JP3536734B2 - Control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an internal combustion engine that controls the engine speed to a target speed when the engine is started.

[0002]

2. Description of the Related Art At the start of an engine, particularly at the time of a cold start of the engine, deterioration of combustion is apt to occur and the engine speed may become unstable. If combustion deteriorates, problems such as deterioration of engine startability and engine exhaust characteristics, vibrations due to instability of the rotation speed after starting, and an increase in noise occur. For this reason, various control devices have been proposed for preventing deterioration of combustion at the time of engine start and stabilizing the engine speed.

[0003] For example, an example of this type of control device is disclosed in Japanese Patent Application Laid-Open No. 62-3139. The apparatus disclosed in the publication discloses an engine cooling water at the time of engine start (in this specification, the period from the start of engine start operation (start of cranking) to the start of steady idle operation after the complete explosion of the engine is called “engine start”). The throttle valve opening is set to a target opening corresponding to the temperature, and the throttle valve opening is set so that the engine speed matches the target value after the complete combustion of the engine.

[0004]

However, if the engine speed is controlled only by the opening degree of the throttle valve at the time of starting the engine as in the device disclosed in the above-mentioned publication, deterioration of engine combustion cannot be suppressed, and conversely, deterioration of combustion may occur. It may increase. For example, in an engine equipped with a fuel injection valve that injects fuel into the engine intake port, during cold start of the engine, the injected fuel does not vaporize but adheres to the intake port wall surface as a liquid and the concentration of vaporized fuel is insufficient. Therefore, there is a case where the air-fuel ratio of the air-fuel mixture becomes lean and combustion deteriorates. In such a case, if the opening of the throttle valve is increased, the intake pipe negative pressure on the downstream side of the throttle valve is reduced (absolute pressure is increased). Increase. For this reason, the rotation speed at the time of starting the engine may not be accurately controlled to the target rotation speed only by adjusting the throttle valve opening.

In order to solve the above-mentioned problem, the applicant of the present application has already disclosed in Japanese Patent Application No. Hei 11-98897, controlling the number of revolutions at the start of the engine by adjusting the opening of the throttle valve. A control device has been proposed which switches from rotational speed control by adjusting the valve opening to rotational speed control by adjusting the engine ignition timing. According to the device disclosed in the publication, the deterioration of the combustion state of the engine is determined based on the peak rotation speed and rotation fluctuation at the time of starting the engine, and if the deterioration has occurred, the engine ignition timing is determined by controlling the rotation speed by adjusting the throttle valve opening. By switching from the rotational speed control by adjustment or the rotational speed control by adjusting the throttle valve opening to the rotational speed control by increasing the fuel injection amount, deterioration of combustion is prevented.

However, as a result of research conducted by the applicant of the present application, in the above-described apparatus, immediately after the deterioration of the combustion state is determined, adjustment to the engine ignition timing or switching to rotation speed control by increasing the fuel injection amount is performed. It has been found that favorable results may not always be obtained in maintaining good exhaust characteristics of the engine. For example, in general, when the engine is started, the engine ignition timing is set to a more retarded side than during normal operation in order to raise the exhaust gas temperature so that the exhaust purification catalyst disposed in the exhaust passage reaches the catalyst activation temperature early. However, when switching from engine speed control by adjusting the throttle valve opening (intake air amount) to engine speed control by adjusting the ignition timing is performed, the engine ignition timing is advanced from the ignition timing at the time of the normal start. As a result, the exhaust gas temperature decreases and the catalyst temperature rise is delayed. Therefore, when the engine speed is controlled by adjusting the engine ignition timing at the time of starting, the time during which the engine is operated with exhaust purification insufficient due to a delay in catalyst warm-up is lengthened. Further, when switching from engine speed control by adjusting the throttle valve opening to engine speed control by increasing fuel injection is performed, the unburned HC and CO components in the exhaust gas increase, and the exhaust characteristics similarly deteriorate. There is. For this reason, it is preferable to maintain the rotation speed control by adjusting the throttle valve opening as much as possible without using the ignition timing adjustment and the rotation speed control by increasing the fuel injection amount when starting the engine. However, in the device according to the above-mentioned application filed by the applicant of the present invention, when combustion deterioration occurs, switching to the rotation speed control by adjusting the ignition timing or increasing the fuel injection amount is performed immediately. Even when combustion deterioration can be suppressed, there is a possibility that exhaust characteristics may be deteriorated due to switching of rotation speed control.

SUMMARY OF THE INVENTION In view of the above problems, the present invention makes it possible to accurately maintain the engine speed at a target speed while effectively suppressing the deterioration of combustion at the time of starting the engine. An object of the present invention is to provide a control device for an internal combustion engine that can suppress deterioration.

[0008]

According to the first aspect of the present invention, when the engine is started, the engine speed is adjusted to the target engine speed by intake air speed control for adjusting the engine intake air amount according to the engine speed. In addition, the presence or absence of deterioration of the engine combustion is determined based on the peak rotation speed immediately after the start of the engine, and when the combustion deteriorates, the engine ignition timing is adjusted according to the engine rotation speed from the intake air speed control to adjust the engine ignition timing. In a control device for an internal combustion engine that switches the engine speed to a target engine speed by switching to an ignition timing speed control that controls the engine speed to a target engine speed, a predetermined reference peak engine speed and an actual engine start time are controlled. Switching means for calculating a peak rotation speed difference, which is a difference from the peak rotation speed, and controlling the switching from the intake air speed control to the ignition timing speed control based on the peak speed difference. Control device for an internal combustion engine is provided.

That is, according to the first aspect of the present invention, the peak rotation speed at the time of starting the engine is compared with a predetermined reference peak rotation speed, and the difference between the reference peak rotation speed and the peak rotation speed (reference peak rotation speed−peak rotation speed) is determined. ), The switching from the intake air speed control to the ignition timing speed control is controlled. If the engine combustion condition is deteriorating, the peak rotation speed at the start of the engine decreases accordingly, and the peak rotation speed difference, which is the difference between the reference peak rotation speed and the peak rotation speed, depends on the deterioration of combustion. It becomes bigger. For this reason, for example, the reference peak rotation speed is set to a standard peak rotation speed after starting when there is no deterioration in combustion, and the combustion state is most deteriorated in a range where the rotation speed control is possible by the intake air rotation speed control. The peak rotational speed difference is set in advance, and when the actual peak rotational speed difference becomes larger than the set peak rotational speed difference, switching from the intake air speed control to the ignition timing rotational speed control is performed. For example, it is possible to prevent the switching to the ignition timing control even though the intake air speed control is possible. As a result, even when the combustion deteriorates, the intake air speed control is performed as much as possible, and the deterioration of the exhaust property is prevented.

