JP4432593B2 - Intake pressure estimation device for internal combustion engine - Google Patents

Description

  The present invention relates to a technique for estimating an intake pressure in the vicinity of an intake valve of an internal combustion engine.

  The in-cylinder gas composition of the internal combustion engine is composed of newly sucked fresh air and residual gas. To know the in-cylinder gas composition, it is necessary to estimate the residual gas amount. In addition to the gas remaining in the gap volume in the cylinder, the residual gas includes exhaust that blows between the exhaust side and the intake side during the overlap period of the intake valve open period and the exhaust valve open period (hereinafter referred to as blow-off gas and There is. Therefore, in order to estimate the residual gas amount with high accuracy, it is necessary to obtain the blown gas amount with high accuracy. The blown-out gas amount depends on the pressure difference between the exhaust side and the intake side, and it is necessary to accurately estimate the intake pressure in the vicinity of the intake valve during the overlap period.

By the way, in Patent Document 1, the engine speed that resonates with intake pulsation (resonance speed) is corrected by the intake air temperature, and the correction amount is applied to the error correction of the intake air flow rate detected by the air flow meter. An error correction amount for the intake air flow rate is obtained based on the engine speed corrected according to the intake air temperature and the temperature ratio in the reference state and the throttle opening.
Japanese Patent Laid-Open No. 10-153465

However, when the throttle opening is used as a parameter representing the amplitude of the intake pulsation as in Patent Document 1, it does not correspond to the case where the internal EGR rate changes and the amplitude of the intake pulsation changes. Even if it is corrected, complicated calculation is required.
The present invention has been made paying attention to such a conventional problem. By appropriately setting a parameter representing the amplitude of the intake pulsation, the intake pressure in the vicinity of the intake valve can be estimated with high accuracy. An object of the present invention is to provide an intake pressure estimation device for an internal combustion engine.

For this reason, the present invention provides means for detecting or estimating the cylinder pressure immediately before opening the intake valve, means for detecting or estimating the intake pressure smoothed by the surge tank in the intake passage, and the previously determined intake pressure and intake valve opening. For each pressure ratio to the immediately preceding cylinder internal pressure, a map that stores the pulsating intake pressure and the difference between the pulsating intake pressure and the smooth pressure in relation to the engine speed as a pulsation correction value, and the equivalent pipe length of the modeled intake pipe The means for calculating the tuning order by dividing the fundamental frequency calculated based on the sound speed and the engine speed, the engine speed when the predetermined tuning order is obtained by the actual intake pipe shape, and the calculation from the engine speed at which the tuning order to be become the previous SL predetermined tuning order and the same, and means for calculating a revolution speed modification component, the intake and the detection or estimated intake pressure valve Hirakijika The pulsation compensation value of the map is set based on the pressure ratio of the cylinder pressure of, in response to the rotational speed correction amount, and means for shifting the rotational speed direction, and the detection or estimated intake pressure, when the Means for calculating a pulsating intake pressure downstream of the surge tank based on the corrected pulsation correction value selected from the shifted map based on the rotation speed of the engine.

  According to the present invention, the intake pulsation is generated as a vibration force by the ratio of the cylinder internal pressure just before the intake valve opening and the intake pipe internal pressure taking into account the internal EGR rate. By correcting the smoothed intake pressure detection value in the pulsation state obtained based on the internal pressure and the intake pipe internal pressure, the intake pressure in the vicinity of the intake valve is estimated with high accuracy without being affected by the change in the internal EGR rate. Can do.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the configuration of an engine according to an embodiment of the present invention.
An air cleaner 12 is attached to the introduction portion of the intake passage 11, and dust or the like in the intake air is removed by the air cleaner 12. In the intake passage 11, an electronically controlled throttle valve 13 is installed downstream of the air cleaner 12. A surge tank 14 is attached downstream of the throttle valve 13, and a branch 15 is attached to the surge tank 14 to constitute an intake manifold. The intake air in the surge tank 14 flows into the cylinder through the branch 15 and the intake port 16 formed in the cylinder head. A fuel supply injector 17 is installed in the intake port 16 of each cylinder.

