JPS5820919A - Exhaust gas cleaner for diesel engine - Google Patents

Abstract

PURPOSE:To detect the clogged condition of a filter for catching carbon particles easily and securely, by a method wherein a pulse current is passed between two electrodes provided in a filter and the current value is measured. CONSTITUTION:To detect the clogged condition of the filter 3 for cathing carbon particles which is provided in a exhaust passage for the engine, the electrodes 4, 5 are provided at separate positions in the filter 3, the pulse current is supplied from a pulse generator 9 to the electrode 4, the current is received by the electrode 5 and the current value is measured by a detecting circuit 15. Since the resistance between the electrodes is reduced when the filter 3 is clogged, the clogged condition can be detected by discriminating the current value, namely, the resistance value. When the filter 3 is clogged, an air pump 34 and a fuel pump 33 are driven by a signal from the detecting circuit 15, and a burner 8 is operated to reburn minute particles caught in the filter 3, thereby regenerating the filter 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for easily and reliably detecting clogging of a filter member provided in an exhaust passage for collecting particulate components such as carbon particles in the exhaust of a diesel engine. This invention relates to an exhaust purification device for a diesel engine.

Conventionally, an exhaust purification device for a diesel engine uses an exhaust pressure detection means to detect exhaust pressure upstream of a filter member in an exhaust passage, and detects clogging of the filter member due to an increase in the exhaust pressure. It is known to detect clogging and operate a burner provided upstream of the filter member to eliminate clogging.

However, in the exhaust gas purification device that uses exhaust pressure to detect clogging as described above, the exhaust pressure does not only depend on clogging of the filter member, but also on operating conditions such as engine speed and load. For example, exhaust pressure increases during high-load operation and decreases during idling.
It is necessary to detect clogging of the filter member by comparing a preset exhaust pressure map according to the operating state with the exhaust pressure detected by the detection means, which makes the circuit configuration complicated. There are drawbacks.

In addition, as an exhaust purification system for diesel engines, the carbon particles in the exhaust gas are deposited in a collection container using a cyclone, and two electrodes are placed at a certain level inside the container. There is also known a device in which the amount of carbon deposited is detected by connecting the electrodes with carbon when the level of carbon deposits exceeds a certain level.

However, the cyclone method described above has a complicated structure, cannot sufficiently collect extremely small particulate components, and requires periodic removal of accumulated carbon in the container.

For this reason, the present applicant disposed two electrodes on a light letter member provided in the exhaust passage of the engine, and applied a predetermined voltage between the electrodes. A diesel engine is provided with a detection circuit that detects a change in resistance between electrodes that changes depending on the amount of carbon particles adhering to a member, and directly detects clogging of a filter member based on an output signal of the detection circuit. proposed a C purification device that discharges carbon (Utility Application No. 88681/1981).

Since a predetermined voltage is always applied between the two electrodes, carbon 15 is deposited on the electrode 4 as shown in FIG.
．． When the resistance value between electrodes 5 and 5 decreases and a large amount of current flows, the electrode section generates heat and the carbon 15a burns. It has also been found that when the carbon around the electrode burns, the electrode is insulated from the remaining deposited carbon, causing a problem in which carbon is not detected even though a predetermined amount of carbon has been deposited.

The present invention was made to solve the above-mentioned problems,
The voltage applied between the electrodes is made into a pulsed voltage, and the time during which the current is applied to the electrodes is reduced to suppress the heat generation of the electrodes, thereby preventing the combustion of deposited carbon and easily preventing clogging of the filter member. It is an object of the present invention to provide an exhaust gas purification device for a diesel engine that can perform accurate detection with an inexpensive configuration.

Next, one embodiment of the present invention will be explained with reference to the drawings which are one embodiment.

In Fig. 1, 1 is an exhaust passage in an exhaust pipe 2 of a diesel engine, and 3 is a honeycomb-shaped non-conductive filter member disposed in the exhaust passage 1. The two holes are closed with blind plugs 8a, and the exhaust gas flowing in from one of the pores flows out to the other through the porous partition wall 3b. 4 and 5 are respectively fixed to the peripheral wall of the exhaust pipe 2 via insulating members 6.7, and inserted into the filter member 3 tightly against the partition wall 8b in a direction perpendicular to the axis of the filter member 3. 8 is a burner provided in the exhaust pipe 2 on the upstream side of the filter member 3, and the burner 8 blows out combustion gas onto the filter member 3. It is designed to burn off attached carbon particles, etc.

