JPS6390650A - Air fuel ratio control device for gas valve type large size engine - Google Patents

Abstract

PURPOSE:To enable an air fuel ratio to be controlled accurately by making a minute control of a boost pressure fed back to a regulator using a value detected by a lean burn sensor. CONSTITUTION:A pulse gear 34 and an electromagnetic pickup 32 are so arranged as a timing signal can be generated when a lift of an exhaust value 10 is at its maximum, and each time this signal is inputted synchronizing with the rotation, a signal from a lean burn sensor 31 is inputted and a measured value lambda of the exhaust gas air fuel ratio is computed. A microcomputer in a control portion 28 makes a comparison, every fixed time, of the measured value lambda of the air fuel with the target value lambda1 of the air fuel ratio set beforehand, gives a driving signal to a step motor 27 so that the two values will coincide with each other and drives an auxiliary valve 26, thus, any boost pressure applied to an auxiliary diaphragm 15 is adjusted. By this method, any boost pressure fed back to a regulator 1 can be controlled, a gas supply pressure can be controlled and the air fuel ratio can be maintained at the target value lambda1.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an improvement of an air-fuel ratio control device for a large gas valve type gas engine.

<Prior art> The most significant feature of large gas valve type gas engines is that gas in the gas pipe for fuel supply is supplied from the gas valve into the intake pipe. Since the valve is controlled to open except when it overlaps with the lift, sufficient scavenging is performed, resulting in reduced heat load, increased knocking limit, extended plug life, improved thermal efficiency, etc. It can be measured.

On the other hand, with such a gas valve system, air-fuel ratio control tends to become difficult as the engine becomes larger. They discovered that the air-fuel ratio can be easily controlled by changing it accordingly.

Air-fuel ratio control using a regulator that performs such supply pressure control by feedback of boost pressure and intake throttle opening Jx, patent application No. 61-76785
proposed as.

<Problems to be Solved by the Invention> In the device proposed above, the air-fuel ratio can be controlled to approximately the target value by feedback of the boost pressure and the throttle opening on the intake side. Due to changes in engine speed and engine speed, the air-fuel ratio becomes λ=
Fluctuations occur within a range of about 1.35 to 1.9. This is mainly due to changes in the time area of the gas valve due to rotation, and the fact that the relationship between boost pressure and control pressure becomes non-linear due to the fixed orifice.

By the way, the NOx concentration contained in exhaust gas generally tends to decrease when the air-fuel ratio is made leaner, but the leaner it is, the lower the combustion speed becomes and the fluctuation in Pmax becomes larger. This caused a misfire and all five engines stopped.

Therefore, in order to reduce NOx in this type of gas engine, it is necessary to always maintain the leanest state within the range where combustion is stable, that is, the cylinder air-fuel ratio at about λ = 1.8 to 1.9. is necessary, and the performance of the air-fuel ratio control device is the key point.

The present invention has been made in view of these problems, and aims to provide an air-fuel ratio control device that can accurately control the air-fuel ratio.

Note that a control device for a gas fuel engine has been proposed in which the oxygen concentration in exhaust gas is detected by an O2 sensor and this is fed back to a fuel adjustment mechanism to control the air-fuel ratio (Japanese Patent Application Laid-Open No. 1983-1991). (Refer to Publication No. 96131), this method does not take into account the overlap between the exhaust valve lift and the intake valve lift, so it cannot be used for large gas valve-type gas engines, and it cannot be used for air-fuel ratio control. Because it relies entirely on oxygen concentration feedback to the fuel adjustment mechanism,
There is also the problem that if a failure occurs in the control system, the engine cannot be operated at all, which makes it impractical.

<Means for Solving the Problems> In order to achieve the above-mentioned object, the air-fuel ratio control device for a gas engine with two large gas valves according to the present invention controls the gas supply pressure according to the boost pressure and the intake throttle opening. In gas valve two-large gas engines equipped with regulators that control the air-fuel ratio of the gas engine by changing the air-fuel ratio by changing the The boost pressure fed back to the regulator is controlled using the detected value of the lean burn sensor during the period when only the valve is open.

FIG. 1 is a diagram showing the basic configuration of the present invention, where A is a gas engine with two large gas valves, B is a supercharger, C is a regulator having a feedback system from an intake pipe and a gas pipe E, and F is a diagram showing the basic configuration of the present invention.
denotes a lean burn sensor provided in the exhaust pipe G, and H denotes a control unit that outputs a boost pressure feedback signal to the regulator C based on the rotation signal of the engine A and the detection value of the lean burn sensor F.

By controlling the gas supply pressure by feeding back the boost pressure and intake throttle opening to the regulator, the air-fuel ratio is maintained at approximately the target value, and the detected value of the lean burn sensor is also used to feed back the gas supply pressure to the regulator. By finely controlling the boost pressure applied, the air-fuel ratio is finely adjusted and precisely controlled to the target value.

<Example> Next, the illustrated embodiment will be described.

First, the outline of the configuration will be explained using the system diagram shown in FIG.

