JPH0543866B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION This invention relates to a catalyst protection device for an internal combustion engine, and in particular to a thermal protection device for a catalytic converter for a gas engine.

BACKGROUND TECHNOLOGY The exhaust pipes of equipment that operates internal combustion engines using city gas or liquefied petroleum gas (LPG) to produce hot water or generate electricity are usually equipped with catalytic converters for exhaust gas purification. Such equipment is equipped with an exhaust gas monitoring system.

By the way, when a misfire occurs during operation of an internal combustion engine, a large amount of unburned mixed gas flows into the catalytic converter. When this mixed gas causes a chemical reaction within a catalytic converter installed in the exhaust pipe of an internal combustion engine, the temperature within the catalytic converter may rise to 900°C or more. If such high-temperature conditions are left unattended, the life of the catalyst will be significantly shortened, and the catalyst will melt away at temperatures above 1000°C. Therefore, in order to avoid such defects, if the outlet temperature of the catalytic converter exceeds an abnormally high temperature inside the catalytic converter (for example, 900°C), the internal combustion engine is stopped to protect the catalytic converter. .

Therefore, two methods are currently generally used to stop the operation of the internal combustion engine when a large amount of unburned mixed gas is generated. One method is to operate a relay based on an alarm output from a temperature sensor provided in the catalytic converter to shut off power to the internal combustion engine. In this method, the on-off valve that controls the inflow of fuel gas automatically closes when the intake negative pressure is lost due to the stoppage of the internal combustion engine. but,
An internal combustion engine continues to operate due to inertia even after the power is turned off, so it continues to inhale the mixed gas and at the same time
The unburned mixed gas for deenergizing the ignition circuit is supplied to the catalytic converter. Therefore, the catalytic converter has the disadvantage that it generates a large amount of reaction heat and the catalyst temperature increases.

In order to overcome these drawbacks, another method is used, namely, closing the fuel valve based on the alarm output of the temperature sensor, counting the time from the valve closing with a timer, and cutting off the power to the internal combustion engine after a few seconds. There is a way. In this method, the timer counting time from closing the fuel valve to shutting off power to the internal combustion engine must be adjusted for each residual gas capacity.

In experiments conducted by the present inventor, when the power supply to the internal combustion engine was cut off under normal operating conditions in which the outlet temperature of the catalytic converter was maintained at approximately 500°C, the temperature of the catalytic converter rose to a maximum of 950°C. In addition, in an experiment in which the power to the internal combustion engine was cut off after a certain period of time (approximately 3 seconds) after the fuel valve was closed, the temperature of the catalytic converter was 600%.
It was found that the temperature reached more than ℃, and the temperature temporarily decreased slightly due to fuel shutoff, but then it rose further by 100 to 150℃ and then dropped again. As described above, it is difficult to adjust the timer counting time from fuel shutoff to power shutoff of the internal combustion engine for each residual gas capacity.

Problems to be Solved by the Invention As described above, in the conventional catalytic converter for an internal combustion engine, the temperature inside the catalytic converter increases and the catalytic converter cannot be protected from high temperatures.

The object of the present invention is to provide a catalyst protection device for an internal combustion engine that does not have the above-mentioned drawbacks.

Means for Solving the Problems The catalyst protection device for an internal combustion engine of the present invention includes a temperature sensor that detects the temperature of a catalytic converter provided in the exhaust pipe of the internal combustion engine, and a gas sensor that detects the gas concentration in the catalytic converter. , a control circuit having a rotation sensor that detects the rotation speed of the internal combustion engine, a plurality of input terminals connected to the temperature sensor, the gas sensor, and the rotation sensor, respectively; and an electromagnetic control fuel connected to one output terminal of the control circuit. and an ignition control circuit connected to the other output terminal of the control circuit.

The control circuit includes a fuel valve control circuit that closes the electromagnetically controlled fuel valve when the temperature sensor detects a temperature higher than abnormally high temperature inside the catalytic converter, and a fuel valve control circuit that closes the electromagnetic control fuel valve when the temperature sensor detects a temperature higher than the abnormally high temperature inside the catalytic converter. A first gate circuit provides an activation signal to the ignition control circuit to deactivate the ignition circuit when detecting a temperature of flammable components in the catalytic converter. When the catalytic converter detects a high combustible component state or a low combustible component state and the temperature sensor detects a temperature below abnormally high temperature within the catalytic converter, the ignition control is activated after the rotation sensor detects automatic stop of the internal combustion engine. and a second gate circuit that applies an activation signal to the circuit to put the ignition circuit in an inactive state.

Operation When the temperature sensor detects abnormally high temperature within the catalytic converter, the fuel valve control circuit of the control circuit closes the electromagnetically controlled fuel valve. After the electromagnetically controlled fuel valve closes, the mixture ratio at which the internal combustion engine can operate is maintained until the high-pressure side fuel gas pressure is transmitted to the low-pressure side gas pressure, so the ignition circuit is kept in the energized state during this time. , the internal combustion engine continues to operate. Thereby, the combustible components in the mixed gas are sufficiently combusted. Since the internal combustion engine continues to operate with the electromagnetically controlled fuel valve closed, the internal combustion engine automatically stops due to lack of fuel, and then the ignition circuit is switched to a de-energized state. Therefore, the internal combustion engine can be stopped with the gas concentration in the catalytic converter sufficiently low.

Embodiments Embodiments of the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 is a circuit diagram of a catalyst protection device according to the present invention, showing an example in which the control circuit is configured by a microcomputer. Each input terminal of the control circuit 30 has a temperature sensor 31 and a gas sensor 32.
and a rotation sensor 33, and an electromagnetic control fuel valve 34 and an ignition control circuit 35 are connected to each output terminal. Although not shown, the temperature sensor 31 and gas sensor 32 are attached to the outlet and inlet portions of the catalytic converter, respectively. The rotation sensor 33 detects the rotation speed of the internal combustion engine. The gas sensor 32 detects the air-unburned gas mixture ratio by measuring the amount of oxygen at the inlet of the catalytic converter with an oxygen sensor. The electromagnetically controlled fuel valve 34 is
The coil 3 includes a coil 36 and a plunger 37.
6 moves the plunger 37 to the valve open position. The ignition control circuit 35 includes a transistor 3 having a base connected to the control circuit 30.
8, a relay coil 39 connected to the collector of the transistor 38, and a pair of contacts 40 that are turned off when the relay coil 39 is energized. Contact 40
is connected between the main switch 41 of the power supply and the ignition plug, and the emitter of the transistor 38 is grounded.

The control circuit 30 shown in FIG. 1, which is composed of a microcomputer, has a programmable ROM. The program to be commanded to this programmable ROM can be determined according to the operating procedure shown in FIG. Although not shown, a gate circuit including a first gate circuit and a second gate circuit is formed in the control circuit 30. In FIG. 2, the temperature inside the catalytic converter is measured by the temperature sensor 31, and it is determined whether or not it is above an abnormally high temperature (900° C.) (step 51). If the temperature inside the catalytic converter does not reach the abnormally high temperature, the process returns to start 50, and if the temperature exceeds the abnormally high temperature, a clutch device (not shown) is operated to release the load (step 5).
2). Next, the coil 36 is de-energized, the electromagnetically controlled fuel valve 34 is closed (step 53), and the fuel supply is cut off.

Next, the temperature sensor 31 detects that the temperature inside the catalytic converter is higher than the critical temperature (300°C).
If the critical temperature is not reached (step 54), the controller 30 provides an activation signal to the base of the transistor 38 to activate the base of the transistor 38.
is turned on, relay coil 39 is energized, and contact 4
0 is opened to deenergize the ignition circuit (step 55).

However, when the temperature inside the catalytic converter is above the critical temperature, it is determined based on the output of the gas sensor 32 whether the inside of the catalytic converter is in a lean state with few combustible gas components (step 56). When it is determined that the state is lean, the temperature sensor 3 again determines whether the temperature is higher than the abnormally high temperature (step 57). At this time, when it is determined that the temperature is higher than the abnormally high temperature, the control circuit 30 is in an uncontrollable state, and to prevent danger, the control circuit 30 has no choice but to supply an activation signal to the base of the transistor 38 to turn on the ignition circuit. is deactivated (step 55).

When it is determined at step 57 that the temperature is below the abnormally high temperature, or when it is determined that the engine is not in a lean state at step 56, it is determined by the rotation sensor 33 whether or not the internal combustion engine has stopped (step 58). If the internal combustion engine stops, the ignition control circuit 3
5 to deenergize the ignition circuit (step 55). However, if the internal combustion engine does not stop at step 58, the process returns to step 54, where it is determined by the temperature sensor 31 whether the temperature is higher than the critical temperature. In this way, after the electromagnetically controlled fuel valve 34 is closed, the mixture that enables the internal combustion engine to operate is maintained until the high-pressure side fuel gas pressure is transmitted to the low-pressure side gas pressure. During this time, the ignition circuit is energized. The internal combustion engine continues to operate until it automatically stops.

Thereby, the combustible components in the mixed gas can be sufficiently combusted. Since the internal combustion engine continues to operate with the electromagnetically controlled fuel valve 34 closed, the internal combustion engine automatically stops due to fuel shortage, and then the ignition circuit is switched to the de-energized state. Therefore, the internal combustion engine can be stopped while the gas concentration in the catalytic converter is sufficiently low.

Control circuit 3 composed of discrete circuits
0 is shown in FIG. The signal of the temperature sensor 31 is supplied to one input terminal of the comparator 60 and compared with the voltage of the power supply 61, which is equal to the abnormally high temperature (900° C.) and applied to the other input terminal of the comparator 60. When the temperature inside the catalytic converter is abnormally high 900℃ or higher,
The output of the comparator 60 becomes H level, and an H level signal is applied to the gate of the SCR 63 through the amplifier 62, turning the SCR 63 on. Therefore relay 6
4 is activated and the contact 65 is opened and separated, so the solenoid 36 is deenergized and the electromagnetically controlled fuel valve 34 is turned off. Note that the switch 68 is closed when the electromagnetically controlled fuel valve 34 is manually turned off. SCR63 is
It remains on even if the temperature inside the converter drops below 900℃.

The signal of temperature sensor 31 is applied to one input terminal of comparator 70 and compared with a voltage of power supply 71 equal to a critical temperature applied to the other input terminal of comparator 70 . The comparator 70 produces an L level output when the temperature sensor 31 gives a signal that the temperature inside the catalytic converter is 300°C or less, and produces an H level output when a signal exceeding 300°C is given. . Therefore, if the temperature inside the catalytic converter does not reach 300°C after the electromagnetically controlled fuel valve 34 is closed,
AND gate 69 with both inverting input terminals produces an output through OR gate 72 to transistor 38.
Turn on and de-energize the ignition circuit. AND
Gate 69 constitutes a first gate circuit.

Next, the gas sensor 32 produces an L level output when the inside of the catalytic converter is in a lean state. AND gate 76 receives the output of comparator 70 and relay 6
Along with receiving the L level signal of the coil 66 of No. 4,
Since the output of the gas sensor 32 is received through the amplifier 75, when the inside of the catalytic converter exceeds 300°C and is in a lean state after the electromagnetically controlled fuel valve 34 is closed, the AND
Generates an output to gate 77. AND gate 7
7 generates a signal by the output of the comparator 60 when the temperature inside the converter is 900°C or higher, and the OR gate 7
2 to turn on transistor 38.

The output of the rotation sensor 33 is applied from an amplifier 78 to a comparator 82 through a diode 81, a smoothing capacitor 79, and a resistor 80. Rotation sensor 33
is at the L level when the internal combustion engine is stopped, and the comparator 8
2 compares with the reference power source 83 to determine whether the internal combustion engine is stopped. Since the comparator 82 produces an L level output when the internal combustion engine is stopped, the AND gate 84 which receives the output from the AND gate 76 outputs an L level output when the internal combustion engine stops and the output of the rotation sensor 33 becomes L level.
When the temperature inside the catalytic converter is below 900°C, an output is generated and the transistor 38 is output through the OR gate 72.
Turn on.

The AND gate 73 sends a signal to the AND gate 74 when the inside of the catalytic converter is at 300° C. or higher and is not in a lean state after the electromagnetically controlled fuel valve 34 is closed. AND gate 74 has one input terminal connected to AND gate 74.
The signal from the gate 73 is received, and the output from the comparator 82 is received at the other opposite input terminal. Therefore, the AND gate 74 produces an output and turns on the transistor 38 through the OR gate 72 when the temperature inside the catalytic converter exceeds 300° C. and the internal combustion engine is not in a lean state and is stopped. In short, in the circuit shown in FIG. 3, when the electromagnetically controlled fuel valve 34 is closed, the AND gate 69,
The internal combustion engine remains in operation until any one of 74, 77, or 84 reaches the H level, and the combustible components in the mixed gas are combusted by the internal combustion engine. In this example
AND gates 73, 74, 76 and 84 constitute a second gate circuit.

Although the embodiment using the microcomputer shown in FIG. 1 and the embodiment using the discrete circuit shown in FIG. 3 have been shown, it will be understood that the present invention can be practiced with either embodiment. In the above embodiment, a thermocouple was used as the temperature sensor and an oxygen sensor (titania type) was used as the gas sensor, but other sensing elements may also be used.

Effects of the Invention In this invention, when the temperature sensor detects abnormally high temperature within the catalytic converter, the electromagnetically controlled fuel valve is closed. Further, while the mixture ratio necessary for combustion in the internal combustion engine is maintained, the ignition circuit is operated to maintain operation of the internal combustion engine. Therefore, by operating the internal combustion engine, the amount of combustible gas supplied to the catalytic converter can be sufficiently reduced, thereby preventing a rise in temperature within the catalytic converter and protecting the catalytic converter from high temperatures.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a catalyst protection device for an internal combustion engine according to the present invention, FIG. 2 is a flowchart showing the operating sequence of this device, and FIG. 3 is a circuit diagram showing another embodiment of the device according to the present invention. It is a diagram. 30... Control circuit, 31... Temperature sensor, 32
... Gas sensor, 33 ... Rotation sensor, 34 ...
Electromagnetic control fuel valve, 35...Ignition control circuit, 36...Coil, 37...Plunger, 38
...Transistor.

Claims (1)

[Claims] 1. A temperature sensor that detects the temperature of a catalytic converter provided in the exhaust pipe of an internal combustion engine, a gas sensor that detects the gas concentration in the catalytic converter, and a rotation sensor that detects the number of revolutions of the internal combustion engine. , a control circuit having a plurality of input terminals connected to the temperature center, the gas sensor, and the rotation sensor, respectively; an electromagnetically controlled fuel valve connected to one output terminal of the control circuit; and the other output terminal of the control circuit. a fuel valve control circuit that closes the electromagnetically controlled fuel valve when the temperature sensor detects a temperature equal to or higher than an abnormally high temperature in the catalytic converter; a first gate circuit that applies an actuation signal to an ignition control circuit to put the ignition circuit into a non-operating state when the temperature sensor detects a temperature below a critical temperature after the valve closing signal is generated; The temperature sensor detects a temperature equal to or higher than a critical temperature, and the gas sensor detects a state in which there are many flammable components in the catalytic converter, or a state in which there are few flammable components in the catalytic converter, and the temperature sensor detects an abnormally high temperature in the catalytic converter. and a second gate circuit that applies an activation signal to the ignition control circuit to deactivate the ignition circuit after the rotation sensor detects automatic stop of the internal combustion engine when a temperature below the temperature is detected. A catalyst protection device for internal combustion engines characterized by: