Control device for a vehicle's braking system, braking system for a vehicle and method for operating a vehicle's braking system

Abstract

Control device (56) for a braking system of a vehicle with: a first receiving device (10) by means of which a provided brake actuation force quantity (s, 14) with respect to an actuation force of an actuation of a brake actuation element (58) arranged on the brake system can be received; and a plunger control device (16) by means of which, taking into account at least the received brake actuation force quantity (s, 14), a target filling level of a plunger (20, 54) can be determined and a plunger control signal (18) corresponding to the determined target filling level can be output to the plunger (20, 54), so that a ratio (F) between an actual fluid volume filled into a storage volume of the plunger (20, 54) and a maximum volume that can be filled into the storage volume can be set according to the determined target filling level; characterized by the fact that the plunger control device (16) is designed to determine, for a given non-actuating force magnitude (s, 14), a fill level that deviates from an empty state of the plunger (20, 54) as the target fill level, and to output a plunger control signal (18) corresponding to the determined target fill level to the plunger (20, 54) such that the plunger (20, 54) is at least partially filled.

Description

[0001] The invention relates to a control device for a vehicle's braking system. The invention also relates to a vehicle's braking system. Furthermore, the invention relates to a method for operating a vehicle's braking system. State of the art

[0002] German patent application DE 10 2007 030 441 A1 describes a braking system for a motor vehicle with a generator and a corresponding method for operating such a braking system. To maintain a total braking torque specified by the driver of the motor vehicle, despite variations in the generator braking torque over time, a simulator unit is controlled such that a volume of hydraulic fluid corresponding to the difference in the generator braking torque is shifted between the braking system and at least one storage chamber of the simulator unit. This is intended to ensure a standard braking feel for the driver despite variations in the generator braking torque over time.

[0003] DE 10 2010 002 406 A1 discloses a hydraulic brake system and a method as well as a control unit for operating the hydraulic brake system. Disclosure of the invention

[0004] The invention provides a control device for a vehicle's braking system with the features of claim 1, a braking system for a vehicle with the features of claim 10, and a method for operating a vehicle's braking system with the features of claim 11. Advantages of the invention

[0005] As explained in more detail below, by setting a fill level for the plunger, taking into account the actuation force, the free play of the brake actuation element that conventionally occurs when the plunger malfunctions can at least be reduced. Thus, despite the plunger's malfunction, the driver can, thanks to the present invention, brake quickly and reliably into at least one wheel brake caliper of the braking system. This ensures improved driving comfort for the driver.

[0006] The present invention eliminates the cost of the shut-off valve. A plunger operated by the present invention, compared to a conventional buffering device for intermediate fluid storage with a shut-off valve, ensures that it is unnecessary to detect a potential defect in the shut-off valve. Likewise, there is no risk that, due to an undetected defective shut-off valve, a large amount of free travel at the brake actuation element must be overcome before pressure can build up in the at least one wheel brake caliper.

[0007] Likewise, the present invention eliminates the need to determine a functional impairment in a locking mechanism, such as a coil spring. Furthermore, the occurrence of a comparatively large free play in the event of a motor failure and / or a defective locking mechanism is not a problem with the present invention.

[0008] Furthermore, the present invention allows for the elimination of a self-locking mechanism on the plunger. By increasing the efficiency of the plunger's non-self-locking mechanism, its motor can be designed more cost-effectively and with a smaller installation space. Moreover, the reduced power required by the motor to operate the non-self-locking plunger mechanism reduces the plunger's energy consumption and the pollutant emissions of the vehicle equipped with it.

[0009] The present invention thus ensures a more cost-effective and energy-efficient design of a plunger in a braking system. Furthermore, the present invention makes it possible to implement a plunger with an energy-efficient gearbox without the need for additional locking mechanisms or further safety requirements. Brief description of the drawings

[0010] Further features and advantages of the present invention are explained below with reference to the figures. They show: Fig. 1 a schematic representation of an embodiment of the control device; Fig. 2a to 2c three coordinate systems to explain a first embodiment of the method for operating a braking system; Fig. 3a to 3d four coordinate systems to explain a second embodiment of the method for operating a braking system; Fig. 4a to 4c three coordinate systems to explain a third embodiment of the method for operating a braking system; Fig. 5 a coordinate system to explain a fourth embodiment of the method for operating a braking system; Fig. 6a and Fig. 6b a schematic overall representation of an embodiment of the braking system and a coordinate system to explain a fifth embodiment of the method for operating a braking system; Fig. 7a to 7c three coordinate systems for explaining a sixth embodiment of the method for operating a braking system; and Fig. 8a to 8c three coordinate systems for explaining a seventh embodiment of the method for operating a braking system. Embodiments of the invention

[0011] Fig. Figure 1 shows a schematic representation of an embodiment of the control device.

[0012] The in Fig. One schematically depicted control device can be used in a vehicle's braking system. A possible design of the usable braking system will be discussed in more detail in the description of the following figures.

[0013] The control device comprises a first receiving device 10 by means of which a brake actuation force signal 12 relating to the actuation force of an actuation of a brake actuation element arranged on the brake system can be received. A brake actuation force quantity 14 corresponding to the brake actuation force signal 12 can be provided by means of the first receiving device 10. The brake actuation force quantity 14 can, for example, include a braking distance, a braking force, and / or a braking pressure. However, the brake actuation force quantity 14 that can be provided is not limited to the examples listed here.

[0014] The control device also has a plunger control unit 16, by means of which a target fill level of a plunger can be determined, taking into account at least the received brake actuation force parameter 14. The definable target fill level can be understood as a target ratio between a volume of liquid filled into a storage volume of the plunger and a maximum volume that can be filled into the storage volume. The definable target fill level can, for example, be a fill level of the plunger and / or a target volume of the liquid filled into the storage volume of the plunger. Similarly, the target fill level can also be defined as the maximum amount of liquid that can still be filled into the storage volume of the plunger.Similarly, the definable target fill level can describe the position of an adjustable piston component / piston of the plunger and / or the position / angle of rotation of a gearbox / motor of the plunger. However, the definable target fill level is not limited to the examples listed here.

[0015] A plunger control signal 18 corresponding to the specified target fill level can be output to a plunger 20 by means of the plunger control device 16. Preferably, the plunger 20 can be controlled by means of the plunger control signal 18 such that an actual ratio between the volume of liquid filled into the storage volume of the plunger 20 and the maximum volume that can be filled into the storage volume can be set according to the specified target fill level.

