ENGINE CONTROLLER
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an engine controller, in particular, an engine controller capable of maintaining an idle speed even if a change in amount of air occurs when a throttle valve is fully closed in a vehicle which cannot use a backup RAM such as a vehicle using a small-capacity battery as in the case of a two-wheel vehicle or a vehicle which does not use a battery.
2. Description of the Related Art
During idling, idle speed control is conventionally performed by comparing an actual revolution speed and a predetermined target revolution speed with each other, and performing feedback control, according to a result of comparison, on a bypass air amount control valve for adjusting a bypass air amount in a bypass air passage which bypasses a throttle valve provided for an intake passage of an engine. Moreover, it is supposed that an amount of air in a fully-closed state of the throttle valve is varied by a change with elapse of time (change in amount of leaked air, which is caused by a dust or carbon in an atmosphere (chongn caused by clogging) when the throttle valve is fully closed) , and thus there has been proposed a method of learning, even for the case where the amount of air in the fully-closed state of the throttle valve is varied.

the change in the amount of air in the fully "Loaed state of the throttlH valve from the feedback contrcjl amouiil: l:c) ntoro bhe change in the amount of air in a backup RAM {for exninple, see JP 3239200 B).
However, there exist vehicles which cannot use the backup RAM, such as a vehicle using a small-capacity battery as in the case of a two-wheel vehicle or a vehicle which does not use a battery. Therefore, in such vehicles, a learned change in the amount of air cannot be stored in the backup RAM, even though the conventional method of learning the change in the amount of air is performed as described above, and hence it is necessary to write the learned change in the amount of air to a non-volatile memory. However, the non-volatile memory has a limit in the number of rewrite times. Therefore, if storage processing is performed each time the change in the amount of air is learned, there is a possibility that the number of rewrite times exceeds its upper limit. If the number of rewrite times exceeds its upper limit, the learned change in the amount of air cannot be stored, and the idle speed control cannot be performed (there is a possibility that the actual revolution speed of the engine may be undesirably increased or lowered).
Further, for the rewrite of the non-volatile memory, a burden rate of a microcomputer (for example, burden on a CPU) is increased. Therefore, load is correspondingly increased when the actual revolution speed of the engine is high. As a result, there ia a

possibllltiy that a delay occurs in control which may cause an engine malfunction.
SUMMARY OF THE INVENTION
The present invention has been mods to anlve the problems as described above, and it is an object of the present invention to provide an engine controller for reducing the number of rewrite times for a non-volatile memory to prevent the number of rewrite times for the non-volatile memory from exceodJ.ng its upper limit by placing a restriction for Judgment of whetlier or not a learned change d.n amount of air (feedback control nmoiuit) ifi to ho stored in the non-volatile memory to restrain the number of rewrite times for the non-volatile memory from exceeding its upper limit, thereby maintaining an idle speed.
An engine controller according to the present invention includes: a bypass air amount control valve for adjusting a bypass air amount in a bypass air passage which is provided for an intake passage of an engine to bypass a throttle valve; sensor means for detecting an operating state of the engine, the operating state including an actual revolution speed of the engine; control means for applying a driving signal to the bypass air amount control valve according to the operating state obtained by the sensor means to control opening and closure of the bypass air amount control valve; feedback control mode judgment means for judging whether or not

a preset predetermined feedback control condition is satisfied based on the opex"ating state obtained by the sensor means ; feedback control amount learning means for comparing, when the feedback control condition is satisfied, the actual revolution speed and a preset predetermined target revolution speed with each other and for obtaining a feedback control amount according to a result of comparison to control the bypass air amount passing through the bypass air amount control valve; a non-volatile memory for storing an initial value of the feedback control amount and the feedback control amount obtained by the feedback control amount learning means; and storage judgment means for judging whether or not the feedback control amount is to be stored in the non-volatile memory, in which the storage judgment means obtains an absolute value of a difference between the feedback control amount obtained by the feedback control amount learning means and l:he feedback control amount already stored in the non-volatile memory, judges whether or not the absolute value of the difference in equal to or larger than a preset predetermined value, and storea, when the absolute value of the difference is equal to oi: Ini.'ner than tho preset predetermined value, the feedback control amount obtained by the feedback control amount leaning means in the non-volatile memory. The engine controller according to the present invention includes : the bypass air amount control valve for adjusting a bypass air amount in the bypass air passage which is provided for the intake

