Straddled vehicle

Abstract

A straddled vehicle (1) includes an engine (2) and a control device (3). The control device (3) is configured to remove a locked state and restart the engine (2) if a restart condition is established while a crankshaft (21) is stopped in a crank angle range (R1), the removal being implemented by accelerating forward rotation of the crankshaft in a low negative pressure expansion stroke, the forward rotation of the crankshaft being forward rotation of the crankshaft that a starter generator (22) has started without rotating the crankshaft in reverse direction or forward rotation of the crankshaft that the starter generator (22) has started after rotating the crankshaft in the reverse direction so as not to go beyond compression top dead center, the low negative pressure expansion stroke being an expansion stroke in which a negative pressure inside a combustion chamber (26) is reduced before completion by a ventilation between the inside and outside of the combustion chamber created by a crankshaft stop ventilation mechanism (27), the acceleration being carried out in at least a part of a crankshaft run-up section.

Description

Technical Field

[0001] The present teaching relates to a straddled vehicle.Background Art

[0002] An idling-stop function (idle reduction function) is known as a means for improving the fuel efficiency of a vehicle. By use of the idling-stop function, an engine in operation is stopped if a predetermined idle stop condition is satisfied, and the stopped engine is restarted if a predetermined restart condition is satisfied. An exemplary application of the idling-stop function to a straddled vehicle as typified by a motorcycle is disclosed in Patent Literature 1 (PTL 1).

[0003] The straddled vehicle disclosed in PTL 1 includes a four-stroke engine and a starter generator. In the straddled vehicle, the engine is stopped if an idle stop condition is satisfied, and the starter generator restarts the engine if a restart condition is satisfied. The straddled vehicle further includes a decompression mechanism. At a time of the restart of the engine, the decompression mechanism reduces a pressure in a combustion chamber in a compression stroke. The decompression mechanism enables the straddled vehicle to smoothly restart the engine that has been stopped due to the idling-stop function.

[0004] The decompression mechanism, though, is actuated in the compression stroke, so the inside of the combustion chamber undergoes a negative pressure in the subsequent expansion stroke. When the engine is stopped by the idling-stop function, the position at which a piston stops is not fixed. If by chance the piston stops in the expansion stroke, the negative pressure in the combustion chamber makes it difficult for the crankshaft to rotate, so a locked state, in which the engine is not able to be restarted, is created. In this respect, in the straddled vehicle according to PTL 1, when restarting the engine while the piston is stopped in the expansion stroke, the locked state is removed by repeating reverse driving and forward driving of the starter generator. After the removal of the locked state, the crankshaft is swung back beyond the compression top dead center, for the engine to be restarted.Citation ListPatent Literature

[0005] PTL 1: Japanese Patent Application Laid-Open No. 2020-165343Summary of InventionTechnical Problem

[0006] The present teaching aims to provide a straddled vehicle equipped with a starter generator, the straddled vehicle being capable of shortening a time taken until restarting of an engine having been stopped by the idling-stop function, and also capable of reducing the electric power consumption in restarting.Solution to the Problem

[0007] To restart an engine, a piston needs to pass beyond the compression top dead center. As the piston approaches the compression top dead center, the pressure in a combustion chamber rises. Thus, when the piston passes beyond the compression top dead center, a starter generator is subjected to a high-pressure load. It is possible for this load on the starter generator to be reduced by a decompression mechanism; however, intake and exhaust valves are closed in an expansion stroke subsequent to a compression stroke, and therefore in the expansion stroke, the pressure in the combustion chamber becomes negative to an extent corresponding to the pressure reduction in the combustion chamber carried out in the compression stroke by the decompression mechanism. As the piston approaches the bottom dead center, the negative pressure rises, and a torque required to rotate a crankshaft increases. When the required torque exceeds an output torque of the starter generator, a locked state, in which the starter generator is not able to rotate the crankshaft, is created, which makes restarting of the engine impossible.

[0008] Here, the straddled vehicle is configured to turn in a driving direction by the rider manipulating a handle and also by shifting their weight. The straddled vehicle, therefore, is required to have a high responsiveness to the driver's manipulation intention. For the straddled vehicle, the agility, lightness, and convenience of the vehicle are important factors. Thus, it is desired that the straddled vehicle be small and lightweight. In the straddled vehicle, restarting the engine after idling is stopped is different from normal starting in that the restarting needs to be done on a travel lane of a road while the vehicle is waiting at a traffic light, for example. This is why a straddled vehicle having the idling-stop function is required to have a higher responsiveness. For this purpose, it is conceivable that a starter generator capable of outputting a higher torque is adopted in the straddled vehicle. If such a starter generator is adopted, however, the external size of the starter generator is large, and therefore reduction in size and weight of the straddled vehicle is made difficult, which may result in poor responsiveness. For this reason, the locked state is more likely to be created in the straddled vehicle as compared to in a four wheeled vehicle, for example. The likelihood that the locked state is created is higher as the compression ratio of the engine is higher.

[0009] In the straddled vehicle according to PTL 1, the locked state is removed by repeating reverse driving and forward driving of the starter generator. After the removal of the locked state, the crankshaft is swung back largely so as to go beyond the compression top dead center, and the engine is restarted. In this manner, the engine is able to be restarted even though the locked state is created in the straddled vehicle equipped with the starter generator. The repetition of reverse driving and forward driving of the starter generator and the large swing-back not only requires a certain length of time, but also consumes a lot of electric power.

