DE102022200157A1 - Confirmation of the ability of a brake system to build up pressure using an electric brake unit - Google Patents

Abstract

The invention relates to a method for checking the functionality of a hydraulic pump in a brake system. To implement the check without additional components, the following steps are carried out: a) Pumping of brake fluid by means of an electric brake booster in fluid connection with the brake system into a low-pressure accumulator of the brake system, b) Return of the brake fluid from the low-pressure accumulator to the electric brake booster by means of the hydraulic pump of the braking system, c) comparison of verification data with target values and evaluation of the operability based on the comparison.

Description

The invention relates to a method for checking the functionality of a hydraulic pump in a brake system and a corresponding brake system.

For autonomous driving or semi-autonomous driving, it is essential that the vehicle can be braked safely above a certain speed threshold. The stability of the vehicle should also be ensured. This typically requires two independent pressure sources, which can provide hydraulic pressure in the brake system and thus at the wheel brakes. In order to maintain high safety standards, the functionality of the braking systems must be guaranteed and must therefore be checked at certain intervals. The test is usually carried out by evaluating integrated pressure sensors during normal braking or in separate test runs. For this purpose, additional pressure sensors are integrated in the systems that are responsible for the pressure build-up in the fallback level. The pressure build-up test in systems with electric brake boosters (EBKV) and wheel-specific pressure control, especially in stability systems (ESC), requires additional pressure sensors in the wheel brake circuits.

The additional pressure sensors are a high cost factor and increase the space required for the units. In addition, the pressure sensors must also be checked for functionality. Pressure build-up via the additional pressure source during normal braking causes noise that is unacceptable to the majority of customers. Separate pressure build-ups for test purposes usually disturb the driver, since the cause of the noise is not comprehensible for him. The same problems also occur with other brake units, such as a brake-by-wire system.

It is therefore the object of the present invention to check the functionality of brake systems with an electric brake unit and a brake system with its own pressure source.

1. a) Fördern von Bremsflüssigkeit mittels einer elektrischen Bremseinheit in fluider Verbindung mit dem Bremssystem in einen Niederdruckspeicher des Bremssystems,
2. b) Rückfördern der Bremsflüssigkeit aus dem Niederdruckspeicher zur elektrischen Bremseinheit mittels der hydraulischen Pumpe des Bremssystems,
3. c) Vergleich von Überprüfungsdaten mit Sollwerten und Evaluierung der Funktionsfähigkeit basierend auf dem Vergleich.

The solution is to use existing properties of the components in the electronic brake unit and brake system system network to ensure that the brake system can build up pressure in the fallback level. This is done according to the invention by a method for checking the functionality of a hydraulic pump in a brake system, using the steps:

1. a) conveying brake fluid by means of an electric brake unit in fluid connection with the brake system into a low-pressure accumulator of the brake system,
2. b) return of the brake fluid from the low-pressure accumulator to the electric brake unit by means of the hydraulic pump of the brake system,
3. c) Comparison of verification data with target values and evaluation of operability based on the comparison.

The brake system can be designed in particular as an ESC system (Electronic Stability Control) which can adjust the brake pressures of the individual wheel brakes independently of one another in order to intervene in the stability of the driving behavior of the vehicle. The functionality is thus checked in a particularly simple manner by displacing brake fluid, which increases safety.

In a preferred embodiment, the electric brake unit is an electric brake booster and/or a brake-by-wire brake system.

• - Kommunizieren einer Druck-, Bremsmoment- und/oder Volumenanforderung an den elektrischen Bremskraftverstärker,
• - Schalten einer Ventilanordnung des Bremssystems zur Herstellung einer strömungsoffenen Verbindung zwischen dem elektrischen Bremskraftverstärker und dem Niederdruckspeicher des Bremssystems.

In a preferred embodiment of the invention, step a) comprises:

• - Communicating a pressure, braking torque and/or volume request to the electric brake booster,
• - Switching a valve assembly of the brake system to produce a flow-open connection between the electric brake booster and the low-pressure accumulator of the brake system.

A value between 10 Nm and 100 Nm, particularly preferably from 30 Nm to 50 Nm, can preferably be transmitted as the braking torque request.

In a further preferred embodiment of the invention, step a) is carried out in an unbraked situation and/or step b) is carried out in a braked situation. During step a), the brake system is therefore currently in an unused state. Possible braking is therefore not affected, which means that safety is always guaranteed. Depending on the version of the electronic brake booster, the pedal movement could also be perceived by the driver in an unbraked situation.

By carrying out step b) during braking, any noises that may occur are well hidden in the general background noise of braking. With an unbraked If step b) were carried out, the evaluation of the measured values would also be more difficult since the displaced volume only corresponds to the requested torque/pressure. In the braked state, the displaced volume corresponds to a significantly higher moment/pressure, which makes the evaluation of the signals easier and more reliable.

In a further preferred embodiment of the invention, the brake fluid is pumped into a master cylinder of the electric brake booster in step b). The brake fluid is thus immediately available for the next braking.

In a further preferred embodiment of the invention, step b) includes regulating a pressure in the master brake cylinder to a target pressure value. The electronic brake booster thus sets a target pressure value that is determined based on an actuation of the brake pedal or a request from an assistance system. For regulation, the current pressure in the master brake cylinder can be measured by a pressure sensor or evaluation of other signals, such as the engine torque.

In a further preferred embodiment of the invention, step b) is carried out when a connection between the main brake cylinder of the electric brake booster and a reservoir is interrupted. Thus, additional volume that is pumped into the master brake cylinder leads to an increase in pressure, which is easy to detect and can therefore be corrected.

In a further preferred embodiment of the invention, step b) is carried out when the setpoint pressure has been constant for a predetermined period of time. In such a stationary situation, the pressure can be regulated particularly well. In a stationary state, the system has little influence from the viscosity of the brake fluid. In addition, the evaluation in step c) is more accurate. In the non-stationary state, it might be unclear whether the change in the actual values was caused by the liquid being pumped back or by a new setpoint. A balancing would have to be carried out accordingly, which can therefore be omitted in the stationary state.

In a further preferred embodiment of the invention, step b) includes the communication of a negative volume request to the electric brake booster, the amount of which corresponds to the volume flow of the hydraulic pump of the brake system. While the filling level of the low-pressure accumulator is reduced by the hydraulic pump, the control does not have to react, but has the opposing volume flow as a requirement. Only fluctuations around the desired volume flow have to be corrected.

• - Feststellen, dass für eine vorbestimmte Zeitdauer keine Bremsung durchgeführt wurde,
• - Kommunizieren einer Volumenanforderung an den elektrischen Bremskraftverstärker, welche Schnüffellöcher in dem Hauptbremszylinder des elektrischen Bremskraftverstärkers gerade verschließt,
• - Schließen der Einlassventile der Radbremsen;

In a further preferred embodiment of the invention, step b) comprises

• - determining that no braking has been carried out for a predetermined period of time,
• - Communicating a volume request to the electric brake booster which just closes snifting holes in the master brake cylinder of the electric brake booster,
• - Closing the inlet valves of the wheel brakes;

The test method can thus be safely completed within a specified time even without braking.

In a further preferred embodiment of the invention, the checking data are recorded during the return conveyance. Monitoring is therefore implemented during the activity of the hydraulic pump, which collects information about its functionality.

In a further preferred embodiment of the invention, the verification data include a travel path of the brake booster. This is particularly easy to measure, with the corresponding sensor technology generally already being available and thus causing no additional costs.

• 1 zeigt schematisch einen elektronischen Bremskraftverstärker,
• 2 zeigt eine Bremsanlage mit einem elektronischen Bremskraftverstärker und einem ESC-System,
• 3 zeigt charakteristische Größen des erfindungsgemäßen Verfahrens,
• 4 zeigt weitere charakteristische Größen des erfindungsgemäßen Verfahrens,
• 5 zeigt weitere charakteristische Größen des erfindungsgemäßen Verfahrens,
• 6 zeigt weitere charakteristische Größen des erfindungsgemäßen Verfahrens,
• 7 zeigt weitere charakteristische Größen des erfindungsgemäßen Verfahrens,
• 8 zeigt einen Schritt des erfindungsgemäßen Verfahrens;

The object is also achieved by a brake system for wheel-specific control of brake pressures in at least one wheel brake, having a hydraulic pump, the pressure side of which has an inlet valve for connection to a wheel brake, and, in particular via an overflow valve, with an inlet port for connection to a master cylinder is connected to an electric brake unit, and whose intake port is connected via a changeover valve to the input port, to an outlet valve, for connection to a wheel brake, and to a low-pressure accumulator, with a control unit being provided for controlling the brake system, which is set up for a above method to perform. If a brake booster is used as the brake unit, the master cylinder can be the known master cylinder of the brake booster. If, on the other hand, another brake unit, in particular a brake-by-wire system, is used, then the master cylinder is preferably the device that includes the electrically moved volume, for example a linear actuator.

