JPH03281965A - Control device for two-cycle engine - Google Patents

Abstract

PURPOSE:To smoothly shift torque characteristics as combustion is changed by providing a mixed combustion zone at a switching point between stratified combustion and uniform combustion in an engine where fuel injection for stratified combustion is controlled at the time of low and intermediate loading, and fuel injection for uniform combustion is controlled at the time of high loading. CONSTITUTION:Three sections are provided, they are a fuel injection timing determination section 54 which inputs both engine revolution Ne by an engine revolution computing section 51, and the quantity of fuel injection Gf by a fuel injection pulse duration computing section 53, an ignition timing determination section 55 and a combustion mode judging section 56. In the combustion mode judging section 56, a switching point between stratified combustion and uniform combustion is set in advance by the map of Ne - Gf, and a mixed combustion zone of both of them is set at a switching point Po where a torque curve TL for stratified combustion at low speed and intermediate loading and a torque curve TH for uniform combustion at high loading are over- lapped. In mixed combustion, fuel is injected 2 times, that is, at the early and later stages of compression stroke, and furthermore, the quantity of fuel injection by an injector 10 is controlled to be great at the early stage as loading is increased, and is also controlled to be less at the later stage.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a control device that controls the fuel injection amount and combustion method according to operating conditions in a two-stroke engine for a vehicle. Concerning measures to smooth engine power characteristics.

[Conventional technology]

Generally, an injector is installed in the combustion chamber of a two-stroke vehicle engine, and fuel is injected directly into the cylinder at high pressure at least during the compression stroke after the exhaust hole is closed and before ignition.

The applicant has already proposed a system in which the timing of fuel injection is set early to achieve uniform combustion, and the timing is set late to achieve stratified combustion.

In such a combustion method switching type, the engine output torques for stratified combustion and uniform combustion are set in advance using a map so as to match each other at the switching point, and the torque is changed continuously. However, for example, atmospheric conditions such as atmospheric pressure, temperature,
If the actual output torque characteristics of each combustion method differ due to significant changes in humidity, etc. or changes over time, it is possible that the torque at the switching point will be stepped, giving a sense of discomfort.

Therefore, it is desirable to take measures in advance to always maintain smooth characteristics at the combustion method switching point against changes in atmospheric conditions, aging, etc.

Therefore, conventionally, in the above-mentioned combustion method switching type engine,
Regarding measures for smoothing the output characteristics at the switching point, for example, there is a prior art technique disclosed in Japanese Patent Laid-Open No. 60-36719. Here, the intake air density is detected, and if the intake air density decreases, the switching point from stratified charge combustion to uniform combustion is shifted to the low negative side, and if the intake air density increases, the switching point is shifted to the high load side. It has been shown that there is a transition to

[Problem to be solved by the invention]

By the way, the prior art described above requires a sensor for detecting intake air density, and cannot deal with changes over time other than intake air density. Furthermore, since the method changes the switching point based on two types of combustion methods, even if combustion is improved, stepped torque changes remain. Furthermore, switching the combustion method greatly affects the quality of combustion in the case of a two-stroke engine, and since it is optimally set in advance, changing this switching point may disrupt the overall combustion pattern and cause undesirable effects. There's a problem.

The present invention has been made in view of these points, and its purpose is to maintain the overall combustion method switching conditions even if the actual output torque characteristics change due to various conditions in the combustion method switching system. To provide a control device for a two-stroke engine that can always smoothly change torque without changing it.

[Means to solve the problem]

In order to achieve the above object, the two-stroke engine control device of the present invention determines the combustion method based on operating conditions, controls fuel injection and ignition timing for stratified combustion at least at low and medium loads, and controls uniform combustion at high loads. In the control system of a two-stroke engine that controls fuel injection and ignition timing, a mixed combustion region is provided at the switching point between stratified combustion and uniform combustion, and mixed combustion from one of the stratified combustion method and uniform combustion method to the other. This is a method of transition.