  In the engine body, the combustion chamber 18 is formed as a space sandwiched between the cylinder head and the piston 19. The combustion chamber 18 is connected to the intake port 16 on one side with respect to the cylinder center axis, and the intake port 16 is opened and closed by the intake valve 20. The intake valve 20 is driven by an intake cam 21. In addition, the combustion chamber 18 is connected to the exhaust port 22 on one side opposite to the intake port 16, and the exhaust port 22 is opened and closed by an exhaust valve 23. The exhaust valve 23 is driven by an exhaust cam 24. An intake side variable valve device 25 is provided for the intake cam 21, and an exhaust side variable valve device 26 is provided for the exhaust cam 24, and the intake cam 21 or the exhaust cam is provided by these variable valve devices 25, 26. The operation characteristic of the intake valve 20 or the exhaust valve 23 can be changed by changing the phase of each of the 24 camshafts. The variable valve operating devices 25 and 26 may adopt any type such as a hydraulic type and a solenoid type, but in this embodiment, the opening / closing timing (that is, the valve timing) of the intake valve 20 or the exhaust valve 23 is determined. By changing, an overlap period between the intake valve opening period and the exhaust valve opening period (hereinafter simply referred to as “overlap period”) is adopted. A spark plug 27 is installed in the cylinder head so as to face the substantially upper center of the combustion chamber 18.

A first catalytic converter 29 is interposed in the exhaust passage 28 immediately after the exhaust manifold, and a second catalytic converter 30 is interposed downstream thereof. The exhaust gas flowing out to the exhaust port 22 passes through the catalytic converters 29 and 30 and the muffler 31 and is released into the atmosphere.
The operations of the injector 17, the spark plug 27, and the variable valve gears 25 and 26 are controlled by an engine control unit (hereinafter referred to as “ECU”) 41. The ECU 41 includes an intake air amount detection signal from the air flow meter 51, an intake air pressure detection signal from the pressure sensor 52, an intake air temperature detection signal from the temperature sensor 53, a cooling water temperature detection signal from the temperature sensor 54, and a crank angle sensor 55. Unit crank angle and reference crank angle detection signal (the ECU 41 calculates the engine speed NE based on this), an exhaust pressure detection signal from the pressure sensor 56, an exhaust temperature detection signal from the temperature sensor 57, The air-fuel ratio detection signal from the oxygen sensor 58, the accelerator opening detection signal from the accelerator sensor 59, and the cam angle detection signals from the cam angle sensors 60 and 61 (based on this, the actual position of the cam and the camshaft). The phase difference can be detected). The intake pressure detected by the pressure sensor 52 is detected as a pressure in which the pulsation is smoothed in the surge tank 14 having a large capacity. However, it may be smoothed by performing an averaging process. Further, the smoothed intake pressure may be estimated based on the engine operating state. The ECU 41 sets the control amount of each device described above based on each input signal.

Hereinafter, estimation of the intake pressure in the vicinity of the intake valve by the ECU 41, in particular, the intake pressure during the overlap period necessary for calculating the residual gas amount (internal EGR amount) will be described.
In this embodiment, when estimating the pulsating intake pressure, the pulsation correction value corresponding to the pulsation change is calculated using the pulsation amplitude parameter and the phase parameter, and the smoothed intake air detected by the pressure sensor 52 is calculated. The pressure is estimated by correcting with the pulsation correction value.

  First, the outline of the phase parameter of the pulsation will be explained. The tuning order is calculated from the fundamental frequency calculated based on the intake pipe shape and the sound speed and the engine speed, and the intake pulsation pressure (pressure wave) is calculated using the tuning order. ) Is calculated. The tuning frequency of the intake pulsation pressure is the engine speed (synchronization speed) synchronized with the intake pulsation pressure. Here, since the intake pulsation pressure is synchronized with the opening and closing of the intake valve, that is, a traveling wave according to the engine speed, the tuning order characteristic with respect to the engine speed is corrected according to the traveling wave, and will be described later. Thus, the speed of sound changes with the intake air temperature, and therefore the engine speed corrected with the intake air temperature is used as the phase parameter of the intake pulsation pressure.

