CN111791853A

CN111791853A - Determination of a brake pedal characteristic curve for a vehicle brake system having regenerative brakes

Info

Publication number: CN111791853A
Application number: CN202010249868.0A
Authority: CN
Inventors: S.弗罗伊登贝格; 姚迅
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-04-02
Filing date: 2020-04-01
Publication date: 2020-10-20
Anticipated expiration: 2040-04-01
Also published as: CN111791853B; JP2020185984A; DE102019204687A1

Abstract

The present invention relates to a vehicle brake system having regenerative brakes, in particular to a method for modifying a brake pedal characteristic curve for actuating a brake pedal of a brake system of a vehicle, which brake system is provided for generating a braking action for the vehicle. The brake system has: a friction brake hydraulically connected with the electromechanical actuator by means of a hydraulic device assembly; and a regenerative brake. The brake pedal characteristic is a function of pressure in the hydraulic assembly in relation to the electromechanical actuator stroke. The brake pedal characteristic has a lost motion and stiffness coefficient. The method comprises the following steps: the measurement of the brake pedal characteristic curve is carried out by means of an electromechanical actuator according to dynamically known criteria, in particular according to a predefined number of operating brake systems, at least a part of the braking action being generated by means of a friction brake; storing the measured brake pedal characteristic curve; the brake pedal characteristic curve is replaced by the measured brake pedal characteristic curve.

Description

Determination of a brake pedal characteristic curve for a vehicle brake system having regenerative brakes

Technical Field

The present invention relates to a vehicle brake system having a regenerative brake (brake). In particular, the invention relates to a method for modifying a brake pedal characteristic curve for a brake system. Furthermore, the invention relates to a control device, an application, a program element and a computer-readable medium.

Background

Energy efficiency is becoming increasingly important in vehicles, especially in electric and hybrid vehicles. It is therefore attempted to operate the electric motor of an electric or hybrid vehicle as a generator as often as possible in the braking process and thus to use the braking process for energy recovery. This is often referred to as regeneration. In many cases, it is attempted to obtain a brake pedal feel for the driver who intends to initiate braking by actuating the brake pedal, as is the brake pedal feel the driver has when braking with conventional hydraulic friction brakes. This achieves that the driver has a respectively similar or comparable brake pedal feel in a similar braking action. For this purpose, a brake pedal characteristic curve for the brake system is stored in the vehicle, for example in the control system. However, the hydraulic system and the brake mechanism of the friction brake may change over the service life of the vehicle, so that the stored brake pedal characteristic no longer corresponds to the actual brake pedal characteristic of the friction brake. Thus, at least in some vehicles, a braking can be regularly performed in which only the friction brakes contribute to the deceleration. In this case, a measurement of the brake pedal characteristic curve can be carried out and the brake pedal characteristic curve can be updated; otherwise, the brake pedal feel may no longer be adapted to the braking action. By frequently measuring the brake pedal characteristic, a large degree of agreement between the stored and the actual brake pedal characteristic can thus be achieved. However, in particular in electric and hybrid vehicles, in contrast to this, the loss of potential regenerative energy by the braking required for the measurement, i.e. due to friction in the brake, and therefore deceleration by means of the friction brake, should occur as rarely as possible.

Disclosure of Invention

The object of the present invention is to provide a method which provides a balance between, on the one hand, as little deviation as possible between stored and actual brake pedal characteristics and, on the other hand, as little braking as possible by means of friction brakes.

This object is achieved by the subject matter of the independent claims. Further developments of the invention result from the dependent claims and the following description.

A first aspect relates to a method for modifying a brake pedal characteristic curve for a brake pedal for actuating a brake system of a vehicle, wherein the brake system is provided for generating a braking action for the vehicle. Here, the brake system includes: a friction brake hydraulically connected with the electromechanical actuator by means of a hydraulic device assembly; and a regenerative brake. The brake pedal characteristic curve is a function of the pressure in the hydraulic component and the stroke of the electromechanical actuator. The brake pedal characteristic has a lost motion and stiffness coefficient.

