JPH0713464B2 - Two-cycle fuel injection internal combustion engine - Google Patents

Description

The present invention relates to a fuel injection type two-cycle internal combustion engine.

[Conventional technology and problems]

In a two-cycle gasoline engine, it is necessary to take a long period of communication between the intake side and the exhaust side for scavenging. Therefore, there is a problem that the fuel blowout increases and a misfire occurs or the fuel consumption rate deteriorates. Therefore, there is a two-cycle internal combustion engine in which an injector for fuel injection is provided, and the injection of the injector is selected slightly before the exhaust valve is closed to prevent blow-through of fuel. See, for example, JP-A-53-27731. However, even if the fuel injection method is adopted, misfire is likely to occur on the low load side of the engine, particularly in an extremely low load range such as idle operation. This is because scavenging is insufficient on the low rotation side and the amount of residual exhaust gas increases.

An object of the present invention is to improve the ignitability of an air-fuel mixture during extremely low load operation such as idle operation in a two-cycle engine. As prior art, Japanese Patent Laid-Open Nos. 53-27731 and 52-
See 104613, issue.

[Means for solving problems]

The two-cycle internal combustion engine of the present invention has a means for keeping the intake port closed at a low load of the engine, an injection means for simultaneously injecting fuel and air into the combustion chamber, and a combustion chamber from the intake port at a low load of the engine. Intake air amount control means for reducing the amount of air supplied to the combustion chamber, and controlling the amount of air directly injected from the injection means into the combustion chamber when the engine load is low.

〔Example〕

In FIG. 1, 10 is a cylinder block, 12 is a piston,
16 is a crankshaft, 18 is a cylinder head, 20 is a combustion chamber, 21
Is a spark plug, 22 is an intake valve, 24 is an intake port, 26 is an exhaust valve,
28 is an exhaust port. The intake port 24 is connected to an air flow meter 36 via an intake pipe 30, a mechanical supercharger 32 as a scavenging pump, and a throttle valve 34.

A mixture injection valve 38 is attached to the cylinder head 18 so as to inject the mixture directly into the combustion chamber 20. The mixture injection valve 38 is
As shown in FIG. 2, a main body 40, a needle 42, and a piezo (PZT) piezoelectric element 44 as a high-speed driving unit are the basic constituent elements. The needle 42 is configured as an open valve that is opened by popping out. needle
42 is biased upward in the figure by a spring 46. Needle 42
Form a first pressure receiving surface 48 and a second pressure receiving surface 50. First
The air pressure of the air chamber 52 acts on the pressure receiving surface 48, and the fuel pressure in the fuel chamber 54 acts on the second pressure receiving surface 50. The air pressure and the fuel pressure respectively urge the needle 42 upward in the drawing and the spring 46
When the needle 42 lifts against the
The fuel from 54 is introduced into the combustion chamber 20 as an air-fuel mixture.

The air chamber 52 communicates with an air passage 62, and high pressure air is introduced into the air passage 62 as described later. On the other hand, the fuel chamber 54 is selectively communicated with a fuel passage 68 communicating with an external fuel supply source via a valve body 66 driven by the piezoelectric element 44. The disc spring 69 generates a force to lift the valve element 66 from the valve seat 67.

The air passage 62 is connected to an intake pipe downstream of the air flow meter 36, though it is upstream of the throttle valve 34 via the air conduit 70 of FIG. 1 and an air pressurizing compressor 72 driven by a crankshaft. A bypass passage 74 that bypasses the compressor 72 is connected to the air conduit 70 and a bypass control valve 76 is installed. The bypass control valve 76 has a function as a relief valve that keeps the air pressure supplied from the air conduit 70 to the mixture injection valve 38 constant. A pressure control valve 78 for controlling the amount of air introduced into the mixture injection valve 38 from the air conduit 70 is provided downstream of the bypass passage 74.

Mixture injection valve and bypass control valve 76 Pressure control valve described above
Reference numeral 78 is the same as that disclosed in Japanese Patent Application Laid-Open No. 63-012875 filed by the present applicant, and operates as follows. The high pressure air from the compressor 72 is filled in the air chamber 52 prior to the injection. Before injection, the piezoelectric element 44 is energized, and its extension causes the valve element 66 to close the valve seat 67. Therefore, the force applied to the needle 42 is only the air pressure applied to the first pressure receiving portion 48, and the needle 42 does not open. Piezoelectric element during fuel injection
Since the energization of 44 is released, the piezoelectric element 44 is contracted, the valve body 66 is lifted from the valve seat 67 by the force of the disc spring 69, the fuel is introduced into the fuel chamber 54, and the fuel is received in the pressure receiving portion 50. Pressure is applied. Therefore, the needle 42 springs due to the resultant force with the air pressure.
Lifting against 46, the fuel is introduced into the air chamber 52, forms a mixture, and is injected from the injection port 86.

In FIG. 1, an intake valve stop mechanism 81 is for restricting the intake valve 22 to a closed state during extremely low load operation such as engine idle. Various mechanisms have been proposed as such a mechanism, and an appropriate mechanism can be adopted among them. Instead of closing the intake valve 22, a butterfly valve may be provided in the intake port 24 and the butterfly valve may be closed.

The control circuit 84 performs engine control such as mixture injection control and ignition control, and is configured as a microcomputer system. The control circuit 84 has a micro processing unit (MPU) 86, a memory 88, an input port 90, an output port 92, and a bus 94 connecting these units as basic components. Further, it has two comparison registers 95 and 97 for controlling the fuel system control signal and the air system control signal, and further has a down counter 99 for controlling the duty ratio.
It is equipped with. The input port 90 is connected to a required sensor group, and an engine operating condition signal is input. A signal corresponding to the intake air amount Q introduced into the engine is obtained from the air flow meter 36. The crank angle sensor 96 obtains a pulse signal according to the rotation angle of the crankshaft 16. Various other sensors are provided, but the description thereof is omitted because they are not directly related to the present invention. The output port 92 is a piezoelectric element of the mixture injection valve 38.
44, actuator 76A of relief valve 76, air control valve 78
Actuator 78A, intake valve stop mechanism 81, and other engine control actuators.

To explain the operation of the present invention, the control circuit 84 sends a signal to the intake valve stop mechanism 81 to keep the intake valve 22 closed regardless of the rotation of the cam shaft (not shown) during an extremely low load such as idling. Therefore, the introduction of air from the intake port 24 is stopped. The control circuit 84 sends a signal to the mixture injection valve 38, and the mixture injection valve 38 injects air and fuel as a mixture as described above. FIG. 3 is an angle diagram showing the operation timing of the exhaust valve 26 by a cam (not shown). The exhaust valve starts opening sufficiently before the bottom dead center BDC, and completes closing after sufficiently passing BDC. EX indicates the opening period of the exhaust valve 26. The mixture injection valve 38 executes the mixture injection near the closing of the exhaust valve 26, but in a crank angle range sufficiently before the ignition timing before TDC. 1 shows an injection period. The intake valve 22 is restrained in a closed state, and the air is injected from the mixture injection valve 38 in a state of being mixed with the fuel, but the injection timing is near the closing timing of the exhaust valve 26, that is, immediately before ignition. As a result, the air-fuel mixture from the air-fuel mixture injection valve 38 is concentrated near the spark plug electrode 21A in the upper portion of the combustion chamber 20, so stratification is performed with the residual exhaust gas portion in the lower portion of the cylinder bore, and ignition performance is improved. Can be improved. It should be noted that the amount of air that can be covered by the injection from the mixture injection valve 38 cannot be so large, but the required amount of air can be small during idle operation, so idle operation can be prevented. . In FIG. 4, (a) shows the waveform of the drive signal to the actuator 78A of the air control valve 78, which is driven by the pulse signal. On the other hand, (B) shows a drive signal to the piezoelectric element 44 of the mixture injection valve 38. The air control signal is output prior to the fuel control signal for improving atomization at the start of injection, and continues until after the fuel control signal in order to prevent the fuel from dripping after injection. The duty ratio B / A, which is the ratio of one pulse width of the pulse signal for air control to one cycle, is changed by, for example, the intake air amount-rotation speed ratio Q / NE that represents the load of the engine at that time, and The ratio between the amount and the fuel amount is maintained at a predetermined value such as the theoretical air-fuel ratio. That is, when the duty ratio increases, the air amount in the injected air-fuel mixture increases and the air-fuel ratio increases, and conversely, when the duty ratio decreases, the air-fuel ratio in the injected air-fuel mixture decreases and the air-fuel ratio decreases. In the present invention, since the intake valve 22 is kept closed when the load is low, the duty ratio of the air signal is manipulated to change the air amount.

When the load increases from the idle operation, the control circuit 84 releases the restraint state of the intake valve 22 by the intake valve stop mechanism 81, so that the intake valve 22 exerts its original operation in addition to the exhaust valve 26. In FIG. 3, the dotted line represents the operation timing of the intake valve, which is opened after the opening of the exhaust valve is started, is closed after the closing of the exhaust valve, and is shown by the intake valve opening period and IN. The fuel injection period I can be optimally changed depending on the load and the engine speed of the engine, but the operation of the mixture injection valve must be completed at least by the completion of closing the exhaust valve. In FIG. 5, as in FIG. 4, (a) shows the waveform of the drive signal to the actuator 78A of the air control valve 78, and (b) shows the drive signal to the piezoelectric element 44 of the mixture injection valve 38. Show. When the load is higher than idle, the main air is introduced from the intake port 24, and the share of the mixture injection valve decreases, so the duty ratio B / A decreases. The amount of air from the mixture injection valve is selected to achieve optimum fuel atomization.

FIGS. 6, 7, and 8 are operation flowcharts of the control circuit for obtaining the air control signal and the fuel control signal as shown in FIGS. 4 and 5. FIG. 6 shows a crank angle interruption routine which is executed for each crank angle of 30 ° C., for example. In step 110, it is judged whether or not it is the timing for calculating the fuel and air control for that cylinder. That is, in FIG. 9, (B) is the calculation timing, which is naturally selected before the rising of the air system operation signal (D). At step 112, it is judged if the intake valve 22 is in a stopped state, that is, if the load is low. When the intake valve is in the stopped state, the flow proceeds to step 114, and the duty ratio B / A of the air control pulse signal suitable for low load is calculated. As described above with reference to FIG. 4, when the load is low, the duty ratio is calculated according to the intake air amount-rotational speed ratio Q / N so that an appropriate air-fuel ratio can be obtained regardless of the load.

The intake valve 22 is operating during operation other than low load,
The flow proceeds to 116, and the duty ratio B / A of the air control pulse signal suitable for high load is calculated. As described above with reference to FIG. 5, the duty ratio is selected so that proper atomization is performed at high load.

Step 118 shows the calculation of the fuel injection time τ _i . The fuel injection amount is the same as that of a normal electronically controlled fuel injection internal combustion engine, and basically, it is a load factor, that is, the intake air amount-rotational speed ratio Q /
Determined by NE.

In step 120, the start time t _ai and the stop time t _ae of the air control valve actuation signal are calculated. T in Fig. 9 (d)
₁ indicates the period of the air control valve actuation signal, and these times are calculated so as to obtain an appropriate interval Δt ₁ with the ignition signal. In step 122, the start time t _fi and the end time t _fe of the fuel injection signal are calculated from the fuel injection time τ _i and the time Δt ₂ until the end of the air control valve drive signal. Step 12
In 4 the start time t _ai of the air control signal is set in the B register 97 for air control, and in step 126 A for fuel control is set.
The disclosure time t _fi of the fuel injection signal is set in the register 95.

FIG. 7 shows a time coincidence interrupt routine of the A register 95. That is, when the time t _fi arrives this routine is executed, it is determined whether or not the step 130 the flag F ₁ = 1.
Since F ₁ = 0 at the start of fuel injection, the routine proceeds to step 132, where a signal for starting fuel injection is sent to the piezoelectric element 44. In step 134, the flag F ₁ = 1 is set, and in step 136, the end time t _fe is set in the A register.

When the time reaches t _fe , the routine of FIG. 7 is started again,
In step 130, the flow then proceeds to step 138 and the piezoelectric element 44
A signal for stopping the fuel injection is sent to, and the flag F ₁ = 0 is reset in step.

FIG. 9 shows a time coincidence interrupt routine of the B register 97. This routine is started when the current time = t _ai ,
In step 140, the counter n is incremented, and in step 142, the rising time TON of the pulse signal according to the value of the duty ratio B / A is calculated. In step 144, the down counter (first counter for forming the duty ratio
TON is set in the figure). In step 146, it is judged whether or not one cycle Δt × n ≧ T _{1 of the} air control signal, that is, the time _tae has arrived. If No, the process proceeds to step 148 and Δt is entered in the B register. That is, the routine of Figure 8 the same time Δt has elapsed to one cycle of an air system driving pulse signal is performed again, the time t _ae arrives at step 146 proceeds to Yes, and step 150, the counter n
Is cleared. Then, the air control signal is stopped because it bypasses step 148. In FIG. 9, (f) shows the timing of the counter, the countdown is performed every Δt, the air-fuel ratio control signal rises during the countdown, and the duty ratio B / A corresponding to TON is obtained.

Although the embodiment has been described as applied to a two-cycle internal combustion engine having an intake valve and an exhaust valve, the idea of the present invention can be applied to a normal two-cycle internal combustion engine of a piston valve type.

〔The invention's effect〕

According to the present invention, in the two-cycle internal combustion engine, the amount of air into the combustion chamber is reduced during low load operation, and the amount of air directly injected from the injection means into the combustion chamber is controlled when the engine is under low load. Blow-through of the air-fuel mixture during loading is prevented, and ignitability can be improved. Therefore, 4
Idle stability comparable to that of a cycle can be obtained, and exhaust emission can be improved.

[Brief description of drawings]

FIG. 1 is an overall system configuration diagram of the present invention. FIG. 2 is a sectional view of the mixture injection valve. FIG. 3 is an angle diagram showing the operation timing of the intake valve and the exhaust valve. FIG. 4 is a diagram for explaining the timing of the air control signal and the fuel injection signal when the load is low. FIG. 5 is a diagram for explaining the timing of the air control signal and the fuel injection signal when the load is high. 6 to 8 are flowcharts for explaining the operation of the control circuit. FIG. 9 is a timing chart for explaining the operation of the control circuit. 20 ... Combustion chamber 22 ... Intake valve 24 ... Intake port 30 ... Intake pipe 32 ... Scavenging pump 38 ... Mixture injection valve 42 ... Needle 52 ... Air chamber 54 ... Fuel chamber 81 ... Intake Valve stop mechanism 84 ... Control circuit

Claims (1)

[Claims] 1. In a two-cycle internal combustion engine, means for maintaining an intake port closed at a low load of the engine, injection means for simultaneously injecting fuel and air into a combustion chamber, and an intake port at a low load of the engine. Intake air amount control means for reducing the amount of air from the engine to the combustion chamber, and controlling the amount of air directly injected from the injection means into the combustion chamber when the engine has a low load. Internal combustion engine.