DE102019212967A1 - Method for generating a predetermined hydraulic pressure and braking system - Google Patents

Abstract

The invention relates to a method for generating a predetermined hydraulic pressure by means of a pressure generator in a braking system for a motor vehicle, wherein a characteristic curve is first calibrated and then used to generate pressure. The invention also relates to an associated brake system.

Description

The invention relates to a method for generating a predetermined hydraulic pressure by means of a pressure generator in a braking system for a motor vehicle. The invention also relates to an associated brake system.

Brake systems are typically used in automobiles to achieve deceleration. Brake systems are increasingly being designed in such a way that a pressure is no longer, or at least no longer completely, generated manually in some or also typical operating situations, but rather a pressure is provided by means of an electrically operated pressure generator.

It is an object of the invention to provide a method for generating a predetermined hydraulic pressure by means of a pressure generator in a braking system for a motor vehicle, which method is designed as an alternative or better than known designs. It is also an object of the invention to provide a brake system for carrying out such a method.

According to the invention, this is achieved by a method and a braking system in accordance with the respective main claims. Advantageous refinements can be found in the respective subclaims, for example. The content of the claims is made part of the description by express reference.

• - Bereitstellen einer Kennlinie, welche einen Zusammenhang zwischen einem Parameter des Druckerzeugers und dem Druck angibt,
• - Erfassen, dass bei einem Kalibrierwert des Parameters ein Kalibrierdruck erzeugt wird,
• - Kalibrieren der Kennlinie mittels des Kalibrierwerts und des Kalibrierdrucks,
• - Ermitteln eines Arbeitswerts des Parameters, welcher zum vorgegebenen Druck korrespondiert, anhand der kalibrierten Kennlinie und
• - Anlegen des Arbeitswerts des Parameters an den Druckerzeuger.

The invention relates to a method for generating a predetermined hydraulic pressure by means of a pressure generator in a braking system for a motor vehicle. The procedure consists of the following steps:

• - Provision of a characteristic curve which indicates a relationship between a parameter of the pressure generator and the pressure,
• - Detecting that a calibration pressure is generated for a calibration value of the parameter,
• - Calibrating the characteristic using the calibration value and the calibration pressure,
• - Determination of a working value of the parameter, which corresponds to the predetermined pressure, based on the calibrated characteristic and
• - Application of the working value of the parameter to the pressure generator.

By means of the method according to the invention, a characteristic curve can be used which indicates the aforementioned relationship between parameter and pressure and thus enables a defined function of the pressure generator apart from a required calibration.

Through the calibration, a current state of the pressure generator or a brake system is determined promptly and taken into account. It was recognized that such a characteristic curve describes the pressure generator in an advantageous manner, but that influences such as aging, leakage, changes in the composition of a fluid or the presence of air are to be expected, which would prevent reliable operation if only a characteristic curve were used. This can be taken into account by the calibration in the manner described, so that reliable operation of the pressure generator or reliable generation of hydraulic pressure at a desired level can be achieved in a simple manner.

The characteristic curve can in particular be stored in an electronic control device. It can be used for the life of a braking system or updated from time to time. The parameter can be, for example, a voltage or a current or also a power consumption of the pressure generator, there typically being a relationship such that a higher pressure is also generated with a higher parameter.

The calibration can in particular be carried out in an electronic control device.

In particular, a linear actuator or a pump can be used as the pressure generator. A linear actuator is typically understood to mean a device with a displaceable piston, wherein the piston can push a previously charged volume of fluid out of a cylinder and this volume can then be used to actuate brakes. This corresponds to a hydrostatic design. A pump is typically designed for the continuous delivery of fluid and can also build up a pressure in this way.

The parameter can, for example, be a volume displaced in the pressure generator. For example, the more air there is in a braking system, the more volume it may be necessary to displace. Precisely this can be taken into account in a simple and up-to-date manner via the calibration.

The parameter can also be a motor torque or a current intensity of the pressure generator. These are typical operating variables of a pressure generator, which is typically driven by an electric motor, with a higher motor torque or a higher current, a higher pressure is generated.

• - Anlegen des Kalibrierwerts des Parameters an den Druckerzeuger,
• - Messen des Kalibrierdrucks solange der Parameter anliegt.

