JPH04116654U - Diesel engine exhaust recirculation control device - Google Patents

Abstract

(57) [Summary] [Purpose] To control the exhaust gas recirculation rate so that the excess air ratio does not fall below a certain value, and to suppress the smoke emission amount so that it does not exceed the permissible limit. [Configuration] A means 52 for setting a target exhaust recirculation rate according to the operating state, a means 53 for measuring the intake amount of fresh air in the intake passage upstream of the exhaust recirculation position, and a means 53 for measuring the intake amount of fresh air in the intake passage upstream of the exhaust recirculation position, means 54 for calculating a target intake amount of fresh air;
Means 55 for feedback controlling the opening degree of the exhaust recirculation control valve so that the measured fresh air intake amount matches the target fresh air intake amount, and means 56 for setting the limit air amount for the smoke discharge limit according to the operating state. Means 5 for comparing the target fresh air intake amount during exhaust gas recirculation and the limit air amount at that time.
7, and means 58 for correcting the opening degree of the exhaust gas recirculation control valve so that the target fresh air intake amount does not fall below the limit air amount.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

The present invention relates to an improvement of an exhaust gas recirculation control device for a diesel engine.

0002

[Conventional technology]

In order to accurately control the exhaust recirculation amount of a diesel engine to a target value, Feeds the opening degree of the exhaust recirculation control valve while measuring the amount of intake air that changes with the flow. There is a back control device (Japanese Patent Laid-Open No. 61-215426, etc.).

0003 The flow rate of fresh air taken into the engine is greater when there is exhaust recirculation than when there is no exhaust recirculation. The total amount decreases by an amount equivalent to the reflux amount. Therefore, the exhaust gas recirculation rate under that operating condition can be determined. Then, the exhaust recirculation amount relative to the total intake air amount can be estimated from the intake amount of fresh air, and the target exhaust To control the reflux amount, measure the amount of fresh air inhaled at that time, and make sure that this measured value is the target. The opening degree of the exhaust recirculation control valve may be controlled to match the amount of fresh air taken in.

0004 In other words, first find the characteristics of the intake air amount (total intake air amount) when there is no exhaust gas recirculation. Based on this, calculate the exhaust recirculation amount from the exhaust recirculation rate depending on the operating condition. Then, the target fresh air is calculated by subtracting this exhaust recirculation amount from the total intake air amount. The opening of the exhaust recirculation control valve is adjusted so that the intake amount of fresh air matches the target value. Through feedback control, the exhaust recirculation amount can be adjusted accurately according to the operating conditions. can be controlled.

[0005] The recirculated exhaust gas contains soot, and compared to measuring the intake amount of fresh air, the recirculated exhaust gas contains soot, etc. It is difficult to accurately measure the amount of air, so it is difficult to measure the amount of exhaust gas recirculated indirectly. I try to keep it under control.

[0006] In addition, in this way, the amount of exhaust recirculation can be controlled while measuring the amount of intake air. However, depending on the individual engine or due to changes over time, the intake Operating range in which exhaust gas recirculation is stopped as it may cause variations in air volume characteristics. Based on the actually measured intake air amount, the intake air amount characteristics are learned and corrected, and exhaust recirculation is controlled. A device has been proposed by the applicant that increases the accuracy of the control.

[0007]

[Problem that the idea aims to solve]

By the way, in this case, the air cleaner may be clogged or soot may enter the engine intake port. As intake resistance continues to increase due to sludge accumulation, etc., the amount of intake air gradually decreases. It will continue to decrease. For the amount of air required to burn the fuel supplied to the engine The ratio of the amount of fresh air actually drawn into the engine is called the excess air ratio. When the excess rate falls below a certain value, there is a problem that smoke in the exhaust gas increases.

[0008] In general, the exhaust recirculation rate is affected by the deterioration of engine performance and smog under the operating conditions at that time. appropriate measures to effectively reduce NOx without causing an increase in However, when the amount of fresh air inhaled relative to the fuel supplied to the engine falls below a certain value. Therefore, even though the exhaust recirculation rate itself remains the same, the amount of smoke generated increases. There is a phenomenon in which relatively new There is a lack of energy and the smoke tends to increase temporarily.

[0009] This invention determines the excess air ratio and prevents the excess air ratio from falling below a certain value. The exhaust recirculation rate is controlled to prevent smoke emissions from exceeding permissible limits. The purpose is to suppress this so that it does not occur.

0010

[Means to solve the problem]

Therefore, the present invention connects the intake passage and exhaust passage of the engine, as shown in Figure 1. An exhaust gas recirculation control valve 50 interposed in the exhaust gas recirculation passage, and a means 51 for detecting the operating state. , a means 52 for setting the exhaust gas recirculation rate according to the operating state, and a means 52 upstream of the exhaust gas recirculation position. means 53 for measuring the intake amount of fresh air in the intake passage of the target exhaust gas recirculation rate; means 54 for calculating a target intake amount of fresh air to be inhaled into the device; Feedback the opening degree of the exhaust recirculation control valve 50 to match the target fresh air intake amount In an exhaust gas recirculation control device for a diesel engine, the device includes: A means 56 for setting the limit air amount for the smoke emission limit according to the operating condition, and an exhaust means 57 for comparing the target fresh air intake amount during air recirculation with the limit air amount at that time; , the exhaust recirculation control valve is opened so that the target fresh air intake amount does not fall below the limit air amount. and means 58 for correcting the degree.

[0011]

[Effect]

The limit air amount is based on the relationship with the engine load (fuel supply amount) at that time. When the excess air ratio is below this value, the excess air ratio becomes small and the amount of smoke generated is permissible. Exceed your capacity.

0012 The amount of fresh air intake is determined by the relative relationship with the amount of exhaust gas recirculation, and this target fresh air intake amount When the amount of air approaches the limit air amount, the exhaust recirculation should be control, that is, the amount of exhaust gas recirculation is reduced to ensure the amount of fresh air taken in, so the smoke The emission of water is suppressed.

[0013]

【Example】

Figures 2 and 3 show examples of the present invention, and in Figure 2, 1 is a V8 type diesel engine. In the engine, 2 indicates an intake passage, and 3 indicates an exhaust passage. The amount of fresh air taken into intake passage 2 is An air flow sensor 4 for measurement and an intake shutter 6 are provided downstream thereof. intake The shutter 6 receives negative pressure from the vacuum pump 35 guided through the control valve 5. more driven.

[0014] An exhaust brake shutter 8 is provided in the exhaust passage 3, and an exhaust brake shutter 8 is provided in the exhaust passage 3. It is operated by compressed air from the air tank 36. exhaust brake shutter Exhaust air connecting the exhaust passage 3 downstream of the shutter 8 and the intake passage 2 downstream of the intake shutter 6 A recirculation passage (EGR passage) 9 is provided, and the EGR passage 9 is provided with the intake shutter. Exhaust recirculation control valve to control the exhaust gas recirculation amount (EGR amount) in cooperation with 6. (EGR valve) 11 is installed. The EGR valve 11 is guided through the control valve 10. It operates in response to negative pressure from the vacuum pump 35.

[0015] A control unit for controlling each of the control valves 5, 7, and 10 is provided. A port 12 is provided. The control unit 12 includes a signal representing the operating state. As, the fresh air intake amount signal from the air flow sensor 4, the engine rotation sensor 1 3, the load signal from the fuel injection pump rack position sensor 14, the cooling Water temperature signal from cooling water temperature sensor 15, atmospheric pressure signal from atmospheric pressure sensor 16, exhaust valve Various operation switch signals are input from the rake switch 17, etc., and based on these Exhaust gas recirculation control is performed as described below.

[0016] As shown in FIG. 3, the control unit 12 controls the standard intake air amount of the engine. A means 18 for calculating and storing it, a means 19 for learning the actual intake air amount, and a means 19 for learning the actual intake air amount; Means 20 for storing the standard intake air amount correction factor based on the setting E according to the operating condition Means 21 for storing the GR rate, means for calculating the target fresh air intake amount based on the EGR rate 22. Lambda limit air amount from smoke limit air excess rate depending on operating condition The means 30 for determining the target fresh air intake amount and the lambda limit air amount are compared. The determining means 31 controls the signal according to the deviation between the target fresh air intake amount and the actual fresh air intake amount. Comparison means 23 outputs to control output calculation means 24, control from control output calculation means 24 Means 2 for outputting a drive signal for controlling the opening degree of the EGR valve 11 based on duty Consists of 5th grade.

[0017] The standard intake air amount storage means 18 stores information from the engine speed calculation means 26. Rack rotation speed signal and rack via multiplexer 27 and A/D converter 28 Based on the position signal, the engine standard intake air amount is calculated and stored in a map. studies The learning means 19 receives signals from the intake air amount learning region determining means 33 and various operating state detection signals. Based on the above, in the operating range where EGR is stopped (e.g. idle and full load) , the intake air amount is measured based on the fresh air intake amount signal from the air flow sensor 4, and this The result is output to the learning intake air amount correction factor storage means 20.

[0018] The learning intake air amount correction factor storage means 20 stores a standard value based on the engine speed and load. Learning data from the quasi-intake air amount map and the actually measured intake air amount when EGR is stopped Calculate the correction factor for the intake air amount using the data and store it in the learning correction factor map. Ru.

[0019] In other words, the standard intake of the engine is set based on the preset rotation speed and load. Based on the difference between the intake air amount and the actually measured intake air amount, the operating conditions are determined respectively. By calculating the correction factor at the Compensates for irregularities and changes over time.

[0020] As shown in FIG. 5, the set EGR rate storage means 21 controls the The flow rate is stored in a map, and these standard intake air amount storage means 18 and learning intake air flow rate are stored in a map. Each output from the intake air amount correction factor storage means 20 and the set EGR rate storage means 21 is the target It is input to the fresh air intake amount calculation means 22.

[0021] The target intake air amount calculation means 22 calculates the standard intake air amount at that time based on the correction factor. From the corrected intake air amount and target EGR rate, determine the target fresh air intake amount during EGR. It is used to calculate. When exhaust gas is recirculated, the intake amount of fresh air decreases by that amount, reducing the total intake. The intake amount of fresh air is the amount of air minus the EGR flow rate. By subtracting the EGR flow rate according to the EGR rate from the corrected standard intake air amount at the time, the target The amount of fresh air inhaled is calculated, and the actual amount of fresh air inhaled matches this target amount of fresh air inhaled. By controlling the opening degree of the EGR valve 11 so that the It manifests itself.

[0022] The lambda limit air amount determining means 30 is configured to combust the fuel supplied to the engine. air excess, which is the ratio of the actual amount of intake air to the minimum amount of air needed to Limit intake where the rate (λ) is the permissible limit of smoke emissions under that operating condition. Limit intake with a set air volume and corrected based on the current atmospheric pressure The air amount and the target fresh air intake amount are compared in the size determining means 31, and a limit intake amount is determined. When the target fresh air intake amount is smaller than the intake air amount, the target fresh air intake amount during EGR Instead, the limit air amount is output to the comparing means 23.

[0023] As shown in Figure 6, excess air based on the target fresh air intake amount in that operating state If the intake air rate is smaller than the limit intake air amount, there will be insufficient fresh air and the amount of smog discharged will be reduced. In this case, the target amount of fresh air intake is By replacing this with this limit intake air amount, smoke generation is suppressed. It is. In addition, the smoke transmittance is expressed in PHS, and the smaller the value, the Smoke concentration is high.

[0024] Figure 7 shows the characteristics of the lambda limit air amount, and shows the relationship between engine speed and fuel injection. The allowable smoke limit is determined based on the injection pump rack position (fuel supply amount). The limit air amount (Kg/min) may be selected according to the relationship between

[0025] In addition, the limit air amount is corrected by atmospheric pressure according to the correction characteristics shown in Figure 8. will be carried out. Since the air concentration decreases in proportion to the decrease in atmospheric pressure, the limit air amount The volumetric flow rate increases.

[0026] The control output calculation means 24 compares the target fresh air intake amount and the actual fresh air intake amount, and calculates the result. Read the control duty ratio corresponding to the deviation from the map or respond to the deviation. EGR valve drive signal output means 2 via output switching means 32. Output to 5.

[0027] Note that the output switching means 32 uses a signal from the EGR control region determining means 29 to In the EGR region, the signal from this control output calculation means 24 is taken, but in the EGR stop region Then, set the control duty to 0 and fully close the EGR control valve.

[0028] Next, the control operation executed by the control unit 12 will be described in the flowchart of FIG. Explain according to the following.

[0029] First, in steps 1 to 5, various sensor outputs representative of the current operating state are Read the power and operation command output from various operation operation switches, and in step 6 Search EGR rate Regr from the EGR map and check whether it is in the EGR region in step 7. judge whether

[0030] When it is not in the EGR region, the EGR control duty is set to 0, and the EGR valve 11 is fully closed, and the intake shutter 6 is fully opened. Then, the cooling water temperature is set to the specified value. Is it possible to learn the amount of intake air under the condition that the temperature is above (for example, 50 degrees Celsius)? (Steps 8 to 11). If the area is learnable, the airflow - Calculated from the intake air amount measured by the sensor and the standard intake air amount map when EGR is stopped. Calculate the correction factor LNCO for the intake air amount from the deviation from the standard intake air amount calculated, and make the correction. Store it in the map (steps 12, 13).

[0031] On the other hand, when it is not in the learning possible area, the EGR valve 11 is fully closed and , return to the original position with the intake shutter 6 fully open.

[0032] If it is determined in step 7 that the area is in the EGR region, step 14 , 15, and calculate the intake air amount G'o during non-EGR from the standard intake air amount map. Search for the intake air amount correction factor LNCO, and calculate the target fresh air intake amount G from these and Regr. Find as. Then, in step 17, limit air from the lambda limit map. Search for the quantity Gal and calculate G’al by correcting this Gal based on atmospheric pressure data. put out

[0033] In step 19, the corrected target fresh air intake amount and limit air amount are determined respectively. If the target fresh air intake amount is small, set the limit as the target fresh air intake amount. (step 20).

