DE102019210623A1 - Method for ensuring the functionality of a braking system of a motor vehicle in the event of a reduced braking performance of the braking system - Google Patents

Abstract

The invention relates to a method for ensuring the functionality of a braking system of a motor vehicle in the event of reduced braking power of the braking system, the braking system being designed in the form of an electrohydraulic brake-by-wire system having a hydraulic fallback level, with an estimate being made in the case of reduced braking power whether the reduced braking power is due to a vapor bubble in the hydraulic brake circuit of the brake-by-wire system or a defective piston seal of the brake piston of the brake-by-wire system. According to the method, it is provided that if the estimation results in the presence of a vapor bubble, brake fluid is replenished into the hydraulic brake system, if the estimation results in the presence of a defective piston seal, the hydraulic fallback level is released, and if the estimation results in a defective piston seal There is uncertainty, brake fluid is replenished in the hydraulic brake system or the hydraulic fallback level is released.

Description

The invention relates to a method for ensuring the functionality of a brake system of a motor vehicle in the event of a reduced braking performance of the brake system according to the type specified in claim 1.

In the premium segment, vehicles are often equipped with electro-hydraulic brake-by-wire braking systems. A characteristic of these systems is that when the driver mechanically actuates the brake pedal, the driver's braking request is detected by means of sensors, whereupon a control unit controlled by the sensors generates a pressure via a pressure transducer in a hydraulic brake system, on the basis of which the brakes are controlled Perform the appropriate braking intervention as requested by the driver. As a fall-back level (safety path), such brake systems have a hydraulic cylinder that can be actuated with the brake pedal, which is connected to the brake system via isolating valves and is available, for example, if the electronics fail. Such electrohydraulic brake-by-wire brake systems are sufficiently known from the prior art. The EP 3 178 712 A1 referenced.

A well-known problem with hydraulic brakes is the so-called vapor lock: when braking, considerable heat is generated. So that the brake fluid can withstand these temperatures without boiling, it has a high boiling point. However, since brake fluid is hygroscopic, the brake fluid absorbs moisture over time, which lowers the boiling point of the brake fluid. When the moisture content in the brake fluid has reached a certain level, this can cause the brake fluid to boil and vapor bubbles to form, especially when braking for a long time or when braking heavily. In contrast to brake fluid, these vapor bubbles can be compressed, which means that the brake pressure no longer reaches the brake piston and the brake pedal “sags”.

In other words, in the event of a vapor bubble, the driver only notices for the first time that he is pressing the brake pedal, but not decelerating the vehicle. Thus, the braking system must find a way to meet the driver's braking request and achieve the desired deceleration. As a rule, the brake system will try to detect a leak in the hydraulic circuit and compensate for the lack of delay by adding more volume. A disadvantage here is that the brake system, due to the back pressure in the system and the hydraulic lines, cannot distinguish whether it is a leak or a vapor bubble or a defective piston seal of the brake piston. For this reason, the brake system will stop adding volume after a relatively short period of time, possibly before the build-up of brake pressure, and open the isolating valves for the fall-back level so that the driver can obtain the necessary brake pressure even in the event of a defective piston seal to be built up via the hydraulic fallback level.

A method for predicting vapor lock formation in a hydraulic brake system of a motor vehicle is disclosed in US Pat FR 2 960 203 A1 described.

The invention is based on the object of specifying a method by means of which the functionality of the brake system is guaranteed in the event of a fault, with high safety requirements.

This object is achieved by the features of patent claim 1.

The subclaims 2 to 5 form advantageous developments of the invention.

According to the method for ensuring the functionality of a braking system of a motor vehicle in the event of a reduced braking power of the braking system, the braking system is designed as an electrohydraulic brake-by-wire system having a hydraulic fallback level.

