JP2590579B2 - Diesel engine exhaust gas recirculation system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust gas recirculation device for a diesel engine equipped with an exhaust brake.

[Conventional technology]

2. Description of the Related Art There has been proposed an engine in which an exhaust brake device is provided in an exhaust system of an internal combustion engine and a strong engine braking performance is exhibited by operating the exhaust brake device during deceleration operation. The exhaust gas recirculation device includes an on-off valve arranged in an exhaust system and an actuator for driving the on-off valve, and the on-off valve is normally in an open position,
The actuator closes the on-off valve during the deceleration operation required for engine braking.

On the other hand, there is an engine provided with an exhaust gas recirculation (EGR) device to reduce the amount of nitrogen oxide components emitted from a diesel engine. In a system in which this exhaust gas recirculation device is used in combination with an exhaust brake device, the exhaust gas recirculation operation is prohibited during the operation of the exhaust brake. For example, see Japanese Utility Model Laid-Open No. 63-79463. This is because if the exhaust gas is recirculated during the operation of the exhaust brake, the effectiveness of the exhaust brake deteriorates. In the above system, when the exhaust brake is released, the operation returns to the exhaust gas recirculation operation, and the entire amount of exhaust gas is immediately recirculated.

[Problems to be solved by the invention]

In the related art, there is a problem that a large amount of black smoke is easily discharged immediately after the exhaust gas recirculation operation is temporarily prohibited due to the exhaust brake, and then immediately after the exhaust brake is released. This is because the exhaust pressure is increased because the exhaust system is closed during the operation of the exhaust brake, and the so-called internal EGR amount increases. When the exhaust gas recirculation operation is resumed by releasing the exhaust brake, the internal
The sum of the amount of exhaust gas by the EGR and the amount of recirculated exhaust gas by the original exhaust gas recirculation operation is the total amount of recirculated exhaust gas, and the EGR amount is excessive. Therefore, the result of observing the generation of black smoke is obtained.

It is an object of the present invention to suppress the generation of black smoke when the exhaust brake is released in a diesel engine using both an exhaust brake and exhaust gas recirculation.

[Means for solving the problem]

The exhaust gas recirculation device for a diesel engine according to the present invention includes:
As shown in FIG. 1, an exhaust gas recirculation passage A connecting an exhaust system and an intake system of a diesel engine, an exhaust gas recirculation control valve B provided in the exhaust gas recirculation passage, and an exhaust brake device C An exhaust brake operating means D for controlling the operation of the exhaust brake during a predetermined operation and closing the exhaust gas recirculation control valve when the exhaust brake is operating, and an exhaust detecting means for detecting the time of switching from the operation of the exhaust brake to the release. Exhaust of a diesel engine comprising a brake release detection means E and a recirculation operation control means F for temporarily prohibiting the exhaust gas recirculation in total or temporarily increasing the exhaust gas recirculation amount to a target value when the exhaust brake release is detected. A gas recirculation device.

[Action]

The exhaust brake operating means D operates the exhaust brake at the time of a predetermined operation requiring engine braking. At the same time as the operation of the exhaust brake, the exhaust gas recirculation control valve B is closed, and the exhaust gas recirculation is stopped.

The exhaust brake release time detecting means E detects when the exhaust brake operation is released.

When the release of the exhaust brake is detected, the exhaust gas recirculation operation control means F temporarily prohibits all exhaust gas recirculation or temporarily increases the exhaust gas recirculation amount to a target value.

〔Example〕

2 and 3, reference numeral 10 denotes an engine body,
An intake pipe 12 and an exhaust pipe 14 are connected. The exhaust pipe 14 is connected to an exhaust brake device 16 and a particulate trapper 18 (or an exhaust gas purifying device such as a catalytic converter). The exhaust brake device 16 includes a main body 20 through which exhaust gas flows.
, An on-off valve 22, and a negative pressure actuator 24 for driving the on-off valve 22. One end of a lever 26 is fixed to a valve shaft of the on-off valve 22, and the other end of the lever 26 is connected to a diaphragm 30 of an actuator 24 via a rod 28. Spring 32
Urges the diaphragm 30 downward, and this downward movement is transmitted to the lever 26 via the rod 28, and the on-off valve 22 is normally in the fully open position in FIG. The lower diaphragm chamber 34 of the diaphragm 30 is open to the atmosphere, and the upper diaphragm chamber 36 is connected to an electromagnetic three-way switching valve 40.
In the OFF state, the diaphragm chamber 36 is connected to the air filter 42 via the passage 41 in the OFF state, and to the negative pressure pump 48 of the diesel engine in the ON state. In this embodiment, the operation of the exhaust brake is performed when the exhaust brake operation switch 50 is turned on and the accelerator pedal 52 is released. The accelerator pedal switch 54 detects release of the accelerator pedal 52.

