JP3760480B2 - EGR control apparatus and method for diesel engine - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an EGR control method for suppressing the generation of black smoke during acceleration or the like in a diesel engine vehicle (EGR: Exhaust Gas Recirculation).
[0002]
[Prior art]
As an apparatus for reducing nitrogen oxides (hereinafter referred to as “NOx”) in exhaust gas of a diesel engine, an EGR apparatus that recirculates a part of exhaust gas to an intake system is known. The EGR device is provided with an EGR valve in the middle of the exhaust gas recirculation pipe, and opens (ON) when recirculating and closes (OFF) when not recirculating.
[0003]
When exhaust gas is recirculated, NOx is reduced, but black smoke increases. Therefore, EGR control is performed in consideration of whether NOx reduction should be emphasized or black smoke suppression should be emphasized while looking at the operating state of the engine. Normal EGR control in a diesel engine that performs electronically controlled fuel injection is performed according to an EGR valve control map determined in association with a fuel injection amount control map.
[0004]
FIG. 5 is a diagram showing an example of an EGR valve control map. The horizontal axis is the engine speed (N), and the vertical axis is the fuel injection amount (Q). Curve A is the maximum injection amount curve when the accelerator is fully open, and shows the relationship between the engine speed and the fuel injection amount when the accelerator opening (K) is 100% (when the accelerator pedal is fully depressed). Yes. Curve D is the EGR valve operation border region between this and the curve b is a EGR valve OFF region E _1. The region inside the curve D is an EGR valve ON area E _2.
It should be noted that the EGR valve operation boundary line is appropriately determined depending on when the engine operating state is better to turn on or off the EGR valve.
[0005]
By the way, in a diesel engine, it is known that black smoke increases when exhaust gas recirculation is performed during acceleration. In particular, in a diesel engine employing electronically controlled fuel injection, since the opening / closing speed of the EGR valve cannot follow the change in the injection amount, the generation of black smoke tends to further increase. This is because although the injection amount has already been increased due to acceleration, the closing speed of the EGR valve cannot be closed because it is slow, and exhaust gas recirculation is still performed during that time.
[0006]
Japanese Patent Laid-Open No. 5-340310 proposes a technique for reducing the generation of black smoke during acceleration. This is to turn off (close) the EGR valve for a predetermined time τ when sudden acceleration occurs when the engine speed is a predetermined low speed (N _L , for example, 1000 rpm) or less. Whether or not sudden acceleration has occurred is calculated by calculating the rate of change of the accelerator opening and determining whether or not the acceleration rate has reached or exceeded a predetermined value (D _H ).
[0007]
[Problems to be solved by the invention]
The technique disclosed in Japanese Patent Application Laid-Open No. 5-340310 has a problem in that although it is possible to suppress an increase in black smoke during sudden acceleration at a predetermined low rotational speed, it cannot be suppressed during operation outside the conditions. Examples of such operation include, for example, when accelerating from a medium to high speed rotation speed, or when performing relatively gentle acceleration.
Social demands and regulations for the reduction of black smoke and NOx are becoming stricter year by year, and there is a demand not only for reduction in specific operating conditions but also in any operating condition. However, the prior art cannot meet such a demand.
[0008]
If the above-mentioned prior art is applied at the time of acceleration from medium to high speeds, etc., and applied by changing the values of the set speed N _L and accelerator opening change rate D _H , NOx is generated this time. Another problem is that the amount is too large. Because, when accelerating from medium to high speed, or at relatively slow acceleration, the amount of black smoke generated is less than that at the time of sudden acceleration at low speed, but sudden acceleration at low speed This is because the EGR valve is turned off for a predetermined time determined in the same manner as in the case of time, but the OFF period is too long and NOx increases. However, if the predetermined time is shortened so as to be suitable for acceleration from high rotation, the amount of black smoke during acceleration at low rotation increases.
An object of the present invention is to solve such problems.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention relates to the combination of the engine speed sensor, the accelerator opening sensor, the EGR valve provided in the middle of the exhaust gas recirculation pipe, and the engine speed and the fuel injection amount. In the EGR control device for a diesel engine having a built-in EGR valve control map for determining ON / OFF of the EGR valve and controlling the ON / OFF of the EGR valve , the range of engine speed from small to large defining a region on the map by a combination of the division ranges obtained by dividing the range leading to large multiple of the sub-segments were divided range and the accelerator opening change rate into a plurality, corresponding to each region, an abnormal increase in NOx forcing the EGR valve forced with individually determined time to OFF the EGR valve from the perspective of reducing the smoke without causing An FF time map is further built in the controller, and when the OFF time value obtained from the EGR valve forced OFF time map is not zero, the EGR valve forced OFF time is controlled rather than the control based on the EGR valve control map. The EGR control is performed with priority given to the control by the map.
[0010]
Further, according to the present invention, the EGR valve control in which ON / OFF of the EGR valve is determined in correspondence with the combination of the engine speed and the fuel injection amount is performed for the control of the EGR valve provided in the exhaust recirculation pipe of the diesel engine. In the EGR control method of the diesel engine performed according to the map, there are a divided range in which the range from small to large in the engine speed is divided into a plurality and a divided range in which the range from small to large in the accelerator opening change rate is divided into a plurality . defining a region on the map by a combination, corresponding to each area, EGR was individually determined time to forcibly OFF the EGR valve from the perspective of reducing the smoke without causing an abnormal increase in NOx A separate valve forced OFF time map is provided, and the OFF time value obtained from the EGR valve forced OFF time map is zero. If not, said EGR than control by the valve control map with priority control by the EGR valve forced OFF time map and to the EGR control.
[0011]
[Operation]
In addition to the EGR valve control map used for normal EGR control, a new EGR valve forced OFF time map is set. The EGR valve forced OFF time map defines the time to forcibly turn off the EGR valve from the standpoint of reducing black smoke and suppressing NOx increase, corresponding to the combination of engine speed and accelerator opening change rate. It is a map. Then, the EGR valve forced OFF time map is applied with priority, and when the forced OFF time is 0, the EGR valve control map is applied.
This makes it possible to reduce black smoke while suppressing an increase in NOx not only during sudden acceleration at low speeds, but also during acceleration from medium to high speed speeds or during relatively slow accelerations. It becomes.
[0012]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 2 is a block diagram showing an electronically controlled fuel injection apparatus to which the apparatus of the present invention is applied. 1 is an injection pump, 2 is an engine speed sensor, 3 is a fuel pipe, 4 is an electric governor, 5 is a timing control valve, 6 is a fuel pipe, 7 is a controller, 7-1 is a timer, 8 is an accelerator opening sensor, 9 is an EGR valve, 10 is an EGR valve sensor, 12 is an intake pipe, 13 is an injection nozzle, 14 is a diesel engine, 15 is an exhaust recirculation pipe, 16 is an exhaust pipe, and 17 is a turbocharger. The EGR valve sensor 10 is a sensor that detects whether the EGR valve 9 is closed or open.
[0013]
Although the engine is a diesel engine with a turbocharger, it can of course be applied to an engine without it. The intake air to the engine 14 is supercharged by the turbocharger 17. The fuel is supplied from the fuel pipe 3 to the injection pump 1, sent to the injection nozzle 13 through the fuel pipe 6, and injected into the diesel engine 14. The injection amount is controlled by the electric governor 4, and the injection timing is controlled by the timing control valve 5.
[0014]
Control signals to the electric governor 4 and the timing control valve 5 are generated by the controller 7 based on signals from various sensors (not shown) or a control map preset in the controller 7. The fuel injection amount is obtained by applying the engine speed detected by the engine speed sensor 2 and the accelerator opening detected by the accelerator opening sensor 8 to an injection amount control map set in the controller 7. The controller 7 is provided with a timer 7-1 for measuring time, but this may be provided outside the controller 7.
[0015]
The EGR device includes an exhaust gas recirculation pipe 15 and an EGR valve 9 provided in the middle thereof. The EGR control is performed by controlling the opening and closing of the EGR valve 9 with a control signal from the controller 7. In addition to the normal EGR valve control map (see FIG. 5) conventionally used, the controller 7 newly sets an EGR valve forced OFF time map described later with reference to FIG. Based on these maps, a control signal for the EGR valve 9 is generated. The order of map application will be described later.
First, each map will be described.
[0016]
FIG. 4 is a diagram showing an EGR valve control map drawn together with the injection amount control map. Reference numerals correspond to those in FIG. Curve B is a curve for obtaining the injection amount when the accelerator opening (K) is 80%, and curve C is a curve for obtaining the injection amount when the accelerator opening (K) is 15%. Incidentally, when the detected engine speed is N _A and the accelerator opening is 15% (when the operating point is point A), the amount of fuel to be injected is obtained as Q _A.
According to this map, an operating point A, since located EGR valve ON area E _2, for the EGR valve 9 from the controller 7, ON (open) signal is emitted, is made as an exhaust gas recirculation . When the operating point is located in the EGR valve OFF region E ₁ as C is, OFF (close) signal is issued, the exhaust gas recirculation is stopped.
[0017]
FIG. 6 is a diagram showing an EGR valve forced OFF time map. The horizontal axis represents the engine speed (N), and the vertical axis represents the accelerator opening change rate (D). The accelerator opening change rate D is a change amount of the accelerator opening per unit time. For example, if the accelerator opening changes from K _{1 to} K ₂ during Δt seconds, D is obtained by the following equation.
D = (K ₂ −K ₁ ) / Δt
[0018]
This map divides the region by the engine speed N and the accelerator opening change rate D, and sets the time for which the EGR valve 9 is forcibly turned OFF in consideration of the operation state of each region. The length of the forced OFF time is set from the standpoint of reducing black smoke without causing an abnormal increase in NOx while taking into consideration the operating situation corresponding to that region.
[0019]
For example, the area A corresponds to the driving situation where the engine speed is in the range of 0 to N ₁ and the accelerator opening change rate is in the range of 0 to D ₁ , but the forced OFF time at this time is 0 (Zero) is set. That is, the forced OFF is not performed. On the other hand, the region B corresponds to the driving situation where the engine speed is in the range of 0 to N ₁ and the accelerator opening change rate is in the range of D _{3 to} D _4. The forced OFF time at this time is T ₃ is set.
In this way, T ₃ represents the forced OFF time set for the area B, but T ₁ , T ₂ , T _{4 to} T ₁₂ are similarly in the area where they are written. It represents the forced OFF time set for each.
[0020]
FIG. 1 is a flowchart illustrating an EGR control method for a diesel engine according to the present invention. In the EGR control method of the present invention, first, the EGR valve forced OFF time map is applied with priority, and the EGR valve control map is applied when the forced OFF time obtained thereby is zero.
[0021]
Step 1 First, the accelerator opening detected by the accelerator opening sensor 8 in FIG. 2 is read. The accelerator opening at this time is K _1.
Step 2 ... Next, the engine speed N detected by the engine speed sensor 2 is read.
[0022]
Step 3: Time measurement is started by the timer 7-1.
Step 4... Check whether a predetermined time Δt seconds has elapsed. Δt seconds is, for example, a time of about 20 msec. The timer 7-1 is reset when the time Δt is measured.
Step 5: Read the accelerator opening K ₂ when Δt has elapsed.
Step 6: The accelerator opening change rate D is calculated by D = (K ₂ −K ₁ ) / Δt.
[0023]
Step 7: The calculated accelerator opening change rate D and the engine speed N read in Step 2 are applied to the EGR valve forced OFF time map of FIG. 6 to obtain the EGR valve forced OFF time T.
