JP3329711B2 - Exhaust gas recirculation control device for internal combustion 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 exhaust gas recirculation control device applied to an internal combustion engine for recirculating a part of exhaust gas to an intake system and suitably controlling the amount of exhaust gas recirculation.

[0002]

2. Description of the Related Art As one method for reducing nitrogen oxides (NOx) in exhaust gas, an exhaust gas recirculation device (hereinafter, referred to as an EGR device) that recirculates a part of the exhaust gas to an engine intake pipe has been embodied. I have. In an internal combustion engine equipped with such an EGR device, the oxygen concentration in the exhaust gas discharged from the cylinder is detected, and the exhaust gas recirculation amount (EGR amount) is controlled according to the detected exhaust gas oxygen concentration. In particular,
An EGR valve is provided in the middle of an EGR passage connecting the engine exhaust pipe and the engine intake pipe, and the opening of the EGR valve is adjusted. In this case, generally, the exhaust gas oxygen concentration is detected for each exhaust stroke of the cylinder, and the control command value of the EGR valve is calculated using the exhaust gas oxygen concentration detected one combustion cycle before.

[0003]

However, in the above prior art, when the amount of EGR is small and the time required for the exhaust gas to return to the engine intake pipe via the EGR passage (return delay time) is prolonged, the exhaust gas may be exhausted. There arises a problem that the oxygen concentration deviates from the actual value, and eventually the control accuracy of the EGR control deteriorates. This is because the EGR control is performed based on the exhaust gas oxygen concentration one combustion cycle before,
It is considered that this is because the oxygen concentration of the exhaust gas (EGR gas) actually returned to the engine intake pipe is erroneously detected.

For example, when the vehicle is accelerating, the amount of fuel supplied to the internal combustion engine is increased, and the EGR valve is controlled to be closed so as to maintain the balance between the amount of fuel supplied and the amount of in-cylinder intake oxygen. . At the time of this fuel increase, the exhaust gas oxygen concentration decreases. In addition, the recirculation delay time increases as the EGR amount decreases. At this time, the EGR gas (exhaust gas sucked into the cylinder) that is actually recirculated to the engine intake pipe during the intake stroke of the engine temporarily stays in the EGR passage, so that the oxygen before the acceleration is originally required. Although it has a concentration value, the conventional apparatus does not consider the reflux delay time, and thus considers this oxygen concentration as a value smaller than the actual value. As a result, there is a problem in that more oxygen than the optimal in-cylinder intake oxygen amount for the fuel supply amount is sucked into the cylinder, and NOx excessively increases.

The present invention has been made in view of the above-mentioned problems, and has as its object to accurately grasp the oxygen concentration of the exhaust gas recirculated to the intake system, and to control the exhaust gas recirculation control with high accuracy. An object of the present invention is to provide an exhaust gas recirculation control device for an internal combustion engine that can be implemented.

[0006]

In order to achieve the above object, according to the first aspect of the present invention, the exhaust gas recirculation of the internal combustion engine recirculates a part of the exhaust gas of the internal combustion engine to an intake system through an exhaust gas recirculation passage. In the control device, exhaust gas recirculation amount detection means for detecting an exhaust gas recirculation amount for each intake stroke through the exhaust gas recirculation passage, exhaust gas oxygen concentration detection means for detecting an oxygen concentration in the exhaust gas for each exhaust stroke, A memory for storing the history of the detected oxygen concentration in the exhaust gas at any time, and a length in the exhaust gas recirculation passage occupied by the detected exhaust gas recirculation amount is obtained, and stored before the exhaust gas recirculation delay time corresponding to the length. Recirculated gas oxygen concentration calculating means for calculating the oxygen concentration of the exhaust gas recirculated to the intake system from the obtained memory value,
Exhaust gas recirculation amount control means for controlling the amount of recirculated exhaust gas using the calculated oxygen concentration of the recirculated exhaust gas.

[0007] According to the above configuration, the exhaust gas oxygen concentration detected for each exhaust stroke is stored in the memory in order from the oldest data, and the memory value is appropriately read when controlling the exhaust gas recirculation amount. Further, the length of the exhaust gas recirculation passage occupied by the exhaust gas recirculation amount at each time, that is, how much exhaust gas in the recirculation passage is recirculated to the intake system during the intake stroke of the engine is determined. In this case, the oxygen concentration of the exhaust gas (recirculated exhaust gas) actually recirculated is calculated using the memory value (detected value of the exhaust gas oxygen concentration) preceding by the recirculation delay time corresponding to the length of the exhaust gas recirculation passage. By controlling the exhaust gas recirculation amount based on the calculated value, the in-cylinder intake oxygen amount can be appropriately controlled even during transient operation such as vehicle acceleration / deceleration. That is, unlike the conventional apparatus, the problem that the NOx emission amount excessively increases can be solved. as a result,
Accurately grasp the oxygen concentration of the exhaust gas recirculated to the intake system,
As a result, the exhaust gas recirculation control can be performed with high accuracy. By the way, the memory value before the recirculation delay time refers to the oxygen concentration data of the exhaust gas closest to the engine intake pipe in the exhaust gas recirculation passage, that is, the exhaust gas immediately before being discharged to the intake system.

