JP4470765B2 - 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.

  A multi-cylinder internal combustion engine having a variable valve mechanism that can change the phase angle, operating angle, and lift amount of an intake valve and an exhaust valve is known. In a multi-cylinder internal combustion engine having such a variable valve mechanism, the pump loss caused by reducing the opening of the throttle valve is reduced by operating with a small operating angle and small lift amount without using a throttle valve. Therefore, fuel consumption can be improved.

  However, if the operation is performed with a small operating angle and small lift amount, the opening time of the intake valve is shortened or the opening of the intake valve is reduced. For example, deposits near the intake valve or between cylinders Variations between cylinders in the in-cylinder charged air amount remarkably appear due to poor adjustment of the operating angle and lift amount of the intake valve. Thus, when the variation in the cylinder filled air amount between the cylinders becomes large, the air-fuel ratio varies between the cylinders, leading to deterioration of exhaust emission and torque fluctuation.

  Therefore, conventionally, the cylinder charge air amount to each cylinder is estimated in consideration of the variation in cylinder charge air amount between cylinders, and the fuel to each cylinder is calculated based on the estimated cylinder charge air amount to each cylinder. A control device for a multi-cylinder internal combustion engine that controls operation parameters of the internal combustion engine such as an injection amount is known.

  For example, in the control device described in Patent Document 1, the amount of air in the intake pipe downstream of the throttle valve detected by the intake pressure sensor and the temperature sensor is calculated from the amount of air passing through the throttle calculated based on the output of the throttle opening sensor or the like. The in-cylinder charged air amount to each cylinder is calculated by subtracting the increase amount of the air in the intake pipe on the downstream side of the throttle valve calculated based on the pressure and temperature. Based on the calculated in-cylinder charged air amount for each cylinder, the in-cylinder variation of the in-cylinder charged air amount is estimated, and the fuel injection amount to each cylinder is adjusted according to this variation. This suppresses variation in the air-fuel ratio of the air-fuel mixture charged in each cylinder.

JP 2001-234798 A JP 2002-70633 A

  As described above, an intake pressure sensor for detecting the pressure in the intake pipe is required in order to obtain the cylinder-to-cylinder variation in the in-cylinder charged air amount. Such an intake pressure sensor can detect the pressure in the intake pipe in an analog manner, but the output of the intake pressure sensor is converted into digital data by an AD converter when input to an electronic control unit (ECU). . Therefore, the intake pressure cannot be accurately detected depending on the resolution of the AD converter. For this reason, when the intake pressure is detected by the intake pressure sensor, the variation between cylinders in the in-cylinder charged air amount may not be accurately estimated.

  Accordingly, an object of the present invention is to provide a control device for a multi-cylinder internal combustion engine that controls the internal combustion engine in consideration of the variation between cylinders in the cylinder air filling amount without directly using the value of the intake pressure detected by the intake pressure sensor. It is to provide.

In order to solve the above-described problem, in the first invention, an intake pressure sensor that detects an intake pressure downstream of the throttle valve, and an intake valve that corresponds to each cylinder is opened based on the output of the intake pressure sensor. A descent time calculating means for calculating the descent time required for the intake air pressure to drop, an inter-cylinder variation obtaining means for obtaining a variation between the cylinders in the descent time calculated by the descent time calculating means, and There is provided a control device for a multi-cylinder internal combustion engine, comprising: engine control means for controlling the internal combustion engine based on the variation between the cylinders of the above-described descent time obtained by the dispersion obtaining means.
In general, even when the resolution of the output from the intake pressure sensor is low, the descent time can be calculated almost accurately. That is, even if there is an error in the intake pressure detected by the intake pressure sensor, the error in the descent time calculated from this value is small. Further, the descent time associated with the opening of the intake valve of a certain cylinder is substantially proportional to the amount of air charged in the cylinder of the cylinder. Therefore, according to the first aspect of the present invention, the descent time can be calculated relatively accurately even when the resolution of the output from the intake pressure sensor is low, and the in-cylinder charged air amount can be estimated relatively accurately. Can do. Furthermore, since the internal combustion engine is controlled based on the inter-cylinder variation of the descent time, which is a value related to the inter-cylinder variation of the in-cylinder charged air amount, it is possible to suppress exhaust emission deterioration and torque fluctuation.

