JPH0437264B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel injection control device for a spark ignition type direct injection internal combustion engine.

[Conventional technology]

In spark ignition internal combustion engines, in-cylinder injection is performed in which fuel is directly injected into the cylinder in order to reduce fuel transport delay time and improve responsiveness. In this case, for example, in the case of a direct spray type, an injection valve is provided in the cylinder, and in the case of a subchamber type, an injection valve is provided in the subchamber.

In the spark ignition type direct injection internal combustion engine described above, fuel is supplied to each cylinder through one injection for one combustion.

[Problem to be solved by the invention]

However, in the conventional type described above, the amount of fuel injected at one time changes depending on the load of the engine, so the state of the air-fuel mixture formed in the gap of the spark plug changes. For example, if the amount of fuel injected at one time is large, the fuel will be too rich, and conversely, if the amount of fuel injected at one time is small, it will be too lean. As a result, for all load conditions, an ignitable air-fuel mixture cannot be created in the spark gap within an extremely short spark duration, and therefore ignition is not always reliable.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to ensure ignition in a spark ignition direct injection internal combustion engine by generating an appropriate air-fuel mixture state in the spark gap for all load conditions.

[Means to solve the problem]

The means to solve the above problems is Article 10A
10B.

In FIG. 10A, the sub-injection means generates a sub-injection signal near the compression top dead center of the engine, performs sub-injection INJ-B of a constant injection amount q _B regardless of the engine load, and the ignition means The igniter is driven based on the sub-injection signal to ignite the sub-injection spray. The main injection means is the main injection INJ-C that follows after the sub-injection stops.
I do. The sum of the injection amount q _B of the sub-injection and the injection amount q _C of the main injection is made to correspond to the engine load.

Furthermore, in FIG. 10B, a preceding main injection means for performing the preceding main injection INJ-A at a point slightly after the compression bottom dead center of the engine is added to the components shown in FIG. 10A.

[Effect]

According to the above means, the state of the air-fuel mixture when ignited by the ignition means depends on the injection amount q _B of the sub-injection INJ-B, and since the amount q _B is constant regardless of the load, It becomes constant.

In other words, the appropriate amount of sub-injection INJ-B necessary for ignition
is supplied to the spark plug gap, so
Total injection amount (q=q _B +q _C or q=
q _A + q _B + q _C ) In other words, the proper air-fuel mixture will be formed in the spark plug gap regardless of the engine load.

Adjustment of the injection amount q required for engine operation is performed using the sub-injection.
This is performed by main injection INJ-A after the ignition of INJ-B is completed or by preceding main injection INJ-A sufficiently before sub-injection INJ-B.

Embodiment A fuel injection control device for a spark ignition type direct injection internal combustion engine as an embodiment of the present invention is shown in FIG. In FIG. 1, E is a schematic diagram of the combustion chamber of the engine. Since the engine shown in FIG. 1 does not look much different from those commercially available as direct injection diesel engines, detailed illustrations of its structure are omitted. However, it has the following three characteristics.

The first feature is that the compression ratio of the engine shown in FIG. 1 is as low as 8-14, while the compression ratio of a general direct-injection diesel engine is 16-18. This is because the engine shown in FIG. 1 does not want to spontaneously ignite the fuel due to compression as in the original diesel engine, and instead has a spark plug 3 as a second feature. The spark plug 3 is generally used in gasoline engines (automatic engines), and is equipped with an ignition coil 42 and an igniter 41 as is well known. This spark plug 3
is attached to the injection valve 1 so as to be located near the forward direction of the swirl SWR. swirl
SWR is an airflow obtained by changing the shape of the intake port to a well-known shape called tangential or helical, and is quite natural for direct injection diesels.

The third feature of the engine shown in Fig. 1 is that the injection valve 1 is electrically driven to open and close, and a constant high-pressure fuel is continuously supplied to the injection valve 1. ,That's what it means. In order to electrically drive the injection valve 1, it is effective to use the piezo effect. An electric control circuit 5 is used to control and drive the injection valve 1 and to drive the igniter 41. The electric control circuit 5 receives inputs such as accelerator opening L, engine speed N, fuel calorific value G (kcal/Kg), crank signal θ, etc., and determines the optimum fuel amount, that is, the optimum valve opening time and the optimum injection. The timing etc. are determined, the injection valve 1 is driven, and the igniter 41 is driven based on these drive signals. This injection valve 1 always has a constant pressure of, for example, 200 kg/
In order to continuously supply fuel pressure of ^cm2 , a high pressure pump and a pressure regulator (not shown) are used, and the system is such that the fuel pressure is stored in the accumulator 2 and then supplied to the injection valve 1. It's summery.

The injection valve 1 is a hole nozzle with a single nozzle, and the nozzle faces the forward direction of the swirl SWR.
That is, it faces toward the spark gap of the spark plug 3. The structural features of this engine E are the three points mentioned above.

For one explosion stroke of this engine, three fuel injections are required at high loads, and two fuel injections are required at low loads.
This is done by the injection valves 1. Repeat this operation as a second
This will be explained using figures. Figure 2 shows the valve opening signal of the injection valve 1 at four different loads of the engine E: (1) full load, (2) high load, (3) medium load, and (4) light load. The voltage is converted into a drive voltage for the valve 1 to open the injection valve 1, and all processing is performed by the electric control circuit 5. Note that the horizontal axis is the crank phase of engine E, and time passes to the right.

First, at full load, advance main injection INJ-A, sub-injection
INJ-B and subsequent main injection INJ-C are performed three times. The injection start timing of INJ-A is the timing when the intake valve is completely closed, slightly after the compression bottom dead center (BDC) of the engine 1, and this timing is fixed regardless of the operating conditions of the engine E. The injection period of INJ-A, which corresponds one-to-one to the injection amount of INJ-A, is variably controlled by the engine speed, atmospheric pressure, atmospheric temperature, etc. so as not to exceed the smoke limit.

INJ-B injection start time is 50 degrees crank angle (℃A) before top dead center (TDC) of compression.
It is variably controlled within a range of 10 degrees crank angle (℃A) depending on engine speed, accelerator opening, etc. The spark plug 3 generates a spark in synchronization with this injection of INJ-B to ignite the spray of INJ-B, and the details of the synchronization method will be described later. INJ-
The injection amount of B is INJ-A and INJ- at full load.
Approximately 10% of the total injection amount of B and INJ-C is appropriate; if it is too little, ignition by spark will fail, and if it is too much, the ignition delay will become large and unburned hydrocarbons (HC) from engine E will be ejected. emissions increase. This tendency is shown in Figure 3.

In FIG. 3, the horizontal axis represents the injection amount (%) of the INJ-B zone, and the vertical axis represents the unburned hydrocarbon (HC) emission amount (PPMC). However, the range of appropriate values for the injection amount for INJ-B is quite large as shown in Figure 3, so a constant amount is sufficient over all operating conditions, and
The injection period of B is fixed in time. The injection period is about 100μsec.

The injection start timing of INJ-C is delayed by about 1 msec from the end of injection of INJ-B, and this delay time remains unchanged under all operating conditions of the engine. INJ-C
The injection amount remains unchanged under all load conditions, and the amount is determined so that the injection amount of INJ-A is appropriate. Since the fuel injected by INJ-A undergoes premix combustion during the explosion stroke, INJ-B and INJ
Compared to diffusion combustion such as -C, it is advantageous to have more output, but when the cetane number of the fuel is high or the octane number is low, pre-ignition may occur if the amount exceeds a certain amount, resulting in a decrease in output. Since there is a risk of damage to the engine, there is a maximum permissible value depending on the type of fuel.

In the case of light oil with a cetane number of 40, as shown in Figure 4,
The maximum allowable injection amount for INJ-A is INJ-A, INJ
This is about 50% of the total injection amount of -B and INJ-C. In Fig. 4, the horizontal axis represents the INJ-A zone injection amount, and the vertical axis represents the output (Kg·m).

As mentioned above, INJ-A, INJ-B, INJ-
The total amount of C injection is determined by the smoke limit at full load, and since the smoke limit varies depending on the engine speed and atmospheric pressure, the INJ
The injection amount of INJ-C is adjusted so that the injection amount of INJ-A never exceeds the maximum allowable value mentioned above. It is predetermined. As shown in Fig. 4, if the injection amount of INJ-C is set too large for safety reasons, the injection amount of INJ-A will decrease too much, resulting in a decrease in output.

