JPS63297746A - Air-fuel ratio controller for engine equipped with supercharger - Google Patents

Abstract

PURPOSE:To improve the control precision for air-fuel ratio by calculating the fuel injection quantity on the basis of the value which is obtained by subtracting the intake quantity blasted to the exhaust side from the intake air quantity, in the constitution in which the overlap quantity for each opening period of the intake and exhaust ports can be varied. CONSTITUTION:Two suction ports 3 and 4 are opened on the combustion chamber 2 of an engine 1, and the first and second suction passages 6 and 7 are connected to the suction ports 3 and 4. The overlap period with the valve opening time of an exhaust valve 13 at the second suction port 4 is larger than that of the first suction port 3 and can be varied according to the operation states, and this change is performed by revolving a worm gear 24 by a driving motor 22. In this case, the air blasting quantity is searched from a prescribed map on the basis of the revolution speed and load of the engine, and the corrected intake air is obtained by subtracting the blasting quantity from the intake air quantity searched from an air flow meter 17, and then the fundamental operation fuel injection quantity is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides a supercharged engine that improves fuel efficiency and output performance by effectively scavenging the exhaust gas remaining in the combustion chamber. The present invention relates to an air-fuel ratio control device.

In prior art supercharged engines, residual exhaust gas in the combustion chamber is scavenged using supercharging pressure, and the residual exhaust gas in the combustion chamber causes the combustion chamber temperature to rise, causing knocking, etc. There are known products that prevent this from occurring and improve combustibility and output. For example, JP-A-61-1
No. 85628 discloses that while the supercharger is running, the so-called overlap period from when the intake valve begins to open to when the exhaust valve finishes closing is changed according to the operating state of the engine, and the supercharged air is The present disclosure discloses a supercharged engine in which exhaust gas is pushed out of the combustion chamber by the pressure of

Problems to be Solved by the Invention However, when the periods during which the intake port and the exhaust port are open overlap in this way and the supercharging pressure is used to scavenge the residual exhaust gas in the combustion chamber, the intake It is inevitable that some of the air will blow through to the exhaust side, and the amount of intake air filled into the combustion chamber will be smaller than the amount of intake air measured with an air flow meter, etc. When injecting fuel according to the fuel injection time calculated based on
There was a problem in that the air-fuel mixture became richer than the desired value, and the air-fuel ratio became smaller than the desired value.

Purpose of the Invention The present invention provides a method for controlling the air-fuel ratio of a supercharged engine in a desired manner to improve fuel efficiency and output performance by effectively scavenging exhaust gas remaining in a combustion chamber. It is an object of the present invention to provide an air-fuel ratio control device that can control the air-fuel ratio.

Structure of the Invention This object of the present invention is achieved by providing means for calculating the fuel injection amount based on the value obtained by subtracting the amount of intake air flowing through to the exhaust side from the amount of intake air detected by the intake air amount detection means. . .

In the present invention, the amount of intake air that blows through to the exhaust side is determined experimentally in advance as a function of engine speed and engine load, and is stored in the control unit in the form of a map, etc., and is adjusted depending on each operating state. , can be easily calculated using a map or the like according to the detected engine speed and engine load values.

EXAMPLES Hereinafter, examples of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 is a schematic diagram of a supercharged engine according to an embodiment of the present invention, and FIG. 2 is a road view of a cylinder portion thereof.

1 and 2, a first intake port 3, a second intake port 4, and an exhaust port 5 are open in a combustion chamber 2 of an engine 1, and a first intake port 3 and an exhaust port 5 are opened, respectively.
The first intake passage 6 is connected to the second intake port 4, and the first intake passage 6 is connected to the second intake port 4.
A second intake passage 7 independent of the intake passage 6 is connected to the exhaust port 5, and an exhaust passage 8 is connected to the exhaust port 5, respectively. 1st
A fuel injection valve 9 is provided upstream of the first intake port 3ρ in the intake passage 6, and an open/close control valve 10 is provided upstream of the second intake port 4 in the second intake passage 6. 1st
The intake port 3, the second intake port 4, and the exhaust port 5 are connected to the first intake valve 11 and the second intake valve 12, respectively.
In this embodiment, the opening/closing timing of the first intake port 3 and the exhaust port 5 is constant, and the opening/closing of the second intake port 4 is determined by its opening period and the opening/closing timing of the exhaust port 5. The opening/closing timing of the second intake valve 12 is set so that the overlap period between the opening period of the first intake port 3 and the opening period of the exhaust port 5 is greater than the overlap period between the opening period of the first intake port 3 and the opening period of the exhaust port 5, and can be changed depending on the operating condition. and controlled. First intake passage 6
The second intake passage 7 joins the intake passage 14 upstream of the fuel injection valve 9 and the opening/closing control valve 10, and a throttle valve 15 is provided in the intake passage 14 on the upstream side of the merging part. , an air cleaner 16 and an air flow meter 17 are provided upstream of the throttle valve 15, respectively. In the intake passage 14 between the throttle valve 15, the fuel injection valve 9 and the opening/closing control valve 100,
A mechanical supercharger 18 is provided, as well as a bypass passage 19 that bypasses the mechanical supercharger 18 , and a control valve 20 that opens and closes the bypass passage 19 is provided in the bypass passage 19 . The control unit 21 receives an intake air amount detection signal detected by the air flow meter 17, an engine rotation speed signal detected by a crank angle sensor (not shown), etc., and the control unit 21 controls the intake valve according to these input signals. A drive signal is output to the drive motor 22 and the opening/closing control valve drive means 23, respectively, and the intake valve drive motor 22 rotates the worm gear 24 according to the drive signal, and the second intake valve drive motor 22 rotates the worm gear 24 at a predetermined timing depending on the operating state. Valve 12
The on-off control valve driving means 23 opens and closes the on-off control valve 10 at a predetermined timing according to the operating state according to the drive signal.

FIG. 3 is a graph showing the relationship between the engine operating range and the opening/closing control of the opening/closing control valve 10 in this embodiment.
The figure is a time chart showing the opening/closing timing of the first intake port 3, second intake boat 4, and exhaust port 5 in this embodiment, that is, the opening/closing timing of the first intake valve 11, the second intake valve 12 right side, and the exhaust valve 13. It is.

In FIG. 3, a region A indicated by a matte finish is a low-speed, low-load operating region in which the on-off control valve 10 is closed and no air is taken from the second intake boat 3.

In the low-speed, low-load operating region, no supercharging effect can be obtained, and if the opening periods of the second intake valve 12 and exhaust valve 13 overlap, combustion becomes unstable, so the on-off control valve 10 is closed. , the second intake port 4 for scavenging is closed. Area B shown with diagonal lines is the opening/closing control valve 1
0 is opened and the remaining exhaust gas in the combustion chamber is scavenged by intake air from the second intake boat 4. Region C between region A and region B is a transition region, and in this region, the on-off control valve 10 is opened, but the opening degree is controlled to gradually change. In FIG. 4, the curve X is
The lift curve of the first intake valve 11, curve Y is the lift curve of the second intake valve 12, and the curve Z is the lift curve of the exhaust valve 1.
3, the overlapping period between the opening period of the first intake valve 11 and the opening period of the exhaust valve 13 is set so that there is almost no overlap, while The overlap period between the opening period of the first intake valve 12 and the opening period of the exhaust valve 13 is always greater than the overlap period between the opening period of the first intake valve 11 and the opening period of the exhaust valve 13. The opening and closing timings of the two intake valves 12 are set. In this way, since the opening/closing timing of the first intake valve 11, second intake valve 12, and exhaust valve 13 is set and controlled, in the operating range where the opening/closing control valve 10 is open except for low rotation and low load, During the opening period of the exhaust valve 13, the second intake pulp I2 is opened, and the supercharged intake air flows into the combustion chamber 2 from the second intake port 4, and the exhaust gas remaining in the combustion chamber 2 is removed. Gas is scavenged. Further, the fuel injection valve 9 has a first intake port 3 connected to the first intake port 3 opened and closed by the first intake valve 11 whose opening period hardly overlaps with the opening period of the exhaust valve 13. aisle 6
Since the fuel is injected into the combustion chamber 2 through the first intake port 3, the fuel injected into the combustion chamber 2 can immediately flow out of the combustion chamber 2 through the exhaust port 5. Prevented. Furthermore, in the low rotation and high load operating region, it is desirable that the amount of overlap between the opening periods of the second intake valve 12 and the exhaust valve 13 be 10 degrees or more in terms of crank angle. In this way, the second intake valve 1
2 and the opening period of the exhaust valve 13 is set, the scavenging effect prevents knocking in the low-speed, high-load operating range. In order to prevent this, even in supercharged engines where the effective compression ratio was set low, the effective compression ratio can be set to 8.5 or higher, and the combustibility and fuel efficiency are within the practical operating range. This makes it possible to improve the rate.

