Method and apparatus for ignition system spark timing control where exhaust gas recirculation is used

A method and apparatus for controlling ignition system spark timing where exhaust gas recirculation is employed. The value of spark advance is determined based upon engine operating parameters and exhaust gas recirculation rate is sensed. Correction means is provided which corrects the value of spark advance in accordance with the sensed value or actual valve of exhaust gas recirculation rate.

CROSS-REFERENCES TO RELATED APPLICATONS 
References are made to the following related co-pending applications, each 
filed in the name of Kenji Ikeura on Apr. 3, 1980: (1) U.S. patent 
application Ser. No. 137,001; (2) U.S. patent application Ser. No. 
136,959; (3) U.S. patent application Ser. No. 137,000; (4) U.S. patent 
application Ser. No. 136,996. 
BACKGROUND OF THE INVENTION 
The present invention relates to a method and apparatus for the control of 
an ignition system spark timing for a spark ignition internal combustion 
engine, and more particularly to a method and apparatus for the control of 
an ignition system spark timing where not only fuel consumption and power 
output are required, but also purification of exhaust gases is required. 
Conventionally, the spark timing control where the exhaust gas 
recirculation (hereinafter abbreviated as EGR) takes place, employs a 
two-way or three-way ON-OFF valve, often called as "TV valve," which in 
response to the engine coolant temperature effects on-off control of 
atmosphere passages leading to an EGR control unit and a spark timing 
control unit, respectively. (For example, if the atmosphere passages are 
open, EGR is suspended and the spark advance is also suspended.) FIG. 1 
shows the open and close states of the TV valve, wherein the axis of 
abscissa designates the coolant temperature of the engine, the wave-form 
line (1) represents the open and close states of the atmosphere passage 
leading to the EGR control unit, and the wave-form line (2) represents the 
open and close states of the atmosphere passage to the spark timing 
control unit. From this it will be understood that when the coolant 
temperature is higher than 95.degree. C., the atmosphere passage to the 
EGR control unit is open to suspend EGR for the purpose of engine 
protection. When the coolant temperature is lower than 60.degree., the 
atmosphere passage to the EGR control unit is open to suspend EGR for the 
purpose of preventing deterioration in driveability. As will be understood 
from the wave-form line (2), when the coolant temperature is from 
15.degree. C. to 60.degree. C. representing warm-up period of the engine, 
the atmosphere passage leading to the spark ignition control unit is open, 
thereby to suspend the spark advance control, suppressing the spark 
advance to a small value. This causes rapid warm-up and facilitates 
warm-up of the exhaust gas purifier. Within a range when the coolant 
temperature is lower than 15.degree. C., an increase in spark advance is 
allowed to provide a sufficient increase in spark advance for the purpose 
of preventing deterioration in driveability. If EGR is effected during a 
temperature range from 15.degree. C. to 60.degree. C. when spark advance 
control is suspended, the driveability drops excessively because 
driveability which has been worsened during this temperature range owing 
to the suspension of spark advance control is further worsened by the 
addition of EGR, and besides no appreciable effect in reducing NOx is seen 
because during this range the amount of NOx has already been suppressed as 
a result of suspension of spark advance control. This explains the reasons 
why, as shown by wave-form lines (1) and (2), it has been desired to use 
the same temperature for the beginning temperature of the EGR and for the 
resuming temperature of the spark advance control, wherein the EGR begins 
above 60.degree. C. and the spark advance control resumes above 60.degree. 
C. 
For the reason set forth above, it has been the conventional practice to 
combine spark timing control with EGR control to effect a control in 
response to the engine coolant temperature. 
However, in this conventional combination control, disabling and enabling 
of EGR and spark advance control are effected in response to coolant 
temperature and the correction of spark advance value is not effected in 
response to a rise or drop in the exhaust gas recirculation rate, so that 
even if EGR is suspended, the value of spark advance remains unchanged 
such as at a coolant temperature of 95.degree. C. shown in FIG. 1, thus 
causing knocking. The same phenomenon takes place too within a low 
temperature range. Besides, since the control is characterized by so 
called "two-values control" wherein there occurs a disabled-state or an 
abled-state, the value of spark advance can not correspond to the change 
even if minute EGR control is effected. 
SUMMARY OF THE INVENTION 
An object of the present invention is to correct value of spark advance in 
accordance with exhaust gas recirculation rate. 
The method and apparatus of the invention concerns the control wherein 
value of spark advance is determined based upon engine operating 
parameters, exhaust gas recirculation rate is sensed, and the value of 
spark advance which is determined based upon engine operating parameters 
is corrected in accordance with the sensed value of exhaust gas 
recirculation rate. 
Another aspect of the invention is in that a target value of exhaust gas 
recirculation is found by digital operation and a spark advance value is 
increased in accordance with an increase in the target value of exhaust 
gas recirculation rate. 
Still another aspect of the invention is in that spark advance is decreased 
to a small value when exhaust gas recirculation is suspended. 
Still another aspect of the invention is in that spark advance value is 
corrected in accordance with a difference between a target value of 
exhaust gas recirculation rate which is found by digital operation based 
upon various engine operating parameters and an actual value of exhaust 
gas recirculation rate which is sensed by an exhaust gas recirculation 
rate sensor. The correction is effected by digital calculation using a 
mathematical formula K(T-A), where: K is a correction coefficient, T is a 
target value of EGR rate, and A is an actual value of EGR rate. 
The invention may be better understood by reference to the detailed 
description which follows and to the drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 2, the control system employed in the present invention 
will be concretely described. In FIG. 2, the axis of abscissa designates 
exhaust gas recirculation rate, the axis of ordinate spark advance value, 
solid line knocking (knocking is high as the number increases), one-dot 
chain line fuel consumption rate (unit; g/PS.hr), broken line the amount 
of NO.sub.x emission (unit; g/PS.hr). This graph shows the case of an 
electronic fuel injection type 6-cylinder gasoline engine. In this type of 
engine, when operated at the illustrated point A wherein exhaust gas 
recirculation rate is 15% and spark advance value is 50.degree., NO.sub.x 
emission from the engine is little and the fuel consumption is optimum, 
and therefore the engine is set at this point. When, however, EGR is 
suspended to prevent the tendency of the engine from being over heated, 
the exhaust gas recirculation rate=0%, and this means that the engine 
operates at a point B whereat the knocking is greater than 3, thus 
providing unallowable driveability state. Thus according to the present 
invention, concurrently with a decrease in the exhaust gas recirculation 
rate from 15% to 0%, the spark advance value is decreased by 15.degree. 
from 50.degree. down to 35.degree., thus arriving at the illustrated point 
C'. With this, the occurrence of knocking is prevented, the fuel 
consumption is improved by 15 g/PS.hr as compared to the point B, and 
NO.sub.x emission is decreased. If, instead of simply suspending the EGR 
to decrease the exhaust gas recirculation rate to 0%, an illustrated point 
C is selected where the spark advance value is 35.degree. the same as that 
at the point C' and the exhaust gas recirculation rate is 5%, it is enough 
as a counter-measure to engine overheat, besides NO.sub.x emission level 
is less than that at the point C', and the fuel consumption rate is the 
same as that at the point C'. 
FIG. 3 is a block diagram showing an embodiment of the present invention. 
In FIG. 3, 1 designates a temperature sensor which provides a signal 
S.sub.1 representing the coolant temperature of an engine, 2 designates an 
induction vacuum sensor which detects the induction vacuum of the engine 
to provide an induction vacuum signal S.sub.2, 3 designates a basic angle 
sensor which provides basic angle pulses S.sub.3 each upon expiration of a 
basic angle (for example, 120.degree.) as the engine crank shaft rotates, 
4 designates an unit angle sensor which provides unit angle pulses S.sub.4 
each upon expiration of an unit angle (for example, 1.degree.) as the 
engine crank shaft rotates, 5 designates an exhaust gas recirculation rate 
sensor which detects the exhaust gas recirculation rate to provide an 
exhaust gas recirculation rate signal S.sub.5. 
These signals S.sub.1 to S.sub.5 (If necessary, another signals including a 
fuel injection pulse signal, a gear shift position signal, a vehicle speed 
signal may be employed) are read in via an input-output control unit 6 
which is constructed of semiconductors by a central processor 7 including 
a ROM (read only memory), a RAM (random access memory), and a CPU (central 
processor unit). The central processor 7 detects the revolution speed of 
the engine from the basic angle pulse signal S.sub.3 and the unit angle 
pulse signal S.sub.4 of all of the read-in signals and detects the load of 
the engine from the signal S.sub.2 from the load sensor 2, and finds from 
the detected revolution speed and load of the engine an exhaust gas 
recirculation rate to be issued to the EGR control unit and spark advance 
value to be issued to the spark advance control unit, and furthermore 
effects correction of the exhaust gas recirculation rate and correction of 
the spark advance value in response to the temperature signals S.sub.1 
from the temperature sensor 1, and issues the corrected exhaust gas 
recirculation rate and spark advance value to the EGR control unit 8 and 
the spark timing control unit 9 via the input-output control unit 6. It 
will be noted that, the signal S.sub.5 from the exhaust gas recirculation 
rate sensor 5 is not used. 
The operation of the central processor 7 to perform the above-mentioned 
function is illustrated by a flow chart shown in FIG. 4. When the program 
starts, in a step P.sub.1 and in a step P.sub.2 a spark advance value and 
an exhaust gas recirculation rate are found based upon the revolution 
speed and load of the engine, in the subsequent step P.sub.3 the decision 
is made whether or not the condition including engine coolant temperature, 
load, vehicle speed, etc demands a reduction in the exhaust gas 
recirculation rate, and if the result of the decision is "NO" the program 
goes to a step P.sub.4 to allow the output of the spark advance value and 
the exhaust gas recirculation rate determined by the steps P.sub.1 and 
P.sub.2, respectively, and if it is decided, in the step P.sub.3, that the 
exhaust gas recirculation rate be decreased, the program goes to a step 
P.sub.5 wherein the correction of the exhaust gas recirculation rate takes 
place, in the following step P.sub.6, value of spark advance is corrected 
in accordance with the corrected value of exhaust gas recirculation rate, 
and these corrected values (the correction is effected in accordance with 
the characteristic shown in FIG. 2) of the exhaust gas recirculation rate 
and spark advance value are issued via the step P.sub.4. 
FIG. 5 is a flow chart of the operation wherein there is employed the 
output signal S.sub.5 of the exhaust gas recirculation rate sensor 5 which 
is shown in FIG. 3. In a step P.sub.1 a value of spark advance is found by 
calculation based upon the engine revolution speed and load. In the 
subsequent step P.sub.7 the amount of correction is calculated based upon 
exhaust gas recirculation rate signal S.sub.5, if necessary another 
information such as engine coolant temperature, intake air flow, engine 
revolution speed and throttle opening degree may be used for the 
calculation. In a step P.sub.8 that value of spark advance which has been 
calculated in the preceding step P.sub.1 is corrected by that correction 
amount which has been calculated in the step P.sub.7 and then issued via 
step P.sub.9. In this case, the value of spark advance calculated in the 
step P.sub.1 is determined on the assumption that there is no EGR, the 
correction of this value is in a direction so as to increase the value of 
spark advance in response to EGR control. 
FIG. 6 is a flow chart illustrative of the operation of the central 
processor 7 to determine value of an operating or control signal for EGR. 
In a step P.sub.10 the target value of exhaust gas recirculation rate is 
decided based upon the engine revolution speed and load, in the subsequent 
step P.sub.11 the deviation or difference between the target value of 
exhaust gas recirculation rate and the actual value of exhaust gas 
recirculation rate, i.e., signal S.sub.5 of the exhaust gas recirculation 
rate sensor 5, is found, and such an operating signal as to reduce the 
deviation to zero is issued via a step P.sub.12 to the EGR control unit. 
In the preceding embodiment the description went on the assumption that the 
exhaust gas recirculation rate is used, but the exhaust gas recirculation 
rate may be replaceable with exhaust gas recirculation amount because they 
are interchangeable if reference is made to the other informations 
representing the operating state of the engine. The exhaust gas 
recirculation rate can be provided from such a value as the pressure of 
the exhaust gas recirculation passageway, which varies in response to the 
variation of the exhaust gas recirculation only by suitable calculation. 
It will now be understood from the preceding description that according to 
the present invention, the conventional insufficiencies, such as the 
occurrence of knocking upon suspension of EGR, the deterioration of fuel 
economy, and excessive emission of NO.sub.x, are solved and, furthermore. 
The start switch 1 is entirely conventional and may be a pair of contacts 
which are closed while the engine startor motor is in operation. 
The basic angle sensor and unit angle sensor are also conventional and may 
be in the form of a detecting unit 24 described in and is incorporated 
herein by reference in U.S. Pat. No. 4,015,565, filed Apr. 5, 1977 in the 
name of Aono et al. and entitled "SK-ADVANCE CONTROL APATUS FOR 
INTERNAL COMBUSTION ENGINE" or may be in the form of a speed-electrical 
transducer 10 described in and is incorporated herein by reference in U.S. 
Pat. No. 3,853,103, filed Dec. 10, 1974 in the name of Wahl et al. 
(assignee: Robert Bosch GmbH) and entitled "IGNITION TIMING CONTROL SYSTEM 
FOR INTERNAL COMBUSTION ENGINE IGNITION SYSTEMS." 
A way to find or sense revolution speed of engine, i.e., engine rpm, based 
upon signal from the unit angle sensor is conventional and described in 
the above-mentioned U.S. Pat. No. 3,853,103. In this respect, reference is 
made to U.S. Pat. No. 3,969,614, filed July 13, 1976 in the name of Moyer 
et al. and entitled "METHOD AND APATUS FOR ENGINE CONTROL" and 
reference is also made to U.S. Pat. No. 4,009,699, filed Mar. 1, 1977 in 
the name of Hetzler et al. and entitled "DIGITAL IGNITION SK TIMING 
ANGLE CONTROL WITH READ ONLY MEMORY." 
The inventor has used a breakerless ignition system employing an ignition 
coil and a power transistor. 
A way to determine the instance of ignition based upon binary signals of 
the basic angle sensor and unit angle sensor is disclosed in U.S. Pat. No. 
3,853,103 in the name of Wahl et al. and U.S. Pat. No. 4,015,565 in the 
name of Aono et al. 
In a four-cylinder, four-cycle internal combustion engine, one each 
ignition pulse must be obtained after each revolution of the crank shaft 
by 180.degree.; 180.degree. after the first ignition pulse is derived, a 
second basic angle pulse must then be provided by the basic angle sensor. 
In this case, the basic angle sensor must be designed to provide a basic 
angle pulse after each revolution of the crank shaft by 180.degree.. 
In a six-cylinder, four-cycle internal combustion engine, one each ignition 
must be obtained after each revolution of the crank shaft by 120.degree.; 
120.degree. after the first ignition pulse is derived, a second basic 
angle pulse must then be provided by the basic angle sensor. In this case, 
the basic angle sensor must be designed to provide a basic angle pulse 
after each revolution of the crank shaft by 120.degree..