JP2915255B2 - 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]

By the way, when the engine is operated near the stoichiometric air-fuel ratio using natural gas as fuel,
In particular, when the load is high, the temperature of the combustion exhaust gas becomes too high (800 to 900 ° C.), and there is a problem that the engine durability reliability due to the heat load is reduced.

On the other hand, the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio based on the output of the exhaust sensor up to a predetermined load and rotation speed. In some systems, the control is released to switch to a constant lean air-fuel ratio.

In this case, although effective in terms of engine durability, new problems such as a reduction in exhaust gas purification efficiency and a reduction in output performance due to the three-way catalyst arise. Just because the operating condition has reached a certain condition does not mean that the combustion temperature does not always reach the vicinity of the upper limit.In this case, if the feedback control is released and fixed to a constant lean air-fuel ratio, the exhaust Purification efficiency is reduced. Conversely, even if the lean air-fuel ratio is set to lower the combustion temperature, the operating state fluctuates before the temperature is sufficiently lowered, and if the rotational speed or the load falls below a certain level, the air-fuel ratio is switched again to the stoichiometric air-fuel ratio. In this case, even if the load and the number of revolutions are not so high, the combustion gas temperature remains high, and the thermal durability reliability may be impaired.

An object of the present invention is to solve such a problem, that is, to improve the engine output and the exhaust composition while maintaining the thermal durability of the engine.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a method as shown in FIG.
As shown in (1), in a gas engine using high-pressure natural gas as fuel, fuel supply means (11) provided in an intake passage
Means (8, 18) for detecting an operating state, means (A) for setting a target air-fuel ratio based on a stoichiometric air-fuel ratio according to the operating state, and means (9) for detecting an exhaust air-fuel ratio. This
And means for air-fuel ratio of the feedback control of the fuel supply quantity so as to coincide with the target air-fuel ratio (B), and means (16) for detecting the exhaust gas temperature, the target air-Once beyond the temperature at which the exhaust temperature is preset Means for correcting fuel ratio to lean side (C)
And

[0008]

[Function] Basically, the operation is performed with a mixture of the stoichiometric air-fuel ratio. For example, when the exhaust gas temperature becomes higher than a set value at a high load, the target air-fuel ratio is shifted to a lean side according to the temperature, and if the temperature falls, Return to the stoichiometric air-fuel ratio. For this reason, the air-fuel ratio is not controlled to the lean side more than necessary, and high durability reliability against the thermal load of the engine can be maintained while ensuring exhaust performance and output performance in a wide operating range.

[0009]

FIG. 2 shows an embodiment of the present invention, in which a throttle valve 19 is provided in an intake passage 17 of the gas engine 1.
Is linked to an accelerator pedal (not shown), and the amount of intake air is controlled according to the throttle valve opening. A mixer 10 is provided upstream of the throttle valve 19 as a main fuel supply system, and mixes gas fuel in accordance with the intake air amount to generate a predetermined lean air-fuel mixture. Fuel from a gas cylinder 15 filled with high-pressure natural gas is guided to the mixer 10 in a state where the fuel is reduced to a predetermined pressure via a gas regulator 13, and negative pressure generated in a venturi portion in proportion to the amount of intake air. Inhaled according to pressure.

A part of the fuel is guided to a fuel solenoid valve 11 as an auxiliary fuel supply system provided upstream of the throttle valve 19 in the vicinity of the throttle valve 19, and gas fuel is added to the intake passage 17 by opening the solenoid valve 11. Supply.

The engine combustion chamber 24 is provided with an ignition plug 7 for igniting the air-fuel mixture near the compression top dead center.

A control unit 2 for controlling the operation of the solenoid valve 11 and the spark plug 7 and for controlling the fuel pressure regulated by the gas regulator 16 is provided. The control unit 2 supplies fuel from the solenoid valve 11. The amount is controlled so that the air-fuel ratio of the air-fuel mixture supplied to each cylinder coincides with a target air-fuel ratio determined according to the operation state, and the ignition plug 7 is controlled to be ignited at the optimum ignition timing.

For this reason, the control unit 2 includes:
Crank angle sensor 8 for detecting engine speed and crank angle, negative pressure sensor 18 for detecting suction negative pressure downstream of the throttle valve
, An exhaust sensor (inclined O ₂ sensor) 9 for detecting an exhaust air-fuel ratio (oxygen concentration) in an exhaust passage 19 downstream of the exhaust valve 22, and an exhaust temperature for detecting an exhaust temperature. A signal from the sensor 16 is input, and based on these, a target air-fuel ratio is determined according to the driving state,
The supply amount of the additional fuel injected from the fuel injection valve 11 is calculated based on the deviation between the actual air-fuel ratio and the target air-fuel ratio from the output of the exhaust sensor 9 and the exhaust temperature from the exhaust temperature sensor 16. Further, the conduction of the power transistor 5 is controlled so that the ignition plug 7 is ignited at an optimum ignition timing according to the operation state, and a high voltage is applied to the ignition plug 7 from the ignition coil 6.

A signal from an ignition switch 3 connected to the battery 4 is also input to the control unit 2, whereby fuel shutoff valves 12 and 14 for shutting off a fuel passage from the gas cylinder 15 are turned on when the ignition switch 3 is turned on. It is designed to open.

Here, the fuel control of the fuel solenoid valve 11 by the control unit 2 will be described in more detail with reference to the flowchart of FIG.

