JPH10103206A - Ignition timing control device for lean-burn engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the capacity of a memory used by a map for correcting the ignition timing in lean-burn, as well as to obtain an optimum ignition timing corresponding to the degree of lean. SOLUTION: A basic angle of lead value ADV BASE which determines a basic ignition timing corresponding to a normal air/fuel ratio on the basis of the number of revolutions of an engine NE and a basic fuel injection pulse width TP representing the engine load is set (S11), a real air/fuel ratio λa is detected on the basis of the output value a linear O2 sensor (S13), an ignition timing correction factor KADV which increases the angle of lead correction relative to said basic angle of lead value as the degree of lean of the air/fuel ratio becomes high is set by a table retrieval based upon the real air/fuel ratio λa (S15), and is set a control angle of lead ADV which determines the ignition timing by correcting the basic angle of lead value ADV BASE with the ignition timing correction factor KADV (S16). It is thereby possible to obtain an optimum ignition timing which is suitable for the lean burn and corresponds to the degree of lean, as well as to reduce substantially the usable capacity of a memory (ROM 42) since said ignition timing correction factor table is constituted as a unidimensional table with a single parameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ignition timing control device for a lean burn engine which sets an appropriate ignition timing according to an air-fuel ratio.

[0002]

2. Description of the Related Art Conventionally, when the engine operating state is low load operation or the like, the air-fuel ratio is made lean (lean air-fuel ratio) to improve fuel efficiency and exhaust emission. Lean-burn engines that ensure engine output with a stoichiometric fuel ratio (stoichiometric air-fuel ratio) are employed.

[0003] In this lean burn engine,
Since the combustion characteristics are changed according to the air-fuel ratio, it is necessary to set the ignition timing accordingly. That is, during stoichiometric operation, uniform mixed combustion is performed, and when the air-fuel mixture flowing into the combustion chamber of the engine is diffused and homogeneously mixed, ignition occurs, whereas in lean-burn operation, in which stratified combustion is performed, combustion is performed. It is necessary to ignite before the air-fuel mixture flowing into the chamber is diffused, and therefore, the ignition timing must be advanced with respect to the stoichiometric operation.

For this reason, conventionally, two ignition timing maps each having the engine speed and the engine load as parameters corresponding to the stoichiometric operation and the lean burn operation are provided, and the lean corresponding ignition is performed during the lean burn control. The ignition timing is set by the timing map, and the ignition timing is set by the ignition timing map corresponding to the stoichiometric air-fuel ratio during the stoichiometric control.

In Japanese Patent Application Laid-Open No. 6-173732, a lean region and a stoichiometric region of the air-fuel mixture are determined based on the operating state of the engine. When the engine is in the region, the air-fuel ratio is controlled to stoichiometric, and a map for searching for an ignition timing basic value corresponding to the stoichiometric operation using the engine speed and the accelerator opening corresponding to the engine load as parameters is used. And a map for retrieving an ignition timing correction value for advancing the ignition timing during lean burn operation using the accelerator opening as a parameter, and a map for retrieving the ignition timing basic value during stoichiometric control. The basic ignition timing is set as the final ignition timing, and during lean burn control,
By correcting the basic value of the ignition timing by the ignition timing correction value retrieved from the ignition timing correction value search map and setting the final ignition timing, the ignition timing conforming to the stoichiometric operation and the lean burn operation can be set. The techniques obtained are disclosed.

[0006]

However, as described above, two ignition timing maps based on a plurality of parameters of the engine speed and the engine load are provided for the stoichiometric operation and the lean burn operation, respectively. In such a case, the memory (ROM) of the control device based on these maps
However, there is a disadvantage that the used capacity increases. For example, when the number of divisions by each parameter is 16, one map requires an area of 16 × 16 = 256, and if two maps are provided, an area of 256 × 2 = 512 is required. The data usage area of the memory for storing the map is significantly increased. To cope with this, if the number of divisions by each parameter is reduced, the control in accordance with the engine operating state becomes rough due to the decrease in the number of divisions, and the ignition timing control accuracy deteriorates.

[0007] Further, during the lean burn operation, the ignition timing is uniquely set by a single map regardless of the degree of lean, so that the optimal ignition timing according to the degree of lean cannot be obtained. In other words, when the air-fuel ratio is lean and close to stoichio, if the ignition timing is advanced too much for stratified combustion, ignition becomes impossible due to the rich mixture before diffusion, and after the mixture has diffused to some extent Otherwise, it cannot ignite. Therefore, it is necessary to advance the ignition timing as the air-fuel ratio increases from stoichiometric to lean. Furthermore, the combustion characteristics when switching between stratified combustion during lean burn operation and uniform mixed combustion during stoichiometric operation vary between these two combustion states, and it is not possible to obtain an optimum ignition timing corresponding to this. There is also.

Further, the above prior art (Japanese Patent Laid-Open No. 6-17373)
No. 2), an ignition timing correction value search map for storing an ignition timing correction value for correcting an ignition timing basic value at the time of lean burn is also provided in the same manner as the ignition timing basic value search map. Since the map is constituted by a plurality of parameters of the accelerator opening, there is a disadvantage that the use of the memory of the control device by these maps is increased, and when the air-fuel ratio is lean, irrespective of the lean degree, Since the ignition timing correction value is uniquely set by one ignition timing correction value search map, it is not possible to obtain the optimum ignition timing according to the degree of leanness.

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention can reduce the amount of memory used by a map for correcting the ignition timing at the time of lean burn, and obtain an optimum ignition timing according to the degree of lean. It is an object of the present invention to provide a lean-burn engine ignition timing control device capable of performing the above-described steps.

[0010]

To achieve the above object, according to the first aspect of the present invention, when the engine operating state is in a predetermined range, a lean burn operation based on a lean air-fuel ratio is performed, and the engine operating state is set in a predetermined area. When it is outside, the ignition timing control device for a lean burn engine that operates at a predetermined air-fuel ratio, based on the engine speed and the engine load, as shown in the basic configuration diagram of FIG. Basic ignition timing setting means for setting a basic ignition timing corresponding to, ignition timing correction coefficient setting means for setting an ignition timing correction coefficient for correcting the basic ignition timing based on the air-fuel ratio, and Ignition timing setting means for setting the ignition timing by correcting the ignition timing with the ignition timing correction coefficient.

According to a second aspect of the present invention, a lean burn operation with a lean air-fuel ratio is performed when the engine operation state is in a predetermined range, and a lean burn operation with a predetermined air-fuel ratio is performed when the engine operation state is outside the predetermined range. In the ignition timing control device for a burn engine, as shown in a basic configuration diagram of FIG. 1B, a basic ignition timing setting for setting a basic ignition timing corresponding to the predetermined air-fuel ratio based on an engine speed and an engine load. Means for judging whether or not the vehicle is in a lean burn operation state based on the air-fuel ratio; and setting an ignition timing correction coefficient for correcting the basic ignition timing based on the current air-fuel ratio in the lean burn operation state. And an ignition timing correction coefficient setting means for correcting the basic ignition timing with the ignition timing correction coefficient when in the lean burn operation state. Set, when not in the lean burn operation state, characterized in that the basic ignition timing and a spark timing setting means for setting the ignition timing without correcting in the ignition timing correction factor.

According to a third aspect of the present invention, in the first or second aspect, the ignition timing correction coefficient setting means sets the ignition timing correction coefficient by searching a table using the air-fuel ratio as a parameter. The table stores an ignition timing correction coefficient that increases the advance correction with respect to the basic ignition timing as the degree of leanness of the air-fuel ratio increases.

That is, according to the first aspect of the present invention, the basic ignition timing corresponding to the normal air-fuel ratio is set based on the engine speed and the engine load, and the ignition timing correction coefficient is set based on the air-fuel ratio. The basic ignition timing is corrected according to the air-fuel ratio using the ignition timing correction coefficient to set the ignition timing. Since the ignition timing correction coefficient for correcting the basic ignition timing is set by one parameter, the used capacity of the memory can be reduced, and the basic ignition timing can be reduced by the ignition timing correction coefficient set according to the air-fuel ratio. Since the ignition timing is set by correcting the timing, it is possible to obtain the optimum ignition timing suitable for the air-fuel ratio at that time.

According to the second aspect of the present invention, the basic ignition timing corresponding to the normal air-fuel ratio is set based on the engine speed and the engine load, and it is determined whether or not the vehicle is in the lean burn operation. At this time, the ignition timing correction coefficient is set based on the current air-fuel ratio, the basic ignition timing is corrected according to the lean air-fuel ratio by the ignition timing correction coefficient, and the ignition timing is set.When not in the lean burn operation, The ignition timing is set without correcting the basic ignition timing with the ignition timing correction coefficient. Since the ignition timing correction coefficient corresponding to the air-fuel ratio is set only during the lean burn operation, the ignition timing correction coefficient only needs to correspond to the lean air-fuel ratio, and the used capacity of the memory can be further reduced.

In this case, according to the third aspect of the present invention, an ignition timing correction coefficient for increasing the advance correction with respect to the basic ignition timing is set by a table search based on the air-fuel ratio as the degree of leanness of the air-fuel ratio increases. .

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

First, a schematic configuration of the engine will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes a horizontally opposed four-cylinder lean burn engine. When the engine is operating in a lean region such as a low load operation, the air-fuel ratio is controlled to lean (lean air-fuel ratio) and lean burn (lean burn) is performed by stratified combustion. When the engine is operating in a stoichiometric region such as a high-load operation, the air-fuel ratio is controlled to stoichiometric (the stoichiometric air-fuel ratio) or the like, and normal mixed uniform combustion is performed.

During high load operation, the air-fuel ratio may become rich due to an increase in fuel due to an increase in acceleration during acceleration or the like, and the stoichiometric (stoichiometric air-fuel ratio) is not always achieved.

A cylinder head 2 is provided in each of the left and right banks of a cylinder block 1a of the engine 1, and an intake port 2a and an exhaust port 2b are formed in each cylinder head 2.

In the intake system of the engine 1, an intake manifold 3 communicates with each intake port 2a, and a throttle chamber 5 communicates with the intake manifold 3 via an air chamber 4 in which intake passages of respective cylinders gather. An air cleaner 7 is attached to the upstream side of the throttle chamber 5 via an intake pipe 6, and the air cleaner 7 is connected to the air intake chamber 8.

The throttle chamber 5 is provided with a throttle valve 5a linked to an accelerator pedal. The intake pipe 6 is connected to a bypass passage 9 that bypasses the throttle valve 5a.
At the time of idling, the bypass passage 9 depends on the valve opening.
An idle speed control valve (ISC valve) 10 for controlling the idle speed by adjusting the amount of bypass air flowing through the engine is provided.

On the other hand, a partition wall 3a is formed for each cylinder so as to partition the intake passage into a main air passage 11a and a sub intake passage 11b from the middle of the intake manifold 3 to the intake port 2a (see FIG. 11). ). Further, an injector 12 is disposed immediately upstream of the intake port 2a of each cylinder of the intake manifold 3 so as to be directed in the direction of the intake air flow from the auxiliary intake passage 11b.

