JPS62218647A - Air-fuel ratio control method for gas fuel engine and device thereof - Google Patents

Abstract

PURPOSE:To control a air-fuel ratio to an optimum value in accordance with the composition of gas fuel, by setting the quantity of gas fuel to be supplied based on a predetermined air-fuel ratio depending on an engine load and the specific gravity of the gas fuel. CONSTITUTION:A cylinder 10 containing gas fuel is coupled with a mixing unit 38 through a regulator 22 and an actuator 42. A control circuit 32 is supplied with signals from a gas specific gravity sensor 25 as well as from an air intake pipe pressure sensor 48 and an engine r.p.m. sensor for reading out an air-fuel ratio from a data map using an air intake pipe pressure, an engine r.p.m. and a gas specific gravity as parameters. Then, the control circuit 32 sets the quantity of gas fuel to be supplied for obtaining the air-fuel ratio read out and permits an actuator 42 to supply a prescribed quantity of gas fuel. With this arrangement, the decline of an engine performance caused by the change in the gas fuel composition can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an air-fuel ratio control method and apparatus for an engine that uses gas such as compressed natural gas (CNG) as fuel, and in particular, to The present invention also relates to an air-fuel ratio control method and apparatus for a gas fuel engine that can always set the optimum air-fuel ratio.

BACKGROUND OF THE INVENTION In recent years, natural gas has been reconsidered as an alternative energy source to oil, and the movement to utilize it as a fuel for automobiles has become active, especially in natural gas producing countries. Natural gas has methane (C1l) as its main component, which has a low boiling point, and this is the main difference from petroleum gas, which has relatively high boiling points, such as propane and butane, as its main components. Therefore, when using natural gas as a fuel for automobiles, LPG (liquefied petroleum gas), which has traditionally been used in some automobile fuels, is used.
It is difficult to store liquids at room temperature, such as compressed natural gas (compressed natural gas).
It is generally stored and used as a gas (also referred to as CNG for short).

In vehicles that use CNG as fuel, CNG is normally sealed at high pressure in a cylinder, and the pressure is reduced to approximately atmospheric pressure using a regulator, etc., and the mixture is mixed with air using a mixer using a venturi, etc., and then supplied to the engine. I try to do that.

Problems to be Solved by the Invention In general, the composition of natural gas often differs depending on the country and region where it is extracted, and therefore the ratio of natural gas to air (the ratio of natural gas to air) also varies. There was a problem that the performance changed.

That is, the above-mentioned mixer t is normally prepared in advance so that a predetermined air-fuel ratio is achieved for the gas fuel having the composition of l! Since it is set to one section, if the gas composition changes each time the cylinder is filled with gas fuel, the engine output will also change.

For example, for CNG of a certain composition (specific gravity), the excess air ratio λ - engine torque characteristic as shown in Figure 5 is obtained at full load, but the engine torque is maximum at the stoichiometric air-fuel ratio (excess air ratio λ - 1). This characteristic of becoming 100% does not change even if the composition (specific gravity) of CNG changes. However, as shown in FIG. 6, when the gas composition, that is, the gas specific gravity changes, the stoichiometric air-fuel ratio also changes. Therefore, the fifth
As shown in figure a, when the gas composition changes, if the engine is operated at the same air-fuel ratio as before, the engine torque T will decrease by ΔT (or ΔT2), so the change in gas composition (specific gravity) will occur. It is necessary to adjust the air-fuel ratio accordingly.

- On the other hand, when CNG filled in a cylinder is gradually consumed, methane, which has a lower specific gravity among the components, tends to be consumed first. As shown in Figure 7, CNG immediately after filling,
CN in a cylinder whose remaining amount has decreased due to the number of days of use
G and G have different specific gravity and methane content, and the same problem as mentioned above occurs even though the gases are from the same source.

Therefore, an object of the present invention is to focus on gas specific gravity as a substitute characteristic for the composition of gas fuel, and to set an optimal air-fuel ratio according to the gas specific gravity.

