JPH0533709Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a fuel injection control device for a two-stroke internal combustion engine.

[Conventional technology]

In a two-stroke internal combustion engine, the period during which the intake port and exhaust port are in communication for scavenging is extremely long. When fuel is normally supplied to the cylinder in the form of a mixture using a carburetor, it is often discharged directly into the exhaust system through blow-through. Therefore, a system has been proposed in which a fuel injector is installed and fuel is injected only during a predetermined period in the intake cycle of the engine. The amount of fuel to be injected is determined based on operating conditions such as load and engine speed, as in the case of a four-cycle internal combustion period fuel injection system. For example, see Japanese Patent Application Laid-Open No. 53-27731. In order to exhibit the best characteristics in each load range, we installed an intake valve and an exhaust valve, and formed two intake ports in one cylinder.
It is conceivable to install a fuel injector in each cylinder.

[Problem that the invention attempts to solve]

In a two-cycle fuel injection internal combustion engine, the fuel injection timing is set slightly before the intake valve closes. This is based on the idea of trying to reduce the number of open spaces as much as possible. However, just before the intake valve closes, the lift of the intake valve is small, so the flow rate of intake air is low and it is difficult for fuel to enter. This caused problems during high loads when a large amount of fuel was required.

The purpose of this idea is to achieve a balance between fuel flow and performance under high loads.

[Means for solving problems]

According to this invention, as shown in FIG. 1, one cylinder has first and second fuel injectors 38a,
38b is provided, and part of the injector 38a,
38b is activated or deactivated depending on operating conditions, and in a two-stroke internal combustion engine having an intake valve 24 and an exhaust valve 26, the intake valve 24 is opened after the exhaust valve 26 is opened, and the exhaust valve 26 is opened. The intake valve 24 is closed after the valve is closed, and the fuel injection amount calculation means 1 calculates the fuel injection amount from each injector 38a, 38b according to the engine load, and the first injector 38a, A first injector operating means 2 for injecting at the end of the engine when the intake valve 24 is opened, including at least after the exhaust valve is closed, over a load range of the engine from low load to high load; There is provided a fuel injection control device for a two-stroke internal combustion engine, comprising a second injector operating means 3 for operating the injector 38b to perform injection at the maximum intake flow velocity in the intake stroke only during high-load operation of the engine. Ru.

[Effect]

When the load of the engine is low, after the exhaust valve is closed, fuel is injected only from the first injector 38a so as to perform injection at least at the end of the opening period of the intake valve 24.

When the engine is under high load, the first injector 38a
In addition to the injection from the second injector 38b, injection is performed at the maximum intake flow velocity in the intake stroke.

〔Example〕

FIG. 2 shows the general structure of a six-cylinder two-stroke internal combustion engine having an intake valve and an exhaust valve to which this invention is applied, and FIG. 3 shows one cylinder. As will be explained later, this type of two-stroke internal combustion engine generates an exhaust swirl during the backflow of exhaust gas after blowdown, creating a stratification effect in which fresh air is concentrated near the spark plug at the top of the combustion chamber. This was devised to improve ignitability during operation. In FIGS. 2 and 3, 10 is the main body of the internal combustion engine, which includes a cylinder block 12, a cylinder bore 14, a crankshaft 15, and a piston 16.
, a combustion chamber 17 , a cylinder head 18 , and a spark plug 19 . The cylinder head 18 has two intake ports 20a, 20b and two exhaust ports 2.
It is a so-called four-valve type having intake valves 2a, 22b, intake valves 24a, 24b, and exhaust valves 26a, 26b for opening and closing the respective intake ports and exhaust ports. The intake valve and exhaust valve each have a dedicated cam 27,
It is driven to open and close by 28. 30 and 31 are valve springs. Exhaust ports 22a, 22b
is selected in such a shape that a swirl of the exhaust gas is obtained in the cylinder bore about its vertical axis when the exhaust gas flows back into the cylinder bore due to its negative pressure after blowdown.

