JPH0559246B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a device for purifying particulate matter in the exhaust gas of a diesel engine, and particularly to a device for regenerating the particulate trap.

2. Description of the Related Art A technique is known in which a trap is provided in an exhaust pipe to collect particulate matter in the exhaust gas of a diesel engine. The particulate collection capacity of the trap becomes saturated in a relatively short period of time. Therefore, in order to refresh the trap, it is necessary to remove the particulate collected in the trap. Therefore, when the particulate matter has accumulated, the trap is heated by a heater to incinerate the deposited particulate matter. As a conventional technique for detecting the amount of particulate build-up, a method is known that detects the exhaust pipe back pressure upstream of the trap (Japanese Patent Application Laid-open No. 48831/1983). That is, back pressure is simply detected during engine operation, and when the trap reaches saturation in its adsorption capacity, the back pressure increases. The back pressure sensor can detect this and use it as a signal to start regenerating the trap. In other words, back pressure corresponds to operating conditions such as engine speed and accelerator opening, and the computer's memory stores upper limit back pressure values according to operating conditions such as engine speed and accelerator opening. During driving, the rotation speed and accelerator opening degree are measured, a predetermined back pressure is calculated according to the rotation speed, and a clogged trap is detected by comparing this calculated value with the actually measured back pressure. However, with this conventional method, erroneous detection of the regeneration timing is likely to occur during transient operation, for example, during acceleration/deceleration operation in which the accelerator pedal is depressed. In other words, the rotational speed and accelerator opening are changing during acceleration/deceleration operation, and the set back pressure value calculated from the actual rotational speed and accelerator opening due to the delay factor is the same as the saturation level of the trap's adsorption capacity. This is because errors will occur in the correspondence.

Problems to be Solved by the Invention It is an object of the present invention to eliminate the influence of load fluctuations before determining the regeneration time, and to make it possible to accurately determine the regeneration time.

Means for Solving Problems The structure of the present invention is that a particulate purifying device for a diesel engine is shown in FIG. 1, and includes a particulate trap 36 provided in the exhaust pipe of the engine;
A back pressure sensor 64 installed in the exhaust pipe upstream of the particulate trap, sensors 61 and 62 for detecting engine load, and means A for calculating a set back pressure value during regeneration according to the engine load; An engine load state stability determining means that calculates the amount of change in the engine load over a predetermined period from the detected engine load, compares the amount of change with a predetermined value, and determines that the engine load state is stable when the amount of change is smaller than the predetermined value. B, and regeneration determination means C for determining whether or not the back pressure detected by the back pressure sensor exceeds a set back pressure value when the engine load state is determined to be stable by the engine load state stability determination means B. , and an incineration means 42 which is driven by a regeneration signal from the regeneration determination means C and regenerates and incinerates the particulate collected in the trap 36.

Operation The operating condition stability determining means B calculates the amount of change in the load over a predetermined period from the detected engine load, compares the amount of change with a predetermined value, and determines that the engine load state is stable when the amount of change is smaller than the predetermined value. When the amount of change is larger than a predetermined value, the engine load state is determined to be unstable. When it is determined that the trap 36 is unstable, even if the back pressure exceeds a predetermined value obtained by the set back pressure value calculation means A, the trap 36 does not start the regeneration process. If the regeneration determination means C determines that the back pressure exceeds a predetermined value when the operating conditions are determined to be stable, a regeneration signal is sent to the incineration means 42, and the trap 36 is regenerated.

Embodiment FIG. 2 illustrates the invention by way of an embodiment. The diesel engine includes an engine body 8, a fuel injection pump 9, an intake manifold 11, and an exhaust manifold 12. 14 is a turbo charger,
It consists of a compressor 15 and a turbine 16. The compressor 15 is connected via an inlet pipe 17 to an air cleaner 18 and an outlet pipe 19 to the intake manifold 11. Compressa 15
The turbine 16 that rotates integrally with the inlet pipe 20
It is connected to the exhaust manifold 12 via.
The compressor outlet pipe 21 is connected to a particulate trap 26.

The particulate trap 26 is the inlet pipe 2.
8, an outlet pipe 30, and a bypass pipe 32. A trap case 34 is fixed to the bypass pipe 32, and a trap 36 made of porous ceramic is disposed within the trap case 34. A heater 42 is located in front of the trap 36. 44 is a shutoff valve, the valve shaft of which is connected to a diaphragm 50 of a negative pressure actuator 48 via a lever 46. The shutoff valve 44 is normally in a fully closed state as shown by the solid line due to the spring 52. The diaphragm 50 is a switching valve 54
is selectively connected to an atmospheric filter 56 or a negative pressure pump 58 driven by a crankshaft.

60 is a heater 42 during incineration and regeneration of the trap 26
This is a control circuit that controls the shutoff valve 44 and performs regeneration control based on signals from each sensor. That is, at the combustion injection pump 9, there is a sensor 6 that detects the rotation angle of the accelerator control lever 24 connected to the accelerator pedal 23, that is, the accelerator pedal opening degree.
1 and the rotation speed of the governor shafts of the injection pumps 9 and 10, that is, an engine rotation speed sensor 62 is provided,
Signals from the accelerator opening sensor 61 and the engine speed sensor 62 are sent to the control circuit 6 via lines _l1 and _l2 .
Applied to 0. A backpressure signal from backpressure sensor 64 is also applied to control circuit 60 via line _l3 . The back pressure sensor 64 includes an exhaust gas chamber 641 and a diaphragm 642 that defines the exhaust gas chamber 641.
And the strain gauge 643 on this diaphragm 642
The strain gauge 643 detects the force applied to the diaphragm 642 according to the pressure in the chamber 641. The control circuit 60 determines the regeneration start timing based on the signals from these sensors, as will be described later, and drives the cutoff valve 44 and the heater 42.

The control circuit is configured as a microcomputer. That is, the control circuit 60 has a microprocessing unit (MPU) 65 and a memory 66.
Incineration control is performed according to a control program stored in the memory. Furthermore, the control circuit 60 has an input port 67 and an output port 68, and the input port 6
7, a back pressure sensor 64 and an accelerator opening sensor 61 are connected via analog-to-digital converters 69 and 70, respectively. Further, the engine speed sensor 62 is also connected to the input port 67 . The output port 68 is connected to a drive transistor 76 of the heater 42 and a drive transistor 78 of the switching valve 54 through respective latches 70 and 71 as flip-flop circuits.

An example of the control program will be shown below using a flowchart.

FIG. 4 shows the main routine. When the program starts at 80, initialization is performed at 82, thereby clearing the registers of the MPU 65 and the memory 66, and resetting the latches 70 and 71. Resetting latches 70 and 71 causes transistors 76 and 78 to be cut off. Therefore, the heater 42 is not energized and the electromagnetic switching valve 54 is not energized. By de-energizing the switching valve, the switching valve 54 assumes the white port position in FIG. 2, atmospheric pressure acts on the diaphragm 50 of the actuator 48, the shutoff valve 44 becomes fully closed as shown by the solid line, and the entire exhaust gas is discharged. can go to trap,
Adsorption purification of particulate is carried out.

Next, the main routine enters a routine for measuring the maximum and minimum accelerator openings of 84 or less. i.e. at 84
The MPU 65 inputs the A/D converted opening signal θ from the accelerator opening 61 into an internal register. next
In step 86, it is determined whether the detected θ is greater than θMAX. If Yes, go to 87 and update that θ to θMAX and the maximum value; if No, go to 90 and leave θMAX unchanged. The maximum value θMAX calculated in this manner is temporarily stored in the memory 66. The minimum value θMIN is calculated in the same manner at 92, 94, and 96, and the calculated θMIN is stored in the memory 66. In this way, in the main routine, a process is performed in which the values of θMAX and θMIN at the accelerator opening are constantly measured.

In the next step 97, the MPU 65 inputs the back pressure value from the back pressure sensor 64 into the register and stores it in the PB storage area of the memory. PB changes as shown in FIG. 8C. In step 98, the MPU 65 inputs the rotational speed signal from the engine rotational speed sensor 62 and transfers it to the memory area where the rotational speed N is stored.

FIG. 5 shows a routine that is executed every 1000 msec, and this process starts at 140. 145, the difference between the maximum value θMAX and minimum value θMIN of the accelerator opening stored in the memory, that is, θMAX−
The value of θMIN is calculated as shown in FIG. 8B. next
At step 150, it is determined whether the difference between θMAX and θMIN is smaller than a predetermined value K. If the determination is No, it is considered that the accelerator opening is not stable, and in this case, no regeneration is performed. The program then proceeds to step 155, where θMAX and θMIN are initialized, and preparations are made to calculate the maximum and minimum values for the next 1 second.

If 150 is Yes, that is, the accelerator opening is stable, the process proceeds to 160, where the set value of the regeneration start back pressure is calculated. This process is performed in detail as shown in FIG. That is, at 300, the rotation speed N is input, and at 302, the accelerator opening degree θ is input. In step 304, PMAP is calculated according to the measured rotational speed and accelerator opening using a map as shown in FIG. Such maps are stored in memory. In other words, when the accelerator opening is fixed as θ ₁ , θ ₂ , etc., the rotation speed N
The set back pressure value at the start of regeneration is as shown in FIG. Therefore, there is a map of set back pressure values for each combination of rotation speed and accelerator opening, and PMAP is calculated based on this map.

Returning to FIG. 5 again, in step 170, it is determined whether the measured back pressure PB is greater than the set back pressure PMAP at the time of starting the regeneration. If No, the process branches to 180 and resets the playback timing flag F. This flag F is 2
This detects whether a regeneration command has been issued repeatedly. 8 in FIG. 8 represents the magnitude relationship between the actually measured back pressure PB and the set back pressure PMAP for each measurement period of 1 second. Back pressure PB and set back pressure PMAP at step 170
The actual comparison with
If PB≦PMAP at 170, F is reset to 0. Also, when θMAX−θMIN≧K, the step
170, no actual comparison of the size relationship between PB and PMAP is made. That is, when θMAX-θMIN≧K as shown by X ₀ in Figure 8 (b), the flag F is maintained at 0 as shown by X' in (e) even if PB>PMAP as shown by Ru.

As shown by Y ₀ in B, when θMAX−θMIN<K, the actual back pressure PB is equal to the set back pressure as shown in Y in D.
If PMAP is exceeded, the judgment of 170 becomes Yes, and 190
The flag F is incremented by 1 (Y' in Figure 8). In the next step 200, it is determined whether the flag F is 2 or not. If no, exit the routine. If PB > PMAP twice in a row, F = 2 (8th
Y'' in Figure E), the judgment for step 200 is Yes.
Therefore, the process proceeds to 210, where the MPU 65 sets the timer to the heater operating time T when the trap 36 is regenerated. Next, at 220, the MPU 65 outputs a set signal to the latch 71 from the output port 68, and sets the output of the latch 71 to a high level. Therefore transistor 7
2 is turned on, the switching valve 54 is excited and takes the black port position, negative pressure from the negative pressure pump 58 acts on the diaphragm 50, and the cutoff valve 44 opens as shown by the broken line. As a result, a portion of the exhaust gas is not directed to the bypass 32 but directly to the outlet pipe 30. In the next step 220, a set signal is output from the output port 68 to the latch 70, and the transistor 7
6 is turned on and the heater 42 is activated. Therefore, the trap 36 becomes hot due to the decrease in the amount of passing gas due to the opening of the valve 44.
The particulate collected by the trap element 36 is ignited. At the next step 240 in FIG. 5, the flag F is reset, and at 155, θMAX, θMIN
will be reset.

When the timer reaches the appropriate time T to complete the burnout of the particulate matter in the trap, the time interrupt routine of FIG. Shutoff valve 14 is closed. At 420, latch 70 is reset, transistor 76 is turned off, and heater 42 is de-energized (FIG. 8).

Effects of the invention Calculate the amount of change in engine load over a predetermined period,
After comparing the amount of change with a predetermined value and determining that the engine load condition is stable when the amount of change is smaller than the predetermined value,
Since it is determined whether it is time for regeneration by comparing the back pressure with a predetermined value, it is not affected by fluctuations in engine load during the transient period until the time for regeneration is reached, and the time to start regeneration is determined. be able to judge accurately. Therefore, the incineration process can be properly controlled. In contrast,
If there is a false detection, the heater will be controlled when there is little accumulation of particulate matter. If the heater is controlled when there is little particulate buildup, only the particulate near the heater will burn, and the fire will not spread to the rear and will not ignite. If this happens several times, even if a large amount of particulate matter accumulates at the rear, the particulate matter near the heater is so small that it cannot ignite all the way to the rear, leading to problems such as filter clogging, large pressure loss, and poor fuel efficiency.
In addition, even if it eventually becomes possible to ignite, the amount of heat generated by the rear particulate is too large and the trap (catalyst-carrying ceramic filter)
The heat generation load was large, and there was a risk that durability would be impaired. The present invention eliminates such concerns.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of the present invention, FIG. 2 is an overall configuration diagram of an embodiment of the present invention, FIG. 3 is a block diagram of a control circuit, and FIGS. 4 to 7 are diagrams of the present invention. Flowchart showing the software of the invention, No. 8
The figure is an operation timing diagram of the present invention, and FIG. 9 is a diagram showing the regeneration start back pressure setting value with respect to rotation speed and accelerator opening degree. 8... Engine body, 36... Trap, 42
... Heater, 44 ... Shutoff valve, 60 Control circuit, 6
1... Accelerator opening sensor, 62... Rotation speed sensor, 64... Back pressure sensor.

Claims (1)

[Scope of Claims] 1. A particulate purification device for a diesel engine, comprising: (a) a particulate trap provided in an exhaust pipe of the engine; (b) a particulate trap disposed in the exhaust pipe upstream of the particulate trap; (c) a sensor that detects the engine load; (d) means for calculating a set back pressure value during regeneration according to the engine load; an engine load condition stability determining means for calculating an amount of change, comparing the amount of change with a predetermined value, and determining that the engine load condition is stable when the amount of change is smaller than the predetermined value; Regeneration time determination means for determining whether the back pressure detected by the back pressure sensor exceeds a set back pressure value when the load condition is determined to be stable, and (g) a regeneration signal from the regeneration time determination means. An apparatus for purifying particulate matter for a diesel engine, comprising: an incineration means driven by a trap to regenerate and incinerate particulate matter collected in a trap.