[0016] Furthermore, the plunger control device 16 is designed to define a fill level of the plunger 20 that deviates from an empty state when the brake actuation force 14 corresponds to a predetermined non-actuation force. It then outputs a plunger control signal 18 corresponding to this predetermined target fill level to the plunger 20, such that the plunger 20 is at least partially filled (despite the brake actuation force 14 being equal to the non-actuation force). This can be understood to mean that, when the brake actuation force 14 corresponds to the predetermined non-actuation force, a fill level corresponding to a non-zero volume of fluid filled into the plunger's storage volume can be defined as the target fill level.Accordingly, even with a brake actuation force of 14, a position of the adjustable piston component / piston of the plunger and / or a position / angle of rotation of the plunger's gearbox / motor can be defined as the target fill level, corresponding to the specified non-actuation force. This position ensures that the plunger's storage volume is at least partially filled. Likewise, with a brake actuation force of 14, the receiving volume that can still be filled into the plunger's storage volume, corresponding to the specified non-actuation force, can be less than 100%.

[0017] The term "non-actuation force" can be understood as the braking force when the brake actuation element is not actuated, or when the brake actuation element is in its initial / non-actuated position. In particular, the non-actuation force can be zero.

[0018] For example, the plunger control device 16 can be designed to define a target fill level of at least 20% for a brake actuation force 14 corresponding to the non-actuation force 14, and to output a plunger control signal 18 corresponding to the defined fill level to the plunger 20 such that the actual fluid volume filled into the storage volume can be controlled to at least 20% of the maximum volume. Thus, if the driver refrains from actuating the brake actuation element, the plunger 20 can be controlled by the control device such that the actual fluid volume filled into the storage volume can be controlled to at least 20% of the maximum volume.This can also be described as follows: if the brake actuation element is not actuated, an actual ratio of at least 20% between the fluid volume filled into the storage volume of the plunger 20 and the maximum volume that can be filled into the storage volume can be controlled.

[0019] Preferably, the plunger control device 16 is designed to set a target fill level of at least 50% for a brake actuation force 14 corresponding to the non-actuation force, such that the actual fluid volume filled into the storage volume can be controlled to at least 50% of the maximum volume. A plunger control signal 18 corresponding to the set fill level can also be output to the plunger 20 in this case. This can be understood to mean that, for a brake actuation force 14 corresponding to the specified non-actuation force, a target fill level corresponding to a volume of fluid filled into the plunger's storage volume of at least 50% of the maximum volume can be set.Accordingly, even with a brake actuation force of 14, a position of the adjustable piston component / piston of the plunger and / or a position / angle of rotation of the plunger's gearbox / motor can be defined as the target fill level, corresponding to the specified non-actuation force. This position must be at least 50% full. Likewise, with a brake actuation force of 14, the target fill level for the intake volume that can still be filled into the plunger's storage volume can be less than 50%.

[0020] By filling the reservoir volume of the plunger 20 to at least 50% when the brake actuator is in its initial / non-actuated position, a comparatively large quantity of fluid is already present in the reservoir volume of the plunger 20 before the driver even activates the brake actuator. Completely filling the plunger 20, which is already at least 50% pre-filled, therefore requires a significantly smaller quantity of brake fluid than filling an empty plunger with the same maximum volume.If a malfunction occurs in at least one component of the plunger 20, which is already at least 50% pre-filled, such as a malfunction of a motor and / or a locking component of the plunger 20, preventing the control of brake fluid injection during pressure increases in the brake system, only a comparatively small volume of brake fluid will be forced into the plunger 20 before it is completely filled and further filling becomes impossible. In contrast, a significantly larger volume of brake fluid will be unintentionally forced into the plunger if a component of an empty plunger with the same maximum volume malfunctions.

[0021] As a rule, the elimination of the ability to control the flow of brake fluid into a plunger mechanism results in a comparatively long, undesirable shift of brake fluid into the plunger, significantly increasing the free play a driver must overcome when actuating the brake lever. This can also be described as follows: without the ability to control the flow of brake fluid into the plunger mechanism, the driver must first move a comparatively large amount of brake fluid into the plunger by actuating the brake lever before (after overcoming this free play) brake pressure builds up in at least one wheel caliper.In contrast, pre-filling the plunger 20 to at least 50% has the advantage that even if at least one component of the plunger 20 malfunctions, the plunger 20 is filled completely relatively quickly, and the driver can thus initiate the brake pressure build-up in at least one wheel brake caliper by actuating the brake actuation element at an early stage.

[0022] Pre-filling the plunger 20 to at least 20% allows its advantages, particularly compared to a pump, to be utilized. These advantages include its suitability for additionally filling at least one wheel brake caliper without the occurrence of pulsations, and without the delay in brake pressure build-up that conventionally occurs when at least one of its components fails. Further advantages of the plunger 20 being at least 50% filled before the brake actuation element is applied are explained in more detail below.

[0023] In a preferred embodiment, the plunger control device 16 can be designed to define a target fill level of at least 70%, preferably at least 90%, preferably at least 97%, and in particular 100%, of the maximum volume for a brake actuation force 14 corresponding to the non-actuation force. In the latter case, in particular, unwanted filling of the plunger 20 in the event of a malfunction of at least one of its components during the initial actuation of the brake actuation element is (almost) prevented.Therefore, the loss of the ability to control the filling of brake fluid into the plunger does not / hardly cause the brake fluid, which is forced out of a master cylinder of the brake system by a subsequent actuation of the brake actuator, to be undesirably shifted into the plunger 20 (instead of at least one wheel brake caliper), and thus delay the build-up of brake pressure in the at least one wheel brake caliper until the plunger 20 is completely filled. This can also be described as follows: even if at least one component of the plunger 20 malfunctions, the driver has to overcome hardly any / no free travel before the plunger 20 is completely filled and thus brake pressure can begin to build up in the at least one wheel brake caliper using the brake fluid forced out of the master cylinder.By advantageously controlling the plunger 20 by means of the control device, the occurrence of an undesired free stroke in the event of a functional impairment of at least one component of the plunger 20 can be prevented.

[0024] The plunger control device 16 can be designed, in particular, to define the target fill level as a continuously decreasing function of the brake actuation force 14 / brake actuation force when the brake actuation force is between the non-actuation force and a predetermined first limit actuation force. In addition, the plunger control device 16 can further define the target fill level as a continuously increasing function of the brake actuation force when the brake actuation force 14 is between a predetermined second limit actuation force, which is greater than or equal to the first limit actuation force, and a predetermined third limit actuation force. The advantages of such a design of the plunger control device 16 are discussed in more detail below.