According to the second aspect of the present invention, when the peak rotational speed difference is a negative value, the switching means continues the intake air amount rotational speed control, and when the peak rotational speed difference is positive. If the value is smaller than the upper limit which is a predetermined positive value, the reference air amount is set according to the peak rotation speed difference, and the actual intake air amount of the engine is smaller than the reference air amount. When the intake air speed control becomes larger, the switching from the intake air speed control to the ignition timing speed control is performed, and when the peak speed difference is larger than the upper limit value, the switch from the intake air speed control to the ignition timing speed control is immediately performed. A control device for an internal combustion engine according to claim 1, which performs switching to numerical control.

In other words, according to the second aspect of the present invention, when the difference between the peak rotational speeds is a negative value, that is, when the actual peak rotational speed at the start of the engine is larger than the reference peak rotational speed, the combustion is not deteriorated. The quantity rotation speed control is continued, and switching to the ignition timing rotation speed control is not performed. Further, when the peak rotation speed difference exceeds the positive upper limit value, that is, when the actual peak rotation speed decreases by a predetermined deviation or more compared to the reference peak rotation speed, the degree of deterioration of engine combustion is large. The switching from the intake air speed control to the ignition timing speed control is immediately performed.

On the other hand, when the peak rotation speed is other than the above, that is, when the peak rotation speed difference is a positive value but smaller than the upper limit value (the actual peak rotation speed is lower than the reference peak rotation speed and the reference peak rotation speed). In the case where there is a region between the predetermined rotation speed and the combustion speed, although the combustion is deteriorated, there is a possibility that the rotation speed can be controlled by the intake air rotation speed control without immediately switching to the ignition timing rotation speed control. If the peak rotational speed difference is in this region, whether or not the rotational speed can be controlled by the engine intake air amount while continuing the intake air rotational speed control without immediately switching to the ignition timing rotational speed control. Judge. In the intake amount rotation speed control, when the engine rotation speed decreases, control is performed to increase the engine intake air amount and maintain the engine rotation speed at the target rotation speed. For this reason, when the degree of combustion deterioration is large and the rotational speed cannot be controlled to the target rotational speed by the intake air rotational speed control, the engine intake air amount continues to increase. According to the present invention, the upper limit value (reference air amount) of the engine intake air amount is set when the intake air amount control is performed, and when the actual engine intake air amount increases to the reference air amount, depending on the intake air speed control, It is determined that rotation speed control cannot be performed, and switching to ignition timing rotation speed control is performed. If the peak rotation speed difference is in the above range, the reference air amount is set based on the difference between the reference peak rotation speed and the starting peak rotation speed.
For example, the larger the deviation between the reference value and the peak rotation speed,
In other words, the lower the peak rotation speed is and the worse the combustion is, the smaller the reference air amount is set. As a result, the switching to the ignition timing speed control is performed earlier as the deterioration of the combustion is larger, and even when the deterioration of the combustion is larger, the engine speed can be converged to the target speed in a short time. It becomes.

According to the third aspect of the invention, the engine speed is controlled to the target speed by the intake air speed control for adjusting the engine intake air amount according to the engine speed when the engine is started, and the engine is started. It is determined whether the engine combustion has deteriorated based on the immediately following peak rotational speed.When the combustion deteriorates, the engine rotational speed is adjusted to the target rotational speed by adjusting the engine ignition timing according to the engine rotational speed from the intake air rotational speed control. A control device for an internal combustion engine that controls the ignition speed at engine start to a target engine speed by switching to ignition timing speed control to be controlled, wherein a first predetermined engine speed at engine start reaches the peak engine speed. An internal combustion engine having a switching means for switching from the intake air speed control to the ignition timing speed control when the engine speed falls below the engine speed regardless of the value of the peak engine speed; Control device is provided.

That is, according to the third aspect of the present invention, if the engine speed drops to or below the first predetermined speed after reaching the engine start peak speed, the start time peak speed is reduced to the reference peak speed. Even in the case described above, the switching to the ignition timing speed control is immediately performed. For example, when a heavy fuel having low volatility is used, the normal start-up peak rotation speed becomes lower due to deterioration of combustion at the time of starting the engine. However, if the fuel is leaked from the fuel injection valve or the residual fuel remains in the cylinder while the engine is stopped, the peak rotation speed at the start may increase even if heavy fuel is used. However, also in this case, after reaching the peak rotation speed, the engine combustion deteriorates and the engine rotation speed decreases. For this reason, if the deterioration of combustion is determined only by the peak rotation speed at the time of starting, there may be cases where the true combustion state cannot be accurately determined. According to the third aspect of the invention, when the engine speed after reaching the starting peak rotation speed falls below a predetermined value, the switching to the ignition timing rotation speed control is performed regardless of the starting peak rotation speed. Even when the combustion state cannot be accurately determined depending on the peak rotation speed at the time of starting, the engine rotation speed can be made to converge to the target value.