Step 8: Check whether the obtained time T is greater than zero. If 0, the routine proceeds to step 13 in order to perform normal EGR control based on the EGR valve control map.
Step 9... If T is greater than 0, it means that the EGR valve 9 is forcibly turned off for the time T, and therefore a control signal is issued to the EGR valve 9 for turning it off.
[0024]
Step 10... Whether or not the EGR valve 9 is turned off is checked by a detection signal from the EGR valve sensor 10.
Step 11: If it is OFF, the timer 7-1 starts measuring time T. (Note that if the time required for the EGR valve 9 to turn from ON to OFF is T ₀ , T ₀ is a substantially constant time determined by the mechanical structure of the EGR valve 9, and therefore the time measurement by the timer 7-1 is performed in step 9. (It may be started from the time when the OFF signal is output, and the length of time to be measured may be T ₀ + T. In such a case, it is not necessary to provide the EGR valve sensor 10).
Step 12: It is checked whether or not the time T has elapsed, and when it has elapsed, the routine proceeds to Step 13 in order to perform normal EGR control based on the EGR valve control map. The timer 7-1 is reset when the time T is measured.
[0025]
Step 13: The accelerator opening is read.
Step 14: The engine speed is read.
Step 15... These are applied to the EGR valve control map of FIG. 5 to determine whether the EGR valve 9 should be turned on or off. If the operating point is within the EGR valve OFF region E ₁ , it is turned OFF, and if it is within the EGR valve ON region E ₂ , it is turned ON.
Step 16... A control signal is issued to the EGR valve 9 according to the determination.
[0026]
Next, changes in various amounts related to the engine when the present invention is applied will be described with reference to FIG. 3 (a) shows changes in accelerator opening, and FIGS. 3 (b), (c), (d), (e), and (f) respectively show changes in fuel injection amount, changes in engine speed, It shows ON / OFF changes of the EGR valve, changes in the amount of black smoke generated, and changes in the amount of NOx generated. t _{0 to} t ₄ are times, T _{0 in} FIG. 3 (d) is the time required for the EGR valve 9 to turn off from ON, and T is a forced OFF time.
[0027]
Figure 3 (b), the accelerator opening was K _A is the accelerator pedal indicates that started to be increased from the time t _0. The changing accelerator opening is detected every moment, and the calculation of the accelerator opening change rate D is repeated. Then, based on the accelerator opening change rate calculated at time t ₁ (accelerator opening change rate of the point P), was determined the forced OFF time T from the map of FIG. 6, the value is greater than 0. Suppose there was.
Then, a signal to turn off the EGR valve 9 is issued, and the EGR valve 9 starts to move toward OFF as shown in FIG. Although the mechanical valve operates and closes, it takes a time T ₀ until it is completely turned off. However, the turning-off continues for the forced OFF time T after turning off. After that, it is determined whether to turn on or off by the normal control of the EGR valve control map (see the one-dot chain line in FIG. 3D).
[0028]
Accelerator opening K _A = 15%, When was the engine speed = N _A, the operating point in Figure 4 becomes A on curve (c), the injection quantity is Q _A. If the accelerator pedal is depressed this time, the accelerator opening is increased to K _C (for example, about 95%), and the operating point shifts to C, the injection amount will eventually become the operating point C It is increased to a Q _C corresponding to.
[0029]
In FIG. 4, the operating point moves in the order of A → P → B → C. Time T calculated in the EGR valve forced OFF time map of Figure 6, when it comes to larger than 0 at the operating point P, without waiting for the operating point B to get out of the EGR valve ON area E _2, the EGR valve 9 is made me OFF start.
Figure 3 (b) is shows the relationship between the injection quantity of these operating points, when the injection quantity becomes Q _P corresponding to the point P, OFF of the EGR valve 9 is started.
[0030]
During this time, since the injection amount is increasing rapidly, black smoke increases when the EGR valve 9 is turned on, but in the present invention, OFF is commanded early (at the operating point P instead of the operating point B), and Even after the engine is turned off, the engine is forcibly kept off for a time when the injection amount seems to continue to increase while taking into account the driving situation, so that the generation of black smoke is reduced and the increase in NOx is also suppressed. (FIG. 3 (e), reference t ₃ or later (f)).
When the operating point is P, since P is inside the EGR valve operating boundary line D, the EGR valve is ON in the conventional control. However, in the present invention, as described above, control is performed such that the power is forcibly turned off for a predetermined time and then turned back on.
[0031]
【The invention's effect】
As described above, according to the EGR control device and method of the diesel engine of the present invention, in addition to the EGR valve control map used for normal EGR control, a new EGR valve forced OFF time map is provided, and the EGR valve forced OFF Since the time map is given priority, NOx increases not only during sudden acceleration at low revolutions, but also during acceleration from medium to high revolutions, or during relatively slow accelerations. It is now possible to reduce black smoke while suppressing
[Brief description of the drawings]
FIG. 1 is a flowchart for explaining an EGR control method for a diesel engine according to the present invention. FIG. 2 is a block diagram showing an electronically controlled fuel injection device to which an EGR control apparatus for a diesel engine according to the present invention is applied. FIG. 4 is a diagram showing changes in various amounts related to the engine when the invention is applied. FIG. 4 is a diagram showing an EGR valve control map drawn together with an injection amount control map. FIG. 5 is a diagram showing an EGR valve control map. ] Diagram showing EGR valve forced OFF time map [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Injection pump, 2 ... Engine speed sensor, 3 ... Fuel pipe, 4 ... Electric governor, 5 ... Timing control valve, 6 ... Fuel pipe, 7 ... Controller, 7-1 ... Timer, 8 ... Accelerator opening sensor, DESCRIPTION OF SYMBOLS 9 ... EGR valve, 10 ... EGR valve sensor, 12 ... Intake pipe, 13 ... Injection nozzle, 14 ... Diesel engine, 15 ... Exhaust gas recirculation pipe, 16 ... Exhaust pipe, 17 ... Turbocharger

Claims (2)

An engine speed sensor, an accelerator opening sensor, an EGR valve provided in the middle of the exhaust gas recirculation pipe, and an EGR valve that determines ON / OFF of the EGR valve in accordance with a combination of the engine speed and the fuel injection amount In an EGR control device for a diesel engine comprising a control map and a controller for controlling ON / OFF of the EGR valve,
Areas on the map are defined by combining the divided ranges that divide the range from small to large engine speeds into multiple and the divided ranges that range from small to large in the accelerator opening change rate. The controller further incorporates an EGR valve forced OFF time map that individually defines the time to forcibly turn off the EGR valve from the viewpoint of reducing black smoke without causing an abnormal increase in NOx. Configured to let
When the value of the OFF time obtained from the EGR valve forced OFF time map is not zero, the EGR control is prioritized over the control by the EGR valve forced OFF time map over the control by the EGR valve control map. EGR control device for diesel engine characterized by A diesel engine that controls an EGR valve provided in the exhaust gas recirculation pipe of a diesel engine in accordance with an EGR valve control map that determines ON / OFF of the EGR valve corresponding to the combination of the engine speed and the fuel injection amount. In the EGR control method,
Areas on the map are defined by combining the divided ranges that divide the range from small to large engine speeds into multiple and the divided ranges that range from small to large in the accelerator opening change rate. a is associated, separately provided EGR valve forced OFF time map defining individual time to OFF compulsorily the EGR valve from the perspective of reducing the smoke without causing an abnormal increase of NOx, the EGR When the value of the OFF time obtained from the valve forced OFF time map is not zero, the EGR control is performed by giving priority to the control based on the EGR valve forced OFF time map over the control based on the EGR valve control map. EGR control method for diesel engine.

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