According to the present invention, the problem of the prior art described above can be solved by detecting the load condition of the engine and the specific gravity of the gas fuel, and determining the gas fuel supply amount from the air-fuel ratio set in advance according to these. Set,
This set supply is solved by a method for controlling the air-fuel ratio of a gas-fueled engine, characterized in that the gas fuel is supplied to the engine at random.

In addition, the devices used to carry out the method include an intake pipe pressure detection means 1 for detecting the intake pipe pressure of the engine, and a rotation speed detection means 2 for detecting the engine rotation speed, as shown in FIG. , a means 7 for determining the load condition from the intake pipe pressure and the engine speed, a gas specific gravity detection means 3 for detecting the ratio m of the gas fuel, and an engine intake pipe pressure, the engine speed, and the specific gravity of the gas fuel. The air-fuel ratio storage means 4 stores in advance data regarding the air-fuel ratio of the mixture of gas fuel and air as a data map with parameters, and the engine load and a fuel supply gL setting means 5 for reading an air-fuel ratio corresponding to the specific gravity of the gas fuel from the storage means and setting the gas fuel supply amount so as to match the air-fuel ratio;
The present invention provides an air-fuel ratio control device for a gas fuel engine characterized by comprising a fuel supply means 6 for supplying gas fuel to the engine at the set supply amount.

Function: In the method and apparatus of the present invention, the engine load condition is detected from the intake pipe negative pressure and the engine rotation speed, and the specific gravity of the gas fuel in the cylinder is also detected, and the engine load condition and the specific gravity of the gas fuel are detected. A preset air-fuel ratio is selected from the air-fuel ratio storage means according to the air-fuel ratio, and fuel is supplied to the engine at this air-fuel ratio.

Embodiments Hereinafter, preferred embodiments of the present invention will be explained with reference to the drawings.

Referring to FIG. 2, an example of the air-fuel ratio control device of the present invention is shown. In the figure, 10 is a cylinder filled with gas fuel such as CNG at a pressure of 200 kg/cm2, 12 is a valve provided in the cylinder 10 and used for filling and taking out the gas fuel, and 18 is a high-pressure pipe 14 and the fuel A high pressure regulator is connected to the valve 12 via a shutoff valve 16, and a low pressure regulator 22 is connected to the high pressure regulator 18 via a pipe 20, respectively. The fuel cutoff valve 16 is configured to operate in conjunction with, for example, an ignition switch (not shown), and when the switch is turned on and this valve is open, the gas fuel is first supplied to the high pressure regulator 18 from 5 to 6.
After the pressure is reduced to 2, the pressure is reduced by the low pressure regulator 22 to o, i to 0.2 Kg/α2.

26 is a gas specific gravity sensor provided between the branch pipes 24 and 24 connected to the pipe 20, and a check valve 2 is installed in the downstream branch pipe 2/'I of this sensor to prevent backflow of gas.
8 is set. As the gas specific gravity sensor, a known Lauter gas hydrometer that measures the specific gravity of gas fuel with respect to air based on the density of gas fuel and air can be used. When a Lautergas hydrometer is used in the present invention, the device is configured so that its output can be taken out, for example, as a voltage signal, and this voltage signal is input to the control circuit 32 via line 30. Lauter gas hydrometers are usually equipped with a pressure reducing valve and a flow rate control valve (not shown), but if the operating pressure of the hydrometer and the outlet pressure of the high pressure regulator 18 are matched, this pressure reducing valve is unnecessary. be.

On the other hand, a venturi portion 4o is formed in a mixer 38 attached to an intake passage 36 of the engine 34, and a nozzle (not shown) of an actuator 42 is opened in this venturi portion 40. The actuator 42 is configured using, for example, a step motor, a proportional solenoid, etc., so as to adjust the opening degree of the nozzle in response to an electric signal sent from the control circuit 32 via a line 46. The gas fuel is sent at a predetermined pressure from the low pressure regulator 22 via the low pressure piping 44 at a predetermined supply amount determined by the nozzle opening degree of the actuator 42 and the negative pressure of the venturi section 40.
It is mixed with air from an air intake (not shown) and sent into a combustion chamber (not shown) of the engine 34. Exhaust gas after being combusted in the combustion chamber is discharged into the atmosphere via the exhaust passage 52 and a catalytic converter 54 provided in the middle thereof.

