JPH052813B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a particulate removal device for a diesel engine, and more particularly to a diesel particulate removal device that prevents the particulate collecting material of a trap from being eroded.

[Prior art] Exhaust gas discharged from a diesel engine is passed through a trap provided in the exhaust passage, and particulates such as soot (hereinafter referred to as particulate) contained in the exhaust gas are removed from the trap made of porous ceramics, etc. It is collected by a collection material. Particulate matter accumulates in the trap over time,
Since the pressure loss increases and the power loss of the engine increases, it is necessary to burn off the particulate and regenerate the trap once the particulate has accumulated to some extent.

This regeneration is performed by igniting the particulate matter adhering to the collection material using an electric heater or the like and burning the particulate matter. However, the combustion of the particulate during regeneration increases the temperature inside the trap, and if this temperature becomes abnormally high, the collection material will be eroded and damaged, so measures must be taken to prevent this from occurring. .

As a countermeasure, conventional efforts have been to reduce the oxygen concentration in the exhaust gas by using an intake throttle to slow down the combustion of the particulate and lower its combustion temperature. However, in order to optimally control the oxygen concentration in exhaust gas by throttling the intake air in all engine operating ranges, it is necessary to sufficiently increase the responsiveness of the intake throttle valve and to control it precisely. This was a rather difficult control method.

[Problems to be Solved by the Invention] The present invention does not involve difficult control such as when controlling the oxygen concentration in exhaust gas by throttling an intake throttle valve, which is difficult to control sensitively and precisely. ,
Another object of the present invention is to provide a diesel particulate removal device that can easily lower the combustion temperature inside the trap during trap regeneration by slightly improving the existing device, thereby preventing the collection material from being eroded. do.

[Means for Solving the Problems] A diesel particulate removal device according to the present invention for achieving the above object includes a trap installed in the exhaust passage of a diesel engine, an electric heater provided in the trap, and a trap installed in the exhaust passage of the diesel engine. The EGR pipe is branched from a more downstream part, and a single EGR valve is installed in the EGR pipe, and the EGR valve is designed to recirculate a larger amount of EGR gas than during normal operation during trap regeneration. It consists of a computer connected to the EGR valve that controls the EGR valve in order to reduce the increase in the EGR rate compared to normal operation as the torque increases.

[Function] The diesel particulate removal device of the present invention does not use conventional combustion temperature control by throttling the intake and exhaust gases, but increases the amount of EGR gas during trap regeneration to reduce the oxygen concentration in the exhaust gas. This method uses a control method that slows down the combustion of particulate and lowers the combustion temperature in the trap.
EGR devices themselves have been in existence for some time, but there are no improved EGR devices that have been used as a means to prevent erosion of the collection material of particulate removal devices.

In the diesel particulate removal device of the present invention, since EGR gas is taken from downstream of the trap,
Oxygen is consumed by combustion in the trap, and the exhaust gas with less oxygen is returned to the intake system, which reduces the oxygen concentration in the exhaust gas that flows into the trap again. Slowing is effectively achieved.

In addition, since the increase rate of the EGR rate is made smaller as the shaft torque increases, an almost constant excess air ratio in the exhaust gas is obtained in the engine operating range, the combustion rate of the particulate is almost constant, and excessive temperature rise is prevented. This ensures prevention of trap erosion.

[Embodiments] Preferred embodiments of the diesel particulate removal device of the present invention will be described below with reference to the drawings.

FIG. 1 shows a system of a diesel particulate removal device according to an embodiment of the present invention. In the diagram, 1 is the diesel engine body, 2 is the intake manifold, and 3 is the diesel engine body.
is an exhaust manifold, and 4 is an exhaust passage consisting of an exhaust pipe. A trap 5 is provided in the middle of the exhaust passage 4, and a trap 5 is provided inside thereof for collecting particulate matter such as soot in the exhaust gas. The collection material 6 is provided with an electric heater 7 on the upstream side of the exhaust gas flow, and the particulate is ignited by energizing the electric heater 7 during trap regeneration. The electric heater 7 is connected to a battery 8, and a relay 9 is provided on the electric circuit and is turned on during playback. Trap 5 has body ground 10.

In the exhaust passage 4, there is an EGR on the downstream side of the trap 5.
A conduit 11 is branched off and connected to the intake system. An EGR valve 12 is provided in the middle of the EGR conduit 11 to control the amount of EGR gas. The EGR conduit 11 and the EGR valve 12 are made large so that a larger amount of EGR gas than the EGR%α required in a normal EGR system, for example (α+5)%, can be returned to the intake system. There is. The EGR valve is driven by a vacuum diaphragm 13, and the negative pressure from the vacuum pump to the vacuum diaphragm 13 is controlled by a vacuum controller 14.

The vacuum controller 14 is, for example, a second
As shown in the figure, it consists of two vacuum switching valves (VSV) 14a and 14b. Here, one VSV14a is connected to the vacuum pump,
The other VSV14b is connected to the atmosphere, and VSV14
By switching a and 14b, negative pressure or atmospheric pressure is introduced to the vacuum diaphragm 13.

The EGR valve 12, more specifically the vacuum controller 14, is electrically connected to the computer 15, and operates according to instructions from the computer 15.
EGR valve 12 is activated. An engine water temperature sensor 16, an engine rotation speed sensor 17, and an engine load sensor 18 are connected to the computer 15, and signals of engine water temperature, engine rotation speed, and engine load are input from each of them. Of these, the engine water temperature is 8% when the engine is cold.
Since the battery is not sufficiently charged, it is measured to determine whether it is time to perform regeneration. The engine speed is measured in order to integrate the engine speed and determine whether it is time for regeneration. In addition, the excess air ratio usually changes depending on the engine load, so in order to control the excess air ratio, it is necessary to know the state of the engine load from moment to moment. It is something that will be done.

The computer 15 has a control function shown in the flow diagram of FIG. That is, in step 101, an interrupt is made every engine revolution, and in step 102, the engine revolution number n is integrated. And step 103
It is determined whether the engine rotation speed n accumulated in step 1 is equal to or greater than a predetermined reproduction rotation speed N, for example, 200,000 rotations, and if the following is the case, proceed to step 112 to end the calculation for that time, and repeat the steps above. If so, it is assumed that the playback time has come and the process moves to step 104. Step 104
Then, the timer is turned on, and then in step 105 it is determined whether or not the count time t of the timer is less than or equal to a predetermined time t1.If it is less than or equal to the predetermined value _t1 , the process proceeds to step 106, where the electric heater 7 is turned on and energized, and when t becomes _t1. When the temperature exceeds 100, the power to the electric heater 7 is turned off. The electric heater 7 is energized by turning on the relay 9. By the operations in steps 105-107, the electric heater 7 is energized for only _t1 , after which the particulate is combusted by self-combustion. Then step
Proceeding to step 108, it is determined whether the timer count time t is less than or equal to _t2 , and if it is less than that, a signal is sent to the vacuum controller 14 to increase the opening degree of the EGR valve 12, and the EGR% characteristic during regeneration is changed. let This EGR% during regeneration is read from the map shown in Figure 4, and is determined during normal operation (not during regeneration).
It is set to be larger than the EGR% of the engine, and the increase rate of the EGR rate relative to normal operation becomes smaller as the shaft torque becomes larger. Trap 5 is played back in this state, but once the playback time _t2 has passed, the playback is assumed to have ended and step 5 is started.
Proceed from 108 to 110, Vacuum Controller 14
A signal is sent to the EGR valve 12 to return the opening degree of the EGR valve 12 to the original small opening degree. This completes the playback routine, clears n and t in step 111, and returns to the original state.
Accumulation of engine speed will start again at the next interrupt.

In the apparatus having the above configuration and control function, removal of particulate in exhaust gas and prevention of melting damage are carried out as follows. First, exhaust gas from the diesel engine body 1 passes through the trap 5, where particulate matter is collected by a collection material 6.

As the accumulation of particulates progresses, the computer 15 determines that it is time to regenerate, and the regeneration is performed under the control of the computer 15 having the above-mentioned functions. That is, the electric heater 7 is energized to ignite the particulate, and the trap 5 is regenerated with the EGR valve 12 switched to regeneration.

