Straddle type vehicle

1. Field of the Invention

The present invention relates to straddle type vehicles and more specifically to a straddle type vehicle including an operation portion used to control driving of an engine.

2. Description of the Related Art

There are known straddle type vehicles including an engine and an operation portion that is operated by a rider to control driving of the engine. JP S53-13726 A discloses a snowmobile as such a straddle type vehicle. According to the disclosure of JP S53-13726 A, the snowmobile includes an engine and a throttle lever that is operated by a rider to control driving of the engine. The snowmobile is provided with a carburetor used to supply fuel into an intake path for the engine. The carburetor is provided with a throttle valve that can open/close the intake path. The throttle valve is connected to the throttle lever by a Bowden cable (wire). The Bowden cable is moved in response to the movement of the throttle lever when the throttle lever is operated by a rider. The throttle valve is opened/closed according to the movement of the Bowden cable, so that the amount of air-fuel mixture to be taken into the engine is regulated.

The snowmobile disclosed by JP S53-13726 includes a lever switch used to detect the presence/absence of operation input to a throttle lever. The lever switch detects operation input before the throttle lever is rotated in response to operation by a rider.

As in the snowmobile disclosed by JP S53-13726 A, operation input is detected by the lever switch before the throttle lever is rotated, so that the rider's explicit intention of operation can be confirmed. However, it is difficult to detect operation input by the lever switch for a short period before the rotation of the throttle lever starts.

Unlike the arrangement disclosed by JP S53-13726 A in which the throttle valve is controlled by a mechanical wire, a throttle valve may be controlled electrically. In this case, no wire is provided between a throttle lever and the throttle valve, and therefore, a force required for operating the throttle lever is reduced. This makes it more difficult to detect timing before the rotation of the throttle lever starts.

In view of the above, a straddle type vehicle according to a preferred embodiment of the present invention includes an engine, an engine power controller, an operation portion, an operation input detector, an operation amount detector, and a control portion. The engine power controller controls driving of the engine. The operation portion is arranged to control the engine. The operation input detector detects whether the operation portion is operated. The operation amount detector electrically detects the operation amount of the operation portion. The control portion controls the engine by controlling the engine power controller based on the detection results of the operation input detector and the operation amount detector. The control portion does not control the engine power controller based on the operation amount detected by the operation amount detector in a first region in which the operation amount detected by the operation amount detector is at most equal to a first operation amount, a second operation amount smaller than the first operation amount is set in the first region, and if an operation amount detected by the operation amount detector is greater than the first operation amount, the control portion controls the engine power controller based on the operation amount detected by the operation amount detector, provided that operation corresponding to the second operation amount is detected by the operation input detector.

Thus, a preferred embodiment of the present invention provides a vehicle that achieves engine control according to the rider's intention by clearly determining whether the operation portion is operated by the rider.

Other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

FIG. 1 is a side view of an entire structure of a snowmobile according to a preferred embodiment of the present invention.

FIG. 2 is a system diagram of a peripheral structure of an ECU in the snowmobile.

FIG. 3 is a perspective view of a handle.

FIG. 4 is a plan view of the handle.

FIG. 5 is an enlarged plan view of the handle.

FIG. 6 is a rear sectional view of an internal structure of an operation portion.

FIG. 7 is a timing chart for illustrating an example of how a throttle lever and a throttle valve operate.

FIGS. 8 and 9 are flowcharts for illustrating a method of controlling the throttle valve using an ECU.

FIG. 10 is a timing chart for illustrating an example of how a throttle lever and a throttle valve operate.

Preferred embodiments of the present invention will be described. According to the preferred embodiments, a snowmobile will be described as an example of a straddle type vehicle according to the present invention. In the drawings, the arrow FWD refers to the forward advancing direction of the snowmobile 1 . In the following description, the “front-back” direction and the “right” and “left” refer to these directions viewed from a rider on the snowmobile 1 unless otherwise specified.

FIG. 1 is a left side view of an entire structure of the snowmobile 1 according to a first preferred embodiment of the present invention. As shown in FIG. 1 , a front frame 2 is provided in the front portion of the vehicle. A main frame 3 is connected to the upper portion of the front frame 2 . The main frame 3 extends backward and upward. An under frame 5 is connected to the rear portion of the front frame 2 . The rear portions of the main frame 3 and the under frame 5 are coupled by a coupling frame 6 . A rear frame 7 is connected to the rear portions of the under frame 5 and the coupling frame 6 . The rear frame 7 extends backward. The front frame 2 , the main frame 3 , the under frame 5 , the coupling frame 6 , and the rear frame 7 define the body frame.