Next, the high load shown in FIG. 2 will be explained. When the accelerator opening is slightly reduced from full load, the fuel amount is reduced only by reducing the injection period of INJ-A. Injection amount of INJ-B and INJ-C, that is, INJ
-B and INJ-C injection periods remain exactly the same as at full load. Accelerator opening further decreases and INJ
- the injection period of A is the limit value of the metering accuracy of the injection valve 1;
For example, when the time reaches 50 μsec, the injection of INJ-A is made to disappear. When the accelerator opening further decreased after the INJ-A injection disappeared, the second
As shown in the medium load and light loads in the figure, the fuel amount is reduced by reducing the injection period of INJ-C.

The functions and operations of the electric control circuit 5 that performs the above control will be explained. Regarding injection control, this electric control circuit 5 is similar to an ECU for an electronically controlled gasoline injection engine that has been put into practical use and is commercially available.

The configuration and functions of the electric control circuit 5 are as follows. The electric control circuit 5 uses sensors (not shown) to control engine rotation speed N (rpm) and accelerator opening L.
(deg.), a crank signal θ for every 1°C A (crank angle) is input. Any sensor that has already been put into practical use can be used. The electric control circuit 5 includes a clock signal generating circuit every 1 μsec.

In the electric control circuit 5, if N and L are given, the injection amount q (mm ³ /st) uniquely corresponding to them is determined.
A map from which you can draw is stored in the ROM. Further, in the electric control circuit 5, N
and L, it corresponds uniquely to it.
A map from which the injection start timing θ _B (°C A) of INJ-B can be derived is stored in the ROM. Further, in the electric control circuit 5, when an injection amount is given, the opening time of the injection valve 1 for realizing the injection amount is stored in the ROM.

Maximum allowable value of INJ-C injection amount q _C (MAX)
(mm ³ /st) can be set using a dial attached to the outside of the casing of the electric control circuit 5. The electric control circuit 5 drives the igniter 41 to cause the spark plug 3 to generate a spark,
This will be discussed later.

Next, the operations are listed in order.

() Deriving θ _B using the given N and L, using the crank signal and clock signal,
INJ-A injection start timing θ _A (10 after bottom dead center of compression
) and INJ-B injection start timing θ _B
and INJ-C injection start timing θ _C (=θ _B +1msec)
emits a trigger signal.

() Derive q using the given N and L. INJ-B whose value of q is set in advance
injection quantity q _B , for example 3 mm ³ /st, and q _C (MAX),
For example, compare it with the sum of 15mm ³ /st.

() If q<q _B +q _C (MAX), do as follows. In other words, no injection is performed at θ _A , a valve opening signal is sent to the injection valve 1 for a period τ _B (μsec) corresponding to q _B at θ _B , and _a period corresponding to the injection amount q C of q-q _B at θ _C. τ _C
(μsec) Sends a valve opening signal to the injection valve 1.

() If q≧q _B +q _C (MAX), do as follows. In other words, calculate the injection amount q _A = q - q _B - q _C (MAX) at θ _C , and if _the period τ _A corresponding to q _A is 50 μsec _or more, the injection amount is A valve opening signal is sent to the injection valve 1 for a period of τ _B at θ _B , and a valve opening signal is sent to the injection valve 1 for a period corresponding to q _C (MAX) at θ _C.

If the aforementioned τ _A is τ _A < 50μsec, no injection is performed at θ _A , a valve opening signal is sent to injection valve 1 for a period of τ _B at θ _B , and an injection is performed for a period corresponding to q−q _B at θ _C. Sends a valve opening signal to valve 3.

In this case, it is allowed as an exception that q _C exceeds q _C (MAX).

() When the injection of INJ-B starts at θ _B or after a delay of tμsec, the igniter 41
send a signal to. The igniter 41 drives the ignition coil 42 according to the signal, and the spark plug 3
generate a spark.

