DE102016203105A1 - Method and device for diagnosing a brake assist system in a motor vehicle - Google Patents

Abstract

The invention relates to a method for checking a function of a brake assist system with a vacuum pump, comprising the following steps: determining an evacuation performance of the vacuum pump; - Modeling a course of a brake chamber pressure in a brake chamber of the brake assist system based on the evacuation performance; - After releasing an actuation of an actuator, detecting an error when at least one deviation between a modeled course of a brake chamber pressure and a course of the actual brake chamber pressure is detected.

Description

Technical area

The invention relates to brake assist systems with so-called brake booster, which provide a pressure difference with the aid of a vacuum pump. Upon actuation of a brake pedal, a brake assist force resulting from the pressure difference is accordingly provided.

Technical background

In a brake booster, an adjustable pressure difference between two brake chambers is converted into a braking force for a downstream brake system. For this purpose, a negative pressure relative to an ambient pressure is provided in the brake chambers, which is generated by a mechanically, electrically or otherwise driven vacuum pump. During a braking operation, a pressure in one of the brake chambers of the brake booster is increased in accordance with an actuating force predetermined by the driver, and the resulting pressure difference is converted into the braking force that supplements the actuating force.

The vacuum pump ensures after each braking for a rebuild of the negative pressure in the corresponding brake chamber of the brake booster. In case of failure or deterioration of the performance of the vacuum pump is a brake assist only for a few braking operations available because there is no rebuilding the negative pressure by the vacuum pump. As a result, the operating force required to achieve the required braking power can be very high during a journey. Thus, the functionality of the brake booster and in particular the vacuum pump is safety relevant.

From the publication DE 10 2009 011 280 A1 For example, a method for checking the operation of a brake system of a vehicle having a brake booster is known. For this purpose, the braking force is detected in a braking operation of the vehicle, wherein the output signal of the pressure sensor is stored before the start of the braking process in a memory when the brake pressure is within a predetermined first pressure range. After completion of the braking operation, a difference is formed from a current output signal of the pressure sensor and the output signal stored in the memory, the difference serving as an indication of the functionality of the brake system.

From the publication DE 199 35 899 A1 a brake booster system is known in which an actuation of the brake is monitored. An error occurring in the brake booster system is detected by evaluating an intake manifold pressure detected by the pressure sensor as a function of the actuation of the brake.

According to the document DE 199 29 880 A1 is provided for a brake booster to activate the vacuum pump in the presence of certain operating conditions of the drive unit of the vehicle and to perform a diagnosis of the vacuum pump and the connecting lines of the vacuum reservoir.

From the publication DE 100 52 257 A1 a method for checking the operation of a brake booster is known in which the pressure of the brake booster is monitored by a pressure sensor. The plausibility of the pressure sensor values is checked by recording the measured values of the pressure sensor for a predetermined period of time when the brake pedal is actuated and determining, after release of the brake, a difference between the last stored pressure sensor value and a previously recorded pressure sensor value.

However, the above methods for checking the operation of the vacuum pump for a brake booster are unable to detect a gradual degradation of the vacuum pump before it fails.

It is therefore an object of the present invention to provide an improved method for diagnosing a brake assist system in a motor vehicle, with which a gradual degradation of a vacuum pump can already be detected.

Disclosure of the invention

This object is achieved by the method for checking a function of a vacuum pump of a brake assist system, in particular for a motor vehicle, according to claim 1 and by the device and by the brake assist system according to the independent claims.

Further embodiments are specified in the dependent claims.

• – Bestimmen einer Evakuierungsleistung der Unterdruckpumpe;
• – Modellieren eines Verlaufs eines Bremskammerdrucks in einer Bremskammer des Bremsunterstützungssystems basierend auf der Evakuierungsleistung; und
• – nach dem Lösen einer Betätigung einer Betätigungseinrichtung, Feststellen eines Fehlers, wenn eine Abweichung zwischen einem modellierten Verlauf eines Bremskammerdrucks und einem Verlauf des tatsächlichen Bremskammerdrucks festgestellt wird.