A tumble control valve (hereinafter abbreviated as "TCV") 14 is provided immediately upstream of each main air passage 11a as an intake control valve which is operated by a diaphragm actuator 13 to open and close the main air passage 11a. Have been. The working chamber in which the spring of each of the diaphragm actuators 13 is housed is connected to a TCV control solenoid valve 16 through a control pressure passage 15. This TCV control switching solenoid valve 16
Selectively causes an atmosphere port communicating with the atmosphere and a negative pressure port communicating with the surge tank 17 to act on the working chamber of the diaphragm actuator 13. The above surge tank 1
Reference numeral 7 communicates with the intake manifold 3 via a check valve 18 to store a negative pressure generated downstream of the throttle valve 5a.

That is, the electronic control unit 40 (see FIG. 14) which will be described later determines whether the engine operation state is a lean region such as a low load operation or a normal region such as a high load operation. The fuel injection amount is reduced and the air-fuel ratio is controlled to be lean.
The CV switching solenoid valve 16 is turned off to communicate the atmospheric pressure port with the control pressure passage 15, and the atmospheric pressure is led to the working chamber of the diaphragm actuator 13, whereby the biasing force of the spring provided in the working chamber of the diaphragm actuator 13 is applied. As shown by the solid line in FIG.
Close.

As shown in FIG. 11, the intake port 2a
Is formed in a straight port shape.
When the main air passage 11a is closed by closing the valve 14, when the intake valve 19 is opened, the air-fuel mixture flowing into the combustion chamber 20 is caused to flow into the air-fuel mixture flowing into the combustion chamber 20 by an arrow in FIG. As shown, a vertical eddy current, a so-called tumble flow, is generated. This tumble flow enables stratified combustion, and lean burn is performed.

When the engine operating state is in a stoichiometric range such as a high load operation, the air-fuel ratio is controlled to stoichiometric by the electronic control unit 40, and the TCV switching solenoid valve 16 is turned ON to connect the negative pressure port to the control pressure. By communicating with the passage 15 and introducing a negative pressure into the working chamber of the diaphragm actuator 13, as shown by a one-dot chain line in FIG.
Open V14. At this time, by opening the valve of the TCV 14, intake air flows from both the main air passage 11a and the sub intake passage 11b, the intake resistance is reduced, and ordinary uniform mixed combustion is performed.

On the other hand, an ignition plug 21 for exposing a discharge electrode at the tip end to the combustion chamber 20 is attached to each cylinder of the cylinder head 2, and an ignition coil provided for each cylinder is mounted on the ignition plug 21. Igniter 2 through 22
3 are connected.

In the exhaust system of the engine 1, an exhaust pipe 25 is communicated with a collection portion of an exhaust manifold 24 communicating with each exhaust port 2b of the cylinder head 2, and a catalytic converter 26 is interposed in the exhaust pipe 25. And is communicated with the muffler 27.

Next, sensors for detecting the operating state of the engine will be described. Immediately downstream of the air cleaner 7 of the intake pipe 6, a thermal intake air amount sensor 28 using a hot wire or a hot film is interposed, and a throttle valve 5 a provided in the throttle chamber 5 has a throttle valve 5 a. A throttle sensor 29 having a built-in opening sensor 29a and an idle switch 29b that is turned on when the throttle valve 5a is fully closed is provided in series.

The cylinder block 1a of the engine 1
A knock sensor 30 is attached to the cooling water passage 3 communicating the left and right banks of the cylinder block 1a.
1, a cooling water temperature sensor 32 is provided, and a linear O / F for detecting an air-fuel ratio is provided upstream of the catalytic converter 26.
Two sensors 33 are provided. This linear O2 sensor 3
3 has a linear output voltage characteristic corresponding to the actual air-fuel ratio λa, as shown in FIG. 7, and the leaner the air-fuel ratio λa, the higher the output voltage Vλ. When the actual air-fuel ratio λa is the stoichiometric air-fuel ratio λa = 14.7, a voltage of 3 V is output. In FIG. 7, the numerical value in parentheses is the excess air ratio.

The crankshaft 34 of the engine 1
A crank angle sensor 36 is provided on the outer periphery of a crank rotor 35 axially mounted on the cam shaft 37. Further, a cam angle 38 for cylinder identification is provided on a cam rotor 38 connected to a cam shaft 37 that makes a half turn with respect to the crank shaft 34 A sensor 39 is provided opposite.

As shown in FIG. 12, the crank rotor 35 has projections 35a, 35b and 35c formed on the outer periphery thereof, and these projections 35a, 35b and 35c are connected to the cylinders (# 1, # 2 and # 2). 3, # 4) before compression top dead center (BTD
C) It is formed at the positions of θ1, θ2, and θ3. In the present embodiment, θ1 = 97 ° CA, θ2 = 65 ° CA, θ3 =
10 ° CA.

As shown in FIG. 13, on the outer periphery of the cam rotor 38, projections 38a, 38b,
A projection 38a is formed at a position θ4 after the compression top dead center (ATDC) of the # 3 and # 4 cylinders.
b is composed of three protrusions, and the first protrusion is A of the # 1 cylinder.
It is formed at the position of TDCθ5. Further, the protrusion 38c
Is composed of two projections, and the first projection is the AT of the # 2 cylinder.
It is formed at the position of DCθ6. In this embodiment,
θ4 = 20 ° CA, θ5 = 5 ° CA, θ6 = 20 ° CA.

As shown in the time chart of FIG. 9, the crankshaft 34 and the camshaft 37 rotate with the operation of the engine, and each protrusion of the crank rotor 35 is detected by the crank angle sensor 36. 36 to θ1, θ2, θ3 (BTDC97
°, 65 °, 10 °) of the engine 1
/ 2 rotations (180 ° CA), while θ3
Each protrusion of the cam rotor 38 is detected by the cam angle sensor 39 between the crank pulse and the θ1 crank pulse, and the cam angle sensor 39 outputs a predetermined number of cam pulses.

