JP2582972B2 - Exhaust recirculation system for diesel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an exhaust gas recirculation system for a diesel engine.

[0002]

2. Description of the Related Art An exhaust gas recirculation device provided in a diesel engine recirculates a part of exhaust gas, which is inactive according to an operation state, to an intake system, thereby lowering the maximum temperature during combustion to generate NOx. (See JP-A-58-72665, JP-A-61-55358, and JP-A-61-205345).

On the other hand, there is a diesel engine provided with a trap having a heat-resistant filter structure in an exhaust passage to collect particulates such as carbon particles contained in exhaust gas. A regenerator for burning at a predetermined time is provided to prevent the exhaust pressure from excessively increasing due to the accumulation of particulates.

[0004] As this trap regeneration device, for example, one disclosed in Japanese Patent Application Laid-Open No. 58-51235 has an intake throttle valve interposed in an intake passage so as to reduce the opening of the intake throttle valve at a predetermined time. The temperature of the exhaust gas rises due to a decrease in the intake air amount, and the particulate matter collected in the trap is reburned by the heat of the exhaust gas.

[0005]

However, in a diesel engine equipped with this type of trap regeneration device,
If the deceleration operation is performed during regeneration of the trap, the supply of fuel is stopped, so that the temperature of the exhaust gas flowing out of the cylinder to the exhaust passage without combustion is reduced, and the temperature of the trap is reduced to enable regeneration. The possibility of disappearing was considered.

The present invention has been made in view of the above problems, and has as its object to prevent the temperature of the trap from lowering during deceleration.

[0007]

According to a first aspect of the present invention, as shown in FIG. 1, an exhaust gas recirculation passage 3 that connects an intake passage 1 and an exhaust gas passage 2 of an engine, and is interposed in the exhaust gas recirculation passage 3. An exhaust gas recirculation control valve 4, an intake throttle valve 8 interposed in the intake passage 2 upstream of the junction of the exhaust gas recirculation passage 3, a means 91 for detecting operating conditions of the engine, and the detected operating conditions And a means 92 for controlling the amount of exhaust gas recirculation via the exhaust gas recirculation control valve 4 and the intake throttle valve 8 based on the exhaust gas recirculation control valve 4 and the exhaust gas recirculation device. Trap 9
Regenerating means 93 for reducing the opening of the intake throttle valve 8 during regeneration of the trap 9 based on the detected operating conditions, and determining the opening of the intake throttle valve 8 by determining the time of deceleration operation in which fuel supply is stopped. And a deceleration control means 94 for fully opening the exhaust gas recirculation control valve 4.

As shown in FIG. 2, the second invention has an exhaust throttle valve 55 interposed upstream of the trap 9 in the exhaust passage 2, and the deceleration control means 94 stops the fuel supply. The throttle operation of the intake throttle valve 8 is determined.
, The exhaust gas recirculation control valve 4 is fully opened, and the opening of the exhaust throttle valve 55 is reduced.

[0009]

When the trap 9 is not regenerated, the exhaust gas recirculation control means 9
The opening degrees of the intake throttle valve 8 and the exhaust gas recirculation control valve 4 are controlled by the control value calculated in step 2, so that the amount of exhaust gas recirculated according to the engine operating conditions is obtained, and the emission of NOx is suppressed.

When the trap 9 is regenerated, the opening degree of the intake throttle valve 8 is reduced by the regenerating means 93, and the amount of intake air is reduced to raise the temperature of the exhaust gas. To reburn.

When the deceleration control means 94 determines that the fuel supply is stopped during regeneration, the exhaust gas recirculation control valve 4 is fully opened, and the exhaust gas recirculation control valve 4 is fully opened. The amount of exhaust gas recirculated to the exhaust gas is increased to prevent the exhaust gas whose temperature decreases with the stop of fuel supply from being introduced into the trap 9, and the exhaust gas is circulated through the exhaust gas recirculation passage 3 during deceleration. By doing so, a decrease in the temperature of the exhaust gas is suppressed, and the regeneration of the trap 9 is promoted.

Further, in the second aspect, the opening of the exhaust throttle valve 55 is also reduced during the deceleration operation, so that the amount of exhaust gas introduced into the trap 9 can be reliably reduced.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 3 schematically shows an exhaust gas recirculation device provided in a diesel engine with a supercharger. A trap 9 for collecting particulates is provided downstream of the exhaust passage 2, and a trap 9 is provided in the intake passage 1. An intake throttle valve 8 is interposed upstream of the junction of the exhaust gas recirculation passage 3. The intake throttle valve 8 is driven to open and close according to engine operating conditions by a signal from the control unit 60 via a step motor 31.

An exhaust gas recirculation passage 3 connecting the exhaust gas passage 2 and the intake air passage 1 is provided, and a diaphragm type exhaust gas recirculation control valve 4 is interposed in the exhaust gas recirculation passage 3. A negative pressure passage 5 is connected to the negative pressure chamber 46 of the exhaust gas recirculation control valve 4. A negative pressure from a vacuum tank (not shown) is introduced through the orifice 35, and one end of the negative pressure passage 5 is connected to the negative pressure passage 5. The exhaust gas recirculation control valve 4 is connected to the control valve 6, and the negative pressure control valve 6 appropriately dilutes the signal negative pressure.
Is controlled.

The exhaust gas recirculation control valve 4 has a valve body 41 that can be seated on a valve seat 42 formed in the middle of the exhaust gas recirculation passage 3 and is disposed on the exhaust passage 2 side of the valve seat 42, that is, on the upstream side of the exhaust gas recirculation passage 3. Is done. The valve body 42 has a conical seat surface 42a.
On the other hand, a conical seating surface 41 a is also formed on the valve body 41. As a result, even under operating conditions in which the exhaust pressure of the exhaust passage 2 rises significantly, the valve body 41 and the valve seat 42
The opening area of the gap 40 defined therebetween can be accurately controlled.

The exhaust gas recirculation control valve 4 has a valve body 41
3 and is connected to the diaphragm 45. A negative pressure chamber 46 and a back pressure chamber 47 are defined by the diaphragm 45 interposed in the casing 44. In this embodiment, atmospheric pressure is introduced into the back pressure chamber 47 through a hole 49.

A predetermined spring load is applied to the diaphragm 45 by a spring 48 interposed in a negative pressure chamber 46 in a compressed state, and the valve body 41 is urged in the valve opening direction. That is, as the signal negative pressure guided to the negative pressure chamber 46 increases, the diaphragm 45 draws the valve body 41 to the valve seat 42 while compressing the spring 48, and eventually seats the valve body 41.

As shown in FIG. 3, the negative pressure control valve 6 has a lower diaphragm valve portion 32 for performing basic negative pressure control according to the exhaust pressure, and further changes the control characteristics to desired characteristics. And a step motor 33 on the upper side.

The diaphragm valve portion 32 includes a casing 34
The diaphragm 35 disposed therein has a main body, and the diaphragm 35 defines a discharge chamber 36 and a dilution chamber 37.

An orifice 30 is interposed between the exhaust gas recirculation passage 3 and the exhaust gas recirculation control valve 4 on the intake passage 1 side, that is, downstream of the exhaust gas recirculation control valve 4, and the pressure therebetween is introduced into the exhaust pressure chamber 36.

A predetermined spring load is applied to the diaphragm 35 by a spring 38 which is interposed in a compressed state in the exhaust pressure chamber 36, and the valve body 3 is provided on the dilution chamber 37 side.
9 are attached.

The dilution chamber 37 is connected to the intake throttle valve 8 through the passage 7.
A port 10 is opened in the dilution chamber 37 so as to face the valve 39, and the negative pressure passage 5 is connected to the port 10. Thereby, the dilution chamber 37
Is introduced from the upstream side of the intake throttle valve 8 through the passage 7, the diaphragm 35 is pushed up more than necessary even if the pressure introduced into the exhaust pressure chamber 36 increases at the time of high supercharging. Can be prevented.

On the other hand, the step motor 33 includes a pair of stators 13 fixed to the casing 12 and a bearing 1.
And a rotor 16 rotatably supported via four and fourteen. The step motor 33 is provided with the stator 13
The rotation angle is controlled stepwise by applying a predetermined pulse signal from the control unit 60 to the coil.

The rotor 16 has a cylindrical shape, and a female screw 17 is formed on the inner peripheral surface thereof. 18 is a guide member fixed to the inner peripheral side of the bearing 15 of the casing 12, 19
Is a plunger guided by the guide member 18 so as to be non-rotatable and slidable in the axial direction. The plunger 19 has a male screw 20 formed at an upper portion thereof, which is screwed to the female screw 17 of the rotor 16. ing. That is,
The plunger 19 is configured to linearly move in the axial direction according to the rotation angle of the step motor 33. A disc-shaped spring seat 21 is provided at the lower end of the plunger 19.
Are fixed by a lock nut 21a.

An intermediate member 22 transmits the operation of the plunger 19 to the diaphragm 35. This intermediate member 2
2 includes a disc-shaped spring seat portion 22a and a push rod portion 22b extending from one side of the spring seat portion 22a in the axial direction of the plunger 19, and the push rod portion 22b is provided in the dilution chamber 37 of the casing 34. It is disposed so as to penetrate the upper surface portion. An auxiliary spring 23 is interposed between the spring seat portion 22a and the spring seat 21 in a compressed state, whereby the push rod portion 22b of the intermediate member 22 is pressed against the upper retainer 24 of the diaphragm 35. .

The stepping motor 33 makes one rotation in four steps. In this embodiment, the operation range is defined in 32 steps from 0 to 32. FIG. 4 shows a state where the number of steps of the step motor 33 is at an appropriate intermediate value, and the tip of the plunger 19 and the intermediate member 22 are separated to some extent. In this state, a differential pressure between the exhaust pressure and the intake pressure acts on the diaphragm 35, and is urged in the closing direction by the set spring 38 and urged in the opening direction by the auxiliary spring 23. Therefore, the port 10 is opened when the differential pressure is lower than the pressure (valve opening pressure) determined by the spring loads of the springs 38 and 23, and when the differential pressure is higher than that, the port 10 is opened.
Is closed.

Here, since the spring load of the auxiliary spring 23 changes according to the position of the spring seat 21 supporting the upper end thereof, when the step motor 33 rotates and the spring seat 21 moves upward, the valve is opened. The pressure decreases, and conversely, when the spring seat 21 moves downward, the valve opening pressure increases. That is, the step motor 33
The opening / closing characteristics of the port 10 can be corrected by the rotation angle control described above, whereby the final exhaust gas recirculation amount characteristics can be set to desired characteristics. FIG. 5 illustrates the characteristics of the valve opening pressure obtained corresponding to the number of steps of the step motor 33.

As shown in the block diagram of FIG. 6, the control unit 60 includes a CPU 61, a RAM 63, a ROM 62,
The I / O 64 includes a microcomputer including an engine speed sensor 65, an accelerator opening sensor 66, an intake air temperature sensor 67, an exhaust air temperature sensor 68, and an intake air pressure. Signals from the sensor 69, the water temperature sensor 70, and the fuel temperature sensor 71 are input. The CPU 61 fetches information from the I / O 64 according to a program stored in the ROM 62, performs arithmetic processing, and controls a fuel injection pump 73 for controlling a fuel injection timing and an injection amount, an intake throttle valve 8 for controlling an exhaust gas recirculation amount, a negative pressure. Data, which is a control amount for controlling the control valve 6, is set in the I / O 64. The RAM 63 is a CPU
61 is used to temporarily save data related to the arithmetic processing. The I / O 64 controls the fuel injection pump 73, the intake throttle valve 8, and the negative pressure control valve 6 based on the data output from the CPU 61.

The CPU 61 controls the amount of exhaust gas recirculation via the exhaust gas recirculation control valve 4 and the intake throttle valve 8 based on the detected operating conditions, while reducing the opening of the intake throttle valve 8 during regeneration of the trap 9. The deceleration operation state in which the fuel supply is stopped is determined, the opening degree of the intake throttle valve 8 is reduced, and the exhaust recirculation control valve 4 is fully opened.

Next, the control operation of the CPU 61 will be described with reference to FIG.
This will be described with reference to the flowchart of FIG.

First, at step 101, the engine speed N
e, various data of operating conditions such as accelerator opening Acc and cooling water temperature Tw are read.

Next, based on the data read in step 102, the basic injection amount QN and the basic injection timing ITN are shown in FIGS.
Is calculated according to the control map shown in FIG.

Subsequently, in step 103, it is determined whether or not the trap 9 is being reproduced. The control for determining the regeneration time of the trap 9 is, for example, filed by the present applicant as Japanese Patent Application No. 1-339044, and is based on engine load, rotation speed, mileage, mileage, fuel consumption, and the like. The trapping amount is calculated by calculating the trapping amount of the particulates or by detecting the differential pressure across the trap 9 to determine that the trapping amount of the particulates becomes a predetermined value or more.
Playback.

If it is determined in step 103 that the regeneration is not being performed, the routine proceeds to step 104, in which the basic opening degree WN of the intake throttle valve 8 and the basic step number STEP of the step motor 33 are shown in FIGS. The calculation is performed in accordance with the control map shown in FIG. In this way, the throttle valve 8 is throttled according to the engine speed Ne or the fuel injection amount Q according to the control map shown in FIG. 10, and the step number STEP of the step motor 33 is changed according to the control map shown in FIG. Ne
Alternatively, the exhaust gas recirculation control valve 4 is increased in accordance with the fuel injection amount Q.
Is determined, the exhaust gas recirculation amount corresponding to the engine operating conditions can be obtained. This constitutes the exhaust gas recirculation amount control means 92 of FIG.

If it is determined in step 103 that regeneration is being performed, it is determined in step 105 whether or not the vehicle is in a deceleration state in which fuel cut is performed.

If it is determined in step 105 that the fuel cut is not being performed at the time of deceleration, the routine proceeds to step 106, in which the opening WS of the intake throttle valve 8 during regeneration, the number of steps STEP of the step motor 33, the intake throttle valve, 8 and the number of correction steps Δ of the step motor 33
STEP is calculated in accordance with the control maps of FIGS. 11, 12, 13, and 14, and the process proceeds to step 108.

As described above, at the time of regeneration, the opening degree of the intake throttle valve 8 is changed to the engine speed Ne according to the control map of FIG.
Alternatively, the exhaust air temperature is raised by reducing the intake air amount by being throttled according to the fuel injection amount Q, and the particulates collected in the trap 9 are reburned. Thus, the reproducing means 93 of FIG. 1 is configured.

At the time of this regeneration, the number of steps STEP of the step motor 33 is reduced according to the engine speed Ne or the fuel injection amount Q in accordance with the control map of FIG. 11, and the opening degree of the exhaust gas recirculation control valve 4 is determined. Then, exhaust gas recirculation is performed, and the amount of NOx emission during regeneration can be reduced.

At this time, the correction value ΔSTEP is determined according to the control map shown in FIG.
e or the fuel injection amount Q, the opening degree of the exhaust gas recirculation control valve 4 decreases and the exhaust gas recirculation passage 3
Is relatively small. Further, according to the control map of FIG. 13, the opening degree of the intake throttle valve 8 is controlled to be further reduced as the fuel injection charge Q is smaller, so that the intake air amount is also reduced. As a result, since the exhaust gas recirculation amount and the intake air amount decrease, the total intake air amount decreases, the exhaust temperature can be sufficiently increased, and the particulate discharge amount during regeneration can be reduced.

If it is determined in step 105 that the vehicle is being decelerated so that the fuel cut is performed, the routine proceeds to step 107, where the opening W of the intake throttle valve 8 is set to the opening W during regeneration shown in FIG.
S is set to the minimum value Wmin, and the number of steps STEP of the step motor 33 is set to 0. This constitutes the deceleration control means 94 of FIG.

At the time of the regeneration in which the fuel cut is performed, the opening degree of the intake throttle valve 8 is reduced to the minimum value Wmin, thereby suppressing the inflow of fresh air and setting the step number STEP of the step motor 33 to 0. As a result, the negative pressure control valve 6 is opened to reduce the signal negative pressure, and the exhaust gas recirculation control valve 4 is fully opened. As a result, the amount of exhaust gas recirculated from the exhaust passage 2 to the intake passage 1 through the exhaust gas recirculation passage 3 is maximized, and the exhaust gas whose temperature is reduced due to the fuel cut during deceleration is introduced into the trap 9. The exhaust gas is circulated through the exhaust gas recirculation passage 3 at the time of deceleration, whereby a decrease in the temperature of the exhaust gas is suppressed, and the particulates collected in the trap 9 are reburned. As a result, clogging and melting of the trap 9 can be prevented.

Finally, at step 108, the injection amount Q, the injection timing IT, the opening W of the intake throttle valve 8, the step motor 33
Is calculated, stored in a predetermined address, and the processing ends.

Next, in another embodiment shown in FIG. 15, an exhaust throttle valve 55 is provided upstream of the trap 9 in the exhaust passage 2.

The control unit 60 determines that the deceleration operation is performed when the trap 9 is regenerated, and
Is fully opened and the opening degree of the exhaust throttle valve 55 is throttled through an actuator (not shown), whereby the amount of exhaust gas introduced into the trap 9 is reliably reduced, and the particulates trapped in the trap 9 are reduced. Reburn.

[0046]

As described above, according to the present invention, the exhaust gas recirculation control valve is fully opened by judging the time of deceleration at which the fuel cut is performed at the time of trap regeneration, and by maximizing the intake throttle valve and fully opening the exhaust gas recirculation control valve. Is circulated through the exhaust gas recirculation passage to prevent the exhaust gas whose temperature decreases with the fuel cut during deceleration from being introduced into the trap, thereby preventing the temperature of the trap from decreasing during deceleration, and Can be regenerated, and clogging and melting of the trap can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims of the first invention.

FIG. 2 is a diagram corresponding to a claim of the second invention.

FIG. 3 is a schematic configuration diagram of an exhaust gas recirculation device showing an embodiment of the present invention.

FIG. 4 is a sectional view of the same negative pressure control valve.

FIG. 5 is a characteristic diagram of the valve opening pressure of the negative pressure control valve.

FIG. 6 is a block diagram showing details of a control unit.

FIG. 7 is a flowchart of the exhaust gas recirculation amount control.

FIG. 8 is a control map of the fuel injection amount.

FIG. 9 is a control map of the fuel injection timing.

FIG. 10 is also a control map of an intake throttle valve opening degree.

FIG. 11 is a control map of the number of steps of the step motor.

FIG. 12 is a control map of the intake throttle valve opening during trap regeneration.

FIG. 13 is a control map of the intake throttle valve correction opening during trap regeneration.

FIG. 14 is a control map of the number of correction steps of the step motor during trap regeneration.

FIG. 15 is a schematic configuration diagram of an exhaust gas recirculation device showing another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Intake passage 2 Exhaust passage 3 Exhaust recirculation passage 4 Exhaust recirculation control valve 8 Intake throttle valve 9 Trap 55 Exhaust throttle valve 92 Exhaust recirculation amount control means 93 Regeneration means 94 Deceleration control means

Claims (2)

(57) [Claims] 1. An exhaust gas recirculation passage connecting an intake passage and an exhaust gas passage of an engine, an exhaust gas recirculation control valve interposed in the exhaust gas recirculation passage, and an exhaust gas recirculation control valve disposed in the exhaust gas recirculation passage. A diesel engine comprising: an interposed intake throttle valve; means for detecting operating conditions of the engine; and means for controlling the amount of exhaust gas recirculation via the exhaust gas recirculation control valve and the intake throttle valve based on the detected operating conditions. In the exhaust gas recirculation device, a trap interposed in the exhaust passage for collecting particulates in the exhaust gas, and a regeneration means for reducing the opening of the intake throttle valve during regeneration of the trap based on the detected operating conditions, A diesel engine comprising: a deceleration control unit that determines a deceleration operation state in which fuel supply is stopped, reduces an opening of the intake throttle valve, and fully opens the exhaust recirculation control valve. Seki's exhaust gas recirculation system. 2. An exhaust throttle valve interposed upstream of the trap in the exhaust passage, wherein the deceleration control means determines a deceleration operation state in which fuel supply is stopped to open the intake throttle valve. 2. The exhaust gas recirculation device for a diesel engine according to claim 1, wherein the exhaust gas recirculation control valve is fully opened while the exhaust gas recirculation control valve is fully opened, and the opening degree of the exhaust throttle valve is reduced.