According to the fourth aspect of the present invention, the switching means further includes a second predetermined rotation speed that is smaller than the first predetermined rotation speed after the rotation speed at the time of starting the engine reaches the peak rotation speed. A control device for an internal combustion engine according to claim 3, wherein the amount of fuel supplied to the engine is increased when the internal combustion engine speed decreases. That is, in the invention of claim 4, in the case of claim 3, when the rotation speed continues to decrease after reaching the peak rotation speed and reaches the second predetermined rotation speed smaller than the first predetermined rotation speed, It is determined that the degree of deterioration of the combustion is so large that the target rotational speed cannot be maintained only by controlling the ignition timing rotational speed. In this case, in addition to the ignition timing rotation speed control, switching to the rotation speed control by increasing the fuel amount is performed. As a result, even when the deterioration of combustion is large, the engine speed increases and the target speed can be maintained.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing the overall configuration when the present invention is applied to an internal combustion engine for a vehicle. In FIG. 1, 1 is an internal combustion engine main body, 2 is a surge tank provided in an intake passage of the engine 1, 2a is an intake manifold connecting the surge tank 2 and an intake port of each cylinder, 1
Reference numeral 6 denotes a throttle valve arranged in an intake passage on the upstream side of the surge tank 2, and reference numeral 7 denotes a fuel injection valve for injecting pressurized fuel into an intake port of each cylinder of the engine 1.

In this embodiment, the throttle valve 16 is provided with an actuator 16a such as a stepper motor, and employs a so-called electronically controlled throttle valve which takes an opening in accordance with a control signal input from the ECU 10 described later. The throttle valve 16 is provided with a throttle opening sensor 17 for generating a voltage signal corresponding to the operation amount (opening) of the throttle valve.

In FIG. 1, reference numeral 11 denotes an exhaust manifold for connecting the exhaust port of each cylinder to a common collective exhaust pipe 14;
Is a three-way catalyst disposed on the exhaust pipe 14, 13 is an upstream air-fuel ratio sensor disposed on the exhaust junction of the exhaust manifold 11 (upstream of the three-way catalyst 20), and 15 is an exhaust pipe on the downstream side of the three-way catalyst 20. 14 is a downstream air-fuel ratio sensor arranged at 14. The three-way catalyst 20 can exhaust air-fuel ratio flowing to purify HC in the exhaust gas when in the vicinity of the stoichiometric air-fuel ratio, CO, three components of the NO _X at the same time. The air-fuel ratio sensors 13 and 15 are used for exhaust air-fuel ratio detection when performing feedback control of the fuel injection amount to the engine so that the engine air-fuel ratio becomes a predetermined target air-fuel ratio during normal engine operation.

In this embodiment, an intake pressure sensor 3 for generating a voltage signal corresponding to the intake pressure (absolute pressure) in the surge tank is provided in the surge tank 2 in the intake passage.
The water jacket 8 of the cylinder block is provided with a water temperature sensor 9 for generating an analog voltage electric signal corresponding to the temperature of the cooling water. The output signals of the throttle valve opening sensor 17, the intake pressure sensor 3, the water temperature sensor 9, and the air-fuel ratio sensors 13 and 15 are supplied to an ECU described later.
It is input to ten A / D converters 101 with a built-in multiplexer.

In FIG. 1, reference numerals 5 and 6 denote crank angle sensors arranged near the camshaft and the crankshaft (not shown) of the engine 1, respectively. For example, the crank angle sensor 5 generates a reference position detection pulse signal every 720 ° in terms of a crank angle, and the crank angle sensor 6 generates a crank angle detection pulse signal every 30 ° of the crank angle. The pulse signals of these crank angle sensors 5 and 6 are
The output of the crank angle sensor 6 is supplied to the CPU 103 of the ECU 10.
Is supplied to the interrupt terminal. The ECU 10 calculates the rotation speed (rotation speed) of the engine 1 based on the crank angle pulse signal interval from the crank angle sensor 6 and uses it for various controls.

Electronic control unit (ECU) 10 of engine 1
Is configured as, for example, a microcomputer, in addition to an A / D converter 101 with a built-in multiplexer, an input / output interface 102, a CPU 103, a ROM 104,
A RAM 105, a backup RAM 106 capable of holding data even when the main switch is turned off, a clock generation circuit 107, and the like are provided.

The ECU 10 performs basic control of the engine 1 such as fuel injection amount control and ignition timing control of the engine 1 based on the intake pressure, the throttle valve opening, and the engine speed. At the start of the engine (from the start of cranking to the steady idle operation after the complete explosion), the engine speed at the start is controlled to maintain the engine speed at the target speed. In order to perform the above control, the ECU 10 executes an A / D conversion routine that is executed at regular intervals to execute an intake pressure (P
M) signal, throttle opening (TA) signal from the throttle opening sensor 17, cooling water temperature (T
HW) signal is A / D converted and input.

The input / output interface 102 of the ECU 10 is connected to the fuel injection valve 7 via a drive circuit 108, and controls the fuel injection amount and injection timing from the fuel injection valve 7. Further, an input / output interface 102 of the ECU 10 is connected to each ignition plug 111 of the engine 1 through an ignition circuit 110, controls the ignition timing of the engine, and is connected to an actuator 16a of the throttle valve 16 through a drive circuit 113. Then, the opening of the throttle valve 16 is controlled by driving the actuator 16a.

Next, the start-time rotational speed control of the present embodiment will be described. In the present embodiment, the ECU 10 sets the engine rotation speed to a predetermined target rotation speed at the time of engine start, that is, from the start of the engine start operation (start of cranking) to the start of stable idle operation after the complete combustion of the engine. Start speed control to maintain the speed. Normally, at the start of engine cranking, the fuel injection amount of the engine is set to an amount obtained by adding a correction according to the intake air temperature (atmospheric temperature) and the atmospheric pressure to the basic start-up injection amount determined from the cooling water temperature and the engine speed. You.
Then, after the cranking is started, after the engine speed exceeds a predetermined speed (for example, about 400 rpm) higher than the cranking speed, it is determined that the combustion is started in each cylinder and the engine is in a complete explosion state. After that, the fuel injection amount is set to an amount obtained by multiplying a basic fuel injection amount according to the engine intake air amount and the engine speed by a predetermined coefficient. The basic fuel injection amount is a fuel injection amount required to maintain the engine combustion air-fuel ratio at the stoichiometric air-fuel ratio. The predetermined coefficient is for compensating the adhesion of the injected fuel to the intake port wall surface at the time of engine start and the deterioration of the fuel vaporization state due to the low temperature, and the predetermined coefficient is larger than 1 at the time of engine start. And the engine combustion air-fuel ratio is set richer than the stoichiometric air-fuel ratio.