As will be described later, the electronic control unit 40 calculates the engine speed NE based on the input interval time of the crank pulse output from the crank angle sensor 36, and calculates the engine stroke NE in the order of the combustion stroke of each cylinder (for example, , # 1 cylinder → #
3 cylinders # 2 cylinders # 4 cylinders) and the cam angle sensor 3
Based on the pattern of the cam pulse from No. 9 and the value counted by the counter, cylinder discrimination of the fuel injection target cylinder and the ignition target cylinder is performed.

The injector 12, the spark plug 21,
TCV for switching operation of ISC valve 10 and TCV 14
The calculation of the control amounts for the actuators such as the switching solenoid valve 16 and the output of the control signals, that is, engine control such as fuel injection control, ignition timing control, idle speed control, intake control, etc. ECU)
40.

The ECU 40 includes a CPU 41, a ROM 4
2, RAM 43, backup RAM 44, counter
A timer group 45 and an I / O interface 46 are mainly configured by a microcomputer connected to each other via a bus line, and are connected to the constant voltage circuit 47 for supplying a stabilized power to each unit, and to the I / O interface 46. And a peripheral circuit such as an A / D converter 49.

The counter / timer group 45 includes various counters such as a free-run counter, a counter for counting the input of a cam angle sensor signal (cam pulse), a fuel injection timer, an ignition timer, and a timer for generating a periodic interrupt. Various timers such as a periodic interrupt timer, a timer for measuring the input interval of a crank angle sensor signal (crank pulse), and a watchdog timer for monitoring a system abnormality are collectively referred to for convenience. Is sometimes used.

The constant voltage circuit 47 is connected to a battery 51 via a first relay contact of a power supply relay 50 having two circuit relay contacts, and a relay coil of the power supply relay 50 is connected to an ignition switch 52 by the battery 51.
Connected through. The constant voltage circuit 47
When the ignition switch 52 is turned on and the contact of the power supply relay 50 is closed, power is supplied to each unit in the ECU 40 while the ignition switch 52 is turned on and the ignition switch 52 is turned on and off. Instead, the backup power is always supplied to the backup RAM 44.

The input port of the I / O interface 46 includes an idle switch 29b and a knock sensor 3
0, a crank angle sensor 36, and a cam angle sensor 39 are connected. Further, via the A / D converter 49, an intake air amount sensor 28, a throttle opening sensor 29a, a cooling water temperature sensor 32, and a linear O2 While the sensor 33 is connected, the battery voltage VB is input and monitored.

On the other hand, the output port of the I / O interface 46 has an ISC valve 10, an injector 12, a T
The CV switching solenoid valve 16 is connected via the drive circuit 48, and the igniter 23 composed of four power transistors for driving the ignition coils 22 of the # 1, # 2, # 3 and # 4 cylinders is connected. Have been.

The power supply to the primary side of each ignition coil 22 is connected to a power supply line extending to supply power to each actuator from the battery 51 via the second relay contact of the power supply relay 50. Have been.

In accordance with the control program stored in the ROM 42, the CPU 41 processes the detection signals from the sensors and switches, which are input via the I / O interface 46, the battery voltage, and the like, and stores them in the RAM 43. Based on various data, various learning value data stored in the backup RAM 44, fixed data stored in the ROM 42, and the like, a fuel injection amount, an ignition timing, a duty ratio of a drive signal for the ISC valve 11, and the like are calculated. O of switching solenoid valve 16 for TCV
N and OFF are set, and engine control such as fuel injection control, ignition timing control, idle speed control, intake control and the like is performed.

In such an engine control system, EC
In U40, it is determined whether the engine operation state is a lean region such as a low load operation or a stoichiometric region such as a high load operation based on the engine operation state detected by each sensor. For improvement, the fuel injection amount is reduced and the air-fuel ratio is controlled to be lean, the TCV switching solenoid valve 16 is turned off, the TCV 14 is closed, the main air passage 11a is closed, and the sub intake passage 11b is closed. Of the combustion chamber 20
A tumble flow is generated in the inside (see FIG. 11), and lean burn is performed by stratified combustion. Further, when the engine operating state is in the stoichiometric range, the air-fuel ratio is controlled to stoichiometric to secure the engine output, and the TCV switching solenoid valve 16 is turned on to open the TCV 14 and the TCV
By opening the valve V14, the main air passage 11a and the sub intake passage 1
1b to supply intake air, reduce intake resistance,
Perform homogeneous mixed combustion.

Here, at the time of homogeneous mixture combustion in the stoichiometric region, ignition is performed when the air-fuel mixture flowing into the combustion chamber 20 is diffused to form a uniform mixture, whereas in the case of stratified combustion in the lean region, It is necessary to ignite the mixture immediately before the mixture flowing into the combustion chamber 20 is diffused, and it is necessary to advance the ignition timing with respect to the time of uniform mixture combustion. Also, when the air-fuel ratio is lean and close to stoichio, if the ignition timing is advanced too much for stratified combustion, ignition becomes impossible due to the rich mixture before diffusion, and after the mixture has diffused to some extent If not, ignition cannot be performed, and as the air-fuel ratio increases from stoichiometric to lean,
It is necessary to advance the ignition timing. Further, at the time of switching between stratified combustion and uniform mixed combustion, the flow characteristics of the air-fuel mixture in the combustion chamber 20 change between the tumble flow and the normal state, and it is necessary to set the ignition timing accordingly. is there.