In FIG. 2, 32 indicates a surge tank.
It is connected to the number of intake pipes 33 that corresponds to the number of cylinders.
The intake pipe 33 has an internal partition wall 33-1, and two intake passages 34a and 34b are formed therein and connected to the intake ports 20a and 20b, respectively. The second intake passage 34b has an effective dimension equal to that of the first intake passage 34b.
a, and an intake control valve 36 is installed. The intake control valve 36 of each cylinder is connected to a link means 36'.
is connected to the actuator 37 by. The actuator 37 is, for example, a diaphragm mechanism operated under negative pressure, and is switched between negative pressure and atmospheric pressure by a switching valve (not shown).
can selectively take a position where the intake passage 34b is opened or a position where it is closed. Intake control valve 3
6 is closed when the load is light and opened when the load is high, as will be described later. Fuel injector 38a, 38b
are arranged in the intake passages 34a, 34b. 40
Reed valves a and 40b are arranged as necessary to control backflow.

An intercooler 42, a mechanical supercharger 44, a throttle valve 46, an air flow meter 48, and an air cleaner 50 are arranged in this order in the intake system upstream of the surge tank 32. The mechanical supercharger 44 is constituted by, for example, a roots pump or a vane pump, and a pulley 44-2 is provided on the drive shaft 44-1, and a belt 44-3 drives the crankshaft 15.
It is connected to the upper pulley 15'. Mechanical supercharger 4
A bypass control valve 45 is installed in a bypass passage 44' that bypasses the intake pipe 4, and serves to adjust the intake pipe pressure. In this embodiment, the intercooler 42 is configured as an air-cooled type, and has an inlet container 42-1.
, an outlet container 42-2, a heat exchange tube 42-3 communicating therebetween, and a fin 42-4 attached to the heat exchange tube 42-3.

The exhaust manifold 54 is #1 in this example.
Two separate cylinder groups are installed for cylinder groups up to #3 and cylinder groups #4 through #6, respectively. This grouping is such that ignition alternates between these two groups. That is, in this embodiment, the firing order is #1, #6,
Assume that the order is #2, #4, #3, and #5. By grouping the engines with alternating ignition, the exhaust pressure of one cylinder during the scavenging stroke is not affected by the exhaust pressure of other cylinders. The exhaust manifolds 54 of the cylinder groups #1 to #3 and the cylinder groups #4 to #6 are each connected to a dedicated catalytic converter 56 (which may also be used as a muffler or a dedicated muffler may be installed separately).

A distributor 58 is connected to the spark plug 19 of each cylinder, as is well known, and is controlled by an igniter and an ignition coil (not shown) so that ignition is performed at a desired crank angle.

According to this invention, the control circuit 60 controls the operation of the injectors 38a and 38b so as to obtain a desired air-fuel ratio, and is configured as a microcomputer system. The control circuit 60 is a microprocessing unit (MPU) 60
-1, memory 60-2, and input port 60-3
, an output port 60-4, and a bus 60-5 connecting these. Input port 60-
Each sensor is connected to 3, and an operating condition signal is inputted thereto. The air flow meter 48 may be of a volumetric flow rate type, and measures the flow rate Q of intake air passing through the intake pipe. This idea can also be applied to a fuel injection system that is equipped with a pressure sensor that detects intake pipe pressure instead of an air flow meter. In this case, a semiconductor-type intake pipe pressure sensor is installed, for example, downstream of the throttle valve 46 and upstream of the supercharger 44, and generates a signal corresponding to the intake pipe pressure PM. crank angle sensor 62,
64 is installed in the distributor 58. The first crank angle sensor 62 is connected to a magnetic piece 58-1 fixed on the distributor shaft 58-1.
2 and facing each other, for example, the crank angle is 360°.
A pulse signal is generated every cycle (equivalent to one engine cycle) and serves as a reference signal. On the other hand, the second crank angle sensor 64 is installed facing the magnet piece 58-3 on the distributor shaft 58-1, and generates a pulse signal every 30 degrees of the crank angle, so that the engine speed can be determined. At the same time, it becomes the start signal for the fuel injection routine.

The MPU 60-1 executes arithmetic processing according to the program and data stored in the memory 60-2, and executes processing for forming drive signals for the intake control valve actuator 37 and injectors 38a and 38b. The output port 60-4 is connected to the actuator 37 and the fuel injectors 38a and 38 of each cylinder.
b to which a drive signal is applied.

FIG. 4 shows the intake valve 24a in one cylinder determined by the profile and orientation of the cams 27 and 28.
24b and the operation timings of the exhaust valves 26a and 26b. First, the exhaust valves 26a, 26
b begins to open at 80° before bottom dead center (BDC) and finishes closing at 40° after bottom dead center (BDC). On the other hand, the intake valve 24
a and 24b begin to open at 60° before bottom dead center (BDC),
Closes at 60° after bottom dead center (BDC). Ia indicates the fuel injection period of the first injector 38a that operates over the entire range, and is set so that the fuel injection is completed slightly before the intake valve closes, as described later. Ib is the second injector 38b that operates only in the high load range
The fuel injection period is set so that the injection is performed approximately at the center of the intake valve opening period.

Next, the combustion operation of a two-stroke internal combustion engine equipped with an intake valve and an exhaust valve to which this invention is applied will be explained. When the engine is under light load, the intake control valve 36 is closed and the intake air is passed through the first intake passage 34.
It is introduced into the institution only through a. piston 1
6. In the process of descending, first the bottom dead center (BDC)
The exhaust valves 26a and 26b begin to open at around 80 degrees forward.
Therefore, the exhaust gas from the combustion chamber flows out to the exhaust ports 22a, 22b as indicated by arrow P in FIG. When the piston 16 further descends, the inside of the cylinder bore 14 becomes weakly negative, so the exhaust ports 22a, 22b
Due to the pressure difference between the two cylinders, the exhaust gas flows back toward the cylinder bore as shown by arrow Q (Fig. 5b). Because of the shapes of the exhaust ports 26a and 26b, a swirl of exhaust gas as shown by arrow R is formed within the cylinder bore. Around this time, intake valve 24
a (also 24b) begins to open, but its lift is still small, the throttle valve 46 is throttled, the intake control valve 36 is closed, the intake passage 34b with a large effective dimension is closed, and the Since air can flow only through the intake passage 34a, substantially no fresh air is introduced. When the piston 16 further descends, the swirl of exhaust gas continues, and on the other hand, the lift of the intake valves 24a and 24b increases, so fresh air is introduced into the cylinder bore as shown by arrow S. At this time, the exhaust gas rides on the swirl and flows into the cylinder bore. 14, the fresh air mixed with the injected fuel collects in the vicinity of the spark plug electrode above the swirled exhaust gas portion (FIG. 5C), thus achieving stratification. This stratified state of the exhaust gas R and the fresh air S is maintained even when the piston reaches the bottom dead center (BDC) (FIG. 5D).
In E, the intake valves 24a and 24b are closed to prevent fresh air from blowing back. The piston then moves upward, but this stratified state is maintained until compression is completed, making it easy to ignite the fresh air near the spark plug.

In high engine load conditions, the intake control valve 36 is opened. Therefore, the intake passage 34b, which has been closed until now, is opened. In FIG. 6, when the exhaust valves 26a and 26b open during the downward movement of the piston 16, the exhaust gas in the cylinder bore 14 is discharged to the exhaust ports 22a and 22b by a blowdown P, but the blowdown is performed under a light load. It is strong and lasts for a long time (Fig. 6A), and a large amount of exhaust gas is discharged to the exhaust port. The intake valves 24a and 24b begin to open at the point in FIG.
It is done like this. At this time, the intake port 20a,
Fresh air is introduced from both ports 20b, and this fresh air flows from top to bottom along the cylinder bore wall as shown by arrow T, causing the exhaust gas to flow out to exhaust ports 22a and 22b as shown by arrow U. Scavenging is achieved. At the time point (c) in FIG. 6, a negative pressure component appears in the pressure fluid pulse due to strong blowdown, and the exhaust ports 22a and 22b temporarily become negative pressure, which further promotes the introduction of fresh air T into the cylinder bore. A part of the fresh air flows out to the exhaust ports 22a and 22b like V and is stored. When the pressure in the exhaust ports 22a, 22b returns to positive pressure, this stored fresh air flows back into the cylinder bore as shown by arrow W, generating a swirl X of fresh air (FIG. 6D). This causes turbulence and improves flame propagation after ignition. At the time point E in FIG. 6, the intake valves 24a and 24b have completed closing, and fresh air is prevented from blowing back.

Next, the operation of the control circuit 60 that operates the intake control valve 36 in the combustion operation described above will be explained with reference to the flowchart of FIG. This routine can be executed at regular intervals.
In step 100, it is determined whether the flag FTVIS=1. When FTVIS=0, proceed to step 102,
When the intake air amount-rotation speed ratio Q/NE is a predetermined value (Q/
It is determined whether or not the rotational speed _NE is greater than a predetermined value (NE) ₀ in step 104. Intake air amount-rotation speed ratio Q/NE>predetermined value (Q/NE) ₀ or rotation speed NE>predetermined value (NE) If ₀ , proceed to step 106, and connect the intake control valve to the actuator 37 from the output port 60-4. A signal for opening 36 is output. At step 108, the flag FTVIS is set to 1. When FTVIS = 1, the process proceeds to step 110, where it is determined whether the intake air amount - rotation speed ratio Q/NE is smaller than a predetermined value (Q/NE) ₁ , and in step 112, the rotation speed NE is the predetermined value (NE). It is determined whether it is smaller than ₁ . When the intake air amount-rotational speed ratio Q/NE<predetermined value (Q/NE) ₁ and the rotational speed NE<predetermined value (NE) ₁ , the process advances to step 114, and the actuator 37 is connected to the output port 60-4.
A signal is output to close the intake control valve 36. At step 116, the flag FTVIS=0 is set.

Next, Figure 8 shows the fuel injection routine.
This routine is located in the middle of the crank angle interrupt routine that is executed every time the 30° CA signal from the second crank angle sensor 64 arrives. In step 120, it is determined whether or not it is fuel injection calculation timing. As shown in Fig. 4, the first injector Ia is operated near the closing of the intake valve, and the second injector Ib is operated just in the middle of the intake valve lift. This operation is executed. This timing is based on the signal from the first crank angle sensor 62.
This can be determined by the value of the counter that is cleared by the 360° CA signal and incremented by the 30° CA signal from the second crank angle sensor 64. If it is determined that it is the fuel injection calculation timing, the process proceeds to step 122, where the basic fuel injection amount Tp is calculated by Tp=k(Q'/NE). Here, Q' is the intake air amount Q converted to mass, and the air flow meter 48
This is the value after correcting the measured value by intake air temperature, etc. (PM can be used instead of Q'/NE in a system that determines the fuel injection amount based on the intake pipe pressure PM.) In step 124, the final fuel injection amount is
TAU is calculated by TAU=Tp×α+β. Here, α and β represent representative correction coefficients and correction amounts whose explanations are omitted because they are not directly related to this invention.

In step 126, it is determined whether the flag FTVIS=1, that is, whether the intake control valve 36 is in an open state or a closed state. When the intake control valve 36 is closed, the process advances to step 128 and then to step 130, where the first
TAU is entered into the address TAUa which stores the fuel injection time of the second fuel injector 38a, and zero is entered into the address TAUb which stores the fuel injection time of the second fuel injector 38b. That is, only the first injector 38a is operated, and the second injector 38b is not operated. step 126
When the intake control valve 36 is open, the step
132 and then 134, an address for storing the fuel injection time of the first fuel injector 38a.
1/3 of the TAU is placed in TAUa, and the remaining 2/3 of the TAU is placed in the address TAUb that stores the fuel injection time of the second fuel injector 38b. Here, 1/3 and 2/3 have no specific meaning and are compatibility constants, and since the effective dimension of the second intake passage 34b > the effective dimension of the first intake passage 34a, the air-fuel ratio can be set either way. Since it is constant, it merely indicates that the amount of fuel injected from the second injector 38b is greater than the amount of fuel injected from the first injector 38a.

In step 136, the injection start time t _ia and the injection end time of the first injector 38a, which is operated in the entire area, are determined.
Calculation of t _ea is performed. As shown by Ia in FIG. 4, the operating range of the first injector 38a is slightly before the intake valve closes. To calculate t _ia and t _ea , for example, there is a map of the injection end time t _ea , and a method can be used to determine the injection start time t _ia from this map. In other words, in order to end the injection a little before the intake valve closes, the injection end time t _ea is stored in the map as crank angle data with respect to the load and rotation speed, and is calculated by interpolation from the current load and rotation speed. The injection end time t _ea is calculated. At this calculated injection end time t _ea , the fuel injection time TAUa
The injection start time t _ia can be found by adding .

