JPH09228859A - Intake device for gas engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen the effect of air pulsation, and stably execute air-fuel ratio control by providing a resonator at the halfway of an air feed pipe through a large diameter connecting pipe in the device where an air feed pipe for an air compressor is connected with the upstream side of a venturi part within an air intake passage. SOLUTION: In the fuel feed system of a gas engine, a gas mixer 8 is disposed at the venturi part 7 of an air intake passage 2, and a gas feed path composed of a gas cylinder 10 and a regulator 11 is connected with the gas mixer 8 through a main fuel passage 12 and a sub fuel passage 13. The suction port of an air compressor 16 for which an engine is driven to feed compressed air to be used for a brake and the like, is connected with the connection part 17a at the upstream of the venturi 7 by way of an air feed pipe 17. In this case, a resonator 22 is connected with the air feed pipe 17 at its halfway by a large diameter connecting pipe 23, and thereby the suction passage 2 is prevented from being affected by the pulsation of the air compressor 16, so that stable air-fuel ratio control is thereby executed.

Description

Detailed Description of the Invention

The present invention relates to an intake system for a gas engine that uses gas such as compressed natural gas or liquefied natural gas as a fuel.

[0002]

2. Description of the Related Art As shown in FIG. 6, a gas engine having a diesel engine as a basic structure has an intake passage 2 having an air cleaner 1, a three-way catalytic converter 4, and an O upstream of the three-way catalytic converter 4. ₂ An exhaust pipe 6 provided with a sensor 5 is connected to the engine body 3 respectively.

As a fuel supply system, a gas mixer 8 is arranged in the venturi portion 7 of the intake passage 2, a throttle valve 9 is arranged behind it, and a gas cylinder 10 filled with high-pressure fuel gas is provided with a regulator 11. The passage is branched into a main fuel passage 12 and a sub fuel passage 13 and connected to the gas mixer 8, and a gas flow rate control valve 14 (electromagnetic solenoid valve) is provided in the sub fuel passage 13 to control the duty ratio of the fuel gas flow rate. It is supposed to do.

Further, a detection signal of the oxygen concentration in the exhaust gas by the O ₂ sensor 5 provided on the upstream side of the three-way catalytic converter 4 is input to the control device 20 to create a control signal, and the control signal is used to generate the gas. The flow rate control device 14 is adapted to control the duty ratio. On the other hand, in a large vehicle or the like, an air compressor 16 (usually a piston type air compressor) is attached to supply compressed air to an air tank that stores compressed air used for a brake or the like, and the air compressor 16 is driven by the engine body 3. I am doing it. The air supply pipe 17 to which the air compressor 16 is connected is connected to the upstream connecting portion 17a of the venturi portion 7 so that air is sucked from the intake passage 2 through this portion and compressed.

Usually, a diesel engine or the like often injects fuel directly into the combustion chamber and does not strictly control the air-fuel ratio. In this case, the inside of the intake passage 2 is affected by air pulsation by the air compressor 16. Even if it receives, it doesn't matter so much for the operation of the engine. On the other hand, an engine that treats exhaust gas by using a three-way catalyst has been proposed and implemented as a method for comprehensively removing HC, CO, and NO _x in the exhaust gas, but this three-way catalyst operates efficiently. In order to achieve this, it is necessary to strictly control the engine within a narrow range (commonly called a window) that sandwiches the theoretical air-fuel ratio that provides good conversion rates for all three exhaust gas components.

Further, in order to detect the stoichiometric air-fuel ratio, an O ₂ sensor whose output voltage suddenly changes at the stoichiometric mixture ratio is used in combination. Therefore, when this air-fuel ratio deviates from the theoretical value, that is, the window, The three-way catalyst cannot remove the components in the exhaust gas without bias. Especially,
In the case of a gas engine using a three-way catalyst, because the fuel is gas and the gas mixer part has a Venturi structure that is affected by the flow velocity of gas, the air from the piston type air compressor is in the intake passage. There is a problem that the air-fuel ratio cannot be controlled accurately due to the influence of pulsation.