According to a first aspect, a method for checking a function of a brake assist system with a vacuum pump is provided, comprising the following steps:

• Determining an evacuation capacity of the vacuum pump;
• - Modeling a course of a brake chamber pressure in a brake chamber of the brake assist system based on the evacuation performance; and
• After releasing an actuation of an actuator, determining an error if a deviation between a modeled course of a brake chamber pressure and a profile of the actual brake chamber pressure is detected.

With increasing wear, the vacuum pump of a brake booster on an ever-decreasing evacuation performance. However, this reduction in evacuation efficiency is usually initially unnoticed since, for a majority of the braking events, the brake chamber of the brake booster is not fully vented, i. H. not the maximum pressure difference is needed to provide the brake assist force. The reduced evacuation performance can thus ensure a sufficient vacuum supply for most of the braking operations. However, if the progressive wear of the vacuum pump eventually leads to failure and thus to the elimination of the braking force assistance, this event occurs from the perspective of the driver abruptly and without warning. It can occur safety-relevant driving situations.

One idea of the above method for checking the operation of a vacuum pump for a brake assist system is to model the progress of the brake chamber pressure in the negative pressure brake chamber by means of a suitable predetermined brake booster model. The brake booster model models a pressure curve of the brake chamber pressure when the vacuum pump is activated, starting from an initial pressure (which may correspond to the maximum pressure reached in the brake chambers or a momentary pressure in the brake chambers during the last braking operation) and closed to the environment brake chambers, ie a situation at full release the operation of the actuator is present. By comparing and evaluating a difference / deviation between the course of the actual brake chamber pressure and the modeled course of the brake chamber pressure at at least one temporal position, an error in the vacuum system of the brake booster can be detected early, i. H. an error can be detected before z. B. a vacuum pump completely fails. Depending on the amount of difference / deviation, a degree of operability, in particular wear or failure, of the vacuum pump can be determined.

Furthermore, the evacuation performance can be specified or determined as a function of a rotational speed of the vacuum pump and an ambient pressure, and in particular depending on a temperature of the extracted gas.

It can be provided that an error is detected if at least one of the measured values of the actual brake chamber pressure deviates from a corresponding model value of the brake chamber pressure at a respective particular point in time by more than a predetermined degradation threshold value.

• – dass eine vorbestimmte Anzahl von Abweichungen zwischen jeweils einem Modellwert des modellierten Verlaufs des Bremskammerdrucks und einem entsprechenden Messwert des Verlaufs des tatsächlichen Bremskammerdrucks, die jeweils größer sind als ein vorgegebener Degradationsschwellenwert, übersteigt, und/oder
• – dass die Summe einer vorbestimmten Anzahl von Abweichungen zwischen jeweils einem Modellwert des modellierten Verlaufs des Bremskammerdrucks und einem entsprechenden Messwert des tatsächlichen Bremskammerdrucks einen vorgegebenen Integrationsschwellenwert übersteigt.

In particular, a degradation error may be signaled when the presence of a degradation condition is detected, the degradation condition indicating

• A predetermined number of deviations between in each case a model value of the modeled curve of the brake chamber pressure and a corresponding measured value of the curve of the actual brake chamber pressure, which are each greater than a predefined degradation threshold, and / or
• - That the sum of a predetermined number of deviations between each a model value of the modeled course of the brake chamber pressure and a corresponding measured value of the actual brake chamber pressure exceeds a predetermined integration threshold.

In particular, this makes it possible to debounce the method for determining an error.

It may be provided that a degradation error is signaled as a dynamic degradation error when the presence of the degradation condition is detected during a first time period after the actuation of the actuator is released, and a degradation error is signaled as a static degradation error if the presence of the degradation Degradationsbedingung is determined during a second period of time, wherein the end of the first time period and the beginning of the second time period until reaching a predetermined target brake chamber pressure is fixed or specified by reaching a predetermined transition pressure value. This makes it possible to distinguish between types of degradation of the vacuum pump depending on whether the deviations occur in the dynamic or stationary range of the course of the brake chamber pressure.

Furthermore, a function failure error can be signaled if at least one deviation between a model value of the modeled progression of the brake chamber pressure and a corresponding measured value of the actual brake chamber pressure is determined, which is greater than a predefined failure threshold value. In particular, the failure threshold may be greater than the degradation threshold.

