JP2002147237A - Combustion control device for two-cycle engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the stabilized combustion over the whole operation range in a two-cycle engine. SOLUTION: An operation range is determined on the basis of the engine speed Ne and the engine load Lo (S3), and a stratified charge combustion mode is selected in the low-rotation and low-load range (S4), and a self-ignition control combustion mode is selected in a medium load range (S), and an even combustion mode is selected in a high-load range (S7). Stabilized combustion without a misfire can be obtained over the whole operation range by selecting the optimal combustion mode per each operation range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion control device for a two-stroke engine which switches a combustion mode according to an operation range.

[0002]

2. Description of the Related Art Generally, in a two-cycle engine, during low-speed low-load operation, a misfire easily occurs due to a high residual gas concentration in the cylinder, and unburned HC is easily discharged by the misfire. There is a problem of bad.

[0003] In addition, since the two-cycle engine scavenges with an air-fuel mixture, unburned HC is liable to be discharged even by fuel blow-through, and there is a problem that fuel efficiency is further deteriorated.

[0004] In order to solve these problems, recently, various techniques have been proposed for adopting an in-cylinder injection system and a self-ignition combustion system in a two-cycle engine.

In the in-cylinder injection system, fuel can be supplied into the cylinder at an arbitrary time. Therefore, during the compression stroke in which both the scavenging port and the exhaust port are closed, fuel is injected into the cylinder to blow through. Can be prevented. In this case, as disclosed in, for example, Japanese Patent Application Laid-Open No. 3-33422, when the operation range is in the low and medium load range,
By setting the fuel injection timing immediately before the ignition timing, the combustion mode can be stratified combustion.

On the other hand, in the self-ignition combustion system, fresh air is heated by the thermal energy contained in the residual gas of the previous cycle to create an environment in the cylinder which is easy to ignite and self-ignite near the end of the compression stroke. For example, see JP-A-7-71
Japanese Patent Publication No. 279 discloses an in-cylinder condition capable of self-ignition combustion by variably setting an opening timing of an exhaust port according to an engine rotation speed and a throttle valve opening by an exhaust control valve provided in the exhaust port. The techniques obtained are disclosed.

[0007]

In the technology employing the in-cylinder injection system, when the operating region is in a medium load region, turbulence tends to occur in fresh air, and control of fresh air for generating stratified combustion is performed. Not only is it difficult, but also near the ignition portion of the air-fuel mixture, a relatively high temperature state is maintained for a long time, so that the NOx emission tends to increase.

On the other hand, the self-ignition combustion is multipoint ignition, so that not only stable combustion can be obtained even with a lean mixture, but also the combustion at a relatively low temperature suppresses the emission of NOx. However, since it is difficult to control the ignition timing and the combustion period in the full load range, there is a problem that stable combustion cannot be obtained.

In view of the above circumstances, the present invention can not only obtain stable combustion in a wide operating range, but also
It is an object of the present invention to provide a combustion control device for a two-cycle engine that can reduce the amount of Ox emissions and can achieve low fuel consumption.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a fuel injector having an in-cylinder injector, an exhaust control valve for variably setting exhaust timing, and a spark plug.
In a cycle engine, the engine includes an operating region determining unit that determines an operating region based on at least an engine rotation speed and an engine load, and a combustion mode switching unit that switches a combustion mode according to the operating area. When the region is a low-speed low-load region, the fuel injection timing is set in the latter half of the compression stroke, the exhaust control valve is operated to delay the exhaust timing, and an ignition signal is output to the ignition plug to perform stratified combustion by spark ignition. Do
When the operation region is in the middle load region, the fuel injection timing is set to the compression stroke, and the exhaust timing of the exhaust control valve is set based on at least the engine speed and the engine load to perform self-ignition control combustion. In the load range, the fuel injection timing is set in the first half of the compression stroke, the exhaust control valve is operated in the fully open direction, and an ignition signal is output to the spark plug to perform uniform combustion by spark ignition.