According to an advantageous embodiment, the acquisition step can be carried out as follows:

• - Applying the calibration value of the parameter to the pressure generator,
• - Measure the calibration pressure as long as the parameter is present.

This allows a simple determination of the relationship between the calibration value and the calibration pressure at any point in time at which such a calibration is to take place.

The steps of applying the calibration value and measuring the calibration pressure can be carried out in particular with closed wheel valves, inlet valves and / or connecting valves between pressure generators and a master brake cylinder and / or a simulator. In particular, the valves can be switched in such a way that the pressure can be measured as accurately as possible in the respective configuration.

• - Schalten eines Ventils in einen Schaltzustand durch Anwenden eines Schaltstroms als Betätigungsstrom, wobei das Ventil mittels des Betätigungsstroms steuerbar ist und wobei an dem Ventil der Kalibrierdruck anliegt,
• - Verändern des Betätigungsstroms,
• - Erkennen einer Zustandsänderung des Ventils und ansprechend darauf Ermitteln eines Betätigungsstroms, bei welchem das Ventil seinen Zustand geändert hat, als Änderungsstrom,
• - Ermitteln des Kalibrierdrucks in Abhängigkeit von dem Änderungsstrom.

The calibration pressure can be measured in particular by the following steps:

• Switching a valve into a switching state by applying a switching current as the actuating current, the valve being controllable by means of the actuating current and the calibration pressure being applied to the valve,
• - changing the actuation current,
• - Detecting a change in state of the valve and, in response to this, determining an actuating current at which the valve has changed its state, as a change current,
• - Determining the calibration pressure as a function of the change current.

As a result, a valve such as an inlet valve, which can be controlled by means of an actuating current, can be used to determine the calibration pressure.

The switching state can in particular be a closed state or an open state. The switching current is typically of a size that ensures that the respective switching state is adopted.

The valve can in particular be a wheel valve and / or an inlet valve of the brake system. Such an inlet valve is typically a valve with which pressure-generating devices such as master brake cylinders, pressure generators or linear actuators are connected to a respective wheel brake.

According to one embodiment, the switching state is a closed state and the actuation current is reduced when it is changed. This means that the valve is initially closed and is opened by the hydraulic pressure applied when the actuating current is no longer sufficient to maintain the closed state.

According to one embodiment, the switching state is an open state and the actuation current is increased when it is changed. This means that the valve is initially open and will close when the actuation current is sufficient to close it.

The procedure described so far is based on a normally open valve, as is typically the case with an inlet valve, which is typically designed to enable actuation in a hydraulic fallback level. If, on the other hand, a normally closed valve is used, the specified change in the current can also be reversed in order to carry out the method. The actuating current can therefore be increased starting from a closed valve or the actuating current can be reduced starting from an open valve.

The valve can in particular be assigned to a wheel brake. The wheel brake can also be assigned an outlet valve. Such an outlet valve can typically produce a switchable connection between a wheel brake and a pressure sink such as a brake fluid reservoir. While the method is being carried out, in which the calibration pressure is measured by means of a valve, or while the actuating current is being changed, the outlet valve is typically open.

The valve and the outlet valve are typically each directly connected to the wheel brake. This corresponds to a simple implementation.

The outlet valve is preferably connected to a pressure sink or a brake fluid container opposite the wheel brake. This allows brake fluid or pressure to be discharged directly from the wheel brake. As a result, a pressure-free reference is achieved on the side of the valve opposite the pressure applied, with which the pressure determination is carried out.

The actuation current can in particular be changed uniformly and / or continuously. This allows the process to be carried out in a simple manner.

The opening of the valve is preferably recognized on the basis of a movement of a component of the pressure generator. This is based on the knowledge that when a valve is opened, pressure can flow out immediately and thus a pressure-building component typically no longer remains in its state immediately before the valve was opened. For example, this can lead to a jerky movement in a piston. This can be detected accordingly and thus the opening of the valve can be recognized.

The pressure can in particular be generated by a pressure generator designed as a linear actuator, the change in state of the valve preferably being able to be recognized on the basis of a movement of a piston of the linear actuator. This corresponds to a procedure in a typical braking system which has a linear actuator for generating pressure, which can also be used accordingly in the context of the method. A movement of the piston can be detected, for example, by means of a piston position sensor.