Therefore, the air compressor 16 and the intake passage 2
It is necessary to install a means for canceling the air pulsation in the air supply pipe 17 and the device in which a "surge tank" is provided in the air supply pipe 17 is proposed in Japanese Utility Model Laid-Open No. 7-28625. However, while this device has the effect of suppressing the pulsation in the intake passage 2, a part of the air is disturbed or delayed due to the buffering action of the surge tank to change the air-fuel ratio, and the throttle opening There is a problem in that it is difficult to accurately adjust the fuel flow rate when adjusting the.

[0008]

In particular, in a gas engine in which a three-way catalytic converter is provided in the exhaust pipe and feedback control is performed as described above, stable control of air-fuel ratio is achieved by the conventional device described above. Have difficulty. In the gas engine shown in FIG. 6, when the surge tank is not provided in the air supply pipe 17, the gas flow rate control valve 14 is controlled and the characteristic (no load characteristic) in the unloaded state is shown in FIG. The data is obtained by changing the ratio. Line A has a duty ratio of 0%, line B has a duty ratio of 50%, and line C has a duty ratio of 100%. The horizontal axis indicates the throttle opening and the vertical axis indicates the air-fuel ratio (A / F: a portion above the stoichiometric air-fuel ratio λ = 1.0 indicates a thin portion of the fuel gas, and a lower portion indicates a portion of the rich fuel gas) and the fuel flow rate. It should be noted that this figure shows a state in which the amount of air taken into the cylinder is small when the engine load is not applied, and is most susceptible to the influence of air pulsation.

As can be understood from FIG. 7, when the surge tank is not provided in the air supply pipe 17, the fuel flow rate does not increase in proportion to the opening degree of the throttle valve 9 and the duty ratio is high, particularly 100%. Then the throttle opening is 6
The fuel flow rate becomes unstable at ~ 8 °, and the air-fuel ratio cannot be kept constant. Therefore, it is impossible to perform accurate air-fuel ratio control with an apparatus having this characteristic, and it is difficult to perform exhaust gas treatment efficiently using a three-way catalyst.

FIG. 8 shows the gas engine shown in FIG.
The data in the case where the "surge tank" described in Japanese Utility Model Laid-Open No. 7-28625 is installed in the air supply pipe 17 is shown. Comparing FIG. 8 with FIG. 7, FIG.
It can be understood that the above device has a slight improvement in the fuel flow rate and the air-fuel ratio with respect to the opening of the throttle valve 9.

However, it can be seen that there is almost no change in the fuel flow rate when the duty ratio is 0% indicated by the line A and when it is 50% indicated by the line B. Further, looking at the air-fuel ratio, even if the gas flow rate control valve 14 is operated to switch the duty ratio from 0% indicated by the line A to 50% indicated by the line B, both lines follow substantially the same route. Since the air-fuel ratio is changing, the air-fuel ratio is not changing according to the duty ratio, and it is impossible to approach the theoretical air-fuel ratio that is absolutely necessary when using the three-way catalyst.

Without using a three-way catalyst as in the above-mentioned known technique,
When the feedback control to the theoretical air-fuel ratio is not performed, the air-fuel ratio A / F according to the throttle opening may be linearly stabilized. However, when a three-way catalyst is used, this three-way catalyst will not operate effectively unless the stoichiometric air-fuel ratio or a state close to this is controlled, so that the surge tank shown in FIG. An engine with such characteristics cannot use a three-way catalyst.

That is, a line in which the air-fuel ratio is substantially parallel to the theoretical air-fuel ratio λ = 1.0 is drawn, and the duty ratios 0%, 50%, 100
The distance from the stoichiometric air-fuel ratio λ = 1.0 must be accurately maintained according to%. Further, it is necessary that the fuel flow rate also be a straight line that rises to the right and that the fuel flow rate be distributed at a distance according to the duty ratio. 10 (a), (b),
(C) schematically shows the output signal of the O ₂ sensor and the air-fuel ratio control signal (PI signal) with respect to the change of the air-fuel ratio A / F.