In such a configuration, the operating range is determined based on at least the engine speed and the engine load.
When the operating region is in the low-speed low-load region, the fuel injection timing is set in the latter half of the compression stroke, the exhaust timing is retarded by the exhaust control valve, and an ignition signal is output to the spark plug to perform stratified combustion by spark ignition. When the region is the medium load region, the fuel injection timing is set to the compression stroke, and the exhaust timing of the exhaust control valve is set at least based on the engine speed and the engine load to perform self-ignition control combustion. In this case, the fuel injection timing is set in the first half of the compression stroke, the exhaust control valve is operated in the fully open direction, and an ignition signal is output to the spark plug to perform uniform combustion by spark ignition. By selecting the combustion mode for each operation region, stable combustion can be obtained in almost all operation regions.

In this case, preferably, 1) the combustion mode switching means fully opens the exhaust control valve when the engine speed is high when the operating range is in the high load range, and when the engine speed is low, The exhaust control valve is operated in a valve closing direction.

2) A transition region is provided on each of the low-speed low-load region side and the high-load region side of the medium-load region, and in the combustion mode switching means, the operation region is on the low-speed low load region side. The fuel injection timing is retarded within the auto-ignition possible range as the vehicle approaches the low-speed low-load region,
Also, the fuel injection timing is advanced in a self-ignitable range as it approaches the high load region when in the transition region on the high load side.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 to 8 show a first embodiment of the present invention. FIG. 1 shows a vertical sectional view of a spark ignition type two-cycle engine.

1 is a spark ignition type two-stroke engine, 2 is a crankcase, 3 is a cylinder block,
Is a cylinder head, in which a piston 6 is slidably fitted in a cylinder bore 5 formed in the cylinder block 3, and the piston 6 and a crankshaft 7 are connected to each other via a connecting rod 8. The crankshaft 7 is driven to rotate in conjunction with the vertical movement of the crankshaft.

An intake port 9 is opened in the crank chamber 2a. The intake port 9 communicates with an intake passage 10 in which a throttle valve (not shown) is provided halfway.

The cylinder block 3 includes a crank chamber 2a.
A scavenging passage 11 that communicates with the cylinder bore 5 is formed, and a scavenging port 11 a of the scavenging passage 11 is opened to the cylinder bore 5. Further, an exhaust port 12 a of the exhaust passage 12 is opened in the cylinder bore 5.

A combustion chamber 14 is formed at a substantially central top surface above the cylinder bore 5. The combustion chamber 14 is formed on the bottom surface of the cylinder head 4, and a spark plug 16 is fixed substantially at the center of the combustion chamber 14, and the ignition portion is exposed to the combustion chamber 14.

An in-cylinder injector 15 whose injection hole is exposed in a squish area formed around the combustion chamber 14 is fixedly provided on one side of the cylinder head 4. A cavity 6a for guiding the fuel injected from the injector 15 is formed.

As the piston 6 rises, the scavenging port 11a and the exhaust port 12a opened in the cylinder bore 5 are first closed, and then the exhaust port 12a is closed. On the other hand, when the piston 6 descends, the exhaust port 12a opens first, and
Next, the scavenging port 11a is opened.

An exhaust control valve 17 is interposed in the exhaust port 12a. As shown in FIG.
Is formed by bending a flat plate into a U-shape, and has a support hole 17b formed at the tip of a flange portion 17a formed on both sides. Further, the front surface of the exhaust control valve 17 is curved in an arc shape centering on the support hole 17b.

As shown in FIG. 1, a concave groove 18 is formed in the upper part of the passage of the exhaust port 12a for accommodating the exhaust control valve 17 so as to be able to protrude and retract. The concave groove 18 is provided in the exhaust control valve 1.
Support shaft 19 for supporting a support hole 17b formed in
Are formed in an arc shape with the center as the center.

The exhaust control valve 17 is swingably supported about a support shaft 19, and when the exhaust control valve 17 is immersed in the concave groove 18, the opening ratio of the exhaust port 12a becomes 100%. As the valve 17 is exposed to the exhaust port 12a, the exhaust port 12a is narrowed. When the exhaust port 12a is closed by the exhaust control valve 17, the opening ratio becomes 0%. The support shaft 19 is connected to an exhaust control actuator 20 such as a stepping motor, and the opening ratio of the exhaust port 12a is controlled by operating the exhaust control valve 17 by the exhaust control actuator 20.

