JP2616075B2 - Engine exhaust purification device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust gas purification device for an engine.

(Prior Art) In an engine (particularly, a diesel engine) in which fine particles (particulates) such as carbon contained in exhaust gas are trapped by a trap provided in an exhaust passage, the exhaust pressure becomes excessive due to accumulation of the particulates. In order to reduce the engine and emission performance, a device for burning the accumulated particulates at a predetermined time to regenerate the trap is provided (Japanese Patent Application Laid-Open No.
58-51235).

Referring to FIG. 8, the particulates discharged from the engine 1 are collected by a trap 3 having a heat-resistant filter structure provided in the exhaust passage 2.

On the other hand, a butterfly type throttle valve 6 for reducing the intake flow rate is provided in the intake passage 5, and one end of the throttle valve 6 has a throttle valve 6.
The diaphragm actuator 8 is connected via a lever 7 which is fixed to the valve shaft and is rotatably attached at the other end to a rod 8d.

The actuator 8 and the pressure chamber of the actuator 8
An electromagnetic valve 9 that can change the control negative pressure guided to 8b according to the duty signal from the control device 15 constitutes a throttle valve driving device. For example, when the duty value (valve opening time ratio) of the duty signal is increased to increase the negative pressure to the pressure chamber 8b, the diaphragm 8a moves the rod 8d rightward in the figure against the return spring 8c. So throttle valve 6
Is closing. 10 is a negative pressure pump.

Signals from a load sensor 12 and a rotation speed sensor 13 of the engine 1 provided in the combustion injection pump 11 and an intake pressure sensor 14 provided in the intake passage 5 downstream of the throttle valve 6 are input to the control device 15. The control device 15 performs the following control.

If it is determined that the trap 3 is to be regenerated from a predetermined traveling distance or traveling time, the operating condition determined from the engine load and the rotation speed at that time is determined as an operating condition in which a large amount of excess air flows into the engine 1. Is determined. If it is determined that the vehicle is in this operating state, the throttle valve 6
A feedback signal is output so that the intake negative pressure downstream of the throttle valve 6 becomes substantially constant based on a signal from the intake pressure sensor 14 in order to increase the control accuracy by outputting a duty signal so that the intake valve is closed to a predetermined angle. I do.

As described above, when the amount of air introduced into the engine 1 is reduced, the exhaust gas temperature rises. Therefore, the particulates collected in the trap 3 are reburned by the heat of the heated exhaust gas, and the trap 3 is regenerated. You.

(Problems to be Solved by the Invention) By the way, in such an apparatus, a predetermined time is set as a reproduction time, and when the time ends, it is considered that the trap has been completely reproduced.

However, even after the regeneration time, a part of the collected amount may remain unburned. In addition, the unburned amount fluctuates due to a difference in operating conditions.

For this reason, in the case where the regeneration timing is determined based on the collection amount history, an error corresponding to the remaining combustion occurs, and the regeneration timing may be too late. As a result, the trapping amount exceeds the limit, and when the regeneration is performed, the particulates burn rapidly and the trap is disadvantageously melted.

The present invention has been made in view of such conventional problems, and limits the differential pressure at a trapping amount at which traps do not melt due to combustion heat even if the trapped particulates burn. By determining the differential pressure in advance and grasping the amount of unburned trapped amount from the ratio between the differential pressure before and after the trap immediately after regeneration and the limit differential pressure, an error does not occur in the regeneration timing determination based on the collected amount history. It is an object of the present invention to provide a device which has been described.

(Means for Solving the Problems) As shown in FIG. 1, the present invention comprises a trap 53 for collecting particulates in exhaust gas and reburning the collected particulates when the temperature exceeds a regeneration temperature.
A device 54 for raising the temperature of the trap 53, sensors 55 and 56 for detecting the load Q and the rotational speed Ne of the engine, and a means for calculating the amount of collected particulates ΔPCT per unit time according to the detected values. 57, means 58 for accumulating the trapped amount ΔPCT at predetermined time intervals, means 59 for judging whether or not the regeneration time is reached based on the accumulated value SUM, and when the regeneration time comes, the temperature raising device 54 is operated. Means 60, a sensor 61 for detecting the pressure difference ΔP before and after the trap 53, means 62 for judging whether or not immediately after the regeneration, and a detection value for the pressure difference between before and after when it is determined that it is immediately after the regeneration. Means 63 for calculating the ratio of the predetermined limit differential pressure ΔPmax, means 64 for calculating the unburned trapped amount ZAN immediately after regeneration according to this ratio, and the integrated value SUM And means 65 for setting the initial value of.