Furthermore, the course of the brake chamber pressure in the brake chamber of the brake assist system may be determined based on the evacuation performance after releasing the operation of the actuator once or repeatedly or continuously after releasing the operation of the actuator and before reaching a predetermined target brake chamber pressure.

• – eine Evakuierungsleistung der Unterdruckpumpe zu bestimmen;
• – einen Verlaufs eines Bremskammerdrucks in einer Bremskammer des Bremsunterstützungssystems basierend auf der Evakuierungsleistung zu modellieren; und
• – nach dem Lösen einer Betätigung einer Betätigungseinrichtung, einen Fehler festzustellen, wenn mindestens eine Abweichung zwischen einem modellierten Verlauf eines Bremskammerdrucks und einem Verlauf des tatsächlichen Bremskammerdrucks festgestellt wird.
• Gemäß einem weiteren Aspekt ist ein Bremsunterstützungssystem vorgesehen, umfassend:
• – ein Bremsunterstützungssystem mit zwei Bremskammern
• – eine Unterdruckpumpe, die ausgebildet ist, um die Bremskammern zu evakuieren; und
• – die obige Vorrichtung.

According to a further aspect, an apparatus, in particular a control unit for checking a function of a brake assist system with a vacuum pump is provided, the apparatus being designed to:

• To determine an evacuation capacity of the vacuum pump;
• To model a history of a brake chamber pressure in a brake chamber of the brake assist system based on the evacuation performance; and
• - after releasing an actuation of an actuator to detect an error, if at least one deviation between a modeled course of a brake chamber pressure and a course of the actual brake chamber pressure is detected.
• In another aspect, a brake assist system is provided, comprising:
• - A brake assist system with two brake chambers
• - A vacuum pump, which is designed to evacuate the brake chambers; and
• - The above device.

Brief description of the drawings

Embodiments are explained below with reference to the accompanying drawings. Show it:

1 a schematic representation of a brake assist system;

2 a flowchart for illustrating a method for checking the function of a vacuum pump; and

3 a diagram illustrating the course of an actual brake chamber pressure with respect to a modeled course of the brake chamber pressure.

Description of embodiments

In 1 is a schematic representation of a brake assist system 1 shown. The brake force assistance system 1 has a vacuum pump 2 to provide an evacuation performance for generating a negative pressure. The vacuum pump 2 can be driven directly by an output shaft of an internal combustion engine of a motor vehicle or driven by an electric motor.

The brake force assistance system 1 has a brake booster 3 which is in a brake booster housing 35 a first brake chamber 31 and a second brake chamber 32 includes. The two brake chambers 31 . 32 are by a movable diaphragm or a movable piston 33 separated from each other. The piston 33 is with a piston rod 34 firmly connected, which acts to provide a braking force for the brake system (not shown). The piston rod 34 is moveable air and pressure tight in the brake booster housing 35 stored.

It is an actuator 4 z. B. provided in the form of a brake pedal, which has a brake rod 41 a valve 5 inside the piston rod 34 actuated. The valve 5 is designed in a known manner so that when unactuated actuator 4 the first and second brake chamber 31 . 32 together by a fluidic connection 51 are connected, so that with active vacuum pump 2 in the first and second brake chambers 31 . 32 a negative pressure is generated. At the same time by a return spring 36 The piston 33 or the piston rod 34 moved in a first position or held in a first position in which no braking force is exerted on the brake system.

By an actuation of the actuator 4 becomes the valve 5 operated and by the appropriate movement of the brake rod 41 becomes the fluidic connection 51 between the first and second brake chambers 31 . 32 closed. At the same time, an operating force of the operation acts on the piston 33 , After closing the fluidic connection 51 between the brake chambers 31 . 32 becomes another previously closed fluidic connection 52 the second brake chamber 32 open to the environment. As a result, ambient air flows into the second brake chamber 32 and the pressure in the second brake chamber 32 rises. Through the between the brake chambers 31 . 32 adjusting pressure difference acts on the piston 33 and thus on the piston rod 34 a corresponding braking force.