• • Abschätzen, ob im Falle einer verminderten Bremsleistung die verminderte Bremsleistung auf eine Dampfblase im hydraulischen Bremskreislauf des Brake-by-Wire-Systems oder eine defekte Kolbendichtung des Bremskolbens des Brake-by-Wire-Systems zurückzuführen ist;
• • Ergibt die Abschätzung als Ergebnis das Vorliegen einer Dampfblase, so wird Bremsflüssigkeit in das hydraulische Bremssystem nachgefördert;
• • Ergibt die Abschätzung als Ergebnis das Vorliegen einer defekten Kolbendichtung des Bremskolbens, so wird durch ein entsprechendes Öffnen von Ventilen die hydraulische Rückfallebene freigegeben;
• • Ergibt die Abschätzung als Ergebnis das Vorliegen einer Unbestimmtheit, so wird entweder Bremsflüssigkeit in das hydraulische Bremssystem nachgefördert oder es wird die hydraulische Rückfallebene freigegeben.

The method according to the invention is characterized by the following method steps:

• • Estimate whether, in the case of reduced braking performance, the reduced braking performance is due to a vapor bubble in the hydraulic brake circuit of the brake-by-wire system or a defective piston seal on the brake piston of the brake-by-wire system;
• • If the result of the estimate is the presence of a vapor bubble, then brake fluid is replenished into the hydraulic brake system;
• • If the result of the assessment is the presence of a defective piston seal of the brake piston, the hydraulic fallback level is released by opening valves accordingly;
• • If the result of the estimation is the existence of an indeterminacy, either brake fluid is replenished in the hydraulic brake system or the hydraulic fallback level is released.

The method according to the invention proves to be particularly advantageous because the estimation of the fault, ie the positive prediction about the presence of a vapor bubble or the positive prediction about the presence of a defective piston seal, ensures that the brake system is equipped with a corresponding one for the present In the event of a fault, it can respond to a suitable strategy to support the driver. In particular, the method according to the invention ensures that the driver is given maximum support by identifying the "occurrence of a vapor bubble" fault, or by identifying the "presence of a defective piston seal" fault and the immediate resultant subsequent delivery of brake fluid Release of the hydraulic fallback level, the safety of the driver or the occupants is guaranteed. In addition, since in the undefined case, i.e. no positive statement about the presence of a vapor bubble and no positive statement about the presence of a defective piston seal, the brake system either replies with additional delivery of brake fluid or with the release of the hydraulic fallback level, it is guaranteed that the brake system will also operate in this case Case with the "safe variant", eg in the case of a small leak in the hydraulic line system with additional volume or if the leak results in a larger escape of brake fluid, with the release of the hydraulic fallback level.

For the estimation, a plurality of parameters are preferably considered, which are weighted in relation to the occurrence of a vapor bubble and in relation to the occurrence of a defective piston seal.

Due to the use of several parameters and their weighting, a reliable estimation result is ensured in an advantageous manner.

• • wenn die Wahrscheinlichkeitsbetrachtung ergibt, dass eine Dampfblase ursächlich zu sein scheint, das Ergebnis der Abschätzung auf Vorliegen einer Dampfblase festgesetzt wird,
• • wenn die Wahrscheinlichkeitsbetrachtung ergibt, dass eine defekte Kolbendichtung ursächlich zu sein scheint, das Ergebnis der Abschätzung auf Vorliegen einer defekten Kolbendichtung festgesetzt wird,
• • und dass in allen anderen Fällen, das Ergebnis der Abschätzung auf Unbestimmtheit festgesetzt wird.

According to a particularly advantageous embodiment of the method according to the invention, a probability analysis is carried out on the basis of the parameters, their weighting and their correlation, with

• • if the probability analysis shows that a vapor bubble appears to be the cause, the result of the assessment is determined as to whether a vapor bubble is present,
• • if the probability analysis shows that a defective piston seal appears to be the cause, the result of the assessment is determined whether a defective piston seal is present,
• • and that in all other cases, the result of the estimation is set for uncertainty.

Since appropriate control units, which enable a probability analysis and comparisons to be carried out, are usually available as standard in today's motor vehicles, a low-cost, low-cost estimate, namely the presence of a vapor bubble or the presence of a defective piston seal or the presence of an indeterminacy, is ensured .

• • gebremstes Rollen in Neutralstellung N;
• • Bergabfahrt;
• • Temperatur Reibscheiben;
• • Fahrzeuggewicht;
• • Eigenschaft der Bremsflüssigkeit;
• • Eigenschaften des Bremssystems;
• • Bremsentyp;
• • Historie Bremssystem;
• • aktueller Bremsvorgang, und/oder
• • Anzeichen für eine Leckage im Bremssystem

betrachtet.In particular, the following parameters, namely

• • braked rolling in neutral position N;
• • downhill;
• • temperature friction disks;
• • vehicle weight;
• • property of the brake fluid;
• • characteristics of the braking system;
• • type of brake;
• • Brake system history;
• • current braking process, and / or
• • Signs of a leak in the braking system

considered.

0

kein Einfluss erwartet,

+

geringer Einfluss erwartet, und

++

großer Einfluss erwartet

zu verstehen ist.With regard to the occurrence of a vapor bubble, the above parameters are preferably weighted as follows: • "Braked rolling in neutral position N" Duration of scrolling t _R if 0 min ≤ t _R <5 min => 0 if 5min ≤ t _R <15 min => + if t _R ≥ 15min => ++ • "Downhill" Duration of the departure t _A if 0 min ≤ t _A <5 min => 0 if 5min ≤ t _A <15 min => + if t _A ≥ 15min => ++ • "Temperature friction disks T _R " if 0 ° C ≤ T _R <100 ° C => 0 if 100 ° C ≤ T _R <500 ° C => + if T _R ≥ 500 ° C => ++ if T _R ≥ 400 ° C for more than 30 min => ++ • "Vehicle weight" Trailer operation: (Yes) => ++ (No) => 0 Load B _vehicle if 0 kg ≤ B _vehicle <300 kg => 0 if 300 kg ≤ B _vehicle <400 kg => + if B _vehicle ≥ 400 kg => ++ • "Property of brake fluid" Age A _{Bf of} the brake fluid if 0 years ≤ A _Bf <2 years => 0 if 2 years ≤ A _Bf <3 years => + if A _Bf ≥ 3 years => ++ Water content W _{Bf of} the brake fluid if 0% ≤ W _Bf <2% => 0 if 2% ≤ W _Bf <3% => + if W _Bf ≥ 3% => ++ • "Brake system property" Age A _{BS of} the braking system if 0 years ≤ A _BS <3 years => 0 if 2 years ≤ A _BS <4 years => 0 if A _BS ≥ 4 years => 0 Service life G _{d of} the braking system if 0 years ≤ G _d <4 years => 0 if 4 years ≤ G _d <5 years => 0 if G _d ≥ 5 years => 0 • "Brake type" Floating saddle (Yes) => + (No) => 0 Fixed saddle (Yes) => + (No) => 0 • "History of the braking system" if one of the number of applied braking and intensity of the applied brake pressure resulting Load profile of the braking system <load profile, this for the entire service life of the braking system is provided => 0 if one of the number of applied braking and intensity of the applied brake pressures Load profile of the braking system ≥ load profile, this for the entire service life of the braking system is provided => 0 • "Current braking process" Brake pressure if brake pressure of the current braking process < as a mean value of the braking pressures of the braking processes of the last 30 min => 0 if the brake pressure of the current braking process is ≥ as a mean value of the braking pressures of the braking processes of the last 30 min => 0 Pressure build-up speed if pressure build-up speed of the current Braking process <as a mean value of the pressure construction speeds of the braking processes of the last 30min => 0 if pressure build-up speed of the current Braking process ≥ as a mean value of the pressure construction speeds of the braking processes of the last 30min => 0 • "Signs of a leak in the brake system" if the brake system already has a brake loss of fluid was detected => 0 being under

0

no influence expected,

+

low impact expected, and

++

great impact expected

is to be understood.

