JPH0819881B2 - Exhaust gas recirculation rate detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an E measuring EGR rate by an oxygen concentration sensor.
Regarding improvement to GR rate detector.

[Conventional technology]

It is known that an exhaust gas recirculation (EGR) device of an internal combustion engine is provided with an oxygen concentration sensor for detecting an exhaust gas recirculation rate (EGR rate). (For example, JP-A-60-13
See No. 8263. This type of EGR detector has the advantage of being able to know the exact EGR rate without being affected by exhaust gas deposits. That is, the oxygen concentration sensor detects the oxygen concentration in the total intake air including the recirculated exhaust gas. Therefore, assuming that the air-fuel ratio is controlled to be constant, the signal level from the oxygen concentration sensor changes according to the change in the flow rate of the reflux gas, and the signal level of the oxygen concentration sensor represents the EGR rate. Become. Then, the EGR valve can be controlled by the signal from the oxygen concentration sensor so as to achieve the desired EGR rate.

[Problems to be solved by the invention]

The oxygen concentration detected by the oxygen concentration sensor arranged in the intake pipe changes periodically due to the influence of intake pulsation. For example, in a 4-cylinder internal combustion engine, the crank angle changes at a wavelength of 180 °. Therefore, there is a problem that the measured value of the oxygen concentration, that is, the measured value of the EGR rate is affected by the crank angle at the time of measurement, and the EGR rate cannot be accurately measured.

In addition, the output of the oxygen concentration sensor changes even with the same oxygen concentration value due to differences between solids and changes over time.
Affects accurate measurement of EGR rate.

An object of the present invention is to enable accurate measurement of the EGR rate regardless of the influence of pulsation and the difference between individuals and the influence of change over time on the output value of the oxygen concentration sensor.

[Means for solving problems]

According to the present invention, in FIG. 1, the flow rate of the recirculated exhaust gas from the exhaust pipe 1a of the internal combustion engine 1 to the intake pipe 1b is set to the desired EGR.
Control device for exhaust gas recirculation 2
In the internal combustion engine equipped with, the oxygen concentration detection means 1c installed in the intake pipe downstream of the position of introduction of the recirculated exhaust gas to the intake pipe 1b, the operating conditions of the internal combustion engine not performing the exhaust gas recirculation operation By comparing the output value of the oxygen concentration detecting means 1c with a predetermined value in the operating state of the internal combustion engine that does not perform exhaust gas recirculation, the oxygen concentration detecting means 1c
Means for calculating the correction value of the output value of EGR rate detecting means 5 for calculating the EGR rate from the oxygen concentration in the total intake air to the internal combustion engine including the recirculated exhaust gas from the exhaust gas recirculation device And a crankshaft position detecting means 6 for detecting a crankshaft position having a phase difference of approximately 180 ° in the output waveform of oxygen concentration, and an average value of the EGR rate based on the oxygen concentration at each crank angle having a phase difference of approximately 180 °. Means 7
And a means 8 for correcting the calculated EGR rate with the correction value.

[Action]

The oxygen concentration detection means 1c detects the oxygen concentration at the downstream side of the position where the recirculated exhaust gas is introduced into the intake pipe 1b, and the non-EGR operation determination means 3 determines and corrects when the exhaust gas recirculation operation is not performed. The value calculating means 4 compares the output value of the oxygen concentration detecting means 1c with a predetermined value when the non-EGR operation determining means 3 determines that the internal combustion engine is in the operating state in which the exhaust gas recirculation is not performed, and thereby the oxygen concentration detecting means 1c. The correction value of the output value of is calculated.

The EGR rate detecting means 5 calculates the EGR rate from the oxygen concentration detected by the oxygen concentration detecting means 1c including the recirculated exhaust gas from the exhaust gas recirculation device.

The crankshaft position detecting means 6 detects a crankshaft position having a phase difference of approximately 180 ° in the output waveform of the oxygen concentration detecting means 1c, and the average value calculating means 7 has a phase detected by the crankshaft position detecting means 6 of approximately 180 °. The average value of the EGR rate at each different crank angle is calculated.

The correction means 8 calculates the EGR rate by the correction value calculation means 6
It is corrected by the correction value calculated by.

〔Example〕

In FIG. 2, 10 is a cylinder block, 12 is a piston, 14 is a connecting rod, 16 is a combustion chamber, 18 is a cylinder head, 20 is an intake valve, 22 is an intake port, 24 is an exhaust valve, and 26 is an exhaust port. . The intake port 22 is an intake pipe 28,
It is connected to an air cleaner 34 via a surge tank 30 and a throttle valve 32. Reference numeral 35 is a fuel injector, which is arranged in the intake pipe 28 adjacent to the intake port 22. Exhaust port
26 is connected to the exhaust manifold 36. 38 indicates a distributor.

An exhaust gas recirculation passage (EGR passage) 40 that connects the exhaust manifold 36 and the intake pipe 28 is provided, and an exhaust gas recirculation control valve (EGR valve) 42 is installed on the EGR passage 40. The EGR valve 42 is connected to the diaphragm 44, and the opening degree of the EGR valve 42 is controlled according to the negative pressure applied to the diaphragm 44. Diaphragm 44
Are connected by a first pressure conduit 46 to the negative pressure port 30a of the surge tank 30 and by a second pressure conduit 48 to an atmospheric pressure port 50 upstream of the throttle valve 32. A negative pressure control valve 52 is provided in the first pressure conduit 46, and
An atmospheric pressure control valve 54 is installed in the pressure conduit 48 of the. By controlling the opening of the negative pressure control valve 52 and the atmospheric pressure control valve 54,
The negative pressure acting on the diaphragm 44 is controlled, the diaphragm 44 takes a lift that balances with the urging force of the compression spring 56, and the amount of recirculated gas can be controlled arbitrarily.

The control circuit 60 operates to detect the EGR rate according to the present invention,
It controls the EGR rate and is configured as a microcomputer system. That is, the control circuit 60 includes a micro processing unit (MPU) 60a and a memory 60b.
The input port 60c, the output port 60d, and the bus 60e connecting them are the basic components. Input port 6
0d is connected to various sensors, and each operating condition signal is input. The throttle sensor 62 is connected to the throttle valve 32 and generates a signal according to the opening degree of the throttle valve 32. The intake pipe pressure sensor 64 is connected to the surge tank 30 and generates a signal according to the intake pipe pressure in the surge tank 30. The crank angle sensor 66 is provided in the distributor 38,
It is possible to know the engine speed as is well known by generating a pulse signal for every 30 ° CA according to the angular position of the crankshaft. The first oxygen concentration sensor 68 is installed in the exhaust manifold 36. The first oxygen concentration sensor 68 is configured as a linear O ₂ sensor (or a lean sensor) that generates a signal of a level that continuously changes according to the oxygen concentration, and as is well known, the fuel from the signal from the O ₂ sensor is used. The fuel injection amount from the injector 35 is controlled and maintained at a predetermined air-fuel ratio.

According to the present invention, the second oxygen concentration sensor 70 is the intake pipe.
The oxygen concentration in the total intake air including the recirculation gas from the EGR passage 40 provided in 70 can be known. The second oxygen concentration sensor 70 is also linear O ₂ similarly to the first oxygen concentration sensor.
The sensor (or lean sensor) has a well-known configuration and can detect a continuous change in oxygen concentration. Then, the EGR rate can be detected by combining with the intake pipe pressure detected by the intake pipe pressure sensor 64. The principle of measuring the EGR rate will be described. The second oxygen concentration sensor 70 can detect the oxygen concentration MPO ₂ in the total intake air including the EGR gas. By dividing the oxygen concentration MPO ₂ detected in this way by the air density of 0.21, it is possible to know the partial pressure of fresh air in the total intake air. Therefore, if the pressure of all intake air including EGR gas is PM, the measured EGR rate (E
GRc) can be basically calculated by (PM-MPO ₂ /0.21)/PM. Incidentally, FIG. 3 is a graph showing the relationship between the EGR rate and the oxygen concentration MPO ₂ for each intake pipe pressure PM. Furthermore, the value measured by the second oxygen concentration sensor 70
MPO ₂ measures the oxygen concentration remaining in the reflux exhaust gas. In order to eliminate the influence of the oxygen concentration remaining in the recirculated exhaust gas, when the oxygen concentration in the exhaust pipe measured by the first oxygen concentration sensor is EPO ₂ , the above equation for measuring the EGR rate is (PM- It is corrected to (MPO ₂ −EPO ₂ ) /0.21) / PM, which makes it possible to know a more accurate EGR rate.

Then, in the EGR rate detection according to the present invention, since there is a pulsation in the oxygen concentration detection value, the oxygen concentration signal level is measured at each point separated by a crank angle which is half the cycle of the pulsation, and the EGR rate is calculated by the average value thereof. I try to measure the rate. That is, in a four-cylinder internal combustion engine, as shown in FIG. 4, the signal level from the second oxygen concentration sensor 70 has a pulsation with a cycle of 180 ° at a crank angle that is 1/4 of one engine cycle. In the present invention, the sensor output values Vox (0), Vox (9
0) is detected and the EGR rate is calculated from the average value.

The control circuit 60 for detecting the EGR rate according to the present invention will be described below.
The operation of will be described with a flowchart. Figure 5 shows EG
The input routine of the output value of the 2nd oxygen concentration sensor 70 for measuring R rate is shown. This routine has a crank angle of 30
It can be a crank angle interrupt routine executed every °. At step 74, it is judged if the crank angle is at the first reference position (this is assumed to be 0 °). When the determination is affirmative, the routine proceeds to step 75, where the current output value Vox of the oxygen concentration sensor 70 is stored in Vox (0). When No is determined in step 74, the process proceeds to step 76, and a half cycle (90 °) of pulsation from the first reference position.
Second crank angle position away from the crankshaft (determined whether this is the position of 90 °. If affirmative, step
Proceed to 77 and the current output value Vox of the oxygen concentration sensor 70 is Vox.
Stored in (90). Step 78 outlines another routine that is performed every 30 ° CA.

FIG. 6 shows an EGR rate control routine. At step 80, it is judged if the engine is currently in the EGR operating range. For example, the low load operating range where the throttle valve 32 is slightly opened
It is the EGR region. If it is not in the EGR range, proceed to step 82,
It is determined whether or not it is an idle condition. The idle condition can be grasped when the throttle valve 32 is at the idle opening and the engine speed is smaller than a predetermined value. If it is in the idle state, the routine proceeds to step 84, and AirPO ₂ which is the reference value of the oxygen concentration in the intake pipe in the idle state is input 5 from the memory 60b. Step 86
Then, the output calibration value K is the _second reference value of the idle reference value AirPO ₂ .
It is calculated as the ratio of the oxygen concentration MPO ₂ actually measured by the oxygen concentration sensor 70. That is, the EGR rate and the second oxygen concentration sensor 7
As shown in FIG. 3, there is a linear relationship with the oxygen concentration MPO ₂ actually measured by 0 if the intake pipe pressure is fixed. In this case, the proportional constant, that is, the slope of the straight line is shown in FIG. There are variations. If this is left as it is, an accurate EG
R rate control becomes impossible. Therefore, during a constant operation without EGR, for example, the reference value of the oxygen concentration during idling is stored, and the oxygen concentration value MPO ₂ during idling actually measured by the second oxygen concentration sensor 70 during actual operation is stored. By calculating the output calibration value K which is the ratio of the output calibration value K and multiplying the output calibration value K by the actual measurement value of the sensor, the actual measurement value MPO ₂ of the oxygen concentration sensor is calibrated to prevent variations.

At step 88, the memory address EGRD storing the EGR valve opening signal is filled with 0, which is a value corresponding to the full closure of the EGR valve 42. Therefore, as will be described later, the EGR valve 42 is closed.

If the EGR condition is determined in step 80, step 90
And the calculation of EGR ₀ , which is the target EGR rate determined by the engine operating conditions, is executed. The value of EGR ₀ depends on the operating state, for example, the intake pipe pressure as a load and the number of revolutions. That is, the memory 60b stores the EGR ₀ value for the combination of the load and the rotational speed, and the EGR ₀ value for the load and the rotational speed measured by the sensors 64 and 66 is interpolated.

In the next step 92, the target EGR valve opening (EGR ₀ D) that can obtain the EGR rate target value EGR ₀ calculated in step 90 is calculated. The calculation method of EGR ₀ D is the same as the calculation method of EGR ₀ , the data of EGR ₀ D corresponding to the load and the rotation speed are stored in the memory, and the load and the rotation speed measured by the sensors 64 and 66 are calculated. The interpolation calculation is executed.

In step 93, the crank angle position of 0 ° and 90 °
Output value of the second oxygen concentration sensor 70 at the crank angle position of
The average value of Vox (0) and Vox (90) is calculated and put in the address storing the oxygen concentration signal value MPO ₂ .

In step 94, the oxygen concentration signal value MPO ₂ calculated by the second oxygen concentration sensor 70 is multiplied by the calibration value K calculated in step 86 to correct the variation in the oxygen concentration signal.