[0025] In a preferred embodiment, the control device also includes a second receiving device 22, by means of which a provided blending parameter signal 24 relating to a temporal change in a braking torque to be blended can be received. A blending parameter 26 corresponding to the blending parameter signal 24 can then be provided to the plunger control device 16 by means of the second receiving device 22. In this case, the plunger control device 16 is advantageously additionally designed to reduce the target fill level when the braking torque to be blended decreases over time.Preferably, as the braking torque to be blended decreases over time, the target fill level can be redefined by the plunger control device 16 such that, by reducing the actual fill level of the controlled plunger 20, a volume of brake fluid can be transferred into the at least one wheel brake caliper, increasing the hydraulic braking torque of the at least one wheel brake caliper by a difference corresponding to the decrease in the braking torque to be blended over time. In this way, by controlling the plunger 20, a total braking torque specified by the driver can be reliably maintained despite the decrease in the braking torque to be blended over time.

[0026] Additionally, the plunger control unit 16 can be designed to increase the target fill level as the braking torque to be blended increases over time. Advantageously, the target fill level is redefined by the plunger control unit 16 as the braking torque to be blended increases over time, such that the increased actual fill level of the controlled plunger 20 allows a volume of brake fluid to be drawn from at least one wheel brake caliper into the storage volume. This volume reduces the hydraulic braking torque of at least one wheel brake caliper by a difference corresponding to the increase in the braking torque to be blended over time. Thus, the plunger 20 can also be used to compensate for the increase in the braking torque to be blended over time.Alternatively, the plunger control device 16 can also be configured to define a target intake volume of a storage chamber 28 corresponding to the rate of increase of the braking torque to be masked, and to output a storage control signal 30 corresponding to the target intake volume to an actuator unit of the storage chamber 28. The advantages resulting from the use of the storage chamber 28 to mask the rate of increase will be discussed below.

[0027] The braking torque to be masked can, in particular, be the generator braking torque of a generator. Using this control device, a total vehicle deceleration specified by the driver can thus be reliably maintained despite the generator's availability varying over time due to vehicle speed and / or battery charge level, while simultaneously ensuring frequent generator use for rapid battery charging. However, other braking torques besides generator braking torque can also be masked using this control device. Therefore, the applicability of the control device described here is not limited to a braking system equipped with a generator.

[0028] Optionally, a third receiving device 32 can also be provided on the control device, by means of which a provided direction-of-travel signal 34 relating to a change in the direction of travel of a vehicle equipped with the control device, such as a steering angle, can be received. In this case, a direction-of-travel parameter 36 corresponding to the direction-of-travel signal 34 can be transmitted to the plunger control device 16 by means of the third receiving device 32. The plunger control device 16 can additionally be configured to compare the direction-of-travel parameter 36 with at least one predefined reference angle parameter.After receiving a brake actuation force value 14 that deviates from the non-actuation force value, the plunger control device 16 can redefine the target fill level by additionally comparing the direction change value 36 with the reference angle value. In particular, if the direction change value 36 is less than the reference angle value, the plunger control device 16 can define a first fill level as the target fill level, taking the brake actuation force value 14 into account. If the direction change value 36 is greater than the reference angle value, a second fill level, smaller than the first fill level, can advantageously be defined as the target fill level by the plunger control device 16, taking the brake actuation force value 14 into account.As explained in more detail below, reducing the actual fill level of the plunger 20 and the additional brake fluid shifted into the brake system can overcome air play in a brake caliper that occurs when driving around a curve.

[0029] Alternatively or additionally, the control device can also include a fourth receiving device 38, by means of which a provided plunger usage strength signal 40 regarding the duration and / or intensity of plunger usage 20 can be received and a usage strength value 42 corresponding to the plunger usage strength signal 40 can be output to the plunger control device 16. In this case, the plunger control device 16 is preferably also designed to compare the usage strength value 42 with at least one predetermined reference usage value. In this case as well, if a brake actuation strength value 14 deviates from the non-actuation strength value occurs subsequently, the target fill level can be redefined taking into account the comparison of the usage strength value 42 with the reference usage strength value.If the usage intensity value 42 is below the reference usage intensity value, a third fill level value can be set as the target fill level value by means of the plunger control device 16, taking into account the brake actuation intensity value 14. Conversely, if the usage intensity value 42 is above the reference usage intensity value, a fourth fill level value, smaller than the third fill level value, can be set as the target fill level value by means of the plunger control device 16, again taking into account the brake actuation intensity value 14. By reducing the actual fill level of the plunger 20 when the usage intensity value 42 is above the reference usage intensity value, wear effects of the brake system can be compensated for by additionally filling at least one wheel brake caliper. This is explained in more detail with reference to the following figures.

[0030] Fig. Figures 2a to 2c show three coordinate systems to illustrate a first embodiment of the method for operating a braking system.

[0031] In the execution of the method, a target fill level of a plunger is defined, taking into account at least one actuation force of an actuation element arranged in the brake system. The plunger is then controlled according to the defined target fill level such that an actual ratio is established between the volume of fluid filled into the plunger's storage volume 20 and the maximum volume that can be filled into the storage volume, corresponding to the defined target fill level. This can also be described as setting an actual ratio between the volume of fluid filled into the storage volume and the (maximum fillable) maximum volume of the plunger's storage volume, corresponding to the defined target fill level. Examples of the definable target fill level, or the adjustable actual ratio, have already been mentioned above.

[0032] The abscissa of the coordinate system of Fig. 2a specifies a brake actuation travel s [in mm] (entry rod travel) by which the brake actuation element is adjusted when actuated by a driver. The ordinate of the coordinate system of Fig. 2a corresponds to the actual fill level F [in %] set as a function of the brake actuation distance s using the method, or to a further intake volume V [in mm²] that can be filled into the storage volume at the actual fill level F. 2 The intake volume V can also be described as the difference between the maximum volume and the volume of liquid already filled into the storage volume.

[0033] In the execution of the method, the brake actuation force s is compared to a zero-actuation force specified as the actuation force. If the brake actuation force s is equal to zero, or the brake actuation force corresponds to the zero-actuation force, a target fill level of at least 20%, for example at least 50%, preferably at least 70%, in particular at least 90%, and preferably at least 95% (of the maximum volume) is set. Subsequently, the plunger is actuated according to the specified target fill level such that the actual fill level F is preferably set to the target fill level. This can also be described as controlling for at least one actual fill level F of at least 20%, for example at least 50%, preferably at least 70%, in particular at least 90%, and preferably at least 95%.In the illustrated embodiment, when the brake actuation travel s is zero, an actual fill level of 100%, or a receiving volume V, is advantageously set. Thus, in the event of a plunger component failure, an undesirable shift of brake fluid into the plunger during the initial actuation of the brake actuator is prevented, even at a comparatively high pressure.

[0034] In this method, during a brake actuation travel s between zero and a predetermined first limit brake actuation travel s1, or during a brake actuation force between the non-actuation force and a predetermined first limit actuation force, the target fluid level is determined as a continuously decreasing function of the brake actuation travel s / brake actuation force. Preferably, during a brake actuation travel s between zero and the first limit brake actuation travel s1, the actual fluid level F is reduced such that the increased intake volume V corresponds to the additional volume of brake fluid filled into the at least one wheel brake caliper of the brake system during the brake actuation travel s (compared to a brake actuation travel s equal to zero).In this way, it is possible to ensure that, during a brake actuation distance s between zero and the first limit brake actuation distance s1, just enough brake fluid can be filled into the plunger to reduce the hydraulic braking torque of at least one wheel brake caliper to zero. Thus, during a brake actuation distance s between zero and the first limit brake actuation distance s1, it is always guaranteed that a non-hydraulic braking torque, such as a generator braking torque, can be masked by reducing the hydraulic braking torque of at least one wheel brake caliper.At the same time, it is ensured that even in the event of a malfunction of at least one component of the plunger during a brake actuation distance s between zero and the first limit brake actuation distance s1, the driver only has to overcome a comparatively small free distance before the plunger is fully filled and the driver can increase the brake pressure in the at least one wheel brake caliper by actuating the brake actuation element.

[0035] The procedure can also be described as follows: As deceleration is required (between zero and the first limit of brake actuation s1), the plunger pushes additional fluid into the brake system. This displaced brake fluid can be sufficient to generate a brake pressure of 24 bar (3 m / s²) if needed. 2 ) to blend.

[0036] The plunger can additionally be equipped with a locking device by means of which, even after a brake actuation distance s exceeding the first limit brake actuation distance s1, the actual fill level F remains at 0% and can be maintained even against a comparatively high pressure. Since a suitable locking device is not the subject of this invention, it will not be discussed in more detail here.

[0037] Based on the Fig. 2b describes the veneering process again. The abscissa of the coordinate system of the Fig. 2b is the time axis t. The ordinate of the coordinate system of Fig. 2b indicates the current fill level of the plunger [in %], or the fillable intake volume V [in mm²] in the plunger. 3 The advantageous procedure is shown in graph g. (The dashed line I corresponds to a conventional operating strategy for operating a plunger.)

[0038] Before the driver activates the brake actuator at time t0, the plunger is already full. Therefore, the actual fill level before time t0 is 100%. (In the conventional operating strategy represented by the dashed line I, the plunger is completely emptied after each regenerative braking action.)

[0039] From time t0, the driver activates the brake actuator. Only from the start of the brake actuator's activation is the plunger's blending start position replenished with increasing brake application force (depending on the driver's braking request). To this end, the plunger's actual fill level F is continuously reduced until time t1, when the brake application force equals the predetermined first limit. The plunger preferably only pushes as much brake fluid into the brake system as it needs to reduce the hydraulic braking torque of at least one wheel brake caliper for blending a non-hydraulic braking torque, such as generator braking torque. This ensures that the plunger can extract precisely the volume from the brake system required to reduce the hydraulic braking torque of at least one wheel brake caliper for blending.

[0040] In this way, the plunger can provide a sufficient absorption volume V to reduce the brake pressure in at least one wheel brake caliper.

[0041] Therefore, from time t2, the plunger can reduce the hydraulic braking torque of at least one wheel brake caliper to zero by taking in brake fluid, or by increasing the actual fill level F, until time t3. From time t3, by pushing back the volume of brake fluid taken in for blending, the brake pressure prevailing in at least one wheel brake caliper before blending can be built up again until time t4. Thus, despite a decrease in the non-hydraulic braking torque over time, such as a generator braking torque, a total braking torque specified by the driver can be maintained by returning the volume of brake fluid taken in for blending to the braking system.

[0042] Fig. Figure 2c shows the pressure-displacement characteristic at the master cylinder as it changes when the plunger is emptied during a brake actuation travel s between zero and the first limit brake actuation travel s1. While the abscissa of the coordinate system of Fig. 2c specifies the brake actuation distance [in mm], the ordinate of the coordinate system corresponds to the Fig. 2c the pressure p [in bar] prevailing in the master brake cylinder. The brake actuation distance-pressure characteristic curve p1 achievable using the method described here is compared with a brake actuation distance-pressure characteristic curve p0 of a conventional procedure.

[0043] Performing the procedure described here results in a steeper slope of the brake actuation travel-pressure characteristic curve p1. Therefore, a higher brake pressure can be built up more quickly in the master brake cylinder, or in at least one wheel brake caliper, using this procedure. This can thus provide an additional increase in braking force.

[0044] Alternatively, the brake actuation distance-pressure characteristic curve p1 can also be easily adapted to the conventional brake actuation distance-pressure characteristic curve p0 by means of elasticities that can be developed in the brake system. Since the development of suitable elasticities is not the subject of the procedure described here, it will not be discussed further.

[0045] In addition to carrying out the procedure of Fig. 2a to 2c, the plunger can also be equipped with a locking mechanism or a shut-off valve. In this case, the plunger itself does not need to withstand high pressures and can therefore be designed with lower performance requirements. This is achieved by carrying out the procedure of Fig. 2a to 2c resulted in a lower probability of a high volume loss, allowing the interlock to be designed for lower safety requirements. Therefore, cost-effective mechanisms can be used for the interlock or the shut-off valve.

[0046] Fig. Figures 3a to 3d show four coordinate systems to illustrate a second embodiment of the method for operating a braking system.

[0047] The abscissa of the coordinate system of Fig. 3a indicates the brake actuation distance s [in mm] (entry rod travel). The ordinate of the coordinate system of Fig. 3a corresponds to the actual fill level F [in %], or the intake volume V [in mm²]. 2 ].

[0048] In addition to the method described above, in this embodiment, for a brake actuation distance s between a predetermined second limit brake actuation distance s2 and a predetermined third limit brake actuation distance s3, where the second limit brake actuation distance s2 is greater than or equal to the first brake actuation distance s1, the target fluid level is defined as a continuously increasing function of the brake actuation distance s / the brake actuation force. This can also be described as follows: when deceleration is increased between a brake actuation distance s = zero and the first limit brake actuation distance s1, the plunger delivers additional fluid into the brake system, while from the second limit brake actuation distance s2 onwards, the plunger is refilled.This ensures that the plunger reliably withstands high pressures in the brake system, which can occur from the second limit of the brake actuation travel onwards, even if at least one of its components malfunctions. Therefore, there is no need to equip the plunger with a locking mechanism to withstand high pressures.