A brake pedal characteristic is a characteristic which describes the pressure over the pedal travel of the brake pedal, which pressure can be detected at the brake pedal. The brake pedal characteristic curve can be perceived by the driver as a brake pedal feel, for example. The brake pedal characteristic can be implemented by means of a single (sub-) system in the vehicle, for example by means of a brake pedal simulator. The brake pedal characteristic curve can also be generated by the interaction of a plurality of (sub-) systems in the vehicle, for example by means of the (sub-) systems, i.e. at least one of the brake booster, the brake pedal simulator and/or the electromechanical actuator. Accordingly, the brake pedal characteristic curve may be stored in a single (sub-) system or in a plurality of (sub-) systems. The brake system is actuated by means of a brake pedal in order to generate a braking action for the vehicle.

The vehicle may be, for example, a land vehicle, and may be, in particular, a passenger car, a transport vehicle, a truck, a land-based utility vehicle, or an amphibious vehicle. The vehicle may be an electric or hybrid vehicle. The vehicle may comprise at least one large electric motor. The large electric motor is here an electric motor which contributes to the movement of the vehicle. Such large electric motors can have a high regenerative potential, that is to say, contribute significantly to the energy recovery during braking.

A friction brake of a brake system is a brake that contributes to the deceleration of a vehicle by friction. The friction brake may be operated at least partially by means of an electromechanical actuator. The electromechanical actuator can be actuated by a control system and is, for example, a component of a brake-by-wire system. The friction brakes are hydraulically connected with the electromechanical actuators by means of a hydraulic assembly. The hydraulic assembly may be a simple hydraulic circuit, for example in those cases where each electromechanical actuator is connected to a wheel of the vehicle, respectively. The hydraulic device assembly may include and/or be a component of a multi-circuit brake system. In some embodiments, the hydraulic device assembly may be connected to the brake pedal, for example, via a master brake cylinder that is connected to the brake pedal.

A regenerative brake of a brake system is a brake that operates at least one electric motor that contributes to the movement of the vehicle as a generator. The regenerative brakes can be actuated by a control system and are, for example, components of a brake-by-wire system. In order to generate a braking action for the vehicle when braking, only regenerative brakes may be used, only friction brakes may be used, or the two sub-brake systems may be used in a freely selectable relationship in principle. The distribution of the braking action to these sub-brake systems can be associated, for example, with an expected deceleration, with driving conditions, with whether a brake assist, for example an ABS (antilock brake system) or an ESC (electronic stability control), should be used, and/or how effective the electric motor and the sub-brake system are in the vehicle.

In one embodiment, it is possible that the components of the invention are also used at least in braking systems which, instead of or in addition to regenerative brakes, have motor brakes, eddy current brakes or the like, as is the case in at least some trucks. With the involvement of these systems, it is also possible to reduce the share of the friction brakes during braking and to obtain a similar brake pedal feel for a particular deceleration.

The brake pedal characteristic is a function of the pressure in the hydraulic assembly in relation to the stroke of the electromechanical actuator. The brake pedal characteristic, and thus the so-called brake pedal feel, therefore corresponds to the pressure relationships in the hydraulic assemblies and/or to a "replica" of the pressure relationships in the hydraulic assemblies. In a simplified manner, the driver should be given a brake pedal feel as he would have if he were actuating a purely hydraulic brake (if necessary with a service brake system). For this purpose, a brake pedal characteristic curve for the brake system is stored in the vehicle, for example in the control system. The brake pedal characteristic curve may be stored, for example, as a function and/or as a quantity of support points, between which an interpolation is made. The brake pedal characteristic may resemble the "conventional" pV characteristic (pressure-volume characteristic) of a brake system. The brake pedal characteristic has a lost motion and stiffness coefficient. The idle stroke corresponds to the idle stroke that a purely hydraulic brake system would have before the sniffer hole (Schn ü ffelborhungen) was closed and no braking action occurred therein. The stiffness factor corresponds approximately to the gradient of the brake pedal characteristic curve at a predefined point, for example above a pressure in the range of approximately 10bar or in the case of a pressure measured in the master brake cylinder, or for example at a lower pressure in the hydraulic assembly (for example approximately 5 bar).

