Fuel supply control method for internal combustion engines at low temperature

A fuel supply control method for an internal combustion engine in a cold state. A basic value of fuel supply quantity is corrected to an increased value by the use of a correction variable set based upon engine temperature and engine load. Intake air temperature is detected, and the correction variable is corrected by the detected intake air temperature. Preferably, the correction variable is corrected to a larger value as the detected intake air temperature is lower.

BACKGROUND OF THE INVENTION 
This invention relates to a method of controlling the quantity of fuel 
being supplied to an internal combustion engine when the engine is in a 
cold state. 
A fuel supply control method for internal combustion engines has been 
proposed, e.g. by Japanese Provisional Patent Publication (Kokai) No. 
57-137633, which is adapted to control the air-fuel ratio of an air-fuel 
mixture being supplied to an internal combustion engine by electrically 
controlling the valve opening period of a fuel injection valve through 
which fuel is supplied to the engine, that is, by controlling the fuel 
injection quantity. 
According to this proposed fuel supply control method, the valve opening 
period of the fuel injection valve is determined by adding values of 
various correction variables such as an intake air temperature-dependent 
correction variable and a warming-up fuel increasing correction variable 
to and/or multiplying thereby a basic value of valve opening period 
corresponding to the enging rotational speed and a parameter representing 
the engine load, e.g. intake pipe absolute pressure. 
Since the above basic value is set based on air density at a predetermined 
reference value of intake air temperature (e.g. 30.degree. C.), the intake 
air temperature-dependent correction variable is used to correct the basic 
value in order to compensate for a change in the air density caused by 
deviation of the intake air temperature from the predetermined reference 
value. On the other hand, since there can be a difference between the 
quantity of fuel injected and that actually drawn and burnt in the 
cylinder, depending upon the atomization degree of injected fuel and the 
quantity of the injected fuel adhering to the wall of the intake pipe, the 
warming-up fuel increasing correction variable is used to correct the 
basic value to compensate for the difference. 
The warming-up fuel increasing correction variable is determined based not 
only on engine temperature, e.g. engine cooling water (coolant) 
temperature, but also on the intake pipe absolute pressure, because, even 
if the engine temperature remains unchanged, a change in the intake pipe 
absolute pressure, i.e., a change in the flow rate of air in the intake 
pipe can result in a corresponding change in the quantity of fuel adhering 
to the intake pipe wall as well as a change in the fuel atomization 
degree. 
However, the atomization degree of injected fuel also varies as a function 
of the intake air temperature, too, and hence a further correction with 
regard thereto is required. In particular, when the intake air temperature 
is low, it is difficult for the conventional fuel supply control method to 
secure the supply of such a proper quantity of an air-fuel mixture to the 
engine as to obtain stable combustion and stable engine rotation, thus 
suffering from degradation in the driveability of the engine, etc. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a fuel supply control method 
for internal combustion engines, which is adapted to use the intake air 
temperature as one of the determinants of the engine temperature-dependent 
fuel increasing correction variable to stabilize the engine rotation, 
thereby improving the driveability the engine, especially when the intake 
air temperature is low. 
According to the present invention, there is provided a method of 
controlling the quantity of fuel being supplied to an internal combustion 
engine in a cold state, wherein a basic value of the quantity of fuel 
being supplied to the engine is corrected to an increased value by the use 
of a fuel increasing correction variable which is set based upon a 
temperature of the engine and a load on the engine. The method is 
characterized by comprising the following steps: (1) detecting a 
temperature of intake air being supplied to the engine, and (2) correcting 
the fuel increasing correction variable by the intake air temperature 
detected. 
Preferably, the fuel increasing correction variable is corrected to a 
larger value as the intake air temperature detected is lower. 
Also, the temperature of the engine is preferably the temperature of engine 
coolant. 
Further, the load on the engine is preferably the absolute pressure in an 
intake pipe of the engine. 
Still more preferably, the fuel increasing correction variable is a 
coefficient by which the basic value is multiplied. 
The above and other objects, features and advantages of the invention will 
be more apparent from the ensuing detailed description taken in 
conjunction with the accompanying drawings.