FIG. 2 is a flowchart of a tuning rotation speed (tuning frequency) calculation routine.
The ECU 41 stores a tuning order table shown in FIG. 6 (a straight line L2 indicated by a solid line in FIG. 6). Using this tuning order table, the tuning rotational speed corresponding to the actual operating conditions is obtained as shown in FIG. Calculation is performed as in step 1 (indicated by S1 in the figure, the same shall apply hereinafter) and step 2.

Here, the process of creating the tuning order table will be described with reference to the flowchart of FIG.
The tuning order table is set by correcting the theoretical expression of the tuning order at the reference intake air temperature (for example, 25 ° C.) by the result of simulation or experiment.
In step 11, the equivalent pipe length Le when the intake valve is closed is set as shown in the following equation (1).
Le = 2 (Lint + ΔLint) (1)
Lint is the actual pipe length of the intake passage, and ΔLint is the open end correction.

In step 12, the fundamental frequency Fint at the reference intake air temperature of 25 ° C. is calculated from the following equation (2) for calculating the fundamental frequency Fint from the sound velocity Spsd and the equivalent pipe length Le and the equation (3) for calculating the sound velocity.
Fint = Spsd / (2 × Le) (2)
Spsd = √ {κair × Rair × Tint} (3)
Here, Tint is the intake air temperature, κair is the specific heat ratio, and Rair is the gas constant. In this step 12, Tint = 25 ° C.

  In step 13, the tuning order characteristic when the pressure wave in the intake pipe is assumed to be a standing wave is obtained. This calculates the tuning order Mint0 at the modeled equivalent pipe length Le corresponding to the engine speed NE at the reference intake air temperature of 25 ° C. from the basic frequency Fint and the engine speed NE in step 12, and is shown by the dotted line in FIG. The tuning order characteristic represented by the straight line L1 is obtained. The straight line L1 indicates the reciprocal of the tuning order Mint0 and is expressed by the following equation.

1 / Mint0 = (1 / (120 × Fint)) × NE (4)
In step 14, the traveling wave correction is performed on the tuning order characteristic of step 13 as follows, the tuning order characteristic after traveling wave correction of the straight line L2 shown by the solid line in FIG. 4 is obtained, and the basic tuning order is set. First, the intake / exhaust pressure ratio Ppr at the reference intake air temperature (25 ° C. in the present embodiment) corresponding to the engine speed NE obtained in the actual intake pipe shape is obtained as a parameter by simulation or experiment. Here, the intake / exhaust pressure ratio Ppr is calculated as a ratio between the intake pressure detected by the pressure sensor 52 and the exhaust pressure detected by the pressure sensor 56, and used as an amplitude parameter of the intake pulsation pressure as will be described later. It is done. FIG. 5 shows a waveform of the intake pressure in the vicinity of the intake valve at the intake / exhaust pressure ratio Ppr = 1 corresponding to the fully opened state that generates a large intake pulsation pressure. A predetermined tuning order Mint = A in actual characteristics is read from the obtained waveform of FIG. 5, and the engine speed NEa1 at a point corresponding to the tuning order Mint = A is read. Here, the tuning order Mint is n (integer) when it corresponds to the valley of the pressure wave, and n + 1/2 when it corresponds to the peak. N can be calculated and determined from the engine speed. A ratio between the engine speed NEa1 and the engine speed NEa0 at the same tuning order A in the straight line L1 in FIG. 4 is obtained, and a correction coefficient K is set by the following equation (5). Using this correction coefficient K, the slope of the straight line L1 is corrected by the following equation (6) so that the modeled tuning order Mint0 in step 3 matches the actual tuning order Mint, and the tuning shown by the straight line L2 in FIG. The order characteristic is obtained, and this is set as the basic tuning order.

K = NEa0 / NEa1 (5)
1 / Mint = (1 / (120 × Fint)) × K × NE (6)
In the ECU 41, the basic tuning order characteristic (straight line L2) after traveling wave correction obtained in step 4 is stored as a tuning order table. The basic tuning order characteristic may be stored as a function instead of the table.

  When actually calculating the tuning rotational speed, the intake air temperature Tint and the engine rotational speed NE are read in Step 1 of FIG. In step 2, a tuning rotational speed NEK at the detected intake air temperature Tint is calculated. Here, the detected tuning order B at the engine speed NER is searched from the basic tuning order characteristic (straight line L2) at the reference intake air temperature shown in the tuning order table of FIG. Further, the fundamental frequency Fint at the detected intake air temperature Tint (for example, 70 ° C.) is calculated from the equations (2) and (3). Then, from the retrieved tuning order B and the calculated fundamental frequency Fint, the engine speed NEa2 calculated using the equation (6) is set as the actual tuning speed NEK.

In this way, the tuning order is calculated from the fundamental frequency of the intake air and the engine speed, and the tuning speed of the engine is calculated using this tuning order, so that not only the intake air temperature but also the engine speed is taken into account. Numerical characteristics can be calculated.
Further, by using the tuning order characteristic (basic tuning order characteristic) corrected in the traveling wave in step 14, the attenuation in the period from the start of the intake to the start of the next intake is considered, and the influence of the intake stroke of the other cylinders is taken into consideration. Thus, the tuning rotational speed characteristic can be calculated with higher accuracy. Since the tuning rotational speed characteristic correlates with the pulsation phase of the intake pressure, the use of this characteristic improves the estimation accuracy of the intake pressure pulsation described later.

  Using the tuning rotational speed characteristic calculated as described above, the intake pressure in the vicinity of the intake valve in consideration of the pulsation is estimated using the intake / exhaust pressure ratio as the amplitude parameter of the intake pulsation and the engine speed as the phase parameter. Here, the intake pulsation is generated as a vibration force by the ratio between the cylinder pressure just before the intake valve is opened and the intake pressure in the intake pipe, and the amplitude of the pulsation correlates with the vibration force. Since the exhaust valve is opened, the cylinder pressure immediately before the intake valve is opened can be the exhaust pressure, and therefore the intake / exhaust pressure ratio Ppr can be used as the amplitude parameter of the intake pulsation. Further, the cylinder internal pressure (exhaust pressure) immediately before the intake valve is opened may be estimated using the engine operating state.

  Further, if the intake / exhaust pressure ratio Ppr is used as an amplitude parameter, the exhaust pressure used as the cylinder pressure immediately before the intake valve is opened is equal to the internal EGR rate even if the internal EGR rate is changed by changing the valve timing. Since it is a value detected including a change due to a change, the amplitude of the intake pulsation is compared with that using the throttle opening as an amplitude parameter, which cannot detect the influence of the amplitude change due to the change in the internal EGR rate as in Patent Document 1. Can be captured with high accuracy, and there is no need for correction and re-adaptation due to changes in the internal EGR rate.

  The ECU 41 stores a pulsation correction map in addition to the tuning order table of FIG. The pulsation correction map obtains the characteristics of the intake pressure pulsating according to the engine speed for each of a plurality of different intake / exhaust pressure ratios Ppr at a reference intake air temperature of 25 ° C. by simulation (see FIG. 7). The difference (+, − value) of the intake pressure with respect to the smooth pressure is stored as the pulsation correction value DPint.

FIG. 8 is a flowchart of an intake pressure estimation routine according to the present invention. This routine is executed every predetermined time.
In step 21, the intake air temperature Tint, the intake pressure Pmani, the exhaust pressure Pex, and the engine speed NE detected by various sensors are read.
In step 22, the tuning rotational speed NEK at the intake air temperature Tint detected as described above is calculated. For example, if the tuning order Mint = B and the detected intake air temperature Tint = 70 ° C., the engine speed NEa2 is calculated as the tuning speed NEK.

  In step 23, a difference DNE between the tuning rotational speed NEK (= NEa2) calculated in step 22 and the detected current engine rotational speed NER is calculated, and the detected intake pressure Pmani and exhaust pressure in the pulsation correction map are calculated. The characteristic curve of the pulsation correction value DPint corresponding to the ratio of Pex (shown by a broken line in FIG. 9) is shifted by the difference DNE with respect to the engine speed, and the characteristic of the pulsation correction value DPint in the pulsation correction map is shown by the solid line in FIG. Modify as follows.

