GB2352785A

GB2352785A - A method of indicating a malfunction in a brake booster system

Info

Publication number: GB2352785A
Application number: GB0018134A
Authority: GB
Inventors: Ernst Wild; Kristina Eberle
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-07-30
Filing date: 2000-07-24
Publication date: 2001-02-07
Anticipated expiration: 2020-07-24
Also published as: GB2352785B; KR100628853B1; DE19935899B4; JP2001055135A; DE19935899A1; KR20010076167A; GB0018134D0

Abstract

A method of indicating a malfunction in a brake booster system comprises measuring, by sensor (DS, Fig.1), the pressure P in a brake pressure storage device of the system, comparing this value, in unit 10, with a reference pressure ps+DPS (ps= I/C engine intake pipe pressure and DPS being a first pressure tolerance), and providing a malfunction signal to OR gate 50 in dependence on P>ps+DPS and no actuation of the brake(BRN) for a time T1. A second malfunction signal, from unit 20, is supplied by comparator 22 if P>pu+DPU (pu=ambient pressure at the I/C engine and DPU being a second pressure tolerance). A third malfunction signal, from unit 30, is dependent on brake release (BRL, Fig.3), a time delay (T =TTBRL), the difference between final (pe) and initial (pa) pressures measured by the sensor being greater than a maximum increase (DPLE), and BRN. A fourth malfunction signal, from unit 40, is dependent on the brake pressure not increasing over a time period on brake actuation (BR, Fig.4).

Description

2352785 1 Metho of operating a- brake bogstgr system in a reliabIV nmwier;

bra)gz bootrstem and c'r _I cuit f gr same for the purnose of implementinazffie method

Prior art

The inveation relates to a method of operatitig in a reliable manner a brake booster system for a braking system of a vehicle, in particWar a vehicle which is driven by an internal combustion en gine.. wherein a pressure sensor serves to measure a pmssure value preyailing in the brake pressure storge device of the brake booster system- Moreover, the invention relates to a brake bopster system, in particular a suction-air brake booster SYSICm, for a vehicle braking sys= which is to be actisted by means of an actuating mechanism and has a brake pyessuru storage device and dispose d thereon a pressure sensor which measures the pressure value prevailing in the brake press= storage device of the brake booster systvn. Furthermore, the invention relates to a circuit for implementing the meth)nd stated above and for installation iato the aforementioned brake booster system- Vehicles, in pardoular vehicles which are driven by internal combustion engines, am frequently inst4led with braking systems which are provided with a brake booster system for the purpo:ste of assisting the muscle power of the driver by virtue of an awcUiary force. Ln the so- cpAudhydraulic brake booster systems, this aiDdliary force is generated by virtue of excess/pressure which prev0s in the brake pressure storage device and which is pro-vido by a hydraulic pump. In the so-called suction-air brake booster systems, this au:ciloq force is generated by virtue of negative pressure which prevails in the brake pre.vure. storage device and which originates fmm t4e intake pipe of the internal combustion engine or is provided by a vacuum punp. in order to operate the brakc 2 booster system in a reliable manner, a pressure sensor is conventionally installed in the brakt pressure storage device to check whether sufficient pmssure prevails at this site, The pressure sensor is connected to a brake pressure control which increases or decreases the brake pressure in the brake pressure storage device by reason of the pressire value measured by the pressure sensor- In the case of a conymtional method of operating a suction-air brake booster system by the pressure suu-;or, a higher -throttle ratio (intake pipe pressure divided by the pressure upstream of the throttle flap) is required if an excessively low level of negativc, pressure is measured in the brake pressure storage devicg,-. However, this knovm method has the disadvantage that the brake pressure control functions incorreWy if a malfunction occurs in the brake booster system, in particular if a defective prtissue sensor has been inadvertently iwtalled in the brake pressure storage device. However, it is desirablu that sufficient pressure for the brake booster system can also be gaaranter--d in such cases.

It is the -object of the invention to improve the method and the brak-e booster system mentioned in the introduction, so that it can also be operated in a reliable, manner if a malfimction occurs, in particular if the pressure sensor is defective, Moreover, a circuit for impleineriting the aforementioned method and for installation into the brake, booster system shall be proposed.

The object is achieved by a method having the features of claim 1, and by a brake booster system and a circuit for same according to any of the parallel independent claims.

Accordingly, it is proposed that -die actuation of the brake is monitored and that a malfunction in the brake booster system is identified in that the pressure value measured by the pressure sensor is evaluated in dependence upon the actuation of the brake, To this end, the brake booster system in accordance with the invention has a diagnostic circuit which is connected to the pressure sensor and to the actuating mechanism of the brake and whieb for the purpose of identifying a malfimction in the brake booster system evaluate$ the pressure value, which is measured by the pressure sensor, in dependence upon the actuation of the brake.

The invention is based UP,033 tile recognition that a fmctional pressure sensor must measure chmcteristio PI'esSUre values or pressure value pmgmssions in the brake pressure storage device which are determined in dependence upon the ar,=tion of the brake. However, if the measured pressure -values deviate too severely from these cbm-acteristic pressure values, there is a defect in the brake booster sYstem and the brake Plessure MaTuj,r, The invention. has the. advantage that control is not able to fimction in the correct during the operation of the brake booster system, it is possible to diagnose malfunctions, in particular a defective pressure sensor and leakages in the brake booster. systeuL Moreover, the invention can be applied to hydraulic brake booster systems and also to suction-air brake booster systems.

in the case of one advantageous embodiment of the invention for use in a suction-air brake booster systern, the intake pipe press= in the intemal combustion engine of the vehicle is measured and influenced with a predeterminable first pressure tolerance. A check is then made as to whether the measured pressure value is less than t1le influenced intake pipe pressure, if no actuation of the brake takes place for a predetelTninable period of time. These features render it possible to diagnose in a continuous manner the stand-by state of the brake booster systern, ix- the state in which the brake has not recently been actuated and is ready for a new actuation, which substantially increases the operational reliability of the braking system.

In this connection, it is particularly advantageous if the ambient pressure at the internal combustion engine of the vehicle is also meas=d and influenced with a predeterminable second pressure tolerance, and if a check is made as to whether the measured pressure value is less than the influenced ambient pressure. This renders it possible to identify a maMnction either in the stand-by state or in the activation state of the brake booster system, wlAch increases thereliability during the, entire operating time; of the braking system, i.e. for the total duration of the driving operation.

In the case of a farther advantageous embodiment of the invention, the measured pressure value is monitored with respect to time and a pressure increase is determined therefrom, 4 and thez a check is made as to whether this presswe i=rease is less than a prede-terminable maximuza increase value, as Jong as Do actuation of the brake takes place. These features render it possible to make an extremely rapid diagnosis of leakages, should they occur in the stand-by state of the brake booster zystern.

In the case of another advantageous embodiment of the invention, a chc'ck is made as to whether the mewured pnssure value increases if the brake is actuated. As a consequence, a ie.,age occurring in the, activation state of the brake booster system is immediately identified.

Further features, possible applications and advantages of the invention are evident in the description hereinunder of exemplified embodiments which are illustrated in the drawings. All of the features described form, in their own right or in any combination, the subject matter of the invention, imspective of how they = described iii the claims or of their relation to othei claims, and irrespective of the manner in which they are worded and illustrated respectively in the description and the following drawings, in which

Figure I,hows a schematic illustration of the structure of a brake booster system in accordance with the invention-, Figure 2 showg the schematic block diagram of a diagnostic circuit which is incorporated in the brake booster system and Ainctions according to the method in accordance with the invention; Figure shows a schematic illustration of the structure of an evaluating urdt which forms part of the diagnostic ciicuit in accordance with the invention, and Figure 4 shows a schematic illustration of the sLru=e of a ftther evaluatinc, unit Z5 which also forms part of the diagnostic circuit in accordance with the invention.