(Operation) The ratio between the trapping differential pressure ΔP and the critical differential pressure ΔPmax immediately after the regeneration corresponds to the regeneration efficiency, and a large ratio means that the trapped amount that remains unburned immediately after the regeneration is large. Therefore, if the amount of collection is the same as before, the next regeneration time must be advanced.

In the present invention, since the unburned trapped amount ZAN is set as the initial value of the integrated value SUM, the next regeneration time comes earlier. The greater the amount of unburned trapped, the earlier the regeneration time.

(Embodiment) FIG. 2 is a system diagram of one embodiment of the present invention. In the drawing, reference numeral 6 denotes a normally-open butterfly type throttle valve provided in the intake passage 5, and a diaphragm actuator 8 is connected to the intake throttle valve 8.

A three-way solenoid valve 19 is interposed in a passage communicating the pressure chamber of the actuator 8 with a negative pressure source (for example, a negative pressure pump). A constant negative pressure is introduced instead of the atmospheric pressure, and the intake throttle valve 6 is closed to a certain angle. The actuator 8 and the solenoid valve 19 constitute an intake throttle valve driving device.

Similarly, a normally-open butterfly-type throttle valve 21 is provided in the exhaust passage 2 upstream of the trap 3, and a normally-closed butterfly-type bypass valve 25 is provided in a passage 24 that bypasses the throttle valve 21 and the trap 3 from upstream of the exhaust throttle valve 21. Are respectively provided. An exhaust throttle valve driving device includes a diaphragm actuator 22 connected to the exhaust throttle valve 21 and a three-way solenoid valve 23, and a bypass valve.
A diaphragm actuator 26 connected to 25 and a three-way solenoid valve 27 constitute a bypass valve driving device.

A heater 29 is provided near the upstream of the trap 3 and is heated when receiving a communication signal from the control unit 41.

31 is a semiconductor type pressure sensor which is a differential pressure Δ
Detect P. Reference numeral 32 denotes a temperature sensor composed of a thermocouple, which detects an inlet temperature T _IN of the trap 3. Reference numeral 34 denotes a sensor (crank angle sensor) for detecting the rotation speed Ne of the engine 1, reference numeral 35 denotes a sensor composed of a potentiometer for detecting the accelerator lever opening (engine load) Q, and reference numeral 36 denotes a sensor for detecting the cooling water temperature Tw.

Signals from these sensors are input to a control unit 41 composed of a microcomputer.
An ON / OFF signal is output to the three three-way solenoid valves 19, 23 and 27, and an energization signal is output to the heater 29, respectively.

FIG. 3 shows a routine for reproducing a trap.

In S1, the engine speed Ne, engine load Q, cooling water temperature Tw,
The trap inlet temperature T _IN , the differential pressure ΔP before and after the trap, and the travel distance KM from the integrator are read.

S2 is a part that performs the function of the reproduction timing determination means 59 in FIG. 1 together with S7 and S8 described later. In S2, it is checked whether or not it is the regeneration time, and if it is determined that it is not the regeneration time, the process proceeds to S3. In this case, the reproduction time is determined based on the value of the flag F1, and F1 = 0 when the reproduction time is not reached.

S3 is a part that fulfills the function of the immediately after reproduction determination means 62 in FIG. 1 together with S18 and S26 to be described later. In S3, it is determined whether or not it is immediately after the reproduction. If not, the process proceeds to S4. Here, the value immediately after the reproduction is determined based on the value of the flag F2, and F2 = 0 when the reproduction is not immediately after.

In S4, it is determined whether or not it is time to accumulate the particulate collection amount. In this case, the integration time comes at a fixed time interval ΔT ₁ (for example, several seconds).

S5, in sections that act trapping amount calculating means 57 of FIG. 1, where is obtained by performing a map search for particulate collection amount ΔPCT of [Delta] T ₁ per (per unit time).

 In S6, ΔPCT is integrated for each unit time by the following equation.

SUM = SUM + ΔPCT... That is, ΔPCT is added to SUM at each integration time, and SUM represents the integrated value of ΔPCT. Steps S6 and S4 are parts that fulfill the function of the trapping amount integrating means 58 in FIG.

Note that the initial value of SUM is not zero, but a value set in S25 described later.

FIG. 4 shows the contents of the map of ΔPCT, which is a positive maximum in a low-load low-speed range and a negative value in a high-load high-speed range. The reason for setting the negative value is that the region where the map value is negative is the self-regeneration region, and since the exhaust temperature is high in this region, part of the collected particulates will not be burned, so the amount of the collected amount will be reduced. This is because it is necessary to subtract as an integrated value.

Note that ΔPCT increases due to engine durability deterioration as the total mileage becomes longer.
The travel distance correction may be performed on ΔPCT in step 5.

In S7, by comparing the integrated value SUM with a predetermined reference value (constant value), if SUM ≧ reference value, it is determined that it is time to reproduce, and the process proceeds to S8.

At S8, a reproduction timing flag F1 is set (F1 = 1).
That is, F1 = 1 means that it is in the reproduction time.

In S9, the exhaust and intake throttle valves 21 and 6, the bypass valve 25,
On the other hand, if F1 = 1 in S2, it is determined that the regeneration time has come, and the process proceeds to S10 to S18, where the three-way solenoid valve 19, Instructions are given to 23, 27 and heater 29. In other words, S10 to S18 are portions that fulfill the function of the operating means 60 in FIG.

At S10, it is determined whether the trap inlet temperature (exhaust gas temperature) T _IN is equal to or higher than the regeneration temperature T ₁ (for example, 400 ° C.), and T _IN
Without having to do anything if ≧ T _1, the process proceeds to S12 because the trap 3 is played.

Conversely, if T _IN <T ₁ , the process proceeds to S11, and it is determined whether the cooling water temperature Tw is equal to or higher than a predetermined value (for example, 50 ° C.). If so, the process proceeds to S13.

In S13, both exhaust and intake are throttled and heater 29 is turned on
To With these operations, the exhaust gas temperature is raised to the regeneration temperature, and the regeneration of the trap 3 is performed.

If Tw is lower than the predetermined value in S11, the process proceeds to S14, where both throttle valves
Open all 21, 21 and bypass valve 25. The reason that both throttle valves 21 and 6 are open is that when the water temperature is low before warm-up, the exhaust temperature is lower than after the warm-up is completed, so it is not possible to regenerate the trap. This is because, at a low water temperature where combustion is not stable, the engine is misfired, the operability is deteriorated, and the particulate matter increases due to the misfire. The reason why the bypass valve 25 is opened is to prevent the trap 3 from being excessively cooled by cold exhaust.

In S15 and S16, the reproduction time is counted, and the process proceeds to S17. S17
Then, the counted playback time is set to a predetermined time (for example, 10
If the predetermined time has elapsed, it is determined that the reproduction has been completed, and the process proceeds to S18.

In S18, the flag F2 indicating immediately after the reproduction is set (F2 = 1), and in S19, the data used for judging the reproduction time is deleted.

 When the flag F2 is set, the process proceeds from S3 to S20 and thereafter.

In S20, it is determined whether the sample condition is ΔP, and if this condition is satisfied, the process proceeds to S21. In this case, the sample condition is a case where the engine load Q and the rotational speed Ne are each equal to or more than a predetermined value, and all the intervals from the previous sample exceed a predetermined value (for example, 20 seconds).

In S21, ΔP is stored in the memory, and the temperature is corrected by the following equation.

ΔP = ΔP × K _{TW In the} equation, K _TW is a water temperature correction coefficient. The map of this K _TW is shown in FIG. This is because ΔP becomes small in a cold state because the exhaust gas temperature is low, so that it is necessary to consider ΔP large at low temperatures. This improves the measurement accuracy of ΔP. Note that the correction may be made according to the exhaust gas temperature instead of the cooling water temperature Tw.

S22 is a part which performs the functions of the ratio calculating means 63 and the unburned trapped amount calculating means 64 in FIG. 1. Here, the ratio between ΔP and the limit differential pressure ΔPmax is calculated, and from this ratio ΔP / ΔPmax, The remaining collection amount ZAN is obtained by searching the map. FIG. 7 shows the map characteristics of ZAN. It is determined that the higher the ratio, the more unburned, the higher the ratio, the higher the ZAN value. The obtained ZAN is stored in the memory.

Note that ΔPmax is a differential pressure at a trapping amount at which the trap does not melt due to the heat of combustion even if the particulate matter trapped in the trap burns, and is set in advance so that the trap does not melt during regeneration. ing.

Specifically, ΔPmax differs depending on the operating conditions,
It is determined by searching the map shown in FIG. For example, in FIG. 6, ΔPmax increases as the rotation speed Ne increases. This is for the following reason. Even if the trapped amount of particulates is constant, the differential pressure increases as the flow rate of exhaust gas passing through the trap increases. That is, an increase in the number of revolutions means an increase in the flow rate of the exhaust gas. Therefore, ΔPmax is set to be larger as the number of revolutions increases.

In FIG. 6, ΔPm
ax is changing. This is for the following reason. An increase in load means an increase in the amount of fuel supplied to the engine. As the amount of fuel increases, the temperature of the exhaust also increases. In a diesel engine, the change in the amount of air taken into the engine is very small depending on the load, but when the load is high, the exhaust gas temperature becomes high, so that the exhaust flow rate apparently increases and the differential pressure increases. Therefore, ΔPmax increases as the load increases.

In S23, it is determined whether the number of ZAN data obtained every time the sample condition in S20 is satisfied has reached a predetermined number (for example, 4).