[0008] In the invention described in claim 2, the memory has a plurality of storage areas, an apparatus for storing and maintaining the history of the exhaust gas oxygen concentration for each area, the return gas oxygen concentration calculation means, The oxygen concentration memory values of the number corresponding to the detected exhaust gas recirculation amount are read, and the oxygen concentration of the recirculated exhaust gas is calculated based on the read memory values. Here, as described in claim 3, the memory value of the oxygen concentration may be averaged to calculate the oxygen concentration of the recirculated exhaust gas.

According to the second and third aspects of the present invention, the oxygen concentration of the recirculated exhaust gas reflecting the recirculation delay time can be easily and accurately calculated by reading out the memory values of the oxygen concentration corresponding to the exhaust gas recirculation amount. . At this time, if all the oxygen concentrations of the exhaust gas present in the exhaust gas recirculation passage are the same, the same memory value is read out when calculating the recirculated exhaust gas oxygen concentration, and the oxygen concentration of the exhaust gas existing in the same passage is different. If so, a different memory value is read out when calculating the recirculated exhaust gas oxygen concentration.

According to the present invention, the detected value of the exhaust gas oxygen concentration at that time is stored in the memory areas corresponding to the detected exhaust gas recirculation amount. In this case, the same detection value is written in the number of memory areas corresponding to the exhaust gas recirculation amount, and is read out appropriately when calculating the oxygen concentration of the recirculated exhaust gas thereafter.

According to the fifth aspect of the present invention, when controlling the exhaust gas recirculation amount using the memory value of the exhaust gas oxygen concentration, the used memory value of the exhaust gas oxygen concentration is erased, and instead, the exhaust stroke and The memory is updated with the exhaust gas oxygen concentration of another cylinder. In this case, the exhaust gas oxygen concentration detected for each cylinder of the multi-cylinder internal combustion engine can be managed by the same memory, which can contribute to a reduction in memory capacity.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram illustrating an outline of an electronic control system for a vehicle diesel engine according to the present embodiment. An electronic control unit (hereinafter, referred to as an ECU) 10 in the electronic control system of FIG.
The microcomputer mainly includes a well-known CPU, a ROM, a RAM, a backup RAM, and the like.
, The electromagnetically driven distribution type fuel injection pump 11 is driven to supply high-pressure fuel to the diesel engine 20. That is, the high-pressure fuel compressed by the distribution type fuel injection pump 11 is supplied to the fuel injection nozzle 13 through the fuel distribution passage 12, and the fuel injection nozzle 13 injects the fuel into the sub combustion chamber 21 of the diesel engine 20. Note that the diesel engine 20 of the present embodiment
Fourth (# 1 to # 4) four cylinders, and the combustion order of each cylinder is # 1 → # 3 → # 4 → # 2.

The diesel engine 20 has an intake pipe 22 and an exhaust pipe 23. The intake pipe 22 and the exhaust pipe 23 are connected to the main combustion chamber 2 via an intake valve 24 and an exhaust valve 25.
It communicates with 6. The main combustion chamber 26 communicates with the auxiliary combustion chamber 21 via a communication passage 27. Therefore, when the in-cylinder intake air is compressed due to the upward movement of the piston 28, when fuel is injected and supplied from the fuel injection nozzle 13 into the sub-combustion chamber 21, the fuel is compression-ignited and used for combustion.

The diesel engine 20 has a turbocharger 14 constituting a supercharger, and a compressor 14a of the turbocharger 14 is provided in the intake pipe 22.
The exhaust pipe 23 is provided with a turbocharger 14.
Exhaust turbine 14b is provided. As is well known, the turbocharger 14 uses the energy of the exhaust gas to rotate the exhaust turbine 14b, and rotates the compressor 14a on the same axis to increase the pressure of the intake air. When the intake air is pressurized, high-density air is sent into the main combustion chamber 26 and the diesel engine 20
Is amplified.

An intake throttle valve 16 is provided downstream of the compressor 14a in conjunction with an accelerator pedal 15. The open / close position of the intake throttle valve 16 is detected as an accelerator opening by an accelerator opening sensor 17, and the detected accelerator opening signal is input to the ECU 10.

On the upstream side of the compressor 14a, there is provided a fresh air intake sensor 30 for detecting the amount of fresh air to be sucked into the intake pipe 22. The fresh air intake sensor 30 detects the amount of fresh air. The fresh air intake signal is
Is input to The fresh air intake amount sensor 30 is composed of a hot wire air flow meter configured by arranging a hot wire in the intake pipe 22, and the mass flow rate of the fresh air to be sucked in accordance with the dissipation of heat from the heated hot wire (resistor). Is detected.

In addition, the intake pipe 22 is provided with a fresh air temperature sensor 31 for detecting the temperature of fresh air and an intake pressure sensor 32 for detecting the pressure of the intake pipe. The detection signal of 32 is input to the ECU 10.
Further, a drive speed sensor 33 for detecting an engine speed is provided on a drive shaft (not shown) of the distribution type fuel injection pump 11, and a detection signal of the sensor 33 is input to the ECU 10.

Next, an outline of the EGR device provided in the engine system will be described. In the exhaust pipe 23, an EGR passage 35 is provided in a branched manner on the upstream side of the exhaust turbine 14b.
It is connected to the intake pipe 22 via the R valve 36. This EG
A part of the exhaust gas in the exhaust pipe 23 is recirculated to the vicinity of the intake port of the intake pipe 22 by the R passage 35.

The EGR valve 36 for adjusting the exhaust gas recirculation amount (EGR gas amount) has a valve element 37 for opening and closing the EGR passage 35, and the valve element 37 is operated by a diaphragm 38. The EGR gas amount is determined by the lift amount of the valve body 37. A pressure chamber 40 in which a compression coil spring 39 is installed is formed behind the diaphragm 38, and a negative pressure control valve 42 is connected to the pressure chamber 40 via a pressure introducing pipe 41. The negative pressure control valve 42 has an air introduction port 42 a communicating with the atmosphere and a vacuum pump 4.
3 is provided with a negative pressure introduction port 42b.
The negative pressure in the pressure chamber 40 is adjusted by switching control between the atmosphere and the negative pressure by the negative pressure control valve 42.

For example, when the negative pressure in the pressure chamber 40 increases, the diaphragm 38 is displaced upward in the drawing against the compression coil spring 39, and the valve body 37 is driven to lift. The lift of the valve body 37 in this manner causes the EGR passage 3
5, the EGR guided from the exhaust pipe 23 to the intake pipe 22
The gas volume is adjusted. The lift operation of the valve body 37 is performed by the ECU.
10 is controlled by a lift command signal output to the negative pressure control valve 42. The details will be described later.

An EGR gas temperature sensor 44 for detecting the temperature of the EGR gas is provided in the middle of the EGR passage 35, and a detection signal of the sensor 44 is input to the ECU 10.

The ECU 10 detects the operating state of the engine based on the detection signals of the various sensors described above. Specifically, the accelerator opening VA based on the detection signal of the accelerator opening sensor 17, the fresh air intake amount GA based on the detection signal of the fresh air intake sensor 30, and the detection signal of the fresh air temperature sensor 31 are used. Based on the fresh air temperature TA, the intake pressure PM based on the detection signal of the intake pressure sensor 32, the engine speed NE based on the detection signal of the rotation speed sensor 33, based on the detection signal of the EGR gas temperature sensor 44. EGR gas temperature TE
Are calculated respectively.

Further, the ECU 10 controls the distribution type fuel injection pump 11 in accordance with the engine operating state calculated as described above.
, And outputs a command signal based on the calculated value to the fuel injection pump 11 to supply fuel from the fuel injection nozzle 13 to the diesel engine 20. Further, the ECU 10 determines a target opening of the EGR valve 36 (a lift command value of the valve body 37) according to the engine operating state, and based on the command value, determines the negative pressure control valve 4.
2 is driven.

On the other hand, the ECU 10 detects the oxygen concentration (exhaust gas oxygen concentration ΨO2) in the exhaust gas discharged from each cylinder of the diesel engine 20, and stores the detected value in the EGR gas oxygen concentration memory 10a as needed. As shown in FIG. 8, the memory 10a has ten areas of memory addresses "m" to "m + 9", and each area has an exhaust gas oxygen concentration detected for each of the exhaust strokes of the # 1 to # 4 cylinders. ΨO2 is stored and held. Here, the same subscript (cylinder number) of the ΨO2 value indicates the same value (a value detected in the same exhaust stroke), and the number of areas where the same value is stored is determined by the EGR valve 36.
Corresponds to the amount of EGR gas recirculated to the intake pipe 22 via. The memory addresses m to m + 9 indicate positions in the EGR passage 35 from the branch point to the exhaust pipe 23 to the EGR valve 36.

The individual exhaust gas oxygen concentration ΨO2 stored in the memory 10a is stored in the EGR passage 35 and sequentially returned to the intake pipe 22 in the EGR gas.
It corresponds to GR gas oxygen concentration (EO2) and ECU1
In the case of “0”, the “$ O2 value” in the memory 10a is appropriately read to calculate the “$ EO2 value”. The ΨO2 value at address m in the memory 10a (ΨO2 # 3 on the left side in FIG. 8) is the oldest, and this is substantially the value of E in the region closest to the EGR valve 36.
This corresponds to the oxygen concentration of the GR gas. Also, m + 9 address Ψ
The O2 value (ΨO2 # 2 on the left side of FIG. 8) is the latest, which substantially corresponds to the oxygen concentration of the EGR gas in a region farthest from the EGR valve 36.

Next, the operation of the electronic control system according to the present embodiment will be described. FIGS. 3 and 4 are flowcharts showing an EGR valve control routine for realizing the control operation in the present embodiment. The routine is performed for each fuel injection of each cylinder (180 ° CA for four cylinders). ECU1
Performed by 0. According to this routine, the lift command value of the EGR valve 36 is calculated so that the in-cylinder intake oxygen amount matches the target value, and the opening degree of the EGR valve 36 is controlled based on the lift command value.

When the above routine starts, E
First, at step 110, the CU 10 sets the accelerator opening VA,
The engine speed NE, fresh air intake amount GA, intake pressure PM, fresh air temperature TA, and EGR gas temperature TE are read. Also, E
The CU 10 calculates the fuel injection amount QF in a subsequent step 120 by a known method. Generally, the fuel injection amount QF is
It is calculated by searching a map in the ROM of the ECU 10 according to the accelerator opening VA and the engine speed NE at that time.

Thereafter, the ECU 10 proceeds to step 130,
At 140, EG is performed by searching each map in the ROM.
The basic lift amount of the R valve 36 (hereinafter, the basic lift command value SB)
S) and a target value of the intake oxygen amount into the cylinder (hereinafter, referred to as a target intake oxygen amount GTT) is calculated. That is,
In steps 130 and 140, the current fuel injection amount Q
Basic lift command value SBS from F and engine speed NE
And the target intake oxygen amount GTT are calculated. Here, the target intake oxygen amount GTT is equal to the accelerator opening degree V as the acceleration request.
A may be provided as a map value that also reflects A.

Next, the ECU 10 determines in step 150 that E
The GR gas oxygen concentration ΨEO2 is calculated. At this time, EC
In U10, the exhaust gas oxygen concentration ΨO2 in the EGR gas oxygen concentration memory 10a, other engine speed NE, fresh air intake amount GA, intake pressure PM, fresh air temperature TA, EGR gas temperature TE, and the like are stored in accordance with the procedure of FIG. Is used to calculate the EGR gas oxygen concentration ΨEO2.

In step 160, the ECU 10 calculates the in-cylinder intake oxygen amount GTO2. At this time, the ECU 1
0 calculates the in-cylinder intake oxygen amount GTO2 using the EGR gas oxygen concentration ΨEO2 calculated in step 150 according to the procedure of FIG.

Thereafter, the ECU 10 uses the in-cylinder intake oxygen amount GTO2 and the target intake oxygen amount GTT calculated in step 170, and calculates the absolute value of the difference between them (| GTO2-GT).
T |) is within a predetermined allowable range. |
If GTO2-GTT | is out of the allowable range, the ECU 10
Deems that the EGR lift command value needs to be corrected. In this case, the ECU 10 makes a negative determination in step 170 and performs the processing in steps 180 and 190, and after that processing proceeds to step 200 in FIG.

That is, if | GTO2-GTT | is out of the allowable range, the ECU 10 determines in step 180 the difference ΔGT (= GTO2) between the target value and the actual value of the in-cylinder intake oxygen amount.
-GTT) is calculated. Further, the ECU 10 calculates the lift command correction value SK of the EGR valve 36 in the following step 190 using the calculated difference ΔGT according to, for example, a well-known PID control method.

If | GTO2-GTT | is within the allowable range, the ECU 10 determines that the correction of the EGR lift command value is unnecessary. In this case, the ECU 10 determines in step 170
Is affirmatively determined and steps 180 and 190 are skipped.
Proceed directly to step 200 in FIG.

In step 200 of FIG.
Calculates the final lift command value SED of the EGR valve 36. Here, if step 170 is YES, the ECU 1 determines that the lift command correction value SK has not been calculated.
0 sets the basic lift command value SBS calculated in the step 130 as the final lift command value SED (SED = SB
S). If step 170 is NO, EC
U10 is the lift command correction value SK of step 190.
Is added to the basic lift command value SBS of step 130 to calculate the final lift command value SED (SED = S
BS + SK).

The opening of the EGR valve 36 is controlled based on the calculated final lift command value SED. Specifically, the negative pressure controlled by the negative pressure control valve 42 is controlled to a value corresponding to the final lift command value SED, and the controlled negative pressure is introduced into the pressure chamber 40 of the EGR valve 36. And
The EGR valve 36 opens or closes by the amount of the negative pressure introduced into the pressure chamber 40, and the EGR gas is increased or decreased.

In step 210 after the calculation of the SED value,
The ECU 10 calculates the oxygen concentration in the exhaust gas discharged after the combustion (exhaust gas oxygen concentration ΨO2). At this time, EC
U10 calculates the exhaust gas oxygen concentration ΨO2 using the calculated fuel injection amount QF, the in-cylinder intake oxygen amount GTO2, and the like according to the procedure of FIG. 7 described later.

Also, the ECU 10 stores the exhaust gas oxygen concentration ΨO2 calculated in step 220 in the EGR gas oxygen concentration memory 10a with the cylinder number (# 1 to # 4) which is the exhaust stroke at that time, Thereafter, this routine ends. At this time, the ΨO2 value stored in the memory 10a is
The latest $ O2 value is stored in the free memory area of FIG. 8 (for example, addresses m + 8 and m + 9 on the right side of FIG. 8).

FIG. 5 is a flowchart showing step 150 in FIG.
Is a flowchart showing a subroutine for calculating the EGR gas oxygen concentration ΨEO2 in FIG. In FIG. 5, the ECU 10
Is the fresh air intake amount G read in step 151
The unit of A is converted from [g / cyl] to [mol / cyl] convenient for the subsequent calculation, and the fresh air intake amount GA ′ in [mol / cyl] unit is calculated. Further, the ECU 10 determines in the subsequent step 152 that the in-cylinder intake gas amount (the total amount of gas sucked into the cylinder) GT when the in-cylinder intake gas temperature is 300 [K].
Calculate 300 ′ [mol / cyl]. At this time, RO
Engine speed NE at each time by searching the map in M
GT300 'value is calculated according to and intake pressure PM.

Thereafter, the ECU 10 determines in step 153 that the calculated fresh air intake amount GA ′ [mol / cyl] is equal to 3
In-cylinder intake gas amount GT300 '[mol / c] at 00 [K]
yl], and the in-cylinder intake gas amount GT '[mol / cy] corresponding to the fresh air temperature TA and the EGR gas temperature TE at that time.
1] is calculated. In detail, a relational expression in which the in-cylinder intake gas amount is inversely proportional to the in-cylinder intake gas temperature and a relational expression in which the in-cylinder intake gas temperature is obtained from the ratio of the respective gas amounts of the fresh air temperature TA and the EGR gas temperature TE. The in-cylinder intake gas amount GT ′ [mol / cyl] is calculated according to the following equation (1).

[0040]

(Equation 1)

Thereafter, the ECU 10 calculates the fresh air intake amount GA ′ calculated in step 154 and the in-cylinder intake gas amount G
From T ′, the amount of EGR gas GE ′ [mol / cyl] sucked into the cylinder is calculated as GE ′ = GT′−GA ′.

Next, in step 155, the ECU 10 calculates the volume (EGR gas volume VE [liter]) occupied by the calculated EGR gas amount GE 'in the EGR passage 35. Here, the exhaust pressure PE is obtained from the engine speed NE and the fuel injection amount QF at that time by searching a map in the ROM.
[Atm. abs. ] And the following equation (2)
EGR gas volume VE [liter] is calculated by the following formula.

[0043]

(Equation 2)

That is, the EGR gas volume VE is equal to the exhaust pressure P
E, is calculated based on the EGR gas amount GE ′ and the EGR gas temperature TE. In the above equation (2), the coefficient “22.
"4" corresponds to the gas volume per mole under standard conditions (atmospheric pressure).

Thereafter, at step 156, the ECU 10
Means that the EGR gas sucked into the cylinder during this intake stroke is E
The passage length LE [mm] occupied in the GR passage 35 is calculated based on the calculated EGR gas volume VE.

LE = VE · 1000 / AE (3) In the above equation (3), “AE” is a sectional area [mm 〔2] of the EGR passage 35. Thereafter, the ECU 10 calculates the number of addresses N of the ΨO2 value to be read from the memory 10a from the path length LE calculated in step 157 and the path length ΔL per address of the EGR gas oxygen concentration memory 10a, It is calculated by the following equation (4).

N = LE / ΔL (4) However, in the N value calculated by the equation (4), the fractional part is omitted. Here, as shown in FIG.
Is set to "10" and the total length of the EGR passage 35 (the length from the branch point to the exhaust pipe 23 to the EGR valve 36) is set to "L", the passage length .DELTA.L per memory address Is ΔL = L / 10. Incidentally, ΔL is a unique value for each system determined by the total length L of the EGR passage 35 and the total number of memory areas.

Finally, based on the memory value (ΨO2 value) for the number of addresses N calculated in step 158, the ECU 10 calculates the EGR gas oxygen concentration ΨEO2 using the following equation (5).
Is calculated.

ΨEO2 = (ΨO21 + ΨO22 +... + ΨO2N) / N (5) That is, the ΨO2 value corresponding to the number N of addresses in the EGR gas oxygen concentration memory 10a is read from the oldest one, and the read ΨO2
The two values are integrated and averaged.

The EGR gas oxygen concentration memory 10 shown in FIG.
a, for example, when N = 2, two ΨO2 values with small memory addresses, that is, “ΨO2 values at addresses m and m + 1”
2 # 3 "is read and the same value is integrated and averaged, whereby the EGR gas oxygen concentration ΨEO2 is calculated.

FIG. 6 is a flowchart showing the operation of step 160 in FIG.
Is a flowchart showing a subroutine for calculating the in-cylinder intake oxygen amount GTO2 in FIG. In FIG. 6, the ECU 10
In step 161, the in-cylinder intake oxygen amount GTO2 'in units of [mol / cyl] is calculated. At this time, the in-cylinder intake oxygen amount GA ′ [mol / cyl] is obtained according to the following equation (6) derived from the relationship obtained from the sum of the oxygen amount in the fresh air and the oxygen amount in the EGR gas. ], The in-cylinder intake gas amount GT '[mol / cyl], and the EGR calculated in step 150.
From the gas oxygen concentration ΨEO2, the in-cylinder intake oxygen amount GTO
2 ′ is calculated.

GTO2 ′ = 0.21 · GA ′ + ΨEO2 · (GT′−GA ′) (6) In the equation (6), the preceding term on the right side represents the fresh air intake amount GA ′ and the oxygen concentration in the fresh air ( (About 21%) to calculate the amount of oxygen in the fresh air.
T′−GA ′) and the oxygen concentration in the EGR gas ΔEO2
The oxygen amount in the EGR gas is calculated from the product of

The ECU 10 proceeds to the next step 162
The unit of the in-cylinder intake oxygen amount GTO2 ′ calculated above is
[Mol / cyl] is converted to [g / cyl] and [g / cyl]
[cyl] unit, the in-cylinder intake oxygen amount GTO2 is calculated.
After the unit conversion of the GTO2 value, this subroutine ends.
The in-cylinder intake oxygen amount GTO2 calculated in this way is used for feedback control of the in-cylinder intake oxygen amount as described above (steps 170 to 190 in FIG. 3).

FIG. 7 is a flowchart showing step 210 in FIG.
Is a flowchart showing a subroutine for calculating exhaust gas oxygen concentration ΨO2 in FIG. In FIG. 7, the ECU 10 first sets the unit of the fuel injection amount QF to [g / cy] in step 211.
l] to [mol / cyl] units converted to CH2, and the fuel injection amount QCH2 ′ [mol / cyl converted to CH2]
1] is calculated. Here, the CH2 conversion means “CHn”
The composition of the fuel (light oil) represented by is replaced by "CH2" to simplify and calculate the reaction during fuel combustion.

In the following step 212, the ECU 10
The oxygen concentration in the exhaust gas discharged in the exhaust stroke after combustion, that is, the exhaust gas oxygen concentration ΨO2 is calculated. At this time, the in-cylinder intake oxygen amount GTO is calculated according to the following equation (7), which is obtained assuming that the in-cylinder intake gas and the fuel injected into the cylinder are completely burned.
2 '[mol / cyl], the in-cylinder intake gas amount GT' [mol / cyl], and the fuel injection amount QCH2 '[mol / cyl]
Is used to calculate the exhaust gas oxygen concentration ΨO2.

[0056]

(Equation 3)

In short, assuming that 1 mole of fuel "CH2" is completely burned, 1 mole of CH2 and 3/2 mole of O2 burn, resulting in the formation of 1 mole of CO2 and 1 mole of H2O. (CH2 → CO2 + H2 O-3 /
2O2). In such a case, in the above equation (7), the denominator on the right side corresponds to the total gas amount discharged when the fuel has completely burned, and the numerator corresponds to the total oxygen amount discharged when the fuel has completely burned. . Therefore, the exhaust gas oxygen concentration ΨO2 can be calculated by dividing the total oxygen amount in the exhaust gas by the total gas amount.

The ECU 10 stores the exhaust gas oxygen concentration ΨO2 calculated as described above in the EGR gas oxygen concentration memory 10a as needed. The exhaust gas oxygen concentration ΨO2 stored in the memory 10a is equal to the EGR gas oxygen concentration ΨEO as described above.
2 are sequentially read (step 158 in FIG. 5).

Here, the EGR gas concentration memory 10a
Will be described. As shown in FIG. 8, in the memory 10a before updating (left side in the figure), for example, # 3, # 4,
Exhaust gas oxygen concentration of # 2 cylinder ΨO2 # 3, ΨO2 # 4, ΨO2
# 2 is remembered. The same "@O" is set at addresses m to m + 3.
2 # 3 ”is the same“ @ O2 # 4 ”at addresses m + 4 to m + 6.
However, the same “$ O2 # 2” is stored at addresses m + 7 to m + 9. The number of areas where the same value is stored corresponds to the EGR gas amount at the time of detecting the ΨO2 value.

When the next combustion cylinder is the # 2 cylinder, the EGR gas amount GE is calculated for the # 2 cylinder, the exhaust gas passage length LE occupied by the EGR gas, and the number of memory addresses corresponding to the LE. N is calculated (steps 154 to 157 in FIG. 5). At this time, if the number N of the memory addresses is “2”, the values of the addresses m and m + 1 from the memory 10a (left side in FIG. 8) before the update (both in FIG.
3) is read out and used for calculating the EGR gas oxygen concentration ΨEO2 (step 158 in FIG. 5). The value (@ O2 # 3) of the address m, m + 1 is read out, and at the same time, the value is erased. Then, the values of the addresses m + 2 to m + 9 are moved up and stored so as to fill the empty area of the memory 10a.

Thereafter, the exhaust gas oxygen concentration ΨO2 of the cylinder in which the # 2 cylinder is in the exhaust stroke during the intake stroke, that is, the # 1 cylinder is calculated (step 21 in FIG. 4).
0). Then, the calculated exhaust gas oxygen concentrationΨO2 # 1
Are stored in the empty area (addresses m + 8 and m + 9) of the memory 10a. As described above, in the EGR gas oxygen concentration memory 10a, the outflow and inflow operations of the ２O2 value are repeatedly performed.

FIG. 2 is a time chart showing the outline of the above operation more specifically. In FIG. 2, before time t1 (the same applies after time t2), the accelerator pedal opening VA is kept substantially constant, and the vehicle is traveling normally. Therefore, the engine speed NE, the fuel injection amount QF, the EGR gas oxygen concentration ΨEO2, the EGR opening degree (the opening degree of the EGR valve 36), the in-cylinder intake oxygen amount GTO2, and the NOx generation amount are maintained at substantially constant values. .

When the accelerator pedal 15 is depressed at time t1 to start acceleration, the fuel injection amount QF increases and the engine speed NE increases accordingly. Note that the period during which the engine speed NE fluctuates in response to the accelerator operation is actually slightly delayed from the accelerator operation period, but for convenience, FIG. 2 shows the accelerator depression period (time t1 to t2). Engine speed NE
Are shown in the same manner.

At time t1, the EGR is caused by the accelerator operation.
The opening starts to decrease. Further, since the exhaust gas oxygen concentration detected for each exhaust stroke decreases due to an increase in the fuel injection amount QF, the EGR gas oxygen concentration ΨEO2 also starts to decrease. At this time, the recirculation delay time of the exhaust gas increases due to the decrease in the EGR opening, and the EGR gas oxygen concentration 実 際 EO2 actually decreases little by little due to the recirculation delay time. EGR gas oxygen concentrationΨEO
Since 2 (exhaust gas oxygen concentration) is handled, the recirculation delay time is not reflected, and the EGR gas oxygen concentration ΨEO2 is estimated to be lower than the true value (solid line) as shown by the broken line in the figure.
Therefore, as also indicated by the broken line, the EGR opening becomes small, and the in-cylinder intake oxygen amount GTO2 is controlled to be larger than the optimum value. As a result, the NOx generation amount excessively increases.

On the other hand, in the present embodiment, time t1 to time t1
At t2, the EGR gas oxygen concentration ΨEO2 is calculated in consideration of the recirculation delay time of the EGR gas (exhaust gas) staying in the EGR passage 35. Therefore, even when the exhaust gas recirculation delay time increases when the EGR opening decreases, the ΨEO2 value does not deviate from the true value. Therefore, the in-cylinder intake oxygen amount GTO2 corresponding to the ΨEO2 value is controlled to the optimal value. As a result, a good combustion state is maintained, and an excessive increase in the amount of generated NOx is prevented.

In this embodiment, step 154 in FIG. 5 corresponds to the exhaust gas recirculation amount detecting means, step 210 in FIG. 4 corresponds to the exhaust gas oxygen concentration detecting means, and step 158 in FIG. Steps 170 to 200 in FIGS. 3 and 4 correspond to the gas oxygen concentration calculating means and the exhaust gas recirculation amount controlling means, respectively.

According to the embodiment described above, the following effects can be obtained. (A) In the present embodiment, the history of the exhaust gas oxygen concentration ΨO2 detected for each exhaust stroke is stored as needed in the EGR gas oxygen concentration memory 10a, and the length of the EGR passage 35 occupied by the EGR gas amount at that time. The oxygen concentration of the exhaust gas (EGR gas) recirculated to the intake pipe 22 (EGR gas oxygen concentrationΨEO2) is calculated from the memory value stored before the exhaust gas recirculation delay time corresponding to the length. I made it. Then, the exhaust gas recirculation amount (the opening degree of the EGR valve 36) is controlled using the calculated ΔEO2 value.
Therefore, even during a transient operation such as vehicle acceleration / deceleration, the in-cylinder intake oxygen amount can be appropriately controlled, and the problem that the NOx emission amount excessively increases can be solved. As a result, EGR
The gas oxygen concentration can be accurately grasped, and the EGR control can be accurately performed.

(B) A plurality of storage areas are provided in the EGR gas oxygen concentration memory 10a, and a memory value corresponding to the EGR gas amount is read out to calculate the EGR gas oxygen concentration ΨEO2. In this case, the EGR gas oxygen concentration ΨEO2 reflecting the recirculation delay time can be easily and accurately calculated.

(C) In the EGR control, the memory value of the exhaust gas oxygen concentration ΨO2 after use is deleted, and the memory 10a is updated with the exhaust gas oxygen concentration ΨO2 of another cylinder at the time of the exhaust stroke instead. did. In this case, the exhaust gas oxygen concentration ΨO2 detected for each cylinder is stored in the same memory 10.
a and can contribute to a reduction in memory capacity.

(D) In this embodiment, the exhaust gas recirculation amount (the opening of the EGR valve 36) is controlled so that the in-cylinder intake oxygen amount GTO2 becomes the target intake oxygen amount GTT according to the engine operating state. And During vehicle acceleration, the EGR gas amount is suppressed (the EGR valve 36 is controlled to the closed side) to increase the in-cylinder intake oxygen amount GTO2 in accordance with the target intake oxygen amount GTT, and an increase in the fresh air intake amount is encouraged. In such a case, ideal combustion can be realized without shortage of the amount of oxygen taken into the cylinder. At this time, the acceleration performance is not impaired.

(E) When calculating the EGR gas oxygen concentration ΨEO2, the in-cylinder intake oxygen amount GTO2, and the exhaust gas oxygen concentration ΨO2, calculations are performed in terms of moles. for that reason,
Each value of ΨEO2, GTO2, ΨO2 can be calculated accurately.

The embodiment of the present invention can be realized in the following modes other than the above. In the above embodiment, the EGR
Although ten regions were provided in the gas oxygen concentration memory 10a,
Change this configuration. The memory 10a is provided with 10 or more (for example, 20) areas, and the exhaust gas oxygen concentration ΨO2 is stored in these areas as needed. In this case, the passage length ΔL per memory address becomes shorter, and the number of memory addresses N becomes 1 to
20 (step 15 in FIG. 5).
7). By increasing the total number of areas of the memory 10a, fine control becomes possible.

Further, the total number n of the used regions of the EGR gas oxygen concentration memory 10a is made variable, and the passage length ΔL per address of the memory (= full length L / n) is appropriately changed. For example, during steady operation, the total number n is set to a relatively small value, and during transient operation due to acceleration or deceleration of the vehicle, the total number n is set to a relatively large value. According to the present embodiment, when the oxygen concentration in the EGR passage 35 is substantially uniform (during steady operation), the area of the memory 10a to be used can be minimized,
When the oxygen concentration in the EGR passage 35 is different between the exhaust pipe side and the intake pipe side (during transient operation), highly accurate EGR control can be performed in consideration of the recirculation delay time.

In the above embodiment, in the routine of FIG. 5, the exhaust gas oxygen concentration ΨO2 (ΨO21, 1O22,...) For the number N of addresses in the memory 10a according to the EGR gas amount.
(ΨO2N) is read, and the EGR gas concentration ΨEO2 is calculated from the integrated average of the read ΨO2 values. This configuration is changed. For example, as shown in FIG. 8, when a plurality of memory values to be read are the same (in FIG.
3) The value of 積 算 O2 # 3 is read as it is without performing the integrated averaging process. Only when the memory values to be read are different, the process of the integrated averaging is performed. In this case, the calculation load on the integrated average can be reduced.

The configuration may be such that the cylinder discrimination data is not added to the ΨO2 value stored in the EGR gas oxygen concentration memory 10a. In the above embodiment, the memory 10a
Although the number of the same ２O2 values in corresponds to the EGR gas amount, this configuration is changed. For example, the data of $ O2 itself and the number data of $ O2 corresponding to the EGR gas amount are separately stored.