Figure I shows as a possible oxemplified embodiment of the invention a suction-air brake booster system BKV having a brake pressure storage device S, in which there is negative press-ore which originates from the intake pipe of the inimal combiLsfion engine. Disposed on the brake pressure storage device S is a pressure sensor DS which measures the negative pressure. The measured pressure value P is 8upplicd to a brake pressure control R which controls the throttle ratio A (intakc pipe pressum. divided bv the pressure upstrewn of the throttle flap) for the internal combustion engine.

Moreover, the brake booster system BKV in =cordarice with the invention cont9ins a diagnostic circuit I which is connected to the pressure sensor DS and to tht: actuating mechaiiism M (bralce pedal etc.) for the brake. Consequently, the diagnostic circuit I is provided with input variables such as the measured pressure value P and the signals transmitted from the braking mechanism M, in particular the signal BRN "brake not actuated7, the signal BIZ "brake actuated" or the signal BRL "brake released". The diagnostic circuit I evaluates these input variables and establishes whether a malfunction is occurring in the brake booster system BKV, in order then to generate a maMnetion signal F where appropriate.

Figure 2 sbows a block diagram for the diagnostic cimuit I w1dch contains four evaluating units 10, 20, 30 and 40 which will be described in more detail hereinundur. The evaluating units are each supplied with the pressure value P measured by the pressure sensor. Each evaluating unit is able to gene-rate a nuilfunction signal. Tbertfore, an outputs of the evaluating units are guided to an OR-gate 50 which always generates a malf=ction signal F, if at least one of the evaluating units identifies a malfunction in the brake booster system, The first evaluating unit 10 will first be described in more detail:

The input variables for this first evaluating unit 10 are the measwed pressure value P, the C3 iniake pipe pressure ps in the internal combustion engine, a predeterminab)e first pressure tolerance DPS and the signal BRN "brake not actuated7which is transmitted by the 6 actuating mechanism of the brake. The evaluating unit 10 contains an adder 11, in which the intake pipe pressire ps is influenced with the pressure tolerance DPS, and a comparator 12 which compares this influenced intake pipe pressure (ps+DPS) to the measured pressure value P. Moreover, the evaluating unit 10 contains an AND-gate 14, of which the first input is connected to the output of the comparator 12 and of wbich - the second input is connected to the output of a time switching member 13. The time switching member 13 is adjusted to a predeterminable puriod of d= TI =d is triggered by the signal BRN. This serves to establish whether no brake actuation takes place for this predetcrminable peliod of time T. If this is the -ease and if the measured pressure value P is greater than tht influenced intake pipe pressure (ps+DPS), then the time switcbing member 13 and the comparator 12 cacb provide a logic ONE. The AND-gate likewise. now produces a logic ONE, which corresponds to a first maffimction signal which is sirpplied to the OR-gate 50.

With the aid of the first evaluating unit 10, the intake pipe pressure ps in the. internal combustion engine is measured and is influenced with the predeterminable pressure tolerance DPS, in order to check whether the pressure vulue P measured by the pressure sensor assumes a value which is characteristic of the malfunction-free, operation of the brake booster system, Le, to check whether the pressure value P is less than the iafluenced intake pipe pressure (ps+DPS), if no attuation of the brake takes place for the predeterminable period of time TL However, if during the stand-by state of the brake, i.e. for as long as the brake is not actuated, the meamired pressure value P is greater, the first evaluating unit 10 identifies a malfunction 10 which can be attributed to a defect in the pressure sensor.