The pressure can be determined in particular as a function of the change in current on the basis of a stored characteristic opening curve of the valve. Such opening characteristics typically indicate a relationship between pressure, actuation current and the state of a respective valve. They are known very precisely and can be stored in control devices.

The change in state of the valve is preferably recognized during the change in the actuation current. Typically, the actuation current is increased or decreased and this change in state is recognized at a certain actuation current, whereupon an evaluation can be made to determine the calibration pressure.

• - Erzeugen eines Ausgangsdrucks in einem Teil des Bremssystems, welcher von dem Druckerzeuger durch ein Zuschaltventil getrennt ist,
• - Schließen des Zuschaltventils,
• - Messen des Ausgangsdrucks,
• - Variieren des Parameters,
• - Erkennen einer Öffnung des Zuschaltventils und ansprechend darauf Setzen des momentanen Werts des Parameters als Kalibrierparameter und Setzen des Ausgangsdrucks als Kalibrierdruck.

According to one embodiment, the acquisition step can be carried out, for example, by the following steps:

• - Generating an output pressure in a part of the brake system, which is separated from the pressure generator by a connecting valve,
• - closing the sequence valve,
• - measuring the outlet pressure,
• - Varying the parameter,
• - Detecting an opening of the connecting valve and, in response to this, setting the current value of the parameter as the calibration parameter and setting the output pressure as the calibration pressure.

As a result, a typical property of connecting valves can be used, such connecting valves typically being used to connect or disconnect pressure generators such as linear actuators or pumps in brake systems. The relevant property is that they open even in a closed state in the event that a higher pressure is applied on the side of the pressure generator than on the opposite side. In this way, a known pressure can be locked in and it can be checked at which parameter such a pressure is achieved. As a result, a pressure sensor present, for example, in another part of the brake system can be used indirectly to determine the calibration pressure.

The parameter can in particular be varied in such a way that the pressure is increased. For example, a voltage or a current can be increased.

The outlet pressure can in particular be measured by means of a pressure sensor. As mentioned, this can, for example, also be located away from the pressure generator, in which case it can be connected directly to a master brake cylinder or a simulator, for example.

The output pressure can be generated, for example, by means of a manually operated master brake cylinder. For example, a driver can press a brake pedal and thereby generate the output pressure, which can then be used as just described. However, other possibilities for generating the output pressure are also conceivable, in particular the output pressure can also be generated automatically or by a further pressure generator.

An opening of the valve or isolating valve can in particular be recognized on the basis of a movement of part of the pressure generator or of a piston of the pressure generator. This is based on the knowledge that a pressure can typically be built up to a certain degree at which, when the valves are closed, no further movement of a component such as a piston is possible. If a respective valve is opened and thus a reduction or further distribution of the pressure is possible, the corresponding component moves.

According to one embodiment, the calibration pressure can be measured by means of a pressure sensor. Such a pressure sensor can, for example, be connected directly to the pressure generator or separately via only one connecting valve.

The acquisition and calibration steps can be repeated, for example, at predetermined time intervals and / or under predetermined conditions. Such a condition can be, for example, a vehicle start, a visit to the workshop or a recognized malfunction of the braking system. This enables the method to be carried out in such a way that a meaningful current calibration is available in all or at least typical operating situations.

According to a preferred embodiment, the work value is approached from an initial value with a superimposed oscillation. As a result, hysteresis effects that occur with typical pressure generators can be compensated so that more reliable operation is possible.

The invention also relates to a braking system for a motor vehicle. The brake system has at least one pressure generator and a number of valves. In addition, the brake system has a control device which is configured to carry out a method according to the invention. With regard to the method according to the invention, all embodiments and variants described herein can be used.

The invention further relates to a non-volatile computer-readable storage medium, on which program code is stored, which, when executed, a processor carries out a method according to the invention. With regard to the method according to the invention, all embodiments and variants described herein can be used.

