Engine fuel injection controller

A fuel injection amount in an engine is determined based on a cylinder air volume equivalent fuel injection amount and a wall flow correction amount. The fuel injection amount is also decreased in an initial injection when fuel injection is restarted after it is has been stopped. In this way, sudden torque increases are suppressed without causing a loss of engine rotation speed when fuel injection is restarted after it has been stopped.

FIELD OF THE INVENTION 
This invention relates to fuel feed control when fuel supply to an engine 
is restarted from a fuel cut condition. 
BACKGROUND OF THE INVENTION 
In an automobile engine, some time is required until the air-fuel ratio 
reaches a target air-fuel ratio when fuel injection is restarted from a 
fuel cut condition. During this time the air-fuel ratio is lean, and as it 
may not be possible to obtain ignition, the engine speed may fall. 
This can be explained in more detail as follows. 
During fuel cut, fuel which adhered to wall surfaces and valves before fuel 
cut flows into the cylinders, and when fuel injection starts again, there 
is almost no fuel adhering to wall surfaces and valves. However when fuel 
injection is restarted, some of the injected fuel becomes wall flow, and 
this wall flow enters the cylinders later than vaporized fuel which enters 
the cylinders immediately. Hence, the air-fuel ratio needs some time to 
reach its target value immediately after fuel injection restart and during 
this time interval the air-fuel ratio is lean. 
To resolve this problem, Tokkai Hei 5-71402 published by the Japanese 
Patent Office in 1993 proposes increasing a wall flow correction amount 
when fuel injection is restarted after fuel cut. The wall flow correction 
is based on a variation of a basic fuel injection amount relative to the 
amount of air aspirated to the cylinders, and on engine cooling water 
temperature. The basic fuel injection amount is then corrected with the 
wall flow correction amount in order to obtain the final fuel injection 
amount for each cylinder. 
In the calculation of wall flow correction, by correcting a stored value of 
the basic fuel injection amount to be smaller depending on the fuel cut 
time period, a difference or variation from a current calculated value is 
set large, and the wall flow correction amount is thereby increased. 
This enables the air-fuel ratio to reach its target value more rapidly 
after restarting fuel injection. 
In general, the air aspirated into the cylinder of an engine when the 
intake stroke is completed contains a part of the combustion gases 
produced in the immediately preceding combustion. 
One reason for this is that the opening periods of the exhaust valves and 
intake valves overlap with one another at the end of the exhaust stroke, 
therefore some of the combustion gas flows into the intake passage and is 
again led into the cylinder when it comes to the intake stroke. 
Another reason is that the volume of a combustion chamber in the cylinder 
is not zero even at the end of the exhaust stroke so that some combustion 
gas remains in the combustion chamber. 
However during fuel cut, combustion does not take place, consequently 
exhaust gas does not remain in the cylinder and the cylinder is full of 
fresh air when fuel injection is restarted. Therefore, if a large wall 
flow correction is applied when fuel injection is performed, an excessive 
torque is generated which gives a shock to the driver of the vehicle and 
its passengers. 
SUMMARY OF THE INVENTION 
It is therefore an object of this invention to suppress shock when fuel 
injection is restarted from a fuel cut condition. 
It is a further object of this invention to prevent the aforesaid shock 
without causing a decline of engine speed. 
In order to achieve the above objects, this invention provide a fuel 
injection controller for such an engine that comprises a cylinder, a fuel 
injector which performs fuel injection in synchronism with a combustion 
cycle of the cylinder and a mechanism for stopping the fuel injection 
under a predetermined engine running condition. The controller comprises a 
mechanism for calculating a cylinder air volume equivalent fuel injection 
amount corresponding to an air volume aspirated into the cylinder, a 
mechanism for calculating a wall flow correction amount, a mechanism for 
calculating a final fuel injection amount from the cylinder air volume 
equivalent fuel injection amount and the wall flow correction amount, a 
mechanism for controlling the fuel injector such that the injector injects 
the final fuel injection amount, and a mechanism for decreasing the final 
fuel injection amount in the initial injection when fuel injection is 
restarted after fuel injection is stopped by the stopping mechanism. 