A fuel injection pump 60 is driven by the engine and pumps fuel for fuel injection to a fuel injection valve (not shown).

The exhaust gas recirculation passage 62 connects the exhaust pipe upstream of the exhaust brake device 16 and the intake pipe. Exhaust gas recirculation passage
An EGR valve 64 is provided on 62, and the EGR valve 64 has a valve body 66 and a valve body 66.
And a spring 70, which urges the diaphragm 68 so that the valve body 66 closes. When the electromagnetic three-way switching valve 72 is in the OFF state, the atmospheric pressure acts on the diaphragm 68, and the EGR valve 64 is in the closed position. When the switching valve 72 is ON, the diaphragm 68 is connected to the negative pressure pump 48, the diaphragm 68 is pulled against the spring 70 by the negative pressure, the valve body 66 is lifted, and the exhaust gas recirculation operation is performed. In this embodiment, as will be described later, the switching valve 72 is driven by a duty signal, and can take an arbitrary opening degree between fully closed and fully opened.

The control circuit 80 is configured as a microcomputer system, and controls an exhaust brake operation and an exhaust gas recirculation operation as described later. Various sensors are connected to the control circuit, first the load sensor 81 measures the load factor of the engine,
For example, the position of an adjusting lever that determines the fuel injection amount of the fuel injection pump 82 of the diesel engine is detected.
The engine speed sensor 84 detects an engine speed factor, and detects, for example, the speed of the rotation shaft of the fuel injection pump 82. The accelerator pedal switch 54 and the exhaust brake operation switch 50 are connected to a control circuit 80.

FIG. 3 and FIG. 4 are flowcharts schematically explaining the operation of the control circuit 80. FIG. 3 shows how the exhaust gas recirculation operation is performed. The routine of FIG. 3 can be executed in the main routine. Step 10
If it is 0, it is determined whether or not the exhaust brake setting mode is set, that is, whether or not the exhaust brake operation switch 50 is turned on. When not in the exhaust brake setting mode, that is, when the switch 50 is
When F, the flow goes to step 102, and the electromagnetic three-way switching valve 40 is turned off.
It is said. Therefore, the atmospheric pressure is introduced from the air filter 42 into the diaphragm chamber 36, the diaphragm 30 is driven downward by the spring 32, and the on-off valve 22 assumes the fully open position in FIG. Therefore, the exhaust brake operation is not performed.

Exhaust brake operating mode (Yes in step 100)
Step 104 when the accelerator pedal 52 is released
Proceeding to step 106, the electromagnetic three-way switching valve 40 is set to NO. Therefore, the negative pressure from the negative pressure pump 48 is introduced into the diaphragm chamber 36, and the diaphragm 30 is pressed against the spring 32.
Is driven upward in the figure, the on-off valve 22 assumes the fully closed position, and the exhaust brake operation is performed.

FIG. 4 shows an exhaust gas recirculation control routine, which can be executed at regular intervals (for example, every 20 milliseconds). Step 110 the engine speed NE is determined whether greater than a predetermined value NE _0, the engine load L in step 112 it is determined whether or not larger than the predetermined value L _0. NE
When> NE ₀ or when L> L ₀ , the high-speed, high-load range is an operation range in which the exhaust gas recirculation operation is not performed. ₀ is entered. Next, the routine proceeds to step 114, where the duty ratio Duty in the drive signal of the switching valve 72 is set to zero. Next, at step 116, a signal of Duty = 0 (that is, a continuous OFF signal) is applied from the control circuit 80 to the switching valve 72, and the EGR valve 64 is closed. Therefore, the EGR operation is not performed.

