JPS636409Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an exhaust gas treatment device for a diesel engine, and more specifically, it uses a physical method to remove carbon particles and similar particulate matter (hereinafter referred to as particulates or exhaust particulates) contained in exhaust gas. The present invention relates to an exhaust particulate purification device (diesel particulate trap) suitable for collecting exhaust particulates on a suitable collecting material, periodically incinerating the collected exhaust particulates, and regenerating the collecting material.

Most of these types of exhaust particulates are flammable, such as carbon particles, and conventional methods have been used to collect these flammable particulates, incinerate the collected particulates, and regenerate the collection material. Since then, heaters have generally been used. That is, an electric heater is attached to the front surface of the collection material to burn the exhaust particulates adhering to the surface of the collection material, and use this as a heat source to cause the downstream particulates to self-combust.

In such an exhaust particulate purification device, the quality of ignition by the heater is an important issue. It has also been found that ignitability is influenced by the flow rate of exhaust gas. That is, if the flow rate (flow rate) of exhaust gas passing through the heater is high when igniting by the heater, it is difficult to ignite. This is because diesel particulate combustion involves first heating and igniting the exhaust particulates collected by the collecting material near the heater, and then the combustion propagates to the exhaust particulates in the collecting material downstream. However, when exhaust gas flows at a high flow rate to the heater during ignition, the heating of the collected particulates near the heater is suppressed by the exhaust gas flow, and as a result, they are not heated to the temperature required for combustion. For this reason, it is preferable to prevent exhaust gas from flowing into the heater during ignition by the heater. In other words, the flow velocity of exhaust gas is reduced to zero. Therefore, a bypass pipe is provided in the exhaust pipe to bypass the particulate trap, and a normally closed on-off control valve that opens only when the heater is ignited is provided in the bypass pipe to allow the exhaust gas to pass through the particulate trap when the heater is ignited. A device has been proposed that allows the water to flow through a bypass pipe instead of water.

Opening/closing control of the above control valve is generally performed by a negative pressure operated diaphragm device, and this diaphragm device itself is controlled by a negative pressure switching valve (VSV) which is switched and controlled by a control unit (ECU) for controlling the ignition timing of the heater. be activated.

However, conventionally, when the negative pressure switching valve is switched, the switching pressure directly acts on the diaphragm device, and therefore the opening/closing operation of the control valve is controlled.
It started happening rapidly at the same time as VSV was activated. This is particularly a serious problem when the control valve is closed again after the heater has completed ignition. i.e. heater heating (usually for 30-90 seconds)
As soon as the exhaust particulates near the heater are ignited, the power supply to the heater is stopped and the subsequent combustion is carried out by propagation. When the valve is closed again at the same time as the heater is energized, if the valve closes suddenly, the exhaust gas that had previously been flowing into the bypass pipe will flow into the particulate trap trap. The combustion particles were cooled by the flow, and the propagation of combustion was interrupted, causing them to disappear.

The purpose of the present invention is to gradually close the control valve after ignition of exhaust particulates in order to eliminate the inconvenience of interruption of combustion propagation due to the sudden inflow of exhaust gas. .

The present invention will now be described in detail with reference to the accompanying drawings, in which:
1 shows a trap container mounted in the exhaust pipe 4 of the engine.

A collection material (trap material) is provided inside the trap container 10. The trap material does not impose excessive restrictions on the exhaust gas flow, allows the exhaust gas to flow through it, and is capable of trapping a significant amount of exhaust particulates contained in the exhaust gas. There is. The trap material must be made of a suitable material that can withstand the elevated temperatures reached during periodic combustion and ashing of the trapped exhaust particles during engine operation. is made into a suitable shape. Examples of materials suitable for such purposes include three-dimensional network foam ceramics, monolithic ceramics, bulk screen elements such as metal wire mesh or stainless steel.

In order to burn and ash the exhaust particulates collected by the trap material, it is usually necessary to raise the exhaust temperature to a level of approximately 560°C. Therefore,
The material of which the trap is constructed must be sufficiently resistant to this temperature.

An electric heater 16 is provided at the upstream end of the trap material 12 for igniting and burning exhaust particulates collected on the trap material.

The heater 16 may be, for example, a heater wire bent in a zigzag pattern so as to be uniformly positioned throughout the circular or rectangular cross-sectional entrance of the trap container, and its positive terminal is connected to the battery 22 via the relay 21, and the negative terminal is connected to the battery 22 via the relay 21. The side terminal is connected to the container 10 (ground voltage). Alternatively, it is also possible to arrange a large number of heater wires and heat them in sequence. The number, size, and arrangement of the heater wires are selected so as not to impede exhaust gas flow and thus minimize exhaust gas backpressure build-up.

The timing of starting energization and the duration of energization to the heater 16 are controlled by an ECU (control unit) 15 as is well known. Parameter signals S such as engine speed, engine load, engine water temperature, pre-trap exhaust pressure (indicated by S ₁ ), and after-trap exhaust pressure (indicated by S ₂ ) are input to the ECU 15, and the trap is activated according to these signals. The regeneration timing is determined, but the control method is not directly related to the present invention and will not be described in detail. Further, the regeneration time is determined mainly based on the back pressure of the exhaust gas. In other words, the exhaust gas discharged from the diesel engine flows as shown by the arrow.
The particulates contained therein are collected by the trap material 12, and as the particulates accumulate, the back pressure of the exhaust gas upstream of the trap container 10 increases, and this back pressure signal _S1 becomes an indicator of particulate accumulation. . still,
The ECU 15 controls the trap so that it can be regenerated when necessary in all operating ranges.