When carbon particles 15 adhere to the partition wall 8b of the filter member 8 as shown in FIG. It has a decreasing characteristic as shown in the figure.

An oscillator 9, which is a pulse voltage application circuit, is connected to one electrode 4, and an eye consisting of a resistor 16, a peak hold circuit 17, a reference value setting device (reference voltage) 19, and a comparator 18 is connected to the other electrode 5. A blockage detection circuit 15 is connected.

Therefore, the value of the current flowing to the gap electrode 4.5 in response to the pulse voltage from the oscillator 9 is determined by the electrical resistance between the electrodes 5.4, which decreases as the amount of carbon particles 15 on the filter member 3 increases. It is supposed to be done. Therefore, the difference in voltage across the resistor 16 increases as shown by curve B in FIG. 4 as the amount of attached carbon particles 15 increases.

On the other hand, the voltage across the resistor 16 is input to the peak hold circuit 17, and the difference between the voltages across the resistor 16 is detected. The peak hold circuit 17 outputs a signal representing the difference between the voltages to the comparator 18. Further, a reference value representing the reference amount of carbon deposited at which the burner 8 should be activated is set in the reference value setting device 19, and the reference value signal is sent to the comparator 18.
Output to .

The comparator 18 compares the signal representing the voltage difference with the reference value signal, and if the signal representing the voltage difference is larger than the reference value signal, that is, the amount of carbon deposit is larger than the reference value signal. For example, a high level signal is output to the judgment circuit 21 shown in FIG.

The judgment circuit 21 is composed of an AND gate and is designed to operate the burner 8 only under certain conditions.

The determination circuit 21 receives output signals from an accelerator switch 23 for detecting deceleration and a vehicle speed switch 24 to determine whether or not it is idling, and is provided downstream of the filter member 8. The output signal from the exhaust gas temperature sensor 25 is input, and the output signal from the exhaust gas temperature sensor 25 is input.
The comparator 18 is connected to the battery B via the ignition switch 26 and is idling.
Only when the output signal from is at a high level and the temperature detected by the exhaust temperature sensor 25 is 700°C or less,
The judgment circuit 21 outputs a no-repel signal as a movement command signal.

In this way, the fuel and air of the engine 8 can be easily controlled by operating the engine 8 only during idling, when the exhaust volume is low and in a stable state. Further, the burner 8 is operated only when the temperature detected by the exhaust temperature sensor 25 is 700°C or lower, and in other words, the operation of the burner 8 is stopped when the detected temperature is 700°C or higher, thereby preventing overheating. The filter member 3 is protected from the ignition switch 26.
When the ignition switch 26 is turned off, the stoppage of the engine is detected by turning off the ignition switch 26, and the output of the signal for operating the burner control device 22 from the judgment circuit 21 is stopped to protect the battery B.

When the burner control device 22 receives an operation command signal from the judgment circuit 21, it first outputs a signal to heat the ignition heater 81 of the burner 8, and then, when the temperature of the ignition heater 31 reaches 900° C. or higher, When this is detected by the output signal from the ignition heater temperature sensor 32, a signal is output to drive the fuel pump 33 and the air pump 84, so that good combustion gas is ejected from the burner 8 into the exhaust passage l. . In this way, only when the ignition heater 31 reaches a certain temperature or higher, fuel and air are supplied to the burner 8 for complete combustion.
This is to prevent secondary pollution caused by the release of unburned gas. In addition, when stopping the operation of the burner 8, conversely, after stopping the driving of the fuel pump 33 and the air pump 34, the heating to the ignition heater is stopped, so that complete combustion is performed, and 2 We are trying to prevent further contamination.

The diesel engine exhaust gas purification device configured as described above detects the amount of carbon deposited on the filter member 8 and operates the burner 8 as described below.

Assume that this diesel engine is currently idling, the temperature detected by the exhaust temperature sensor 25 is 700° C. or less, and carbon particles 15 of a standard amount or more have adhered to the filter member 3.

Then, the electrical resistance between the electrodes 4 and 5 becomes smaller depending on the amount of carbon particles 15 attached.

Therefore, the current value flowing through the resistor 16 and the electrodes 4 and 5 becomes smaller, and the difference in voltage across the resistor 16 detected by the peak hold circuit 17 is the reference adhesion amount shown by the straight line (b) in FIG. It becomes larger than the reference voltage representing . Therefore, the comparator 18 outputs a no/no level signal to the judgment circuit 21.

The judgment circuit 21 receives both signals for idling detection input from the accelerator switch 23 and the vehicle speed switch 24,
Signal input from exhaust temperature sensor and comparator 18
The engine is in an idling state due to the level signal inputted from the engine, and the exhaust temperature downstream of the filter member 8 is 700°C or less, and carbon particles are attached to the filter member 3. It is determined that the amount is equal to or greater than the reference amount and that the burner 8 is in a state where it should be operated, and an operation command signal is output to the burner control device 8.

In response to the operation command signal, the burner control device 22 first outputs a signal for heating the ignition heater 31, and then inputs from the ignition heater temperature sensor 32 that the ignition heater 31 has been heated to 900°C or higher. When detected by the signal, it outputs a signal that activates the fuel pump 3B and the air pump 34, supplies fuel and air to the burner 8, and blows out combustion gas from the burner 8. Since the burner 8 is provided upstream of the filter member 3, the combustion gas is blown onto the filter member 8 together with the exhaust gas, burns carbon particles adhering to the filter member 3, and burns the filter member 3. To recover from clogging of one member 3.

On the other hand, if the amount of carbon particles attached to the filter member 3 is less than the reference amount and the comparator 18 outputs a low level signal, or if the accelerator outputs a low level signal, the signal from the switch 23 and the vehicle speed switch 24 or when the exhaust temperature detected by the output signal from the exhaust temperature sensor 25 is 7.
If the temperature is 00° C. or higher, the judgment circuit 21 does not output an operation command signal and stops the operation of the burner 8 to prevent energy loss and overheating of the filter member 8.

In the embodiment described above, the burner 8 is operated during idling operation, but the burner 8 may be operated during high load operation. Further, the clogging detection circuit is not limited to that of the embodiment described above, and may be a detection circuit 15a that directly detects the value of the current flowing through the electrodes 4 and 5, for example. Further, an electrode 4.5 disposed on the filter member 3
For example, as shown in FIG. 9, an electrode 5 is fixed to one blind plug 41 of the filter member 3 through the electrode 5, while a conductive material 43 such as stainless steel, gold, or platinum is fixed to the other blind plug 42. The conductive material 48 may be used as an electrode by being fixed by vapor deposition, baking, etc. so as to be in contact with the carbon particles 15.
As is clear from the above description, according to the present invention, two electrodes are disposed on the filter member in the exhaust passage of the engine, and a predetermined pulse voltage is applied between the electrodes to remove the filter. In order to detect clogging of a filter member by providing a detection circuit that detects the resistance change between the electrodes that changes depending on the amount of carbon particles attached to the filter member, as shown in Figs. 7 and 8, The amount of heat generated by the electrode is extremely small compared to the conventional method in which a constant voltage is applied all the time.Furthermore, since the cooling period begins after that, the accumulated carbon around the electrode does not burn, and the clogging of the filter material is prevented. Accurate detection is possible with a simple and inexpensive configuration.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the main parts of a diesel engine exhaust purification device showing an embodiment of the present invention, and FIG.
Line cross-sectional view, Figure 3 is a graph showing the relationship between the amount of carbon and the resistance between the electrodes, Figure 4 is a graph showing the relationship between the amount of carbon and the voltage difference between both ends of the resistance, and Figure 5 is the graph shown in Figure 1. 6 is a detailed diagram of a pulse voltage application circuit and a clogging detection circuit, FIG. 7 is a pulse voltage diagram, and FIG. FIG. 9 is a cross-sectional view showing a modification of the electrode, and FIG. 10 is an explanatory view showing the combustion state of carbon. 1... Exhaust passage, 8... Filter member, 4.5...
・Electrode, 9...Pulse voltage application circuit (transmitter), 15
...Clogging detection circuit.

Claims (1)

[Claims] (1) In a diesel engine in which a filter member for collecting carbon particles, etc. in exhaust gas is disposed in the exhaust passage of the engine, two filter members disposed at a predetermined interval on the filter member an electrode, a pulse voltage application circuit that applies a pulsed voltage between the electrodes, and a pulse voltage application circuit that applies a voltage between the electrodes depending on the amount of carbon particles that adhere to the filter member when the voltage is applied between the electrodes by the pulse voltage application circuit; 1. An exhaust gas purification device for a diesel engine, comprising: a detection circuit for detecting a change in resistance between electrodes that changes due to a change in resistance; and a detection circuit for detecting clogging of the filter member.