An intake pipe pressure sensor 4 is connected to the intake passage 36 via a conduit 47.
8 is provided, and this intake pipe pressure sensor 48 sends a voltage signal generated in response to the negative pressure in the intake passage 36 to the control circuit 32 via a line 50 as information regarding the engine load.

The engine distributor 56 is provided with a rotation speed sensor (not shown) that outputs a pulse signal every time the crankshaft rotates by a predetermined angle. ) to the control circuit 32 via line 60.

FIG. 3 shows the control circuit 32 and various sensors shown in FIG.
FIG. 3 is a block diagram showing the relationship with an actuator.

The voltage signal from the intake pipe pressure sensor 48 and the voltage signal from the gas specific gravity sensor 26 are sent to an analog-to-digital (A/D) converter 70 having an analog multiplexer function, and are sent to a central processing unit (CPU) 72. The signals are sequentially converted into two communication signals according to the instructions from .

Pulse signals for each predetermined angle from the rotational speed sensor are sent to a well-known speed forming circuit provided in the input interface circuit (110 circuit) 74, thereby forming two signals representing the rotational speed of the engine. .

The output interface circuit (1/○ circuit) 76 is a CP
Based on the data regarding the gas fuel supply sent from U72, for example, a pulse signal is generated to instruct the nozzle opening of the actuator 42 to correspond to the supply layer. This signal is sent to the actuator 42 via a drive circuit (not shown), and the nozzle opening degree is set.

The A/D converter 70 and I10 circuits 74 and 76 are connected via a common bus 82 to a CPU 72, a random access memory (RAM) 78, and a read only memory (ROM) 80, which are the main components of the microphone computer. Data and instructions are transferred via this bus 82.

In the ROM 80, air data is preset as three-dimensional parameters, including intake pipe negative pressure data from the intake pipe pressure sensor 48, engine rotation speed data from the sensor, and fuel gas specific gravity data from the gas specific gravity sensor 26. Fuel ratio data is stored. This setting selects the stoichiometric air-fuel ratio of the gas composition (specific gravity) at that time in the full load range to obtain maximum output, and in the partial load range, selects the stoichiometric air-fuel ratio of the gas composition (specific gravity) at that time to improve fuel efficiency. 30-4 than the stoichiometric air-fuel ratio of
The air-fuel ratio on the 0% lean side is selected.

Note that the stored data is not limited to air-fuel ratio data;
For example, data on the fuel supply amount or the nozzle opening degree of the actuator 42 to achieve the air-fuel ratio may be directly stored.

The ROM 80 also stores a routine program for setting the fuel supply amount based on the air-fuel ratio data and driving the actuator, other programs, and various data necessary for these calculation processes.

Next, the operation of the microcomputer described above will be explained.

During its main processing routine, the CPU 72 sends the latest data representing the engine rotational speed N to the I10 circuit 74.
, and store it in the RAM 78. Also, A/D
Due to the A/D conversion completion interrupt from the converter 70, the latest data representing the engine intake pipe negative pressure [] and the latest data representing the fuel gas ratio ff1D are fetched from the A/D converter 70 and stored in the RAM 78. Store.

The CPU 72 executes a processing routine as shown in FIG. 4 in response to an interrupt request signal generated at a predetermined crank angle position, and sets the nozzle opening degree of the actuator 42. First, in step 90, the intake pipe negative pressure P representing the engine load and the engine rotation speed N are stored in the RAM 78.
, and the fuel gas ratio ff1D, and in step 91, data A/F regarding the air-fuel ratio stored in a predetermined area of the ROM 80 is read using the three data as parameters. Next, in step 92, a predetermined calculation is performed using the data A/F regarding the air-fuel ratio to calculate the fuel supply amount), and in step 93, the nozzle opening degree of the actuator 42 is determined according to the temperature and this fuel supply ff1F. A signal to drive the actuator 42 is set in a register in the I10 circuit 76, and the actuator 42 is actually driven by this signal.

In this case, it is determined whether the engine is in the full load range from the data of engine speed N and intake pipe negative pressure P, and if the engine is in the full load range that requires the most output, the gas at that time is The supply amount of gas fuel is determined by selecting the stoichiometric air-fuel ratio of the composition (specific gravity), and selecting an air-fuel ratio leaner than the stoichiometric air-fuel ratio when the load is in another partial load range.

Effects of the Invention As detailed above, according to the present invention, since the air-fuel ratio is set in advance according to the specific gravity of the gas fuel,
Not only gas fuels with different compositions due to different extraction regions, but also gas fuels whose compositions have changed during the consumption process.
Maximum output can always be obtained in the entire engine load range, and engine performance will not deteriorate due to changes in the composition of the gas fuel. In addition, technology to control the air-fuel ratio by detecting LPG pressure and vapor pressure (Japanese Patent Application Laid-open No. 118543/1983,
Compared to Japanese Unexamined Patent Publication No. 57-131853), the present invention detects and controls the specific gravity of the gas, so the composition of the gas fuel in the cylinder can be known with high accuracy regardless of the amount of gas remaining or the amount remaining. , it is possible to control the engine with high precision.

[Brief Description of the Drawings] Fig. 1 is a functional block diagram of a microcomputer showing the basic configuration of the present invention, Fig. 2 is a system configuration diagram showing an embodiment of the present invention, and Fig. 3 is a functional block diagram of a microcomputer showing the basic configuration of the present invention. Figure 4 is a flow chart showing the routine program for driving the actuator for gas fuel supply; Figure 5 is a block diagram showing the relationship between the control circuit and peripheral equipment; Figure 5a is a graph showing an example of the relationship between excess air ratio λ and engine torque. Figure 5a is a graph showing the relationship between air-fuel ratio A/F and engine torque based on Figure 5. Figure 6 is a graph showing the relationship between gas specific gravity and theory. Graph showing the relationship between air-fuel ratio FIG. 7 is a graph showing the relationship between gas fuel consumption in the cylinder (number of elapsed days), gas specific gravity, and methane content rate. 10...Cylinder, 18...High pressure regulator, 22
...Low pressure regulator, 26...Gas specific gravity sensor, 32...Control circuit, 34
...Engine, 36...Intake passage, 38...Mixer, 40...Venturi section, 42...Actuator, 48...Intake pipe pressure sensor, 52...Exhaust passage. Applicant: Toyota Motor Corporation Aisan Industry Co., Ltd.

Claims (3)

[Claims] (1) Detecting the load condition of the engine and the specific gravity of the gas fuel, setting the gas fuel supply amount from a preset air-fuel ratio according to these, and supplying the gas fuel to the engine at this set supply amount. An air-fuel ratio control method for a gas fuel engine, characterized by: (2) An intake pipe pressure detection means for detecting the intake pipe pressure of the engine, a rotation speed detection means for detecting the engine rotation speed, a means for determining the load condition from the intake pipe pressure and the engine rotation speed, and a gas fuel gas specific gravity detection means for detecting the specific gravity of the gas, and data regarding the air-fuel ratio of the mixture of gas fuel and air that is stored in advance as a data map using the engine intake pipe pressure, the engine rotation speed, and the specific gravity of the gas fuel as parameters. an air-fuel ratio storage means which is stored, and an air-fuel ratio corresponding to the engine load and the specific gravity of the gas fuel at that time is read from the storage means according to the operating state of the engine and the specific gravity of the fuel gas, and the air-fuel ratio is set to that air-fuel ratio. An air-fuel ratio control device for a gas fuel engine, comprising: a fuel supply amount setting means for setting a gas fuel supply amount; and a fuel supply means for supplying gas fuel to the engine at the set supply amount. (3) The air-fuel ratio control device for a gas fuel engine according to claim 2, wherein the gas specific gravity detection means is a Lauter gas analyzer.