0

kein Einfluss erwartet,

+

geringer Einfluss erwartet, und

++

großer Einfluss erwartet

zu verstehen ist.With regard to the event of a defective piston seal, the above parameters are preferably weighted as follows: • "Braked rolling in neutral position N" Duration of scrolling t _R if 0 min ≤ t _R <5 min => 0 if 5min ≤ t _R <15 min => 0 if t _R ≥ 15min => 0 • "Downhill" Duration of the departure t _A if 0 min ≤ t _A <5 min => 0 if 5min ≤ t _A <15 min => 0 if t _A ≥ 15min => 0 • "Temperature friction disks T _R " if 0 ° C ≤ T _R <100 ° C => 0 if 100 ° C ≤ T _R <500 ° C => 0 if T _R ≥ 500 ° C => 0 if T _R ≥ 400 ° C for more than 30 min => 0 • "Vehicle weight" Trailer operation: (Yes) => 0 (No) => 0 Load B _vehicle if 0 kg ≤ B _vehicle <300 kg => 0 if 300 kg ≤ B _vehicle <400 kg => 0 if B _vehicle ≥ 400 kg => 0 • "Property of brake fluid" Age A _{Bf of} the brake fluid if 0 years ≤ A _Bf <2 years => 0 if 2 years ≤ A _Bf <3 years => 0 if A _Bf ≥ 3 years => 0 Water content W _{Bf of} the brake fluid if 0% ≤ W _Bf <2% => 0 if 2% ≤ W _Bf <3% => 0 if W _Bf ≥ 3% => 0 • "Brake system property" Age A _{BS of} the braking system if 0 years ≤ A _BS <3 years => 0 if 2 years ≤ A _BS <4 years => + if A _BS ≥ 4 years => ++ Service life G _{d of} the braking system if 0 years ≤ G _d <4 years => 0 if 4 years ≤ G _d <5 years => + if G _d ≥ 5 years => ++ • "Brake type" Floating saddle (Yes) => 0 (No) => 0 Fixed saddle (Yes) => 0 (No) => 0 • "History of the braking system" if one of the number of applied braking and intensity of the applied braking pressures Load profile of the braking system <load profile, this for the entire service life of the braking system is provided => 0 if one of the number of applied braking and intensity of the applied braking pressures Load profile of the braking system ≥ load profile, this for the entire service life of the braking system is provided => ++ • "Current braking process" Brake pressure if brake pressure of the current braking process < as a mean value of the braking pressures of the braking processes of the last 30 min => 0 if the brake pressure of the current braking process is ≥ as a mean value of the braking pressures of the braking processes of the last 30 min => ++ Pressure build-up speed if pressure build-up speed of the current Braking process <as a mean value of the pressure construction speeds of the braking processes of the last 30min => 0 if pressure build-up speed of the current Braking process ≥ as a mean value of the pressure construction speeds of the braking processes of the last 30min => ++ • "Signs of a leak in the brake system" if the brake system already has a brake loss of fluid was detected => ++ being under

0

no influence expected,

+

low impact expected, and

++

great impact expected

is to be understood.

Further advantages and possible applications of the present invention emerge from the following description in conjunction with the exemplary embodiment shown in the drawing.

• 1 eine schematische Darstellung eines Kraftfahrzeugs zur Verdeutlichung des Verfahrens zur Gewährleistung der Funktionsfähigkeit eines Bremssystems eines Kraftfahrzeugs im Falle einer verminderten Bremsleistung des Bremssystems.

In the drawing means:

• 1 a schematic representation of a motor vehicle to illustrate the method for ensuring the functionality of a brake system of a motor vehicle in the event of a reduced braking power of the brake system.

1 shows a schematic representation of an overall with the reference number 10 designated motor vehicle. The front axle is marked with the reference number VA and the rear axle is indicated by the reference number HA designated.