The applied braking force depends on the actuation of the brake rod 41 , as with a movement of the piston 33 in the direction of the brake rod 41 the further fluidic connection 52 the second brake chamber 32 closed to the environment again.

A critical component of such a brake assist system 1 puts the vacuum pump 2 This can fail, and it is thus no longer available to a driver of a motor vehicle brake assistance. As a result, the required actuating forces for a braking operation can be very high.

A common cause of failure of a vacuum pump is a wear of moving parts in the vacuum pump, z. B. pump impeller blades. Such wear can already occur before a complete failure of the vacuum pump 2 in a decrease in the evacuation capacity of the vacuum pump 2 impact. Thus, the wear of the vacuum pump 2 be determined by continuous monitoring of the evacuation performance. For the diagnosis, one in the first brake chamber 31 arranged pressure sensor 6 be used.

Furthermore, a control unit 10 provided with the pressure sensor 6 is coupled to an indication of the brake chamber pressure in the first brake chamber 31 to obtain. Furthermore, the control unit receives 10 Information about the current oil temperature, the current speed of the vacuum pump 2 and via the ambient pressure either via sensors or via a separate control unit, such as an engine control unit for operating an internal combustion engine. Instead of the speed of the vacuum pump 2 can also be one of the vacuum pump 2 supplied electric power in the case of an electrically operated vacuum pump can be provided. From the information, in particular from the speed of the vacuum pump 2 or the supplied electrical power, an evacuation performance of a functioning vacuum pump 2 without closure phenomena in a manner known per se (for example, with the aid of a given pump model).

In 2 FIG. 4 is a flowchart illustrating one in the control unit. FIG 10 executed method for the diagnosis of the vacuum system and in particular the vacuum pump 2 shown.

In step S1, first operating parameters of the vacuum pump 2 determined, which may relate in particular to a speed and the ambient pressure. Furthermore, an indication of a temperature of the vacuum pump, in particular when arranged on an internal combustion engine, an oil temperature can be provided.

In step S2, based on the operating parameters of the vacuum pump 2 Based on the given pump model, an evacuation performance (or a size representing this) can be determined. Alternatively, the vacuum pump 2 be formed with a known constant evacuation performance.

After pressing an actuator 4 to activate the braking system, the pressure in the first brake chamber increases 31 due to the piston movement (the piston movement causes a reduction of the first brake chamber 31 ). In step 33 is therefore checked cyclically, whether after a previous actuation of the actuator 4 has been solved. If this is the case (alternative: yes), ie when the actuator is released 4 , the process proceeds to step S4. If the actuation has not been released (alternative: no), then the method is continued with step S1 or alternatively (in particular with known evacuation performance) with step S3.

In step S4, the actual brake chamber pressure using the pressure sensor 6 measured.

In step S5, based on the modeled evacuation performance and that provided by the pressure sensor 6 measured brake chamber pressure a time course of the brake chamber pressure at complete release of the actuator 4 calculated. This calculation can be performed on a physical brake chamber pressure model. The brake chamber pressure model may be a model calibrated by measurement in a fully functional vacuum pump and / or a physical model of the volumes of the brake chambers to be evacuated 31 . 32 correspond. Through the first and the second brake chamber 31 . 32 There is a defined volume in which a predefined, measured by the pressure sensor pressure prevails and that by the vacuum pump 2 to be evacuated to a predetermined vacuum level. This can be in knowledge of the volume to be evacuated at unconfirmed actuator 4 interconnected brake chambers 31 . 32 done in a conventional manner. The evacuation is carried out with an evacuation performance that is constant or whose instantaneous value is continuously measured and provided.

To model the course of the brake chamber pressure, it is necessary to determine the timing of release of the actuator. This time can be through a suitable sensor on the brake rod 41 be determined. Alternatively, the timing may also be through Evaluation of two consecutively detected measured values of the brake chamber pressure can be detected. Signals the difference between two consecutively detected brake chamber pressures that a negative pressure in the first brake chamber 31 is rebuilt, this may be taken as the time of stopping the braking operation, since the fluidic connection between the second brake chamber 32 and the environment is closed again and the fluidic connection 51 between the first and second brake chambers 31 . 32 has been opened again.

