Two-wheeled motor vehicle

A two-wheeled motor vehicle prevents a belt from slipping in a continuously variable transmission even when support by a center stand is released and a rear wheel thus lands while spinning. The two-wheeled motor vehicle includes a hydraulic continuously variable transmission that transmits torque via a belt, and a control device includes a stand position obtaining unit that obtains position information about the center stand, and an add-at-support-position unit that increases oil pressure generated in a primary oil chamber and a secondary oil chamber by a predetermined amount when the center stand is at the support position.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to two-wheeled motor vehicles including a belt-type continuously variable transmission.

2. Description of the Related Art

Some two-wheeled motor vehicles have a center stand for supporting the vehicle body while keeping the rear wheel, which is a driving wheel, floating above the ground. For such a two-wheeled motor vehicle, when the acceleration grip is operated while the vehicle body is supported by the center stand, the rear wheel will spin. Then, when the support by the center stand is released and the rear wheel thus lands while spinning, an abrupt change will occur to the torque in the torque transmission path to the rear wheel.

The above mentioned abrupt change in torque causes a belt slip in a two-wheeled motor vehicle having a belt-type continuously variable transmission. In a hydraulic continuously variable transmission for transmitting torque via a metallic belt, in particular, belt slip is not preferable in view of durability of a belt and a pulley.

SUMMARY OF THE INVENTION

In view of the above described situation, preferred embodiments of the present invention provide a two-wheeled motor vehicle that reduces belt slip in a continuously variable transmission even though support by a center stand is released and a rear wheel thus lands while spinning.

A two-wheeled motor vehicle according to a preferred embodiment of the present invention includes an engine and a continuously variable transmission. The continuously variable transmission includes a primary pulley and a second pulley. The primary pulley includes a first sheave and a first oil chamber to hydraulically move the first sheave, to which torque is transmitted from the engine. The secondary pulley includes a second sheave and a second oil chamber to hydraulically move the second sheave, to which the torque is transmitted from the primary pulley via a belt. The two-wheeled motor vehicle further includes a control device to change oil pressure generated in the first oil chamber and the second oil chamber to thereby control the speed reduction ratio of the continuously variable transmission; a driving wheel to which the torque is transmitted from the secondary pulley; and a center stand. The center stand moves between a support position with a vehicle body supported with the driving wheel floating above the ground and a release position with the support released. The control device further includes a stand position obtaining unit that obtains position information of the center stand; and an add-at-support-position unit that increases the oil pressure generated in the respective oil chambers by a predetermined amount when the center stand is at the support position.

According to various preferred embodiments of the present invention, as the oil pressure in each oil chamber increases when the center stand is at the support position, it is possible to prevent the occurrence of belt slip even though the support by the center stand is released and the rear wheel thus lands while spinning.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, preferred embodiments of the present invention will be described with reference to the accompanying drawings.FIG. 1is a side view of a two-wheeled motor vehicle1, which is an example of a preferred embodiment of the present invention.FIG. 2is a schematic view showing a control device10, an engine20, a continuously variable transmission30, and a hydraulic circuit50of the two-wheeled motor vehicle1.

As shown inFIG. 1or2, the two-wheeled motor vehicle1preferably includes a front wheel2, which is a following wheel, and a rear wheel3, which is a driving wheel. The two-wheeled motor vehicle1further includes an engine20, a continuously variable transmission30to reduce the rotation speed of the engine20and transmit a rotation force to the rear wheel3, a control device10arranged and programmed to control the engine20and the continuously variable transmission30, and a hydraulic circuit50. A center stand9is provided on a lower portion of the two-wheeled motor vehicle1. The center stand9can move between a support position A where the vehicle body is supported with the rear wheel3floating above the ground and a release position B where the support is released.

As shown inFIG. 1, the front wheel2is attached to the lower end of the front suspension4so as to rotate. A steering shaft5is attached to an upper portion of the front suspension4so as to rotate in the left and right directions. A handle6is provided to an upper portion of the steering shaft5. The handle6, the steering shaft5, the front suspension4, and the front wheel2are arranged so as to integrally rotate in the left and right directions. Operating the handle6enables steering the front wheel2. An accelerator grip (not shown) is provided on the right side of the handle6to be operated by a passenger.

As shown inFIG. 1, a seat7is mounted behind the handle6so that a passenger can straddle the seat7to sit thereon. The engine20is mounted below the seat7. The engine20includes a cylinder21and a crankcase23. As shown inFIG. 2, a suction pipe24is connected to the cylinder21. The suction pipe24includes a fuel supply device26that feeds fuel in a fuel tank (not shown) to the cylinder21. The fuel supply device26may be, e.g., an electronically controlled fuel injection system that is controlled by the control device10. The fuel supply device26may be a carburetor, for example.

A throttle body25is connected to the suction pipe24, wherein a throttle valve25athat adjusts the amount of air flowing through the suction pipe24is formed inside the throttle body25. The air having flown through the throttle body25flows further into the cylinder21via the suction pipe24. The throttle valve25amay be, e.g., an electronically controlled valve that is actuated by an actuator that is controlled by the control device10or a valve that is connected via a wire to and operates in connection with the accelerator grip provided to the handle6.

Inside the cylinder21is provided a piston21athat reciprocatingly moves as the fuel ignited by the ignition plug29burns. The piston21ais connected to the crankshaft23aso that the crankshaft23arotates as the piston21areciprocatingly moves which causes the engine20to output torque. An emission pipe27that emits exhaust gas produced by the fuel burning is connected to the cylinder21.

Upstream of the continuously variable transmission30in the torque transmission path between the engine20and the continuously variable transmission30, that is, from the engine20to the rear wheel3is provided a clutch61that transmits the torque output from the engine20to the continuously variable transmission30or reducing torque transmission to the continuously variable transmission30. The clutch61preferably is a centrifugal clutch that is automatically connected or disconnected according to the rotation speed of the engine20. In this example, the clutch61includes a driving member61athat rotates integrally with the crankshaft23aand a driven member61cthat rotates integrally with a primary shaft36provided to the continuously variable transmission30. The driving member61amoves in the radial direction due to a centrifugal force to contact with the driven member61c. The driven member61crotates integrally with the driving member61adue to a friction force between itself and the driving member61a, whereby the torque from the engine20is transmitted via the clutch61to the primary shaft36.

The continuously variable transmission30is a belt-type continuously variable transmission, and preferably includes a primary pulley31that rotates integrally with the primary shaft36and a secondary pulley32that is provided to and rotates integrally with the secondary shaft34. The continuously variable transmission30includes an annular belt33that is wound around the primary pulley31and the secondary pulley32to transmit the rotation of the primary pulley31to the secondary pulley32. The belt33preferably is, e.g., a metallic belt or a resin belt.

The primary pulley31includes a movable sheave (first sheave)31aprovided so as to move in the axial direction of the primary shaft36and a stationary sheave31bprovided so as to be opposed to the movable sheave31ain the axial direction. The secondary pulley32also includes a movable sheave (second sheave)32aprovided so as to move in the axial direction of the secondary shaft34and a stationary sheave32bprovided so as to be opposed to the movable sheave32ain the axial direction.

The movable sheaves31a,32amove in the axial direction and the respective intervals between the movable sheaves31a,32aand the stationary sheave31b,32bare accordingly changed, whereby the speed reduction ratio of the continuously variable transmission30is changed. The speed reduction ratio of the continuously variable transmission30is changed between a speed reduction ratio with the movable sheave31apositioned closest to the stationary sheave31band the movable sheave32apositioned farthest from the stationary sheave32b(hereinafter referred to as “top”, or the minimum speed reduction ratio) and a speed reduction ratio with the movable sheave31apositioned farthest from the stationary sheave31band the movable sheave32apositioned closest to the stationary sheave32b(hereinafter referred to as “low”, or the maximum speed reduction ratio).

The secondary shaft34is connected to the wheel shaft of the rear wheel3via a gear, so that the rotation transmitted from the primary pulley31to the secondary pulley32is further transmitted from the secondary shaft34to the wheel shaft of the rear wheel3via the gear.

The continuously variable transmission30is a continuously variable transmission of which speed reduction ratio is controlled by oil pressure. The primary pulley31includes a first oil chamber (hereinafter referred to as a primary oil chamber)51to which hydraulic oil is supplied from the second oil passage59b, while the secondary pulley32has a second oil chamber (hereinafter referred to as a secondary oil chamber)52to which hydraulic oil is supplied from the first oil passage59a. The movable sheave31amoves in the axial direction due to the oil pressure of the primary oil chamber51to sandwich the belt33together by the stationary sheave31bdue to the oil pressure. Meanwhile, the movable sheave32amoves in the axial direction due to the oil pressure of the secondary oil chamber52to sandwich the belt33together by the stationary sheave32bdue to the oil pressure.

The hydraulic circuit50preferably is a circuit that generates oil pressure in the primary oil chambers51,52according to an electric signal input from the transmission control device14. In this example, the hydraulic circuit50includes a shift control valve55and a clamp force control valve56. The shift control valve55includes a solenoid valve that operates according to a current supplied from the transmission control device14and a pressure reducing valve that operates according to a signal pressure output from the solenoid valve. The clamp force control valve56includes a solenoid valve that operates according to a current supplied from the transmission control device14and a relief valve that operates according to a signal pressure output from the solenoid valve.