  According to a second invention, in the first invention, the engine control means estimates the cylinder-to-cylinder variation of the in-cylinder charged air amount based on the cylinder-to-cylinder variation of the descent time obtained by the cylinder-to-cylinder variation obtaining means. Then, the internal combustion engine is controlled based on the inter-cylinder variation in the estimated cylinder air charge amount.

  In a third invention, in the first invention, the inter-cylinder variation obtaining means obtains a difference between the maximum value and the minimum value among the descent times corresponding to all the cylinders as the inter-cylinder variation.

  According to a fourth invention, in the first invention, the inter-cylinder variation obtaining means includes an average value of descent times corresponding to all the cylinders, and a descent time corresponding to each cylinder calculated by the descent time calculating means. Is obtained as the variation between cylinders.

  According to a fifth aspect, in the first aspect, the inter-cylinder variation obtaining means is predicted based on an operating parameter of the internal combustion engine other than the descent time when it is assumed that there is no inter-cylinder variation in the descent time. The difference between the descent time and the descent time corresponding to each cylinder calculated by the descent time calculating means is obtained as the variation between the cylinders.

  According to the present invention, there is provided a control device for a multi-cylinder internal combustion engine that controls the internal combustion engine in consideration of the variation between cylinders in the cylinder air charge amount without directly using the value of the intake pressure detected by the intake pressure sensor. The

  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 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 operating angle and the lift amount of the intake valve 6 change as the intake valve driving device 22 is operated. As shown in FIG. 2, the operating angle and lift amount of the intake valve 6 are continuously changed by the intake valve driving device 22. In particular, according to the intake valve drive device 22 of the present embodiment, as the operating angle of the intake valve 6 is increased, the operating angle of the intake valve 6 is increased (solid line → broken line → dashed line).

  By the way, in a multi-cylinder internal combustion engine, due to assembly tolerances and machine differences related to the valve portion, wear of the valve portion, adhesion of deposits, and the like, variations in the amount of in-cylinder charged air between the cylinders occur, which causes torque fluctuations. There is a problem that the exhaust emission is deteriorated due to the generation or the air-fuel ratio of the air-fuel mixture varies between the cylinders. Such a problem may occur similarly in a multi-cylinder internal combustion engine of the type that controls the working angle and the like as in the present embodiment to control the amount of in-cylinder charged air. It is known that the larger the working angle and the lift amount are, the smaller the working angle and the lift amount are, for example, the smaller the working angle and the lift amount of the intake valve 6 are.

  Therefore, in the present embodiment, the cylinder-to-cylinder variation in the in-cylinder charged air amount is estimated directly or indirectly, and the influence of the estimated in-cylinder charged air amount between the cylinders is reduced or estimated cylinder. By controlling the multi-cylinder internal combustion engine so as to compensate for the variation in the amount of internal charge air between cylinders, the occurrence of torque fluctuations and the deterioration of exhaust emissions are suppressed.

  First, in the present embodiment, a method for directly or indirectly estimating the cylinder-to-cylinder variation in the in-cylinder charged air amount will be described. In this embodiment, when estimating the cylinder-to-cylinder variation in the in-cylinder charged air amount, the descent time (hereinafter simply referred to as “descent time”) required for the intake pressure to drop as the intake valve corresponding to each cylinder opens. Δtdwni is used. The descent time will be described with reference to FIGS.

  FIG. 3 shows the intake pressure Pm detected by the pressure sensor 41 over, for example, a 720 ° crank angle at regular time intervals. The intake order in the multi-cylinder 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 the maximum value Pmmaxi and the intake pressure Pm at the downward peak DNi is referred to as the minimum value Pmmini, the intake pressure is increased by the intake to the i-th cylinder. Pm decreases from the maximum value Pmmaxi to the minimum value Pmmini. Therefore, the intake pressure decrease amount ΔPmdwni in this case is expressed by the following equation (1).
ΔPmdwni = Pmmaxi−Pmmini (1)

On the other hand, as shown in FIG. 4, the time when the intake pressure Pm takes the maximum value Pmmaxi at the upward peak UPi is called tmaxi, and the time at which the intake pressure Pm takes the minimum value Pmmini at the downward peak DNi is called tmini. Time (descent time) Δtdwni required for the atmospheric pressure Pm to drop from the maximum value Pmmaxi to the minimum value Pmmini is expressed by the following equation (2).
Δtdwni = tmini−tmaxi (2)

  The inventors of the present application have found that there is a certain relationship between the descent time Δtdwni calculated in this way and the in-cylinder charged air amount to each cylinder. More specifically, it is considered that the descent time Δtdwni and the in-cylinder charged air amount to each cylinder are substantially proportional as shown in FIG. That is, when the descent time Δtdwni associated with the opening of the intake valve corresponding to a certain cylinder is short, this means that the amount of air charged into the cylinder is small, and conversely, the intake valve corresponding to a certain cylinder. When the descent time Δtdwni accompanying the opening of the valve is long, it means that the amount of air charged in the cylinder is large. Therefore, it can be said that the inter-cylinder variation in the descent time Δtdwni represents the inter-cylinder variation in the in-cylinder charged air amount. In other words, if the inter-cylinder variation in the descent time Δtdwni can be obtained, the inter-cylinder variation in the in-cylinder charged air amount can be estimated.

  Note that the ECU 31 is referred to as a descent time calculation means and an inter-cylinder variation acquisition means because the calculation of the descent time Δtdwni based on the output from the intake pressure sensor 41 and the inter-cylinder variation of the descent time Δtdwni are performed by the ECU 31. be able to.

  By the way, when the intake air pressure drop amount ΔPmdwni flows into the intake pipe portion IM through the throttle valve 18 by the amount of air passing through the throttle valve mt and intake into the i-th cylinder is performed, When considering that the air flows out through the valve 6 by the in-cylinder intake air flow rate mci, the in-cylinder intake air flow rate mci, which is the outflow, temporarily exceeds the throttle valve passage air flow rate mt, which is the inflow. This is the amount of decrease in pressure in the intake pipe portion IM that has been reduced by. Since the intake pressure decrease amount ΔPmdwni shows such physical characteristics, it is considered that the intake pressure decrease amount ΔPmdwni changes according to the in-cylinder charged air amount for each cylinder. For this reason, it is considered that the intake pressure decrease amount ΔPmdwni can be calculated based on the output of the intake pressure sensor 41, and the in-cylinder variation in the cylinder charge air amount can be estimated based on the value of the intake pressure decrease amount ΔPmdwni. .

  However, when the intake pressure sensor 41 detects the intake pressure Pm in the intake pipe portion, the analog signal of the intake pressure sensor 41 is converted into a digital signal by the AD converter 36. Therefore, the intake pressure data detected by the intake pressure sensor 41 is a digital signal when input to the ECU 31. Here, the AD converter 36 has a resolution, and can output intake pressure data only for every fixed value.

  FIG. 6 is an example of a plot of the intake pressure input from the intake pressure sensor 41 to the ECU 31 when the intake pressure sensor 41 detects a change in the intake pressure as shown by the solid line. As can be seen from FIG. 6, in the vicinity of the upward peak UPi, a deviation ΔDFi may occur between the input value (plot) from the intake pressure sensor 41 and the actual intake pressure (solid line). This is caused by the low resolution of the AD converter 36. On the other hand, there may be a difference between the input value from the intake pressure sensor 41 and the actual intake pressure similarly in the vicinity of the downward peak DNi. However, in the illustrated example, the input value is in the vicinity of the downward peak DNi. There is no deviation between the actual intake pressure and the actual intake pressure. Therefore, as shown in FIG. 6, the intake pressure decrease amount ΔPmdwni calculated from the input value from the intake pressure sensor 41 is smaller than the actual intake pressure decrease amount by a deviation ΔDFi. For this reason, if the inter-cylinder variation in the in-cylinder charged air amount is estimated based on the intake pressure decrease amount ΔPmdwni, a large error occurs in the estimated inter-cylinder variation.

  On the other hand, the descent time Δtdwni can be calculated relatively accurately even when the resolution of the AD converter 36 is low. That is, when the resolution of the AD converter 36 is low, the input value from the intake pressure sensor 41 is the same over a certain period as shown in FIG. 6 in the vicinity of the upward peak UPi and the downward peak DNi. In this case, if the detection time in the middle of the period in which the input values are the same or in the vicinity of the center of this period is detected as the time at which the intake pressure Pm is maximum or minimum, the detected intake pressure Pm is maximum. There is almost no error between the time when the intake pressure Pm is actually maximized, and the time between the time when the detected intake pressure Pm is minimized and the time when the intake pressure Pm is actually minimized is similar. There is almost no error. For this reason, the descent time Δtdwni calculated from these detected values is almost the same as the actual descent time Δtdwni. Therefore, the detection of the descent time Δtdwni can be detected relatively accurately without being affected by the resolution of the input from the intake pressure sensor 41 to the ECU.

  Thus, even when the resolution of the intake pressure sensor 41 is low, the descent time Δtdwni can be detected relatively accurately, and the descent time Δtdwni corresponding to the intake valve opening of each cylinder is filled in the cylinder. Since there is a substantially proportional relationship with the air amount, according to the present invention, it is possible to estimate the cylinder-to-cylinder variation of the in-cylinder charged air amount relatively accurately.

  Next, using the detection result of the inter-cylinder variation of the drop time Δtdwni that is an index of the inter-cylinder variation in the in-cylinder charged air amount, the in-cylinder variation in the in-cylinder charged air amount is reduced or estimated. A method for controlling a multi-cylinder internal combustion engine to compensate for the variation in the amount of charged air between cylinders will be described.

  First, a method for controlling a multi-cylinder internal combustion engine using the detection result of the inter-cylinder variation of the descent time Δtdwni so that the variation of the cylinder air charge amount between the cylinders is reduced will be described. FIG. 7A shows, as an example, the descent time Δtdwni calculated based on the output of the intake pressure sensor 41 for each cylinder as described above in a certain multi-cylinder internal combustion engine. The descent time Δtdwni has a different value for each cylinder, and it can be seen that in this multi-cylinder internal combustion engine, the descent time Δtdwni varies among the cylinders. That is, in this multi-cylinder internal combustion engine, it can be seen that the cylinder air charge amount varies between cylinders.

  In the present embodiment, the maximum value Δtdwnmax of the drop time Δtdwni that varies among the cylinders (the drop time Δtdwn1 of the first cylinder in the case of FIG. 7A) and the minimum value Δtdwnmin of the drop time Δtdwniin (FIG. 7A). In this case, the difference ΔTmm of the descent time from Δtdwni) of the i-th cylinder is calculated. The difference ΔTmm calculated in this way is a value corresponding to the difference between the maximum value and the minimum value of the in-cylinder charged air amount. Therefore, the larger the difference ΔTmm, the greater the variation in the in-cylinder charged air amount between the cylinders. It means that.

  Therefore, in the present embodiment, the internal combustion engine is controlled based on the drop time difference ΔTmm, which is an index of the variation between cylinders in the in-cylinder charged air amount. As described above, the inter-cylinder variation in the cylinder charge air amount due to deposit adhesion, tolerance, and machine difference becomes significant when the operating angle or the lift amount is small. That is, even if the deposit adhesion degree, tolerance, and machine difference are the same, the in-cylinder charge air amount variation between cylinders increases when the working angle and lift amount are small, resulting in large exhaust emission deterioration and torque fluctuation. It becomes. Therefore, in the present embodiment, the operating angle control permission range, that is, the operating angle range of the intake valve 6 that is allowed to be adjusted by the intake valve driving device 22 is changed according to the difference ΔTmm in the descent time. Yes.