[0010] The inventors of the present teaching have focused on the expansion stroke in which the starter generator is not able to start a rotation of the stopped crankshaft due to occurrence of the locked state. The inventors of the present teaching have considered that if no locked state is created in the expansion stroke, the starter generator is able to start rotation of the crankshaft. The inventors of the present teaching have also considered that reducing the negative pressure in the combustion chamber in the expansion stroke, which is a cause of the locked state, can reduce the risk of falling into the locked state. Based on these studies, the present teaching has been accomplished. (1) A straddled vehicle according to the present teaching includes a single-cylinder or two-cylinder engine and a control device. The engine includes a crankshaft capable of rotating in forward and reverse directions, a starter generator capable of rotating the crankshaft in the forward and reverse directions, and a crankshaft forward-rotation ventilation mechanism. The crankshaft forward-rotation ventilation mechanism is configured to, while an idle stop condition is established and a combustion operation is stopped but the crankshaft is rotating in the forward direction, create a ventilation between the inside and outside of a combustion chamber before a compression top dead center is reached, and subsequently block the ventilation between the inside and outside of the combustion chamber before the compression top dead center is reached. The engine is an engine that is brought into a post-idle-stop restarting locked state when in order: the idle stop condition is established, the crankshaft stops in a crank angle range that is after the crankshaft passes beyond the compression top dead center, and is ahead of an exhaust valve being opened, and then a restart condition is established; the post-idle-stop restarting locked state being where a torque required to rotate the crankshaft in the forward direction exceeds a torque that the starter generator gives to the crankshaft.

[0011] The engine further includes a crankshaft stop ventilation mechanism configured to create a ventilation between the inside and outside of the combustion chamber when in order: after the idle stop condition is established, the combustion operation of the engine is stopped, the crankshaft rotating in the forward direction passes through the compression top dead center, and the crankshaft is in any one of the following stages in the crank angle range before the exhaust valve is opened; the crankshaft is about to stop while in the state of rotation, the crankshaft is in a stopped state, or the crankshaft has again started rotation.

[0012] The control device is configured for removal of the post-idle-stop restarting locked state and restart the engine when in order: the idle stop condition is established, the crankshaft stops in the crank angle range that is after the crankshaft passes beyond the compression top dead center, and is ahead of the exhaust valve being opened, and then the restart condition is established, the removal being implemented by acceleration of forward rotation of the crankshaft in a low negative pressure expansion stroke for post-idle-stop restarting, the forward rotation of the crankshaft having been started by the starter generator without any reverse direction rotation of the crankshaft or after rotating the crankshaft in the reverse direction so as not to go beyond the compression top dead center, the acceleration being carried out in at least a part of a crankshaft run-up section for post-idle-stop restarting. The low negative pressure expansion stroke for post-idle-stop restarting is where a negative pressure inside the combustion chamber is reduced before stroke completion by the ventilation between the inside and outside of the combustion chamber created by the crankshaft stop ventilation mechanism. The crankshaft run-up section for post-idle-stop restarting is composed of: a section from the start of the forward rotation of the crankshaft to completion of the low negative pressure expansion stroke for post-idle-stop restarting; and the exhaust stroke; and the intake stroke, which are each subsequent to the low negative pressure expansion stroke for post-idle-stop restarting.

[0013] In the foregoing straddled vehicle, if the idle stop condition is established, the crankshaft forward-rotation ventilation mechanism suppresses an increase of the pressure inside the combustion chamber in the compression stroke. Then, the crankshaft stops in the expansion stroke next to the compression stroke. That is, the crankshaft stops in a state where the post-idle-stop restarting locked state (hereinafter, the locked state) will occur in restarting. In this regard, however, the negative pressure inside the combustion chamber is reduced by the crankshaft stop ventilation mechanism when the crankshaft is in any one of the following stages before the exhaust valve is opened; the crankshaft is about to stop while in the state of rotation, the crankshaft is in a stopped state, or the crankshaft has again started rotation. Since the crankshaft starts rotating in the low negative pressure expansion stroke for post-idle-stop restarting (hereinafter, the low negative pressure expansion stroke) in which the negative pressure is reduced, occurrence of the locked state is suppressed, and acceleration of the crankshaft is allowed. Consequently, even the starter generator mounted in the straddled vehicle is able to resume the forward rotation of the crankshaft without any swing-back of the crankshaft or with just a slight swing-back of the crankshaft. The acceleration of the crankshaft can be made by using at least a part of the crankshaft run-up section for post-idle-stop restarting (hereinafter, the crankshaft run-up section), which is composed of the low negative pressure expansion stroke and subsequent exhaust and intake strokes. This can provide a sufficient moment of inertia. The crankshaft is able to overcome the compression top dead center due to a resultant force of the torque of the starter generator and the moment of inertia of the crankshaft obtained by the crankshaft forward rotation, which is started in the low negative pressure expansion stroke, being accelerated in the crankshaft run-up section. Accordingly, the foregoing straddled vehicle equipped with a starter generator is capable of shortening a time taken to restart an engine having been stopped by the idling-stop function, and also capable of reducing the electric power consumption to restart.

[0014] (2) In the straddled vehicle according to (1) above, the starter generator may be attached to the crankshaft with no reduction gear interposed therebetween. The locked state may be a state where a torque required to rotate the crankshaft in the forward direction exceeds a torque that the starter generator, attached to the crankshaft without interposition of the reduction gear, gives to the crankshaft when in order: the idle stop condition is established, the crankshaft stops in the crank angle range that is after the crankshaft passes beyond the compression top dead center, and is ahead of the exhaust valve being opened, and then the restart condition is established. The control device may be configured for removal of the locked state and restart the engine when in order: the idle stop condition is established, the crankshaft stops in the crank angle range that is after the crankshaft passes beyond the compression top dead center, and is ahead of the exhaust valve being opened, and then the restart condition is established, the removal being implemented by acceleration of the forward rotation of the crankshaft in the low negative pressure expansion stroke, the forward rotation of the crankshaft having been started by the starter generator giving a torque to the crankshaft without interposition of any reduction gear, the acceleration being carried out in at least a part of the crankshaft run-up section.

[0015] If a starter generator is attached to a crankshaft with a reduction gear interposed therebetween, a structure surrounding an engine is complicated, and the size of a straddled vehicle is increased. In the straddled vehicle according to (2) above, an output torque of the starter generator is transmitted to the crankshaft without amplification. This can allow the straddled vehicle to be small and lightweight. On the other hand, a torque that the starter generator is able to give to the crankshaft is low, because no such reduction gear is interposed. This makes the locked state likely to occur if the idle stop condition is established and the crankshaft stops in the expansion stroke. In the straddled vehicle according to (2) above, the crankshaft starts rotating from the low negative pressure expansion stroke, and thus the risk of falling into the locked state can be suppressed even though the starter generator provides a low output torque. In addition, the acceleration of the crankshaft can be made by using at least a part of the crankshaft run-up section, which allows the crankshaft to overcome the compression top dead center, to restart the engine. Accordingly, this straddled vehicle equipped with a starter generator is capable of shortening a time taken to restart an engine having been stopped by the idling-stop function, and also capable of reducing the electric power consumption to restart, while suppressing an increase in size.

[0016] (3) In the straddled vehicle according to (1) or (2) above, the control device may be configured to control both the engine and the starter generator such that the control device restarts the engine, and subsequently further accelerates forward rotation of the crankshaft having been accelerated in at least the part of the crankshaft run-up section, while the control device performs an electric power-running control on the starter generator, to add a driving force of the starter generator to a driving force of the engine. The restart of the engine by the control device may be performed with the locked state removed if the restart condition is established while the crankshaft is stopped in the crank angle range that is located after the crankshaft passes through the compression top dead center subsequent to establishment of the idle stop condition and before the exhaust valve is opened, the removal being implemented by accelerating forward rotation of the crankshaft in the low negative pressure expansion stroke, the forward rotation of the crankshaft being started by the starter generator, the acceleration being carried out in at least a part of the crankshaft run-up section.

[0017] In the straddled vehicle according to (3) above, the starter generator assists the engine. This can, for example, reduce a load on the engine at a time of starting the straddled vehicle. In the straddled vehicle, the crankshaft starts a rotation from the low negative pressure expansion stroke, and the crankshaft is accelerated in at least a part of the crankshaft run-up section. In restarting the engine, therefore, no swing-back of the crankshaft, or just a slight swing-back of the crankshaft is required, which allows the engine to be restarted quickly. This can advance the time at which the starter generator assists the engine after the engine is restarted. As a result, in the straddled vehicle, the starter generator is able to start assisting the engine earlier. Accordingly, this straddled vehicle equipped with a starter generator is capable of shortening a time taken to restart the engine having been stopped by the idling-stop function, also capable of reducing the electric power consumption to restart, and further capable of allow the straddled vehicle to be started smoothly and quickly.

[0018] The "straddled vehicle" is transportation equipment. The straddled vehicle is one driven by a person. The straddled vehicle is a motorcycle, for example. The straddled vehicle is not limited to the motorcycle, and may be a motor tricycle, for example. The straddled vehicle has two or three wheels, for example. The straddled vehicle has at least one front wheel and at least one rear wheel, for example. The type of the straddled vehicle is not particularly limited, and examples thereof include a scooter type, a moped type, an off-road type, and an on-road type. The straddled vehicle is a vehicle of a type in which a driver sits straddling a seat, for example. In the straddled vehicle, for example, the sitting driver has their left leg positioned to the left relative to the center in the left-right direction of the straddled vehicle, and their right leg positioned to the right relative to the center in the left-right direction of the straddled vehicle. The straddled vehicle may have a cabin. The straddled vehicle is also a leaning vehicle, for example. The leaning vehicle includes a vehicle body that leans in either one of the leftward or rightward directions when the leaning vehicle turns in that direction, for example. To be specific, the vehicle body leans in the leftward direction when the leaning vehicle turns left, and leans in the rightward direction when the leaning vehicle turns right. The leaning vehicle includes at least one steered wheel, which leans together with the vehicle body, for example. The leaning vehicle includes at least one driving wheel, which leans together with the vehicle body, for example.

[0019] The "engine" generates power for making the straddled vehicle travel, for example. The power generated by the engine is transmitted to the driving wheel via a transmission, for example. The power generated by the engine is transmitted to the transmission not via a torque converter, for example. The engine is supported by the vehicle body of the straddled vehicle, for example. The engine is an internal combustion engine, for example. The engine is a fuel-injection type engine, for example. The engine is a reciprocating engine, for example. The engine is a four-stroke engine, for example. The engine is a spark-ignition type engine in which fuel combustion is caused by a spark plug, for example. A fuel of the engine is a gasoline, a liquefied petroleum gas (LP gas), hydrogen, an alcohol, a biofuel, a synthetic fuel, or the like, for example.

[0020] The engine includes one combustion chamber, for example. The engine includes a piston that is disposed in the combustion chamber, for example. The engine includes a crankshaft, which is connected to the piston, for example. The engine includes an intake valve for supplying a mixed gas to the combustion chamber, for example. The engine includes an exhaust valve for exhausting a combustion gas of the combustion chamber, for example. The engine may include a valve for creating a ventilation between the inside and outside of the combustion chamber, the valve being such that it is different from the intake and exhaust valves, for example.

[0021] The engine in which the locked state occurs refers to an engine in which the locked state can occur when in order: the idle stop condition is established, the crankshaft stops in the crank angle range that is after the crankshaft passes beyond the compression top dead center, and is ahead of an exhaust valve being opened, and then the restart condition is established, for example. The engine in which the locked state occurs does not necessarily refer to an engine in which the locked state always occurs when in order: the idle stop condition is established, the crankshaft stops in the crank angle range that is after the crankshaft passes beyond the compression top dead center, and is ahead of an exhaust valve being opened, and then the restart condition is established, for example. The engine in which the locked state occurs refers to an engine in which the probability of causing the locked state is more than 0% and not more than 100%, for example. Whether the locked state occurs or not can be checked by restarting the engine without actuating the crankshaft stop ventilation mechanism in the expansion stroke, for example.

[0022] The "forward rotation (rotating in the forward direction)" of the crankshaft indicates that the crankshaft rotates in a direction in which the crankshaft rotates while the engine is in combustion operation, for example. The forward rotation indicates that the crankshaft rotates such that the engine repeats an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke in this order, for example.

[0023] The "reverse rotation (rotating in the reverse direction)" of the crankshaft indicates that the crankshaft rotates in a rotation direction reverse to the direction of the forward rotation of the crankshaft, for example.

[0024] The "crank angle" refers to an angle through which the crankshaft rotates from a reference position, for example. In a case of the four-stroke engine, the crank angle advances by 720 degrees upon completion of a one-cycle combustion operation, which is composed of the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke. The crank angle being zero degrees represents an angle of the crankshaft when the piston is located at a position (compression top dead center) of completion of the compression stroke, for example.

[0025] The "starter generator" serves as both a starter motor and a generator, for example. The starter generator has both a function of starting or restarting the engine by rotating the crankshaft and a function of being driven by the engine to generate electricity while the engine is in combustion operation, for example.

[0026] The starter generator is a permanent magnet type three-phase brushless motor / generator, for example. The starter generator includes a rotor and a stator, for example. The starter generator may be of either an outer rotor type or an inner rotor type. The rotor includes at least one permanent magnet, for example. The stator includes at least one winding having a conductivity, for example. The stator is arranged such that an induced electromotive force occurs in the winding due to rotation of the rotor, for example.

[0027] The starter generator is directly attached to the crankshaft, for example. More specifically, the rotor is directly attached to the crankshaft, for example. The starter generator is attached to the crankshaft with no clutch interposed therebetween, for example. The starter generator rotates with a fixed rotation speed ratio relative to the crankshaft, for example. The starter generator rotates at the same rotation speed as that of the crankshaft, for example. The starter generator may alternatively be attached to the crankshaft with a reduction gear interposed therebetween, for example.

[0028] The "crankshaft forward-rotation ventilation mechanism" suppresses an increase of the pressure inside the combustion chamber in the compression stroke, for example. The crankshaft forward-rotation ventilation mechanism assists the crankshaft rotating in the forward direction in overcoming the compression top dead center, for example. The crankshaft forward-rotation ventilation mechanism creates a ventilation between the inside and outside of the combustion chamber in the compression stroke, for example. The crankshaft forward-rotation ventilation mechanism creates a ventilation between the inside and outside of the combustion chamber in a section from the intake bottom dead center to the compression top dead center, for example. The crankshaft forward-rotation ventilation mechanism creates a ventilation between the inside and outside of the combustion chamber when the idle stop condition is established and the combustion operation of the engine is stopped but the crankshaft is rotating in the forward direction due to inertia, for example. The crankshaft forward-rotation ventilation mechanism creates a ventilation between the inside and outside of the combustion chamber when the restart condition is established and the crankshaft is rotating in the forward direction in order to resume the combustion operation of the engine, for example. The crankshaft forward-rotation ventilation mechanism blocks a ventilation between the inside and outside of the combustion chamber after the ventilation between the inside and outside of the combustion chamber is created and before the compression top dead center is reached, for example.

[0029] The crankshaft forward-rotation ventilation mechanism uses the intake valve and / or the exhaust valve, to create and block a ventilation between the inside and outside of the combustion chamber, for example. The crankshaft forward-rotation ventilation mechanism may use a valve (decompression valve) different from the intake and exhaust valves, to create and block a ventilation between the inside and outside of the combustion chamber, for example. The crankshaft forward-rotation ventilation mechanism uses at least one of the intake valve, the exhaust valve, or the decompression valve, to create and block a ventilation between the inside and outside of the combustion chamber, for example.

[0030] The "idle stop condition" is a condition that stops the combustion operation of the engine by the idling-stop function, for example. If the idle stop condition is satisfied, the engine in the combustion operation is stopped by the idling-stop function.

[0031] The "restart condition" is a condition that resumes the combustion operation of the engine that has been stopped by the idling-stop function, for example. If the restart condition is satisfied, the engine of which the combustion operation has been stopped by the idling-stop function is restarted.

[0032] The idle stop condition and the restart condition are set based on the amount of operation of an accelerator operator, the degree of opening of a throttle valve, a vehicle speed, or the like, for example.

[0033] The "crank angle range that is after the crankshaft passes beyond the compression top dead center ahead of an exhaust valve being opened" corresponds to a partial or the entire range of the expansion stroke, for example. In a case where the exhaust valve starts to open before completion of the expansion stroke, for example, the crank angle range that is after the crankshaft passes beyond the compression top dead center ahead of an exhaust valve being opened corresponds to a part of the expansion stroke.

[0034] The "crankshaft stop ventilation mechanism" suppresses a decrease of the pressure (increase of the negative pressure) inside the combustion chamber in the expansion stroke, for example. To be specific, the crankshaft stop ventilation mechanism changes the expansion stroke into the low negative pressure expansion stroke, for example. The crankshaft stop ventilation mechanism assists the crankshaft in rotating in the forward direction in the low negative pressure expansion stroke, for example.

[0035] The crankshaft stop ventilation mechanism is configured to start creating a ventilation between the inside and outside of the combustion chamber in the low negative pressure expansion stroke, for example. The crankshaft stop ventilation mechanism is configured to start creating a ventilation between the inside and outside of the combustion chamber after the crankshaft passes beyond the compression top dead center and ahead of the exhaust valve being opened, for example. More specifically, the crankshaft stop ventilation mechanism is configured to start creating a ventilation between the inside and outside of the combustion chamber when the idle stop condition is established and the combustion operation of the engine is stopped but the crankshaft is rotating in the forward direction due to inertia, for example. The crankshaft stop ventilation mechanism is configured to start creating a ventilation between the inside and outside of the combustion chamber when the idle stop condition is established, the combustion operation of the engine is stopped, and the crankshaft having rotated in the forward direction due to inertia is stopped, for example. The crankshaft stop ventilation mechanism is configured to start creating a ventilation between the inside and outside of the combustion chamber after the restart condition is established, the combustion operation of the engine is resumed, and the stopped crankshaft resumes rotation (including forward rotation and reverse rotation) and before the crankshaft reaches the crank angle position at which the exhaust valve is opened, for example.

[0036] The crankshaft stop ventilation mechanism is configured to block a ventilation between the inside and outside of the combustion chamber in the low negative pressure expansion stroke or in the exhaust stroke subsequent to the low negative pressure expansion stroke, for example. To be specific, the crankshaft stop ventilation mechanism blocks a ventilation between the inside and outside of the combustion chamber after the ventilation between the inside and outside of the combustion chamber is created and before the crankshaft reaches the crank angle position at which the exhaust valve is opened, for example. The crankshaft stop ventilation mechanism blocks a ventilation between the inside and outside of the combustion chamber when the crankshaft reaches the crank angle position at which the exhaust valve is opened, after the ventilation between the inside and outside of the combustion chamber is created, for example. The crankshaft stop ventilation mechanism blocks a ventilation between the inside and outside of the combustion chamber after the ventilation between the inside and outside of the combustion chamber is created and then the crankshaft passes through the crank angle position at which the exhaust valve is opened, for example. In such a case, the crankshaft stop ventilation mechanism blocks a ventilation between the inside and outside of the combustion chamber after the ventilation between the inside and outside of the combustion chamber is created and before the crankshaft, passing beyond the crank angle position at which the exhaust valve is opened, reaches a crank angle position at which the exhaust valve is opened to the maximum degree, for example.

[0037] In sum, the crankshaft stop ventilation mechanism creates a ventilation between the inside and outside of the combustion chamber at least in the low negative pressure expansion stroke, for example. The crankshaft stop ventilation mechanism may create a ventilation between the inside and outside of the combustion chamber in the low negative pressure expansion stroke and the exhaust stroke subsequent to the low negative pressure expansion stroke, for example. The exhaust valve may start to open in the low negative pressure expansion stroke, or may start to open in the exhaust stroke.

[0038] The crankshaft stop ventilation mechanism uses the intake valve and / or the exhaust valve, to create and block a ventilation between the inside and outside of the combustion chamber, for example. The crankshaft stop ventilation mechanism may use a decompression valve, to create and block a ventilation between the inside and outside of the combustion chamber, for example. The crankshaft stop ventilation mechanism uses at least one of the intake valves, the exhaust valve, or the decompression valve, to create and block a ventilation between the inside and outside of the combustion chamber, for example. The crankshaft stop ventilation mechanism uses at least one valve out of the intake valve, the exhaust valve, and the decompression valve, to create and block a ventilation between the inside and outside of the combustion chamber, the at least one valve being different from the valve used by the crankshaft forward-rotation ventilation mechanism, for example. The crankshaft stop ventilation mechanism may use at least one valve out of the intake valve, the exhaust valve, and the decompression valve, to create and block a ventilation between the inside and outside of the combustion chamber, the at least one valve being the same as the valve used by the crankshaft forward-rotation ventilation mechanism, for example.

[0039] The "low negative pressure expansion stroke" refers to an expansion stroke in which a negative pressure inside the combustion chamber is lower, compared to an expansion stroke in which a ventilation between the inside and outside of the combustion chamber is not created by the crankshaft stop ventilation mechanism, for example.

[0040] The "control device" is electrically connected to the engine, for example. The control device controls the engine, for example. The control device is an electronic control unit (ECU), for example. The control device includes a processor such as a central processing unit (CPU), a digital signal processor (DSP), or the like, for example. The control device may include a nonvolatile memory on which recorded are one or more programs including a part or the whole of arithmetic processing to be executed by the control device, for example. The processor reads out and executes the one or more programs recorded on the nonvolatile memory, which is disposed in the control device or outside the control device, to enable the control device to carry out stopping and restarting of the engine, for example. That is, the control device carries out the idling-stop function of the engine, for example. The control device is disposed in the vehicle body of the straddled vehicle, for example.

[0041] When the restart condition is established, the control device accelerates forward rotation of the crankshaft started by the starter generator, in at least a part of the crankshaft run-up section, for example. The control device may accelerate forward rotation of the crankshaft that the starter generator has started after rotating the crankshaft in the reverse direction (swing-back), in at least a part of the crankshaft run-up section, for example. Here, the control device rotates the crankshaft, which has been stopped in the low negative pressure expansion stroke by the starter generator, in the reverse direction such that the crankshaft does not go beyond the compression top dead center, which is a start position of the low negative pressure expansion stroke, for example. That is, the control device has the crankshaft rotated in the reverse direction by the starter generator, in a range of the low negative pressure expansion stroke, for example. The control device may rotate the crankshaft in the reverse direction, then rotate the crankshaft in the forward direction, and then rotate the crankshaft in the reverse direction, for example. The control device accelerates forward rotation of the crankshaft in at least a part of the crankshaft run-up section, the forward rotation of the crankshaft being started by the control device after the control device rotates the crankshaft in the reverse direction at least once in a range of the low negative pressure expansion stroke, for example.

[0042] The control device may accelerate forward rotation of the crankshaft in at least a part of the crankshaft run-up section, the forward rotation of the crankshaft being started by the starter generator without any reverse rotation of the crankshaft, for example. In this case, since the crankshaft is not rotated in the reverse direction, a path of the crankshaft run-up section is shortened accordingly, which enables early restarting of the engine.

[0043] The "crankshaft run-up section" allows the crankshaft to obtain a moment of inertia for overcoming the compression top dead center when the restart condition is established, for example. In the crankshaft run-up section, the crankshaft keeps rotating in the forward direction, for example. In the crankshaft run-up section, the crankshaft does not rotate in the reverse direction, for example.

[0044] The control device may accelerate forward rotation of the crankshaft over the entire crankshaft run-up section. The control device may accelerate forward rotation of the crankshaft in a part of the crankshaft run-up section. Cases where the control device accelerates forward rotation of the crankshaft in a part of the crankshaft run-up section can be exemplified in the following case.

[0045] The control device may accelerate forward rotation of the crankshaft in a partial section of the crankshaft run-up section, for example. The control device may accelerate forward rotation of the crankshaft amidst the crankshaft run-up section, for example. The control device may accelerate forward rotation of the crankshaft intermittently in the crankshaft run-up section. The acceleration of the crankshaft in the crankshaft run-up section may vary. In sum, the control device accelerating forward rotation of the crankshaft in a part of the crankshaft run-up section means that the rotation speed of the crankshaft at the end point of the crankshaft run-up section is higher than the rotation speed of the crankshaft at the start point of the crankshaft run-up section, for example. How to accelerate the crankshaft in the crankshaft run-up section is not particularly limited.

[0046] The foregoing description deals with a case of the straddled vehicle including the single-cylinder engine. The straddled vehicle may alternatively include a two-cylinder engine. The two-cylinder engine is an in-line type, V-type, or horizontally opposed type engine, for example. The two-cylinder engine includes a 270-degree crankshaft, for example. The two-cylinder engine may include a 180-degree crankshaft, for example. The two-cylinder engine includes two combustion chambers, for example. In the two-cylinder engine, the crankshaft forward-rotation ventilation mechanism for creating and blocking a ventilation between the inside and outside of the combustion chamber is provided for each of the two combustion chambers, for example. In the two-cylinder engine, the crankshaft stop ventilation mechanism for creating and blocking a ventilation between the inside and outside of the combustion chamber is provided for each of the two combustion chambers, for example. In a case of the straddled vehicle including the two-cylinder engine, a consideration is focused on either one of the two combustion chambers. To be specific, a consideration is focused on the combustion chamber that is in the expansion stroke when the idle stop condition is established and the crankshaft is stopped. The foregoing description is applied to the combustion chamber that is focused on.

[0047] In the straddled vehicle including the two-cylinder engine, cases where the control device accelerates forward rotation of the crankshaft in a part of the crankshaft run-up section can be exemplified not only in the same case as in the above-described example case of the single-cylinder engine, but also in the following case, for example.

[0048] Supposing a case in which the engine is restarted while a second combustion chamber is in the low negative pressure expansion stroke, for example. In this case, the control device accelerates forward rotation of the crankshaft in the crankshaft run-up section composed of the low negative pressure expansion stroke and subsequent exhaust and intake strokes in the second combustion chamber, for example. In some cases, however, fuel ignition may occur in the first combustion chamber amidst the crankshaft passing through the crankshaft run-up section. In other words, the engine may be restarted before the crankshaft completes the crankshaft run-up section. Such a case is also encompassed by the cases where the control device accelerates forward rotation of the crankshaft in a part of the crankshaft run-up section.

[0049] These and other objects, features, aspects, and advantages of the present teaching will become more apparent from the following detailed description of embodiment(s) of the present teaching, with reference to 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 terms "including," "comprising," or "having," and variations thereof specify the presence of stated features, steps, operations, elements, components, and / or equivalents thereof, and can include one or more of steps, operations, elements, components, and / or their groups. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present teaching belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the present disclosure and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. It will be understood that the description of the present teaching discloses a number of techniques and steps. Each of these has individual benefit and each can also be used in conjunction with one or more, or in some cases all, of the other disclosed techniques. Accordingly, for the sake of clarity, this description will refrain from repeating every possible combination of the individual steps in an unnecessary fashion. Nevertheless, Description and Claims should be read with the understanding that such combinations are entirely within the scope of the present teaching and the claims. In the description given below, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present teaching. It will be apparent, however, that those skilled in the art may practice the present teaching without these specific details. The present disclosure is to be considered as an exemplification of the present teaching, and is not intended to limit the present teaching to the specific embodiments illustrated by the drawings or descriptions provided below.Advantageous Effects of Invention

[0050] The present teaching enables provision of a straddled vehicle equipped with a starter generator, capable of shortening a time taken until restarting of an engine having been stopped by an idling-stop function, and also capable of reducing the electric power consumption in restarting.Brief Description of Drawings

[0051] [FIG. 1] FIG. 1(A) contains a side view of a straddled vehicle according to an embodiment, a diagram schematically showing an engine, and a diagram schematically showing a starter generator attached to a crankshaft; and FIG. 1(B) shows the relationship of a torque required to restart the engine, the position of the crankshaft, and the degrees of opening of various valves in the straddled vehicle according to the embodiment. [FIG. 2] FIG. 2 shows the relationship of a torque required to restart an engine, the position of a crankshaft, and the degrees of opening of various valves in a case where the straddled vehicle according to the embodiment includes a two-cylinder engine. Description of Embodiments

[0052] In the following, a straddled vehicle according to an embodiment of the present teaching will be described with reference to the drawings. Here, it should be noted that the embodiment described below is merely an example. The present teaching should not be construed as being limited in any way by the embodiment described below.

[0053] FIG. 1(A) contains a side view of the straddled vehicle according to the embodiment, a diagram schematically showing an engine, and a diagram schematically showing a starter generator attached to a crankshaft. A straddled vehicle 1 includes an engine 2 and a control device 3. The engine 2 and the control device 3 are disposed in a vehicle body of the straddled vehicle 1.

[0054] The engine 2 is a single-cylinder four-stroke engine. The engine 2 includes a crankshaft 21, a starter generator 22, and a crankshaft forward-rotation ventilation mechanism 23. The crankshaft 21 is supported by an engine main body so as to be capable of rotating in forward and reverse directions. The starter generator 22 is attached to an end portion of the crankshaft 21 with no reduction gear interposed therebetween. The starter generator 22 is configured to rotate the crankshaft 21 in the forward direction or reverse direction in response to a signal from the control device 3.

[0055] In a case where an idle stop condition is established and a combustion operation of the engine 2 is stopped, the crankshaft forward-rotation ventilation mechanism 23 is actuated before the crankshaft 21, which is rotating in the forward direction in a compression stroke due to inertia, reaches the compression top dead center. To be specific, upon actuation of the crankshaft forward-rotation ventilation mechanism 23, an exhaust valve 24 is opened. Consequently, a ventilation between the inside and outside of a combustion chamber 26 is created, so that a pressure in the combustion chamber 26, which has been raised in the compression stroke, is reduced. The crankshaft forward-rotation ventilation mechanism 23 creates the ventilation between the inside and outside of the combustion chamber 26 in a predetermined section during the compression stroke, and then closes the exhaust valve 24 before completion of the compression stroke. Thus, the ventilation between the inside and outside of the combustion chamber 26 is blocked.

[0056] FIG. 1(B) shows the relationship of a torque required to restart the engine, the position of the crankshaft, and the degrees of opening of various valves in the straddled vehicle according to the embodiment. A crank angle position at which the crankshaft 21 stops after the idle stop condition is established and the combustion operation of the engine 2 is stopped is not fixed. In some cases, the crankshaft 21 may stop in a crank angle range R1, which is located after the crankshaft 21 passes through the compression top dead center (crank angle is zero degrees) and before the exhaust valve is opened. Assumed herein is a case where the crankshaft 21 stops at a position P1 in the crank angle range R1. In the crank angle range R1, which is included in an expansion stroke, the exhaust valve 24 and an intake valve 25 are normally closed. If, in this state, a restart condition is established and the crankshaft 21 resumes forward rotation, the inside of the combustion chamber 26 falls into a negative pressure to an extent corresponding to the pressure reduction carried out in the last compression stroke. This increases a torque required to rotate the crankshaft 21 in the forward direction (in the drawing, illustrated with the dashed line in the required torque graph). If the required torque exceeds an output torque of the starter generator 22, a locked state is created.

[0057] Referring to FIG. 1(A), the engine 2 further includes a crankshaft stop ventilation mechanism 27. If the crankshaft 21 having stopped at the position P1 starts rotation again, the crankshaft stop ventilation mechanism 27 opens the intake valve 25. As the intake valve 25 is opened, the ventilation between the inside and outside of the combustion chamber 26 is created, so that the negative pressure inside the combustion chamber 26 is reduced. In other words, the expansion stroke is changed into a low negative pressure expansion stroke in which the negative pressure is reduced as compared to a normal expansion stroke. Consequently, the torque required to rotate the crankshaft in the forward direction is lowered as shown in FIG. 1(B) (in the drawing, illustrated with the solid line in the low negative pressure expansion stroke), so that creation of the locked state is suppressed. The crankshaft stop ventilation mechanism 27 closes the intake valve 25 before the crankshaft 21 reaches a crank angle position at which the exhaust valve 24 is opened in the low negative pressure expansion stroke.

[0058] If the restart condition is established while the crankshaft 21 is stopped at the position P1, the control device 3 rotates the crankshaft 21 in the reverse direction once in the low negative pressure expansion stroke, and then rotates the crankshaft 21 in the forward direction (in the drawing, (i) of the crankshaft position). Here, the control device 3 rotates the crankshaft 21 in the reverse direction such that the crankshaft 21 does not go beyond the compression top dead center (crank angle is zero degrees) in the low negative pressure expansion stroke. In this case, a long crankshaft run-up section is obtained extending over substantially the entire section of the low negative pressure expansion stroke and subsequent exhaust and intake strokes. This enables the crankshaft 21 to pass through the next compression top dead center (crank angle is 720 degrees), to restart the engine 2. It may be possible that the control device 3 rotates the crankshaft 21 in the forward direction without rotating it in the reverse direction (in the drawing, (ii) of the crankshaft position).

[0059] A case of the straddled vehicle 1 including a single-cylinder engine has been described above. Alternatively, the straddled vehicle 1 may include a two-cylinder engine.

[0060] FIG. 2 shows the relationship of a torque required to restart an engine, the position of a crankshaft, and the degrees of opening of various valves in a case where the straddled vehicle according to the embodiment includes a two-cylinder engine. In the embodiment, the crankshaft is of a 270-degree crank. In the drawing, the piston is positioned at the compression top dead center in a first combustion chamber when the crank angle is zero degrees, and the piston is positioned at the compression top dead center in a second combustion chamber when the crank angle is 270 degrees. In the graph showing the degrees of opening of the valves in FIG. 2, the dashed lines indicate the degrees of opening of the exhaust valve, the intake valve, and valves included in the crankshaft forward-rotation ventilation mechanism and the crankshaft stop ventilation mechanism in the first combustion chamber; and the solid lines indicate the degrees of opening of the exhaust valve, the intake valve, and valves included in the crankshaft forward-rotation ventilation mechanism and the crankshaft stop ventilation mechanism in the second combustion chamber.

[0061] Suppose the idle stop condition is established and the crankshaft 21 stops at a position (the position P1 in the crank angle range R1) near a position of passing through 270 degrees in crank angle. In this case, the second combustion chamber is in the middle of the expansion stroke. In this case, the crankshaft stop ventilation mechanism 27 reduces a negative pressure of the second combustion chamber. As a result, the same effects as described above are obtained.

[0062] The foregoing description illustrates things until the restart of the engine 2 having been stopped by the idling-stop function. It may be acceptable that the control device 3, after restarting the engine 2, controls the starter generator 22 and the engine 2 so as to add a driving force of the starter generator 22 to a driving force of the engine 2.

[0063] The embodiments and variations, of which at least either one of description or illustration has been given herein, are for ease of understanding the present disclosure, and not for limiting the concept of the present disclosure. The foregoing embodiments and variations may be altered and / or adapted without departing from the spirit of the present disclosure. The spirit encompasses equivalent elements, modifications, omissions, combinations (for example, a combination of features of any embodiment and any variation), adaptations and / or alterations as would be appreciated by those skilled in the art based on the embodiments disclosed herein. The limitations in the Claims are to be broadly interpreted based on the language employed in the Claims and not limited to embodiments and variations described herein or during the prosecution of the present application. The embodiments and variations are to be construed as non-exclusive. For example, in this Description, the terms "preferably," "may," and "possible," are non-exclusive and mean "preferably, but not limited to," "may, but not limited to," and "possibly, but not limited to," respectively.Reference Signs List

[0064] 1: straddled vehicle 2: engine 21: crankshaft 22: starter generator 23: crankshaft forward-rotation ventilation mechanism 24: exhaust valve 25: intake valve 26: combustion chamber 27: crankshaft stop ventilation mechanism 3: control device P1: stop position of crankshaft R1: crank angle range in which crankshaft stops

Claims

1. A straddled vehicle comprising: a single-cylinder or two-cylinder engine including a crankshaft, a starter generator, and a crankshaft forward-rotation ventilation mechanism, the crankshaft being capable of rotating in forward and reverse directions, the starter generator being capable of rotating the crankshaft in the forward and reverse directions, the crankshaft forward-rotation ventilation mechanism being configured to, while an idle stop condition is established and a combustion operation is stopped but the crankshaft is rotating in the forward direction, create a ventilation between the inside and outside of a combustion chamber before a compression top dead center is reached, and subsequently block the ventilation between the inside and outside of the combustion chamber before the compression top dead center is reached, the single-cylinder or two-cylinder engine being brought into a post-idle-stop restarting locked state when in order: the idle stop condition is established, the crankshaft stops in a crank angle range that is after the crankshaft passes beyond the compression top dead center, and is ahead of an exhaust valve being opened, and then a restart condition is established; the post-idle-stop restarting locked state being where a torque required to rotate the crankshaft in the forward direction exceeds a torque that the starter generator gives to the crankshaft; and a control device, the engine further including a crankshaft stop ventilation mechanism configured to create a ventilation between the inside and outside of the combustion chamber when in order: after the idle stop condition is established, the combustion operation of the engine is stopped, the crankshaft rotating in the forward direction passes through the compression top dead center, and the crankshaft is in any one of the following stages in the crank angle range before the exhaust valve is opened; the crankshaft is about to stop while in the state of rotation, the crankshaft is in a stopped state, or the crankshaft has again started rotation; the control device being configured for removal of the post-idle-stop restarting locked state and restart the engine when in order: the idle stop condition is established, the crankshaft stops in the crank angle range that is after the crankshaft passes beyond the compression top dead center, and is ahead of the exhaust valve being opened, and then the restart condition is established, the removal being implemented by acceleration of forward rotation of the crankshaft in a low negative pressure expansion stroke for post-idle-stop restarting, the forward rotation of the crankshaft having been started by the starter generator without any reverse direction rotation of the crankshaft or after rotating the crankshaft in the reverse direction so as not to go beyond the compression top dead center, the low negative pressure expansion stroke for post-idle-stop restarting being where a negative pressure inside the combustion chamber is reduced before stroke completion by the ventilation between the inside and outside of the combustion chamber created by the crankshaft stop ventilation mechanism, the acceleration being carried out in at least a part of a crankshaft run-up section for post-idle-stop restarting, the crankshaft run-up section being composed of: a section from start of the forward rotation of the crankshaft to completion of the low negative pressure expansion stroke for post-idle-stop restarting; and exhaust stroke; and intake stroke, each being subsequent to the low negative pressure expansion stroke for post-idle-stop restarting.

2. The straddled vehicle according to claim 1, wherein the starter generator is attached to the crankshaft with no reduction gear interposed therebetween; the post-idle-stop restarting locked state is where a torque required to rotate the crankshaft in the forward direction exceeds a torque that the starter generator, attached to the crankshaft without interposition of the reduction gear, gives to the crankshaft when in order: the idle stop condition is established, the crankshaft stops in the crank angle range that is after the crankshaft passes beyond the compression top dead center, and is ahead of the exhaust valve being opened, and then the restart condition is established; and the control device is configured for removal of the post-idle-stop restarting locked state and restart the engine when in order: the idle stop condition is established, the crankshaft stops in the crank angle range that is after the crankshaft passes beyond the compression top dead center, and is ahead of the exhaust valve being opened, and then the restart condition is established, the removal being implemented by acceleration of forward rotation of the crankshaft in the low negative pressure expansion stroke for post-idle-stop restarting, the forward rotation of the crankshaft having been started by the starter generator giving a torque to the crankshaft without interposition of any reduction gear, the acceleration being carried out in at least a part of the crankshaft run-up section for post-idle-stop restarting.

3. The straddled vehicle according to claim 1 or 2, wherein the control device is configured to control both the engine and the starter generator such that, when in order: the idle stop condition is established, the crankshaft stops in the crank angle range that is after the crankshaft passes beyond the compression top dead center, and is ahead of the exhaust valve being opened, and then the restart condition is established, the control device implements removal of the post-idle-stop restarting locked state and restarts the engine by, in the low negative pressure expansion stroke for post-idle-stop restarting, acceleration of forward rotation of the crankshaft having been started by the starter generator, the acceleration being carried out in at least a part of the crankshaft run-up section for post-idle-stop restarting; and subsequently the control device further accelerates the forward rotation of the crankshaft having been accelerated in at least the part of the crankshaft run-up section for post-idle-stop restarting, while the control device performs an electric power-running control on the starter generator, to add a driving force of the starter generator to a driving force of the engine.

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