It is preferable that the controller further comprises a mechanism for 
detecting an engine cooling water temperature and a mechanism for 
calculating a fuel injection restart correction coefficient of which the 
value is different in the initial injection and in other injections, and 
the wall flow correction amount calculating mechanism comprises a 
mechanism for calculating a variation of the cylinder air volume 
equivalent fuel injection amount, a mechanism for calculating a water 
temperature correction coefficient according to the engine cooling water 
temperature, and a mechanism for computing a wall flow correction amount 
in the cylinder from the variation, water temperature correction 
coefficient and fuel injection restart correction coefficient. 
In this case, it is further preferable that the mechanism for calculating a 
variation of the cylinder air volume equivalent fuel injection amount 
comprises a mechanism for storing a cylinder air volume equivalent fuel 
injection amount calculated for the previous fuel injection mechanism for 
calculating a difference between the cylinder air volume equivalent fuel 
injection amount calculated for a present injection and the cylinder air 
volume equivalent fuel injection amount stored by the storing mechanism 
and a mechanism for progressively decreasing the cylinder air volume 
equivalent fuel injection amount stored by the storing mechanism as the 
combustion cycle proceeds during a period in which fuel injection is 
stopped by the stopping mechanism. 
As for the engine connected to a transmission, it is preferable that the 
controller further comprises a mechanism for detecting a gear position of 
the transmission, and the decreasing mechanism comprises a mechanism for 
correcting the wall flow correction amount such that the final injection 
amount becomes smaller the lower the gear position used. 
When the engine comprises a torque converter comprising a lockup clutch, it 
is preferable that the controller further comprises a mechanism for 
detecting lockup of the lockup clutch, and the decreasing mechanism 
comprises a mechanism for correcting the wall flow correction amount such 
that the final injection amount is smaller during lockup. 
The details as well as other features and advantages of this invention are 
set forth in the remainder of the specification and are shown in the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1 of the drawings, a 4 stroke cycle water-cooled 
automobile engine 1 aspirates air from an air cleaner 2 via an intake 
passage 20 and intake manifold 4. A throttle 3 connected to an accelerator 
pedal is provided in the intake passage 20 to vary the amount of intake 
air. 
A fuel injector 5 is provided in each branch of the intake manifold 4 which 
runs to each cylinder. The fuel injector 5 is an electromagnetic valve 
which is open and shut by the magnetic force of a solenoid, the opening 
time and period of this valve being varied according to a pulse signal 
output by a control unit 10. 
Fuel is constantly supplied at a predetermined pressure to the fuel 
injector 5 from a fuel pump, not shown, via a regulator, and fuel is 
injected at a predetermined pressure into the branch of the manifold when 
the fuel injector opens. 
A spark plug 6 is provided in each cylinder of the engine 1. The fuel mixed 
with air which is led into the cylinder is ignited by the spark plug 6, 
and burns. Burnt gas is led to a catalytic converter 8 through an exhaust 
manifold 7 and exhaust passage 21, and after toxic components, i.e. carbon 
monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx) have been 
removed by a three-way catalyst in the catalytic converter 8, the exhaust 
is discharged into the atmosphere. 
A control unit 10 comprises a microcomputer, and controls the fuel 
injection amount of the injector 5 based on signals from various sensors. 
One of these sensors is a hot wire air flow meter 11 for detecting an 
intake air volume Q which is installed in the intake passage 20 upstream 
of the throttle 3, and a crank angle sensor 12 is also provided to detect 
the rotation angle of a crankshaft, not shown. The crank angle sensor 12 
outputs a REF signal every 180 degrees, and a POS signal every 1 or 2 
degrees of the crankshaft rotation. 
The control unit 10 detects an engine speed N of the engine 1 and a piston 
position in each cylinder by counting these signals. A potentiometer type 
throttle opening sensor 13 for detecting a throttle opening TVO is 
provided in the throttle 3. The throttle opening sensor 13 comprises an 
idle switch which switches ON in the fully shut position of the throttle 
3. 
A water temperature sensor 14 is provided in a water jacket of the engine 1 
to detect a cooling water temperature Tw of the engine 1. 
An oxygen sensor 15 is provided in an exhaust passage 21. The oxygen sensor 
15 detects, from the oxygen concentration of the exhaust, detects whether 
the fuel mixture supplied to the cylinders is rich or lean relative to a 
stoichiometric air fuel ratio. 
For the second and third embodiments described hereafter, a gear position 
sensor 16 for detecting a gear position of a transmission and a lockup 
switch 17 are provided. The lockup switch 17 detects the state of a lockup 
clutch which directly connects the input/output shafts of the torque 
converter of the automatic transmission under predetermined conditions, so 
in automobiles with manual transmission which do not have a torque 
converter, the lockup switch 17 is not provided. 
The signals from all of these sensors are input to the control unit 10. 
Based on these signals, the control unit 10 computes a fuel injection 
amount of the fuel injector 5 according to routines shown by the 
flowcharts of FIGS. 2-6, and controls the fuel injector 5 by outputting a 
pulse signal so as to inject the computed amount of fuel. 
These routines will now be described. 
FIG. 2 is a routine for computing a cylinder air volume equivalent fuel 
injection amount AVTP which is executed for example every 10 ms. 
In a step S1, a basic fuel injection amount Tp is calculated based on the 
intake air amount Q detected by the air flow meter 11 and the engine speed 
N detected by the crank angle sensor 12, as follows: 
##EQU1## 
where, K is a constant. 
In a step S2, the basic injection amount Tp is processed by the following 
first order delay equation taking account of the reaction delay between 
the value detected by the air flow meter 11 and the air actually aspirated 
by the cylinder, and a cylinder intake air volume equivalent fuel 
injection amount AVTP corresponding to the actual cylinder intake air 
volume, is calculated. 
EQU AVTP=Tp.multidot.FLOAD+AVTP.multidot.(1-FLOAD) 
where, FLOAD=weighted average coefficient determined by the throttle 
opening TVO and engine rotation speed N 
EQU (0&lt;FLOAD.ltoreq.1). 
FIG. 3 is a routine for calculating a cylinder specific fuel injection 
amount CTln, and is executed at intervals of e.g. 10 ms as in the case of 
the routine of FIG. 2. 
In a step S11, a fuel injection pulse width Ti is calculated based on the 
cylinder intake air volume equivalent fuel injection amount AVTP obtained 
by the process of FIG. 2, using the following equation. 
EQU Ti=AVTP.multidot.TFBYA.multidot.(ALPHA+LALPHA-1)+Ts 
where, TFBYA=air-fuel ratio correction coefficient 
ALPHA=air-fuel ratio feedback correction coefficient 
LALPHA=learning correction coefficient 
Ts=ineffectual pulse width (voltage compensation) depending on battery 
voltage. 
In a step S12, a cylinder specific wall flow correction amount CHOSn 
described hereafter is added to the fuel injection pulse width Ti to 
calculate a final cylinder specific fuel injection amount CTln. n is the 
cylinder number to which a value ranging from 1 to 4 is assigned in a 
4-cylinder. 
EQU CTln=Ti+CHOSn 
FIG. 4 is a routine which performs determinations related to fuel cut. This 
routine is also executed at intervals of for example 10 ms. 
In a step S21, it is determined whether or not fuel cut is in progress. 
More specifically, it is determined whether or not a fuel cut flag FC is 1 
or 0. When FC=0, it is determined in a step S22 whether or not the idle 
switch is ON or OFF, and in a step S23, it is determined whether or not 
the engine speed N is equal to or greater than a predetermined fuel cut 
rotation speed Nfc. 
The routine proceeds to a step S24 only when the idle switch is ON, i.e. 
when the throttle is fully closed, and the engine rotation speed is equal 
to or greater than the predetermined value Nfc. The fuel cut flag FC is 
then set to 1, and fuel supply is cut. 
When FC=1, it is determined in a step S25 whether or not the idle switch is 
OFF, and in a step S26, it is also determined whether or not the engine 
speed N is less than the predetermined value Nfc. 
When the idle switch is OFF, i.e. when the accelerator pedal is depressed, 
the fuel cut flag FC is set to 0 in a step S27, fuel cut is released and 
fuel injection is restarted. Even when the engine rotation speed is less 
than the predetermined value Nfc in the step S26, the same process is 
performed in the step S27. 
Hence, while fuel cut is in progress, the fuel cut flag FC is 1, and when 
fuel cut is released, the fuel cut flag FC is set to 0. 
FIG. 5 is a fuel injection control routine. This routine is performed prior 
to fuel injection in each cylinder and for each fuel injection. 
In this routine, the number n of the cylinder to be controlled is first 
determined in a step S31. 
In a step S32, it is determined whether or not fuel cut is in progress, 
i.e. whether or not FC=1. 
When FC=0, a pulse signal having a pulse width corresponding to the 
cylinder specific fuel injection amount CTln is output in a step S33 to 
the fuel injector 5 in the cylinder #n. Also in a step S14, a current 
cylinder intake air volume equivalent fuel injection amount AVTP is stored 
as a cylinder air volume equivalent fuel injection amount AVTPOn in the 
immediately preceding fuel injection for the same cylinder. 
When FC=1, only a pulse signal corresponding to the ineffectual pulse width 
Ts is output to the fuel injector 5 of cylinder n in a step S35, and fuel 
injection is not performed. In this case, a cylinder intake air volume 
fuel equivalent amount obtained by subtracting a predetermined amount 
.DELTA.t from the cylinder air volume fuel equivalent amount AVTPOn on the 
immediately preceding occasion is stored as a new value AVTPOn in a step 
S36. However when the result of the subtraction is negative in a step S37, 
AVTPOn is set to 0 in a step S38. 
FIG. 6 is a routine for calculating the cylinder specific wall flow 
correction amount CHOSn. This routine is executed at intervals of for 
example 10 ms as in the case of the routine of FIG. 2. 
In a step S41, it is determined whether or not a fuel cut flag FC=1, i.e. 
whether or not fuel cut is in progress. When FC=1, the routine is 
terminated. 
When FC=0, a variation amount .DELTA.AVTPn of the cylinder air volume 
equivalent fuel injection amount AVTP for each cylinder is calculated in a 
step S42. 
EQU .DELTA.AVTPn=AVTP-AVTPOn 
where, n is the cylinder number, and the calculation is performed from 
.DELTA.AVTPO1 to .DELTA.AVTPO4 for a 4-cylinder engine. 
Next in a step S43, a table of water temperature correction coefficients 
GZTWC is looked up from the cooling water temperature Tw. 
As shown in FIG. 7, the table of water correction coefficients GZTWC is set 
to reflect the characteristics of TGZTWP in the figures when 
.DELTA.AVTPn.gtoreq.0, i.e. when the vehicle is running steadily or 
accelerating, and to reflect the characteristics of TGZTWM in the figures 
when .DELTA.AVTPn&lt;0, i.e. when the vehicle is decelerating. Therefore, 
either one of these tables is selected depending on the value of 
.DELTA.AVTPn so as to determine the water temperature correction 
coefficient GZTWC. In both of these tables, the water temperature 
coefficient GZTWC is set larger the lower the cooling water temperature 
Tw. 
Next, in a step S44, it is determined whether or not fuel injection has 
restarted from the fuel cut state. When FC=1 in the immediately preceding 
determination, and FC=0 in the present determination, it is determined 
that fuel injection has restarted. 
When it is determined that fuel injection has not restarted, a fuel 
injection restart correction coefficient FCRATE is set to 1.0 in a step 
S45, and the routine proceeds to a step S51. 
When it is determined that fuel injection has restarted, FCRATE is set to 
0.6 in a step S46, and the routine proceeds to the step S51. 
In the step S51, the cylinder specific wall flow correction amount CHOSn is 
calculated from the following equation: 
EQU CHOSn=.DELTA.AVTPn.multidot.GZTWC.multidot.FCRATE 
Hence by adding the fuel injection restart correction coefficient FCRATE to 
the equation for calculating the cylinder specific wall flow correction 
amount CHOSn and varying FCRATE according to whether or not fuel injection 
has restarted, the cylinder specific wall flow correction amount CHOSn is 
set small when fuel supply is restarted. As a result, the cylinder 
specific fuel injection amount CTln is reduced when fuel injection is 
restarted, the generated torque is suppressed, a sudden torque is avoided, 
and the driver and passengers do not experience a shock. 
