JPH1150900A - Control device for spark ignition engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always secure a stable combustion so as to expand a lean limit by controlling the current carrying time for ignition coil and an air-fuel ratio according to the loading conditions on an ignition coil when an operation is performed at the lean air-fuel ratio when an engine is operated at the lean air-fuel ratio with an ignition energy increased. SOLUTION: When the coil temperature T of an ignition coil is detected and the ignition coil is overloaded at T>THIGH (THIGH is a set temperature), a dwell time is shortened correlatively from a target dwell time to a minimum range of set dwell time capable of reducing a thermal load on the ignition coil, and an air-fuel ratio is enriched correctively to the set air-fuel ratio so that an ignitability corresponding to an ignition energy in the set dwell time can be secured. By this, a target air-fuel ratio A/F in lean burn control is sifted to a stoichio direction, leading to a lean air-fuel ratio corresponding to an ignition energy in the set dwell time. Thus a stable combustion can be secured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control apparatus for a spark ignition engine in which the ignition energy is increased by varying the energization time of an ignition coil during operation at a lean air-fuel ratio.

[0002]

2. Description of the Related Art Generally, in a spark ignition engine,
Ignition devices that apply a secondary high voltage generated when the primary current of an ignition coil is cut off to an ignition plug to discharge the ignition plug are widely used, but the ignition energy required to ensure stable combustion is as follows: It changes depending on the combustion method and operating conditions.

[0003] For example, a lean burn engine that performs combustion with a lean mixture requires a large amount of ignition energy to ensure stable combustion. For this reason,
Japanese Patent No. 57362 proposes a technique in which the energization time of the ignition coil can be appropriately changed according to the air-fuel ratio during operation, and the discharge energy is increased during lean burn operation to improve the ignition state.

In this case, if the energizing time of the ignition coil is changed to increase the discharge energy, the ignition coil may be overloaded.
No. 8746 discloses that the lean burn operation and the high EG
At the time of R operation, the energizing time of the ignition coil is extended and the elapsed time after the extension is measured, and when the elapsed time exceeds the set time, the extension of the energizing time of the ignition coil is stopped to thereby extend the ignition coil. A technique for increasing ignition energy while preventing overload has been proposed.

[0005]

However, when the ignition energy is to be increased while preventing the overload of the ignition coil, the energization time of the ignition coil must be increased according to the load state of the ignition coil for more precise control. You need to control.

Further, conventionally, when the ignition coil is overloaded during the lean operation, the energization time of the ignition coil must be shortened. Therefore, in order to secure stable combustion, a stoichiometric or rich air-fuel ratio is required. It was necessary to return to driving at the time, which was a constraint on expanding the lean limit.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and when the lean air-fuel ratio is operated by increasing the ignition energy,
It is an object of the present invention to provide a control device for a spark ignition type engine which can always secure stable combustion by controlling an energization time and an air-fuel ratio of an ignition coil according to a load state of the ignition coil and can increase a lean limit. And

[0008]

According to the first aspect of the present invention,
When operating at a lean air-fuel ratio, means for setting the energization time of the ignition coil to a value corresponding to the target air-fuel ratio and the load state of the ignition coil are examined, and this load state exceeds the set state and becomes overloaded. Means for determining whether or not the ignition coil is overloaded, and when it is determined that the ignition coil is overloaded, the energization time of the ignition coil is reduced and corrected, and the target idle time is corrected in accordance with the reduced and corrected energization time. Means for correcting the fuel ratio within the range of the lean air-fuel ratio.

According to a second aspect of the present invention, in the first aspect of the present invention, the load state of the ignition coil is checked based on a coil temperature detected by a temperature sensor.

A third aspect of the present invention is characterized in that, in the first aspect of the present invention, the load state of the ignition coil is checked based on a change in a primary resistance value of the ignition coil.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the load state of the ignition coil is checked based on a weighted average value of the energization time of the ignition coil.

That is, in the control apparatus for a spark ignition engine according to the present invention, the energizing time of the ignition coil is set to a value corresponding to the target air-fuel ratio during operation at a lean air-fuel ratio. When the overload is determined by checking the load state of the ignition coil to increase the ignition energy, the energization time of the ignition coil is reduced and corrected, and the target air-fuel ratio is set to lean air corresponding to the reduced and corrected energization time. By compensating within the fuel ratio range, the stability of combustion is ensured.

In this case, the load state of the ignition coil includes the coil temperature detected by the temperature sensor, the amount of change in the primary resistance of the ignition coil, and the energization of the ignition coil. It can be examined by a weighted average of time.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 relate to an embodiment of the present invention, FIG. 1 is a flowchart of an ignition control routine, FIG. 2 is a flowchart of a fuel injection amount setting routine,
FIG. 3 is an explanatory diagram showing the relationship among the ignition coil temperature, the target air-fuel ratio, and the dwell time, and FIG. 4 is a schematic configuration diagram of an engine control system.

In FIG. 4, reference numeral 1 denotes an engine,
This is a lean burn engine that performs lean burn during high load / acceleration operation requiring high output or in an operation region other than some operation regions such as idling.
Cylinder heads 2 are provided on both left and right banks of a cylinder block 1a of the engine 1, respectively. A combustion chamber 3 for each cylinder formed by the cylinder head 2 and the cylinder block 1a is connected via an intake valve 4. An intake manifold 5 is communicated with the exhaust manifold 7 via an exhaust valve 6.

An injector 8 is located immediately upstream of an intake port in which the intake valve 4 is interposed, and an ignition plug 9 whose tip is exposed to the combustion chamber 3 is provided on the cylinder head 2 for each cylinder. Attached to. An ignition coil 10 is connected to the ignition plug 9, and an igniter 11 is connected to the ignition coil 10.

An air chamber 12 is formed at an upstream gathering portion of the intake manifold 5 and communicates with an intake pipe 13. An air cleaner 14 is attached to an air intake port on the upstream side of the intake pipe 13. A throttle valve 15 is provided. Further, a bypass passage 13a that bypasses the throttle valve 15 is connected to the intake pipe 13. The bypass passage 13a
Idle speed control valve (ISCV) 1
6 are interposed.

On the other hand, an exhaust pipe 17 is communicated with the exhaust manifold 7, and a catalytic converter 18 is provided immediately downstream of the exhaust pipe 17 at the collecting portion of the exhaust manifold 7.
And a muffler 19 at the downstream end.

The engine 1 is provided with various sensors, such as an intake air amount sensor 20 disposed immediately downstream of the air cleaner 14 in the intake pipe 13 and a throttle. A throttle sensor 21 which is connected to the valve 15 and includes a throttle opening sensor for detecting a throttle opening and an idle switch which is turned on when the throttle is fully closed; a knock sensor 22 attached to the cylinder block 1a; A cooling water temperature sensor 23 facing a cooling water passage 1b communicating between the left and right banks, a crank angle sensor 25 for detecting a crank angle provided on an outer periphery of a crank rotor 24 axially mounted on a crankshaft 1c, and a camshaft 1d.
A cam angle sensor 27 for cylinder discrimination, which is provided opposite to a cam rotor 26 connected to the exhaust pipe 18;
There are a wide-range air-fuel ratio sensor 28 facing the upstream side, a temperature sensor 29 for detecting the coil temperature of the ignition coil 10, and various other sensors (not shown).

The various sensors are connected to an electronic control unit (ECU) 50 for electronically controlling the engine 1. The ECU 10 includes a CPU 51, a ROM 52,
A power supply circuit 5 mainly composed of a microcomputer including a RAM 53, a backup RAM 54, an I / O interface 55, and supplies a stabilized voltage to each unit.
6. a driving circuit 57 for driving actuators by a signal from an output port of the I / O interface 55;
A peripheral circuit such as an A / D converter 58 for converting an analog signal from sensors into a digital signal is incorporated.

The input ports of the I / O interface 55 are connected to the crank angle sensor 25, the cam angle sensor 27, other sensors and switches (not shown), and the A / D converter 58 The intake air amount sensor 20, the throttle sensor 21, the intake pipe pressure sensor 22, the cooling water temperature sensor 23, the wide area air-fuel ratio sensor 28, the temperature sensor 29, and the like are connected via the air intake sensor. On the other hand, the igniter 11 is connected to an output port of the I / O interface 55, and the injector 8,
The ISCV 16 and other various actuators (not shown) are connected.

The power supply circuit 56 is connected to a battery 61 via a relay contact of an ECU relay 60, and a relay coil of the ECU relay 60 is connected to the battery 61 via an ignition switch 62. Further, the power supply circuit 56 is directly connected to the battery 6.
1 and the ignition switch 62
Is turned on and the relay contact of the ECU relay 60 is closed, power is supplied from the power supply circuit 56 to each unit, and the ignition switch 62 is turned on and off.
Regardless, the backup RAM 54 is always supplied with power for backup.