This control will be explained in more detail. First, the timing of transmitting the drive signal to the igniter 41, that is, (θ _B
A method for determining the timing of +τ _B +t) will be explained with reference to FIG. In FIG. 5, (1) the phase of the internal combustion engine, (2) the injection valve drive signal, (3) the actual injection amount, (4) the gap spray amount, and (5) the spark current are shown.

First, when the crank phase of the internal combustion engine E is θ _B , the signal for opening the injection valve is τ _B (approximately 100 μsec)
Sent. Injection valve 1 does not open immediately in response to this signal, and actual injection is performed at t ₁ ( _{approximately}
50 μsec). This injection is a sub-injection, and there is an additional delay of _t2 before the spray of this sub-injection reaches the gap of the spark plug 3. This _t2 varies depending on the injection pressure, the strength of the swirl SWR, the distance between the injection valve 1 and the spark plug 3, etc., but is approximately 50 to 150 μsec. A spark is generated against this gap spray to ignite it, and the spark duration t ₃ is about 150 μsec in the case of capacitive discharge ignition (CDI) ignition. Under such a situation, the delay time t of the spark start timing with respect to the valve opening/stop signal of the injection valve 1 is expressed by the following equation.

t ₁ +t ₂ -τ _B -t ₃ <t<t ₁ +t _2If this equation is deviated from, the spray and spark will not meet in the gap, making ignition impossible.

In Fig. 5, the secondary injection time τ _B is 100 μsec, the subsequent main injection time τ _C is 300 to 2000 μsec, the injection valve response delay t ₁ is 50 μsec, the spray flight time t ₂ is 50 to 150 μsec,
Spark time (using CDI) t ₃ is 150μsec, interval t ₄ is
It is 1000-1500μsec.

The electrical control circuit 5 will be described below. FIG. 6 shows the configuration of the electric control circuit 5. 501 is an input interface, for example, a magnetoresistive element (MRE)
Angle sensor 611 and reference position sensor 61 using
2. This is for processing the signal from the stroke discrimination sensor 616 and detecting the rotational phase of the crankshaft and the engine rotation speed. An angle sensor 611 is carved on the outer periphery of a disc 614 attached to a crankshaft 613 of an engine (not shown).
It detects 360 teeth and generates 360 pulses per revolution of the crankshaft, that is, a signal of 1°C per pulse.

The reference position sensor 612 is connected to the rotating disk 614.
One protrusion 615 provided near the outer periphery of the engine is detected, and a signal is generated, for example, at 200° C.A. of the engine BTDC. A stroke discrimination sensor 616 detects a protrusion of a camshaft 617 that rotates at 1/2 the rotation speed of the crankshaft, and generates a signal at, for example, BTDC 210° C. of the compression stroke. Therefore, the reference position signal immediately after the stroke discrimination signal is generated is the compression stroke signal.
The BTDC is 200°C A, and the rotational phase of the crankshaft can be accurately detected based on this reference signal.

From the input interface 501, information on the engine speed is connected to a bus line 506, and the reference signal is connected as an interrupt signal to a CPU 503, which will be described later. Furthermore, a reference signal and an angle signal are connected to an output interface 510, which will be described later.

502 is an AD interface that converts the voltage generated by the potentiometer 622 for detecting the opening degree of the accelerator pedal 621 into AD and connects it to the bus line 506. 530 is a digital interface, and a digital switch 63 has a dial for setting the maximum allowable value q _C (MAX) of INJ-C injection.
This is for connecting the value set in 2 to the bus line 506.

Reference numeral 503 is a CPU, and its interrupt input is provided with information about the compression process from the input interface 501.
A reference signal generated at BTDC200℃A is connected. The CPU 503 is activated by the interrupt signal, determines engine conditions based on the above-mentioned input information, and controls the injection amount, injection timing, and ignition timing, which will be described later. 504 is a ROM that stores a control program for the CPO 503 and various data. 505 is
The RAM is used to perform operations such as data storage for the CPU 503.

506 is a bus line for exchanging data between each component in the electric control circuit 5. 510 is an output interface for generating an energization signal to the injection valve 1 and creating an ignition timing signal to the igniter;
A reference signal from 01, an angle signal, and a clock signal with a period of 1 μsec from a clock generation circuit 520 are connected.

Output interface 510 has seven timing generation circuits inside. 511 is a θ _A generation circuit that generates the INJ-A injection timing θ _A calculated and outputted by the CPU 503 using a reference signal, an angle signal, and a clock signal. This configuration consists of a main counter that starts with a reference signal and counts down with an angle signal, and a sub-counter that counts down with a clock signal by converting the number of angle signals (less than 1°C in this example) into time. Consists of. 512 is a θ _B generation circuit, and 513 is a θ _C generation circuit, which has the same configuration as the θ _A generation circuit.

514 is a τ _A generation circuit that generates the INJ-A injection period τ _A calculated and output by the CPU 503 . This configuration consists of a counter that is started by a signal from the θ _A generating circuit and counts down by a clock signal. 515 is a τ _B generation circuit, and 516 is a τ _C generation circuit, which has the same configuration as the τ _A generation circuit 514.

517 is a t generation circuit that generates an ignition timing signal, which starts at the end of INJ-B injection from the τ _B generation circuit 515, and calculates the delay time t calculated and output by the CPU 503 from a counter that is counted down by a clock signal. Become. 518 is a three-input OR circuit whose inputs are the τ _A generation circuit 514,
The outputs from the τ _B generation circuit 515 and the τ _C generation circuit 516 are connected, and the logical sum of the three inputs is output. That is, the output of the OR circuit 518 is a combination of the three types of signals.

521 is a drive circuit for the injection valve 1, which receives the injection valve energization signal from the OR circuit 518, and supplies -200V to the injection valve 1 when the energization signal is at 1 level, and +500V when it is at 0 level. The injection valve 1 is designed to open at -200V and close at +500V.

Reference numeral 41 denotes an igniter circuit, which is a known CDI ignition circuit, and is triggered with a delay of t seconds after the end of INJ-B injection by the fall of the output signal of the t generation circuit 517 described above. This trigger activates the CDI, a large current flows through the primary coil of the ignition coil 42, a high voltage is generated in the secondary coil, and the ignition plug 3 ignites. 523 is a known DC/DC converter that boosts the low DC voltage from the storage battery 9 using a transformer to generate a DC voltage of about 250V.
This high voltage is supplied to the drive circuit 521 and the igniter 41.

The operation of the electric control circuit 5 in FIG. 6 is shown in FIG.
This will be explained with reference to B, C and FIG. 7A, B, and C are flowcharts (step S101) for explaining the arithmetic control contents of the CPU 503.
to step S125), FIG. 8 is a time chart showing the signals of each part.

In Fig. 8, (1) reference signal, (2) angle signal,
(3) τ _A signal, (4) τ _B signal, (5) τ _C signal, (6) Energization signal, (
7)
The waveforms of the t signal, (8) trigger signal, and (9) spark current are shown. The CPU 503 performs the compression process mentioned above.
It is activated by an interrupt caused by the reference signal of BTDC200℃A. The CPU first uses input interface 5
The engine speed N is read through 01 (S102). Next, the accelerator opening degree L is read through the AD interface 502 (S103). Furthermore, through the digital interface 530, q _C (MAX)
The setting value of q _C (MAX) in the setting section is read (S104). Next, calculate the injection timing.

INJ-A injection timing θ _A is constant at 10℃A after bottom dead center of compression, that is, 170℃A BTDC, so _θA =
Set BTDC to 170℃A (S105). Since the INJ-B injection timing changes depending on the engine conditions, the INJ-B injection timing θ _B under the predetermined engine conditions N and L is calculated from a map obtained in advance through a bench test or the like and stored in the ROM 504 (S106). INJ-C injection timing is
Since it is 1 msec after the INJ-B injection, 1 msec is converted into an angle using the engine rotation speed N, and θ _C =θ _B +N/60×360×10 ⁻³ is calculated (S107).

Next, calculate the injection amount. The total injection amount q is determined in advance through a bench test or the like, and the total injection amount q under predetermined engine conditions N and L is calculated from a map stored in the ROM 504 (S108). INJ-B injection amount q _B is set to a constant value, for example 3 mm ³ /st, so q _B
= 3.0 (S109). Total injection amount q and q _B +q _C
(MAX) (S110), q<q _B +q _C
(MAX), there is no need to perform INJ-A injection. That is, the INJ-A injection period τ _A is set to 0 (S111).
INJ-B injection period τ _B is q _B and flow coefficient k of injection valve 3
Multiply by τ _B = kq _B to find (S112).