  FIG. 8 is a diagram showing the relationship between the descent time difference ΔTmm and the operating angle control permission range. In the figure, the hatched portion indicates the control allowable range of the operating angle. For example, as shown in FIG. 8 (a), when the difference ΔTmm in descent time is relatively small, it is considered that the variation in the in-cylinder charged air amount between the cylinders is small even if the working angle is small. The working angle can be controlled to a small range. Therefore, the operating angle can be changed in a wide range. On the other hand, as shown in FIG. 8B, when the difference ΔTmm in descent time is relatively large, if the working angle is reduced, the variation in the cylinder charge air amount between the cylinders becomes large. It is prohibited to become smaller than a certain value. Therefore, the operating angle is controlled within a limited narrow range.

  In the above embodiment, the operating angle of the intake valve 6 is changed based on the difference ΔTmm in the descent time. However, the control parameter changed based on the difference ΔTmm in the descent time is limited to the operating angle of the intake valve 6. Instead, other control parameters such as the lift amount of the intake valve 6 and the throttle opening may be changed.

  Next, a method for controlling the multi-cylinder internal combustion engine so as to compensate for the variation between cylinders in the in-cylinder charged air amount using the detection result of the variation between cylinders during the descent time Δtdwni will be described.

By the way, in the multi-cylinder 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 the following equation (3), for example.
TAUi = TAUb · ηi · k (3)
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 operation state (for example, engine load and engine speed NE, etc., hereinafter referred to as “operation parameters”), and is stored in the ROM 32 in the form of a map. Or calculated by mathematical formulas based on the 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 the in-cylinder charged air amount Mci, the air amount variation correction coefficient ηi compensates for the variation between the cylinders in the in-cylinder charged air amount Mci. Is to do. The air amount variation correction coefficient ηi of the i-th cylinder is a value that can be expressed, for example, by the following equation (4), and indicates the degree of variation in the in-cylinder charged air amount of each cylinder.
ηi = Mci / Mcave (4)
Here, Mcave represents the average value (= ΣMci / 8, “8” represents the number of cylinders) of the in-cylinder charged air amount Mci of all the cylinders. The average value Mcave is a value calculated from a mathematical formula, a map, or the like based on the throttle opening, the operating angle, the atmospheric temperature, and the like, assuming that there is no inter-cylinder variation in the in-cylinder charged air amount.

  Therefore, if the air amount variation correction coefficient ηi can be calculated, the inter-cylinder variation of the in-cylinder charged air amount can be compensated, and the air-fuel ratio of the air-fuel mixture can be made equal for all the cylinders.

  In the present embodiment, the air amount variation correction coefficient ηi is calculated from the variation between cylinders of the descent time Δtdwni. A method for calculating the air amount variation correction coefficient ηi will be described with reference to FIG.

In calculating the air amount variation correction coefficient ηi, first, the descent time Δtdwni calculated from the output of the intake pressure sensor 41 is totaled for all the cylinders over one cycle, and this is divided by the number of cylinders. An all cylinder average value Δtdwnave (see FIG. 7B) is calculated. Then, by subtracting the all cylinder average value Δtdnave of the descent time from the descent time Δtdwni calculated for each cylinder, a difference ΔTavei between the descent time and the all cylinders average value is calculated for each cylinder. The air amount variation correction coefficient ηi of the i-th cylinder is calculated by the following formula (5) based on the average value Δtdwnave of all the cylinders for the descent time calculated in this way and the difference ΔTavei of each cylinder.
ηi = (Δtdwnave + ΔTavei + a) / (Δtdwnave + a) (5)
Here, a is a constant determined based on parameters such as the throttle opening and the ambient air temperature around the internal combustion engine, and is stored in the ROM 34 of the ECU 31 as a map based on these parameters, or calculated from these parameters using mathematical formulas. The

  Using the air amount variation correction coefficient ηi of the i-th cylinder calculated in this way, the fuel injection amount TAUi to the i-th cylinder is calculated by the above equation (3). As a result, the fuel injection amount TAUi for the i-th cylinder is calculated in consideration of the cylinder-to-cylinder variation in the in-cylinder charged air amount. Therefore, the ratio of the fuel injection amount to the in-cylinder charged air amount for all cylinders, The air-fuel ratio of the air-fuel mixture becomes substantially equal for the cylinders, so that deterioration of exhaust emission can be suppressed.

  However, even if the air-fuel ratio of the air-fuel mixture is almost the same for all the cylinders, the cylinder charge air amount and the fuel injection amount are different among the cylinders, so that the torque generated by the combustion in each cylinder also varies between the cylinders. It becomes different and torque fluctuation occurs.

  Therefore, in this embodiment, the torque generated by combustion is made equal for all the cylinders by adjusting the ignition timing by the spark plug 10.

  FIG. 9 shows the relationship between ignition timing and torque. As can be seen from FIG. 9, in the region that is retarded from a certain ignition timing (usually the region that is used in the operation of the internal combustion engine), the torque generated by combustion decreases with the retard of the ignition timing. . Therefore, in the present embodiment, the ignition timing is advanced in a cylinder with a small in-cylinder charged air amount and fuel injection amount, the torque generated by the combustion in the cylinder is increased, and the in-cylinder charged air amount and fuel injection amount are increased. In many cylinders, the ignition timing is retarded to reduce the torque generated by combustion in the cylinders.

  FIG. 10 is a diagram for explaining that the air-fuel ratio and the torque can be adjusted by adjusting the fuel injection amount and the ignition timing, and the solid line in the figure shows the case where the in-cylinder charged air amount and the ignition timing are the same. The relationship between air-fuel ratio and torque is shown.

  For example, consider the case where it is desired to match the air-fuel ratio and torque to the black circle x in the figure. Generally, in a cylinder having a larger cylinder air charge than other cylinders, the air-fuel ratio becomes leaner and more combustible oxygen than other cylinders unless the fuel injection amount is corrected. Is slightly larger (point y in the figure). When the fuel injection amount is adjusted so that the air-fuel ratio of the air-fuel mixture becomes equal to the air-fuel ratio of the other cylinders from this state, the torque generated by combustion is reduced while the air-fuel ratio of the air-fuel mixture is equal to that of the other cylinders. (Point y ′ in the figure). Therefore, the torque is reduced by retarding the ignition timing in the cylinder. As a result, the air-fuel ratio of the air-fuel mixture and the torque generated by the combustion can be made equal to those of the other cylinders even in the cylinder where the amount of in-cylinder charged air is larger than that of the other cylinders.

  On the other hand, in a cylinder with less cylinder air charge than other cylinders, if the fuel injection amount or the like is not corrected, the air-fuel ratio becomes richer and the combustible oxygen is less than other cylinders. Torque is reduced (point z in the figure). If the fuel injection amount is adjusted from this state so that the air-fuel ratio becomes equal to the air-fuel ratio of the other cylinders, the air-fuel ratio of the mixture is equal to that of the other cylinders, but the torque generated by combustion is smaller than that of the other cylinders. (Point z ′ in the figure). Therefore, the torque is increased by advancing the ignition timing in the cylinder. As a result, the air-fuel ratio of the air-fuel mixture and the torque generated by the combustion can be made equal to those of the other cylinders even in the cylinder where the amount of in-cylinder charged air is smaller than that of the other cylinders.

  The air amount variation correction coefficient ηi can be calculated from the variation between cylinders of the descent time Δtdwni by another calculation method. With reference to FIG. 7C, another method of calculating the air amount variation correction coefficient ηi will be described.

In this calculation method, first, assuming that there is no variation between cylinders in the descent time, the expected descent time Δtdwnx expected based on the operating parameters of the internal combustion engine (for example, engine speed, engine load, etc.) other than the descent time. (See FIG. 7C). Then, by subtracting the average value Δtdwnx of the descent time from the descent time Δtdwni calculated for each cylinder, a difference ΔTxi between the descent time and the average value of all cylinders is calculated for each cylinder. The air amount variation correction coefficient ηi of the i-th cylinder is calculated by the following formula (6) based on the average value Δtdwnx of all the cylinders for the descent time calculated in this way and the difference ΔTxi of each cylinder.
ηi = (Δtdwnx + ΔTxi + a) / (Δtdwnx + a) (6)
Here, a is the same value as the constant a in Equation 5.

  Also in this embodiment, using the air amount variation correction coefficient ηi of the i-th cylinder calculated in this way, the fuel injection amount TAUi to the i-th cylinder is expressed by the above equation (3) as in the above embodiment. Calculated. As a result, the fuel injection amount TAUi for the i-th cylinder is calculated in consideration of the cylinder-to-cylinder variation in the in-cylinder charged air amount. Therefore, the ratio of the fuel injection amount to the in-cylinder charged air amount for all cylinders, The air-fuel ratio of the air-fuel mixture is approximately equal for the cylinder.

1 is an overall view of a multi-cylinder internal combustion engine to which the present invention is applied. It is a figure which shows a mode that the working angle and lift amount of an intake valve are changed. It is a figure which shows the detection result of the intake pressure Pm. It is a time chart for demonstrating fall time (DELTA) tdwni. It is a figure which shows the relationship between descent | fall time and the cylinder air charge amount to each cylinder. It is a figure which shows the input value to ECU from an intake pressure sensor. It is the figure which showed fall time (DELTA) tdwni calculated based on the output of an intake pressure sensor for every cylinder. It is a figure showing the relationship between the difference ΔTmm of the descent time and the controllable range of the operating angle. It is the figure which showed the relationship between the ignition timing of a spark plug and the torque which generate | occur | produces by combustion. It is the figure which showed the relationship between the air fuel ratio of air-fuel | gaseous mixture, and the torque which generate | occur | produces by combustion.

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 (5)

An intake pressure sensor for detecting the intake pressure downstream of the throttle valve;
Based on the output of the intake pressure sensor, a descent time calculating means for calculating a descent time taken for the intake pressure to drop as the intake valve corresponding to each cylinder opens.
An inter-cylinder variation obtaining unit for obtaining an inter-cylinder variation of the descent time calculated by the descent time calculating unit;
A control device for a multi-cylinder internal combustion engine, comprising: an engine control unit that controls the internal combustion engine based on the inter-cylinder variation of the descent time obtained by the inter-cylinder variation obtaining unit.   The engine control means estimates the cylinder-to-cylinder variation of the cylinder filling air amount based on the cylinder-to-cylinder variation of the descent time obtained by the cylinder-to-cylinder variation obtaining means, and determines the estimated cylinder filling air amount. The control apparatus for a multi-cylinder internal combustion engine according to claim 1, wherein the internal combustion engine is controlled based on variation between cylinders.   2. The control apparatus for a multi-cylinder internal combustion engine according to claim 1, wherein the inter-cylinder variation obtaining means obtains the difference between the maximum value and the minimum value among the descent times corresponding to all the cylinders as inter-cylinder variation.   The inter-cylinder variation obtaining unit obtains, as inter-cylinder variation, a difference between an average value of descent times corresponding to all cylinders and a descent time corresponding to each cylinder calculated by the descent time calculating unit. A control device for a multi-cylinder internal combustion engine according to claim 1.   The inter-cylinder variation obtaining means is calculated by the expected descent time based on the operating parameters of the internal combustion engine other than the descent time and the descent time calculating means when it is assumed that there is no inter-cylinder variation in the descent time. 2. The control apparatus for a multi-cylinder internal combustion engine according to claim 1, wherein a difference from the descent time corresponding to each cylinder is obtained as a variation between cylinders.

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