Figure 4 shows EGR% during regeneration. As shown in the figure, during normal operation, not during regeneration,
The EGR gas amount is controlled so that an EGR% larger than EGR% (EGR gas amount/new gas amount x 100) is obtained. If the normal EGR% is α%, it is set to about EGR% (α+5)% or more during regeneration according to the present invention. Generally, the EGR% is about 30% (curve A in FIG. 4), so during regeneration in the present invention, the EGR% is controlled to 35% or more, for example, about 50% (curve B in FIG. 4). That is, the fourth
Controlled by EGR% during playback in the shaded area in the diagram. The reason for setting +5% for α is that a sufficient particulate combustion control effect cannot be obtained unless the value is about 5% larger than α.
The reason why the upper limit is set at 70% is that if it is higher than that, it will not have a positive effect on other things such as output.

By controlling the EGR% as shown in FIG. 4, the excess air ratio in the exhaust gas becomes as shown in FIG. 5. That is, conventionally, the excess air ratio changes depending on the shaft torque of the diesel engine (curve C in Fig. 5), but in the case of the present invention, this change is suppressed, and desirably, the excess air ratio λ is almost constant. For example, it is controlled to λ=1.3 (curve D in FIG. 5). Since the oxygen concentration in the exhaust gas increases or decreases depending on the excess air ratio, in the case of the present invention, even if the shaft torque becomes small, the oxygen concentration in the exhaust gas does not change much and can be kept low.

Therefore, the combustion of the particulate collected by the collection material 6 in the trap 5 is performed in a state where oxygen is not excessive, and the combustion is slow. Therefore, the combustion temperature does not become that high, and the collection material 6
does not exceed the melting temperature, for example 1000° C., and the collection material 6 does not melt.

[Effects of the Invention] According to the diesel particulate removal device of the present invention,
Obtain the following effects.

(b) EGR gas is refluxed in a larger amount than is required in a normal EGR device, and the amount of reflux is controlled by a computer, so the combustion of particulate during regeneration can be controlled, and therefore the trap By controlling the internal temperature, it is possible to prevent the collection material from melting away.

(b) Since EGR is performed from the downstream side of the trap, the exhaust gas that has become depleted due to oxygen being consumed during combustion within the trap is returned to the intake system, and the exhaust gas that flows into the trap again is reduced. Oxygen concentration can be effectively lowered. As a result, combustion in the trap becomes slower and the effect of preventing nourishment damage is increased.

(c) As the shaft torque increases, the increase rate of the EGR rate relative to normal operation is set to be smaller, so it is possible to obtain an almost constant excess air ratio in the exhaust gas in the engine operating range, and the particulate rate is reduced. The combustion rate can be kept almost constant, excessive temperature rise can be prevented, and trap melting can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a diesel particulate removal device according to an embodiment of the present invention, FIG. 2 is a schematic system diagram of the vacuum controller of the device shown in FIG. 1, and FIG. 3 is a system diagram of the computer of the device shown in FIG. FIG. 4 is a flowchart showing the control function, FIG. 4 is a shaft torque-EGR% characteristic diagram in the device shown in FIG. 1, and FIG. 5 is a shaft torque-excess air ratio characteristic diagram in the device shown in FIG. 1... Diesel engine body, 4... Exhaust passage,
5... Trap, 6... Collection material, 7... Electric heater, 9
...Relay, 11...EGR conduit, 12...EGR valve, 1
4... Vacuum controller, 15... Computer.

Claims (1)

[Claims] 1 A trap is installed in the exhaust passage of a diesel engine, an electric heater is provided in the trap, an EGR conduit is branched from a portion of the exhaust passage downstream of the trap, and a single EGR valve is provided in the EGR conduit;
During trap regeneration, the EGR valve is
The feature is that a computer is connected to control the EGR valve in order to circulate a larger amount of EGR gas than the amount of EGR gas, and to reduce the rate of increase in the EGR rate relative to normal operation as the shaft torque increases. Diesel particulate removal equipment.