The reduction due to FCRATE is applied only to the initial injection in 
each cylinder after fuel supply is restarted, and as FCRATE is set to 1.0 
in the second and subsequent injections in each cylinder, it has no effect 
on the calculation of the cylinder specific wall flow correction amount 
CHOSn. In the second and subsequent injections, as part of the burnt gas 
remains in the combustion chamber as described above, a cylinder specific 
wall flow correction amount with FCRATE=1.0 is applied, so the air fuel 
ratio rapidly reaches the target air-fuel ratio. Hence, according to this 
invention, shocks are avoided without any loss of engine speed. 
FIGS. 8A-8C show the variations of engine speed, air-fuel ratio and 
generated torque after fuel supply is restarted according to this fuel 
injection controller. 
A broken line (a) shows the case when the fuel injection amount is not 
corrected by the cylinder specific wall flow correction amount CHOSn. In 
this case, as the fuel injection amount is not increased by the wall flow 
correction amount when fuel injection is restarted, engine speed falls 
after restarting injection as shown in FIG. 8A. 
A dotted line (b) shows the case where the fuel injection amount is 
corrected by the cylinder specific wall flow correction amount CHOSn, 
however the fuel injection restart correction coefficient FCRATE is not 
taken into account in the calculation of the cylinder specific wall flow 
correction amount CHOSn, i.e. FCRATE is always set to 1.0. In this case, 
decrease of engine speed is prevented as shown in FIG. 8A by increasing 
the fuel supply when fuel injection is restarted, however an excessive 
torque is produced immediately after injection as shown in FIG. 8C. 
A solid line (c) shows the case of this invention where FCRATE is set small 
only immediately after restarting fuel injection. In this case, not only 
is decrease of engine speed prevented but also an excessive torque is not 
generated after fuel injection is restarted. 
FIG. 9 shows a second embodiment of this invention. This relates to another 
process for calculating the cylinder specific wall flow correction amount 
CHOSn which is executed instead of the process of FIG. 6. 
According to this process, steps S47 and S48 are provided instead of the 
step S46 of FIG. 6, and the set value of FCRATE after restarting fuel 
injection is varied according to a gear position. 
In the step S47, the present gear position is detected by a signal from a 
gear position sensor 16. In the step S48, the fuel injection restart 
correction coefficient FCRATE is set according to the gear position as 
shown below: 
Neutral: FCRATE=1.0 
First gear: FCRATE=0.3 
Second gear: FCRATE=0.4 
Third gear: FCRATE=0.6 
Fourth gear: FCRATE=0.6 
Fifth gear: FCRATE=0.6 
Even when an excessive shock is produced in neutral, the driver and 
passengers experience hardly any shock so emphasis can be put on 
preventing drop of engine rotation speed. In other gear positions, the 
shock transmitted to the driver and passengers is greater the lower the 
gear, so FCRATE is set to a smaller value the lower the gear. 
FIG. 10 shows a third embodiment of this invention. This embodiment also 
relates to the process of calculating the cylinder specific wall flow 
correction amount CHOSn, and is performed instead of the process of FIG. 
6. 
According to this process, steps S49 and S50 are provided instead of the 
step S46 of FIG. 6. Here, the setting of FCRATE is varied according to the 
operating state of the lockup clutch of the torque converter. 
In the step S49, the lockup state is detected by a signal from the lockup 
switch 17. In the step S50, FCRATE is set as follows according to this 
detection result. 
During lockup: FCRATE=0.6 
Not during lockup: FCRATE=1.0 
During lockup, shocks are easily produced, so emphasis is placed on 
preventing shock. When there is no lockup, shocks are hardly transmitted, 
so emphasis is placed on preventing drop of engine rotation speed. The 
construction of converters which transmit rotation via a fluid is such 
that shocks are not easily transmitted when there is no lockup. 
It will be understood that the values of FCRATE given in the above 
description are only examples, and other values may of course be assigned 
within the spirit and scope of the appended claims. 
This invention has been described in the context of its application to 
synchronous injection at a predetermined crank angle, however it may also 
be applied to a fuel injection controller comprising an interrupt system 
where asynchronous injection is performed, i.e. where injection is 
interrupted when fuel injection is restarted so that an asynchronized 
injection that is not synchronized with the crank angle is performed.