Control device for internal combustion engine

Abstract

Provided is a control device for an internal combustion engine, which is used in a vehicle that comprises: the internal combustion engine; a centrifugal clutch to be engaged when the rotation speed of the internal combustion engine increases; and a catalyst for exhaust gas purification. The control device executes catalyst early activation control for activating the catalyst by increasing the rotation speed during stand-by operation, and can suppress unintended engagement of the centrifugal clutch during the execution of the catalyst early activation control. A control device (1) for an internal combustion engine controls the engine rotation speed such that, when it is determined that the engine rotation speed is included in a loss-torque increase region during the execution of catalyst early activation control, the engine rotation speed becomes lower than the engine rotation speed at the time when it is determined that the engine rotation speed is included in the loss-torque increase region, where the loss-torque increase region denoting a region of the engine rotation speed in which the loss torque of an internal combustion engine (2) increases in association with a shift of a centrifugal clutch (6) from a disengaged state to a fully-engaged state.

Description

Control device for internal combustion engine

[0001] The present invention relates to a control device for an internal combustion engine.

[0002] There is known a control device for an internal combustion engine that is applied to an internal combustion engine mounted on a vehicle and executes idle operation control when in an idle state. For example, Patent Document 1 discloses a control device for an internal combustion engine that performs early activation of a catalyst for exhaust gas purification during idle operation control. According to this control device, when the temperature of the catalyst for exhaust gas purification is relatively low (that is, when catalyst warm-up is required), the intake air amount is increased compared to normal idle operation. The control of increasing the rotational speed of the internal combustion engine (engine rotational speed) during idle operation to increase the intake air amount for catalyst warm-up is also referred to as "catalyst early activation control".

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2000-179439

[0004] By the way, a centrifugal clutch may be interposed in the torque transmission path of a vehicle on which an internal combustion engine is mounted. A centrifugal clutch generally has an input shaft and an output shaft, and when the rotational speed of the input shaft increases, engagement occurs in the centrifugal clutch and torque is transmitted from the input shaft to the output shaft. If the input shaft is connected to the internal combustion engine so as to be torque-transmittable and the output shaft is connected to the drive wheels of the vehicle so as to be torque-transmittable, there is a possibility that unintended torque transmission from the internal combustion engine to the drive wheels may occur due to the engagement of the centrifugal clutch during the execution of idle operation control.

[0005] Therefore, a control device for an internal combustion engine applied to a vehicle equipped with a centrifugal clutch needs to increase the engine rotational speed during the execution of catalyst early activation control while avoiding unintended engagement in the centrifugal clutch. However, in Patent Document 1, no consideration has been made in this regard.

[0006] An object of the present invention is to provide a control device for an internal combustion engine that can execute catalyst early activation control and suppress unintended engagement in a centrifugal clutch.

[0007] The inventors of this application investigated implementing catalyst early activation control, as disclosed in Patent Document 1, in a vehicle equipped with an exhaust gas purification catalyst and a centrifugal clutch.

[0008] In catalytic converter early activation control, it is generally necessary to increase the engine speed. However, if the engine speed exceeds the clutch-engagement speed, rotation is transmitted from the internal combustion engine to the drive wheels due to the engagement of the centrifugal clutch. Therefore, in order to perform catalytic converter early activation control in a vehicle equipped with a centrifugal clutch, it is necessary to increase the engine speed while keeping the engine speed below the clutch-engagement speed.

[0009] Based on the above, the inventors of the present invention considered controlling the internal combustion engine such that, when performing catalyst early activation control, the engine speed is reduced if it exceeds a threshold rotational speed set to be lower than the clutch-in rotational speed.

[0010] In a centrifugal clutch, torque is transmitted from the input shaft to the output shaft by the frictional force generated between a coupling member (e.g., a clutch shoe) located on the input shaft and a coupling member (e.g., a clutch drum) located on the output shaft. Therefore, the clutch-in rotational speed can be said to be the engine rotational speed at which the frictional force in a centrifugal clutch becomes relatively large. As the engine rotational speed increases and the frictional force increases further, the output shaft rotates. That is, rotation is transmitted from the internal combustion engine to the drive system (specifically, the transmission and reduction gears included in the torque transmission path from the centrifugal clutch to the drive wheels).

[0011] The clutch-in rotational speed can vary depending on the environment in which the centrifugal clutch operates and / or individual differences in the centrifugal clutch itself. In other words, the actual clutch-in rotational speed has a range. That is, the actual clutch-in rotational speed is likely to differ from the theoretical clutch-in rotational speed described later. More specifically, the torque transmitted from the input shaft to the output shaft in a centrifugal clutch (transmitted torque) can vary depending on the temperature of the centrifugal clutch and the humidity around the centrifugal clutch. In addition, the transmitted torque can vary depending on individual differences in the centrifugal clutch and changes over time.

[0012] Therefore, the inventors of this invention realized that in order to avoid an increase in transmitted torque when performing catalyst early activation control, the threshold rotational speed needs to be set to a value that is somewhat smaller than the theoretical value of the clutch-in rotational speed (theoretical clutch-in rotational speed). On the other hand, in order to terminate catalyst early activation control early, it is desirable to maintain a relatively high engine rotational speed.

[0013] Therefore, the inventors of the present invention have come to realize that when performing catalyst early activation control in a vehicle equipped with a centrifugal clutch, it is necessary to achieve two conflicting requirements: maintaining a relatively high engine rotation speed and suppressing an increase in the torque transmitted in the centrifugal clutch.

[0014] To achieve these two requirements, the inventors of the present invention considered the following configuration. Specifically, if the region of rotational speed of the internal combustion engine in which the lost torque of the internal combustion engine increases as the centrifugal clutch transitions from the open state to the fully engaged state is defined as the "lost torque increase region," then when it is determined that the rotational speed of the internal combustion engine falls within the lost torque increase region during the execution of catalyst early activation control, the rotational speed of the internal combustion engine is controlled to be smaller than the actual rotational speed of the internal combustion engine when it is determined that the rotational speed of the internal combustion engine falls within the lost torque increase region.

[0015] With this configuration, when catalyst early activation control is performed, the engine speed is maintained at a relatively high level, while if it is determined that the engine speed falls within the range of increased lost torque, the internal combustion engine is controlled to decrease the engine speed.

[0016] More specifically, the inventors of this invention obtained changes in various physical quantities when a centrifugal clutch transitions from an open state to a fully engaged state. Through this, the inventors discovered that there exists a region of engine speed (i.e., a region of increased lost torque) in which the lost torque of the internal combustion engine increases before rotation is transmitted due to the engagement of the centrifugal clutch. This increase in lost torque is due to the frictional force generated when the coupling members of the centrifugal clutch (e.g., the clutch shoe and clutch drum) slide against each other. The region of increased lost torque can also be described as a region where frictional force is generated in the coupling members, while rotation is not yet transmitted from the internal combustion engine to the vehicle's drivetrain.

[0017] With the above configuration, it is possible to detect when the transmitted torque is relatively large before rotation is transmitted in the centrifugal clutch. In addition to (or instead of) this, it is possible to detect when a transmitted torque is being generated in the centrifugal clutch. When these detections are made, the engine rotation speed is reduced, thereby suppressing unintended engagement in the centrifugal clutch (i.e., when the transmitted torque becomes relatively large).

[0018] If the engine speed is not determined to be within the range of increased lost torque, and the internal combustion engine is controlled based on a predetermined threshold speed, then the threshold speed must be set to a small value so that it is not within the range of increased lost torque. In other words, with the above configuration, the engine speed during the execution of catalyst early activation control can be increased compared to control based on the threshold speed.

[0019] Based on the above findings, the control device for an internal combustion engine according to each aspect of the present invention comprises the following configuration.

[0020] (1) A control device for an internal combustion engine used in a vehicle comprising an internal combustion engine, a centrifugal clutch that engages when the rotational speed of the internal combustion engine increases, and a catalyst for exhaust gas purification, wherein during idle operation, the control device performs either a first idle operation control or a catalyst early activation control that activates the catalyst by increasing the rotational speed of the internal combustion engine to a level higher than the rotational speed of the internal combustion engine when the first idle operation control is performed, wherein the region of rotational speed of the internal combustion engine in which the lost torque of the internal combustion engine increases as the centrifugal clutch transitions from an open state to a fully engaged state is defined as the lost torque increase region, and if it is determined that the rotational speed of the internal combustion engine is included in the lost torque increase region during the execution of the catalyst early activation control, the control device controls the rotational speed of the internal combustion engine so that it is lower than the actual rotational speed of the internal combustion engine when it is determined that the rotational speed of the internal combustion engine is included in the lost torque increase region.

[0021] In a centrifugal clutch, friction occurs due to the mutual contact between the clutch shoes and clutch drum (i.e., the coupling members in a centrifugal clutch) as the engine rotational speed increases, transmitting torque, but also increasing lost torque. That is, a difference (rotational speed difference) occurs between the rotational speed of the clutch shoes and the rotational speed of the clutch drum in a centrifugal clutch. The region of increased lost torque is the range of engine rotational speeds in which lost torque increases due to the increase in friction in the centrifugal clutch. In the above configuration, if it is determined that the engine rotational speed is included in the region of increased lost torque, the control device reduces the engine rotational speed. With this configuration, the increase in torque transmitted from the internal combustion engine to the vehicle's drive system (i.e., the side of the torque transmission path of a vehicle equipped with an internal combustion engine that is on the drive wheel side of the centrifugal clutch) as a result of the engine rotational speed further increasing in the region of increased lost torque is suppressed (and consequently, the transmission of rotation).

[0022] As described above, in conventional technology, the target rotational speed when performing catalyst early activation control must be set to a value relatively small compared to the theoretical clutch-in rotational speed. On the other hand, with the above configuration, the internal combustion engine is controlled so that the engine rotational speed decreases when it is determined that the engine rotational speed is included in the region in which the torque transmitted from the internal combustion engine to the drive system increases. Therefore, with the above configuration, it is possible to increase the target rotational speed when performing catalyst early activation control compared to conventional methods, while avoiding an increase in transmitted torque. In other words, unintended engagement in the centrifugal clutch can be suppressed when performing catalyst early activation control.

[0023] According to one aspect of the present invention, the control device for an internal combustion engine can employ the following configuration: (2) The control device for an internal combustion engine according to (1), wherein the catalyst early activation control is performed during the period from the start of the internal combustion engine to the first start of driving in the vehicle.

[0024] During the period between the start of the internal combustion engine and the vehicle's initial movement, the temperatures of the internal combustion engine and catalytic converter are likely to be relatively low. According to the above configuration, even if the internal combustion engine starts with low temperatures, the catalytic converter's temperature is likely to rise by the time the vehicle begins to move.

[0025] According to one aspect of the present invention, the control device for an internal combustion engine can employ the following configuration: (3) The control device for an internal combustion engine according to (1) or (2), wherein the target rotational speed of the internal combustion engine during the execution of the catalyst early activation control is set to a value greater than the clutch-out rotational speed at which the centrifugal clutch transitions from the engaged state to the disengaged state.

[0026] With the above configuration, it is possible to maintain a relatively high engine rotation speed (specifically, a state where the engine rotation speed is greater than the clutch-out rotation speed). Even with this configuration, if it is determined that the engine rotation speed is in the region of increased lost torque, the engine rotation speed can be reduced, thereby suppressing unintended engagement in the centrifugal clutch.

[0027] According to one aspect of the present invention, the control device for an internal combustion engine can adopt the following configuration: (4) A control device for an internal combustion engine according to any one of (1) to (3), wherein, when it is determined that the vehicle has been driven after the internal combustion engine has been started, the target rotational speed of the internal combustion engine during idle operation is set to a value smaller than the clutch-out rotational speed at which the centrifugal clutch transitions from the engaged state to the disengaged state.

[0028] In the above configuration, the engine speed during idle operation (for example, when catalyst early activation control is performed) can be maintained at a level higher than the clutch-out speed during the period before the vehicle first starts moving. Therefore, the likelihood of early catalyst activation increases. On the other hand, after the vehicle has started moving, the target engine speed during idle operation becomes lower than the clutch-out speed. Therefore, if the vehicle comes to a stop after moving, the engine speed will be lower than the clutch-out speed, which suppresses the maintenance of the engagement state in the centrifugal clutch.

[0029] According to one aspect of the present invention, the control device for an internal combustion engine can adopt the following configuration: (5) The control device for an internal combustion engine according to (4), wherein it determines whether or not the vehicle has traveled based on at least one physical quantity among the load state of the internal combustion engine, the rotational speed of the internal combustion engine, the vehicle speed of the vehicle, and the temperature of the internal combustion engine.

[0030] According to the above configuration, it is possible to determine whether or not a vehicle has traveled based on various physical quantities.

[0031] A centrifugal clutch can switch the power of an internal combustion engine on and off by utilizing the centrifugal force acting on the clutch (more specifically, the coupling member of the centrifugal clutch) in accordance with the rotation of the internal combustion engine. The centrifugal clutch according to this disclosure is, for example, a wet multi-plate clutch. Alternatively, a wet shoe clutch may be used. For ease of understanding, this disclosure will use commonly used terminology for wet shoe clutches. In other words, the centrifugal clutch applied in each of the above configurations is not limited to a wet shoe clutch. The centrifugal clutch may be, for example, a dry shoe clutch.

[0032] Clutch-in rotational speed can be defined as the rotational speed of the internal combustion engine at the point when the centrifugal clutch switches from an open state (i.e., a state where torque transmission is interrupted) to an engaged state as the engine rotational speed increases, and rotation begins to be transmitted through the centrifugal clutch. Switching from an open state to an engaged state of the centrifugal clutch means, for example, that the magnitude of the transmitted torque in the centrifugal clutch becomes greater than "0". Alternatively, it may mean that the magnitude of the transmitted torque becomes greater than a predetermined value. The theoretical clutch-in rotational speed (i.e., the theoretical value (design value) of the clutch-in rotational speed) can be determined based on the shape and material of each component constituting the centrifugal clutch. On the other hand, the coefficient of friction between coupling members that come into contact with each other in accordance with the centrifugal force in the centrifugal clutch changes due to various factors such as temperature, humidity, and aging. In other words, the actual transmitted torque in the centrifugal clutch can change depending on the environment and individual differences. Therefore, the actual clutch-in rotational speed in the centrifugal clutch does not necessarily coincide with the theoretical clutch-in rotational speed, and generally has a certain range.

[0033] Idle operation is an operating state in which the internal combustion engine is rotating (operating) but the rotation of the internal combustion engine is not being transmitted to the power transmission mechanism connected to the internal combustion engine. The first idle operation control is, for example, a control performed when the vehicle is temporarily stopped in an internal combustion engine mounted on a vehicle. Catalyst early activation control is performed with the aim of raising the catalyst temperature to activate the catalyst contained in the exhaust gas purification device (i.e., exhaust gas purification catalyst) installed in the exhaust path of the internal combustion engine. Therefore, the rotational speed of the internal combustion engine when catalyst early activation control is performed is greater than the rotational speed when the first idle operation control is performed. Catalyst early activation control is performed, for example, when the internal combustion engine is cold-started. However, the triggers for performing catalyst early activation control are not limited to this.

[0034] For example, if the engine speed during idle operation is greater than or equal to a predetermined percentage compared to the average engine speed when the first idle operation control is performed for a predetermined time, it can be determined that catalyst early activation control is being performed. The determination of whether or not catalyst early activation control is being performed may be based on the opening degree of the bypass valve during idle operation. Alternatively, this determination may be based on both the opening degree of the bypass valve and the engine speed during idle operation control.

