JPH0519005B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust particulate purification device for a diesel engine, and more particularly to a control method for a single flow bypass type exhaust particulate purification device.

Most of these types of exhaust particulates are flammable, such as carbon particles, and diesel engines collect these flammable particulates and incinerate the collected particulates (particulate matter) to regenerate the collection material. Various particulate 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 front end surface of the collection material, and the heater burns the exhaust particulates adhering to the surface of the collection material, which is used as a heat source to cause the downstream particulates to self-combust. The ignition timing of the heater, that is, the regeneration timing of the trap, is determined by a signal from the control device when a predetermined amount of particulate matter has accumulated in the trap and signal parameters such as exhaust gas temperature, engine water temperature, exhaust gas flow rate, etc. satisfy predetermined conditions. This is done based on signals. In addition, the single-flow bypass type exhaust particulate purification device is equipped with one bypass path that bypasses the particulate trap, and opens the on-off valve disposed in the bypass path at a predetermined time to particulate the exhaust gas. This is to prevent it from falling into a trap. For example, if the flow rate of exhaust gas flowing through the trap is too high when the heater starts ignition, the ignition combustion of the particulate will not occur smoothly. It is used to temporarily slow down the flow rate of exhaust gas flowing into the trap by passing the exhaust gas through the bypass.

Assume that in the single flow bypass type exhaust particulate purification device as described above, high load operation such as steep hill climbing or high speed driving is performed continuously with a sufficient amount of particulates collected in the trap. do. Under such operating conditions, the temperature of the exhaust gas becomes quite high and the amount of fuel injected is large, so the concentration of oxygen (O ₂ ) in the exhaust gas is necessarily low. If the access pedal is released in such a state or the engine load side is set to half-open, the O ₂ concentration in the exhaust gas will rapidly increase, considering that diesel engines are originally supplied with excess air. do. As a result, if the collected particulate was burned all at once under such conditions, there was a risk that the trap would be melted and damaged.

In order to solve the above-mentioned drawbacks, the present invention detects when the exhaust gas temperature is higher than a predetermined temperature for a predetermined period of time and the O ₂ concentration in the exhaust gas increases under such conditions, and controls the bypass opening/closing valve. The purpose is to forcibly open the trap and reduce the exhaust gas flow rate on the trap side, thereby lowering the exhaust gas temperature and preventing trap melting.

This will be explained below with reference to the drawings.

FIG. 1 is a diagram showing the overall configuration of a diesel particulate purification device for carrying out the present invention, in which a particulate trap 1 equipped with a collection material for collecting exhaust particulates is installed inside an exhaust pipe 3 of a diesel engine 11. established in A heater 5 is provided at the upstream end of the trap 1 to ignite the collected particles. A single flow bypass 13 bypasses the trap 1 and is connected to the exhaust pipe 3, and is provided with an on-off valve 15 which is normally closed. Open/close valve 1
5 is a diaphragm type actuator 17, for example.
It is operated to open and close by. Note that 19 is a fuel injection valve.

The timing of energizing the heater 5, that is, the timing of regenerating the trap 1, is controlled by a drive relay circuit 21. Actuator 17 and relay circuit 21 are control devices
It is controlled by signals from the ECU 25. Note that the actuator 17 is controlled via a negative pressure switching valve VSV31 operated by a signal from the ECU 25. As is well known, the ECU 25 receives a negative pressure signal Sv and a valve opening signal from the opening sensor 39 of the intake throttle valve 37.
Signals such as Sd, engine water temperature St, engine load Sl, engine rotation speed Sn, etc. are appropriately input, and the opening timing of the on-off valve 15 and the timing of energizing the heater 5 are controlled accordingly. In addition, 41 is an intake throttle valve 37
The actuator 43 is an EGR valve that recirculates exhaust gas to the intake system when necessary, but since it is not directly related to the present invention, its explanation will be omitted.

The configuration and operation described above are well known.

