Method for operating an electromechanical brake booster of a braking system, method for operating a recuperative braking system and control device for at least one electromechanical brake booster of a braking system

Abstract

Method for operating an electromechanical brake booster of a brake system comprising the steps: Determining a virtual target brake pressure value (pv) at least taking into account an actuation travel and / or an actuation force of an actuation of a brake actuation element of the brake system; Determining a target differential travel value (Δ) with respect to a target differential travel to be set between a valve piston and a valve body of the electromechanical brake booster at least by: - determining a first intermediate value (x1) taking into account a first weighting relation (a1) and a minimum (min) from a first set of values ​​comprising the virtual target brake pressure variable (pv) and an entry pressure variable (p0) which corresponds to a virtual target brake pressure variable (pv) from which a gap existing when the brake actuating element is not actuated is closed; and - determining a second intermediate value (x2) taking into account a second weighting relation (a2) and a maximum (max) from a second set of values ​​comprising zero and a value of a difference (d1) with the virtual target brake pressure variable (pv) as the minuend and the entry pressure variable (p0) as the subtrahend; wherein the target differential travel value (Δ) is determined at least taking into account a sum (sum) of the first intermediate value (x1) and the second intermediate value (x2); and Controlling a motor of the electromechanical brake booster in such a way that a differential travel corresponding to the specified target differential travel size (Δ) is set between the valve piston and the valve body of the electromechanical brake booster.

Description

[0001] The invention relates to a method for operating an electromechanical brake booster of a braking system and a method for operating a regenerative braking system. The invention also relates to a control device for at least one electromechanical brake booster of a braking system. Furthermore, the invention relates to an electromechanical brake booster and a braking system for a vehicle. State of the art

[0002] FR 2 947 228 A1 describes a braking system with an electromechanical brake booster. The electromechanical brake booster comprises a boost housing that can be adjusted by means of an electric motor and has a continuous receiving opening for a valve body that is adjustably arranged therein and can be adjusted with the boost housing. Furthermore, the valve body has a continuous central opening within which a valve piston can be adjusted relative to the valve body by means of a driver braking force transmitted thereto. To transmit the driver braking force to the valve piston, an input rod can contact the valve piston at least temporarily. By means of the adjusting movements of the valve body and / or the valve piston, an output piston can also be adjusted such that a braking pressure present in at least one pressure chamber of a master brake cylinder can be increased.

[0003] DE 10 2009 045 415 A1 shows a method for operating a brake-assisted braking system of a vehicle and a control device for a brake-assisted braking system of a vehicle.

[0004] DE 10 2011006411 A1 discloses a brake control system which displaces the primary piston by controlling an operation of the electric motor by means of a master pressure control unit according to the operation amount of the brake pedal, thereby generating a hydraulic pressure in the master cylinder to supply it to the wheel cylinders. Disclosure of the invention

[0005] The invention provides a method for operating an electromechanical brake booster of a braking system having the features of claim 1, a method for operating a recuperative braking system having an electromechanical brake booster having the features of claim 8, a control device for at least one electromechanical brake booster of a braking system having the features of claim 9, an electromechanical brake booster for a braking system having the features of claim 11, and a braking system for a vehicle having the features of claim 12. Advantages of the invention

[0006] The invention provides several possibilities for ensuring a favorable (standard) brake actuation feel (pedal feel) for a driver during deceleration / stopping of their vehicle. As explained in more detail below, the present invention is particularly advantageously applicable to a regenerative braking system. With such use of the present invention, it is ensured that the driver has a favorable (standard) brake actuation feel (pedal feel) regardless of the fluctuations in the master cylinder pressure, despite an increase / decrease in the master cylinder pressure of the regenerative braking system. In particular, a desired restoring force of the brake actuation element of the regenerative braking system, such as a brake pedal, can be adjusted independently of the master cylinder pressure by means of the present invention.Thus, by varying the master brake cylinder pressure, at least one generator braking torque of at least one generator can be blended without this leading to an unusual brake actuation feeling (pedal feeling) for the driver.

[0007] Advantageously, it is primarily ensured that the position of the jump-in point perceptible to the driver remains unchanged. During a braking operation with blending of the generator braking torque, the force feedback felt by the driver at the brake actuation element does not differ from the standard perceptible force feedback during a braking operation performed exclusively by the friction braking torques of the wheel brake cylinders of the regenerative braking system.

[0008] In the preceding paragraph, the advantages of the present invention are explained using the example of a regenerative braking system. However, it should be noted that the applicability of the present invention does not require the use of a braking system designed for regenerative braking.

[0009] The present invention enables the target differential travel value to be set with respect to the target differential travel between the valve piston and the valve body of the electromechanical brake booster, or with respect to a position of a boost body of the electromechanical brake booster, with separate components being used as a first intermediate value and a second intermediate value depending on the respectively set / present operating point of the electromechanical brake booster. As explained in more detail below, setting the first intermediate value ensures that a gap between the valve piston and a reaction disc of the electromechanical brake booster is closed precisely at a desired jump-in pressure.Above all, this allows for the jump-in pressure to be freely adjusted / applied within given physical limits, such as the deformation path of the reaction disc and the mechanical stops. In contrast, the setting of the second intermediate value ensures that force fluctuations on the brake actuation element (brake pedal) are minimized during volumetric blending of at least one generator braking torque, as described in more detail below.

[0010] Preferably, the target differential travel value is determined by additionally taking into account a quotient of a master brake cylinder pressure value with respect to a master brake cylinder pressure present or to be set in a master brake cylinder of the brake system as the dividend and the virtual target brake pressure value as the divisor. The master brake cylinder pressure value can, for example, be a master brake cylinder pressure measured in the master brake cylinder or a value derived therefrom. However, the master brake cylinder pressure value can also correspond to a desired master brake cylinder pressure, which is to be set, for example, to blend a time-varying generator braking torque in the master brake cylinder of the brake system. Thus, the force level in the master brake cylinder can also be taken into account when determining the target differential travel value.The calculation step described here for forming the quotient depending on an operating point of the electromechanical brake booster, which corresponds to the driver's braking request and a pressure set in the master brake cylinder (actual pressure) or the driver's braking request and a pressure to be set in the master brake cylinder (target pressure), ensures a particularly advantageous use of the electromechanical brake booster.

[0011] To determine the target differential travel value, a third intermediate value is preferably determined and taken into account as the product of the sum of the first intermediate value and the second intermediate value, and the quotient of the master brake cylinder pressure value as the dividend and the virtual target brake pressure value as the divisor. This provides a determination of the target differential travel value while taking a gradient into account. Furthermore, the target differential travel value can be determined taking into account a difference value with the sum of the first intermediate value and the second intermediate value as the minuend and the third intermediate value as the subtrahend.

[0012] Optionally, low-pass filtering can be performed to determine the target differential travel value. Alternatively or in addition, gradient limitation can be performed to determine the target differential travel value. Likewise, manipulated variable limitation can be performed to determine the target differential travel value. All procedures described here can be used optionally to ensure a more advantageous determination of the target differential travel value.

[0013] The advantages described above are also ensured when implementing a corresponding method for operating a regenerative braking system with an electromechanical brake booster. For this purpose, at least the following steps are performed during the actuation of the brake actuating element of the regenerative braking system: determining a generator braking torque generated by a generator of the regenerative braking system, at least taking into account the actuation travel and / or the actuation force of the brake actuating element, and controlling the generator accordingly.Varying at least one friction braking torque of at least one wheel brake cylinder of the regenerative braking system, at least taking into account the specified generator braking torque, by setting a target value for a fluid volume to be displaced between at least one accumulator volume and an accumulator-external volume of at least one brake circuit of the regenerative braking system by means of at least one hydraulic device of the regenerative braking system, at least taking into account the specified generator braking torque, and correspondingly controlling the at least one hydraulic device; and varying a restoring force of the brake actuating element by operating the electromechanical brake booster. The method for operating the regenerative braking system can be further developed in accordance with the above explanations regarding the method for operating the electromechanical brake booster.

[0014] In addition, the described advantages are realized by a corresponding control device for at least one electromechanical brake booster of a brake system. The control device is designed to establish a virtual target brake pressure variable, at least taking into account an actuation travel and / or an actuation force of an actuation of a brake actuation element of the brake system, wherein the control device is additionally designed to establish a target differential travel variable with respect to a target differential travel to be set between a valve piston and a valve body of the electromechanical brake booster, at least by determining a first intermediate value, taking into account a first weighting relation and a minimum from a first set of values ​​comprising the virtual target brake pressure variable and an entry pressure variable, which corresponds to a virtual target brake pressure variable,from which a gap existing when the brake actuating element is not actuated is closed, and in that a second intermediate value can be determined taking into account a second weighting relation and a maximum from a second set of values ​​comprising zero and a value of a difference with the virtual target brake pressure variable as the minuend and the entry pressure variable as the subtrahend, wherein the target differential travel variable can be determined at least taking into account a sum of the first intermediate value and the second intermediate value, and wherein the control device is designed to control a motor of the electromechanical brake booster in such a way,that a differential travel corresponding to the specified target differential travel value can be set between the valve piston and the valve body of the electromechanical brake booster. The control device can also be further developed according to the above-described embodiments of the method for operating the electromechanical brake booster.

[0015] In an advantageous development, the control device is additionally designed to determine a generator braking torque implemented by a generator of the braking system, at least taking into account the actuation path and / or the actuation force of the brake actuation element, and to control the generator accordingly. At least taking into account the determined generator braking torque, the control device is designed to determine a target value with respect to a brake fluid volume that varies between at least one storage volume and a storage-external volume of at least one brake circuit of the braking system by means of at least one hydraulic device of the braking system, and to control the at least one hydraulic device accordingly. The control device can thus also realize the advantages of the method for operating a recuperative braking system.

[0016] An electromechanical brake booster for a braking system comprising such a control device and a braking system for a vehicle with a corresponding control device and / or a corresponding electromechanical brake booster can also contribute to the realization of the above-described advantages. The electromechanical brake booster and the braking system can be further developed according to the embodiments described above. Short description of the drawings

[0017] Further features and advantages of the present invention are explained below with reference to the figures. They show: Fig. 1 is a block diagram for explaining an embodiment of the method for operating an electromechanical brake booster of a brake system; and Fig. 2a to 2f coordinate systems for explaining an embodiment of the method for operating a recuperative braking system with an electromechanical brake booster. Embodiments of the invention

[0018] Fig. 1 shows a block diagram for explaining an embodiment of the method for operating an electromechanical brake booster of a brake system.

[0019] The Fig. The method schematically illustrated in Figure 1 can be used to operate a variety of different types of electromechanical brake boosters. For example, all controllable or adjustable electromechanical brake boosters can be operated using the method described in Fig. 1. In particular, the conventional electromechanical brake booster described above can be operated by means of the method shown in Fig. 1. However, it should be noted that the feasibility of the method is not limited to this brake booster type.

[0020] In a method step not shown in detail, a virtual target brake pressure variable pv is determined at least taking into account an actuation travel and / or an actuation force of an actuation of a brake actuation element of the braking system. The virtual target brake pressure variable pv is preferably determined such that it corresponds to a (target) brake pressure that is / would be present during purely hydraulic braking of the braking system in accordance with the driver braking request indicated by the actuation of the brake actuation element. The (target) brake pressure can in particular be determined as the virtual target brake pressure variable pv. However, instead of a pressure variable, the virtual target brake pressure variable pv can also be another variable corresponding to the (target) brake pressure.

[0021] For example, a pedal travel, a rod travel, a driver brake force, and / or a driver brake pressure can be evaluated to determine the virtual target brake pressure value pv. However, the examples listed here for the actuation travel or actuation force are not restrictive. Likewise, the feasibility of the method is not limited to a braking system with a brake pedal as the brake actuation element.

[0022] At least taking into account the specified virtual target brake pressure variable pv, a target differential travel variable Δ is specified with respect to a target differential travel to be set between a valve piston and a valve body or a boost body of the electromechanical brake booster. In particular, the target differential travel to be set can be specified as the target differential travel variable Δ. The valve body or the boost body can be understood as a valve body or a boost body. The valve piston is preferably understood to be a component adjustably arranged in a central opening of the valve body, via which a driver braking force can be transmitted from the brake actuating element to at least one adjustable piston of a master brake cylinder of the braking system.