Reference numeral 1 denotes a regulator, gas is supplied from the gas pipe 2 before pressure regulation, and the pressure is regulated, and the pressure-regulated gas passes from the gas pipe 3 through the gas side throttle 4, passes through the gas valve 5, and enters the intake pipe 6. Become a person. On the other hand, air is supplied to the intake pipe 6 from the supercharger (not shown).
The exhaust gas passes through the intake throttle 7 and is supplied together with the above gas to the combustion chamber 9 by driving the intake valve 8. The exhaust gas is discharged from the exhaust pipe 11 by driving the exhaust valve 10.

The gas side throttle 4 and the intake side throttle 7 are connected to the governor 12.
is controlled by.

The regulator 1 is provided with an auxiliary diaphragm 15 and a gas pressure setting spring 16, and the auxiliary diaphragm 15 pushes up the spring 18 via a shaft 17. Then, the respective pressures are fed back to the regulator 1 through the gas pressure dedicated pipe 19, the boost pressure pipe 20, and the intake negative pressure pipe 21. What is the pressure that regulator 1 adjusts?

This is the sum of the intake negative pressure introduced by the intake negative pressure conduit 21 and the pressure due to the spring force of the spring 18.
This is in addition to the upward force exerted by the auxiliary diaphragm 15 via the auxiliary diaphragm 15. Additionally, the pressure within the auxiliary diaphragm 15 is the same as the pressure within the boost pressure conduit 20.

With the above structure, the regulator 1 changes the gas supply pressure according to the opening degree of the intake throttle 7 in the intake pipe 6 and the pressure inside the intake pipe 6, so as to keep the air-fuel ratio λ constant. works.

The boost pressure conduit 20 is provided with a fixed orifice 25 and an auxiliary valve 26. The auxiliary valve 26 has a structure in which, for example, a needle valve is driven by a direct-acting step motor 27, and the step motor 27 is controlled by a control section 28.

31 is a lean burn sensor disposed in the exhaust pipe 11;
2 is an electromagnetic pickup provided corresponding to a pulse gear 34 fixed to a camshaft that rotates in conjunction with the piston 33, and these detected values are input to the control section 28.

As shown in FIG. 3, the control unit 28 includes an input interface 28a for inputting the detected values of the lean burn sensor 31 and the electromagnetic pickup 32, a microcomputer 28b equipped with arithmetic processing and memory functions, and a Step motor 2 by output signal
Output interface 2 that outputs a drive signal for 7
It consists of 8c etc.

The lean burn sensor 31 is a sensor that measures the oxygen concentration in exhaust gas and outputs a nearly linear voltage signal with respect to the air-fuel ratio in a lean state, and is equipped with a heater to improve responsiveness. .

In addition, in order to prevent fuel gas from blowing through when the intake valve 8 and exhaust valve 10 overlap and from being affected by other cylinders due to pulsation, the mounting position is set at the exhaust manifold 37 as shown in FIG. It is located in the position closest to the exhaust valve. Note that the cylinder to which the lean burn sensor 31 is attached is not particularly specified. 38 is an engine, 39 is an intake manifold, and 40 is a supercharger.

Next, the operation will be explained.

As shown in FIG. 5, the pulse gear 34 and the electromagnetic pickup 32 are arranged so that a timing signal 32a can be obtained when the exhaust valve 10 is at its maximum lift.

Every time this signal is input in synchronization with the rotation, a signal from the re-inburn sensor 31 is input, and a measured value λ of the air-fuel ratio of exhaust gas is calculated. Microcomputer 28b
Then, the target value λ1 of the air-fuel ratio set in advance is compared with the above-mentioned measured value λ at regular intervals, and a drive signal is given to the step motor 27 so that the two match, and the auxiliary valve 26 is driven to perform the auxiliary operation. The boost pressure applied to the diaphragm 15 is adjusted. In other words, if the measured value λ of the air-fuel ratio is larger than the target value λ (leaner than the target), the auxiliary valve 2
6 is closed by a certain amount to increase the boost pressure applied to the auxiliary diaphragm 15. Conversely, if the measured value λ is smaller than the target value λ (richer than the target), the auxiliary valve 26 is opened by a certain amount to reduce the boost pressure applied to the auxiliary diaphragm 15, thereby maintaining the air-fuel ratio at the target value λ1. It turns out. FIG. 6 shows a flowchart of the above control procedure.

The base air-fuel ratio is approximately controlled to a predetermined value by the intake negative pressure downstream of the intake throttle 7, which is led to the regulator 1 by the intake negative pressure conduit 21, and is controlled by the opening and closing of the auxiliary valve 26. Fine adjustments are made to the air-fuel ratio, which varies depending on the operating conditions, and the air-fuel ratio is controlled with high precision.

In the above embodiment, the lean burn sensor 31 is connected to the supercharger 4o.
The exhaust manifold 37 on the inlet side of the exhaust manifold 37 is disposed at a position closest to the exhaust valve, but a modification example in which the inburn sensor 31 is disposed on the outlet side of the supercharger 40 will be shown next.

FIG. 7 is a system diagram showing an outline of the configuration, and the same parts as in the above-described embodiment are indicated by the same numbers.

In this example, a boost sensor 41 for detecting boost pressure P is provided upstream of the intake-side throttle 7 of the intake pipe 6, and an electromagnetic pickup 32 is connected to a pulse gear 34a fixed to a crankshaft that rotates in conjunction with a piston 33. , the lean burn sensor 31 is connected to the supercharger 40 as shown in FIG.
It is placed on the exit side of the This means that the exhaust gas is the supercharger 4
This is to eliminate the effects of exhaust pulsation and fuel gas outflow during overlap by measuring the air-fuel ratio in a well-mixed state at 0.
A stable output voltage can be obtained from the

However, the output voltage obtained here is an apparent air-fuel ratio that is different from the actual air-fuel ratio, and even if the actual air-fuel ratio is the same, it changes depending on the rotation speed and boost pressure. Correction is performed using a stored correction data map as shown below.

First, at regular intervals, the engine speed N is calculated from the detection signal of the electromagnetic pickup 32, the boost pressure P is calculated from the detection signal of the jib sensor 41, and the air-fuel ratio λ is calculated from the detection signal of the lean burn sensor 31. A target apparent air-fuel ratio λ1 is calculated according to the engine speed N and boost pressure P. Next, the target apparent air-fuel ratio λ1 and the measured air-fuel ratio λ are compared, and a drive signal is given to the step motor 27 so that the two match, and the boost pressure is applied to the auxiliary diaphragm 15 by driving the auxiliary valve 26. It is to adjust. As a result, the air-fuel ratio is maintained at the apparent target value λ1, and the actual air-fuel ratio is also maintained at the target value. FIG. 9 shows a flowchart of the above control procedure.

<Effects of the Invention> As is clear from the above embodiments, the air-fuel ratio control device for a gas valve type large gas engine of the present invention is capable of changing the gas supply pressure according to the boost pressure and the intake side Scottle opening degree. In a large gas valve type gas engine equipped with a regulator that controls the air-fuel ratio of the gas engine,
The lean burn sensor is placed in the exhaust manifold at the position closest to the exhaust valve, and the detected value of the lean burn sensor during the period when only the exhaust valve is open is used to control the boost pressure fed back to the above regulator. This is what I did.

Therefore, by controlling the gas supply pressure with the regulator, the air-fuel ratio is maintained at approximately the target value, and then the gas supply pressure is finely adjusted in accordance with the detection value of the lean burn sensor to bring the air-fuel ratio to the target value. Precisely controlled to hold. Therefore, it is possible to reduce NOx by always maintaining the air-fuel ratio in the leanest state within the range where combustion is stable, that is, at around λ = 1.8 to 1.9, and this control is effective as the engine ages. It can respond to changes and institutional variations without any problems. Furthermore, since air-fuel ratio control is not entirely dependent on feedback from the lean burn sensor, even if the feedback system based on the lean burn sensor fails, the air-fuel ratio will still be maintained within a certain range by the regulator. It is possible to operate the engine in the following manner, which is a very advantageous practical advantage.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the basic configuration of the present invention. Figures 2 to 6 show one embodiment of the present invention, with Figure 2 being a system diagram showing an overview of the configuration, Figure 3 being a block diagram of the control section, and Figure 4 showing the lean burn sensor. FIG. 5 is a diagram showing the arrangement, FIG. 5 is a diagram showing the relationship between the valve lift and the timing signal of the lean burn sensor, and FIG. 6 is a control flowchart. 7 to 9 show a modified example of the embodiment, FIG. 7 is a system diagram showing an outline of the configuration, and FIG. 8 is a system diagram showing an outline of the configuration.
The figure shows the arrangement of lean burn sensors, and FIG. 9 is a control flowchart. 1...Regulator, 2.3...Gas pipe, 4...
Gas side throttle, 5... gas valve, 6... intake pipe,
7...Intake side throttle, 8...Intake valve, 10...
- Exhaust valve, 11... Exhaust pipe, 15... Auxiliary diaphragm, 19... Gas pressure conduit, 20... Boost pressure conduit, 21... Intake negative pressure conduit, 25... Fixed orifice, 26... Auxiliary valve, 27... Step motor, 28... Control unit, 28b... Microcomputer, 31... Lean burn sensor, 32... Electromagnetic pickup, 37... Exhaust manifold, 38...
Engine, 39...Intake manifold, 40...Supercharger.

Claims (1)

[Claims] (1) In a large gas valve type gas engine equipped with a regulator that controls the air-fuel ratio of the gas engine by changing the gas supply pressure according to the boost pressure and intake throttle opening, lean burn The sensor is placed in the exhaust manifold at the position closest to the exhaust valve, and the detected value of the lean burn sensor when only the exhaust valve is open is used to control the boost pressure fed back to the regulator. An air-fuel ratio control device for a gas valve type large gas engine, characterized by: