JPH04353267A - Ignition timing controller for engine - Google Patents

Abstract

PURPOSE:To make combustibility excellent and improve a fuel consumption performance by limiting spark retard setting that is by means of a reference ignition time setting means, when deviation quantity of an engine actual rotation number is less than a predetermined value. CONSTITUTION:During engine operation, an spark plug 14 is impressed with predetermined ignition voltage through an igniter by means of an ignition time control signal operated at an ECU 9 into which the output signals of a knock sensor 19, a boost pressure sensor 20 or the like are inputted, and ignites air-fuel mixture in a combustion chamber and burns it. At the time of this ignition time control signal operation at the ECU 9, ignition time that is spark retarded by a predetermined quantity against a reference ignition time at the time of idling operation, is set as the reference ignition time of idling rotation number control. The feedback control of a reference ignition time is conducted according to an engine actual rotation number deviation quantity against a target rotation number at the time of idling operation, and at this time, when the deviation quantity is less than a predetermined value, arrangement is made so that the above spark retard setting may be made to be limited.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine ignition timing control device for controlling the idle speed.

0002

[Prior Art] In the electronically controlled idle speed control device which is widely used in automobile engines in recent years,
For example, an intake air bypass passage is formed to bypass the throttle valve of the engine, and an intake air amount is provided in the intake air bypass passage to adjust the intake air quantity when the throttle valve is in the minimum opening state (idle state). An adjustment means (usually an electromagnetic control valve) is provided, and the intake air amount adjustment means is, for example, feedback-controlled in accordance with the amount of deviation between the actual rotation speed of the engine and a predetermined target rotation speed. Some engines are configured to operate at a target idle speed.

In such an idle speed control device using the intake air amount control method, when an external load of the engine (for example, an air conditioner) is normally applied, the electromagnetic control valve is adjusted according to the amount of the external load. The duty ratio of the engine is increased by a predetermined amount to increase the amount of intake air, and the engine speed is maintained at a constant idle target speed (for example, see Japanese Patent Laid-Open No. 181942/1983).

However, although the idle speed control device using intake air control has a wide control range, the response is inevitably poor, and it is not possible to quickly respond to load fluctuations such as when the external load is turned on as described above. There is a problem with rotational fluctuations.

On the other hand, control of engine output involves control of ignition timing (retard/advance), which affects its combustion performance.
Moreover, the control of the engine output by the ignition timing control has very high responsiveness.

Therefore, recently, the above-described ignition timing control device has been combined with the above-mentioned idle speed control device that controls the intake air amount, and the idle speed can be controlled over a wide range by controlling both the intake air amount and the ignition timing. An engine idle speed control device that controls engine speed with good response has also been proposed (see, for example, Japanese Patent Laid-Open No. 2-149749).

[0007]

[Problems to be Solved by the Invention] The ignition timing control device for controlling the idle rotation speed described above includes a basic ignition timing setting means for setting the basic ignition timing during idling operation, and A reference ignition timing setting means for setting an ignition timing retarded by a predetermined amount with respect to the basic ignition timing set by the setting means as a reference ignition timing for idle speed control, and an ignition timing F/B control means, The actual rotation of the engine is determined by determining the deviation amount of the actual engine rotation speed from the target rotation speed during the idling operation, and feedback correcting the reference ignition timing set by the reference ignition timing setting means according to the deviation amount. A configuration will be adopted in which the number of rotations is controlled to converge to the target rotation speed.

However, the larger the value of the retardation amount of the reference ignition timing set by the reference ignition timing setting means, the larger the amount of advance correction can be taken when the rotational speed changes (decrease). On the other hand, there is a problem in that fuel consumption deteriorates.

On the other hand, if the retard amount is made small, fuel efficiency improves, but the width of the advance angle correction amount becomes smaller and the output contribution is reduced, causing a problem that it becomes difficult to deal with large load fluctuations.

0010

[Means for Solving the Problems] The inventions described in each of claims 1 to 5 of the present application have been made for the purpose of solving the above problems, and are each constructed as follows. .

(1) Configuration of the invention according to claim 1 The ignition timing control device for an engine according to the invention includes a basic ignition timing setting means for setting a basic ignition timing during idling operation, and a basic ignition timing setting means for setting a basic ignition timing during idling operation. a reference ignition timing setting means for setting an ignition timing delayed by a predetermined amount with respect to the basic ignition timing set as a reference ignition timing for idle speed control; and a deviation of the actual engine speed from the target speed during idle operation. ignition timing control means for controlling the actual rotational speed of the engine to converge to the target rotational speed by feedback correcting the reference ignition timing set by the reference ignition timing setting means according to the deviation amount; The ignition timing control device for an engine is characterized in that a retardation limiting means is provided for limiting the retardation setting by the reference ignition timing setting means when the deviation amount of the actual rotational speed of the engine is below a predetermined value. That is.