The brake pedal characteristic curve is applied to a brake pedal simulator. The brake pedal simulator may be implemented, for example, as a separate element and contain a spring, a mechanical resistance (e.g., a damping element), and/or another element. The brake pedal simulator may also be implemented as a component of a service brake system of a vehicle. The brake pedal therefore no longer acts directly and no longer exclusively on the hydraulic components of the brake system, but rather operates the brake system via a brake pedal simulator. Thus, the brake pedal feel may be substantially the same in a particular deceleration situation when the vehicle is decelerated purely by means of friction brakes, purely by means of regenerative brakes, or by means of a "hybrid" of these brakes. The brake pedal feel but should still follow the pressure relationships in the (hydraulic) friction brake or hydraulic device package; this is achieved by means of a brake pedal characteristic curve and a brake pedal simulator.

The method for modifying a brake pedal characteristic has the following steps:

-performing a measurement of a brake pedal characteristic curve by means of an electromechanical actuator after a predefined number of actuations of the brake system, wherein at least a part of the braking action is generated by means of the friction brake and the remaining part is generated by means of the regenerative brake;

-as an optional step: storing the measured brake pedal characteristic curve;

-replacing the brake pedal characteristic curve by the measured brake pedal characteristic curve.

Since the brake pedal characteristic is a function of the pressure in the hydraulic assembly as a function of the stroke of the electromechanical actuator, a brake pedal characteristic measurement, also referred to as "stiffness determination", is carried out in the actuator stroke and the hydraulic assembly by means of a sensor (or sensors). In braking systems where there is a hydraulic coupling between the electromechanical actuator and the brake pedal, a sensor (or sensors) in the brake pedal may also be used instead of, or in addition to, the sensor in the actuator stroke. In the measurement, the stroke of the electromechanical actuator or brake pedal and the pressure acting thereon in the hydraulic assembly are determined at predefined support points and/or continuously. To this end, at least part of the braking action is generated by means of a friction brake. The remainder of the braking action is generated by means of regenerative brakes. Thus, when stiffness determination is often performed, the energy efficiency is influenced in an unwanted manner, since no (re-) generated energy used in the friction brake is (re-) provided. On the other hand, it is significant that the stiffness determination is carried out more frequently in order to avoid large deviations between the actual and stored characteristic curve. In order to provide the best possible compromise between these divergent requirements, the measurement of the brake pedal characteristic curve is carried out by means of the electromechanical actuator only after a predefined number of actuations of the brake system.

Alternatively or additionally, further dynamic criteria can also be selected, for example brake wear and/or other criteria based on the current measurement and/or history of acceleration sensors, height measuring instruments, temperature measuring instruments. For example, the stiffness determination can take place more frequently in urban traffic or when driving uphill than, for example, when driving on a largely undisturbed highway. A predefined number of actuations of the brake system (or other criteria) can be known dynamically per se. For example, the number of maneuvers may be related to the type and/or life of the vehicle and/or to the brake configuration, e.g., relating to the size, number, etc. of linings (e.g., "asbestos free organics" NAO or otherwise), brake calipers, brake pistons. The predefined number of maneuvers can be reduced, for example, in stop-and-go traffic situations or uphill driving, and additional criteria can be increased and/or selected in highway driving.

After the measurement of the brake pedal characteristic curve has been carried out, the measured brake pedal characteristic curve can be stored in an optional step. For example, this measured brake pedal characteristic can be stored in the control system of the vehicle and therefore also used in brakes in which a regenerative brake is involved ("regenerative brake"). It may be expedient here that not every measured brake pedal characteristic curve is stored, for example if the measurement is inconsistent or not sufficiently complete. When, for example, a peak or a further deviation is measured which can lead back to EMV interference, the measurement can then be identified as inconsistent, for example. When only a small portion of the actuator stroke and/or too large dynamic effects are measured, the measurement may then be considered to be insufficiently complete, for example.

Finally, the brake pedal characteristic curves used in the brake systems to date are replaced by the measured brake pedal characteristic curves. "substitution" in many cases means that instead of a complete change of the brake pedal characteristic, the brake pedal characteristic can be adapted in real systems exactly in a plurality of small steps ("gradual" or "incremental" change). Strong deviations of the measured brake pedal characteristic can also be used at least several times as (negative) plausibility criteria; a strong deviation of the brake pedal characteristic curve used up to now may therefore require a removal of the measured brake pedal characteristic curve as unreliable. Other predefined criteria may also be applied to the measured brake pedal characteristic curve for replacement. These criteria may, for example, consider whether the deviation was captured by another mechanism. For example, a reduction in the braking action (fade) of the brake system (for example in steep uphill driving) can be compensated by a further (sub-) system of the vehicle, so that the brake pedal characteristic curve does not have to be adapted to this type of deviation. In the case of these criteria, for example, also: the deviation (possibly or actually) is caused by a change in the braking system, either short-term or long-term. The replacement may involve incremental adaptation in the lost motion and stiffness coefficients.