A pair of right and left ski holding frames 8 is provided under the front frame 2 . A pair of right and left skis 9 is provided at the lower end of the pair of ski holding frames 8 . The skis 9 turn to the right and the left as the ski holding frames 8 turn to the right and the left. A front cowling 10 arranged to cover the front portion of the vehicle body is provided in front of and above the front frame 2 .

A handle 11 connected to the ski holding frames 8 is provided above the main frame 3 . As the handle 11 is turned, the skis 9 are turned to the right or left, so that the advancing direction of the snowmobile 1 can be determined.

A seat 12 is provided above the rear frame 7 . A driving track 13 is provided under the rear frame 7 . The driving track 13 includes a rubber track belt 13 a , front and rear axles 13 b and 13 c provided inside the track belt 13 a , and a suspension 13 d used to absorb impact. The front axle 13 b rotates the track belt 13 a by driving power of the engine 4 . This allows the snowmobile 1 to travel. A plurality of guide wheels 13 e and 13 f used to prevent the loosening of the track belt 13 a are provided inside the track belt 13 a.

The engine 4 is provided in front of the front axle 13 b . The engine 4 is supported by the body frame.

FIG. 2 is a system diagram of the engine 4 and a peripheral structure of an ECU (Engine Control Unit) 26 . As shown in FIG. 2 , the engine 4 includes a cylinder 14 , a piston 15 arranged to move in the vertical direction in the cylinder 14 and a cylinder head 16 provided above the cylinder 14 . One end of a connecting rod 17 is rotatably attached to the piston 15 . The cylinder head 16 is arranged to close one opening of the cylinder 14 . The cylinder head 16 includes an intake port 16 a and an exhaust port 16 b . The intake and exhaust ports 16 a and 16 b are provided with an intake valve 18 and an exhaust valve 19 , respectively. A combustion chamber 16 c is provided in the lower portion of the cylinder head 16 .

The intake port 16 a is provided to supply an air-fuel mixture containing air and fuel to the combustion chamber 16 c . The intake port 16 a is connected with an intake pipe 20 . The exhaust port 16 b is arranged to discharge residual gas after combustion from the combustion chamber 16 c . An exhaust pipe 21 is connected to the exhaust port 16 b . A muffler 22 is connected to the rear end of the exhaust port pipe 21 as shown in FIG. 1 .

As shown in FIG. 2 , a throttle valve 23 is attached to the intake pipe 20 so that it can be opened/closed. The throttle valve 23 is an example of the “intake control valve” according to a preferred embodiment of the present invention. The throttle valve 23 is arranged to control driving of the engine 4 . The throttle valve 23 rotates to control the open state and the closed state of the intake pipe 20 and regulates the amount of air to be taken into the intake port 16 a of the engine 4 from the intake pipe 20 .

A TPS (Throttle Position Sensor) 23 a that detects the rotation position of the throttle valve 23 is provided near the throttle valve 23 of the intake pipe 20 . A valve driving motor 23 b that drives the throttle valve 23 is provided near the TPS 23 a . The throttle valve 23 is an example of the “engine power controller” and the “intake control valve” according to a preferred embodiment of the present invention. The TPS 23 a is an example of the “control state detector” and the “opening/closing detector” according to a preferred embodiment of the present invention. The valve driving motor 23 b is an example of the “engine power controller” and the “control valve driving portion” according to a preferred embodiment of the present invention.

An injector 24 that injects fuel toward the engine 4 is attached between the throttle valve 23 in the intake pipe 20 and the intake port 16 a . An ignition plug 25 used to ignite air-fuel mixture from the intake port 16 a is attached to the combustion chamber 16 c.

An ECU (Engine Control Unit) 26 that receives a detection signal transmitted from the TPS 23 a is connected to the TPS 23 a . The ECU 26 is an example of the “control portion” according to a preferred embodiment of the present invention. The ECU 26 controls driving of the engine 4 based on a predetermined opening degree for the throttle valve 23 during idling, a threshold opening degree in a preliminary zone (that will be described), a detection signal for the rotation amount (operation amount) of a thumb throttle 31 (that will be described) by the rider. More specifically, based on these parameters, the opening/closing of the throttle valve 23 , the injection amount of fuel by the injector 24 , and the ignition by the ignition plug 25 are controlled.