In accordance with the control program stored in the ROM 52, the CPU 51 processes detection signals from sensors and switches, which are input via the I / O interface 55, battery voltage, and the like.
And various data stored in the backup RAM 54,
Based on the fixed data and the like stored in the ROM 52, a fuel injection amount, an ignition timing, a duty ratio of a drive signal for the ISCV 16 and the like are calculated, and various engine controls such as a fuel injection control, an ignition timing control, and an idle speed control are performed. .

In this engine control, in order to save fuel, the air-fuel ratio control for stoichiometric air-fuel mixture is switched from the normal air-fuel ratio control to lean air-fuel ratio control, that is, lean burn control. During the burn control, a large ignition energy is required as compared with the normal control because the ignitability of the air-fuel mixture is poor.

For this reason, the ECU 50 ensures the required ignition energy according to the operating state of the engine, and
The load state of the ignition coil 10 with the increase of the ignition energy is monitored so that a stable combustion state is always maintained.

Hereinafter, processing relating to an increase in ignition energy during lean burn control will be described with reference to the flowcharts of FIGS.

FIG. 2 shows a fuel injection amount setting routine that is executed at predetermined intervals after the system initialization, and a fuel injection pulse width Ti that determines the fuel injection amount is set for each fuel injection target cylinder.

In this fuel injection amount setting routine, in step S101, a unit rotation is determined from the engine speed NE based on the output signal of the crank angle sensor 25 and the intake air amount Q based on the output signal from the intake air amount sensor 20. Calculate the intake air flow rate per cylinder Qcy as the engine load (Qcy ← Q
/ NE), in step S102, based on the engine speed NE and the intake air flow rate Qcy per unit rotation, refer to a map in which the air-fuel ratio target value is stored for each operating region, and set the target air-fuel ratio A / F. Set. For example, when performing the lean burn control in the low load and the medium load regions excluding the extremely low load low rotation region and the high load region, a lean target air-fuel ratio is set for each region.

Next, the routine proceeds to step S103, where the ignition coil 1
When a later-described air-fuel ratio correction value KIG for correcting the air-fuel ratio according to the energization time (dwell time) of 0 is read from a predetermined address in the RAM 54, in step S104, the target air-fuel ratio A / F, the corrected target air-fuel ratio A / F and the intake air flow rate Qcy per unit rotation.
, The basic fuel injection pulse width Tp that determines the basic fuel injection amount is calculated (Tp ← K × Qcy / ((A / F) −K
IG); where K is an injector characteristic correction constant).

In the following step S105, the cooling water temperature sensor 2
3, based on the cooling water temperature, the throttle opening output from the throttle sensor 21 and the idle output, and the like, set various correction coefficients COEF related to cooling water temperature correction, acceleration / deceleration correction, full-open increase correction, post-idle increase correction, and the like. In step S106, the air-fuel ratio feedback correction coefficient λ set according to the deviation between the actual air-fuel ratio based on the output of the wide area air-fuel ratio sensor 28 and the target air-fuel ratio is read from a predetermined address in the RAM 53.

Further, at step S107, the battery voltage VB
When the voltage correction coefficient TS for interpolating the invalid injection time of the injector 8 is set based on the above, in step S108, the basic fuel injection pulse width Tp is multiplied by the various increase correction coefficient COEF and the air-fuel ratio feedback correction coefficient λ to perform voltage correction The coefficient TS is added, the air-fuel ratio correction and the voltage correction are performed, and the fuel injection pulse width Ti that determines the final fuel injection amount is set (Ti ← Tp × COEF × λ + TS). Then, in step S109, the fuel injection pulse width Ti is set in the injection timer of the fuel injection target cylinder, and the routine exits.

Since the required ignition energy increases during the execution of the lean burn control in the above fuel injection amount setting routine, the dwell time of the ignition coil 10 is set in the ignition control routine of FIG. Energy to be increased.

In this ignition control routine, first, in step S201, the engine speed NE and the basic fuel injection pulse width Tp
When the basic advance value ADVBASE is set with reference to the basic advance value table (see FIG. S201) based on the above, in step S202, the knocking based on the cooling water temperature or the occurrence of knocking based on the signal from the knock sensor 22 is determined. The ignition timing correction value ADVK is set.