passage of the engine to bypass the throttle valve; the sensor means for detecting an operating state of the engine, the operating state including an actual revolution speed of the engine; the control means for applying a driving signal to the bypass air amount control valve according to the operating state obtained by the sensor means to control opening and closure of the bypass air amount control valve; the feedback control mode judgment means for judging whether or not a preset predetermined feedback control condition is satisfied basedon the operating state obtained by the sensor means; the feedback control amount learning means for comparing, when the feedback control condition is satisfied, the actual revolution speed and a preset predetermined target revolution speed with each other and for obtaining a feedback control amount according to a result of comparison to control the bypass air amount passing through the bypass air amount control valve; the non-volatile memory for storing an Initial value of the feedback control amount and the feedback control amount obtained by the feedback control amount learning means; and the storage judgment means for judging whether or not the feedback control amount is to be stored in the non-volatile memory, in which the storage judgment means obtains an absolute value of a difference between the feedback control amount obtained by the feedback control amount learning nioanH eind the f eodback control amount already stored In the non-volatile memory, judges whether or not the absolute value of the difference is equal to or larger

than a pi:edetermined value, and stores, whan the abaolute value of the difference is equal to or larger than tliB p:regnl: predetermined value, the feedback control amount obtained by l:he ioedback control amount loaning means in the non-volatile mtiirioiy. 1'herel-ore, the number of rewrite times for the non-volatile memory is reduced by placing a restriction for judgment of whether or not a learned change in the amount of air (feedback control amount) is to be stored in the non-volatile memory to prevent the number of rewrite times for the non-volatile memory from exceeding its upper limit. In this manner, the number of rewrite times for the non-volatile memory is restrained from exceeding its upper limit, whereby an idle speed can be maintained.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a diagram illustrating a configuration of an engine controller according to a first embodiment of the present invention;
FIG. 2 is a flowchart illustrating an initial operation of a control unit of the engine controller according to the first embodiment of the present invention;
FIG. 3 is a flowchart illustrating a bypass air amount setting operation of the control unit of the engine controller according to the first embodiment of the present invention;
FIG. 4 is a flowchart illustrating a feedback control amount

setting operation illustrated in FIG. 3; and
FIG. 3 is a flowchart illustrating an oporatinii of feedback control amount storage processing of the contro.l. unit of the engine controller according to the first embodiment of the present Invention.
PKTAILEDDESCRIFTIOM OF THE PRKFHHREn EMBODIMENT
First Embodiment
Helierring to FIGS. 1 to 5, an engine oonti.oilejr flccording to a first embodiment of the present invention .In deHci;J.bod. FIG. 1 is a configuration diagram illustrating n atsite in wh Lch the engine controiler according to the first embodinmut of thepveaent .Invention is mounted to an engine.
As Illustrated in FIG. 1, the engine controller according to the first embodiment of the present invention is provided with a control unit 10 constituting a main part of the engine controller. The control unit 10 Includes a microcomputer including a CPU, a ROM, a RAM and an I/O interface etc. , and stores programs and maps for controlling an entire operation of an engine 25. The control unit 10 includes a non-volatile memory 11. An initial value Qeep of a feedback control amount Qfb with respect to a bypass air amount in a bypass air passage is prestored in the non-volatile memory 11. In addition, the feedback control amount Qfb {updated value) obtained by learning is also stored in the non-volatile memory 11.

For an Intake passage 22 for introducing an intake air into the engine 25, an air cleaner 21, an intake air temperature sensor 1, a throttle valve 23, a bypass air passage (not shown), a bypass air amount control valve (throttle actuator) 24 , a throttle position sensor 2, an intake air pressure sensor 3, and a fuel injection module 27 are provided. The air cleaner 21 removes foreign substances in the air to generate the Intake air for the engine 25. The intake air tempei:ature sensor 1 measures a temperature of the intake air. The throttle valve 23 is driven to be opened/cJ.osed by the bypass air amount control valve 24. The bypass air pnssage is provided to bypass the throttle valve 23 . The bypaso ad r amount control valve 24 adjusts a bypass air amount in the bypass air passage. The throttle position sensor 2 measures an opening degree TH of the throttle valve 23. The Intake air pressure sensor 3 maaaures a pressure of the intake air at the downstream of the throttle valve 23. The fuel Injectdon module 27 injects a fuel stored in n fuel tank 26 to the engine 25.
The engine 25 is provided with an engine bemperature sensor 4 , a crank angle sensor 5 , and a sparkplug 29 . Tlie eniilne teriipernCure sensor 4 measures a wall temperature WT of l:he eiiolne 2 5 (hereinafter, referred to simply as a temperature WT of the oiigine 25) . The crank angle sensor 5 measures a revolution speed Ne of the engine 25 and a crank position of the engine 25 to output a crank angle signal (pulse) corresponding to the crank position. The spark plug 29 is

driven by an Ignition coil 28.
Further, an exhaust passage 30 for exhausting an exhaust gas from the engine 25 is provided with an oxygen concentration sensor (air-fuel ratio sensor) 6 and an exhaust gas purification catalyst (three-way catalyst) 31. The oxygen concentration sensor 6 detects a concentration of oxygen in the exhaust gas. The exhaust gas purification catalyst 31 removes NO^, HC, and CO contained In the exhaust gas to purify the exhaust gas.
Next, referring to'FIGS. 2 to 5, an operation of the engine controller according to the first embodiment is described. FIG. 2 is a flowchart illustrating an initial operation of the control unit 10 of the engine controller according to the first embodiment of the present invention, FIG. 3 is a flowchart illustrating a bypass air amount setting operation of the control unit 10. Further, FIG. 4 is a flowchart illustrating a feedback control amount setting operation of the control unit 10, which is illustrated in FIG. 3. FIG. 5 is ei flowchart illustrating an operation of feedback control amount storage processing of the control unit 10.
The control unit 10 follows a routine illustrated in FIGS. 2 to 5 to compute a bypass air amount for controlling an idle speed, to thereby output a driving signal Q to the bypass air amount control valve 24.
Further, the control unit 10 coiiipul.oH appropriate fuel Injection timing and fuel injection amount bnaed on information

regard:l.ng an operating state of a vehicle, whicli includes at least one oJ: the intake air temperature detiectod by t;he in Lake air temperature sensor 1, the opening degriiti 'I'll of: I he throttle valve, which 1H detected by the throttle position wensor 2, llie intake air preaaure detected by the intake air praeauro sensof 3, the temperature WT of the engine 25, which is detected by the engine temperature sensor 4, an actual revolution speed Ne (or crank position) of the engine 25, which is detected by the crank angle sensor 5, and the oxygen concentration detected by the oxygen concentration sensor 6 . Then, the control unit 10 outputs a driving signal corresponding to the obtained fuel injection timing and fuel injection amount to the fuel injection module 27.
Similarly, the control unit 10 computes appropriate ignition timing and energization time based on the information regarding the operating state of the vehicle, which includes at least one of the detection values from the sensors 1 to 6 described above. Then, the control unit 10 outputs a driving signal corresponding to the obtained ignition timing and energization time to the ignition coil 28.
First, referring to FIG. 2, the initial operation of the control unit 10 of the engine controller is described.
In Step SlOl, when powered ON, the control unit 10 reads out the value Qeep stored in the non-volatile memory 11 as an initial value to set the read value Qeep as the feedback control amount
10

Qfb.
Next, referring to FIG. 3, the bypafis air amount setting operation of the control unit 10 of the engine control] er ia described.
In Htep S201, the control unit 10 uiaes a map TQBASE (WT) to calculate a basic air amount Qi based on the temperature WT of the engine 25, which is detected by the engiii© temperature sensor 4, Namely, a basic air amount TQBASE (WT) cor rrea pond Lng to the temperature WT is stored in the map TQBASB (WT) for oaoh temperature WT of the engine 25. Therefore, the basic air nmount correBponding to the detected temperature WT of the engine 25 is t-ead fx-om the map TQBASE (WT) to set the basic air amount Ql. eo ati Lo establish the relation: Qi » TQBASE (WT).
yuhaequently, in Step S202, the oontiroi unil: 10 nets the feedback control amount Qfb. The details of a method of setting the feedback control amount Qfb are described below referring to FIG. 4.
Next, in Step S203, the control unit 10 calculates a bypass air amount Q based on the basic air amount Qi set in Step S201 and the feedback control amount Qfb set in Step S202. Namely, the control unit 10 sets the bypass air amount Q based on an arithmetic expression: Q = Qi + Qfb. The control unit 10 outputs a driving signal corresponding to the calculated bypass air amount Q to the bypass air amount control valve 24.
After being powered ON, the control unit 10 repeats the
11