FIG. 3 is a perspective view of a right handle 11 R. As shown in FIG. 3 , the right handle 11 R includes a grip 11 a grasped by the rider and an operation portion 30 provided near the grip 11 a . The operation portion 30 is operated by the right hand of the rider to control driving of the engine 4 . More specifically, the operation portion 30 controls driving of the engine 4 by controlling the open/closed state of the throttle valve 23 . The operation portion 30 includes a resin thumb throttle 31 operated by the rider's right hand and a case 32 that supports the thumb throttle 31 . The thumb throttle 31 is rotatably supported at the case 32 . The thumb throttle 31 is an example of the “operation portion” and the “throttle lever” according to a preferred embodiment of the present invention.

In the specification, the throttle lever refers to an operation tool provided separately from the grip 11 a in the vicinity of the grip 11 a and used to control driving of the engine 4 . More specifically, in the described arrangement, driving of the engine is not controlled by operating the grip 11 a itself but a separate operation tool is provided near the grip 11 a . The operation tool is not limited to such a rotational lever or any particular kind.

The handle 11 includes a left handle 11 L (see FIG. 1 ) symmetrically positioned to the right handle 11 R. However, the left handle 11 L does not include the operation portion 30 .

FIG. 4 is a plan view of the right handle 11 R. As shown in FIG. 4 , the grip 11 a extends to the right of the vehicle (in the X2-direction). The thumb throttle 31 extends rightward and backward (opposite to the direction of the arrow FWD).

FIG. 5 is an enlarged plan view of the right handle 11 R. As shown in FIG. 5 , the thumb throttle 31 can rotate in the horizontal direction around the rotation shaft 33 . The rotation shaft 33 is preferably made of metal and rotatably attached to the resin case 32 . The rotation shaft 33 is provided behind the grip 11 a . The rotation shaft 33 is provided in a position nearer to the rider on the snowmobile 1 than the grip 11 a . The position of the rotation shaft 33 is not particularly limited. The rotation shaft 33 may be provided ahead of the grip 11 a.

The rider controls the thumb throttle 31 by the thumb of the right hand while grasping the grip 11 a by the right hand. When the rider pushes the thumb throttle 31 forward by the thumb of the right hand, the thumb throttle 31 is rotated forward.

FIG. 6 is a rear sectional view of an internal structure of the operation portion 30 . As shown in FIG. 6 , a flange 33 a is provided at the upper end of the rotation shaft 33 . Two rubber O-rings 34 arranged to apply resistance to the rotation operation of the thumb throttle 31 are provided between the flange 33 a and the upper surface of the case 32 . A flange 33 b is provided at the lower end of the rotation shaft 33 . Further two O-rings 34 arranged to apply resistance to the rotation operation of the thumb throttle 31 are provided between the flange 33 b and the lower surface of the case 32 .

An end of a metal arm 35 is attached (e.g., welded) to the rotation shaft 33 . The arm 35 extends outward (in the X2-direction) in the widthwise direction of the vehicle from the connection portion with the rotation shaft 33 . The other end of the arm 35 is fixed to the thumb throttle 31 . The arm 35 is therefore rotated integrally with the rotation operation of the thumb throttle 31 . The arm 35 transmits the rotation operation of the thumb throttle 31 to the rotation shaft 33 .

A torsion coil spring 36 includes a coil portion 36 a provided around the rotation shaft 33 . The torsion coil spring 36 has one end 36 b hooked at the inner wall surface of the case 32 . The other end 36 c of the torsion coil spring 36 is in contact with the arm 35 from the front. In this way, the torsion coil spring 36 pressurizes the thumb throttle 31 backward through the arm 35 . The pressurizing force of the torsion coil spring 36 causes the thumb throttle 31 to be rotated to the initial position on the backside when the operation force of the rider is not applied.

A pressure sensor 37 is provided in the thumb throttle near the end of the arm 35 on the outer side (in the X2-direction) in the widthwise direction of the vehicle. The pressure sensor 37 is an example of the “operation input detector” according to a preferred embodiment of the present invention. The pressure sensor 37 detects whether the rider operates the thumb throttle 31 by detecting an operation load applied to the thumb throttle 31 . As shown in FIG. 5 , when the rider rotates thumb throttle 31 , the thumb throttle 31 is pushed forward (in the direction of the arrow FWD). The pressure is transmitted to the arm 35 from the thus pushed thumb throttle 31 . The pressure sensor 37 detects the pressure and detects an operation load when the thumb throttle 31 is operated by the rider.

