FR2769343A1 - METHOD AND DEVICE FOR DETECTING THE CUTTING OF A GLOW PLUG OF A MOTOR VEHICLE DIESEL ENGINE - Google Patents

Abstract

This method for detecting the cut out of a glow plug of a diesel engine of a motor vehicle, comprising at least two supply branches of at least two glow plugs each, is characterized in that it comprises the steps following: - we measure (at 25), each time the engine is started, the currents (IB1, IB2) flowing in the two branches, - we calculate (at 26) a ratio (Kcal) of these two currents, and - we compare (in 27) the calculated ratio (Kcal) to a reference ratio (Kref) for detecting a cut candle if the calculated ratio differs from the reference ratio, by at least one predetermined coefficient (S).

Description

The present invention relates to a method and a dis-

  positive detection of the cut out of a glow plug

  fage of a diesel engine of a motor vehicle.

  More particularly, the invention relates to the detection of a cut spark plug for a diesel vehicle engine.

  automobile branch, comprising at least two branches of supply

  tation of at least two glow plugs each.

  Such a method and such a device are intended for

  be associated with an electronic control unit for pre-

post-heating.

  This pre-postheating electronic unit is in

  makes a power interface that fits into a sys-

  check engine control between the calculation

  injector and the glow plugs of this engine

tor.

  One of the functions of this box is to energize the glow plugs when it receives them

the order of the calculator.

  In addition, such a box must incorporate a number of security and fault detection functions.

to meet certain standards.

  Thus, for example, such a housing must

  for candle feeding when it detects a surin-

  supply voltage or overvoltage.

  In addition, such a box must detect all the failures of the spark plugs and corresponding relays and transmit a status signal, i.e. a diagnostic signal, to the

  calculator for the evaluation of the functioning of the function

tion of these candles.

  The object of the invention is to propose a method and a device for detecting the cut out of a glow plug of a diesel engine of a motor vehicle which are simple, reliable and easy to implement in

such a context.

  To this end, the subject of the invention is a method for detecting the cut out of a glow plug of a diesel engine of a motor vehicle, comprising at least

  two supply branches of at least two pre-

  heating each, characterized in that it comprises the steps

following pes:

  - we measure, each time the engine is started, the

  rants circulating in the two branches, - we calculate a ratio of these two currents, and

  - the calculated ratio is compared to a reduction ratio

  reference to detect a cut candle if the ratio calculated

  the differs from the reference ratio by at least one predetermined coefficient. Advantageously, the baseline report is established

  during an initialization phase of the device at the first

  supply of the latter, by reading the circulating currents

  culvert in the supply branches during this initialization phase, calculation of the ratio of these currents and

  storing this report as a baseline report.

  Advantageously also, the coefficient predeter-

mined is 0.7.

  According to another aspect, the invention also relates to a detection device for the implementation of a

such process.

  The invention will be better understood using the

  description which will follow, given solely by way of example and made with reference to the appended drawings, in which:

  - Fig.l shows a block diagram illus-

  trating the general structure of an electronic preheating diesel control unit;

  - Fig.2 shows a block diagram illus-

  trating the general structure of an exemplary embodiment of a detection device according to the invention; and - Fig.3 illustrates a flowchart representing an example of operation of a detection method according to the invention. We recognize in fact in Figure 1, a housing

  preheating electronics for diesel engine

  automobile vehicle, this electronic unit being designated by

  the general reference 1 in this figure 1.

  As indicated above, this box constitutes

  demment, a power interface which is integrated in the engine operation control system between an injection computer designated by the general reference 2 and the glow plugs, designated by the reference

general 3 in this figure 1.

  In the embodiment, these candles are re-

  parts in pairs, the candles 1 and 2 being associated in a first pair 3a and the candles 3 and 4 being associated

in a second pair 3b.

  Each pair of candles is then supplied via a supply branch respectively

  4 and 5, from electronic unit 1.

  This box receives as input the mass, the most

  statement from the vehicle battery and a signal

command + APC.

  This housing 1 in fact comprises a power supply module.

  tion designated by the general reference 6, a communication module

  candle candles designated by the general reference 7 and a safety and diagnostic module designated by the reference

general 8.

  The spark plug control module 7 receives a control signal by a control line (Co) 9 from the

  injection computer 2, and this computer receives a

  general diagnosis by a diagnostic line (Di) 10 ema-

  from the safety and diagnostic module 8.

  The safety and diagnostic module fills more

  several protective functions as indicated above

  cedent. In addition, it may include a device for detecting the cutout of a glow plug, one of which

  exemplary embodiment is illustrated in FIG. 2.

  We know that such a security and

  diagnosis must be able to detect a good working

  glow plugs, cutting at least

  one of the candles and cutting all of the candles.

  In the detection device according to the invention, the currents flowing in branches 4 and 5 are analyzed

feeding these candles.

  Indeed, the detection device according to the invention

  tion includes means 11 and 12 for measuring currents

  IB1 and IB2 circulating in branches 4 and 5, respectively-

  connecting the control module 7 of the power supply

candles to them.

  This current information IB1 and IB2 is then transmitted to a central information processing unit designated by the general reference 13 in FIG. 2, which is suitable for calculating a ratio K of these two currents and for delivering this calculated ratio Kcal to means of comparison 14 of the latter with a reference ratio Kref, for detecting a cut candle if the ratio calculated by the unit 13 differs from the reference ratio by at least one predetermined coefficient S.

  In fact, the corresponding entry of the means of com-

  paraison receives Kref.S information established by

  calculation means 15, by multiplying the pre-

  determined S stored in storage means 16 and of the ratio Kref stored in storage means 17. The comparison of this information then makes it possible to detect a

cut candle.