[0035] The region of increased lost torque is, as described above, the range of engine speeds in which lost torque increases due to increased friction in the centrifugal clutch. More specifically, as the engine speed increases, the centrifugal clutch transitions from an open state to a fully engaged state. During this process, when the centrifugal clutch is in a partially engaged state, a rotational speed difference occurs between the rotational speed of the clutch shoes and the rotational speed of the clutch drum. In other words, while torque is transmitted from the internal combustion engine to the drive system, rotation is not transmitted (i.e., lost torque, which is transmitted torque that is not transmitted as rotation, is generated). In this state, as the engine speed increases, lost torque increases. When this state is present, the engine speed is included in the region of increased lost torque. As the centrifugal clutch approaches the fully engaged state from a partially engaged state, the rotational speed difference decreases, and therefore lost torque decreases. In the above configuration, if it is determined that the engine speed is included in the region of increased lost torque, the engine speed is reduced, thereby suppressing the transmission of rotation to the drive system when catalyst early activation control is performed.

[0036] Whether or not the engine rotational speed is included in the region of increased lost torque may be determined based on the amount of change in engine rotational speed (rotational speed fluctuation) caused by the increase in friction in the centrifugal clutch, as described below. The rotational speed fluctuation is a value corresponding to the change in rotational speed in one cycle of the internal combustion engine. Alternatively, this determination may be made based on the detected or estimated value of the torque actually transmitted to the vehicle's drivetrain. Alternatively, the engine rotational speed may be obtained for each predetermined crank angle over multiple cycles of the internal combustion engine, and if the engine rotational speed for a certain cycle is less than or equal to a predetermined value than the engine rotational speed for the same crank angle in the previous cycle, it may be determined that the engine rotational speed is included in the region of increased lost torque.

[0037] As a rotational speed fluctuation, for example, the magnitude of the difference between the maximum engine rotational speed that appears due to the combustion of the air-fuel mixture near the compression top dead center (often immediately after the compression top dead center) and the engine rotational speed at the next exhaust top dead center can be obtained. In this case, if the rotational speed fluctuation becomes larger than a predetermined value (first threshold), it can be determined that the engine rotational speed is in the region of increased lost torque.

[0038] Alternatively, the magnitude of the difference between the engine speed at top dead center and the maximum engine speed immediately thereafter may be obtained as the rotational speed fluctuation. In this case, it can be determined that the engine speed is in the region of increased lost torque when the rotational speed fluctuation becomes smaller than a predetermined value (second threshold). The first and second thresholds may be fixed values ​​determined according to the combination of the internal combustion engine and the centrifugal clutch. Alternatively, the first and second thresholds may be values ​​that change according to the amount of fuel injected by the fuel injector of the internal combustion engine.

[0039] Control to reduce engine speed when it is determined that the engine speed falls within the range of increased lost torque is performed, for example, by reducing the amount of intake air flowing into the combustion chamber of the internal combustion engine. Alternatively, this control may be performed by retarding the ignition timing of the fuel spark plug or by temporarily not igniting the fuel spark plug.

[0040] The clutch-out rotational speed can be defined as the engine rotational speed at which rotation is no longer transmitted by the centrifugal clutch due to a decrease in centrifugal force caused by the decrease in engine rotational speed. Generally, the clutch-out rotational speed is smaller than the clutch-in rotational speed. Similar to the theoretical clutch-in rotational speed, the theoretical clutch-out rotational speed (i.e., the theoretical value (design value) of the clutch-out rotational speed) can be determined based on the shape and material of each component constituting the centrifugal clutch. However, the actual clutch-out rotational speed, like the clutch-in rotational speed, can vary depending on the environment and individual differences. In other words, the actual clutch-out rotational speed is likely to differ from the theoretical clutch-out rotational speed.

[0041] Vehicle movement detection can be performed based on vehicle speed (i.e., the vehicle's travel speed). Specifically, if the vehicle speed exceeds a threshold (vehicle speed threshold), it is determined that the vehicle is moving. This vehicle speed threshold is set to "0" or a relatively small value. Similarly, vehicle movement detection may be performed based on one or more values ​​among the internal combustion engine load (output), engine rotational speed, and internal combustion engine temperature.

[0042] The technical terms used herein are intended to define only specific embodiments and are not intended to limit the invention. The term "and / or" as used herein includes any or all combination of one or more related enumerated components. Where used herein, the use of the terms "including," "comprising," or "having" and their variations identifies the presence of described features, processes, operations, elements, components and / or equivalents thereof, but may include one or more of the steps, operations, elements, components and / or groups thereof. Where used herein, the terms "attached," "connected," "joined" and / or equivalents are used broadly and include both direct and indirect attachment, connection and joining. Furthermore, "connected" and "joined" are not limited to physical or mechanical connection or joining, but may include direct or indirect electrical connection or joining. Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as generally understood by those skilled in the art to whom the invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant technology and this disclosure, and not as ideal or overly formal unless expressly defined herein. In the description of the present invention, it is understood that a number of technologies and steps are disclosed. Each of these has its own individual benefit, and each may be used in conjunction with one or more, or possibly all, of the other disclosed technologies. Therefore, for clarity, this description refrains from unnecessarily repeating all possible combinations of individual steps. Nevertheless, the specification and claims should be read with the understanding that all such combinations are within the scope of the invention and claims. This specification describes a control device for a new internal combustion engine. In the following description, for explanatory purposes, a number of specific details are given to provide a complete understanding of the invention.However, it is clear to those skilled in the art that the present invention can be implemented without these specific details. This disclosure should be considered as an exemplification of the present invention and is not intended to limit the present invention to the specific embodiments shown in the following drawings or description.

[0043] According to the present invention, it is possible to maintain the engine rotational speed at as large a value as possible during the execution of catalyst early activation control and suppress an unintentional engagement in the centrifugal clutch.

[0044] It is a time chart showing an example of changes in the engine rotational speed of an internal combustion engine controlled by a control device for an internal combustion engine according to a first embodiment, and the rotational speed (transmission rotational speed) of the output shaft of a centrifugal clutch whose input shaft is connected to the internal combustion engine. It is a diagram schematically showing an internal combustion engine and a centrifugal clutch. It is a time chart showing an example of changes in the engine rotational speed in one cycle of the internal combustion engine. It is a time chart showing another example of changes in the engine rotational speed. It is a time chart showing an example of changes in the engine rotational speed of an internal combustion engine controlled by a control device for an internal combustion engine according to a third embodiment and the transmission rotational speed.

[0045] Hereinafter, the present invention will be described based on embodiments with reference to the drawings.

[0046] [First Embodiment] FIG. 1 is a time chart showing an example of changes in the engine rotational speed NE, which is the rotational speed of the internal combustion engine 2 according to the first embodiment, and the transmission rotational speed ND described later. FIG. 2 is a diagram schematically showing the internal combustion engine 2 and the centrifugal clutch 6. The internal combustion engine 2 is mounted as a driving power source, for example, on a saddle-type vehicle (not shown, also referred to as a "mounted vehicle"). The internal combustion engine 2 is controlled by an ECU 1 (control device, control unit, control means).

[0047] The internal combustion engine 2 is a four-stroke single-cylinder engine that repeats an intake stroke, a compression stroke, a combustion stroke (expansion stroke), and an exhaust stroke. The internal combustion engine 2 may be a multi-cylinder engine. As shown in FIG. 2, in the internal combustion engine 2, the reciprocating motion of the piston 21 is transmitted to the crankshaft 23 via the connecting rod 22, and as a result, the crankshaft 23 rotates.

[0048] The internal combustion engine 2 will be described more specifically. The intake pipe 31 and the intake port 32 form an intake passage for introducing intake air (fresh air) into the combustion chamber 33 of the internal combustion engine 2. The intake valve 34 opens and closes the communication portion between the intake port 32 and the combustion chamber 33 according to the rotational position of a camshaft (not shown) of the internal combustion engine 2. A throttle valve 35 is disposed in the intake pipe 31. The throttle valve 35 adjusts the opening degree of the intake pipe 31 (i.e., the throttle opening degree) according to the instruction of the ECU 1. A fuel injection valve 36 is disposed in the intake port 32. The fuel injection valve 36 injects fuel into the intake port 32 according to the instruction of the ECU 1.

[0049] Furthermore, a bypass passage 37 that bypasses the throttle valve 35 is disposed in the intake pipe 31. A bypass valve 38 is disposed in the bypass passage 37. The bypass valve 38 adjusts the bypass valve opening degree Vb according to the instruction of the ECU 1. The bypass valve opening degree Vb is the opening degree of the bypass valve 38.

[0050] An ignition plug 39 is disposed in the combustion chamber 33. The ignition plug 39 ignites the air-fuel mixture (i.e., the intake air including the fuel injected from the fuel injection valve 36) in the combustion chamber 33 according to the instruction of the ECU 1.

[0051] The exhaust port 41 and the exhaust pipe 42 form an exhaust passage for discharging the exhaust gas (combustion gas) generated in the combustion chamber 33. The exhaust valve 43 opens and closes the communication portion between the combustion chamber 33 and the exhaust port 41 according to the rotational position of the camshaft. An exhaust gas purification catalyst 44 is interposed in the exhaust pipe 42. The catalyst 44 is an exhaust gas purification device that contains a catalyst substance.

[0052] The rotation of the crankshaft 23 is transmitted to the drive transmission device 54 (drive system) via the centrifugal clutch 6, outer shaft 51, gears 52a to 52b that mesh with each other, and drive shaft 53. The crankshaft 23 is the input shaft of the centrifugal clutch 6, and the drive shaft 53 is the output shaft of the centrifugal clutch 6. The drive transmission device 54 includes a transmission and reduction gears, etc., and forms a torque transmission path from the drive shaft 53 to the drive wheels (not shown) of the mounted vehicle. In the mounted vehicle according to this embodiment, rotation is transmitted from the crankshaft 23 to the drive shaft 53 using gears 52a to 52b, but rotation may be transmitted by a belt and / or chain instead of gears 52a to 52b.

[0053] The centrifugal clutch 6 includes an inner disc 61, an outer drum 62, and a plurality of clutch shoes 63. Each of the outer drum 62 and clutch shoes 63 is a coupling member in the centrifugal clutch 6.

[0054] The inner disc 61 is mounted on the crankshaft 23. Therefore, the crankshaft 23 and the inner disc 61 rotate as a single unit. The outer drum 62 and the gear 52a are mounted on the outer shaft 51. Therefore, the outer drum 62, the outer shaft 51, and the gear 52a rotate as a single unit. The engine rotational speed NE mentioned above is the rotational speed of the crankshaft 23. The rotational speed of the outer shaft 51 is also referred to as the transmission rotational speed ND.

[0055] Each of the clutch shoes 63 is disposed on the inner disc 61 and rotates integrally with the inner disc 61. The inner disc 61 is provided with a plurality of elastic bodies (not shown; in this embodiment, coil springs) that bias the clutch shoes 63 toward the axis of the crankshaft 23.

[0056] As the rotational speed of the inner disc 61 (i.e., the engine rotational speed NE) increases, the clutch shoe 63 moves away from the axis of the crankshaft 23 against the biasing force of the elastic body due to centrifugal force. As a result, the clutch shoe 63 approaches the inner surface of the outer drum 62. When the clutch shoe 63 comes into contact with the inner surface of the outer drum 62 due to centrifugal force (i.e., the clutch shoe 63 and the outer drum 62 engage and slide against each other), a frictional force is generated between the clutch shoe 63 and the outer drum 62. As a result, torque is transmitted from the crankshaft 23 to the driveshaft 53 via the clutch shoe 63 and the outer drum 62.

[0057] When the torque transmitted from the crankshaft 23 to the driveshaft 53 (transmitted torque) increases, the driveshaft 53 rotates. That is, rotation is transmitted from the crankshaft 23 to the driveshaft 53. When rotation is transmitted from the crankshaft 23 to the driveshaft 53, the drive wheels of the vehicle rotate. Weights may be provided on each of the clutch shoes 63 so that the clutch shoes 63 and the outer drum 62 engage even when the engine rotation speed NE is relatively low. By providing weights, the centrifugal force acting on the clutch shoes 63 increases. In the vehicle equipped with this embodiment, the centrifugal clutch 6 is provided on the crankshaft 23, but the centrifugal clutch 6 may also be provided on the driveshaft 53.

[0058] The ECU 1 is an electronic control unit that includes a CPU, RAM, and non-volatile memory (none of which are shown). The ECU 1 is connected to a crank angle sensor 71, a cam position sensor 72, an accelerator pedal operation amount sensor 73, an intake air volume sensor 74, a vehicle speed sensor 75, and temperature sensors 76a to 76b. The crank angle sensor 71 outputs a pulse signal to the ECU 1 each time the crankshaft 23 rotates by a predetermined angle. The cam position sensor 72 outputs a signal to the ECU 1 corresponding to the rotational position of the camshaft of the internal combustion engine 2.

[0059] The ECU 1 acquires the engine rotational speed NE based on the signal input from the crank angle sensor 71. In addition, the ECU 1 acquires the crank angle CA based on the signals input from the crank angle sensor 71 and the cam position sensor 72. The crank angle CA is a value that falls within the range of 0° to 720°. When the piston 21 is at top dead center of compression, the crank angle CA is 0°. When the piston 21 is at top dead center of exhaust, the crank angle CA is 360°.

[0060] The accelerator pedal operation amount sensor 73 acquires the accelerator pedal operation amount Ap. The accelerator pedal operation amount Ap is a value that represents the amount of operation (rotation angle) relative to the accelerator grip (not shown) located on the handlebars of the vehicle on which the vehicle is installed. When the accelerator grip is not operated by the driver of the vehicle on which the vehicle is installed, the accelerator pedal operation amount Ap is "0". When the accelerator grip is operated, the accelerator pedal operation amount Ap becomes greater than "0".

[0061] The intake air volume sensor 74 is positioned upstream of the bypass passage 37 in the intake manifold 31. The intake air volume sensor 74 acquires the intake air volume Ga. The intake air volume Ga is the amount of intake air flowing into the combustion chamber 33 per unit time. The vehicle speed sensor 75 acquires the vehicle speed Vs. The vehicle speed Vs is the driving speed of the vehicle on which the system is installed.

[0062] The temperature sensor 76a is positioned upstream of the catalyst 44 in the exhaust pipe 42. The temperature sensor 76a acquires the exhaust temperature Te1. The exhaust temperature Te1 is the temperature of the exhaust gas flowing into the catalyst 44. The temperature sensor 76b is positioned downstream of the catalyst 44 in the exhaust pipe 42. The temperature sensor 76b acquires the exhaust temperature Te2. The exhaust temperature Te2 is the temperature of the exhaust gas flowing out of the catalyst 44. The ECU 1 acquires the catalyst temperature Tc based on the exhaust temperatures Te1 to Te2. The catalyst temperature Tc is the temperature of the catalytic material contained in the catalyst 44. The catalyst temperature Tc may also be acquired directly by a temperature sensor installed in the catalyst 44.

[0063] (Control of the internal combustion engine by the ECU) The ECU 1 controls the throttle opening via the throttle valve 35 while the internal combustion engine 2 is operating. Generally, the larger the accelerator pedal input Ap, the larger the throttle opening, and as a result, the intake air volume Ga increases. In addition, the ECU 1 determines the fuel injection amount Qinj based on the intake air volume Ga. Generally, the larger the intake air volume Ga, the larger the fuel injection amount Qinj. When the crank angle CA reaches the fuel injection timing Cinj, the ECU 1 injects an amount of fuel equal to the fuel injection amount Qinj into the fuel injector 36.

[0064] (Idle Operation Control) Furthermore, when the ECU 1 determines that the internal combustion engine 2 should be in an idle state, it executes "idle operation control". Specifically, the ECU 1 executes idle operation control when the accelerator pedal input amount Ap is "0". When idle operation control is executed, the ECU 1 maintains the throttle valve 35 in a fully closed state. In addition, the ECU 1 controls the intake air volume Ga by adjusting the bypass valve opening Vb.

[0065] Idle operation control includes "first idle operation control" and "catalyst early activation control". First idle operation control is performed, for example, when the vehicle is in a stationary state. When first idle operation control is performed, ECU 1 adjusts the bypass valve opening Vb by feedback control so that the engine rotational speed NE approaches the reference idle rotational speed Nib. More specifically, ECU 1 sets the target rotational speed Ntgt to a value equal to the reference idle rotational speed Nib. In addition, ECU 1 adjusts the bypass valve opening Vb so that the difference between the target rotational speed Ntgt and the engine rotational speed NE becomes small.

[0066] On the other hand, if the ECU 1 determines that it is necessary to raise the temperature of the catalyst 44 early in order to activate it, it executes catalyst early activation control as idle operation control. For example, if the catalyst temperature Tc is lower than the threshold temperature Tth, the ECU 1 determines that it is necessary to raise the temperature of the catalyst 44 early. When executing catalyst early activation control, the ECU 1 sets the target rotational speed Ntgt to a value equal to the first temperature-raising rotational speed Nr1. The first temperature-raising rotational speed Nr1 is greater than the reference idle rotational speed Nib (i.e., Nr1 > Nib).

[0067] (Specific control in idle operation control) Furthermore, when the ECU 1 determines that the engine rotation speed NE is included in the region of increased lost torque during the execution of catalyst early activation control, it executes "specific control" that reduces the engine rotation speed NE by the rotation speed reduction value Nf.

[0068] The specific control will be explained with reference to the solid line L1a and dashed line L2a shown in Figure 1. The solid line L1a shows an example of the change in engine rotational speed NE. The dashed line L2a shows the change in transmission rotational speed ND in this example. Note that the actual vehicle on which this system is installed does not have a sensor that directly detects the transmission rotational speed ND. During the period shown in Figure 1, the accelerator pedal input amount Ap is maintained at "0". In addition, during the period shown in Figure 1, the braking system (not shown) installed in the vehicle on which this system is installed is not operating.

[0069] In this example, cranking begins at time ta0. More specifically, from time ta0 onward, the starter motor (not shown) rotates the crankshaft 23. As a result, the internal combustion engine 2 begins operation. Since the accelerator input amount Ap is "0", the ECU 1 performs idle operation control at the same time as the start of operation (start) of the internal combustion engine 2. More specifically, since the catalyst temperature Tc at time ta0 is less than the threshold temperature Tth, the ECU 1 performs catalyst early activation control as idle operation control. That is, the ECU 1 sets the target rotational speed Ntgt to a value equal to the first temperature rise rotational speed Nr1.

[0070] Therefore, at time ta1, the engine rotation speed NE reaches the first heating rotation speed Nr1, and thereafter, the engine rotation speed NE is maintained in the vicinity of the first heating rotation speed Nr1. More specifically, the engine rotation speed NE fluctuates in the vicinity of the first heating rotation speed Nr1. In other words, "fluctuations" occur in the engine rotation speed NE.

[0071] As time approaches ta2, fluctuations in the engine rotational speed NE increase, and as a result, the engine rotational speed NE becomes relatively larger than the first heating rotational speed Nr1. More specifically, the engine rotational speed NE at time ta2 is the rotational speed na2. The rotational speed na2 is greater than the first heating rotational speed Nr1.

[0072] Due to the increase in engine rotational speed NE, ECU1 determines at time ta2 that engine rotational speed NE is included in the region of increased lost torque. The process that ECU1 performs to determine whether or not engine rotational speed NE is included in the region of increased lost torque (also referred to as the "determination process") will be described later. Rotational speed na2 can also be said to be the actual engine rotational speed NE (actual rotational speed) when it is determined that engine rotational speed NE is included in the region of increased lost torque.

[0073] ECU1 determines that the engine rotational speed NE is in the region of increased lost torque, and therefore executes specific control at time ta2. More specifically, ECU1 sets the target rotational speed Ntgt to a value that is smaller than the rotational speed na2 by the rotational speed reduction value Nf. In this example, the target rotational speed Ntgt is the rotational speed na1. The rotational speed na1 is the difference between the rotational speed na2 and the rotational speed reduction value Nf (i.e., na1 = na2 - Nf). As a result, from time ta2 onward, the engine rotational speed NE is maintained in the vicinity of the rotational speed na1.

[0074] Subsequently, at time ta6, ECU1 determines that it is no longer necessary to prematurely heat up the catalyst 44. For example, ECU1 determines that it is no longer necessary to prematurely heat up the catalyst 44 when the catalyst temperature Tc becomes greater than the threshold temperature Tth. Therefore, from time ta6 onward, ECU1 replaces the catalyst early activation control with the first idle operation control as the idle operation control. That is, ECU1 sets the target rotational speed Ntgt to a value equal to the reference idle rotational speed Nib. As a result, from time ta6 onward, the engine rotational speed NE is maintained near the reference idle rotational speed Nib.

[0075] (Decision Processing in Specific Control) The decision processing (i.e., the processing for determining whether the engine rotational speed NE is included in the loss torque increase region) will be explained with reference to the solid line L3 shown in Figure 3. When executing the decision processing, the ECU 1 refers to, for example, the rotational speed fluctuation amount Nfa. In this embodiment, the rotational speed fluctuation amount Nfa is the difference between the upper end rotational speed Npk and the exhaust top dead center rotational speed Nte (Nfa = Npk - Nte). If the rotational speed fluctuation amount Nfa becomes greater than the first threshold Nth1 during the execution of catalyst early activation control, the ECU 1 determines that the engine rotational speed NE is included in the loss torque increase region.

[0076] The solid line L3 in Figure 3 shows an example of the change in engine rotational speed NE. In Figure 3, the passage of time is shown by the change in crank angle CA. Figure 3 shows a period slightly earlier than time ta2 in Figure 1.

[0077] The upper end rotational speed Npk is the maximum value of the engine rotational speed NE that appears due to the combustion of the air-fuel mixture near the compression top dead center. The exhaust top dead center rotational speed Nte is the engine rotational speed NE at the first exhaust top dead center that occurs after the upper end rotational speed Npk is obtained. In the change of engine rotational speed NE shown by the solid line L3, the upper end rotational speed Npk is rotational speed nb3, and the exhaust top dead center rotational speed Nte is rotational speed nb2. Therefore, the rotational speed fluctuation amount Nfa in this example is equal to the difference between rotational speed nb3 and rotational speed nb2 (i.e., Nfa = nb3 - nb2). In the example in Figure 3, since the rotational speed fluctuation amount Nfa is greater than the first threshold Nth1, the ECU1 determines that the engine rotational speed NE is included in the region of increased lost torque.

[0078] The ECU1 may also obtain the difference between the upper end rotational speed Npk and the lower end rotational speed Nbt as the rotational speed fluctuation amount Nfa (Nfa = Npk - Nbt). The lower end rotational speed Nbt is the engine rotational speed NE at the last compression top dead center that occurs before the upper end rotational speed Npk is obtained. In the example in Figure 3, the lower end rotational speed Nbt is the rotational speed nb1. Therefore, in this example, the rotational speed fluctuation amount Nfa is equal to the difference between the rotational speed nb3 and the rotational speed nb1 (i.e., Nfa = nb3 - nb1). When the rotational speed fluctuation amount Nfa is the "difference between the upper end rotational speed Npk and the lower end rotational speed Nbt", the ECU1 determines that the engine rotational speed NE is in the region of increased lost torque when the rotational speed fluctuation amount Nfa becomes greater than the second threshold Nth2 (not shown).

[0079] (Other examples of specific control being performed) Other examples of specific control being performed will be explained with reference to the solid line L4 shown in Figure 4. The solid line L4 shows an example of a change in engine rotational speed NE. During the period shown in Figure 4, the accelerator operation amount Ap is maintained at "0" and the braking system of the vehicle on which it is mounted is not activated. In the example of Figure 1, specific control was performed after the engine rotational speed NE reached the first temperature rise rotational speed Nr1. In contrast, in the example of Figure 4, specific control is performed before the engine rotational speed NE reaches the first temperature rise rotational speed Nr1.

[0080] In the example shown in Figure 4, ECU 1 starts cranking at time tc0. Furthermore, ECU 1 starts catalyst early activation control at the same time as the internal combustion engine 2 starts operating. As a result, the engine rotational speed NE increases toward the first temperature rise rotational speed Nr1.

[0081] Next, ECU1 determines that at time tc1, the engine rotational speed NE is in the region of increased lost torque. Therefore, ECU1 executes specific control. More specifically, at time tc1, the engine rotational speed NE is the same as rotational speed nc2. Rotational speed nc2 is smaller than the first temperature rise rotational speed Nr1. Therefore, ECU1 sets the target rotational speed Ntgt to a value smaller than rotational speed nc2 by the rotational speed reduction value Nf. In this example, the target rotational speed Ntgt becomes rotational speed nc1. Rotational speed nc1 is the difference between rotational speed nc2 and the rotational speed reduction value Nf (i.e., nc1 = nc2 - Nf). As a result, from time tc1 onward, the engine rotational speed NE is maintained in the vicinity of rotational speed nc1.

[0082] (Significance of Specific Control) The reason why ECU1 performs specific control will be explained with reference to the dashed-dotted line L1b and the double-dotted-dotted line L2b shown in Figure 1. The dashed-dotted line L1b shows an example of the change in engine rotational speed NE assuming that the specific control was not started at time ta2. The double-dotted-dotted line L2b shows the change in transmission rotational speed ND under this assumption. Note that in Figure 1, the illustration of the dashed-dotted line L1b and the double-dotted-dotted line L2b for periods prior to time ta2 is omitted.

[0083] In this assumption, no specific control is performed, so from time ta2 onward, the engine speed NE temporarily rises above the rotational speed na2. On the other hand, in this assumption, ECU1 sets the target rotational speed Ntgt to a value equal to the reference idle rotational speed Nib around time ta6. That is, as idle operation control, the first idle operation control is performed instead of the catalyst early activation control. Therefore, after the engine speed NE temporarily rises, the engine speed NE decreases to the reference idle rotational speed Nib.

[0084] In this case, as shown by the dashed line L2b, the transmission rotational speed ND increases from "0" from time ta3, and at time ta4, the transmission rotational speed ND is equal to the engine rotational speed NE. Subsequently, from time ta5, the transmission rotational speed ND becomes less than the engine rotational speed NE, and at time ta7, the transmission rotational speed ND is approximately "0". That is, the vehicle speed Vs is greater than "0" during the period from time ta3 to time ta7.

[0085] In other words, during the period from time ta3 to time ta4, and from time ta5 to time ta7, the transmitted rotational speed ND is greater than "0" and the rotational speed difference ΔN is greater than "0". The rotational speed difference ΔN is the difference between the engine rotational speed NE and the transmitted rotational speed ND (i.e., ΔN = NE - ND). Figure 1 shows an example of the rotational speed difference ΔN at time ta3a.

[0086] Specifically, during the period from time ta3 to time ta4, and from time ta5 to time ta7, the centrifugal clutch 6 is in a semi-engaged state (more specifically, a state in which rotation is transmitted). During the period from time ta4 to time ta5, the centrifugal clutch 6 is in a fully engaged state. During the period up to time ta3, and from time ta7 onward, rotation is not transmitted through the centrifugal clutch 6. At time ta3, the engine rotational speed NE is the clutch-in rotational speed Nci. At time ta7, the engine rotational speed NE is the clutch-out rotational speed Nco. Specifically, when the engine rotational speed NE decreases from a value greater than the clutch-out rotational speed Nco to the clutch-out rotational speed Nco, the transmission of rotation through the centrifugal clutch 6 stops.

[0087] As can be seen from Figure 1, the first heating rotation speed Nr1 is greater than the clutch-out rotation speed Nco. In addition, the clutch-in rotation speed Nci is greater than the first heating rotation speed Nr1 (i.e., Nco < Nr1 < Nci). The reason why the clutch-in rotation speed Nci is greater than the clutch-out rotation speed Nco is that when the transmitted rotation speed ND is greater than "0", the torque generated by the internal combustion engine 2 and acting on the inner disc 61 must be greater than "the torque required to start rotating each component included in the torque transmission path from the outer drum 62 to the drive wheels of the mounted vehicle against the maximum static friction force".

[0088] As can be understood from this assumption, if specific control is not performed when it is determined that the engine rotational speed NE is included in the region of increased lost torque, the likelihood of unintended engagement in the centrifugal clutch 6 increases. That is, the transmitted torque in the centrifugal clutch 6 increases, and as a result, the transmission rotational speed ND is likely to become greater than "0". On the other hand, as shown by the solid line L1a, if specific control is performed when it is determined that the engine rotational speed NE is included in the region of increased lost torque, the likelihood of unintended engagement in the centrifugal clutch 6 being suppressed increases. In other words, before the transmitted torque in the centrifugal clutch 6 increases and the transmission rotational speed ND becomes greater than "0", the engine rotational speed NE decreases, and as a result, a state is achieved in which the engine rotational speed NE does not reach the clutch-in rotational speed Nci.

[0089] Incidentally, the engine rotational speed NE at which the centrifugal clutch 6 transitions from the open state to the semi-engaged state can change. Similarly, the clutch-in rotational speed Nci and the clutch-out rotational speed Nco can each change. More specifically, as described above, the transmission of torque (and consequently, the transmission of rotation) in the centrifugal clutch 6 is due to the frictional force generated when the clutch shoe 63 contacts (engages) with the inner circumferential surface of the outer drum 62. The frictional force (clutch friction force) between the clutch shoe 63 and the outer drum 62 can change depending on the temperature of the clutch shoe 63 and the outer drum 62, as well as the surrounding humidity, etc. In addition, the clutch friction force can change due to wear and deformation of the clutch shoe 63, etc.

[0090] Furthermore, clutch friction may increase due to a decrease in the biasing force of the elastic body (i.e., coil spring) that biases the clutch shoe 63 toward the axis of the crankshaft 23, due to aging. In other words, a decrease in the biasing force of the elastic body may cause clutch friction to occur even at relatively low engine rotational speeds NE. Similarly, a decrease in the biasing force of the elastic body may cause clutch friction to occur even at relatively low engine rotational speeds NE.

[0091] In the example shown in Figure 4, when the catalyst early activation control is executed, it is determined that the engine rotational speed NE is included in the region of increased lost torque before it reaches the first temperature-raising rotational speed Nr1, and as a result, specific control is executed. That is, clutch friction force is generated when the engine rotational speed NE is relatively low, and the ECU 1 reduces the engine rotational speed NE accordingly. In other words, according to the ECU 1, even when the engine rotational speed NE at which clutch friction force is generated in the centrifugal clutch 6 decreases, there is a higher possibility that unintended engagement in the centrifugal clutch 6 can be suppressed.

[0092] Therefore, the ECU 1 can maintain the engine speed NE at the largest possible value when performing catalyst early activation control, while suppressing unintended engagement in the centrifugal clutch 6 (for example, transmission of rotation in the centrifugal clutch 6). The region of increased lost torque can also be described as the range (region) of engine speed NE in which the centrifugal clutch 6 is in a semi-engaged state.

[0093] In other words, in order to suppress unintended engagement in the centrifugal clutch 6 by specific control, the first threshold Nth1 and / or second threshold Nth2 related to the determination process described above may be set such that the following condition (a) is more likely to be met when the rotational speed fluctuation amount Nfa becomes equal to the first threshold Nth1 and / or second threshold Nth2. By setting the first threshold Nth1 and / or second threshold Nth2 in this way, when the engine rotational speed NE approaches the clutch-in rotational speed Nci during idle operation control, the likelihood of specific control being executed increases. Condition (a): The engine rotational speed NE is less than the clutch-in rotational speed Nci and the difference between the engine rotational speed NE and the clutch-in rotational speed Nci is relatively small.

[0094] For example, condition (a) may be a condition that is satisfied when the engine rotational speed NE is approximately equal to the average value (i.e., the median value) of the first temperature-raising rotational speed Nr1 and the clutch-in rotational speed Nci. Alternatively, condition (a) may be a condition that is satisfied when the engine rotational speed NE is approximately equal to the average value of the clutch-out rotational speed Nco and the clutch-in rotational speed Nci.

[0095] The clutch-in rotational speed Nci and / or clutch-out rotational speed Nco, which are referenced when determining the first threshold Nth1 and / or the second threshold Nth2, may be the theoretical clutch-in rotational speed and / or theoretical clutch-out rotational speed. The theoretical clutch-in rotational speed and / or theoretical clutch-out rotational speed are theoretical values ​​(design values) obtained based on the shape and material of each component constituting the centrifugal clutch 6 (i.e., the inner disc 61, outer drum 62, clutch shoe 63, and coil spring, etc.). If the actual clutch-in rotational speed Nci is smaller (or larger) than the theoretical clutch-in rotational speed, it is highly likely that the engine rotational speed NE at which the rotational speed fluctuation Nfa is larger than the first threshold Nth1 or the second threshold Nth2 will decrease (or increase). Therefore, even if the clutch-in rotational speed Nci differs from the theoretical clutch-in rotational speed, it is highly likely that specific control will be executed before the engine rotational speed NE reaches the clutch-in rotational speed Nci.

[0096] In the vehicle equipped with this actual configuration, the rotational speed of the inner disc 61 of the centrifugal clutch 6 (input shaft rotational speed) was equal to the engine rotational speed NE, but the input shaft rotational speed may be different from the engine rotational speed NE. For example, a gear mechanism may be interposed in the torque transmission path from the crankshaft 23 to the inner disc 61. Even in this case, the input shaft rotational speed increases as the engine rotational speed NE increases. Therefore, when the transmitted torque of the centrifugal clutch 6 increases due to an increase in the engine rotational speed NE, the ECU 1 determines that the engine rotational speed NE is included in the region of increased lost torque and executes specific control.

[0097] The first heating rotation speed Nr1 was greater than the clutch-out rotation speed Nco, but it may also be less than the clutch-out rotation speed Nco and greater than the reference idle rotation speed Nib.

[0098] The ECU 1 may perform idle operation control that is different from the first idle operation control and the catalyst early activation control. For example, when the vehicle on which it is installed is traveling in an area with relatively low atmospheric pressure (e.g., high altitude), the ECU 1 may perform a "second idle operation control" as the idle operation control.

[0099] When ECU 1 performs catalyst early activation control, it previously set the target rotational speed Ntgt to a value equal to the first temperature-boosting rotational speed Nr1. That is, ECU 1 set the target rotational speed Ntgt to a predetermined value. Alternatively, when ECU 1 performs catalyst early activation control, it may gradually increase the target rotational speed Ntgt from the reference idle rotational speed Nib until it is determined that the engine rotational speed NE is included in the loss torque increase region.

[0100] The ECU 1 adjusted the bypass valve opening Vb according to the difference between the target rotational speed Ntgt and the engine rotational speed NE. In other words, when the ECU 1 decreases the engine rotational speed NE, it decreases the bypass valve opening Vb, thereby decreasing the amount of air flowing into the combustion chamber 33. However, the ECU 1 may also decrease the engine rotational speed NE by decreasing the fuel injection amount Qinj. Alternatively, the ECU 1 may decrease the engine rotational speed NE by retarding the ignition timing. The ECU 1 may also decrease the engine rotational speed NE by applying an electrical load. The ECU 1 may also decrease the engine rotational speed NE by temporarily causing a misfire (i.e., temporarily stopping fuel injection by the fuel injector 36 and ignition by the spark plug 39).

[0101] [Second Embodiment] The second embodiment will now be described. In the first embodiment, the ECU 1 terminated the catalyst early activation control and performed the first idle operation control as idle operation control when the catalyst temperature Tc became greater than the threshold temperature Tth. In contrast, in the second embodiment, after the internal combustion engine 2 starts operating and the vehicle on which it is installed has driven for the first time, the first idle operation control is performed as idle operation control regardless of the catalyst temperature Tc.

[0102] More specifically, the ECU 1a determines that the vehicle has started moving when the vehicle speed Vs becomes greater than "0" after the internal combustion engine 2 has started operating. During the period after the ECU 1a determines that the vehicle has started moving, it executes the first idle operation control as idle operation control. In other words, the ECU 1a executes catalyst early activation control as idle operation control during the period from the start of the internal combustion engine 2 to the first start of driving in the vehicle.

[0103] Although not shown in the diagram, if ECU 1a determines that the engine rotational speed NE is within the range of increased lost torque while catalyst early activation control is being performed, it will execute specific control in the same manner as ECU 1.

[0104] The determination of whether the mounted vehicle is running (running determination), performed by the ECU 1a, can be based on various physical quantities (determination physical quantities). The determination physical quantities referenced in the running determination may include, in addition to or instead of the vehicle speed Vs, engine rotational speed NE, fuel injection amount Qinj, exhaust temperature Te1, gear position, clutch position, acceleration obtained from the acceleration sensor, and the coolant temperature of the internal combustion engine 2. The fuel injection amount Qinj can also be said to be a physical quantity correlated with the load state of the internal combustion engine 2. The coolant temperature of the internal combustion engine 2 can also be said to be a physical quantity correlated with the temperature of the internal combustion engine 2. The ECU 1a may be configured to determine that the mounted vehicle is running when one or more determination physical quantities exceed a predetermined value (threshold). Alternatively, the ECU 1a may be configured to determine that the mounted vehicle is running when the state in which the determination physical quantities are greater than the predetermined value continues for a predetermined time. Furthermore, the ECU 1a may be configured to determine that the vehicle is running if the engine rotational speed NE and the fuel injection amount Qinj remain greater than their respective predetermined values ​​for a predetermined period of time.

[0105] [Third Embodiment] The third embodiment will be described with reference to Figure 5. Figure 5 is a time chart showing an example of the change in engine rotational speed NE of the internal combustion engine 2 controlled by the ECU 1b according to the third embodiment. The solid line L5 shown in Figure 5 represents the change in engine rotational speed NE. The dashed line L6 represents the change in transmission rotational speed ND in this example.

[0106] When the ECU 1b starts idle control after the vehicle has been driven, it temporarily sets the target rotational speed Ntgt to a value equal to the release rotational speed Nm. The release rotational speed Nm is set to be less than the (potentially variable) clutch-out rotational speed Nco. Alternatively, the release rotational speed Nm may be set such that there is a very high probability that the centrifugal clutch 6 will be released (more specifically, that the clutch shoe 63 and the outer drum 62 will separate) when the engine rotational speed NE decreases to the release rotational speed Nm.

[0107] In other words, when the ECU 1b determines that the vehicle has been driven after the internal combustion engine 2 has been started, it sets the target rotational speed Ntgt during idle operation to a value smaller than the clutch-out rotational speed Nco (or an engine rotational speed NE that is smaller than the clutch-out rotational speed Nco and reliably transitions to the open state of the centrifugal clutch 6). In this embodiment, the open rotational speed Nm is smaller than the reference idle rotational speed Nib.

[0108] In the example shown in Figure 5, the accelerator pedal input amount Ap is "0" during the period from time td0 to time td2. The catalyst temperature Tc at time td0 is less than the threshold temperature Tth. Cranking begins at time td0, and the internal combustion engine 2 starts operating. During the period shown in Figure 5, the braking system of the vehicle is not operating.

[0109] Since the catalyst temperature Tc is less than the threshold temperature Tth, the ECU 1b performs catalyst early activation control as idle operation control. Immediately after starting the internal combustion engine 2, the vehicle on which it is installed is not yet running, so the ECU 1b sets the target rotational speed Ntgt to a value equal to the first temperature-raising rotational speed Nr1 (not the open rotational speed Nm). As a result, at time td1, the engine rotational speed NE reaches the first temperature-raising rotational speed Nr1.

[0110] Subsequently, due to the driver's operation of the vehicle, the accelerator pedal input amount Ap becomes greater than "0", and as a result, the engine speed NE increases from time td2. At time td3, the engine speed NE reaches the clutch-engagement speed Nci, and as a result, the transmission speed ND begins to increase from "0". That is, the vehicle has started to move. At this time, the vehicle speed Vs becomes greater than "0", and the ECU1b determines that the vehicle is moving.

[0111] At time td4, the centrifugal clutch 6 is fully engaged, and therefore the rotational speed difference ΔN is approximately "0". Subsequently, due to the operation of the driver of the vehicle, the accelerator operation amount Ap becomes "0", and the engine rotational speed NE decreases accordingly, so at time td5 the centrifugal clutch 6 becomes partially engaged, and therefore, from time td5 onward, the rotational speed difference ΔN is greater than "0".

[0112] At time td6, the engine rotational speed NE decreases to the clutch-out rotational speed Nco, and as a result the transmission rotational speed ND becomes approximately "0". That is, the vehicle on which it is installed is stopped. At this point, the catalyst temperature Tc is still lower than the threshold temperature Tth, so the ECU 1b performs catalyst early activation control as idle operation control. However, since the vehicle on which it is installed has already been driven, the ECU 1b sets the target rotational speed Ntgt to a value equal to the open rotational speed Nm. As a result, at time td7, the engine rotational speed NE reaches the open rotational speed Nm. That is, the ECU 1b decreases the target rotational speed Ntgt, thereby ensuring that the centrifugal clutch 6 transitions to the open state. Next, the ECU 1b sets the target rotational speed Ntgt to a value equal to the first temperature rise rotational speed Nr1.

[0113] More specifically, when the accelerator input amount Ap becomes approximately "0" and the vehicle speed Vs becomes approximately "0" (in this example, time Td6), the ECU 1b changes the target rotational speed Ntgt from the open rotational speed Nm to the first temperature-raising rotational speed Nr1 after the release transition time Tm has elapsed. In this example, when the release transition time Tm has elapsed from time td6 to time td8, the ECU 1b sets the target rotational speed Ntgt to a value equal to the first temperature-raising rotational speed Nr1, and as a result the engine rotational speed NE reaches the first temperature-raising rotational speed Nr1.

[0114] Subsequently, at time td9, the catalyst temperature Tc rises to a value greater than the threshold temperature Tth, and therefore, ECU1b executes the first idle operation control as idle operation control. That is, ECU1b sets the target rotational speed Ntgt to a value equal to the reference idle rotational speed Nib. As a result, the engine rotational speed NE reaches the reference idle rotational speed Nib.

[0115] If the catalyst temperature Tc at time td8 is greater than the threshold temperature Tth, the ECU 1b sets the target rotational speed Ntgt to a value equal to the reference idle rotational speed Nib (not the first heating rotational speed Nr1). That is, from time Td8 onward, the ECU 1b executes the first idle operation control as idle operation control.

[0116] In any case, when the vehicle on which the ECU 1b is installed stops after driving, the ECU 1b can more reliably transition the centrifugal clutch 6 to the open state by temporarily setting the target rotational speed Ntgt to a value equal to the open rotational speed Nm. If the accelerator operation amount Ap remains approximately "0", the ECU 1b temporarily sets the target rotational speed Ntgt to a value equal to the open rotational speed Nm, and then performs idle operation control.

[0117] Although not shown in the diagram, if ECU 1b determines that the engine rotational speed NE is in the region of increased lost torque while catalyst early activation control is being performed, it performs specific control in the same way as ECU 1. ECU 1b determines that the vehicle is running when the vehicle speed Vs is greater than "0", but as with ECU 1a in the second embodiment, the determination of whether the vehicle is running may be made based on various determination physical quantities.

[0118] The timing at which the ECU 1b changes the target rotational speed Ntgt from the open rotational speed Nm to the first temperature rise rotational speed Nr1 or the reference idle rotational speed Nib (target change timing) was determined to be when the open transition time Tm elapsed from the point at which the accelerator operation amount Ap became approximately "0" and the vehicle speed Vs became approximately "0". The target change timing may be different from this. For example, the ECU 1b may determine that the target change timing has arrived when the magnitude of the difference between the engine rotational speed NE and the open rotational speed Nm is smaller than a predetermined value for a predetermined time.

[0119] Furthermore, when the catalyst early activation control is being performed, if the vehicle on which it is installed is not yet running, the ECU 1b may set the target rotational speed Ntgt to a value equal to a second temperature-raising rotational speed Nr2 (not shown), which is different from the first temperature-raising rotational speed Nr1. The second temperature-raising rotational speed Nr2 may be greater than or less than the first temperature-raising rotational speed Nr1.

[0120] 1, 1a, 1b ECU 2 Internal Combustion Engine 21 Piston 22 Connecting Rod 23 Crankshaft 31 Intake Pipe 32 Intake Port 33 Combustion Chamber 34 Intake Valve 35 Throttle Valve 36 Fuel Injector 37 Bypass Passage 38 Bypass Valve 39 Spark Plug 41 Exhaust Port 42 Exhaust Pipe 43 Exhaust Valve 44 Catalytic Converter 51 Outer Shaft 52a, 52b Gears 53 Drive Shaft 54 ​​Drive Transmission 6 Centrifugal Clutch 61 Inner Disc 62 Outer Drum 63 Clutch Shoes 71 Crank Angle Sensor 72 Cam Position Sensor 73 Accelerator Pitch Sensor 74 Intake Air Volume Sensor 75 Vehicle Speed ​​Sensor 76a, 76b Temperature Sensor

Claims

1. A control device for an internal combustion engine used in a vehicle comprising an internal combustion engine, a centrifugal clutch that engages when the rotational speed of the internal combustion engine increases, and a catalyst for exhaust gas purification, wherein during idle operation, the control device performs either a first idle operation control or a catalyst early activation control that increases the rotational speed of the internal combustion engine to a level higher than the rotational speed of the internal combustion engine when the first idle operation control is performed to activate the catalyst, wherein, if the region of rotational speed of the internal combustion engine in which the lost torque of the internal combustion engine increases as the centrifugal clutch transitions from an open state to a fully engaged state is defined as the lost torque increase region, the control device for an internal combustion engine controls the rotational speed of the internal combustion engine so that, when it is determined that the rotational speed of the internal combustion engine falls within the lost torque increase region during the execution of the catalyst early activation control, the rotational speed of the internal combustion engine is lower than the actual rotational speed of the internal combustion engine when it is determined that the rotational speed of the internal combustion engine falls within the lost torque increase region.

2. A control device for an internal combustion engine according to claim 1, wherein the control device for an internal combustion engine performs the catalyst early activation control during the period from the start of the internal combustion engine to the first start of driving in the vehicle.

3. A control device for an internal combustion engine according to claim 1 or 2, wherein the target rotational speed of the internal combustion engine during the execution of the catalyst early activation control is set to a value greater than the clutch-out rotational speed at which the centrifugal clutch transitions from an engaged state to an unengaged state.

4. A control device for an internal combustion engine according to any one of claims 1 to 3, wherein, when it is determined that the vehicle has been driven after the internal combustion engine has been started, the control device sets the target rotational speed of the internal combustion engine during idle operation to a value smaller than the clutch-out rotational speed at which the centrifugal clutch transitions from an engaged state to an unengaged state.

5. A control device for an internal combustion engine according to claim 4, wherein the control device determines whether or not the vehicle has traveled based on at least one physical quantity among the load state of the internal combustion engine, the rotational speed of the internal combustion engine, the vehicle speed of the vehicle, and the temperature of the internal combustion engine.

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