JPS584183B2 - Mixing ratio control device for LPG engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mixture ratio control device for an LPG engine.

The LPG mixer of a conventional LPG engine has only a main fuel supply system (main system), and has the disadvantage that the mixture ratio varies widely because the venturi negative pressure (main nozzle negative pressure) decreases during idling operation.

For this reason, in recent years, a low-speed fuel supply system (slow system) has been provided to supply fuel using negative pressure downstream of the throttle valve, or to supply fuel with positive pressure applied upstream of the throttle valve.

However, in these methods, slow fuel is supplied at a nearly constant flow rate over the entire range of engine operating conditions, so the ratio between the main system and the slow fuel is greater than the mixture ratio determined by the main system fuel (theoretically constant). The total mixture ratio of the two systems will have a richer part and a thinner part depending on the engine operating conditions.

This is because if the air flow rate flowing through the venturi section is Qas, the fuel flow rate of the main system is Qfm, and the fuel flow rate of the slow system is Qfs, the negative pressure in the venturi section is determined by Qa, so it is approximately QavQfm, and therefore The mixing ratio (X) is expressed by the following formula.

Here, since Qfs is approximately constant, as the air flow rate Qa increases, the mixture ratio tends to become thinner.

Therefore, it was extremely disadvantageous as a system aiming at stoichiometric mixing ratio operation.

In view of these circumstances, the present invention includes a main system and a slow system, a correction fuel passage that corrects the fuel flow rate of the main system, and a throttle valve part that communicates with the upstream of the venturi part of the intake passage of the LPG mixer. The correction air passage opens downstream, and the correction fuel passage and the correction air passage each include a fuel and air flow rate control device, and the air flow is controlled via a common solenoid valve based on a signal from an exhaust sensor installed in the exhaust system. The present invention provides a mixture ratio control device for an LPG engine configured to control the mixture supplied to the engine to a predetermined mixture ratio by controlling the operations of the respective control devices.

Hereinafter, the present invention will be explained according to an embodiment shown in the drawings.

In FIG. 1, reference numeral 1 denotes an intake passage of an LPG mixer, which includes a venturi section 2 and primary and secondary throttle valves 3 and 4, and mixes air and LPG fuel.

Note that 5 is an intake pipe, 6 is a combustion chamber of the engine, and 7 is an exhaust pipe.

Reference numeral 8 denotes a paperizer, which is a device that supplies LPG fuel at a constant pressure, and automatically adjusts the pressure in the primary pressure chamber 8a to 1.3 atm and the pressure in the secondary pressure chamber 8b to around 1.0 atm. be done.

Reference numeral 9 denotes a main passage of the main fuel supply system, which communicates with the secondary pressure chamber 8b of the paper riser 8, and has one end connected to the intake passage 1.
It opens into the venturi section 2 of.

This main passage 9 is equipped with a main jet 10.

A correction fuel passage 11 branches from the main passage 9 upstream of the main jet 10 and communicates downstream of the main jet 10, and this passage 11 is provided with a fuel flow rate control device (variable jet).

This fuel flow control device uses a diaphragm 1 by balancing the negative pressure in the negative pressure chamber 12a and the elastic force of the spring 12b.
The control valve 12 is configured such that the valve body 12d moves up and down through the valve 2c, and the valve opening decreases when the operation control negative pressure increases.
Consisting of

Reference numeral 13 denotes a slow passage of the slow fuel supply system, which communicates with the primary pressure chamber 8a of the paperizer 8, and has one end connected to the intake passage 1.
It opens downstream of the primary throttle valve 3.

This slow passage 13 is provided with a slow jet, that is, a slow fuel adjustment screw 14.

Reference numeral 15 denotes a correction air passage, which communicates with the upstream side of the venturi portion 2 of the intake passage 1, and has one end opening downstream of the secondary throttle valve 4 of the intake passage 1.

This air passage 15 is provided with an air flow rate control device.

This air flow control device uses a balance between the negative pressure in the negative pressure chamber 16a and the elastic force of the spring 16b to
The control valve 1 is configured such that the valve body 16d moves up and down as shown in the figure via the valve body 6c, and the valve opening degree increases when the operation control negative pressure increases.
Consists of 6.

Each negative pressure chamber 12a, 16a of the two control valves 12, 16
The operation control negative pressure led to is the same, and the negative pressure passage 17 communicates with the suction negative pressure source via the orifice 18 and the constant pressure valve 119, and also communicates with the suction negative pressure source through the orifice 20 and the solenoid valve 2.
1 to the atmosphere.

Therefore, the operation control negative pressure is obtained by controlling the constant negative pressure obtained by the constant pressure valve 19 to be diluted with the atmosphere by the electric valve 21 using the suction negative pressure as the negative pressure source.

This solenoid valve 21 is operated by a drive pulse output from an electronic control circuit 22, and the electronic control circuit 22 receives a signal from an 02 sensor 23 that detects the oxygen concentration in the exhaust gas, and adjusts the air-fuel mixture to the stoichiometric mixing ratio. It performs calculations and outputs drive pulses.

