JP2009293514A - Controller of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controller of an internal combustion engine capable of detecting deterioration in detection accuracy of combustion fluctuation of each cylinder. <P>SOLUTION: The internal combustion engine controller is suitably used for an internal combustion engine including a plurality of cylinders, a crank angle detection means for detecting the crank angles of the plurality of cylinders, and a cylinder internal pressure detection means for detecting the internal pressure of at least one of the cylinders. The internal combustion engine controller includes a judgment means. As for the internal pressure detected cylinder that is a cylinder the internal pressure of which is detected, the judgment means judges that torsional vibration occurs in a crankshaft to which torque is transmitted from the plurality of cylinders when a difference between the combustion fluctuation calculated based on the crank angle and the combustion fluctuation calculated based on the cylinder internal pressure is not smaller than a predetermined value. It is thus possible to judge whether or not the detection accuracy of combustion fluctuation calculated based on the crank angle is deteriorated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine that corrects variations in combustion fluctuations between cylinders.

  2. Description of the Related Art Conventionally, there has been known a technique for detecting variations in combustion fluctuations between cylinders and correcting the fluctuations in combustion fluctuations between cylinders by adjusting control parameters of the internal combustion engine based on the detected fluctuations. For example, Patent Document 1 describes a technique for detecting torque variation between cylinders based on crank angle or in-cylinder pressure fluctuation, and controlling an intake valve based on the detected torque variation between cylinders. . Patent Document 2 also describes a technique related to the present invention.

JP 2004-316613 A JP 2004-84607 A

  However, since the technique described in Patent Document 1 does not consider the occurrence of torsional vibration in the crankshaft, the detection accuracy may be deteriorated when torque variation between cylinders is detected based on the crank angle. There is. If feedback control is performed based on the torque variation between the cylinders whose detection accuracy has deteriorated, engine damage, fuel consumption, emission, and drivability may be deteriorated. In addition, when detecting torque variation between cylinders based on in-cylinder pressure fluctuations, it is necessary to provide in-cylinder pressure sensors for all cylinders, which is costly.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a control device for an internal combustion engine that can detect deterioration in accuracy of combustion fluctuations.

  In one aspect of the present invention, a plurality of cylinders, a crank angle detection unit that detects crank angles of the plurality of cylinders, and an in-cylinder pressure detection unit that detects an in-cylinder pressure of at least one of the plurality of cylinders. An internal combustion engine control device applied to an internal combustion engine comprising: a cylinder pressure detection cylinder, which is a cylinder in which cylinder pressure is detected, calculated based on combustion fluctuations calculated based on a crank angle and cylinder pressure When the difference between the generated combustion fluctuation is equal to or greater than a predetermined value, there is provided determination means for determining that torsional vibration is generated in the crankshaft to which torque is transmitted from the plurality of cylinders.

  The control apparatus for an internal combustion engine includes a plurality of cylinders, crank angle detection means for detecting crank angles of the plurality of cylinders, and in-cylinder pressure detection for detecting an in-cylinder pressure of at least one of the plurality of cylinders. And is suitably applied to an internal combustion engine including the means. The crank angle detection means is, for example, a crank angle sensor, and the in-cylinder pressure detection means is, for example, an in-cylinder pressure sensor. The control device for the internal combustion engine includes determination means such as an ECU (Electronic Control Unit), for example, and the determination means is calculated based on a crank angle for an in-cylinder pressure detection cylinder that is a cylinder in which the in-cylinder pressure is detected. When the difference between the combustion fluctuation and the combustion fluctuation calculated based on the in-cylinder pressure is a predetermined value or more, a torsional vibration is generated on the crankshaft to which torque is transmitted from the plurality of cylinders. It is determined that In this way, it is possible to determine whether or not the accuracy of the combustion fluctuation calculated based on the crank angle is deteriorated due to torsional vibration.

  Another aspect of the control device for an internal combustion engine described above performs feedback control for suppressing variation in combustion fluctuation among the plurality of cylinders based on combustion fluctuation for each of the plurality of cylinders calculated based on a crank angle. The control means prohibits the feedback control when the determination means determines that torsional vibration is occurring. The control means is, for example, an ECU. By doing in this way, it can prevent performing feedback control based on combustion fluctuation with low accuracy.

  In a preferred embodiment of the control apparatus for an internal combustion engine, the determination unit is configured to determine, for the in-cylinder pressure detection cylinder, a statistical amount of torque variation calculated based on a crank angle and a torque calculated based on the in-cylinder pressure. When it is determined that the difference between the statistic of variation and a predetermined value is greater than or equal to a predetermined value, it is determined that the torsional vibration has occurred.

  In another aspect of the control apparatus for an internal combustion engine, the in-cylinder pressure detecting unit detects an in-cylinder pressure of a cylinder at which the influence of the torsional vibration is maximized. By doing in this way, it can be determined more reliably whether torsional vibration has occurred or not.

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

[Device configuration]
FIG. 1 shows a schematic configuration of an internal combustion engine according to the present embodiment. In FIG. 1, broken line arrows indicate the flow of signals. The internal combustion engine 10 (hereinafter referred to as “engine”) is mounted on a vehicle as a driving power source, and is, for example, a gasoline engine, a diesel engine, or the like. In FIG. 1, only the main part of the engine 10 is shown.

  The engine 10 includes four cylinders (cylinders) 11a to 11d (hereinafter, simply referred to as “cylinder 11” when the cylinders are not distinguished from each other), and is connected to the piston 12 and the connecting rod 16 in each cylinder 11. The crankshaft 17 is held rotatably. The engine rear (rear) side of the crankshaft 17 is connected to the transmission. Spark plugs 19 are provided at the head portions of the cylinders 11a to 11d. The ignition timing of the spark plug 19 in each of the cylinders 11a to 11d is controlled by a control signal from the ECU 20, respectively. An in-cylinder pressure sensor 31 is provided at the head portion of the cylinder 11a located on the engine front (front) side farthest from the transmission. The in-cylinder pressure sensor 31 detects the in-cylinder pressure of the cylinder 11a and transmits a detection signal corresponding to the detected in-cylinder pressure to the ECU 20.

  Here, the operation stroke of the cylinder 11 will be described with reference to FIG. FIG. 2 shows a cross-sectional configuration inside the cylinder 11. In FIG. 2, broken-line arrows indicate the flow of signals. An intake passage 3 and an exhaust passage 4 are connected to the combustion chamber 15 of the cylinder 11. An intake valve 13 and an exhaust valve 14 are provided in the combustion chamber 15 of the cylinder 11. The intake valve 13 controls conduction / interruption between the intake passage 3 and the combustion chamber 15 by opening and closing. The exhaust valve 14 controls opening / closing of the exhaust passage 4 and the combustion chamber 15 by opening and closing. Specifically, one cycle of the operation stroke of the cylinder 11 includes four strokes of an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. First, in the intake stroke, a mixture of fuel and air injected from the fuel injection valve 18 is supplied from the intake passage 3 into the combustion chamber 15 of the cylinder 11. Next, in the compression stroke, the piston 12 rises to the top dead center (TDC), and the air-fuel mixture is compressed. In the combustion stroke, the combustion of the air-fuel mixture is started by igniting the spark plug 19, and the piston 12 is pushed down to the bottom dead center (BDC) by the expansion of the air-fuel mixture due to the combustion. Thereafter, in the exhaust stroke, the piston 12 rises and the exhaust gas is discharged into the exhaust passage 4. The force that pushes down the piston 12 to the bottom dead center in the combustion stroke is transmitted as torque to the crankshaft 17 through the connecting rod 16, and the crankshaft 17 rotates. Here, in the vicinity of the crankshaft 17, as shown in FIG. 1, a crank angle sensor 41 that detects the rotation angle of the crankshaft 17 and transmits a detection signal corresponding to the detected rotation angle to the ECU 20 is provided. It has been.

  Returning to FIG. 1 and continuing the description, the ECU (Electronic Control Unit) 20 has a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like (not shown). Based on detection signals from various sensors, The engine 10 is controlled. Specifically, the ECU 20 detects torque variations of the cylinders 11a to 11d based on the detection signal from the crank angle sensor 41, and controls the ignition timing of the spark plug 19 based on the detected torque variation. Control to suppress torque variation is performed.

[Control method]
Next, the internal combustion engine control method according to the present embodiment will be specifically described.

  In a general internal combustion engine control method, combustion fluctuation for each cylinder (cycle fluctuation for each cylinder, for example, torque fluctuation for each cylinder) based on the crank angle detected by the crank angle sensor. Is calculated, and feedback control for suppressing variation in combustion fluctuation among the cylinders is performed by controlling the engine control parameter based on the calculated combustion fluctuation for each cylinder. For example, the ECU calculates the torque generated by the combustion in the cylinder for each cylinder based on the crank angle detected by the crank angle sensor. Then, the ECU calculates the torque variation between the cycles of each cylinder (hereinafter simply referred to as “torque variation for each cylinder”), and the torque variation between the cylinders is calculated based on the torque variation for each cylinder. Feedback control is performed to control the ignition timing of the spark plug so that the difference falls within a predetermined range.

  However, when torsional vibration occurs in the crankshaft, the combustion fluctuation for each cylinder calculated based on the crank angle is calculated as information including the influence of torsional vibration. It becomes impossible to accurately calculate the fluctuation of combustion. In a general control method for an internal combustion engine, the ECU performs feedback control based on the erroneous combustion fluctuation information, which may cause deterioration of engine damage, fuel consumption, emission, and drivability. On the other hand, in order to eliminate the influence of torsional vibration of the crankshaft, when calculating the combustion fluctuation for each cylinder based on the in-cylinder pressure, it is necessary to provide in-cylinder pressure sensors for all the cylinders, which is expensive. .

  Therefore, in the control method for an internal combustion engine according to the present embodiment, an in-cylinder pressure sensor is provided for the cylinder having the greatest influence of torsional vibration, and the ECU 20 determines the crank angle for the cylinder provided with the in-cylinder pressure sensor. It is determined whether the difference between the combustion fluctuation calculated based on the combustion fluctuation calculated based on the in-cylinder pressure is equal to or greater than a predetermined value. If the ECU 20 determines that the difference is greater than or equal to a predetermined value, the ECU 20 determines that the torsional vibration is generated in the crankshaft 17 and determines each cylinder calculated based on the crank angle. Assuming that the combustion fluctuation has low accuracy, the feedback control for suppressing the variation of the combustion fluctuation among the cylinders is prohibited. Hereinafter, as an example of the combustion fluctuation, a torque variation for each cylinder will be described as an example.

  First, a method for calculating the torque variation for each cylinder based on the crank angle will be described. First, the relationship between the crank angle and each torque is expressed by the following equation (1).

式（１）の左辺において、慣性質量Ｊは混合気の燃焼によって駆動されるピストン１２などの駆動部材の慣性質量、ｄω／ｄｔはクランク軸１７の角加速度、を示している。式（１）の右辺において、筒内ガス圧トルクＴｐは気筒１１の筒内ガス圧によるトルク、即ち、気筒内の混合気の燃焼によって発生するトルクを示し、往復質量慣性トルクＴｍはピストン１２などの往復慣性質量による慣性トルク、フリクショントルクＴｆは気筒１１におけるフリクショントルク、負荷トルクＴｌｅは走行時に路面から受ける負荷トルク、をそれぞれ示している。

In the left side of the equation (1), the inertia mass J represents the inertia mass of a drive member such as the piston 12 driven by the combustion of the air-fuel mixture, and dω / dt represents the angular acceleration of the crankshaft 17. In the right side of the equation (1), the in-cylinder gas pressure torque Tp indicates the torque due to the in-cylinder gas pressure of the cylinder 11, that is, the torque generated by the combustion of the air-fuel mixture in the cylinder, and the reciprocating mass inertia torque Tm is the piston 12 or the like. Inertia torque due to reciprocating inertia mass, friction torque Tf indicates friction torque in the cylinder 11, and load torque Tle indicates load torque received from the road surface during traveling.