A further malfunction in tht brake booster system is identified by the second evaluating unit 20 which will now be described in more detail with reference to Figure 2:

This second evaluating xmit 20 has as input variables the measured pressure value P, the ambient pressure pu at the internal combustion engine and a second predeterminable pressure tolerance DPU. The. second evaluating unit 20 contains am adder 2 1, in which 7 the ambient pressure pu is influenced with the predetermiuable pressure tolerance DPU Moreover, the evaluating urit.20 contains a comparator 22 which compares the measured prcssure value P to the lafluenced ambient pressure (pu+DPU). This p"al circuit serves to identify dufing the activation state of the brake C'brake actuated"), whether the pressure value P measined by the pressure sensor is less than the influenced ambient press= (pu+DP(D, which La turn means that the pressure sensor is defective, In this case, the comparator 22 provides a logic ONE which indicates Us malftrution in the bTake booster system. The output signal of the comparator 22 is transmitted as the second malfunction signal to the OR-gate SO.

Nloreover the diagnostic circuit I illustrated in Figure 2 contains also a fliird evaluating unit 30 and a fourth evaluating =it 40 which eacb identify a further malfunction in the brake booster system and transmit correspondiag maifunction signals to the OR-gate 50. These. evaluating units 30 and 40 will be described in detail hercinunder with reference to Figures 3 and 4 respectively; Fig= 3 shows the block diagram for the third evaluatiug unit 30 which identifies whether a leakage is occurring in the brake booster system and which generates a malfuncdon signal where appropriate. The available iiiput vadabies for the third evaluating uriit 30 = the meas:ured pressure value P, the signals BRL "brake released" and 13RN "brake not aCtUated77 as Mmsmitted by the actuating mechanism of the brake, and a predetem)inable maximum increwe value DPLE. The measured pressure value P is written into two storage cells (RAM-cells), of which one is formed as the time switching member 32 and the other is formed as the sample-and- hold circuit 33. The sample-and. hold circuit 33 is triggered by a holding signal ("hold") and generates at the output a signal which indicates theinitial pressure value parneasured by the pressure sensor. The time switching member 32 is triggered by a switch 31 and generates a signal which indicates the final pressure value pe measured by the pressure sensor. A subtracter 37 is used to form a difference (pe-pa) from the:Bnal pressure value pt! and the initial pressure value pa, said diffca-ence representing the pressure increasr, within the brake pressure storage device.

8 In order to e.stablish the initial value pa, the trigger input of the sample-and-bold circuit 33 is connected to the output of a comparator 3 5 which compares the signal BRL "brake release&' trailsmitted by WaY Of a time switching member 34 to the output of a differmt comparator 36. Tls different comparator 36 inturn compares the measui-ed pressure value P to the initial pressure Vgue Pa provided at the beginning by the sample-and-hold circuit 33.

D-ke final pressure value pt is established by transmitting the measured pressure -value, P to the first-narned time switching member 32 which also serves as a storage cell, wherein this time switching member 32 is controlled by way of a sWitch 3 1 and is adjusted to a predetermined period of time T which corresponds to a predeterminable delay time (T = TTBRL). The s,%;vitch 31 is controlled in turn bY the Output Of the comparator '35 which is connected to the trigger iuPut Of the samPle-andhold circuit 33. Consequently, the measured pressure value P is vMtten juto the storage cells 32 aDd 33 after the period of time T2 which has elapsed after the release of the brake. If -the pressure value P continues to fall, then the new lower presse value is written i-ato the storage cells. In addition, the pressure value is written into the first storage cell 32 after the delay time TTBRL has elapsed. Therefore, the storage cells provide the aal pressvx value pe and the initial pressure value pa which are used to form the, difference: pe-pa far the purpose of calculating the pressure increase. This difference (press= increase) is compared in a subsequent comparator 308 to a predeternlinabic maximum increase value DFLE wbich indicates an unacceptable pressure increase in the event of a leakage. if the estabLished pressure increase (pe-pa) is not less than this maximulu inacase -yalue DPLE, then the comparator 38 generates a logic ONE which is suppi. ied to an AND-gate 39. This AND gate 39 is also suppJied with the sigrial BRN "brake not actuateel, so that the AND-gate 39 then transmits a third malfunction signal F, if a nlativelY high pressure increase occurs despite the non-actuation of the brake. In other words, it is assumed that a malfunction has occurred as a resWt of a leakage in the brake booster system, if the pressure increase is not less than the m&xi-m-um. increase value during the period of time, in which the brake is 'not actuated, 9 figure 4 shows the block diagram for the fourth evaluating unit 40 which checks whether the pressure micreases upon actuation of the brake. If this is not the case, then a fourth malfunction signal F is generated. The input variables which are applied to the inputs of the evaluating unit 40 are the measured presswe value P aud the signal BR "brake actuated" which is trantted by the actuating mechanism of the brake, The signal BR "brake actuatedl is b-ansmitted to a slope detector 43 whi-oh is conuected to tL6-, input of an AND-gate 44. The measured pressure value P is transmitted to the first input of a comparator 42 and to the input of a time switching member 41, which in turn, is connected to the second input of the comparator 42. This cimuit has the fimcdon of a differentiating, inember which establishes whether the pressure value P measttred over the period of time. T is increasing.

