GB2245027A - I.c. engine misfire diagnosis apparatus - Google Patents

Description

DESCRIPTION "A MISFIRE DIAGNOSIS APPARATUS FOR AN INTERNAL COMBUSTION

ENGINW

The present invention relates to a misfire diagnosis apparatus for an engine, in particular wherein a misfire judgement is temporarily stopped at the start of the engine.

In general, it is ideal for producing a stable output that combustion in a multicylinder engine undergoes the same process every cycle. In the multicylinder engine, however, the combustion is liable to deviate for such reasons as listed below: (1) Nonuniformity in the distribution rate of intake air attributed to the complication of the shape of an intake pipe, the interferences of the intake air among cylinders, etc. (2) Some differences among the combustion temperatures of the individual cylinders attributed to cooling routes. (3) Manufacturing dispersions in the volumes of the combustion chambers of the individual cylinders, the shapes of pistons, etc. (4) Slight discrepancies of the air fuel ratios of the individual cylinders caused by unequal fuel injection quantities ascribable to the manufacturing errors of injectors, etc.

Heretofore, the so-called combustion fluctuation has been suppressed to the minimum by the air fuel ratio controls and ignition timing controls of the individual cylinders. In a modern high-performance engine tending toward a higher output and a lower fuel cost, however, when any of the injectors, ignition plugs etc. has degraded or broken down, intermittent misfire arises and produces a lowering of output.

Even when the intermittent misfire has occurred in one cylinder in the multicylinder engine, a driver often drives an automobile without noticing the misfire. Besides, it is difficult to diagnose during driving whether the cause of the misfire is temporary or is the degradation or the like of any of the injectors, the ignition plugs etc.

Therefore, according to the official gazette of Japanese Patent Application Laid-open No. 258955/1986 by way of example, a comparison is made between the difference of the minimum value and maximum value of the r.p.m. of an engine corresponding to a cylinder at the previous combustion stroke and the difference of the minimum value and maximum value of the engine r.p.m. corresponding to the cylinder at the present combustion stroke. The combustion condition of the pertinent cylinder is discriminated, depending upon whether or not the discrepancy between the compared -3values falls within a preset reference value. In a case where abnormal combustion has occurred in excess of a predetermined number of times, a misfire is judged, and warning is given.

With the prior-art technique mentioned above, the misfire condition is discriminated by grasping or sensing the revolution fluctuation of the engine. However, when the misfire is diagnosed at the cranking of the engine or at the initial stage of complete explosion at which the revolution fluctuation is great, the diagnosis is liable to become erroneous and poses a problem in reliability.

The present invention has been made in view of the above circumstances, and has for its object to provide a misfire diagnosis apparatis for an engine which can reduce erroneous diagnoses and attain a high reliability.

The present invention provides a misfire diagnosis apparatus for an internal combustion engine having a crankshaft for outputting power and a camshaft for actuating valves, the apparatus comprising a crank plate connected to said crankshaft for indicating a crank angle, a crank angle sensor for detecting said crank angle of said crankshaft and for generating a crank angle signal, a cam plate connected to said camshaft for indicating a cam position, a cam angle sensor for detecting said cam position of said camshaft and for producing a cam angle signal, a starter motor for starting said engine for producing a starter signal. and control means responsive to said crank angle and said cam angle for controlling an ignition timing of said engine, the apparatus further comprising: a plurality of even numbers of projections provided on a periphery of said crank plate for indicating said crank angle, said projections be--ng diametrically symmetrically arranged on said periphery and each pair of said projections being spaced apart by at least three different specific angles; a plurality of cam projections provided on a periphery of said cam plate and spac ed angularly apart at a predetermined angle on said periphery for indicating said cam position; discriminating means responsive to said crank angle signal and said cam angle signal for discriminating a cylinder number at a combustion stroke and for producing a cylinder number signal; misfire judgement stopping means responsive to said starter signal for stopping a misfire judgement for a predetermined period and for producing a stopping signal; misfire judgement means responsive to said stopping signal, said cylinder number signal, said crank angle signal and said cam angle signal for calculating a differentiated engine speed and for deciding a misfire of said cylinder number at said combustion stroke in order to generate a misfire signal; and warning means responsive to said misfire signal for storing a number of said misfire corresponding to said cylinder number and for indicating a malfunction of said internal combustion engine.

With the above construction, first, the misfire judgement stopping means M1 operates to stop the misfire judgement for the time period taken since the starter motor begins to be driven, until the predetermined time period lapses after the end of the drive of the starter motor.

Subsequently, the misfire judging means M2 operates to start the misfire judgement after the lapse of the misfire judgement stopping time period.

The present invention also includes an internal combustion engine comprising a misfire diagnosis apparatus in accordance with the present invention.

By way of example only, specific embodiments of the present invention will now be described, with reference to the accompanying drawings, in which:

Fig. 1 is a diagram showing the fundamental arrangement of the present invention; Figs. 2 - 9 illustrate the first embodiment of the present invention, in which Fig. 2 is a schemati- diagram of an engine control system, Fig. 3 is a front view of a crank plate and a crank angle sensor, Fig. 4 is a front view of a cam plate and a cam angle sensor, Fig. 5 is a time chart of pressure fluctuations in cylinders, crank pulses, cam pulses and engine r.p.m.,, Fig. 6 is a conceptual diagram of a misfire judgement level map, Fig. 7 is a time chart of differentiated r.p.m. and a misfire judgement level, Fig. 8 is a flow chart showing misfire diagnosis stopping steps, and Fig. 9 is a flow chart showing misfire judgement steps; Fig. 10 is a flow chart showing misfire judgement steps according to the second embodiment of the present invention; Fig. 11 is a flow chart showing misfire judgement steps according to the third embodiment of the present invention; and Fig. 12 is a flow chart showing misfire judgement steps according to the fourth embodiment of the present invention.

A misfire diagnosis apparatus for an engine according to the present invention comprises, as shown in Fig. 1, misfire judgement stopping means M1 for stopping a misfire judgement for a time period taken since a starter motor begins to be driven, until a predetermined time period lapses after end of the drive of said starter motor; and misfire judging means M2 for starting the misfire judgement after lapse of the misfire judgement stopping time period.

Figs. 2 - 9 illustrate the first embodiment of the present invention.

Numeral 1 in Fig. 2 indicates an engine proper. and a four-cylinder horizontally-opposed engine is shown in the figure.

An intake pipe 4 communicates with the intake port 2a of the engine proper 1 through an intake manifold 3, and an intake air quantity sensor 6 is incorporated in the part of the intake pipe 4 immediately downstream of an air cleaner 5. Also, an idling switch 8 which turns ON under a fully-closed throttle condition is joined to a throttle valve 7 which is incorporated midway of the intake pipe 4. Further, (multipoint) injectors 9 whose injection ports are directed toward the intake port 2a are disposed downstream of the intake manifold In addition, a crank rotor or crank plate 15 is secured on the crankshaft lb of the engine proper 1, and a crank angle sensor 16 which includes an electromagnetic pickup or the like for detecting a crank angle is mounted in opposition to the outer periphery of the crank rotor 15. Further, a cam rotor or cam plate 17 is secured on a camshaft ic which of 1/2 relative to the crankshaft sensor 18 for detecting a cam opposition to the outer periphery revolves at a rate 1b, and a cam angle angle is mounted in of the cam rotor 17.

As shown in Fig. 3, the outer periphery of the crank rotor 15 is formed with projections 15a, ISb and 15c. The respective projections 15a,!5b and ISc are formed at positions el, e2 and 0 before the top dead center QTDC) of compression in each cylinder, and an engine speed N is calculated from a time period in which the section between the projections 15b and 15c passes.

Meanwhile, in general, the crank angle (CA) which exhibits the maximum combustion pressure in the MBT -9(most best torque) control is substantially constant in the entire operating region, and the combus-L-Jon pressure does not abruptly rise before about 10' in terms of the BTDC crank angle yet.

Besides, as shown in Fig. 5, in the embodiment, the valve opening timing of the exhaust valve of each cylinder is set at the side of a somewhat retarded angle with respect to the ignition reference crank angle BTDC e2 of the next combustion cylinder. Since, however, the combustion pressure usually lowers abruptly immediately after the opening of the exhaust valve, it exerts almost no influence at the crank anale BTDC e3.

Accordingly, when the crank angle 63 of the projection 15c is set at an advanced anale side with respect to the BTD\-- CA of 100, the section between the crank angles BTDC e2 and 63 of the respective Jons 15b and 15c is hardly influenced by the project combustion between the cylinders. That Is, a work based on the combustion between the cvl-nder at a combustion stroke and the cylinder at the next on.

combustion stroke is not done in the sect- Also, as shown in Fig. 4, the outer periphery Of Lhe cam roror 17 is formed with projections 17a, 'c for discriminating the cylinders. The 17b and 11 -10projections 17a are respectively formed positions e4 after the top dead centers compression, of the cylinders #3 and #4.

at the (ATDC) of Besides, the projection group 17b is configured of three projections, the first one of which is formed at the position e5 after the top dead center (ATDC) of compression, of the cylinder #1. Further, the projection group 17c is configured of two projections, the first one of which is formed at the position K after the top dead center (ATDC) of compression, of the cylinder #2.

By the way, in the illustrated embodiment, there are held 61 97' CA, e2 = 65' CA, e3 = 10' CA, N = 20' CA, V So CA, e6 = 20' CA and e(2 - 3) = 55' CA. Owing to this arrayal, as indicated in Fig. 5, in a case where the cam angle sensor 18 has detected cam pulses at the angle eS (the projections 17b) by way of example, it can be discriminated that a crank pulse to be subsequently detected by the crank angle sensor 16 is a signal which indicates the crank angle of the cylinder #3.

Also, in a case where a cam pulse at the angle 64 (the projection 17a) has been detected after the cam pulses of the angle 65, it can be discriminated that the subsequent crank pulse to be detected by -lithe crank angle sensor 16 indicates the crank angle of the cylinder #2. Similarly, it can be discriminated that a crank pulse after the detection of cam pulses at the angle e6 (the projections 17c) indicates the crank angle of the cylinder #4. 13esides, in a case where a cam pulse at the angle e4 (the projection 17a) has been detected after the cam pulses of the angle e6, it can be discriminated that a crank pulse to be subsequently detected indicates the crank angle of the cvlinder #1.

Further, it can be discriminated that the crank nuise which is detected by the crank angle sensor 16 after the detection cf: the cam pulse(s) by the cam angle sensor 18 indicates the reference crank angle (---1) of the corresponding cylinder.

-ronJc Meanwhile, numeral 21 designates an elect - control unit which is con:Eigured of a microcomputer etc. CPU (central processing unit) 22, a ROM 23, a RAM 24, a back-up RAM 25 and an I/0 interface 26, which constitute the electronic control unit (ECU) 21, are interconnected through bus lines 27. The sensors 6, 16 and 18, the idling switch 8, a vehicle speed sensor 19 and a starter switch 32 are connected t ports of the I/0 interface 26, while Lo the input the injectors.0 and warning means, such as an indicator -12lamp, 29 disposed on an instrument panel or the like not shown are connected to the output ports c--F the 1/0 interface 26 through a driver circuit 28.

A control program, fixed data, etc. are stored in the ROM 23. The fixed data includes a misfire judgement level map MPLN LEVEL to be described later.

Besides, the output signals of the sensors S4 subjected to data proces Ing and data arithmetically i'Drocessed bv the CPU 22 are stored in the RAM 24, and trouble data items such as the misfire -judgement data of each cvlinder are stored in the back-un RAM 25.

--her, a trouble diagnos. Eor 30 is Fur'L. Jng conneci -he 1/0 inzerace connected to the output port oJ t 26. The trouble data stored in the backuz R.:.M 25 can be read out bv connectina a trouble diagnosing serial monitor 31 to the trouble diagnosing connectcr 30. in addift-Jor., a starter motor 33 and a power source "A are connected throuah -he starter switch --2.

- L_ _L - Incidentally, the ECU 21 is 'Led with a contrcilling 3 5 and a supply voltage through an ignition relay voltacre regulator circuit 36 from the power source 34, and the back-up RAM 25 with a backing-up supply -age. Besides, numeral 37 denotes an ignition volt switch.

"ire diaanosina function of Moreover, the mi4s- L -13the electronic control unit 21 includes Misfire judgement stopping means for stopping a misfire judgement for a time period taken since the starter motor begins to be driven, until a predetermined time period lapses after the end of the drive of the starter motor; and misfire judging means for starting '%.-he misfire judgement after the lapse of the misfire judgement stopping time period.

Next, misfire diagnosis -ronic steps in the elect controll unit 21 will be described in conjunction with the flow charts of Fias. 8 and 9. Diagnos-'s Stopping Steps: MI sf - This flow chart is started simultaneously with the closure of the power source of the ECU.

own 8, a misfire diaanosis -op As sh Fig. J_ - st -'alize a misf-I-re diagnosis is cleared so as to init-L stop flag at a step (hereinbelow, abbreviated l -G ing the m-s-f-4--e diagnosis to "S") 101 " 0, resett fire diaanosis is ston), and whether or not a mis.' stopped is judged at S102 et sea.

First, the S102 judaes if the starter sw-Lch 32 OIN. 1In a case where the starter switch 32 is OFF, the control flow returns to the S101. Bv the starter switch 32 is not ON after the power source of the ECU L-he misfire way, while the closure of the -14diagnosis stop flag FLAG A maintaJLns the status off: resetting the stop (FT AG, - 0). Since, however, the enaine is not started, a misfire diagnosing program to be described later is not executed.

On the other hand, when t-he starter switch 32 is judged 0'-,'i at the S102, the control flow proceeds to an S103, at which a delay timer TIMER1 is set at a set value nSET (corresponding to, for example, 2 sec.) (TIMER1 - nS-T). At an S104, the misfire is set (FLtlG. - 1, stopping diagnosis stop flag FLAC, M ]-he misfire diagnosi When the enaine is cranked b,,- the -starter motcr 333, tt-he crank rotor 15 ar,-,,' cam rotor 177 are rotated, and hence, the crank pulses and cam, pulses are respectively detected by and cam angle sensor 18. cranking is unstable and, width. Therefore, unless c ' 1 be tlag FLAG, is set, a misfire condition erroneously diagnosed in the Misfire d--aancsiJng program to be described later.

Subsequently, the control flow proceeds to an S105, which Judges if the starter switch 32 is OFF. in a case where the starter switch 33.2 -Js 0.N, judged that the engine is under the crankina -he crank anale sensor 16 r'he enaine r.

L -15the control flow returns to the S103. in a case where it, is OFF, it is tentatively judged that the enaine has undergone the complete explosion, and the S105 is followed by an S106.

At the S106, the set value nSET of the delay timer TIMER1 set at the S103 is decremented (TIMER1 - TIMER1 - 1).

Then, an S107 judges if the delay timer TIMERI has become zero. In case of TIMER1;e 0, it is judged that the timer is being decremented, the control flow returns to the S105, which judges again if the starter -heref Z1 switch 32 is OFF. The reason Lor hat, when t he engine was not started by the first cranking, the cranking operation might be conducted again. on the other hand,in case of TIMER1 = 0, the control flow oroceeds to an a predetermined time period S108 upon judging that has 'Lapsed, and the misfire diagnosis stop flag FWS.G A is cleared (FLAG, - 0), whereuiDon the routIne is left.

As a result, the misfire diagnosis is stopped during the cranking and during the predetermined time period since the complete explosion, during which the r. p. m. fluctuations are comparatively great. Therefore, erroneous diagnoses are diminished, the diagnostic accuracy is enhanced, and a high -reliability -16 can be attained.

Misfire Diagnosing Steps:

The misfire diagnosis is interruptingly executed for each cylinder in synchronism with the r. p. m.

of the engine.

As shown in Fig. 9, first of all, an S201 decides if the misfire diagnosis stop flag FLAG A of the misfire - stat diagnosis stopping program is in its reselL =s (FLAG A ": 0, resetting the misfire d-Jaanos-Js stop).

in case of FLAG A = 1 (stopping the misfire di4aanosis), it- is judged that the engine is under the cranking and the routine is lef t without making the misf ire diagnosis.

on. the other hand, in case of F-WIG, = 0 (resettina PI.

t11- lúe misfire diagnosis ston), in order to r7,a'--- the m-;s.'-re d-Jac:r.-.os-i-c:, an S202 discriminates the c,,,1i:-,der i (i = 1, 3, 2, 4) at a combustion s--ro--- on the -he crank r)-1se an,2 cam mulse(s) are bas-'s of 4L respectively delivered from the crank angle sensor 16 and cam angle sensor 18, and an S203 counts up I of "nent the calculative cycle number C he nert- C Z 1 cylinder #i at the combustion stroke (Cill - -- + incidentally, during the ston of the enaine, even when FLAG, = 0 holds, the d-Japncsz-ic proz-ram ri 1).

-17is not executed because no pulse is o sensors 16 and 18.

Subsequently, at an S204, the crank pulses for detecting the angles BTDC \112 and e3 as delivered from the crank angle sensor 16 are discriminated on the -" the interrupt of the cam pulses, and at an basis oi S205, a period f2,3 is calculated from the elapsed time interval t2,3 between the crank pulses for detecting the angles BTDC e2 and 1:113, and the angular difference (e2 - e3) between the angles 62 and e3 (f72,3 - dt2,3/d(e2 e3)).

Thereafilter, at an S206, the present engine r.::. m. value N NEW is calculated from the period f 2, 3 (N N --- W - 60/(2-,,..-F2,3)), and at an S207, 'Llhe dif-ferentiated r. p. m. value L.Ni (i = 1, 3, 2, 4) - e3) in which no work is done o f IC-h e s e c t i c n ( l- - by combustion of the clinder ii at the combustion s -s cal cula ted from the between the present engine r. p. m. N NEW and engine r. p. m. N OLD evaluated in the last routine (LNi - N NEW - N OLD)' As shown in Fig. 5, in the case of the four-cycle four-cylinder engine, the calculation of the engine r. p. m. N NEW in the section in which no work is done by the combustion is executed every 1800 C111.. rPherefore, when note is taken of the cylinder #1 by way P the ut- from.1.

0 -18of example, the differentiated r. p. m. =1 of the cylinder #1 can be obtained by subtracting the engine r. p. m. N OLD calculated at the last time, from the engine r. p. m. N NEW calculated at the present time. On the other hand, when the cylinder #3 is noticed, the engine r. p. m. N NEW of the cylinder #1 is set as the value N OLD' whereupon the differentiated r. p. m. W3 can be obtained from the subsequent engine r. p. m. N NEW of the cylinder #3.

Letting N4.1, N1.3, N3.2 and N2.4 denote the engine r. p. m. values common to each other between the cylinders, respectively, the differentiated r. p. m. values of the individual cylinders are as follows:

N i N, N 1.iEW OLD W1 N1.3 N4.1 LN3 = N3.2 - N1.3 W2 = N2.4 - N3.2 LN4 = N4.1 - N2.4 Meanwhile, it has been experimentally revealed that the differentiated r. intensely correlated with p. m. values LNi are illustrated average effective pressures Pi, namely, the combustion conditions of the cylinders. Accordingly, whether the combustion condition of each cylinder A (the illustrated average -19effective pressure) is good or bad can be conjectured by evaluating the differentiated r. p. m. -'Ni.

The relationships between the differentiated r. p. m. LNi and the illustrated average effective Dressure will be explained below.

First, the state in which the engine is rotating is expressed by the following equation:

I 2 7 -N = Ti - Tf... (1) dt I: moment of inertia, N: enaine r. p. m., torque, friction toraue.

Ti:

Tf:

a. (1) is simplified into: mf -L Further, in terms of Pressures, this equation is ex-resse--',' b,,-:

!71 d N Pi - Pf Cit ..(2) .. (3) Pi: illustrated average effective pressure, Pf: frictional-loss effective pressure.

Experimentally, as to the four-cycle fou-r-cylinder engine, 'the crank angle widths 11-2.3 for detecting -he the r. n. m. were set to be before and after t ' Ea. 3-) combustion stroke, and the value dN/dt o - was found on the basis of the differentiated r. p. m.

-20L.Ni and a temporal change LT (1800 CIP1) taken meantime. As a result, a very intense correlation was exhibited. In this case, when it is considered that the fluctuation of the change LT (1800 CA) is a negligible amount and that the frictional-loss effective pressure 4 ng holds in view of Pf s also constant, the follow Eq. (3):

LN = K x Pi + PF... (4) Pi, PF: constants.

Accordingly, the illustrated average effective pressures Pi, namely, the combustion conditions can be conjectured for the by evaluating the dii-Eferentiated r. p. m. values L:4L of the resnective cvlinders.

!'hen, when t'he differentiated r. n. -. values of the resz)ec---ve cv1inders:i are brought close to "0", the combustion con,'-J-cD..s all the cvl-inders can be re.-idere,,' uniform.

rictional On the other hand, when in Ea. (3), the :'f ect average ef L-ive pressure Pf is regarded as being constant and is denoted by a constant C, and proportionality constant is denoted by K, the holds:

dN lt = K.Pi - C a r followina .. (5) I'ccord-4nQ!v, the illustrated average el-fective pressure 2- -21Pi can be calculated by evaluating the constants K and C beforehand.

According to Eq. (5), the differentia-Led r. p. m. value LT.,,i is differentiated with respect to time, whereby the illustrated average effective pressure Pi can be more accurately conjectured from the differentiated r. p. m. N.

The engine r. p. m. value N NEW calculated in the section (62 - e3) in which no work based on the combustion is done does not contain anv fluctuatina -or f the r. p. in. attributed to the combustion fac 0; L pressure, and it is therefore commaratively stable.

Moreover, the two enaine r. p. m. values N and NEW N OLD to be compared are detected under the same condition, so that the correlation be-tween the d-J'-"feren-n-'La.-ed r. n. m. LNi and the combustion state Of 'Ll-e peertinent cylinder rui at the combustion stroke s clari-f-ed. Accordingly, the combustion state can be conjectured at high precision.

Thereafter, at an S208, engine load data fundamental fuel injection pulse width) Tp 4s calculat -he engine r. p. m. N and an ed on the basis of t I NEW intake air cuantity Q evaluated in the routine at me (To - K x Q/N K: cons' -).

L.he zresen-. L-1 NEW' ant Then, at an S209, a misfire judgement level -22 411111\1 LEVEL is set in the light of a misfire judgement level mar) MPLN LEVEL' using the engine load data Tp and the engine r. D. m. N NEW as parameters.

As shown in Fig. 6, the misfire judgement level map MPLN LEVEL is a threedimensional man whose parameters are the engine r. p. m. N NEE'A' and the engine load data Tp, and in which the misfire judgement level AN LEVEL evaluated by, e. g., an experiment beforehand is stored in each mesh reaion.

: at As shown in Fig. 7, the different ed r. p. m. ANi exhibit a comparatively large value in a transient state, but the fluctuating width thereof depending upon the operating conditions c-':' the enane. Therefore, the fluctuating widths of th.e individual operating conditions are evaluated bY, e. g., an exneriment beforehand, and the misfire -udaement levels 12z LEVEI con=orming to the w-d-hs are set Ecr the misfire and manned, whereby a high accuracy judgement can be attained.

Subsequently, an S210 compares the d-4---f:eren.L---ated r. P. m. LNi and the judgement level -'N EL LEVEE In a case where LNi < LN LEVEL holds, t._Lat Ls, where 1 fere.

the dLf- ntiated r. p. m. LN.i c the pert c-,-linder;9'L at the combu Stlon stroke s -:udced to be lower thari the misfire judaement!eve-' Z k in case of LNi (refer to Fig. 7), a misfire is decided, and the control flow proceeds to an S211. On the other hand, -ion is decided, LN L LEVEL, normal combust and the control flow proceeds to an S212.

At the S211, the misfire number Ci2 of each cylinder as corresponds to the pertinent cylinder #i at the combustion stroke is counted up (Ci2 -<- Ci2 + 1), whereupon the control flow proceeds to the S212.

Then, the S212 makes the comparison between the calculative cycle number Cil of the pertinent cylinder #i at the combustion stroke and a preset sampling cvcle number Cil SET (for example, 100 cycles). In a case (Cil < Cil SET) where the calculative cycle number C-41 does not reach the sampling cycle number Cil SET' ' the control flow jumps to an S220. On the other hand, in a case (C-41 Cil SET) where the calculative cvcle number C4 1 reaches the sampling cycle number C-41 SET' the control flow proceeds to an S213, at which the calculative cycle number Cil is reset (Cil - 0).

Subsequently, at an S214, the average misfire number Ci2(-l) of each cylinder corresponding to the pertinent cylinder #1 at the combustion stroke, the number having been calculated in the las-, sampling period, is read out, and at an S215, the average -24misfire number M2 of each cylinder at the present time is evaluated from the weighted average of weight coefficients r on the basis of the average misfire number MJ-1) of each cylinder and the misfire number CH of each cylinder counted in the sampling cycle number Cil SET at the present time (Ci2 - ((2 r - 1) x n2(-1) + Ci2J2 r).

Since the average misfire number = of each cylinder is evaluated in accordance with the weighted average, it is possible to correct the misfire judgement error of the pertinent cylinder C at the combustion stroke and a temporary misfire misjudgement ascribable to an abrupt combustion fluctuation.

Thereafter, at an S216, the misfire number CO of each cylinder is reset (M2 0), and at an S217, the average misfire number Ci2(-!) of each cylinder calculated in the last sampling period is updated into the average misfire number M2 of each cylinder calculated at the present time (Ci2(-1) - Ci2).

Subsequently, an S218 makes the comparison between the average misfire number = of each cylinder at the present time and a misfire abnormalitydeciding reference number CK SET previously set. In a case where C= > =2 SET holds, that is, where the average misfire number CW of each cylinder exceeds the misfire -25 abnormality deciding reference number C2 SET' is judged that the pertinent cylinder #i undergoes a misfire abnormality, and the control flow proceeds to an S219. Here. the misfire abnormality data of the pertinent cylinder #i is stored in the predetermined address of the back-up RAM 25, and the driver is warned of the misfire abnormality by lighting up the warning means such as indicator lamp 29. Thereafter, the S219 is followed by the S220. In a case where U712):5 c n SET is decided, it is judged that the pertinent cylinder il-,'i does not undergo a misfire abnormalitv.-et, and the S218 is followed bv the S220.

At the S220, the engine r. p. m. value NOLD calculated in the last routine is undated into the enaine r. o. m. N NEW calculated at the nresent time (N D "- N 1ZE W and the routine is left.

- -!v, J_ - - ic-dental the misfire abnormality data of the pertinent cylinder rJJ-i stored in the memory means (back-un RAM) 25 can be read out by connecting the serial monitor 31 in, e. g., the service station of a car dealer. Also, the misfire abnor.-,ia-',-,t, data stored in the memory means 25 can be cleared through the serial monitor 31.

Fig. 10 is a flow chart showing a misfire judging procedure according to the second embodiment of the -26present invention.

Here, steps having functions similar to those of the first embodiment are denoted by the same symbols as in the first embodiment and shall be omitted from description.

In this embodiment, the number of misfires is sequentially stored for each cylinder. Moreover, in a case where the misfire number has reached the maximum count number, the maximum misfire number is fixed and stored.

First, an S201 judges if a misfire diagnosis stop is reset (FLAG, = 0), and it is followed by an S202, at which cylinder #i at a combustion stroke is discriminated. Thereafter, an S301 discriminates whether the maximum misfire counz number flag Fi of the pertinenr cylinder Pi at the combustion stroke is in a set status (Fi = 1) or a reset staous (Fi = 0) Here, in case of the set status (Fi = 1), the control flow proceeds to an S302, at which the warning means such as indicator lamp 29 is brought inic a!it-up state to warn the driver of a misfire alnormality. Then, the routine is left.

On the other hand, when the maximum misfire count number flag Fi is judged to be in the reset status Pi = 0), the same steps S204 - S210 as in the first -27embodiment described before are executed.

Then, when the S210 decides that the pertinent cylinder #i at the combustion stroke undergoes a misfire (,,Ni < LN LEVEL), it is followed by an S303, and when it decides normal combustion (ANi -k LN LEVEL)' it is followed by an S304, at which the maximum misfire count number flag Fi is reset (Fi -- 0).

A the S303, the warning means such as indicator lamp 29 is lit ulp ffor a very short time, thereby to warn the driver of the occurrence of the misfire.

The driver recoanizes the lighting frequence of the warning means 29, and can thus grasp the misfiring situation of the engine, namely, the operating conditions of the engine under which the Eires are liable to occur.

misf Subsequently, at an S305, the misfire number Ci2 of the pertinent cylinder #i is counted up (Ci2 - Ci2 + 1), whereuDon the value Ci2 counted up is stored in the predetermined address of the memory means (back-up RAM) 25.

In, e. cr., the service station of the car dealer, L-he serial monitor 31 is connected to read out the misfire number data of each cvlinder stored in the memory means 25, and the misfiring s-JL-ua-ion is judged bv, e. c., reference to a manual.

Thereafter, an S306 makes the compar _4 son between 1-inent CV14 the misfire number C-42 of the pert nder #i and the maximum count number Ci2 MAX previously set (for example, FFH corresponding to 2 bytes). In case of Ci2 = Ci2 MAX' the control flow proceeds to an S307, and in case of Ci2 < Ci2 MAX' the control flow proceeds to the S304.

When the control flow proceeds to the S307 upon judging that the misfire number Ci2 reaches the maximum count number Ci2 (Ci2 = Ci2 th _4_ Jsfire number MAX MAX)' _ mi - Ci2 stored in the predetermined address of the memory X 4 rr,, I- the ma count means 25 is held aL C-2 MAX At an S308, the max..-,-,ium, misfire count number flag ri is set (Fi - 1).

At an S309 following the S308 or engine r. o. m. value N OLD calculated time is undated into the engine r. m.

ed at the presen- time (IN N, OLD routine is left.

-he S304, -he at the llast calculatThen, the Fig. 11 is a flow chart showing a misfire Judging procedure according to the third embod4ment of the present invention.

Si M4 la- to those Here, steps having functions of the first and second embodiments are denoted by the same svmbols and shall be cm-ted from, descrintion.

1 In this embodiment, a misfire judgement is made during an idling operation.

During the idling operation, the engine speed 0 is low, and the load fluctuation is little. Therefore, the misfire judgement level LN LEVEL need not be set at the fluctuating value (S209) as in the first embodiment described before. Even when the level is set at a fixed value obtained by, e. g., an exmeriment beforehand, no misjudgement is made.

Accordingly, the misfire judging procedure based - is substantially the same as the on this embodiment 1 is judged at flow chart si-lown in Fig. 9. First, it AG an S201 that the misfire diagnosis stop flag F. A is in its reset status (FLAG A 0, resetting the misfire diagnosis stop). Then, unlike the foregoing flow chart, the control flow proceeds to an S401, at which the idling is decided on the basis o:E the 01.1,1 state of the idling switch 8 (the ON, state corresiDonds to the full closure of the throttle, and the OFF state the full opening) and the output value of the vehicle speed sensor 19. In a case where a non-idling condition (under which the idling switch is OFF or the vehicle speed; 0) is discriminated, Lhe routine is left, and in a case where the idling operation (under which the idling switch is ON and -30the vehicle speed = 0) is discriminated, the control flow proceeds to an S202. Further, instead of the S208 and S209 of the first embodiment, an S402 reads out the fixed misfire judgement level LN LEVEL stored in the ROM 23 beforehand.

Fig. 12 is a flow chart showing a misfire judging procedure according to the fourth embodiment of the present invention.

Here, steps having functions similar to those of the second and third embodiments are denoted by the same symbols and shall be omitted from description.

In this embodiment, the number of misfires during an idling operation is sequentially stored for each cylinder, and when the misfire number has reached the maximum count number, this maximum misfire number is fixed and stored.

The misfire judging procedure based on this embodiment is substantially the same as the flow chart shown in Fig. 10. However, it differs in that the idling is decided at an S401 and that the fixed misfire judgement level LN LEVEL previously set is read out at an S402.

Here, the S401 and S402 are the same as in the third embodiment described before (Fig. 11) and shall be omitted from description.

1 Incidentally, the present invention is not restricted to the foregoing embodiments. By way of example, although the engine r. p. m. value is employed as a momentum in each embodiment, it may well be replaced with a period, an angular velocity or an angular acceleration.

As described above, according to the present invention, there are comprised misfire judgement stopping means for stopping a misfire judgement for a time period taken since a starter motor begins to be driven, until a oredetermined time period lapses after end of the drive of said starter motor; and misfire judging means for starting the misfire judaement after lanse of the misfire judgement stopping time neriod. Therefore, the invention achieves such excellent effects that the erroneous diagnoses of misfires attributed to revolution fluctuations during cranking and at the initial stage of complete explosion diminish, that the accuracy of diagnoses is enhanced and that a high reliability can be attained.

Claims (3)

-32CLAIMS

1. A misfire diagnosis apparatus for an internal combustion engine having a crankshaft for outputting power and a camshaft for actuating valves, the apparatus comprising a crank plate connected to said crankshaft for indicating a crank angle, a crank angle sensor for detecting said crank angle of said crankshaft and for generating a crank angle signal, a cam plate connected to said camshaft for indicating a cam position, a cam angle sensor for detecting said cam position of said camshaft and for producing a cam angle signal, a starter motor for starting said engine for producing a starter signal, and control means responsive to said crank angle and said cam angle for controlling an ignition timing of said engine, the apparatus further comprising:

a plurality of even numbers of projections provided on a periphery of said crank plate for indicating said crank angle, said projections being diametrically symmetrically arranged on said periphery and each pair of said projections being spaced apart by at least three different specific angles; a plurality of cam projections provided on a periphery of said cam plate and spaced angularly apart -33at a predetermined angle on said periphery for indicating said cam position; discriminating means responsive to said crank angle signal and said cam angle signal for discriminating a cylinder number at a combustion stroke and for producing a cylinder number signal; misfire judgement stopping means responsive to said starter signal for stopping a misfire judgement for a predetermined period and for producing a stopping signal; misfire judgement means responsive to said stopping signal, said cylinder number signal, said crank angle signal and said cam angle signal for calculating a differentiated engine.speed and for deciding a misfire of said cylinder number at said combustion stroke in order to generate a misfire signal; and warning means responsive to said misfire signal for storing a number of said misfire corresponding to said cylinder number and for indicating a malfunction of said internal combustion engine.

2. A misfire diagnosis apparatus for an internal combustion engine, substantially as herein described with reference to, and as illustrated in, Figs. 1 to 9 -34or Figs. 1 to 9 as modified by Fig.. 10, Fig. 11 or Fig.12.

3. An internal combustion engine comprising a misfire diagnosis apparatus as claimed in claim 1 or claim 2.

Published 1991 at The Patent Office. Concept House. Cardiff Road. Newport. Gwent NP9 I RH. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point, Cwmfelinfach. Cross Keys. Newport. NP1 7HZ. Printed by Multiplex techniques lid. St Mary Cray. Kent.