The INJ-C injection amount q _C is the remaining q-q _B obtained by subtracting q _B from the total injection amount (S113), and τ _C =kq _C is calculated from this (S114). The comparison result of q and q _B +q _C (MAX) is q
When q _B + q _C (MAX), INJ-A injection will be performed. INJ-A injection amount q _A is q-q _B −q _C
(MAX) (S115). This is converted into INJ-A injection period τ _A =kq _A (S116).

Next, it is checked whether τ _A is 50 μsec or more (S117), and if it is less than 50 μsec, it is below the response limit of the injection valve 1, so as a special case, INJ-A injection is not performed. In this case, the process branches to the previous routine for τ _A =0 (S111). If τ _A is 50μsec or more,
Since INJ-A injection is possible, the following τ _B = kq _B ,
Calculate q _C = q _C (MAX), τ _C = kq _C (S118,
S119, S120) Find the injection period of each injection. θ _A , θ _B , θ _C , τ _A , τ _B , and τ _C thus determined are output to the output interface 510 (S121, S122).
The actual creation of the drive signal is automatically performed by the output interface hardware.

Next, calculation of ignition timing will be explained. In the above explanation, it was stated that the ignition timing should be determined based on the INJ-B injection end timing so as to satisfy the relationship: t ₁ +t ₂ -τ _B -t ₃ <t<t ₁ +t ₂ . this house,
The spray flight time _t2 changes depending on the engine speed, but
t ₁ and t ₃ are constant.

The above relationship is shown in FIG. In Fig. 9, the horizontal axis represents the engine rotation speed N (rpm), and the vertical axis represents the time t.
(μs). The shaded area is the area where t can exist. This includes t = 0, that is, simply INJ-
It can be seen that ignition may be performed at the end of B injection. However, it is desirable to have the spark with the maximum energy immediately after the ignition voltage is generated slightly inside the spray tip. This timing is shown by the thick line in FIG.

This is a function of engine speed and t≒
It can be approximated by 75000/Nμsec. Therefore, the CPU
calculates t=75000/Nμsec (S123), outputs t to the output interface (S124), and returns (S125). As described in the configuration section, the ignition signal is generated by the t generation circuit 517 generating a trigger signal t after the end of INJ-B injection, the igniter 41 operates to generate ignition voltage, and the plug 3 ignites the ignition signal. will be held.

In carrying out the present invention, various modifications are possible in addition to the embodiments described above. For example, the configuration and operation of the electric circuit 5 described above are just one example, and various other configurations are possible, but detailed description thereof will be omitted. Further, in the above description, only one cylinder was described to simplify the explanation, but it is easy to extend this to multiple cylinders. Further, in an actual engine, it is common sense to provide inputs such as a water temperature sensor and an intake pressure sensor to correct the injection amount and injection timing, but a detailed explanation is omitted.

In the above-mentioned equipment, INJ is used during light and medium loads.
Two injections are performed as -B and INJ-C.
The injection temperature of INJ-B is 50 to 10°C before compression top dead center, and the injection period is about 100 μsec. The fuel injected from the injection valve 1 reaches the spark plug 3 after about 100μsec.
A mixture with air is formed in the spark gap of the engine, and at that time a spark is generated in this gap and the mixture is ignited. After an ignition delay of just under 1msec, INJ
The entire spray produced by the injection of -B emits a flame, but the spray produced by the injection INJ-C jumps into this flame, and diffusion combustion known as diesel combustion progresses.

In this case, there are the following advantages. That is, firstly, a high cetane number fuel is not necessarily required for ignition with a spark plug;
In addition, ignition is performed only on the spray from the injection of INJ-B, and since the injection amount of INJ-B is constant regardless of engine conditions, the spark gap of spark plug 3 always has a constant mixture at the ignition timing. Thirdly, gas is formed and reliable ignition is possible.
Since the ignition timing (spark generation timing) only needs to be synchronized with the injection of INJ-B, there is no need for a separate control circuit to determine the ignition timing.Fourthly,
INJ-C injection combustion is completely diffusive combustion, so there is no need to control the amount of intake air, and of course there is no need for an intake throttle valve, and the pump loss is smaller than that of a normal gasoline engine, resulting in fuel consumption. Less is.

INJ-A, INJ-B, INJ- at high/full load
C3 injections are performed. The injection temperature of INJ-A is 10℃A after the bottom dead center of compression, and this spray is swirled.
It is diffused into the combustion chamber by SWR and sufficiently premixed with intake air. The air-fuel mixture at this time has an excess air ratio that is more than twice the stoichiometric mixture ratio, and even if it is a low-octane fuel, spontaneous combustion will not occur. If there is such a risk, the injection amount of INJ-C is increased and the injection amount of INJ-A is reduced by that amount, so that the excess air ratio increases accordingly and the risk of spontaneous ignition can be eliminated. This premixture with a large excess air ratio is
Although some combustion occurs due to the ignition of the INJ-B injection, most of the combustion occurs due to diffusion combustion caused by the INJ-C injection, resulting in so-called torch combustion. In this case, in addition to the first to fourth advantages mentioned above, fifthly,
Because it is so-called torch combustion, which causes premix combustion along with diffusion combustion, it has the advantage of increasing the excess air ratio of the premix to the minimum necessary, thereby achieving the ultimate goal of preventing spontaneous ignition and increasing output.

Further, in carrying out the present invention, the following matters are also included within the scope of carrying out the present invention. For example, secondary injection
The injection amount of INJ-B may exceed the injection amount of subsequent main injection INJ-C. It simply defines the earlier one as the secondary injection. In addition, the injection amount of the sub-injection INJ-B is generally constant, but the injection amount of the subsequent main injection INJ-C changes depending on the accelerator opening L, and exceptionally during low load or deceleration, the injection amount of the subsequent main injection INJ-C is The injection amount of C disappears. However, this case is also within the scope of the present invention. Furthermore, when using fuel with a not so low cetane number, the method of the present invention may be used only during startup or warm-up, and sub-injection or spark ignition may be stopped after complete explosion or warm-up. It is within the scope of implementing the present invention.

In addition, in the above embodiments, the fuel is a petroleum-based fuel such as naphtha, gasoline, kerosene, light oil, heavy oil, or a mixture thereof, and the calorific values of these fuels are not very different, but for example, methyl alcohol When using fuels with significantly different calorific values such as , ethyl alcohol, and vegetable oil,
It is preferable to increase or decrease the amount of each injection of INJ-A, INJ-B, and INJ-C in proportion to the calorific value, and an adjustment dial for this purpose should be attached to the outside of the casing of the electric control circuit 5. For example, it is effective as a multi-fuel engine.

In addition, in the above-mentioned embodiment, the maximum value of the injection amount of INJ-C is set by the driver himself using a dial attached to the outside of the casing of the electric control circuit 5, but a commercially available knob control In a similar manner to the system, when a knock is detected, the injection amount of INJ-C is increased and INJ-C is replaced with
It is easy to reduce the injection amount of A.

Furthermore, in the above-mentioned embodiment, it is assumed that two injections, INJ-B and INJ-C, exist under any operating conditions, but INJ-B injection occurs at extremely light loads or during deceleration. However, even if the injection amount of INJ-B is slightly increased or decreased, this is within the scope of the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, the sub-injection amount
q _B makes it possible to keep the air-fuel mixture in the gap of the spark plug at the time of ignition constant, that is, the state necessary for ignition, so ignition can be achieved reliably regardless of the load. Furthermore, the load can be compensated for by main injection other than sub-injection and by preceding main injection.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a fuel injection control device for a spark ignition type direct injection internal combustion engine as an embodiment of the present invention;
Figure 2 is a waveform diagram explaining the operation of the apparatus shown in Figure 1, Figures 3 and 4 are characteristic diagrams showing the operating characteristics of the apparatus shown in Figure 1, and Figure 5 explains the operation of the apparatus shown in Figure 1. FIG. 6 is a diagram showing the configuration of the electric control circuit in the device shown in FIG. 1, FIG. 7 A, B, and C are flow charts showing the operation of the circuit shown in FIG. 6, and FIG. A waveform diagram explaining the operation, Figure 9 is a characteristic diagram explaining the operating characteristics of the circuit in Figure 6, Figures 10A and 10B.
The figure is a block diagram showing the basic configuration of the present invention. Explanation of symbols, 1... Injection valve, 2... Accumulator, 3... Spark plug, 41... Igniter, 42... Ignition coil, 5... Electric control circuit,
611... Angle sensor, 612... Reference position sensor, 613... Crankshaft, 614... Disc, 615... Protrusion, 616... Stroke discrimination sensor, 617... Camshaft, 621... Accelerator pedal, 622 ...Potentiometer, 63...
...Digital switch, 9...Storage battery, E...Combustion chamber of internal combustion engine.

