JP2806507B2 - Fuel injection control device for two-cycle engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for a two-stroke engine in which fuel is directly injected into a cylinder every one revolution of a crankshaft, and particularly, when a spark plug is hot. The present invention relates to a fuel injection control device capable of preventing knocking due to preignition and ignition of end gas that occur as points by correcting fuel injection timing.

2. Description of the Related Art A two-stroke engine equipped with an air fuel injection device for directly injecting fuel into a cylinder together with compressed air has attracted attention recently. In this type of engine, for example, in a low-speed low-load operation range, fuel is supplied to a partial area of a combustion chamber in a cloud form, and the fuel cloud is ignited, so-called stratified combustion is performed. Therefore, the spark plug is generally arranged such that its electrode portion protrudes into the cylinder in order to confirm the ignition of the cloud.

[Problems to be solved by the invention]

However, when the spark plug is protruded into the cylinder as described above, the temperature of the electrode of the spark plug tends to become high during operation, so that there is a problem that the electrode portion becomes a hot point and preignition is apt to occur.

Further, in an operation region in which the injected fuel is widely diffused into the combustion chamber, that is, in an operation region where so-called premixed combustion is performed, the flame by spark ignition adiabatically compresses the end gas located at the end of the combustion chamber. Become. Then, such end gas ignites and burns at a time when the temperature becomes equal to or higher than a predetermined value, and a sharp pressure non-equilibrium state, that is, so-called knocking occurs due to the rapid combustion.

An object of the present invention is to provide a fuel injection control device for a two-stroke engine that can prevent the above-mentioned preignition and knocking.

[Means for solving the problem]

The present invention includes a combustion injection device that directly injects fuel into a cylinder for each rotation of a crankshaft, and a spark plug that ignites fuel injected from the injection device, wherein a piston moves from a top dead center to a bottom dead center. The exhaust port and the scavenging port provided in the combustion chamber are sequentially opened during the moving down stroke, and after closing the scavenging port during the up stroke when the piston moves to the bottom dead center or the top dead center, In a two-cycle engine having an exhaust port closed, a fuel injection control device for controlling the fuel injection timing and the injection period, wherein detection means for detecting the occurrence of preignition or knocking;
If the detection means does not detect the occurrence of preignition or knocking, the piston closes the exhaust port from the bottom dead center during the ascent stroke when the fuel injection from the fuel injection device starts and ends. If the detection means detects the occurrence of preignition or knocking, the injection is delayed at least until the piston closes the exhaust port during the ascent stroke of the fuel. And timing correction means.

Here, in the present invention, delaying at least the injection end timing of the fuel means that both the injection start timing and the end timing are delayed, that is, when the entire injection is delayed, and only the end timing is delayed while the start timing is unchanged. The purpose is to include both cases.

[Action]

According to the fuel injection control device of the present invention, when the detection means for detecting the occurrence of preignition or knocking does not detect the occurrence of preignition or knocking, the fuel injection start timing and the injection of the fuel from the fuel injection device are performed. Since the end time is during the period from the bottom dead center of the piston to the closing of the exhaust port during the ascent stroke, the fuel injection is terminated before the piston closes the exhaust port and enters the compression stroke. Premixed combustion.

In such a case, when preignition or knocking occurs, at least the fuel injection end timing is retarded until after the piston closes the exhaust port during the rising stroke, so that the cylinder internal pressure increases. As a result, fuel is injected also in the latter half of the compression stroke in which preignition is likely to occur, and the spark plug is cooled by the injected fuel, whereby a temperature rise near the electrode is suppressed, and preignition hardly occurs.

Further, since the fuel injection end timing is delayed, the fuel is injected when the pressure in the cylinder increases. Therefore, the difference between the pressure in the cylinder and the fuel injection pressure becomes smaller, and the penetration force of the spray becomes weaker, making it difficult for the fuel to diffuse in the cylinder, thereby reducing the amount of end gas generated and consequently suppressing knocking. Is done.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

1 to 5 are views for explaining an air fuel injection control device of an air fuel injection type two-stroke engine according to one embodiment of the present invention. FIG. 1 is a configuration diagram thereof, and FIG. FIG. 3 is a sectional side view of an air fuel injection type two-stroke engine, FIG. 4 is a crank angle-cylinder pressure characteristic diagram for explaining a preignition and knocking state, and FIG. It is a flowchart figure for demonstrating operation | movement.

In the figure, reference numeral 1 denotes a water-cooled two-cycle parallel three-cylinder engine configured to directly inject air and fuel into a cylinder.
The three cylinders 3a have a structure in which a cylinder body 3 formed in parallel in the crankshaft direction is mounted and fixed by bolting, and a cylinder head 4 is fixed on the cylinder body 3 by fastening bolts 4b. Here, a load washer type pressure sensor 23 is mounted on the fastening bolt 4b, and detects a pressure fluctuation in the combustion chamber 17 described later.