(2) Configuration of the invention as claimed in claim 2 The engine ignition timing control device of the invention has the basic configuration of the engine ignition timing control device of the invention as claimed in claim 1, and an engine with the same configuration. The present invention is characterized in that the amount of deviation in rotational speed is determined by the operation of engine auxiliary equipment.

(3) Configuration of the invention according to claim 3 The engine ignition timing control device of the invention has the configuration of the invention according to claim 2 as a basic configuration, and the engine auxiliary equipment in the same configuration is a vehicle air conditioner. It is characterized by being a machine.

(4) Configuration of the invention according to claim 4 The engine ignition timing control device according to the invention has the configuration of the invention according to claim 1 as a basic configuration, and the determination of the deviation amount of the engine speed is performed based on the engine speed. This is characterized in that it is performed by making predictions based on water temperature.

(5) Configuration of the invention according to claim 5 The engine ignition timing control device of the invention has the basic configuration of the invention according to claim 1, and the reference ignition timing setting means in the same configuration sets the ignition timing. The retardation amount of the standard ignition timing is determined according to the engine water temperature, and the determined retardation amount is increased as the engine water temperature is lower.

[0016]

[Function] As a result of each of the inventions described in claims 1 to 5 of the present application being constructed as described above, each of the inventions exhibits the following functions corresponding to each of the structures.

(1) Effect of the invention according to claim 1 The engine ignition timing control device according to the invention according to claim 1, as described above, includes basic ignition timing setting means for setting the basic ignition timing during idling operation; a reference ignition timing setting means for setting an ignition timing retarded by a predetermined amount with respect to the basic ignition timing set by the basic ignition timing setting means as a reference ignition timing for idle speed control; and a target rotation during idle operation. Determine the amount of deviation of the actual engine rotation speed from the number,
ignition timing control means for controlling the actual rotational speed of the engine to converge to the target rotational speed by feedback-correcting the reference ignition timing set by the reference ignition timing setting means in accordance with the deviation amount; The ignition timing control means performs feedback control of the idle speed with good responsiveness based on the rotational deviation between the target idle speed and the actual speed.

In particular, with this configuration, the reference ignition timing set by the reference ignition timing setting means is retarded from the original basic advance value in accordance with the deviation amount of the engine speed, so that, for example, When the deviation of the engine speed is larger than normal, such as when the engine external load is turned on, and if the original ignition timing control is performed, the output will decrease and the engine will stall. As a result of being able to secure a large advance angle correction amount, it becomes possible to reliably avoid engine stalling.

On the other hand, in the engine ignition timing control device of the present invention, contrary to the above case, when the deviation amount of the actual engine speed is smaller than a predetermined value, that is, there is not a large advance angle correction amount. A retardation limiting means is provided for limiting the retardation setting by the reference ignition timing setting means when the rotational speed fluctuation can be accommodated. This improves combustibility and improves fuel efficiency.

(2) Effect of the invention claimed in claim 2 The engine ignition timing control device of the invention claimed in claim 2 has the same effect as the invention claimed in claim 1 due to its basic configuration, and also Since the amount of deviation in engine speed is specifically determined based on the operation of the engine auxiliary equipment itself, for example, it is possible to determine engine speed fluctuations that cause a large decrease in engine speed before the engine speed actually starts to decrease. In particular, the control responsiveness of idle rotation speed control can be improved.

(3) Effect of the invention set forth in claim 3 The ignition timing control device for an engine according to the invention set forth in claim 3 has the basic configuration of the invention set forth in claim 2. Therefore, first of all, in addition to the same effect as described above with the same configuration, the configuration of the present invention is characterized in that the engine auxiliary equipment is a vehicle air conditioner, and the engine auxiliary equipment is a vehicle air conditioner. Using the operation of the vehicle air conditioner, which is the most typical auxiliary equipment, as a parameter, it determines fluctuations in engine external load, especially decreases in rotational speed, with good responsiveness, and determines a sufficiently large retardation amount. setting, thereby ensuring a sufficient advance angle correction amount for ignition timing control.

As a result, fluctuations in the idle rotation speed when the vehicle air conditioner is turned on are reliably prevented.