As shown in FIG. 10 (a), during operation of the engine, the air-fuel ratio fluctuates up and down around the theoretical air-fuel ratio λ = 1.0. This change changes the air-fuel ratio theoretical air-fuel ratio λ =
This is to keep it at 1.0, and as shown in Fig. 10 (b), O
₂ The output voltage Vs of the sensor 5 changes sensitively to changes in oxygen concentration near the stoichiometric air-fuel ratio. Upon receiving the signal from the O ₂ sensor 5, as shown in FIG.
While changing the I signal to the duty ratio, the gas flow control valve 14 in the gas engine shown in FIG. 6 is operated to increase or decrease the gas fuel supplied to the intake passage 2 through the gas mixer 8.

In this case, the gas flow rate control valve 14 is controlled by changing the duty ratio depending on the P value and the I value. In order for this air-fuel ratio control to be performed normally, the fuel flow rate is changed by changing the duty ratio. Changes widely and accurately. The air-fuel ratio A / F is proportionally controlled by the duty ratio, that is, when the duty ratio is 50%, the air-fuel ratio (A / F) at 0% and 100%, for example.
It is necessary to have a characteristic that is located near the middle of.

However, in the characteristics of the air-fuel ratio A / F in FIGS. 7 and 8, there is almost no change in the fuel flow rate even if the duty ratio is changed from 30% to 50%. This means
It means that the air-fuel ratio is not improved. Further, for example, when the duty ratio is changed from 60% to 80%, the distance between the line B and the line C is larger than the distance between the line A and the line B, so that the fuel flow rate rapidly increases and becomes large. Air-fuel ratio A /
F will change.

This cannot be used at all when a three-way catalyst is used for the exhaust system of the engine and feedback control is performed. In addition, the fuel flow rate changes smoothly according to the throttle opening, the air-fuel ratio A / F is controlled so as to be parallel to the theoretical air-fuel ratio λ = 1.0, and the theoretical air-fuel ratio λ changes according to the duty ratio. It is necessary to be at a target position away from = 1.0.

An object of the present invention is to solve the above problems of the conventional gas engine, in which an air supply pipe of an air compressor is connected to an intake passage, and an exhaust system includes a three-way catalyst and an O gas. _Two sensors are provided and this O ₂
It is an object of the present invention to provide an intake system for a gas engine that can perform feedback control using a signal from a sensor.

[0019]

In order to achieve the above object, an intake system for a gas engine according to the present invention comprises an air compressor 16 upstream of a venturi portion 7 provided in an intake passage 2 connected to an engine body 3. In a gas engine in which an air supply pipe 17 is connected, a three-way catalytic converter 4 and an O ₂ sensor 5 are provided in an exhaust pipe 6 provided in the engine body 3, and feedback control is performed according to the amount of oxygen in the exhaust gas, The resonance box 2 is provided in the middle of the air supply pipe 17 via a connecting pipe a having a diameter larger than that of the air supply pipe 17.
2 is provided.

A connecting pipe a connected to the air supply pipe 17
Is orthogonal to the air supply pipe 17, has one end slightly protruding from the air supply pipe 17, and the other end fixed to the top plate of the resonance box 22.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an intake system for a gas engine according to an embodiment of the present invention will be described with reference to FIG. A gas engine based on a diesel engine according to the embodiment of the present invention has an intake passage 2 having an air cleaner 1, a three-way catalytic converter 4, and a three-way catalytic converter 4 as in the device shown in FIG. An exhaust pipe 6 provided with an O ₂ sensor 5 on the upstream side is connected to the engine body 3 to form an engine that performs feedback control according to the amount of oxygen in the exhaust gas.

As a fuel supply system, a gas mixer 8 is arranged in the venturi portion 7 of the intake passage 2, and a throttle valve 9 is arranged behind it. A gas supply passage consisting of a gas cylinder 10 filled with high-pressure fuel gas and a regulator 11 is connected to the gas mixer 8 via a main fuel passage 12 and a sub fuel passage 13, and a gas flow control valve is further provided in the sub fuel passage 13. 14 (electromagnetic solenoid valve) is provided for duty-controlling the flow rate of the fuel gas.

Also in this engine, an air compressor 16 is attached to supply compressed air to an air tank for storing compressed air used for braking or the like, and the air compressor 16 is driven by the engine body 3. . The air supply pipe 17 is the venturi portion 7.
The air is sucked from the intake passage 2 through the connecting portion 17a on the upstream side.