When the engine is started, the temperature of the exhaust purification catalyst (indicated by reference numeral 20 in FIG. 1) disposed in the exhaust passage is low, and the catalyst cannot exhibit the exhaust purification function. Therefore,
After starting the engine, it is necessary to raise the catalyst temperature to the activation temperature as soon as possible to start purifying the exhaust gas with the catalyst. For this reason, at the time of normal engine startup, the engine ignition timing is retarded as compared with the normal operation in order to raise the exhaust gas temperature and raise the temperature of the catalyst in a short time.

As described above, the fuel injection amount at the time of starting the engine is appropriately set in accordance with various factors. Therefore, if the engine is normally in a normal state, the rotation speed fluctuation due to deterioration of combustion at the time of starting the engine is unlikely to occur. Has become. However, even when the engine is normal, there is a case where the rotation speed fluctuates due to deterioration of combustion at the time of starting. For example, if the properties of the fuel (gasoline) used for the engine are different, combustion deterioration at the time of starting is likely to occur. The fuel injection amount at the time of starting the engine is set based on a case where a fuel having a standard property is used. Therefore, for example, when a fuel having a lower volatility than the standard fuel (hereinafter, referred to as "heavy fuel") is used in the engine, the combustion may be deteriorated particularly at the time of the cold start of the engine. That is, since the heavy fuel has low volatility, even when the same amount of fuel as the standard fuel is injected, the ratio of the fuel adhering to the intake port wall as a liquid without vaporizing increases and is actually supplied into the cylinder. The amount of fuel used is reduced. As a result, the combustion air-fuel ratio of the engine shifts to a leaner side than normal, and the engine speed becomes unstable due to deterioration of combustion.

Generally, as a method of preventing the engine speed from becoming unstable at the time of starting and maintaining the engine speed at a predetermined target speed, feedback control of the engine intake air amount based on the engine speed (intake air amount) Rotation speed control) is performed. In the intake air speed control, when the engine speed is lower than the target speed, the opening of the throttle valve 16 is increased (the engine intake air amount is increased) to increase the speed, and the speed is higher than the target speed. In this case, the rotation speed is maintained at the target rotation speed by performing feedback control based on the rotation speed for reducing the rotation speed by reducing the throttle valve opening (reducing the intake air amount). However, when heavy fuel is used, deterioration of combustion in the engine cannot be suppressed by intake air speed control, and the start speed may not be maintained at the target speed.

For example, when the combustion air-fuel ratio of the engine becomes lean at the start of the engine due to the use of heavy fuel and the combustion deteriorates, in the intake air speed control, when the engine speed decreases due to the combustion deterioration, the engine speed is reduced. The throttle valve opening is increased to increase the number. However, when the opening degree of the throttle valve is increased, the negative pressure in the intake passage downstream of the throttle valve decreases (the absolute pressure increases), so that the injected fuel becomes more difficult to vaporize. For this reason, the engine combustion air-fuel ratio may shift further in the lean direction, and the deterioration of combustion may increase.

In this embodiment, when the engine speed decreases due to deterioration of combustion at the time of starting the engine, the engine speed is reduced by the following method according to the degree of combustion deterioration (according to the degree of fuel heaviness). The target speed is maintained. In this embodiment, when it is determined that the intake amount rotational speed control cannot compensate for the decrease in the starting rotational speed due to deterioration of combustion, the ignition timing rotational speed control is performed instead of the intake amount rotational speed control. . In the ignition timing rotation speed control, an operation of maintaining the engine rotation speed at the target rotation speed by performing feedback control of the ignition timing based on the engine rotation speed is performed. When the engine is started, the engine ignition timing is retarded for warming up the catalyst as described above. On the other hand, when heavy fuel is used, the combustion speed of the in-cylinder air-fuel mixture decreases due to a lean air-fuel ratio or the like. Therefore, by advancing the engine ignition timing to compensate for the decrease in the combustion speed, the output torque in the cylinder increases, and the engine speed increases. However, when the ignition timing rotational speed control is performed, the engine ignition timing is on the more advanced side than during normal startup, so that the exhaust gas temperature decreases and the time required for warming up the catalyst becomes longer. Therefore, when the ignition timing speed control is performed, the exhaust properties deteriorate due to a delay in activation of the catalyst.

If the deterioration of the combustion is large and the reduction of the rotation speed due to the deterioration of the combustion cannot be compensated for even by performing the ignition timing rotation speed control, the increase of the fuel injection amount in addition to the ignition timing rotation speed control is required. Done. By increasing the fuel injection amount, it is possible to supply sufficient vaporized fuel to the cylinders while compensating for the deterioration of vaporization due to heavy fuel, so that the engine speed increases.

However, the increase in the fuel injection amount depends on the unburned H in the exhaust gas.
Since the C and CO components are increased, the deterioration of the exhaust properties is further increased as compared with the case of controlling the ignition timing rotation speed. As described above, when the ignition timing is controlled or the fuel injection amount is increased when the combustion is deteriorated at the time of starting the engine, there is a possibility that the exhaust properties may deteriorate. Therefore, in the embodiment described below, even when combustion deteriorates, the engine speed is controlled using the intake air speed control as much as possible, and the ignition timing is controlled only when the intake speed control cannot control the combustion deterioration. By switching to rotation speed control, deterioration of exhaust characteristics is suppressed.

Hereinafter, a specific embodiment of the start-time rotational speed control of the present invention will be described. (1) First Embodiment In this embodiment, the engine combustion state is determined by comparing the peak value (peak rotation speed) of the engine rotation speed at the time of engine start with a preset reference peak rotation speed, and the intake air amount is determined. Switching between rotation speed control and ignition timing rotation speed control is controlled.

FIG. 2 is a diagram showing a change in the number of revolutions when the engine is started. In FIG. 2, the horizontal axis represents the time from the start of cranking, and the vertical axis represents the engine speed. Further, the solid line in FIG. 2 shows a change in rotation speed when combustion is not deteriorated, and the dotted line shows a change in rotation speed when combustion is deteriorated (when heavy fuel is used). In FIG. 2, the solid line represents a change in the number of revolutions when the engine is started using, for example, a standard fuel having good volatility. The engine speed rises after the start of cranking, and when an explosion occurs in all cylinders (complete explosion), the engine speed rises sharply and peaks (Fig. 2,
After reaching point (b), the rotation speed drops again to idle rotation (c).
point). On the other hand, the dotted line in FIG. 2 corresponds to a change in the rotation speed when a heavy fuel with low volatility is used. In this case as well, the engine speed sharply rises at the time of the complete combustion of the engine, but the combustion state is deteriorated and the generated torque of the cylinder is also small, so that the peak engine speed (point a in FIG. 2) is smaller than the solid line. The peak rotation speed in each case corresponds to the cylinder generated torque due to combustion, and can be used as an index of the combustion state in each case. That is, the peak rotational speed NEP ₀ in the case where the combustion state is good using the standard fuel (FIG. 2, solid line) and the peak in the case where the combustion state is deteriorated using the heavy fuel (FIG. 2, dotted line). It is considered that the difference from the rotational speed NEP indicates the difference in the combustion state in each case.

In this embodiment, the starting peak rotational speed NEP ₀ in a standard state (when a standard fuel having good volatility is used) is set in advance as a reference peak rotational speed.
At the time of actual engine start, the peak rotational speed NE
P is measured, the combustion state is determined based on the difference between the reference peak rotation speed NEP ₀ and the actual peak rotation speed NEP, DNP (= NEP ₀ −NEP), and the intake air speed control is performed based on the determination result. And the ignition timing control.

FIG. 3 is a flow chart for explaining the starting speed control operation of the present embodiment. This operation is performed by the ECU
10 is performed as a routine executed at regular intervals. When the operation starts in FIG.
In 01, it is determined whether or not the engine is currently started, that is, whether or not it is a period in which the engine speed control is to be performed. In step 301, for example, if the predetermined time has not elapsed from the start of the engine start operation (cranking), it is determined that the engine is currently started. It should be noted that whether or not the engine is currently started is determined not by the time from the start of the engine start operation, but by determining, for example, whether or not the engine cooling water temperature has reached a predetermined value and has reached the predetermined value. When there is no engine (when the engine warm-up is not completed), it may be determined that the engine is present at the time of starting.

If the engine is not started at step 301, the engine has been warmed up and the combustion is stable, so there is no need to control the engine speed at startup. The value of the execution flag CN and the value of the ignition timing rotation speed control execution flag IN are both set to 0, and the operation ends. As will be described later, when the value of the flag CN is set to 0, the execution of the intake air speed control (FIG. 6) is stopped, and when the value of the flag IN is set to 0, the ignition timing speed control ( The execution of FIG. 7) is stopped. In the present embodiment, the initial value of the intake air speed control flag CN is set to 1 (execution), and the initial value of the ignition timing speed control flag IN is set to 0 (prohibited).

On the other hand, if it is determined in step 301 that the engine is currently being started, then in step 303, the difference DNP between the pre-stored reference peak rotation speed NEP ₀ and the current startup rotation speed NEP is calculated. You. FIG. 4 is a flowchart for explaining the start-time peak rotation speed NEP calculation operation used in step 303 of FIG. This operation is EC
This is performed by a routine executed at regular intervals by U10.

In the operation of FIG. 4, from the start of the engine start operation
Predetermined time (Even if the combustion is deteriorated, the engine will be completely exploded
Until a sufficient time has elapsed (step 40).
1) The engine speed NE is read each time the operation is executed (step
403), the engine speed NE at the time of the previous operation execution_i-1And N
Compare with E (step 405). Then, NE ≧ NE
_i-1That is, the engine speed is currently increasing.
If this is the case, measure the value of the peak rotation speed NEP at startup this time.
Operation (step 40)
Perform 7). As a result, the engine speed continues to rise
During this time, the peak engine speed NEP is calculated using the current engine speed.
It is updated, but when the engine speed starts decreasing, NEP
Since the value will not be updated, NEP will be
Then, the peak rotation speed at the time of starting is set.
This operation is performed until the complete explosion of the engine in step 401.
You. In FIG. 4, step 409 is a step N for preparing for the next operation execution.
E_i-1This is the operation of updating the value of.

In FIG. 3, in step 303, the peak rotational speed difference DNP is calculated using the value of the starting peak rotational speed NEP set as described above. After calculating the peak rotational speed difference DNP in step 303, next, in steps 305 to 313
Then, the upper limit value EQ _MAX of the intake feedback correction amount in the intake amount rotation speed control described later is set according to the calculated peak rotation speed DNP. In the present embodiment,
By changing the value of the intake feedback correction amount upper limit value EQ _MAX , the timing of switching from the intake air speed control to the ignition timing speed control is controlled.

Before describing steps 305 to 313, first, the intake air speed control and the ignition timing speed control in this embodiment will be described with reference to FIGS. FIG. 6 is a flowchart for explaining the intake amount rotation speed control operation. This operation is performed as a routine executed by the ECU 10 at regular intervals. In the operation of FIG. 6, first, at step 601, it is determined whether or not the value of the intake air amount rotation speed control flag CN is set to 1. If CN ≠ 1, control for rotating the intake air amount is currently permitted. Since there is no operation, the operation immediately ends without executing steps 603 and subsequent steps.

If the value of the flag CN is 1 at step 601, the routine proceeds to step 603, where the current engine speed NE is read, and at step 605, the predetermined idle target engine speed NE ₀ and the current engine speed NE ₀ are set. Difference DN from number NE
E is calculated as DNE = NE ₀ −NE. And
In steps 607 and 609, PI control (proportional integral control) of the engine intake air amount is performed based on the calculated value of the deviation DNE. That is, in step 607, the deviation D
The integral term IDNE of NE is calculated, and in step 609, the feedback correction amount EQ of the engine intake air amount is calculated by using the integral term IDNE and the proportional term DNE, and EQ = α × DNE.
It is calculated as + β × IDNE. And step 6
In 11, the calculated feedback correction amount EQ is determined whether the host vehicle has reached the upper limit EQ _MAX described above, EQ _MAX
Is not reached, a value obtained by adding the feedback correction amount EQ to the current engine intake air amount target value QT in step 613 is set as a new intake air amount target value, and in step 615, the target value QT The actuator 16a is driven to adjust the opening of the throttle valve 16 so as to obtain the intake air amount. As a result, the engine speed NE
Is lower than the idle target rotational speed NE ₀ , the engine intake air amount QT is increased each time the operation is performed, and if NE is higher than the target rotational speed NE ₀ , the intake air amount QT is reduced each time the operation is performed. , The engine speed becomes equal to the target value NE ₀ .

In the intake air speed control, for example, when heavy fuel is used, the engine speed becomes lower than the target speed due to deterioration of combustion, so that the value of the feedback correction amount EQ increases. . Therefore, if the engine speed cannot be increased to the target speed by the intake air speed control, the value of the feedback correction amount EQ continues to increase. In step 611, the intake quantity speed control if the value of EQ has reached the upper limit EQ _MAX increases the rotational speed ignition timing to cancel the decision to intake air quantity engine speed control and can not control the engine speed Control is started. That is, when the value of the feedback correction amount EQ has reached the upper limit value EQ _MAX in step 611, the intake air speed control execution flag C is set in step 617.
The value of N is set to 0 (stop execution), and the value of the ignition timing rotation speed control execution flag IN is set to 1 (execution). As a result, the operation of FIG. 6 ends immediately after the execution of step 601 from the next time, and the intake air speed control is not executed. Further, since the value of the ignition timing rotation speed control execution flag IN is set to 1, the ignition timing rotation speed control operation (FIG. 7) is executed instead of the intake air rotation speed control operation of FIG.

FIG. 7 is a flowchart for explaining the ignition timing rotation speed control operation of this embodiment. This operation is performed by the ECU
The routine is executed by a routine executed every time the engine crankshaft rotates at a predetermined angle. In the operation of FIG.
In step 1, it is determined whether the value of the ignition timing rotation speed control execution flag IN is set to 1 or not. Only when IN = 1, the ignition timing rotation speed control in step 703 and subsequent steps is executed.
In the ignition timing speed control of the present embodiment, the difference DNE (= N) between the idle target speed NE ₀ and the current engine speed NE.
E ₀ −NE) (steps 703 and 704), and D
NE> 0 if (when the engine speed NE is lower than the target rotational speed NE ₀₎ To agencies that current ignition timing AOP (expressed before top dead center crank angle) is advanced by a predetermined amount ΔA ignition Set as time AOP (steps 707, 70
9). As a result, the engine speed increases and approaches the target speed. If DNE <0, that is, if the actual rotational speed NE is higher than the target rotational speed NE _{0, the} current ignition timing AOP is retarded by a fixed amount ΔA (steps 711 and 713). As a result, the engine speed decreases and approaches the target engine speed NE ₀ . Then, the ignition timing AOP set as described above is set in the ignition circuit (step 715), and the operation ends. By the operation in FIG. 7, the engine speed is maintained at the target speed NE ₀ .

As described above, in the present embodiment, the intake air amount feedback correction amount EQ is controlled during the intake amount rotation speed control.
When the value reaches the upper limit value EQ _MAX , switching from the intake air speed control to the ignition timing speed control is performed. Therefore, as the upper limit value EQ _MAX of the feedback correction amount EQ is set to a smaller value, the switching from the intake amount rotation speed control to the ignition timing rotation speed control is performed earlier.

As described above, in the starting speed control (FIG. 3) of the present embodiment, the value of the feedback correction upper limit EQ _MAX of the intake air amount is changed according to the value of the peak speed difference DNP. Thus, the switching from the intake air speed control to the ignition timing speed control is controlled in accordance with the degree of deterioration of the combustion state (volatility of heavy fuel). Hereinafter, FIG.
And the feedback correction amount EQ _MAX of the intake air amount with reference to FIG.
The setting will be described.

In the operation shown in FIG. 3, after calculating the peak rotational speed difference DNP in step 303, it is first determined in step 305 whether or not DNP is a negative value. DNP is the case is negative, the combustion state of the starting peak rotational speed NEP is reference peak rotational speed NE ₀ greater than for the engine is considered to not worsening. Therefore, when the value of DNP is negative, the feedback correction amount upper limit value EQ _MAX is set to a relatively large value (positive constant value) EQ _MAX0 in step 307. If DNP <0 in step 303, the starting peak rotational speed NEP is smaller than the reference peak rotational speed NEP ₀ , and the combustion has deteriorated. judge.

As described above, the starting peak rotational speed NEP
Is considered to decrease in accordance with the degree of combustion deterioration at the start. Therefore, in step 309, the value of EQ _MAX is determined based on how much the actual start-time peak rotational speed NEP is lower than the reference peak rotational speed NEP ₀ , that is, how large the peak rotational speed difference DNP is. Set.

[0048] That is, the value of the peak rotational speed difference at step 309 DNP is determined whether a positive value DNP ₁ below a predetermined, if DNP is larger than DNP _1, i.e. reduction in the peak rotational speed NEP is If the degree of combustion deterioration is considerably large, it is difficult to recover from the combustion deterioration even if the intake air speed control is continued.
Proceeding to 13, the value of the feedback correction amount EQ _MAX is set to 0.

As a result, the operation shown in FIG.
In the work, EQ> EQ immediately in step 611_MAXIs established
In step 617, the intake air speed control is stopped.
At the same time, the ignition timing speed control operation of FIG. 7 is started.
Become so. On the other hand, in step 309, DNP ≦ DNP₁
In the case of
Immediately switch from intake air speed control to ignition timing speed control
Even without replacement, the combustion will not worsen as it is.
If this is the case, it is possible to control the rotation speed while controlling the intake air speed.
May be possible. Therefore, in this case, step 3
11 and EQ according to the value of DNP_MAXSet the value of
The intake air speed control as much as possible.
You. In this case, if the current degree of combustion deterioration is large
(When the value of the peak rotational speed difference DNP is large)
If the combustion deteriorates even a little, intake air speed control
Then, there is a possibility that the rotation speed cannot be controlled. On the other hand,
When the degree of deterioration of baking is relatively small (peak rotation speed difference D
(When the value of NP is small)
Even so, still controlling the rotation speed with intake air speed control
Could be possible. Therefore, in this embodiment, the peak
If the value of the rotational speed difference DNP is 0 ≦ DNP ≦ DNP₁In the area of
Is, the greater the value of DNP, the greater the EQ_MAXSet the value of
I am trying to do it. That is, combustion is worse than the current situation
Then, the value of the feedback correction amount becomes the value of Step 609 in FIG.
Is increased by Therefore, EQ _MAXSet the value of
As a result, even if combustion deteriorates slightly,
Switching to fire timing speed control is now performed.
You.

FIG. 5 shows steps 305 to 313 in FIG.
Feedback correction amount upper limit value EQ _MAX set by
FIG. 4 is a diagram showing a relationship between the value of the peak rotation speed difference DNP and the value of the peak rotation speed difference DNP. As shown in FIG. 5, the value of EQ _MAX is a relatively large constant value EQ _{MAX0 in} a region where DNP <0 (FIG. 5, region I).
(Steps 305 and 307 in FIG. 3). Also,
In the present embodiment, 0 ≦ DNP ≦ DNP ₁ region (Fig. 5,
In region II), the value of EQ _{MA X} is set so as to decrease linearly from 0 to EQ _MAX0, DNP> DNP ₁ region (Fig. 5, is secured to the region III) in 0. Since the value of DNP ₁ differs for each engine type, it is preferable to actually determine it by experiment or the like.

As described above, in the present embodiment, the feedback correction amount EQ is set according to the value of the peak rotational speed difference DNP.
By setting the value of _MAX , it is possible to continue the intake air speed control as much as possible to prevent deterioration of the engine exhaust characteristics at the time of starting. Also, as described above, EQ _MAX
Is set to a smaller value as the deterioration of combustion is larger (the larger the value of DNP), the earlier the degree of deterioration of combustion is, the earlier the switching from the intake air speed control to the ignition timing speed control is performed. You will be For this reason, in this embodiment, even when combustion deteriorates, it becomes possible to converge the starting rotation speed to the target rotation speed in a short time. (2) Second Embodiment Next, a second embodiment of the present invention will be described.

In the first embodiment, the peak engine speed at the time of starting the engine is used as a parameter indicating the degree of combustion deterioration, and the intake air speed control and the ignition timing speed control are performed in accordance with the degree of combustion deterioration. Switching to was controlled. However, although the start-time peak rotation speed almost exactly indicates the degree of deterioration of combustion, even when deterioration of combustion occurs, the start-time peak rotation speed may increase.

For example, when a small amount of fuel leaks from the fuel injection valve while the engine is stopped, a larger amount of fuel than usual is supplied to the cylinder when the engine is started. In such a case, even when heavy fuel is used and the combustion state is deteriorated, the generated torque in the cylinder becomes large, so that the peak rotation speed at the start is higher than the reference peak rotation speed. There is. In such a case, even if the peak rotation speed at startup is high, if the fuel that has leaked during stoppage has burned out, the engine rotation speed will decrease as in the case where there was no leak. Moreover, in this case, it is determined that the peak rotation speed at the start is high and the combustion is not deteriorated. Therefore, for example, in the first embodiment, the feedback correction amount EQ _MAX is set to a large value EQ _MAX0 . Therefore, the timing of switching from the intake air speed control to the ignition timing speed control is delayed, and the combustion may be further deteriorated.

Therefore, in this embodiment, in parallel with the switching of the rotation speed control based on the starting peak rotation speed described in the first embodiment, the determination of the deterioration of combustion and the switching of the rotation speed control are performed by another method. ing. FIG. 8 is a flowchart illustrating a rotation speed control switching operation according to the present embodiment.
This operation is performed by a routine executed by the ECU 10 at regular intervals.

Also in the present embodiment, apart from the operation of FIG.
An operation of switching between the intake air speed control and the ignition timing speed control (for example, the switching control described in the first embodiment or another similar control) is performed. As described above, if heavy fuel is used and fuel leaks from the fuel injection valve while the fuel is stopped, the peak rotation speed at startup increases, so combustion is performed based on the peak rotation speed at startup. Is determined, it is determined that combustion has not deteriorated. However, when the combustion is deteriorated, the engine speed becomes much lower after reaching the peak engine speed than when the combustion is not deteriorated.
In the operation shown in FIG. 8, when the engine speed decreases after reaching the start-time peak rotation speed and becomes lower than the first predetermined value, regardless of the determination of combustion deterioration based on the start-time peak rotation speed, the ignition timing The rotation speed control is started. If it is not possible to determine the deterioration of the combustion at the start-time peak rotation speed, the switching to the ignition timing rotation speed control is delayed, and the deterioration of the combustion state may be large. In such a case, the convergence of the engine speed to the target speed is delayed only by performing the ignition timing speed control, and the deterioration of the engine exhaust properties may be continued for a long time. Therefore, in the operation of FIG. 8, when the deterioration of combustion is large, that is, when the engine speed is greatly reduced and becomes lower than the second predetermined value smaller than the first predetermined value, the ignition timing speed control is performed. And the amount of fuel injected into the engine is further increased to increase the rotational speed.

The operation of FIG. 8 will be described below.
In step 801, it is determined whether or not the engine is in a state after the complete explosion. This determination can be made, for example, by determining that the engine has completely exploded when a predetermined time has elapsed after the start of engine cranking, as in step 401 of FIG. If the engine has not reached the complete explosion in step 801, this operation ends immediately without executing step 803 and the subsequent steps.
The following operations are performed.

[0057] That is, in step 803, the engine speed NE is read, whether the engine rotational speed NE read in step 805 is in the first lower than the predetermined rotational speed NE ₁ is determined. NE is higher than NE ₁ is institution because it is operated without greatly reduced rotation after starting peak rotational speed reaches, it is not necessary to perform switching to the ignition timing speed control. Therefore, also in this case, this operation ends immediately. As a result, when the intake air speed control is being performed, the intake air speed control is continued.

[0058] engine speed NE in step 805 if that was lower than the first predetermined rotational speed NE _1, it is necessary to immediately ignition timing speed control for the combustion of the engine is deteriorated. Therefore, in this case, the process proceeds to step 807, in which the value of the intake air speed control execution flag CN is set to 0 (execution stopped), and the ignition timing speed control execution flag IN
Is set to 1 (execute), and the operation is terminated. As a result, the intake air speed control is stopped as described with reference to FIGS. 6 and 7, and instead, the ignition timing speed control is executed.

After execution of step 807, step 80
9, the engine speed NE whether or not reduced to below a predetermined value NE ₂ lower second than the first predetermined value NE ₁ described above is determined. NE is if not reduced to a second predetermined value NE _2, the rotational speed decreases due to worsening of combustion to be determined to be sufficiently recoverable by rotation speed control ignition timing, the operation is terminated immediately . On the other hand, when NE is lower than the second predetermined value NE ₂ , the engine speed is greatly reduced due to deterioration of combustion, and it is difficult to control the engine speed to the target engine speed only by controlling the ignition timing. Because it is difficult, the process proceeds to step 811 and the fuel increase flag FI
Is set to 1 and the operation is terminated.

When the value of the fuel increase flag FI is set to 1, the ECU 10 increases and corrects the fuel injection amount by a predetermined amount to increase the torque generated in each cylinder. As a result, even when the deterioration of combustion is large, the engine speed increases quickly, and the engine engine speed matches the target engine speed. Note that the initial value of the fuel increase flag FI is set to 0.

As described above, according to the present embodiment, even when it is not possible to determine the deterioration of combustion from the peak rotation speed at the time of starting, the deterioration of combustion is determined without fail, and the target engine speed is set in a short time. It is possible to match the rotation speed. In the present embodiment, the case where the method of the first embodiment is used as the rotation speed control switching operation based on the starting peak rotation speed which is separately performed is described. Needless to say, the present invention can also be applied to other rotation speed control based on the starting peak rotation speed.

In each of the above embodiments, the case of using an electronic throttle valve which can be operated independently of the driver's operation of the accelerator pedal at the time of controlling the intake air speed is described as an example. The present invention is also applicable to a device that controls the intake air amount rotation speed by using other means. For example, a bypass intake passage that bypasses the engine throttle valve is provided,
The present invention is also applied to an engine having a so-called idle speed control device (ISC device) that controls the intake air amount rotation speed by controlling a control valve (ISC valve) provided on the bypass intake passage independently of a throttle valve. It goes without saying that can be applied.

[0063]

According to the invention described in each of the claims, it is possible to effectively suppress a decrease in the engine speed due to deterioration of combustion at the time of starting the engine, and to accurately maintain the engine engine speed at the target engine speed. In addition, even when combustion deteriorates, a common effect is obtained in which deterioration of exhaust properties at the time of engine start can be minimized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment when a control device of the present invention is applied to an internal combustion engine for a vehicle.

FIG. 2 is a diagram illustrating a general rotation speed change at the time of engine start.

FIG. 3 is a flowchart illustrating a start-time rotational speed control operation according to the first embodiment of the present invention.

FIG. 4 is a flowchart illustrating a start-time peak rotational speed detection operation in the embodiment of FIG. 3;

FIG. 5 is a graph showing setting of variables used in the flowchart of FIG. 3;

FIG. 6 is a flowchart illustrating an intake air speed control operation.

FIG. 7 is a flowchart illustrating ignition timing rotation speed control.

FIG. 8 is a flowchart illustrating a rotation speed control switching operation according to a second embodiment of the present invention.

[Explanation of symbols]

1. Internal combustion engine body 5, 6… Crank angle sensor 10. Electronic control unit (ECU) 16 Electronically controlled throttle valve 110 ... Ignition circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-224707 (JP, A) JP-A-6-101609 (JP, A) JP-A-62-2139 (JP, A) JP-A-9-209 303189 (JP, A) JP-A-11-13611 (JP, A) JP-A-3-81544 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 41/06 310 F02D 43/00 301 F02D 45/00 362 F02P 5/15 F02D 45/00 368

Claims (4)

(57) [Claims] When the engine is started, the engine speed is controlled to a target speed by an intake air speed control that adjusts an engine intake air amount according to the engine speed, and based on a peak speed immediately after the engine is started. Judging the presence or absence of engine combustion deterioration, when the combustion is deteriorated, from the intake air speed control to the ignition timing speed control for controlling the engine speed to the target speed by adjusting the engine ignition timing according to the engine speed. In a control device for an internal combustion engine that switches to control the engine speed at engine start to a target engine speed, a peak speed difference that is a difference between a predetermined reference peak engine speed and an actual peak engine speed at engine start is calculated. A control device for an internal combustion engine, comprising switching means for controlling switching from the intake air speed control to the ignition timing speed control based on the peak speed difference. 2. The switching means continues the intake air speed control when the peak speed difference is a negative value, wherein the peak speed difference is a positive value, and When the actual intake air amount of the engine becomes larger than the reference air amount, the intake air amount rotational speed is set when the reference air amount is set in accordance with the peak rotational speed difference. Switching from control to the ignition timing speed control, and immediately switching from the intake air speed control to the ignition timing speed control when the peak speed difference is greater than the upper limit value. Item 2. The control device for an internal combustion engine according to Item 1. 3. When the engine is started, the engine speed is controlled to a target speed by an intake air speed control for adjusting an engine intake air amount according to the engine speed, and based on a peak speed immediately after the engine is started. Judging the presence or absence of engine combustion deterioration, when the combustion is deteriorated, from the intake air speed control to the ignition timing speed control for controlling the engine speed to the target speed by adjusting the engine ignition timing according to the engine speed. In a control device for an internal combustion engine, which switches to control the engine speed at the time of engine start to a target engine speed, when the engine speed at engine start falls below a predetermined first predetermined engine speed after reaching the peak engine speed, Is a control device for an internal combustion engine, comprising: switching means for switching from the intake air speed control to the ignition timing speed control regardless of the value of the peak speed. 4. The switching means further supplies to the engine when the rotation speed at the time of starting the engine further falls below a second predetermined rotation speed which is smaller than the first predetermined rotation speed after reaching the peak rotation speed. The control device for an internal combustion engine according to claim 3, wherein the amount of fuel to be increased is increased.