JPH03117643A - Fuel injection control device for two-cycle internal combustion engine - Google Patents

Abstract

PURPOSE:To reliably maintain an air-fuel ratio at a target value by a method wherein based on actual oxygen concentration, a remaining rate of intake air remaining in a cylinder is determined, and based on the remaining rate, a fuel injection time is decided so that an actual air-fuel ratio is maintained at a target value. CONSTITUTION:A relation responding to an engine running state between oxygen concentration detected by an oxygen concentration sensor 25 and actual oxygen concentration is predetermined by experiment to store a result in a memory means A. From detected oxygen concentration, actual oxygen concentration is calculated by a calculating means B, and based on the actual oxygen concentration, a remaining rate of intake air remaining in an engine cylinder is calculated by a calculating means C. Based on the remaining rate of intake air, an injection time calculating means D decides a fuel injection time in which an actual air-fuel ratio in the engine cylinder is adjusted to a target value. This constitution reliably maintains an actual air-fuel ratio in the engine cylinder at a target value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel injection control device for a two-stroke internal combustion engine.

[Conventional technology]

In a two-stroke internal combustion engine, not all of the intake air supplied into the engine cylinders contributes to combustion, and some of the intake air blows into the exhaust passage without contributing to combustion. Therefore, if the amount of intake air supplied to the engine cylinder is determined and the fuel injection amount is determined from this amount of intake air so that the air-fuel ratio becomes the target air-fuel ratio, some of the intake air will blow through, so the actual amount of air inside the engine cylinder will be The air-fuel ratio becomes richer than the target air-fuel ratio, and the actual air-fuel ratio in the engine cylinder cannot be made to match the target air-fuel ratio.

Incidentally, the amount of intake air vented varies depending on the operating state of the engine, but the amount of intake air vented in a particular steady operating state is constant. Therefore, if the amount of the air vents used in various steady-state operating conditions is determined in advance through experiments, the amount of the intake air vents can be determined if the current operating state of the engine is known.

Therefore, by actually measuring the amount of intake air and the amount of air vent supplied into the engine cylinder under various steady operating conditions, we calculated the fresh air capture coefficient ((amount of intake air - amount of air vent/amount of intake air), that is, the amount of intake air supplied to the engine cylinder. The proportion of fresh air remaining in the engine is determined in advance through an experiment, the fresh air capture coefficient determined through this experiment is stored in advance, and the operating state of the engine is detected to determine the fresh air capture coefficient corresponding to this operating state. and measure the amount of intake air,
A two-cycle system that calculates the amount of intake air that actually contributes to combustion from the measured intake air amount and fresh air capture coefficient, and then determines the fuel injection amount based on this intake air amount so that the air-fuel ratio becomes the target air-fuel ratio. Internal combustion engines are well known (Japanese Patent Laid-Open No. 63-1
83231 to JP-A-63-183236). In these two-stroke internal combustion engines, the fuel injection amount is determined based on the amount of intake air that actually contributes to combustion, so the actual air-fuel ratio within the engine cylinder can be made to closely match the target air-fuel ratio.

[Problem to be solved by the invention]

By the way, even if the fuel injection time is controlled using such a fresh air capture coefficient, there is a limit to maintaining the actual air-fuel ratio in the engine cylinder at the target air-fuel ratio. In order to accurately maintain the air-fuel ratio, it is necessary to actually measure the amount of intake air vented and to control the fuel injection time based on the measured amount of intake air. Conventionally, in a 4-stroke internal combustion engine, feedback control is performed so that the air-fuel ratio becomes the target air-fuel ratio based on the output signal of an oxygen concentration sensor that detects the oxygen concentration in the exhaust gas, but in a 2-stroke internal combustion engine, a large amount of intake air is Blow through into the exhaust passage,
Moreover, since a difference occurs between the oxygen concentration detected by the oxygen sensor and the actual oxygen concentration depending on the strength of exhaust blowdown, the feedback control used in 4-stroke internal combustion engines cannot be directly applied to 2-stroke internal combustion engines. The problem is that it is not possible.

[Means to solve the problem]

In order to solve the above problems, according to the present invention, as shown in the block diagram of the invention in FIG. Storage means A stores in advance the relationship between the concentration and the actual oxygen concentration in exhaust gas depending on the engine operating state, and the oxygen detected by the oxygen concentration sensor 25 based on the relationship stored in the storage means A. an oxygen concentration calculation means B that calculates the actual oxygen concentration from the concentration; a residual ratio calculation means C that calculates the residual rate of the intake air remaining in the engine cylinder based on the actual oxygen concentration; and injection time calculation means for determining the fuel injection time so that the actual air-fuel ratio in the engine cylinder becomes the target air-fuel ratio.

[For production]

The relationship between the oxygen concentration detected by the oxygen concentration sensor and the actual oxygen concentration depending on the engine operating state is determined in advance through experiments or the like and stored. Therefore, the actual oxygen concentration can be determined from the oxygen concentration detected by the oxygen sensor. If the actual oxygen concentration is known, the residual rate of intake air remaining in the engine cylinder can be determined, and if the residual rate is known, the fuel injection time required to bring the actual air-fuel ratio in the engine cylinder to the target air-fuel ratio can be calculated. be able to.

〔Example〕

FIG. 2 shows an overall diagram of a two-stroke internal combustion engine.

Referring to FIG. 2, 1 is a cylinder block, 2 is a piston that reciprocates within the cylinder block l, 3 is a cylinder head fixed on the cylinder block 1, and 4 is a cylinder formed between the piston 2 and the cylinder head 3. combustion chamber,
Reference numeral 5 indicates an intake valve, 6 indicates an intake port, 7 indicates an exhaust valve, 8 indicates an exhaust port, and 9 indicates an air blast valve that injects fuel together with compressed air into the combustion chamber 4. Although not shown in the drawings, an ignition plug is arranged at the center of the inner wall surface of the cylinder head 3. The air supply port 6 is connected to a surge tank 11 via an air supply branch pipe 10, and the surge tank 11 is connected to an engine-driven mechanical supercharger 12, an air supply duct 13, and an air flow meter 1.
It is connected to the air cleaner 15 via 4. A throttle valve 16 is arranged within the air supply duct 13.

FIG. 3 shows an enlarged sectional view of the air blast valve 9.

Referring to FIG. 3, the housing 30 of the air blast valve 9
A compressed air passage 31 extending straight is formed inside.
A nozzle port 32 located within the combustion chamber 4 (FIG. 2) is formed at the tip of this compressed air passage 31. An on-off valve 33 is disposed within the compressed air passage 31, and a valve body 34 for controlling opening and closing of the nozzle port 32 is integrally formed at the outer end of the on-off valve 33. A movable core 36 that is disposed coaxially with the on-off valve 33 and urged toward the on-off valve 33 by a compression spring 35, and a solenoid 37 for attracting the movable core 36 are arranged within the housing 30. The inner end of the on-off valve 33 is brought into contact with the end surface of the movable core 36 by a compression spring 38, and the spring force of the compression spring 38 is
Since the spring force is stronger than the spring force of 5, the nozzle port 32 is normally used as the on-off valve 3.
It is closed by a valve body 34 of No. 3. solenoid 37
When the movable core 36 is energized, the movable core 36 moves toward the on-off valve 33, and as a result, the valve body 34 of the on-off valve 33 opens the nozzle port 32.

On the other hand, a compressed air passage 39 that extends obliquely from the compressed air passage 31 branches off from the compressed air passage 31, and this compressed air passage 39 is connected to a compressed air supply port 40.

A fuel injection valve 41 is attached to the housing 30 , and fuel is injected into the compressed air passage 39 from a nozzle hole 42 of the fuel injection valve 41 .

As shown in FIG. 2, an air blasting air passage 17 is branched from the air supply duct 13 between the air flow meter 14 and the throttle valve 16.
7 is an engine-driven vane pump 8 and a compressed air passage 1
It is connected via 9 to a compressed air distribution chamber 20 . This compressed air distribution chamber 20 is connected to a compressed air supply port 40 of an air blast valve 9 provided for each cylinder. A sub-pressure valve 21 is disposed in the compressed air passage 19 to maintain the compressed air pressure in the compressed air distribution chamber 20 at a predetermined constant pressure, and excess compressed air is returned to the supply air via the compressed air return passage 22. It is returned into the duct 13. The compressed air passages 31, 39 of the air blast valve 9 are therefore filled with compressed air at a constant pressure.

FIG. 4 shows the opening period of the intake valve 5 and the exhaust valve 7, the period of fuel injection from the fuel injection valve 41, and the valve body 34 of the on-off valve 33.
In other words, the valve opening period of the air blast valve 9 is shown.

As shown in FIG. 4, in the embodiment shown in FIG. 2, the exhaust valve 7 opens before the intake valve 5 and closes before the intake valve 5. Also,
As shown in FIG. 4, before the valve body 34 of the on-off valve 33 opens, that is, before the air blast valve 9 opens, the fuel injection valve 41 directs the compressed air into the compressed air passage 39. Fuel is injected. Next, when the air blast valve 9 is opened, the injected fuel is injected from the nozzle port 32 into the combustion chamber 4 together with compressed air. On the other hand, as shown in FIG.
A mask wall 23 that covers the opening of the side air supply valve 5 over the period when the air supply valve 5 is fully open is formed on the inner wall surface of the cylinder head 3. Therefore, when the air supply valve 5 opens, fresh air flows into the air supply boat 6.
The air is supplied into the combustion chamber 4 through the opening of the intake valve 5 on the side opposite to the exhaust valve 7. As a result, the fresh air flows along the peripheral wall surface of the combustion chamber 4 as shown by arrow S, thus achieving good loop scavenging. As shown in FIG. 2, the exhaust boat 8 is connected to an exhaust manifold 24, and an oxygen concentration sensor 25 is disposed within the exhaust manifold 24.

As shown in FIG. 2, the air blast valve 9 is controlled based on an output signal from an electronic control unit 50.

This electronic control unit 50 includes ROM (read only memory) 52 interconnected by a bidirectional bus 51.
, RAM (random access memory) 53, and CP
It has a U (microprocessor) 54, an input port 55, and an output port 56. The air flow meter 14 generates an output voltage proportional to the amount of intake air, and this output voltage is input to the input port 55 via the AD converter 57. The oxygen concentration sensor 25 generates an output voltage proportional to the oxygen concentration (weight %) in the exhaust gas, and this output voltage is input to the input port 55 via the AD converter 58. Further, an output signal from the rotation speed sensor 26 indicating the engine rotation speed is input to the input port 55 .

On the other hand, the output port 56 has a corresponding drive circuit 59. '60
It is connected to the solenoid 37 of the air blast valve 9 and the fuel injection valve 41 via.

In the present invention, the fuel injection time TAU is calculated based on the following equation.

TAtl=K-TP-F・to Here K is a constant TP is the basic fuel injection time F is the residual rate of intake air remaining in the engine cylinder C is a correction coefficient based on engine cooling water temperature, etc.

The basic fuel injection time TP is a function of the engine load Q/N (amount of intake air supplied into the engine cylinder Q/engine speed N) and the engine speed N, and all the intake air supplied into the engine cylinder is It represents the fuel injection time required to bring the air-fuel ratio in the engine cylinder to the target air-fuel ratio, assuming that the fuel remains in the cylinder without blowing through. This basic fuel injection time TP is stored in advance in the ROM 52 in the form of a map as a function of the engine load Q/N and the engine speed N, as shown in FIG.

On the other hand, the residual rate F of intake air is calculated based on the following equation.

F=1-[02]. /[ozlt here [0□]. is the actual oxygen concentration (weight %) in the exhaust gas; [0□ko1 is the oxygen concentration (weight %) of the intake air supplied into the engine cylinder. The oxygen concentration of this intake air [o
zlt is approximately 21% by weight.

In a two-stroke internal combustion engine, a portion of the intake air is sent to exhaust port 8.
The exhaust gas consists of burnt gas and intake air that has blown through. The exhaust gas therefore consists of blown-through intake air in a weight percent of burnt gas. On the other hand, burnt gas consists of % of fuel by weight and intake air that contributed to combustion of % by weight, but since the weight of fuel is negligible compared to the weight of intake air that contributed to combustion, exhaust gas consists of % of fuel by weight. It can be considered that the weight percent of the intake air that has been blown through constitutes the intake air that contributed to combustion. If you think about it this way, [0□ko]. /[0□ko1 represents the proportion of air that has blown through, (1-[02]./[0□],)
It can be seen that represents the proportion of intake air that contributed to combustion, that is, the proportion of intake air that remained in the engine cylinder. Therefore, it can be seen that the intake air remaining ratio F described above represents the proportion of the intake air remaining in the engine cylinder. When the basic fuel injection time TP is multiplied by the residual rate F, this T
P-F represents the fuel injection time required to adjust the actual air-fuel ratio in the engine cylinder to the target air-fuel ratio, and also represents the oxygen concentration [Oz] of the intake air supplied into the engine cylinder.
is constant, so the actual oxygen concentration in the exhaust gas [02]
. If this is known, the actual air-fuel ratio in the engine cylinder can be set to the target air-fuel ratio by setting the fuel injection time to TP-F.

As shown in FIG. 6, the oxygen concentration sensor 25 generates an output voltage V corresponding to the oxygen concentration [0□]k in the exhaust gas, so this oxygen concentration [0□] is the actual oxygen concentration in the exhaust gas. [0□]. By calculating the survival rate F from the output voltage V of the oxygen concentration sensor 25, the actual air-fuel ratio in the engine cylinder can be set as the target air-fuel ratio.

However, the oxygen concentration [02]k detected by this oxygen concentration sensor 25 is not necessarily the actual oxygen concentration [02]k in the exhaust gas. Therefore, even if the survival rate F is calculated based on the oxygen concentration [02]k detected by the oxygen concentration sensor 25, the actual air-fuel ratio in the engine cylinder cannot be set as the target air-fuel ratio.

That is, in a two-stroke internal combustion engine, when the exhaust valve 7 opens, the burned gas in the combustion chamber 4 suddenly blows out into the exhaust port 8.
A so-called blowdown occurs.

After such blowdown occurs, the burned gas within the combustion chamber 4 flows out into the exhaust port 8 relatively slowly. Next, when the intake valve 5 opens, fresh air, that is, intake air, begins to flow into the combustion chamber 4, and a portion of this intake air blows into the exhaust port 8.

By the way, the oxygen concentration sensor 25 generates an output voltage V corresponding to the average oxygen concentration [oz]h of the exhaust gas that comes into contact with the oxygen concentration sensor 25. That is, when the exhaust valve 8 opens, the burnt gas is discharged, and then the blown-through intake air is discharged, but the oxygen concentration sensor 25 detects the average oxygen concentration [02] of these burnt gases and the entire blown-through intake air. Detect k. However, in this case, even if the amount of burned gas and the amount of intake air blown through are constant, if the contact time between the burned gas and the oxygen concentration sensor 25 and the contact time between the intake air blown through and the oxygen concentration sensor 25 change, the oxygen concentration sensor 2
The average oxygen concentration [0,]k detected by 5 changes. For example, when the flow rate of the burned gas around the oxygen concentration sensor 25 is faster than the flow rate of the intake air that has blown through, the amount of burned gas is determined by the oxygen concentration sensor 25 because the contact time between the burned gas and the oxygen concentration sensor 25 is shortened. is detected to be less than the actual amount of burned gas. That is, the amount of intake air that has blown through is detected in many ways, and therefore the oxygen concentration [02]k detected by the oxygen concentration sensor 25 is the actual oxygen concentration [0□]. becomes more expensive than This phenomenon occurs when the flow rate of the burnt gas around the oxygen concentration sensor 25 becomes faster (indeed, it becomes more intense).The flow rate of the burnt gas around the oxygen concentration sensor 25 becomes faster as the blowdown becomes stronger. The oxygen concentration [0□1] detected by the concentration sensor 25 is the actual oxygen concentration [0,].

becomes more expensive than

Incidentally, the higher the engine load, the higher the combustion pressure, and therefore the higher the engine load, the stronger the blowdown.

Therefore, as the engine load increases, the oxygen concentration [02] k detected by the oxygen concentration sensor 25 becomes smaller than the actual oxygen concentration [
0□]. It will be higher than that. Therefore [02]. /[02
] If k is expressed as H, the engine load Q is expressed as shown in Fig. 7.
/N (Intake air amount Q supplied into the engine cylinder/engine speed N) becomes smaller as H becomes smaller. As mentioned above, H=[02].

/[:ozlk, so if you multiply [0□3k by H, you get [[12].

will be found, and hereinafter this H will be referred to as a correction coefficient.

Further, this correction coefficient H is influenced by the engine speed N.

That is, as the engine speed N increases, the amount of burnt gas discharged into the exhaust port 8 per unit time increases, so the pressure within the exhaust port 8, that is, the back pressure increases. When the back pressure increases, it becomes difficult for burned gas to flow out when the exhaust valve 7 is opened, so that blowdown becomes weaker. Therefore, the engine load Q
If /N is the same, the correction coefficient H becomes larger as the engine speed N becomes higher. Therefore, the correction coefficient H is the engine load Q/N
is a function of the engine speed N. Each curve in Fig. 8 shows the same correction coefficient H, so from Fig. 8 it can be seen that the engine load Q/
It can be seen that the higher N and the lower the engine speed N, the larger the correction coefficient H becomes. This correction coefficient H has been determined in advance through an experiment, and the correction coefficient H determined through this experiment is stored in the ROM 52 in advance.

FIG. 9 shows a routine for calculating the fuel injection time TAU, and this routine is executed by interrupts at fixed time intervals.

Referring to FIG. 9, first, in step 70, a basic fuel injection time TP is calculated from the output signals of the air flow meter 14 and the rotational speed sensor 26 based on the relationship shown in FIG. Next, in step 71, the oxygen concentration sensor 2
The output voltage V of No. 5 is read, and then in step 72, the oxygen concentration [02]k is calculated from this output voltage V based on the relationship shown in FIG.

Next, in step 73, a correction coefficient H is determined based on the relationship shown in FIG. 8, and by multiplying this correction coefficient H by [0□]k, the actual oxygen concentration [0□]
Ko. is calculated. Next, in step 74, this [02
]. The residual rate F of the intake air is calculated using the following equation.

F=1-[02]. /[02]1 As mentioned above, [0□]1 is approximately 21% by weight.

Next, in step 75, a correction coefficient C based on the engine cooling water temperature, etc. is calculated, and then in step 76, the actual fuel injection time TAU is calculated based on the following equation.

TAU = TP-F-C [Effects of the Invention] In a two-stroke internal combustion engine, the actual air-fuel ratio in the engine cylinder can be reliably maintained at the target air-fuel ratio.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the invention, Fig. 2 is an overall view of a two-stroke internal combustion engine, Fig. 3 is an enlarged side sectional view of an air blast valve, and Fig. 4 shows the opening period of the air supply and exhaust valves, and the opening period of the air blast valve. 5 is a diagram showing the basic fuel injection time, 6 is a diagram showing the output voltage of the oxygen temperature sensor, 7 is a diagram showing the correction coefficient H, 8 is a diagram showing the valve opening period, etc. The figure shows the correction coefficient H.
FIG. 9 is a flowchart for calculating fuel injection time. 5...Air supply valve, 7...Exhaust valve, 9...
・Air blast valve, 25...Oxygen concentration sensor.

Claims (1)

[Claims] an oxygen concentration sensor that detects the oxygen concentration in the exhaust gas; and a storage means that stores in advance a relationship between the oxygen concentration detected by the oxygen concentration sensor and the actual oxygen concentration in the exhaust gas according to the engine operating state. , an oxygen concentration calculation means for calculating the actual oxygen concentration from the oxygen concentration detected by the oxygen concentration sensor based on the relationship stored in the storage means; and residual intake air remaining in the engine cylinder based on the actual oxygen concentration. and an injection time calculation means for determining the fuel injection time so that the actual air-fuel ratio in the engine cylinder becomes the target air-fuel ratio based on the residual ratio of intake air. Engine fuel injection control device.