above-described bypass air amount setting operation (Steps S201 to S203) for each predetermined time period or each predetermined number of revolutions of the engine 25.
Referring to FIG. 4, the feedback control amount setting operation of the control unit 10 of the engine controller is now described.
InStepS301, the control unit 10 judgeswhether or not a feedback control condition is satisfied (a feedback control mode is estabJ.iahed) based on the actual revolution speed Ne of the engine 25, the temperature WT of the engine 25, and the opening degree TH of the throttle valve . The control unit 1.0 jnclges that the feedback control condition is satisfied (the feedback control mode is established) when, for example, the actual revolution speed Ne of the engine 25 is within a predetermined range, the temperature WT of the engine 25 ia within a predetermined range, and the opening degree TU of the throttle valve is within n predetermined range. When the feedback control condition ia aailsfled (the feedback control mode is established), the proceaeing proceeda to next Step S302. On the other hand, when the feedback aontrol condition is not satiHfied (the feedback control mode la not est;abliBhad) , the proceasilig proceeds to RETURN because the faedback ciont.rn.l IB not performed in this case.
In Step S302, the control unit 10 uses a map TNTRGT (WT) to calculate a target revolution speed Ns based on the temperature
12

WT of the engine 25, which is detected by the engine temperature sensor 4. Namely, a target revolution speed TNTRGT (WT) corresponding to the temperature WT is stored in the map TNTRGT (WT) for each temperature WT of the engine 25 . Therefore, the control unit 10 reads the target revolution speed corresponding to the detected temperature WT of the engine 25 from the map TNTRGT (WT) to set the target revolution speed Ns so as to establish the relation: Ns = TNTRGT (WT).
In Step S303 , the control unit 10 compares the actual revolution speed Ne of the engine 25 and the target revolution speed Ns with each other. When the relation: Ne < Ns is established, the processing proceeds to Step S304 . On the other hand, when the relation: Ne > Ns is established, the processing proceeds to Step S305. When the relation: Ne = Ns is established, the processing proceeds to RETURN.
In Step S304, the control unit 10 adds a preset predetermined value Qd to the feedback control amount Qfb to obtain the learned feedback control amount Qfb. Then, the processing proceeds to RETURN.
In Step S305, the control unit 10 subtracts a preset predetermined value Qd from the feedback control amount Qfb to obtain the learned feedback control amount Qfb. Then, the processing proceeds to RETURN.
Next, referring to FIG. 5 , the opera 1.1-on o(f l;he f aadbaak control
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amount «l:orage processing of the control un 11 1(J 131: the engine controller la described.
Iii!3tepS40X , the control unit 10 Jurigos wli« l;her DI, not a feedback control mnount storage condition is satlHEltul (a fBodback control amount Htorage mode is established). The ouiiLroI unit 10 judges that the feedback control amount storage condition 1B satisfied (the feedback control amount storage mode la established) when conditions that the actual revolution speed Ne of the engine 25 is within a predetermined range (for example, within a range of from 1,250 rpm to 2,000 rpm) and that the opening degree TH of the throttle valve is equal to or less than a predetermined value {for example, 3.0 degrees) are satisfied. When the feedback control amount storage condition is satisfied (the feedback control amount storage mode is established) , the processing proceeds to next Step S402. On the other hand, when the feedback control amount storage condition is not satisfied (the feedback control amount storage mode is not established) , the processing proceeds to RETURN because the feedback control amount is not stored in the non-volatile memory 11 in this case.
Next, in Step S402, the control unit 10 judges whether or not the feedback control amount Qfb calculated in Step S304 or S305 is to be stored in the non-volatile memory 11. Namely, the control unit 10 judges that the feedback control amount Qfb is to be stored in the non-volatile memory 11 when an absolute value of a difference
14

between the calculated feedback control amount Qfb and the value Qeep utored in the non-volatile memory 1.1 .l.s equal to or larger than a prtJdetermined value (for example, a duty of 5%). Namely, when the relation: |Qfb-Qeep|2the predetermined value IH established, the control unit io judges that the feedback control amount Qfb is to be stored in the non-volatile memory 11. Therefore, when the relation; |Q£b-Qeep|a:the predetermined value ia eatabliehed, the processing proceeds to Step S403. On tlio iithier hmitl, when the relation 1 |Qfb-Qeep|