DETAILED DESCRIPTION 
The invention will now be described in detail with reference to the 
drawings showing an embodiment thereof. 
Referring first to FIG. 1, there is illustrated the whole arrangement of an 
internal combustion engine equipped with a fuel supply control system to 
which the method of the present invention is applied. Reference numeral 1 
designates the engine which may be a four cylinder type. Connected to each 
cylinder are an intake pipe 2 and an exhaust pipe 3. 
Fuel injection valves 4 are inserted in the intake pipe 2 in the vicinity 
of the engine 1, and an air cleaner 5 is provided at an inlet end of the 
intake pipe 2 opening into the atmosphere. Arranged across the intake pipe 
2 at a location upstream of the fuel injection valves 4 is a throttle 
valve 6, to which a throttle valve opening (.theta.TH) sensor 7 is 
connected for detecting the valve opening. The throttle valve opening 
sensor 7 converts the detected throttle valve opening into an electrical 
signal to supply same to an electronic control unit (hereinafter called 
"ECU") 8 to which it is electrically connected. 
An absolute pressure (PBA) sensor 10 communicates through a conduit 9 with 
the interior of the intake pipe 2 at a location between the throttle valve 
6 and the fuel injection valves 4, to detect the absolute pressure in the 
intake pipe 2 and convert same into an electrical signal to supply same to 
the ECU 8, to which it is connected. 
Further, an intake air temperature (TA) sensor 11 is inserted in the intake 
pipe 2 at a location between the conduit 9 and the fuel injection valves 
4, to detect the temperature of intake air passing in the intake pipe 2 
and convert the detected intake air temperature into an electrical signal 
to supply to the ECU 8, to which it is also connected. 
The fuel injection valves 4 are each connected to a fuel pump (not shown), 
and electrically connected to the ECU 8 to have its valve opening period 
controlled by a driving signal supplied from the ECU 8. 
Mounted on the cylinder block of the engine 1 are an engine rotational 
speed (Ne) sensor 12 and an engine temperature (TW) sensor 13. The latter 
13 is adapted to detect the temperature of engine cooling water (coolant) 
as an engine temperature and convert same into an electrical signal to 
supply to the ECU 8, to which it is electrically connected. 
The engine rotational speed sensor 12 is adapted to generate one pulse of a 
crank-angle-position signal (hereinafter called "TDC signal") at a 
particular crank angle position of each cylinder of a predetermined crank 
angle before a top-dead-center of the cylinder corresponding to the start 
of the suction stroke each time the engine crankshaft rotates through 180 
degrees. The TDC signal thus generated is supplied to the ECU 8 to which 
the sensor 12 is connected. 
An O.sub.2 sensor 14 is inserted in the exhaust pipe 3 for detecting oxygen 
concentration in the exhaust gases and converting same into an electrical 
signal to supply to the ECU 8, to which it is electrically connected. A 
three-way catalyst 15 is arranged across the exhaust pipe 3 at a location 
downstream of the O.sub.2 sensor 14 for purifying ingredients HC, CO and 
NOx contained in the exhaust gases. 
Further connected to the ECU 5 are other parameter sensors 16 such as an 
atmospheric pressure sensor for detecting atmospheric pressure, and a 
starting switch 17 for actuating the engine 1, the other parameter sensors 
16 being also electrically connected to the ECU 8 to supply same with 
respective electrical signals representing the detected values. 
The ECU 8 comprises an input circuit 8a having such functions as shaping 
the waveforms of signals inputted from various sensors, shifting the 
voltage levels of other input signals to a predetermined level, and 
converting the values of analog signals into degital values, a central 
processing unit (hereinafter called "CPU") 8b, storage means 8c for 
storing various calculation programs to be executed in the CPU 8b, the 
results of calculations, etc., and an output cirucuit 8d having such 
functions as supplying the fuel injection valves 6 with driving signals to 
open them in response to the results of calculations. 