Next, the routine proceeds to step S203, where the ignition timing correction value ADVK is added to the basic advance value ADVBASE to set the control advance angle ADV (ADV ← ADVBASE + ADV).
K), In step S204, it is checked whether or not the vehicle is in a lean operation state. When the vehicle is not in the lean operation state, step S205
Then, the basic dwell time DWLB of the ignition coil 10 at the stoichiometric or rich air-fuel ratio is set by referring to a table or the like based on the battery voltage VB. The basic dwell time DWLB is a basic energizing time based on the coil primary current that changes depending on the battery voltage VB. The higher the battery voltage VB, the shorter the basic dwell time DWLB is stored in the table.

Further, the steps S205 to S2
In step 06, a rotation correction coefficient KDWLN is set by referring to a table based on the engine speed NE. The rotation correction coefficient KDWLN is a coefficient for correcting the influence 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. The correction coefficient KDWLN is stored in the table.

Thereafter, from step S206 to step S2
Go to 07 and add the rotation correction coefficient KDWLN to the basic dwell time DWLB.
To set the target dwell time DWL at the stoichiometric or rich air-fuel ratio (DWL ← DWLB × KDWLN).
Then, in step S208, the air-fuel ratio correction value KIG is set to 0 (KIG
← 0), in step S217, the control timer ADV and dwell time (target dwell time) are set in the ignition timer of the cylinder to be ignited.
Set DWL and exit the routine.

As a result, at a predetermined timing, the ECU 50
An ignition signal is output to the igniter 16 to the ignition target cylinder to start energization of the ignition coil 10. When the ignition timing is reached, a dwell is cut off, a high secondary voltage is induced in the ignition coil 10, and the ignition target The spark plug 9 of the cylinder sparks.

On the other hand, if it is determined in step S204 that the engine is in the lean operation state, the process proceeds from step S204 to step S209 to set the target dwell time DWL at the lean air-fuel ratio. The target dwell time DWL is a dwell time for increasing the ignition energy so that misfire does not occur with respect to the target air-fuel ratio A / F at the time of the lean burn control. The target air-fuel ratio A / F, the battery voltage VB, the engine The dwell time is set based on the rotational speed NE and the like, and is generally set to a dwell time longer than the target dwell time at the stoichiometric or rich air-fuel ratio.

In the following steps S210 and S211, the load state of the ignition coil 10 is detected, and it is checked whether or not this load state exceeds a set state and is overloaded. Ignition coil 1
The load state of 0 can be checked by the coil temperature T of the ignition coil 10. In step S210, the temperature sensor 2
9, the coil temperature T of the ignition coil 10 based on the output from
Is detected, and in a step S211, it is checked whether or not the coil temperature exceeds the set temperature THIGH. This set temperature THI
GH is an upper limit temperature that can be used continuously determined in consideration of the capacity, specifications, durability and the like of the ignition coil 10.

As a result, when the ignition coil 10 is in an overload state with T> THIGH, steps S211 to S212 are performed.
Then, the dwell time of the ignition coil 10 is reduced and corrected from the target dwell time set in step S209 to a set dwell time in a minimum range in which the thermal load on the ignition coil 10 can be reduced.

Further, in step S213, an air-fuel ratio correction value KIG (initial value is 0) is set to richly correct the air-fuel ratio toward the set air-fuel ratio so that ignitability corresponding to the ignition energy at the set dwell time can be secured. ) Is increased to the plus side, and the routine exits through the ignition timer set in step S217.

The set air-fuel ratio is a lean limit air-fuel ratio given as a function of the set dwell time. In the above-described fuel injection amount setting routine, the target air-fuel ratio A / F during the lean burn control is adjusted by the air-fuel ratio correction. By shifting the value in the stoichiometric direction by the value KIG and calculating the basic fuel injection pulse width Tp (step S104), the target air-fuel ratio is substantially corrected in the stoichiometric direction within the range of the lean air-fuel ratio. Thus, a lean air-fuel ratio commensurate with the ignition energy of the engine can be obtained, and stable combustion can be ensured.

If T.ltoreq.THIGH in step S211 and the coil temperature T of the ignition coil 10 does not exceed the set temperature THIGH, the process proceeds from step S211 to step S211.
The process branches to S214 to check whether the coil temperature T is lower than the set temperature TLOW. The set temperature TLOW is the temperature of the ignition coil 10 that can be continuously used at the target air-fuel ratio set in a table according to the operation range during the lean burn control.
W <THIGH.

When T ≧ TLOW, the process jumps from step S214 to step S217 for setting the ignition timer of the corresponding cylinder while maintaining the current corrected dwell time. When T <TLOW, the process proceeds from step S214. Proceed to S215 and the current dwell time is the above step
Enlargement correction is performed so as to reach the target dwell time set in S209.