[For production]

Based on the above configuration, during low and medium load operation of a 2-stroke engine, slow fuel injection in the latter half of compression allows stable stratified combustion even with a small amount of fuel, and at high loads,
By injecting a large amount of fuel early at the beginning of compression, uniform combustion with high air utilization efficiency is achieved. At the switching point between the two combustion methods, by switching to a mixed combustion method, the torque characteristics change smoothly with the combustion state, and the torque characteristics change smoothly even in the case of atmospheric conditions or changes over time.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

In FIG. 2, the overall configuration of a two-stroke direct injection gasoline engine is described. Reference numeral 1 is the main body of the two-stroke engine, in which a piston 3 is inserted into a cylinder 2 so as to be able to reciprocate, and a crank in a crank chamber 4 is inserted. The piston 3 is connected by a connecting rod 6 provided eccentrically with respect to the shaft 5, and a balancer 7 is provided on the crankshaft 5 so as to offset the reciprocating inertia force of the piston 3. The combustion chamber 8 has an offset, wedge, or semicylindrical shape, and a high-pressure single-fluid injector IO is located at a high position near the center top.
It is installed so that it is open for the ON time (pulse width) of the pulse signal. Further, the spark plug 9 is installed at an angle so that the electrode 9a is located directly below the injector 10 in the injection direction.

The distance between the injector lO and the electrode bulb 9a is set in consideration of the cone-shaped fuel spray that is injected just before ignition at low/medium loads. That is, when the distance is short, atomization is insufficient, and when the distance is long, the spray diffuses, so that between the two, the rear end of the spray can be ignited and stratified combustion can occur.

In addition, since the injector IO is located approximately on the center line of the cylinder 2, a large amount of fuel injected at an early stage under high load quickly diffuses throughout the cylinder 2 from its internal center and is uniformly premixed. This makes it possible to burn evenly.

The cylinder 2 has an exhaust port 11 opened and closed at a predetermined timing by the piston 3, and an exhaust pipe from the exhaust port 11! 2. Catalyst device 13. A muffler I4 is provided.

Here, an exhaust rotary valve 15 is installed in the exhaust port 11, and is connected to the crankshaft 5 by a belt means 16 to individually determine opening and closing of the exhaust port 11. That is, when the piston 3 rises, the exhaust port 11 is closed early by the exhaust rotary valve 15 on the bottom dead center side, making it possible to set the timing of fuel injection early in the uniform combustion method under high load.

Further, in the cylinder 2, a scavenging boat 17, which is similarly opened and closed at a predetermined timing by the piston 3, is provided at a position shifted by 180 degrees and about 90 degrees in the circumferential direction with respect to the exhaust port 11. and scavenging boat 1
The air supply pipe 18 of No. 7 has an air cleaner 19. A throttle valve 20 is provided which opens according to the opening degree of the accelerator, and a scavenging pump 21 is connected to the crankshaft 5 by a belt means 22 downstream of the throttle valve 20, and is constantly driven by the engine power to generate scavenging pressure. established in here,
The throttle valve 20 is set to open slightly even when the accelerator is fully closed, allowing suction by the scavenging pump 21, and when this play range is exceeded, the throttle valve 20 opens according to the accelerator opening to control the amount of air. The scavenging pressure of air alone is used to forcefully scavenge air, supplying air with high filling efficiency.

Regarding the high pressure fuel system of the injector 10, the fuel tank 30 is connected to the filter 31. Fuel pump 32. Fuel pressure regulator 38. Accumulator 3 absorbs pressure fluctuations
4, and a return passage 3B from the fuel pressure regulator 33 communicates with the fuel tank 30. The fuel pressure regulator 33 then adjusts the return of high-pressure fuel from the fuel pump 82 to control the fuel pressure of the injector IO. Here, when the amount of charged air is small under low load, the fuel pressure is low, and when the amount of filled air increases due to an increase in load, the fuel pressure is also controlled to be high.

Next, in FIG. 1, a fuel injection 9 ignition timing control system will be described as an electronic control system.

First, the crank angle sensor 40. It has a cylinder discrimination sensor 41 and an accelerator opening sensor 42, and these sensor signals are input to a control unit 50. The control unit 50 has an engine rotation speed calculating section 51 that manually calculates the crank angle θ of the crank angle sensor 40, and calculates the engine rotation speed No. based on the time of the crank pulse and the like.