To explain the mode of mixture ratio control with reference to FIG. 2, the output voltage of the 02 sensor 23 according to the oxygen concentration in the exhaust gas is compared with a comparison voltage corresponding to the theoretical mixture ratio in the electronic control circuit 22. An output is obtained, which is subjected to proportional and integral operations to calculate the duty ratio (ratio of pulse width to pulse period) of the drive pulse, and based on this, the drive pulse is output to the electromagnetic valve 21.

As a result, an operation control negative pressure is obtained by operating the solenoid valve 21, and when this negative pressure decreases, that is, when the oxygen concentration in the exhaust gas is low and the mixture ratio is lean, the opening degree of the control valve 16 of the correction air passage 15 decreases. At the same time, the opening degree of the control valve 12 of the correction fuel passage 11 increases, enriching the mixture ratio and bringing it closer to the stoichiometric mixture ratio.

Note that the mixture ratio control in this case causes a time delay by the length of the control period.

Thus, the main system controls the fuel flow rate by the control valve 12 of the correction fuel passage 11, and the slow system controls the fuel flow rate by the control valve 12 of the correction fuel passage 11.
The air flow rate is controlled by the control valve 16 of No. 5.

Particularly regarding the mixture ratio control during idle-link operation, air whose flow rate is controlled by the control valve 16 is supplied through the correction air passage 15 to the positive pressure fuel supplied through the slow passage 13.

Here, if the fuel flow rates flowing through the main jet 10 and the correction fuel passage 11 are respectively Q'fm and Q''fm, and the air flow rate flowing through the correction air passage 15 is Qas, the mixture ratio (-) is expressed by the following equation.

Therefore, if the slow system correction air amount Qas is controlled during idle link operation where the required fuel amount is small, and the main system correction fuel amount Q″fm is controlled during other operations where the required fuel amount is large, the mixture ratio will always be maintained. It is easy to maintain a constant mixing ratio and maintain a uniform mixing ratio over the entire range of engine operating conditions, so it is easy to control the mixing ratio to the stoichiometric ratio.

In addition, controlling the fuel flow rate in the slow system during idling is difficult because it involves controlling a very small fuel flow rate, and since the area of the fuel passage is extremely small, impurities such as tar may accumulate, resulting in poor control accuracy. However, in the present invention, since the mixing ratio is controlled by controlling the air flow rate, which has a large flow rate, these drawbacks can be overcome.

Note that the air flow rate control device for the correction air passage 15 may be configured to operate only during idling.

Further, the fuel flow rate control device and the air flow rate control device may be configured with electromagnetic valves operated by an electronic control circuit.

Furthermore, one end of the slow passage 13 may be communicated with the vicinity of the outlet of the main passage 9 to the intake passage 1, as shown by the broken line in FIG.

As explained above, according to the present invention, there is an air flow control device that mainly corrects the air amount during idling operation, a fuel flow control device that corrects the fuel amount during non-idling operation, and communication between the two flow rate control devices. a common negative pressure source to
Since a common solenoid valve that is interposed between the negative pressure source and both flow rate control devices and controls the operating negative pressure is provided, the control negative pressure can be controlled by one solenoid valve, and the control of both flow rate control devices can be controlled by one solenoid valve. The signal negative pressure is unified, the connection from the slow system to the main system is made continuously with good synchronization, and the mixture ratio can be accurately maintained at a predetermined value over a wide range via the exhaust sensor and control means. can be simplified.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the apparatus of the present invention, and FIG. 2 is a timing chart illustrating aspects of mixing ratio control. 1... Intake passage, 2... Venturi section, 3, 4... Primary side and secondary side throttle valve, 8...
...Paperizer, 9...Main passage,
10...Main jet, 11...Correction fuel passage, 12.16...Control valve, 13...
... Slow passage, 15... Correction air passage,
16... Control valve, 19... Constant pressure valve, 2
1...Solenoid valve, 22...Electronic control circuit, 23...02 sensor.

Claims (1)

[Claims] I. The LPG mixer of the LPG engine includes a main fuel supply system, a low-speed fuel supply system, a correction fuel passage, a fuel flow control device provided in the correction fuel passage, and a venturi section of the intake passage of the LPG mixer. A correction air passage that communicates upstream and opens downstream of the throttle valve portion, an air flow control device provided in the correction air passage, and a device other than the air flow control device and idle link that mainly corrects the air amount during idling operation. a common negative pressure source communicating with the fuel flow control device that corrects the amount of fuel during operation; a common solenoid valve interposed between the negative pressure source and both flow rate control devices to control the operating negative pressure; and an exhaust gas flow control device. The system includes an exhaust sensor provided in the system, and a control means that issues a control output based on a signal from the sensor, and the control means controls the operation of each of the flow rate control devices via the solenoid valve. A mixture ratio control device for an LPG engine, characterized in that it is configured to control the mixture supplied to the engine to a predetermined mixture ratio.