JP2935625B2 - Air-fuel ratio control device for gas engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for a gas engine using high-pressure natural gas as fuel.

[0002]

2. Description of the Related Art A gas engine using high-pressure natural gas as fuel is disclosed, for example, in Japanese Utility Model Laid-Open Publication No. 60-92742. The fuel from a high-pressure cylinder is depressurized by a pressure reducing valve (gas regulator). The mixture is mixed with the engine intake air at a predetermined ratio by a mixer, and this mixture is supplied to the engine.

[0003]

However, the mixing of air and fuel in the mixer is difficult to be carried out sufficiently homogeneously, since both are gaseous. The air-fuel ratio of the air-fuel mixture tends to vary. Variations in air-fuel ratio between cylinders make combustion uneven and unstable,
This causes a torque difference between cylinders and causes deterioration of fuel efficiency and exhaust composition.

An object of the present invention is to solve such a problem, that is, to eliminate variations in the air-fuel ratio between cylinders, and to improve output performance and exhaust composition.

[0005]

According to the present invention, as shown in FIG. 1 , intake air is provided upstream of an engine intake manifold.
Gas fuel to produce a predetermined lean mixture depending on the amount
(5), which is arranged for each cylinder.
From the mixer through the intake manifold branch.
Auxiliary fuel supply to add gaseous fuel to the supplied lean mixture
Means (12) , an air-fuel ratio detecting means (13) for detecting an air-fuel ratio for each cylinder, and a fuel supply amount of each auxiliary fuel supply means.
The detected air-fuel ratio of the corresponding cylinder depends on the operating condition.
Comprising a means for controlling such that the target air-fuel ratio (12), the.

[0006]

The basic fuel is mixed with the intake air by the mixer so as to have a substantially constant lean air-fuel ratio, and this air-fuel mixture is sucked into each cylinder through the branch of the intake manifold.
It becomes a uniform mixed state before being charged . On the other hand,
Air-fuel ratio is detected for each cylinder by the air-fuel ratio detecting means, this
Of the intake manifold from the mixer according to the air-fuel ratio of the
Supplementary fuel added to the lean mixture supplied via the punch
The amount is controlled for each cylinder, the air-fuel ratio among the cylinders is to match the accuracy target air-fuel ratio.

In this case, instead of controlling the total amount of required fuel for each cylinder, an air-fuel mixture having a substantially constant concentration is generated in advance, and the supply amount of auxiliary fuel for each cylinder is determined according to the detected air-fuel ratio. Responsiveness and stability of the air-fuel ratio control are improved. In addition, since a large amount of fuel is previously mixed with intake air in the mixer, the mixture of fuel and air taken into each cylinder is sufficiently uniform compared to supplying the entire amount to each cylinder. A stable combustion state with less uneven combustion can be obtained.

In this case, the total amount of fuel required is not controlled for each cylinder, but a mixture of approximately constant concentration is generated in advance, and the fuel additionally supplied for each cylinder is detected. Since the control is performed according to the air-fuel ratio, the responsiveness and stability of the control of the air-fuel ratio are improved. In addition, since a large amount of fuel is preliminarily mixed with air in the mixer, the mixing of fuel and air sucked into each cylinder is sufficiently promoted as compared with the case where the entire amount is supplied to each cylinder, and combustion is improved. Stable combustion with less unevenness can be obtained.

[0009]

In the embodiment shown in FIG. 2, 1 is a six-cylinder engine main body, 2 is an intake passage, 3 is an exhaust passage, and a throttle valve 4 linked to an accelerator pedal (not shown) provided in the intake passage 2.
A mixer 5 for mixing the intake air and the gaseous fuel is installed upstream of the mixer.

The mixer 5 has a venturi section 6, and a fuel nozzle 7 is opened in the venturi section 6, and the gas fuel is supplied from the fuel nozzle 7 according to the amount of intake air passing through the venturi section 6 according to the throttle valve opening. Is sucked out. Reference numeral 8 denotes a high-pressure cylinder filled with high-pressure natural gas. The fuel passage 11 from the high-pressure cylinder 8 is connected to a fuel nozzle 11 via a shut-off valve 9 that closes when the engine is stopped or the like and a pressure reducing valve 10 that reduces the pressure of the high-pressure gas to a predetermined pressure. Connect to 7. As a result, the mixer 5 generates an air-fuel mixture having a substantially constant concentration, which is leaner than the stoichiometric air-fuel ratio, and supplies the mixture to the engine body 1.