Now, in the present invention, the air supply pipe 1
7 is provided with a resonance box 22. As shown in FIGS. 2 and 3, the resonance box 22 has a connecting pipe 2 having a diameter larger than that of the air supply pipe 17.
The air supply pipes 17 are connected to both sides of 3 so as to be orthogonal to each other, one end of the connection pipe 23 is closed by a lid a, and the open end is fixed to a lid c of the resonance chamber b. The bottom plate d that closes the bottom of the resonance chamber b is provided with a drain drain e, and a mounting bracket f is fixed to the side surface of the resonance chamber b, and is fixed to the engine portion with a bolt g fixed to the center of the bracket f. It is like this.

As shown in the drawing, the diameter of the connecting pipe 23 is larger than that of the air supply pipe 17, and the air supply pipe 17 is connected to the midway portion of one end of the connecting pipe 23 at right angles. The connecting pipe 23 forms a resonance cylinder that cooperates with the resonance chamber b. If the diameter of the connecting pipe 23 is equal to or smaller than that of the air supply pipe 17, the influence of the pulsation of the air compressor 16 in the intake passage 2 is exerted. give. Therefore, the diameter of the connecting pipe 23 is preferably larger than the diameter of the air supply pipe 17.

FIG. 4A shows a resonance box 22 according to the present invention,
(B) shows a resonance box 22a with a similar structure, and (c)
FIG. 4 is a cross-sectional view showing an expansion type surge tank described in the above-mentioned known example for comparison with the present invention. FIG. 5 is a resonance box 2 according to the present invention shown in FIGS. 2, 3 and 4 (a).
2 is installed in the middle of the air supply pipe 17 of the compressor 16 (Note: No load characteristic) (Note: In the test for evaluating no-load operation, engine characteristics in a region where the amount of fuel and air is small, especially The operation under the condition is likely to be affected by the intake pulsation and the duty ratio is not stable, and it is possible to determine the characteristic of the engine based on the quality of this characteristic.).

In the lower graph showing the relationship between the air-fuel ratio A / F and the throttle opening, the line A is 0% (the sub fuel flowing through the sub fuel passage 13 is zero), and the line B is 50%.
(Sub fuel is 50%), and line C is 100% (sub fuel is flowing without restriction). According to this graph, line B with a duty ratio of 50%
Shows a value close to the theoretical air-fuel ratio λ = 1.0, and it can be seen that the line A and the line C are spaced apart from the line B at equal intervals.

Further, in the upper graph showing the relationship between the fuel flow rate and the throttle opening, the line A is a straight line rising to the right, and the lines B and C are drawn along the line A. What can be said from this graph is the resonance box 22 of the present invention.
Is attached in the middle of the air supply pipe 17 of the air compressor 16, the pulsation of the air compressor 16 does not affect the intake passage 2, and even in the device in which the three-way catalytic converter 4 is provided in the exhaust pipe 6, feedback control is performed. Can also perform sufficient air-fuel ratio control, and can perform control in the vicinity of the window, which has the highest exhaust gas purification efficiency of the three-way catalyst, and as a result, shortens the life of the three-way catalyst and deteriorates exhaust characteristics. You can operate a gas engine without.

Reference Example 1 FIG. 7 is a characteristic diagram similar to that of FIG. 5, and is shown for comparing the characteristic of the conventional gas engine shown in FIG. 6 with the present invention. According to this figure,
The air-fuel ratio A / F is not constant when the duty ratio is changed, and the fuel flow rate cannot be linearly changed according to each duty ratio. Therefore, the three-way catalytic converter 4 is attached to this engine. It proves difficult to use and operate efficiently.

Reference Example 2 FIG. 8 is a characteristic diagram similar to that of FIG. 5, in which the expansion type surge tank 23 shown in FIG.
Is provided in the middle of the air supply pipe 17 of FIG. According to this FIG. 8, in the curve of the air-fuel ratio A / F,
The duty ratios are not drawn at even intervals at 0% indicated by line A, 50% of line B, and 100% of line C, and the fuel flow rate is such that lines A and B follow substantially the same path. It turns out that the air-fuel ratio control cannot be performed accurately.

FIG. 4B shows a resonance box 22a having a structure similar to the resonance box 22 of the present invention shown in FIG. 4A, but the resonance box 22 in FIG. A connecting pipe 23 thicker than this is used, while FIG.
The device (b) is different in that a connecting pipe 23a having the same diameter as or a diameter close to that of the air supply pipe 17 is used. FIG. 9 shows a graph of the resonance box 22a of FIG. 4B, in which the air-fuel ratio A / F is 0%, 50%, 100%.
The lines A, B, C indicating% are not parallel to each other, and the lines A and B
While and are close, the line B and the line C are wide open. Although the fuel flow rate changes according to the throttle opening, the distance between the line A and the line B is close. Therefore, although the fuel flow rate is improved as compared with the case where the expansion type surge tank 25 of FIG. 4C is provided in the air supply pipe 17, the air-fuel ratio A / F and the fuel flow rate are controlled according to the duty ratio. There are some difficulties.

[0032]

In the intake system for a gas engine according to the present invention, the air supply pipe 17 of the air compressor 16 is connected to the upstream side of the venturi portion 7 provided in the intake passage 2 connected to the engine body 3, and the engine main body is connected. Exhaust pipe 6 provided in 3
In a gas engine in which a three-way catalytic converter 4 and an O ₂ sensor 5 are provided and feedback control is performed according to the amount of oxygen in the exhaust gas, in the middle of the air supply pipe 17, a diameter larger than the diameter of the air supply pipe 17 is provided. Since the resonance box 22 is provided via the diameter connecting pipe 23, the following effects can be obtained.

The pulsation of the air compressor 16 is caused by the intake passage 2
The three-way catalytic converter 4 without affecting the exhaust pipe 6
Even in the device provided in the three-way catalyst, sufficient air-fuel ratio control can be performed even in the feedback control, and control in the vicinity of the window, which has the highest exhaust gas purification efficiency of the three-way catalyst, can be performed. Shorten the life,
The gas engine can be operated without deteriorating the exhaust characteristics.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a gas engine of the present invention.

FIG. 2 is a cross-sectional view of a resonance box used in the gas engine of the present invention.

FIG. 3 is a plan view of the resonance box of FIG.

FIG. 4A is a schematic sectional view of the resonance box of the present invention, and FIG.
FIG. 3 is a schematic sectional view of a resonance box having a structure similar to the resonance box of the present invention, and (c) is a side sectional view of an expansion type surge tank.

FIG. 5 is a characteristic diagram of the gas engine of the present invention.

FIG. 6 is a schematic view of a conventional gas engine.

FIG. 7 is a characteristic diagram of a gas engine in which a pulsation damper is not provided in a conventional air supply pipe.

FIG. 8 is a characteristic diagram of a conventional gas engine in which a surge tank is provided in an air supply pipe.

FIG. 9 is a characteristic diagram of a gas engine in which a resonance box is provided in an air supply pipe.

10 (a), (b), and (c) are diagrams showing signal changes in air-fuel ratio control.

[Brief description of reference numerals]

1 air cleaner 2 intake passage 3 engine body 4 three-way catalytic converter 5 O ₂ sensor 6
Exhaust pipe 7 Venturi section 8 Gas mixer 9 Throttle valve 12 Main fuel passage 13 Sub fuel passage 14
Gas flow control valve 16 Air compressor 17 Air supply pipe 17
a connection part 20 control device 22 resonance box 23 connection pipe

Claims (2)

[Claims] 1. An air compressor 16 is provided upstream of a venturi portion 7 provided in an intake passage 2 connected to an engine body 3.
In a gas engine in which the air supply pipe 17 is connected, the exhaust pipe 6 provided in the engine body 3 is provided with the three-way catalytic converter 4 and the O ₂ sensor 5, and feedback control is performed according to the amount of oxygen in the exhaust gas. An intake system for a gas engine in which a resonance box 22 is provided in the middle of the air supply pipe 17 via a connecting pipe a having a diameter larger than that of the air supply pipe 17. 2. The connecting pipe a connected to the air supply pipe 17,
The air supply pipe 1 is orthogonal to the air supply pipe 17 and has one end
7. The intake system for a gas engine according to claim 1, wherein the intake system slightly protrudes from the second end and is fixed to the top plate of the resonance box 22 at the other end.