The ECU 26 determines whether operation of the thumb throttle 31 is carried out by the rider based on the operation load detected by the pressure sensor 37 . As shown in FIG. 2 , a detection signal for the operation load detected by the pressure sensor 37 is transmitted to the ECU 26 . A threshold value is set for the load detected by the pressure sensor 37 and when the thumb throttle 31 is operated with a load greater than the threshold value, the ECU 26 determines that the thumb throttle 31 is operated by the rider.

As shown in FIG. 6 , an APS (Accelerator Position Sensor) 38 is provided coaxially under the rotation shaft 33 in the case 32 . The APS 38 is an example of the “operation amount detector” according to a preferred embodiment of the present invention. The APS 38 electrically detects the rotation amount of the thumb throttle 31 . The rotation shaft 33 is inserted in the APS 38 and the APS 38 detects the rotation angle of the rotation shaft 33 from the initial position. Using the APS 38 , the amount of operation of the thumb throttle 31 by the rider can be detected.

As shown in FIG. 2 , the APS 38 transmits a detection signal for the operation amount of the thumb throttle 31 to the ECU 26 . The ECU 26 calculates the opening degree of the throttle valve 23 , a fuel injection amount and injection timing by the injector 24 and ignition timing by the ignition plug 25 based on the detection signals from the APS 38 and the TPS 23 a . The ECU controls driving of the engine 4 based on the results of calculation. The ECU 26 controls the opening degree of the throttle valve 23 . The ECU 26 controls the engine 4 as a result through the control of the throttle valve 23 .

According to the present preferred embodiment, when the operation amount (accelerator opening degree) of the thumb throttle 31 detected by the APS 38 is not more than a prescribed value, the ECU 26 does not control the valve driving motor 23 b based on the detected accelerator opening degree. A preliminary zone (electrically idle region) is set for the ECU 26 . In the preliminary zone, if the thumb throttle 31 is operated by the rider, the accelerator opening degree is not reflected upon driving of the valve driving motor 23 b . The preliminary zone is an example of the “first region” according to a preferred embodiment of the present invention. A preliminary zone opening degree is an upper limit for the preliminary zone. When the accelerator opening degree detected by the APS 38 is greater than the preliminary zone opening degree, the ECU 26 controls the valve driving motor 23 b based on the accelerator opening degree. The preliminary zone covers the region between the state in which the thumb throttle 31 is not operated (when the accelerator opening degree is zero) and the state in which the APS 38 detects the preliminary zone opening degree.

In the preliminary zone, the ECU 26 maintains control so that the opening degree of the throttle valve 23 is at an idling opening degree. At the idling opening degree, the engine speed of the engine 4 can be maintained so that the rotation power of the engine 4 is not transmitted to the driving track 13 . The power transmission member between the engine 4 and the driving track 13 is provided with a clutch that turns on/off power transmission. The clutch turns on/off in response to the engine speed of the engine 4 . When the opening degree of the throttle valve 23 is regulated at the idling opening degree, the power of the engine 4 is not transmitted to the driving track 13 . The ECU 26 controls the valve driving motor 23 b so that the throttle valve 23 is maintained at the idling opening degree in the preliminary zone.

When the accelerator opening degree detected by the APS exceeds the preliminary zone opening degree, the ECU 26 controls the valve driving motor 23 b so that the opening degree of the throttle valve 23 exceeds the idling opening degree. The state of the engine 4 changes from the idling state to a traveling state, and the snowmobile 1 starts to travel.

FIG. 7 is a timing chart for illustrating an example of how the thumb throttle 31 and the throttle valve 23 operate. In FIG. 7 , the uppermost stage indicates change in load applied to the thumb throttle 31 . The middle stage in FIG. 7 indicates change in the rotation amount of the thumb throttle 31 and the rotation shaft 33 , in other words, change in the accelerator opening degree. In FIG. 7 , the lowermost stage indicates the throttle valve opening degree. FIGS. 8 and 9 are flowcharts about the ECU 26 for illustrating a method of controlling the throttle valve 23 . With reference to FIGS. 7 to 9 , the content of the control of the throttle valve 23 by the ECU 26 will be described.

Referring to FIG. 8 , it is determined by the ECU 26 in step S 1 whether the engine 4 is in a driven state. If it is determined that the engine 4 is in a driven state (YES in step S 1 ), the control proceeds to step S 2 . This timing comes in and before timing T 1 in FIG. 7 . In the state in and before timing T 1 in FIG. 7 , the accelerator opening degree detected by the APS 38 is zero and the throttle valve opening degree detected by the TPS 23 a equals the idling opening degree. The engine 4 is in an idling state. The engine 4 is controlled to attain an idling state as an initial state before attaining a traveling state by the operation of the rider. If the engine 4 is not in a driven state (NO in step S 1 ), the control returns to step S 1 , and the determination process is repeatedly carried out.

As shown in FIG. 7 , between timings T 1 and T 2 , the engine 4 is in an idling state. When the rider operates the thumb throttle 31 and a load is applied between timings T 1 and T 2 , the rotation shaft 33 rotates together with the thumb throttle 31 . The APS 38 detects the rotation angle of the rotation shaft 33 as an accelerator opening degree.

As shown in FIG. 8 , it is determined by the ECU 26 in step S 2 whether the accelerator opening degree (the rotation angle of the thumb throttle 31 and the rotation shaft 33 ) detected by the APS 38 is greater than zero. If it is determined that the accelerator opening degree is greater than zero (YES in step S 2 : in and after timing T 1 in FIG. 7 ), and the control proceeds to step S 3 . As shown in FIG. 7 , between timings T 1 and T 2 , the ECU 26 controls the valve driving motor 23 b so that the throttle valve 23 maintains the idling opening degree as the initial state.

As shown in FIG. 8 , if it is determined that the accelerator opening degree is not greater than zero, in other words, if it is determined that the accelerator opening degree is zero (NO in step S 2 : in or before timing T 1 in FIG. 7 ), the control proceeds to step S 10 in FIG. 9 . In step S 10 , the valve driving motor 23 b is controlled so that the throttle valve 23 maintains the idling opening degree.

As shown in FIG. 7 , between timings T 1 to T 2 , when the rider increases the load applied to the thumb throttle 31 , the rotation angle of the thumb throttle 31 and the rotation shaft 33 increases. The APS 38 detects the rotation angle of the rotation shaft 33 , so that increase in the accelerator opening degree is detected.

As shown in FIG. 8 , it is determined in step S 3 whether the load applied to the thumb throttle 31 detected by the pressure sensor 37 is not less than a threshold value. The ECU determines whether operation of the thumb throttle 31 is carried out by the rider based on the determination. If the ECU 26 determines that the load applied to the thumb throttle 31 by the rider is not less than the threshold value (YES in step S 3 : in and after timing T 2 in FIG. 7 ), the control proceeds to step S 4 .

If it is determined that the load applied to the thumb throttle 31 is less than the threshold value (NO in step S 3 : between timings T 1 to T 2 in FIG. 7 ), the control proceeds to step S 11 .

As shown in FIG. 7 , the critical point for determining whether operation is carried out to the thumb throttle 31 is timing T 2 in the period where the accelerator opening degree detected by the APS 38 changes from zero to a preliminary zone opening degree (from timings T 1 to T 3 in FIG. 7 ).

About a half of the rotation angle of the thumb throttle 31 when the accelerator opening degree reaches the preliminary zone opening degree (the rotation angle in timing T 3 in FIG. 7 ) is defined as a reference angle. The load applied to the thumb throttle 31 that reaches the threshold value is a load necessary for the rotation angle of the thumb throttle 31 to reach the reference angle. In timing T 2 , the thumb throttle 31 attains about a half of the rotation angle where the accelerator opening degree reaches the preliminary zone opening degree, in other words, attains the reference angle. At the time, it is determined that the load applied to the thumb throttle 31 is not less than the threshold value and that operation input to the thumb throttle 31 by the rider has been carried out.

As shown in FIG. 7 , in timings T 2 to T 3 , if the rider increases the load applied to the thumb throttle 31 beyond the threshold value, the APS 38 detects the rotation angle of the rotation shaft 33 . After the load applied to the thumb throttle 31 exceeds the threshold value (in and after timing T 2 in FIG. 7 ), the control proceeds to step S 4 as shown in FIG. 8 . It is determined by the ECU 26 in step S 4 whether the accelerator opening degree detected by the APS 38 is greater than the preliminary zone opening degree.

If it is determined that the accelerator opening degree is greater than the preliminary zone opening degree (YES in step S 4 : in and after timing T 3 in FIG. 7 ), the control proceeds to step S 5 . If it is determined that the accelerator opening degree is not more than the preliminary zone opening degree (NO in step S 4 : in and before timing T 3 in FIG. 7 ), the control proceeds to step S 10 in FIG. 9 , and the valve driving motor 23 b is controlled so that the throttle valve 23 maintains the idling opening degree.

In step S 5 shown in FIG. 8 , the opening degree of the throttle valve 23 is controlled based on the accelerator opening degree output by the APS 38 . More specifically, the preliminary zone opening degree is subtracted from the accelerator opening degree output by the APS 38 to produce a differential opening degree. The valve driving motor 23 b is controlled so that the opening degree of the throttle valve 23 equals an opening degree produced by adding the idling opening degree to the valve opening degree calculated based on the differential opening degree.

As shown in FIG. 7 , the ECU 26 controls the valve driving motor 23 b in response to the accelerator opening degree that changes according to the operation of the thumb throttle 31 by the rider. The accelerator opening degree detected by the APS 38 is raised to an accelerator opening degree at which the thumb throttle 31 reaches the full opening degree from the preliminary zone opening degree between timings T 3 and T 4 . During the period, the ECU 26 controls the valve driving motor 23 b so that the opening degree of the throttle valve 23 is increased.

As shown in FIG. 8 , it is determined in step S 6 whether the accelerator opening degree detected by the APS 38 is reduced. If it is determined that the accelerator opening degree is reduced (YES in step S 6 : in and after timing T 4 in FIG. 7 ), the control proceeds to step S 7 .

As shown in FIG. 7 , during the period before the accelerator opening degree detected by the APS 38 reaches the preliminary zone opening degree from the full opening degree of the thumb throttle 31 (between timings T 4 and T 5 ), the ECU 26 controls the valve driving motor 23 b so that the opening degree of the throttle valve 23 is reduced.

As shown in FIG. 8 , if it is determined that the accelerator opening degree is not reduced (NO in step S 6 : between timings T 3 and T 4 in FIG. 7 ), the control proceeds to step S 3 . It is determined in step S 3 whether the load applied to the thumb throttle 31 detected by the pressure sensor 37 is not less than the threshold value. If the load applied to the thumb throttle 31 is not less than the threshold value (YES in step S 3 : between timings T 2 and T 6 in FIG. 7 ), steps S 4 to S 6 are repeatedly carried out. In this way, the ECU 26 repeatedly determines whether the load applied to the thumb throttle 31 is not less than the threshold value. It is continuously determined whether operation of the thumb throttle 31 is carried out by the rider.

It is determined in step S 7 whether the load applied to the thumb throttle 31 detected by the pressure sensor 37 is less than the threshold value. If the load applied to the thumb throttle 31 is less than the threshold value (YES in step S 7 : in and after timing T 6 in FIG. 7 ), the control proceeds to step S 8 in FIG. 9 . If it is determined that the load applied to the thumb throttle 31 is not less than the threshold value (NO in step S 7 : between timings T 4 to T 6 in FIG. 7 ), the control returns to step S 3 . It is determined in step S 3 whether the load applied to the thumb throttle 31 detected by the pressure sensor 37 is not less than the threshold value.

It is determined in step S 8 whether the opening degree of the throttle valve 23 detected by the TPS 23 a equals the idling opening degree. If it is determined that the opening degree of the throttle valve 23 equals the idling opening degree (YES in step S 8 : between timings T 5 to T 7 in FIG. 7 ), the processing ends.

As shown in FIG. 7 , between timings T 5 and T 7 , the accelerator opening degree detected by the APS 38 is reduced from the preliminary zone opening degree to zero. During the period, the accelerator opening degree is within the range of the preliminary zone (electrical idling region), and therefore the ECU 26 controls the valve driving motor 23 b so that the opening degree of the throttle valve 23 is maintained at the idling opening degree.

If it is determined in step S 8 that the opening degree of the throttle valve 23 does not equal the idling opening degree (is greater than the idling opening degree) (NO in step S 8 ), the control proceeds to step S 9 . In step S 9 , the valve driving motor 23 b is controlled so that the throttle valve 23 is gradually closed.

If it is determined in step S 3 that the load applied to the thumb throttle 31 is less than the threshold value (NO in step S 3 ), the control proceeds to step S 11 . The ECU 26 determines that the operation of the thumb throttle 31 by the rider is stopped. It is determined in step S 11 whether the load detected by the pressure sensor 37 has continued to be less than the threshold value for a prescribed period. If it is determined that the load detected by the pressure sensor 37 has continued to be less than threshold value for a prescribed period (YES in step S 11 ), the control proceeds to step S 12 . The ECU 26 determines that the operation of the thumb throttle 31 by the rider is no longer carried out.

If it is determined that the state in which the load detected by the pressure sensor 37 is less than the threshold value did not continue for a prescribed period (NO in step S 11 ), it is determined that the operation of the thumb throttle 31 by the rider continues, and the control proceeds to step S 4 .

It is determined in step S 12 whether the throttle valve opening degree detected by the TPS 23 a equals the idling opening degree. If it is determined that the throttle valve opening degree equals the idling opening degree (YES in step S 12 ), the control proceeds to step S 10 . In step S 10 , the valve driving motor 23 b is controlled so that the throttle valve 23 maintains the idling opening degree.

If it is determined that the throttle valve opening degree does not equal the idling opening degree (is greater than the idling degree)(NO in step S 12 ), the control proceeds to step S 13 and the valve driving motor 23 b is controlled so that the throttle valve 23 is gradually closed.

After the series of processing steps, the control returns to step S 1 and the processing is repeated.

According to the present preferred embodiment, the threshold value for operation input is set in the preliminary zone, and it is determined by the pressure sensor 37 whether operation of the thumb throttle 31 is carried out. Unlike the case in which the presence/absence of operation input is detected for a very short period before the rotation operation of the thumb throttle 31 , sufficient time can be secured for detecting the presence/absence of operation input. While driving of the engine 4 is electrically controlled by operating the thumb throttle 31 , the presence/absence of operation input can be detected accurately by the pressure sensor 37 .

When the accelerator opening degree is greater than the preliminary zone opening degree, the ECU 26 carries out engine control using the valve driving motor 23 b based on the accelerator opening degree. In the preliminary zone, the presence/absence of operation of the thumb throttle 31 by the pressure sensor 37 is determined. Engine control based on the accelerator opening degree without detecting operation of the thumb throttle 31 can be prevented.

According to the present preferred embodiment, if no operation of the thumb throttle 31 is detected and the throttle valve opening degree detected by the TPS 23 a is greater than the idling opening degree in the preliminary zone, the ECU 26 controls the valve driving motor 23 b so that the engine 4 is maintained in an idling state. More specifically, the ECU 26 controls the valve driving motor 23 b so that the engine speed of the engine 4 is not more than a prescribed engine speed at which the vehicle does not start to move. If no operation of the thumb throttle 31 is carried out and the throttle valve opening degree is greater than the idling opening degree because of freezing or the like, the engine 4 can be kept automatically in an idling state.

According to the present preferred embodiment, the pressure sensor 37 used to detect the load applied to the thumb throttle 31 as pressure is preferably provided. If application of a load equal to or larger than the threshold value to the thumb throttle 31 is determined by the pressure sensor 37 , it is determined that operation of the thumb throttle 31 has been carried out. The presence/absence of operation of the thumb throttle 31 based on the rider's explicit intention can be determined.

Approximately a half of the rotation angle of the thumb throttle 31 when reached at the preliminary zone opening degree is set as a reference angle. According to the present preferred embodiment, the threshold value for the load detected by the pressure sensor 37 is set as the load at which the thumb throttle attains the reference angle. The relationship between the load applied to the thumb throttle 31 and the angle of the thumb throttle 31 rotated by the load slightly changes because of change with time in the rotation mechanism of the thumb throttle 31 . According to the present preferred embodiment, the threshold value for the load detected by the pressure sensor 37 can be prevented from departing from the preliminary zone even if such change occurs.

According to the present preferred embodiment, if the thumb throttle 31 is operated with a load equal to or greater than the threshold value (in the range of timings T 2 to T 6 in FIG. 7 ), the presence/absence of operation input to the thumb throttle 31 continues to be determined by the pressure sensor 37 . When the state of the thumb throttle 31 changes from the state in which it is operated with a load at least equal to the threshold value to the state in which it is operated with a load less than the threshold value, control in response to the presence/absence of operation input to the thumb throttle 31 can be carried out.

According to the present preferred embodiment, if the accelerator opening degree detected by the APS 38 is greater than the preliminary zone opening degree, the valve driving motor 23 b is controlled at least based on the accelerator opening degree. If the accelerator opening degree detected by the APS 38 exceeds the preliminary zone opening degree, the vehicle can be switched to a traveling state.

According to the present preferred embodiment, if the accelerator opening degree detected by the APS 38 is greater than the preliminary zone opening degree and operation input to the thumb throttle 31 is detected by the pressure sensor 37 , the valve driving motor 23 b is controlled according to the value produced based on the accelerator opening degree detected by the APS 38 and the preliminary zone opening degree. If the accelerator opening degree detected by the APS 38 exceeds the preliminary zone opening degree, the vehicle can be switched to a traveling state.

According to the present preferred embodiment, if no operation is carried out on the thumb throttle 31 and the throttle valve 23 is controlled based on the accelerator opening degree, the ECU 26 stops engine control based on the accelerator opening degree and controls the valve driving motor 23 b so that the throttle valve 23 attains an idling opening degree. If no operation of the thumb throttle 31 is detected and the throttle valve 23 is not at the idling opening degree, the throttle driving motor 23 b is controlled automatically so that the throttle valve 23 attains an idling opening degree. In this way, engine control according to the rider's intention can be carried out.

According to the present preferred embodiment, if no operation of the thumb throttle 31 has been detected for a prescribed period and the throttle valve 23 is controlled based on the accelerator opening degree, the driving control based on the accelerator opening degree is stopped. Then, the valve driving motor 23 b is controlled so that the throttle valve 23 attains an idling opening degree. The engine 4 can be prevented from attaining an idling state if the rider releases the thumb throttle 31 only for a short period.

According to the present preferred embodiment, if the accelerator opening degree changes from a value greater than the preliminary zone opening degree to a value equal to or smaller than the preliminary zone opening degree, the valve driving motor 23 b is controlled so that the engine 4 is maintained in an idling state. During deceleration, control based on the preliminary zone can be carried out.

Note that the “idling state” according to the present preferred embodiment includes a fast idling state in which the engine speed is intentionally increased to warm up the engine 4 from its cold state.

According to the present preferred embodiment, the ECU calculates the accelerator opening degree based on the rotation state of the rotation shaft 33 electrically detected by the APS 38 . Then, the valve driving motor 23 b is controlled based on the accelerator opening degree. The throttle valve can be controlled without using a mechanism such as a wire.

According to the present preferred embodiment, a snowmobile is described as an example of a vehicle including an engine and an operation portion that controls driving of the engine. The present invention is not limited to the above and may be applied to a straddle type vehicle other than the snowmobile such as an SSV (Side by Side Vehicle) and an ATV (All Terrain Vehicle).

According to the preferred embodiments of the present invention, a pressure sensor used to detect pressure applied by the rider during operation is described as an example of the operation input detector. The present invention is not limited to the above, and a deformation detector such as a distortion gauge that detects deformation at a portion pressurized by the thumb throttle during the rider's operation may be used.

According to the present preferred embodiments of the present invention, the ECU adds the idling opening degree to the value produced based on the accelerator opening degree and the preliminary zone opening degree to produce the opening degree of the throttle valve by way of illustration. The present invention is not limited to the above and a map used to produce the opening degree of the throttle valve based on the relationship between the accelerator opening degree and the preliminary zone opening degree may be used.

According to the preferred embodiments of the present invention, the pressure sensor detects the load in order to determine the presence/absence of operation input to the thumb throttle by the rider. The present invention is not limited to the above and the presence/absence of detection of operation input to the thumb throttle may be determined based on the operation amount (accelerator opening degree) of the thumb throttle operated by the rider. In this way, when operation is carried out with an accelerator opening degree (the operation amount of the thumb throttle) smaller than the preliminary zone opening degree in the preliminary zone, the presence/absence of detection of operation input of the thumb throttle by the rider is determined.

According to the preferred embodiments of the present invention, the thumb throttle is gradually operated (see FIG. 7 ) by way of illustration. The present invention is not limited to the above and may be applied to the arrangement in which the thumb throttle is abruptly operated. For example, the ECU may be controlled as shown in the timing chart in FIG. 10 . In this way, the ECU controls the throttle valve to be gradually closed even if the thumb throttle is suddenly closed and the accelerator opening degree is abruptly dropped in timing T 10 in FIG. 10 . During such control, if the thumb throttle is fully close and the accelerator opening degree becomes zero in timing T 11 , the throttle valve is gradually closed. In timing T 11 , the throttle valve opening degree is greater than the idling opening degree and then the throttle valve is gradually closed until reaching the idling opening degree.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.