For this reason, in the ignition timing control, the basic ignition timing corresponding to stoichiometry is set based on the engine speed and the engine load, and the actual ignition timing is controlled based on the output value of the linear O2 sensor 33 during the lean burn operation. The air-fuel ratio λa is detected, and a table search is performed on the basis of the actual air-fuel ratio λa to set an ignition timing correction coefficient that increases the advance correction with respect to the basic ignition timing as the lean degree of the air-fuel ratio increases. By setting the ignition timing by correcting the basic ignition timing with the correction coefficient, an optimum ignition timing suitable for lean burn due to the air-fuel ratio lean and according to the degree of lean air-fuel ratio is obtained. In the stoichiometric operation, the ignition timing is set without correcting the basic ignition timing with the ignition timing correction coefficient, so that the optimum ignition timing suitable for the stoichiometric operation is obtained.

That is, the functions of the basic ignition timing setting means, the determination means, the ignition timing correction coefficient setting means, and the ignition timing setting means according to the present invention are realized by the ECU 40.

Hereinafter, the ignition timing control processing according to the present invention by the ECU 40 will be described with reference to the flowcharts shown in FIGS.

First, the ignition switch 52 is turned on.
Then, when the power is supplied to the ECU 40, the system is initialized, and each flag and each counter are initialized except for data such as various learning values stored in the backup RAM 44. And the starter switch is O
N and the engine starts, the crank angle sensor 36
Each time the crank pulse is input from the
An engine speed calculation routine is executed.

In this cylinder discriminating / engine rotational speed calculating routine, when the crank rotor 35 rotates with the engine operation and the crank pulse from the crank angle sensor 36 is input, first, in step S1, the crank input at this time is inputted. Whether the pulse corresponds to the crank angle of θ1, θ2, or θ3 is determined based on the input pattern of the cam pulse from the cam angle sensor 39. In step S2, the cylinder to be ignited is determined from the input pattern of the crank pulse and the cam pulse. And the like.

That is, as shown in the time chart of FIG. 9, for example, if there is a cam pulse input between the previous crank pulse input and the present crank pulse input, the current crank pulse is θ1 crank pulse. It can be identified as a pulse, and the crank pulse input next time can be identified as a θ2 crank pulse.

If there is no cam pulse input between the previous and current crank pulse inputs and there is a cam pulse input between the last and previous crank pulse inputs, the current crank pulse can be identified as the θ2 crank pulse, and The input crank pulse can be identified as a θ3 crank pulse. Further, when there is no cam pulse input between the previous and current times and between the last and last crank pulse inputs, the currently input crank pulse can be identified as the θ3 crank pulse, and the next input crank pulse is It can be identified as a θ1 crank pulse.

Further, three cam pulses are input between the previous and current crank pulse inputs (θ corresponding to the projection 38b).
When 5 cam pulses are obtained, it can be determined that the next compression top dead center is the # 3 cylinder and the ignition target cylinder is the # 3 cylinder. When two cam pulses are input between the previous and current crank pulse inputs (θ6 cam pulse corresponding to the projection 38c), the next top dead center is # 4 cylinder,
The cylinder to be ignited can be determined to be a # 4 cylinder.

One cam pulse is input between the previous and current crank pulse inputs (θ4 corresponding to the projection 38a).
When the previous compression top dead center determination is # 4 cylinder, the next compression top dead center is # 1 cylinder and the ignition target cylinder can be determined as # 1 cylinder. Similarly, if one cam pulse is input between the previous and current crank pulse inputs and the previous compression top dead center determination was # 3 cylinder, the next compression top dead center is # 2 cylinder and the ignition target The cylinder can be determined to be a # 2 cylinder.

As the cylinder discrimination, in addition to the ignition target cylinder discrimination, the fuel injection target cylinder discrimination is also performed, but will not be described in detail here.

Thereafter, the process proceeds from step S2 to step S3, where the time from the previous crank pulse input to the present crank pulse measured by the crank pulse input interval timer, ie, the crank pulse input interval time (θ1 crank pulse and θ2 An input interval time Tθ12 of the crank pulse, an input interval time Tθ23 of the θ2 crank pulse and the θ3 crank pulse, or an input interval time Tθ31 of the θ3 crank pulse and the θ1 crank pulse are read, and the crank pulse input interval time Tθ is detected.

Next, the process proceeds to step S4, in which the angle between the crank pulses corresponding to the crank pulse identified this time is read out, and the current engine speed N is determined based on the angle between the crank pulses and the crank pulse input interval time Tθ.
E is calculated and stored at a predetermined address in the RAM 43, and the routine exits. The angle between the crank pulses is known and is stored in advance in the ROM 42 as fixed data. In the present embodiment, the angle between the θ1 crank pulse and the θ2 crank pulse is 32 ° CA,
The angle between the θ2 crank pulse and the θ3 crank pulse is 55
° CA, the angle between the θ3 crank pulse and the θ1 crank pulse is 93 ° CA.

The engine speed NE calculated by the above-described cylinder discrimination / engine speed calculation routine is read out in the ignition timing setting routine shown in FIG. 3 and is used for setting the ignition timing.

Next, the ignition timing setting routine of FIG. 3 will be described. This ignition timing setting routine is started at predetermined intervals after the system initialization. First, in step S11, a basic fuel injection pulse width Tp representing an engine load and determining a basic fuel injection amount (calculated in a fuel injection amount setting routine not shown). Tp ← K × Q / NE; K
Is the injector characteristic correction constant, Q is the intake air amount) and the engine speed NE is referred to the basic advance value table stored in the ROM 42 with interpolation calculation, and the basic ignition timing corresponding to the stoichiometric value is obtained. ADV ADV
Set BASE.