An intake port of each cylinder of the engine body 1 has an auxiliary fuel supply valve 12 for supplementarily supplying fuel.
Are operated in synchronism with the engine rotation in response to a fuel injection signal from the control device 15, and additionally supply fuel in the intake stroke of each cylinder. Auxiliary fuel supply valve 12
The fuel from the pressure reducing valve 10 is guided to the auxiliary fuel supply valve 12, and the auxiliary fuel supply valve 12 is supplied with gas fuel of a predetermined pressure to each intake port while the valve is opened. Further, an oxygen sensor 13 for detecting an exhaust air-fuel ratio is provided at an exhaust port of each cylinder, and an oxygen concentration (air-fuel ratio) detected by the oxygen sensor 13 is fed back to the control device 15 so that the actual The supply amount of the auxiliary fuel is corrected for each cylinder so that the air-fuel ratio of the cylinder matches the target air-fuel ratio set based on the operating state.

The control device 15 includes a speed sensor 16 for detecting the engine speed, a negative pressure sensor 17 for detecting a suction negative pressure downstream of the throttle valve, and an opening degree (fully closed) of the throttle valve 4. Each signal from the throttle opening sensor 18 is input, and a target air-fuel ratio is set according to these operating conditions.
Also, an engine key switch 19, a start switch 2
Signals from 0 are also input, and these are used to set a target air-fuel ratio when the engine is started.

The shut-off valve 9 is energized by turning on the engine key switch 19 and opens.

Next, the overall control operation will be described with reference to the flowcharts of FIGS.

In FIG. 3, when the engine key switch 19 is first turned on, the primary shut-off valve 9 of the fuel is opened, and when the start switch 20 is turned on, the auxiliary fuel is set so that the air-fuel ratio required for starting is attained. Is set, and the auxiliary fuel supply valve 12 is driven (steps 1 to 3).

At this time, the air-fuel mixture having a predetermined air-fuel ratio is generated by the mixer 5, which is thinner than the air-fuel ratio required at the time of starting. Therefore, the auxiliary fuel is supplied from the auxiliary fuel supply valve 12. Accordingly, the air-fuel mixture becomes rich to a predetermined concentration.

In step 4, the engine speed is detected,
If there is no increase in the number of revolutions, the engine stall is determined at step S5 after a lapse of a predetermined time (short time), the auxiliary fuel supply valve 12 is turned off, and a restart is waited.

On the other hand, if the engine speed has increased, the routine proceeds to step 8, where the engine stall determination is turned off, that is, it is determined that the engine has entered into an independent operation.
The process shifts to normal air-fuel ratio control (step 9).

When the start of the engine is completed in this way, the process proceeds to an air-fuel ratio control routine (contents of step 9) also shown in FIG.

The engine speed and the engine load (throttle valve opening or suction negative pressure) are detected, and the target air-fuel ratio λA corresponding to the operating state at that time is calculated (steps 11 to 1).
3). Then, the cylinder to be controlled in step 14 is set to # 1, CYL = 1 is set, and the oxygen sensor 13 of that cylinder is set.
, An actual air-fuel ratio λB is detected from the output. A deviation Δλ = λA−λB between the target air-fuel ratio and the actual air-fuel ratio is obtained, and PID, which is an operation of normal feedback control, is obtained from the deviation.
A correction value of λ is calculated by (proportional, integral, differential) control (steps 15 to 19). An opening value (control duty) of the auxiliary fuel supply valve 12 is calculated based on the correction value λ, and is output to the auxiliary fuel supply valve 12 (step 2).
0, 21).

Accordingly, the auxiliary fuel supplied from the auxiliary fuel supply valve 12 to the intake port is subjected to correction control so that the detected air-fuel ratio matches the target air-fuel ratio. It is controlled to the target value.

In step 22, to control the next cylinder, CYL = CYL + 1, and the number of cylinders is CYL = 6.
Until, the process returns to step 15 and the same operation as described above is repeated. When the control cylinder ends up to # 6 cylinder,
It returns to the start again, and repeats the same operation again in the next cycle (step 23).

In this way, the air-fuel ratio supplied to each cylinder is feedback-controlled while detecting the actual air-fuel ratio for each cylinder, so that the air-fuel ratio of each cylinder can be accurately converged to the target value. .