(4) Effect of the invention claimed in claim 4 The engine ignition timing control device of the invention claimed in claim 4 has the same function as the invention claimed in claim 1 due to its basic configuration, and also has the following functions in the same configuration. Since the deviation amount of the engine speed is judged based on the engine water temperature, the combustion state is unstable like when it is cold, and the viscosity of the engine oil is also high, so the engine drive resistance is It is possible to reflect a state in which a large rotational speed drop is particularly likely to occur in an accurately set retard amount.

(5) Effect of the invention set forth in claim 5 In the engine ignition timing control device of the invention set forth in claim 5, in the structure of the invention set forth in claim 1, the reference ignition timing setting means sets the reference ignition timing. The invention is characterized in that the amount of retardation of the reference ignition timing is determined according to the engine water temperature, and the lower the engine water temperature, the larger the retardation amount is determined. To achieve this effect, the reference ignition timing is retarded to a greater extent during cold periods when the engine water temperature is low, engine drive resistance is high, and combustion stability is poor, ensuring a large amount of advance correction, which is effective against rotational fluctuations. Respond accordingly.

[0025]

Therefore, according to the engine ignition timing control device of the present invention, it is possible to achieve an action of increasing the idle speed and an action of improving fuel efficiency in accordance with the operating state of the external load of the engine. It becomes possible to control the idle rotation speed while achieving both of these requirements.

[0026]

[Embodiment] First, FIGS. 1 and 2 show an ignition timing control device for an automobile gasoline engine in which the present invention is applied to an idle speed control device for the engine. FIG. 2 is a schematic diagram of the control system of the apparatus, and is a flowchart showing the ignition timing control operation of the engine control unit in the control system.

First, the outline of the control system according to the embodiment of the present invention will be explained with reference to FIG. 2, and then the control of the main parts will be explained.

In FIG. 2, reference numeral 1 denotes an engine body, in which intake air is taken in from the outside via an air cleaner 30, and then supplied to each cylinder via an air flow meter 2 and a throttle chamber 3. Further, fuel is supplied from the fuel tank 12 to the engine side by the fuel pump 13 and injected by the fuel injector 5.

In this embodiment, a so-called split injection method is adopted in which the fuel injection is performed in both the intake stroke and the combustion stroke of the engine.

Further, in this embodiment, fuel injection is performed as an external factor that influences the degree of fuel evaporation.
After a portion of the fuel adheres to the wall of the intake passage, the adhering fuel can evaporate until it evaporates and is inhaled into the combustion chamber. Specifically, fuel injection is performed by considering the early or late timing of fuel injection. Is going. This is based on the fact that the earlier the injection timing, the greater the amount of evaporation of the adhering fuel, and as a result, the ratio of the amount carried away to the total fuel intake into the combustion chamber increases.

More specifically, the fuel injection is performed based on input signals such as the intake air amount, water temperature, and crank angle by the engine control unit 9, which will be described later. This is now done by calculating the amount of fuel supplied in accordance with the amount of remaining fuel (hereinafter referred to as the amount of adhesion to the intake manifold) and the degree of evaporation of the fuel, and controlling the opening time of the fuel injector 5. ing.

The amount of air taken into the cylinder during running is controlled by a throttle valve 6 provided in the throttle chamber 3. The throttle valve 6 is operated in conjunction with the accelerator pedal, and is maintained at the minimum opening state in the idling state.

The throttle chamber 3 is provided with a bypass intake passage 7 that bypasses the throttle valve 6, and the bypass intake passage 7 is provided with an intake air amount adjusting means for controlling the engine speed during idling. A current controlled solenoid valve (ISC valve) 8 is provided. Therefore, in the idle operating state, the intake air that has passed through the air flow meter 2 is supplied to each cylinder via the bypass intake passage 7, and the amount of intake air supplied is adjusted by the solenoid valve 8. The opening/closing state of the electromagnetic valve 8 is controlled by the duty ratio D of a control signal supplied from the engine control unit 9.

Further, reference numeral 10 indicates a three-way catalytic converter 1
1 shows an exhaust pipe with 1.

On the other hand, reference numeral 14 denotes a spark plug provided in the cylinder head of the engine body 1, and a predetermined ignition voltage is applied to the spark plug 14 via a distributor 17 and an igniter 18. The application timing of this ignition voltage, that is, the ignition timing, is controlled by the ignition timing control signal Igt (thtig) supplied from the ECU 9 to the igniter 18. Further, the reference numeral 19 indicates the engine main body 1
This is a knock sensor installed in the cylinder block of the engine, and the voltage output V corresponds to the intensity of engine knocking.
o is output and input to the ECU 9. Furthermore, code 2
0 is a boost pressure sensor 20 that detects an engine boost pressure B corresponding to the engine load and inputs it to the ECU 9.

The ECU 9 has, for example, a microcomputer (CPU) which is an arithmetic unit, a knock determination circuit, memory (ROM and RAM), and an interface (
It is configured with an I/O) circuit, etc. In addition to the above-mentioned detection signals, the interface circuit of the ECU 9 includes, for example, an engine starting signal (ECU trigger) from a starter switch (not shown), an engine rotation speed detection signal Ne from the engine rotation speed sensor 15, and a water temperature thermistor. 16, the throttle opening detection signal TVO detected by the throttle opening sensor 4, the intake air amount detection signal Q detected by the air flow meter 2, etc. Signals are also input respectively.

Next, the operation of controlling the idle speed by controlling the ignition timing of the engine of this embodiment by the engine control unit 9 will be explained.

That is, first, in step S1, various data necessary for the following control, such as engine water temperature Tw and engine rotational speed Ne, are read. Then, in the following step S2, it is determined whether the current operating state is in the idle operating region of the engine.

If the result is YES (idle), the process further advances to step S3, where it is determined whether or not an external engine load such as an air conditioner is turned on (a in FIG. 3).
When the result of the same judgment is YES (load ON), the load judgment flag XL is set to XL=1 in step S4, and the other (load ON) is set to XL=1.
FF), the same flag is set to XL=0 in step S5.

On the other hand, when the operating state of the engine is in the non-idle region, which is determined as NO in step S2, the process proceeds to steps S26 and S27, and first, in step S26, for example, the engine rotation speed Ne and the engine load are determined. In step S27, the solenoid valve 8 is opened so that the intake air flow rate of the intake bypass passage 7 becomes a predetermined flow rate. After setting the degree to a predetermined fixed value Cecont, the control proceeds to the final steps S24 and S25. And step S
In step S24, the control setting time of the ignition timing control timer Tig that specifically sets the ignition timing is set, and in step S
At step 35, a duty value corresponding to the set time is set.

Next, go back to the above steps S4 and S.
When the setting operation of the load judgment flag XL=1, XL=0 corresponding to the ON/OFF state of the engine external load is completed in Step 5, the process proceeds to step S6, and the value of the set load judgment judgment flag XL is changed from the previous time. Load judgment flag XL
Whether it is the same as the value of 0, that is, whether the above external load is ON
It is determined whether this is a continuation from the previous state or whether it is turned on for the first time (determination of load fluctuation), and if YES (it was also ON last time), the process goes to step S7; If it is ON for the first time, the process proceeds to step S8. In step S7, the counter value Cret of the ignition timing retard counter that determines the retard amount of the reference value for performing F/B control of the ignition timing, which has already been set in the previous control cycle, is decremented by one cycle (Cret =Cr
et-1). On the other hand, in step S8, the counter value Cret of the same ignition timing retard counter is set to the load O
After setting the initial value Kcret with N as a condition (see b in FIG. 3), the process proceeds to step S11, which will be described later. As shown in FIG. 4, for example, the counter value of the ignition timing retard counter Cret is set to be larger as the water temperature Tw is lower, taking into consideration the magnitude of the engine drive resistance.

When the decrement operation in step S7 is completed, the process further advances to step S9, and as a result of the decrement, the value of the counter value Cret becomes 0.
It is determined whether or not it is smaller than , and YES (Cret<
0), the value of Cret is set to 0 in step S10, that is, the counter value Cret of the ignition timing retard counter is reset, and then the process proceeds to step S11. Also, NO(Cr
et>0), the process jumps to step S10 and proceeds to step S11.

In step S11, the value of the current load judgment flag XL is set (memory) to the load judgment completion value (data to be stored for the next time) XL0, and then in step S12
Specifically, the retard amount thtret of the reference ignition timing with respect to the basic ignition timing shown in FIG. 3(e) is calculated using the calculation formula t
Calculate by htret=Kret·Cret (however, Kret is a constant). That is, the retard amount thtretf of the ignition timing, the ignition timing retard counter Cre
It is determined in proportion to the counter value of t (see b in Figure 3).
.

In this way, the ignition timing retard amount th
When the calculation of tret is completed, the process proceeds to step S13, where the idle intake air correction amount (IG correction amount) Ce is determined by the intake air amount control corresponding to the ignition timing retard amount.
Using ret in the same way, the formula Ceret=Kcer・Cr
Calculate by et (however, Kcer is a constant). As a result, the correction amount Ceret of the idle intake air amount is also proportional to the counter value Cret of the ignition timing retard counter (see c in FIG. 3).

Based on the above premise, the process further advances to step S14, where the basic amount Ceb of the idle intake air amount is calculated based on the indicated water temperature map. Also, after that, step S
At step 15, the basic ignition timing thtb is calculated based on the illustrated rotation map.

[0046] After that, the process further advances to step S16.
It is reconfirmed whether the value of the load determination flag XL mentioned above is XL=1 (external load ON state).

If the result is YES, the process advances to step S17, where the idle intake air amount load correction amount Ceid is set to K.
ceid, and if NO, proceed to step S18 and set the same load correction amount Ceid to Ceid=0, and then
Proceeding to step S19, the gain G (fb) of the ignition timing feedback control by the ignition timing control means is calculated. The gain G(fb) is calculated using the calculation formula G(fb)=Kg1-K
Calculated based on g2・thtret (however, Kg1,
Kg2 is an arbitrary constant).

Then, the process further proceeds to step S20, where the ignition is determined based on the ignition timing F/B gain G (fb) and the deviation (no-ne) of the actual engine speed ne (Ne) from the idle target speed no. The timing feedback control amount (g in FIG. 3) thtfb is calculated.

Thereafter, the process proceeds to step S21, where a feedback correction amount Cfb of the idle intake air amount is calculated. Further, in steps S22 and S23, the final ignition timing (h in FIG. 3) thtig and the final idle intake air control amount (d in FIG. 3) Cecont are calculated based on the calculation formulas shown in the diagram, respectively, and the final ignition timing (h in FIG. 3) is calculated based on the calculation formulas shown in the figure. The ignition timing control timer Tig is set in step S25, and the corresponding duty value is set in step S25 to control the ignition timing.

As is clear from the above control details, in the configuration of this embodiment, the external engine load such as the air conditioner is turned off and turned on, for example, as shown in FIGS. 5A and 5B. The reference value (its retard amount) of the ignition timing feedback control is set to different values. As a result, for example, the engine external load is turned off.
When the engine is turned on from the above state and there is a large drop in rotation, the reference ignition timing is set to the retard side as shown in the diagram (A) to ensure a sufficient amount of advance angle correction within the idle F/B region and the engine is idle. Ensure stability. On the other hand, when the amount of rotation reduction when the engine external load is OFF is small, the reference ignition timing is set as advanced as possible to improve combustion performance and achieve good fuel efficiency, as shown in figure (B). It has become.

Therefore, according to this embodiment, it is possible to prevent the engine from stalling when the external engine load is ON and to improve fuel efficiency when the engine is idling.

(2) Second Embodiment Next, FIG. 6 shows an ignition timing control system for an engine according to a second embodiment of the present invention, which takes into account the magnitude of driving resistance due to oil viscosity when the engine is cold, for example. Indicates control details.

That is, first, in step S1, various data necessary for the following control, such as engine water temperature Tw and engine rotational speed Ne, are read. Then, in the following step S2, it is determined whether or not the current operating state is in the idle operating region of the engine, as in the case of the first embodiment.

If the result is YES (idle), the process further advances to step S3.

On the other hand, when the operating state of the engine is in the non-idle region, which is determined as NO in step S2, the process proceeds to steps S5 and S6, and first, step S
5, for example, the ignition timing tht during normal control is determined from a map of the engine speed Ne and the engine load amount (intake air filling amount) Ce.
In addition to reading and setting ig, step S
6, the opening degree of the solenoid valve 8 is set to a predetermined fixed value Cec so that the intake air flow rate of the intake bypass passage 7 becomes a predetermined flow rate.
ont, and then the final step S17 of this control
, the process advances to step S18. Then, in step S17, the ignition timing control timer Tig is set to specifically set the ignition timing.
In step S18, a duty value corresponding to the control setting time is set.

Next, when returning to the original state and proceeding to step S3, the ignition timing retard amount thtret is specifically calculated using the formula thtret=Kret·Cr.
(However, as shown in FIG. 4, Cret here is the counter value of the ignition timing retard counter, which is set to a larger value as the water temperature Tw is lower, and Kret is a constant). In other words, the retard amount thtret of the ignition timing
is determined in proportion to the counter value of the ignition timing retard counter Cret.

In this way, the ignition timing retard amount th
When the calculation of tret is completed, the process proceeds to step S4, where the idle intake air correction amount Ceret by the intake air amount control corresponding to the retard amount of the ignition timing is similarly calculated using the calculation formula Ceret=Kcer·Cret (
However, Kcer is a constant). As a result, the correction amount Ceret of the idle intake air amount is also equal to the counter value Cret of the retard counter of the ignition timing.
It will be proportional to.

Based on the above premise, the process further advances to step S7, and this time, the basic amount Ceb of the idle intake air amount is calculated based on the indicated water temperature map. Also, after that, step S8
Then, the basic ignition timing thtb is calculated based on the illustrated rotation map.

Thereafter, the process further advances to step S9 to check whether the value of the water temperature determination flag XL corresponding to the load determination flag described above is XL=1 (below a predetermined water temperature).

If the result is YES, the process advances to step S10, where the load correction amount Ceid for the idle intake air amount is set to K.
ceid, and when NO is not cold, the process proceeds to step S11 to set the same load correction amount Ceid to Ceid=0, and then proceeds to step S12 to set the gain G (fb) of the ignition timing feedback control by the ignition timing control means. ) is calculated. The gain G(fb) is calculated using the calculation formula G(fb)=Kg
Calculated based on 1-Kg2・thtret (however, K
g1 and Kg2 are arbitrary constants).

Then, the process further proceeds to step S13, where the ignition is determined based on the F/B gain G (fb) of the ignition timing and the deviation (no-ne) of the actual engine speed ne (Ne) from the idle target speed no. Calculate the timing feedback control amount thtfb.

[0062] Then, the process proceeds to step S14, where a feedback correction amount Cfb of the idle intake air amount is calculated. In addition, in steps S15 and S16, the final ignition timing thtig and the final idle intake air control amount Cecont are respectively calculated, and the setting of the ignition timing control timer Tig in step S17 and the corresponding duty value in step S18 are performed. Go to each of the above first
Ignition timing control similar to the embodiment is executed.

Therefore, in the case of this embodiment, when the engine is cold and the engine water temperature is below a predetermined value, the same retard control as in the first embodiment is performed, and the magnitude of the engine drive resistance and the combustion Appropriate advance angle correction can be made in response to instability.

[Brief explanation of the drawing]

FIG. 1 is a control system diagram of an engine ignition timing control device according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing the ignition timing control operation of the device.

FIG. 3 is a time chart showing the operating state of each part corresponding to the control operation of FIG. 2;

FIG. 4 is an ignition timing retard map used in the ignition timing control operation shown in FIG. 2 above.

FIG. 5 is a torque characteristic diagram showing the operational characteristics of the control operation shown in FIG. 2;

FIG. 6 is a flowchart showing the control operation of the engine ignition timing control device according to the second embodiment of the present invention.

[Explanation of symbols]

1 is an engine body, 2 is an air flow meter, 5 is a fuel injector, 14 is a spark plug, 15 is an engine rotation speed sensor, and 18 is an igniter.

Claims (5)

[Claims] 1. A basic ignition timing setting means for setting a basic ignition timing during idling operation, and an ignition timing that is retarded by a predetermined amount with respect to the basic ignition timing set by the basic ignition timing setting means to control the idle rotation speed. a reference ignition timing setting means that sets the reference ignition timing for the engine, and a deviation amount of the actual engine rotation speed from the target rotation speed during idling operation, and the reference ignition timing setting means sets the reference ignition timing according to the deviation amount. and ignition timing control means for controlling the actual rotation speed of the engine to converge to the target rotation speed by feedback-correcting the reference ignition timing, wherein the deviation in the actual rotation speed of the engine is controlled. 1. An ignition timing control device for an engine, characterized in that the ignition timing control device for an engine is provided with a retardation limiting means for limiting the retardation setting by the reference ignition timing setting means when the amount is less than a predetermined value. 2. The engine ignition timing control device according to claim 1, wherein the deviation amount of the engine rotational speed is determined by the operation of an engine auxiliary machine. 3. The engine ignition timing control device according to claim 2, wherein the engine auxiliary equipment is a vehicle air conditioner. 4. The ignition timing control device for an engine according to claim 1, wherein the determination of the deviation amount of the engine speed is performed by predicting the engine water temperature. 5. The amount of retardation of the reference ignition timing set by the reference ignition timing setting means is determined according to the engine water temperature, and the lower the engine water temperature, the larger the determined amount of retardation. The ignition timing control device for an engine according to claim 1, characterized in that: