JPS589262B2 - Air-fuel ratio control device for internal combustion engines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for maintaining the air-fuel ratio of a mixed gas supplied to an internal combustion engine at a target value.

Generally, in a normal internal combustion engine, the relationship between the air-fuel ratio of the supplied mixed gas and the oxygen concentration or carbon monoxide concentration of the exhaust gas derived from the air-fuel ratio is the same as when the fuel and oxygen in the mixed gas have sufficiently reacted. This is shown by the broken line in Figure 1.

The downward right line CO on the left side of the figure corresponds to carbon monoxide, and the upward right line 02 on the right side corresponds to oxygen, and an air-fuel ratio of about 15 where both concentrations are O is the stoichiometric air-fuel ratio.

Therefore, the ratio of the oxygen concentration and carbon monoxide concentration of the exhaust gas resulting from incomplete combustion of the mixed gas at the stoichiometric air-fuel ratio is considered to be constant.

Next, as shown in the cross section in Figure 2, one side of zirconium oxide or tin oxide 4-1 is coated with platinum and 4-2 so that the platinum coated side is in contact with the exhaust gas and the opposite side is in contact with the atmosphere. The electromotive force generated between both sides changes depending on the air-fuel ratio of the mixed gas originating from the exhaust gas that comes into contact with it, for example, as shown in FIG.
A stoichiometric air-fuel ratio sensor 4 is known that has a stoichiometric air-fuel ratio sensor 4 that is configured to suddenly occur in the vicinity.

The above-mentioned characteristics of the stoichiometric air-fuel ratio sensor 4 are related to the air-fuel ratio of the mixed gas from which the exhaust gas is derived, and therefore to the ratio of the oxygen concentration and monoxide gas concentration of the exhaust gas, and are not actually related to the respective values of both concentrations. It is considered a thing.

It has a structure similar to the stoichiometric air-fuel ratio sensor 4 shown in FIG. Analog sensors that gradually change depending on the situation are known.

Compared to this, the stoichiometric air-fuel ratio sensor is superior in that it is less susceptible to changes in atmospheric pressure and temperature, but as it is, it cannot detect air-fuel ratios outside the stoichiometric air-fuel ratio. It has been difficult to achieve both insensitivity to changes in atmospheric pressure and temperature and control of air-fuel ratios other than the stoichiometric air-fuel ratio. In order to realize an air-fuel ratio control device capable of controlling air-fuel ratios other than the fuel ratio, in an internal combustion engine, an exhaust gas passage is provided in the exhaust manifold as a side passage for guiding exhaust gas, and a stoichiometric air-fuel ratio sensor 4 is provided in this,
A blending device is provided upstream of the stoichiometric air-fuel ratio sensor in the exhaust gas passageway to blend oxygen, carbon monoxide, or a gas containing these at known concentrations at a fixed ratio to the flow rate of the exhaust gas flowing therethrough. In the case of exhaust gas originating from a mixed gas having an air-fuel ratio of a target value, the ratio of the oxygen concentration and carbon monoxide concentration of the gas downstream of the blending device is made to match that of the exhaust gas originating from a mixed gas having a stoichiometric air-fuel ratio, A mixture supply device that supplies mixed gas to the internal combustion engine is provided with an adjustment device that adjusts the air-fuel ratio of the mixture gas, and further, the adjustment device is driven in response to a signal from the stoichiometric air-fuel ratio sensor to adjust the air-fuel ratio of the mixture gas. An air-fuel ratio control device for an internal combustion engine has been proposed, which includes a control circuit unit that returns the fuel ratio to the target value.

The present invention relates to the specific structure of the blending device, which will be explained next based on examples.

The embodiment shown in its entirety in FIG. 4 and in part in FIG. The stoichiometric air-fuel ratio sensor 4 is provided at the stoichiometric air-fuel ratio sensor 4, and a venturi 5 is provided upstream of the stoichiometric air-fuel ratio sensor 4 in the exhaust gas passage 3.

6 is a blended gas source such as a cylinder filled with pressurized oxygen, carbon monoxide, or a gas containing these at a fixed ratio, or a pump that pumps these gases; these gases are depressurized by a pressure reducing valve 7, and the blended gas is It communicates with the venturi 5 through a gas passage 8 and an adjustment throttle 9.