As shown in FIG. 8, as the opening ratio of the exhaust port 12a shifts from the fully opened state of 100% to the fully closed state of 0%, the opening timing of the exhaust port 12a opened by the vertical movement of the piston 6 is changed. The exhaust timing at the time of the exhaust stroke, that is, the opening timing of the exhaust port 12a associated with the lowering operation of the piston 6, gradually moves in the retard direction.

An ignition drive circuit 21 for outputting an ignition signal to the ignition plug 16, an injector drive circuit 22 for outputting a drive signal to the in-cylinder injector 15, and an exhaust control actuator 20 are connected to an electronic control unit (ECU) 23. It is connected.

Sensors for detecting the operating state of the engine, such as an engine speed sensor 24, a throttle opening sensor 25 for detecting the opening of a throttle valve (not shown), and switches are connected to the input side of the electronic control unit 23. ing.

The electronic control unit 23 determines an engine operating region based on the engine rotational speed Ne detected by the engine rotational speed sensor 24 and the throttle opening θth detected by the throttle opening sensor 25 and responds to each operating region. The fuel injection timing, ignition timing, and exhaust control valve opening are set to control the combustion state of the engine. This combustion control is specifically processed according to the flowcharts of FIGS.

When the engine is started, an operation region determination routine shown in FIG. 3 is started. First, at step S1, the engine speed Ne and the throttle opening θth are read, and at the next step S2, the engine speed Ne and the throttle opening are set. Based on the degree θth, the engine load Lo is set by referring to the map with interpolation calculation.

Thereafter, in steps S3 and S4, the engine operation area is determined based on the engine speed Ne and the engine load Lo.

As shown in FIG. 7, in this embodiment, the engine operation range is a low-speed low-load range I, a medium load range II,
The combustion mode of each of the regions I, II, and III is divided into three regions of a high-load region III, stratified combustion is selected in the low-speed low-load region I, and auto-ignition control combustion is selected in the medium-load region II. In the load region III, uniform combustion is selected.

When it is determined that the operation region is the low rotation and low load region I, the process proceeds from step S3 to step S5, executes the stratified combustion mode, and exits the routine. or,
If it is determined that the engine is in the middle load range II, the process proceeds from step S4 to step S6, executes the self-ignition control combustion mode, and exits the routine. When it is determined that the load is high, the process branches from step S4 to step S7, executes the uniform combustion mode, and exits the routine.

When the stratified combustion mode is selected as the combustion mode, a stratified combustion mode routine shown in FIG. 4 is executed.

In this routine, first, at step S11
Then, based on the engine rotation speed Ne and the engine load Lo, an opening ratio of the exhaust port 12a is set by referring to a map (not shown) with interpolation calculation, and a drive signal for achieving this opening ratio is subjected to exhaust control. Output to the actuator 20.
Then, the exhaust control actuator 20 moves the exhaust control valve 17
Is rotated to set the opening of the exhaust control valve 17, and the exhaust port 12a is opened at a predetermined position.

In this map, based on the engine speed Ne and the engine load Lo, the gas flow in the cylinder during the exhaust stroke is suppressed, and the residual gas promotes the rise of the gas temperature during the next compression stroke. The optimal aperture ratio that does not cause autoignition combustion but can obtain stable stratified combustion is obtained in advance from experiments and stored.

Next, the routine proceeds to step S12, in which the compression stroke second-half injection control is executed. In the latter half of the compression stroke injection control, a mixture of fuel and fresh air injected from the in-cylinder injector 15 is stratified, and an ignitable mixture is formed around the ignition portion of the ignition plug 16 to provide a stable mixture. In order to obtain combustion, the fuel injection timing is set immediately before ignition, and an injection start signal is output to the injector drive circuit 22 when a predetermined crank angle is reached.

Thereafter, the routine proceeds to step S13, where normal ignition timing control is executed, and the routine exits.

In the normal ignition timing control, an optimum ignition timing is set by referring to a map with interpolation calculation based on the engine speed Ne and the engine load Lo, or a fixed ignition timing set in advance (for example, BTDC 10 ° CA). And outputs an ignition command signal to the ignition drive circuit 21 when the crank angle reaches the set ignition timing. Then
An ignition signal is output from the ignition drive circuit 21 to the ignition plug 16.

As described above, when the engine operation region is in the low-speed and low-load region I, the exhaust port 12a is throttled by the exhaust control valve 17, so that scavenging can be performed at a relatively high flow rate, and good scavenging can be achieved. Not only efficiency is obtained, but also because the scavenging flow is relatively fast, good stratified combustion can be obtained by the vortex generated in the compression stroke.

On the other hand, when the self-ignition control combustion mode is selected as the combustion mode, the self-ignition control combustion mode routine shown in FIG. 5 is executed. In this routine, first, in step S21, the engine speed Ne and the engine load Lo are determined.
Based on the above, a map (not shown) is referred to with interpolation calculation to set the opening ratio of the exhaust port 12a, and a drive signal for achieving this opening ratio is output to the exhaust control actuator 20. Then, the exhaust control actuator 20 rotates the exhaust control valve 17, sets the opening of the exhaust control valve 17, and opens the exhaust port 12a to a predetermined value.

In this map, based on the engine speed Ne and the engine load Lo, the self-ignition is performed at the most preferable timing, and the exhaust port 12a of the exhaust port 12a at which the residual gas concentration at which the stable active hot atmosphere combustion can be obtained is obtained. The aperture ratio is obtained from experiments and stored. The opening ratio of the exhaust port 12a set with reference to this map is:
This value is narrower than the opening ratio described in the map referred to during low-speed low-load operation.

Then, the process proceeds to a step S22, wherein the compression stroke second-half injection control is executed. In the latter half of the compression stroke injection control, the fuel injection timing from the in-cylinder injector 15 is set so as to self-ignite at the optimum timing in the cylinder.
Based on o, the injection timing is set by referring to a map, and when a predetermined crank angle is reached, an injection start signal is output to the injector drive circuit 22.

Then, fuel is injected from the in-cylinder injector 15 into the cylinder at an optimal timing, and stable active hot atmosphere combustion by self-ignition is obtained.

Thereafter, the process proceeds to step S23, in which ignition cut control is performed, and the routine exits. This ignition cut control prohibits the output of an ignition signal to the ignition drive circuit 21 of the cylinder to be injected.

As described above, when the operation region is in the medium load region II, by setting the combustion mode to the self-ignition combustion control mode, it is possible to obtain stable combustion while suppressing the amount of NOx emission.

When the uniform combustion mode is selected as the combustion mode, the uniform combustion mode shown in FIG. 6 is executed.

In this routine, first, at step S31
To the exhaust control actuator 20 and the exhaust control valve 1
A drive signal for fully opening the valve 7 is output, and the exhaust control valve 17 is fully opened. Then, the exhaust control valve 17 is set to the exhaust port 1
2a is immersed in a concave groove 18 formed in the upper part of the passage,
The opening ratio of the exhaust port 12a becomes 100%, and the exhaust port 12a is opened at an early timing (see FIG. 8).

Next, the routine proceeds to step S32, where the compression stroke first half injection control is executed. In the first half of the compression stroke injection control, the mixing of the fuel injected from the in-cylinder injector 15 and fresh air is promoted, and the homogenized fuel mixture is used.
In order to obtain good uniform combustion, the fuel injection timing is set at the early stage of the compression stroke, and an injection start signal is output to the injector drive circuit 22 when a predetermined crank angle is reached.

Thereafter, the routine proceeds to step S33, executes normal ignition timing control, and exits the routine. In this normal ignition timing control, the same processing as that in step S13 in FIG. 4 is performed, and thus the description is omitted.

As described above, when the operation region is in the high load region III, by setting the combustion mode to the uniform combustion mode, the combustion under the high load operation is stabilized, and a good engine output can be obtained.

As described above, according to the present embodiment, the operation region is divided, the stratified combustion mode is selected in the low-speed low-load region I, and the self-ignition combustion control mode is selected in the middle-load region II. By selecting the optimal combustion mode in each of the operation regions I, II, and III, such as selecting the uniform combustion mode in the load region III, stable combustion can be obtained in all operation regions, and low fuel consumption and exhaust emissions can be achieved. Reduction and improvement in drivability can be realized.

FIG. 9 shows a uniform combustion mode routine according to the second embodiment of the present invention. In the present embodiment, when the uniform combustion mode is selected as the combustion mode when the operation region is in the high load region III, the opening ratio of the exhaust port 12a is switched according to the engine rotation speed Ne. . This embodiment is different from the first embodiment in FIG.
Is adopted in place of the uniform combustion mode shown in FIG. 7, and the other points are the same as those in the first embodiment.

In this routine, first, at step S41
The engine rotation speed Ne and the low rotation determination value Nl (about 30
00 rpm), and when it is determined that the rotation speed is low (Ne ≦ N1), the process proceeds to step S42, where the exhaust control valve 17 is opened to the exhaust control actuator 20 (opening ratio 40).
(Up to 60%) is output, the exhaust control valve 17 is opened midway, and the opening timing of the exhaust port 12a is slightly retarded.

On the other hand, when it is determined that the rotation speed is Ne> Nl, the process branches to step S43, and the exhaust control valve 17 is fully opened (opening ratio 100
%), The exhaust control valve 17 is fully opened, and the opening timing of the exhaust port 12a is advanced.

Then, the process proceeds to step S44, in which the fuel injection timing is set to the first half of the compression stroke and the normal ignition timing control is performed in steps S44 and S45, similarly to steps S32 and S33 shown in FIG. 6 of the first embodiment. Do,
Exit the routine.

As described above, in the present embodiment, when the uniform combustion mode is selected as the combustion mode in the high load region III, the opening ratio of the exhaust port 12a is changed to the engine rotation speed N
When e is low, the exhaust timing is retarded by decreasing it, so that the actual expansion ratio is increased, and the torque in the low rotation speed region can be improved by increasing the effective stroke.

As a result, the controllability of the exhaust control valve 17 is
Although it is slightly more complicated than the embodiment, not only can stable combustion without misfire be obtained in the entire operation range, but also the full load output is improved in the entire rotation speed range, and good operability is obtained. be able to.

FIGS. 10 and 11 show a third embodiment of the present invention. In the present embodiment, transition regions IV and V are provided on the low-speed low-load region I side and the high-load region III of the medium load region II, respectively, and when the operation region is in the transition regions IV and V, the fuel injection is performed. The timing is set so as to be close to the fuel injection timing set in the adjacent region I or III within a self-ignitable range.

That is, in the self-ignition control combustion mode routine shown in FIG. 10, first, in step S51, as in step S21 shown in FIG. 5 of the first embodiment, based on the engine speed Ne and the engine load Lo, The opening degree of the exhaust control valve 17 (the opening ratio of the exhaust port 12a) is set.

Next, the process proceeds to step S52, and in this step S52 and the next step S53, it is checked whether or not the operating state of the engine is in any of the transition regions IV and V.
If it does not belong to any of the areas, the process proceeds to step S54, and in steps S54 and S55, FIG.
As in steps S22 and S23, the fuel injection timing is set in the latter half of the compression stroke, ignition cut control is performed, and the routine exits.

On the other hand, if it is determined in step S52 that the current state is in the transition region IV, the process branches to step S56, executes transition region IV injection control, and exits the routine.

In the transition region IV injection control, as the fuel injection timing approaches the low-speed low-load region I, the self-ignition occurs with respect to the fuel injection timing set in the low-speed low-load region I (the latter half of the compression stroke injection control). Control is performed such that the fuel injection timing is gradually approached as much as possible, that is, the fuel injection timing is gradually retarded.

