JPH07208272A - Egr control device of engine - Google Patents

Abstract

PURPOSE:To realize the EGR control where the reduction of the NOX rate of discharge and the supression of the combustion fluctuation ratio are consistent. CONSTITUTION:The combustion fluctuation ratio is calculated by a combustion fluctuation ratio calculating means M4 based on the pressure in the cylinder to be detected by an in- cylinder pressure sensor, and the combustion fluctuation ratio is compared with the allowable limit value of the combustion fluctuation ratio in the present operating condition by a combustion fluctuation ratio comparing means M5. On the other hand, NOX ratio of discharge is obtained by the NOX concentration detected by a NOX concentration sensor and the sucked air volume by a NOX ratio of discharge calculating means M6, and the NOX ratio of discharge is compared with the NOX ratio of discharge allowable limit value by a NOX ratio of discharge comparing means M7. The target EGR ratio is set by a target EGR ratio setting means M9 so that the combusion fluctuation ratio may be lower than the combustion fluctuation ratio allowable limit value, and the NOX ratio of discharge may be lower than the NOX ratio of discharge allowable limit value. The driving signal corresponding to this target EGR is outputted to an EGR valve 18 through an EGR valve driving circuit 30. The EGR control is realized both from the combustion fluctuation ratio and from the NOX ratio of discharge, and the reduction of the NOX ratio of discharge can be consistent with the improvement of the traveling performance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EGR control device for an engine which achieves both reduction of nitrogen oxide emission rate in exhaust gas and improvement of running performance.

[0002]

2. Description of the Related Art Conventionally, nitrogen oxides during combustion (hereinafter referred to as
As an effective means of suppressing the generation of “NOX”, exhaust gas recirculation (hereinafter, referred to as “NOX”) increases a heat capacity of in-cylinder gas by mixing a part of exhaust gas with intake air to relatively lower the gas temperature during combustion. Abbreviation as "EGR") control is widely adopted. However, it is also known that if the amount of EGR is large, the fluctuation in combustion causes the decrease in output, the deterioration in fuel consumption, and the instability of the running performance, and therefore the amount must be kept to the minimum necessary.

For example, in Japanese Unexamined Patent Publication No. 2-252958, the EGR control range is defined into a feedback control range and an open loop control range according to the operating conditions of the engine. In the feedback control range, the accelerator opening and the engine speed are set. A technique is disclosed in which a target EGR rate in the operating state is set by a map search as a parameter and the EGR supply amount is controlled.

Further, in Japanese Unexamined Patent Publication No. 2-298657, the EGR amount is controlled according to the intensity of the combustion light generated in the combustion chamber to avoid a rapid increase of the combustion speed.
A technique for suppressing the generation of OX is disclosed.

[0005]

However, the above-mentioned Japanese Unexamined Patent Application Publication No.
In the EGR control disclosed in Japanese Patent No. 252958, the target EGR rate is determined by the operating condition, so it is possible to perform the EGR control corresponding to the NOx generation amount, but NO
It is not possible to suppress combustion fluctuations due to the reduction of the X emission amount, and it is not possible to always obtain good running performance in the EGR control range.

In this respect, in the above-mentioned Japanese Patent Laid-Open No. 2-298657, since the combustion state is detected by the light intensity, it is possible to perform EGR control corresponding to the combustion state, but NOX.
Since the emission amount is not detected, there is a problem in the control accuracy of the EGR supply amount.

The present invention has been made in view of the above circumstances, and it is possible to obtain good control accuracy while achieving both suppression of combustion fluctuation and reduction of NOx emission amount.
It is an object of the present invention to provide an EGR control device for an engine that can obtain driving performance that meets the driver's requirements.