According to the present invention, the ECU 25 receives an incoming gas temperature signal Se and an O ₂ concentration increase signal Sa from an exhaust temperature sensor 51 that detects the temperature of exhaust gas (incoming gas) on the upstream side of the trap. The O ₂ concentration signal can be detected by, for example, a micro switch that mechanically detects release of an accelerator pedal (not shown) or a lean sensor (which detects the absolute value of the O ₂ concentration).

In the present invention, the inlet gas temperature is set to a predetermined temperature t°C (for example,
600℃) or higher and the O ₂ concentration increases
The ECU 25 forcibly opens the valve via the second VSV 33 regardless of the original operation of the on-off valve 17 to reduce the exhaust gas flow rate on the trap side, thereby lowering the exhaust gas temperature. The following measures have been taken to measure the temperature of the incoming gas. That is, the trap temperature becomes high only when the exhaust gas temperature remains above t° C. for a certain period of time. In other words, the incoming gas temperature temporarily becomes t°C.
Cases where the temperature rises above t°C and immediately returns to below t°C may or should be excluded from the scope of the present invention. FIG. 2 shows an example of such a change in inlet gas temperature. In the same figure
During the times x ₁ , x ₂ , x ₃ , the incoming gas temperature is t°C or higher,
During times y ₁ and y _{2 ,} the incoming gas temperature is below t°C. That is, only the shaded area indicates the area where the temperature is t° C. or higher.
Now, if the measurement time from x ₁ to x ₃ is T ₁ , then T ₁ = x ₁ + y ₁ + x ₂ + y ₂ + x ₃ .

Therefore, the total time of x ₁ + x ₂ + x ₃ is the total time T ₁
It can be assumed that the trap reaches a critical temperature for melting only when the temperature exceeds A% of the trap. That is, A=x ₁ +x ₂ +x ₃ /T ₁ ×100 (%) This A actually differs depending on the average temperature level Tf of the trap for T ₂ seconds before t°C. That is, there is a relationship of T ₁ =f(Tf) as shown in FIG.

FIG. 4 is a block diagram showing the control method of the present invention. It goes without saying that the flowchart in the figure is carried out with priority over the normal trap regeneration program.

As is clear from FIG. 4, according to the present invention, when the gas temperature entering the trap reaches t°C or higher, the temperature continues to be measured for T ₁ seconds ₍ for example, 90 seconds). Preparatory conditions for opening the bypass on-off valve are completed only in certain cases. Under these conditions, the O ₂ concentration after T ₁ second has elapsed, and only when the O 2 concentration increases (for example, 3% or more) does the bypass on/off valve operate independently of and in priority to the normal trap regeneration program. By opening the trap, melting and damage of the trap can be prevented.

In addition, the on-off valve is operated when the inlet gas temperature is continuously below t℃.
T will be closed again if it lasts for ₂ seconds.

Incidentally, the opening operation range of the on-off valve as described above is actually limited to when the engine is at full load or in the vicinity thereof. Therefore, during normal acceleration/deceleration driving or uphill driving, a normal trap regeneration program is executed.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of an apparatus for carrying out the present invention, FIG. 2 is a graph showing an example of a change in gas temperature entering the trap, and FIG. 3 is a graph showing an example of the change in temperature of the gas entering the trap _. A graph showing the relationship between and the inlet gas temperature Tf,
FIG. 4 is a block diagram showing the control method of the present invention. 1...Trap, 3...Exhaust pipe, 5 Heater, 13...
Bypass, 15...open/close valve.

Claims (1)

[Claims] 1. A method for controlling a single flow bypass type diesel exhaust particulate purification device having a particulate trap provided in the exhaust pipe of a diesel engine and a bypass passage with an on-off control valve that bypasses the particulate trap. Then, measure the temperature of the exhaust gas (incoming gas) on the inlet side of the particulate trap for a predetermined time (T ₁ second), and calculate this T ₁
The inlet gas temperature is above the predetermined temperature (t°C) for a predetermined percentage (A%) or more of the time, and the oxygen concentration of the exhaust gas measured after the above predetermined T ₁ hour has increased by more than the predetermined value. A method of controlling a diesel exhaust particulate purification device, comprising, at times, forcibly opening an opening/closing control valve of the bypass passage.