[0049] The plunger control concept achievable through this method reduces the level and probability of pedal travel extension due to a malfunction of at least one plunger component. This will be demonstrated below using the following examples: Fig. 3b explained: In the coordinate system of Fig. 3b the abscissa is a deceleration a [in m / s] performed by the braking system 2 ] (negative acceleration, e.g. total deceleration) and the ordinate a volume loss N [in %].

[0050] The solid graph n1 represents the volume loss when the plunger is operated according to the procedure described here. At a deceleration a = zero, the plunger is (completely) filled. At a deceleration a = non-zero, a blending start state of the plunger is activated, depending on the deceleration a. At a deceleration a between zero and a first limit deceleration a1, the plunger only moves as much fluid into the brake system as it needs to blend the brake pressure built up in at least one wheel brake caliper. From a deceleration a of at least the second limit deceleration a2, the plunger is refilled.

[0051] In this way, it can be ensured that a volume loss N of 100% is only incurred when the brake application distance is between the first limit brake application distance s1 and the second limit brake application distance s2, or when the deceleration a is between the first limit deceleration a1 and the second limit deceleration a2. In contrast, the volume loss N can be reduced to 0% using the advantageous method, especially for the more frequently occurring decelerations a between zero and half of the first limit deceleration a1. Likewise, no volume loss N is incurred when the vehicle decelerates sharply with a deceleration a >> a2.

[0052] The dashed graph n0 represents the volume loss N during a conventional plunger operation procedure, where the plunger is emptied before veneering. Therefore, a maximum volume loss N of 100% can occur due to plunger failure at any delay a.

[0053] In Fig. Figure 3c shows a pressure-displacement characteristic obtained using the method described here. The abscissa of the coordinate system of the Fig. 3c is the brake actuation distance s [in mm]. The ordinate of the coordinate system of Fig. 3c corresponds to the pressure p [in bar] prevailing in the master brake cylinder. The brake actuation distance-pressure characteristic curve p1 achievable using the method described here is compared with the brake actuation distance-pressure characteristic curve p0 of the conventional procedure.

[0054] The brake actuation distance-pressure characteristic curve p1 achievable using the method described here is steeper than the brake actuation distance-pressure characteristic curve p0 of the conventional approach at a small brake actuation distance s. From the second limit actuation distance onwards, at which point the plunger is again controlled towards 100% fill level, the brake actuation distance-pressure characteristic curve p1 again approaches the brake actuation distance-pressure characteristic curve p0.

[0055] In the coordinate system of Fig. 3d represents the abscissa, the brake pressure pb [in bar] present in at least one wheel brake caliper, and the ordinate, the maximum pressure reduction Δpb [in bar] achievable using the plunger at a given brake pressure pb. Graph v1 indicates the pressure reduction achievable with the blending method described here, while graph v0 shows the corresponding values ​​for a conventional approach.

[0056] Comparing the two graphs v1 and v0 reveals that the advantageous method described here ensures a favorable blending of the generator braking torque, particularly at low brake pressure pb or low vehicle deceleration. This is advantageous because low decelerations are frequently encountered in urban traffic. Therefore, the advantageous method described here ensures that a generator can be used frequently for the rapid charging of a vehicle battery.

[0057] Fig. Figures 4a to 4c show three coordinate systems to illustrate a third embodiment of the method for operating a braking system.

[0058] In the coordinate system of Fig. 4a The abscissa gives the brake actuation distance s [in mm] (entry rod travel) and the ordinate the actual filling level F [in %], or the intake volume V [in mm 2 ], on.

[0059] In the embodiment of the method described here, the second limit brake actuation travel s2 differs from the first limit brake actuation travel s1. Furthermore, when the brake actuation travel s is zero, the plunger is only partially filled, for example, to 57%.

[0060] Into the coordinate system of Fig. Figure 4b shows the brake actuation distance-pressure characteristic curve p1 achievable by means of the procedure described here and the brake actuation distance-pressure characteristic curve p0 of the conventional procedure for comparison, where the abscissa indicates the brake actuation distance [in mm] and the ordinate indicates the pressure p [in bar] prevailing in the master brake cylinder.

[0061] As shown by the Fig. As can be seen in section 4b, the pedal characteristics can be adjusted differently by setting different limit brake actuation distances s1 and s2. Thus, the pedal characteristics can be customized more precisely by adjusting the limit brake actuation distances s1 and s2. In particular, the discontinuous slope of the brake actuation distance-pressure characteristic curve p1 can be at least partially smoothed out by selecting the second limit brake actuation distance s2 (independent of the first limit brake actuation distance s1).

[0062] The pedal free travel can also be adjusted more variably by setting the values ​​for the limit brake actuation distances s1 and s2.

[0063] In the coordinate system of Fig. 4c, the abscissa is the brake pressure pb [in bar] present in at least one wheel brake caliper, and the ordinate is the maximum pressure reduction Δpb [in bar] achievable by means of the plunger at a specific brake pressure pb. For comparison, the graph v1, which represents the pressure reduction achievable with the method described here, and the corresponding graph v0 in the conventional procedure are plotted in the coordinate system of Fig. 4c entered.

[0064] By defining different limit brake actuation distances s1 and s2, the blending capacity can also be defined more freely. For example, by defining the values ​​for the limit brake actuation distances s1 and s2, the graph v1 can be approximated to a standard blending capacity.

[0065] Fig. Figure 5 shows a coordinate system to illustrate a fourth embodiment of the method for operating a braking system.

[0066] The abscissa of the coordinate system of Fig. 5 is the time axis t. The ordinate of the coordinate system of Fig. 5 indicates the current fill level F of the plunger [in %], or the fillable intake volume V [in mm²] in the plunger. 3 ], an. The procedure described below is represented by the graph g.

[0067] The brake actuation element can be, for example, the brake pedal. If the brake actuation element is not actuated until time t0, the plunger is almost or completely filled with brake fluid. However, an initial state can be set in the plunger during the transition from the accelerator pedal to the brake actuation element, in which it preferably exists at / around time t0. To set the initial state, the plunger is preferably adjusted from the accelerator pedal actuation level to the target fill level of the initial state by slightly emptying the plunger.The target fill level of the initial state can be set to a value of at least 20%, taking into account at least one provided brake actuation force and / or one provided generator usability, such as a switching time between the accelerator and brake pedal actuation, a speed of brake pedal actuation, a vehicle speed, an available generator braking torque, a battery charge level and / or a preferred recuperation mode, in particular selected from at least one comfort mode and one maximum recuperation mode.

[0068] During the driver's actuation of the brake actuator between times t0 and t1, the blending start position of the plunger is adjusted depending on the level of the driver's braking request. The other parameters already listed above can also be considered for determining the blending start position. Even after the initial position, or blending start position, has been set, the plunger can still draw sufficient brake fluid volume from the brake system to reduce brake pressure for blending. By pumping brake fluid through the plunger, a preferred overall braking torque can be maintained despite a decrease in the braking torque to be blended over time. For further executable process steps, please refer to the description of... Fig. 2b referred.

[0069] Fig. 6a and Fig. Figure 6b shows a schematic overall representation of an embodiment of the braking system and a coordinate system to explain a fifth embodiment of the method for operating a braking system.

[0070] The in Fig. Figure 6a, a schematically represented braking system for a vehicle, comprises a master brake cylinder 50, at least one wheel brake caliper 52 hydraulically connected to the master brake cylinder 50, at least one plunger 54 hydraulically connected to the at least one wheel brake caliper 52, and a control device 56 as described above. Optionally, a brake actuation element 58, which may be designed, for example, as a brake pedal, is also arranged on the master brake cylinder 50. A brake booster 60 allows the driver to be relieved of braking force when applying the brakes to the master brake cylinder 50 by actuating the brake actuation element 58. Preferably, at least one brake actuation force sensor 62 is also arranged on the brake actuation element 58, which can output a sensor signal regarding the brake actuation force to the control device 56 and / or to a brake booster control device 64.The at least one brake actuation force sensor 62 can, for example, be a rod travel sensor and / or a force sensor.

[0071] The braking system operable by the method described here is not limited to a specific number of wheel brake calipers 52 or brake circuits. Likewise, the operable braking system is not limited to a specific design of the at least one brake circuit or to a required configuration of the at least one brake circuit with a high-pressure switching valve 66, a changeover valve 68 with a parallel bypass line 70 and a check valve, at least one wheel inlet valve 72 with a parallel bypass line 74 and a check valve, at least one wheel outlet valve 76, a pump 78, and a spring check valve 80 arranged between at least one wheel outlet valve 76 and a pump 78.To carry out the embodiment of the method described here, it is assumed that the brake system is equipped with at least one storage chamber 82 (in addition to the plunger 54). (However, it should be noted that other embodiments of the method described here can also be implemented without such a storage chamber 82.) There are considerable degrees of freedom regarding the arrangement and design of the at least one storage chamber 82 in the brake system.

[0072] The embodiment of the method described here is based on the coordinate system of the Fig. Figure 6b is shown. The abscissa represents the time axis t, and the ordinate represents the current filling level F of the plunger 54 and the current storage volume Vsp of the at least one storage chamber 82.

[0073] Before and after actuation of the brake actuation element 58, the plunger 54 is at least partially filled, preferably to at least 20%, for example to 50%, and particularly to 100%. Neither the increase in brake actuation force between times t0 and t1, nor the constant maintenance of the brake actuation force between times t1 and t2, influences the actual fill level F of the plunger 54.

[0074] Preferably, the at least one storage chamber 82 is in an empty state between times t0 and t2.

[0075] From time t2 onwards, the braking torque to be blended increases. In order to maintain a total braking torque specified by the driver despite the increase in the braking torque to be blended, the at least one storage chamber 82 is used to reduce brake pressure in the at least one wheel brake caliper 52. For this purpose, brake fluid is drained into the at least one storage chamber 82. For example, the at least one wheel outlet valve 76, if present, can be designed for the controlled draining of brake fluid into the storage chamber 82. In this case, the at least one wheel outlet valve 76 can be closed again to maintain a set brake pressure.

[0076] This can also be described as follows: when the braking torque to be masked increases over time, a target intake volume corresponding to this increase is set for the at least one storage chamber 82 of the brake system, and the at least one storage chamber 82 is controlled to draw in an actual intake volume corresponding to the target intake volume, or for a corresponding actual storage volume Vsp. At least one storage chamber 82 of the ESP system can be used for this purpose. The method can therefore be implemented using a component that is generally already present in a brake system.

[0077] To mask a decrease in the braking torque to be masked from time t3 onwards, brake pressure is built up in the at least one wheel brake caliper 52 by means of the plunger 54. While pumping brake fluid out of the at least one storage chamber 82 may cause pulsations that the driver may perceive as vibration / shaking / recoil of the brake actuation element 58, the brake pressure build-up carried out by means of the plunger 54 between times t3 and t4 is imperceptible to the driver. Furthermore, if the braking torque to be masked increases after time t4, brake fluid can be added to the plunger 54 until it is again 100% full.

[0078] Fig. Figures 7a to 7c show three coordinate systems to illustrate a sixth embodiment of the method for operating a braking system.

[0079] In the coordinate systems of Fig. 7a and Fig. 7b the ordinates are a brake actuation distance s and the abscissas are a braking force Fb caused by this for braking in at least one brake caliper of the brake system. Fig. 7a and Fig. Figure 7b illustrates the influence of a centrifugal force acting on the vehicle on the brake actuation distance-braking force characteristic of the braking system. Fig. Figure 7a shows the brake application distance-braking force characteristic before driving the vehicle equipped with the braking system around a sharp curve. In contrast, in Fig. 7b shows the brake travel-braking force characteristic after the vehicle has driven around the sharp curve. As in a comparison of the Fig. 7a and Fig. As noted in section 7b, after driving around the sharp curve, an additional brake application distance / curve-related free travel Δ must be overcome to apply braking force. It should be noted that no brake pressure is built up or braking force is applied to the corresponding wheel during this additional brake application distance / curve-related free travel Δ.

[0080] The free play Δ caused by cornering can be attributed to the fact that, during driving around a sharp curve, displacements / adjustments occur within at least one component of the braking system due to the centrifugal force. For example, the centrifugal force can move at least one piston in at least one wheel brake caliper. This can, for example, mean that the respective piston has to be moved a greater distance before contact is made between the brake pads and the rotor.

[0081] This effect can also be described as knock-back. Knock-back is primarily caused by air play when driving around a curve, where, for example, the piston of the brake caliper is moved by centrifugal force. Additionally, seal expansion due to age and / or frequent use can occur. Similarly, seal expansion and / or a loss of frictional torque can also occur on at least one brake caliper when driving around a curve.

[0082] Using the method described here, it is possible to eliminate this effect, known as knock-back, which often occurs when driving around a sharp bend, and thus suppress the cornering-related free travel Δ despite frequent driving around sharp bends: To carry out the method, the master cylinder internal pressure and the wheel brake pressure in at least one wheel brake caliper can be determined and evaluated, preferably after closing at least one pressure equalization port of the master cylinder, such as a vent hole. Subsequently, if an imbalance is detected between the increase in the master cylinder internal pressure and the increase in the wheel brake pressure, the knock-back can be rectified by transferring volume from the already pre-filled plunger into the at least one wheel brake caliper.