Thus, a brake pedal characteristic curve in the brake system which is close to reality is provided at most or frequently during the operating time of the vehicle by this method. At the same time, the number of unwanted measurements-and thus unwanted friction braking-is reduced; the energy efficiency of the vehicle can thereby be significantly improved. Furthermore, the load on the friction brake, and thus the wear and other losses of the friction brake, can be reduced thereby. Furthermore, the NVH effect (NVH: Noise, Vibration, Harshness, i.e. Noise, Vibration, roughness) may be reduced on the basis of deviating brake pedal characteristics. Therefore, so-called brake pedal stimulation (bremspiedal-Irritationen) can also be avoided. Such brake pedal stimuli may, for example, include a counter depression of the pedal (for example, in the event of an incorrect or insufficient adaptation of the brake pedal characteristic curve). Furthermore, it may be necessary to receive and provide a new brake pedal characteristic curve to the driver relatively quickly, for example after a return to the factory with a brake change, so that a sensible pedal feel is available relatively quickly and/or relatively often.

Other disadvantages can also be avoided by the illustrated method. Therefore, in particular in hybrid electric cross brake systems (hev-X), brake pedal characteristics deviating from reality, such as erroneously determined stiffness values, may lead to deceleration disturbances, for example in situations in which the driver is braking constantly and the generator is no longer able or should bring the required braking power, but the target pressure known in the hydraulic assembly cannot be achieved by the displaced volume. For example, in hybrid electric parallel brake systems (hev-II), an overpressure of the sniffing opening in the hydraulic cylinder may also occur when the brake pedal characteristic curve is determined to be insufficiently accurate, which may lead, for example, to hydraulic short circuits, NVH problems and/or increased component loading — as, for example, the loading of the hydraulic pump increases-.

In one embodiment, the method has the further step of: -incrementing a counter containing the number of performed braking processes when the vehicle is in motion and when a braking action is generated for the vehicle, wherein the highest part of the braking action is generated by means of the friction brake.

For example, a counter may be selected as a dynamic criterion that indicates whether a measurement of the brake pedal characteristic should be performed. Therefore, when braking is performed in which measurement of the brake pedal characteristic curve cannot be performed, the counter may then be incremented. This may be the case, for example, if the friction brake is not or not sufficiently involved in braking, or if the measurement of the brake pedal characteristic curve is not performed with sufficient quality, for example if the measurement is not uniform or not sufficiently complete. This can be the case, for example, when an intervention is set (for example, by a brake assistance system), when driving excessively dynamically and/or when braking excessively dynamically. The state of the counter (counter value) may, for example, reflect a predefined number of actuations of the brake system — or a function thereof — after which a measurement of the brake pedal characteristic curve is carried out. The number of times braking should be performed without measuring the brake pedal characteristic can be vehicle-specific and/or, for example, current and/or previous traffic conditions can be taken into account. The initial counter value can be known, for example, prior to the delivery of the vehicle or a series of vehicles and/or a plurality of series of vehicles for the vehicle. After exceeding a predefined counter value, a forced measurement can be carried out by means of the friction brake, for example by limiting the generator torque of the regenerative brake. As long as the brake pedal characteristic can be measured and used, the counter stores back and stores the brake pedal characteristic for the subsequent regenerative braking.

In one embodiment, the method has the further step of:

-setting the counter to zero when the vehicle (10) is moving and when braking action is generated for the vehicle (10), wherein the entire braking action is generated by means of the friction brake (20).

If the entire braking action is produced by means of the friction brake and a successful measurement can take place, the counter is set to zero (reset). If a successful measurement of the brake pedal characteristic curve, for example, only by means of the friction brake, is possible when braking is carried out without generator torque being available, the counter can also be reset. This may lead to a further improvement in the energy efficiency of the vehicle.

In one embodiment, the method has the following additional steps:

-storing a counter in a non-volatile memory in case of switching off the vehicle; and

reading in the counter from the non-volatile memory when the vehicle is switched on.

Advantageously, the standard "current state of the counter" can thus be reused or retained by restarting the vehicle (gerettet).

In one embodiment, the measurement of the brake pedal characteristic is carried out by means of an electromechanical actuator if the vehicle is at a standstill. In one embodiment, the measurement of the brake pedal characteristic can also be carried out independently of a predefined number of actuations of the brake system, and for example independently of the state of a counter.

In this case, the vehicle is "at rest" when the vehicle is stopped or parked and stopped. The driver may have left the vehicle here. For example (if necessary additionally) it is possible to check: whether a mechanical fuse, for example a handbrake and/or the P-point of the automatic transmission, is inserted. In the measurement in the stationary state, advantageously no actuation of the brake pedal is required; in particular, the driver does not have to be required to operate the brake pedal.

In this embodiment, it is advantageous if the brake pedal characteristic curve and in particular the stiffness of the brake system can be determined with high quality. This is facilitated, for example, in the following respects:

when the vehicle is in a stationary state, no lateral acceleration occurs. The lateral acceleration may affect the quality of the measurement based on dynamic effects.

When the vehicle is in a stationary state, there is no disk impact of the brake disk, so that a deviation in the measurement accuracy also does not occur as a result.

Since the actuator can be moved virtually statically, no dynamic effects of the measured pressure in the hydraulic device assembly occur, for example due to the mass of the hydraulic liquid.

Furthermore, different influences on the vehicle may be given when the vehicle is moving, which influences may falsify the measurement of the brake pedal characteristic curve. For example, it can be expected that short-term influences, such as a reduction in temperature or braking effect, are not or only slightly added to the stiffness coefficient. For this reason, long-term effects should be added to the measurement more accurately and/or at an earlier time. It is possible that this is the case in the higher ranges in static or nearly static measurements. The measurement can therefore also be advantageous when the vehicle is at a standstill, since the necessity of performing the measurement during driving is less necessary or can even be eliminated, for example, in more frequent standstill states. In certain brake architectures, there may be better frame conditions for the measurements in the case of measurements in the stationary state. Thus, for example, in the case of a hybrid electric parallel brake system (hev-II), it may be necessary for the sniffing hole to be closed, for the determination of the lost motion at the start of braking to be terminated successfully, for no volume reduction at the front axle and/or no intervention in regulation to occur; see, for example, the following further explanation (in the description of the figures). These frame conditions can be satisfied exactly in the static attitude of the vehicle.

In one embodiment, a complete pedal characteristic with hysteresis may be received. Hysteresis can occur in many real hydraulic braking systems. The formation of this phenomenon therefore constitutes another component for a realistic pedal feel.

In one embodiment, the measurement of the brake pedal characteristic takes into account systematic deviations of the measurement when the brake pedal characteristic is measured when the vehicle is at a standstill relative to the measurement when the vehicle is moving. The differences in the case of these different measurements are explained in detail above.

In one embodiment, the method has the following additional steps:

-determining a difference between the measured brake pedal characteristic and the stored brake pedal characteristic;

-varying the predefined number of brake system actuations in relation to the difference.

The difference between the measured brake pedal characteristic and the stored brake pedal characteristic can be determined, for example, from a plurality of measurement points and/or by comparing the idle stroke and the stiffness coefficient of the two brake pedal characteristics. The difference value may also be analyzed based on a list of measurements. The column of measurements may also take into account the time trend. The predefined number of actuations of the brake system is changed on the basis of and/or in relation to the evaluation of the difference or differences. Thus, large differences and/or rapid growth of differences may result in a reduced number of operating brake systems. Here, the threshold values for these changes may be confirmed specifically for the vehicle and/or hardware. A tolerance range may also be provided in which the difference does not cause a change. When this tolerance range is exceeded, the distinction between real and stored characteristic curve is so great that there is an increased risk of damage to hardware and/or NVH problems, which may then lead to a reduction in the number of brake systems operated, so that the measurement of the brake pedal characteristic curve is again carried out or forced as quickly as possible.

In one embodiment, long term changes to parameters of the brake system are considered more than short term changes. The parameters of the brake system can be, for example, the thickness of the brake lining, the material of the brake lining, the amount of brake fluid in the hydraulic assembly and/or the installation (for example, the installation position) of the hydraulic device (Verbauung).