• 1: ein Bremssystem,
• 2: eine Schaltung mit einem hydraulischen Kurzschluss,
• 3: ein Phasenmodell,
• 4: ein weiteres Phasenmodell,
• 5: einen Satz von Öffnungskennlinien,
• 6: ein weiteres Phasenmodell,
• 7: einen Zusammenhang zwischen Druck und Motormoment, und
• 8: einen weiteren Zusammenhang zwischen Druck und Motormoment.

The person skilled in the art will learn further features and advantages from the exemplary embodiments described below with reference to the accompanying drawings. Show:

• 1 : a braking system,
• 2 : a circuit with a hydraulic short circuit,
• 3rd : a phase model,
• 4th : another phase model,
• 5 : a set of opening curves,
• 6th : another phase model,
• 7th : a relationship between pressure and engine torque, and
• 8th : another relationship between pressure and engine torque.

1 shows a braking system 10 according to an embodiment of the invention, by means of which a method according to an embodiment of the invention can be carried out.

The braking system 10 has a master cylinder 20th on. In this there is a brake piston 24 , which by means of a brake pedal 22nd can be operated.

The braking system 10 assigns a simulator 30th on, which via a simulator valve SV with the master cylinder 20th connected is.

The braking system 10 has a linear actuator 40 on, in which there is a piston 42 moved, which in turn by a motor 44 is driven, whereby the motor is also marked with M.

The braking system 10 has a first inlet valve E1 , a second inlet valve E2 , a third inlet valve E3 and a fourth inlet valve E4 on. These establish a connection between the pressure-generating components of the master brake cylinder already described 20th and linear actuator 40 to the respective wheel brakes B1 , B2 , B3 , B4 represent.

The braking system 10 has a brake fluid reservoir 50 on which exhaust valves A1 , A2 , A3 , A4 are connected, each outlet valve A being assigned to a respective inlet valve E. A respective wheel brake B is actuated and controlled by means of an outlet valve A and an inlet valve E.

The first inlet valve E1 and the second inlet valve E2 together form a first brake circuit, which has an isolating valve TV with the master cylinder 20th as well as the simulator valve SV connected is. The second inlet valve E3 and the fourth inlet valve E4 together form a second brake circuit, which via a connecting valve ZV with the linear actuator 40 connected is. The two brake circuits are via a circuit separation valve as shown KTV connected with each other. The linear actuator 40 is via a check valve 46 with the brake fluid reservoir 50 connected so that brake fluid can be sucked in. Also the master cylinder 20th is for replenishing with the brake fluid reservoir 50 connected.

The braking system 10 has a first pressure sensor 12th which as shown on the master cylinder 20th and on the simulator valve SV connected. This first pressure sensor 12th can thus create a pressure in this area of the braking system 10 measure up. The braking system 10 also has a second pressure sensor 14th which as shown on the third inlet valve E3 and on the fourth inlet valve E4 connected. This second pressure sensor 14th can thus measure a pressure in this area of the brake system.

The linear actuator 40 can in particular be used to ensure that pressure is generated for braking in normal braking operation. For this purpose, for example, the isolating valve TV be closed and the simulator valve SV can be opened. If a driver then steps on the brake pedal 22nd , the brake piston moves 24 To the right. However, the resulting pressure is not directed to the inlet valves E, but rather is via the open simulator valve SV directly on the simulator 30th directed. The corresponding movement of the brake piston 24 is detected, with this movement indicating the driver's braking request. The control device 60 then activates the motor 44 such that in the linear actuator 40 a corresponding pressure is generated. This is in the control device 60 a suitable characteristic is stored, which indicates a relationship between a current to be applied and a pressure generated in the process. However, this characteristic curve is only valid up to a calibration, ie the current state of the brake system in each case 10 which can be changed compared to an original state, for example due to wear, leakage or air entry, must first be determined before the characteristic curve can be used meaningfully. It will be described below how such a calibration can be done.

In particular, the case is considered that, for example, the second pressure sensor 14th fails and a reliable pressure control should still be possible. For example, the procedures described below can, however, also be used if an alternative to direct pressure regulation is to be found or if the second pressure sensor 14th does not exist at all, whereby, for example, the execution of the braking system 10 can be simplified.