The motor vehicle has a in its entirety with the reference number 100 designated break-by-wire braking system. From the break-by-wire braking system 100 are presently only schematically the wheels 12 , 14th the front axle VA associated front friction braking devices 110 who have favourited the wheels 16 , 18th the rear axle HA associated rear friction braking devices 120 as well as the regulation control unit 130 over which the break-by-wire braking system 100 can be regulated / controlled in a known manner. The hydraulic fallback level has not been shown for reasons of clarity.

The method according to the invention is explained below using two scenarios:

Scenario 1:

The car 10 is loaded with four people and the corresponding luggage in the trunk and the motor vehicle 10 is currently on a hill descent when a reduced braking power occurs during braking.

From corresponding, in the motor vehicle 10 It is known that the load B _{Kfz of} the motor vehicle B _{Kfz is} 400 kg, the downhill descent has already lasted more than 15 minutes and the temperature T _{R of} the friction disks is currently at T _R = 600 ° C. In the regulation / control unit 130 is also stored that the motor vehicle 10 already three years old and the braking system at this time 100 is installed unchanged, and the brake fluid has not yet been changed. From a corresponding evaluation of the braking processes of the last 30 minutes, it is also known that the current braking process was started slowly, i.e. with a low pressure build-up rate, and that a load profile of the braking system resulting from the number of braking processes applied and the intensity of the braking pressures applied 100 is smaller than one in the control unit 130 stored, critical, ie a load profile intended for the entire service life of the brake system.

In the present case, the probability analysis carried out on the basis of the parameters loading, downhill travel, temperature T _{R of} the friction disks, property of the brake system, property of brake fluid, current braking process and history of the brake system, their weighting and their correlation shows that a vapor bubble appears to be the cause of the reduced braking performance with a high degree of probability and the result of the estimation is determined to be the presence of a vapor bubble.

As a result of this, a countermeasure is provided that the subsequent delivery of brake fluid is extended over time.

Scenario 2:

The car 10 is only equipped with the driver and is on a motorway trip. The reduced braking power occurs when the driver quickly depresses the brake pedal due to an unexpected lane change in another vehicle.

The motor vehicle is almost 8 years old and the braking system - with the exception of the friction disks - has been in use for 8 years. The last service was less than two years ago; The brake fluid was also changed during this service. It is also known that the rule control unit 130 stored critical, for the entire service life of the braking system 100 The load profile provided is smaller than the load profile of the brake system resulting from the number of braking processes applied and the intensity of the braking pressures applied 100 .

As corresponding evaluations and sensors have shown, almost no braking processes were carried out in the last 10 minutes and as a result, the temperature T _{R of} the friction disks was below 50 ° C before the last braking process. As the evaluation of the braking processes of the last 30 minutes also shows, the current braking process was started very quickly, ie with a high pressure build-up speed.

The probability analysis carried out on the basis of the parameters vehicle weight, property of the brake system, property of brake fluid, history of the brake system, temperature T _{R of} the friction disks and the current braking process, their weighting and their correlation shows that a defective piston seal appears to be the cause of the reduced braking performance with a high degree of probability and the result of the assessment is based on the presence of a defective piston seal.

As a result, the hydraulic fallback level is released as a countermeasure.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was 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.

Patent literature cited

• EP 3178712 A1 [0002]
• FR 2960203 A1 [0005]

Claims (5)