First, in steps 1 to 3, the rotation speed sensor 8
Then, the operating state is read based on the signal from the intake negative pressure sensor 18 and the target air-fuel ratio (basically, the stoichiometric air-fuel ratio) is determined by searching a map even in response to the operating state to determine the target air-fuel ratio.

Next, the exhaust gas temperature is read from the output of the exhaust gas temperature sensor 16 and it is determined whether or not it is higher than a preset exhaust gas temperature (steps 4 and 5). If the temperature is equal to or higher than the set temperature, the process proceeds to step 6, where the target air-fuel ratio is corrected to a lean side by a fixed amount.

In step 7, the actual air-fuel ratio is read from the output of the exhaust sensor 9, and the fuel supply amount is calculated so that the corrected target air-fuel ratio matches the actual air-fuel ratio. Output to the valve 11 (step 8,
9).

When the exhaust temperature is equal to or lower than the set temperature in step 5, the fuel supply amount is calculated in step 8 based on the target air-fuel ratio calculated in step 3.

Thus, the control unit 2
Controls the amount of fuel supplied from the solenoid valve 11 for each cycle.

Next, the overall operation will be described.

The air-fuel mixture supplied to the gas engine 1 is generated in the mixer 10 in the intake passage 17 upstream of the throttle valve 19 so as to have a predetermined lean air-fuel ratio in advance. Although this air-fuel mixture has a substantially constant value irrespective of the operation state, it is thinner than the required air-fuel ratio and does not burn smoothly by itself. However, fuel is supplementarily supplied by the electromagnetic valve 11 provided in the vicinity of the throttle valve 23, and feedback control is performed so that the target air-fuel ratio (the stoichiometric air-fuel ratio) is obtained. The purification efficiency of the catalyst is high and the output performance of the engine is well maintained.

On the other hand, when the exhaust gas temperature rises above a set temperature determined from the thermal durability of the engine during operation, the target air-fuel ratio is corrected to a lean side, thereby suppressing the temperature rise. In this case, while the temperature is higher than the set value, the air-fuel ratio is reduced, so that the temperature can be surely lowered.

FIG. 4 is a characteristic diagram showing the relationship between the air-fuel ratio and the combustion exhaust gas temperature when the engine speed and the ignition timing are constant. The maximum temperature is obtained near the stoichiometric air-fuel ratio.
It can be seen that the temperature decreases with dilution.

Then, when the exhaust gas temperature falls below the set temperature, the air-fuel ratio returns to the target air-fuel ratio determined by the operating condition, and thus, in principle, the target air-fuel ratio is maintained.
Only when the temperature is high, the air-fuel ratio is diluted as needed, so that the output and exhaust performance can be maintained in the best state while ensuring the thermal durability of the engine.

In this embodiment, the mixer 10 and the solenoid valve 11 are provided as the fuel supply system, and the solenoid valve 11 is feedback-controlled. However, only the mixer 10 or the fuel injection valve is provided. Alternatively, the fuel supply amount may be controlled.

As described above, according to the present invention, in a gas engine using high-pressure natural gas as a fuel, a fuel supply means provided in an intake passage, a means for detecting an operation state, and a stoichiometric air-fuel ratio in accordance with the operation state are provided. means for setting a target air-fuel ratio of the basic means for detecting an exhaust air-fuel ratio, and means for feedback controlling a fuel supply amount so that the air-fuel ratio coincides with the target air-fuel ratio, means for detecting the exhaust gas temperature , due to a means for correcting the target air-fuel ratio when exceeding the temperature at which the exhaust temperature is preset to lean side is basically operated with the air-fuel mixture of the stoichiometric air-fuel ratio is made the exhaust, for example when a high load When the temperature is equal to or higher than the set value, the target air ratio is shifted to the lean side in accordance with the temperature, and is returned to the stoichiometric air-fuel ratio side when the temperature is lowered.Therefore, the air-fuel ratio is not controlled to the lean side more than necessary, Wide driving While ensuring the exhaust performance and power performance in range, it is possible to maintain high endurance reliability against thermal load of the engine.

[Brief description of the drawings]

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

FIG. 2 is a structural sectional view showing an embodiment of the present invention.

FIG. 3 is a flowchart showing a fuel control operation.

FIG. 4 is a characteristic diagram showing a relationship between an air-fuel ratio and a combustion exhaust temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas engine 2 Control unit 7 Spark plug 8 Crank angle (rotation speed) sensor 9 Exhaust sensor 10 Mixer 11 Solenoid valve 15 Gas cylinder 18 Suction negative pressure sensor

Continuing on the front page (72) Inventor Hiroshi Takada Ichibanchi, Dai-Chome, Ageo-shi, Saitama Nissan Diesel Kogyo Co., Ltd. (72) Inventor Nobuo Hamasaki Nissan Diesel Industrial Co., Ltd. (56) References JP-A 5-24922 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) F02M 21/02 F02D 19/02 F02D 41/14 F02D 45/00

Claims (1)

(57) [Claims] 1. A gas engine using high-pressure natural gas as a fuel, a fuel supply means provided in an intake passage, a means for detecting an operation state, and a stoichiometric air-fuel ratio based on the operation state.
Means for detecting and means for setting a target air-fuel ratio, means for detecting the exhaust air-fuel ratio, and means for feedback controlling a fuel supply amount so that the air-fuel ratio coincides with the target air-fuel ratio, the exhaust gas temperature to, air-fuel ratio control system for a gas engine, characterized in that the target air-fuel ratio When exceeding the temperature at which the exhaust temperature is preset and means for correcting the lean side.