At a portion corresponding to each of the cylinders 3a on the lower surface of the cylinder head 4, a combustion recess 4a that forms a combustion chamber 17 with a recess 5a formed on an upper surface of the piston 5 inserted into the cylinder 3a is formed. The electrode part 18a of the ignition plug 18 is inserted into the combustion chamber 17. An air fuel injection device 19 is mounted on an upper portion of each combustion chamber 17 on the upper surface of the cylinder head 4. Each of the air fuel injection devices 19 mainly includes an injection body 20 inserted and fixed to the cylinder head 4 and a valve mechanism 21 that opens and closes an air chamber and an injection port of a fuel chamber formed in the injection body 20 with a valve body. And a fuel injection valve 22 mounted on the rear side of the outer wall of the injection body 20 and supplying fuel to the fuel chamber. 14a is a fuel rail for supplying fuel, and 14b is an air rail for supplying compressed air. While the valve mechanism 21 opens the injection port with the valve element, the compressed air in the air chamber is injected into the cylinder and the fuel injection valve is opened.
Fuel from 22 is injected into the cylinder.

Each piston 5 is a crank arm 6a of a crank shaft 6.
The crank arm 6a is located in the crank chamber 2a. An outside air inlet 2b is formed on the back side of each crank chamber 2a. Each intake port 2b is provided with a reed valve 7 for opening and closing the intake port 2b, and is further connected to an intake manifold 8.

Further, each branch of an exhaust pipe 16 is connected to an exhaust port 3b formed above the intake port 2b of the cylinder body 3, and the exhaust pipe 16 is bent downward after merging into one. And extend to the rear of the vehicle.

Reference numeral 24 denotes an injection timing, an injection period, etc. of air and fuel by the valve mechanism 21 and the fuel injection valve 22, and an ignition device 25.
ECU that controls the ignition timing of the ECU. The ECU 25 receives a pressure signal a from a pressure sensor 23 attached to the fastening bolt 4b and a signal b indicating an engine operation state such as an accelerator opening, an engine rotation speed, a crank angle, etc. An air injection control signal A for controlling the period is output to the valve mechanism 21, a fuel injection control signal B for controlling the fuel injection timing and the injection period is output to the fuel injection valve 22, and an ignition timing control signal C is output to the ignition device 25. Output to

Here, the ECU 24 determines the occurrence of pre-ignition or knocking based on the pressure waveform from the pressure sensor 23. For example, in a normal operation state (see FIG. 4 (a)) in which the cylinder pressure p1 reaches a maximum value from the top dead center (TDC) at a predetermined crank angle θ, the pressure p2 is changed to the predetermined angle θ
When the pressure reaches the maximum pressure later and then shows a pressure fluctuation at a frequency of several KHZ (see FIG. 4 (b)), it is determined that knocking has occurred, and the pressure p3 reaches the maximum pressure near the top dead center and the normal maximum pressure is reached. If the pressure is significantly higher (for example, 30kg at low load)
/ cm ² , full load 70 kg / cm ² , see FIG. 4 (c)), it is determined that preignition has occurred.

The ECU 24 also functions as a means for correcting the injection timing and the ignition timing. If it is determined that pre-ignition has occurred, the ECU 24 controls the control signals A and A to delay the air and fuel injection end timings. Corrects and outputs B. In this case, as shown in FIG. 2, for example, during a rising stroke in which the piston 5 moves from the bottom dead center BDC to the top dead center while the crankshaft 6 makes one rotation, the piston 5 connects the exhaust port from the bottom dead center BDC to the exhaust port. If pre-ignition occurs in the injection condition R1 during the period until closing, a method of delaying only the injection end timing while leaving the injection start timing as it is (R2),
Alternatively, either of the methods (R3) for delaying both the injection start timing and the end timing is adopted. Further, the larger the occurrence frequency of the preignition is, the larger the retard amount is set.

When it is determined that knocking has occurred, if the occurrence intensity and frequency of knocking are relatively small, only the timing control signal C is corrected so that the ignition timing is retarded. And the control signals A and B are corrected so that the air fuel injection end timing is retarded. In this case, any of the above methods R2 and R3 may be adopted.

Next, the operation and effect of this embodiment will be described with reference to FIG.

After the pressure signal a from the pressure sensor 23 is amplified by the amplifier circuit, a noise component is removed by a high-pass filter, and it is determined whether knocking has occurred (steps S1 to S4). If knocking has not occurred, the control signals A to C are output as they are, and operation is performed at the usual ignition timing and air fuel injection timing (step S6). On the other hand, if it is determined that knocking has occurred, only the control signal C is corrected and output according to the intensity and frequency of occurrence so that the ignition timing is retarded, or the air fuel injection is terminated. The control signals A and B are corrected and output so that the timing is retarded (steps S5 and S6).