Method for ensuring the functionality of a braking system of a motor vehicle in the event of a reduced braking power of the braking system, the braking system being designed in the form of an electrohydraulic brake-by-wire system having a hydraulic fall-back level, wherein in the case of a reduced braking power, it is estimated whether the reduced braking power Braking power is due to a vapor bubble in the hydraulic brake circuit of the brake-by-wire system or a defective piston seal of the brake piston of the brake-by-wire system, whereby if the result of the estimation shows the presence of a vapor bubble, brake fluid is replenished in the hydraulic brake system, if the assessment shows the presence of a defective piston seal as a result, the hydraulic fallback level is released, and if the estimation results in an indeterminacy, brake fluid is replenished in the hydraulic brake system or the hydraulic fallback level is released. Procedure according to Claim 1 , characterized in that several parameters are considered for the estimation, which are weighted in relation to the event of the presence of a vapor bubble and in relation to the event of the presence of a defective piston seal. Procedure according to Claim 2 , characterized in that on the basis of the parameters, their weighting and their correlation, a probability analysis is carried out, and that if the probability analysis shows that a vapor bubble is the cause, the result of the assessment is determined as to the presence of a vapor bubble, and that if the probability analysis results, that a defective piston seal is the cause, that the result of the assessment of the presence of a defective piston seal is established, and that in all other cases, the result of the assessment of the existence of an indeterminacy is established. Method according to one of the Claims 2 or 3 , characterized in that the parameters of braked rolling in neutral position N, downhill travel, temperature of friction disks, vehicle weight, property of the brake fluid, properties of the brake system, brake type, history of the brake system, current braking process and / or signs of a leak in the brake system are considered for the assessment. Procedure according to Claim 4 , characterized in that the parameters are weighted according to the following table: parameter Weighting vapor bubble Weighting piston seal Braked rolling in N Duration of scrolling t _R if 0 min ≤ t _R <5 min 0 0 if 5min ≤ t _R <15 min + 0 if t _R ≥ 15min ++ 0 Downhill Duration of the departure t _A if 0 min ≤ t _A <5 min 0 0 if 5min ≤ t _A <15 min + 0 if t _A ≥ 15min ++ 0 Temperature friction disks T _R : if 0 ° C ≤ T _R <100 ° C 0 ++ if 100 ° ≤ T _R <500 ° + 0 if T _R ≥ 500 ° ++ 0 if T _R ≥ 400 ° for more than 30 min ++ 0 Vehicle weight: Trailer operation (Yes) ++ 0 (No) 0 0 Load B _vehicle if 0 kg ≤ B _vehicle <300 kg 0 0 if 300 kg ≤ B _vehicle <400 kg + 0 if B _vehicle ≥ 400 kg ++ 0 Property brake fluid: Age A _{Bf of} the brake fluid if 0 years ≤ A _Bf <2 years 0 0 if 2 years ≤ A _Bf <3 years + 0 if A _Bf ≥ 3 years ++ 0 Water content W _{Bf of} the brake fluid if 0% ≤ W _Bf <2% 0 0 if 2% ≤ W _Bf <3% + 0 if W _Bf ≥ 3% ++ 0 Property braking system: Age A _{BS of} the braking system if 0 years ≤ A _BS <3 years 0 0 if 2 years ≤ A _BS <4 years 0 + if A _BS ≥ 4 years 0 ++ Service life G _{d of} the braking system if 0 years ≤ G _d <4 years 0 0 if 4 years ≤ G _d <5 years 0 + if G _d ≥ 5 years 0 ++ Brake type: Floating saddle (Yes) + 0 (No) 0 0 Fixed saddle (Yes) + 0 (No) 0 0 History braking system: if a load profile of the brake system <load profile resulting from the number of braking processes applied and the intensity of the applied brake pressures, which is provided for the entire service life of the brake system if 0 0 a load profile of the brake system ≥ load profile resulting from the number of braking processes applied and the intensity of the applied braking pressures, which is provided for the entire service life of the brake system 0 ++ Current braking process if Brake pressure of the current braking process <as an average of the braking pressures of the braking processes of the last 30 minutes 0 0 if Brake pressure of the current braking process ≥ as a mean value of the braking pressures of the braking processes of the last 30 minutes 0 ++ if Pressure build-up speed of the current braking process <an average value of the pressure build-up speeds of the braking processes over the last 30 minutes 0 0 if Pressure build-up speed of the current braking process ≥ an average value of the pressure build-up speeds of the braking processes over the last 30 minutes 0 ++ Signs of leakage in the braking system: if the brake system has already detected a loss of brake fluid 0 ++ in which : 0: no influence expected + Influence expected ++ great influence means.

Images