WO2015001715A1

WO2015001715A1 - Engine system and saddle-straddling type motor vehicle

Info

Publication number: WO2015001715A1
Application number: PCT/JP2014/003040
Authority: WO
Inventors: Kosei Maebashi; Tetsuhiko Nishimura
Original assignee: Yamaha Hatsudoki Kabushiki Kaisha
Priority date: 2013-07-03
Filing date: 2014-06-06
Publication date: 2015-01-08
Also published as: TW201512517A

Abstract

An engine includes a decompression mechanism. The decompression mechanism is configured to be switchable between an operation state in which a gas in a cylinder is exhausted, so that a pressure in the cylinder is reduced, and a non-operation state in which the gas in the cylinder is not exhausted. The engine is controlled in a normal mode in which the ignition of a fuel-air mixture by an ignition device is performed, and in an idle stop mode in which the ignition of the fuel-air mixture by the ignition device is not performed. In the idle stop mode, the decompression mechanism is controlled in a state of being kept in the non-operation state such that the rotation of a crank shaft is stopped.

Description

ENGINE SYSTEM AND SADDLE-STRADDLING TYPE MOTOR VEHICLE

The present invention relates to an engine system and a saddle-straddling type motor vehicle that includes the engine system.

In recent years, in a saddle-straddling type motor vehicle such as a motorcycle, technique that automatically performs an idle stop has been developed. Specifically, when a vehicle is temporarily stopped to wait at the traffic light or the like, an engine is automatically stopped. Thereafter, when the vehicle starts moving, the engine is automatically re-started. In order to prevent deterioration in driving performance, the re-start after the idle stop is required to be performed in a short period of time as compared to the normal start-up. Therefore, it is suggested to keep a fuel-air mixture in a combustion chamber at the time of stopping the engine, and perform the ignition of the fuel-air mixture compressed in a first compression stroke after the re-start (see JP 4419655 B, for example).

An object of the present invention is to provide an engine system that can quickly perform re-start of an engine, and a saddle-straddling type motor vehicle that includes the engine system.

This object is achieved by an engine system according to claim 1, and by a saddle-straddling type motor vehicle according to claim 12.

The inventors of the present invention recognized that a conventional engine control device as it is described in JP 4419655 B has some drawbacks. A decompression mechanism is used in order to improve the startability of the engine. The decompression mechanism reduces the pressure in a cylinder in a compression stroke. Thus, the piston easily goes over a compression top dead center. Therefore, it is possible to easily start the engine without using a large-size starter motor.

When the decompression mechanism is automatically controlled, the decompression mechanism is generally controlled based on a rotation speed of a crank shaft. Specifically, the decompression mechanism operates when the rotation speed of the crank shaft is lower than a threshold value, so that the pressure inside of the cylinder is reduced. On the other hand, when the rotation speed of the crank shaft is not less than the threshold value, the decompression mechanism does not operate.

When the decompression mechanism is controlled in this manner, however, a stop position for the crank shaft is not stable at the time of an idle stop, and the rotation of the crank shaft is likely to be stopped in other than the compression stroke. Therefore, it may not be possible to quickly perform the re-start after the idle stop. Specifically, the rotation of the crank shaft is stopped in other than the compression stroke, whereby it may require some time until the first ignition time point arrives. Further, when the rotation of the crank shaft is stopped with an intake port or an exhaust port being open, the fuel-air mixture cannot be kept in the combustion chamber, and the first ignition after the re-start cannot be appropriately performed.

(1) According to one aspect of the present invention, an engine system includes an engine, and a controller configured to control the engine, the engine includes a cylinder, an ignition device configured to ignite a fuel-air mixture in a combustion chamber in the cylinder, a first detection subject (a first subject for detection) provided to be rotated together with a crank shaft, a first detector provided to detect the first detection subject, and a decompression mechanism configured to be switchable between an operation state in which a gas in the cylinder is exhausted such that a pressure in the cylinder is reduced, and a non-operation state in which the gas in the cylinder is not exhausted, wherein the controller is configured to be capable of controlling the engine in a normal mode in which ignition of the fuel-air mixture by the ignition device is performed and in an idle stop mode in which the ignition of the fuel-air mixture by the ignition device is not performed, the ignition device is controlled to ignite the fuel-air mixture compressed in a first compression stroke after a change from the idle stop mode to the normal mode based on detection of the first detection subject by the first detector, and the decompression mechanism is controlled in a state of being kept in the non-operation state in the idle stop mode such that rotation of the crank shaft is stopped.

In the engine system, the engine is controlled in the normal mode and the idle stop mode. In the normal mode, the fuel-air mixture compressed in the combustion chamber is ignited by the ignition device. Thus, the crank shaft is driven to be rotated. At the time of an engine start-up, the decompression mechanism is kept in the operation state, whereby the pressure in the cylinder is reduced. Thus, the rotational load of the crank shaft is reduced, and the piston easily goes over the pressure top dead center. Therefore, the engine can be smoothly started.

After the change from the normal mode to the idle stop mode, the ignition of the fuel-air mixture is stopped. Thus, the rotation speed of the crank shaft is gradually reduced, and the rotation of the crank shaft is stopped. In this case, because the decompression mechanism is kept in the non-operation state, the rotational load of the crank shaft is not reduced. Therefore, the rotation of the crank shaft can be stopped in the compression stroke in which the rotational load is increased.

Because the intake port and the exhaust port are both closed in the compression stroke, the fuel-air mixture can be kept in the combustion chamber in a period in which the rotation of the crank shaft is stopped. Further, after the change from the idle stop mode to the normal mode, the first opportunity instantly arrives. Thus, the engine can be quickly re-started.

(2) The engine may further include a rotation member, a reference detection subject (a reference subject for detection), a plurality of second detection subjects (second subjects for detection) and a second detector, the rotation member may be rotated together with the crank shaft, the reference detection subject and the plurality of second detection subjects may be arranged at the rotation member in a rotation direction of the rotation member, and the plurality of second detection subjects may include a detection subject for ignition, the first detection subject may be provided at the rotation member to be arranged at a position different from the reference detection subject and the plurality of second detection subjects in a direction along a rotation axis of the rotation member, the first detector may be provided at a first fixed position to be capable of detecting the first detection subject at the time of rotation of the rotation member, the second detector may be provided at a second fixed position to be capable of sequentially detecting the reference detection subject and the plurality of second detection subjects at the time of rotation of the rotation member, the first fixed position may be different from the second fixed position in the direction along the rotation axis of the rotation member, the first detection subject may be arranged to be detected by the first detector in the compression stroke, the reference detection subject may be arranged to be detected by the second detector in any one stroke of an intake stroke, an expansion stroke and an exhaust stroke, the controller may be capable of identifying detection of the detection subject for ignition by the second detector based on detection of the reference detection subject by the second detector, and may be capable of identifying detection of the detection subject for ignition by the second detector based on detection of the first detection subject by the first detector in a case in which the first detection subject is detected by the first detector before the reference detection subject is first detected by the second detector after rotation is started in an engine stop state, and the ignition device may be controlled to ignite the fuel-air mixture compressed in the compression stroke in response to detection of the identified detection subject for ignition.