In step 86 is again checked whether the actuation of the actuator 4 is still solved. If this is not the case (alternative: no), the method is continued with step S1. Otherwise (alternative: Yes), the method continues with step S7.

In step S7, the actual brake chamber pressure using the pressure sensor 6 measured again.

In step S8, a time corresponding to the elapsed time after the release timing of the operation of the actuator becomes 4 determined model value of the brake chamber pressure (value of the brake chamber pressure model at the time after the elapsed time) compared with the measured actual brake chamber pressure. If no deviation between the model value and the actual brake chamber pressure is determined in step S8 (alternative: no), the method is continued with step S6. Otherwise (alternative: yes), an error handling in step S9 can be performed.

If after releasing the actuator 4 the actual pressure in the first brake chamber 31 corresponds to the modeled course of the brake chamber pressure, so can on a proper function of the vacuum pump 2 getting closed. If the course of the actual brake chamber pressure deviates from the modeled brake chamber pressure, then it is possible for the vacuum pump to have limited functionality 2 , z. B. by a degradation of the vacuum pump 2 , or insufficient functioning of the vacuum pump 2 getting closed.

The modeled course of the brake chamber pressure can once after reaching the maximum pressure in the brake chambers 31 . 32 and after releasing the operation of the actuator 4 be determined on the basis of the determined evacuation performance. Alternatively, the modeled course of the brake chamber pressure multiple or continuous after reaching the maximum pressure in the brake chambers 31 . 32 and after releasing the operation of the actuator 4 be determined until reaching a target brake chamber pressure to account for varying evacuation performance, which arise in accordance with the pump model in the modeled course of the brake chamber pressure. The desired brake chamber pressure is a predetermined pressure value, up to which the pressure in the brake chambers 31 . 32 when not operating the actuator 4 should fall.

It should be noted in particular that, depending on the error, errors only in transient or only in stationary operation of the vacuum pump 2 may occur. That is, it can in case of failure, a slower build-up of the negative pressure in the first brake chamber 31 Although the expected negative pressure in the stationary case, the negative pressure at a proper vacuum pump 2 equivalent.

Another error case may provide that the course of the brake chamber pressure the modeled course of the brake chamber pressure in the transient / dynamic operation, ie immediately after the release of the actuator 4 However, this will be for a proper vacuum pump 2 expected stationary negative pressure, ie the negative pressure after a certain period of time after completion of the braking process (after releasing the actuation of the actuator 4 ), not reached.

Therefore, it may be provided that a dynamic degradation error is detected or signaled, if in step S8, a deviation between the model value and the actual brake chamber pressure during a first time period after releasing the actuation of the actuator 4 is detected. Similarly, a static degradation error can be detected or signaled if in step S8 a deviation between the model value and the actual brake chamber pressure during a second time period until reaching a predetermined target brake chamber pressure is detected. The end of the first time period and the beginning of the second time period may be fixed or indicated by reaching a predetermined transition pressure value.

These two error cases can be evaluated in the error handling of step S9 regarding the deviation between the modeled brake chamber pressure and the actual brake chamber pressure.

If the deviation or the difference between the model value of the brake chamber pressure and the actual measured value of the brake chamber pressure corresponds to a value that is greater than a predefined failure threshold value, then a failure or an insufficient functioning of the Vacuum pump can be determined and an appropriate emergency measure to be initiated. The emergency measure may, for example, in a corresponding signaling a failure of the brake assist system 1 in the form of a functional failure error are communicated to the driver, for example, by a particular red warning light.

If the deviation between the model value and the actual brake chamber pressure corresponds to a value which is smaller than the predetermined failure threshold but a value that is greater than a predefined degradation threshold value, then a degradation of the vacuum pump may occur 2 getting closed. Such a degradation can be communicated to the driver by a corresponding signaling, for example by a particularly yellow warning light.

In order to detect only short-term deviations between the model value and the actual brake chamber pressure as a degradation error, the detection of a degradation error can be debounced. In particular, the detected deviations can be integrated into an integrator value within a predefined time period and a maintenance or replacement of the vacuum pump depending on the exceeding of a predefined integration threshold value by the integrator value 2 recommended or an emergency operation of the brake assist system or the entire engine system of the motor vehicle are activated.