Crank angle sensor 40. The signal from the cylinder discrimination sensor 41 is input to a crank position detection section 52, which detects the reference position before the top dead center of each cylinder.

Further, the fuel injection pulse width calculation unit 5 receives the engine rotation speed Ne and the accelerator opening degree φ of the accelerator opening degree sensor 42.
3, and a map search is performed for the fuel injection amount Gf according to each operating condition based on the engine speed No. and the accelerator opening degree φ.

Then, the fuel injection pulse width Ti is calculated by adding -Gf+Ts to Ti- by adding the voltage correction numerator s to the coefficient corresponding to the fuel pressure.

The engine rotational speed Ne and the fuel injection amount Gf are inputted to a fuel injection timing determining section 541, an ignition timing determining section 55, and further inputted to a combustion method determining section 56. In the combustion method determining section 56, a switching point between the stratified combustion method and the uniform combustion method is set in advance using a map of NeGf.

Here, in the present invention, as shown in FIG.
A switching point P where the torque curve T for medium-load stratified combustion and the torque curve T for high-load uniform combustion overlap. In this step, a mixed combustion region for both is set. and a switching point P where the torque curve TM in the mixed combustion region is provided straddling the torque curve Tl of stratified combustion and the torque curve T0 of uniform combustion, and the torque curve T and TM coincide;
A switching point P2 is set where the torque curve T&4 and To match. Therefore, we have fuel injection amount setting values Gf+ and Gf2 corresponding to the switching points p, , p2, and these and the fuel injection amount f
f1Gf, stratified combustion is determined when Gf<Gf, and uniform combustion is determined when Gf≧Gf2, and these combustion method signals are sent to the fuel injection timing determining unit 541.
The signal is input to the ignition timing determining section 55.

Further, mixed combustion is determined when Gf, ≦Gf<Gf2.

The fuel injection timing determining unit 54 has a map of fuel injection timings θlE and θis for each stratified and uniform combustion method based on the engine speed Ne and the fuel injection amount Gf, and in the case of stratified combustion, the fuel injection timing of the stratified combustion method is determined. In the case of uniform combustion, θILE is output by searching a map for the fuel injection timing θIS of the uniform combustion method. Here, in stratified charge combustion, it is necessary to end injection with a predetermined atomization time left immediately before ignition, so in this case, injection end timing θIIE is set. On the other hand, in uniform combustion,
Since it is necessary to start the injection early after the exhaust gas closes, the injection start timing θIS is set in this case. The ignition timing determining unit 55 also determines the engine speed Ne and the fuel injection amount G.
It has a map of ignition timing θg for each combustion method based on It has become.

Fuel injection pulse width Ti and fuel injection timing θiE or θ1
s is input manually to the fuel injection timing setting section 57, and a fuel injection signal corresponding to the fuel injection pulse width Ti, fuel injection timing θIF, or θIS is sent to the injector via the drive section 58 based on the crank angle reference position. Output to 0. The ignition timing θg is manually input to the ignition timing setting section 59, and ignition signals such as ignition timing and dwell time are outputted to the spark plug 9 via the drive section 60 based on the crank angle reference position. It is composed of

Next, we will discuss the control system for the mixed combustion method.

In this mixed combustion, fuel is injected at least twice, at the beginning and the end of the compression stroke, and as the load increases, the initial (front) fuel injection amount is increased and the late (rear) fuel injection amount is decreased. (The engine speed Ne, fuel injection fiGf, and fuel injection pulse width Ti are input to the two-time fuel injection amount calculation section 61. Two injections are performed with a pulse width Ti and a post-fuel injection pulse width Ti2.As shown in Fig. 3(b), the pre-fuel injection pulse width Tt1m at the start of mixed combustion is uniform. The required minimum fuel injection amount for lean combustion only, and the necessary minimum fuel injection amount for stratified combustion only for the after-fuel injection pulse width T i 2 at P2 when the mixture combustion shifts from mixed combustion to uniform combustion, respectively. In addition, the engine rotation speed Ne, the fuel injection amount Gf,
Mixed combustion method signal and old fuel injection pulse width Ti,
, the post-fuel injection pulse width Ti2 is input to the mixed combustion fuel injection timing determination unit 62, and the uniform fuel injection timing θIs is used to determine the fuel injection timing θ1 according to the pre-fuel injection pulse width Ti1.
1 and the stratified fuel injection timing θICE, the fuel injection timing θ12 corresponding to the post-fuel injection pulse width Ti2 is determined, and this signal is manually input to the fuel injection timing setting section 57.