In the routine of FIG. 3 in the above embodiment, the determination processing of step 170 is deleted. In this case, the deviation ΔGT of the in-cylinder intake oxygen amount and the lift command correction value SK are always calculated, and the EGR gas oxygen concentration ΨEO2
Is reflected in the hourly EGR control.

For example, the EGR gas amount for each intake stroke is detected by a flow meter, or the exhaust gas oxygen concentration for each exhaust stroke is detected by an oxygen concentration sensor (for example, a limiting current type oxygen concentration sensor). You may. in this case,
The exhaust gas recirculation amount detecting means and the exhaust gas oxygen concentration detecting means described in the claims are constituted by the respective sensors.

In the above embodiment, the in-cylinder intake oxygen amount GTO2 is controlled to the target value by adjusting the opening of the EGR valve 36, but this is changed. The intake throttle valve 16 may be of an electronic control type, and the in-cylinder intake oxygen amount GTO2 may be controlled to a target value by adjusting the opening of the intake throttle valve 16. In such a case, for example, when the vehicle is accelerated due to the operation of depressing the accelerator pedal, the intake throttle valve 16 is controlled to the open side, and an increase in the fresh air intake amount is promoted, so that the in-cylinder intake oxygen amount increases. Even with this configuration, ideal combustion can be realized.

In the above embodiment, the present invention is embodied in the EGR device of the four-cylinder diesel engine, but this is changed. The present invention may be applied to a multi-cylinder engine other than a four-cylinder engine, a single-cylinder engine, or a gasoline engine. In such a case, NO
x Emissions can be reduced, and the object of the present invention can be achieved.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing an outline of an engine control system according to an embodiment of the present invention.

FIG. 2 is a time chart for explaining an operation in the embodiment.

FIG. 3 is a flowchart showing an EGR valve control routine.

FIG. 4 is a flowchart showing an EGR valve control routine continued from FIG. 3;

FIG. 5 is a flowchart showing a subroutine for calculating an EGR gas oxygen concentration.

FIG. 6 is a flowchart showing a subroutine for calculating an in-cylinder intake oxygen amount.

FIG. 7 is a flowchart showing a subroutine for calculating an exhaust gas oxygen concentration.

FIG. 8 is a schematic diagram showing a configuration of an EGR gas oxygen concentration memory.

[Explanation of symbols]

10: ECU (electronic control device) constituting exhaust gas recirculation amount detection means, exhaust gas oxygen concentration detection means, recirculation gas oxygen concentration calculation means, exhaust gas recirculation amount control means, 10a: EGR gas oxygen concentration memory, 20: diesel engine, 22 …
Intake pipe, 35 ... EGR passage (exhaust gas recirculation passage), 36 ...
EGR valve.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI F02D 41/02 351 F02D 41/02 351 45/00 368 45/00 368F 376 376B (56) References JP-A-5-18324 ( JP, A) JP-A-2-275055 (JP, A) JP-A-63-140856 (JP, A) JP-A-59-120770 (JP, A) (58) Fields studied (Int. Cl. ⁷ , (DB name) F02M 25/07 550 F02M 25/07 570 F02D 21/08 301 F02D 35/00 368 F02D 41/02 351 F02D 45/00 368 F02D 45/00 376

Claims (5)

(57) [Claims] An exhaust gas recirculation control device for an internal combustion engine for recirculating a part of exhaust gas of an internal combustion engine to an intake system through an exhaust gas recirculation passage, wherein the amount of exhaust gas recirculated for each intake stroke through the exhaust gas recirculation passage is determined. Exhaust gas recirculation amount detecting means for detecting; exhaust gas oxygen concentration detecting means for detecting oxygen concentration in exhaust gas for each exhaust stroke; memory for storing the history of the detected oxygen concentration in exhaust gas as needed; Calculate the length of the exhaust gas recirculation passage occupied by the flow rate and calculate the oxygen concentration of the exhaust gas recirculated to the intake system from the memory value stored just before the recirculation delay time of the exhaust gas corresponding to the length. Exhaust gas recirculation control for an internal combustion engine, comprising: concentration calculation means; and exhaust gas recirculation amount control means for controlling the exhaust gas recirculation amount using the calculated oxygen concentration of the recirculated exhaust gas. Location. 2. The apparatus according to claim 2, wherein the memory has a plurality of storage areas, and stores and retains a history of the exhaust gas oxygen concentration for each of the areas. Read the corresponding number of oxygen concentration memory values,
2. The exhaust gas recirculation control device for an internal combustion engine according to claim 1, wherein an oxygen concentration of the recirculated exhaust gas is calculated based on the read memory value. 3. The exhaust gas recirculation control device according to claim 2, wherein the recirculated gas oxygen concentration calculating means averages a memory value of the oxygen concentration to calculate an oxygen concentration of the recirculated exhaust gas. apparatus. 4. The exhaust gas recirculation control device according to claim 2, wherein the detected value of the exhaust gas oxygen concentration at that time is stored in a memory area corresponding to the detected exhaust gas recirculation amount. Exhaust gas recirculation control device. 5. An exhaust gas recirculation control device applied to a multi-cylinder internal combustion engine, wherein when the exhaust gas recirculation amount is controlled using the memory value of the exhaust gas oxygen concentration, the memory value of the used exhaust gas oxygen concentration is deleted. The exhaust gas recirculation control device for an internal combustion engine according to any one of claims 1 to 4, wherein the memory is updated with the exhaust gas oxygen concentration of another cylinder which is in an exhaust stroke at that time.