Multi-cylinder engine unit

Abstract

To improve detection accuracy in a multi-cylinder engine unit for detecting inter-cylinder imbalance in an air-to-fuel ratio using fluctuation of rotating speed of a crank shaft.SOLUTION: In a multi-cylinder engine unit 1, a control device 14 detects inter-cylinder imbalance in an air-to-fuel ratio in the plurality of cylinders 11A and 11B using fluctuation of rotating speed of a crank shaft 12 appearing at any one of combustion intervals (A)-(C). (A) a combustion interval of 360-720 degrees in a crank angle. (B) a combustion interval of 240-720 degrees in the crank angle. (C) a combustion interval of 240 degrees or more in the crank angle, and a combustion interval of 240-720 degrees in the crank angle in a cross plane type crank shaft configured so that inertia torque is reduced.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a multi-cylinder engine unit, and more particularly to a multi-cylinder engine unit that detects imbalance in air-fuel ratios among a plurality of cylinders by using fluctuations in the rotation speed of a crankshaft. [Background technology]

[0002] An apparatus for detecting an imbalance in the air-fuel ratio between multiple cylinders using the fluctuation in the rotation speed of the crankshaft is disclosed, for example, in Patent Document 1. This apparatus detects the degree of unevenness in the fluctuation in the rotation speed of the crankshaft using, for example, the amount of change per unit time in the rotation speed of the crankshaft, and detects the imbalance in the air-fuel ratio between the cylinders. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5256233 specification Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to improve the detection accuracy in a multi-cylinder engine unit that detects imbalance in air-fuel ratio between cylinders using fluctuations in the rotation speed of a crankshaft. [Means for solving the problem]

[0005] (1) A multi-cylinder engine unit according to an embodiment of the present invention includes a plurality of cylinders each forming a combustion chamber together with a piston, a crankshaft that rotates as fuel is burned in the combustion chamber, a generator that generates electric power as the crankshaft rotates, and a control device that detects an imbalance in the air-fuel ratio between the plurality of cylinders using a fluctuation in the rotation speed of the crankshaft. The generator includes a rotor having a permanent magnet, fixed to the crankshaft so as to be coaxial with the crankshaft, and rotating at a fixed gear ratio relative to the crankshaft, and a stator having a coil that generates an electromotive force as the rotor rotates. The control device detects an imbalance in the air-fuel ratio between the plurality of cylinders using the fluctuation in the rotation speed of the crankshaft during a combustion interval in which a fluctuation in the rotation speed of the crankshaft due to combustion appears, and satisfies any one of the following (A) to (C). (A) Detecting inter-cylinder imbalance in air-fuel ratio among multiple cylinders using fluctuations in rotation speed that occur in a combustion interval that is equal to or greater than 360 degrees in crank angle and equal to or less than 720 degrees in crank angle in a crankshaft that is configured so that at least one combustion interval in the rotation cycle of the crankshaft is equal to or greater than 360 degrees in crank angle. (B) Detecting inter-cylinder imbalances in air-fuel ratios among multiple cylinders using fluctuations in rotation speed that occur in combustion intervals of 240 degrees or more and 720 degrees or less in crank angle in a crankshaft configured so that all combustion intervals in the crankshaft rotation cycle are 240 degrees or more in crank angle. (C) At least one combustion interval in the rotation cycle of the crankshaft is equal to or greater than 240 degrees in crank angle, and an imbalance in the air-fuel ratio between multiple cylinders is detected using fluctuations in rotation speed that occur in a combustion interval that is equal to or greater than 240 degrees in crank angle and is equal to or less than 720 degrees in crank angle in a cross-plane type crankshaft that is configured to reduce inertia torque.

[0006] In general, in a multi-cylinder engine unit, fuel is burned in a predetermined sequence in the cylinders. The rotation speed of the crankshaft reaches a maximum immediately after a combustion occurs and then decreases until the next combustion occurs. In this way, the rotation speed of the crankshaft repeatedly increases and decreases, fluctuating in a manner that alternates between peaks and valleys. In the above multi-cylinder engine unit, when the control device satisfies the above (A), the crankshaft rotates 360 degrees or more between one combustion and the next combustion. A multi-cylinder engine unit including such a crankshaft is, for example, a two-cylinder engine unit. In this case, the multi-cylinder engine unit has two cylinders. The two-cylinder engine unit is, for example, an equal interval combustion type or an unequal interval combustion type two-cylinder engine unit. The equal interval combustion type two-cylinder engine unit has, for example, a combustion interval of 360 degrees by 360 degrees in crank angle. The unequal interval combustion type two-cylinder engine unit has, for example, a combustion interval of 270 degrees by 450 degrees in crank angle. The unequal interval combustion type two-cylinder engine unit may have a combustion interval of 180 degrees by 540 degrees in crank angle. The control device detects an imbalance of the air-fuel ratio between the cylinders using the fluctuation of the rotation speed during the period when the combustion interval is 360 degrees or more. A combustion interval of 360 degrees or more is a long period that occupies more than half of the rotation cycle (720 degrees) of the crankshaft in a four-stroke engine, for example. Therefore, it is easy to clearly grasp the peaks and valleys of the fluctuations in the rotation speed of the crankshaft. Therefore, it is possible to improve the detection accuracy in a multi-cylinder engine unit that detects an imbalance in the air-fuel ratio between cylinders using the fluctuations in the rotation speed of the crankshaft. When the control device satisfies the above (B), the crankshaft rotates 240 degrees or more between one combustion and the next combustion. A multi-cylinder engine unit including such a crankshaft is, for example, a three-cylinder engine unit. In this case, the multi-cylinder engine unit has three cylinders. The three-cylinder engine unit is, for example, a three-cylinder engine unit with equal interval combustion. The three-cylinder engine unit with equal interval combustion has, for example, a combustion interval of 240 degrees, 240 degrees, and 240 degrees in crank angles. The control device detects the imbalance of the air-fuel ratio between the cylinders using the fluctuation in the rotation speed during the period when the combustion interval is 240 degrees or more. A combustion interval of 240 degrees or more is a long period that occupies more than 1 / 3 of the rotation cycle of the crankshaft in a four-stroke engine, for example. Therefore, it is easy to clearly grasp the peaks and valleys of the fluctuation in the rotation speed of the crankshaft. Therefore, the detection accuracy can be improved in a multi-cylinder engine unit that detects the imbalance of the air-fuel ratio between the cylinders using the fluctuation in the rotation speed of the crankshaft. When the control device satisfies the above (C), the crankshaft is a crossplane type. A multi-cylinder engine unit including such a crankshaft is, for example, a four-cylinder engine unit. In this case, the multi-cylinder engine unit has four cylinders. The four-cylinder engine unit is, for example, a four-cylinder engine unit with an uneven combustion interval. The four-cylinder engine unit with an uneven combustion interval has, for example, a combustion interval of 270 degrees, 180 degrees, 90 degrees, and 180 degrees in crank angle. Here, the fluctuation in the rotation speed of the crankshaft mainly depends on the combustion fluctuation and the torque (also called inertia torque) generated by the piston, connecting rod, and crankshaft moving by the combustion continuing to move. A crossplane type crankshaft has four crankpins arranged at 90 degrees offset from each other when viewed in the axial direction of the crankshaft, and has a shape like a symbol +. In a crossplane type crankshaft with such a configuration, the four pistons connected to each crankpin, which are arranged at 180 degrees offset from each other, move in opposite directions to each other. As a result, the inertial torques generated on the crankshaft by each piston act to cancel each other out. In the cross-plane crankshaft, the inertial torques generated on the crankshaft by each piston are reduced, so that the fluctuation in the rotation speed of the crankshaft can be grasped to practically grasp the fluctuation in the rotation speed due to combustion. In addition, the cross-plane crankshaft rotates 240 degrees or more from one combustion to the next. The control device detects the imbalance of the air-fuel ratio between cylinders using the fluctuation in the rotation speed during the period when the combustion interval is 240 degrees or more. In this way, the control device detects the imbalance of the air-fuel ratio between cylinders during the period when the combustion interval is 240 degrees or more, during which the peaks and valleys of the fluctuation in the rotation speed of the crankshaft are easily grasped clearly, while grasping the fluctuation in the rotation speed due to combustion more accurately. Therefore, the detection accuracy can be improved in a multi-cylinder engine unit that detects the imbalance of the air-fuel ratio between cylinders using the fluctuation in the rotation speed of the crankshaft.

[0007] (2) In the multi-cylinder engine unit of (1) above, the control device may include a rotation speed acquisition unit configured to acquire the rotation speed of the crankshaft, a swell detection unit configured to detect periodic swells included in the fluctuation of the rotation speed of the crankshaft based on the rotation speed acquired by the rotation speed acquisition unit, and a swell removal unit configured to remove the periodic swells detected by the swell detection unit from the rotation speed of the crankshaft. In this case, the swells have an angle period longer than 720 degrees in crank angle. The control device detects an imbalance of the air-fuel ratio between the multiple cylinders using the fluctuation of the rotation speed of the crankshaft calculated from the rotation speed of the crankshaft from which the periodic swells have been removed by the swell removal unit.

[0008] The rotation speed of the crankshaft also varies due to factors other than the combustion in each cylinder. For example, the rotation speed of the crankshaft varies due to external factors such as the load received when the vehicle runs on a slope or a rough road, the structure of the vehicle, etc. In order to improve the detection accuracy of the imbalance of the air-fuel ratio between cylinders, it is desirable to reduce the influence of these external factors and make it easier to grasp the fluctuation of the rotation speed of the crankshaft caused by the combustion. In the engine unit of (2) above, the control device detects the imbalance of the air-fuel ratio between cylinders in the multiple cylinders by using the fluctuation of the rotation speed of the crankshaft from which the swell having an angle period longer than 720 degrees in crank angle has been removed. Therefore, the fluctuation of the rotation speed of the crankshaft caused by the combustion becomes easier to grasp, and the detection accuracy can be improved in the multi-cylinder engine unit that detects the imbalance of the air-fuel ratio between cylinders by using the fluctuation of the rotation speed of the crankshaft.

[0009] (3) In the multi-cylinder engine unit according to (1) or (2) above, When the control device satisfies (A), the multiple cylinders may include a reference cylinder that performs combustion that produces a maximum rotation speed of the crankshaft in a combustion interval of 360 degrees or more and 720 degrees or less, and a target cylinder that is different from the reference cylinder. In this case, the control device detects an imbalance in the air-fuel ratio between the multiple cylinders using a fluctuation in the rotation speed of the crankshaft obtained based on the maximum rotation speed of the crankshaft produced by combustion in the reference cylinder and the maximum rotation speed of the crankshaft produced by combustion in the target cylinder. When the control device satisfies (B), the multiple cylinders may include an arbitrarily selected reference cylinder that performs combustion that produces a maximum rotation speed of the crankshaft in a combustion interval equal to or greater than 240 degrees and equal to or less than 720 degrees, and an arbitrarily selected target cylinder that is different from the reference cylinder. In this case, the control device detects an imbalance in the air-fuel ratio between the multiple cylinders using a fluctuation in the rotation speed of the crankshaft obtained based on the maximum rotation speed of the crankshaft produced by combustion in the reference cylinder and the maximum rotation speed of the crankshaft produced by combustion in the target cylinder. When the control device satisfies (C), the multiple cylinders may include a reference cylinder that performs combustion that produces a maximum rotation speed of the crankshaft in a combustion interval of 240 degrees or more and 720 degrees or less, and a target cylinder that is different from the reference cylinder and is arbitrarily selected. In this case, the control device detects an imbalance in the air-fuel ratio between the multiple cylinders using a fluctuation in the rotation speed of the crankshaft obtained based on the maximum rotation speed of the crankshaft produced by combustion in the reference cylinder and the maximum rotation speed of the crankshaft produced by combustion in the target cylinder.

[0010] In general, to detect an imbalance in the air-fuel ratio between cylinders using the fluctuation in the rotation speed of the crankshaft, the fluctuation in the rotation speed between rotation cycles of the crankshaft is compared. For example, in the case of a four-stroke engine, the imbalance in the air-fuel ratio between cylinders is detected by comparing the average rotation speed of the crankshaft in one rotation cycle (720 degrees) of the crankshaft with the average rotation speed of the crankshaft in the next rotation cycle of the crankshaft. This method is effective for detecting the imbalance in the air-fuel ratio between cylinders in an engine unit in which the fluctuation in the rotation speed between rotation cycles of the crankshaft is not so large under normal conditions. However, in an engine unit in which the fluctuation in the rotation speed between rotation cycles of the crankshaft is large under normal conditions, it is difficult to determine whether the fluctuation in the rotation speed between rotation cycles of the crankshaft is due to the imbalance in the air-fuel ratio between cylinders. Such an engine unit is mounted on an inclined vehicle such as a motorcycle. In contrast, in the engine unit of (3) above, when the control device satisfies (A), for example, the inter-cylinder imbalance of the air-fuel ratio in the multiple cylinders is detected using the maximum rotation speed of the crankshaft caused by combustion in the first cylinder and the maximum rotation speed of the crankshaft caused by combustion in the second cylinder of an even-interval combustion or uneven-interval combustion two-cylinder engine unit. When the control device satisfies (B), for example, the inter-cylinder imbalance of the air-fuel ratio in the multiple cylinders is detected using the maximum rotation speed of the crankshaft caused by combustion in the first cylinder of an even-interval combustion three-cylinder engine unit and the maximum rotation speed of the crankshaft caused by combustion in at least one of the second and third cylinders. When the control device satisfies (C), for example, the inter-cylinder imbalance of the air-fuel ratio in the multiple cylinders is detected using the maximum rotation speed of the crankshaft caused by combustion in the first cylinder of an uneven-interval combustion four-cylinder engine unit and the maximum rotation speed of the crankshaft caused by combustion in at least one of the second to fourth cylinders.Therefore, the fluctuation in the rotation speed of the crankshaft within the same rotation cycle can be used, and it is easy to detect an imbalance in the air-fuel ratio between cylinders even in an engine unit in which the fluctuation in the rotation speed of the crankshaft between rotation cycles is large. Therefore, it is possible to improve the detection accuracy in a multi-cylinder engine unit in which an imbalance in the air-fuel ratio between cylinders is detected using the fluctuation in the rotation speed of the crankshaft.

[0011] The "multi-cylinder engine unit" may include, for example, an intake and exhaust system. The multi-cylinder engine unit includes, for example, an engine that generates power for driving a vehicle in which the multi-cylinder engine unit is mounted. The engine is an internal combustion engine. The engine is not an electric motor. The engine is, for example, a reciprocating engine. The engine is, for example, a four-stroke engine. The engine is, for example, a gasoline engine in which fuel is burned by a spark plug. The engine may be a diesel engine in which fuel is burned by compressed air. The engine is, for example, an in-line, V-type, or horizontally opposed type multi-cylinder engine. The engine includes, for example, a plurality of cylinders, pistons, and a crankshaft. The multi-cylinder engine unit may be a hybrid engine unit including an engine and an electric motor. The hybrid engine unit may be, for example, a parallel type hybrid engine unit or a series type hybrid engine unit.

[0012] The multi-cylinder engine unit is, for example, a non-uniform combustion type multi-cylinder engine unit. The non-uniform combustion type multi-cylinder engine unit means an engine unit configured so that all the combustion intervals expressed in crank angles are not equal in the rotation cycle of the crankshaft. The combustion interval expressed in crank angle means the rotation angle of the crankshaft from the combustion in one cylinder to the combustion in another cylinder that will be burned next, when the combustion in one cylinder is taken as the reference (crank angle is 0 degrees). For example, consider a four-stroke two-cylinder engine unit with non-uniform combustion intervals. In this engine unit, when the combustion in the first cylinder is taken as the reference, the combustion in the second cylinder occurs when the crankshaft has rotated 270 degrees since the combustion in the first cylinder. The combustion in the first cylinder occurs again when the crankshaft has rotated 450 degrees since the combustion in the second cylinder. In this case, the non-uniform combustion type two-cylinder engine unit has a combustion interval of 270 degrees and 450 degrees in crank angle. The two-cylinder engine unit of the variable combustion interval type may have a combustion interval of 180° to 540° in crank angle. The multi-cylinder engine unit is, for example, a two- or four-cylinder engine unit of the variable combustion interval type. The four-cylinder engine unit of the variable combustion interval type has a combustion interval of, for example, 270° to 180° to 90° to 180° in crank angle. The multi-cylinder engine unit does not include, for example, a three-cylinder engine unit of the variable combustion interval type. The multi-cylinder engine unit does not include, for example, an engine unit of five or more cylinders of the variable combustion interval type.

[0013] The multi-cylinder engine unit is, for example, an equal-interval combustion type multi-cylinder engine unit. The equal-interval combustion type multi-cylinder engine unit means an engine unit configured such that all combustion intervals expressed in crank angles are equal in the rotation cycle of the crankshaft. The multi-cylinder engine unit is, for example, an equal-interval combustion type two- or three-cylinder engine unit. The multi-cylinder engine unit does not include, for example, an equal-interval combustion type four- or more-cylinder engine unit.

[0014] The multi-cylinder engine unit includes, for example, a crank angle sensor that detects the rotation angle of the crankshaft. The crank angle sensor sends a signal to the control device when it detects the passage of a detection target provided on the crankshaft. The method of detecting the rotation angle of the crankshaft is not particularly limited, and other well-known methods may be used.

[0015] A multi-cylinder engine unit includes, for example, a plurality of intake passages through which air passes to be supplied to each of the plurality of cylinders. A multi-cylinder engine unit includes, for example, the same number of intake passages as the number of cylinders. The plurality of intake passages are, for example, independent of each other. Each of the plurality of intake passages is connected to a corresponding cylinder. However, the plurality of intake passages may be integrated together at an intake port that takes in outside air.

[0016] The multi-cylinder engine unit is, for example, an independent throttle type engine unit. The multi-cylinder engine unit includes, for example, a throttle valve provided in each of a plurality of intake passages. The plurality of throttle valves, for example, adjust the amount of air flowing into the corresponding cylinders. The plurality of throttle valves are, for example, controlled simultaneously. The plurality of throttle valves may also be controlled individually. The opening degrees of the plurality of throttle valves are, for example, controlled to be the same at a nominal value. The opening degrees of the plurality of throttle valves may also be controlled to be different at a nominal value.

[0017] The multi-cylinder engine unit includes, for example, an injector provided in each of a plurality of intake passages to inject fuel. Each of the plurality of injectors is provided, for example, downstream of a throttle valve in the flow direction of the intake air. Each of the plurality of injectors is, for example, electronically controlled. Each of the plurality of injectors injects fuel into the intake passage. Each of the plurality of injectors does not, for example, directly inject fuel into a cylinder.

[0018] The multi-cylinder engine unit is mounted on, for example, a tilting vehicle. The tilting vehicle is a transportation device. The tilting vehicle is a vehicle driven by a person. The tilting vehicle includes, for example, a vehicle body that tilts to the left when the tilting vehicle turns to the left and tilts to the right when the tilting vehicle turns to the right. The tilting vehicle is, for example, a motorcycle. The tilting vehicle is not limited to a motorcycle, and may be, for example, a three-wheeled motor vehicle or a four-wheeled motor vehicle. The tilting vehicle includes, for example, at least one front wheel and at least one rear wheel. The tilting vehicle is not particularly limited, and examples thereof include a scooter type, a moped type, an off-road type, and an on-road type tilting vehicle.

[0019] The multi-cylinder engine unit is mounted, for example, on a saddle-type vehicle. A saddle-type vehicle is a type of inclined vehicle. A saddle-type vehicle is a type of vehicle in which a driver sits astride a saddle. In a saddle-type vehicle, the left foot of the seated driver is positioned to the left of the center in the left-right direction of the saddle-type vehicle, and the right foot is positioned to the right of the center in the left-right direction of the saddle-type vehicle. The above-mentioned motorcycle and three-wheeled motor vehicle are each an example of a saddle-type vehicle. Further, an example of a saddle-type vehicle is an ATV (All-Terrain Vehicle). An ATV is an example of a saddle-type four-wheeled motor vehicle. Further, a saddle-type vehicle may not have wheels, for example. An example of such a saddle-type vehicle is a snowmobile. A snowmobile has, for example, a track belt instead of wheels.

[0020] Each of the "plurality of cylinders" has, for example, a cylindrical internal space. Each of the plurality of cylinders accommodates a piston in the internal space. The internal spaces of the plurality of cylinders, together with the piston, form a combustion chamber in which a mixture of fuel and air is combusted. The piston reciprocates as the mixture is combusted in each combustion chamber.

[0021] The "crankshaft" includes, for example, a journal, a crank pin that is eccentric with respect to the journal, and a crank arm that connects the journal and the crank pin. The crankshaft is connected to a piston, for example, via a connecting rod. The connecting rod connects the piston and the crank pin. The crankshaft converts, for example, the reciprocating motion of the piston into rotational motion.

[0022] The "generator" generates electricity by utilizing the rotation of the crankshaft, for example. The generator is electrically connected to, for example, an electric storage device. The generator sends the generated electric power to, for example, the electric storage device. The generator includes, for example, a rotor and a stator. The rotor is provided, for example, at an end of the crankshaft. The rotor is fixed, for example, to the crankshaft. The rotor rotates, for example, at the same rotation speed as the crankshaft. The rotor includes, for example, a disk portion extending in the radial direction of the crankshaft, and a cylindrical portion provided on the outer periphery of the disk portion. For example, a plurality of permanent magnets are fixed to the inner circumferential wall of the cylindrical portion in a line in the circumferential direction. The number of permanent magnets is not particularly limited, and may be one or more. The stator is, for example, disposed inside the rotor. The stator includes, for example, a stator core having a cylindrical shape, and a plurality of coils. The stator core includes, for example, a plurality of teeth arranged in the circumferential direction. Each of the plurality of teeth extends, for example, toward the radial direction of the stator core. The multiple coils are provided, for example, on the teeth of the stator core. The multiple coils are provided, for example, so that there is a gap between the multiple permanent magnets of the rotor. The multiple coils are, for example, conductive. The multiple coils are provided, for example, so that they can react with the magnetic fields of the multiple permanent magnets. The multiple coils are provided, for example, so that an induced electromotive force is generated by a change in the magnetic field caused by the rotation of the rotor. The number of coils is not particularly limited, and may be one or more.

[0023] The generator may be, for example, a starter generator that functions as a starter motor in addition to the power generation function. The starter generator functions as a starter motor when the crankshaft is not rotating and functions as a generator when the crankshaft is rotating.

[0024] The "control device" is, for example, an ECU (Electronic Control Unit). The control device includes, for example, a processor such as a CPU (Central Processing Unit) or a DSP (Digital Signal Processor). The control device may include, for example, a non-volatile memory in which one or more programs including part or all of the arithmetic processing executed by the control device are recorded. The control device realizes detection of at least inter-cylinder imbalance in air-fuel ratio, for example, by a processor reading and executing one or more programs recorded in the non-volatile memory.

[0025] The control device uses, for example, an oxygen sensor or an air-fuel ratio sensor to feedback control the amount of fuel supplied to each cylinder so that the air-fuel ratio of the multiple cylinders as a whole falls within a predetermined range from the target air-fuel ratio. The control device, for example, uses the detection result of the oxygen sensor or the air-fuel ratio sensor to reduce the amount of fuel supplied to the multiple cylinders when it determines that the air-fuel ratio is rich, and increases the amount of fuel supplied to the multiple cylinders when it determines that the air-fuel ratio is lean. In this way, the control device maintains the air-fuel ratio of the multiple cylinders as a whole at a value close to the target air-fuel ratio. Note that a state in which fuel is excessive with respect to the target air-fuel ratio is called an air-fuel ratio being rich. A state in which air is excessive with respect to the target air-fuel ratio is called an air-fuel ratio being lean. The target air-fuel ratio may be a value or range that includes the stoichiometric air-fuel ratio, or may be a value or range that is slightly deviated from the stoichiometric air-fuel ratio. However, it is assumed that the air-fuel ratio in a certain cylinder has deviated significantly from the target air-fuel ratio beyond the allowable range due to some factor. In this case, the air-fuel ratio varies greatly among the multiple cylinders, and the components in the exhaust gas differ from those expected, which also affects the purification function of the catalyst. Therefore, in such a case, it is desirable to notify the driver of the vehicle equipped with the multi-cylinder engine unit that the air-fuel ratio is significantly different from the target air-fuel ratio.

[0026] Therefore, the control device detects the inter-cylinder imbalance of the air-fuel ratio in the multiple cylinders, for example, by using the fluctuation in the rotation speed of the crankshaft that occurs at the widest combustion interval in the crank angle. Specifically, in a two-cylinder engine unit with uneven combustion intervals, the widest combustion interval is, for example, a combustion interval of 450 degrees or 540 degrees. This combustion interval of 450 degrees or 540 degrees is the interval from the second combustion in one rotation cycle of the crankshaft to the first combustion in the next rotation cycle. In a four-cylinder engine unit with uneven combustion intervals, the widest combustion interval is, for example, a combustion interval of 270 degrees. This combustion interval of 270 degrees is the interval from the first combustion to the second combustion in the rotation cycle of the crankshaft.

[0027] The control device detects the inter-cylinder imbalance of the air-fuel ratio in the multiple cylinders, for example, by using a fluctuation in the maximum rotation speed of the crankshaft occurring in the widest combustion interval in the crank angle. More specifically, the control device sets, as a reference, for example, the maximum rotation speed of the crankshaft occurring in the widest combustion interval in a rotation cycle of the crankshaft when no inter-cylinder imbalance of the air-fuel ratio occurs. The control device detects the inter-cylinder imbalance of the air-fuel ratio in the multiple cylinders, for example, by using the reference maximum rotation speed and the maximum rotation speed of the crankshaft occurring in the widest combustion interval in a rotation cycle of the crankshaft. The control device detects the inter-cylinder imbalance of the air-fuel ratio in the multiple cylinders, for example, by determining whether or not a difference between the reference maximum rotation speed and the maximum rotation speed of the crankshaft occurring in the widest combustion interval in a rotation cycle of the crankshaft is greater than a threshold value.

[0028] The control device detects an abnormality in the air-fuel ratio in at least one of the multiple cylinders, which is referred to as detecting an inter-cylinder imbalance of the air-fuel ratio. The abnormality referred to here means that the amount of fuel correction by feedback control exceeds a predetermined threshold value. The threshold value may be a constant value at all times, or may be a variable value that is changed according to the situation. For example, when the control device detects an inter-cylinder imbalance of the air-fuel ratio in at least one cylinder, the control device executes a process for notifying a driver or the like to inspect the multi-cylinder engine unit. However, the control device only needs to detect an inter-cylinder imbalance of the air-fuel ratio in the multiple cylinders using a fluctuation in the rotation speed of the crankshaft that appears at least in the widest combustion interval in the crank angle, and the method of detecting an inter-cylinder imbalance of the air-fuel ratio in the multiple cylinders is not limited to the above example.

[0029] The control device may detect the imbalance of the air-fuel ratio between the cylinders by using, for example, a part or all of the maximum rotation speed of the crankshaft that appears in each of a plurality of combustion intervals in the same rotation cycle of the crankshaft. For example, the control device detects the imbalance of the air-fuel ratio between the cylinders by using a fluctuation in the difference between the reference cylinder maximum rotation speed and the target cylinder maximum rotation speed between the rotation cycles of the crankshaft. The reference cylinder maximum rotation speed is the maximum rotation speed of the crankshaft caused by combustion in the reference cylinder. The reference cylinder is, for example, a cylinder that performs combustion that generates the maximum rotation speed of the crankshaft in the widest combustion interval. The target cylinder maximum rotation speed is the maximum rotation speed of the crankshaft caused by combustion in the target cylinder. The target cylinder is, for example, a cylinder that is different from the reference cylinder and is arbitrarily selected. The control device detects the imbalance of the air-fuel ratio between the cylinders by using, for example, whether the fluctuation in the difference between the reference cylinder maximum rotation speed and the target cylinder maximum rotation speed is greater than a threshold value.

[0030] The above and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the embodiments of the present invention taken in conjunction with the accompanying drawings. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. As used herein, the use of the terms "including," "comprising," or "having" and variations thereof identifies the presence of the described features, steps, operations, elements, ingredients, and / or equivalents thereof, but may include one or more of the steps, operations, elements, components, and / or groups thereof. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. Terms, such as terms defined in commonly used dictionaries, should be interpreted to have a meaning consistent with the meaning in the context of the relevant art and this disclosure, and should not be interpreted in an idealized or overly formal sense unless expressly defined herein. In the description of the present invention, it is understood that a number of techniques and steps are disclosed. Each of these has separate benefits, and each can also be used with one or more, or in some cases all, of the other disclosed techniques. Thus, for the sake of clarity, this description will refrain from unnecessarily repeating all possible combinations of the individual steps. Nevertheless, the specification and claims should be read with the understanding that all such combinations are within the scope of the present invention and claims. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the invention can be practiced without these specific details. The present disclosure is to be considered as an example of the invention, and is not intended to limit the invention to the specific embodiments illustrated in the following drawings or description. Effect of the Invention

[0031] According to the present invention, it is possible to improve the detection accuracy in a multi-cylinder engine unit that detects imbalance in air-fuel ratio between cylinders using fluctuations in the rotation speed of the crankshaft. [Brief description of the drawings]

[0032] [Figure 1] FIG. 1(A) is a schematic diagram of a multi-cylinder engine unit of this embodiment, FIG. 1(B) is a schematic diagram of a generator included in the multi-cylinder engine unit of this embodiment, and FIG. 1(C) is a diagram showing the relationship between combustion timing and crankshaft rotation speed in the multi-cylinder engine unit of this embodiment. [Diagram 2] FIG. 2 is a diagram showing changes in fluctuations in the rotation speed of the crankshaft when an imbalance in air-fuel ratio occurs among the cylinders in the multi-cylinder engine unit of this embodiment. [Diagram 3] FIG. 3 is a flowchart showing the process of detecting an imbalance in air-fuel ratio among cylinders according to this embodiment. [Figure 4] FIG. 4 is a block diagram showing the configuration of a control device in a multi-cylinder engine unit according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Hereinafter, a multi-cylinder engine unit according to an embodiment of the present invention will be described with reference to the drawings. Note that the embodiment described below is merely an example. The present invention should not be construed as being limited in any way by the embodiment described below.

[0034] 1A is a schematic diagram of a multi-cylinder engine unit according to the present embodiment. The multi-cylinder engine unit 1 is a two-cylinder engine unit of an independent throttle type and an uneven combustion interval type. The multi-cylinder engine unit 1 includes a plurality of cylinders 11A and 11B, a crankshaft 12, a generator 13, and a control device 14.

[0035] Each of the cylinders 11A, 11B forms a combustion chamber 112 together with a piston 111. The cylinders 11A, 11B are arranged in series. Each of the cylinders 11A, 11B has a cylindrical internal space that forms a part of the combustion chamber 112. The combustion chamber 112 is formed in each of the cylinders 11A, 11B. Each of the combustion chambers 112 is connected to an intake pipe and an exhaust pipe. In each combustion chamber 112, a mixture of fuel and air flowing in from the intake pipe is burned. The combustion of the mixture generates exhaust gas. The generated exhaust gas flows out from the exhaust pipe. Each of the pistons 111 has a cylindrical shape. Each of the pistons 111 is arranged in the internal space of the corresponding cylinder 11A, 11B and reciprocates. Each of the pistons 111 is connected to the crankshaft 12 via a connecting rod.

[0036] The crankshaft 12 rotates as fuel is burned in the combustion chamber 112. The crankshaft 12 converts the reciprocating motion of the piston 111 into rotational motion. In this embodiment, the multi-cylinder engine unit 1 is a two-cylinder engine unit, so the crankshaft 12 includes two crankpins. The two crankpins are positioned 270 degrees apart when viewed in the axial direction of the crankshaft.

[0037] The generator 13 is provided at an end of the crankshaft 12. The generator 13 generates electric power as the crankshaft 12 rotates. The generator 13 includes a rotor 131 and a stator 132.

[0038] FIG. 1B is a schematic diagram of a generator included in the multi-cylinder engine unit of this embodiment. The rotor 131 has a roughly cylindrical shape. The rotor 131 has a plurality of permanent magnets 1311 arranged at equal intervals in the circumferential direction. The rotor 131 is fixed to the crankshaft 12 so as to be coaxial with the crankshaft 12. The rotor 131 rotates at a fixed gear ratio with respect to the crankshaft 12. In this embodiment, the rotor 131 rotates at the same rotation speed as the crankshaft 12. The stator 132 is disposed inside the rotor 131. The stator 132 has a roughly cylindrical shape. The stator 132 has a plurality of coils 1321 arranged at equal intervals in the circumferential direction. The plurality of coils 1321 are provided with a small gap between them and the plurality of permanent magnets 1311 in the radial direction of the rotor 131. An electromotive force is generated in the plurality of coils 1321 when the rotor 131 rotates.

[0039] FIG. 1(C) is a diagram showing the relationship between the combustion timing and the rotation speed of the crankshaft in the multi-cylinder engine unit of this embodiment. In the diagram, the vertical axis indicates the rotation speed of the crankshaft, and the horizontal axis indicates the crank angle. The control device 14 detects the inter-cylinder imbalance of the air-fuel ratio in the multiple cylinders 11A, 11B by using the fluctuation in the rotation speed of the crankshaft 12. In this embodiment, the crankshaft 12 is configured so that one combustion interval T1 in the rotation cycle of the crankshaft 12 is 360 degrees or more in crank angle. The control device 14 detects the inter-cylinder imbalance of the air-fuel ratio in the multiple cylinders 11A, 11B by using the fluctuation in the rotation speed that occurs in the combustion interval T1 that is 360 degrees or more and 720 degrees or less in crank angle.

[0040] <Detection of air-fuel ratio imbalance between cylinders> FIG. 2 is a diagram showing the change in the fluctuation of the rotation speed of the crankshaft when an imbalance of the air-fuel ratio between cylinders occurs in the multi-cylinder engine unit of this embodiment. In the figure, the vertical axis indicates the rotation speed of the crankshaft, and the horizontal axis indicates the crank angle. In this embodiment, the cylinder 11A is defined as the target cylinder, and the cylinder 11B is defined as the reference cylinder. In the target cylinder 11A and the reference cylinder 11B, fuel is burned when the piston 111 reaches the top dead center. The crank angle is defined as zero degrees when the fuel is burned in the target cylinder 11A. However, the timing when the fuel is burned in the target cylinder 11A and the reference cylinder 11B is not limited to when the piston 111 reaches the top dead center, and may be before or after the piston 111 reaches the top dead center. In the figure, the solid line indicates the fluctuation of the rotation speed of the crankshaft when no imbalance of the air-fuel ratio between cylinders occurs in the multi-cylinder engine unit. The dashed line indicates the fluctuation of the rotation speed of the crankshaft when an imbalance occurs between the cylinders, that is, the air-fuel ratio of the target cylinder is lean and the air-fuel ratio of the reference cylinder is rich. The dashed line indicates the fluctuation of the rotation speed of the crankshaft when an imbalance occurs between the cylinders, that is, the air-fuel ratio of the target cylinder is rich and the air-fuel ratio of the reference cylinder is lean.

[0041] Referring to the solid line, when fuel is burned in the target cylinder 11A, the rotation speed of the crankshaft 12 increases, and the rotation speed becomes maximum when the crank angle is about 90 degrees. After that, the rotation speed of the crankshaft 12 decreases, and when fuel is burned in the reference cylinder 11B at a crank angle of about 270 degrees, the rotation speed increases again. The rotation speed of the crankshaft 12 due to the combustion in the reference cylinder 11B becomes maximum when the crank angle is about 360 degrees. The multi-cylinder engine unit 1 of this embodiment is an independent throttle type and unequal interval combustion type multi-cylinder engine unit having a combustion interval of 270 degrees to 450 degrees. In such a multi-cylinder engine unit, the amount of air supplied to the target cylinder 11A and the reference cylinder 11B is likely to vary, and the amount of energy due to combustion is different. Therefore, the maximum value of the rotation speed of the crankshaft 12 due to the combustion in the target cylinder 11A is different from the maximum value of the rotation speed of the crankshaft 12 due to the combustion in the reference cylinder 11B. The difference D0 (positive value) is determined by subtracting the maximum value of the rotation speed of the crankshaft 12 due to combustion in the reference cylinder 11B from the maximum value of the rotation speed of the crankshaft 12 due to combustion in the target cylinder 11A.

[0042] Referring to the dashed line, when the air-fuel ratio of the target cylinder 11A becomes lean, the ratio of fuel in the mixture decreases. Therefore, the maximum value of the rotation speed of the crankshaft 12 due to combustion in the target cylinder 11A becomes lower than that in the case of the solid line. The control device 14 controls the amount of fuel supplied to each of the multiple cylinders so that the air-fuel ratio of the multiple cylinders 11A, 11B as a whole becomes the target air-fuel ratio. If the air-fuel ratio of the target cylinder 11A becomes lean, the control device 14 controls the air-fuel ratio of the reference cylinder 11B to become rich, and tries to maintain the air-fuel ratio of the multiple cylinders 11A, 11B as a whole at the target air-fuel ratio. As a result, the maximum value of the rotation speed of the crankshaft 12 due to combustion in the reference cylinder 11B becomes higher than that in the case of the solid line. The difference D1 is calculated by subtracting the maximum value of the rotation speed of the crankshaft 12 due to combustion in the reference cylinder 11B from the maximum value of the rotation speed of the crankshaft 12 due to combustion in the target cylinder 11A. The difference D1 is a negative value, and is smaller than the difference D0.

[0043] Referring to the dashed line, when the air-fuel ratio of the target cylinder 11A becomes rich, the ratio of fuel in the mixture increases. Therefore, the maximum value of the rotation speed of the crankshaft 12 caused by combustion in the target cylinder 11A becomes higher than that in the case of the solid line. In this case, the control device 14 controls the air-fuel ratio of the reference cylinder 11B to be lean. As a result, the maximum value of the rotation speed of the crankshaft 12 caused by combustion in the reference cylinder 11B becomes lower than that in the case of the solid line. The difference D2 is a positive value and is larger than the difference D0.

[0044] In this way, when an imbalance in the air-fuel ratio between the multiple cylinders 11A and 11B occurs, the difference between the maximum rotation speed of the crankshaft 12 caused by combustion in the target cylinder 11A and the maximum rotation speed of the crankshaft 12 caused by combustion in the reference cylinder 11B changes. The control device 14 detects the imbalance in the air-fuel ratio between the multiple cylinders 11A and 11B using the change in this difference. That is, the control device 14 detects the imbalance in the air-fuel ratio between the multiple cylinders 11A and 11B using the maximum rotation speed of the crankshaft 12 caused by combustion in the target cylinder 11A and the maximum rotation speed of the crankshaft 12 caused by combustion in the reference cylinder 11B.

[0045] 3 is a flowchart showing the process of detecting an imbalance in air-fuel ratio among cylinders according to this embodiment, assuming that the multi-cylinder engine unit 1 is already in operation.

[0046] First, the control device 14 acquires the difference D0 when no imbalance in the air-fuel ratio occurs between the multiple cylinders 11A and 11B. The difference D0 is a value obtained by subtracting the maximum rotation speed of the crankshaft 12 caused by combustion in the reference cylinder 11B from the maximum rotation speed of the crankshaft 12 caused by combustion in the target cylinder 11A. The difference D0 may be stored in memory in advance, or may be calculated while the multi-cylinder engine unit 1 is operating (step S11).

[0047] Next, the control device 14 acquires the crank angle from a crank angle sensor (not shown). The control device 14 acquires the crank angle periodically or irregularly over a rotation cycle (720 degrees) of the crankshaft 12 (step S12).

[0048] Next, the control device 14 uses the acquired crank angle to calculate the rotation speed of the crankshaft 12 at that crank angle. The control device 14 calculates the rotation speed of the crankshaft 12 over a rotation cycle of the crankshaft 12 (step S13).

[0049] Next, the control device 14 calculates a difference D by subtracting the maximum rotational speed of the crankshaft 12 caused by combustion in the reference cylinder 11B from the maximum rotational speed of the crankshaft 12 caused by combustion in the target cylinder 11A based on the rotational speed of the crankshaft 12 calculated over the rotation cycle of the crankshaft 12 (step S14).

[0050] Next, the control device 14 compares the value obtained by subtracting the difference D from the difference D0 with a threshold value. The threshold value is stored in advance in the memory (step S15).

[0051] If the difference D0 minus the difference D is equal to or smaller than the threshold (NO in step S15), the control device 14 repeats steps S12 and after. If the difference D0 minus the difference D is greater than the threshold (YES in step S15), the control device 14 determines that an inter-cylinder imbalance in the air-fuel ratios of the multiple cylinders 11A, 11B has occurred (step S16).

[0052] <Other embodiments> 4 is a block diagram showing the configuration of a control device in a multi-cylinder engine unit of another embodiment. The control device 14 includes a rotation speed acquisition section 141, a swell detection section 142, and a swell removal section 143.

[0053] The rotation speed acquisition unit 141 is configured to acquire the rotation speed of the crankshaft 12. Specifically, the rotation speed acquisition unit 141 acquires the crank angle detected by the crank angle sensor 121. The rotation speed acquisition unit 141 calculates the rotation speed of the crankshaft 12 using the acquired crank angle. The rotation speed acquisition unit 141 sends the calculated rotation speed of the crankshaft 12 to the swell detection unit 142 and the swell removal unit 143.

[0054] The swell detection unit 142 is configured to detect periodic swells included in fluctuations in the rotation speed of the crankshaft 12, based on the rotation speed of the crankshaft 12 received from the rotation speed acquisition unit 141. The swells have an angle period longer than 720 degrees in crank angle. When the swell detection unit 142 detects a periodic swell, it notifies the swell removal unit 143 that a swell has been detected.

[0055] The swell removal unit 143 is configured to receive a notification from the swell detection unit 142 and remove the periodic swell detected by the swell detection unit 142 from the rotation speed of the crankshaft 12 acquired from the rotation speed acquisition unit 141.

[0056] The control device 14 detects imbalance in the air-fuel ratio between the multiple cylinders 11A, 11B using the fluctuation in the rotation speed of the crankshaft 12 calculated from the rotation speed of the crankshaft 12 from which periodic swells have been removed by the swell removing unit 143.

[0057] In the above description, the multi-cylinder engine unit 1 is a two-cylinder engine unit, and the control device 14 detects the imbalance of the air-fuel ratio between cylinders using the fluctuation of the rotation speed occurring in the combustion interval of 360 degrees or more and 720 degrees or less. However, the multi-cylinder engine unit may be a three-cylinder engine unit. In this case, the control device 14 detects the imbalance of the air-fuel ratio between cylinders using the fluctuation of the rotation speed occurring in the combustion interval of 240 degrees or more and 720 degrees or less. In addition, the multi-cylinder engine unit may be a four-cylinder engine unit, and the crankshaft may be a cross-plane type crankshaft configured to reduce inertia torque. In this case, at least one combustion interval in the rotation cycle of the crankshaft is 240 degrees or more in crank angle. The control device 14 detects the imbalance of the air-fuel ratio between cylinders using the fluctuation of the rotation speed occurring in the combustion interval of 240 degrees or more and 720 degrees or less in crank angle.

[0058] The embodiments and modifications described and / or illustrated in this specification are intended to facilitate understanding of the present disclosure and are not intended to limit the spirit of the present disclosure. The above-mentioned embodiments and modifications may be modified or improved without departing from the spirit of the present disclosure. The spirit of the present disclosure includes equivalent elements, modifications, deletions, combinations (e.g., combinations of features across the embodiments and modifications), improvements, and modifications that may be recognized by a person skilled in the art based on the embodiments disclosed in this specification. The limitations in the claims should be interpreted broadly based on the terms used in the claims and should not be limited to the embodiments and modifications described in the specification or prosecution of this application. Such embodiments and modifications should be interpreted as non-exclusive. For example, in this specification, the terms "preferably" and "good" are non-exclusive and mean "preferably but not limited to" and "good but not limited to". [Explanation of symbols]

[0059] 1: Multi-cylinder engine unit 11A, 11B: Cylinder 111: Piston 112: Combustion chamber 12: Crankshaft 121: Crank angle sensor 13: Generator 131: Rotor 1311: Permanent magnets 132: Stator 1321: Coil 14: Control device 141: Rotation speed acquisition unit 142: Swell detection section 143: Waviness removal section

Claims

1. The multi-cylinder engine unit is A plurality of cylinders each forming a combustion chamber together with a piston; a crankshaft that rotates as fuel is combusted in the combustion chamber; A generator that generates electricity by rotating the crankshaft; a control device that detects an imbalance in air-fuel ratio among the plurality of cylinders using a fluctuation in the rotation speed of the crankshaft, The generator includes: a rotor having a permanent magnet, fixed to the crankshaft so as to be coaxial with the crankshaft, and rotating at a fixed speed ratio relative to the crankshaft; a stator having a coil that generates an electromotive force when the rotor rotates; The multi-cylinder engine unit is a two- or four-cylinder engine unit of a variable combustion interval type, in which a throttle valve and an injector are provided in each of a plurality of intake passages, or a two- or three-cylinder engine unit of a uniform combustion interval type, which is mounted on a saddle-ride type vehicle and satisfies any one of the following (A) to (C): the rotor is a rotor for a saddle-ride type vehicle used in the saddle-ride type vehicle, The control device detects an imbalance in the air-fuel ratio between cylinders by detecting an abnormality in the air-fuel ratio in at least one of the plurality of cylinders using fluctuations in the rotational speed of the crankshaft during a combustion interval that is the widest, equal to or greater than 240 degrees in crank angle, and in which fluctuations in the rotational speed of the crankshaft due to combustion occur, in a rotation cycle of the crankshaft of the saddle-ride type vehicle in which the rotor for the saddle-ride type vehicle is fixed to an end and in which fluctuations in the rotational speed are likely to occur. (A) At least one combustion interval in the rotation cycle of the crankshaft is configured to be 360 ​​degrees or more in crank angle, and the widest combustion interval is 360 degrees or more and 720 degrees or less in crank angle. (B) All combustion intervals in the rotation cycle of the crankshaft are configured to be 240 degrees or more in crank angle, and the widest combustion interval is 240 degrees or more and 720 degrees or less in crank angle. (C) A cross-plane type in which at least one combustion interval in the rotation cycle of the crankshaft is 240 degrees or more in crank angle and inertia torque is reduced, and the widest combustion interval is 240 degrees or more and 720 degrees or less in crank angle.

2. 2. The multi-cylinder engine unit according to claim 1, The control device includes: a rotation speed acquisition unit configured to acquire a rotation speed of the crankshaft; a swell detection unit configured to detect periodic swells included in fluctuations in the rotation speed of the crankshaft based on the rotation speed obtained by the rotation speed acquisition unit; and a swell removing unit configured to remove the periodic swell detected by the swell detecting unit from the rotation speed of the crankshaft, The swell has an angular period longer than 720 crank angles, The control device detects an imbalance in the air-fuel ratio between cylinders in at least one of the plurality of cylinders by using fluctuations in the rotational speed of the crankshaft calculated from the rotational speed of the crankshaft from which the periodic swell has been removed by the swell removal unit.

3. 3. The multi-cylinder engine unit according to claim 1 or 2, When the multi-cylinder engine unit satisfies (A), the plurality of cylinders include a reference cylinder that performs combustion that generates a maximum rotation speed of the crankshaft in the combustion interval of 360 degrees or more and 720 degrees or less, and a target cylinder that is different from the reference cylinder, the control device detects an imbalance in the air-fuel ratio between at least one cylinder among the plurality of cylinders using a fluctuation in the rotation speed of the crankshaft obtained based on a maximum rotation speed of the crankshaft generated by combustion in the reference cylinder and a maximum rotation speed of the crankshaft generated by combustion in the target cylinder; When the multi-cylinder engine unit satisfies (B), the plurality of cylinders include an arbitrarily selected reference cylinder that performs combustion that produces a maximum rotation speed of the crankshaft in the combustion interval of 240 degrees or more and 720 degrees or less, and a target cylinder that is different from the reference cylinder and is arbitrarily selected, the control device detects an imbalance in the air-fuel ratio between at least one cylinder among the plurality of cylinders using a fluctuation in the rotation speed of the crankshaft obtained based on a maximum rotation speed of the crankshaft generated by combustion in the reference cylinder and a maximum rotation speed of the crankshaft generated by combustion in the target cylinder; When the multi-cylinder engine unit satisfies (C), the plurality of cylinders include a reference cylinder that performs combustion that produces a maximum rotation speed of the crankshaft in the combustion interval of 240 degrees or more and 720 degrees or less, and a target cylinder that is different from the reference cylinder and is arbitrarily selected, The control device detects an imbalance in the air-fuel ratio between at least one of the plurality of cylinders by using a fluctuation in the rotational speed of the crankshaft obtained based on a maximum rotational speed of the crankshaft generated by combustion in the reference cylinder and a maximum rotational speed of the crankshaft generated by combustion in the target cylinder.

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