Long-term changes in the brake system can be caused, for example, by vehicle tolerances from the end of the production line (Bandende), aging of the brake system, wear and tear. Short-term changes can be caused, for example, by temperature, reduced braking action, etc. Short term changes are often compensated for by additional systems of the vehicle. Too rapid and/or too large a change in the brake pedal characteristic can lead to an increased risk of damage to the hardware and/or NVH problems. More accounting for long-term changes may be achieved, for example, by comparing a series of measurements and/or by weighting the measurements more heavily in a quiescent state.

Another aspect relates to a control device of a vehicle, which is configured to perform a method as described above and/or in the following.

Another aspect relates to a vehicle having the control apparatus described above.

Another aspect relates to the use of a method for determining a brake pedal characteristic of a vehicle as described above and/or in the following.

Another aspect relates to a program element which, when implemented on a control device as described above, starts to perform a method as described above.

Another aspect relates to a computer readable medium having stored thereon a program element as described above.

Drawings

Further measures which improve the invention are subsequently shown in detail together with a description of preferred embodiments of the invention on the basis of the drawing.

Examples

Wherein:

FIG. 1 shows a schematic view of a vehicle according to an embodiment;

FIG. 2 shows a schematic view of a brake pedal characteristic according to an embodiment;

FIG. 3 shows a schematic view of an apparatus for stiffness determination, according to an embodiment;

FIG. 4 shows a schematic view of a measurement of a brake pedal characteristic according to one embodiment;

FIG. 5 shows a schematic view of a method according to an embodiment;

FIG. 6 shows a schematic view of a further method according to an embodiment.

Detailed Description

Fig. 1 shows a schematic view of a vehicle 10 according to an embodiment. The vehicle has a controller 35 of the brake system 25. The control unit 35 is actuated by means of the brake pedal 12 for actuating the brake system 25, wherein the brake system 25 is provided for generating a braking action for the vehicle 10. The brake pedal 12 has a brake pedal simulator 14 to which a brake pedal characteristic 30 (see fig. 2) is applied. The brake system 25 has four friction brakes 20, which are hydraulically connected to electromechanical actuators 21 by means of a respective hydraulic assembly 22, here illustrated schematically as brake lines. Furthermore, the brake system 25 has a regenerative brake 15, which is likewise actuated by the control unit 35. The control unit 35 has a memory 37, in which, for example, the brake pedal characteristic 30 can be stored. In order to generate a braking action for the vehicle 10 during braking, only the regenerative brakes 15 can be used, only the friction brakes 20 can be used, or the two

partial braking systems

15 and 20 can be used in a freely selectable relationship in principle.

Fig. 2 shows a schematic illustration of a brake pedal characteristic 30, 31 according to an embodiment. The brake pedal characteristic 30 is a function of the pressure in the hydraulic assembly 22 as a function of the stroke of the electromechanical actuator 21 (see fig. 1). The pressure p in the hydraulic assembly 22 is given on the y-axis in relation to the stroke s of the electromechanical actuator 21 on the x-axis. The pressure p can, depending on the embodiment of the brake system, additionally or alternatively take into account the pressure of a main cylinder (master cylinder) which is actuated and/or mechanically coupled by the brake pedal 12. In the illustrated fig. 2, the first brake pedal characteristic 30 is opposite the measured brake pedal characteristic 31. In this case, it is clear that the change in the idle stroke s0 and the stiffness f can be recognized between the two brake pedal characteristics. In this case, the measurement of the brake pedal

characteristic curves

30, 31 may require a plurality of individual measurements — and thus braking-.

Fig. 3 shows a schematic view of an apparatus 50 for stiffness determination according to an embodiment. The pressure p of the hydraulic assembly 22 (see fig. 1) and the stroke s of the electromechanical actuator 21 are provided as input data on the input 51. The pressure p and the stroke s (see fig. 2) are used to (re-) determine the stiffness f in the assembly 52. The stroke s and stiffness f are used to estimate the lost motion s 0. The lost motion s0 may be approximately 0 to 6 mm. The idle stroke s0 is used together with the brake pedal characteristic 30 to determine the target pressure p. The brake pedal characteristic 30 is additionally added to the determination of the stiffness f, for example, in order to eliminate unreliable measurements. The target pressure p and the stiffness f are used to determine a virtual target pressure pv. The virtual target pressure pv and the pressure p are communicated to the transition logic 54. The transition logic 54 causes the transition of the hydraulic brake to regenerative braking and back to be barely or imperceptible to the driver. The transition logic 54 can furthermore take into account the signal "hybrid mode" b, by means of which: braking is to be assisted purely hydraulically (that is to say only by means of the friction brakes 20) or else by a generator (by means of the regenerative brake 15). Further, the transition logic 54 may take into account brake pedal movement 56, by which dynamic aspects of the movement of the brake pedal 12 are incorporated into the controller. As a result, the transition logic 54 provides the target deceleration td. This target deceleration is provided on the output 59 of the device 50 together with the virtual target pressure pv.

FIG. 4 is a diagram according to an embodimentThe exemplary embodiment shows a schematic representation 60 of a measurement process of the brake pedal characteristic 30. Here, the architecture of the brake system is used, in which the pressure of the main cylinder (master cylinder) is taken into account, which is actuated by the brake pedal 12 and/or is mechanically coupled. In this illustration 60, a time t is applied on the x-axis, during which the brake pedal 12 (see fig. 1) is actuated and during which a measurement is carried out. The stroke s of the brake pedal 12 is shown as an upper dashed curve s and the speed v of the brake pedal 12 is shown as a lower curve v. In this embodiment, the speed v of the brake pedal 12 is not allowed to exceed the maximum speed v_maxSo that dynamic effects (e.g. brake fluid) do not render the measurement unusable. The measurement 62 occurs between a start time ts and an end time te. The determination of the idle stroke s0 (see fig. 3) must be successfully terminated at the start time ts. Before the start time ts, the sniffer hole has to be closed at time t 0. No volume reduction (volumenverbendan) is required (e.g., on the anterior bridge) during measurement 62. Shown as a volume reduction is a process in which the volume displaced by the pedal actuation of the brake pedal 12 is not pushed into the wheel brake caliper, but rather is stored at another location and thus prevents the build-up of hydraulic braking torque in order to fully use the provided generator torque in this way. Furthermore, no intervention in the regulation (controller mediation, for example by the ABS) is allowed to take place.

FIG. 5 illustrates a schematic view of a method in a flow chart diagram 80 according to an embodiment. In step 81, a measurement of the brake pedal characteristic 30 (see fig. 2) is carried out. The measurement of the brake pedal characteristic 30 is carried out, for example, after a predefined number of actuations of the brake system 25 (and/or further dynamically known criteria). The measurement takes place by means of an electromechanical actuator 21. In some embodiments, an architecture of the brake system is used in which the pressure of a main cylinder (master cylinder) is alternatively or additionally taken into account, which is actuated by the brake pedal 12 and/or mechanically coupled. In the measurement, at least part of the braking action is generated by means of the friction brake 20. In step 82, the measured brake pedal characteristic 31 is stored in a memory. For example, the brake pedal characteristic 31 may be stored in the control system of the vehicle and may also be used in the braking in which regenerative braking takes place. It may be expedient here not to store each measured brake pedal characteristic curve, for example if the measurements are inconsistent or incomplete. In step 83, the brake pedal characteristic curve used in the brake system up to now is replaced by the measured brake pedal characteristic curve. In this case, predefined criteria for the replacement can be applied to the measured brake pedal characteristic curve. For example, a strong deviation of the brake pedal characteristic curve used up to now can be removed as an implausible deviation.

FIG. 6 illustrates a schematic view of another method in a flow chart 100 according to an embodiment. The method starts in step 101. In step 102 it is checked whether the vehicle 10 (see fig. 1) is stationary or moving. If the vehicle 10 is stationary, then in step 103 a measurement in a stationary state is performed, as explained in detail above. In this case, for example, electromechanical actuators can be actuated in order to thus carry out braking in the stationary state and to carry out and optionally store measurements. In one embodiment, the measurement of the brake pedal characteristic curve can be carried out in the stationary state, even independently of the actuation of the brake system by a predefined number, and for example also independently of the state of a counter which counts the number of non-measured brakes. In this measurement situation in a stationary state, the driver may be outside the vehicle 10. In step 104 it is checked: whether the measurement meets certain criteria (see above) or whether the measurement has to be removed. If the measurement is determined to be successful, the brake pedal characteristic curve used in the brake system up to now is replaced by the measured brake pedal characteristic curve in step 105 and a counter is set to zero. Next, the method may be terminated in step 114 or started from a new one in step 101.

If the vehicle 10 is not stationary, then in step 106 it is checked: whether a restart of the vehicle 10 has occurred. When so, a counter is read in step 107. Next, in step 108 it is checked: whether the counter exceeds a predefined value. If so, then in step 109 the engagement of the friction brake 20 (see fig. 1) is forced in the next braking and/or the next braking is performed solely by means of the friction brake 20. The brake pedal characteristic curve used up to now in the brake system is then replaced in step 112 by the measured brake pedal characteristic curve and the counter is set to zero. When it is established in step 108 that the counter has not exceeded the predefined value, then "normal" braking is performed in step 110. If a successful measurement of the brake pedal characteristic has taken place during this braking in step 110, the brake pedal characteristic used up to now in the brake system is replaced by the measured brake pedal characteristic in step 112, or is adapted in a plurality of small steps ("gentle" or "incremental") and a counter is set to zero. Otherwise, the counter is incremented in step 113. Next, the method may be terminated in step 114 or started from a new one in step 101.

Claims

1. Method for modifying a brake pedal characteristic curve (30) for a brake pedal (12) for actuating a brake system (25) of a vehicle (10), wherein the brake system (25) is provided for generating a braking action for the vehicle (10),

the brake system (25) has:

a friction brake (20) hydraulically connected to an electromechanical actuator (21) by means of a hydraulic assembly (22); and

a regenerative brake (15),

wherein the brake pedal characteristic (30) is a function of the pressure in the hydraulic assembly (22) in relation to the stroke of the electromechanical actuator (21) and has a lost motion and a stiffness coefficient,

wherein the method has the following steps:

-performing a measurement of the brake pedal characteristic (30) by means of the electromechanical actuator (21) after a predefined number of actuations of the brake system (25), wherein at least a part of the braking action is generated by means of the friction brake (20) and the remaining part is generated by means of the regenerative brake (15);

-replacing the brake pedal characteristic (30) by the measured brake pedal characteristic (31).

2. The method according to claim 1, having the further step of:

-storing said measured brake pedal characteristic (31).

3. The method according to claim 1 or 2, having the further step of:

-incrementing a counter when the vehicle (10) is in motion and when a braking action is generated for the vehicle (10), the counter containing the number of braking processes performed,

wherein at most a part of the braking action is generated by means of the friction brake (20).

4. The method according to claim 1 or 2, having the further step of:

-setting the counter to zero when the vehicle (10) is in motion and when a braking action is generated for the vehicle (10),

wherein the entire braking action is generated by means of the friction brake (20).

5. The method according to any of the preceding claims, having the further step of:

-storing the counter in a non-volatile memory (37) when the vehicle (10) is switched off; and

-reading in the counter out of the non-volatile memory (37) when the vehicle (10) is switched on.

6. The method according to claim 1 or 2,

wherein the measurement of the brake pedal characteristic curve (30) is carried out by means of the electromechanical actuator (21) when the vehicle (10) is in a stationary state.

7. The method of claim 6, wherein the first and second light sources are selected from the group consisting of,

wherein the measurement of the brake pedal characteristic curve (30) takes into account systematic deviations of the measurement when the brake pedal characteristic curve (30) is measured when the vehicle (10) is in a stationary state relative to the movement of the vehicle (10).

8. The method according to any one of the preceding claims,

with the additional steps of: wherein the brake pedal characteristic curve (30) has a hysteresis.

9. The method according to any one of the preceding claims,

-determining a difference (33) between the measured brake pedal characteristic (30) and the stored brake pedal characteristic (31);

-varying a predefined number of actuations of the braking system as a function of the difference (33).

10. The method according to any one of the preceding claims,

wherein long-term changes of parameters of the brake system are taken into account more than short-term changes.

11. Control device (35) of a vehicle (10), which is provided for carrying out the method according to any one of the preceding claims.

12. Vehicle (10) having a control device (35) according to claim 11.

13. The method according to one of claims 1 to 10 for determining the application of a brake pedal characteristic curve (30) of a vehicle (10).

14. Program element, which, when it is implemented on a control device (35) according to claim 11, the control device (35) starts to perform the method according to any one of claims 1 to 10.

15. Computer readable medium on which a program element according to claim 14 is stored.