[0023] The target differential travel value Δ is determined, at least taking into account the specified virtual target brake pressure value pv, by setting a first intermediate value x1, taking into account a first weighting relationship a1 and a minimum min from a first set of values. The first set of values ​​comprises the virtual target brake pressure value pv and a step-in pressure value p0. The step-in pressure value p0 is understood to be a value that corresponds to a virtual target brake pressure value pv, above which a gap existing when the brake actuating element is not actuated is closed. When the brake actuating element is not actuated, a gap / gap often exists between a reaction disc of the electromechanical brake booster and the valve piston.The jump-in pressure variable p0 can thus correspond to a target brake pressure which, during purely hydraulic braking, is present at the point in time at which the actuation of the brake actuating element causes the gap / gap to close, whereas previously a transmission of the driver's braking force to the at least one adjustable piston of the master brake cylinder is prevented due to the gap / gap not being closed. The jump-in pressure variable p0 can be a pressure value or a corresponding variable. The jump-in pressure variable p0 generally corresponds to the jump-in range of the electromechanical brake booster and is often also described as the jump-in point or as the (desired) jump-in pressure limit value. The jump-in pressure variable p0 can either be predetermined by the mechanics of the electromechanical brake booster or set via programming of its electronics.

[0024] The process step described in the previous paragraph ensures that the gap (e.g., between the reaction disc and the valve piston) is closed precisely at a desired entry point / entry pressure limit. As explained in more detail below, even during a blending of at least one generator braking torque due to a volume shift within the brake system's hydraulics, it is still ensured that no deviating return behavior / braking actuation feel of the brake actuating element occurs, particularly at the entry point.

[0025] In the embodiment of the Fig. 1, the virtual target brake pressure variable pv is fed to a block 10, which determines the minimum min from the first set of values. (The initial pressure variable p0 can, for example, be stored in a memory unit not shown.) Subsequently, the minimum min is fed to a block 12, in which the first intermediate value x1 is calculated as the product of the minimum min and the first weighting relation a1.

[0026] In addition, a second intermediate value x2 is determined taking into account a second weighting relation a2 and a maximum max from a second set of values. The second set of values ​​comprises the number 0 and a value of a difference d1. The difference d1 is calculated in a block 14 with the virtual target brake pressure variable pv as the minuend and the step-in pressure variable p0 as the subtrahend. The difference d1 is fed to a block 16, which determines the maximum max from the second set of values. Subsequently, in a block 18, a product of the maximum max and the second weighting relation a2 is calculated as the second intermediate value x2. Using the second intermediate value x2, it is possible to adapt a force curve of a restoring force of the actuated brake actuating element to a desired characteristic curve after the gap has closed.

[0027] The first weighting relation a1 and / or the second weighting relation a2 can each be a weighting factor, at least two factors, or a characteristic curve. The first weighting factor a1 preferably corresponds to a quotient of a gap actually present in the unconfirmed state of the electromechanical brake booster and a desired jump-in pressure limit.

[0028] The procedure of Fig. 1 thus realizes at least a two-factor force compensation. As a supplement to the two-factor pedal force compensation, a multi-factor pedal force compensation can also be implemented. Blocks 10 and 16 identify whether the virtual target brake pressure value pv is smaller or larger than the (to be set / specified) step-in pressure value p0. The first intermediate value x1 ensures that the gap is closed exactly at the specified step-in point / step-in pressure limit. The second mean value x2 can ensure that fluctuations at the brake actuating element / brake pedal are minimized. Thus, the advantages of a single-factor pedal force compensation are also achieved when executing the method of Fig. 1 is still guaranteed.

[0029] The desired differential travel value Δ is determined at least taking into account a sum of the first intermediate value x1 and the second intermediate value x2. For this purpose, the intermediate values ​​x1 and x2 can be fed to a block 20 for summation. This can also be described as an addition of offset setpoints for a desired position of the valve body / boost body.

[0030] Advantageously, the target differential travel variable Δ is determined with additional consideration of a (current) master brake cylinder pressure variable pa with respect to a master brake cylinder pressure present or to be set in the master brake cylinder of the brake system. The master brake cylinder pressure variable pa can thus be either a variable with respect to an actual pressure in the master brake cylinder or with respect to a desired target pressure in the master brake cylinder. In particular, such a pressure value or a corresponding variable can be used as the master brake cylinder pressure variable pa. Preferably, the target differential travel variable Δ is determined with additional consideration of a quotient, which is derived with the master brake cylinder pressure variable pa as the dividend and the virtual target brake pressure variable pv as the divisor.

[0031] To ensure this, the procedure of Fig. 1, a third intermediate value x3 is calculated to determine the target differential travel variable Δ. The third intermediate value x3 is a product of the sum (from the first intermediate value x1 and the second intermediate value x2) and the quotient (with the master brake cylinder pressure variable pa as the dividend and the virtual target brake pressure variable pv as the divisor). The third intermediate value x3 is taken into account when determining the target differential travel variable Δ. To derive the third intermediate value x3, a reciprocal value k of the virtual target brake pressure variable pv is determined in a block 22. The reciprocal value k is multiplied by the sum sum by means of a block 24. The product p formed in this way is fed together with the master brake cylinder pressure variable pa to a block 26, which calculates the third intermediate value x3 by multiplying the product p by the master brake cylinder pressure variable pa.

[0032] Setting the third intermediate value x3 allows a master brake cylinder force level (depending on the operating point of the electromechanical brake booster and / or depending on the sum sum) to be taken into account when setting the target differential travel value Δ by determining a gradient for taking the actual pressure or the target pressure into account.

[0033] In the proceedings of the Fig. 1, the target differential travel value Δ is determined taking into account a value of a difference d2 with the sum sum (from the first intermediate value x1 and the second intermediate value x2) as the minuend and the third intermediate value x3 as the subtrahend. For this purpose, the sum sum and the third intermediate value x3 are fed to a block 28 for subtraction. (Thus, when executing the method, a difference between the target and actual pressure for the various areas above and below the entry point is also weighted with different weighting relationships a1 and a2.)

[0034] Optionally, a low-pass filter, a gradient limitation and / or a manipulated variable limitation can also be carried out to determine the desired differential travel value Δ. In the method of Fig. 1, the difference d2 output by block 28 is first fed to a block 30 for low-pass filtering, then as signal d2' to a block 32 for manipulated variable limitation and as signal d2" to a block 34 for gradient limitation. Between blocks 32 and 34, a switch 36 is arranged which controls the forwarding of the signal d2" to block 34 depending on an actuation state S of the brake actuation element (not actuated, adjusted, held constant).

[0035] In a final step of the procedure of Fig. 1, a motor of the electromechanical brake booster is controlled in such a way that a target differential travel between the valve piston and the valve body, or the boost body of the electromechanical brake booster, corresponding to the specified target differential travel value Δ is set. A variety of control options can be used in this procedure. Therefore, it will not be discussed in detail.

[0036] During execution of the procedure of Fig. 1, the brake pressure present in at least one wheel brake cylinder of the brake system can be varied independently of the position / actuation of the brake actuation element, particularly at the master brake cylinder level. Regardless of whether the brake pressure is modulated, the haptic feedback for the driver remains unchanged. A particularly advantageous application is discussed below.

[0037] Fig. 2a to 2f show coordinate systems for explaining an embodiment of the method for operating a recuperative braking system with an electromechanical brake booster.

[0038] Various types of regenerative braking systems equipped with an electromechanical brake booster can also be used to implement the method described below. Some braking system components suitable for performing specific method steps are listed below. However, it should be noted that the regenerative braking system used to implement the method is not limited to being equipped with precisely these braking system components. Likewise, the regenerative braking system suitable for implementing the method is neither restricted to a specific brake circuit design, nor are there any obstacles to integrating a multitude of additional braking system components.

[0039] Fig. Figure 2a indicates a desired relationship r1 between a restoring force Fr of a brake actuating element (e.g., a brake pedal), which is to be applied as a driver braking force to the driver's braking request, and a resulting output force Fout. The output force Fout, which results from the driver braking force and a motor force of a motor of the electromechanical brake booster, is transmitted to at least one adjustable piston of a master brake cylinder of the regenerative braking system and causes a corresponding brake pressure buildup in the master brake cylinder and in at least one connected wheel brake cylinder of the regenerative braking system. In the coordinate system of the Fig. 2a, an abscissa is the restoring force Fr and an ordinate is the output force Fout.

[0040] Fig. Figure 2b shows a second desired relation r2 between an input rod travel sΔ (as an example for a brake actuation travel) and the restoring force Fr, where an abscissa indicates the input rod travel sΔ and an ordinate indicates the restoring force Fr.

