JPH0151900B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for a gas engine that can control the air-fuel ratio of an air-fuel mixture to a predetermined value with a relatively simple configuration.

In gas engines, a mixer is generally installed upstream of an intake manifold to generate a mixture, and the jet of the mixer is adjusted to generate the mixture. In this case, it is possible to obtain a predetermined air-fuel ratio with a certain degree of accuracy by setting the mixer, but in order to always maintain a predetermined air-fuel ratio under various operating conditions such as rotation speed and load conditions, , the structure of the mixer becomes complex, and delicate setting based on experience and intuition is required. In addition, in order to simultaneously satisfy low fuel consumption, low exhaust emissions, and high output, it is necessary to change the air-fuel ratio depending on the rotation speed and load conditions, and it is no longer possible to meet these demands with a mixer. be.

In other words, for example, in order to make a three-way catalyst function effectively and keep exhaust emissions low, the air-fuel ratio of the air-fuel mixture is controlled so that the air-fuel ratio of the exhaust gas before the catalyst is set to λ = 1.
It is necessary to precisely control the air in the vicinity of the exhaust manifold, and in order to cope with this, a lambda type O ₂ sensor is installed downstream of the exhaust manifold, and the amount of intake gas or intake air is controlled based on the feedback signal from this sensor. A means of doing so is necessary.
Specifically, the method involves adjusting the amount of gas entering the mixer using a throttle valve driven by a step motor;
Alternatively, a method is generally adopted in which a gas passage is provided that bypasses the mixer, and the amount of bypassed gas is adjusted using an injector or a throttle valve.

However, control using such a lambda type O ₂ sensor to maintain λ = 1 requires a complicated air-fuel ratio control mechanism, and in addition, in λ = 1 control, the lambda type O ₂ sensor is a digital sensor. Because there is
It is difficult to accurately control λ=near 1 for all rotational speeds and all load conditions, and there is a problem that the control device tends to be complicated and expensive.

The present invention focuses on the above-mentioned problems, and generates an air-fuel mixture with a predetermined air-fuel ratio under all operating conditions, including different rotational speeds and load conditions, without the need for a mixer and with a relatively simple configuration. The purpose of this device is to provide an air-fuel ratio control device that can control the air-fuel ratio, and includes a gas injection means that injects gas into the air path in the intake pipe to generate a mixture, and a gas injection device that injects gas into the air path in the intake pipe to generate a mixture. A lean burn sensor is installed to detect the air-fuel ratio of exhaust gas, and when the engine is started, it outputs a control signal corresponding to the preset starting injection amount, and during normal operation, it outputs a control signal corresponding to the preset air-fuel ratio setting value and Calculating means for calculating an optimum injection amount based on input information including at least a value detected by the lean burn sensor and outputting a control signal corresponding to the optimum injection amount; and controlling the gas injection means in accordance with the control signal of the calculating means. The invention is characterized by comprising an injection amount control means.

The above-mentioned gas injection means include those that can control the gas flow rate in an analog manner, such as a gas injector that controls the gas flow rate by changing the valve opening time rate (duty), and an actuator such as a needle valve that is operated by a step motor. is used.

Next, the present invention will be specifically explained with reference to illustrated embodiments.

Figure 1 is a conceptual system diagram, where 1 is a gas engine, 2
is an intake pipe, 3 is a gas injector, 4 is a throttle valve, 5 is an exhaust pipe, 6 is a lean burn sensor, 7
is a microcomputer.

The gas injector 3, as shown in FIG.
By changing the injector duty, the gas flow rate can be controlled in an analog manner, and by applying positive pressure, the fuel gas 11 is transferred to the intake pipe 2.
It is designed to be injected inside. The injected fuel gas 11 is mixed with air 12 in the intake pipe 2 to generate an air-fuel mixture, which is supplied to the engine 1 via the throttle valve 4 and is exhausted as exhaust gas 13 from the exhaust pipe 5. . In the figure, the gas injector 3 is provided upstream of the throttle valve 4, but depending on the shape of the intake manifold etc.
A gas injector 3 can also be provided downstream of the throttle valve 4.

As shown in FIG. 3, the lean burn sensor 6 has a well-known structure that generates a linear output voltage with respect to changes in oxygen concentration. This sensor can accurately detect the fuel ratio (excess air ratio).

The microcomputer 7 has a CPU 21 and a ROM.
22, RAM23, I/O interface 2
4, a system bus line 25 etc. are provided, and the output signal of the lean burn sensor 6 as an analog quantity is converted into a digital quantity by a multiplexer A/D converter 26 and inputted to the microcomputer 7, and an air-fuel ratio setting means. The air-fuel ratio setting signal from 27 is similarly input to the microcomputer 7 via the A/D converter 26. The air-fuel ratio setting means 27 may be manually operated, for example, or may be one that automatically sets the air-fuel ratio setting value according to the detection outputs of various other sensors (not shown) and issues a setting signal. It's okay.
A calculation control program is stored in the ROM 22, and calculations as described later are performed according to the detection value of the lean burn sensor 6 and the setting value of the air-fuel ratio setting means 27, and the resulting control signal is sent to the I/F. It is output from the O interface 24. This signal is amplified by the power transistor array 28 to control the gas injector 3, and the gas injector 3 is operated at a predetermined injector duty to adjust the injection amount of the fuel gas 11.

Next, this control procedure will be explained with reference to the flowchart shown in FIG.

FIG. 4a is a flowchart of basic feedback control, in which interrupts are applied by the microcomputer 7 at regular sampling intervals. In this interrupt routine, the air-fuel ratio setting value λ _r by the air-fuel ratio setting means 27 and the air-fuel ratio detection value λ _n by the lean burn sensor 6 are input to calculate the deviation e=λ _n −λ _r between the two. , PID calculation, etc. are performed to calculate the injector duty D=f(e) such that the deviation e becomes zero. A control signal obtained as a result of this calculation is output, and the gas injector 3 is controlled so that the air-fuel mixture supplied to the gas engine 1 is controlled to a predetermined air-fuel ratio.

FIG. 4b shows the above procedure plus the startup procedure, and this kind of control is actually performed. In other words, Fig. 4a shows the gas engine 1 in steady operation, and as it is, control is impossible at startup when the lean burn sensor 6 does not function effectively. A determination step is added to output the starting injector duty D _S that enables the gas engine 1 to start at the time of starting, and the feedback control described above is performed from the time the steady state is entered. It is. Injector duty at startup
D _S is preset to a constant value that ensures reliable startup under various conditions, or is preset to an appropriate value depending on factors that affect startup performance, such as temperature.

With the above configuration and operation, the object of the present invention has been achieved to a certain extent. Next, another embodiment will be described in which it is possible to cope with rapid load fluctuations.

Now, when the control system as described above is stable and the gas amount is constant, if the load fluctuates, the governor (not shown) operates in response to the load fluctuation.
The opening degree of the throttle valve 4 is adjusted. When the opening degree of the throttle valve 4 changes, the intake air amount changes, and the air-fuel ratio also changes, so the gas injection amount of the gas injector 3 changes to follow the load fluctuation by the above-mentioned feedback control, and the predetermined set value The air-fuel ratio is automatically controlled during this period, but because the lean burn sensor 6 has a slight response delay, changes in the air-fuel ratio cannot be detected immediately, and during that delay time the air-fuel ratio is automatically controlled. The actual air-fuel ratio is different from the fuel ratio. Therefore, if the load changes suddenly, the actual air-fuel ratio will deviate significantly from the set value, and the engine 1 will no longer operate properly, resulting in higher exhaust emissions and lower output. Or, in the worst case scenario, the engine may stop.

Fig. 5 shows an embodiment in which a so-called feed forward control function is added to the one shown in Fig. 1 in order to solve this problem. Detector 3
1, and if the change is large enough to cause a large fluctuation in the air-fuel ratio, a correction value based on the feed forward is added to the injector duty value calculated by the feedback loop. be.

That is, the output of the throttle valve opening detector 31 is inputted to the microcomputer 7 via the A/D converter 26, and as shown in the flowchart of FIG. 6, the amount of change Δθ in the throttle valve opening is detected. . Then, this amount of change △θ is set to a constant reference value θ ₀
If the amount of change is greater than the reference value, the injector duty correction amount D ₁ =g(△θ) is calculated, and the previously determined injector duty D
D ₂ =D+D ₁ is output as a control signal, and the air-fuel mixture supplied to the gas engine 1 is immediately controlled to a predetermined air-fuel ratio in response to load fluctuations.

Note that the injector duty can also be corrected automatically or manually based on factors other than the throttle valve opening, if necessary.

As described above, the present invention provides a gas injection means in the intake pipe and a lean burn sensor in the exhaust pipe, controls the gas injection amount to the startup injection amount when starting the engine, and controls the lean burn sensor during steady operation. The gas injection amount is feedback-controlled using the detection output, and a mixer is not required, the structure of the intake system is simple, and an air-fuel mixture with a predetermined air-fuel ratio is generated under all operating conditions. This has the advantage that it is possible to easily obtain a gas engine with low fuel consumption, low exhaust emissions, and high output.

[Brief explanation of drawings]

Fig. 1 is a conceptual system diagram of one embodiment of the present invention;
The figure is an example of the flow rate characteristic diagram of a gas injector.
The figure is an example of an output characteristic diagram of a lean burn sensor, Figure 4a is a basic control flowchart of the same embodiment, Figure 4b is an actual control flowchart of the same as above, and Figure 5 is a diagram of another embodiment. The conceptual system diagram, FIG. 6, is the same control flowchart. 1... Gas engine, 2... Intake pipe, 3... Gas injector, 5... Exhaust pipe, 6... Lean burn sensor, 7... Microcomputer, 21...
CPU, 22...ROM, 24...I/O interface, 27...Air-fuel ratio setting means, 28...Power transistor array.

Claims (1)

[Claims] 1. A gas injection means that injects gas into an air passage in an intake pipe to generate a mixture; A lean burn sensor that is installed in an exhaust gas passage in an exhaust pipe and detects the air-fuel ratio of exhaust gas; , outputs a control signal corresponding to a preset startup injection amount when starting the engine, and outputs a control signal corresponding to a preset starting injection amount during steady operation, and uses input information including at least an air-fuel ratio setting value that is arbitrarily set in advance and a value detected by the lean burn sensor. It is characterized by comprising: calculation means for calculating an optimum injection amount and outputting a control signal corresponding to the optimum injection amount; and injection amount control means for controlling the gas injection means in accordance with the control signal of the calculation means. Air-fuel ratio control device for gas engines.