Low rotation L ≦ L ₀ in NE ≦ NE _0, the low load region is an operating region to re-circulation operating exhaust gas, the flow advances from step 110 to step 120, the current exhaust brake 16 is judged whether or not the operation . Step 12 if the exhaust brake is not operating
Proceeding to 2, it is determined whether or not the exhaust brake 16 was operated last time (that is, when this routine was executed 20 milliseconds ago).
If not the last in the exhaust brake operation proceeds from step 122 to step 124, the value C ≧ C ₀ of the counter is determined whether or not satisfied. Since there is a C = C ₀ at step 113, the process proceeds to step 126, the opening degree of the EGR valve 64, i.e., the duty ratio Duty in accordance with the EGR amount is calculated engine speed NE, the engine load L. That is, there is a map Map of the EGR amount according to the combination of the value of the engine speed and the value of the engine load, and the duty ratio Dut which is the EGR valve opening corresponding to the engine speed NE and the engine load L at that time.
y is calculated. In step 116, the duty ratio signal is output, and the EGR valve 64 turns the EGR valve according to the operating condition at that time.
You will get the amount.

When the accelerator pedal is released from the normal running state described above and the exhaust brake operation is started, the result in Step 120 becomes Yes, the process proceeds to Step 114 through Step 113, and the duty ratio in the operation pulse signal of the drive electromagnetic switching valve 72 of the EGR valve is changed. Duty =
Set to 0, EGR valve 64 is closed. That is, during the operation of the exhaust brake, the operation of the EGR device is canceled even if the rotation is low and the load is low, and the operation is originally in the EGR operation range.

When the exhaust brake is released from the state in which the exhaust brake is actuated, the process proceeds from step 120 to step 122, and the previous time (ie, when this routine is executed 20 milliseconds before this routine)
It is determined whether 16 has been activated. If the determination in step 122 is Yes, it means that it is time to switch from the operation of the exhaust brake to the release, and the process proceeds to step 128,
The counter C is cleared. This counter C monitors the elapsed time from the switching from the operation of the exhaust brake to the release. Next, to proceed to step 114, the exhaust gas recirculation operation is continued. That is, when the operation is switched from the exhaust brake operation to the release, the exhaust gas recirculation operation is not immediately restored even in the EGR region.

Then during execution of this routine, it is determined No in step 122, the process proceeds to step 124, it is determined whether or not has reached a value or a predetermined value C ₀ of the counter C. The size of the predetermined value C ₀ corresponds to the period when smoke enters the case of executing the exhaust gas recirculation of the total amount instantly from exhaust brake release. For C <C ₀ considered smoke generation period, the process proceeds to step 130, the counter C is incremented.
Next, the routine proceeds to step 114, where the EGR valve 64 is still basically in the exhaust gas recirculation operating condition, but the prohibition of the exhaust gas recirculation is continued.

When the counter value ≧ C _0, i.e., the time that also perform EGR in the total amount from the release of the exhaust brake does not look at the generation of the black smoke has passed, the process proceeds to the aforementioned step 126 from step 124,
The duty ratio becomes a map value, and exhaust gas recirculation of the entire amount is executed.

FIG. 5 is a timing chart for explaining the operation of the embodiment shown in FIGS. When the accelerator pedal is released (time t ₀ ), the exhaust brake is activated (A), and at the same time, the EGR valve 64 is fully closed (B). When the exhaust brake at time t ₁ is released, then the counter value C is gradually increased (d), EG
The R valve is kept fully closed. A predetermined time τ corresponding to C = C ₀
Has elapsed since the release of the exhaust brake (t ₁ ) (time
t ₂ ), the EGR valve returns to the original opening.

FIG. 6 shows an EGR valve control routine of the second embodiment. In this embodiment, steps 200 and 202 are provided instead of steps 113, 124, 128 and 130 in FIG. If not in the exhaust gas recirculation operating area (Yes in step 110 or step 112)
Or, in the exhaust gas recirculation operation area, while the exhaust brake is operating (Yes in step 120), the process proceeds to steps 114 and 116, and the EGR
The valve 64 is fully closed.

When the exhaust brake operation is released, first, at step 114, D
uty = 0 is set, and thereafter, the process proceeds from step 122 to step 200, where it is determined whether or not Duty ≧ Map (N, L). Map (N, L)
Is a duty ratio corresponding to a predetermined EGR amount at the engine speed NE and the load L as described in step 126 of FIG. At first, Duty <Map (N, L), the process proceeds to step 202, and Duty is incremented (increment value = α), and the opening degree according to the duty ratio is determined by EG.
The R valve 64 will have.

If Duty ≧ Map (N, L), step 1 from step 200
Proceeding to 26, the drive duty signal Duty of the EGR valve becomes a map value, and the desired EGR amount is obtained.

The operation of the second embodiment is shown in FIG. That is, the EGR valve is fully closed during the exhaust braking. After the release of the exhaust brake, the opening of the EGR valve gradually increases toward the map value with time.

FIG. 8 is a timing chart of the conventional control, in which the entire amount of EGR is restarted immediately after the release of the exhaust brake. In this case, the total amount of EGR gas immediately after the return of the EGR is P P in FIG.
As shown by, black smoke may be generated locally. That is, during the operation of the exhaust brake, the exhaust gas is recirculated from the upstream of the exhaust brake to the engine side by the so-called internal EGR, and the amount of recirculation by the internal EGR is indicated by δ. When the exhaust brake is released and the EGR valve 64 is opened, the internal EGR amount δ
Since the gas amounts overlap, a temporary excessive amount of reflux occurs. According to the present invention, when the exhaust gas recirculation operation is restarted by releasing the exhaust brake, the amount of circulation is suppressed to be less than the original amount of circulation, thereby making it possible to suppress a temporary excessive amount of recirculation as in the related art.

In the case of a system provided with the particulate trapper 18 as in the embodiment, there is an effect of improving the durability. That is, when the EGR is restarted by releasing the exhaust brake, if the amount of EGR is large, the amount of unburned fuel in the exhaust gas introduced into the particulate trapper 18 increases, and this reacts quickly in the trapper 18 and the trapper 18 Although there is a possibility of melting, according to the present invention, by suppressing the EGR amount at the time of release of the exhaust brake, the amount of unburned fuel can also be suppressed, and the risk of melting can be eliminated.

〔effect〕

According to the present invention, in the system for stopping exhaust gas recirculation during operation of the exhaust brake, the total amount of exhaust gas recirculation immediately after the release of the exhaust brake is eliminated by not performing the entire amount of exhaust gas recirculation immediately after the release of the exhaust brake. The amount can be appropriately suppressed, and generation of black smoke can be suppressed.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing the configuration of the present invention. FIG. 2 is an overall schematic diagram of an embodiment of the present invention. 3 and 4 are flowcharts for explaining the operation of the control circuit of FIG. FIG. 5 is a timing chart for explaining the operation of the control circuit according to the embodiment of the present invention. FIG. 6 is a flowchart for explaining the operation of the second embodiment. FIG. 7 is a timing chart of the operation of the second embodiment. FIG. 8 is a similar timing chart for explaining the operation of the prior art. 10 ... engine body, 12 ... intake pipe, 14 ... exhaust pipe, 16 ... exhaust brake device, 18 ... particulate trapper (or catalytic converter), 22 ... on-off valve, 24 ... actuator, 30 …… diaphragm, 32 …… spring, 36 …… diaphragm chamber, 40 …… electromagnetic 3-way switching valve, 48 …… negative pressure pump, 50 …… exhaust brake actuation switch, 52 …… accelerator pedal, 54 …… accelerator pedal Switch, 60: Fuel injection pump, 64: EGR valve, 80: Control circuit, 84: Rotation speed sensor.

Claims (1)

(57) [Claims] An exhaust gas recirculation passage connecting an exhaust system and an intake system of a diesel engine; an exhaust gas recirculation control valve provided in the exhaust gas recirculation passage; an exhaust brake device; Exhaust brake operating means for controlling the operation of the exhaust brake and closing the exhaust gas recirculation control valve when the exhaust brake is activated, and exhaust brake release time detecting means for detecting when the exhaust brake is switched from operation to release, An exhaust gas recirculation apparatus for a diesel engine, comprising: recirculation operation control means for temporarily prohibiting exhaust gas recirculation for a time when exhaust brake release is detected or gradually increasing the exhaust gas recirculation amount to a target value.