In advance, using 2 a hydraulic short-circuit explained. Here are the fourth inlet valve E4 , the fourth exhaust valve A4 , the fourth wheel brake connected to it B4 as well as the second pressure sensor 14th shown.

As in 2 can be seen, the fourth exhaust valve is located A4 present in an open state. This creates a direct hydraulic connection between the fourth wheel brake B4 and the brake fluid reservoir already mentioned above 50 produced. The fourth wheel brake B4 is thereby placed in a defined manner on a pressureless state, which in turn is a pressureless reference for the right side of the fourth inlet valve E4 represents. The pressure on the left side of the fourth inlet valve E4 can thus be regarded as the pressure that is passed through the fourth inlet valve E4 is applied. This pressure can, for example, by means of the second pressure sensor 14th be measured.

The inlet valves or the fourth inlet valve shown here can in particular be operated analogously. A volume flow through the inlet valve E can be better regulated by the already described pressure reference of zero.

In order to now carry out a calibration, the following procedure can be used, for example.

First is by depressing the brake pedal 22nd a pressure built up. The pressure is measured by the first pressure sensor 12th measured. Then the isolation valve TV and / or the circuit isolation valve KTV closed to this known pressure in the lower part of the braking system 10 imprison.

With the sequence valve closed ZV a motor movement in the direction of pressure build-up is then started, whereby it is known that the sequence valve ZV will open when in the linear actuator 40 the imprisoned pressure has been built up. When the sequence valve ZV is open, the motor stops 44 the position against the pressure rise. This can be detected accordingly. Using the procedure just described, a relationship between a parameter of the motor can thus be established 44 , for example, a motor current, and a generated pressure. The parameter at the moment the sequence valve opens ZV is referred to as the calibration value of the parameter. The pressure generated in the process, which was measured and locked in as described, is referred to as the calibration pressure. Calibration value and calibration pressure can be stored in the control device for calibrating the characteristic curve already mentioned above 60 is saved. In this way, influences that change over time, such as aging or air entry, can be taken into account, and a currently calibrated characteristic curve is always used.

The initial pressure build-up via the brake pedal 22nd has the advantage that a clearance has already been overcome.

Based on an exemplary pressure-volume characteristic, the additional calibration can also be used in the event of a pressure build-up by the linear actuator 40 a clearance can be overcome and an operating point can be defined in the characteristic.

Typically one space is the linear actuator 40 stiff, where volume, motor torque, motor current and / or pressure are known.

A possible process sequence is based on 3rd explained in four phases. The top line indicates a pedal pressure. The second line from the top shows a pressure on the front axle, ie on the first inlet valve E1 and at the second inlet valve E2 at. The third line from the top shows a pressure on the rear axle, ie on the third inlet valve E3 and the fourth inlet valve E4 at. The bottom line, which is drawn in with a dashed line, shows a position of the piston 42 of the linear actuator 40 at.

In phase 1, the circuit separation valve is open KTV , opened isolation valve TV and closed sequence valve ZV first of all an initial pressure build-up through the brake pedal 22nd initiated. In phase 2 the circuit isolation valve is KTV closed, at which time also the pressure applied by means of the first pressure sensor 12th is measured. This pressure is through the closed circuit separation valve KTV now locked on the rear axle. In phase 2 the linear actuator is used 40 Moment built up until a positive movement was detected. During the transition to phase 3, the sequence valve became ZV by the linear actuator 40 pushed open, which means that the linear actuator 40 has built up a pressure identical to the known enclosed pressure. Phase 3 is also used here to match the pressure on the rear axle to the front axle. Then, when transitioning to phase 4, the circuit isolating valve is activated KTV opened again. In phase 4, normal operation, for example by-wire operation, is possible again.

Using the procedure just described, a calibration pressure can thus be determined in such a way that it occurs when the connection valve is opened ZV corresponds to the enclosed pressure, and it can be the value of a parameter of the motor which is present at this point in time 44 can be saved as calibration parameters. This allows calibration of the characteristic curve already mentioned.

4th shows an alternative embodiment in which the circuit separation valve is not used during the transition from phase 1 to phase 2 KTV but only the isolation valve TV is closed. Otherwise, the course of the procedure corresponds to that which has just been given with reference to 3rd has been described.