[0041] As a rule, drivers are accustomed to the fact that after overcoming a free travel range A1 (almost) effortlessly, an initial actuation of the brake actuating element is possible by means of a constant driver braking force (with a constant restoring force Fr). The free travel range A1 is therefore followed by a jump-in range A2, within which a constant restoring force Fr counteracts an increase in the input rod travel sΔ. Within the jump-in range A2, the output force Fout is usually only caused by the motor of the electromechanical brake booster. Thus, the electromechanical brake booster in the jump-in range A2 is a power braking system (i.e., the driver braking force does not increase the output force Fout). In the jump-in range A2, the gap (e.g.between the input rod and the reaction disc), which prevents the driver's braking force from being transmitted toward the master brake cylinder, is still open. As the input rod travel sΔ increases in the jump-in area A2, the boost body / valve body is moved toward the master brake cylinder, and the reaction disc bulges due to the pressure load on a side facing the input rod.

[0042] The gap is only closed at an entry point P1, so that upon further actuation of the brake actuation element, the driver's braking force can be transmitted to the at least one adjustable piston of the master brake cylinder to increase the braking pressure. In a linear amplification range A3 following the entry point P1, there is therefore a constant relationship between the restoring force Fr and the output force Fout. Above a control point P2, an increase in the driver's braking force cannot be accompanied by an increase in the engine's power, so that any further increase in the output force Fout on the at least one adjustable piston must be provided as driver braking force. Above the control point P2, the restoring force Fr therefore increases at a comparatively steep rate.

[0043] The following is based on the Fig. 2c to 2f describe the advantageous method for operating the regenerative braking system, wherein the abscissas of the Fig. 2c to 2f the input rod travel sΔ and the ordinates of the Fig. 2c to 2f show the restoring force Fr. In all coordinate systems of the Fig. 2c to 2f also show the second target relation r2, which is to be maintained during braking of the vehicle equipped with the recuperative braking system.

[0044] In the case of the Fig. In the method illustrated in Figures 2c to 2f, a generator braking torque generated by a generator of the regenerative braking system is applied during the actuation of the brake actuating element of the regenerative braking system. The generator braking torque is determined at least taking into account the actuation travel and / or the actuation force of the brake actuating element. The generator is then controlled in such a way that a generator braking torque corresponding to the determined value is applied to decelerate the vehicle. By activating the generator, the deceleration of the vehicle can be used to charge a vehicle battery.

[0045] However, various factors, such as vehicle speed and / or the charge level of the vehicle battery, can impair the usability of the generator to simultaneously brake the vehicle and charge the vehicle battery. This is preferably taken into account when setting the generator braking torque. Furthermore, it is desirable if using the generator to brake the vehicle does not result in the driver's braking command being exceeded. To ensure this, the method described here varies at least one friction braking torque of the at least one wheel brake cylinder of the recuperative braking system, at least taking into account the set generator braking torque, such that the driver's braking command is not exceeded or is barely exceeded.For this purpose, a target value is determined with respect to a brake fluid volume between at least one storage volume and an external storage volume of at least one brake circuit of the regenerative braking system, which is determined by means of at least one hydraulic device of the regenerative braking system, at least taking into account the specified generator braking torque. Subsequently, the at least one hydraulic device is controlled in such a way that a brake fluid volume corresponding to the target value is shifted between the at least one storage volume and the external storage volume.

[0046] For example, an electric motor-driven volume blending actuator, such as a plunger, and / or an ESP device capable of volume absorption and discharge can be used as the at least one hydraulic device. Using such a hydraulic device, brake fluid can be drawn into and expelled from at least one actuator-specific storage volume, an external storage volume, and / or a brake fluid reservoir as needed. The volume blending actuator can be configured either with a self-locking gear or with a high-efficiency gear.

[0047] For example, an increase in the generator braking torque (e.g., at the beginning of the actuation of the brake actuating element) can be compensated by a reduction of the at least one friction braking torque by shifting brake fluid from the external storage volume into the at least one storage volume. In particular, the volume shifted from the master brake cylinder to the wheel brake cylinders upon slow actuation of the brake actuating element by the driver can be shifted immediately into the at least one storage volume. This causes the Fig. 2c shows the example relation f1, which can be described as a shift of the second target relation r2 parallel to the abscissa in the direction of increasing the input rod travel sΔ.

[0048] A situation often occurs in which the generator is deactivated during a braking process and the vehicle is only slowed down further by means of at least one wheel brake cylinder of the regenerative braking system. In the example of Fig. 2d, starting from a limit input rod travel s0, a phase Δt1 of the regenerative braking of the vehicle is terminated and a phase Δt2 of the purely friction brake-based braking is started.