• 1 shows schematically an electronic brake booster,
• 2 shows a brake system with an electronic brake booster and an ESC system,
• 3 shows characteristic variables of the method according to the invention,
• 4 shows other characteristic variables of the method according to the invention,
• 5 shows other characteristic variables of the method according to the invention,
• 6 shows other characteristic variables of the method according to the invention,
• 7 shows other characteristic variables of the method according to the invention,
• 8th shows a step of the method according to the invention;

In 1 an electronic brake booster (EBKV) 1 is shown, as is known from the prior art. This has a reservoir 2 in which the brake fluid is stored. A first piston 3 is connected via a piston rod 9 to an electric drive unit which can linearly move the first piston. The electronic brake booster 1 also has a second piston 4, with the first piston 3 supplying a first brake circuit 5 and the second piston 4 supplying a second brake circuit 6 with brake fluid. The second piston 4 moves via the hydraulic coupling and a spring together with the first piston 3. A first snifting hole 7 is arranged in the hydraulic chamber of the first piston 3 and a second snifting hole 8 is arranged in the hydraulic chamber of the second piston 4, which is always closed when the retracted piston 3, 4 represents a flow-open connection to the reservoir 2. Alternatively, a single-piston master cylinder can be used.

As in 2 shown, an electronic brake booster 1 can be equipped with a downstream ESC system 10 in order to be able to carry out wheel-specific brake pressure modulations. The ESC system 10 has a hydraulic pump 17 as a core element, the suction side of which is connected to the electronic brake booster 1 via a switchover valve 12 and the pressure side of which is connected to the electronic brake booster 1 via an isolating valve 11 . At the same time, the pressure side of the hydraulic pump 17 has a connection to at least one wheel brake 16 via at least one inlet valve 13 . The intake side is connected to the wheel brakes 16 via an outlet valve 14 each. In addition, a low-pressure accumulator 15 is arranged on the suction side of the hydraulic pump 17 . In 2 A diagonal brake circuit layout is shown, but it can also be split between the front wheel brakes and the rear wheel brakes (black and white). The second brake circuit has an equivalent structure.

In 3 a first step of the method according to the invention is now shown for the case in which the ESC system 10 and the electronic brake booster 1 are connected via a total braking torque interface via which they communicate. In this first step, brake fluid volume is stored in the ESC system (brake system) 10 . In an unbraked situation, the ESC system 10 requests a total braking torque, ie a setpoint braking torque 20, greater than zero, in particular from 30 Nm to 50 Nm, and prohibits implementation via regenerative braking. The ESC system 10 activates the outlet valves 14 and thus stores the volume of brake fluid in the low-pressure accumulator (LPS) 15. The outlet valves 14 are opened in order not to build up any effective braking torque 21. The request for the target braking torque 20 is terminated as soon as the fill level 22 of the low-pressure accumulator 15 is sufficiently high. To implement this requirement, the electronic brake booster 1 moves forward in order to deliver brake fluid volume and the travel distance 23 of the electronic brake booster (EBKV) increases accordingly.

The system now waits for a braking request ( 4 ). This can be triggered by the driver actuating a brake pedal or it can be a request from an assistance system. If there is a stationary state, ie a state with a constant setpoint braking torque 20 , the volume from the low-pressure accumulator 15 is conveyed back into the master brake cylinder of the electronic brake booster 1 . For this purpose, the hydraulic pump 17 of the ESC system is activated accordingly. The associated increase in pressure is recognized and corrected accordingly. The effective braking torque 21 therefore remains essentially constant apart from small fluctuations. The fact that the pressure was increased, ie volume was conveyed into the master brake cylinder, can be seen in the travel path 23 of the electronic brake booster 1, which has to compensate for the introduced volume by moving back. In particular, the travel of the actuator can be used as the travel of the electronic brake booster. The pressure increase can also be detected using a pressure sensor.

From this it can be concluded that the ESC system is able to build up pressure and is therefore functional.

During the return flow, the connection between the main cylinder and the reservoir is interrupted, ie the snifting holes are closed. For this purpose, the EBKV traverse path can be greater than a minimum value s0. In this way, pressure can be built up without valve switching and the pressure sensor connected to the master brake cylinder can be used to measure the pressure.

In the event of braking with purely regenerative deceleration, the ESC system can request conversion as pure friction braking torque or request partial conversion as friction braking torque.

It is possible for a control unit of the ESC system and a control unit of the electric brake booster to communicate with one another and in particular to find out about an active or upcoming test.

Alternatively, the ESC system 10 communicates a volume flow request 25 to the electronic brake booster 1 instead of the total braking torque, as is shown in 5 is shown. This is set to a predetermined value Q3 and maintained for a certain period of time until the fill level 22 of the low-pressure accumulator 15 is large enough. In this case, too, the outlet valves 14 are opened in order not to build up any effective braking torque.

The return is then carried out according to 6 , waiting again for normal braking or autonomous braking. Correspondingly, braking torque 26 is greater than zero again. At the same time, a volume flow request 28 is sent to the ESC hydraulic pump 17 . It is thus promoted volume from the low-pressure accumulator 15 back to the electronic brake booster 1, whereby the fill level 22 of the low-pressure accumulator 15 decreases. Meanwhile, the master cylinder pressure 27 is kept at the pressure value required for the current braking and disturbances are corrected. The volume introduced by the ESC hydraulic pump 17 is therefore compensated for by retracting the EBKV, which in turn is reflected in the travel path 23 of the EBKV.

A slightly modified version is in 7 shown. Here, too, a volume flow request 28 is sent to the ESC hydraulic pump 17 when braking is present, ie a braking torque 26 greater than zero. At the same time, an opposing volume flow requirement 25 is sent to the electronic brake booster 1, which volume flow requirement 28 to the ESC hydraulic pump 17 just compensates for. While the fill level 22 of the low-pressure accumulator 15 is reduced as a result, the regulation of the master cylinder pressure 27 is much more precise, since the regulation does not have to react, but instead receives the opposing current as a request. Only fluctuations around the desired volume flow 25, 28 therefore have to be corrected. It is particularly advantageous to take the system parameters into account in the volume flow specification for the EBKV.

As described above, the brake system waits for braking before pumping back the volume flow. However, if there is no braking with a pressure build-up for an inadmissibly long time, another part of the process can be implemented, which is shown schematically in 8th is shown. For this purpose, the EBKV is moved to a position in which the snifting holes are just closed via a volume flow request. Thereafter, the inlet valves 13 of all wheel brakes 16 are closed and the return pumping is started. As soon as the master cylinder pressure exceeds a certain value, it is proven that the ESC system can build up pressure. Ideally, this takes place when the vehicle is safely stationary, but this is not absolutely necessary.

The invention thus makes it possible to monitor the operability of the ESC hydraulic pump without changes in the structure of the brake system.

reference list

1

Electronic brake booster

2

reservoir

3

First Piston

4

Second Piston

5

First brake circuit

6

Second brake circuit

7

First snoop

8th

Second snoop

9

piston rod

10

ESC system

11

isolation valve

12

switching valve

13

intake valve

14

outlet valve

15

low-pressure accumulator

16

wheel brake

17

hydraulic pump

20

target braking torque

21

Effective braking torque

22

NDS fill level

23

EBKV travel

25

Volume flow requirement EBKV

26

braking torque

27

master cylinder pressure

28

Volumetric flow request to the hydraulic pump of the ESC

Claims (13)

Method for checking the functionality of a hydraulic pump (17) in a brake system (10), characterized by the steps: a) conveying brake fluid by means of an electric brake unit (1) in fluid connection with the brake system (10) into a low-pressure accumulator (15) of the brake system (10), b) return of the brake fluid from the low-pressure accumulator (15) to the electric brake unit (1) by means of the hydraulic pump (17) of the brake system (10), c) comparison of test data with target values and evaluation of the functionality based on the Comparison. procedure after claim 1 , characterized in that the electric brake unit is an electric brake booster (1) and/or a brake-by-wire brake system. procedure after claim 1 or 2 , characterized in that step a) comprises: - communicating a pressure, braking torque and/or volume requirement (25) to the electric brake booster (1), - switching a valve arrangement of the brake system to produce a flow-open connection between the electric brake booster (1 ) and the low-pressure accumulator (15) of the brake system (10). Method according to one of the preceding claims, characterized in that step a) is carried out in an unbraked situation and/or step b) is carried out in a braked situation Method according to one of the preceding claims, characterized in that in step b) the brake fluid is conveyed into a master brake cylinder of the electric brake booster (1). Method according to one of the preceding claims, characterized in that step b) comprises: - Regulating a pressure in the master brake cylinder to a desired pressure value. Method according to one of the preceding claims, characterized in that step b) is carried out when a connection between the main brake cylinder of the electric brake booster (1) and a reservoir is interrupted. Method according to one of the preceding claims, characterized in that step b) is carried out when the target pressure has been constant for a predetermined period of time. Method according to one of the preceding claims, characterized in that step b) comprises: - Communicating a negative volume request to the electric brake booster (1), the amount of which corresponds to the volume flow of the hydraulic pump (17) of the brake system (10). Method according to one of the preceding claims, characterized in that step b) comprises: - determining that no braking has been carried out for a predetermined period of time, - communicating a negative volume request to the electric brake booster, which snifter holes in the master brake cylinder of the electric brake booster (1) just closed, - closing of the inlet valves of the wheel brakes; Method according to one of the preceding claims, characterized in that the checking data are recorded during the return conveyance. Method according to one of the preceding claims, characterized in that the checking data include a travel distance of the brake booster (1). Brake system for wheel-specific regulation of brake pressures in at least one wheel brake, having a hydraulic pump (17), the pressure side of which is connected to an inlet valve for connection to a wheel brake and to an input port for connection to a master cylinder of an electric brake power unit (1), and whose suction port is connected via a switching valve (12) to the input port, to an outlet valve for connection to a wheel brake, and to a low-pressure accumulator (15). is, characterized in that a control unit is provided for controlling the brake system, which is set up to a method according to one of Claims 1 until 12 to perform.

Images