In 3 a diagram is shown, the curves of the modeled curve of the brake chamber pressure p (curve K1), the actual course of the brake chamber pressure p (curve K2) in the event of degradation of the vacuum pump 2 represents. It can be seen that a deviation between the modeled and the actual course of the brake chamber pressure can already be detected in transient operation, ie immediately after termination of the braking process at time T0.

LIST OF REFERENCE NUMBERS

1

Brake assist system

2

Vacuum pump

3

Brake booster

31, 32

brake chambers

33

piston

34

piston rod

36

Return spring

35

Brake booster housing

4

actuator

41

brake rod

5

Valve

51

fluidic connection

52

further fluidic connection

6

pressure sensor

10

control unit

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009011280 A1 [0004]
• DE 19935899 A1 [0005]
• DE 19929880 A1 [0006]
• DE 10052257 A1 [0007]

Claims (9)

Method for checking a function of a brake assist system ( 1 ) with a vacuum pump ( 2 ), comprising the following steps: - determining (S2) an evacuation performance of the vacuum pump ( 2 ); Modeling (S5) a time course of a brake chamber pressure in a brake chamber ( 31 ) of the brake assist system based on the evacuation performance; After releasing an actuation of an actuator ( 4 ), Determining (S8) an error if at least one deviation between a modeled course of a brake chamber pressure and a course of the actual brake chamber pressure is detected. Method according to claim 1, wherein the evacuation power depends on a rotational speed of the vacuum pump ( 2 ) and an ambient pressure, and in particular is determined depending on a temperature of the extracted gas. The method of claim 1 or 2, wherein a deviation between the modeled course of the brake chamber pressure and the course of the actual brake chamber pressure is determined, if at least one of the values of the course of the actual brake chamber pressure deviates from a corresponding model value of the brake chamber pressure by more than a predetermined Därradationsschwellenwert. The method of claim 3, wherein a degradation error is signaled when the presence of a degradation condition is detected, wherein the degradation condition indicates A predetermined number of deviations between in each case a model value of the modeled curve of the brake chamber pressure and a corresponding measured value of the curve of the actual brake chamber pressure, which are each greater than a predefined degradation threshold, and / or - That the sum of a predetermined number of deviations between each a model value of the modeled course of the brake chamber pressure and a corresponding measured value of the actual brake chamber pressure exceeds a predetermined integration threshold. A method according to claim 4, wherein a degradation error is signaled as a dynamic degradation error if the presence of the degradation condition during a first time period after the release of actuation of the actuator ( 4 ), and a degradation error is signaled as a static degradation error when the presence of the degradation condition is detected during a second time period until a predetermined target brake chamber pressure is reached, the end of the first time period and the beginning of the second time period being fixed or by reaching a predetermined transition pressure value. Method according to one of claims 1 to 5, wherein a function failure error is signaled when at least one deviation between a model value of a modeled curve of the brake chamber pressure and a corresponding measured value of the actual brake chamber pressure is determined which is greater than a predetermined failure threshold. Method according to one of claims 1 to 6, wherein the course of the brake chamber pressure in the brake chamber ( 31 ) of the brake assist system ( 1 ) based on the evacuation performance after releasing the operation of the actuator ( 4 ) is determined once or repeatedly or continuously after releasing the actuation of the actuator ( 4 ) and before reaching a predetermined target brake chamber pressure is determined. Device, in particular control unit ( 10 ) for checking a function of a brake assist system ( 1 ) with a vacuum pump ( 2 ), the device being designed to: - an evacuation capacity of the vacuum pump ( 2 ) to determine; A course of a brake chamber pressure in a brake chamber ( 31 ) of the brake assist system based on the evacuation performance; After releasing an actuation of an actuator ( 4 ) to detect an error if at least one deviation between a modeled course of a brake chamber pressure and a course of the actual brake chamber pressure is detected. Brake Assist System ( 1 ), comprising: a brake assist system having two brake chambers; a vacuum pump configured to evacuate the brake chambers; - A device according to claim 7.

Images