As shown in FIG. 3, the overlap period between the opening periods of the second intake valve 12 and the exhaust valve 13 is the period when the opening/closing control valve l
In the low-speed, high-load operation region where O is open, the engine speed is controlled to increase as the engine speed increases. Even if the amount of overlap indicated by the crank angle is the same, when the engine speed is low, the actual overlap time during which both the second intake valve 12 and the exhaust valve 13 are open becomes longer; When the height increases, the second intake valve 12 and exhaust valve 13
The actual overlap time when both are open is necessarily shorter, so in the operating range where engine speed is low
If the amount of overlap indicated by the crank angle is not controlled to be small, the amount of fresh air blown into the exhaust side will increase, leading to a decrease in the charging amount, resulting in a decrease in output, and the engine speed will also decrease. In a high operating range, a sufficient scavenging effect cannot be expected unless the amount of overlap indicated by the crank angle is largely controlled. However, in the high-speed, high-load operating range, as the engine speed increases, the exhaust pressure increases and may become greater than the intake pressure.
In such an operating range, when increasing the overlap period, there is a risk of fuel blowing back toward the second intake passage 7, so conversely, the overlap period is controlled to become smaller as the engine speed increases. There is. Further, in the low load operation region, the overlap period is controlled to be smaller than that in the high load operation region.

In this way, by controlling the overlap period between the opening periods of the second intake valve 12 and the exhaust valve 13, the exhaust gas remaining in the combustion chamber 2 can be effectively scavenged, and the combustibility can be greatly improved. can be improved, but the second
As long as the opening periods of the intake valve 12 and the exhaust valve 13 overlap, it is impossible to completely prevent two parts of the intake air taken into the combustion chamber 2 from blowing through from the exhaust port 5 to the exhaust passage 8. Therefore, when calculating the fuel injection amount to give a desired air-fuel ratio based on the intake air amount detected by the air flow meter 17, the intake air amount used for combustion is determined based on the detected intake air amount. As a result, the actual air-fuel ratio will inevitably be smaller than the desired value.

Therefore, in this embodiment, the amount of intake air that blows through to the exhaust side is experimentally determined in advance based on the engine speed and engine load, and is stored in the control unit 21 in the form of a map. According to the detected value of the intake air and the engine load, the control unit 7) 21) calculates the amount ΔQ of the intake air vent, and subtracts this from the intake air amount Q detected by the air flow meter 17 to obtain the corrected intake air amount. The basic fuel injection amount is calculated based on the air amount Q. The amount of intake air blowing ΔQ varies depending on the amount of overlap between the opening periods of the second intake valve 12 and the exhaust valve 13, but in this embodiment, this amount of overlap is a function of the engine speed and the engine load. Therefore, the intake air blowout amount ΔQ is determined by the engine speed and engine load.

FIG. 5 is a flowchart of fuel injection amount control according to this embodiment.

In FIG. 5, first, the intake air amount Qm detected by the air flow meter 17, and the engine rotation speed and crank angle detected by a crank angle sensor (not shown) are input manually to the control unit 21, respectively. Next, according to the input engine speed and the detected value of the engine load, the amount ΔQ of the intake air blowout is calculated using a map stored in the control unit 21 in advance, and the amount ΔQ is corrected using the following formula. The intake air amount Q is calculated.

Q=Q, -ΔQ According to the corrected intake air amount Q obtained in this way, the control unit 211. : Using the stored map etc., the basic fuel injection amount is calculated in the form of injection time. Thereafter, necessary corrections are made to determine the injection time of the fuel to be injected, and when the fuel injection timing is reached, the fuel is injected.

According to this embodiment, the exhaust gas remaining in the combustion chamber 2 can be effectively scavenged, and the air-fuel ratio can be controlled as desired while improving combustibility and fuel efficiency.