The output of ft comparatpT 42 is connected to the iiiput of the AND-gate 44, whereby the AND-gate 44 then generutes a log;ic ONE, if there is no pressure increase, even though the brake is being actuated. 1herefore, leakages are identified and indicated as a malfunction during the activation state of the brake.

The invezition has been described vAth refarenv4: to possible applications in a suction-air brake booster systems. However, this does not represent a limitation of the applications in accordance with the invention in the case of btake boosters in general. For example, the inven4on is also suitable for use in hydia-ulic brake booster systems. Sir"arly, the hivention can be applied not only to vehicles operated by internal combustion engines, such as road vehicles, but also to vehi-cles in general which are equipped with brake booster systems, such as electrically operated rail-bamt- vehicles.

Claims

1. IAethod of operafiDg hi a reliable marmer a brake booster system (BK'V), i-a particular a suction-air brake boosteT system. for a braklincr system of a vehicle, in particular a vehicle which is driven by an intemal combustion engine., wherein a pressure sc-nsor (DS) serves to measure a prcssun- vaiue (P) prevailing in the brake press= storage deNricee (S) of the brake booster system (DKV), characterised in that the actuation (BRN; BR, BRI.) of the brake is monitored and that a malfunction (F) which occurs in the brake booster system (BKV.) is identified in that the pressure value (P) measuxed by the pressure sensor (DS) is evaluated in dependence upon the actuation (BRNI; BR; B.U) of the brake.

2. Method according to claim -.haracterised in that the intake pipe press= (ps) in the interilal combustion engine of the vehicle is measured and influenced,;,rith a predete=inalble first pressuie toleran= (DPS), and that a check is carried out as to whether the measured pressure value (P) is less tluan the influcnced iTitake pipe pressure (ps+DPS), if no actuation (BRN) of the brake takes piace for a pre,determinable period of time (T).

3. -Iviethod acQordinc, to c lairn 2, charazterised. in that the ambient pressure (pu) at the internal combustion enolne of 'the vehicle is measured and infl. uenced with a przdettrminable second pressure tolerance (DFU, and that a check, is carried out as to -whether the rne=ed pressure value (P) is less than Lhtt influenced ambient pressure (t)-U-DPU)- 11

4. Method according to any one of the preceding claims, characterised in that the measured prmure value (P) is monitored with respect to time and a pressure increase (pe-pa) is determined thcxefrorri, and that a cbeck i5 carried out as to whether this pressure increase (pe-pa) is It,-!ss than a predeterminable third preasure tolerance (DPLE), as long as no actuation (DRN) of the brake takes place.

5. Method according to any vac of the preceding claims, characteriscd in that a check is carried out as to whether the measured pressure value (P) increases if the brake is actuated (BR).