In the basic advance value table, the optimum ignition timing is determined in advance by an experiment or the like for each engine operation region based on the engine speed NE and the basic fuel injection pulse width Tp in the homogeneous mixed combustion during the stoichiometric operation. BTDC is set as a basic advance value ADVBASE that determines at what CA the BTDC is to be ignited, as a table using the engine speed NE and the basic fuel injection pulse width Tp as parameters, and stored in a series of addresses in the ROM 42. Yes, for example, 16 grids × 16 grids = 256
It is configured as an area table.

Next, at step S12, knock sensor 3
The ignition timing learning correction value AD for learning the amount of retard or advance for each operation region according to the presence or absence of knock detected by 0
VKR is calculated based on the engine speed NE and the basic fuel injection pulse width Tp.
Based on the above, the ignition timing learning correction value table stored in the backup RAM 44 is set with reference to interpolation calculation.

In the following step S13, the linear O2 sensor 3
3, the actual air-fuel ratio λa is detected based on the output voltage Vλ.
As shown in FIG. 6, the linear O2 sensor 33 has a linear output voltage characteristic corresponding to the actual air-fuel ratio λa, and this output characteristic is stored in a series of addresses of the ROM 42 as a table using the output voltage Vλ as a parameter. By storing in the memory, the actual air-fuel ratio λa can be detected by searching the table.

Next, the routine proceeds to step S14, where the actual air-fuel ratio λa is compared with the stoichiometric air-fuel ratio λs (= 14.7) to determine whether the current air-fuel ratio state is stoichiometric (including a rich air-fuel ratio) or lean. That is, it is determined whether or not the operation is lean burn based on the actual air-fuel ratio λ.

When λa> λs is lean,
Proceeding to step S15, the ignition timing correction coefficient table is searched based on the actual air-fuel ratio λa, and the ignition timing correction coefficient KADV is set by interpolation calculation.

That is, the basic advance value ADVBASE, which determines the basic ignition timing, corresponds to the mixed homogeneous combustion during the stoichiometric operation, and the air-fuel mixture flowing into the combustion chamber 20 diffuses and becomes a uniform mixed state. In some cases, the ignition is performed. In the case of lean burn, it is necessary to ignite the mixture before flowing into the combustion chamber 20 before the mixture is diffused in order to perform the stratified combustion. For this reason, the basic advance value ADVBASE corresponding to the uniform mixed combustion is changed to the ignition timing correction coefficient KADV.
Is used to correct the advance angle.

The air-fuel ratio is controlled lean during stratified combustion, and stoichiometric during uniform mixed combustion. Therefore, the actual combustion state, that is, stratified combustion or homogeneous mixed combustion, is determined by the actual air-fuel ratio λa. It can be determined, and the transition of switching between stratified combustion and homogeneous mixed combustion can also be determined.

In the ignition timing correction coefficient table, an ignition timing correction coefficient KADV for obtaining an optimum ignition timing corresponding to the actual air-fuel ratio λa by performing advance correction of the basic advance value ADVBASE under an air-fuel ratio lean condition is obtained in advance by experiments or the like. , And stored in a series of addresses of the ROM 42 as a table using the air-fuel ratio λa as a parameter, and as shown in FIG.

Here, since the ignition timing correction coefficient table for correcting the ignition timing at the time of lean burn is constituted as a one-dimensional table with a single parameter, a plurality of parameters used at the time of the conventional lean burn are used. , It is possible to significantly reduce the used capacity of the memory (ROM 42).

As shown in FIG. 8, in the ignition timing correction coefficient table, the higher the degree of leanness of the air-fuel ratio, the larger the ignition timing of the basic advance value ADVBASE. The correction coefficient KADV is stored.

That is, as described above, if the air-fuel ratio is lean but close to stoichiometric, if the ignition timing is advanced too much for stratified combustion, ignition becomes impossible due to the rich mixture before diffusion, and to some extent Only after the air-fuel mixture has diffused can ignition occur, and when switching between stratified combustion during lean burn operation and uniform mixed combustion during stoichiometric operation,
The flow characteristics of the air-fuel mixture in the combustion chamber 20 change between the tumble flow and the normal state, and accordingly, it is necessary to advance the ignition timing as the lean degree of the air-fuel ratio increases. Then, from the ignition timing correction coefficient table, the higher the degree of lean of the actual air-fuel ratio λa, the larger the ignition timing correction coefficient KADV is set.

The output voltage V of the linear O2 sensor 33
λ is directly used, the output voltage Vλ is compared with a voltage value (3 V in this embodiment) corresponding to stoichiometry to determine the air-fuel ratio state, and the ignition timing is corrected based on the output voltage Vλ of the linear O2 sensor 33. The coefficient KADV may be set.

Next, the routine proceeds to step S16, in which the basic advance value ADVBASE is multiplied by the ignition timing correction coefficient KADV to correct the ignition timing in accordance with the air-fuel ratio, that is, the combustion characteristic at that time, to correspond to the combustion characteristic based on the air-fuel ratio. The obtained optimal ignition timing is obtained, the ignition timing learning correction value ADVKR is added to perform learning correction, a control advance angle ADV that determines the ignition timing is set (ADV ← ADVBASE × KADV + ADVKR), and the routine proceeds to step S18.

On the other hand, when the stoichiometric condition of λa ≦ λs is satisfied in step S14, the process proceeds to step S17, where the ignition timing learning correction value ADVKR is added to the basic advance value ADVBASE to set the control advance angle ADV (ADV ← ADVBASE + A
DVKR), and proceeds to step S18.

Here, as described above, the basic advance value A
DVBASE corresponds to stoichio, so
When the air-fuel ratio λa is stoichiometric, the control advance angle ADV that determines the ignition timing is set without correcting the basic ignition advance value ADVBACE with the ignition timing correction coefficient KADV.