[0083] As an alternative or supplement, a change in direction of travel can also be evaluated to detect a possible knockback and, if necessary, quickly compensate for it. For example, a change in direction of travel of a vehicle equipped with the brake system can be examined for exceeding a predefined reference angle. If no exceedance of the predefined reference angle is detected, a first fill level can be defined as the target fill level, taking the brake application force into account, at the next brake application force that deviates from the non-application force. After exceeding the predefined reference angle, a second fill level, smaller than the first fill level, can be defined as the target fill level, taking the brake application force into account, at the next brake application force that deviates from the non-application force.By reducing the target fluid level after driving around at least one sharp bend, an additional volume of brake fluid is shifted from the plunger into at least one wheel brake caliper. This allows additional pressure to be exerted, particularly on the adjustable piston of the wheel brake caliper. This pressure can, for example, return the piston to its initial position, which it held before driving around the sharp bend. This is demonstrated by the... Fig. 7c is illustrated below: In the coordinate system of Fig. 7c represents the abscissa, the brake actuation distance s, and the ordinate, the piston travel k of a brake caliper piston. Graph k0 depicts the brake actuation distance-piston travel relationship before a vehicle drives around a sharp curve. In contrast, graph k1 shows the brake actuation distance-piston travel relationship after a vehicle drives around the sharp curve, unless the procedure described above for preventing the curve-induced free travel Δ is applied.

[0084] The piston travel k is directly proportional to the brake travel s in both brake travel-piston travel relationships k0 and k1. However, the brake travel-piston travel relationship k1 shows a significant delay in the increase of the piston travel k above zero despite a minimum brake travel sm not being equal to zero.

[0085] Using the method described above for preventing the cornering-induced free travel Δ, an additional volume of brake fluid can be transferred from the actuated plunger to at least one wheel brake caliper, even up to the minimum brake actuation travel sm (by reducing the actual fill level of the plunger). As indicated by arrow 100, the advantageous brake actuation travel-piston travel ratio k0 can thus be achieved despite driving around at least one sharp curve. Using the method described above, the otherwise lost input rod / pedal travel can be compensated for even without feedback from the driver. After overcoming the jump-in range, the driver also receives the same feedback from the braking system as with conventional operation of the braking system.

[0086] It should be noted that the embodiment of the method described here can be carried out on a braking system without requiring any structural modifications to the braking system.

[0087] Fig. Figures 8a to 8c show three coordinate systems to illustrate a seventh embodiment of the method for operating a braking system.

[0088] In the coordinate system of Fig. 8a The abscissa represents the volume of brake fluid (Vbf) displaced during brake application, while the ordinate represents the resulting brake pressure pb. A minimum brake pressure pbm should be achieved during both the first braking operation (with pV characteristic b1) and the second braking operation (with pV characteristic b2). The time profiles of the brake pressure pb and the displaced volume Vbf are shown in the coordinate systems of the Fig. 8b and Fig. Figure 8c shows the abscissas representing the time axis t.

[0089] When considering the in Fig. Figure 8a shows that the pV characteristic of the brake system changes with repeated pressure modulations. This change in the pV characteristic can be caused, for example, by compression at the seals and / or brake pads. This can result in additional free travel. Therefore, during prolonged operation of the brake system without fully releasing the pedal (no fluid recirculation, e.g., during significant fluctuations in the generator braking torque, which often leads to large pressure modulations), a larger volume is conventionally required to adjust the brake pressure to the desired minimum brake pressure pbm.

[0090] The method described here, however, implements an operating strategy in which the plunger is at least partially filled at the start of pressure modulation. Thus, before pressure modulation begins, the plunger always contains a sufficient volume of brake fluid to compensate for wear on the brake system by additionally pumping brake fluid into at least one wheel brake caliper.

[0091] The procedure examines the duration and / or intensity of plunger / brake system usage to determine if a predefined reference usage threshold is exceeded. If no exceedance of the predefined reference usage threshold is detected, a third fill level can be set as the target fill level, taking the brake application force into account, at the next brake application force that deviates from the non-use force. Conversely, if the predefined reference usage threshold is exceeded, a fourth fill level, lower than the third, is set as the target fill level at the next brake application force that deviates from the non-use force, again taking the brake application force into account. By reducing the actual fill level, additional brake fluid volume is automatically delivered to the wheel calipers to compensate for wear on the brake system.In this way, reliable operation of the braking system can be guaranteed even after prolonged use.

[0092] It should be noted that all methods described here can be implemented using a cost-effective plunger 54 that requires little installation space. Thus, the technology according to the invention can be used to reduce the cost and installation space requirements of a plunger interacting with a braking system. Furthermore, a high-efficiency gearbox can be used for the plunger using the technology described here.