[0049] As in Fig. As can be seen in Figure 2d, the temporal decrease in the generator braking torque can be compensated by increasing the at least one friction braking torque by shifting the brake fluid volume back from the at least one storage volume to the external storage volume. This results in an example relation f2, which corresponds to the example relation f1 below the limit input rod travel s0 and lies on the second target relation r2 above the limit input rod travel s0.

[0050] However, by means of the method steps described above for operating an electromechanical brake booster of a braking system, the return behavior of the brake actuating element can be adapted even better to the second target relationship r2. In particular, it should be noted that the method steps described above are even more advantageous than single-factor pedal force compensation. With single-factor pedal force compensation, a compensation factor for an offset movement of the boost body, proportional to the deviation between the target value and the actual value of the at least one friction braking torque, is calculated and subsequently adjusted using the electromechanical brake booster.However, with the one-factor pedal force compensation, particularly in a range ΔA close to the entry point P1, deviations still occur that are perceptible to the driver between the second target relation r2 and the example relation f3 realized by means of the one-factor pedal force compensation, as shown in . Fig. 2e. These deviations can also be referred to as entry errors.

[0051] Advantageously, however, in the method described here, instead of a single-factor pedal force compensation, a variation of a restoring force of the brake actuating element is also carried out by operating the electromechanical brake booster according to the procedure of Fig. 1. The method thus implements at least a two-factor pedal force compensation according to the procedure described above. As a supplement to the two-factor pedal force compensation, a multi-factor pedal force compensation can also be implemented.

[0052] The effect of at least two-factor pedal force compensation is in Fig. 2f, where the realized actual relation r3 lies on the second target relation r2. By considering different adjustment factors for the difference between the target pressures and the current pressures below and above a desired entry pressure limit, it can be ensured that the gap between the pressure piece and the reaction disc is closed at the correct location. The entry point P1 can thus be set as desired.

[0053] As shown by the Fig.As can be seen in Figure 2f, the method described here enables a standard pedal feel for the driver to be achieved despite the changes in the generator braking torque during braking. This prevents the temporal changes in at least one friction braking torque from causing noticeable changes in the return behavior of the brake actuation element. Furthermore, the occurrence of undesirable movements in the driver's foot is prevented, thus also preventing undesirable changes in the driver's braking request.

[0054] When applying the method, even when switching between purely hydraulic braking (using only the wheel brake cylinders) and braking using the generator, there are no changes in the brake actuation feel / haptic feedback (braking characteristics). In particular, the pedal force / actuation travel curve does not change during blending of the generator braking torque. This advantage is guaranteed even though the driver is connected to the master brake cylinder during actuation of the brake actuation element, as soon as the gap is closed and the brake booster switches from the external power brake to the auxiliary power brake. The shape of the entry point transition in the pedal force / actuation travel curve can be easily and reliably influenced using software parameterization.

[0055] The methods described above can also be carried out by a control device for at least one electromechanical brake booster. An electromechanical brake booster for a braking system comprising such a control device, as well as a braking system for a vehicle with a corresponding control device and / or a corresponding electromechanical brake booster, also ensure the advantages described above.