  Here, the indicated torque TK, which is the torque generated in the crankshaft 17 by combustion in each cylinder 11, is calculated by integrating the sum of the in-cylinder gas pressure torque Tp and the reciprocating mass inertia torque Tm with the crank angle θ. Therefore, the following equation (2) is obtained by using equation (1).

ここで、式（２）において、右辺第２項のフリクショントルクＴｆの積分項と右辺第３項の負荷トルクＴｌｅの積分項との和は、どの気筒についても一定とみなすことができる。従って、各気筒１１毎のトルクばらつきに影響を及ぼすのは、式（２）の右辺第１項に示す、慣性質量Ｊに角加速度ｄω／ｄｔをかけた値の積分項である。以下では、ＥＣＵ２０は、慣性質量Ｊに角加速度ｄω／ｄｔをかけた値の積分項を、規格化された図示トルクとして算出することとする。ここで、慣性質量Ｊは各気筒１１毎の形状や質量等により予め規定された値であるので、ＥＣＵ２０は、クランク角センサ４１により検出されたクランク角に基づいて、角加速度ｄω／ｄｔを算出し、算出された角加速度ｄω／ｄｔに対し、予め規定された慣性質量Ｊをかけることにより、規格化された図示トルクを算出することができる。なお、以下では、規格化された図示トルクを「図示トルク」と称することとする。

Here, in equation (2), the sum of the integral term of the friction torque Tf in the second term on the right side and the integral term of the load torque Tle in the third term on the right side can be regarded as constant for any cylinder. Therefore, it is the integral term of the value obtained by multiplying the inertial mass J by the angular acceleration dω / dt, which is shown in the first term on the right side of the equation (2), which affects the torque variation for each cylinder 11. Hereinafter, the ECU 20 calculates an integral term of a value obtained by multiplying the inertial mass J by the angular acceleration dω / dt as a normalized indicated torque. Here, since the inertia mass J is a value defined in advance by the shape and mass of each cylinder 11, the ECU 20 calculates the angular acceleration dω / dt based on the crank angle detected by the crank angle sensor 41. Then, the normalized indicated torque can be calculated by multiplying the calculated angular acceleration dω / dt by a predetermined inertial mass J. Hereinafter, the standardized indicated torque is referred to as “indicated torque”.

  FIG. 3 is a graph showing changes of the indicated torque with respect to time in each of the cylinders 11a to 11d. In the graph of FIG. 3, the horizontal axis indicates time, and the vertical axis indicates the indicated torque. In FIG. 3, X indicates the calculated indicated torque, the alphabetic subscripts indicated by a to d indicate the cylinders 11a to 11d, respectively, and the numerical subscript indicates the number of cycles of the operation stroke. For example, Xa1 indicates the indicated torque of the cylinder 11a calculated in the first cycle, and Xa2 indicates the indicated torque of the cylinder 11a calculated in the second cycle.

  As described above, the ECU 20 can obtain the indicated torque by calculating the angular acceleration dω / dt. As a specific method for calculating the angular acceleration dω / dt, for example, the ECU 20 in each cylinder 11 is based on a detection signal from the crank angle sensor 41 and each angular velocity when the piston 12 is at TDC and BDC. The angular acceleration dω / dt is calculated by calculating ω (TDC) and ω (BDC) and dividing the difference ω (BDC) −ω (TDC) by the time during which the piston 12 moves from TDC to BDC. The ECU 20 calculates the indicated torque by multiplying the calculated angular acceleration dω / dt by the inertial mass J, and integrating the crank angle displacement when changing from TDC to BDC, for example, with the crank angle θ.

  Since the timing at which the piston 12 moves from TDC to BDC is different in each of the cylinders 11a to 11d, as shown in FIG. 3, for example, the cylinders 11a, 11b, and 11c with respect to the passage of time in one cycle. , 11d, the indicated torque X is calculated.

  Next, the ECU 20 calculates a statistical amount of the indicated torque X. For example, the ECU 20 calculates the relative standard deviation (coefficient of variation) CV for the indicated torque X obtained in each of a plurality of cycles using the following formula (3) for each cylinder 11. In the equation (3), the relative standard deviation CV is shown as a percentage by multiplying by 100.

式（３）において、Ｘの添え字ｉ（ｉ＝ａ〜ｄ）は気筒１１ａ〜１１ｄを示し、添え字１〜ｎはサイクルの回数を示している。

In Expression (3), the subscript i (i = a to d) of X indicates the cylinders 11a to 11d, and the subscripts 1 to n indicate the number of cycles.

  For example, when calculating the relative standard deviation CV of the indicated torque of the cylinder 11a, the ECU 20 determines the standard deviation STD for the indicated torques Xa1, Xa2,..., Xan of the cylinder 11a calculated in n cycles. (Xa1,..., Xan) and average value AVE (Xa1,..., Xan) are obtained, and the standard deviation STD is divided by the average value AVE to calculate the relative standard deviation CV of the indicated torque. For each of the other cylinders 11b to 11d, the relative standard deviation CV is calculated by performing the same calculation using Expression (3). That is, the ECU 20 calculates a standard deviation and an average value for the indicated torque calculated in n cycles for each cylinder 11b to 11d, and calculates the relative standard deviation CV of the indicated torque by dividing the standard deviation by the average value. To do. The relative standard deviation CV for each of the cylinders 11a to 11d calculated in this way indicates the variation in the indicated torque between cycles for each of the cylinders 11a to 11d.

  FIG. 4 is a graph showing the relative standard deviation of the indicated torque for each of the cylinders 11a to 11d. In FIG. 4, white circles indicate the relative standard deviation of the indicated torque for each cylinder calculated based on the crank angle. Specifically, CVa is a relative standard deviation of the indicated torque of the cylinder 11a, CVb is a relative standard deviation of the indicated torque of the cylinder 11b, CVc is a relative standard deviation of the indicated torque of the cylinder 11c, and CVd is a relative standard deviation of the indicated torque of the cylinder 11d. Standard deviation is shown respectively.

  In the example shown in FIG. 4, the relative standard deviation CVd of the indicated torque of the cylinder 11d is larger than the relative standard deviations CVa to CVc of the indicated torque of the other cylinders 11a to 11c. From this, it can be seen that the indicated torque of the cylinder 11d has a larger variation between cycles than the indicated torque of the other cylinders 11a to 11c. That is, it can be seen that the combustion state of the cylinder 11d is worse than the combustion states of the other cylinders 11a to 11c.

  Next, a method for calculating the torque variation for each cylinder based on the in-cylinder pressure will be described. As described above, in the present embodiment, the in-cylinder pressure sensor 31 is provided only in the head portion of the cylinder 11a located on the front side farthest from the transmission. Therefore, in the present embodiment, the ECU 20 calculates only the torque variation of the cylinder 11a based on the in-cylinder pressure.

  First, the ECU 20 detects the in-cylinder pressure in the cylinder 11a based on the detection signal from the in-cylinder pressure sensor 31, and calculates the indicated torque using the following equation (4).

式（４）では、筒内圧をＰ、燃焼室１５の容積である筒内容積をＶ、筒内容積Ｖの単位クランク角に対する変化量をｄＶ／ｄθとして示している。ＥＣＵ２０は、筒内圧Ｐと筒内容積Ｖの単位クランク角に対する変化量ｄＶ／ｄθとの積をクランク角θで積分することにより、筒内圧Ｐに基づいた図示トルクを算出する。

In the equation (4), the in-cylinder pressure is P, the in-cylinder volume that is the volume of the combustion chamber 15 is V, and the change amount of the in-cylinder volume V with respect to the unit crank angle is dV / dθ. The ECU 20 calculates the indicated torque based on the in-cylinder pressure P by integrating the product of the in-cylinder pressure P and the variation dV / dθ of the in-cylinder volume V with respect to the unit crank angle by the crank angle θ.

  Then, after calculating the indicated torque of the cylinder 11a based on the in-cylinder pressure for each of a plurality of cycles, the ECU 20 performs a statistical amount of the indicated torque of the cylinder 11a, such as relative A standard deviation CV is calculated. In FIG. 4, the relative standard deviation of the indicated torque of the cylinder 11a calculated based on the in-cylinder pressure is shown as CVSa (triangle mark).

  Next, a method for determining whether or not torsional vibration has occurred will be described.

  In FIG. 4, when the torsional vibration is not generated on the crankshaft 17, the relative standard deviation CVa of the indicated torque of the cylinder 11a calculated based on the crank angle and the cylinder 11a calculated based on the in-cylinder pressure. The relative standard deviation CVSa of the indicated torque is substantially the same. More specifically, in FIG. 4, the difference between the relative standard deviation CVa and the relative standard deviation CVSa is less than the predetermined value β, as indicated by CVSa indicated by a broken triangle. When the difference between the relative standard deviation CVa and the relative standard deviation CVSa is less than the predetermined value β, the ECU 20 determines that the crankshaft 17 is not twisted and vibration is not generated. Here, the predetermined value β is obtained in advance by experiments or the like, and is recorded in the ROM or the like of the ECU 20.

  When it is determined that the torsional vibration is not generated in the crankshaft 17, the ECU 20 performs feedback control for correcting the control parameter so as to suppress the variation in the relative standard deviation of the indicated torque between the cylinders 11a to 11d. In the example shown in FIG. 4, as feedback control, the ECU 20 determines that the difference between the relative standard deviation CVd of the indicated torque of the cylinder 11d and the relative standard deviations CVa to CVc of the indicated torque of the other cylinders 11a to 11c is a predetermined value α. In order to improve the combustion state of the cylinder 11d, the ignition timing of the cylinder 11d is controlled so as to be as follows. Here, the predetermined value α is obtained in advance by experiments or the like, and is recorded in the ROM or the like of the ECU 20.

  Needless to say, the control parameter to be corrected is not limited to the ignition timing. Alternatively or in addition, other control parameters such as the fuel injection amount and the intake air amount may be corrected. . Further, in the case of a direct injection engine in which the fuel injection valve is directly attached to the combustion chamber, the fuel injection timing may be corrected. Further, in a direct injection type engine, when a fuel injection valve is also attached to the intake passage, the fuel injection valve in the intake passage and the fuel injection valve directed into the combustion chamber are each It is also possible to correct the distribution ratio of the fuel injection amount.

  On the other hand, when the torsional vibration is generated in the crankshaft 17, the relative standard deviation CVa of the indicated torque of the cylinder 11a calculated based on the crank angle and the indicated torque of the cylinder 11a calculated based on the in-cylinder pressure. The relative standard deviation CVSa is not substantially the same. More specifically, in FIG. 4, the difference between the relative standard deviation CVa and the relative standard deviation CVSa is equal to or greater than a predetermined value β, as indicated by CVSa indicated by a solid triangle. In this case, since the torsional vibration is generated in the crankshaft, it is considered that the accuracy of the relative standard deviation of the indicated torque of each of the cylinders 11a to 11d calculated based on the crank angle is deteriorated. Accordingly, at this time, the relative standard deviation of the indicated torque for each cylinder 11 calculated based on the crankshaft is not appropriate information for performing feedback control.

  Therefore, for the cylinder 11a, the ECU 20 has a difference between the relative standard deviation CVa of the indicated torque calculated based on the crank angle and the relative standard deviation CVSa of the indicated torque calculated based on the in-cylinder pressure not less than a predetermined value β. If it is, it is determined that the torsional vibration is generated in the crankshaft 17, and in that case, the accuracy of the relative standard deviation of the indicated torque of the cylinders 11a to 11d calculated based on the crank angle is determined. As a result, the feedback control for suppressing the variation in the relative standard deviation of the indicated torque between the cylinders 11a to 11d is not performed. By doing in this way, it can prevent performing feedback control based on the relative standard deviation of the indicated torque with low accuracy.

  In the above-described embodiment, the in-cylinder pressure sensor is provided only in the cylinder 11a, but is not limited thereto. Instead of this, an in-cylinder pressure sensor may be provided in any of the other cylinders 11b to 11d. Preferably, an in-cylinder pressure sensor is provided in a cylinder at a position where the influence of the torsional vibration of the crankshaft 17 is greatest, such as the cylinder 11a. Therefore, for example, when a balancer is attached to the front end of the crankshaft 17, the influence of torsional vibration is greatest in the cylinder in the middle of the engine 10, for example, the cylinders 11b and 11c. In this case, it is preferable to provide the cylinder pressure sensors in the cylinders 11b and 11c. As described above, since the cylinder pressure sensor is provided in the cylinder at the position where the influence of the torsional vibration of the crankshaft 17 is the largest, it is possible to more reliably determine whether or not the torsional vibration is generated in the crankshaft. Can be done.

  In the above-described embodiment, the relative standard deviation of the indicated torque is calculated based on the in-cylinder pressure only for the cylinder 11a. However, the present invention is not limited to this. Instead, in-cylinder pressure sensors are provided in two or more cylinders 11, and the relative standard deviation of the indicated torque based on the in-cylinder pressure is provided for each of the two or more cylinders 11 provided with the in-cylinder pressure sensors. Of course, the difference between the relative standard deviation of the indicated torque based on the in-cylinder pressure and the relative standard deviation of the indicated torque based on the crank angle may be calculated. This also makes it possible to more reliably determine whether torsional vibration has occurred on the crankshaft.

  In the above-described embodiment, the relative standard deviation is calculated as the indicated torque statistic for each of the cylinders 11a to 11d. However, the present invention is not limited to this. Other statistics such as deviation (RMS) may be calculated.

  That is, in the control method for the internal combustion engine according to the present embodiment, for the in-cylinder pressure detection cylinder in which the in-cylinder pressure is detected, the statistical amount of torque variation calculated based on the crank angle and the torque calculated based on the in-cylinder pressure. It is determined whether or not the difference between the statistic of variation is a predetermined value or more, and if the difference is a predetermined value or more, it is determined that torsional vibration has occurred. In this way, it is possible to determine whether or not the accuracy of the statistical amount of torque variation calculated for each cylinder based on the crank angle has deteriorated.

[Control processing]
Next, the control process for the internal combustion engine will be described with reference to the flowchart of FIG. In the following internal combustion engine control process, the ECU 20 determines whether the difference between the cylinder combustion fluctuation calculated based on the crank angle and the cylinder combustion fluctuation calculated based on the in-cylinder pressure is equal to or greater than a predetermined value. By determining whether or not torsional vibration has occurred, it is determined whether or not to perform feedback control according to the determination result.

  In step S101, the ECU 20 calculates the combustion fluctuation for each cylinder from the crank angle. In the above example, the ECU 20 calculates the indicated torque in each of a plurality of cycles based on the crank angle detected by the crank angle sensor 41 for each of the cylinders 11a to 11d, and performs a plurality of cycles. The relative standard deviation CV of the indicated torque is calculated based on the indicated torque calculated in each of the above.

  In step S102, the ECU 20 calculates the combustion fluctuation for each cylinder based on the detection signal from the in-cylinder pressure sensor. In the above example, the ECU 20 calculates the indicated torque in each of a plurality of cycles based on the in-cylinder pressure detected by the in-cylinder pressure sensor 31 for the cylinder 11a, and calculates in each of the plurality of cycles. Based on the indicated torque, the relative standard deviation of the indicated torque for the cylinder 11a is calculated.

  In addition, the process of step S101 and S102 may be performed prior to the process of step S101, or both may be performed in parallel. When the ECU 20 finishes the processes of steps S101 and S102, it proceeds to the process of step S103.

  In step S103, the ECU 20 determines whether torsional vibration is generated in the crankshaft 17. In the above example, for the cylinder 11a, the ECU 20 calculates the difference between the relative standard deviation CVa of the indicated torque calculated based on the crank angle and the relative standard deviation CVSa of the indicated torque calculated based on the in-cylinder pressure. Is determined to be greater than or equal to a predetermined value β. If it is determined that the difference is equal to or greater than the predetermined value β, it is determined that torsional vibration is generated in the crankshaft 17, and If it is determined that the difference is less than the predetermined value β, it is determined that no torsional vibration has occurred in the crankshaft 17. Here, the predetermined value β is obtained in advance by an experiment or the like, and is recorded in the ROM or the like of the ECU 20.

  When it is determined that the torsional vibration is not generated in the crankshaft 17 (step S103: No), the ECU 20 proceeds to the process of step S104 and performs feedback control. In the above example, the ECU 20 performs feedback control so that the variation of the relative standard deviation of the indicated torque between the cylinders 11a to 11d is equal to or less than the predetermined value α. Here, the predetermined value α is obtained in advance by an experiment or the like and recorded in the ROM of the ECU 20 or the like. On the other hand, when the ECU 20 determines that the torsional vibration is generated in the crankshaft 17 (step S103: Yes), the relative standard deviation of the indicated torque of the cylinders 11a to 11d calculated based on the crank angle is determined. Assuming that the accuracy has deteriorated, the process proceeds to step S105, and execution of feedback control is prohibited. By doing in this way, it can prevent performing feedback control based on the relative standard deviation of the indicated torque with low accuracy. ECU20 complete | finishes this control process after the process of step S104 or S105.

  As can be seen from the above description, in the control method of the internal combustion engine according to the present embodiment, the combustion fluctuation of the internal combustion engine calculated based on the crank angle and the internal combustion engine calculated based on the in-cylinder pressure. It is determined whether or not the difference with the combustion fluctuation is equal to or greater than a predetermined value, and when it is determined that the difference is equal to or greater than the predetermined value, it is determined that torsional vibration has occurred. Thereby, it can be determined whether the accuracy of the combustion fluctuation calculated based on the crank angle is deteriorated.

It is a mimetic diagram of an internal-combustion engine concerning each embodiment. The cross-sectional structure inside a cylinder is shown. It is a graph which shows the change with respect to time of the indicated torque in each cylinder. It is a graph which shows the relative standard deviation in each cylinder. It is a flowchart which shows the control processing which concerns on this embodiment.

Explanation of symbols

10 Engine 11 Cylinder 12 Piston 17 Crankshaft 20 ECU
31 In-cylinder pressure sensor 41 Crank angle sensor

Claims (4)

Applied to an internal combustion engine comprising a plurality of cylinders, crank angle detection means for detecting crank angles of the plurality of cylinders, and cylinder pressure detection means for detecting the cylinder pressure of at least one of the plurality of cylinders. A control device for an internal combustion engine,
When the difference between the combustion fluctuation calculated based on the crank angle and the combustion fluctuation calculated based on the in-cylinder pressure is greater than or equal to a predetermined value with respect to the in-cylinder pressure detection cylinder that is the cylinder in which the in-cylinder pressure is detected. The control device for an internal combustion engine, further comprising: a determination unit that determines that torsional vibration is generated in a crankshaft to which torque is transmitted from the plurality of cylinders. Control means for performing feedback control for suppressing variation in combustion fluctuation among the plurality of cylinders based on combustion fluctuation for each of the plurality of cylinders calculated based on a crank angle;
The control device for an internal combustion engine according to claim 1, wherein the control means prohibits the feedback control when the determination means determines that torsional vibration is occurring.   The determination means has a difference between a statistical value of torque variation calculated based on the crank angle and a statistical value of torque variation calculated based on the in-cylinder pressure for the in-cylinder pressure detection cylinder equal to or greater than a predetermined value. The control apparatus for an internal combustion engine according to claim 1 or 2, wherein if it is determined that the torsional vibration has occurred, the torsional vibration is determined to have occurred.   The control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the in-cylinder pressure detecting means detects an in-cylinder pressure of a cylinder at which the influence of the torsional vibration is maximized.

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