moreover, an undesired brake pressure buildup in the at least one second wheel brake cylinder  14  of second brake circuit  52  connected to brake fluid reservoir  42  can be prevented. A vehicle axle assigned to second brake circuit  52  can thus easily be braked by a generator. 
     The specific embodiment of the method in accordance with the present invention described herein also ensures the advantages named above. Therefore, these advantages will not be listed again here. 
       FIGS. 4 a  and 4 b    show schematic representations of a specific embodiment of the vehicle brake system and its control device in accordance with an example embodiment of the present invention.  FIGS. 4 a  and 4 b    schematically show a vehicle brake system that, in addition to control device  60 , also includes at least one brake pressure buildup device  61 , a first wheel brake cylinder  12  having a first wheel inlet valve  16  assigned to first wheel brake cylinder  12  and a first wheel outlet valve  18  assigned to first wheel brake cylinder  12 , and a second wheel brake cylinder  14  having a second wheel inlet valve  20  assigned to second wheel brake cylinder  14  and a second wheel outlet valve  22  assigned to second wheel brake cylinder  14 . The at least one brake pressure buildup device  61  is designed and situated in the vehicle brake system in such a way that a flow of brake fluid through at least the open first wheel valve  16  into first wheel brake cylinder  12  can be brought about by an operation brought about by driver&#39;s force and/or motorically of the at least one brake pressure buildup device  61 , and likewise a flow of brake fluid through at least the open second wheel inlet valve  20  into second wheel brake cylinder  14  can be brought about by the operation of the at least one brake pressure buildup device  61 . As is shown in  FIG. 4 a   , at least one motorized plunger device  61 , such as in particular at least one integrated motor brake  61  (Integrated Power Brake, or IPB), can also be used as the at least one brake pressure buildup device  61 . Only as an example, for this purpose first and second wheel brake cylinders  12  and  14  of a brake circuit  10  and  52  are connected to master brake cylinder  36  via a respective separating valve  54 , and are connected to motorized plunger device  61  via a further respective separating valve  54 . Further examples of the at least one brake pressure buildup device  61  have been indicated above. Here it is also expressly to be noted that the vehicle brake system equipped with control device  60  may also have all features of the above-described vehicle brake systems, instead of or in addition to the features shown in  FIG. 4 a   . Moreover, the practicability of the vehicle brake system is limited neither to a particular brake system type nor to a specific vehicle type/motor vehicle type of the vehicle/motor vehicle equipped with the vehicle brake system. 
     Using control device  60 , during the operation of the at least one brake pressure buildup device first wheel inlet valve  16  is controllable/controlled into its open state, first wheel outlet valve  18  is controllable/controlled into its closed state, second wheel inlet valve  20  is controllable/controlled into its closed state, and second wheel outlet valve  22  is at least at times controllable/controlled into its open state, so that a first brake pressure in first wheel brake cylinder  12  can be increased/is increased, while simultaneously an increase of a second brake pressure in second wheel brake cylinder  14  is at least limitable/is limited. For this purpose, control device  60  is designed to, during operation of the at least one brake pressure buildup device  61 , control second wheel outlet valve  22  with a pulse width-modulated signal  60   a  in such a way that second wheel outlet valve  22  controlled by pulse width-modulated signal  60   a  is permanently in its open state. Control device  60  thus ensures the advantages already described above. In particular, using control device  60  all method steps of the above-described method can be carried out. 
     As is shown in  FIG. 3 , control device  60  includes at least one flyback diode  62 . Moreover, control device  60  is designed to output pulse width-modulated signal  60   a  to second wheel outlet valve  22  using flyback diode  62 . However, the electronic design of control device  60  shown schematically in  FIG. 3 , made up of diodes D 1  to D 4  (and coils configured parallel thereto), transistors T 1  to T 5 , resistors R 1  and R 2 , circuits S 1  and S 2 , and an electronics device  64 , is to be interpreted only as an example.