Regarding the ignition timing in the mixed combustion method, for example, the ignition timing determining section 55 has a dedicated ignition timing θg, searches this map, and outputs an ignition timing signal.

Next, let's talk about the operation of the control device for a two-stroke engine with this configuration.

First, during engine operation, the throttle valve 20 opens according to the accelerator opening and air is sucked into the scavenging pump 21 to generate a predetermined scavenging pressure.When the piston 3 descends, the exhaust boat 11 opens, and then the scavenging boat 17 is also opened, this pressurized air flows into the interior of the cylinder 2 from the scavenging boat I7. This vertical swirl flow of the supply air pushes out the residual gas in the cylinder 2 from the exhaust boat 11, and performs a scavenging action to fill the supply air with high filling efficiency. On the other hand, piston 3
When the engine starts to rise from the bottom dead center, the exhaust rotary valve 15 closes and scavenging ends, making it possible to inject fuel without fuel blow-through, and then the scavenging boat 17 closes and the compression stroke begins. . On the other hand, at this time, in the high-pressure fuel system of the injector IO, the fuel pressure is controlled by the fuel pressure regulator 33 according to the operating conditions, and this fuel is supplied to the injector I.
Guided by O.

Further, the fuel injection pulse width calculation section 53 of the control unit 50
Then, the fuel injection amount Gf is searched on a map according to the engine speed No. and the accelerator opening degree φ, and the fuel injection pulse width Ti is further calculated based on the fuel injection amount Gf. At the same time, the combustion method determining section 5B determines the combustion method, and the map of the fuel injection timing determining section 541 and the ignition timing determining section 55 is selected based on this determination.

Therefore, at low/medium load, the fuel injection timing determining section 54 selects the stratified combustion map, and thereby the fuel injection timing θ
IB is determined to be close to the ignition timing, and the ignition timing determining section 55
However, the ignition timing θg is determined relatively close to top dead center by the stratified combustion map. Then, the injection signal based on the fuel injection pulse width Ti and the fuel injection timing θIP is output to the injector IO.
As shown in FIG. 4(a), a relatively small amount of fuel is injected toward the electrode 9a of the spark plug 9 in the late stage of compression, and immediately after that, an ignition signal based on the ignition timing θg is sent to the spark plug. Output to 9. For this reason, before the cone-shaped fuel spray diffuses, it is ignited by the electrode 9a at its rear end, resulting in stratified combustion.In this way, even if the fuel is very small compared to the amount of air, a rich mixture of fuel can be effectively used. Stable combustion is achieved using this method.

Subsequently, when the combustion method determining section 56 determines mixed combustion at the switching point of the combustion method from medium load to high load, the double fuel injection amount calculating section 61 executes two fuel injections, front and rear. As shown in FIG. 4(b), the fuel injection pulse widths Ti, Ti2 are divided into two, and the mixed combustion fuel injection timing determination unit 62 determines the fuel injection timings θiI+θ12 in the early and late stages of compression. Fuel is injected twice. Therefore, as shown in FIG. 5(a), the minimum necessary fuel F, which burns lean at least uniformly at the beginning of compression, is
is injected from the injector 10, and when the fuel injection is completed as shown in FIG. 5(b), the fuel F1 is diffused and mixed uniformly as the piston 3 rises, as shown in FIG. 5(c). . Then, as shown in FIG. 5(d), a small amount of fuel F is again injected into the homogeneous mixture A, and immediately after this, the fifth
As shown in Figure (e), the spark plug 9 is connected to the spray of fuel F2.
is ignited. Therefore, the mixture A of the first fuel F burns uniformly using the second fuel F2 as the ignition source, resulting in a combustion state in which stratified and homogeneous combustion is mixed. As the load increases, the pre-fuel injection amount is increased as shown in Figure 3(b).
The amount of post-fuel injection is reduced, and ultimately the amount of post-fuel injection is set to the minimum necessary amount for combustion only through stratification.

Next, when the load is high, when the fuel injection amount Gf increases, a map for the uniform combustion method is selected by the fuel injection timing determining section 54 and the ignition timing determining section 55. Therefore, the fuel injection timing θIs is set early after the exhaust rotary valve 15 is closed, and the ignition timing θg
is determined to be the optimal value, and therefore, as shown in Fig. 4 (C
), a large amount of fuel is injected into the cylinder 2 from the injector IO at the beginning of compression, and the fuel and air are sufficiently mixed during compression. After this uniform mixing, the spark plug 9 ignites the mixture, resulting in uniform combustion with a high air utilization rate, increasing engine output. In this case,
As shown in FIG. 3(a), the torque characteristic is determined by the uniform combustion torque curve T via the mixed combustion torque curve TM described above.
+ White color will transition smoothly.

It goes without saying that even in the case of a decrease in engine output, the combustion method is switched from the homogeneous combustion method to the stratified combustion method via mixing.

In this way, mixed combustion between stratified combustion and uniform combustion is present at the switching point, thereby smoothing the torque change at the switching point. Furthermore, even if one or both of the actual stratified and uniform combustion conditions changes due to atmospheric conditions or changes over time, the transition between the two will be smooth.

〔Effect of the invention〕

As described above, according to the present invention, in a two-cycle direct injection engine that switches between the stratified combustion method and the uniform combustion method, a mixed combustion region of both is provided at the switching point, so that the combustion at the switching point The state and torque characteristics change smoothly,
Especially atmospheric conditions.

It is possible to reduce steps in torque due to aging.

Furthermore, in mixed combustion, fuel is injected twice and combustion is controlled to have a stratified and uniform tendency, so the torque curve at the switching point can be set to change smoothly, which is highly effective.

Further, since a dedicated sensor is not required and the switching point of the combustion method is fixed, the overall combustion form is always constant and an optimum combustion state can be maintained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an electronic control system showing an embodiment of a control device for a two-stroke engine according to the present invention, and FIG.
Figure 3 (a) is a diagram showing the overall configuration of a cycle engine; Figure 3 (a) is a torque characteristic diagram for stratified, mixed, and uniform combustion methods; Figure 3 (b) is a map showing the setting of the amount of fuel injected twice in mixed combustion. Figures 4(a) to 4(c) show fuel injection for each combustion method. Figures 5(a) to 5(o) are diagrams showing the timing of ignition timing, and Figures 5(a) to 5(o) are diagrams showing states of fuel injection, etc. in the mixed combustion system. l... 2-stroke engine body, 9... spark plug, 10... injector, 50... control unit,
53...Fuel injection pulse width calculation unit, 54...Fuel injection timing determination unit, 55...Ignition timing determination unit, 56...
Combustion method determination section, 61... Twice fuel injection amount calculation section, 6
2...Mixed combustion fuel injection timing determination part diagram (a) Gf. f 2 Fuel injection amount Gf- (Pl) (P2) Fig. 5

Claims (3)

[Claims] (1) A two-stroke engine control system that determines the combustion method based on operating conditions, and controls fuel injection and ignition timing for stratified combustion at least at low and medium loads, and controls fuel injection and ignition timing for uniform combustion at high loads. A two-stroke engine characterized in that a mixed combustion region is provided at the switching point between stratified combustion and uniform combustion, and a transition is made from one of the stratified combustion method and the uniform combustion method to the other through the mixed combustion method. Control device. (2) The control system for the mixed combustion method uses a combustion method determining means that determines the mixed combustion region, a double fuel injection amount calculation means that divides the fuel injection amount into two before and after, and stratification and uniform fuel injection timing. 2. The control device for a two-stroke engine according to claim 1, further comprising a mixed combustion fuel injection timing determining means for determining fuel injection timing according to two fuel injection amounts before and after. (3) The two-cycle engine according to claim 1, wherein the second fuel injection amount calculation means sets the pre-fuel injection amount using an increasing function and the post-fuel injection amount using a decreasing function depending on the load. control device.