Claims

[1] Method for operating an electromechanical brake booster of a braking system, comprising the steps: Determining a virtual target brake pressure value (pv) at least taking into account an actuation travel and / or an actuation force of an actuation of a brake actuation element of the brake system; Determining a target differential travel value (Δ) with respect to a target differential travel to be set between a valve piston and a valve body of the electromechanical brake booster at least by: - determining a first intermediate value (x1) taking into account a first weighting relation (a1) and a minimum (min) from a first set of values ​​comprising the virtual target brake pressure variable (pv) and an entry pressure variable (p0) which corresponds to a virtual target brake pressure variable (pv) from which a gap existing when the brake actuating element is not actuated is closed; and - determining a second intermediate value (x2) taking into account a second weighting relation (a2) and a maximum (max) from a second set of values ​​comprising zero and a value of a difference (d1) with the virtual target brake pressure variable (pv) as the minuend and the entry pressure variable (p0) as the subtrahend; wherein the target differential travel value (Δ) is determined at least taking into account a sum (sum) of the first intermediate value (x1) and the second intermediate value (x2); and Controlling a motor of the electromechanical brake booster in such a way that a differential travel corresponding to the specified target differential travel size (Δ) is set between the valve piston and the valve body of the electromechanical brake booster. [2] Method according to claim 1, wherein the determination of the target differential travel value (Δ) is carried out with additional consideration of a quotient of a master brake cylinder pressure value (pa) with respect to a master brake cylinder pressure present or to be set in a master brake cylinder of the brake system as a dividend and the virtual target brake pressure value (pv) as a divisor. [3] Method according to claim 2, wherein, in order to determine the desired differential travel value (Δ), a third intermediate value (x3) is determined and taken into account as the product of the sum (sum) of the first intermediate value (x1) and the second intermediate value (x2) and the quotient of the master brake cylinder pressure value (pa) as the dividend and the virtual desired brake pressure value (pv) as the divisor. [4] Method according to claim 3, wherein the target differential travel size (Δ) is determined taking into account a value of a difference (d2) with the sum (sum) of the first intermediate value (x1) and the second intermediate value (x2) as the minuend and the third intermediate value (x3) as the subtrahend. [5] Method according to one of the preceding claims, wherein a low-pass filtering is carried out to determine the desired differential path size (Δ). [6] Method according to one of the preceding claims, wherein a gradient limitation is carried out to determine the desired differential path size (Δ). [7] Method according to one of the preceding claims, wherein a manipulated variable limitation is carried out to determine the desired differential travel variable (Δ). [8] Method for operating a regenerative braking system with an electromechanical brake booster: Perform at least the following steps while operating the brake actuation element of the regenerative braking system: - Determining a generator braking torque carried out by means of a generator of the recuperative braking system, at least taking into account the actuation path and / or the actuation force of the brake actuation element, and controlling the generator accordingly; - Varying at least one friction brake torque of at least one wheel brake cylinder of the regenerative braking system, at least taking into account the specified generator braking torque, by setting a target value with respect to a brake fluid volume to be shifted by means of at least one hydraulic device of the regenerative braking system between at least one storage volume and an external storage volume of at least one brake circuit of the regenerative braking system, at least taking into account the specified generator braking torque, and correspondingly controlling the at least one hydraulic device; and - Varying a restoring force of the brake actuating element (Fr) by operating the electromechanical brake booster according to the method according to one of the preceding claims. [9] Control device for at least one electromechanical brake booster of a brake system, wherein the control device is designed to determine a virtual target brake pressure variable (pv) at least taking into account an actuation travel and / or an actuation strength of an actuation of a brake actuation element of the brake system, and wherein the control device is additionally designed to determine a target differential travel variable (Δ) with regard to a target differential travel to be set between a valve piston and a valve body of the electromechanical brake booster, at least by determining a first intermediate value (x1) taking into account a first weighting relation (a1) and a minimum (min) from a first set of values ​​comprising the virtual target brake pressure variable (pv) and an entry pressure variable (p0) which corresponds to a virtual target brake pressure variable (pv),from which a gap existing when the brake actuating element is not actuated is closed, and in that a second intermediate value (x2) can be determined taking into account a second weighting relation (a2) and a maximum (max) from a second set of values ​​comprising zero and a value of a difference (d1) with the virtual target brake pressure variable (pv) as the minuend and the step-in pressure variable (p0) as the subtrahend, wherein the target differential travel variable (Δ) can be determined at least taking into account a sum (sum) of the first intermediate value (x1) and the second intermediate value (x2), and wherein the control device is designed to control a motor of the electromechanical brake booster such that a differential travel corresponding to the defined target differential travel variable (Δ) can be set between the valve piston and the valve body of the electromechanical brake booster. [10] Control device according to claim 9, wherein the control device is additionally designed to determine a generator braking torque carried out by means of a generator of the braking system, at least taking into account the actuation path and / or the actuation force of the actuation of the brake actuating element, and to control the generator accordingly, and to determine a target value with respect to a brake fluid volume to be displaced by means of at least one hydraulic device of the braking system between at least one storage volume and a storage-external volume of at least one brake circuit of the braking system, at least taking into account the determined generator braking torque, and to control the at least one hydraulic device accordingly. [11] Electromechanical brake booster for a braking system comprising a control device according to claim 9 or 10. [12] Braking system for a vehicle with a control device according to claim 9 or 10 and / or an electromechanical brake booster according to claim 11.

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