JPH059612B2 - - 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 or gaseous fuel to promote the reaction by the catalyst of the catalytic filter and the combustion by the auxiliary fuel. Therefore, it is known that the collected combustible particles are burned and removed by heating the exhaust gas to a temperature higher than the ignition temperature of the combustible particles.

In the above-mentioned conventional exhaust gas purification device, in the normal operating range where the exhaust gas temperature is low, the exhaust gas temperature does not reach the ignition temperature of the combustible particles, so the combustible particles remain without burning. There is a problem in that the catalytic filter is clogged with combustible particles, and as a result, the back pressure in the exhaust system increases, making it impossible to operate the engine normally.

For this reason, a method has been proposed in which a catalyst solution is supplied upstream of the filter and the catalyst is deposited on the surface of the combustible particles, thereby lowering the ignition temperature of the combustible particles through the reaction of the catalyst. There is.

By the way, when supplying a catalyst solution as described above to promote the combustion of combustible particles, the catalyst component is not consumed directly by combustion, so the catalyst component is repeatedly injected and supplied. It will accumulate in the filter little by little, but if you ignore the amount of catalyst components accumulated above and always supply a fixed amount of catalyst solution, a large amount of catalyst components will accumulate in the filter and the filter will not be ventilated. The resistance increases and the back pressure in the exhaust passage increases, resulting in worsening fuel efficiency.
In addition, excessive catalyst components significantly accelerate the combustion of combustible particles, causing the filter to reach an abnormally high temperature, and the resulting thermal stress may cause cracks in, for example, ceramic particulate filters, making them unusable as filters. Further, problems arise, such as an increase in the consumption of an expensive catalyst solution, resulting in an increase in running costs.

(Object of the Invention) The present invention has been made to solve the above-mentioned problems, and can prevent deterioration of engine fuel efficiency, prevent damage to the particulate filter, and reduce the consumption of catalyst solution. 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 an exhaust system, an injection means for injecting a catalyst solution that promotes combustion of the combustible particles upstream of the particulate filter. and detecting means for detecting the amount of catalyst components accumulated in the particulate filter, and receiving the output of the detecting means and detecting the amount of catalyst components accumulated in the particulate filter. A control means is provided for controlling the amount of catalyst components to be injected and supplied.

As the detection means, a counting means for counting the number of times the catalyst solution is injected since the start of engine use may be used, or a detection means for detecting the electrical resistance of the filter, which decreases approximately in proportion to the amount of accumulated catalyst components, may be used. Alternatively, a detection means for detecting the pressure loss of the filter, which increases approximately in proportion to the accumulated amount of catalyst components, may be used.

(Effects of the Invention) In the engine exhaust gas purification device according to the present invention, as explained above, the catalyst component accumulated in the filter is detected by the detection means, and the filter is controlled by the control means based on the output. Since the amount of catalyst components newly injected and supplied is controlled according to the amount of catalyst components accumulated in the filter, the appropriate amount of catalyst components is always supplied by taking into consideration the amount of catalyst components accumulated in the filter. You can.

Therefore, by appropriately promoting the combustion of combustible particles within the filter with an appropriate amount of catalyst component, it is possible to control the filter so that it does not reach an abnormally high temperature, and it is possible to prevent the use of expensive catalyst components. It is possible to reduce consumption, and at the same time, it is possible to prevent engine fuel efficiency from deteriorating due to increased ventilation resistance of the filter due to accumulation of catalyst components.

(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.

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 the 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 installed in the guide hole 23 so as to be slidable in the axial direction, and the rod 27
A flange-shaped spring receiving part 27c is disposed in the spring mounting hole 24, and a compression spring 28 sheathed on the rod 27 between the spring receiving part 27c and the proximal wall of the spring mounting hole 24 prevents the rod 27 from becoming clogged in the distal direction. A solenoid 29 is mounted on the outside of the rod 27 within the solenoid mounting hole 25, and an auxiliary solenoid 29 is mounted between the flange 27d at the proximal end of the rod 27 and the proximal wall of the solenoid mounting hole 25. A 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 and the engine rotation speed is calculated, in S3 the detection signal from the load sensor 20 is read and the engine load is calculated, and in S4 The back pressure in the exhaust passage 2 is determined by reading the detection signal from the back pressure sensor 15.

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 judgment in S5 is YES, move to S6,
If NO, move 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. accumulate 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 operating condition of the engine, 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. Because 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. be.

In S9, the detection signal from the first exhaust gas temperature sensor 16 is read and the exhaust gas temperature T1 on the upstream side of the filter 3 is determined, and in S10, the above exhaust gas temperature _T1 is determined.
It is determined whether or not T ₁ is lower than a preset predetermined temperature T _A. If it is lower, the process moves to S11, and if it is not lower, 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 the drive of the pump 9 is started, and at the same time
In S12, the solenoid 29 of the injector 7 is energized to open the valve of the injector 7 to start injection, 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 a relatively short predetermined time set in the timer has elapsed, and after the predetermined time has elapsed, a timer is set.
The process moves to S16, and the timer is reset in S16.

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 on the downstream side of the filter 3 is determined.
It is determined whether T ₂ is higher than a preset predetermined temperature T _B , and if it is higher, it is determined that the combustion of carbon particles, etc. is progressing sufficiently actively, so there is no need to continue injecting catalyst solution, etc., and the process proceeds to S21. The pump 8 is then stopped, and if the temperature is not high, it is determined that there is a need to continue injection, and the process moves to S19.

In S19, it is determined whether a predetermined pump driving time corresponding to the injection amount determined in S8 has elapsed.
When it has passed, move to S20 and switch to injector 7.
valve is closed to stop the injection, and if the predetermined time has not elapsed, the process returns to S17.

When the injector 7 is closed in S20, the drive of the pump 9 is stopped in S21, and the injection flag F is set to F=0 in S22.

Next, the flowchart in 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 processing, 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's low
In S32, a signal for driving the throttle valve 5 in the closing direction is output to the duty solenoid valve 12, and if the duty solenoid valve is not low, the throttle valve 5 is driven in S33.
A signal for driving the valve in the opening direction is output to the duty solenoid valve 12.

From S32 and S33, the process moves to S34. In S34, it is determined whether the injection flag F is F=1, that is, whether or not injection is in progress. When F=1, the process returns to S30 and repeats steps S30 to S33, and F= When it is 0, the process moves to S35 and the throttle valve 5 is operated to close the bypass passage 4. 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 achieved under a stable flow rate of exhaust gas.

In the above embodiment, the injection amount is set according to the number of injections based on the premise that the amount of catalyst components accumulated in the filter 3 is approximately proportional to the number of injections. may be detected in the following manner, and the injection amount may be set based on the detected signal.

That is, since the catalyst component contains metal as mentioned above, the more the catalyst component accumulated in the filter 3, the more the conductivity of the ceramic particulate filter 3 increases and the electrical resistance thereof decreases. Therefore, by installing a pair of electrodes in the filter 3 and applying a predetermined voltage between the electrodes and detecting the current flowing between the electrodes, the electrical resistance between the electrodes is determined and the accumulated amount of the catalyst component is detected. I can do it.

Alternatively, since the ventilation resistance of the filter 3 increases as the catalyst components accumulated in the filter 3 increase, the amount of back pressure detected by the back pressure sensor 15 on the upstream side of the filter 3 indicates that the accumulation of catalyst components In this case, the back pressure value is measured when the operating state of the engine 1 is constant and the adhesion state of the carbon particles is constant after burning the carbon particles etc. by injecting the catalyst solution etc. It is necessary to compare.

[Brief explanation of drawings]

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.

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, combustion of the combustible particles is promoted upstream of the particulate filter. An injection means for injecting the catalyst solution is provided, a detection means for detecting the amount of the catalyst component accumulated in the particulate filter, and a catalyst component accumulated in the particulate filter receives the output of the detection means. 1. An exhaust gas purification device for an engine, comprising: control means for controlling the amount of a catalyst component to be newly injected and supplied according to the amount.