After the noise component is removed by the low-pass filter, it is determined whether or not pre-ignition has occurred in the amplified signal (steps S7 and S8). If not, the amplified signal is operated at a normal injection timing. (Step S1
0). On the other hand, if preignition has occurred,
Control signals A and B such that the air fuel injection end timing is retarded
Is corrected and output, and the vehicle is operated in the retarded state (steps S9 and S10).

As described above, in the present embodiment, when preignition occurs, the fuel fuel injection end timing is retarded, so that fuel is injected even in the second half of the compression stroke in which the temperature of the electrode 18a of the ignition plug 18 tends to rise. That is, this fuel can cool the electrode 18a and suppress the temperature rise,
Pre-ignition can be suppressed. Here, when the method (R2) of delaying only the injection end timing is adopted, the injection time is extended and the injection amount is increased, so that the cooling effect is further improved.

Further, when knocking occurs, the injection timing of the air fuel is retarded in accordance with the intensity and frequency, so that the fuel is injected when the pressure in the cylinder increases.
Therefore, the difference between the pressure in the cylinder and the fuel injection pressure becomes smaller, and the penetration force of the spray becomes weaker, making it difficult for the fuel to diffuse in the cylinder, thereby reducing the amount of end gas generated and consequently suppressing knocking. Is done. If only the injection timing is retarded with the ignition timing unchanged, the time from the injection of the air fuel to the ignition, that is, the time during which the fuel can be diffused, is shortened, and the diffusion of the fuel is also suppressed from this point. The amount of end gas generated is reduced, and as a result, knocking is suppressed. Furthermore, since the fuel injection timing is retarded, the scavenging flow in the cylinder is attenuated, and from this point the diffusion of fuel is suppressed.

In the above embodiment, the case where the fuel is injected together with the compressed air has been described. However, the present invention can of course be applied to an engine of the type in which only the fuel is injected.

〔The invention's effect〕

As described above, according to the fuel injection control device for a two-stroke engine according to the present invention, when the detection unit that detects the occurrence of preignition or knocking does not detect the occurrence of preignition or knocking, the fuel injection device The fuel injection start timing and the injection end timing are set during the period from the bottom dead center to the closing of the exhaust port during the ascent stroke, so that the fuel is injected before the piston closes the exhaust port and enters the compression stroke. Is terminated, and the premix combustion can be reliably performed.

Then, when the detection means detects the occurrence of preignition or knocking, at least the injection end timing is retarded until after the piston closes the exhaust port during the ascent stroke, so in the late stage of the compression stroke, Fuel is also injected, the spark plug is cooled by the injected fuel, preventing the spark plug from becoming a hot point and controlling the preignition,
In addition, there is an effect that knocking can be suppressed by reducing the generation amount of end gas.

[Brief description of the drawings]

1 to 5 are views for explaining a fuel injection control device according to one embodiment of the present invention, FIG. 1 is a configuration diagram thereof, FIG. 2 is a characteristic diagram showing the fuel injection timing thereof, and FIG. 3 is a sectional side view of a two-cycle engine, FIGS. 4 (a), (b) and (c) are crank angle-cylinder pressure characteristic diagrams, respectively, and FIG. 5 is a flowchart. In the figure, 1 is a two-stroke engine, 3a is a cylinder,
18 is a spark plug, 22 is a fuel injection valve (fuel injection device), 23
Is a pressure sensor (pressure detecting means), 24 is an ECU (injection timing correcting means), and a is a detected pressure signal.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-49939 (JP, A) JP-A-60-11651 (JP, A) JP-A-56-66426 (JP, A) JP-A-57- 131825 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) F02D 41/02 F02D 41/04 F02D 41/34 F02B 25/20

Claims (1)

(57) [Claims] 1. A fuel injection device for directly injecting fuel into a cylinder for each revolution of a crankshaft, and a spark plug for igniting fuel injected from the injection device, wherein a piston is moved from a top dead center to a bottom dead center. After the exhaust port and the scavenging port provided in the combustion chamber are sequentially opened during the descending stroke to move to, and the scavenging port is closed during the ascent stroke when the piston moves from bottom dead center to top dead center, The exhaust port is closed 2
In a cycle engine, a fuel injection control device that controls the fuel injection timing and the injection period, wherein a detection unit that detects the occurrence of preignition or knocking, and the detection unit does not detect the occurrence of preignition or knocking The fuel injection from the fuel injection device, the injection start timing and the injection end timing during the period from the bottom dead center of the piston to close the exhaust port during the ascent stroke, the detection means pre-ignition or knocking Injection timing correction means for delaying at least the fuel injection end timing until after the piston closes the exhaust port during the ascent stroke when the occurrence of the fuel injection is detected. Engine fuel injection control device.