[0008]

In order to achieve the above object, an EGR control device for an engine according to the present invention comprises a combustion fluctuation rate calculating means for calculating a combustion fluctuation rate based on the in-cylinder pressure detected by the in-cylinder pressure detecting means. With the nitrogen oxide emission rate calculation means for calculating the nitrogen oxide emission rate based on the nitrogen oxide concentration in the exhaust gas detected by the nitrogen oxide concentration detection means and the intake air amount, the combustion fluctuation rate and the current operating conditions Combustion fluctuation rate comparison means for comparing with the combustion fluctuation rate allowable limit value, and nitrogen oxide discharge rate comparison means for comparing the nitrogen oxide discharge rate with the nitrogen oxide discharge rate allowable limit value under the current operating conditions. , The EGR rate is increased when the nitrogen oxide emission rate is higher than the nitrogen oxide emission rate allowable limit value, and the EGR rate is reduced when the combustion variation rate is higher than the combustion variation rate acceptable limit value, and Above combustion fluctuation Is lower than the combustion fluctuation rate allowable limit value and the nitrogen oxide discharge rate is lower than the nitrogen oxide discharge rate allowable limit value, the EGR rate is increased / decreased in accordance with the driver's request. Target E to set the rate
And a GR rate setting means.

[0009]

[Operation] In the present invention, the combustion fluctuation rate of the engine is obtained based on the in-cylinder pressure detected by the in-cylinder pressure detection means, and the nitrogen oxide in the exhaust gas and the intake air amount detected by the nitrogen oxide concentration detection means are calculated. Calculate the nitrogen oxide emission rate from

Next, the combustion fluctuation rate and the combustion fluctuation rate allowable limit value under the operating condition are compared, and the nitrogen oxide discharge rate and the nitrogen oxide discharge rate allowable limit value under the operating condition are compared. Compare with.

When the combustion fluctuation rate is higher than the combustion fluctuation rate allowable limit value, the GER amount is decreased, while the nitrogen oxide discharge rate is higher than the nitrogen oxide discharge rate allowable limit value. At this time, the EGR amount is increased to reduce the nitrogen oxide emission amount.

When the combustion fluctuation rate and the nitrogen oxide discharge rate are within the EGR control range set by the combustion fluctuation rate allowable limit value and the nitrogen oxide discharge rate allowable limit value, the driver The EGR rate is appropriately set according to the preference. In other words, if the driver prioritizes running performance, set the EGR rate to the lower side within the limit of the nitrogen oxide emission rate,
When priority is given to fuel efficiency, EGR should be within the limit of combustion fluctuation rate.
Set the rate higher.

[0013]

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

FIG. 1 shows an embodiment of the present invention, and FIG.
2 is a flowchart showing an EGR control procedure, FIG. 3 is a conceptual diagram showing an EGR control range, FIG. 4 is a schematic diagram of an engine, and FIG. 5 is a circuit diagram of the control device.

Reference numeral 1 in FIG. 4 denotes an engine body, and an intake manifold 2 is connected to the upstream side of the engine body 1, and an intake valve (not shown) provided in an intake port of each cylinder of the intake manifold 2 is directly connected to the intake manifold. The injector 3 faces the upstream side. Further, a throttle valve 5 is provided in an intake pipe 4 communicating with the intake manifold 2, and an air cleaner 6 is provided at an intake port of the intake pipe 4.
Is installed.

An exhaust pipe 8 is connected to the downstream side of the engine body 1 via an exhaust manifold 7, a muffler 9 is connected to the downstream side of the exhaust pipe 8, and exhaust gas is exhausted in the middle of the exhaust pipe 8. A catalyst 10 for purification is installed. It should be noted that the engine shown in the embodiment of the figure controls the theoretical air-fuel ratio, and a three-way catalyst is used as the catalyst 10.

Further, at the intake port of the intake pipe 4 of the intake system,
An air flow meter 11 that detects the mass flow rate of intake air is provided. Further, a throttle sensor 12 for detecting the opening of the throttle valve 5 is connected to the throttle valve 5.

On the other hand, an O2 sensor 13 for detecting the oxygen concentration in the exhaust gas and NO, NO2 in the exhaust gas are provided between the catalyst 10 and the collecting portion of the exhaust manifold 7 of the exhaust system.
And a NOX concentration sensor 14 for detecting the concentration of nitrogen oxides (NOX).

Further, the engine body 1 is provided with an in-cylinder pressure sensor 15 for detecting the in-cylinder pressure of a specific cylinder, and a crank angle sensor 16 is provided opposite to a crank rotor 1b axially attached to the crank shaft 1a. There is. The crank angle sensor 16 detects protrusions and the like formed on the outer circumference of the crank rotor 1b at predetermined intervals. The control unit (ECU) 21 described later determines the engine from the interval time when the protrusions and the like are detected. The number of revolutions, ignition timing, etc. are calculated.

Further, the collecting portion of the exhaust manifold 7 and the collecting portion of the intake manifold 2 are EGR.
The EGR passage 17 is communicated through the passage 17.
An EGR valve 18 is interposed midway. This EG
When the R valve 18 is opened, a part of the exhaust gas is returned to the intake system and reburned according to the opening degree.

As shown in FIG. 5, the ECU 21 is
PU22, ROM23, RAM24, oscillator 25, input ports 26a and 26b, and output ports 26c and 26d.
Is mainly composed of a microcomputer connected via a bus line.

At one input port 26a, analog signals from the air flow meter 11, the NOx concentration sensor 14, and the O2 sensor 13 are sent to the A / D via the multiplexer 22.
It is converted into a digital signal by the converter 23 and sequentially input. Further, the crank angle signal from the crank angle sensor 16 is subjected to predetermined waveform shaping by the shaping circuit 27 and input to the other input port 26b, and the signal from the throttle sensor 12 is input via the input circuit 28, \ u For example, it is determined whether the throttle valve 5 is in the open state or the fully closed state, and the peak value of the output from the in-cylinder pressure sensor 15 is waveform-shaped via the waveform circuit 29. It has been entered.

Further, the mode selection switch 19 is connected to the input port 26b. The mode selection switch 19 selects whether the driver performs EGR control with priority on fuel economy or traveling performance. When the fuel economy priority mode is selected by the mode selection switch 19, EGR control is performed. EGR control is performed with a value that maximizes the EGR rate within the control range, while if the travel performance priority mode is selected, EG is controlled with a value that minimizes the EGR rate within the EGR control range.
R control. \ u Furthermore, the above output ports 26c, 26
The EGR valve 18 and the injector 3 are connected to d via drive circuits 30 and 31, respectively. The opening of the EGR valve 18 is controlled by a control signal of a predetermined duty ratio output from the ECU 21.

Next, the functional configuration of the EGR control in the ECU 21 will be described.

As shown in FIG. 1, the EGR control is performed by detecting the peak value of the in-cylinder pressure for each cycle from the output value of the in-cylinder pressure sensor 29, or the in-cylinder pressure for detecting the in-cylinder pressure at a constant crank angle during the combustion stroke. Detection means M1 \ u, NOx concentration sensor 1
NOx concentration detecting means M2 for detecting the NOx concentration in the exhaust gas from the output value of No. 4, engine speed NE and intake air amount Q
Or the like, the operating condition detecting means M3 for detecting the operating condition of the engine, the ratio between the weighted average value of the peak value of the in-cylinder pressure for each \ u cycle detected by the in-cylinder pressure detecting means M1 and the in-cylinder pressure detected this time, or , A combustion variation rate calculating means M4 \ u for calculating a combustion variation rate from a ratio of a weighted average of the in-cylinder pressure at a constant crank angle for each combustion cycle and a currently detected in-cylinder pressure at the crank angle, and this combustion variation rate calculating means M4 The basic fuel injection amount obtained on the basis of the combustion fluctuation rate calculated in step S1, the engine speed NE and the engine load detected by the operating condition detecting means M3 (for example, the basic fuel injection amount obtained based on the engine speed NE and the intake air amount Q is set as the engine load). ) Is used as a parameter to compare with a combustion fluctuation rate allowable limit value set by a map search, and NOX is calculated from the ratio between the NOX concentration in the exhaust gas and the intake air amount Q. The NOX emission rate calculation means M6 for calculating the output rate, the NOX emission rate calculated by the NOX emission rate calculation means M6, the engine speed NE detected by the operating condition detection means M3, and the engine load (for example, engine speed NE (NOX emission rate comparison means M7 for comparing the basic fuel injection amount obtained based on the intake air amount Q with the engine load) as a parameter and the allowable limit value of NOX emission rate set by map search, mode selection switch 1
Based on the output value of 9, the fuel consumption priority mode or the driving performance priority mode is selected to set the operation mode, the operation mode setting means M8, and the combustion variation rate comparison means M.
If it is determined in step 5 that the combustion fluctuation rate is lower than the combustion fluctuation rate allowable limit value, and if the NOx emission rate comparison means M7 determines that the NOx emission rate is lower than the NOx discharge rate allowable limit value, the driver's Target E according to the selected operation mode
When the GR rate is set and when the combustion fluctuation rate exceeds the combustion fluctuation rate allowable limit value, the target EGR rate is set with a value that reduces the EGR rate, while the NOX emission rate is N
When it is larger than the OX emission rate allowable limit value, the target EGR rate setting means M9 for setting the target EGR rate with a value that increases the EGR rate, and the drive signal corresponding to this target EGR rate is EG.
It is composed of an EGR valve drive circuit 30 for outputting to the R valve 18.

Next, the EGR control procedure by the ECU 21 will be described with reference to the flowchart of FIG.

This flow chart is a routine executed every predetermined crank angle or every predetermined calculation cycle. First, at step S1, various data such as the current engine speed NE, the intake air amount Q and the like which are the operating conditions of the engine are detected. To do. Then, in step S2, the in-cylinder pressure of the current combustion cycle is detected, and in step S3, the combustion fluctuation rate is calculated from the ratio of the weighted average of the in-cylinder pressure of each combustion cycle and the in-cylinder pressure of the current fuel cycle. On the other hand, in step S4, the NOX concentration in the exhaust gas during the current operation is detected based on the output signal of the NOX concentration sensor 14, and in step S5 the NOX emission rate in the exhaust gas is calculated from the ratio of the intake air amount Q and the NOX concentration. calculate.

Then, in step S6, the combustion fluctuation rate is compared with the combustion fluctuation rate allowable limit value set in advance by a map search using the engine speed NE and the engine load as parameters.

FIG. 3 shows the relationship between the EGR rate and the combustion fluctuation rate under certain operating conditions. As shown in the figure, when the EGR rate is increased, the combustion fluctuation rate has a characteristic that it rapidly increases in the middle of the EGR rate. The allowable value of the firing fluctuation rate indicated by point a differs for each operating condition, and In the above map for setting the permissible limit value of the burning fluctuation rate in the above, the permissible limit of the combustion fluctuation for each operating condition is obtained in advance by experiments and stored.

When it is determined in step S6 that the combustion fluctuation rate under the current operating condition is lower than the combustion fluctuation rate allowable limit value, the process proceeds to step S7, while the combustion fluctuation rate is the combustion fluctuation rate. When it is determined that the value is higher than the allowable limit value (point a in FIG. 3), the process jumps to step S10, the target EGR rate is set to a value that reduces the EGR rate to a predetermined value, and the routine exits.

When it is determined in step S6 that the combustion fluctuation rate is lower than the combustion fluctuation rate allowable limit value,
In step S7, the NOX emission rate is compared with the NOX emission rate allowable limit value set in advance by map search using the engine speed NE and the engine load as parameters.

FIG. 3 shows the EGR rate and N under certain operating conditions.
The relationship with the OX emission rate is shown. As shown in the figure, the NOX emission rate fluctuates almost in inverse proportion to the EGR rate, and the NOX emission rate gradually increases as the EGR rate is reduced. Varies according to each operating condition. The allowable limit of the NOx emission rate for each operating condition is obtained in advance from experiments or the like and stored in the map for setting the allowable limit value of the NOx emission rate.

When it is determined in step S7 that the NOX emission rate is larger than the NOx emission rate allowable limit value (point b in FIG. 3), the process jumps to step S9 and E
The target EGR rate is set with a value obtained by increasing the GR rate to a predetermined value, and the routine exits.

On the other hand, if it is determined in step S7 that the NOX emission rate is lower than the NOx emission rate allowable limit value, the process proceeds to step S8, in which the driver selects the fuel consumption priority mode from the output signal from the mode selection switch 19. It is determined whether the driving performance priority mode is selected.

Then, if the fuel economy priority mode is selected, the routine proceeds to step S9, where the target EGR rate is set to a value obtained by increasing the EGR rate by a predetermined amount, and the routine is exited. If the driving performance priority mode is selected, the process proceeds to step S10, the target EGR rate is set to a value obtained by reducing the EGR rate to a predetermined value, and the routine exits.

The drive circuit 30 is attached to the EGR valve 18.
A control signal having a predetermined duty ratio corresponding to the target EGR rate is output via.

Here, the target E is set to a value for increasing the EGR rate.
When the GR rate is set, the opening degree of the EGR valve 18 becomes large, and when the target EGR rate is set to a value that reduces the EGR rate, the opening degree of the EGR valve 18 becomes small. As a result, the EGR rate that recirculates to the intake system by the opening degree of the EGR valve 18 falls within the range from the NOx emission rate allowable limit value (point b in FIG. 3) to the combustion fluctuation rate allowable limit value (point a in FIG. 3). Controlled to fit in.

If the driver selects the driving performance priority mode, the EGR rate is controlled to decrease within the EGR control range, and if the fuel economy priority mode is selected,
Since the EGR rate is controlled to increase within the EGR control range, it is possible to obtain driving performance that meets the driver's request.

The present invention can also be applied to lean air-fuel ratio control. In this case, a lean NOx catalyst is used as the catalyst 10, and an O2 sensor is unnecessary.

[0040]

As described above, according to the present invention,
Since the EGR control under each operating condition is performed based on the combustion variation rate and the NOx emission rate, both suppression of the combustion variation rate and reduction of the NOx emission rate can be satisfied, and highly reliable control accuracy. Can be obtained.

Further, within the range of the EGR control range, control is performed such that the EGR rate is increased when the driver prioritizes fuel consumption, while the EGR rate is decreased when the driver prioritizes running performance. Therefore, it is possible to obtain driving performance that meets the driver's requirements and is convenient.

[Brief description of drawings]

FIG. 1 is a functional block diagram of an EGR control device.

FIG. 2 is a flowchart showing an EGR control procedure.

FIG. 3 is a conceptual diagram showing an EGR control range.

FIG. 4 is a schematic diagram of an engine.

FIG. 5 is a circuit diagram of a control device.

[Explanation of symbols]

 M1 ... In-cylinder pressure detection means M2 ... Nitrogen oxide concentration detection means M4 ... Combustion fluctuation rate calculation means M5 ... Combustion fluctuation rate comparison means M6 ... Nitrogen oxide emission rate calculation means M7 ... Nitrogen oxide emission rate comparison means M9 ... Target EGR Rate setting means Q ... Intake air amount

Claims (1)

[Claims] 1. A combustion variation rate calculating means (M4) for calculating a combustion variation rate based on the in-cylinder pressure detected by the in-cylinder pressure detecting means (M1) and an exhaust gas detected by a nitrogen oxide concentration detecting means (M2). Oxide discharge rate calculation means (M for calculating the nitrogen oxide discharge rate based on the nitrogen oxide concentration of the air and the intake air amount (Q)
6), a combustion fluctuation rate comparison means (M5) for comparing the combustion fluctuation rate with a combustion fluctuation rate allowable limit value under the current operating conditions, and the nitrogen oxide discharge rate and the nitrogen oxide discharge under the current operating conditions. Oxide discharge rate comparison means (M7) for comparing the rate with an allowable limit value, and increasing the EGR rate when the nitrogen oxide discharge rate is higher than the allowable limit for the nitrogen oxide discharge rate, and the combustion fluctuation rate Is lower than the combustion fluctuation rate allowable limit value, the EGR rate is reduced, the combustion fluctuation rate is lower than the combustion fluctuation rate allowable limit value, and the nitrogen oxide discharge rate is the nitrogen oxide discharge rate allowable limit. An EGR control device for an engine, comprising: a target EGR rate setting means (M9) for setting a target EGR rate by increasing or decreasing the EGR rate in a range lower than a value according to a driver's request.