[0034] Next, the fresh air intake amount Gai measured by the air flow sensor and this target fresh air intake Calculate the deviation from the input amount Gas and perform feedback control so that this deviation becomes zero The control duty of the EGR control valve is calculated in order to The opening degree of the GR valve 11 is controlled and the intake shutter 6 is narrowed down to a predetermined opening degree.

[0035] In this way, during exhaust recirculation control, the intake amount of fresh air, which decreases with EGR, can be controlled. Set a target value and feed the EGR amount so that the actually measured fresh air intake amount matches the target value. By back-controlling, it is possible to accurately measure the EGR amount without measuring the actual amount of EGR. It is possible to converge to the target EGR rate.

[0036] Also, prevents clogging of the air cleaner and accumulation of deposits on the intake port. As a result, the passage resistance in the intake system increases, and the flow rate of fresh air sucked into the engine decreases. As shown in Figures 9 and 10, the EGR rate itself changes depending on the operating condition. Even if an appropriate value is maintained, smoke will gradually increase as the excess air ratio decreases. Emissions will increase, but the target amount of fresh air intake under that operating condition will reach the smoke limit. When the amount of air is less than the preset limit air amount based on the relationship with the field, the This limit intake air is used instead of the target fresh air intake amount as the target value for back-back control. Since air volume is used, the amount of exhaust recirculation does not increase any more, and the amount of smoke emitted is limited. This allows it to be suppressed so that it does not exceed the limit value.

[0037] Note that the above lambda limit air amount is corrected based on atmospheric pressure, but To calculate the surplus rate, the supplied fuel flow rate (weight) must also be corrected based on the fuel temperature. This makes it possible to realize EGR control with even higher precision in suppressing smoke emissions.

[0038]

[Effect of the idea]

As described above, according to the present invention, smoke is allowed to be discharged while determining the excess air ratio. Since the exhaust gas recirculation amount is controlled so as not to exceed the capacity limit, the amount of smoke emitted is reduced. It is possible to effectively reduce NOx while keeping it below a predetermined standard, especially against changes over time. The amount of fresh air intake decreases due to increased resistance in the intake system, especially when the amount of fuel increases suddenly. Even when the excess air ratio temporarily decreases during transient operation, smoke will not occur. It is possible to prevent exceeding the permissible limit.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing the configuration of the present invention.

FIG. 2 is a schematic configuration diagram showing an embodiment of the present invention.

FIG. 3 is a block diagram of a control unit.

FIG. 4 is a flowchart showing control operations executed by the control unit.

FIG. 5 is a characteristic diagram showing the characteristics of the exhaust gas recirculation rate based on the rotation speed and load.

FIG. 6 is an explanatory diagram showing the relationship between excess air ratio and smoke emission concentration.

FIG. 7 is a characteristic diagram showing the characteristics of the lambda limit air amount based on the rotation speed and load.

FIG. 8 is an explanatory diagram showing correction characteristics of the lambda limit air amount depending on atmospheric pressure.

FIG. 9 is an explanatory diagram showing changes in engine intake air amount and fresh air intake amount when the same exhaust gas recirculation rate is maintained.

FIG. 10 is an explanatory diagram showing the relationship between excess air ratio (λ) and smoke concentration depending on operating conditions.

[Explanation of symbols]

1 diesel engine 2 Intake passage 3 Exhaust passage 4 Air flow sensor 9 EGR passage 11 EGR valve 12 Control unit 13 Engine speed sensor 14 Rack position sensor 50 Exhaust recirculation control valve 51 Operating state detection means 52 Exhaust gas recirculation rate setting means 53 Fresh air intake amount measuring means 54 Target fresh air intake amount calculation means 55 Feedback control means 56 Limit air amount setting means 57 Means of comparison 58 Correction means

Claims (1)

[Scope of utility model registration request] 1. An exhaust recirculation control valve interposed in an exhaust recirculation passage connecting an intake passage and an exhaust passage of an engine, means for detecting an operating state, and means for setting an exhaust recirculation rate according to the operating state. means for measuring the intake amount of fresh air in the intake passage upstream of the exhaust gas recirculation position; means for calculating the target intake amount of fresh air taken in when the target exhaust gas recirculation rate is reached; In the exhaust recirculation control device for a diesel engine, the exhaust recirculation control device for a diesel engine includes means for feedback controlling the opening degree of the exhaust recirculation control valve so that the amount of fresh air intake matches the target fresh air intake amount, means for comparing the target fresh air intake amount during exhaust gas recirculation with the limit air amount at that time, and means for opening the exhaust recirculation control valve so that the target fresh air intake amount does not fall below the limit air amount. 1. An exhaust recirculation control device for a diesel engine, characterized in that it is equipped with a means for correcting the temperature.