In S24, statistical processing is performed on data of a predetermined number of ZANs.
The statistical processing in this case is a weighted average and the first data ZA
N ₁ is stored in the memory of the same name by the following equation.

ZAN ₁ = ZAN ₁ ... Next, a weighted average value is calculated from the value ZAN ₁ stored in this memory and the second data ZAN ₂ by the following equation, and this is stored in the memory having the same name.

ZAN ₂ = (3ZAN ₁ + ZAN ₂ ) / 4 In the same manner, a weighted average value is sequentially obtained by the following equation.

ZAN ₃ = (3ZAN ₂ + ZAN ₃ ) / 4... ZAN ₄ = (3ZAN ₃ + ZAN ₄ ) / 4... The value finally stored in the memory ZAN ₄ is the value to be obtained.

S25 performs the function of the initial value setting means 65 in FIG. 1, and stores the value of ZAN ₄ as the initial value of SUM.

In S26, the flag F2 indicating immediately after the reproduction is cleared (F2 = 0).

 Here, the operation of this example will be described.

In this example, the efficiency of regeneration is grasped from the ratio between the trapping differential pressure ΔP and the critical differential pressure ΔPmax immediately after regeneration, and the trapped amount ZAN that remains unburned immediately after regeneration is calculated according to the regeneration efficiency. Then, using this unburned collection amount ZAN as an initial value of the integrated SUM, it is determined when the next regeneration should be performed.

Therefore, if the particulate remains unburned after the lapse of the reproduction time, the reproduction time comes earlier. Moreover, the regeneration time becomes earlier as the amount of unburned material increases. In other words, the regeneration time is appropriate regardless of the remaining amount of combustion.

As a result, it is possible to prevent a situation where the trapping amount exceeds the limit during the next regeneration due to the regeneration timing being too late and the particulates are rapidly burned and the trap is melted when the regeneration is performed.

Further, the control is simpler than that in which the regeneration time is determined by using both the pressure and the operation history.

(Effects of the Invention) In the present invention, the amount of unburned residue immediately after regeneration is calculated according to the ratio between the differential pressure across the trap immediately after regeneration and the critical differential pressure, so that the particulates trapped in the trap are calculated. However, even if the garbage remains unburned immediately after the regeneration, the regeneration time can be advanced by that much, and the melting of the trap can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims of the present invention, FIG. 2 is a system diagram of one embodiment, FIG. 3 is a flow chart for explaining a braking operation of this embodiment, and FIGS. FIG. 8 is a characteristic diagram of ΔPCT, K _TW , ΔPmax and ZAN of the example, and FIG. 8 is a system diagram of a conventional example. 2 ... exhaust passage, 5 ... intake passage, 6 ... intake throttle valve, 8 ... diaphragm actuator, 19 ... three-way solenoid valve, 21 ... exhaust throttle valve, 22 ... diaphragm actuator, 23 ... three-way solenoid valve, 24 ... bypass passage, 25 ... bypass valve, 26 ... diaphragm actuator, 27 ... three-way solenoid valve, 29 ... heater,
31: pressure sensor, 32: trap inlet temperature sensor, 34: crank angle sensor (engine speed sensor), 35: accelerator lever opening sensor (engine load sensor), 41: control unit, 53: trap, 54: temperature rise Equipment, 55 ...
Engine load sensor, 56… Engine speed sensor, 57…
Collection amount calculation means, 58: Collection amount integration means, 59: Regeneration timing determination means, 60: Activation means, 61: Differential pressure sensor, 62: Regeneration immediately determination means, 63: Ratio calculation means, 64: Remaining unburned Collection amount calculation means, 65: Initial value setting means.

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Nobukazu Kanesa 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. (56) References JP-A-60-111013 (JP, A) JP-A-1 163412 (JP, A) JP-A-3-18614 (JP, A)

Claims (1)

(57) [Claims] 1. A trap for collecting particulates in exhaust gas and reburning the collected particulates when the temperature exceeds a regeneration temperature, a device for raising the temperature of the trap, and a load and rotation speed of an engine. A sensor for detecting, a means for calculating a particulate collection amount per unit time according to the detected values, a means for integrating the collected amount at predetermined time intervals, and whether a regeneration time is determined based on the integrated value. Means for determining whether or not the regeneration time is reached, means for operating the temperature raising device, a sensor for detecting a differential pressure across the trap, means for determining whether or not immediately after regeneration, Means for calculating the ratio between the detected value of the front-rear differential pressure and a predetermined limit differential pressure, and determining the amount of unburned residue immediately after regeneration according to the ratio. An engine exhaust gas purification apparatus, comprising: means for calculating; and means for setting the unburned trapped amount as an initial value of the integrated value.