In step 138, the second
The injection start time t _ib and injection end time t _eb of the injector 38b are calculated. As shown as Ib in FIG. 4, the operating range of the second injector 38b is:
This is approximately the middle of the intake valve operating period. A similar interpolation operation is performed to calculate t _ib and t _eb . In other words, the injection end time _teb is stored in the map as data of the crank angle with respect to the load and rotation speed so that the injection is performed in a crank angle range with a large lift in which the intake valve is operating, and the current load The injection end time t _eb is calculated from the rotation speed and the rotation speed by interpolation calculation. The injection start time t _ib is determined by adding the fuel injection time TAUb to the calculated injection end time t _eb.
can be known.

In step 140, the injection start time t _ia of the first injector 38a and the injection start time t _ib of the second injector 38b are set in respective comparison registers (not shown). FIG. 9 shows the first injector 38
The comparison register time match interrupt routine for a is activated when the injection start time _tia arrives, and the injection end time _tea is set at step 140. 1st
FIG. 0 shows the time coincidence interrupt routine of the comparison register for the second injector 38b, which is activated when the injection start time _tib arrives, and the injection end time _teb is set at step 144.

FIG. 11 shows the timing of fuel injection calculation, the first injector 38a, and the second injector 38b.
This explains the operating timing. FIG. 12 shows the intake flow rate, the first injector 38a, and the second injector 38a.
The relationship with the operating period of the injector 38b is shown.
The first injector 38a, which has a small injection amount, injects near the closing of the intake valve like Ia, and this is a countermeasure for the light load range where blow-by is a problem. On the other hand, the second injector 38b with a large injection amount
Since the injected fuel is injected at the maximum intake speed, the injected fuel can easily enter the cylinder and a sufficient amount can be supplied to the cylinder bore.

[Effect of idea]

In this design, a first and a second injector are provided in one cylinder, and when the engine is under low load, the first injector injects only at the end of the intake valve opening period, which includes at least after the exhaust valve is closed. It is possible to avoid the timing of valve opening and overlapping as much as possible, reducing fuel blow-through, and supplying the necessary amount of fuel into the cylinder at low loads when the fuel injection amount itself is small. On the other hand, at high loads when the amount of fuel required by the engine increases, fuel from the second injector is injected at the maximum intake flow velocity in the intake stroke in addition to the fuel from the first injector, so a large amount of fuel enters. This makes it easier to supply the required amount of fuel into the cylinder. Therefore, it is possible to harmonize the requirements for blow-through prevention at low loads and engine output at high loads.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of this invention. FIG. 2 is a schematic diagram of the entire system according to the embodiment of this invention. FIG. 3 is a diagram showing a cross section of one cylinder (a diagram taken along the - line in FIG. 2). FIG. 4 is an angle diagram of the operation timing of the intake valve and exhaust valve of one cylinder in one cycle of the engine. Figure 5 shows one example of a two-stroke internal combustion engine with an intake valve and an exhaust valve according to an embodiment of this invention under light load.
The figure explaining the combustion operation in a cycle. FIG. 6 is a diagram illustrating combustion operation in one cycle of a two-stroke internal combustion engine with an intake valve and an exhaust valve according to an embodiment of the present invention under high load. Figure 7, Figure 8,
9 and 10 are flowcharts illustrating the operation of the control circuit. FIG. 11 is a timing diagram of fuel injection. FIG. 12 is a graph illustrating the relationship between the intake flow rate and the operating period of the first injector and the second injector. 10...Engine body, 17...Combustion chamber, 24a,
24b...Intake valve, 26a, 26b...Exhaust valve,
34a, 34b...Intake passage, 36...Intake control valve, 38a, 38b...Fuel injector, 42
...Intercooler, 44...Mechanical supercharger, 48
... Air flow meter, 54 ... Exhaust manifold, 60 ... Control circuit, 62, 64 ... Crank angle sensor.

Claims (1)

[Claims for Utility Model Registration] A two-stroke engine that has a first and second fuel injector in one cylinder, some of the injectors are activated or stopped depending on operating conditions, and has an intake valve and an exhaust valve. In an internal combustion engine, the intake valve opens after the exhaust valve opens, the intake valve closes after the exhaust valve closes, and the amount of fuel injected from each injector is calculated according to the engine load. a fuel injection amount calculation means for injecting the first injector at the end of the opening period of the intake valve, which includes at least the closing period of the exhaust valve, over a load range of the engine from low load to high load; a first injector operating means for operating the second injector to perform injection at the maximum intake flow velocity in the intake stroke only during high load operation of the engine; Fuel injection control device for cycle internal combustion engines.