If it is determined in step S53 that the transition region is V, the process branches to step S57, executes transition region V injection control, and exits the routine.

In the transition region V injection control, as the fuel injection timing approaches the high load region III, the high load region III
The fuel injection timing (the first half of the compression stroke injection control), which is set in step (1), is controlled so as to gradually approach the self-ignitionable range, that is, to gradually advance the fuel injection timing.

As described above, in this embodiment, when the operating state of the engine is in the transition region IV or V of the medium load region II, the fuel injection timing is set in the low rotation low load region I or the high load region V. Control is performed so that the fuel injection timing is gradually approached within the range where self-ignition is possible.
In the transition region IV, the combustion mode can be smoothly shifted from the self-ignition control combustion mode to the stratified combustion mode. In the transition zone V, the combustion mode can be smoothly shifted from the self-ignition control combustion mode to the uniform combustion mode. it can. As a result, good drivability can be obtained.

[0065]

As described above, according to the present invention,
Since the optimum combustion mode is selected according to the operating state of the engine, not only can stable combustion be obtained in a wide operating range, but also NOx emissions can be reduced, and low fuel consumption can be achieved. Can be realized.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a spark ignition type two-stroke engine according to a first embodiment.

FIG. 2 is a perspective view of the exhaust control valve.

FIG. 3 is a flowchart showing a combustion region determination routine.

FIG. 4 is a flowchart showing a stratified combustion mode routine;

FIG. 5 is a flowchart showing a self-ignition control combustion mode.

FIG. 6 is a flowchart showing a uniform combustion mode.

FIG. 7 is an explanatory diagram showing a combustion mode for each engine operation region.

FIG. 8 is a characteristic diagram showing a relationship between an exhaust port opening ratio and exhaust timing.

FIG. 9 is a flowchart showing a uniform combustion mode according to a second embodiment.

FIG. 10 is a flowchart showing a self-ignition combustion control mode according to a third embodiment.

FIG. 11 is an explanatory diagram showing a combustion mode for each engine operation region.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Spark ignition type 2 cycle engine 15 In-cylinder injector 16 Spark plug 17 Exhaust control valve Lo Engine load Ne Engine speed I Low rotation low load region II Medium load region III High load region V, IV transition region

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Claims (3)

[Claims] 1. A two-stroke engine including an in-cylinder injector, an exhaust control valve for variably setting exhaust timing, and a spark plug, wherein an operating range is determined based on at least an engine speed and an engine load. Determination means; and combustion mode switching means for switching the combustion mode in accordance with the operation range, wherein the combustion mode switching means sets the fuel injection timing in the latter half of the compression stroke when the operation range is in the low rotation and low load range. By operating the exhaust control valve to delay the exhaust timing, output an ignition signal to the ignition plug to perform stratified combustion by spark ignition, and set the fuel injection timing to the compression stroke when the operation region is a medium load region. At the same time, the exhaust timing of the exhaust control valve is set based on at least the engine speed and the engine load. When the ignition control combustion is performed and the operation region is in the high load region, the fuel injection timing is set in the first half of the compression stroke, the exhaust control valve is operated in the fully open direction, and an ignition signal is output to the ignition plug to generate spark ignition. A fuel control device for a two-cycle engine, which performs uniform combustion. 2. The combustion mode switching means fully opens the exhaust control valve when the engine speed is high when the operating range is in a high load range, and closes the exhaust control valve when the engine speed is low. The combustion control device for a two-stroke engine according to claim 1, wherein the combustion control device is operated in a valve direction. 3. A transition region is provided on each of the low-speed and low-load region side and the high-load region side of the medium-load region, and in the combustion mode switching means, the operation region is on the low-speed and low load region side. The fuel injection timing is retarded within the auto-ignition possible range as the vehicle approaches the low-speed low-load region, and the fuel injection timing is self-ignitable as the vehicle approaches the high-load region during the high-load side transition region. 3. The method according to claim 1, wherein the angle is advanced.
Cycle engine combustion control device.