  As will be described in more detail below, the Kref reference report can be established during a

  initialization phase of the detection device, upon

  better supply thereof, by calculating the ratio of the currents flowing in the branches 4 and 5, during this

  initialization phase and storage thereof.

  Of course, other embodiments of this

  device can be considered.

  In fact and as can be seen in FIG. 3, the operation of such a device begins with a step 20 of initialization and entry into the device of the value of the predetermined coefficient S. This coefficient constitutes a detection threshold who

  can for example be equal to 0.7.

  Then, during step 21, the information processing unit 13 for example, determines whether it is the first supply of the device to determine if the

  device requires an initialization phase.

  If so, this information processing unit

  mations 13 ensures in 22, the acquisition of circulating currents

  lant in branches 4 and 5 of candle supply,

  ie for example the currents IB1 and IB2 respectively-

ment in branches 4 and 5.

  After this acquisition of currents at 22, which can be carried out after a determined time for feeding the candles, this time being able to be established experimentally to obtain a stabilization of these, the central information processing unit calculates in 23, the report of

  reference Kref, from these currents IB1 and IB2, in use

  reading the relationship Kref = IB1 / IB2, for example.

  This reference report Kref is then stored during step 24 for example in the storage means 17 described with reference to FIG. 2. This then allows the

  calculation means 15 described with reference to FIG. 2, of

  blir the Kref product. x S, S being stored in the means of

storage 16 of FIG. 2.

  Once this initialization phase is complete and each time this device is powered up, that is to say each time the vehicle engine is started, the central information processing unit 13 reports during step 25 , the currents flowing in branches 4 and 5, that is to say

the currents IB1 and IB2.

  From these currents acquired for each new spark plug supply at each engine start,

  this central information processing unit 13 deter-

  mine in step 26, a calculated ratio Kcal in use

  sant the relation Kcal = IB1 / IB2, for example.

  It is understood that in normal operation, that is to say when all the plugs are operational, this calculated ratio Kcal must be equal to the ratio Kref established during

  the device initialization phase.

  On the other hand, if one of the candles is cut, for example the candle 1 or the candle 2 supplied by the supply branch 4, the calculated Kcal ratio differs from the ratio

  Kref established during the initialization phase.

  Indeed, one of the candles being cut, the current

  IB1 circulating in the corresponding branch is modified.

  To avoid any problem of inadvertent detection of a candle cut, linked to dispersions or drifts thereof, a detection threshold is then established using the coefficient S. Indeed, a cut candle is detected only if the ratio calculated Kcal differs from the reference ratio Kref by at least this predetermined coefficient S. Thus, for example, during step 27, the central information processing unit 13 compares the calculated ratio Kcal with the reference ratio Kref multiplied by the predetermined detection coefficient S to detect a cut candle in case of agreement and an operation

normal in case of discrepancy.

  Put in the form of an equation, the operation of this device can then be summarized as follows: - in normal operation: IB1 = KIB2, - if one of the spark plugs is cut, for example in the supply branch 4: IB1 <to KS IB2, - while if the four candles are cut:

IB1 = IB2 = O.

  We can then see that the coefficient S must be con-

  served in memory in the device and is used each time

  starting the engine of the vehicle to ensure the function-

  correct glow plugs.

  It goes without saying of course that different modes of

  operation of this device can be envisaged.

Claims (7)

  1. A method for detecting the cut out of a glow plug of a diesel engine of a motor vehicle, comprising at least two branches (4,5) supplying at least two glow plugs each, characterized in that '' it comprises the following stages: - the currents (IB1, IB2) in the two branches are measured (at 25), at each engine start-up,   - we calculate (at 26) a ratio of these two   rants, and - we compare (in 27) the calculated ratio (Kcal) to a reference ratio (Kref) to detect a cut candle if the calculated ratio (Kcal) differs from the reference ratio   (Kref) of at least one predetermined coefficient (S).   2. Method according to claim 1, characterized in that one establishes the reference ratio (Kref) during a   device initialization phase at the first power supply   tion thereof, by reading (at 22) the currents (IB1, IB2) flowing in the supply branches (4,5) during this initialization phase, calculation (at 23) of the ratio of these currents and storage of this report (in 24) as baseline report (Kref).   3. Method according to claim 1 or 2, character-   se in that the predetermined coefficient (S) is equal to 0.7.   4. Device for detecting the cut of a plug   Preheating unit for a diesel engine in a motor vehicle   bile, comprising at least two branches (4,5) supplying at least two glow plugs each, characterized   in that it includes means (11,12) for measuring the   rants circulating in the two branches (4,5), at each   engine setting, means (13) for calculating a ratio   (Kcal) of these two currents, and means (14) of comparing   sound of the calculated ratio (Kcal) to a reference ratio (Kref) to detect a cut candle if the calculated ratio differs from the reference ratio by at least one coefficient predetermined (S).   5. Device according to claim 4, characterized   in that it comprises means (16) for storing the coefficient   cient predetermined (S) and means (17) for storing the   reference report (Kref), delivered by the cal-   cul (13) of this reference report, from the currents flowing in the supply branches (4,5), during a   initialization phase of this device at the first power mention of it.   6. Device according to any one of the claims.   tions 4 or 5, characterized in that the coefficient predeter- mined (S) is equal to 0.7.   7. Device according to claim 4,5 or 6, ca-   characterized in that the comparison means (14) receive on one input the calculated ratio (Kcal) and on another input, the product of the reference ratio (Kref) by the   predetermined coefficient (S), established by means of cal- ass (15).