6. Brake booster system (BKV), in particular a suciion-air bralce, booster System, for U braking system, whicb, is, to be actuated by means of an aenuiting mechanism of a vehicle, in particular a vehicle which is driven by an internal combustion engine, having a brake pressure storage dcvice (9) and disposed thereon a pressure sensor (DS) which measures the pressure value (P) prevailing in the brake pressure storage device (S) of the brake booster system (BKV), ebaracterised by a diagno-stic circuit (1) wbich is connected to the pressure sensor (DS) and to the actuating mechanism (M) of the brake and which for the purpose of identifying a malfunction (F) in the brake booster system (BKV) evaluates the pressure value (P), Wbich is measured by the pressure semor (DS), in dependence upon the actuation (BRN; BR; BRL) of the brake.

7. Brake booster system (BKV) according to claim 6, chardeterised in that the diagnostic oircuit (1) conuins a first evaluating unit (10) which mewsures die intake pipe pressure (ps) in the internal combustion en&e of the vehicle and influeum it with a predeterminabIc fnt pressure tolerance (DPS) and checks whether the measured presore value (P) is less than the influenced intake pipe pressure (ps+DPS), if no actuation (BRN) of the brake takes place for a predeterminable period of time C11).

12

S. Brake booster system. (BKV) according to claim 6 or 7, characterised in that the diagnostic, circuit (1) contains a sevond evaluating unit (20) whirh Measures; the ambient presmze (pu.) at the internal combustion engine of the vehicle and influencei it with a predetenninable second pressure tolerance (DPLD and which checks whether the. me-asured pressure value, (P) is legs, than the influenced ambieat pressure (ptI-f-DPTJ).

9- Brake booster system (BKV) according to any one of the claims 6 to 9, characturised in that the diagnostic circuit (1) contains a third evaluating wait (30) which monitors ft measured pressure value (P) with respect to time and de,termines therefrom a pressiare increase (pe-pa) and which checks whether this pressure iucreasc (pe-pa) is less than a predeterminable maximum increase value (DPLE), as long as Do actuation (BRN) of the brake takes place.

10, Brake booster systern (BKV) according to ctaim 9, characterised in that the third evaluating twit (30) contains a first and a second storage cell (32; 33) which st:rVes to store the pressure value (P) after completion of a predetcrminable time interval (T2), which commences with the release (BRL) of the brake, and if the pressure value (P) decreases, said evaluatinp, unit vaites the new pressure value into the second storage cell (3-1) after completion of a predeterminable delay time (ITIM).

11. Rrake booster systein. (BKV) according to any one of the claims 6 to 10, chamettrised in that the diagnostic circuit (1) contains a fourth evaluating urdt (40) which checks whether the measured pressure valut: (P) increases if an actuation (BR) of the brake, takes place.

12. Circuit (1) for the purpose of iraplementiag a method according to any one of Ihe clai= I to 7 and for installation into a brake booster system (BK-V), in particular into a suction-air brake booster system, for a braking systern, which is to be actuated by means of an actuating mechanism (N, of a vehicle, in particular a

13 vehicle which is driven by an internal combustiori engine, having a brake pressure Storage device (S) and disposed thereon a pressure sensor (DS) which measurcs the press-ure value (P) prevailing in the brake pressure storage device (S) of the brak-e. booster system (BKV), chw-acterised in that the circuit is a dia'gnostic circuit (1) which is connected to the pressure sensor (DS) and to the actuating mechanism (W of the brake and which for the purpose of identifying a malfunction (T) in the brake booster system (BKV) evaluate& the pres.,mre value (P), which is ineasizcd by th,-, pressure sensor (DS), in dependence upon the actiiation (BRN; BR; BRL) of the brake.

I I Method of operating a brake booster system substantially as hereinbefore described with reference to the accompanying drawings.

14. Brake booster system substantially as hereinbefore described with reference to the accompanying drawings.

15. Circuit for implementing a method of operating a brake booster system substantially as herembefore described with reference to the accompanying drawings.