When the heater 16 is energized and heated, it burns exhaust particulates adhering to the vicinity thereof, and the combustion flame is propagated downstream.

As previously mentioned, a bypass pipe 18 is provided to prevent exhaust gas from flowing into the trap during heating by the heater. The bypass pipe 18 connects the exhaust pipes 4 upstream and downstream of the trap 10, and a normally closed on-off control valve 8 is disposed inside the bypass pipe 18. The control valve 8 is normally in the closed position so that exhaust gas flows into the trap 10 so that exhaust particulates flow into the trap material 1.
Collected by 2. The control valve 8 is connected to a diaphragm device 7 as its actuator, and is opened and closed according to the movement of the diaphragm. The negative pressure working chamber of the diaphragm device 7 is the negative pressure pipe 2
It is connected to a negative pressure switching valve (VSV) 6 via.
The VSV 6 may be a solenoid valve that selectively communicates the negative pressure working chamber of the diaphragm device 7 with the atmosphere or a negative pressure region in response to an ON or OFF signal from the ECU 15. As the negative pressure area, a vacuum pump or a negative pressure area of an intake pipe can be used. the result
When VSV6 is turned on, negative pressure is applied to the diaphragm chamber of the diaphragm device and the control valve 8 is opened.

According to the present invention, in the configuration as described above,
In the negative pressure pipe 2 that communicates the VSV 6 and the negative pressure working chamber of the diaphragm device 7, there is a rate or speed at which the atmosphere is transmitted to the negative pressure working chamber of the diaphragm device 7 when the VSV 6 is turned off and communicated with the atmosphere side. Negative pressure damping means are provided for damping. As this negative pressure damping means, for example, a negative pressure delay valve 5 as shown can be used. The negative pressure delay valve 5 delays only the transmission of atmospheric air from the VSV 6 side to the negative pressure diaphragm device 7 side. Thus, according to the present invention, the control valve 8, which is opened when the heater is energized, is opened at the same time as the energization to the heater is stopped after the heater has completed ignition.
When the VSV 6 is switched to the atmospheric side and the valve is closed again, the negative pressure delay valve 5 gradually closes the valve.

FIG. 2 is a flow diagram of the operation of the device of the present invention.

When the trap regeneration period is determined, ECU15
The heater 16 and VSV 6 are turned on at the same time. The heater 16 is activated for a predetermined time t ₁ (generally t ₁ >
After heating for 30 to 90 seconds, the power is cut off. When the electricity supply to the heater is cut off, the collected particulate matter near the heater is already ignited and burned, and the collected particulate matter downstream from it is already ignited and burned by the propagation of the flame. On the other hand, the VSV 6 is turned on at the same time as the heater is energized, and the control valve 8 is temporarily opened to prevent exhaust gas from flowing to the trap side. By locating the bypass pipe 18 on an extension of the exhaust pipe and bending the main pipe provided with the trap 10 from the exhaust pipe as shown in the figure, most of the exhaust gas flows into the bypass pipe 18 when the control valve 8 is opened. It can be made to flow. After turning on VSV6 for a predetermined time _t2 and opening control valve 8,
The VSV 6 is turned off and the control valve 8 is opened, but at this time, if the control valve 8 is opened at the same time as the VSV 6 is switched off, the problem described at the beginning will occur. However, according to the present invention, even when the VSV 6 is turned off, the atmospheric air is gradually transmitted to the negative pressure diaphragm device 7, so the control valve 8 closes little by little, and the combustion of the collected particulate is interrupted. This solves the problem of

Incidentally, the time t ₂ for operating the VSV 6 is determined as follows. That is, if t ₂ is too small, the exhaust gas will flow into the trap before the initial ignition by the heater is completed, so the provision of the bypass pipe 18 and the control valve 8 becomes meaningless. On the other hand, if _t2 is too large, the flame will not propagate even after ignition by the heater, and the trap will not be regenerated. is necessary).
From the above point of view, it is appropriate that _t2 is, for example, about 3 to 5 seconds.

As described above, according to the present invention, by causing exhaust gas to flow through the bypass pipe at the start of energization of the heater, it is possible not only to prevent the heater from being cooled by the exhaust gas, but also to effectively use the amount of heat generated by the heater to ignite the particulate. After the particulate ignition, combustion propagation is maintained by gradually increasing the flow of exhaust gas to the trap, thereby ensuring regenerative combustion even when the amount of particulate adhering is small.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the device according to the present invention, and FIG. 2 is a flow diagram showing the trap regeneration operation. 4... Exhaust pipe, 5... Negative pressure delay valve, 6... Negative pressure switching valve, 7... Diaphragm device, 8... Control valve, 10... Trap container, 16... Heater, 1
8...Bypass pipe.

Claims (1)

[Scope of utility model registration request] A diesel particulate trap having an exhaust particulate collecting material and an electric heater for igniting and burning the exhaust particulates collected by the collecting material is disposed in the exhaust pipe line of the diesel engine, and the diesel particulate trap is provided in the exhaust pipe. A diesel engine exhaust particulate purification system comprising a bypass pipe that bypasses the diesel particulate trap, and an opening/closing control valve that is opened by a negative pressure actuator that operates simultaneously with the operation of the electric heater. An exhaust particulate purification device for a diesel engine, characterized in that the negative pressure actuator is provided with gradual negative pressure damping means for gradually opening a control valve when the actuator stops operating.