JPS6319532Y2 - - 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 exhaust particulates or particulates) contained in exhaust gas. The present invention relates to an exhaust particulate purification device suitable for collecting on a suitable trapping material such as a filter element, periodically incinerating the collected exhaust particulates, and regenerating the trapping material.

Most of these types of exhaust particulates are flammable, such as carbon particles, and diesel particulates collect these flammable particulates and incinerate them to regenerate the collection material. Various traps are known. An electric heater is generally used as a means for burning the collected particulate and regenerating the trap. That is, an electric heater is attached to the entire surface of the collection material, and the heater burns the exhaust particulates adhering to the surface of the collection material, and uses this as a heat source to cause the downstream particulates to self-combust.

However, if the flow velocity of the exhaust gas flowing through the trap at the time of heater ignition is too high, the particulate matter collected in the vicinity of the heater that is heated by the heater will lose heat and be cooled by the exhaust gas flow, resulting in ignition failure. Therefore, in the past, the regeneration range of the trap was extremely limited, and efficient regeneration was not possible.
For this reason, for example, as disclosed in JP-A-56-118514, while the trap is being regenerated, exhaust gas is guided from the trap to a bypass pipe, and air is supplied upstream of the trap to ignite and burn the particulate. There is a method for regenerating the trap, but this method requires an air supply means and has a problem in that the structure is complicated.

The purpose of the present invention is to solve this problem by expanding the reproducible area of the trap and by easily controlling the regeneration.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In Figure 1, 5 is the diesel engine body;
Reference numeral 9 indicates an exhaust manifold, and reference numeral 11 indicates a main exhaust pipe. A trap 13 having a trap material 12 for collecting exhaust gas particulates is installed in the main exhaust pipe 11. The trap 13 has an electric heater 16 at its upstream end. By energizing the electric heater 16, the particulate collected on the trap material 12 near the heater is first ignited, and then the flame is carried downstream by the exhaust gas flow. propagate and perform combustion regeneration of the entire trap. As is well known, the timing of energizing the heater 16 (regeneration timing) is determined by detection signals S such as engine rotation speed, engine load, engine water temperature, exhaust gas pressure, exhaust gas temperature, etc.
is controlled by a microcomputer (CPU) 21 under predetermined operating conditions.

The main exhaust pipe 11 is provided with a bypass pipe 3 that connects the upstream and downstream sides of the trap 13. When the bypass pipe 3 is provided, a part of the exhaust gas always flows through the bypass pipe without being treated by the trap, so it is necessary to make the pipe diameter smaller than the main exhaust pipe 11 in order to improve the exhaust emission. Figure 2 shows the inner diameter D ₁ of the main exhaust pipe and the inner diameter D 2 of the bypass pipe ₃ with respect to the regulatory critical value of exhaust emission.
This shows the results of an experiment to determine the relationship between According to this, for example, when D ₁ =50φ, D ₂ ≈20φ. If we focus only on improving exhaust emissions,
When D ₁ =50φ, D ₂ ≦20φ may be satisfied, but since substantially all of the exhaust gas flows through the bypass pipe 3 when the control valve 31 (described later) is closed, the output is reduced by the reduction in the pipe diameter. Therefore, it is preferable to select the maximum value of D ₂ within the allowable range of the emission.

A control valve 31 is provided downstream (or upstream) of the trap 13 to shut off the flow of exhaust gas from the main exhaust pipe 11 as necessary. The control valve 31 is simply an ON-OFF valve that opens and closes the passage of the main exhaust pipe 11. As an actuator for the control valve 31, a diaphragm device 33 as shown can be used. The negative pressure working chamber of the diaphragm device 33 is selectively connected to the atmosphere or a vacuum pump via a negative pressure switching valve (VSV) 35. That is, when the diaphragm device 33 is connected to a vacuum pump or other negative pressure region, the on-off valve 31 closes;
The passage of the main exhaust pipe 11 is closed. As shown in FIG. 3, the control valve 31 preferably has a slight clearance G with respect to the inner diameter surface of the main exhaust pipe 11 even in its closed position.
(preferably G≦0.2 mm), thereby preventing the valve from becoming stuck to the inner diameter of the main exhaust pipe 11 due to particulation.

Switching control of the VSV 35 is performed using the output signal from the CPU 21 in the following manner. That is, when the heater 16 starts igniting the particulate, as described above, if the flow velocity of the exhaust gas is too high, ignition failure will occur. Therefore, when starting ignition, the control valve 31 is closed to prevent exhaust gas from flowing into the trap 13. After the ignition is completed, the control valve 31 is quickly reopened to allow the exhaust gas to flow into the trap 13, causing the ignition flame to propagate to the collection particulate downstream of the trap. At this time, if there is a large amount of exhaust gas flowing into the trap, there is a possibility that the ignition flame will be blown out, but since a portion of the exhaust gas always flows into the bypass pipe, the amount of exhaust gas flowing into the trap is relatively small. Therefore, combustion propagates without the ignition flame being blown out. In this way, the CPU
21 controls the actuator 33 to close the control valve 31 only when the heater starts ignition.

FIG. 4 is a flow chart showing an example of trap regeneration operation. First, conditions such as engine speed, engine load, engine water temperature, and vehicle speed are input to the CPU 21 (FIG. 1) as information. The regeneration time is determined mainly based on the back pressure of the exhaust gas. That is, the exhaust gas discharged from the diesel engine flows as shown by the arrow, and 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 13 increases. Therefore, this back pressure is an indicator of particulate accumulation. When it determines that it is time for regeneration, the engine water temperature is checked. This is to prevent regeneration from starting immediately after the engine is started. When the engine water temperature is, for example, 110°>T>80°C, the VSV 35 is switched and the actuator 33 closes the control valve 31. Next, or at the same time, energization of the heater 16 is started (usually for 20 to 40 seconds). When ignition is completed, the power supply to the heater is stopped, and at the same time, the control valve 31 is opened again.

As described above, according to the present invention, simply ON-
The OFF-operated control valve makes it easy to reliably regenerate the trap, and the bypass pipe, which is smaller in diameter than the main exhaust path and which bypasses the trap and allows exhaust gas to constantly flow, prevents deterioration of exhaust emissions and prevents ignition. It is possible to reliably regenerate the trap by preventing the flame from being blown out by exhaust gas.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the exhaust system of a diesel engine using the device according to the present invention; Fig. 2 is a diagram showing the relationship between the inner diameter of the main exhaust pipe and the inner diameter of the bypass pipe shown in Fig. 1; FIG. 3 is an enlarged illustrative view of the control valve, and FIG. 4 is a flow diagram showing an example of trap regeneration operation. 3... Bypass pipe, 5... Diesel engine body, 9... Exhaust manifold, 11... Main exhaust pipe, 12... Trap material, 16... Heater, 31
...control valve.

Claims (1)

[Scope of utility model registration request] Exhaust particulate purification for a diesel engine in which a particulate trap is provided in the exhaust gas path of the diesel engine, which has a trap material that collects exhaust particulates and an electric heater that ignites and burns the exhaust particulates collected by the trap material. In the device, a bypass pipe having a diameter smaller than the main exhaust path is provided, which bypasses the particulate trap and through which exhaust gas always flows, and the main exhaust path is provided in the main exhaust path upstream or downstream of the particulate trap. A diesel engine exhaust particulate purification device characterized by being equipped with an ON-OFF control valve that controls opening and closing.