Next, the process proceeds to step S216, in which the air-fuel ratio correction value KIG is reduced to a negative value so as to lean-correct the air-fuel ratio toward the target air-fuel ratio so that the air-fuel ratio corresponds to the dwell time corrected in step S215. Then, the routine exits through the ignition timer set in step S217. Accordingly, in the above-described fuel injection amount setting routine, the target air-fuel ratio A / F during the lean burn control is shifted toward the lean side by the air-fuel ratio correction value KIG to calculate the basic fuel injection pulse width Tp (step S104). It approaches the original target air-fuel ratio during lean burn control.

Note that T <TLO at the beginning of the lean burn control.
In the state of W, or once T> HIGH, the temperature of the ignition coil 10 is reduced by the above-described processing, and T <THIGH.
When TLOW is reached and the dwell time of the ignition coil 10 reaches the target dwell time DWL set in step S209, KIG = 0 is set.

That is, at the time of the lean burn control, the energy stored in the primary side of the ignition coil 10 is increased to increase the discharge energy from the ignition plug 10 to secure the combustibility, but as shown in FIG. When the temperature of the ignition coil 10 exceeds the set temperature THIGH, the dwell time is immediately reduced to eliminate the thermal overload state, and the air-fuel ratio is reduced within the range of the lean air-fuel ratio in response to the reduced dwell time. Since the correction is performed in the stoichiometric direction, stable combustion can be ensured in the lean operation region, and generation of a surge or the like can be avoided.

Instead of checking the load state of the ignition coil 10 based on the coil temperature T based on the output from the temperature sensor 29, the load state of the ignition coil 10 may be checked based on a change in the resistance value on the primary winding side. In this case, the average coil temperature calculated from the change in the resistance value is set to the set temperature THI.
The values may be compared with GH and TLOW, or the amount of change in the resistance value may be directly compared with the values corresponding to the set temperatures THIGH and TLOW.

Further, the dwell time may be weighted by the following equation, and the load state of the ignition coil 10 may be checked from the dwell time based on the weighted average. In this case, the coil temperature is determined from the dwell time based on the weighted average. It may be estimated and compared with the set temperatures THIGH and TLOW, or the dwell time after the weighted average may be directly compared with a value corresponding to the set temperatures THIGH and TLOW.

NTD = {TD + NTD. (N-1)} / n where NTD: dwell time by weighted average TD: dwell time n: smoothing constant

[0051]

As described above, according to the present invention, when operating at a lean air-fuel ratio, the energization time of the ignition coil is set to a value corresponding to the target air-fuel ratio, and the load state of the ignition coil is checked to determine the excess. When the load is determined, the ignition coil is overloaded because the energization time of the ignition coil is reduced and corrected, and the target air-fuel ratio is corrected within the range of the lean air-fuel ratio in accordance with the reduced and corrected energization time. Even in this case, excellent effects such as stable combustion can be secured without returning to the stoichiometric or rich air-fuel ratio, and the lean limit can be expanded.

[Brief description of the drawings]

FIG. 1 is a flowchart of an ignition control routine.

FIG. 2 is a flowchart of a fuel injection amount setting routine;

FIG. 3 is an explanatory diagram showing a relationship among an ignition coil temperature, a target air-fuel ratio, and a dwell time.

FIG. 4 is a schematic configuration diagram of an engine control system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine 10 ... Ignition coil 50 ... ECU DWL ... Target dwell time A / F ... Target air-fuel ratio

Claims (4)

[Claims] 1. An operation for setting an energization time of an ignition coil to a value corresponding to a target air-fuel ratio during an operation at a lean air-fuel ratio, a load state of the ignition coil is examined, and the load state exceeds a set state. Means for determining whether or not an overload has occurred, and, when it is determined that the ignition coil has been overloaded, the energization time of the ignition coil is reduced and corrected, and Means for correcting the target air-fuel ratio within the range of the lean air-fuel ratio. 2. A control device for a spark ignition type engine according to claim 1, wherein a load state of said ignition coil is checked by a coil temperature detected by a temperature sensor. 3. The control apparatus for a spark ignition engine according to claim 1, wherein a load state of said ignition coil is checked by an amount of change in a primary resistance value of said ignition coil. 4. The control device for a spark ignition engine according to claim 1, wherein a load state of said ignition coil is checked based on a weighted average value of a current supplied to said ignition coil.