ENGINE CONTROL APPARATUS
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an engine control apparatus capable of operating an engine efficiently even in the case where a fuel containing an alcohol of plant origin such as bioethanol is used in a vehicle that does not allow a backup RAM to be employed, for example, a vehicle employing a small-capacity battery such as a two wheeler, or a vehicle employing no battery.
2. Description of the Related Art
In recent years, flexible fuel vehicles (FFV), which can run with a fuel containing alcohol or a fuel made only from alcohol in addition to gasoline fuel, have been put into practical use. In each of these FFVs, the correction of a fuel injection amount is required so as to maintain an actual rotational speed of an engine with various fuels.
There is proposed a method of estimating an alcohol concentration based on an air-fuel ratio feedback correction coefficient calculated based on an exhaust air-fuel ratio to correct a fuel injection amount using the estimated alcohol concentration and the feedback correction coefficient (e.g., see JP• 3903925 B). In this method, the estimated alcohol concentration is stored, and the fuel injection amount is corrected using the stored alcohol

concentration until an alcohol concentration is estimated and calculated next time.
However, in the above-mentioned conventional method of correcting the fuel injection amount, the estimated alcohol concentration cannot be stored into a backup RAM in a vehicle that does not allow the backup RAM to be employed, for example, a vehicle employing a small-capacity battery such as a two wheeler, or a vehicle employing no battery, so the value of the estimated alcohol concentration needs to be written into a nonvolatile memory. However, there is an upper limit to the number of times of rewriting the nonvolatile memory. If the processing of storage is performed every time an alcohol concentration is estimated, the upper limit of the number of times of rewriting the nonvolatile memory may be exceeded. When the upper limit of the number of times of rewriting the nonvolatile memory is exceeded, the value of the estimated alcohol concentration cannot be stored, so the fuel injection amount cannot be corrected. As a result, there arises a problem of an overrich/overlean phenomenon.
The feedback correction coefficient is not initialized when the alcohol concentration is estimated, so the fuel injection amount is doubly corrected using the estimated alcohol concentration and the feedback correction coefficient. As a result, there arises a problem of the overrich/overlean phenomenon.

SUMMARY OF THE INVENTION
The present invention has been made to solve the above-mentioned problem, and it is therefore an obj ect of the present invention to provide an engine control apparatus capable of reducing the number of times of rewriting a nonvolatile memory, preventing an upper limit of the number of times of rewriting the nonvolatile memory from being exceeded, and hence preventing the occurrence of an overrich/overlean phenomenon by setting a limit in storing an alcohol concentration estimate into the nonvolatile memory so that the upper limit of the number of times of rewriting the nonvolatile memory is not exceeded.
Further, the present invention has been made to solve the above-mentioned problem, and it is therefore another object of the present invention to provide an engine control apparatus capable of eliminating double correction of a fuel injection amount and preventing the occurrence of the overrich/overlean phenomenon by initializing a feedback correction amount when an alcohol concentration estimate is calculated.
An engine control apparatus according to the present invention includes : a nonvolatile memory for storing an alcohol concentration estimate; a crank angle sensor for detecting an actual rotational speed of an engine; an intake air pressure sensor for detecting an intake air pressure; an intake air temperature sensor for detecting a temperature of intake air; a throttle position sensor for detecting

an opening degree of a throttle valve; an engine temperature sensor for detecting a temperature of the engine; an oxygen concentration sensor for detecting a concentration of oxygen in exhaust gas of the engine; a fuel injection module for injecting fuel into the engine; and a control unit that reads a value stored in the nonvolatile memory to set the value as an alcohol concentration estimate when a power supply is turned ON, calculates a base fuel injection amount based on an actual rotational speed of the engine detected by the crank angle sensor and an intake air pressure detected by the intake air pressure sensor, sets a correction coefficient based on a temperature of intake air detected by the intake air temperature sensor, an opening degree of the throttle valve detected by the throttle position sensor, and a temperature of the engine detected by the engine temperature sensor, sets a feedback correction amount based on a concentration of oxygen detected by the oxygen concentration sensor, corrects the alcohol concentration estimate based on the actual rotational speed of the engine detected by the crank angle sensor and the opening degree of the throttle valve detected by the throttle position sensor to set an air-fuel ratio learning correction coefficient, sets a voltage correction amount based on a battery voltage, corrects the base fuel injection amount based on the correction coefficient, the feedback correction amount, the air-fuel ratio learning correction coefficient, and the voltage correction amount to calculate a fuel injection amount, and outputs

a drive signal corresponding to the calculated fuel injection amount to the fuel injection module, in which the control unit calculates an alcohol concentration estimate based on the feedback correction amount when an air-fuel ratio learning mode is established, and stores the calculated alcohol concentration estimate into the nonvolatile memory when an absolute value of a difference between the calculated alcohol concentration estimate and the alcohol concentration estimate stored in the nonvolatile memory is equal to or larger than a predetermined value, and the actual rotational speed of the engine is within a predetermined range.
The engine control apparatus according to the present invention achieves an effect of enabling to reduce the number of times of rewriting the nonvolatile memory, and hence to prevent the occurrence of the overrich/overlean phenomenon.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a diagram showing the construction of an engine control apparatus according to a first embodiment of the present invention;
FIG. 2 is a flowchart showing an initial operation of a control unit of the engine control apparatus according to the first embodiment of the present invention;
FIG. 3 is a flowchart showing a fuel injection amount setting operation of the control unit of the engine control apparatus

according to the first embodiment of the present invention; and FIG. 4 is a flowchart showing a feedback correction amount setting operation of FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT First Embodiment
An engine control apparatus according to the first embodiment of the present invention will be described with reference to FIGS.
I to 4 . FIG. 1 is a diagram showing the construction of the engine
control apparatus according to the first embodiment of the present
invention.
Referring to FIG. 1, the engine control apparatus according to the first embodiment of the present invention is provided with an intake air temperature sensor 1 for measuring a temperature of intake air of an engine 25, a throttle position sensor 2 for measuring an opening degree of a throttle valve 23, an intake air pressure sensor 3 for measuring a pressure of intake air downstream of the throttle valve 23, an engine temperature sensor 4 for measuring a temperature of a wall surface of the engine 25, a crank angle sensor 5 for measuring a crank position of the engine 25, an oxygen concentration sensor 6 for detecting a concentration of oxygen in exhaust gas of the engine 25, a control unit 10 having a CPU, a ROM, a RAM, an I/O interface, and the like, and a nonvolatile memory
II incorporated in the control unit 10.

In addition, the engine control apparatus is provided with an air cleaner 21, an intake passage 22, an idle speed controller (ISC) 24 for supplying intake air bypassing the aforementioned throttle valve 23, a fuel tank 26 in which any one of "gasoline," "a blended fuel containing gasoline and alcohol," and "alcohol" is stored, a fuel injection module 27 for injecting fuel into the engine 25, an ignition coil 28, an ignition plug 29, an exhaust passage 30, an exhaust gas purification catalyst 31 for purifying NOx, HC, and CO, and the like.
Next, the operation of the engine control apparatus according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a flowchart showing the initial operation of the control unit of the engine control apparatus according to the first embodiment of the present invention. FIG.
3 is a flowchart showing the fuel injection amount setting operation
of the control unit of the engine control apparatus according to
the first embodiment of the present invention. In addition, FIG.
4 is a flowchart showing the feedback correction amount setting
operation of FIG. 3.
The control unit 10 calculates a suitable fuel injection timing and a suitable fuel injection amount based on pieces of information from the intake air temperature sensor 1, the throttle position sensor 2, the intake air pressure sensor 3, the engine temperature sensor 4, the crank angle sensor 5, and the oxygen concentration

sensor 6, and outputs a drive signal T to the fuel injection module 27. By the same token, the control unit 10 calculates a proper ignition timing and a suitable energization time based on the pieces of the information from the above-mentioned various sensors, and outputs a drive signal to the ignition coil 28.
First of all, the initial operation of the control unit of the engine control apparatus will be described with reference to FIG. 2.
In Step S101, the control unit 10 reads a value Keep stored in the nonvolatile memory 11 and sets the read value as an alcohol concentration estimate Kirn when a power supply is turned ON.
Subsequently, the fuel injection amount setting operation of the control unit of the engine control apparatus will be described with reference to FIG. 3.
In Step S2 01, the control unit 10 calculates a base fuel injection amount Ti based on a map TINJMAP (Ne, Pb) of an actual rotational speed Ne of the engine 25 detected by the crank angle sensor 5 and an intake air pressure Pb detected by the intake air pressure sensor 3. That is, the control unit 10 sets the base fuel injection amount Ti based on a relationship: Ti = TINJMAP (Ne, Pb) .
Then in Step S2O2, the control unit 10 sets a correction coefficient K based on a temperature of intake air detected by the intake air temperature sensor 1, an opening degree TH of the throttle valve 23 detected by the throttle position sensor 2, and a temperature

of the wall surface of the engine 25 detectedby the engine temperature sensor 4.
Then in StepS 2 03, the control unit 10 sets a feedback correction amount Kfb based on an oxygen concentration detected by the oxygen concentration sensor 6. The setting of this feedback correction amount Kfb will be described later in detail with reference to FIG. 4.
Then in Step S2O4, the control unit 10 corrects the alcohol concentration estimate Kirn using a correction map TKLRNAF (Ne, TH) that is set based on the actual rotational speed Ne of the engine 25 detected by the crank angle sensor 5 and the opening degree TH of the throttle valve 23 detected by the throttle position sensor 2, and calculates an air-fuel ratio learning correction coefficient Kaf. That is, the control unit 10 sets the air-fuel ratio learning correction coefficient Kaf based on a relationship: Kaf = Kirn*TKLRNAF (Ne, TH).
Then in Step S2O5, the control unit 10 sets a voltage correction amount Tb based on a battery voltage.
Then in Step S2O6, the control unit 10 calculates a fuel injection amount T based on the base fuel injection amount Ti, the correction coefficient K, the feedback correction amount Kfb, the air-fuel ratio learning correction coefficient Kaf, and the voltage correction amount Tb. That is, the control unit 10 sets the fuel injection amount T based on a relationship: T = TixKxKfbxKaf+Tb.

The control unit 10 outputs the drive signal T corresponding to the calculated fuel injection amount T to the fuel injection module
27.
The control unit 10 repeats the aforementioned fuel injection amount setting operation (Steps S201 to S2O6) at intervals of a certain period after the power supply is turned ON.
Now, the feedback correction amount setting operation of the control unit of the engine control apparatus will be described with reference to FIG. 4.
In Step S301, the control unit 10 determines, based on the actual rotational speed Ne of the engine 25, the temperature of the engine 25, and the opening degree TH of the throttle valve 23, whether or not a feedback condition is fulfilled. For example, when the actual rotational speed Ne of the engine 25 is within a predetermined range, the temperature of the engine 2 5 is within a predetermined range, and the opening degree TH of the throttle valve 23 is within a predetermined range, the control unit 10 determines that the feedback condition is fulfilled. When the feedback condition is fulfilled, the control unit 10 proceeds to the subsequent Step S3O2. On the other hand, when the feedback condition is not fulfilled, the control unit 10 proceeds to Step S310.
Then in Step S3O2, the control unit 10 determines whether or not an alcohol concentration estimate was calculated last time.

When a flag FL indicating that the alcohol concentration estimate was calculated last time is set (to 1) , the control unit 10 determines that the alcohol concentration estimate was calculated last time. When the alcohol concentration estimate was calculated last time, the control unit 10 proceeds to the subsequent Step S3O3. On the other hand, when the alcohol concentration estimate was not calculated last time, the control unit 10 proceeds to Step S3O4.
Then in Step S3O3, the control unit 10 initializes the feedback correction amount Kfb to "1." The control unit 10 also resets (to 0) the flag FL indicating that the alcohol concentration estimate was calculated last time.
Then in Step S3O4, the control unit 10 performs a known processing of calculating the feedback correction amount Kfb. That is, when the alcohol concentration estimate was calculated last time, the control unit 10 integrates (adds) a feedback correction amount Kfb calculated this time with (to) the feedback correction amount Kfb initialized in Step S3O3 ♦ When the alcohol concentration estimate was not calculated last time, the control unit 10 integrates jadds) the feedback correction amount Kfb calculated this time with (to) the feedback correction amount Kfb calculated last time.
Then in Step S3O5, the control unit 10 determines whether or not an air-fuel ratio learning mode is established. When a state in which the actual rotational speed Ne of the engine 25 is within a predetermined range (e.g., within a range from 1250 rpm to 2000

rpm) , a state in which the temperature of the engine 25 is within a predetermined range (e.g., within a range from 8O°C to HO°C), and a state in which a change in the opening degree TH of the throttle valve 23 is equal to or smaller than a predetermined value (e.g., 1.34 deg) are all established, the control unit 10. determines that the air-fuel ratio learning mode is established. When the air-fuel ratio learning mode is established, the control unit 10 proceeds to the subsequent Step 306. On the other hand, when the air-fuel ratio learning mode is not established, the control unit 10 proceeds to a block of "RETURN."
Then in Step S3O6, the control unit 10 performs a processing of averaging the feedback correction amount Kfb. The control unit 10 integrates the feedback correction amount Kfb calculated in Step S3O4 a predetermined number of times (e.g., 256 times) and divides the integrated value by the predetermined number of times (e.g., 256 times) to calculate a feedback correction amount average.
Then in Step S3O7, the control unit 10 integrates (adds) the feedback correction amount average calculated this time in Step S3O6 with (to) a feedback correction amount average calculated last time to calculate the alcohol concentration estimate Kirn. The control unit 10 also sets (to 1) the flag FL indicating that the alcohol concentration estimate was calculated last time.
Then in Step S3O8, the control unit 10 determines whether or not the alcohol concentration estimate Kirn calculated in Step S3O7

should be stored into the nonvolatile memory 11. That is, when the absolute value of a difference between the alcohol concentration estimate Kirn calculated in Step S3O7 and the value Keep stored in the nonvolatile memory 11 is equal to or larger than a predetermined value 1 (e.g., 0.1), and when the actual rotational speed Ne of the engine 25 is within a predetermined range (within a range from a predetermined value 2 (e.g., 500 rpm) to a predetermined value 3 (e.g., 2000 rpm) ) , the control unit 10 determines that the calculated alcohol concentration estimate Kirn should be stored into the nonvolatile memory 11. That is, when a relationship: |Kirn-Keep| ^ the predetermined value 1 and a relationship: the predetermined value 2 ^ Ne ^ the predetermined value 3 are established, the control unit 10 determines that the calculated alcohol concentration estimate Kirn should be stored into the nonvolatile memory 11. When the calculated alcohol concentration estimate Kirn should be stored into the nonvolatile memory 11, the control unit 10 proceeds to Step S3 09. On the other hand, when the calculated alcohol concentration estimate Kirn shouldnot be stored into the nonvolatile memory 11, the control unit 10 proceeds to the block of "RETURN."
Then in Step S3O9, the control unit 10 stores the alcohol concentration estimate Kirn calculated in Step S3O7 into the nonvolatile memory 11, and then proceeds to the block of "RETURN."
In Step S310, the control unit 10 initializes the feedback correction amount Kfb to "1." The control unit 10 also resets (to

0) the flag FL indicating that the alcohol concentration estimate was calculated last time, and then proceeds to the block of "RETURN. " In the first embodiment of the present invention, the limit is set in storing the alcohol concentration estimate for correcting the fuel injection amount into the nonvolatile memory 11 so that the upper limit of the number of times of rewriting the nonvolatile memory 11 is not exceeded. That is, the occurrence of the overrich/overlean phenomenon can be preventedby reducing the number of times of rewriting the nonvolatile memory 11 and hence ensuring that the upper limit of the number of times of rewriting the nonvolatile memory 11 is not exceeded. The occurrence of the overrich/overlean phenomenon can also be prevented by initializing the feedback correction amount to eliminate double correction of the fuel injection amount when the alcohol concentration estimate was calculated.

WHAT IS CLAIMED IS:
1. An engine control apparatus, comprising:
a nonvolatile memory for storing an alcohol concentration estimate;
a crank angle sensor for detecting an actual rotational speed of an engine;
an intake air pressure sensor for detecting an intake air pressure;
an intake air temperature sensor for detecting a temperature of intake air;
a throttle position sensor for detecting an opening degree of a throttle valve;
an engine temperature sensor for detecting a temperature of the engine;
an oxygen concentration sensor for detecting a concentration of oxygen in exhaust gas of the engine;
a fuel injection module for injecting fuel into the engine; and
a control unit that
reads a value stored in the nonvolatile memory to set the value as an alcohol concentration estimate when a power supply is turned ON,
calculates a base fuel injection amount based on an actual rotational speed of the engine detected by the crank angle

sensor and an intake air pressure detected by the intake air pressure sensor,
sets a correction coefficient based on a temperature of intake air detected by the intake air temperature sensor, an opening degree of the throttle valve detected by the throttle position sensor, and a temperature of the engine detected by the engine temperature sensor,
sets a feedback correction amount based on a concentration of oxygen detectedby the oxygen concentration sensor,
corrects the alcohol concentration estimate based on the actual rotational speed of the engine detected by the crank angle sensor and the opening degree of the throttle valve detected by the throttle position sensor to set an air-fuel ratio learning correction coefficient,
sets a voltage correction amount based on a battery voltage,
corrects the base fuel injection amount based on the correctioncoefficient, the feedback correction amount, theair-fuel ratio learning correction coefficient, and the voltage correction amount to calculate a fuel injection amount, and
outputs a drive signal corresponding to the calculated fuel injection amount to the fuel injection module, wherein the control -unit
calculates an alcohol concentration estimate based on

the feedback correction amount when an air-fuel ratio learning mode is established, and
stores the calculated alcohol concentration estimate into the nonvolatile memory when an absolute value of a difference between the calculated alcohol concentration estimate and the alcohol concentration estimate stored in the nonvolatile memory is equal to or larger than a predetermined value, and the actual rotational speed of the engine is within a predetermined range.
2. An engine control apparatus according to claim 1, wherein the control unit
determines that the air-fuel ratio learningmode is established when the actual rotational speed of the engine is within a predetermined range, the temperature of the engine is within a predetermined range, and a change in the opening degree of the throttle valve is equal to or smaller than a predetermined value, and
stores the calculated alcohol concentration estimate into the nonvolatile memory when the absolute value of the difference between the calculated alcohol concentration estimate and the alcohol concentration estimate stored in the nonvolatile memory is equal to or larger than 0.1, and the actual rotational speed of the engine is within a range from 500 rpm to 2000 rpm.
3 . An engine control apparatus according to claim 1 or 2, wherein

the control unit initializes the feedback correction amount when the alcohol concentration estimate is calculated last time.
4. An engine control apparatus according to claim 3, wherein the control unit initializes the feedback correction amount to 1 when the alcohol concentration estimate is calculated last time.
5. An engine control apparatus, comprising:
a nonvolatile memory for storing an alcohol concentration estimate;
a crank angle sensor for detecting an actual rotational speed of an engine;
an intake air pressure sensor for detecting an intake air pressure;
an intake air temperature sensor for detecting a temperature of intake air;
a throttle position sensor for detecting an opening degree of a throttle valve;
an engine temperature sensor for detecting a temperature of the engine;
an oxygen concentration sensor for detecting a concentration of oxygen in exhaust gas of the engine;
a fuel injection module for injecting fuel into the engine; and

a control unit that
reads a value stored in the nonvolatile memory to set the value as an alcohol concentration estimate when a power supply is turned ON,
calculates a base fuel injection amount based on an actual rotational speed of the engine detected by the crank angle sensor and an intake air pressure detected by the intake air pressure sensor,
sets a correction coefficient based on a temperature of intake air detected by the intake air temperature sensor, an opening degree of the throttle valve detected by the throttle position sensor, and a temperature of the engine detected by the engine temperature sensor,
sets a feedback correction amount based on a concentration of oxygen detected by the oxygen concentration sensor,
corrects the alcohol concentration estimate based on the actual rotational speed of the engine detected by the crank angle sensor and the opening degree of the throttle valve detected by the throttle position sensor to set an air-fuel ratio learning correction coefficient,
sets a voltage correction amount based on a battery voltage,
corrects the base fuel injection amount based on the correction coefficient, the feedback correction amount, theair-fuel

ratio learning correction coefficient, and the voltage correction amount to calculate a fuel injection amount, and
outputs a drive signal corresponding to the calculated fuel injection amount to the fuel injection module,
wherein the control unit initializes the feedback correction amount when the alcohol concentration estimate is calculated last time.
6. An engine control apparatus according to claim 5, wherein the control unit initializes the feedback correction amount to 1 when the alcohol concentration estimate is calculated last time.