The respective engine parameter signals from the aforementioned sensors and 
the on-off signal from the starting switch 17 are supplied to the CPU 8b 
through the input circuit 8a in the ECU 8. The CPU 8b determines operating 
conditions of the engine by processing the engine parameter signal values 
and the on-off signal value through a predetermined control program, and 
calculates the quantity of fuel to be supplied to the engine 1, i.e., the 
fuel injection period TOUT of the fuel injection valves 4, and then 
supplies the fuel injection valves 4 via the output circuit 8d with the 
driving signals to drive same in response to the result of the 
calculation. 
The fuel injection period TOUT for the fuel injection valves 4 is 
calculated by the following equation (1): 
EQU TOUT=Ti.times.KTA.times.KTW.times.K1+K2 (1) 
where Ti is a basic value of the fuel injection period, for which a 
plurality of predetermined values are stored in the storage means 8c in 
the ECU 8, each of the predetermined values corresponding to a respective 
one of combinations of values of intake pipe absolute pressure PBA and 
engine rotational speed Ne and being set at such a value as to supply an 
optimal fuel quantity on condition that the intake air temperature TA and 
the engine cooling water temperature TW assume respective predetermined 
reference values. Thus, the basic value Ti is set to a value read from the 
storage means 8c in response to the values PBA and Ne detected. 
KTA is an intake air temperature correction coefficient to compensate for a 
deviation of the detected intake air temperature from the predetermined 
reference value (e.g. 30.degree. C.), the value of the coefficient KTA is 
read from a table as shown in FIG. 2 in response to the intake air 
temperature TA detected. KTW is a warming-up fuel increasing correction 
coefficient, or a coolant temperature-dependent fuel increasing correction 
coefficient, which will be described later in detail. 
K1 and K2 are correction coefficients and correction variables, 
respectively, which are determined as functions of the values of various 
engine parameters except for the intake air temperature TA and the engine 
temperature TW, and are set to such values as to achieve optimal operating 
characteristics of the engine such as fuel consumption and emission 
characteristics. 
The engine coolant temperature-dependent fuel increasing correction 
coefficient KTW is read from tables shown in FIGS. 3 and 4, for instance. 
FIGS. 3 and 4 show examples of the relationship between the engine water 
temperature TW and the engine coolant temperature-dependent fuel 
increasing correction coefficient KTW. FIG. 3 is applied when the intake 
air temperature TA is equal to or lower than a predetermined value TAS 
(e.g. 20.degree. C.), and FIG. 4 when the intake air temperature TA 
exceeds the predetermined value TAS, respectively. It is so arranged that 
the value KTW read from FIG. 3 is greater than that read from FIG. 4 at 
the same value of engine water temperature TW and the same value of intake 
pipe absolute pressure PBA. 
Now the manner of obtaining the engine coolant temperature-dependent fuel 
increasing correction coefficient KTW from the tables of FIGS. 3 and 4 
will be described with reference to FIG. 5 and FIG. 6. 
First, it is determined at step 1 in FIG. 6 whether or not the actual 
intake air temperature TA is higher than the predetermined value TAS. If 
the answer is negative (No), the program proceeds to step 2, where a value 
of the engine coolant temperature-dependent fuel increasing correction 
coefficient KTW is read from the table of FIG. 3 based on the detected 
intake pipe absolute pressure PBA and the detected engine water 
temperature TW. If the answer is affirmative (Yes), the program proceeds 
to step 3, where a value of the correction coefficient KTW is read from 
the table of FIG. 4 based on the detected intake pipe absolute pressure 
PBA and the detected engine water temperature TW. 
By way of example, let it be assumed that the detected intake air 
temperature TA is equal to or lower than the predetermined value TAS 
(20.degree. C.), reading from the table of FIG. 3 is effected as follows: 
In, FIG. 3, the curve I indicates values KTWPBA1 to be selected at a first 
predetermined value PBA1 of intake pipe absolute pressure (e.g. 300 mmHg), 
and II values KTWPBA2 to be selected at a second predetermined value PBA2 
of intake pipe absolute pressure (e.g. 650 mmHg), respectively. Thus, 
values KTWPBA.sub.1 and KTWPBA.sub.2 are selectively read in response to 
the detected water temperature TW, depending upon the detected intake pipe 
absolute pressure. As is learned from the table, when the water 
temperature TW exceeds a predetermined value TW.sub.5 (e.g. 60.degree. 