Claims

[1] Control device (56) for a braking system of a vehicle comprising: a first receiving device (10), by means of which a provided brake actuation force variable (s, 14) relating to an actuation force of an actuation of a brake actuation element (58) arranged on the brake system can be received; and a plunger control device (16), by means of which, taking into account at least the received brake actuation force value (s, 14), a desired fill level of a plunger (20, 54) can be determined and a plunger control signal (18) corresponding to the determined desired fill level can be output to the plunger (20, 54), so that a ratio (F) of an actual fluid volume filled into a storage volume of the plunger (20, 54) and a maximum volume that can be filled into the storage volume can be set in accordance with the determined desired fill level; characterized by , that the plunger control device (16) is designed to define a filling level value that deviates from an empty state of the plunger (20, 54) as the target filling level value when the brake actuation force value (s, 14) corresponds to a predetermined non-actuation force value, and to output a plunger control signal (18) corresponding to the defined target filling level value to the plunger (20, 54) in such a way that the plunger (20, 54) is at least partially filled. [2] Control device (56) according to claim 1, wherein the plunger control device (16) is designed to set a filling level of at least 20% as the target filling level for a brake actuation force value (s, 14) corresponding to the non-actuation force value and to output a plunger control signal (18) corresponding to the set filling level value to the plunger (20, 54) in such a way that the actual fluid volume filled into the storage volume can be controlled to at least 20% of the maximum volume. [3] Control device (56) according to claim 2, wherein the plunger control device (16) is designed to define a filling level of at least 50% as the target filling level for a brake actuation force value (s, 14) corresponding to the non-actuation force value and to output a plunger control signal (18) corresponding to the defined filling level value to the plunger (20, 54), so that the actual fluid volume filled into the storage volume can be controlled to at least 50% of the maximum volume. [4] Control device (56) according to claim 3, wherein the plunger control device (16) is designed to define a filling level value of at least 70% as the target filling level value for a brake actuation force value (s, 14) corresponding to the non-actuation force value. [5] Control device (56) according to claim 4, wherein the plunger control device (16) is designed to set a filling level value of at least 90% as the target filling level value for a brake actuation strength value (s, 14) corresponding to the non-actuation strength value. [6] Control device (56) according to one of the preceding claims, wherein the plunger control device (16) is additionally designed to define the desired fill level value as a continuously decreasing function of the brake actuation force value (s, 14) when the brake actuation force value (s, 14) is between the non-actuation force value and a predetermined first limit actuation force value (s1). [7] Control device (54) according to claim 6, wherein the plunger control device (16) is additionally designed to set the target fill level as a continuously increasing function of the brake actuation force (s, 14) when the brake actuation force (s, 14) is between a predetermined second limit actuation force (s2) greater than or equal to the first limit actuation force (s1) and a predetermined third limit actuation force (s3). [8] Control device (56) according to one of the preceding claims, wherein the control device (56) comprises a second receiving device (22) by means of which a provided blending variable (26) can be received with respect to a temporal change in a braking torque to be blended, and wherein the plunger control device (16) is additionally designed to reduce the target filling level variable in the event of a temporal decrease in the braking torque to be blended. [9] Control device (56) according to claim 8, wherein the plunger control device (16) is additionally designed to increase the desired filling level size in the event of a temporal increase in the braking torque to be blended or to determine a desired intake volume of a storage chamber (28, 82) of the braking system corresponding to the temporal increase and to output a storage control signal (30) corresponding to the desired intake volume to a control unit of the storage chamber (28, 82). [10] Control device (56) according to one of the preceding claims, wherein the control device (56) comprises a third receiving device (32), by means of which a provided change in direction variable (36) relating to a change in direction of travel of a vehicle equipped with the control device (56) can be received, and wherein the plunger control device (16) is additionally designed to compare the received change in direction variable (36) with at least one predetermined comparison angle variable, and, in the case of a brake actuation force variable (s, 14) deviating from the non-actuation force variable, if the change in direction variable (36) is below the comparison angle variable, to define a first fill level variable as the target fill level variable taking into account the brake actuation force variable (s, 14), and, if the change in direction variable (36) is above the comparison angle variable,to define a second fill level value smaller than the first fill level value as the target fill level value, taking into account the brake actuation force value (s, 14). [11] Control device (56) according to one of the preceding claims, wherein the control device (56) comprises a fourth receiving device (38), by means of which a provided usage intensity variable (42) relating to a duration and / or an intensity of use of the plunger (20, 54) and / or the braking system can be received, and wherein the plunger control device (16) is additionally designed to compare the received usage intensity variable (42) with at least one predetermined comparison usage intensity variable, and, in the case of a brake actuation intensity variable (s, 14) that differs from the non-actuation intensity variable, if the usage intensity variable (42) is below the comparison usage intensity variable, to define a third fill level variable as the target fill level variable taking into account the brake actuation intensity variable (s, 14), and, if the usage intensity variable (42) is above the comparison usage intensity variable,to specify a fourth fill level value smaller than the third fill level value as the target fill level value, taking into account the brake actuation force value (s, 14). [12] Braking system for a vehicle with: a master brake cylinder (50); at least one wheel brake caliper (52) hydraulically connected to the master brake cylinder (50); at least one plunger (20, 54) hydraulically connected to the at least one wheel brake caliper (52); a control device (56) according to one of the preceding claims. [13] A method for operating a braking system of a vehicle comprising the steps of: Determining a target filling level of a plunger (20, 54) taking into account at least one actuation force (s, 14) of an actuation of a brake actuation element (58) arranged on the brake system; and Controlling the plunger (20, 54) in accordance with the specified target filling level, so that a ratio (F) of an actual liquid volume filled into a storage volume of the plunger (20, 54) and a maximum volume that can be filled into the storage volume is set in accordance with the specified target filling level; characterized by the steps: Comparing the brake application force (s, 14) with a predetermined non-application force; if the brake actuation force (s, 14) corresponds to the non-actuation force, setting a filling level that differs from an empty state of the plunger (20, 54) as the target filling level; and Controlling the plunger (20, 54) according to the specified filling level so that the plunger (20, 54) is at least partially filled. [14] Method according to claim 13, wherein a filling level of at least 50% is defined as the desired filling level, and wherein the plunger (20, 54) is controlled in accordance with the defined filling level of at least 50% such that the actual liquid volume filled into the storage volume is set to at least 50% of the maximum volume. [15] Method according to claim 13 or 14, wherein, for a brake actuation force (s, 14) between the non-actuation force and a predetermined first limit actuation force (s1), the target fill level is defined as a continuously decreasing function of the brake actuation force (s, 14), and wherein, for a brake actuation force (s, 14) between a predetermined second limit actuation force (s2) greater than or equal to the first brake actuation force (s1) and a predetermined third limit actuation force (s3), the target fill level is defined as a continuously increasing function of the brake actuation force (s, 14). [16] Method according to one of claims 13 to 15, wherein a temporal change of a braking torque to be blended is determined, and wherein in the case of a temporal decrease in the braking torque to be blended, the target filling level is reduced, and in the case of a temporal increase in the braking torque to be blended, a target intake volume of a storage chamber (28, 82) of the braking system corresponding to the temporal increase is determined and the storage chamber (28, 82) is controlled to suck in an actual intake volume (Vsp) corresponding to the target intake volume. [17] Method according to one of claims 13 to 16, wherein an exceedance of a predetermined comparison angle value is examined during a change of direction of travel of a vehicle, and wherein, if no exceedance of the predetermined comparison angle value is determined, a first filling level is set as the target filling level taking into account the brake actuation strength (s, 14) at the next brake actuation strength (s, 14) deviating from the non-actuation strength, and, after an exceedance of the predetermined comparison angle value, a second filling level smaller than the first filling level is set as the target filling level taking into account the brake actuation strength (s, 14) at the next brake actuation strength (s, 14) deviating from the non-actuation strength. [18] Method according to one of claims 13 to 17, wherein an exceedance of a predetermined comparison usage intensity value is examined on the basis of a duration and / or an intensity of use of the plunger (20, 54) and / or the brake system, and wherein, if no exceedance of the predetermined comparison usage intensity value is determined, a third filling level is set as the target filling level taking into account the brake application intensity (s, 14) at the next brake application intensity (s, 14) deviating from the non-application intensity, and, after an exceedance of the predetermined comparison usage intensity value, a fourth filling level less than the third filling level is set as the target filling level taking into account the brake application intensity (s, 14) at the next brake application intensity (s, 14) deviating from the non-application intensity.

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