Claims (1)

[Scope of Claims] 1. In a spark-ignition direct injection internal combustion engine in which fuel is injected into a cylinder and ignited by an igniter, an auxiliary injection signal is generated near the compression top dead center of the engine to reduce the load on the engine. a sub-injection means for performing a sub-injection INJ- _B of a constant injection amount qB unrelated to the sub-injection, an ignition means for driving the igniter based on the sub-injection signal to ignite the spray of the sub-injection, and the sub-injection. main injection means for performing a subsequent main injection INJ- _C after the stop of the main injection _; A fuel injection control device for a spark ignition type direct injection internal combustion engine, characterized in that: 2. The fuel injection control device according to claim 1, wherein the ignition means ignites the sub-injection simultaneously with the stop of the sub-injection. 3. Claim 1, wherein the ignition means ignites the sub-injection after a predetermined time t after the sub-injection stops.
The fuel injection control device described in Section 1. 4 The predetermined time t is t ₁ +t ₂ −τ _B −t ₃ <t<t ₁ +t ₂ However, t ₁ is the response delay time of the injection valve that performs injection, and t ₂ is the ignition time of the spray of the sub-injection. 4. The fuel injection control device according to claim 3, wherein: the flight time of the means to the spark gap, τ _B is the sub-injection time, and _t3 is the ignition duration of the ignition means. 5. In a spark-ignition direct injection internal combustion engine that injects fuel into a cylinder and ignites it with an igniter, a preceding injection means that performs a preceding main injection INJ-A at a point slightly after the compression bottom dead center of the engine; , a sub-injection means that generates a sub-injection signal near the compression top dead center of the engine and performs sub-injection INJ-B of a constant injection amount q _B unrelated to the load of the engine; and based on the sub-injection signal. ignition means for driving the igniter to ignite the spray of the sub-injection, and main injection means for performing the subsequent main injection INJ-C after stopping the sub-injection, the injection amount of the preceding main injection being Fuel injection for a spark ignition type direct injection internal combustion engine, characterized in that the sum of q _A , the injection amount of the auxiliary injection, q _B , and the injection amount q _C of the main injection corresponds to the load of the engine. Control device. 6. The preceding main injection means reduces the injection amount q A of the preceding main injection INJ-A in accordance with the reduction in the load of the engine, and the main injection means reduces the injection quantity q _A of the preceding main injection INJ-A in accordance with the reduction in the load on the engine. The fuel injection control device according to claim 5, wherein the injection amount τ _C of the main injection INJ-C is decreased when the injection amount q _A of the main injection INJ-C becomes 0. 7. The fuel injection control device according to claim 6, wherein the ignition means ignites the sub-injection simultaneously with the stop of the sub-injection. 8. Claim 6, wherein the ignition means ignites the sub-injection after a predetermined time t after the sub-injection stops.
The fuel injection control device described in Section 1. 9 The predetermined time t is t ₁ +t ₂ −τ _B −t ₃ <t<t ₁ +t ₂ However, t ₁ is the response delay time of the injection valve that performs injection, and t ₂ is the ignition time of the spray of the sub-injection. 9. The fuel injection control device according to claim 8, wherein τ B is the flight time of the means to the spark gap, τ _B is the sub-injection time, and t ₃ is the ignition duration of the ignition means.