In the pressure reducing valve 7, the lower surface of the diaphragm 10 receives the pressure of the reduced gas, and the upper surface receives the pressure of the portion 12 upstream of the exhaust gas passage 3 in the exhaust manifold 2 via the pressure guide path 11, reducing the pressure on both the upper and lower surfaces. The difference drives the valve body 14 via the bell crank 13 to adjust the passage area with the valve seat 15 and change the pressure in the blended gas passage 3 in response to the pressure in the upstream 12, As a result, the ratio between the amount of exhaust gas flowing into the venturi 5 and the amount of mixed gas flowing through the regulating throttle 9 is maintained at a predetermined value.

Therefore, the side passage 3, the venturi 5, the mixed gas source 6, the pressure reducing valve 11, the mixed gas passage 8, the regulating throttle 9, etc. are arranged at a predetermined ratio with respect to the flow rate of the exhaust gas flowing through the exhaust manifold 2.
A blending device 16 is configured to blend oxygen, carbon monoxide, or a gas containing these at high concentrations.

Then, a target value for the air-fuel ratio of the mixed gas to be supplied to the internal combustion engine 1 is determined, and when the air-fuel ratio of the mixed gas is at this target value, the blending device 16 adds the blended gas to the exhaust gas derived therefrom at a fixed ratio. When blended, the ratio of oxygen concentration to monoxide gas concentration of the resulting gas is made to match that of the exhaust gas derived from a mixed gas at a stoichiometric air-fuel ratio.

Therefore, in this device, the stoichiometric air-fuel ratio sensor 4 is
A signal is emitted when the air-fuel ratio of the gas mixture supplied to the internal combustion engine 1 changes through the target value.

Next, the carburetor 17, which serves as a mixture control device that supplies mixed gas to the internal combustion engine 1, is equipped with an electromagnetic control device, which controls the air flow of the main air bleeder when normally closed, as an adjustment device that adjusts the air-fuel ratio of the mixed gas. A valve 18 is provided.

Reference numeral 19 denotes a control circuit unit having a circuit shown in FIG. 6, which energizes the solenoid valve 18 only for a time t in a constant operating cycle T to pass air when the electromagnetic valve 18 is repeatedly turned on, as shown in FIG.
Therefore, the air flow rate is made proportional to the duty ratio (t/T).

The main air bleed in the carburetor 17 is determined so that when the duty ratio (t/T) changes in the range of 0 to 100%, the air-fuel ratio changes as shown in FIG.

The circuit in FIG. 6 consists of resistors 401 to 414 and capacitor 4.
15-417, diodes 418-419, operational amplifiers 420-422, duty ratio converter 423, oscillator 4
24, composed of transistors 425 to 426, impedance conversion is performed on the signal shown in diagram a in FIG. amplifier 422
, a resistor 408, and a capacitor 417, the signal is integrated and input to a duty ratio converter 423, and the signal is switched by transistors 425 and 426, and adjusted by a solenoid valve 18 as a regulating device. .

According to this control circuit unit 19, when the air-fuel ratio of the mixed gas supplied to the internal combustion engine 1 is lower than the target value, that is, when the fuel concentration of the mixed gas is too high, the signal voltage of the stoichiometric air-fuel ratio sensor 4 is high, As shown in diagram b of the figure, integrators 422,4
The output voltage of 08,417 gradually increases as shown in line C in Figure 9.
As shown in , the duty ratio (t/T) gradually increases, the air flow rate of the solenoid valve 18 gradually increases, and the air-fuel ratio is restored.

When the air-fuel ratio is higher than the target value, that is, the fuel concentration of the mixed gas is too low, the signal voltage of the stoichiometric air-fuel ratio sensor 4 is low, and the integrators 422, 408, 41 as shown by line b in FIG.
7 gradually decreases, the duty ratio (t/T) gradually decreases as shown in line C of FIG. 9, and the air flow rate of the solenoid valve 18 gradually decreases to restore the air-fuel ratio.