With reference to the 5 and 6th describes how a calibration can be determined by means of an opening characteristic of an inlet valve E.

The circular isolating valve, for example, can be used to measure a pressure generated KTV as well as the third inlet valve E3 closed and the sequence valve ZV be opened. The fourth inlet valve E4 is closed and the fourth exhaust valve A4 will be opened. The latter measure provides a pressure reference in the form of a pressureless state on the fourth wheel brake B4 reached. An actuation current that the fourth intake valve E4 holds in the closed state, is then continuously lowered. This happens while the linear actuator 40 generates a constant pressure, but cannot deliver it to another component because all valves are closed and the piston 42 thus cannot move. From a certain actuation current, which can be referred to as the change current, there is a change in the position of the piston 42 detected. This indicates that the fourth inlet valve E4 was opened at exactly this change stream. From this, conclusions can now be drawn about the pressure prevailing in this change current, which represents the calibration pressure.

The in 5 The opening characteristic curves shown for the inlet valves E. An applied pressure difference delta_P is plotted on the horizontal axis. An applied actuation current I is plotted on the vertical axis. A bold line is drawn in, which at the same time represents the top line, which corresponds to a current at the respective pressure difference delta_P at which the respective inlet valve E closes. The lines below show a respective flow rate with a correspondingly lower current. The upper line is decisive for the implementation of the method according to the invention, since in the present case it can also be used in such a way that an applied pressure difference can be determined for a measured change current. Since the pressure reference on the opposite side is set to zero, as mentioned, the pressure difference delta_P corresponds to the pressure applied. This enables one of the linear actuator to be measured 40 generated pressure without the need for an additional pressure sensor. In particular, the pressure measurement can be carried out without the second pressure sensor 14th be performed.

6th shows a phase model of the measurement. A distinction is made between three phases. In phase 1, pressure is first applied using the linear actuator 40 by varying a parameter, for example increasing a current, built up, with a position of the piston 42 , which is shown in the uppermost curve, changes, ie the piston 42 moves to the right. The system pressure, which is in shown on the middle curve increases accordingly.

In phase 2 the circuit isolation valve KTV as well as the third inlet valve E3 and the fourth inlet valve E4 closed. There is no further pressure generation, so that the system pressure remains constant.

The lower curve shows the actuation current at the fourth inlet valve E4 at. This is initially relatively high in order to bring about a reliable closure. It remains correspondingly high in phase 2. In phase 3, the actuation current is reduced in a controlled manner so that the pressure can be determined. At the end of phase 3 there will be a movement of the piston 42 detected. This can again be seen in the top curve. This now means that with the associated actuation current, which can be referred to as the change current, an opening of the fourth inlet valve E4 is done leading to the movement of the piston 42 has led.

Overall, a connection between a calibration parameter and an associated calibration pressure can thus be established by means of an inlet valve.

With the calibration options described above, the characteristic curve already mentioned above can now be adjusted or calibrated.

Motor position control or motor speed control can be carried out based on a PV (pressure-volume) characteristic curve, for example. This can be calibrated using the options described. A corresponding calibration can take place, for example, after certain periods of time, with certain temperature changes or after volume has been released through the wheel valves.

A motor torque-to-pressure characteristic can also be used. A relationship between the engine torque and the resulting pressure is typically proportional or almost proportional, but can also be of a different type. With the pressure determination methods mentioned above, a ratio of engine torque to pressure can be learned and then the engine torque can be regulated.

However, since the mechanics are typically provided with friction and play, hysteresis and saturation effects are to be expected. 7th shows an exemplary characteristic curve which indicates a relationship between engine torque and pressure. It can be seen here that the pressure, which corresponds to a specific engine torque, is typically higher when the pressure is increased than when the pressure is reduced.

To avoid or reduce these effects, an oscillation of the engine torque can be used. A correspondingly modified characteristic curve with such an oscillation is shown 8th . The respective pressures, which correspond to an engine torque, which occur when the pressure increases and when the pressure decreases, are here much closer to one another.

As with a pressure-volume characteristic curve, the characteristic curve can preferably also be re-learned after a certain period of operation in the case of torque control. The particular advantage over a pressure-volume characteristic is that the engine torque-to-pressure characteristic is not sensitive to wheel pressure regulator activities.

In the embodiments described herein, it can be achieved in particular that a calibration of the characteristic curve of the linear actuator 40 is still possible even if the second pressure sensor 14th has failed. This can also be dispensed with if necessary.

If a brake system is operated, for example, with an additional brush motor and an overflow valve, the overflow valve can be used, for example, to learn the system pressure. This extension would be analogous to the procedures described above.

Mentioned steps of the method according to the invention can be carried out in the order given. However, they can also be carried out in a different order if this is technically sensible. The method according to the invention can be carried out in one of its embodiments, for example with a specific combination of steps, in such a way that no further steps are carried out. In principle, however, further steps can also be carried out, including those which are not mentioned.

It should be pointed out that features can be described in combination in the claims and in the description, for example to facilitate understanding, although these can also be used separately from one another. The person skilled in the art recognizes that such features can also be combined with other features or combinations of features independently of one another.

References back in subclaims can identify preferred combinations of the respective features, but do not exclude other combinations of features.

Claims (15)

A method for generating a predetermined hydraulic pressure by means of a pressure generator (40) in a brake system (10) for a motor vehicle, the method comprising the following steps: - Providing a characteristic curve which indicates a relationship between a parameter of the pressure generator (40) and the pressure, - Detecting that a calibration pressure is generated for a calibration value of the parameter, - Calibrating the characteristic using the calibration value and the calibration pressure, - Determination of a working value of the parameter, which corresponds to the predetermined pressure, based on the calibrated characteristic curve, and - Applying the working value of the parameter to the pressure generator (40). Procedure according to Claim 1 - A linear actuator or a pump being used as the pressure generator (40). Method according to one of the preceding claims, - The parameter being a volume displaced in the pressure generator (40). Method according to one of the Claims 1 or 2 - wherein the parameter is a motor torque or a current strength of the pressure generator (40). Method according to one of the preceding claims, wherein the step of recording is carried out as follows: - Applying the calibration value of the parameter to the pressure generator (40), - Measure the calibration pressure as long as the parameter is present. Procedure according to Claim 5 - The steps of applying the calibration value and measuring the calibration pressure are carried out with the wheel valves, inlet valves (E) and / or connecting valves between the pressure generator (40) and a master brake cylinder (20) and / or a simulator (30) closed. Method according to one of the Claims 5 or 6th , the calibration pressure being measured by the following steps: switching a valve (E) into a switching state by applying a switching current as the actuating current, the valve (E) being controllable by means of the actuating current and the calibration pressure being applied to the valve (E), Changing the actuating current, recognizing a change in the state of the valve and, in response to this, determining an actuating current at which the valve (E) has changed its state as a change current, determining the calibration pressure as a function of the change current. Method according to one of the Claims 1 to 4th , the step of detection being carried out by the following steps: - generating an output pressure in a part of the brake system (10) which is separated from the pressure generator (40) by a connecting valve (ZV), - closing the connecting valve (ZV), - Measuring the output pressure, - Varying the parameter, - Detecting an opening of the connection valve (ZV) and, in response to this, setting the current value of the parameter as a calibration parameter and setting the output pressure as the calibration pressure. Procedure according to Claim 8 - wherein the outlet pressure is measured by means of a pressure sensor (12). Method according to one of the Claims 8 or 9 - wherein the output pressure is generated by means of a manually operated master brake cylinder (20). Method according to one of the Claims 7 to 10 - wherein an opening of the valve (E) or the isolating valve (TV) is detected on the basis of a movement of part of the pressure generator (40) or a piston (42) of the pressure generator (40). Method according to one of the Claims 1 to 4th - wherein the calibration pressure is measured by means of a pressure sensor (12, 14). Method according to one of the preceding claims, - wherein the steps of recording and calibrating are repeated at predetermined time intervals and / or under predetermined conditions. Method according to one of the preceding claims, - The work value is approached from an initial value with a superimposed oscillation. Brake system (10) for a motor vehicle, the brake system (10) having the following: - at least one pressure generator (40), - a number of valves, and - A control device (60) which is configured to carry out a method according to one of the preceding claims.

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