  In step 24, using the characteristic of the corrected pulsation correction value DPint, the pulsation correction value DPint (point X in FIG. 9) at the detected engine speed NE is searched. Here, in order to clarify the content, the map is shifted and searched. However, in practice, it is a complicated process to shift the entire characteristic data of the pulsation correction map by the difference DNE. Therefore, the pulsation correction map is left as it is, and the rotation speed shifted by the difference DNE in the direction opposite to the shift direction of the map with respect to the detected value NE of the engine speed (if DNE is positive, NE to DNE is changed. Subtraction, if DNE is negative, the same value X is retrieved even if retrieval is performed from the original map shown by the dotted line using NEH (the rotational speed obtained by adding DNE to DNE), and simple processing is sufficient.

In step 25, the detected pulsation correction value DPint is added to the detected intake pressure Pmani to calculate the intake pressure Pint near the intake valve in consideration of the pulsation.
Pint = Pmani + DPint (7)
Thus, since the intake pressure is estimated using the intake / exhaust pressure ratio Ppr as the amplitude parameter and the engine speed as the phase parameter, the estimation accuracy of the intake pressure near the intake valve can be improved.

Configuration diagram of an engine according to an embodiment of the present invention Flow chart of tuning rotation speed calculation routine Flow chart explaining the tuning order table creation process Illustration of creation of basic tuning order characteristics A diagram showing the relationship between the intake pressure near the intake valve and the engine speed in the fully open state and the reference intake air temperature Diagram showing tuning order table A graph showing the relationship between the intake pressure near the intake valve and the engine speed using the intake / exhaust pressure ratio at the reference intake temperature as an amplitude parameter Flow chart of intake pressure detection routine The figure explaining search of a pulsation correction value

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 11 Intake passage 13 Throttle valve 16 Intake port 18 Combustion chamber 20 Intake valve 22 Exhaust port 23 Exhaust valve 28 Exhaust passage 41 Engine control unit 52 Manifold pressure sensor 53 Intake temperature sensor 55 Crank angle sensor 56 Exhaust pressure sensor

Claims (3)

Means for detecting or estimating the pressure in the cylinder immediately before the intake valve is opened;
Means for detecting or estimating the intake pressure smoothed by the surge tank in the intake passage;
A map for storing the pulsating intake pressure and the difference between the pulsating intake pressure and the smooth pressure in association with the engine speed as a pulsation correction value for each pressure ratio between the intake pressure obtained in advance and the cylinder internal pressure immediately before opening the intake valve; ,
Means for calculating the tuning order by dividing the fundamental frequency calculated based on the modeled equivalent pipe length and sound speed of the intake pipe by the engine speed;
Actual engine speed at which a predetermined tuning orders are example by the intake pipe shape from an engine rotational speed when the tuning order that the calculated is the same as the previous SL predetermined tuning order, rpm Means for calculating the correction amount;
Means for shifting the pulsation correction value of the map set based on the pressure ratio between the detected or estimated intake pressure and the cylinder internal pressure immediately before opening the intake valve in the rotation speed direction according to the rotation speed correction; ,
Means for calculating the pulsating intake pressure downstream of the surge tank based on the detected or estimated intake pressure and the corrected pulsation correction value selected from the shifted map based on the rotational speed at that time;
An intake pressure estimation device for an internal combustion engine, comprising: The rotational speed correction amount calculating means includes:
Correction coefficient from the ratio of the engine speed when the predetermined tuning order obtained by the actual intake pipe shape is equal to the engine speed when the calculated tuning order is the same as the predetermined tuning order To calculate
The basic tuning order is obtained by correcting the tuning order at the modeled reference intake air temperature according to the correction coefficient,
Furthermore, the difference between this basic tuning order and the engine speed that becomes the same tuning order at the intake air temperature at that time is obtained,
The intake pressure estimation device for an internal combustion engine according to claim 1, wherein the difference in the rotational speed is used as the rotational speed correction.   The exhaust pressure in the exhaust pipe is used as the cylinder internal pressure immediately before the intake valve opening when estimating the pulsating intake pressure while the open periods of the intake valve and the exhaust valve overlap. Or the intake pressure estimating device for an internal combustion engine according to 2;

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