In this way, when the air-fuel ratio of the mixed gas supplied to the internal combustion engine 1 changes through the target value, the control circuit section 19 receives the signal emitted by the stoichiometric air-fuel ratio sensor 4 and controls the solenoid valve 18 as a regulating device. and adjusts the air flow rate of the main air bleed to return the air-fuel ratio of the mixed gas to the target value.

In this embodiment, a stoichiometric air-fuel ratio sensor is used for the air-fuel ratio of the mixed gas when 0 or 1 times as much air as the exhaust gas is mixed in by the blending device 16, and when 0.2 times as much carbon monoxide as the exhaust gas is mixed. The electromotive force characteristics of No. 4 are as shown by solid lines and horizontal lines in FIG. 3, respectively, when the target air-fuel ratio is set to 13.
5 and 16.5.

According to this invention, since the stoichiometric air-fuel ratio sensor 4 is used, it is not affected by external conditions such as exhaust gas temperature and atmospheric pressure, and therefore no compensating device is required. It is possible to realize an air-fuel ratio control device that sets an air-fuel ratio other than that as a target value, and the structure is simple.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the air-fuel ratio of the mixed gas supplied to the internal combustion engine and the oxygen concentration and monoxide gas concentration of the exhaust gas derived from it, and Figure 2 is a cross-section of an example of the stoichiometric air-fuel ratio sensor. Figure 3 is a diagram showing the electromotive force against the air-fuel ratio of the stoichiometric air-fuel ratio sensor and the device of this invention, Figure 4 is a diagram of the overall principle of this invention, Figure 5 is a diagram of the principle of the blending device, and Figure 6 is a diagram showing the electromotive force with respect to the air-fuel ratio of the stoichiometric air-fuel ratio sensor and the device of this invention. Figure 7 is a circuit diagram of the control circuit section, Figure 7 is a diagram showing the relationship between the operating period T and valve opening time t of the normally closed solenoid valve for main air bleed by the control circuit unit, and Figure 8 is a diagram showing the relationship between the duty ratio (t /T) and the air-fuel ratio, and FIG. 9 is a diagram illustrating the operation of the control circuit section. 1... Internal combustion engine, 2... Exhaust manifold, 3... Exhaust gas passage, 4... Theoretical air-fuel ratio sensor, 5... Venturi, 7...
...Pressure reducing valve, 9... Throttle, 16...
Blending device, 17...Mixed gas supply device, 18.
...Adjusting device, 19...Control circuit section.

Claims (1)

[Claims] 1 In an internal combustion engine, an exhaust gas passage is provided in the exhaust manifold as a side passage for guiding exhaust gas, and a stoichiometric air-fuel ratio sensor 4 is provided in this passage, and a stoichiometric air-fuel ratio sensor 4 is provided in the exhaust gas passage, and a passageway for exhaust gas flowing through the exhaust gas passage is provided upstream of the stoichiometric air-fuel ratio sensor. A blending device that blends oxygen, carbon monoxide, or a gas containing these at a known concentration at a fixed ratio to the flow rate is installed, and the blending device is installed to mix exhaust gas derived from a mixed gas having an air-fuel ratio of a target value. The ratio of the oxygen concentration and carbon monoxide concentration of the gas downstream of the device is made to match that of the exhaust gas derived from the mixed gas at the stoichiometric air-fuel ratio, and the air-fuel ratio of the mixed gas is sent to the mixture supply device that supplies the mixed gas to the internal combustion engine. an air-fuel ratio adjustment device for an internal combustion engine, further comprising a control circuit unit that drives the adjustment device in response to a signal from the stoichiometric air-fuel ratio sensor to return the air-fuel ratio of the mixed gas to the target value. In the fuel ratio control device, in order to constitute the blending device, a venturi is provided upstream of the stoichiometric air-fuel ratio sensor in the exhaust gas passage, and the mixture is to be blended in response to the pressure upstream of the exhaust gas passage in the exhaust manifold. An air-fuel ratio control device for an internal combustion engine, characterized in that a pressure reducing valve for changing the pressure of gas is provided, and the gas to be blended whose pressure has been reduced by the pressure reducing valve is made to flow into the venturi via a throttle.