The air-fuel mixture supplied to the engine body 1 is basically controlled by the mixer 5 to have an air-fuel ratio that is thinner than the stoichiometric air-fuel ratio and has a substantially constant concentration. The gaseous fuel and the air are sufficiently mixed before the mixture is sucked into the engine body 1. Auxiliary fuel is supplied from the auxiliary fuel supply valve 12 for supplying auxiliary fuel to the previously generated air-fuel mixture, and the air-fuel ratio as a whole becomes the target air-fuel ratio.

What is corrected by the feedback control is not the entire fuel but only the additional fuel from the auxiliary fuel supply valve 12. Therefore, the response of the feedback control is excellent and the stability is very high. In addition, mixer 5
Since the additional fuel from the auxiliary fuel supply valve 12 is mixed with the air-fuel mixture generated at the intake port at the intake port, the mixing of the gaseous fuel and air is improved as compared with injecting the entire amount to the intake port. , The variation of the mixture in each cylinder is eliminated,
The combustion stabilizes accordingly.

As a result, variations in the air-fuel ratio between the cylinders are eliminated, torque fluctuations between the cylinders are reduced, fuel efficiency is improved, and the exhaust composition is made uniform. Fuel ratio window (catalyst required air-fuel ratio)
Control becomes easy, high exhaust purification efficiency is obtained,
In the case of lean combustion, the trade-off between NOx and HC or CO can be eliminated.

[0027]

As described above, according to the present invention, the engine intake
Predetermined lean according to the intake air amount upstream of the manifold
A mixer for mixing the gaseous fuel to produce an air-fuel mixture ;
The intake manifold is located for each cylinder and
Gaseous fuel into the lean mixture supplied through the
Auxiliary fuel supply means for adding fuel , air-fuel ratio detection means for detecting the air-fuel ratio of each cylinder, and fuel for each auxiliary fuel supply means.
The detected air-fuel ratio of the cylinder corresponding to the supply amount is the operating state
Because of and means for controlling so that the target air-fuel ratio in accordance with the air-fuel ratio in each cylinder is coincident with accurately the target air-fuel ratio, moreover, to control the total amount of fuel required for each cylinder Instead, an air-fuel mixture of approximately constant concentration is generated in advance, and the amount of auxiliary fuel supplied is controlled for each cylinder, so that the responsiveness and stability of the air-fuel ratio control are improved, Since the auxiliary fuel is mixed with the generated air-fuel mixture,
The mixture between fuel and air drawn into each cylinder is improved,
As a result, variations in the air-fuel ratio between the cylinders are eliminated,
Stable combustion with little torque fluctuation between cylinders is secured,
The effect of improving fuel efficiency and uniform improvement of exhaust composition can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing the present invention.

FIG. 2 is an overall configuration diagram showing an embodiment of the present invention.

FIG. 3 is a flowchart showing an overall control operation.

FIG. 4 is a flowchart illustrating an operation of air-fuel ratio control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 2 Intake passage 3 Exhaust passage 5 Mixer 8 High pressure cylinder 10 Pressure reducing valve 12 Solenoid valve 13 Oxygen sensor 15 Control device

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Takada Nissan Diesel Kogyo Co., Ltd. (72) Inventor Nobuo Hamasaki Nissan Diesel Kogyo 1 (56) References JP-A-64-73158 (JP, A) JP-A-2-233867 (JP, A) JP-A-5-10212 (JP, A) JP-A-3-194144 (JP, A) A) JP-A-1-200053 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F02D 41/14 310 F02D 41/14 330 F02D 19/02 F02D 41/36 F02M 21 / 02 311

Claims (1)

(57) [Claims] 1. Intake at an upstream side of an engine intake manifold
Gas to generate a predetermined lean mixture according to the amount of air
A mixer for mixing the fuel and a cylinder
From the mixer through the branch of the intake manifold
Supplementary fuel supplier to add gaseous fuel to the lean mixture
Stage , air-fuel ratio detection means for detecting the air-fuel ratio of each cylinder,
The fuel supply amount of each auxiliary fuel supply means is
The detected air-fuel ratio of the cylinder becomes the target air-fuel ratio according to the operating condition.
Air-fuel ratio control system for a gas engine, characterized in that it comprises means for controlled so, the.