In the above-mentioned configuration, the crank shaft is rotated, so that the rotation member is rotated. At the time of the rotation of the rotation member, the first detection subject is detected in the compression stroke by the first detector. Further, at the time of the rotation of the rotation member, the reference detection subject and the plurality of second detection subjects are sequentially detected by the second detector. In this case, the reference detection subject is detected in any one stroke of the intake stroke, the expansion stroke and the exhaust stroke.

The plurality of second detection subjects include the detection subject for ignition. In the normal mode, the detection of the detection subject for ignition by the second detector is identified based on the detection of the reference detection subject by the second detector. The ignition of the fuel-air mixture compressed in the compression stroke is performed in response to the detection of the identified detection subject for ignition. Thus, the series of operation including the intake, the compression, the expansion and the exhaustion is repeated.

At the time of changing from the idle stop mode to the normal mode, the first detection subject is detected in the first compression stroke by the first detector before the reference detection subject is first detected by the second detector after the rotation of the crank shaft is started in the engine stop state. Thus, the detection of the detection subject for ignition by the second detector is quickly identified based on the detection of the first detection subject by the first detector before the reference detection subject is detected. The ignition device is controlled to ignite the fuel-air mixture compressed in the first compression stroke in response to the detection of the identified detection subject for ignition. Thus, the engine re-start can be quickly performed.

(3) A fuel injection device of the engine may be controlled such that the fuel-air mixture is kept in the combustion chamber when rotation of the crank shaft is stopped in the idle stop mode. That is, in a period from the time when the idle stop mode is started until the time when the rotation of the crank shaft is stopped, the ignition by the ignition device is stopped, and the injection of the fuel by the fuel injection device is performed.

In this case, at the time of the change from the idle stop mode to the normal mode, the first explosion can be efficiently generated. Thus, the engine can be quickly re-started.

(4) The engine may further include a third detector provided to detect a rotation speed of the crank shaft, and the decompression mechanism may be controlled to be kept in the operation state in a period from a time when the rotation of the crank shaft is started in the normal mode until a time when a rotation speed detected by the third detector reaches a predetermined first value, and to be switched from the operation state to the non-operation state when a rotation speed detected by the third detector reaches the first value.

In this case, the pressure in the cylinder is reduced at the time of the engine start-up by the decompression mechanism. Thus, because the piston easily goes over the compression top dead center, the engine can be smoothly started.

Whereas, because the rotation of the crank shaft is stopped with the decompression mechanism being kept in the non-operation state in the idle stop mode, the rotation of the crank shaft can be stopped in the compression stroke. Therefore, at the time of the change from the idle stop mode to the normal mode, the engine can be quickly re-started.

(5) The decompression mechanism may be controlled to be kept in the non-operation state in a period in which the rotation speed detected by the third detector is not more than a predetermined second value in the idle stop mode.

In this case, even if the rotation speed of the crank shaft is reduced in the idle stop mode, the decompression mechanism is not switched to the operation state. Therefore, the rotation of the crank shaft can be stably stopped in the compression stroke. Therefore, at the time of the change from the idle stop mode to the normal mode, the engine can be quickly re-started.

(6) The decompression mechanism may be controlled to be kept in the non-operation state in a period of the idle stop mode.

In this case, even if the rotation speed of the crank shaft is reduced in the idle stop mode, the decompression mechanism is not switched to the operation state. Therefore, the rotation of the crank shaft can be stably stopped in the compression stroke. Therefore, the engine can be quickly re-started at the time of the change from the idle stop mode to the normal mode.

(7) The engine may be a single-cylinder engine. In the single-cylinder engine, the rotational load of the crank shaft in the compression stroke is large as compared to the multi-cylinder engine. Therefore, the decompression mechanism is kept in the non-operation state, whereby the rotation of the crank shaft is likely to be stopped in the compression stroke. On the other hand, in the single-cylinder engine, if the first explosion fails at the first opportunity for the ignition, it is necessary to rotate the crank shaft twice until the next opportunity for the ignition arrives. In the present invention, because the rotation of the crank shaft can be stopped in the compression stroke in the idle stop mode, and the first explosion can be appropriately generated at the first opportunity for the ignition at the time of the change from the idle stop mode to the normal mode, the engine re-start can be quickly performed.

(8) The controller may change from the normal mode to the idle stop mode when a predetermined idle stop condition is satisfied. In this case, the controller can be changed from the normal mode to the idle stop mode at an appropriate time point.

(9) The idle stop condition may include a condition that relates to at least one of a throttle opening (a degree of opening), a vehicle speed and an engine rotation speed. In this case, the controller can be appropriately changed from the normal mode to the idle stop mode according to at least one of the throttle opening, the vehicle speed and the rotation speed of the engine.

(10) The controller may change from the idle stop mode to the normal mode when a predetermined re-start condition is satisfied. In this case, the controller can change from the idle stop mode to the normal mode at an appropriate time point.

(11) The re-start condition may include a condition that relates to the throttle opening. In this case, the controller can appropriately change from the idle stop mode to the normal mode according to the throttle opening.

(12) According to another aspect of the present invention, a saddle-straddling type motor vehicle includes a main body that has a drive wheel, and the above-mentioned engine system that generates power for rotating the drive wheel.

In the saddle-straddling type motor vehicle, the drive wheel is rotated by the power generated by the engine system. Thus, the main body is moved. In this case, because the above-mentioned engine system is used, the engine can be quickly re-started.

The present invention enables the engine to be quickly re-started.

FIG. 1 is a schematic side view showing the schematic configuration of a motorcycle according to one embodiment of the present invention. FIG. 2 is an external perspective view showing the configuration of a handle. FIG. 3 is a schematic diagram for explaining the configuration of an engine. FIG. 4 is a schematic side view for explaining a crank angle detection mechanism. Fig. 5 is a development diagram of an outer peripheral surface of a rotor. Fig. 6 is a timing chart showing the relation between a position of a piston that changes in one cycle, and crank pulses and re-start pulses generated in the one cycle. Fig. 7 is a block diagram showing a control system of the motorcycle. Fig. 8 is a timing chart showing the one control example of the engine 10 by a normal mode and an idle stop mode. Fig. 9 is a diagram for explaining the operation of a decompression mechanism. Fig. 10 is a diagram for explaining the operation of the decompression mechanism. Fig. 11 is a diagram for explaining the operation of the decompression mechanism.

An engine system and a saddle-straddling type motor vehicle that includes the engine system according to embodiments of the present invention will be described below.

(1) Motorcycle
Fig. 1 is a schematic side view showing the schematic configuration of a motorcycle according to one embodiment of the present invention. The motorcycle of the present embodiment is one example of the saddle-straddling type motor vehicle. In the following description, the front, the rear, the left, and the right mean the front, the rear, the left, and the right based on a viewpoint of a rider of the motorcycle.

In the motorcycle 100 of Fig. 1, a front fork 2 is provided at a front portion of a vehicle body 1 to be swingable to the right and the left. A handle 4 is attached to an upper end of the front fork 2, and a front wheel 3 is attached to a lower end of the front fork 2 to be rotatable.

A seat 5 is provided at an upper portion of substantially the center of the vehicle body 1. A control device 6 and an engine 10 are provided below the seat 5. In the present embodiment, the control device 6 is an ECU (Electronic Control Unit), for example, and the engine 10 is a four-stroke single-cylinder engine. An engine system ES is constituted by the control device 6 and the engine 10. A rear wheel 7 is attached to a lower portion of the rear end of the vehicle body 1 to be rotatable. The rear wheel 7 is driven to be rotated by the power generated by the engine 10.

Fig. 2 is an external perspective view showing the configuration of the handle 4. In Fig. 2, appearance of the handle 4 viewed from the rider who is seated on the seat 5 is shown. As shown in Fig. 2, the handle 4 includes a handle bar 40 that laterally extends. A grip 41 is provided at the left end of the handle bar 40, and an accelerator grip 42 is provided at the right end of the handle bar 40. The accelerator grip 42 is provided to be rotatable in a predetermined range of a rotation angle with respect to the handle bar 40. The accelerator grip 42 is operated, whereby an opening degree of a below-mentioned throttle valve SL (Fig. 3) is adjusted.

A brake lever 43 for operating the brake of the rear wheel 7 (Fig. 1) is arranged in front of the grip 41, and a brake lever 44 for operating the brake of the front wheel 3 (Fig. 1) is arranged in front of the accelerator grip 42. The handle bar 40 is covered by a handle cover 45. A starter switch 46 for starting the engine 10 (Fig. 1) is provided at a portion of the handle cover 45 that is adjacent to the accelerator grip 42.

Further, a speed meter 47, an engine rotation speed meter 48, various types of switches and the like are provided at the handle cover 45. Further, a main switch (not shown) is provided below the handle cover 45. The main switch is operated by the rider in order to supply electric power from a battery to an electrical system such as the control device 6.

Fig. 3 is a schematic diagram for explaining the configuration of the engine 10. As shown in Fig. 3, the engine 10 includes a cylinder CY, a piston 11, a connecting rod 12, a crank shaft 13 and a starter motor 14. Further, the engine 10 includes an intake valve 15, an exhaust valve 16, a valve driver 17, a decompression mechanism DE, an ignition device 18, an injector 19, a crank angle detection mechanism 60 and a throttle opening sensor SE1.

The piston 11 is provided to be capable of reciprocating in the cylinder CY, and is connected to the crank shaft 13 via the connecting rod 12. The reciprocating motion of the piston 11 is converted into the rotational motion of the crank shaft 13. The starter motor 14 and a rotor 61 are attached to the crank shaft 13.

The starter motor 14 rotates the crank shaft 13 at the time of the start-up of the engine 10. A crank angle detection mechanism 60 includes the rotor 61, a crank angle sensor SE11 and a reference angle sensor SE12. The rotor 61 is fixed to the crank shaft 13. Thus, at the time of the rotation of the crank shaft 13, the rotor 61 is integrally rotated with the crank shaft 13 around a rotation axis C of the crank shaft 13. Further, the rotor 61 has an outer peripheral surface 61a that is formed to extend along a circle with the rotation axis C of the crank shaft 13 used as a center. The crank angle sensor SE11 and the reference angle sensor SE12 are arranged in the vicinity of the rotor 61. A rotation position (a crank angle) of the crank shaft 13 is detected by the crank angle detection mechanism 60.

Further, a generator (not shown) is attached to the crank shaft 13. The generator generates electrical power by the rotation of the crank shaft 13. A battery (not shown) is charged by the generated electrical power. The electrical power stored in the battery is supplied to each constituent element of the motorcycle 100. The rotor included in the generator may be used as the above-mentioned rotor 61.

A combustion chamber 31 is partitioned by the cylinder CY and the piston 11. The combustion chamber 31 communicates with an intake passage 22 through an intake port 21, and communicates with an exhaust passage 24 through an exhaust port 23. The intake valve 15 is provided to open and close the intake port 21, and the exhaust valve 16 is provided to open and close the exhaust port 23. The intake valve 15 and the exhaust valve 16 are driven by the valve driver 17. The valve driver 17 is a cam shaft that is rotated in conjunction with the crank shaft 13, for example. A hydraulic valve mechanism, an electromagnetic valve mechanism or the like may be used as the valve driver 17.

The decompression mechanism DE includes a solenoid actuator, for example, and is configured to be capable of separately driving an exhaust valve 16 from the valve driver 17. This decompression mechanism DE reduces the pressure in the combustion chamber 31 by lifting the exhaust valve 16.

In the following description, the function that reduces the pressure in the combustion chamber 31 by the decompression mechanism DE is referred to as decompression function. That the decompression function is turned on means that the exhaust valve 16 is lifted by the decompression mechanism DE, and that the decompression function is turned off means that the exhaust valve 16 is not lifted by the decompression mechanism DE. In any one of the case in which the decompression function is turned on, and the case in which the decompression function is turned off, the lifting operation of the exhaust valve 16 by the valve driver 17 is separately performed from the lifting operation of the exhaust valve 16 by the decompression mechanism DE.

The throttle valve SL for adjusting a flow rate of air that flows in from outside is provided at the intake passage 22. As described above, the accelerator grip 42 of Fig. 2 is operated, whereby the opening degree of the throttle valve SL (hereinafter referred to as a throttle opening) is adjusted. A throttle opening sensor SE1 is arranged in the vicinity of the throttle valve SL. The throttle opening sensor SE1 detects the throttle opening.

The ignition device 18 includes an ignition coil 18a and an ignition plug 18b, and is configured to ignite a fuel-air mixture in the combustion chamber 31. The ignition coil 18a is connected to the ignition plug 18b. The ignition coil 18a stores electrical energy for generating spark discharge at the ignition plug 18b.

A fuel pump (not shown) is connected to the injector 19. The injector 19 is configured to inject the fuel supplied from the fuel pump to the intake passage 22. In the present embodiment, the injector 19 is arranged such that the fuel is injected toward the intake port 21.

(2) Crank Angle Detection Mechanism
Fig. 4 is a schematic side view for explaining the crank angle detection mechanism 60, and Fig. 5 is a development diagram of the outer peripheral surface 61a of the rotor 61. In Fig. 5, the outer peripheral surface 61a of the rotor 61 is shown as a strip-shaped plane. The crank shaft 13 and the rotor 61 are rotated in a direction indicated by the thick arrows of Figs. 4 and 5 during the rotation of the engine 10. In the following description, the direction in which the thick arrows of Figs. 4 and 5 are directed toward is referred to as a rotation direction RD.

As shown in Fig. 5, the outer peripheral surface 61a of the rotor 61 is divided into substantially equal regions R1, R2 with a boundary line BL that extends in a circumferential direction held therebetween. A toothless portion N is set at a predetermined position in the region R1 of the outer peripheral surface 61a of the rotor 61. Details of the position at which the toothless portion N is set will be described below.

As shown in Figs. 4 and 5, in the region R1 of the outer peripheral surface 61a, detection subjects P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11 are sequentially provided to line up from the toothless portion N along the boundary line BL at constant intervals. On the other hand, in the region R2 of the outer peripheral surface 61a, a detection subject PS is provided to be adjacent to one (the detection subject P9 in the present example) of the detection subjects P1 to P11 in a direction parallel with a rotation axis C (hereinafter referred to as an axis direction).

The detection subjects P1 to P11, PS are projections that are formed to project a constant height from the outer peripheral surface 61a. A projection is not present at the toothless portion N. The detection subject PS is integrally formed with the detection subject P9. Further, the detection subjects P1 to P11, PS have a common width W in the circumferential direction of the outer peripheral surface 61a of the rotor 61, and a common length L in the axis direction. Further, each of the detection subjects P1 to P11, PS has a front end f that is positioned on the downstream side, and a rear end b that is positioned on the upstream side in the rotation direction RD.

As shown in Fig. 4, in the present example, the rear ends b of the detection subjects P1 to P11 are arranged on the outer peripheral surface 61a of the rotor 61 at angular intervals of 30 degrees with respect to the rotation axis C. The angular interval between the rear end b of the detection subject P11 and the rear end b of the detection subject P1 that are arranged to sandwich the toothless portion N therebetween is 60 degrees.

The crank angle sensor SE11 and the reference angle sensor SE12 are constituted by an electromagnetic pickup or an optical pick up, for example, and are fixed to a crank case (not shown).

As described above, the detection subjects P1 to P11 are arranged to line up along the boundary line BL that extends in the circumferential direction of the outer peripheral surface 61a of the rotor 61, and the detection subject PS is arranged to be adjacent to the detection subject P9 in the axis direction. Therefore, at the time of the rotation of the rotor 61, the detection subjects P1 to P11 move on the common trajectory, and the detection subject PS moves on a trajectory different from the trajectory of the detection subjects P1 to P11.

The crank angle sensor SE11 outputs an electric signal that corresponds to an object that passes through the detection region SR1. The crank angle sensor SE11 is arranged such that the detection region SR1 is positioned on the trajectory on which the detection subjects P1 to P11 move. Thus, the detection subjects P1 to P11 sequentially pass through the detection region SR1 at the time of the rotation of the rotor 61. In this case, after the front end f of each detection subject P1 to P11 enters the detection region SR1, its rear end b enters the detection region SR1. The crank angle sensor SE11 outputs pulses that respectively correspond to the front end f and the rear end b when the front end f and the rear end b of each detection subject P1 to P11 pass through the detection region SR1. A crank pulse is generated by a below-mentioned crank pulse generating circuit 74 (Fig. 7) based on the pulse that is output when the rear end b of each detection subject P1 to P11 passes through the detection region SR1.

A reference angle sensor SE12 outputs an electric signal that corresponds to an object that passes through the detection region SR2. The reference angle sensor SE12 is arranged such that the detection region SR2 is positioned on the trajectory on which the detection subject PS moves. Further, relative positions of the crank angle sensor SE11 and the reference angle sensor SE12 are set such that the detection region SR2 is spaced apart from the detection region SR1 by an angular interval that is larger than 90 degrees and smaller than 120 degrees in a direction opposite to the rotation direction RD. At the time of the rotation of the rotor 61, the detection subject PS passes through the detection region SR2. In this case, after the front end f of the detection subject PS enters the detection region SR2, its rear end b enters the detection region SR2. The reference angle sensor SE12 outputs pulses that respectively correspond to the front end f and the rear end b when the front end f and the rear end b of the detection subject PS pass through the detection region SR2. A re-start pulse is generated by a below-mentioned re-start pulse generating circuit 75 (Fig. 7) based on the pulse that is output when the rear end b of the detection subject PS passes through the detection region SR2.

As described above, the detection subjects P1 to P11 and the detection subject PS are arranged at positions different from each other in a direction along the rotation axis C. Therefore, the trajectory on which the toothless portion N and the detection subjects P1 to P11 move, and the trajectory on which the detection subject PS moves are different. In this case, because the detection region SR1 of the crank angle sensor SE11 is positioned on the trajectory of the detection subjects P1 to P11, false detection of the detection subject PS by the crank angle sensor SE11 is prevented. Further, because the detection region SR2 of the reference angle sensor SE12 is positioned on the trajectory of the detection subject PS, false detection of the detection subjects P1 to P11 by the reference angle sensor SE12 is prevented.

Fig. 6 is a timing chart showing the relation between the position of the piston 11 that changes during one cycle, and the crank pulses and the re-start pulses generated during the one cycle in the engine 10 of Fig. 3.

In the following description, rotating the engine 10 first by the starter switch 46 (rotating the crank shaft 13) is referred to as a start-up of the engine 10. Further, rotating the engine 10 (rotating the crank shaft 13) first after the engine 10 is stopped in a below-mentioned idle stop mode is referred to as a re-start of the engine 10. Further, a top dead center through which the piston 11 passes at the time of changing from a compression stroke to an expansion stroke is referred to as a compression top dead center, and a top dead center through which the piston 11 passes at the time of changing from an exhaust stroke to an intake stroke is referred to as an exhaust top dead center. A bottom dead center through which the piston 11 passes at the time of changing from the intake stroke to the compression stroke is referred to as an intake bottom dead center, and a bottom dead center through which the piston 11 passes at the time of changing from the expansion stroke to the exhaust stroke is referred to as an expansion bottom dead center.

First, the start-up of the engine 10 will be described. Generally, in the compression stroke, because the pressure in the cylinder CY increases, the rotational load of the crank shaft 13 increases. Therefore, at the time of stopping the engine 10, the rotation of the crank shaft 13 is likely to be stopped in the compression stroke. Specifically, as indicated by the thick arrow in Fig. 6, the rotation of the crank shaft 13 is likely to be stopped when the piston 11 is positioned at an intermediate point (hereinafter referred to as a compression intermediate point) between the intake bottom dead center and the compression top dead center or a position in the vicinity of the compression intermediate point.

Therefore, at the time of the start-up of the engine 10, the piston 11 moves from the compression intermediate point or a position in the vicinity of the compression intermediate point towards the compression top dead center. Thereafter, the piston 11 sequentially moves to the expansion bottom dead center, the exhaust top dead center and the intake bottom dead center.

The crank pulse is used for controlling a time point for the injection of the fuel and the ignition of the fuel-air mixture. In the four-stroke engine 10, the rotor 61 is rotated two times per one cycle. Thus, the crank pulses that respectively correspond to the detection subjects P1 to P11 are generated two times per one cycle.

In the present example, the toothless portion N is provided at the outer peripheral surface 61a of the rotor 61 to pass through the detection region SR1 right before the piston 11 reaches the bottom dead center. The angular interval between the rear end b of the detection subject P11 and the rear end b of the detection subject P1 is larger than the angular interval between the rear end b of a detection subject Pn (n is an integer that is not less than 1 and not more than 10) and the rear end b of the detection subject Pn+1. Thus, as shown in Fig. 6, the interval between the crank pulses that respectively correspond to the detection subjects P11, P1 is large as compared to the interval between the crank pulses that respectively correspond to the detection subjects Pn, Pn+1. Therefore, that the toothless portion N passes through the detection region SR1 is detected based on the interval between the each two adjacent crank pulses.

In the present example, the detection subjects P1 to P11 sequentially pass through the detection region SR1 after the toothless portion N passes through the detection region SR1. Therefore, the crank pulses that are generated after the detection of the toothless portion N are counted, whereby the detection subjects P1 to P11 that pass through the detection region SR1 are identified. Thus, the position of the piston 11 is determined based on the crank pulse. That is, the rotation position (the crank angle) of the crank shaft 13 is detected.

As described above, because the pressure in the cylinder CY rapidly increases in the compression stroke, the rotational load of the crank shaft 13 increases. Therefore, the rotation speed of the engine 10 is likely to be unstable when the piston 11 is positioned at the compression top dead center or a position in the vicinity of the compression top dead center. On the other hand, the rotation speed of the engine 10 is relatively stable when the piston 11 is positioned at the bottom dead center or a position in the vicinity of the bottom dead center. In the present example, as described above, the position of the toothless portion N is set such that the toothless portion N passes through the detection region SR1 right before the piston 11 reaches the bottom dead center. Thus, the toothless portion N can be detected with a high degree of accuracy regardless of the rotation speed of the engine 10.

As described above, the rotation position (the crank angle) of the crank shaft 13 is detected, whereby the injection of the fuel by the injector 19 (Fig. 3) is performed in the exhaust stroke at a time point at which the crank pulse that corresponds to the detection subject P5 is generated. In this case, the fuel-air mixture is produced in the intake passage 22, and the fuel-air mixture is introduced from the intake passage 22 to the combustion chamber 31 in the following intake stroke. Further, the energization to the ignition coil 18a (Fig. 3) is started in the compression stroke at a time point at which the crank pulse that corresponds to the detection subject P6 is generated. Thereafter, the energization to the ignition coil 18a (Fig. 3) is stopped at a time point at which the crank pulse that corresponds to the detection subject P7 is generated. At this time, the ignition plug 18b (Fig. 3) generates spark discharge. In this manner, the ignition of the fuel-air mixture by the ignition device 18 is performed right before the piston 11 reaches the compression top dead center.

Next, the re-start of the engine 10 will be described. Even at the time of stopping the engine 10 in the idle stop mode, the piston 11 is positioned at the compression intermediate point or in the vicinity of the compression intermediate point. Therefore, at the time of the re-start of the engine 10, similarly to the start-up of the engine 10, the piston 11 moves from the compression intermediate point or a position in the vicinity of the compression intermediate point towards the compression top dead center.

As described below, the injection of the fuel by the injector 19 is performed in a plurality of cycles including the cycle right before the engine 10 is stopped in the idle stop mode. Therefore, the fuel-air mixture is kept in the combustion chamber 31 after the stop and before the re-start of the engine 10.

The positional relation between the detection subject PS and the detection region SR2 is set such that the re-start pulse is generated after the piston is started to move and before a time point at which the fuel-air mixture is to be ignited. Specifically, the positional relation between the detection subject PS and the detection region SR2 is set such that the detection subject PS passes through the detection region SR2 after the piston 11 is started to move from the compression intermediate point or a position in the vicinity of the compression intermediate point, and before the detection subject P6 passes through the detection region SR1. In the present example, the detection subject PS is arranged at the outer peripheral surface 61a of the rotor 61 such that the detection subject PS passes through the detection region SR2 in a period from the time when the detection subject P5 passes through the detection region SR1 until the time when the detection subject P6 passes through the detection region SR1 (see Fig. 5).

In this case, after the detection subject PS passes through the detection region SR2, the detection subject P6 passes through the detection region SR1 first, and the detection subject P7 passes through the detection region SR1 second. That is, the first crank pulse after the generation of the re-start pulse corresponds to the detection subject P6, and the second crank pulse corresponds to the detection subject P7. Therefore, the crank pulse is counted after the generation of the re-start pulse, whereby the detection subjects P6, P7 that pass through the detection region SR1 are quickly identified. Thus, in the first compression stroke after the change from the idle stop mode to the normal mode, the ignition of the fuel-air mixture by the ignition device 18 is performed based on the crank pulses that respectively correspond to the detection subjects P6, P7.

The positional relation between the detection subject PS and the detection region SR2 is set as described above, whereby the detection subject PS is arranged to be detected by the reference angle sensor SE12 when the piston 11 is positioned between the compression intermediate point and the compression top dead center in the present example.

The rotation speed of the crank shaft 13 is low right after the re-start of the engine 10. Therefore, even when the rotation speed of the crank shaft 13 is temporarily reduced in the compression stroke because the piston 11 approaches the compression top dead center from the compression intermediate point, the detection subject PS is accurately detected by the reference angle sensor SE12. Therefore, the detection subject PS is likely to be detected in the first compression stroke by the reference angle sensor SE12 before the toothless portion N is first detected by the crank angle sensor SE11 after the rotation of the crank shaft 13 is started in a state in which the engine 10 is stopped. Thus, the quick re-start of the engine 10 can be stably performed.

(3) Control System of Motorcycle
Fig. 7 is a block diagram showing the control system of the motorcycle 100 of Fig. 1. As shown in Fig. 7, the control device 6 of Fig. 1 includes a CPU (Central Process Unit) 71, a ROM (Read Only Memory) 72, a RAM (Random Access Memory) 73, a crank pulse generating circuit 74 and a re-start pulse generating circuit 75.

A vehicle speed sensor SE2 that detects a traveling speed is provided at the motorcycle 100 of Fig. 1. The signals that are respectively output from the starter switch 46, the throttle opening sensor SE1, the vehicle speed sensor SE2 and the main switch (not shown) are supplied to the CPU 71.

The crank pulse generating circuit 74 generates the crank pulse based on the pulse that is output from the crank angle sensor SE11. The crank pulse generated by the crank pulse generating circuit 74 is supplied to the CPU 71.

The re-start pulse generating circuit 75 generates the re-start pulse based on the pulse output from the reference angle sensor SE12. The re-start pulse generated by the re-start pulse generating circuit 75 is supplied to the CPU 71.

The ROM 72 stores control program of the CPU 71 and the like. The RAM 73 stores various data, and functions as a process area of the CPU 71. The CPU 71 realizes the function of an engine controller 111, a mode determiner 112 and a decompression controller 113 by operating the control program stored in the ROM 72.

The engine controller 111 operates the starter motor 14 at the time of the start-up and the re-start of the engine 10. Further, the engine controller 111 supplies the injection pulse (Fig. 8) that instructs the injector 19 the injection of the fuel, and supplies the ignition pulse (Fig. 8) that instructs the ignition device 18 to ignite. The injection pulse is generated in response to the detection of the rear end b of the detection subject P5 (the generation of the crank pulse that corresponds to the detection subject P5) by the crank angle sensor SE11 (Fig. 4). The ignition pulse is generated in response to the detection of the rear end b of the detection subjects P6, P7 (the generation of the crank pulses that correspond to the detection subjects P6, P7) by the crank angle sensor SE11 (Fig. 4).

In the present example, the energization to the ignition coil 18a (Fig. 3) is started in response to a falling edge of the ignition pulse, and the energization to the ignition coil 18a (Fig. 3) is stopped in response to the rising edge of the ignition pulse. Further, the injector 19 may start the injection of the fuel in response to the falling edge of the injection pulse, and the injector 19 may stop the injection of the fuel in response to the rising edge of the injection pulse. In this case, the injection amount of the fuel can be appropriately adjusted.

The engine controller 111 controls the engine 10 in any one mode of the below-mentioned normal mode and the idle stop mode. In the following description, the condition for the engine controller 111 to change from the normal mode to the idle stop mode is referred to as an idle stop condition. Further, the condition for the engine controller 111 to change from the idle stop mode to the normal mode is referred to as a re-start condition.

The mode determiner 112 determines whether or not the idle stop condition is satisfied in a state in which the engine 10 is controlled by the normal mode. The idle stop condition includes the condition that relates to at least one of the throttle opening, the vehicle speed and the engine rotation speed. The idle stop condition is that the throttle opening detected by the throttle opening sensor SE1 is 0, the travelling speed (the vehicle speed) of the motorcycle 100 is 0, and the rotation speed of the engine 10 is larger than 0 rpm and not more than 2500 rpm, for example. Further, the idle stop condition may include another condition such as that the brake levers 43, 44 (Fig. 2) are operated and the like.

Further, the mode determiner 112 determines whether or not the re-start condition is satisfied in a state in which the engine 10 is controlled in the idle stop mode. The re-start condition includes the condition that relates to the throttle opening. The re-start condition is that the throttle opening detected by the throttle opening sensor SE1 is larger than 0, for example. Further, the re-start condition may include another condition such as that the operation of the brake levers 43, 44 (Fig. 2) is released and the like.

The decompression controller 113 switches on and off of the decompression function by controlling the decompression mechanism DE according to the rotation speed of the engine 10. In the present embodiment, the decompression controller 113 controls the decompression mechanism DE such that the rotation of the crank shaft 13 is stopped in a state in which the decompression function is turned off in the idle stop mode. The rotation speed of the engine 10 (the rotation speed of the crank shaft 13) is detected based on the crank pulse generated by the crank pulse generating circuit 74.

While each of the engine controller 111, the mode determiner 112 and the decompression controller 113 is realized by hardware and software in the example of Fig. 7, the invention is not limited to this. Each of the engine controller 111, the mode determiner 112 and the decompression controller 113 may be realized by hardware such as an electronic circuit, and part of these may be realized by hardware such as a CPU and a memory, and software such as computer program.

(4) Normal Mode and Idle Stop Mode
As described above, the engine controller 111 of Fig. 7 controls the engine 10 in the normal mode or the idle stop mode. Fig. 8 is a timing chart showing one control example of the engine 10 by the normal mode and the idle stop mode. In Fig. 8, the rotation speed of the engine 10 is shown in the upper column, the injection pulse is shown in the middle column and the ignition pulse is shown in the lower column.

In the example of Fig. 8, the engine 10 is controlled in the normal mode from a time point t0 to a time point t1. In the normal mode, the engine controller 111 respectively supplies the injection pulse and the ignition pulse to the injector 19 and the ignition device 18 every one cycle. Thus, the fuel-air mixture is introduced into the combustion chamber 31 in the intake stroke of each cycle, the fuel-air mixture is compressed in the combustion chamber 31 in the compression stroke and the fuel-air mixture is combusted in the expansion stroke.

At the time point t1, when the above-mentioned idle stop condition is satisfied, the engine controller 111 changes from the normal mode to the idle stop mode. In the idle stop mode, the engine controller 111 does not generate the ignition pulse. In this case, because the combustion of the fuel-air mixture is not performed, the rotation speed of the engine 10 is gradually reduced, and the rotation of the engine 10 is stopped at a time point t2.

In the example of Fig. 8, in the plurality (three cycles in the present example) of cycles right before the time point t2 at which the engine 10 is stopped, the engine controller 111 supplies the injection pulse to the injector 19. Thus, the rotation of the crank shaft 13 is stopped in a state in which the fuel-air mixture is kept in the combustion chamber 31.

The fuel is injected in the plurality of cycles, whereby the combustion chamber 31 can be sufficiently wetted by the fuel by the last cycle in which the rotation of the crank shaft 13 is stopped. Thus, the fuel-air mixture can be appropriately led into the combustion chamber 31 in the last cycle, and the fuel-air mixture can be kept in the combustion chamber 31 at the time of the idle stop. Further, even if there are variations in the number of cycles until the rotation of the crank shaft 13 is stopped in the idle stop mode, the fuel is not injected in the last cycle and the rotation of the crank shaft 13 is prevented from being stopped.

The cycle in which the fuel is injected in the idle stop mode may be determined in advance by an experiment or the like, or may be appropriately determined according to the traveling state of the motorcycle 100 or the like.

At a time point t3, when the above-mentioned re-start condition is satisfied, the engine controller 111 changes from the idle stop mode to the normal mode.

(5) Operation of Decompression Mechanism DE
Figs. 9 to 11 are diagrams for explaining the operation of the decompression mechanism DE. In Fig. 9, an example of switching on and off of the decompression function at the time of the start-up of the engine 10 is shown. In Fig. 10, an example of switching on and off of the decompression function in the idle stop mode is shown. In Fig. 11, an example of switching on and off of the decompression function at the time of the re-start of the engine 10 is shown. In each of Figs. 9 to 11, the rotation speed of the engine 10 is shown in the upper column, and the turn-on and turn-off of the decompression function is shown in the lower column.

In the example of Fig. 9, in a period from a time point t10 to a time point t11, the rotation of the engine 10 is stopped. In this period, the decompression function is kept turned off. At the time point t11, the starter switch 46 is operated, whereby the engine 10 is started and the decompression function is switched to turn-on. That is, the decompression mechanism is switched to an operation state at the time of the engine start-up. Thus, the rotation speed of the engine 10 increases. At a time point t12, when the rotation speed of the engine 10 reaches a specified value TH1, the decompression function is switched to turn-off. The specified value TH1 is the rotation speed in a state in which the rotation of the engine 10 is stable, and is determined in advance by an experiment or simulation.

In this manner, at the time of the start-up of the engine 10, the decompression function is switched to turn-on, whereby the piston 11 (Fig. 3) easily goes over the compression top dead center, and the engine 10 can be smoothly started. Thereafter, when the rotation of the engine 10 is stable, the decompression function is turned off. Thus, the energy loss due to the decompression function is eliminated, and the energy can be efficiently generated in the engine 10.

In the example of Fig. 10, because the engine 10 is controlled in the idle stop mode, the rotation speed of the engine 10 is gradually reduced in a period from a time point t20 to a time point t22. At the time point t21, the rotation speed of the engine 10 is not more than the specified value TH1, and the rotation of the engine 10 is stopped at the time point t22. In this case, in a period from the time point t20 to the time point t22, and in the period onward, the decompression function is kept turned off.

In this manner, in the idle stop mode, even if the rotation speed of the engine 10 is not more than the specified value TH1, the decompression function is kept turned off. In this case, because the rotational load of the engine 10 in the compression stroke is not reduced, the rotation of the engine 10 is stopped due to the rotational load. That is, the rotation of the engine 10 is stopped in the compression stroke.

In the example of Fig. 11, in a period from a time point t30 to a time point t31, the engine 10 is controlled in the idle stop mode, and the engine 10 is not rotated. At a time point t31, the engine controller 111 changes from the idle stop mode to the normal mode, and the engine 10 is re-started. Thus, the rotation speed of the engine 10 increases. In this case, in a period from the time point t30 to the time point t31 and in the period onward, the decompression function is kept turned off.

At the time of the re-start of the engine 10, because the inside of the combustion chamber 31 is wetted and the temperature of the engine 10 is high, the piston 11 can relatively easily go over the compression top dead center. In particular, in the present example, because the ignition is performed right before the piston 11 reaches the compression top dead center, the piston 11 easily goes over the compression top dead center. Therefore, at the time of the re-start of the engine 10, the necessity for turning on the decompression function is low.

Further, the decompression function is kept turned off, whereby the fuel-air mixture kept in the combustion chamber 31 is not exhausted from the exhaust port 23, and a state in which the fuel-air mixture is kept in the combustion chamber 31 is maintained until the first opportunity for ignition arrives. Thus, the re-start of the engine 10 can be appropriately performed.

Note that, if the re-start of the engine 10 can be appropriately performed, the decompression function may be turned on at the time of the re-start of the engine 10 similarly to at the time of the start-up of the engine 10.

Further, when the rotation of the engine 10 is stopped in other than the idle stop mode (in a case in which the main switch is turned off, for example), the decompression function may be kept turned off similarly to the example of Fig. 10, or the decompression function may be turned on at a time point at which the rotation speed of the engine 10 is less than the specified value TH1.

(6) Effects
In the engine system ES according to the present embodiment, the decompression mechanism DE is controlled in the idle stop mode such that the rotation of the crank shaft 13 (the rotation of the engine 10) is stopped in a state in which the decompression function is kept turned off. In this case, in the idle stop mode, the rotational load of the crank shaft 13 is not reduced by the decompression function. Therefore, the rotation of the crank shaft 13 can be stopped in the compression stroke in which the rotational load increases.

Because the intake port 21 and the exhaust port 23 are both closed in the compression stroke, the fuel-air mixture can be kept in the combustion chamber 31 in a period in which the rotation of the crank shaft 13 is stopped. Further, after the change from the idle stop mode to the normal mode, the first opportunity for the ignition instantly arrives. Thus, the engine 10 can be quickly re-started.

Further, in the present embodiment, the injector 19 is controlled such that the fuel-air mixture is kept in the combustion chamber 31 when the rotation of the crank shaft 13 is stopped in the idle stop mode. Thus, at the time of the change from the idle stop mode to the normal mode, the first explosion can be efficiently generated. Thus, the engine 10 can be quickly re-started.

Further, in the present embodiment, at the time of the start-up of the engine 10, the decompression function is kept turned on until the rotation speed of the crank shaft 13 reaches the specified value TH1. Thus, because the piston 11 easily goes over the compression top dead center, the engine 10 can be smoothly started. Thereafter, when the rotation of the engine 10 is stable, the decompression function is turned off. Thus, the energy loss due to the decompression function is eliminated, and the energy can be efficiently generated in the engine 10.

On the other hand, in the idle stop mode, even if the rotation speed of the crank shaft 13 is not more than the specified value TH1, the decompression function is kept turned off. Thus, the rotation of the crank shaft 13 can be stopped in the compression stroke. Therefore, at the time of the change from the idle stop mode to the normal stop mode, the engine 10 can be quickly re-started.

Further, in the present embodiment, a single-stroke engine is used as the engine 10. In the single-stroke engine, the rotational load of the crank shaft 13 in the compression stroke is large as compared to a multi-cylinder engine. Therefore, the decompression function is kept turned off, whereby the rotation of the crank shaft 13 is more likely to be stopped in the compression stroke. On the other hand, in the single-stroke engine, if the first explosion fails at the first opportunity for the ignition, it is necessary to rotate the crank shaft 13 twice until the next ignition opportunity arrives. In the present embodiment, because the rotation of the crank shaft 13 can be stopped in the compression stroke, and the first explosion can be appropriately generated in the first period for the ignition at the time of the change from the idle stop mode to the normal mode, the re-start of the engine 10 can be quickly performed.

(7) Other Embodiments
(7-1)
While the decompression function is turned on only at the time of the start-up of the engine 10 in the above-mentioned embodiment, the decompression function may be turned on in another period. However, the decompression mechanism DE is controlled such that the decompression function is not turned on under a constant condition. In this case, the rotation of the crank shaft 13 is stopped in a state in which the decompression function is kept turned off in the idle stop mode. For example, the decompression mechanism DE may be controlled such that the decompression function is kept turned off in a period in which the rotation speed of the engine 10 is not more than the specified value TH1 in the idle stop mode. Alternatively, the decompression mechanism DE may be controlled such that the decompression function is kept turned off in an entire period of the idle stop mode.

(7-2)
While the decompression function is continuously turned on in a period until the rotation speed of the engine 10 reaches the specified value TH1 at the time of the start-up of the engine 10 in the above-mentioned embodiment, the invention is not limited to this. For example, the decompression function may be turned on only in the compression stroke during the above-mentioned period, or the decompression function may be turned on only from the latter half of the compression stroke to the anterior half of the expansion stroke in the above-mentioned period.

(7-3)
While the decompression mechanism DE is separately provided from the valve driver 17 in the above-mentioned embodiment, the invention is not limited to this. The decompression mechanism DE may be integrally provided with the valve driver 17. For example, a decompression cam for realizing the decompression mechanism may be provided at the cam shaft. In this case, the cam shaft is configured to be switchable between a state in which the decompression cam works on the exhaust valve 16 and the decompression cam does not work on the exhaust valve 16.

(7-4)
While the decompression mechanism DE lifts the exhaust valve 16, so that the pressure in the combustion chamber 31 is reduced in the above-mentioned embodiment, the invention is not limited to this. For example, a gas exhauster for exhausting the gas in the combustion chamber 31 may be separately provided from the exhaust port 23, and the gas in the combustion chamber 31 is exhausted from the gas exhauster, whereby the pressure in the combustion chamber 31 is reduced.

(7-5)
While the injector 19 is configured to inject the fuel into the intake passage 22 in the above-mentioned embodiment, the invention is not limited to this. The injector 19 may be configured to inject the fuel into the combustion chamber 31.

(7-6)
While the rear wheel 7 is driven by the engine 10 in the above-mentioned embodiment, the invention is not limited to this. The front wheel 3 may be driven by the engine 10.

(7-7)
While the above-mentioned embodiment is an example in which the present invention is applied to the engine system ES that includes a single-stroke engine, the invention is not limited to this. The present invention may be applied for another engine system that includes a multiple-stroke engine.

(7-8)
While the above-mentioned embodiment is an example in which the present invention is applied to the motorcycle, the invention is not limited to this. The present invention may be applied to another saddle-straddling type motor vehicle such as a motor tricycle, an ATV (All Terrain Vehicle) or the like.

(7-9)
In the above-mentioned embodiment, the toothless portion N that passes through the detection region SR1 is detected in order to identify the detection subjects P1 to P11 that pass through the detection region SR1. The configuration to be detected in order to identify the detection subjects P1 to P11 is not limited to the toothless portion N. A projection for identification that has a detectable shape to be differentiated from the detection subjects P1 to P11 by the crank angle sensor SE11 may be provided in the region R1 of the outer peripheral surface 61a of the rotor 61. As the projection for identification, a projection that has a width W larger than the detection subjects P1 to P11 in a circumferential direction (or a projection that has a smaller width W in the circumferential direction) or the like can be used, for example.

(8) Correspondences between Constituent Elements in Claims and Parts in Preferred Embodiments
In the following paragraphs, non-limiting examples of correspondences between various elements recited in the claims below and those described above with respect to various preferred embodiments of the present invention are explained.

In the above-mentioned embodiment, the engine system ES is an example of an engine system, the engine 10 is an example of an engine, the control device 6 is an example of a controller, the cylinder CY is an example of a cylinder, the ignition device 18 is an example of an ignition device, the detection subject PS is an example of a first detection subject, the reference angle sensor SE12 is an example of a first detector and the decompression mechanism DE is an example of a decompression mechanism. Further, a state in which the decompression mechanism is turned on is an example of an operation state, and a state in which the decompression state is turned off is an example of a non-operation state.

Further, the rotor 61 is an example of a rotation member, the toothless portion N is an example of a reference detection subject, the detection subjects P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11 are examples of a plurality of second detection subjects, the crank angle sensor SE11 is an example of second and third detectors, the detection subject P6 is an example of a detection subject for ignition, the rotation axis C of the crank shaft 13 is an example of a rotation axis of a rotation member and the injector 19 is an example of a fuel injection device. Further, the motorcycle 100 is an example of a saddle-straddling type motor vehicle, the rear wheel 7 is an example of a drive wheel and the vehicle body 1 is an example of a main body.

As each of constituent elements recited in the claims, various other elements having configurations or functions described in the claims can be also used.

The present invention can be effectively utilized for various types of vehicles.

Claims

An engine system comprising:
an engine; and
a controller configured to control the engine,
the engine comprising:
a cylinder;
an ignition device configured to ignite a fuel-air mixture in a combustion chamber in the cylinder;
a first detection subject provided to be rotated together with a crank shaft;
a first detector provided to detect the first detection subject; and
a decompression mechanism configured to be switchable between an operation state in which a gas in the cylinder is exhausted such that a pressure in the cylinder is reduced, and a non-operation state in which the gas in the cylinder is not exhausted, wherein
the controller is configured to be capable of controlling the engine in a normal mode in which ignition of the fuel-air mixture by the ignition device is performed and in an idle stop mode in which the ignition of the fuel-air mixture by the ignition device is not performed,
the ignition device is controlled to ignite the fuel-air mixture compressed in a first compression stroke after a change from the idle stop mode to the normal mode based on detection of the first detection subject by the first detector, and
the decompression mechanism is controlled in a state of being kept in the non-operation state in the idle stop mode such that rotation of the crank shaft is stopped.
The engine system according to claim 1, wherein
the engine further includes a rotation member, a reference detection subject, a plurality of second detection subjects and a second detector,
the rotation member is rotated together with the crank shaft,
the reference detection subject and the plurality of second detection subjects are arranged at the rotation member in a rotation direction of the rotation member, and the plurality of second detection subjects include a detection subject for ignition,
the first detection subject is provided at the rotation member to be arranged at a position different from the reference detection subject and the plurality of second detection subjects in a direction along a rotation axis of the rotation member,
the first detector is provided at a first fixed position to be capable of detecting the first detection subject at the time of rotation of the rotation member,
the second detector is provided at a second fixed position to be capable of sequentially detecting the reference detection subject and the plurality of second detection subjects at the time of rotation of the rotation member,
the first fixed position is different from the second fixed position in the direction along the rotation axis of the rotation member,
the first detection subject is arranged to be detected by the first detector in the compression stroke,
the reference detection subject is arranged to be detected by the second detector in any one stroke of an intake stroke, an expansion stroke and an exhaust stroke,
the controller is capable of identifying detection of the detection subject for ignition by the second detector based on detection of the reference detection subject by the second detector, and is capable of identifying detection of the detection subject for ignition by the second detector based on detection of the first detection subject by the first detector in a case in which the first detection subject is detected by the first detector before the reference detection subject is first detected by the second detector after rotation is started in an engine stop state, and
the ignition device is controlled to ignite the fuel-air mixture compressed in the compression stroke in response to detection of the identified detection subject for ignition.
The engine system according to claim 1 or 2, wherein
a fuel injection device of the engine is controlled such that the fuel-air mixture is kept in the combustion chamber when rotation of the crank shaft is stopped in the idle stop mode.
The engine system according to any one of claims 1 to 3, wherein
the engine further includes a third detector provided to detect a rotation speed of the crank shaft, and
the decompression mechanism is controlled to be kept in the operation state in a period from a time when rotation of the crank shaft is started in the normal mode until a time when a rotation speed detected by the third detector reaches a predetermined first value, and to be switched from the operation state to the non-operation state when a rotation speed detected by the third detector reaches the first value.
The engine system according to claim 4, wherein
the decompression mechanism is controlled to be kept in the non-operation state in a period in which the rotation speed detected by the third detector is not more than a predetermined second value in the idle stop mode.
The engine system according to any one of claims 1 to 4, wherein
the decompression mechanism is controlled to be kept in the non-operation state in a period of the idle stop mode.
The engine system according to any one of claims 1 to 6, wherein
the engine is a single-cylinder engine.
The engine system according to any one of claims 1 to 7, wherein
the controller changes from the normal mode to the idle stop mode when a predetermined idle stop condition is satisfied.
The engine system according to claim 8, wherein
the idle stop condition includes a condition that relates to at least one of a throttle opening, a vehicle speed and an engine rotation speed.
The engine system according to any one of claims 1 to 9, wherein
the controller is configured to change from the idle stop mode to the normal mode when a predetermined re-start condition is satisfied.
The engine system according to claim 10, wherein
the re-start condition includes a condition that relates to the throttle opening.
A saddle-straddling type motor vehicle comprising:
a main body that has a drive wheel; and
the engine system according to any one of claims 1 to 11 configured to generate power for rotating the drive wheel.