JP4696617B2 - Control device for multi-cylinder internal combustion engine - Google Patents

Description

  The present invention relates to a control device for a multi-cylinder internal combustion engine.

  In recent years, in addition to the throttle valve, a device for controlling on-off valve characteristics such as the phase angle, operating angle, and lift amount of the intake valve and exhaust valve has been provided, and the on-off valve characteristics are also controlled along with the throttle valve opening degree to control the combustion chamber An internal combustion engine that controls the amount of air charged in the engine has been developed and is publicly known.

  On the other hand, conventionally, in a multi-cylinder internal combustion engine, the amount of air charged in the cylinder varies among cylinders due to assembly tolerances and machine differences related to the valve part, or wear and deposit adhesion of the valve part, resulting in torque fluctuations. Or the exhaust emission deteriorates due to variations in the air-fuel ratio of the air-fuel mixture. Such a problem may occur similarly in a multi-cylinder internal combustion engine equipped with the above-described device for controlling the on-off valve characteristics, and in particular, the on-off valve characteristics such that the amount of in-cylinder charged air is reduced, In other words, it is known that the smaller the working angle and lift amount of the intake valve, the larger the value.

  Therefore, conventionally, the cylinder charge air amount to each cylinder is estimated in consideration of the variation between cylinders in the cylinder fill air amount, and fuel injection to each cylinder is performed based on the estimated cylinder fill air amount to each cylinder. A control device for a multi-cylinder internal combustion engine that controls engine operating parameters such as quantity has been proposed.

  For example, in the control device described in Patent Document 1, the intake pressure and temperature in the intake pipe portion detected by the intake pressure sensor and the temperature sensor from the amount of air passing through the throttle calculated based on the output of the throttle opening sensor or the like. By subtracting the increase amount of air in the intake pipe portion calculated based on the above, the in-cylinder charged air amount to each cylinder is calculated. Based on the in-cylinder charge air amount to each cylinder calculated in this way, the in-cylinder charge air amount variation is estimated, and the fuel injection amount to each cylinder is adjusted according to the inter-cylinder variation. By doing so, the air-fuel ratio of the air-fuel mixture filled in each cylinder is suppressed from varying.

JP 2002-70633 A JP 2001-234798 A

  By the way, in the control device described in Patent Document 1, as described above, the intake pressure in the intake pipe portion is used to calculate the amount of increase in the air in the intake pipe portion. In particular, it is considered that the intake pressure in the intake pipe is used on the assumption that the intake pressure of the air in the intake pipe changes gently. It goes up and down due to pulsation. Therefore, it is difficult to accurately calculate the in-cylinder charged air amount and the in-cylinder variation of the in-cylinder charged air amount based on the intake pressure in the intake pipe portion without considering such intake pulsation. .

  Accordingly, an object of the present invention is to accurately calculate the in-cylinder charged air amount or the cylinder-to-cylinder variation of the cylinder charged air amount to each cylinder while taking into account the intake pulsation, and to control the internal combustion engine based on the calculated amount. The object is to provide a control device for a multi-cylinder internal combustion engine.

In order to solve the above-described problem, in the first invention, in a control device for a multi-cylinder internal combustion engine that controls an intake valve so that an on-off valve time of the intake valve becomes a target on-off valve time, a cylinder with an in-cylinder charged air amount is provided. When the estimated in-cylinder filling air amount is less than a predetermined level, the in-cylinder filling air amount to each cylinder is estimated and estimated based on the target on-off valve time. If the variation in the cylinder air charge amount between the cylinders is larger than the predetermined level, at least one engine operating parameter required for estimating the opening / closing valve time of the intake valve is detected by the operating parameter detecting means. Estimates the in-cylinder charge air amount to each cylinder based on the estimated opening / closing valve time of the intake valve estimated based on one engine operating parameter, and multi-cylinder based on the estimated in-cylinder charge air amount to each cylinder Internal combustion machine To control.

  According to a second aspect, in the first aspect, the cylinder-to-cylinder variation in the in-cylinder charged air amount is estimated based on an intake pressure drop time associated with opening of the intake valve corresponding to each cylinder.

  According to a third aspect, in the first aspect, the cylinder-to-cylinder variation in the in-cylinder charged air amount is estimated based on an intake pressure drop amount associated with the opening of the intake valve corresponding to each cylinder.

  In order to solve the above problems, in a fourth aspect of the invention, in the control device for a multi-cylinder internal combustion engine that controls the intake valve so that the open / close valve time of the intake valve becomes the target open / close valve time, the target open / close valve time is predetermined. If the value is less than the value, the cylinder charge air amount to each cylinder is estimated based on the target opening / closing valve time, and if the target opening / closing valve time is larger than the predetermined value, it is detected by the operating parameter detection means. The cylinder charge air amount to each cylinder is estimated based on the estimated opening / closing valve time of the intake valve estimated based on at least one engine operating parameter, and the estimated cylinder charge air amount to each cylinder is calculated. Based on this, the multi-cylinder internal combustion engine is controlled.

  In a fifth aspect of the invention, in any one of the first to fourth aspects, the at least one engine operating parameter is a time period during which the intake pressure drops when the intake valve corresponding to each cylinder opens.

  In a sixth aspect of the invention, in any one of the first to fifth aspects of the invention, the estimation of the in-cylinder charged air amount to each of the cylinders includes the in-cylinder charged air amount to each cylinder, the basic air amount, and the intake air As the valve is opened, the flow rate of the throttle valve passing air flows into the cylinder from the intake pipe portion exceeding the throttle valve passing air flow rate and flows into the cylinder through the throttle valve. The basic air amount is calculated based on the target on-off valve time or the estimated on-off valve time of the intake valve, and the excess air amount is calculated based on the amount of decrease in the intake pressure accompanying the opening of the intake valve corresponding to each cylinder, This is done by adding the basic air amount and the excess air amount.

In the seventh invention, in any one of the first to fifth inventions, when estimating the in-cylinder charged air amount to each cylinder based on the target on-off valve time of the intake valve, The in-cylinder charged air amount is divided into two parts: the basic air amount and the excess air amount that flows into the cylinder from the intake pipe portion exceeding the throttle valve passing air flow rate as the intake valve opens. The basic air amount is calculated based on the flow rate of air passing through the throttle valve through the throttle valve and the target opening / closing valve time of the intake valve, and the excess air is calculated based on the amount of decrease in intake pressure accompanying the opening of the intake valve. By calculating the amount and summing these basic air amount and excess air amount, the in-cylinder charge air amount to each cylinder is estimated, and the in-cylinder charge to each cylinder is based on the estimated opening / closing valve time of the intake valve. When estimating the air volume, Based on at least one engine operating parameter to derive the near-Nishiki-cylinder intake air flow rate of the transition to each cylinder, each cylinder by integrating over the near-Nishiki the estimated off valve time that is detected by the The amount of air filled in the cylinder is estimated.

In order to solve the above-mentioned problem, in the eighth invention, the intake pressure of the intake pipe portion is detected, and the transition of the in-cylinder intake air flow rate to each cylinder is detected based on the detected intake pressure of the intake pipe portion. derives Nishiki, it estimates the cylinder air charge amount to each cylinder by integrating over the near-Nishiki the estimated off valve time, based on the in-cylinder charged air amount of each cylinder is estimated Control a multi-cylinder internal combustion engine.

In a ninth aspect, in the invention of the seventh or eighth, upper KiKon Nishiki is a quadratic approximate expression.

In the tenth invention, in any one invention of the seventh to ninth, the transition of the cylinder intake air flow rate to each cylinder is approximated by a plurality of approximate expressions.

  In order to solve the above-described problem, in the eleventh aspect of the invention, the intake pressure of the intake pipe is detected, and the intake pressure drop time associated with the opening of the intake valve corresponding to each cylinder is detected based on the detected intake pressure. And the opening / closing valve time of the intake valve corresponding to each cylinder is estimated based on the calculated intake pressure drop time associated with the opening of the intake valve corresponding to each cylinder, and corresponding to each estimated cylinder A multi-cylinder internal combustion engine is controlled based on the opening / closing valve time of the intake valve.

According to a twelfth aspect, in the eleventh aspect, the on-off valve time of the intake valve is the in-cylinder intake air to each cylinder based on the intake pressure drop time associated with the opening of the intake valve corresponding to each cylinder. together to derive the near-Nishiki flow transition is calculated from the approximation equation issued conductor.

In the thirteenth invention, in the twelfth invention, approximating the transition of the cylinder intake air flow rate to each cylinder by a plurality of approximate expressions.

  According to a fourteenth aspect, in the eleventh aspect, in addition to the intake pressure decrease time associated with the opening of the intake valve corresponding to each cylinder, the average value of all the calculated intake pressure decrease times for all cylinders. Based on the above, the opening / closing valve time of the intake valve corresponding to each cylinder is calculated.

  In the fifteenth aspect, in the eleventh aspect, in addition to the intake pressure drop time associated with the opening of the intake valve corresponding to each cylinder, the intake air expected based on the average value of the intake pressure over one cycle. Based on the average value of all cylinders for the valve opening / closing time, the valve opening / closing time of the intake valve corresponding to each cylinder is calculated.

  According to a sixteenth aspect of the invention, in the invention of any one of the first to fifteenth aspects, an in-cylinder charged air amount to each cylinder is estimated based on the estimated opening / closing valve time of the intake valve corresponding to each cylinder. The multi-cylinder internal combustion engine is controlled based on the estimated in-cylinder charge air amount to each cylinder, and the in-cylinder charge air amount to each cylinder is estimated based on the in-cylinder charge air amount to each cylinder. A throttle that divides into an air amount and an excess air amount that flows into the cylinder from the intake pipe portion over the throttle valve passing air flow rate when the intake valve opens, and flows into the intake pipe portion via the throttle valve The basic air amount is calculated based on the valve passing air flow rate and the estimated opening / closing time of the intake valve, and the excess air amount is calculated based on the amount of decrease in the intake pressure accompanying the opening of the intake valve. This is done by summing the basic air amount and the excess air amount.

  According to the present invention, a multi-cylinder capable of accurately calculating in-cylinder charged air amount to each cylinder or variation between cylinders in the cylinder filled air amount while taking intake pulsation into account, and controlling the internal combustion engine based on the calculated amount. A control device for an internal combustion engine is provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a case where the present invention is applied to a direct injection spark ignition type internal combustion engine. The present invention can also be applied to other spark ignition internal combustion engines and compression self-ignition internal combustion engines.

  As shown in FIG. 1, in this embodiment, for example, an engine body 1 having eight cylinders is fixed on a cylinder block 2, a piston 3 that reciprocates in the cylinder block 2, and the cylinder block 2. And a cylinder head 4. A combustion chamber 5 is formed between the piston 3 and the cylinder head 4. In the cylinder head 4, an intake valve 6, an intake port 7, an exhaust valve 8, and an exhaust port 9 are arranged for each cylinder. Further, as shown in FIG. 1, a spark plug 10 is disposed at the center of the inner wall surface of the cylinder head 4, and a fuel injection valve 11 is disposed around the inner wall surface of the cylinder head 4. Further, a cavity 12 extending from the lower side of the fuel injection valve 11 to the lower side of the spark plug 10 is formed on the top surface of the piston 3.

  The intake port 7 of each cylinder is connected to a surge tank 14 via an intake branch pipe 13, and the surge tank 14 is connected to an air cleaner 16 via an intake pipe 15. A throttle valve 18 driven by a step motor 17 is disposed in the intake pipe 15. In the present specification, a portion of the intake passage composed of the intake pipe 15 downstream of the throttle valve 18, the surge tank 14, the intake branch pipe 13, and the intake port 7, that is, a portion of the intake passage from the throttle valve 18 to the intake valve 6. Is referred to as an “intake pipe portion” IM. On the other hand, the exhaust port 9 of each cylinder is connected to a catalytic converter 21 containing an exhaust purification device 20 via an exhaust branch pipe and an exhaust pipe 19, and this catalytic converter 21 communicates with the atmosphere via a muffler (not shown). Is done. Further, the intake valve 6 of each cylinder is driven to open and close by an intake valve drive device (variable valve mechanism) 22. The intake valve driving device 22 can change the phase angle, the operating angle, and the lift amount of the intake valve 6.

  An electronic control unit (ECU) 31 comprises a digital computer, and is connected to each other via a bidirectional bus 32, a RAM (random access memory) 33, a ROM (read only memory) 34, a CPU (microprocessor) 35, an input A port 36 and an output port 37 are provided. An air flow meter 40 for detecting the flow rate of air (intake gas) passing through the intake pipe 15 is disposed in the intake pipe 15 upstream of the throttle valve 18. The surge tank 14 is provided with an intake pressure sensor 41 for detecting air pressure (hereinafter referred to as “intake pressure”) Pm in the intake pipe portion IM. Further, a load sensor 43 for generating an output voltage proportional to the amount of depression of the accelerator pedal 42 is connected to the accelerator pedal 42, and a throttle opening sensor (see FIG. 5) for detecting the opening of the throttle valve 18 is connected to the throttle valve 18. Not shown). The output signals of these sensors 40, 41 and 43 are input to the input port 36 via corresponding AD converters 38, respectively. Further, a crank angle sensor 44 that generates an output pulse every time the crankshaft rotates, for example, 30 ° is connected to the input port 36. The CPU 35 calculates the engine speed based on the output pulse of the crank angle sensor 44. On the other hand, the output port 37 is connected to the spark plug 10, the fuel injection valve 11, the step motor 17, and the intake valve drive device 22 through corresponding drive circuits 39, which are based on the output from the electronic control unit 31. Be controlled.

  FIG. 2 is a diagram showing how the phase angle, the operating angle, and the lift amount of the intake valve 6 change as the intake valve drive device 22 is operated. Here, the phase angle of the intake valve 6 means the opening / closing valve timing of the intake valve 6. In this embodiment, the phase angle is advanced or retarded (solid line → Dash-dot line). On the other hand, the operating angle means the length of time (open / close valve time) from when the intake valve is opened to when it is closed, and in this embodiment, it is changed along with the lift amount. For example, as the operating angle of the intake valve 6 is decreased, the lift amount of the intake valve 6 is decreased (solid line → broken line). Note that, according to the present embodiment, the phase angle, the working angle, and the lift amount of the intake valve 6 are continuously changed by the intake valve driving device 22.

Incidentally, in the internal combustion engine of the present embodiment, the fuel injection amount (fuel injection time) TAUi of the i-th cylinder (i = 1, 2,..., 8) is calculated based on, for example, the following equation (1).
TAUi = TAUb · ηi · k (1)
Here, TAUb represents a basic fuel injection amount, ηi represents an air amount variation correction coefficient of the i-th cylinder, and k represents another correction coefficient.

  The basic fuel injection amount TAUb is a fuel injection amount necessary to make the air-fuel ratio coincide with the target air-fuel ratio. This basic fuel injection amount TAUb is obtained in advance as a function of parameters relating to the engine operating state (for example, engine load and engine speed NE, etc., hereinafter referred to as “engine operating parameters”) and stored in the ROM 32 in the form of a map. Or is calculated by a mathematical formula based on engine operating parameters. The correction coefficient k is a collective representation of an air-fuel ratio correction coefficient, an acceleration increase correction coefficient, etc., and is set to 1.0 when there is no need for correction.

When the amount of air that is filled in the cylinder when the intake valve is closed in the i-th cylinder is referred to as in-cylinder charged air amount Mci (g), the air amount variation correction coefficient ηi is the in-cylinder charged air amount Mci in each cylinder. This is to compensate for the variation between the cylinders. The air amount variation correction coefficient ηi of the i-th cylinder is calculated based on the following equation (2), for example.
ηi = Mci / Mcave (2)
Here, Mcave represents the average value (= ΣMci / 8, “8” represents the number of cylinders) of the cylinder air charge amount Mci of all cylinders.

  Here, for example, if a deposit mainly made of carbon is formed on the inner peripheral surface of the intake pipe portion IM or the outer peripheral surface of the intake valve 6, the deposit adhesion amount varies from cylinder to cylinder. There is a risk of variation between cylinders. Further, there may be an assembly tolerance or machine difference related to the valve portion between the cylinders. In this case as well, the cylinder charge air amount Mci may vary between the cylinders. If the cylinder charge air amount Mci varies among the cylinders and the fuel injection amount is kept equal for all the cylinders, the air-fuel ratio and the output torque will vary among the cylinders. Therefore, in the present embodiment, an air amount variation correction coefficient ηi is introduced to compensate for the variation between cylinders in the in-cylinder charged air amount.

  In consideration of the fact that the timing at which the fuel injection is actually performed is a certain time ahead of the calculation timing of the fuel injection amount TAUi, the basic fuel injection amount TAUb in equation (1) is the fuel injection by equation (1). The predicted value may be a certain time ahead of the calculation timing of the amount TAUi.

Alternatively, the fuel injection amount TAUi of the i-th cylinder can be calculated based on the following equation (3).
TAUi = Mci · k / AFt (3)
Here, AFt is a target air-fuel ratio.

  As described above, whether the fuel injection amount TAUi is calculated based on the equation (1) or the equation (3), the air-fuel ratio of the air-fuel mixture is made to coincide with the target air-fuel ratio for all the cylinders. In order to eliminate the variation between the air-fuel ratio cylinders, it is necessary to accurately obtain the in-cylinder charged air amount Mci to each cylinder or the in-cylinder charged air amount variation between the cylinders.

  In the present embodiment, the intake pressure drop amount (hereinafter referred to as “the intake pressure drop amount corresponding to the i-th cylinder”) ΔPmdwni, which is the decrease amount of the intake pressure Pm accompanying the opening of the intake valve 6 corresponding to the i-th cylinder. Based on the above, the cylinder air charge amount Mci for each cylinder is calculated. Next, the intake pressure drop amount ΔPmdwni will be described first with reference to FIGS.

  FIG. 3 shows the intake pressure Pm detected by the intake pressure sensor 41 over, for example, a 720 ° crank angle at regular time intervals. The intake order in the internal combustion engine shown in FIG. 3 is # 1- # 8- # 4- # 3- # 6- # 5- # 7- # 2. In FIG. 3, OPi (i = 1, 2,..., 8) represents the on-off valve period of the intake valve 6 of the i-th cylinder, and the 0 ° crank angle represents the intake top dead center of the # 1 cylinder # 1. ing. As can be seen from FIG. 3, when intake into a certain cylinder is started, the intake pressure Pm that has increased starts to decrease, and thus an upward peak occurs in the intake pressure Pm. The intake pressure Pm further decreases and then increases again, so that a downward peak occurs in the intake pressure Pm. As described above, an upward peak and a downward peak are alternately generated in the intake pressure Pm. In FIG. 3, the upward peak generated in the intake pressure Pm when the intake valve 6 of the i-th cylinder is opened is indicated by UPi, and the downward peak is indicated by DNi.

As shown in FIG. 4, when the intake pressure Pm at the upward peak UPi is referred to as a maximum value Pmmaxi, and the intake pressure Pm at the downward peak DNi is referred to as a minimum value Pmmini, the intake pressure to the i-th cylinder is performed. Pm decreases from the maximum value Pmmaxi to the minimum value Pmmini. Therefore, the intake pressure drop amount ΔPmdwni corresponding to the i-th cylinder in this case is expressed by the following equation (4).
ΔPmdwni = Pmmaxi−Pmmini (4)

  On the other hand, as shown in FIG. 4, when the intake valve 6 is opened, the in-cylinder intake air flow rate mci (g) that is the flow rate of air that flows out of the intake pipe portion IM and is sucked into the in-cylinder CYL of the i-th cylinder. / Sec, see FIG. 5) begins to increase. Next, when the in-cylinder intake air flow rate mci becomes larger than the throttle valve passage air flow rate mt (g / sec, see FIG. 5), which is the flow rate of air passing through the throttle valve 18 and flowing into the intake pipe portion IM, The intake pressure Pm starts to decrease. Next, when the in-cylinder intake air flow rate mci decreases and becomes smaller than the throttle valve passage air flow rate mt, the intake pressure Pm starts to increase.

  That is, when air flows into the intake pipe portion IM through the throttle valve 18 by the throttle valve passage air flow rate mt and intake into the i-th cylinder is performed, the air is transferred from the intake pipe portion IM through the intake valves 6 to each cylinder. Considering that the internal intake air flow rate mci flows out, the in-cylinder intake air flow rate mci, which is the outflow, temporarily exceeds the throttle valve passing air flow rate mt, which is the inflow, and thus the pressure in the intake pipe portion IM The intake pressure Pm is reduced by the intake pressure drop amount ΔPmdwni.

ここで、ｉ番気筒への吸気により吸気圧Ｐｍに上向きのピークが発生する時刻である上向きピーク発生時刻をｔｍａｘｉ、ｉ番気筒への吸気により吸気圧Ｐｍに下向きのピークが発生する時刻である下向きピーク発生時刻をｔｍｉｎｉとすると、Δｔｄｗｎｉは上向きピーク発生時刻ｔｍａｘｉから下向きピーク発生時刻ｔｍｉｎｉまでの吸気圧の降下時間（ｓｅｃ、ｔｍｉｎｉ−ｔｍａｘｉ）を、Δｔｏｃは吸気弁の開閉弁時間（ｓｅｃ、吸気弁の開閉弁期間の長さ）を、それぞれ表している（図４参照）。 The in-cylinder charged air amount Mci is obtained by integrating the in-cylinder intake air flow rate mci with time. Accordingly, if the influence of the overlap of the intake valve opening / closing valve timing OPi (see FIG. 3) on the cylinder filling air amount Mci or the air quantity variation correction coefficient ηi can be ignored, the cylinder filling air amount Mci is expressed by the following equation (5). Can be expressed as:

Here, tmaxi is an upward peak generation time, which is a time when an upward peak occurs in the intake pressure Pm due to intake into the i-th cylinder, and is a time when a downward peak occurs in the intake pressure Pm due to intake into the i-th cylinder. Assuming that the downward peak occurrence time is tmini, Δtdwni is the intake pressure fall time (sec, tmini−tmaxi) from the upward peak occurrence time tmaxi to the downward peak occurrence time tmini, and Δtoc is the opening / closing valve time (sec, intake air) of the intake valve The length of the valve opening / closing valve period) is shown (see FIG. 4).

  In Expression (5), the first term on the right side is a portion indicated by T1 in FIG. 4 (hereinafter referred to as “region T1”), that is, a portion surrounded by the cylinder intake air flow rate mci and the throttle valve passing air flow rate mt. The second term on the right side is a portion indicated by T2 in FIG. 4 (hereinafter referred to as “region T2”), that is, the cylinder intake air flow rate mci, the throttle valve passing air flow rate mt, and the straight line mci. The area of the portion surrounded by = 0 is approximated by a trapezoid.

  As described above, the intake air flow rate mci in the cylinder temporarily exceeds the throttle valve passing air flow rate mt due to intake. Therefore, during this period, the cylinder charge air amount Mci obtained by time integration of the cylinder intake air flow rate mci exceeds the time integral value of the throttle valve passage air flow rate mt. The region T1 thus represents an excess of the cylinder charge air amount Mci with respect to the integral value of the throttle valve passage air flow rate mt generated by intake.

  Therefore, in general terms, the in-cylinder charged air amount is divided into a basic air amount represented by the area of the region T2 and an excess air amount represented by the area of the region T1, and the excess air amount is determined by intake air. This is the excess of the in-cylinder charged air amount with respect to the throttle valve passing air amount generated by the engine, and the in-cylinder charged air amount of each cylinder is calculated by summing the basic air amount and the excess air amount for each cylinder. It turns out that.

ここで、Ｖｍは吸気管部分ＩＭの容積（ｍ³）を、Ｒａは気体定数を空気の平均分子量で除算した値（以下、単に「気体定数」と称す）を、Ｔｍは吸気管部分ＩＭ内の空気の温度（Ｋ、以下、「吸気温度」と称す）をそれぞれ表している（図５参照）。式（６）は、Ｖｍ／ＲａをパラメータＫｍとして表すと、次式（７）のように変形される。

On the other hand, the law of conservation of mass for the intake pipe portion IM is expressed by the following equation (6) using the equation of state for the air in the intake pipe portion IM.

Here, Vm is the volume (m ³ ) of the intake pipe portion IM, Ra is a value obtained by dividing the gas constant by the average molecular weight of air (hereinafter simply referred to as “gas constant”), and Tm is in the intake pipe portion IM. (K, hereinafter referred to as “intake air temperature”) (see FIG. 5). Expression (6) is transformed into the following expression (7) when Vm / Ra is expressed as a parameter Km.

Since the intake pressure Pm decreases by the intake pressure drop amount ΔPmdwni from the time tmaxi to the time tmini, the equation (5) can be rewritten as the following equation (8) using the equation (7).

  Then, the intake pressure Pm is detected by the intake pressure sensor 41, the intake pressure drop amount ΔPmdwni is calculated, the above-mentioned parameter Km is obtained, and the air flow rate mt detected by the air flow meter 40 or the throttle opening sensor is obtained. And an average value mtave (hereinafter, “the throttle valve passing air flow rate mt” is described as including the average value mtave) and the time tmaxi and tmini are calculated from the intake pressure Pm. If the descent time Δtdwni (= tmini−tmaxi) is calculated from the above, the in-cylinder charged air amount Mci to each cylinder can be calculated using equation (8).

  The opening / closing valve time Δtoc of the intake valve 6 in the equation (8) is, for example, a target opening / closing valve time Δtoctrg. Here, the ECU 31 sets the target on / off valve time of the intake valve 6 so that the engine operating state is optimized based on the engine load detected by the load sensor 43, the engine speed detected by the crank angle sensor 44, and the like. Δtoctrg is determined, and the intake valve driving device 22 drives the intake valve 6 so that the on-off valve time of the intake valve 6 becomes the target on-off valve time Δtoctrg. Therefore, if there is no wear or the like of the valve portion, that is, if the intake valve driving device 22 can drive the intake valves 6 as designed in all cylinders, basically the open / close valve times of all intake valves 6 are the target open / close valve time Δtoctrg. Thus, the in-cylinder charged air amount Mci to each cylinder can be accurately calculated by setting the opening / closing valve time Δtoc of the intake valve 6 in the equation (8) as the target opening / closing valve time Δtoctrg.

  However, as described above, there is a case where the opening / closing valve time Δtoc of the intake valve 6 does not become the target opening / closing valve time Δtoctrg due to wear of the valve portion or the like. In particular, the opening / closing valve time Δtoc of the intake valve 6 may vary between cylinders. is there. In this way, when the actual opening / closing valve time Δtoc of the intake valve 6 varies between cylinders, the opening / closing valve time Δtoc of the intake valve 6 is set as the target opening / closing valve time Δtoctrg and the cylinders are filled into each cylinder according to the equation (8). When the air amount Mci is calculated, the calculation error of the second term on the right side, that is, the region T2 in FIG. 4 is large, and therefore the cylinder charge air amount Mci to each cylinder cannot be accurately calculated.

  Therefore, especially when the actual variation in cylinder time of the opening / closing valve time Δtoc of the intake valve 6 is large, that is, when the variation in the cylinder charge air amount Mci is large between cylinders, the opening / closing valve time Δtoc of the intake valve 6 is large. Is not set as the target on-off valve time Δtoctrg, and the cylinder charge air amount Mci to each cylinder needs to be calculated as a value that takes into account the inter-cylinder variation of the on-off valve time Δtoc of the intake valve 6. Therefore, in the present invention, the in-cylinder charged air amount Mci for each cylinder is calculated in consideration of the variation between the cylinders in the in-cylinder charged air amount. Hereinafter, a method of calculating the opening / closing valve time Δtoci of the intake valve 6 corresponding to the i-th cylinder in consideration of the cylinder-to-cylinder variation in the in-cylinder charged air amount will be described.

  First, referring to FIG. 6, a first calculation method of the opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder will be described. By the way, when it is assumed that there is no inter-cylinder variation in the cylinder charge air amount, that is, when there is no inter-cylinder variation during the opening / closing valve time of the intake valve 6, as described above, all the cylinders It is considered that the opening / closing valve time Δtoc of the intake valve 6 coincides with the target opening / closing valve time Δtoctrg. In this case, there is no inter-cylinder variation in the descent time Δtdwn associated with the opening of the intake valve 6, and therefore the descent time Δtdwn is the same for all cylinders. Further, in this case, a value (hereinafter referred to as “expected descent time”) Δtdwntrg expected to be taken by the descent time Δtdwn is obtained in advance in consideration of the transition of the valve lift amount of the intake valve 6 from the target opening / closing valve time Δtoctrg. It can be calculated by a map or other maps or mathematical expressions (see the left side of FIG. 6).

On the other hand, it is considered that the variation between cylinders in the opening / closing valve time Δtoc of the intake valve 6 is basically proportional to the variation between cylinders in the drop time Δtdwn. Therefore, the expected fall of Δtdwni calculated by the opening of the intake valve 6 corresponding to the i-th cylinder (hereinafter referred to as “fall time corresponding to the i-th cylinder”) calculated based on the output of the intake pressure sensor 41. The ratio to the time Δtdwntrg is equal to the ratio of the opening / closing valve time Δtoci of the i-th cylinder intake valve 6 to the target opening / closing valve time Δtoctrg (refer to the right in FIG. 6), and therefore the opening / closing valve time Δtoci of the i-th cylinder intake valve 6 is It can be calculated by equation (9).

  That is, according to the first calculation method, the inter-cylinder variation of the on-off valve time Δtoc is estimated from the inter-cylinder variation of the descent time Δtdwn (particularly, the inter-cylinder variation of Δtdwn with respect to the expected descent time Δtdwntrg). The opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder is calculated by correcting the target opening / closing valve time Δtoctrg for each cylinder based on the variation between the cylinders of the time Δtoc. Thus, according to the first calculation method, the opening / closing valve time Δtoci of the intake valve 6 of each cylinder can be calculated relatively accurately. By calculating the cylinder air charge amount Mci, the cylinder air charge amount Mci for each cylinder can be calculated relatively accurately.

Next, a second method of calculating the opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder will be described with reference to FIG. The average value of all cylinders of the descent time Δtdwni corresponding to the i-th cylinder calculated based on the output of the intake pressure sensor 41 (hereinafter referred to as “average descent time”) Δtdwnave is the variation between cylinders of the descent time Δtdwn. Therefore, it is considered that the opening / closing valve time Δtoc of the intake valve 6 is approximately equal to the expected descent time Δtdwntrg, which is a value calculated on the assumption that there is no variation between cylinders. Therefore, in this embodiment, the on / off valve time Δtoci of the i-th cylinder is calculated using the average descent time Δtdwnave instead of the expected descent time Δtdwntrg in the first calculation method described above (see FIG. 7). The opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder can be calculated by the following equation (10).

  That is, according to the second calculation method, the inter-cylinder variation of the on-off valve time Δtoc is estimated from the inter-cylinder variation of the descent time Δtdwn with respect to the average descent time Δtdwnave, and based on the estimated inter-cylinder variation of the on-off valve time Δtoc. By correcting the target opening / closing valve time Δtoctrg for each cylinder, the opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder is calculated. Thus, according to the second calculation method, it is not necessary to calculate the expected descent time Δtdwntrg in advance compared to the first calculation method, and the in-cylinder to each cylinder is reduced while reducing the calculation load in the ECU 31. The filling air amount Mci can be calculated relatively accurately.

  Next, a third method of calculating the opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder will be described with reference to FIG. By the way, in the first and second calculation methods, when it is assumed that there is no inter-cylinder variation in the opening / closing valve time Δtoc of the intake valve 6, the opening / closing valve time Δtoc of the intake valve 6 is the target opening / closing valve time. The opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder is calculated on the assumption that it corresponds to Δtoctrg. However, in practice, when the opening / closing valve time Δtoc of the intake valve 6 is totally deviated, it is assumed that there is no variation between cylinders in the opening / closing valve time Δtoc of the intake valve 6. The on-off valve time Δtoc does not coincide with the target on-off valve time Δtoctrg.

  On the other hand, if the engine operating parameters such as the engine speed and the engine load are the same, the opening / closing valve time Δtoc of the intake valve 6 and one cycle (assuming the internal combustion engine of the present embodiment) when it is assumed that there is no variation between cylinders. Then, there is a relationship as shown in FIG. 8 between the average value of the intake pressure per 720 ° crank angle (hereinafter referred to as “cycle average intake pressure”) Pmave. If the on-off valve time Δtoc of the intake valve 6 is not entirely deviated from the target on-off valve time Δtoctrg, the cycle average intake pressure detected by the intake pressure sensor 41 is the intake pressure Pmavetrg corresponding to the target on-off valve time Δtoctrg in FIG. Matches. However, when the opening / closing valve time Δtoc of the intake valve 6 is totally deviated from the target opening / closing valve time Δtoctrg, the cycle average intake pressure Pmave detected by the intake pressure sensor 41 is equal to the target opening / closing valve time Δtoctrg in FIG. It does not correspond to the corresponding intake pressure Pmavetrg. On the other hand, in this case, based on FIG. 8, the average value of all cylinders (hereinafter referred to as the following) of the open / close valve time of the intake valve 6 when it is deviated from the target open / close valve time Δtoctrg due to the overall deviation from the cycle average intake pressure Pmave. Δtocpm (referred to as “expected on-off valve timing”) can be predicted.

  Therefore, in the third calculation method, the cycle average intake pressure Pmave is calculated based on the output of the intake pressure sensor 41, and the map as shown in FIG. 8 is used based on the calculated cycle average intake pressure Pmave. Then, the expected opening / closing valve timing Δtocpm of the intake valve 6 taking into account the overall deviation is calculated. Then, the calculated expected opening / closing valve timing Δtocpm is used instead of the target opening / closing valve time Δtoctrg in the second calculation method, for example (see FIG. 7).

  That is, in the present embodiment, an overall deviation of the on-off valve timing with respect to the target on-off valve timing Δtoctrg is calculated based on the intake pressure detected by the intake pressure sensor 41, and the expected on-off valve calculated by taking this deviation into account. The opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder is calculated by correcting the timing Δtoctrg for each cylinder based on the variation in the opening / closing valve time between the cylinders. As a result, it is possible to calculate the opening / closing valve time of the i-th cylinder in consideration of the overall deviation of the opening / closing valve time Δtoc and the variation between cylinders. Therefore, this is substituted into the equation (8) and the cylinder to each cylinder is calculated. By calculating the inner charge air amount Mci, the in-cylinder charge air amount Mci for each cylinder can be calculated more accurately.

  FIG. 9 is a flowchart of a control routine for calculating the opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder by the third calculation method. This control routine is performed by interruption at predetermined time intervals.

  As shown in FIG. 9, first, at step 101, the intake pressure Pm is detected by the intake pressure sensor 41, the throttle valve passage air flow rate mt is calculated from the throttle opening detected by the throttle opening sensor, and the like. The intake air temperature Tm is detected by a temperature sensor (not shown) for detecting the temperature in the intake pipe portion IM. Next, in step 102, the intake pressure drop amount ΔPmdwni (= Pmmaxi−Pmmini) and the drop time Δtdwni (= tmini−tmaxi) corresponding to the i-th cylinder are calculated from the transition of the intake pressure Pm detected in step 101. The

  Next, at step 103, it is determined whether one cycle has elapsed since it was determined at the previous step 103 that one cycle has elapsed, or whether the first cylinder intake top dead center has been passed. If it is determined that the first cylinder intake top dead center is not passed, the control routine is terminated. On the other hand, if it is determined in step 103 that the first cylinder intake top dead center has been passed, the routine proceeds to step 104.

In step 104, the average value of the intake pressure Pm detected in step 101 over one cycle, that is, the cycle average intake pressure Pmave is calculated. Further, an average value over one cycle of the descent time Δtdwni corresponding to the i-th cylinder calculated in step 102, that is, the average descent time Δtdnave is calculated. Next, at step 105, the predicted opening / closing valve timing Δtocpm is calculated from the cycle average intake pressure Pmave calculated at step 104 based on the graph shown in FIG. In step 106, the intake of the i-th cylinder is calculated based on the following equation (11) from the predicted opening / closing valve time Δtocpm calculated in step 105, the average descent time Δtdwnave calculated in step 104, and the descent time Δtdwni calculated in step 102. The opening / closing valve time Δtoci of the valve 6 is calculated from the first cylinder to the eighth cylinder.

  In step 107, an equation is established using the on-off valve time Δtoci calculated in step 106, the intake pressure drop amount ΔPmdwni, the intake air temperature Tm, the throttle valve passing air flow rate mt, and the drop time Δtdwni detected or calculated in steps 101 and 102. Based on 8), the in-cylinder charged air amount Mci for the i-th cylinder is calculated for each of the 1st to 8th cylinders.

  Next, a fourth method of calculating the opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder will be described with reference to FIG. By the way, depending on the cam profile of the intake cam when the intake valve drive device 22 uses an intake cam (not shown), depending on the characteristics of the drive device when the intake valve drive device 22 is electromagnetically driven, In many cases, the transition of the in-cylinder intake air flow rate mci to the i-th cylinder can be approximated to a quadratic curve as shown in FIG. Therefore, according to the fourth calculation method, the opening / closing valve timing Δtoci of the intake valve 6 corresponding to the i-th cylinder is calculated by approximating the transition of the in-cylinder intake air flow rate mci to the i-th cylinder to a quadratic curve. Like to do.

More specifically, as shown in FIG. 10, the time (or crank angle) is the x axis, the in-cylinder intake air flow rate mci to the i-th cylinder is the y-axis, and the in-cylinder to the i-th cylinder is Coordinates are set with the time when the intake air flow rate mci reaches a peak as zero. When the coordinates are set in this way, the transition of the cylinder intake air flow rate mci to the i-th cylinder can be approximated by the following equation (12).
y = ax ² + b (12)
Here, a and b in Formula (12) are constants.

As described in FIG. 4, if the descent time corresponding to the i-th cylinder is Δtdwni, the throttle valve passing air flow rate mt and the in-cylinder intake air flow rate mci to the i-th cylinder are equal to the descent time Δtdwni corresponding to the i-th cylinder. Intersect each other with a time interval. Therefore, as shown in FIG. 10, the approximate curve of Expression (12) passes through the point A (−Δtdwni / 2, mt) and the point B (Δtdwni / 2, mt). Substituting this into equation (12) leads to equation (13) below.
mt = a · (Δtdwni / 2) ² + b (13)

この図１０における面積Ｓは図４における領域Ｔ１の面積に相当することから、式（１４）は下記式（１５）のように表すことができる。

On the other hand, the area S (shaded portion) in FIG. 10 can be calculated by the following equation (14) by time-integrating the equation (12) from the point A to the point B.

Since the area S in FIG. 10 corresponds to the area of the region T1 in FIG. 4, the expression (14) can be expressed as the following expression (15).

  Here, the throttle valve passage air flow rate mt is calculated from the output of the air flow meter 40 and the throttle opening sensor, and the intake pressure drop amount ΔPmdwni and the drop time Δtdwni corresponding to the i-th cylinder are calculated from the output of the intake pressure sensor 41 and the like. Therefore, by substituting these calculated values into the equations (13) and (15), the constants a and b in the equation (12) can be calculated. An approximate expression (12) of the air flow rate mci can be obtained.

The two x values calculated when y = 0 in this approximate expression (12) represent the x-coordinates of point C and point D in FIG. 10, respectively, and the difference between these two x values is It represents the opening / closing valve time Δtoci of the intake valve 6 corresponding to the i-th cylinder. Accordingly, the opening / closing valve time Δtoci of the intake valve corresponding to the i-th cylinder can be expressed by the following equation (16).

  That is, in the fourth calculation method, the transition of the in-cylinder intake air flow rate mci is approximated to a quadratic curve, and the approximate expression (12) is calculated based on the output of the intake pressure sensor 41 and the intake pressure drop amount ΔPmdwni. And the opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder is calculated from the obtained approximate expression (12) from the throttle valve passage air flow rate mt calculated from the descent time Δtdwni and the throttle opening. As described above, according to the fourth calculation method, since the open / close valve time Δtoci of the intake valve 6 is calculated using an approximate expression, the open / close valve time Δtoci of the intake valve 6 can be calculated relatively accurately. it can. Thus, the in-cylinder charged air amount Mci for each cylinder is calculated more accurately by substituting the calculated opening / closing valve time Δtoci into the equation (8) to calculate the in-cylinder charged air amount Mci for each cylinder. be able to.

In the above embodiment, the cylinder filling air is calculated by calculating the opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder from the approximate expression (12) and substituting the calculated opening / closing valve time Δtoci into the expression (8). Although the amount Mci is calculated, the in-cylinder charged air amount Mci for each cylinder may be calculated by integrating the approximate expression (12) from the point C to the point D, that is, the following expression (17). When the in-cylinder charged air amount Mci for each cylinder is calculated in this way, if the transition of the in-cylinder intake air flow rate is very close to a quadratic curve, the in-cylinder charged air amount Mci for each cylinder is relatively reduced. It can be calculated accurately.

  Next, a fifth method of calculating the opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder will be described with reference to FIGS. 11 and 12.

  FIG. 11 is a diagram showing the relationship between the opening timing of the intake valve 6 and the transition of the pressure in the cylinder (hereinafter referred to as “in-cylinder pressure”). In the figure, the horizontal axis indicates the crank angle, and the vertical axis indicates the in-cylinder pressure Pci of the i-th cylinder. The solid line x indicates that the intake valve 6 is opened at time X, and the broken line y indicates the intake valve at time Y. When 6 is opened, the alternate long and short dash line z indicates the transition of the in-cylinder pressure Pci when the intake valve 6 is opened at time Z. Further, a two-dot chain line in the figure indicates an average value of the intake pressure Pm in the intake pipe portion IM.

  As can be seen from FIG. 11, the in-cylinder pressure Pci is high immediately after the intake top dead center (TDC in the figure) regardless of the opening timing of the intake valve 6. This is because the in-cylinder volume is minimized by the discharge stroke. Since the in-cylinder volume gradually increases in the subsequent intake stroke, the in-cylinder pressure Pci gradually decreases accordingly. When the opening timing of the intake valve 6 is early, as shown by the solid line x, the intake valve 6 is opened in a state where the in-cylinder pressure Pci is higher than the intake pressure Pm in the intake pipe portion IM. . For this reason, immediately after the intake valve 6 is opened, almost no air is sucked into the cylinder from the intake pipe portion IM, or air is sucked very slowly, and then rapidly increases as the in-cylinder volume increases. Air is sucked into the cylinder. In this way, when the air is suddenly sucked into the cylinder, the rising speed of the in-cylinder intake air flow rate mci is very fast.

  When the opening timing of the intake valve 6 is delayed, the intake valve 6 is opened in a state where the in-cylinder pressure Pci is substantially equal to the intake pressure Pm in the intake pipe portion IM, as shown by the broken line y. For this reason, immediately after the intake valve 6 is opened, the period during which almost no air is sucked from the intake pipe portion IM into the cylinder is shortened as compared with the case shown by the solid line x, and the in-cylinder intake air flow rate mci thereafter The ascending speed will be slower. When the opening timing of the intake valve 6 is further delayed, the intake valve 6 is opened in a state in which the in-cylinder pressure Pci is lower than the intake pressure Pm in the intake pipe portion IM, as indicated by the alternate long and short dash line z. . For this reason, the air is sucked into the cylinder immediately after the intake valve 6 is opened without passing through a period during which almost no air is sucked into the cylinder from the intake pipe portion IM, and the rising speed of the cylinder intake air flow rate mci at this time is slow.

  As described above, the time from when the intake valve 6 is opened until the air is actually sucked into the cylinder, and the rising speed of the cylinder intake air flow rate mci after the air starts to be sucked, are as follows. Varies depending on the valve opening timing. On the other hand, after the in-cylinder intake air flow rate mci reaches its peak, the in-cylinder intake air flow rate mci becomes equal to the intake pressure Pm of the intake pipe portion IM regardless of the opening timing of the intake valve 6 as shown in FIG. Since it converges, the descending speed of the in-cylinder intake air flow rate mci does not change much regardless of the opening timing of the intake valve 6. Therefore, the rising speed to the peak of the in-cylinder intake air flow rate mci differs from the falling speed after the peak according to the opening timing of the intake valve 6.

  Therefore, the fifth calculation method approximates the transition of the in-cylinder intake air flow rate mci to the i-th cylinder with a different quadratic curve when the in-cylinder intake air flow rate mci rises and falls. The approximation between the transition of the cylinder intake air flow rate mci and the quadratic curve is improved.

More specifically, as shown in FIG. 12, the time is the x-axis, the cylinder intake air flow rate mci to the i-th cylinder is the y-axis, and the cylinder intake air flow rate mci to the i-th cylinder is Set the coordinates with zero as the peak time. When the coordinates are set in this way, the transition of the in-cylinder intake air flow rate mci to the i-th cylinder is expressed by the following equation (18) representing the rise of the in-cylinder intake air flow rate mci, and when the in-cylinder intake air flow rate mci is lowered. It can be approximated by the following two expressions:
y = ax ² + b (x <0) (18)
y = cx ² + b (x ≧ 0) (19)
Here, a, b and c in formulas (18) and (19) are constants.

As described with reference to FIG. 10, the straight line of the throttle valve passing air flow rate mt and the curve of the in-cylinder intake air flow rate mci to the i-th cylinder intersect each other with a time interval of the descent time Δtdwni corresponding to the i-th cylinder ( Point A ′ and point B ′ in FIG. However, when the rising speed and the falling speed of the in-cylinder intake air flow rate mci are different, the x coordinate of the center between the point A ′ and the point B ′ does not become zero. Therefore, if the shift amount from zero of the x coordinate at the center between the point A ′ and the point B ′ is α, as shown in FIG. 12, the approximate curve of the equation (18) is the point A ′ (− Δtdwni / 2 + α , Mt), and the approximate curve of equation (19) passes through the point B ′ (Δtdwni / 2 + α, mt). Substituting this into the equations (18) and (19) respectively leads to the following equations (20) and (21).
mt = a · (−Δtdwni / 2 + α) ² + b (x <0) (20)
mt = c · (Δtdwni / 2 + α) ² + b (x ≧ 0) (21)

この図１２における面積Ｓは図４における領域Ｔ１の面積に相当することから、式（１４）は下記式（２３）のように表すことができる。

On the other hand, the area S ′ (shaded portion) in FIG. 12 is obtained by summing up the time integration of the equation (18) from the point A ′ to x = 0 and the equation (19) from x = 0 to the point B ′. Can be calculated by the following equation (22).

Since the area S in FIG. 12 corresponds to the area of the region T1 in FIG. 4, the expression (14) can be expressed as the following expression (23).

  Here, the value of the shift amount α changes according to the rising speed of the cylinder intake air flow rate mci. That is, when the time from when the intake valve 6 is opened until the air is actually sucked into the cylinder is long and the rising speed of the cylinder intake air flow rate mci after the air starts to be sucked is high, the cylinder Since the rising time is shorter than the falling time of the inner intake air flow rate mci, the deviation amount α is a large value. Conversely, when the time from when the intake valve 6 is opened until the air is actually sucked into the cylinder is short and the rising speed of the cylinder intake air flow rate mci after the air starts to be sucked is slow, Compared to the above case, since the rising time of the in-cylinder intake air flow rate mci with respect to the falling time is longer, the shift amount α is a small value. Further, as described above, the time from when the intake valve 6 is opened until the air is actually sucked into the cylinder and the rising speed of the cylinder intake air flow rate mci after the air starts to be sucked are determined by the intake valve 6. It depends on the valve opening time.

  Therefore, in the fifth calculation method, the value of the deviation amount α is calculated by a map or a calculation formula obtained in advance based on the valve opening timing of the intake valve 6. Specifically, the deviation amount α increases when the opening timing of the intake valve 6 is advanced, and the deviation amount α decreases when the opening timing of the intake valve 6 is retarded.

  Further, since the throttle valve passing air flow rate mt, the intake pressure drop amount ΔPmdwni, and the drop time Δtdwni are calculated from the outputs of the air flow meter 40 and the intake pressure sensor 41, the expressions (20), (21), and (23) By substituting these calculated values and deviation amount α into constants a, b, and c in equations (18) and (19), the in-cylinder intake air flow rate to the i-th cylinder can be calculated. The approximate expressions (18) and (19) of mci can be obtained.

In the approximate expressions (18) and (19), the two x values calculated when y = 0 represent the point C ′ and the point D ′ in FIG. 12, respectively. This difference represents the on-off valve time Δtoci of the intake valve 6 corresponding to the i-th cylinder. Accordingly, the opening / closing valve time Δtoci of the intake valve corresponding to the i-th cylinder can be expressed by the following equation (24).

  That is, in the fifth calculation method, the transition of the in-cylinder intake air flow rate mci is approximated by two quadratic curves, and the approximate expressions (18) and (19) are expressed by the intake pressure drop amount ΔPmdwni, the drop time Δtdwni, the throttle An opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder is calculated from a deviation amount α calculated from the valve passage air flow rate mt and the opening timing of the intake valve 6. According to the fifth calculation method, the cylinder intake air flow rate mci is approximated to a different quadratic curve when the cylinder intake air flow rate mci rises and falls, so that even if the cylinder intake air flow rate mci rises, the accuracy increases. In addition, the opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder can be calculated. Thus, the in-cylinder charged air amount Mci for each cylinder is calculated more accurately by substituting the calculated opening / closing valve time Δtoci into the equation (8) to calculate the in-cylinder charged air amount Mci for each cylinder. be able to.

In the fifth calculation method, the open / close valve time Δtoci of the intake valve 6 of the i-th cylinder is calculated from the approximate expressions (18) and (19), and the calculated open / close valve time Δtoci is expressed by Expression (8). The in-cylinder charged air amount Mci for each cylinder is calculated by substituting, but by integrating the approximate expressions (18) and (19) from point C ′ to point D ′ over time, that is, the following expression (25 ) To calculate the in-cylinder charged air amount Mci for each cylinder.

  In the fifth calculation method, the quadratic curve approximated when the in-cylinder intake air flow rate rises and falls is divided, but it does not have to be divided between when it rises and when it falls. An approximate quadratic curve may be divided before or after the inner intake air flow rate reaches a peak.

  In the above embodiment, the transition of the in-cylinder intake air flow rate is approximated by a quadratic curve. However, the approximate curve is not limited to a quadratic curve, and can be approximated to an nth-order curve (n is arbitrary). is there. For example, the lift amount of the intake valve rises and falls more smoothly immediately after opening the intake valve or immediately before closing the intake valve than when approximating the quadratic curve shown in FIGS. 10 and 12 (see the solid line in FIG. 13). ). Therefore, the lift amount of the intake valve immediately after opening the valve or immediately before closing the valve can be accurately approximated by approximating with a quartic curve, so that the operating angle of the intake valve 6 can be calculated relatively accurately. . However, when the lift amount of the intake valve 6 is small, practically little air is sucked into the cylinder from the intake pipe portion IM, and the substantial in-cylinder intake air flow rate is extremely small. Therefore, when calculating the opening / closing valve time Δtoci of the intake valve 6 that effectively acts on the in-cylinder intake air flow rate, it is preferable to approximate the transition of the in-cylinder intake air flow rate with a quadratic curve.

  Further, in the above calculation method, the calculation of the intake pressure decrease amount ΔPmdwn and the decrease time Δtdwn may be performed every cycle, that is, based only on the output of the intake pressure sensor 41 over one cycle, or the engine operating state may be When the engine is in a steady operation state (an operation state in which engine operation parameters such as engine load and engine speed do not change), it may be performed every plural cycles, that is, based on the output of the intake pressure sensor 41 over a plurality of cycles.

  Next, a second embodiment of the present invention will be described.

  By the way, as described above, when there is a large variation between cylinders in the opening / closing valve time Δtoc of the intake valve 6, that is, when there is a large variation between cylinders in the in-cylinder charged air amount, the intake valve 6 of the i-th cylinder in equation (8) When the on-off valve time Δtoci is used as the target on-off valve time Δtoctrg to calculate the in-cylinder charged air amount Mci to each cylinder (hereinafter referred to as “target on-off valve time utilization method”), the in-cylinder charged air amount Mci to each cylinder is calculated. Cannot be calculated accurately.

  On the other hand, in the above-described five calculation methods (hereinafter referred to as “descent time utilization method”), when the variation between the cylinders in the open / close valve time Δtoci of the intake valve 6 is small, the in-cylinder charged air amount Mci to each cylinder Cannot be calculated accurately. That is, in any of the five calculation methods described above, the descent time Δtdwni corresponding to the i-th cylinder is used in calculating the on-off valve time Δtoci of the intake valve 6 corresponding to the i-th cylinder. The descent time Δtdwni corresponding to the i-th cylinder is calculated based on the intake pressure detected by the intake pressure sensor 41, but there is some measurement error.

  If the variation in the cylinder charge air amount between the cylinders is small, an error in the cylinder charge air amount caused by calculation using the target opening / closing valve time method, that is, the opening / closing valve time Δtdwn with the cylinder variation is the target opening / closing. An error in the in-cylinder charged air amount caused by imitating the valve time Δtdwntrg is an error in the in-cylinder charged air amount caused by calculation using the descent time method, that is, an in-cylinder charged air caused by a measurement error in the on-off valve time Δtdwn Less than the quantity error.

  Therefore, in the second embodiment, when the variation in the cylinder charge air amount between the cylinders is small, that is, when the variation in the cylinder charge air amount between the cylinders is equal to or less than a predetermined level, the on-off valve time Δtoc of equation (8). By substituting the target opening / closing valve time Δtoctrg into the target opening / closing valve time utilization method, the in-cylinder charged air amount Mci for each cylinder is calculated. On the other hand, when the variation in the cylinder charge air amount between the cylinders is large, that is, when the variation in the cylinder charge air amount between the cylinders is larger than the predetermined level, any one of the five calculation methods described above is calculated. By a method (fall time utilization method), for example, the cylinder intake air flow rate mci is approximated by a single quadratic curve, and the quadratic curve is integrated to calculate the in-cylinder charged air amount Mci for each cylinder.

  As a result, the in-cylinder charged air amount Mci for each cylinder can be calculated relatively accurately even when the variation between the cylinders in the opening / closing valve time Δtoci of the intake valve 6 is large or small.

  Note that the inter-cylinder variation level of the cylinder air charge amount is determined, for example, by the following two methods. The first determination method is based on the descent time Δtdwn. That is, the cylinder-to-cylinder variation in the drop time Δtdwn represents the cylinder-to-cylinder variation in the in-cylinder charged air amount. Therefore, the cylinder-to-cylinder variation in the in-cylinder charged air amount increases as the in-cylinder variation in the drop time Δtdwn increases. I can judge.

  Therefore, in the first determination method, among the descent times Δtdwn corresponding to all the cylinders, the maximum value (maximum descent time) Δtdwnmax and the minimum value (minimum descent time) Δtdwnmin are calculated, and these maximum descent times Δtdwnmax. And the minimum drop time Δtdwnmin (Δtdwnmax−Δtdwnmin). When the difference calculated in this way is greater than or equal to a predetermined value, it is determined that the cylinder-to-cylinder variation level of the in-cylinder charged air amount is large, and when the difference is smaller than the predetermined value, the cylinder It is determined that the variation level between the cylinders of the inner charge air amount is small.

  The second determination method is based on the intake pressure drop amount ΔPmdwn. That is, the inter-cylinder variation of the intake pressure drop amount ΔPmdwn represents the inter-cylinder variation of the in-cylinder charged air amount similarly to the drop time Δtdwn. Therefore, when the inter-cylinder variation of the intake pressure drop amount ΔPmdwn increases, the in-cylinder charged air amount It can be determined that the variation between the cylinders increases.

  Therefore, in the second determination method, the maximum value (maximum intake pressure decrease amount) ΔPmdwnmax and the minimum value (minimum intake pressure decrease amount) ΔPmdwnmin are calculated among the intake pressure decrease amounts ΔPmdwn corresponding to all the cylinders. Then, the difference (ΔPmdwnmax−ΔPmdwnmin) between the maximum intake pressure decrease ΔPmdwnmax and the minimum intake pressure decrease ΔPmdwnmin is calculated. When the difference calculated in this way is greater than or equal to a predetermined value, it is determined that the cylinder-to-cylinder variation level of the in-cylinder charged air amount is large, and when the difference is smaller than the predetermined value, the cylinder It is determined that the variation level between the cylinders of the inner charge air amount is small.

  The determination of the cylinder-to-cylinder variation level of the in-cylinder charged air amount is not limited to the above two methods. For example, the determination may be made not only based on the difference between the maximum value and the minimum value of the inter-cylinder variation as described above, but also based on the standard deviation of the inter-cylinder variation, for example.

  FIG. 14 is a flowchart of a control routine for calculating the opening / closing valve time Δtoci of the intake valve 6 of the i-th cylinder according to the second embodiment. This control routine is performed by interruption at predetermined time intervals.

  As shown in FIG. 14, first, in step 151, the intake pressure Pm, the throttle valve passage air flow rate mt, and the intake air temperature Tm are detected or calculated in the same manner as in step 101 shown in FIG. Further, at step 151, the target valve opening timing tiv of the intake valve 6 is acquired from the ECU 31. Next, at step 152, the intake pressure drop amount ΔPmdwni and the drop time Δtdwni corresponding to the i-th cylinder are calculated from the transition of the intake pressure Pm detected at step 151.

  Next, at step 153, it is determined whether or not the first cylinder intake top dead center has been passed, as in step 103 of FIG. If it is determined that the first cylinder intake top dead center is not passed, the control routine is terminated. On the other hand, if it is determined in step 153 that the first cylinder intake top dead center has been passed, the routine proceeds to step 154.

  In step 154, the difference between the maximum descent time Δtdwnmax and the minimum descent time Δtdwnmin is calculated based on the intake pressure drop amount ΔPmdwni for each cylinder calculated in step 152, and this difference is set to a predetermined value n. Or less is determined. If it is determined that the difference is smaller than the predetermined value n, the process proceeds to step 155. In step 155, the target opening / closing valve time Δtoctrg of the intake valve 6 is acquired from the ECU 31. Next, at step 156, the values of various parameters (intake pressure drop amount ΔPmdwni, intake air temperature Tm, throttle valve passage air flow rate mt, drop time Δtdwni, target on-off valve time Δtoctrg) calculated at steps 151, 152 and 155 are used. Based on the equation (8), the in-cylinder charged air amount Mci for the i-th cylinder is calculated for each of the 1st to 8th cylinders.

  On the other hand, if it is determined in step 154 that the difference is greater than or equal to a predetermined value n, the process proceeds to step 157. In step 157, the deviation amount α is calculated based on a map or the like obtained in advance using the target valve opening timing tivo of the intake valve 6 calculated in step 151. Next, in step 158, the values of various parameters (intake pressure drop amount ΔPmdwni, intake air temperature Tm, throttle valve passage air flow rate mt, drop time Δtdwni, deviation amount α) calculated in steps 151, 152 and 157 are used. Thus, constants a, b, and c are calculated for each cylinder based on equations (20), (21), and (23). Next, at step 159, the in-cylinder charged air amount Mci is calculated for each cylinder by substituting the constants a, b, and c calculated at step 158 into equation (25).

  Next, a third embodiment of the present invention will be described.

  By the way, when the operating angle of the intake valve 6 becomes large and the opening / closing valve periods of the intake valves 6 corresponding to two cylinders continuing in the order of ignition overlap, or when the opening / closing valve periods of these intake valves 6 overlap, In this case, the ratio of the area of the region T2 to the area of the region T1 in FIG. Therefore, in such a case, the calculation accuracy of the area of the region T2 has a great influence on the calculation accuracy of the in-cylinder charged air amount Mci for the i-th cylinder. For this reason, if the cylinder filling air amount Mci is calculated using the opening / closing valve time Δtoci of the intake valve 6 corresponding to the i-th cylinder as the target opening / closing valve time Δtoctrg in such a case, the calculation accuracy of the cylinder filling air amount Mci deteriorates. . Therefore, in this case, the calculation accuracy of the in-cylinder charge air amount Mci is more calculated by calculating the in-cylinder charge air amount Mci by the descent time use method than by calculating the in-cylinder charge air amount Mci by the target on-off valve time use method. Can be expensive.

  On the other hand, when the operating angle of the intake valve 6 is reduced and the opening / closing valve periods of the intake valves corresponding to the two cylinders consecutive in the firing order do not overlap, or the period during which the opening / closing valve periods of the intake valves 6 overlap is shortened. In this case, the ratio of the area of the region T2 to the area of the region in FIG. 4 is small, and the influence of the calculation accuracy of the area of the region T2 on the calculation accuracy of the in-cylinder charged air amount Mci to the i-th cylinder is small. . Therefore, in such a case, even if the in-cylinder charged air amount Mci is calculated using the opening / closing valve time Δtoci of the intake valve 6 corresponding to the i-th cylinder as the target opening / closing valve time Δtoctrg, the calculation accuracy is relatively high. When the in-cylinder charged air amount Mci is calculated based on the descent time Δtdwni corresponding to the No. cylinder, the calculation accuracy of the in-cylinder charged air amount Mci is relatively low due to the measurement error of the descent time Δtdwni corresponding to the i-th cylinder. Therefore, in such a case, the calculation accuracy of the in-cylinder charge air amount Mci is more calculated by the target on-off valve time use method than by calculating the in-cylinder charge air amount Mci by the descent time use method. Can be high.

  Therefore, in the present embodiment, when the target operating angle of the intake valve 6 is large, the cylinder charge air amount Mci is calculated by the descent time utilization method, and when the target operating angle of the intake valve 6 is small, the target The in-cylinder charged air amount Mci is calculated by the on-off valve time utilization method. As a result, the in-cylinder charged air amount Mci is always calculated by an optimal calculation method, and therefore the in-cylinder charged air amount Mci can be calculated relatively accurately.

  Note that the ratio of the area of the region T2 to the area of the region T1 in FIG. 4 also changes depending on the number of cylinders. That is, the area ratio of the region T2 is larger in the multi-cylinder internal combustion engine having a larger number of cylinders. Therefore, in a multi-cylinder internal combustion engine having a large number of cylinders, the cylinder charge air amount Mci is calculated by the descent time method, and in a multi-cylinder internal combustion engine having a small number of cylinders, the cylinder charge air amount Mci is calculated by the on-off valve time method. May be.

  In the above description, only the fuel injection amount is adjusted for each cylinder based on the cylinder-to-cylinder variation in the cylinder charge air amount. However, the fuel injection is performed based on the cylinder-to-cylinder variation in the cylinder charge air amount. The ignition timing by the spark plug 10 as well as the amount may be adjusted. That is, the air-fuel ratio of the air-fuel mixture can be made equal for all the cylinders by adjusting the fuel injection amount based on the cylinder-to-cylinder variation in the cylinder-filled air amount. Due to the variation in the fuel injection amount, the torque generated for each cylinder differs and torque fluctuations occur. Therefore, by adjusting the ignition timing 10 for each cylinder, the torque generated for all the cylinders can be made equal, and the occurrence of torque fluctuation can be suppressed.

  In the present specification, the on-off valve time Δtoc is basically described as meaning the actual on-off valve time, that is, the operating angle. However, the opening / closing valve time Δtoc more precisely means the opening / closing valve time that affects the in-cylinder charged air amount, that is, the time during which the intake valve is effectively opened to suck air into the cylinder. Is.

1 is an overall view of an internal combustion engine to which the present invention is applied. It is the figure which showed a mode that the phase angle of the intake valve, the working angle, and the lift amount changed with the operation of the intake valve driving device. It is a figure which shows the detection result of the intake pressure Pm. It is a time chart for demonstrating intake pressure fall amount (DELTA) Pmdwni. It is a figure for demonstrating the calculation method of the cylinder filling air amount Mci. It is a figure for demonstrating the 1st calculation method of the on-off valve time of the intake valve of i-th cylinder. It is a figure for demonstrating the 2nd calculation method of the on-off valve time of the intake valve of i-th cylinder. It is a figure which shows the relationship between the on-off valve time of an intake valve when it assumes that the variation between cylinders has not generate | occur | produced, and cycle average intake pressure. It is a flowchart of the control routine for calculating the cylinder filling air amount to the i-th cylinder by the third calculation method. It is a figure for demonstrating the calculation principle of the 4th calculation method of the opening / closing valve time of the intake valve corresponding to the i-th cylinder. It is the figure which showed the relationship between the valve opening time of an intake valve, and transition of in-cylinder pressure. It is a figure for demonstrating the calculation principle of the 5th calculation method of the opening-and-closing valve time (DELTA) of the intake valve corresponding to i-th cylinder. It is a figure which shows the curve which approximated the transition of the in-cylinder intake air flow rate with a quadratic function, and the transition of the lift amount of the intake valve. 12 is a flowchart of a control routine for calculating an in-cylinder charged air amount to an intake valve of an i-th cylinder according to a second embodiment.

Explanation of symbols

1 Engine Body 6 Intake Valve 10 Fuel Injection Valve 18 Throttle Valve 22 Intake Valve Drive Device 31 ECU
40 Air flow meter 41 Intake pressure sensor IM Intake pipe part

Claims (16)

In a control device for a multi-cylinder internal combustion engine that controls an intake valve so that the on-off valve time of the intake valve becomes a target on-off valve time,
Estimate the cylinder-to-cylinder variation in the amount of air charged in the cylinder,
When the estimated cylinder filling air amount is less than a predetermined level, the cylinder filling air amount to each cylinder is estimated based on the target on-off valve time,
When the estimated in-cylinder charged air amount is larger than the predetermined level , it is an engine operating parameter necessary for estimating the opening / closing time of the intake valve and is detected by the operating parameter detecting means. Estimating the in-cylinder charged air amount to each cylinder based on the estimated opening / closing valve time of the intake valve estimated based on at least one engine operating parameter;
A control apparatus for a multi-cylinder internal combustion engine, which controls the multi-cylinder internal combustion engine based on the estimated cylinder air charge amount to each cylinder.   2. The control device for a multi-cylinder internal combustion engine according to claim 1, wherein the inter-cylinder variation in the in-cylinder charged air amount is estimated based on an intake pressure drop time associated with opening of an intake valve corresponding to each cylinder.   2. The control device for a multi-cylinder internal combustion engine according to claim 1, wherein the cylinder-to-cylinder variation in the in-cylinder charged air amount is estimated based on an intake pressure drop amount associated with opening of an intake valve corresponding to each cylinder. In a control device for a multi-cylinder internal combustion engine that controls an intake valve so that the on-off valve time of the intake valve becomes a target on-off valve time,
When the target opening / closing valve time is less than or equal to a predetermined value, the cylinder charge air amount to each cylinder is estimated based on the target opening / closing valve time,
When the target opening / closing valve time is larger than the predetermined value, the cylinders are supplied to each cylinder based on the estimated opening / closing valve time of the intake valve estimated based on at least one engine operation parameter detected by the operation parameter detecting means. Estimate the amount of air filled in the cylinder,
A control apparatus for a multi-cylinder internal combustion engine, which controls the multi-cylinder internal combustion engine based on the estimated cylinder air charge amount to each cylinder.   The control apparatus for a multi-cylinder internal combustion engine according to any one of claims 1 to 4, wherein the at least one engine operating parameter is a time period during which the intake pressure drops when the intake valve corresponding to each cylinder opens.   The cylinder air charge amount to each cylinder is estimated from the intake pipe portion by exceeding the basic air amount and the air flow rate through the throttle valve as the intake valve is opened. The basic air volume is divided into the excess air volume that flows into the cylinder and is divided into two, and the flow rate of the throttle valve passing air that flows into the intake pipe portion via the throttle valve and the target on-off valve time or estimated on-off valve time of the intake valve Is calculated by calculating the excess air amount based on the amount of decrease in the intake pressure associated with the opening of the intake valve corresponding to each cylinder, and summing the basic air amount and the excess air amount. The control apparatus of the multi-cylinder internal combustion engine of any one of 1-5. When estimating the in-cylinder charged air amount to each cylinder based on the target opening / closing valve time of the intake valve, the in-cylinder charged air amount to each cylinder is determined by the basic air amount and the intake valve opening. The throttle valve passing air flow rate is divided into two, the excess air amount flowing into the cylinder from the intake pipe portion, and the throttle valve passing air flow rate flowing into the intake pipe portion via the throttle valve and the target opening / closing of the intake valve The basic air amount is calculated based on the valve time, the excess air amount is calculated based on the intake air pressure drop accompanying the opening of the intake valve, and the basic air amount and the excess air amount are summed. The amount of air filled in each cylinder is estimated,
When estimating the in-cylinder charged air amount to each cylinder based on the estimated opening / closing valve time of the intake valve, the cylinder to each cylinder is based on at least one engine operating parameter detected by the operating parameter detecting means. derives the near-Nishiki inner intake air flow rate changes, the in-cylinder charged air amount of each cylinder by integrating over the near-Nishiki the estimated off valve time is estimated, of claims 1 to 5 The control apparatus of the multi-cylinder internal combustion engine of any one of Claims. Detect the intake pressure of the intake pipe part,
Each cylinder by based on the intake pressure of the detected intake pipe part derives the near-Nishiki-cylinder intake air flow rate of the transition to each cylinder, integrating over the near-Nishiki the estimated off valve Time Estimate the amount of air filled in the cylinder,
A control apparatus for a multi-cylinder internal combustion engine, which controls the multi-cylinder internal combustion engine based on the estimated cylinder air charge amount to each cylinder. Upper KiKon Nishiki is a quadratic approximate expression control apparatus for a multi-cylinder internal combustion engine according to claim 7 or 8. Changes in the cylinder intake air flow rate to each cylinder is approximated by a plurality of approximate expression control apparatus for a multi-cylinder internal combustion engine according to any one of claims 7-9. In addition to detecting the intake pressure in the intake pipe portion, based on the detected intake pressure, calculate the intake pressure drop time associated with the opening of the intake valve corresponding to each cylinder,
Estimating the open / close valve time of the intake valve corresponding to each cylinder based on the calculated intake pressure drop time associated with the opening of the intake valve corresponding to each cylinder,
A control device for a multi-cylinder internal combustion engine that controls the multi-cylinder internal combustion engine based on an estimated opening / closing time of an intake valve corresponding to each cylinder. Off valve time of the intake valve is adapted to derive the near-Nishiki of the cylinder intake air flow rate of the transition to each based on the fall time of the intake pressure accompanying the opening cylinder of the intake valve corresponding to each cylinder, It is calculated from the approximation equation issued conductor control device for a multi-cylinder internal combustion engine according to claim 11. Approximating the transition of the cylinder intake air flow rate to each cylinder by a plurality of approximate expression control apparatus for a multi-cylinder internal combustion engine according to claim 12.   In addition to the intake pressure drop time associated with the opening of the intake valve corresponding to each cylinder, the intake valve opening / closing corresponding to each cylinder is based on the average value of the calculated intake pressure drop times for all cylinders. The control apparatus for a multi-cylinder internal combustion engine according to claim 11, wherein the valve time is calculated.   Based on the average value of all cylinders of the opening / closing valve time of the intake valve predicted based on the average value of the intake pressure over one cycle, in addition to the decrease time of the intake pressure accompanying the opening of the intake valve corresponding to each cylinder. 12. The control device for a multi-cylinder internal combustion engine according to claim 11, wherein an opening / closing valve time of the intake valve corresponding to each cylinder is calculated. The in-cylinder charge air amount to each cylinder is estimated based on the estimated opening / closing valve time of the intake valve corresponding to each cylinder, and the multi-cylinder internal combustion engine is based on the estimated in-cylinder charge air amount to each cylinder Control
The cylinder air charge amount to each cylinder is estimated from the intake pipe portion by exceeding the basic air amount and the air flow rate through the throttle valve as the intake valve is opened. The basic air amount is calculated based on the amount of air passing through the throttle valve that flows into the intake pipe through the throttle valve and the estimated opening / closing valve time of the intake valve. The excess air amount is calculated based on the amount of decrease in the intake pressure accompanying the opening of the intake valve, and the basic air amount and the excess air amount are summed. The control device for a multi-cylinder internal combustion engine according to claim 1.

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