WO2016104160A1

WO2016104160A1 - Air-cooled engine unit

Info

Publication number: WO2016104160A1
Application number: PCT/JP2015/084619
Authority: WO
Inventors: 誠脇村
Original assignee: ヤマハ発動機株式会社
Priority date: 2014-12-22
Filing date: 2015-12-10
Publication date: 2016-06-30
Also published as: BR112017013422A2; EP3239505A4; ES2791149T3; TW201625841A; BR112017013422B1; TWI568923B; EP3239505A1; EP3239505B1

Abstract

Provided is an air-cooled engine unit capable of suppressing the degradation of a catalyst, even when the catalyst is arranged near an engine body. This air-cooled engine unit (11) has a compression ratio of 10 or higher, and comprises a catalyst (53) that is arranged in an exhaust gas passage section (51) and arranged near a combustion chamber. The path length of the exhaust gas passage section (51) from an exhaust gas port to the catalyst (53) is shorter than the path length of the exhaust gas passage section (51) from the catalyst (53) to an atmospheric release opening (64a).

Description

Air-cooled engine unit

The present invention relates to an air-cooled engine unit.

For example, an air-cooled engine unit such as Patent Document 1 has a higher temperature of the engine body than a water-cooled engine unit. Therefore, the air-cooled engine unit is more likely to knock than the water-cooled engine unit. Conventionally, in order to prevent knocking, the compression ratio of the air-cooled engine unit is set lower than that of the water-cooled engine unit.

JP-A-10-067372

The air-cooled engine unit has a catalyst that purifies the exhaust gas. The air-cooled engine unit is required to shorten the time until the catalyst changes from the inactive state to the active state. In the following description, the time required for the catalyst to change from the inactive state to the active state is referred to as the time required for the activation of the catalyst. As a method for shortening the time required for the activation of the catalyst, it is conceivable to dispose the catalyst near the engine body. However, the compression ratio of the air-cooled engine unit is low. Therefore, if the catalyst is disposed near the engine body, the catalyst may be overheated and deteriorated by heat.

An object of the present invention is to provide an air-cooled engine unit that can suppress the deterioration of the catalyst even if the catalyst is arranged near the engine body.

Means for Solving the Problems and Effects of the Invention

The engine unit of the present invention has a compression ratio of 10 or more, an engine main body forming at least one combustion chamber, a heat dissipating part that dissipates heat generated in the engine main body from the surface of the engine main body, and the combustion An exhaust port formed in the chamber is connected to an atmospheric discharge port that discharges exhaust gas to the atmosphere, and the inside is disposed in the exhaust passage unit and an exhaust passage unit through which exhaust gas flows from the exhaust port toward the atmospheric discharge port A combustion chamber adjacently arranged catalyst. The path length from the exhaust port of the exhaust passage portion to the upstream end of the catalyst disposed in the vicinity of the combustion chamber is shorter than the path length from the downstream end of the catalyst disposed near the combustion chamber of the exhaust passage portion to the atmosphere discharge port.

The air-cooled engine unit includes an engine body, a heat radiating section, an exhaust passage section, and a combustion chamber adjacently arranged catalyst. The engine body forms at least one combustion chamber. The heat dissipating part dissipates heat generated in the engine body from the surface of the engine body. The exhaust passage section connects an exhaust port formed in the combustion chamber and an atmospheric discharge port for discharging exhaust gas to the atmosphere. In the exhaust passage portion, exhaust gas flows through the interior from the exhaust port toward the atmospheric discharge port. The combustion chamber adjacently arranged catalyst is arranged in the exhaust passage portion. The path length from the exhaust port of the exhaust passage portion to the upstream end of the catalyst adjacent to the combustion chamber is shorter than the path length from the downstream end of the catalyst adjacent to the combustion chamber of the exhaust passage portion to the atmospheric discharge port. That is, the combustion chamber adjacently arranged catalyst is arranged near the engine body. Thereby, the time required for the activation of the catalyst can be shortened.
Generally, an air-cooled engine tends to have a higher temperature of the engine body than a water-cooled engine. However, the air-cooled engine unit of the present invention has a high compression ratio of 10 or more as compared with the conventional air-cooled engine unit. Due to the high compression ratio, the temperature of the exhaust gas discharged from the combustion chamber can be lowered. Therefore, even if the combustion chamber adjacently disposed catalyst is disposed near the engine body, the temperature of the exhaust gas flowing into the combustion chamber adjacently disposed catalyst can be reduced. Therefore, even if the combustion chamber adjacently disposed catalyst is disposed near the engine body, deterioration due to overheating of the combustion chamber adjacently disposed catalyst can be suppressed.

The air-cooled engine unit of the present invention includes a control device that controls the operation of the air-cooled engine unit, and the control device performs the air-cooling when a predetermined idle stop condition is satisfied during operation of the air-cooled engine unit. An idle stop control unit that automatically stops the operation of the engine unit, and when the predetermined restart condition is satisfied while the operation of the air cooling engine unit is stopped by the idle stop control unit, It is preferable to include a restart control unit that restarts the operation of the engine unit.

The control device includes an idle stop control unit and a restart control unit. The idle stop control unit automatically stops the operation of the air-cooled engine unit when a predetermined idle stop condition is satisfied during the operation of the air-cooled engine unit. This stop may be referred to as idle stop. The restart control unit restarts the operation of the air-cooled engine unit when a predetermined restart condition is satisfied in a state where the operation of the air-cooled engine unit is stopped by the idle stop control unit. That is, if a predetermined idle stop condition is satisfied during idling, the operation is automatically stopped. Thereafter, the operation is restarted if a predetermined restart condition is satisfied.
During idling, the temperature of the exhaust gas discharged from the combustion chamber is lowered. The air-cooled engine unit has a high compression ratio. Therefore, the temperature of the exhaust gas discharged from the combustion chamber is further lowered during idling. However, since the air-cooled engine unit performs idle stop, it can prevent the idle state from continuing for a long time. Thereby, it can prevent that the temperature of a catalyst falls rather than activation temperature. As a result, exhaust purification performance can be improved.

The air-cooled engine unit of the present invention controls a knocking sensor that detects knocking of the engine body, an ignition device that ignites fuel in the combustion chamber, and an ignition timing of the ignition device based on a signal of the knocking sensor. And a control device.

According to this configuration, the air-cooled engine unit includes a knocking sensor, an ignition device, and a control device. The knocking sensor detects knocking that occurs in the engine body. The ignition device ignites the fuel in the combustion chamber. The control device controls the ignition timing of the ignition device that ignites the fuel in the combustion chamber based on the signal of the knocking sensor. Specifically, when knocking is detected, the ignition timing is retarded. Thereby, it is possible to prevent large knocking from occurring.
If the compression ratio of the engine body is high, knocking of the engine body tends to occur. However, the air-cooled engine unit includes a knocking sensor, and retards the ignition timing when knocking occurs. Therefore, it is not necessary to retard the ignition timing excessively to prevent knocking. That is, the retard of the ignition timing can be reduced. Thereby, the temperature of the exhaust gas discharged from the combustion chamber can be lowered. Thus, the temperature of the exhaust gas can be lowered while suppressing the retard of the ignition timing. As a result, it is possible to further suppress deterioration due to overheating of the combustion chamber adjacently arranged catalyst while ensuring torque.

An air-cooled engine unit according to the present invention is disposed upstream of the combustion chamber adjacently arranged catalyst in the exhaust passage portion in the exhaust gas flow direction, detects an oxygen concentration of the exhaust gas in the exhaust passage portion, and the combustion It is preferable to include a fuel supply device that supplies fuel into the room and a control device that controls a fuel supply amount of the fuel supply device based on a signal from the oxygen sensor.

According to this configuration, the air-cooled engine unit includes the oxygen sensor, the fuel supply device, and the control device. The oxygen sensor is arranged upstream of the combustion chamber adjacently arranged catalyst in the exhaust passage portion in the exhaust gas flow direction. The oxygen sensor detects the oxygen concentration of the exhaust gas in the exhaust passage. The fuel supply device supplies fuel into the combustion chamber. The control device controls the fuel supply amount of the fuel supply device based on the signal of the oxygen sensor.
If the compression ratio of the engine body is high, the temperature of the exhaust gas will be low. Therefore, the temperature of the oxygen sensor provided in the exhaust passage portion also decreases. If the temperature of the oxygen sensor becomes too low, the oxygen sensor becomes inactive. Thereby, the detection accuracy of the oxygen sensor decreases. However, the oxygen sensor is disposed upstream of the combustion chamber adjacently disposed catalyst disposed near the engine body. That is, the oxygen sensor is arranged closer to the engine body than the combustion chamber adjacently arranged catalyst. Therefore, the temperature of the exhaust gas that contacts the oxygen sensor can be increased. That is, a decrease in the temperature of the oxygen sensor can be suppressed. Therefore, the active state of the oxygen sensor can be maintained. As a result, the accuracy of control of the fuel supply amount can be maintained.

In the air-cooled engine unit of the present invention, an intake port formed in the combustion chamber is connected to an air intake port for sucking air from the atmosphere, and air flows through the interior from the air intake port toward the intake port. An intake passage portion, an ignition device for igniting fuel in the combustion chamber, a fuel supply device for supplying fuel into the combustion chamber, and a combustion chamber adjacently arranged throttle valve provided in the intake passage portion, the intake passage The combustion is disposed at a position where a path length from the atmosphere intake port of the portion to the throttle valve close to the combustion chamber is longer than a path length from the throttle valve close to the combustion chamber of the intake passage portion to the intake port A close proximity throttle valve, a close proximity throttle opening sensor for detecting an open degree of the close proximity throttle valve, and an engine speed detection Control of the fuel supply amount of the fuel supply device and control of the ignition timing of the ignition device are performed based on an engine rotational speed sensor, a signal from the combustion chamber adjacently arranged throttle opening sensor, and a signal from the engine rotational speed sensor. And a control device.

According to this configuration, the air-cooled engine unit includes an intake passage portion, an ignition device, a fuel supply device, a combustion chamber adjacently disposed throttle valve, a combustion chamber adjacently disposed throttle opening sensor, an engine speed sensor, and a control. Device. The intake passage portion connects an intake port formed in the combustion chamber and an air intake port that sucks air from the air. The air flows in the intake passage portion from the air intake port toward the intake port. The ignition device ignites the fuel in the combustion chamber. The fuel supply device supplies fuel into the combustion chamber. The throttle valve close to the combustion chamber is provided in the intake passage portion. The combustion chamber adjacently arranged throttle opening sensor detects the opening of the combustion chamber adjacently arranged throttle valve. The engine rotation speed sensor detects the engine rotation speed. The control device controls the fuel supply amount of the fuel supply device and the ignition timing of the ignition device based on the signal of the throttle opening sensor disposed close to the combustion chamber and the signal of the engine speed sensor.
The path length from the combustion chamber adjacently arranged throttle valve in the intake passage to the intake port is shorter than the path length from the air intake port of the intake passage to the combustion chamber adjacently arranged throttle valve. That is, the combustion chamber adjacently arranged throttle valve is arranged at a position close to the combustion chamber. Therefore, the delay in the change in the amount of air taken into the combustion chamber can be reduced with respect to the change in the opening degree of the throttle valve close to the combustion chamber.
The control device controls the fuel supply amount and the ignition timing based on the signal of the throttle opening sensor disposed close to the combustion chamber. Therefore, it is possible to reduce the delay in controlling the fuel supply and the ignition timing with respect to the change in the opening degree of the throttle valve close to the combustion chamber. As described above, the delay in the change in the amount of air taken into the combustion chamber is small with respect to the change in the opening degree of the throttle valve close to the combustion chamber. Therefore, when the opening degree of the throttle valve close to the combustion chamber changes, the time difference between the change in the fuel supply amount and the ignition timing and the change in the air amount taken into the combustion chamber can be reduced. Therefore, the accuracy of control of the fuel supply amount and the ignition timing can be improved.
In addition, the following effects can be obtained by improving the accuracy of ignition timing control. That is, even if a knocking sensor is not provided, it is possible to reduce an extra retard of the ignition timing for preventing knocking. Thereby, the temperature of the exhaust gas can be lowered while suppressing the retard of the ignition timing. As a result, deterioration due to overheating of the catalyst adjacent to the combustion chamber can be suppressed while securing torque.

In the air-cooled engine unit of the present invention, an intake port formed in the combustion chamber is connected to an air intake port for sucking air from the atmosphere, and air flows through the interior from the air intake port toward the intake port. An intake pressure sensor that includes an intake passage and is provided in the intake passage and detects the internal pressure of the intake passage, and an intake air temperature sensor that is provided in the intake passage and detects the temperature in the intake passage It is preferable not to have.

According to this configuration, the air-cooled engine unit does not have the intake pressure sensor that detects the internal pressure of the intake passage portion. Further, the air-cooled engine unit does not have an intake air temperature sensor that detects the temperature in the intake passage portion. Therefore, the intake pressure and the intake temperature are not used for controlling the fuel supply amount and the ignition timing. Therefore, the control of the fuel supply amount and the ignition timing can be simplified.

1 is a left side view of a motorcycle to which an air-cooled engine unit according to an embodiment is applied. It is a schematic diagram of an air-cooled engine unit. It is a cross-sectional schematic diagram of a muffler. It is a control block diagram of an air-cooled engine unit. It is a partial detailed view of the control block of the air-cooled engine unit. It is an intake air amount map corresponding to the throttle opening and the engine speed. It is a graph which shows an example of the relationship between a throttle opening degree, an engine speed, and a basic fuel supply amount. It is a figure which shows the relationship between a throttle opening, an engine speed, and an oxygen feedback control area | region. It is a figure which shows the relationship between a throttle opening, an engine speed, and an oxygen feedback learning area | region. It is a graph which shows an example of the relationship between a throttle opening degree, an engine speed, and basic ignition timing. It is a figure which shows the relationship between a throttle opening, an engine speed, and a knocking control area | region.

Hereinafter, embodiments of the present invention will be described. This embodiment is an example of a motorcycle to which the air-cooled engine unit of the present invention is applied. In the following description, the front-rear direction is the vehicle front-rear direction viewed from a rider seated on a seat 9 (described later) of the motorcycle 1. The left-right direction is the left-right direction of the vehicle when viewed from a rider seated on the seat 9. The vehicle left-right direction is the same as the vehicle width direction. Moreover, the arrow F direction and the arrow B direction in FIG. 1 represent the front and back, and the arrow U direction and the arrow D direction represent the upper side and the lower side.

[Overall structure of motorcycle]
As shown in FIG. 1, the motorcycle 1 of the present embodiment includes a front wheel 2, a rear wheel 3, and a vehicle body frame 4. The vehicle body frame 4 has a head pipe 4a at the front thereof. A steering shaft (not shown) is rotatably inserted into the head pipe 4a. The upper end portion of the steering shaft is connected to the handle unit 5. An upper end portion of a pair of front forks 6 is fixed to the handle unit 5. A lower end portion of the front fork 6 supports the front wheel 2.

The handle unit 5 is provided with a right grip (not shown) and a left grip 12. The right grip is an accelerator grip that adjusts the output of the engine. If the accelerator grip is rotated to the front side of the rider while the rider holds the accelerator grip, the engine output increases. Specifically, the throttle opening increases. Further, when the accelerator grip is rotated to the opposite side, the engine output decreases. Specifically, the throttle opening decreases. A brake lever 13 is provided in front of the left grip 12. A display device 14 is disposed in front of the handle unit 5. Although illustration is omitted, the display device 14 displays the vehicle speed, the engine speed, and the like. The display device 14 is provided with an indicator (indicator light).

A pair of swing arms 7 are swingably supported on the body frame 4. The rear end portion of the swing arm 7 supports the rear wheel 3. One end of the rear suspension 8 is attached to a position behind the swing center of each swing arm 7. The other end of the rear suspension 8 is attached to the vehicle body frame 4.

A seat 9 and a fuel tank 10 are supported on the upper part of the body frame 4. The fuel tank 10 is disposed in front of the seat 9. An air-cooled engine unit 11 is mounted on the body frame 4. The air-cooled engine unit 11 is disposed below the fuel tank 10. The vehicle body frame 4 is mounted with a battery (not shown) that supplies power to electronic devices such as various sensors.

[Configuration of air-cooled engine unit]
The air-cooled engine unit 11 is a natural air-cooled engine. The air-cooled engine unit 11 is a 4-stroke single cylinder engine. The 4-stroke engine is an engine that repeats an intake stroke, a compression stroke, a combustion stroke (expansion stroke), and an exhaust stroke. The air-cooled engine unit 11 includes an engine body 20, an intake unit 40, and an exhaust unit 50.

The engine body 20 includes a crankcase 21, a cylinder body 22, a cylinder head 23, and a head cover 24. The cylinder body 22 is attached to the upper end portion of the crankcase 21. The cylinder head 23 is attached to the upper end portion of the cylinder body 22. The head cover 24 is attached to the upper end portion of the cylinder head 23.

A fin portion 25 is formed on at least a part of the surface of the engine body 20. The fin portion 25 is formed on the surface of the cylinder body 22 and the surface of the cylinder head 23. The fin portion 25 is composed of a plurality of fins. Each fin is formed to protrude from the surface of the engine body 20. The fin portion 25 is formed on substantially the entire circumference of the cylinder body 22 and the cylinder head 23. The fin portion 25 radiates heat generated in the engine body 20. The fin portion 25 corresponds to the heat radiating portion of the present invention.

FIG. 2 is a diagram schematically showing the air-cooled engine unit 11. As shown in FIG. 2, the crankcase 21 houses a crankshaft 26, a starter motor 27, a transmission (not shown), a generator (not shown), and the like. The transmission is a device that changes the ratio between the rotational speed of the crankshaft 26 and the rotational speed of the rear wheel 3. The rotation of the crankshaft 26 is transmitted to the rear wheel 3 via the transmission. The starter motor 27 rotates the crankshaft 26 when the engine is started. The starter motor 27 is operated by electric power from a battery (not shown). The generator generates electric power by the rotational force of the crankshaft 26. The battery is charged with the electric power. Instead of arranging the starter motor 27 and the generator, an ISG (Integrated / Starter / Generator) may be arranged. The ISG is an apparatus in which a starter motor 27 and a generator are integrated.

The crankcase 21 is provided with an engine rotation speed sensor 71 and a knocking sensor 72. The engine rotation speed sensor 71 detects the rotation speed of the crankshaft 26, that is, the engine rotation speed. The engine rotation speed is the rotation speed of the crankshaft 26 per unit time. The knocking sensor 72 detects knocking that occurs in the engine body 20. Knocking is a phenomenon in which a metallic striking sound or striking vibration is generated when abnormal combustion occurs in a combustion chamber 30 described later. Normally, the air-fuel mixture starts to burn after being ignited by spark discharge, and the flame propagates to the surroundings. In the present specification, the air-fuel mixture is an air-fuel mixture. Knocking occurs when an unburned air-fuel mixture that has not reached flame propagation spontaneously ignites in the combustion chamber 30. The configuration of knocking sensor 72 is not particularly limited as long as knocking can be detected.

The cylinder body 22 has a cylinder hole 22a. A piston 28 is slidably accommodated in the cylinder hole 22a. The piston 28 is connected to the crankshaft 26 via a connecting rod 29. The engine body 20 is provided with an engine temperature sensor 73. The engine temperature sensor 73 detects the temperature of the engine body 20. Specifically, the temperature of the cylinder body 22 is detected.

The combustion chamber 30 (see FIG. 2) is formed by the lower surface of the cylinder head 23, the cylinder hole 22a, and the piston 28. In the present specification, the space formed by the lower surface of the cylinder head 23, the cylinder hole 22 a and the piston 28 regardless of the position of the piston 28 is defined as the combustion chamber 30. The compression ratio of the engine body 20 is 10 or more. The compression ratio is a value obtained by dividing the volume of the combustion chamber 30 when the piston 28 is at the bottom dead center by the volume of the combustion chamber 30 when the piston 28 is at the top dead center.

In the combustion chamber 30, the tip of the spark plug 31 is disposed. The tip of the spark plug generates a spark discharge. By this spark discharge, the air-fuel mixture in the combustion chamber 30 is ignited. The spark plug 31 is connected to the ignition coil 32. The ignition coil 32 stores electric power for causing spark discharge of the spark plug 31. A device in which the ignition plug 31 and the ignition coil 32 are combined corresponds to the ignition device of the present invention.

An intake port 33 and an exhaust port 34 are formed on the surface defining the combustion chamber 30 of the cylinder head 23. That is, the intake port 33 and the exhaust port 34 are formed in the combustion chamber 30. The intake port 33 is opened and closed by an intake valve 35. The exhaust port 34 is opened and closed by an exhaust valve 36. The intake valve 35 and the exhaust valve 36 are opened and closed by a valve gear (not shown) housed in the cylinder head 23. The valve gear operates in conjunction with the crankshaft 26.

The air-cooled engine unit 11 has an intake passage portion 41 that connects the intake port 33 and an air intake port 41c facing the atmosphere. In addition, a passage part means the wall body etc. which surround a path | route and form a path | route, and a path | route means the space through which object passes. The air inlet 41c sucks air from the atmosphere. The air sucked from the air suction port 41 c flows in the intake passage 41 toward the intake port 33. A part of the intake passage portion 41 is formed in the engine body 20, and the remaining portion of the intake passage portion 41 is formed in the intake unit 40. The intake unit 40 has an intake pipe connected to the engine body 20. Further, the intake unit 40 includes an injector 42, a throttle valve 45, and a bypass valve 46. In the following description, the upstream and downstream in the air flow direction in the intake passage portion 41 may be simply referred to as upstream and downstream.

The air-cooled engine unit 11 has an exhaust passage portion 51 that connects the exhaust port 34 and the atmospheric discharge port 64a facing the atmosphere. The combustion gas generated in the combustion chamber 30 is discharged to the exhaust passage portion 51 through the exhaust port 34. The combustion gas discharged from the combustion chamber is referred to as exhaust gas. The exhaust gas flows in the exhaust passage 51 toward the atmospheric discharge port 64a. The exhaust gas is discharged to the atmosphere from the air discharge port 64a. A part of the exhaust passage portion 51 is formed in the engine body 20, and the remaining portion of the exhaust passage portion 51 is formed in the exhaust unit 50. The exhaust unit 50 has an exhaust pipe 52 (see FIG. 1) connected to the engine body 20. Further, the exhaust unit 50 includes a catalyst 53 and a muffler 54. The muffler 54 is a device that reduces noise caused by exhaust gas. In the following description, the upstream and downstream in the exhaust gas flow direction in the exhaust passage 51 may be simply referred to as upstream and downstream.

In the intake passage 41, an injector 42 is arranged. The injector 42 injects fuel to the air sucked from the air inlet 41c. More specifically, the injector 42 injects fuel to the air in the intake passage 41. The injector 42 corresponds to the fuel supply device of the present invention. The injector 42 is connected to the fuel tank 10 via the fuel hose 43. A fuel pump 44 is disposed inside the fuel tank 10. The fuel pump 44 pumps the fuel in the fuel tank 10 to the fuel hose 43.

The intake passage portion 41 has a main intake passage portion 41a and a bypass intake passage portion 41b. A throttle valve 45 is provided in the main intake passage portion 41a. The throttle valve 45 is disposed upstream of the injector 42. The bypass intake passage portion 41b is connected to the main intake passage portion 41a so as to bypass the throttle valve 45. That is, the bypass intake passage portion 41b communicates the upstream portion and the downstream portion of the throttle valve 45 of the main intake passage portion 41a. The throttle valve corresponds to the throttle valve close to the combustion chamber of the present invention.

The path formed inside the intake passage 41 is referred to as an intake path. The path length of any part of the intake passage 41 is the length of the path formed inside this part. As shown in FIG. 2, the path length from the air inlet 41c of the intake passage 41 to the throttle valve 45 is defined as a path length D1. A path length from the throttle valve 45 of the intake passage portion 41 to the intake port 33 is defined as a path length D2. The path length D2 is shorter than the path length D1. That is, the throttle valve 45 is disposed at a position close to the combustion chamber 30. A volume from the air inlet 41c of the intake passage 41 to the throttle valve 45 is defined as a volume V1. The volume from the throttle valve 45 of the intake passage 41 to the intake port 33 is defined as a volume V2. The volume V1 is larger than the volume V2.

The throttle valve 45 is connected to an accelerator grip (not shown) via a throttle wire. When the rider rotates the accelerator grip, the opening degree of the throttle valve 45 is changed. The air-cooled engine unit 11 has a throttle opening sensor (throttle position sensor) 74 that detects the opening of the throttle valve 45. Hereinafter, the opening degree of the throttle valve 45 is referred to as a throttle opening degree. The throttle opening sensor 74 outputs a signal representing the throttle opening by detecting the position of the throttle valve 45. The throttle opening sensor 74 corresponds to the throttle opening sensor disposed close to the combustion chamber of the present invention.

A bypass valve 46 is provided in the bypass intake passage 41b. The bypass valve 46 is disposed to adjust the flow rate of air flowing through the bypass intake passage portion 41b. The bypass valve 46 is a manually operated valve. The bypass valve 46 is configured by, for example, an adjustment screw. The bypass intake passage portion 41b is not provided with a valve mechanism whose opening degree is controlled by an ECU 80 described later.

The intake passage 41 is not provided with an intake pressure sensor for detecting the internal pressure of the intake passage 41. The internal pressure of the intake passage 41 is referred to as intake pressure. The intake passage portion 41 is not provided with an intake air temperature sensor that detects the temperature in the intake passage portion 41. The temperature of the air in the intake passage portion 41 is referred to as intake air temperature.

In the exhaust passage 51, a catalyst 53 is disposed. The catalyst 53 corresponds to the combustion chamber adjacently arranged catalyst of the present invention. The catalyst 53 is disposed in the exhaust pipe 52 of the exhaust unit 50 (see FIG. 1). A path formed inside the exhaust passage 51 is referred to as an exhaust path. The path length of any part of the exhaust passage 51 is the length of the path formed inside this part. As shown in FIG. 2, the path length from the exhaust port 34 of the exhaust passage 51 to the upstream end of the catalyst 53 is defined as a path length D3. A path length from the downstream end of the catalyst 53 of the exhaust passage 51 to the atmospheric discharge port 64a is defined as a path length D4. The path length D3 is shorter than the path length D4. That is, the catalyst 53 is disposed at a position close to the combustion chamber 30. A volume from the exhaust port 34 of the exhaust passage 51 to the upstream end of the catalyst 53 is defined as a volume V3. The volume from the downstream end of the catalyst 53 of the exhaust passage 51 to the atmospheric discharge port 64a is defined as a volume V4. The volume V3 is smaller than the volume V4. As shown in FIG. 1, the catalyst 53 is disposed below the engine body 20.

Catalyst 53 is a three-way catalyst. The three-way catalyst is a catalyst that is removed by oxidizing or reducing three substances of hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) in the exhaust gas. The catalyst 53 may be a catalyst that removes any one or two of hydrocarbon, carbon monoxide, and nitrogen oxide. The catalyst 53 may not be a redox catalyst. The catalyst 53 may be an oxidation catalyst or a reduction catalyst that removes harmful substances only by either oxidation or reduction. The catalyst 53 has a configuration in which a noble metal having an exhaust gas purification action is attached to a base material. The catalyst 53 of this embodiment is a metal-based catalyst. The catalyst 53 may be a ceramic-based catalyst.

An oxygen sensor 75 is disposed upstream of the catalyst 53 in the exhaust passage 51. The oxygen sensor 75 detects the oxygen concentration in the exhaust gas. The oxygen sensor 75 outputs a voltage signal corresponding to the oxygen concentration in the exhaust gas. The oxygen sensor 75 outputs a signal having a high voltage value when the air-fuel ratio of the air-fuel mixture is rich, and outputs a signal having a low voltage value when the air-fuel ratio is lean. The rich state refers to a state where fuel is excessive with respect to the target air-fuel ratio. The lean state is a state where air is excessive with respect to the target air-fuel ratio. That is, the oxygen sensor 75 detects whether the air-fuel ratio of the air-fuel mixture is in a rich state or a lean state. The oxygen sensor 75 has a sensor element portion made of a solid electrolyte body mainly composed of zirconia. The oxygen sensor 75 can detect the oxygen concentration when the sensor element unit is heated to a high temperature and becomes activated. Note that a linear A / F sensor that outputs a linear detection signal corresponding to the oxygen concentration of the exhaust gas may be used as the oxygen sensor 75. The linear A / F sensor continuously detects a change in oxygen concentration in the exhaust gas.

The muffler 54 is provided downstream of the catalyst 53 in the exhaust passage 51. As shown in FIG. 3, the muffler 54 has an outer cylinder 60, three pipes 61 to 63 accommodated in the outer cylinder 60, and a tail pipe 64. The inside of the outer cylinder 60 is partitioned into three

expansion chambers

60a, 60b, 60c by two

separators

65, 66. One end of the first pipe 61 is connected to the exhaust pipe 52 (see FIG. 1). The first pipe 61 is inserted inside the third pipe 63 that penetrates the separator 65. A gap is formed between the outer peripheral surface of the first pipe 61 and the inner peripheral surface of the third pipe 63. The first pipe 61 passes through the two

separators

65 and 66. The other end of the first pipe 61 is disposed in the first expansion chamber 60a. The second pipe 62 passes through the two

separators

65 and 66. The second pipe 62 communicates the first expansion chamber 60a and the second expansion chamber 60b. The third pipe 63 communicates the second expansion chamber 60b and the third expansion chamber 60c. The tail pipe 64 communicates the third expansion chamber 60 c and the space outside the outer cylinder 60. The end of the tail pipe 64 is exposed to the outside of the outer cylinder 60. An end portion of the tail pipe 64 forms an atmospheric discharge port 64a. In the muffler 54, the first pipe 61, the first expansion chamber 60a, the second pipe 62, the second expansion chamber 60b, the gap between the third pipe 63 and the first pipe 61, the third expansion chamber 60c, and the tail pipe 64 A path through which the exhaust gas flows is formed in order. The length of the path formed in the muffler 54 is longer than the maximum length of the muffler 54. A sound absorbing material such as glass wool may be disposed between the inner surface of the outer cylinder 60 and the outer surfaces of the pipes 61 to 64, but may not be disposed. The structure inside the muffler 54 is not limited to the structure shown in the schematic diagram of FIG.

As shown in FIG. 4, the air-cooled engine unit 11 has an ECU (Electronic Control Unit) 80 that controls the operation of the air-cooled engine unit 11. The ECU 80 corresponds to the control device of the present invention. The ECU 80 is connected to various sensors such as an engine rotation speed sensor 71, a knocking sensor 72, an engine temperature sensor 73, a throttle opening degree sensor 74, and an oxygen sensor 75. The ECU 80 is connected to the ignition coil 32, the injector 42, the fuel pump 44, the starter motor 27, the display device 14, and the like.

The ECU 80 includes a CPU, a ROM, a RAM, and the like. The CPU executes information processing based on programs and various data stored in the ROM and RAM. Thereby, ECU80 implement | achieves each function of a some function processing part. As shown in FIG. 4, the ECU 80 includes a fuel supply amount control unit 81, an ignition timing control unit 82, an idle stop control unit 83, a restart control unit 84, and the like as function processing units. Further, the ECU 80 has an operation instruction unit 85. The operation instruction unit 85 transmits an operation command signal to the ignition coil 32, the injector 42, the fuel pump 44, the starter motor 27, the generator, the display device 14 and the like based on the information processing result of each function processing unit. . The idle stop control unit 83 and the operation instruction unit 85 correspond to the idle stop control unit 83 of the present invention. The restart control unit 84 and the operation instruction unit 85 correspond to the restart control unit 84 of the present invention.

The fuel supply amount control unit 81 determines the fuel supply amount of the injector 42. The fuel supply amount is a fuel injection amount. More specifically, the fuel supply amount control unit 81 controls the fuel injection time by the injector 42. In order to increase the combustion efficiency and the exhaust gas purification efficiency of the catalyst 53, the air-fuel ratio in the air-fuel mixture is preferably the stoichiometric air-fuel ratio (stoichiometry). The fuel supply amount control unit 81 increases or decreases the fuel supply amount as necessary. For example, until the air-cooled engine unit 11 is warmed up, the fuel supply amount is larger than that in the normal time. Also, during acceleration, the amount of fuel supply is larger than usual in order to increase the output of the air-cooled engine unit 11. Further, the fuel supply is cut during deceleration.

5, the fuel supply amount control unit 81 includes a basic fuel supply amount calculation unit 86, a final fuel supply amount calculation unit 87, and an oxygen feedback learning unit 88. The basic fuel supply amount calculation unit 86 calculates a basic fuel supply amount. The final fuel supply amount calculation unit 87 corrects the basic fuel supply amount calculated by the basic fuel supply amount calculation unit 86 to calculate the final fuel supply amount.

The basic fuel supply amount calculation unit 86 calculates the basic fuel supply amount based on the signal from the throttle opening sensor 74 and the signal from the engine speed sensor 71. The basic fuel supply amount calculation unit 86 calculates the basic fuel supply amount in all opening regions of the opening degree of the throttle valve 45 and all rotation speed regions of the engine rotation speed. The basic fuel supply amount calculation unit 86 calculates a basic fuel supply amount for the region based on the two signals. Specifically, the map shown in FIG. 6 is used for calculating the basic fuel supply amount. The map in FIG. 6 shows the intake air amount (A11, A12... A1n, A21, A22,...) With respect to the throttle opening (K1, K2... Km) and the engine speed (C1, C2... Cn). .., Am1, Am2,... The intake air amount is the mass flow rate of the air that is inhaled. In this map, the intake air amount is set for all opening regions of the throttle opening and all rotation speed regions of the engine rotation speed. This map and other maps described later are stored in the ROM. First, the basic fuel supply amount calculation unit 86 obtains the intake air amount based on the map of FIG. The basic fuel supply amount calculation unit 86 determines a basic fuel supply amount that can achieve the target air-fuel ratio with respect to the intake air amount obtained from the map. FIG. 7 is a graph showing an example of the relationship between the throttle opening, the engine speed, and the basic fuel supply amount.

The final fuel supply amount calculation unit 87 includes an oxygen sensor correction cancellation unit 89, an oxygen sensor correction unit 90, an oxygen feedback learning correction unit 91, and an engine temperature sensor correction unit 92. The oxygen sensor correction unit 90 corrects the basic fuel supply amount based on the signal from the oxygen sensor 75. Control of the fuel supply amount based on the signal from the oxygen sensor 75 is referred to as oxygen feedback control.

The oxygen sensor correction cancellation unit 89 determines whether or not to temporarily cancel the correction of the basic fuel supply amount by the oxygen sensor correction unit 90. That is, the oxygen sensor correction cancellation unit 89 determines whether or not to temporarily cancel the oxygen feedback control. This determination is made based on the signal from the throttle opening sensor 74 and the signal from the engine speed sensor 71.

Specifically, the map shown in FIG. 8 is used for this determination. The map of FIG. 8 displays an oxygen feedback control area associated with the throttle opening and the engine speed. The oxygen feedback control region is a hatched region. As shown in FIG. 8, the oxygen feedback control region does not include a region where the throttle opening is particularly large. The oxygen feedback control region does not include a region where the throttle opening is particularly low and the engine speed is high.

The oxygen sensor correction cancellation unit 89 determines whether or not the signal from the throttle opening sensor 74 and the signal from the engine rotation speed sensor 71 are included in the oxygen feedback control region. When both signals are not included in the oxygen feedback control region, the oxygen sensor correction cancel unit 89 determines to cancel the correction. On the other hand, when both signals are included in the oxygen feedback control region, the oxygen sensor correction cancel unit 89 determines not to cancel the correction.

When the oxygen sensor correction canceling unit 89 determines to cancel the correction, the oxygen sensor correction canceling unit 89 cancels the correction by the oxygen sensor correcting unit 90. The cancellation of the correction by the oxygen sensor correction unit 90 specifically means that the arithmetic processing by the oxygen sensor correction unit 90 is not performed. The cancellation of the correction by the oxygen sensor correction unit 90 may be to execute the following processing. In other words, the oxygen sensor correction unit 90 uses the correction value that is not based on the signal from the oxygen sensor 75 to perform a calculation process that results in the same result as when the correction is not performed. For example, when the oxygen sensor correction unit 90 performs a calculation process for adding a correction value to the basic fuel supply amount, the correction value may be zero.

If the oxygen sensor correction cancellation unit 89 determines not to cancel the correction, the oxygen sensor correction unit 90 corrects the basic fuel supply amount. As described above, the oxygen sensor correction unit 90 corrects the basic fuel supply amount based on the signal from the oxygen sensor 75. Specifically, when the signal from the oxygen sensor 75 indicates a lean state, the basic fuel supply amount is corrected so that the next fuel supply amount increases. On the other hand, when the signal from the oxygen sensor 75 indicates a rich state, the basic fuel supply amount is corrected so that the next fuel supply amount is reduced.

When the oxygen sensor correction cancellation unit 89 cancels the correction by the oxygen sensor correction unit 90, the oxygen feedback learning correction unit 91 corrects the basic fuel supply amount. The oxygen feedback learning correction unit 91 corrects the basic fuel supply amount based on an oxygen feedback environment learning correction value and an oxygen feedback bypass valve learning correction value described later.

The result of correcting the basic fuel supply amount by the oxygen sensor correction unit 90 or the oxygen feedback learning correction unit 91 is referred to as a corrected fuel supply amount. The engine temperature sensor correction unit 92 corrects the corrected fuel supply amount or the basic fuel supply amount based on the signal from the engine temperature sensor 73. The final fuel supply amount calculation unit 87 determines the value corrected by the engine temperature sensor correction unit 92 as the final fuel supply amount. The operation instruction unit 85 operates the fuel pump 44 and the injector 42 based on the final fuel supply amount calculated by the final fuel supply amount calculation unit 87.

The air-cooled engine unit 11 of this embodiment does not include an intake pressure sensor. Therefore, the ECU 80 does not directly grasp a change in atmospheric pressure due to a change in altitude or the like. However, when the atmospheric pressure changes, the intake air amount changes. Further, the ECU 80 does not directly grasp the opening degree of the bypass valve 46 disposed in the bypass intake passage portion 41b. However, when the throttle opening is small, the change in the intake air amount due to the change in the opening of the bypass valve 46 is large. When the throttle opening is large, the change in the intake air amount due to the change in the opening of the bypass valve 46 is small.

When performing oxygen feedback control, even if the intake air amount changes due to a change in the atmospheric pressure or a change in the opening degree of the bypass valve 46, the fuel supply amount can be controlled to an appropriate amount. However, when oxygen feedback control is not performed, in order to control to an appropriate fuel supply amount, it is necessary to perform correction corresponding to changes in atmospheric pressure and changes in the opening degree of the bypass valve 46. Therefore, in the present embodiment, the oxygen feedback learning unit 88 is provided in order to control the fuel supply amount corresponding to the change in the atmospheric pressure and the change in the opening degree of the bypass valve 46. The oxygen feedback learning unit 88 performs oxygen feedback learning. Oxygen feedback learning for learning changes in atmospheric pressure is referred to as oxygen feedback environment learning. The oxygen feed learning for learning the change in the opening degree of the bypass valve 46 is referred to as oxygen feedback bypass valve learning. The oxygen feedback learning includes oxygen feedback environment learning and oxygen feedback bypass valve learning. The oxygen feedback learning unit 88 performs oxygen feedback environment learning and oxygen feedback bypass valve learning once for each operation of the air-cooled engine unit 11. That is, it is performed once each from the start to the stop of the air-cooled engine unit 11.

The map shown in FIG. 9 is used for oxygen feedback learning. The map of FIG. 9 displays an oxygen feedback environment learning area associated with the throttle opening and the engine speed. The map of FIG. 9 displays an oxygen feedback bypass valve learning region associated with the throttle opening and the engine speed. The oxygen feedback environment learning area and the oxygen feedback bypass valve learning area are hatched areas. The oxygen feedback environment learning area and the oxygen feedback bypass valve learning area are included in the oxygen feedback control area shown in FIG.

The oxygen feedback learning unit 88 determines whether the signal of the engine speed sensor 71 and the signal of the throttle opening sensor 74 are in the oxygen feedback environment learning region after the air-cooled engine unit 11 is started. When these two signals are in the oxygen feedback environment learning region, the oxygen feedback learning unit 88 performs oxygen feedback environment learning. Specifically, first, the difference between the final fuel supply amount calculated by performing the oxygen feedback control and the basic fuel supply amount obtained from the map shown in FIG. 6 is calculated. This difference is stored in the ROM or RAM as an oxygen feedback environment learning value. Then, the calculated oxygen feedback environment learning value and the already stored oxygen feedback environment learning value are compared with those having the same throttle opening and engine speed. If the two compared values are different, it can be determined that the atmospheric pressure has changed. Therefore, when the two compared values are different, the oxygen feedback learning unit 88 calculates an oxygen feedback environment learning correction value. The oxygen feedback environment learning correction value is calculated based on the difference between the two oxygen feedback environment learning values compared. The oxygen feedback learning correction unit 91 corrects the basic combustion supply amount based on the oxygen feedback environment learning correction value.

The oxygen feedback learning unit 88 determines whether the signal of the engine speed sensor 71 and the signal of the throttle opening sensor 74 are in the oxygen feedback bypass valve learning region after the air-cooled engine unit 11 is started. When these two signals are in the oxygen feedback bypass valve learning region, the oxygen feedback learning unit 88 performs oxygen feedback bypass valve learning. Specifically, first, the difference between the final fuel supply amount calculated by performing the oxygen feedback control and the basic fuel supply amount obtained from the map shown in FIG. 6 is calculated. This difference is stored in the ROM or RAM as the oxygen feedback bypass valve learning value. Then, the calculated oxygen feedback bypass valve learned value and the already stored oxygen feedback bypass valve learned value are compared with those having the same throttle opening and engine speed. If the two compared values are different, it can be determined that the opening of the bypass valve 46 has changed. Therefore, when the two compared values are different, the oxygen feedback learning unit 88 calculates an oxygen feedback bypass valve learning correction value. The oxygen feedback bypass valve learning correction value is calculated based on the difference between the two compared oxygen feedback bypass valve learning values. The oxygen feedback learning correction unit 91 corrects the basic combustion supply amount based on the oxygen feedback bypass valve learning correction value.

The ignition timing control unit 82 calculates the ignition timing. The ignition timing is the discharge timing of the spark plug 31. The ignition timing is represented by the rotation angle of the crankshaft 26 with respect to the compression top dead center. The compression top dead center is the top dead center of the piston 28 between the compression stroke and the combustion stroke. The minimum advance angle corresponding to the ignition timing at which the torque is maximum is called MBT (Minimummadvance for the Best Torque). Hereinafter, the ignition timing is close to the advance corresponding to MBT, the ignition timing is close to MBT, the ignition timing is on the retard side compared to the advance corresponding to MBT, the ignition timing is later than MBT, And so on. In order to increase fuel consumption and output, it is preferable that the ignition timing is closer to MBT. However, knocking easily occurs in MBT. Therefore, the ignition timing is delayed from MBT. Then, the ignition timing is controlled as close as possible to MBT while preventing large knocking.

The ignition timing control unit 82 includes a basic ignition timing calculation unit 93 and a final ignition timing calculation unit 94. The basic ignition timing calculation unit 93 calculates a basic ignition timing. The final ignition timing calculation unit 94 corrects the basic ignition timing calculated by the basic ignition timing calculation unit 93 to calculate the final ignition timing.

The basic ignition timing calculation unit 93 calculates the basic ignition timing based on the signal from the throttle opening sensor 74 and the signal from the engine speed sensor 71. The basic ignition timing calculation unit 93 calculates the basic ignition timing in all opening regions of the throttle valve 45 and all rotation speed regions of the engine rotation speed. The basic ignition timing calculation unit 93 calculates the basic ignition timing for the region based on the two signals. Specifically, the basic ignition timing is obtained using a map (not shown) in which the basic ignition timing is associated with the throttle opening and the engine speed. In this map, the basic ignition timing is set for all opening regions of the throttle opening and all rotation speed regions of the engine rotation speed. FIG. 10 is a graph showing an example of the relationship among the throttle opening, the engine speed, and the basic ignition timing.

The final ignition timing calculation unit 94 includes a knocking sensor correction cancellation unit 95, a knocking sensor correction unit 96, and an engine temperature sensor correction unit 97. The knocking sensor correction unit 96 corrects the basic ignition timing based on the signal from the knocking sensor 72. Control of the ignition timing based on the signal of the knocking sensor 72 is referred to as knocking control. The knocking sensor correction cancellation unit 95 determines whether or not to cancel the correction by the knocking sensor correction unit 96. That is, the knocking sensor correction cancellation unit 95 determines whether or not to perform knocking control. This determination is made based on the signal from the throttle opening sensor 74 and the signal from the engine speed sensor 71.

Specifically, the map shown in FIG. 11 is used for this determination. In the map of FIG. 11, a knocking control region associated with the throttle opening and the engine speed is displayed. The knocking control region is a hatched region. As shown in FIG. 11, the knocking control region is a region where the throttle opening is particularly large. That is, the knocking control region is a region where the engine load is large.

The knocking sensor correction cancellation unit 95 determines whether or not the signal from the throttle opening sensor 74 and the signal from the engine rotation speed sensor 71 are included in the knocking control region. When both signals are not included in the knocking control region, the knocking sensor correction cancellation unit 95 determines to cancel the correction. On the other hand, when both signals are included in the knocking control region, the knocking sensor correction cancellation unit 95 determines not to cancel the correction.

When the knocking sensor correction cancellation unit 95 determines to cancel the correction, the knocking sensor correction cancellation unit 95 cancels the correction by the knocking sensor correction unit 96. The cancellation of the correction by the knocking sensor correction unit 96 specifically means that the arithmetic processing by the knocking sensor correction unit 96 is not performed. The cancellation of the correction by the knocking sensor correction unit 96 may be to execute the following processing. In other words, the knocking sensor correction unit 96 uses a correction value that is not based on the signal of the knocking sensor 72 to perform a calculation process that results in the same result as when the correction is not performed.

When the knocking sensor correction cancellation unit 95 determines that the correction is not canceled, the knocking sensor correction unit 96 corrects the basic ignition timing. The knocking sensor correction unit 96 corrects the basic ignition timing based on the signal from the knocking sensor 72. Specifically, knocking sensor correction unit 96 first determines the presence or absence of knocking of engine body 20 based on a signal from knocking sensor 72. The determination of the presence or absence of knocking is made based on the peak value of the signal from the knocking sensor 72, for example. When it is determined that knocking is present, the knocking sensor correction unit 96 corrects the basic ignition timing so as to retard the basic ignition timing by a predetermined retardation value. Further, when it is determined that there is no knocking, the knocking sensor correction unit 96 corrects the basic ignition timing to advance by a predetermined advance value. As a result, when there is no knocking, the ignition timing approaches the MBT by a predetermined advance value. When knocking occurs, the ignition timing is delayed from the MBT by a predetermined delay value. Thereby, the occurrence of knocking is suppressed. Therefore, it is possible to improve the output and fuel consumption by preventing the occurrence of large knocking and making the ignition timing as close to MBT as possible.

The result of correcting the basic ignition timing by the knocking sensor correction unit 96 is referred to as corrected ignition timing. The engine temperature sensor correction unit 97 corrects the corrected ignition timing or basic ignition timing based on the signal from the engine temperature sensor 73. The final ignition timing calculation unit 94 determines the value corrected by the engine temperature sensor correction unit 97 as the final ignition timing. The operation instructing unit 85 energizes the ignition coil 32 based on the final ignition timing calculated by the final ignition timing calculating unit 94 to operate the spark plug 31.

The air-cooled engine unit 11 of this embodiment does not include an intake pressure sensor. Therefore, the ECU 80 does not grasp changes in atmospheric pressure due to changes in altitude. However, by performing knocking control in the knocking control region, it is possible to make the ignition timing as close to MBT as possible even when the atmospheric pressure changes. Therefore, fuel consumption and output can be increased.

The idle stop control unit 83 stops the operation of the air-cooled engine unit 11 when a predetermined idle stop condition is satisfied during the operation of the air-cooled engine unit 11. A state in which the operation of the air-cooled engine unit 11 is automatically stopped by the control by the idle stop control unit 83 is set as an idle stop state. When a predetermined idle stop condition is satisfied, the idle stop control unit 83 gives the following command to the operation instruction unit 85. The command is a command for stopping the ignition operation of the spark plug 31 and stopping the fuel supply from the injector 42. Thereby, the operation of the air-cooled engine unit 11 is stopped.

The idle stop condition of this embodiment is that all of the following conditions A1 to A6 continue for a predetermined time. The predetermined time is, for example, 3 seconds.
A1: The throttle opening is a predetermined idle opening range (for example, less than 0.3 °).
A2: The vehicle speed is a predetermined value (for example, 3 km / h) or less.
A3: The engine rotation speed is in a predetermined idle rotation speed range (for example, 2000 rpm or less).
A4: The engine temperature is equal to or higher than a predetermined value (for example, 60 ° C.).
A5: The remaining battery level is equal to or greater than a predetermined value.
A6: The oxygen feedback bypass valve learning is not performed.

In the idle stop state, the ECU 80 turns on the indicator of the display device 14. Thereby, the rider can know that it is in an idle stop state. Further, in the idle stop state, the piston 28 stops at or near the bottom dead center. The ECU 80 injects fuel from the injector 42 in the idle stop state.

The restart control unit 84 restarts the operation of the air-cooled engine unit 11 when a predetermined restart condition is satisfied in the idle stop state. The restart condition of the present embodiment is that the throttle opening is equal to or greater than a predetermined opening. Therefore, the rider can restart the operation of the air-cooled engine unit 11 by operating an accelerator grip (not shown).

The restart control unit 84 instructs the operation instruction unit 85 to operate the starter motor 27 when a predetermined restart condition is satisfied. Thereby, the starter motor 27 is operated. Furthermore, the restart control unit 84 starts control by the fuel supply amount control unit 81 and the ignition timing control unit 82 when a predetermined restart condition is satisfied. Thereby, fuel is injected from the injector 42 and spark discharge of the spark plug 31 is performed, and the operation of the air-cooled engine unit 11 is restarted. More specifically, the ignition timing control unit 82 ignites the fuel supplied to the combustion chamber 30 in the idling stop state at the first compression top dead center after the starter motor 27 is operated. To control. Thereby, the operation of the air-cooled engine unit 11 can be restarted quickly. Furthermore, the noise of the starter motor 27 at the time of restart can be suppressed.

In the idle stop state, the throttle opening is almost fully closed. Therefore, the throttle opening and the engine speed when restarting from the idle stop state are not included in the knocking control region. Therefore, the ignition timing control does not have to be complicated at the time of restart.

As described above, the compression ratio of the engine body 20 of the present embodiment is 10 or more. Table 1 shows an example of exhaust gas temperatures of an air-cooled engine having a compression ratio of 11 and an air-cooled engine having a compression ratio of 9.5. The exhaust temperature in Table 1 indicates the temperature of the exhaust gas at the time when it is discharged from the engine body. As is apparent from Table 1, the higher the compression ratio, the lower the temperature of the exhaust gas. This is because the higher the compression ratio, the higher the thermal efficiency.

In the present embodiment, the operation of the air-cooled engine unit 11 is stopped when a predetermined idle stop condition is satisfied. In the idle operation state, the engine speed is low, so the temperature of the exhaust gas is low. Here, it is assumed that the idle operation state is continued after shifting from the normal operation state to the idle operation state. In this case, the temperature of the catalyst 53 decreases as the exhaust gas whose temperature has decreased passes through the catalyst 53. As described above, in the air-cooled engine, the temperature of the exhaust gas is low in the first place. Therefore, in the idle operation state, the temperature of the exhaust gas becomes considerably low. Therefore, at the time of idling, the temperature of the catalyst 53 may be lowered to a temperature at which it becomes inactive. However, in the present embodiment, when the predetermined idle stop condition is satisfied, the operation of the air-cooled engine unit 11 is stopped, so that the exhaust gas whose temperature has decreased can be prevented from passing through the catalyst 53. Thereby, the temperature of the catalyst 53 can be maintained at a high temperature, and the active state of the catalyst 53 can be maintained.

Table 2 below shows an example of the result of comparing the exhaust gas temperature and the catalyst temperature when the idle operation is stopped and when it is not stopped. The Example in Table 2 shows the result 20 seconds after the idle operation state is stopped. In the embodiment, after shifting from the normal operation state to the idle operation state, the idle operation state is stopped. Moreover, the comparative example in Table 2 shows the result 20 seconds after the transition from the normal operation state to the idle operation. The first temperature in Table 2 indicates the temperature of the exhaust gas in the vicinity of the engine body in the exhaust passage portion. The second temperature in Table 2 indicates the temperature of the exhaust gas upstream of the catalyst in the exhaust passage portion and in the vicinity of the catalyst. As is apparent from Table 2, the temperature of the catalyst can be maintained at a higher temperature by stopping the idle operation state than when continuing the idle operation state.

The air-cooled engine unit 11 of the present embodiment has the following characteristics.
A path length D3 from the exhaust port 34 of the exhaust passage portion 51 to the catalyst 53 is shorter than a path length D1 from the catalyst 53 of the exhaust passage portion 51 to the atmospheric discharge port 64a. That is, the catalyst 53 is disposed near the engine body 20. Thereby, the time required for the activation of the catalyst 53 can be shortened.
In general, an air-cooled engine tends to have a higher temperature of the engine body 20 than a water-cooled engine. However, the air-cooled engine unit 11 of the present embodiment has a higher compression ratio of the engine body 20 of 10 or more than the conventional air-cooled engine unit. Due to the high compression ratio, the temperature of the exhaust gas discharged from the combustion chamber 30 can be lowered. Therefore, even if the catalyst 53 is arranged near the engine body 20, the temperature of the exhaust gas flowing into the catalyst 53 can be reduced. Therefore, even if the catalyst 53 is disposed near the engine body 20, deterioration due to overheating of the catalyst 53 can be suppressed.

The idle stop control unit 83 automatically stops the operation of the air-cooled engine unit 11 when a predetermined idle stop condition is satisfied during the operation of the air-cooled engine unit 11. The restart control unit 84 restarts the operation of the air-cooled engine unit 11 when a predetermined restart condition is satisfied in a state where the operation of the air-cooled engine unit 11 is stopped by the idle stop control unit 83. That is, if a predetermined idle stop condition is satisfied during idling, the operation is automatically stopped. Thereafter, the operation is restarted if a predetermined restart condition is satisfied.
During idling, the temperature of the exhaust gas discharged from the combustion chamber 30 decreases. The air-cooled engine unit 11 of this embodiment has a high compression ratio. Therefore, the temperature of the exhaust gas discharged from the combustion chamber 30 is further lowered during idling. However, since the air-cooled engine unit 11 of the present embodiment performs idle stop, it can prevent the idle state from continuing for a long time. Thereby, it can prevent that the temperature of the catalyst 53 falls below active temperature. As a result, exhaust purification performance can be improved.

The ECU 80 controls the ignition timing of the spark plug 31 that ignites the fuel in the combustion chamber 30 based on the signal from the knocking sensor 72. Specifically, when knocking is detected, the ignition timing is retarded. Thereby, it is possible to prevent large knocking from occurring.
If the compression ratio of the engine body 20 is high, the engine body 20 is likely to knock. However, the air-cooled engine unit 11 of the present embodiment includes the knocking sensor 72 and retards the ignition timing when knocking occurs. Therefore, it is not necessary to retard the ignition timing excessively to prevent knocking. That is, the retard of the ignition timing can be reduced. Thereby, the temperature of the exhaust gas discharged from the combustion chamber 30 can be lowered. Thus, the temperature of the exhaust gas can be lowered while suppressing the retard of the ignition timing. As a result, deterioration due to overheating of the catalyst 53 can be suppressed while securing torque.

The ECU 80 controls the fuel supply amount of the injector 42 based on the signal from the oxygen sensor 75. If the compression ratio of the engine body 20 is high, the temperature of the exhaust gas will be low. Therefore, the temperature of the oxygen sensor 75 provided in the exhaust passage portion 51 also decreases. If the temperature of the oxygen sensor 75 becomes too low, the oxygen sensor 75 becomes inactive. Thereby, the detection accuracy of the oxygen sensor 75 decreases. However, the oxygen sensor 75 of the present embodiment is arranged upstream of the catalyst 53 arranged near the engine body 20. That is, the oxygen sensor 75 is arranged closer to the engine body 20 than the catalyst 53. Therefore, the temperature of the exhaust gas that contacts the oxygen sensor 75 can be increased. That is, a decrease in the temperature of the oxygen sensor 75 can be suppressed. Therefore, the active state of the oxygen sensor 75 can be maintained. As a result, the accuracy of control of the fuel supply amount can be maintained.

The path length D2 from the throttle valve 45 to the intake port 33 in the intake passage 41 is shorter than the path length D1 from the air intake port 41c of the intake passage 41 to the throttle valve 45. That is, the throttle valve 45 is disposed at a position close to the combustion chamber 30. Therefore, the delay in the change in the amount of air taken into the combustion chamber 30 with respect to the change in the opening degree of the throttle valve 45 can be reduced. The ECU 80 controls the fuel supply amount of the injector 42 and the ignition timing of the spark plug 31 based on the signal from the throttle opening sensor 74. Therefore, it is possible to reduce the delay in controlling the fuel supply and the ignition timing with respect to the change in the opening degree of the throttle valve 45. As described above, the delay in the change in the amount of air taken into the combustion chamber 30 is small with respect to the change in the opening degree of the throttle valve 45. Therefore, when the opening degree of the throttle valve 45 changes, the time difference between the change in the fuel supply amount and the ignition timing and the change in the air amount taken into the combustion chamber can be reduced. Therefore, the accuracy of control of the fuel supply amount and the ignition timing can be improved.
In addition, the following effects can be obtained by improving the accuracy of ignition timing control. That is, even if the knocking sensor 72 is not provided, it is possible to reduce the excessive retard of the ignition timing for preventing knocking. Thereby, the temperature of the exhaust gas can be lowered while suppressing the retard of the ignition timing. As a result, deterioration due to overheating of the catalyst adjacent to the combustion chamber can be suppressed while securing torque.

The air-cooled engine unit 11 does not have an intake pressure sensor that detects the internal pressure of the intake passage portion 41. Further, the air-cooled engine unit 11 does not have an intake air temperature sensor that detects the temperature in the intake passage portion 41. Therefore, the intake pressure and the intake temperature are not used for controlling the fuel supply amount and the ignition timing. Therefore, the control of the fuel supply amount and the ignition timing can be simplified.

The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims. Moreover, the example of a change mentioned later can be implemented in combination as appropriate. In the present specification, the term “preferred” is non-exclusive, and means “preferably but not limited to”.

The final fuel supply amount calculation unit 87 may include a correction unit that corrects the fuel supply amount in addition to the oxygen sensor correction unit 90 and the engine temperature sensor correction unit 92. For example, the final fuel supply amount calculation unit 87 may include a correction unit that corrects the fuel supply amount according to the transient characteristics during acceleration / deceleration.

The final ignition timing calculation unit 94 may include a correction unit that corrects the ignition timing in addition to the knocking sensor correction unit 96 and the engine temperature sensor correction unit 97. Further, the final ignition timing calculation unit 94 may not include the engine temperature sensor correction unit 97.

In the above embodiment, the operation of the air-cooled engine unit 11 is stopped when a predetermined idle stop condition is satisfied during idling. However, it is not necessary to stop the operation of the air-cooled engine unit 11 during idling. That is, the ECU 80 does not have to include the idle stop control unit 83 and the restart control unit 84.

In the above embodiment, the catalyst 53 is disposed below the engine body, but the position of the catalyst 53 is not limited to this. The arrangement position of the catalyst 53 may be a position where the path length D3 is shorter than the path length D4. The catalyst 53 may be disposed in front of the engine body 20.

Further, a plurality of catalysts may be arranged in the exhaust passage portion 51. In this case, among the plurality of catalysts, the catalyst that most purifies the exhaust gas discharged from the combustion chamber 30 in the exhaust path corresponds to the combustion chamber adjacently arranged catalyst of the present invention. That is, the combustion chamber adjacently arranged catalyst has the highest contribution to purify the exhaust gas. The other catalyst is disposed upstream or downstream of the combustion chamber adjacently disposed catalyst.

The degree of contribution of purification of each of the plurality of catalysts can be measured by the following method.
Here, a case where the number of catalysts is two will be described as an example. Of the two catalysts, the catalyst disposed upstream is referred to as a front catalyst, and the catalyst disposed downstream is referred to as a rear catalyst. First, the engine unit of the modified example is operated, and the concentration of harmful substances contained in the exhaust gas discharged from the atmospheric discharge port 64a in the warm-up state is measured. The exhaust gas measurement method shall be in accordance with European regulations. In the warm-up state, the two catalysts are in an activated state and can sufficiently exhibit purification performance.

Next, remove the rear catalyst of the test engine unit, and place only the rear catalyst carrier instead. The engine unit in this state is referred to as a measurement engine unit A. The measurement engine unit A is operated to measure the concentration of harmful substances contained in the exhaust gas discharged from the atmospheric discharge port 64a in the warm-up state.

Next, the front catalyst of the measurement engine unit A is removed, and only the front catalyst carrier is arranged instead. The engine unit in this state is referred to as a measurement engine unit B. The measurement engine unit B is operated to measure the concentration of harmful substances contained in the exhaust gas discharged from the atmospheric discharge port 64a in the warm-up state.

The measurement engine unit A has a front catalyst and does not have a rear catalyst. The measurement engine unit B does not have a front catalyst and a rear catalyst. Therefore, the degree of contribution of the purification of the front catalyst is calculated from the difference between the measurement result of the measurement engine unit A and the measurement result of the measurement engine unit B. Further, the contribution of the purification of the rear catalyst is calculated from the difference between the measurement result of the measurement engine unit A and the measurement result of the engine unit of the modified example.

In the above embodiment, the injector 42 is disposed so as to inject fuel into the intake passage portion 41, but may be disposed so as to inject fuel into the combustion chamber 30. The injector 42 may be disposed in the engine body 20.

In the above embodiment, the injector 42 corresponds to the fuel supply device of the present invention. However, the fuel supply device of the present invention is not limited to an injector. The fuel supply device of the present invention may be a device that supplies fuel into the combustion chamber. The fuel supply device of the present invention may be, for example, a carburetor that supplies fuel to the combustion chamber by negative pressure.

In the above embodiment, a bypass valve 46 whose opening degree can be manually changed is arranged in the bypass intake passage 41b. However, instead of the bypass valve 46, a valve whose opening degree can be controlled by the ECU 80 may be arranged.

The air-cooled engine unit 11 may have an intake pressure sensor that detects the internal pressure of the intake passage portion 41. In this case, a signal from the intake pressure sensor may be used for controlling the fuel supply amount and / or controlling the ignition timing.

The air-cooled engine unit 11 may have an intake air temperature sensor that detects the temperature of air in the intake passage portion 41. In this case, a signal from the intake air temperature sensor may be used for controlling the fuel supply amount and / or controlling the ignition timing.

The air-cooled engine unit 11 may not include the knocking sensor 72.

The air-cooled engine unit 11 of the above embodiment is a natural air-cooled engine unit. However, the air-cooled engine unit of the present invention may be a forced air-cooled engine unit. The forced air cooling engine unit includes a shroud and a fan. The shroud is disposed so as to cover at least a part of the engine body. Air is introduced into the shroud by driving the fan.

The engine unit 11 of the above embodiment is a single cylinder engine unit, but the air-cooled engine unit of the present invention may be a multi-cylinder engine unit having a plurality of combustion chambers. In this case, the number of the air intake ports 41c may be smaller than the number of the plurality of combustion chambers 30. That is, a portion of the intake passage portion 41 formed for one combustion chamber 30 may also serve as a portion of the intake passage portion 41 formed for another combustion chamber 30. The number of atmospheric inlets 41c may be one. Further, the number of atmospheric discharge ports 64a may be smaller than the number of the plurality of combustion chambers 30. That is, a part of the exhaust passage portion 51 formed for one combustion chamber 30 may also serve as a part of the exhaust passage portion 51 formed for another combustion chamber 30. The number of atmospheric discharge ports 64a may be one. Further, when the number of combustion chambers 30 is an odd number of 4 or more, the atmospheric discharge ports 64a may be arranged one by one on the left and right.

The combustion chamber of the present invention may have a configuration having a main combustion chamber and a sub-combustion chamber connected to the main combustion chamber. In this case, one combustion chamber is formed by the main combustion chamber and the sub-combustion chamber.

The above embodiment is an example in which the air-cooled engine unit of the present invention is applied to a sports type motorcycle. However, the application target of the air-cooled engine unit of the present invention is not limited to a sports type motorcycle. The air-cooled engine unit of the present invention may be applied to a motorcycle other than the sport type. For example, the engine unit of the present invention may be applied to a scooter type motorcycle. The air-cooled engine unit of the present invention may be applied to a lean vehicle other than a motorcycle. A lean vehicle is a vehicle having a vehicle body frame that leans to the right of the vehicle when turning right and leans to the left of the vehicle when turning left. The air-cooled engine unit of the present invention may be applied to a straddle-type vehicle other than a motorcycle. Note that the saddle riding type vehicle refers to all vehicles that ride in a state in which an occupant straddles a saddle. The saddle riding type vehicle includes a motorcycle, a tricycle, a four-wheel buggy (ATV: All Terrain Vehicle), a water bike, a snowmobile, and the like.

In this specification, the route length of an arbitrary portion of the intake passage portion 41 is the length of a route formed inside this portion. The same is true for the path length of any part of the exhaust passage portion 51. In this specification, the path length refers to the path length of the middle line of the path. The path length of the expansion chambers (60a, 60b, 60c) of the muffler 54 means the length of the path connecting the center of the expansion chamber inlet to the center of the expansion chamber outlet at the shortest distance. In this specification, the upstream end of the catalyst 53 means an end where the path length from the combustion chamber 30 in the catalyst 53 is the shortest. The downstream end of the catalyst 53 means an end where the path length from the combustion chamber 30 in the catalyst 53 is the longest. Similar definitions apply to upstream and downstream ends of elements other than the catalyst 53.

11 Air-cooled engine unit 20 Engine body 25 Fin part (heat dissipation part)
30 Combustion chamber 31 Spark plug (ignition device)
32 Ignition coil (ignition device)
33 Intake Port 34 Exhaust Port 41 Intake Passage 41c Air Intake Port 42 Injector (Fuel Supply Device)
45 Throttle valve (throttle valve close to combustion chamber)
51 Exhaust passage part 53 Catalyst (Combustion chamber proximity catalyst)
64a Atmospheric discharge port 71 Engine rotation speed sensor 72 Knocking sensor 73 Engine temperature sensor 74 Throttle opening sensor (throttle opening sensor arranged close to combustion chamber)
75 Oxygen sensor 80 ECU (control device)
81 Fuel supply amount control unit 82 Ignition timing control unit 83 Idle stop control unit 84 Restart control unit 85 Operation instruction unit

Claims

An engine body having a compression ratio of 10 or more and forming at least one combustion chamber;
A heat radiating part for radiating heat generated in the engine body from the surface of the engine body;
Connecting an exhaust port formed in the combustion chamber and an atmospheric discharge port for discharging exhaust gas to the atmosphere, and an exhaust passage portion through which exhaust gas flows from the exhaust port toward the atmospheric discharge port;
A combustion chamber adjacently disposed catalyst disposed in the exhaust passage portion,
The path length from the exhaust port of the exhaust passage portion to the upstream end of the catalyst disposed close to the combustion chamber is shorter than the path length from the downstream end of the catalyst disposed close to the combustion chamber of the exhaust passage portion to the atmospheric discharge port. An air-cooled engine unit characterized by
A control device for controlling the operation of the air-cooled engine unit;
The controller is
An idle stop controller that automatically stops the operation of the air-cooled engine unit when a predetermined idle stop condition is satisfied during the operation of the air-cooled engine unit;
A restart control unit that restarts the operation of the air-cooled engine unit when a predetermined restart condition is satisfied in a state where the operation of the air-cooled engine unit is stopped by the idle stop control unit. The air-cooled engine unit according to claim 1.
A knocking sensor for detecting knocking generated in the engine body;
An ignition device for igniting fuel in the combustion chamber;
The air-cooled engine unit according to claim 1, further comprising a control device that controls an ignition timing of the ignition device based on a signal of the knocking sensor.
An oxygen sensor which is disposed at a position upstream of the combustion chamber adjacently arranged catalyst in the exhaust passage portion in the flow direction of the exhaust gas and detects the oxygen concentration of the exhaust gas in the exhaust passage portion;
A fuel supply device for supplying fuel into the combustion chamber;
The air-cooled engine unit according to any one of claims 1 to 3, further comprising a control device that controls a fuel supply amount of the fuel supply device based on a signal of the oxygen sensor.
Connecting an intake port formed in the combustion chamber and an air intake port for sucking air from the atmosphere, and an intake passage portion through which air flows from the air intake port toward the intake port;
An ignition device for igniting fuel in the combustion chamber;
A fuel supply device for supplying fuel into the combustion chamber;
A combustion chamber adjacently arranged throttle valve provided in the intake passage portion, wherein a path length from the atmospheric intake port of the intake passage portion to the combustion chamber adjacently arranged throttle valve is set to be close to the combustion chamber of the intake passage portion. The throttle valve close to the combustion chamber disposed at a position longer than the path length from the throttle valve to the intake port;
A combustion chamber proximity arrangement throttle opening sensor for detecting an opening degree of the combustion chamber proximity arrangement throttle valve;
An engine speed sensor for detecting the engine speed;
A control device for controlling a fuel supply amount of the fuel supply device and an ignition timing of the ignition device based on a signal of the throttle opening sensor disposed adjacent to the combustion chamber and a signal of the engine speed sensor; The air-cooled engine unit according to any one of claims 1 to 4.
Connecting an intake port formed in the combustion chamber and an air intake port for sucking air from the atmosphere, and having an intake passage portion through which air flows from the air intake port toward the intake port;
An intake pressure sensor that is provided in the intake passage portion and detects an internal pressure of the intake passage portion, and an intake air temperature sensor that is provided in the intake passage portion and detects a temperature in the intake passage portion is not provided. The air-cooled engine unit according to any one of claims 1 to 5.