METHOD FOR DIAGNOSTIC THE PLAINITY OF PRESSURE MEASUREMENT IN A BRAKE BULBER

Description

[0001] The present invention claims priority from French application 2104464 filed on April 29, 2021.

[0002] The invention relates generally to the field of operational safety of a vehicle braking system. More particularly, the invention relates to a method for diagnosing the plausibility of pressure measurement information in a brake booster of a vehicle braking system.

[0003] In the braking system of a motor vehicle, the brake booster, also called "master-vac", is a vacuum assistance device which is inserted between the brake pedal and the master cylinder of the hydraulic braking circuit. The presence of a vacuum in a chamber of the brake booster makes it possible to obtain an amplification of the driver's effort on the brake pedal. This amplification is necessary to obtain sufficient braking pressure in the hydraulic circuits of the braking system when pressing the brake pedal, while avoiding the driver the sensation of a "hard pedal". In vehicles with a gasoline-type combustion engine, the vacuum necessary for the operation of the brake booster can be provided by the combustion engine, more precisely, by the vacuum present in its intake manifold. In other vehicles, a vacuum pump is necessary to provide this vacuum.The vacuum pump can be a coupled vacuum pump, typically in vehicles with a diesel-type thermal engine, or an electric vacuum pump, typically in electrified vehicles such as hybrid or all-electric vehicles.

[0004] The vacuum pump is a critical component for the operation of the brake booster and must constantly provide a sufficient level of vacuum. Document EP2493736A1 discloses a method for diagnosing the operation of the vacuum pump of a vehicle braking system. The vacuum pump is actuated between a switch-on pressure and a switch-off pressure in order to generate a vacuum. A vacuum period between the switch-on pressure and the switch-off pressure is determined and compared with a reference period defined according to the level of the electrical supply voltage in the vehicle. A fault signal is generated in the event that the vacuum period is greater than the reference period.

[0005] Furthermore, it is known in the prior art (see document US 2014 / 110994 A1) to use two pressure sensors of different technology for measuring the vacuum in the brake booster. A consistency diagnosis is carried out on the pressure information delivered by the two pressure sensors. This consistency diagnosis monitors that the pressure information provided by the sensors remains within an acceptable tolerance range and detects an anomaly when a delta between the pressure information becomes greater than a predefined pressure threshold, for example, 100 mbar. In terms of operational safety, the choice of two pressure sensors of different technology provides robustness that makes it possible to satisfy the aforementioned consistency diagnosis to obtain the safety level required in the standard classification "ASIL" (for "Automotive Security Integrity Level" in English).

[0006] On the other hand, in a configuration with two pressure sensors of identical technology, the aforementioned coherence diagnosis is unable to determine a common mode between the sensors and does not allow the detection of a simultaneous and coherent drift between them, nor a freezing of the pressure information provided. In the event of a significant drift of the two sensors which indicate sufficient vacuum when this is not the case, this may result in degraded braking performance, or even no braking, with the vacuum pump only being activated when the vacuum falls below a threshold for activating it. A new diagnosis on the pressure information provided by the sensors is therefore necessary for this configuration, in order to comply with the required “ASIL” safety level.

[0007] It is desirable to provide a method for diagnosing the plausibility of pressure measurement information in a brake booster of a vehicle braking system, making it possible to meet the aforementioned need by being able to detect anomalies in the plausibility of pressure measurement information when the brake booster is equipped with two pressure sensors of identical technology.

[0008] According to a first aspect, the invention relates to a method for diagnosing the plausibility of at least two brake booster pressure information items from separate pressure sensors in a brake booster of a vehicle braking system.According to the invention, the method comprises the steps of a) detecting a valid brake application by comparing a brake pedal depression ratio with a predetermined depression ratio threshold, b) monitoring a change in each piece of brake booster pressure information over a predetermined period of time from the detection in step a) of a valid brake application, c) for each piece of brake booster pressure information, performing during the predetermined period of time a fault detection on the brake booster pressure information by comparing a change delta of the brake booster pressure information with at least one pressure change threshold, and d) establishing a plausibility diagnosis of the brake booster pressure information from the fault detection results obtained in step c).

[0009] According to a particular characteristic, step d) also includes a categorization of the plausibility anomaly.

[0010] According to another particular characteristic, the pressure evolution threshold is a variable threshold determined according to the vehicle's driving speed and the atmospheric pressure.

[0011] According to yet another particular feature, in step a), the brake pedal depression ratio is determined from a hydraulic pressure in a master cylinder of the vehicle braking system.

[0012] According to yet another particular characteristic, the method also comprises a verification of validity conditions of the diagnosis of plausibility of the brake booster pressure information, the validity conditions being satisfied when an active state of a powertrain of the vehicle and a brake application are detected.

[0013] According to yet another particular characteristic, the method also comprises a communication of the plausibility diagnosis to means for managing degraded mode of the vehicle.

[0014] The invention also relates to a vehicle braking system comprising a brake booster equipped with two separate pressure sensors delivering brake booster pressure information and a computer, in which the computer comprises a memory storing program instructions for implementing the method briefly described above. According to a particular characteristic, the two pressure sensors are of the same technology. According to another particular characteristic, the computer is a multifunction engine computer of the vehicle.

[0015] The invention also relates to a vehicle comprising a braking system as briefly described above.

[0016] Other advantages and characteristics of the present invention will appear more clearly on reading the detailed description below of several particular embodiments of the invention, with reference to the appended drawings, in which: [ Fig.1 ] There Fig.1 is a block diagram partially showing the architecture of a braking system of a motor vehicle in which the method of the invention is implemented. Fig.2 ] There Fig.2 is a flowchart of a particular embodiment of the method of the invention. [ Fig.3 ] There Fig.3 shows two schematic diagrams illustrating two life situations in the braking system, without and with fault detection on brake booster pressure information.

[0017] In reference to the Fig.1 , an example of a hardware configuration of a vehicle braking system is described below in which a particular embodiment of the method according to the invention is implemented. The invention is described here in the context of a vehicle equipped with a coupled vacuum pump and a braking system with “HBB / HBC” assistance, for example, a hybrid vehicle. The “HBB / HBC” assistance deploys compensation strategies for lack of braking assistance, called “HBB” for “Hydraulic Brake Booster” in English, and for assistance failure, called “HBC” for “Hydraulic Booster Compensation” in English. These “HBB / HBC” strategies are typically embedded in the computer of the vehicle’s electronic trajectory correction system, called “ESC” or “ESP” corrector, respectively for “Electronic Stability Control” or “Electronic Stability Program” in English.The “HBB / HBC” strategies act on braking by activating an electric hydraulic pump of the “ESC” corrector which increases the braking pressure in the hydraulic braking circuit.

[0018] The vehicle braking system, marked SFA, is only partially represented in the Fig.1 The SFA system includes a PF brake pedal, a SF brake booster, a MC master cylinder topped with an RL brake fluid reservoir, a CF hydraulic braking circuit, a PV vacuum pump, a PH hydraulic pump and command and control means using the vehicle's CMM and C_ESC computers.

[0019] The SF brake booster is inserted between the brake pedal PF and the master cylinder MC and is connected to the vacuum pump PV via a connecting pipe TR and other components not shown, such as flaps or valves. Two pressure sensors CP1 and CP2, using the same technology, are provided for measuring the vacuum pressure in the SF brake booster. In this example, the pressure sensors CP1, CP2 are mounted directly on a wall of the vacuum chamber of the SF brake booster, at separate locations. Alternatively, one of the pressure sensors could be mounted at one end of the connecting pipe TR, at a vacuum connection of the SF brake booster. The pressure sensors CP1 and CP2 provide pressure information PR1 and PR2 respectively.

[0020] The master cylinder MC is connected to the hydraulic brake circuit CF. Pressing the brake pedal AF on the brake pedal PF by the driver causes, via the brake booster SF, the movement of a piston in the master cylinder MC and, correlatively, generates braking pressure in the hydraulic brake circuit CF. The brake fluid pressure in the master cylinder MC, hereinafter referred to as "master cylinder pressure", is measured by a pressure sensor CM which provides master cylinder pressure information PM. As can be seen at Fig.1 , the CM pressure sensor is mounted here on the MC master cylinder.

[0021] In this example configuration, as indicated above, the PV vacuum pump is a pump attached to the thermal engine of the vehicle's powertrain. Generally, the PV vacuum pump can be a coupled pump or an electric pump, depending on the vehicle.

[0022] The PH hydraulic pump is coupled to the CF brake hydraulic circuit. The PH hydraulic pump here is the electric hydraulic pump of the aforementioned "ESC" corrector.

[0023] The CMM is typically the vehicle's multifunction engine control unit that hosts various powertrain and vehicle control and command strategies via embedded software modules. In particular, as seen in the Fig.1 , three software modules SW_CP, SW_PV and SW_GD / GAR are located in a MEM memory of the CMM calculator.

[0024] The software module SW_CP allows the implementation of the method according to the invention by the execution of program code instructions by a processor (not shown) of the CMM computer. In this particular embodiment, as shown in Fig.1 , the software module SW_CP is implemented in the software module SW_PV which is responsible for controlling the vacuum pump PV. For the implementation of the method according to the invention, the software module SW_CP receives as input the brake booster pressure information PR1 and PR2, the master cylinder pressure information PM and other information generally available in the CMM computer, such as information GMP_A indicating the active or inactive state of the powertrain, vehicle speed information VV, atmospheric pressure information PA and brake support information AF.

[0025] In the present invention, depending on the result of the plausibility check performed on the pressure information PR1, PR2, and carried out by the software module SW_CP, the software module SW_PV may be requested by the software module SW_CP to command a re-engagement of the vacuum pump PV. The software module SW_PV operates the vacuum pump PV by means of a command C_PV.

[0026] In general, the SW_GD / GAR software module is responsible for managing diagnostics (GD) and managing arbitrations and reconfigurations (GAR). Thus, the SW_GD / GAR software module performs three general functions which are the post-processing of on-board diagnostics generating fault codes of the so-called “APV” type for after-sales vehicle maintenance operations, the post-processing of on-board diagnostics of the OBD type (for “On-Board Diagnostics” in English) and the triggering of system reconfigurations upon detection of faults reported by the diagnostics. In the present invention, the SW_GD / GAR software module may be requested by the SW_CP software module to trigger a degraded mode depending on the result of the plausibility diagnosis carried out on the PR1 and PR2 pressure information. For this, an exchange of C_GD data takes place between the SW_CP and SW_GD / GAR software modules.

[0027] The C_ESC computer is here the computer of the “ESC” corrector. The C_ESC computer hosts a SW_HBB / HBC software module responsible for implementing the aforementioned “HBB / HBC” assistance. To carry out the “HBB / HBC” strategies, the SW_HBB / HBC software module manages the braking pressure in the CF hydraulic braking circuit by actuating the PH hydraulic pump by means of a C_PH command. In the present invention, the SW_HBB / HBC software module may be requested by the SW_CP software module to trigger “HBB / HBC” assistance depending on the result of the plausibility diagnosis carried out on the PR1 and PR2 pressure information, in particular in the event of a failure of the PV vacuum pump. For this, a C_HB data exchange takes place between the SW_CP and SW_HBB / HBC software modules.

[0028] For example, degraded modes MD1 to MD5 may be activated depending on the result of the plausibility diagnosis carried out on the pressure information PR1 and PR2. In this example, mode MD1 is a fault report indicating a vacuum supply failure for after-sales service, mode MD2 requires restarting the combustion engine and inhibiting the so-called "Stop-and-Go" function for automatically stopping / restarting the combustion engine, mode MD3 is a ban on driving in electric mode, mode MD4 is the illumination of a warning light informing the driver of a fault in their vehicle and mode MD5 is the activation of the "HBB / HBC" assistance described above.

[0029] As shown schematically in the Fig.1 , the various data exchanges, such as pressure measurement information, status information and commands, take place via a vehicle data communication network N_CAN, typically a “CAN” type network. Generally speaking, several pieces of information from vehicle components and sensors may already be available in the CMM computer, as they are acquired by the latter for various other control strategies, and will then be directly usable by the SW_PV software module. Other information may be available in another computer of the vehicle and transmitted, via the N_CAN network, to the SW_PV software module hosted in the CMM computer. Thus, in the embodiment more particularly described here, it is considered that the PR2 and PM pressure information are acquired by the C_ESC computer for its processing and transmitted by the latter to the SW_PV software module hosted in the CMM computer.

[0030] In the concept of the invention, the plausibility of the pressure information PR1, PR2, provided by the pressure sensors CP1, CP2, is checked when the driver presses the brake pedal PF AF, also referred to as a "brake press" hereinafter. Pressing the brake pedal AF consumes vacuum in the brake booster SF and causes a reduction in the vacuum therein.

[0031] During this AF brake application event, if the pressure information PR1, PR2 is consistent with this expected development of the vacuum in the brake booster, it is then considered plausible. Otherwise, a plausibility anomaly in the pressure information PR1, PR2 is detected.

[0032] The detection of a plausibility anomaly in the PR1, PR2 pressure information results in a lack of confidence in this information, which justifies a switch to a degraded mode. The objective of switching to a degraded mode is to avoid the emergence of a life situation in which the vehicle's braking performance is affected by a deficient measurement of the pressure in the vacuum chamber of the brake booster. Operating safety is thus improved.

[0033] In reference to the Fig.2 , an example of a processing process carried out by the SW_CP software module for implementing the method according to the invention is now described above.

[0034] The processing process comprises two functional blocks A and B. Functional block A concerns a verification of validity conditions of the plausibility diagnosis on the pressure information PR1, PR2, provided by the sensors CP1, CP2. Functional block B concerns the processing of establishing the plausibility diagnosis on the pressure information PR1, PR2, simultaneously.

[0035] As visible at the Fig.2 , functional block A essentially comprises three main steps SA1 to SA3.

[0036] The SA1 function detects the active or inactive state of the powertrain from the aforementioned GMP_A information. As long as the powertrain is inactive, this state being indicated by the information GMP_A= "0", a "NOK" output of the SA1 function is validated and this function remains in a waiting loop. When the powertrain is active, this state is indicated by the information GMP_A= "1" and an "OK" output of the SA1 function is validated.

[0037] The SA2 function detects whether or not the driver is pressing the PF brake pedal based on the aforementioned AF information. If the PF brake pedal is not pressed, indicated by the AF= "0" information, a "NOK" output from the SA2 function is validated and this function remains in a waiting loop. When the brake pedal is pressed, this pressure is indicated by the AF= "1" information and an "OK" output from the SA2 function is validated.

[0038] The SA3 function is an "AND" logic function receiving as input the "OK" outputs of the SA1 and SA2 functions. When the powertrain is active GMP_A= "1" and the brake pedal is pressed AF= "1", the SA3 function delivers information CDV= "1" which indicates that the applicability conditions are met.

[0039] In the embodiment described above, the SA2 function uses the AF brake support information available in the CMM computer. Alternatively, this SA2 function could be carried out using the PM master cylinder pressure information, a brake support AF= “1” then being validated when the master cylinder pressure is higher for a certain duration than a pressure threshold with hysteresis.

[0040] As visible at the Fig.2 , functional block B essentially comprises a valid brake application detection function SB0, two fault detection functions SB1 and SB2 dedicated respectively to the pressure information PR1 and PR2 of the pressure sensors CP1 and CP2, and a plausibility anomaly decision function SB3. The processing performed by the fault detection functions SB1 and SB2 is identical. Only the processing performed by the fault detection function SB1 is described below.

[0041] According to the invention, the fault detection on the pressure information PR1, PR2, is carried out on sufficiently strong brake presses AF, for which the tests and simulations carried out by the inventive entity have given optimal results. The valid brake press detection function SB0 quantifies a ratio R_PF of depression of the brake pedal PF and compares the ratio R_PF to a threshold SR to decide on the validity of the corresponding brake press AF to carry out a plausibility diagnosis of the pressure information PR1, PR2. Thus, in the function SB0, a sub-function SB01 quantifies the ratio R_PF, in percent (%), from the master cylinder pressure information PM, by means of the following equality: R_PF=(PM / PMmax)x100, in which PMmax is the maximum master cylinder pressure.Another sub-function SB02 of the SB0 function compares the R_PF ratio obtained with the SR threshold and validates the corresponding AF brake support by activating an “OK” output when the R_PF ratio is greater than the SR threshold (R_PF>SR). Otherwise, activating a “NOK” output invalidates the AF brake support and the SB02 sub-function loops on hold. The “OK” output delivered by the SB02 sub-function activates the execution of the two fault detection functions SB1 and SB2.

[0042] In the fault detection function SB1, at a time t0 corresponding to the activation of the function by the “OK” output of SB02, the pressure information PR1 t0 delivered by the sensor CP1 is stored by the sub-function SB11, with PR1m being the pressure information PR1 t0 stored.

[0043] The SB12 subfunction calculates the evolution delta DIF_PR1=PR1 t -PR1m between the current instantaneous pressure information PR1 t delivered by the CP1 sensor and the stored pressure information PR1m.

[0044] Fault detection on pressure information PR1 uses sub-functions SB13, SB14 and SB15 and is carried out by comparing the evolution delta DIF_PR1 with a pressure evolution threshold S_PR1 and applying a persistence duration TEMP.

[0045] The pressure evolution threshold S_PR1 is variable and is defined by sub-function SB13 according to the vehicle's rolling speed VV and the atmospheric pressure PA, with S_PR1=f(VV, PA). Sub-function SB14 compares the evolution delta DIF_PR1 to the pressure evolution threshold S_PR1 and activates an "OK" output when the evolution delta DIF_PR1 is lower than the pressure evolution threshold S_PR1, DIF_PR1 <S_PR1. Dans le cas contraire, l'activation d'une sortie « NOK » maintient la sous-fonction SB14 dans une boucle d'attente.

[0046] The persistence during the duration TEMP of the inequality DIF_PR1 <S_PR1 est vérifiée par la sous-fonction SB15 qui active une sortie « OK » lorsque cette persistance est effective. Dans le cas contraire, c'est une sortie « NOK » qui est activée par la sous-fonction SB15. L'activation de la sortie « OK » de SB15 correspond une détection de défaut DEF1 sur l'information de pression PR1, détection de défaut DEF1 qui est activée par la sous-fonction SB16 avec DEF1 = « 1 ». L'activation de la sortie « NOK » de SB15 correspond à l'absence de détection de défaut et renvoie le processus à la sous-fonction SB02 en attente d'un prochain appui frein AF valide.

[0047] There Fig.3 illustrates the processing carried out by the fault detection function SB1 (or SB2) for two life situations SV1 and SV2 corresponding respectively to a non-detection of fault DEF1 (DEF2) = “0” and a detection of fault DEF1 (DEF2) = “1”. In the illustrative curves of the Fig.3 , the unit of pressure is the hectopascal (hPa).

[0048] In the life situation SV1, after time t0, the instantaneous pressure PR1 t in the vacuum chamber of the brake booster SF, indicated by the pressure information PR1, changes rapidly and increasingly due to the vacuum consumption resulting from the brake application AF. The evolution delta DIF_PR1 remains below the pressure evolution threshold S_PR1 only for a short time t1-t0, which is less than the persistence time TEMP. The evolution of PR1 t is consistent with that expected in the context of normal operation and no fault (DEF1 = "0") is reported by the process for the pressure information PR1.

[0049] In the life situation SV2, after time t0, the instantaneous pressure PR1 t slowly evolves in an increasing manner and the evolution delta DIF_PR1 remains below the pressure evolution threshold S_PR1 during the persistence duration TEMP. The evolution PR1 t does not conform to that expected in the context of normal operation and a fault (DEF1 = "1") is reported by the process for the pressure information PR1.

[0050] In the embodiment described above of the method according to the invention, a simple fault detection is carried out with a single pressure evolution threshold on the evolution delta (such as S_PR1 for DIF_PR1). It will be noted that it is within the vision of the inventive entity to carry out the fault detection with several pressure thresholds so as to be able to discriminate faults of different types. Thus, in another particular embodiment of the invention, an additional pressure evolution threshold is provided on the evolution delta, namely, a lower pressure evolution threshold, which complements a higher pressure evolution threshold (such as S_PR1 for DIF_PR1), to discriminate a freezing fault where the pressure information given by the sensor evolves very little.

[0051] The plausibility anomaly decision function SB3 processes the results of the fault detections DEF1, DEF2, carried out by the fault detection functions SB1, SB2, and decides whether or not a plausibility anomaly is present on the pressure information PR1, PR2. The SB3 function also categorizes the plausibility anomaly by indicating its type. Thus, the plausibility anomaly can be categorized as a common mode between the two pressure sensors PR1, PR2, a freezing or a higher drift of the sensors PR1, PR2, informing of sufficient depression in the brake booster SF when this is not the case.

[0052] The plausibility anomaly decision function SB3 is also responsible for communications (see G_GD and C_HB on Fig.1 ) in particular with the SW_GD / GAR software module and / or the SW_HBB / HBC software module for the activation of one or more degraded modes, such as for example the MD1 to MD5 modes described with reference to the Fig.1 , following the detection of a plausibility anomaly in the pressure information PR1, PR2. However, before authorizing these communications and the activation of a degraded mode, the process checks that the validity conditions verified by the functional block A are indeed fulfilled. The “AND” type logic function, SB30, receiving as input the CDV information from the functional block A and an output from the function SB3 schematically represents this check before the aforementioned communications with the software module SW_GD / GAR and / or the software module SW_HBB / HBC.

[0053] The invention is not limited to the particular embodiments which have been described here by way of example. Those skilled in the art, depending on the applications of the invention, will be able to make various modifications and variations falling within the scope of protection defined by the claims.

Claims

1. Method for diagnosing the plausibility of at least two pieces of brake pressure information (PR1, PR2) coming from separate pressure sensors (CP1, CP2) in a brake booster (SF) of a vehicle braking system (SFA), characterized in that it comprises the steps of a) detecting (SB0) a valid brake pressure (AF) by comparing a brake pedal depression ratio (R_PF) with a predetermined depression ratio threshold (SR), b) following (SB1, SB11, SB12; SB2) an evolution of each said piece of pressure information servo-brake (PR1, PR2) over a predetermined time period (TEMP) from the detection in step a) of a said valid brake pressure (AF), c) for each said servo-brake pressure information (PR1, PR2), performing (SB1, SB13, SB14, SB15, SB16; SB2) during said predetermined time period (TEMP) a detection of defect (DEF1, DEF2) on said servo-brake pressure information (PR1, PR2) by comparison of an evolution delta (DIF_PR1) from said servobrake pressure information (PR 1, PR 2) to at least one pressure change threshold (S_PR 1), and d) establishing (SB 3) a diagnosis of plausibility of said servobrake pressure information (PR 1, PR 2) from the fault detection results (DEF 1, DEF 2) obtained in step (c).

2. Method according to claim 1, characterized in that the said step d) also comprises a categorization (SB3) of the said plausibility anomaly.

3. Method according to claim 1 or 2, characterized in that the said pressure change threshold (DIF_PR1) is a variable threshold (SB13) determined as a function of the running speed (VV) of the vehicle and of the atmospheric pressure (PA).

4. Method according to any one of claims 1 to 3, characterized in that, in step a), the said brake pedal depression ratio (R_PF) is determined from a hydraulic pressure (PM) in a master cylinder (MC) of the said vehicle braking system (SFA).

5. Method according to any one of claims 1 to 4, characterized in that it also comprises a verification (A, CDV, SB30) of conditions of validity of the said diagnosis of plausibility of the brake booster pressure information (PR1, PR2), the said conditions of validity being satisfied when an active state (SA1, GMP_A) of a power train of the vehicle and a brake support SA2, AF) is detected.

6. Method according to any one of claims 1 to 5, characterized in that it also comprises a communication (C_GD) of the said plausibility diagnosis to means for managing the degraded mode (SW_GD / GAR) of the vehicle.

7. Vehicle braking system (SFA) comprising a brake booster (SF) equipped with two distinct pressure sensors (CP1, CP2) delivering brake booster pressure information (PR1, PR2) and a computer (CMM), characterized in that said computer (CMM) comprises a memory (MEM) storing program instructions for implementing the method according to any one of claims 1 to 6.

8. Vehicle braking system according to claim 7, characterized in that the said two pressure sensors (PR1, PR2) are of the same technology.

9. Vehicle braking system according to claim 7 or 8, characterized in that the said computer is a multifunction engine computer (CMM) of the vehicle.

10. Vehicle comprising a braking system (SFA) according to any one of claims 7 to 9.