JPH0551043B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an engine exhaust gas purification device,
In particular, the present invention relates to an improvement in an exhaust gas purification device that captures combustible particles such as carbon particles contained in exhaust gas with a particulate filter and burns and removes the combustible particles.

(Prior Art) Conventionally, as this type of exhaust gas purification device, for example, as disclosed in Japanese Patent Laid-Open No. 56-98519, there has been a system that collects combustible particles in the exhaust gas in the exhaust system of an engine. A catalytic filter is disposed to cause an oxidation reaction, and an injector is provided upstream of the catalytic filter to inject auxiliary fuel such as liquid fuel as a liquid that promotes combustion of the combustible particles. It is known that the collected combustible particles are burnt and removed by heating the exhaust gas to a temperature higher than the ignition temperature of the combustible particles through a reaction by .

In addition, by supplying a catalyst solution, for example, as a liquid that promotes the combustion of the combustible particles upstream of the filter and depositing the catalyst on the surface of the combustible particles, the combustible particles are reduced by the reaction of the catalyst. There have also been proposals that lower the ignition temperature.

By the way, when using a particulate filter suitable for collecting combustible particles such as carbon particles, if the above auxiliary fuel or catalyst liquid is injected when the exhaust gas temperature is high such as during acceleration or high load, the inside of the filter may be damaged. The combustible particles will rapidly burn, creating an abnormally high temperature state, and the resulting thermal stress will cause cracks in the above-mentioned ceramic particulate filter, making it unusable as a filter. When particles are being collected, even if auxiliary fuel or catalyst liquid is supplied when the exhaust gas temperature is relatively low, the heat of combustion will result in a high temperature state, causing the same problem as described above.

Conversely, if the supply of auxiliary fuel or catalyst liquid is insufficient, there is also the problem that combustible particles cannot be sufficiently burned and removed.

(Object of the Invention) The present invention was made to solve the above-mentioned problems, and can prevent damage to the particulate filter due to abnormal combustion and failure to regenerate the particulate filter due to insufficient combustion. The purpose of the present invention is to provide an exhaust gas purification device for such an engine.

(Structure of the Invention) The engine exhaust gas purification device according to the present invention includes:
In an exhaust gas purification device for an engine equipped with a particulate filter that collects combustible particles in the exhaust system, an injection means for injecting a liquid that promotes combustion of the combustible particles upstream of the particulate filter. a back pressure sensor and a first exhaust gas temperature sensor that respectively detect the exhaust gas pressure and temperature upstream of the particulate filter, and a second exhaust gas temperature sensor that detects the exhaust gas temperature downstream of the particulate filter. a gas temperature sensor, a bypass passage that bypasses the particulate filter, a gas flow rate adjustment means for adjusting the flow rate of exhaust gas flowing through the bypass passage, including a throttle valve interposed in the bypass passage, and the back pressure. A control means receives outputs from the sensor and the first and second exhaust gas temperature sensors, and controls the injection means and the gas flow rate adjustment means based on these outputs, the control means controlling the injection means and the gas flow rate adjusting means, the control means receiving outputs from the sensor and the first and second exhaust gas temperature sensors, The injection means executes a predetermined injection of liquid on the condition that the back pressure is higher than a predetermined back pressure preset for each operating region and the exhaust gas temperature on the upstream side is less than a first predetermined temperature, and the exhaust gas on the downstream side is Control means for controlling the gas flow rate adjusting means to stop liquid injection when the gas temperature becomes higher than a second predetermined temperature, and to keep the upstream exhaust gas pressure below a predetermined value during injection. It is equipped with the following.

(Effect of the invention) In the above engine exhaust gas purification device,
Predetermined injection of liquid to the injection means on condition that the exhaust gas pressure on the upstream side is higher than a predetermined back pressure set in advance for each operating region of the engine, and the exhaust gas temperature on the upstream side is less than a first predetermined temperature. By performing this, it is possible to promote the combustion of the combustible particles accumulated in the particulate filter while preventing abnormal combustion of the combustible particles and thereby preventing damage to the filter (occurrence of cracks).

Moreover, since the liquid injection is stopped when the exhaust gas temperature on the downstream side becomes higher than the second predetermined temperature, damage to the filter due to overheating due to combustion of combustible particles can be reliably prevented.

Furthermore, by providing a bypass passage and a gas flow rate adjustment means, and controlling the gas flow rate adjustment means so that the upstream exhaust gas pressure is below a predetermined value during injection, an abnormally large amount of gas is prevented from entering the filter. This prevents abnormal combustion in the center of the filter due to exhaust gas flowing in, and provides a stable combustion state with a stable exhaust gas flow rate.

In this way, in the engine exhaust gas purification device of the present invention, triple measures are taken to prevent abnormal combustion within the filter.

(Example) Hereinafter, an example in which the engine exhaust gas purification device according to the present invention is applied to a diesel engine will be described with reference to the drawings.

The overall configuration of the above exhaust gas purification device will be explained with reference to FIG. In order to adjust the exhaust gas flow rate, a bypass passage 4 is provided which branches from the exhaust passage 2 on the upstream side of the filter 3 and merges with the exhaust passage 2 on the downstream side of the filter 3, and a throttle is provided at the starting end of the bypass passage 4. A valve 5 is provided.

The filter 3 is a particulate filter made of porous ceramic having minute pores, and has a large number of passages partitioned by a large number of partition walls. It is designed to capture combustible particles such as carbon particles.

In order to burn the combustible particles trapped in the filter 3 and regenerate the filter 3, an injection device 6 is provided for injecting a catalyst aqueous hydrocarbon emulsion into the exhaust passage 2 upstream of the filter 3.

The injection device 6 includes an injector 7 installed in the exhaust passage 2 on the upstream side of the filter 3 toward the filter 3, a tank 10 for storing the catalyst aqueous hydrocarbon emulsion, and the injector 7 connected to the tank 10. The connecting pipe 8 and the communicating pipe 8
It consists of a pump 9 interposed in the middle of the pump.

The composition of the above catalyst aqueous hydrocarbon emulsion is 0.05 to 0.5% by weight of one or more water-soluble compounds of platinum group metals (Pt, Pd, Rh, Ir), or 1 to 10% by weight of one or more of one or more platinum group metals (Pt, Pd, Rh, Ir). A catalyst component consisting of water-soluble salts of base metals (V, Cu, Cr, Fe, Ni, Mo, Ca, Ba) and 10 to 50% by weight of kerosene,
A mixture of hydrocarbons such as light oil, heavy oil, alcohol, or ketones (oxygenated hydrocarbons), 1 to 10% by weight of a surfactant to dissolve the hydrocarbons in water, and the remainder water. This is what I did. Hereinafter, the aqueous catalyst solution hydrocarbon emulsion will be simply referred to as a catalyst solution or the like.

However, the catalyst solution and the hydrocarbon may be stored in separate tanks, and both may be mixed and supplied to the injector 7, or only one may be supplied to the injector 7 as necessary. Of course.

The adjustment mechanism for adjusting the throttle valve 5 of the bypass passage 4 includes a vacuum pump 11, a duty solenoid valve 12 connected to the vacuum pump 11, and a duty solenoid valve 12 connected to the duty solenoid valve 12 and connected to the throttle valve 5. Diaphragm actuator 1
It consists of 3. The throttle valve 5, actuator 13, solenoid valve 12, and vacuum pump 11 correspond to gas flow rate adjusting means.

controlling the injection device 6 according to the combustion state of the combustible particles captured in the filter 3;
A control unit 14 is also provided to adjust and control the opening degree of the throttle valve 5, and detection signals are inputted to the control unit 14 from various sensors described below.

The sensors include a back pressure sensor 15 and a first exhaust gas temperature sensor 1 that detect the back pressure and exhaust gas temperature in the exhaust passage 2 on the upstream side of the filter 3, respectively.
6, and a second exhaust gas temperature sensor 17 that detects the exhaust gas temperature in the exhaust passage 2 on the downstream side of the filter 3.
, a rotation speed sensor 19 that detects the rotation speed of the pump shaft of the fuel injection pump 18 of the engine 1, and a load sensor 20 that detects the position of the control sleeve of the fuel injection pump 18. It is output to unit 14.

A control signal is output from the control unit 14 to the injector 7 to open and close a solenoid valve (see FIG.
A control signal for turning on and off the pump 9 is output from the control unit 14, and a control signal for controlling the throttle valve 5 by changing its duty ratio is output from the control unit 14 to the duty solenoid valve 12.

Next, the injector 7 is configured as shown in FIG. 2, for example.

That is, in the center of the injector body 21, an injection port 22, a guide hole 23, a spring mounting hole 24, a solenoid mounting hole 25, and a supply hole 26 are formed in order from the tip side in a communicating manner. An integral rod 27 is inserted into each of the holes 22 to 25, and a needle valve body portion 27 at the tip of the rod 27 is inserted.
a comes into contact with the valve seat at the far end of the injection port 22 from the inside to form a valve, and the guide portion 27b of the rod 27 is fitted in the guide hole 23 so as to be slidable in the axial direction.
A collar-shaped spring receiving part 27c of 7 is arranged in the spring mounting hole 24, and the rod 27 is moved in the distal direction by a compression spring 28 that is sheathed on the rod 27 between the spring receiving part 27c and the base end wall of the spring mounting hole 24. In other words, the valve is biased in the direction of closing, and the solenoid 29 is mounted on the outside of the rod 27 within the solenoid mounting hole 25, and between the flange 27d at the base end of the rod 27 and the base wall of the solenoid mounting hole 25. An auxiliary compression spring 30 is interposed.

Although not shown in FIG. 2, the communication pipe 8 is connected to the base end of the main body 21, and the catalyst aqueous solution, etc., which is pressure-fed from the communication pipe 8 into the supply hole 26, is passed through the hole on the outer periphery of the rod 27. The liquid then reaches the valve, and when the valve is opened, it is sprayed in the form of mist from the injection port 22 as shown in the figure. However, the above valve is designed to open against the spring force when the solenoid 29 is energized.

The control unit 14 receives signals from each sensor 15, 16, 17, 19, 20, for example.
AD converter that performs AD conversion, input/output interface, read-only memory (ROM), random access memory (RAM), central processing unit (CPU), and output signals to pump 9 and solenoids 12 and 29. It is composed of a drive circuit for conversion and amplification, etc., and a program and various constants for a control routine to be described later are previously input and stored in the read-only memory (ROM).

Next, the control routine performed by the control unit 14 will be explained based on the flowchart of the main routine shown in FIG. 3a and the flowchart of the interrupt processing routine shown in FIG. 3b. S30 to S35 indicate each step.

In S1, necessary data is initialized, in S2, the detection signal from the rotation speed sensor 19 is read to calculate the engine rotation speed, and in S3, the engine rotation speed is calculated by reading the detection signal from the rotation speed sensor 20.
The engine load is determined by reading the detection signal from the back pressure sensor 15, and the back pressure in the exhaust passage 2 is determined by reading the detection signal from the back pressure sensor 15 at S4.

In S5, it is determined whether the back pressure has decreased to a predetermined value at least once after injecting the catalyst solution or the like. That is, if the carbon particles accumulated in the filter 3 are combusted by the combustion promoting action of the catalyst solution etc. after the previous injection, the back pressure will drop below the predetermined value. This is to proceed to the next step on the condition that the lever, that is, the previously injected catalyst solution, etc. has contributed to combustion.

If the result of the determination in S5 is YES, the process moves to S6, and if the result is NO, the process moves to S4.

In S6, it is determined whether the current back pressure is higher than a predetermined back pressure for each operating region.

The more carbon particles etc. are accumulated in the filter 3, the greater the ventilation resistance of the filter 3 becomes, and the back pressure on the upstream side of the filter 3 increases. Therefore, the degree of accumulation of carbon particles is determined based on the value of the back pressure. I have to. However, since the magnitude of back pressure varies depending on the engine operating condition, predetermined allowable back pressure values corresponding to each operating range determined by engine speed and engine load are prepared in advance as a map.
It is input and stored in the only memory (ROM), and in S6, the allowable back pressure value in the operating range corresponding to the current operating state is compared with the current back pressure value,
When the current back pressure is higher than the allowable back pressure value, it is necessary to inject catalyst solution, etc., so the process moves to S7, and when it is not high, the process moves to S2.

In S7, the number of current injections since the start of use of the engine is counted, and in S8, the amount of injection of catalyst solution, etc. is determined based on the number of injections.

The catalytic component contained in the catalytic solution promotes combustion through a catalytic reaction during the combustion of carbon particles, etc. During repeated injections, a portion of the catalytic component is emitted into the atmosphere along with the exhaust gas. Considering that the remainder will gradually accumulate in the filter 3,
As shown in the graph of FIG. 4, the amount of the catalyst solution etc. to be injected is determined depending on the number of times of injection.

In other words, since the amount of accumulated catalyst components is thought to increase approximately in proportion to the number of injections as shown by curve a, the amount of catalyst solution etc. injected per time also increases in proportion to the number of injections as shown by line b. is set to decrease.

However, until the number of injections reaches a predetermined number, the accumulated amount of catalyst components is not so large, so the catalyst components are injected in fixed amounts.

By the way, the newly injected catalyst component is injected in a highly active state in which it is ionized into an aqueous solution under conditions of high exhaust gas temperature due to an increase in back pressure.
Since it is supplied to the surface layer of carbon particles etc. accumulated in the upstream part of the filter 3 and easily comes into contact with oxygen in the exhaust gas, it acts extremely actively as a catalyst to promote combustion, and by the combustion on the upstream side. Combustion on the downstream side will also be significantly promoted.

On the other hand, the catalyst components accumulated in the filter 3 come into contact with carbon particles, etc. in a dry state under conditions of relatively low exhaust gas temperature, and are buried in the accumulated layer of carbon particles, etc., and are contained in the exhaust gas. Since it is difficult to come into contact with oxygen, it does not act as actively as a catalyst for promoting combustion.

Therefore, when setting the amount of catalyst components to be newly injected and supplied according to the amount of catalyst components accumulated in the filter 3, it is necessary to set the amount of catalyst components that have been accumulated and the effectiveness thereof. There is.

In S9, the detection signal from the first exhaust gas temperature sensor 16 is read to determine the exhaust gas temperature _T1 on the upstream side of the filter 3, and in S10, the exhaust gas temperature _T1 is set to a predetermined temperature T _A. It is determined whether or not it is lower than that, and if it is low, the process moves to S11, and if it is not low, the process returns to S9.

If a catalyst solution is injected when the exhaust gas temperature is high, such as during acceleration or under high load, the carbon particles accumulated in the filter 3 will rapidly burn, resulting in an abnormally high temperature, and the thermal stress will damage the ceramic filter. 3 will cause a crack and damage the filter 3. To prevent this, the exhaust gas temperature should be kept at a specified temperature.
This is because the injection is performed on the condition that it is lower than T _A.

In S11, the pump 9 of the injection device 6 is driven for a predetermined time corresponding to the injection amount determined in S8, so that the pump 9 starts to be driven.At the same time, in S12, the solenoid 29 of the injector 7 is activated.
By energizing the injector 7, the valve of the injector 7 is opened and injection is started, and in S13, the injection flag F is set to F=1.

In S14, a timer is set, and in S15, it is determined whether or not a relatively short predetermined time set in the timer has elapsed.After the predetermined time has elapsed, the process moves to S16, and in S16, the timer is reset.

In S17, the detection signal from the second exhaust gas temperature sensor 17 is read to determine the exhaust gas temperature _T2 on the downstream side of the filter 3, and in S18, the exhaust gas temperature _T2 is determined from a preset predetermined temperature _TB. It is determined whether the temperature is high or not, and when the temperature is high, the combustion of carbon particles, etc. is progressing sufficiently actively, so there is no need to continue injecting the catalyst solution, etc., and the process moves to S21, and the pump 8 is stopped, and when it is not high, it continues. It is determined that injection is necessary, and the process moves to S19.

In S19, it is determined whether or not a predetermined pump driving time corresponding to the injection amount determined in S8 has elapsed, and when it has elapsed, the process moves to S20, the valve of the injector 7 is closed and injection is stopped, and the predetermined time has elapsed. If not, the process returns to S17.

When the injector 7 is closed in S20, S2
1, the drive of the pump 9 is stopped, and in S22, the injection flag F is set to F=0.

Next, the flowchart of FIG. 3b shows an interrupt processing routine for controlling the throttle valve 5 of the bypass passage 4, and the interrupt processing is started when the determination in S10 of the main routine is YES, and the interrupt processing is started in S22. Return after completion.

After starting the interrupt process, in S30, the back pressure is determined by reading the detection signal from the back pressure sensor 15 of the exhaust passage 2, and in S31, it is determined whether or not the back pressure is lower than a predetermined value set in advance. When it is low, a signal for driving the throttle valve 5 in the closing direction is sent to the duty solenoid valve 12 in S32.
If it is not low, a signal for driving the throttle valve 5 in the opening direction is output to the duty solenoid valve 12 in S33.

From S32 and S33, the process moves to S34, and then S3
In step 4, it is determined whether or not the injection flag F is F=1, that is, whether or not the injection is in progress. By operating 5, the bypass passage 4 is closed. In this way, the throttle valve 5 of the bypass passage 4 is controlled as described above only during the injection of the catalyst solution or the like.

The current control is performed through S1 to S22 and S30 to S35, and the next control is performed from S22 to S1.

As explained above, by injecting the catalyst solution etc. only when the exhaust gas temperature T ₁ on the upstream side of the filter 3 is lower than the predetermined temperature T _A , the filter 3
In addition, during the injection of catalyst solution, etc., when the exhaust gas temperature _T2 on the downstream side of the filter 3 becomes higher than the predetermined temperature _TB , the filter 3 is prevented from abnormally high temperature by stopping the injection. The filter 3 is doubly protected to prevent it from becoming hot.

In addition, by controlling the interrupt handling routine,
During the injection of catalyst solution, etc., the throttle valve 5 of the bypass passage 4
By controlling this, it is possible to prevent an abnormally large amount of exhaust gas from flowing into the filter 3, causing the catalyst solution, etc. to be biased toward the center of the filter 3, and causing abnormal combustion in the center.
A stable combustion state is obtained under a stable flow rate of exhaust gas.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, in which Fig. 1 is an overall configuration diagram of an exhaust gas purification device for a diesel engine, Fig. 2 is a vertical sectional view of an injector, and Fig. 3 a and b are each a control unit. FIG. 4 is a flowchart of the main routine of control and a flowchart of the interrupt processing routine. 1... Diesel engine, 2... Exhaust passage,
3...Party filter, 7...Injector, 8...Communication pipe, 9...Pump, 10...
Tank, 14... Control unit, 15...
...back pressure sensor, 16...first exhaust gas temperature sensor, 17...second exhaust gas temperature sensor.

Claims (1)

[Scope of Claims] 1. In an exhaust gas purification device for an engine equipped with a particulate filter that collects combustible particles in the exhaust system, a particulate filter is provided upstream of the particulate filter to promote combustion of the combustible particles. a back pressure sensor and a first exhaust gas temperature sensor that detect exhaust gas pressure and temperature upstream of the particulate filter, respectively; and exhaust gas downstream of the particulate filter. A second exhaust gas temperature sensor for detecting temperature, a bypass passage for bypassing the particulate filter, and a gas flow rate for adjusting the flow rate of exhaust gas flowing through the bypass passage, including a throttle valve interposed in the bypass passage. a control means that receives outputs from the back pressure sensor and the first and second exhaust gas temperature sensors and controls the injection means and the gas flow rate adjustment means based on these outputs; A predetermined injection of liquid is made to the injection means on the condition that the exhaust gas pressure on the side is higher than a predetermined back pressure preset for each operating region of the engine, and the exhaust gas temperature on the upstream side is less than a first predetermined temperature. The liquid injection is stopped when the exhaust gas temperature on the downstream side becomes higher than the second predetermined temperature, and the gas flow rate is adjusted so that the exhaust gas pressure on the upstream side is below the predetermined value while the injection is being executed. An exhaust gas purification device for an engine, comprising: a control means for controlling an adjustment means; and a control means for controlling an adjustment means.