In step S18, based on the control advance angle ADV, the energization cutoff timing TAD of the ignition coil 22 based on the input of the θ2 crank pulse corresponding to the ignition timing.
Set V. In the present embodiment, a so-called time control method is employed, and the power cutoff timing is set by time.

That is, since the control advance ADV is angle data (BTDC ° CA), it is necessary to convert the control advance ADV into the time from the input of the θ2 crank pulse to the ignition.
As shown in the time chart of FIG. 9, the time from when the θ1 crank pulse is input to when the θ2 crank pulse is input is Tθ12, and the angle between the θ1 and θ2 crank pulses (for example, 32 ° CA) is θ12. In this embodiment,
The energization cutoff timing TADV is set by the following equation based on the θ2 crank pulse input.

TADV ← (Tθ12 / θ12) × (θ2−ADV) Next, the process proceeds to step S19, where the basic energizing time DWLB of the ignition coil 22 is set by referring to the table with interpolation calculation based on the battery voltage VB. In step S20, a rotation correction coefficient KDWLN is set by referring to the table with interpolation calculation based on the engine speed NE. Above basic energizing time DWLB
Is a basic value of the energizing time based on the coil primary current depending on the battery voltage. The higher the battery voltage VB, the shorter the basic energizing time DWLB is stored in the table. The above-mentioned rotation correction coefficient KDWLN is a coefficient for correcting the effect of the coil non-energization time (pause time) which becomes shorter as the engine speed NE becomes higher, and becomes smaller as the engine speed NE becomes higher. Are stored in the table.

Thereafter, the flow advances to step S21 to multiply the basic energizing time DWLB by the rotation correction coefficient KDWLN to calculate the energizing time DW
L is calculated (DWL ← DWLB × KDWLN), and the following step S
At 22, the energizing time DW is calculated from the energizing cutoff timing TADV.
L is subtracted to set the energization start timing TDWL based on the θ2 crank pulse (TDWL ← TADV−DWL),
In step S23, the energization cutoff timing TADV is set in the ignition timing timer of the relevant cylinder, and in step S24, the energization start timing TDWL is set in the energization start timing timer of the relevant cylinder, and the routine exits.

As a result, each of the timers is started by the θ2 crank pulse interruption routine shown in FIG. 4, which is started in synchronization with the input of the θ2 crank pulse, and ignition is performed.

The routine for interrupting the θ2 crank pulse will be described. The routine is started in synchronization with the input of the θ2 crank pulse. In step S31, the energization start timing timer for the cylinder to be ignited is started.
In step S32, the ignition timing timer of the cylinder to be ignited is started, and the routine exits.

When the power supply start timing reaches the power supply start timing TDWL by measuring the power supply start timing timer, FIG.
Is started by interruption, and in step S41, an energization signal for the corresponding cylinder is output from the ECU 40 to the igniter 23 by the dwell setting of the cylinder to be ignited (see FIG. 9), and energization (dwell) of the ignition coil 22 of the corresponding cylinder is started. Is done.

Thereafter, when the current reaches the energization cutoff timing TADV by the timing of the ignition timing timer, the routine shown in FIG. 6 is started by interruption. In step S51, the dwell of the cylinder to be ignited is cut, and the high voltage The next voltage is induced, the electrode of the ignition plug 21 of the ignition target cylinder is discharged and sparks, and the air-fuel mixture in the combustion chamber 20 is ignited and burned.

At this time, since the control advance angle ADV that determines the ignition timing is set according to the combustion characteristics required by the difference in the air-fuel ratio, the ignition is performed at the optimum ignition timing suitable for the combustion characteristics depending on the air-fuel ratio. As a result, the flammability is improved, and the exhaust emission is effectively improved.

If the ignition timing is advanced too much for stratified combustion when the air-fuel ratio is lean but close to stoichiometric, ignition becomes impossible due to the rich mixture before diffusion, and the mixture is diffused to some extent. After that, ignition cannot be performed, and when switching between stratified combustion and uniform mixed combustion,
It is necessary to advance the ignition timing as the flow characteristics of the air-fuel mixture in the combustion chamber 20 change between the tumble flow and the normal state, and the degree of leanness of the air-fuel ratio increases. Correspondingly, the higher the degree of leanness of the actual air-fuel ratio λa, the larger the ignition timing correction coefficient KADV is set, and the basic advance value ADVBASE is corrected by the ignition timing correction coefficient KADV to determine the ignition timing. Control lead angle AD
Since V is set and the ignition timing is advanced, it is possible to always obtain the optimum ignition timing according to the degree of lean during lean burn operation. It can be effectively eliminated.

The present invention is not limited to the above-described embodiment, and the basic ignition timing AD can be set even during the stoichiometric operation.
VBASE may be corrected by the ignition timing correction coefficient KADV. In this case, KADV = 1.0, that is, a value substantially without correction is stored in the ignition timing correction coefficient table with respect to stoichiometry. Steps S14 and S17 of the ignition timing setting routine are omitted.

Further, in the present embodiment, the basic fuel injection pulse width Tp is used as the engine load, but the present invention is not limited to this, as long as it represents the engine load. Further, in the present embodiment, the ignition timing control based on the so-called time control method is employed, but it is needless to say that the ignition timing control based on the angle control method may be employed.

Further, in the present embodiment, the stoichiometric operation is controlled outside the lean burn operation region, but a predetermined rich operation may be performed.
In this case, the basic ignition timing map is created in advance so as to be suitable for the predetermined rich operation.

[0088]

According to the present invention, the basic ignition timing corresponding to the normal air-fuel ratio is set based on the engine speed and the engine load, and the ignition timing correction coefficient is set based on the air-fuel ratio. The ignition timing correction coefficient is used to correct the basic ignition timing according to the air-fuel ratio and set an ignition timing suitable for the actual air-fuel ratio. Therefore, the ignition timing correction coefficient for correcting the basic ignition timing is determined by one parameter. Since the setting is made, the used capacity of the memory can be reduced.

Further, since the basic ignition timing is corrected by the ignition timing correction coefficient set in accordance with the air-fuel ratio to set the ignition timing, it is possible to obtain the optimum ignition timing suitable for the combustion characteristics based on the air-fuel ratio at that time. Thus, even if the required combustion characteristics change due to the difference in the air-fuel ratio, the combustibility can be improved, and the exhaust emission can be effectively improved.

According to the second aspect of the present invention, the basic ignition timing corresponding to the normal air-fuel ratio is set based on the engine speed and the engine load, and whether or not the engine is in the lean burn operation state is determined based on the air-fuel ratio. Judgment, at the time of lean burn operation, set the ignition timing correction coefficient based on the current air-fuel ratio, correct the basic ignition timing according to the lean air-fuel ratio by this ignition timing correction coefficient, set the ignition timing, When not in the lean burn operation, the ignition timing is set without correcting the basic ignition timing with the ignition timing correction coefficient, so that the ignition timing correction coefficient corresponds to the lean air-fuel ratio in addition to the effect of the invention described in claim 1. Only what you do,
This has the effect that the used capacity of the memory can be further reduced.

According to the third aspect of the present invention, a table search is performed based on the air-fuel ratio to set an ignition timing correction coefficient that increases the advance correction with respect to the basic ignition timing as the lean degree of the air-fuel ratio increases. The ignition timing correction coefficient table for correcting the ignition timing at the time of burn is configured as a one-dimensional table with a single parameter. The used capacity can be significantly reduced.

Further, even if the required combustion characteristics change depending on the degree of lean air-fuel ratio, an optimum ignition timing corresponding to the change can be obtained, and stratified combustion during lean burn and a predetermined air-fuel ratio (stoichio ratio) are used. The optimum ignition timing can be obtained even during the transition of switching to homogeneous mixed combustion,
Misfire and deterioration of flammability due to mismatch of ignition timing can be effectively eliminated.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of the present invention.

FIG. 2 is a flowchart of a cylinder discrimination / engine speed calculation routine.

FIG. 3 is a flowchart of an ignition timing setting routine;

FIG. 4 is a flowchart of a θ2 crank pulse interrupt routine.

FIG. 5 is a flowchart of a TDWL interrupt routine.

FIG. 6 is a flowchart of a TADV interrupt routine.

FIG. 7 is an explanatory diagram showing output characteristics of a linear O2 sensor.

FIG. 8 is an explanatory diagram of an ignition timing correction coefficient table.

FIG. 9 is a time chart showing a relationship among a crank pulse, a cam pulse, and an ignition signal.

FIG. 10 is an overall schematic diagram of an engine.

FIG. 11 is a sectional view showing details of a main part of an intake system.

FIG. 12 is a front view of a crank rotor and a crank angle sensor.

FIG. 13 is a front view of a cam rotor and a cam angle sensor.

FIG. 14 is a circuit configuration diagram of an electronic control system.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Lean burn engine 21 Spark plug 22 Ignition coil 33 Linear O2 sensor 40 Electronic control unit (basic ignition timing setting means, discriminating means, ignition timing correction coefficient setting means, ignition timing setting means) λa Air-fuel ratio NE Engine speed Tp Basic fuel Injection pulse width (engine load) ADVBASE Basic advance value (basic ignition timing) KADV Ignition timing correction coefficient ADV control advance (ignition timing)

Claims (3)

[Claims] An ignition timing control for a lean burn engine that performs a lean burn operation based on a lean air-fuel ratio when the engine operation state is in a predetermined range, and performs a lean burn operation when the engine operation state is out of the predetermined range. A basic ignition timing setting means for setting a basic ignition timing corresponding to the predetermined air-fuel ratio based on an engine speed and an engine load; and an ignition timing correction for correcting the basic ignition timing based on an air-fuel ratio. An ignition timing correction coefficient setting means for setting a coefficient; and an ignition timing setting means for setting the ignition timing by correcting the basic ignition timing with the ignition timing correction coefficient. Control device. 2. An ignition timing control for a lean burn engine that performs a lean burn operation with a lean air-fuel ratio when the engine operation state is in a predetermined range, and performs a lean burn operation with a predetermined air-fuel ratio when the engine operation state is outside the predetermined range. In the device, basic ignition timing setting means for setting a basic ignition timing corresponding to the predetermined air-fuel ratio based on the engine speed and the engine load, and discriminating means for determining whether or not a lean burn operation state is based on the air-fuel ratio. An ignition timing correction coefficient setting means for setting an ignition timing correction coefficient for correcting the basic ignition timing based on the current air-fuel ratio in the lean burn operation state; and the basic ignition timing in the lean burn operation state. Is corrected with the above ignition timing correction coefficient to set the ignition timing. An ignition timing control device for a lean burn engine, comprising: ignition timing setting means for setting the ignition timing without correcting the ignition timing with the ignition timing correction coefficient. 3. The ignition timing correction coefficient setting means sets the ignition timing correction coefficient by searching a table using the air-fuel ratio as a parameter. The basic ignition timing is set in the table as the leanness of the air-fuel ratio increases. 3. An ignition timing control apparatus for a lean burn engine according to claim 1, wherein an ignition timing correction coefficient for increasing an advance angle correction is stored.