C.), the values KTWPBA.sub.1 and KTWPBA.sub.2 are read as 1.0. Besides 
TW.sub.5 there are provided four predetermined coolant temperature values 
TW.sub.1 through TW.sub.4 as calibration variables (increasing in the 
order of the index number), and five predetermined values KTWPBAij 
corresponding to respective predetermined values TW.sub.j (j=1, 2, 3, 4, 
or 5). If the detected coolant temperature assumes a value falling between 
adjacent ones of the predetermined values TW.sub.1 through TW.sub.5, then 
the values KTWPBA.sub.1 and KTWPBA.sub.2 are calculated by means of linear 
interpolation. 
Based on the values KTWPBA.sub.1 and KTWPBA.sub.2 thus obtained, the 
coolant temperature-dependent fuel increasing correction coefficient KTW 
is finally obtained in response to the actual intake pipe absolute 
pressure PBA as shown by FIG. 5. To be specific, if the intake pipe 
absolute pressure PBA is equal to or greater than the second predetermined 
intake pipe absolute pressure value PBA.sub.2 (e.g. 650 mmHg), the value 
KTW is read as KTWPBA.sub.2, and if the intake pipe absolute pressure PBA 
is equal to or less than the first predetermined intake pipe absolute 
pressure value PBA.sub.1 (e.g. 300 mmHg), the value KTW is read as 
KTWPBA.sub.1. If the intake pipe absolute pressure PBA falls intermediate 
between PBA.sub.1 and PBA.sub.2, the value KTW is set to a value 
intermediate between KTWPBA.sub.1 and KTWPBA.sub.2 by means of linear 
interpolation. 
A similar manner of determining the KTW value to the above is applicable in 
the case where the intake air temperature TA detected is higher than the 
predetermined temperature TAS (e.g. 20.degree. C.), i.e., the case where 
the table of FIG. 4 is selected. Therefore, the explanation is omitted. 
The coolant temperature-dependent fuel increasing correction coefficient 
KTW thus obtained is substituted into the equation (1), whereby it is 
assured that a sufficient quantity of fuel is always supplied to the 
combustion chamber of each cylinder of the engine even when the intake air 
temperature is low and accordingly the atomization degree of the injected 
fuel is low, to thereby stabilize the engine rotation and improve the 
driveability. 
Although in this embodiment two TW-KTW tables are provided (FIGS. 3 and 4) 
for determining the KTW value as stated above, which are selected 
depending upon whether the intake air temperature TA is above or below the 
predetermined value TAS, a three-dimensional table, which employs intake 
air temperature TA, engine cooling water temperature TW, and intake pipe 
absolute pressure PBA, as parameters for determining the KTW value, from 
which table the KTW value can be directly read in response to a 
combination of the detected values of these parameters. 
Also, in obtaining the desired cooling water temperature fuel incremental 
correction coefficient KTW interpolation may be conducted with regard to 
intake pipe absolute pressure PBA before conducting interpolation with 
regard to engine cooling water temperature TW. 
Further, the parameter representing the engine load may be throttle valve 
opening or intake air quantity in lieu of intake pipe absolute pressure. 
As set forth above, according to the method of the invention, warming-up or 
engine temperature-dependent fuel increasing correction coefficient 
(engine coolant temperature, dependent fuel increasing correction 
coefficient), which is one of the factors to determine a desired quantity 
of fuel to be supplied to an internal combustion engine, is set to an 
appropriate value as a function of intake air temperature as well as 
engine temperature (engine coolant temperature) and intake pipe absolute 
pressure, to thereby enable compensating for a change in the atomization 
degree of the injected fuel caused by variation in the intake air 
temperature and hence prevent the atomization degree change from affecting 
the engine operating condition, whereby the engine rotation is stabilized 
and the driveability is improved.