JPH0480204B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for regenerating a particulate trap in a diesel engine provided with a particulate trap in the exhaust pipe.

A technique has been proposed in which a particulate trap is provided in an exhaust pipe to remove particulates from exhaust gas discharged from a diesel engine. Particulates are collected in the trap during engine operation. In order to avoid an increase in the pressure loss in the exhaust pipe due to the collection of particulates in the trap, the particulates collected in the trap are incinerated every time the vehicle travels. The regeneration of traps through incineration involves extremely critical issues in selecting the timing. That is, unless a certain amount of fine particles are collected in the trap, ignition will not occur or good combustion will not occur. On the other hand, if the amount exceeds a certain level, combustion will proceed too much and the trapper will reach an extremely high temperature, which may not only lead to melting but also deteriorate the function of the trap. The amount of particles trapped in the trap has a significant impact on regeneration control, but in reality it is difficult to accurately determine the amount of particles trapped in the trap at the start of the regeneration process. It is difficult to know. Traditionally, the regeneration timing has been decided by integrating the engine speed or by detecting an increase in back pressure with a pressure sensor in the exhaust pipe, but the integrated engine speed and back pressure are only used to determine the start of the regeneration period. This is only a guideline. If the amount of particulates is small, this is not a big problem since no combustion reaction will occur, but overheating if the amount of particulates is large must be avoided from the viewpoint of safety measures.

Therefore, in JP-A-56-118514, a bypass passage is provided, and during regeneration, the control valve upstream of the trap is controlled so that the flow rate to the trap is reduced and most of the exhaust gas is diverted to the bypass passage. During regeneration, air for combustion promotion is introduced along with fuel from upstream of the trap, and a temperature sensor is installed inside the trap to ensure that the temperature of the trap reaches a predetermined temperature that is higher than the combustion temperature of carbon (fine particles). When the air intake is stopped. A temperature sensor detects the temperature of the trap, and when it reaches a predetermined temperature above the combustion temperature of carbon (fine particles), the introduction of air is stopped.

Furthermore, in Japanese Patent Application Laid-Open No. 57-8311, a means for introducing air is provided upstream of the trap, and sensors for detecting the temperature are placed near the inlet and outlet of the trap, and when the trap is regenerated, a heater is used to introduce air into the trap. Air introduction is started after the temperature reaches the ignition temperature of the particles, and air introduction is stopped when it is detected that the outlet temperature has reached the ignition temperature.

In the prior art, the amount of oxygen is limited after ignition starts when the temperature inside the trap reaches the combustion temperature (ignition temperature) of the particulates. In other words, once the combustion temperature or ignition temperature is reached, it is determined that combustion can continue without adding any additional air from outside, and once the combustion temperature (ignition temperature) of fine particles is reached, the amount of oxygen is limited. it seems to do. However, when comparing the inner and outer circumferences of a trap, the temperature at the outer circumference tends to drop, so even once the combustion or ignition temperature is reached at the outer circumference, the temperature tends to drop. Therefore, there is a possibility that unburnt remains are likely to occur.

An object of the present invention is to reliably prevent combustion from proceeding excessively while preventing unburned remains due to a temperature drop.

According to this invention, in a diesel engine in which a trap for exhaust particulates is provided in the exhaust pipe and a flow rate control valve for recirculated exhaust gas is provided in the exhaust gas recirculation passage that connects the exhaust pipe to the intake pipe, the regeneration timing of the trap is controlled. The detection starts ignition and incineration of the particulates collected in the trap, and the flow rate is controlled when the temperature in the exhaust pipe downstream of the trap exceeds a predetermined value corresponding to excessive combustion of particulates in the trap. A method of regenerating a diesel engine exhaust particulate trap is provided, the method comprising operating a valve to increase the amount of recirculated exhaust gas.

When the regeneration time of the trap is detected, the regeneration incineration process is started, and when the temperature in the exhaust pipe exceeds a predetermined value corresponding to excessive combustion of particulates in the trap as the regeneration incineration process progresses, the recirculated exhaust gas is The amount of gas is increased. The increase in the amount of recirculated exhaust gas reduces the amount of oxygen in the trap, and together with the decrease in exhaust gas temperature accompanying the increase in the amount of recirculated exhaust gas, the inside of the trap is maintained in a suitable combustion state.

The following will be explained with reference to the drawings. In FIG. 1, 10 is the main body of the diesel engine, 12 is the intake pipe, and 1
Reference numeral 4 indicates an exhaust pipe, and reference numeral 16 indicates an exhaust gas recirculation passage that connects the exhaust pipe 14 to the intake pipe 12. A recirculated exhaust gas flow control valve (EGR) is installed in the exhaust gas recirculation passage 16.
A valve) 18 is provided. A particulate trap 20 is provided in the exhaust pipe 14. The particulate trap 20 is comprised of a filter material 24 (made of, for example, cordierite foam ceramic) provided within a case 22. A heater 26 is provided upstream of the filter material 24 as means for starting ignition and incineration at the start of the regeneration process. An exhaust throttle valve 28 is provided upstream of the heater 26 and is arranged to be switchable between a position where exhaust gas from the exhaust pipe 14 is guided to the filter material 24 and a position where it is guided to a bypass passage 32 that bypasses the trap 20. ing.

Reference numeral 34 denotes a control circuit as a programmable microcomputer system for controlling the regeneration of the trap 24. Drive signals to the actuator 28' of the flow rate control valve 18, heater 26, and exhaust throttle valve 28 are connected to lines l ₁ , l ₂ , Output via _l3 .

In order to detect the start of the regeneration process, this embodiment integrates the engine rotational speed. That is, a pulse generator 40 is provided in close proximity to the crankshaft 10' to generate a pulse for each revolution of the engine, and is connected to a counter 42 via line _l4 . Counter 42 introduces a predetermined number of pulses from pulse generator 40, one pulse for each accumulated engine speed, into control circuit 34 via line _l5 . Further, in order to detect the temperature inside the trap during regeneration, a temperature sensor 46 is provided downstream of the filter material 24 and is connected to the control circuit 34 via a line _l6 .

In the illustrated embodiment, the trap regeneration timing is detected based on the integrated value of the rotational speed from the pulse generator 40, and the exhaust throttle valve 28 and heater 26 are operated to raise the temperature of the filter material 24 and incinerate it. After the particulates in the filter material 24 are ignited, the exhaust throttle 28 is released and the heater 26 is destaticized, and the temperature signal from the temperature sensor 46 is detected to control the flow rate control valve 18 to increase the exhaust gas flow rate (i.e., trap). 20
control to reduce the amount of air in the exhaust gas that goes to the exhaust gas. Such control is performed by a program stored in the control circuit 34, and an example of the routine will be explained with reference to FIGS. 2 to 5.

When the cumulative value of the engine rotation speed reaches a predetermined value, the counter 42 applies a pulse to one interrupt port of the MPU (not shown) in the control circuit 34.
The interrupt routine starts. At 62, the heater 26 is activated, and at 64, the actuator 28' rotates the exhaust throttle valve 28 counterclockwise in FIG. 1 to reduce the flow rate of exhaust gas to the trap 20 to almost zero. As a result, the temperature within the trap 20 rises, and the particles captured by the filter material 24 begin to ignite and burn. At 66, timer 1 is set for a period of time sufficient for ignition and combustion of the particulates to occur. This interrupt routine ends at 68.

When the time t has elapsed, an interrupt routine is started at 70 in FIG.
8 to rotate clockwise in the figure. Trap 20 due to the action of excess air contained in the exhaust gas
The combustion of the collected particulates inside continues. 76 indicates a reset of timer 1, and 78 indicates a return to the main routine.

If excessive combustion of particulates within the trap occurs during the regeneration process, the temperature within the trap will exceed a predetermined value and the interrupt routine of FIG. 4 is initiated at 80.
At 82, the control valve 18 is driven in the open direction to reduce the amount of air occupying the engine intake pipe 12.
As a result, the combustion reaction in the trap 20 is suppressed. The temperature of the exhaust gas at which the routine of FIG. 4 is started is set at a value that causes excessive combustion of particulates within the trap, as described above. That is,
If the temperature rises even slightly above this value, there is a risk of overheating of the trap, so attempts are made to suppress overheating by increasing the amount of recirculated exhaust gas and reducing the amount of oxygen accordingly. In addition, the increase in recirculated exhaust gas suppresses combustion in the engine 10, resulting in a decrease in the temperature of the exhaust gas. As the temperature of the exhaust gas decreases, it is possible to provide sufficient margin against overheating even though the temperature of the trap that stops regeneration is set as high as possible as described above. 84 sets timer 2, trap 20
The time t' is set to be sufficient to reduce the temperature within.
86 indicates the end of this interrupt routine.

88 in FIG. 5 indicates the start of the interrupt routine starting at time t', 90 returns the flow control valve 18 to its original position, 92 resets the timer 2, and 94 indicates the end of this interrupt routine. .

In the embodiments described above, the temperature rise during trapping is detected and the flow rate of the recirculated exhaust gas is increased. Therefore, the amount of air in the exhaust gas is suppressed, thereby preventing overburning of the trap and the resulting deterioration of the trap's function.

In order to detect when the trap 20 is to be regenerated, a pressure increase in the exhaust pipe may be detected using a pressure sensor instead of integrating the number of engine revolutions. Also, instead of using the heater 26 and the exhaust throttle together as the ignition means at the start of regeneration, the exhaust throttle alone, the intake throttle,
Alternatively, ignition using a burner is also optional.

According to this invention, by increasing the amount of recirculated exhaust gas when the amount of recirculated exhaust gas exceeds a predetermined value corresponding to excessive combustion of particulates in the trap after the start of regeneration, the amount of oxygen for combustion in the trap is reduced. Combined with the lowering of the gas temperature, the temperature inside the trap can be maintained as high as possible with sufficient margin against overheating. Therefore, it is possible to satisfy the contradictory demands of preventing unburned remains and preventing early thermal deterioration of the trap. Also, the existing
ECR equipment can be used effectively.

[Brief explanation of the drawing]

FIG. 1 is an overall schematic configuration diagram of a diesel engine that implements the method of the present invention, and FIGS. 2 to 5 are flowcharts showing the method of the present invention. 10...Engine body, 12...Intake pipe, 14
...Exhaust pipe, 18...EGR valve, 20...Trap, 26...Heater, 28...Exhaust throttle valve, 34
...Control circuit, 46...Temperature sensor.

Claims (1)

[Claims] 1. In a diesel engine that has a trap for exhaust particulates in the exhaust pipe and a flow rate control valve for recirculated exhaust gas in the exhaust gas recirculation passage that connects the exhaust pipe to the intake pipe, the trap can be removed by detecting the regeneration timing of the trap. When the temperature in the exhaust pipe downstream of the trap exceeds a predetermined value, which corresponds to excessive combustion of particulates in the trap, the flow control valve starts to ignite and incinerate the collected particulates. A method for regenerating an exhaust particulate trap of a diesel engine, characterized by operating the trap to increase the amount of exhaust gas.