In step 96, EGR _c , which is the currently measured EGR rate, is calculated by (PM− (MPO ₂ −EPO ₂ ) /0.21) / PM. Here, EPO ₂ is the oxygen concentration in the exhaust gas measured by the first oxygen concentration sensor.

In step 98, the deviation Δ from the measured EGR rate EGR _c and the target EGR rate EGR ₀ calculated in step 90 is calculated.

In step 100, the contents of the address storing FEGR which is the EGR rate feedback correction coefficient are updated to the current value plus k × Δ. Here, k is a feedback gain. In step 102, the content of the address EGRD for inputting the EGR valve opening signal is the current value multiplied by the EGR valve opening target value EGR ₀ D by the feedback correction coefficient FEGR.

In this embodiment, the target EGR valve opening is calculated and the target EGR valve opening is calculated.
The EGR valve drive signal is obtained by multiplying the feedback correction coefficient FEGR so that the deviation Δ between the GR rate and the measured EGR rate becomes zero. Therefore, the control speed to the target EGR valve opening can be improved. However, as a simpler feedback control method, step 92 is omitted,
EGRD is increased or decreased according to the deviation between the target EGR rate and the measured EGR rate,
The opening degree of the EGR valve may be controlled to increase or decrease.

In step 104, EGR valve drive signal forming processing is performed, and drive signals for the negative pressure control valve 54 and the atmospheric pressure control valve 52 are formed so that the EGR valve opening degree calculated in step 102 is obtained. For example, a pulse signal having a duty ratio such that the calculated EGR valve opening is obtained is formed and applied to the negative pressure control valve 52 and the atmospheric pressure control valve 54. That is, the negative pressure control valve 52 is driven by a pulse signal having a duty ratio directly proportional to EGRD, and the atmospheric pressure control valve 54 is driven by a pulse signal having a duty ratio inversely proportional to EGRD.

〔The invention's effect〕

In the EGR rate control according to the present invention, the oxygen concentration sensor signal representing the EGR rate is taken in at crank angle positions separated by about half the cycle of the pulsation, and the EG is calculated by the average value of these.
The R rate is calculated, and the oxygen concentration sensor output value is corrected with a correction value calculated by comparing the oxygen concentration sensor output value during non-EGR operation with a reference value. Therefore, regardless of pulsation, inter-individual difference and change over time, accurate EG
The R rate can be detected.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of the present invention. FIG. 2 is a diagram showing the configuration of an embodiment of the present invention. FIG. 3 is a graph showing the relationship between the EGR rate and the output of the oxygen concentration sensor with respect to each intake pipe pressure. FIG. 4 is a graph schematically showing how the output value of the second oxygen concentration sensor for EGR rate measurement changes. 5 and 6 are flowcharts for explaining the operation of the control circuit for EGR control. FIG. 7 is a graph for explaining the EGR rate and the output fluctuation of the oxygen concentration sensor when the intake pipe pressure is fixed. 28 …… Intake pipe 30 …… Surge tank 32 …… Throttle valve 36 …… Exhaust manifold 40 …… EGR passage 42 …… EGR valve 52 …… Negative pressure control valve 54 …… Atmospheric pressure control valve 60 …… Control circuit 64 ...... Intake pipe pressure sensor 68 …… First oxygen concentration sensor 70 …… Second oxygen concentration sensor

Claims (1)

[Claims] 1. An internal combustion engine equipped with an exhaust gas recirculation control device for controlling the flow rate of recirculated exhaust gas from an exhaust pipe of an internal combustion engine to an intake pipe so as to obtain a desired EGR rate. Oxygen concentration detection means installed in the intake pipe downstream of the exhaust gas introduction position, means for discriminating the operating conditions of the internal combustion engine that does not perform exhaust gas recirculation operation, and internal combustion engine that does not perform exhaust gas recirculation A means for calculating a correction value for the output value of the oxygen concentration detecting means by comparing the output value of the oxygen concentration detecting means with a predetermined value in the operating state, and the internal combustion engine including the recirculated exhaust gas from the exhaust gas recirculation device. The EGR rate detection means that calculates the EGR rate from the oxygen concentration in the total intake air to the engine and the phase in the output waveform of the oxygen concentration is approximately 180
° Crankshaft position detecting means for detecting different crankshaft positions, means for calculating the average value of the EGR rate based on the oxygen concentration at each crank angle having a phase difference of approximately 180 °, and the calculated EGR rate as the correction value And an exhaust gas recirculation rate detection device.