The present invention is not limited to the above-mentioned examples, but various modifications can be made within the scope of the invention described in the claims, and these are also included within the scope of the present invention. Needless to say.

For example, in the above embodiment, the second intake valve 12
By controlling the opening/closing timing of the second intake valve 12 and the exhaust valve 13, the amount of overlap between the opening periods of the second intake valve 12 and the exhaust valve 13 is controlled.
It is desirable to control the amount of overlap by controlling the opening/closing timing of the exhaust valve 13. When controlling the second intake valve 12 to open quickly in order to increase the amount of overlap, the piston is still in the rising process, so the rising pressure of the piston causes the combustion chamber 2 to open quickly.
The intake air drawn into the combustion chamber 2 tends to flow over the upper surface of the combustion chamber 2, so that the exhaust gas near the upper surface of the piston is not scavenged.
, and when the piston rises to near top dead center,
Although the rising pressure of the piston becomes weaker, the exhaust valve 13
Since the lift amount of the exhaust valve 13 becomes small, a scavenging effect of the exhaust gas near the top surface of the piston cannot be expected, and in the end, the residual exhaust gas may not be sufficiently scavenged. However, by controlling the timing of closing the exhaust valve 13, When controlling the overlap period, when controlling the overlap period to a large extent, at the time of overlap, the piston is in a descending state, so the pressure in the combustion chamber 2 decreases, and the intake air flows into the vicinity of the top surface of the piston. This makes it possible to sufficiently scavenge exhaust gas near the top surface of the piston, further enhancing the scavenging effect, and making knocking less likely to occur, making it possible to further increase the compression ratio, improving fuel efficiency and output performance. can be further improved. Furthermore,
In this way, when the overlap period is controlled by controlling the opening/closing timing of the exhaust valve 13, the opening/closing timing of the intake port is set so as to increase the filling amount by utilizing the intake resonance effect. Even in supercharged engines, the overlap period can be controlled as desired without impairing the intake resonance effect, which has the advantage of increasing the scavenging effect and improving combustibility. .

Furthermore, in the embodiment described above, the opening/closing timing of the intake valve 12 of the second intake port 4 is continuously controlled depending on the operating condition. It is also possible to control the overlap period by setting several valve periods and selecting one of them depending on the operating state.

The same applies to the case where the overlap period is controlled by controlling the opening/closing timing of the exhaust valve 13.

Furthermore, in the embodiment described above, the fuel injection valve 9 is provided in the first intake passage 6 connected to the first intake port 3; The fuel injection valve 9 may be provided at a position biased towards the first intake passage 6 side.

Effects of the Invention According to the present invention, by effectively scavenging the exhaust gas remaining in the combustion chamber, it is possible to control the air-fuel ratio as desired while improving fuel efficiency and output performance. becomes.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a supercharged engine according to an embodiment of the present invention, and FIG. 2 is a road view of a cylinder portion thereof. FIG. 3 is a graph showing the relationship between the engine operating range and the opening/closing control of the opening/closing control valve in the embodiment of the present invention, and FIG. 4 is a graph showing the opening/closing of the first intake valve, second intake valve, and exhaust valve. It is a time chart showing timing. FIG. 5 is a flowchart of fuel injection amount control in an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Engine, 2... Combustion chamber, 3... First intake port, 4... Second intake port, 5... Exhaust port, 6...
...first intake passage, 7...second intake passage, 8...
Exhaust passage, 9...Fuel injection valve, 10...Opening/closing control valve, 11...First intake valve, 12...Second intake valve, 13...Exhaust valve, 14...Intake passage , 15・
... Throttle valve, 16... Air cleaner, 17... Air flow meter, 18... Mechanical supercharger, 19... Bypass passage, 20... Control valve, 21...
◆9 Control unit, 22... Intake valve drive motor, 23... Opening/closing control valve drive child, 24... Worm gear.

Claims (1)

[Claims] In an air-fuel ratio control device for a supercharged engine that largely controls the amount of overlap between the open periods of the intake port and the exhaust port in an operating range where the engine load is above a predetermined value, the intake air amount detected by the intake air amount detection means is An air-fuel ratio control device for a supercharged engine, comprising means for calculating a fuel injection amount based on a value obtained by subtracting an amount of intake air that blows through to the exhaust side from an amount of air.