An oil pump58is provided so as to operate in connection with the rotation of the engine20, and sucks hydraulic oil in the oil sump57and supplies oil to the first oil passage59a. The first oil passage59ais connected to the secondary oil chamber52and also to the clamp force control valve56via an oil passage59c. To the clamp force control valve56are connected an oil passage59dconnected to a lubrication path to lubricate the respective units of the engine20, and a lubrication path adjusting valve71to adjust the oil pressure in the lubrication path. The clamp force control valve56introduces hydraulic oil from the first oil passage59a, and adjusts the amount of hydraulic oil to be discharged to the oil passage59csuch that the oil pressure (line pressure) of the first oil passage59aand that of the secondary oil chamber52become equal to an oil pressure according to the current supplied from the transmission control device14.

The shift control valve55is connected via an oil passage59eto the first oil passage59aand also via the second oil passage59bto the primary oil chamber51. An exhaust path59fis connected to the shift control valve55. The shift control valve55reduces the oil pressure, that is, line pressure, of the first oil passage59a, and generates oil pressure according to a current input from the transmission control device14in the primary oil chamber51. That is, the shift control valve55feeds hydraulic oil fed from the first oil passage59avia the oil passage59eto the second oil passage59bor exhausts hydraulic oil fed from the second oil passage59bto the exhaust path59fso that the oil pressure in the primary oil chamber51becomes an oil pressure according to a current input from the transmission control device14.

On the throttle body25, a throttle sensor25bto determine a throttle opening is provided. The throttle sensor25bpreferably includes, e.g., a potentiometer, and outputs an electric signal according to a throttle opening. The engine20includes an engine rotation speed sensor23bthat outputs a signal having a frequency according to the rotation speed of the crankshaft23a. The continuously variable transmission30includes a primary rotation speed sensor36athat outputs a signal having a frequency according to the rotation speed of the primary shaft36and a secondary rotation speed sensor34athat outputs a signal having a frequency according to the rotation speed of the secondary shaft34. On the lower end of the front suspension4shown inFIG. 1, a front wheel rotation speed sensor2athat outputs a signal having a frequency according to the rotation speed of the front wheel2is provided. The engine rotation speed sensors23b, primary rotation speed sensor36a, secondary rotation speed sensor34a, and front wheel rotation speed sensor2apreferably are respectively provided by a rotation sensor including, e.g., an electromagnetic pickup and a magnetic resistive element. Further, an oil pressure sensor81including a diaphragm or a piezo element that outputs an electric signal according to the oil pressure of the first oil passage59ais provided to the first oil passage59a, and an oil pressure sensor82similarly including a diaphragm or a piezo element that outputs an electric signal according to the oil pressure of the second oil passage59bis provided to the second oil passage59b.

The control device10includes a transmission control device14and valve driving circuits13,15. The transmission control device14includes a memory unit49including a RAM (Random Access Memory) and a ROM (Read Only Memory), a microprocessor, and the control unit40that executes a program stored beforehand in the memory unit49. In the memory unit49, a map and a threshold for use in a process carried out by the control unit40are stored beforehand in addition to the program to be executed by the control unit40.

Output signals from the engine rotation speed sensor23b, the primary rotation speed sensor36a, and the secondary rotation speed sensor34aare input to the control unit40. The control unit40calculates an engine rotation speed, a rotation speed of the primary shaft36(hereinafter referred to as a primary rotation speed), and that of the secondary shaft34(hereinafter referred to as a secondary rotation speed), based on the signals from these sensors.

An output signal from the front wheel rotation speed sensor2ais also input to the control unit40. The control unit40calculates the rotation speed of the front wheel2(hereinafter referred to as a front wheel rotation speed), based on the output signal (a function as a front wheel rotation speed obtaining unit47to be described later). Further, the control unit40multiplies the secondary rotation speed by a gear ratio between the secondary shaft34and the wheel shaft of the rear wheel3to thereby calculate the rotation speed (a rear wheel rotation speed) of the rear wheel3(a function as a wheel rotation speed obtaining unit48to be described later). Still further, the control unit40is supplied with output signals from the oil pressure sensors81,82and the throttle sensor25b. The control unit40determines the oil pressure of the primary oil chamber51(hereinafter referred to as a primary pressure), that of the secondary oil chamber52(hereinafter referred to as a secondary pressure), and a throttle opening, based on the output signals from these sensors. Based on these data, the control unit40actuates the shift control valve55and the clamp force control valve56to control the continuously variable transmission30. Control by the control unit40will be described later in detail. Note that the respective sensors are connected to the control unit40via an interface circuit (not shown) including an A/D converter, or the like, so that an output signal from each sensor is converted in the interface circuit into a signal that can be processed by the control unit40before being supplied to the control unit40.

The valve driving circuit13supplies a current according to a signal input from the control unit40to a solenoid valve constituting the shift control valve55to thereby activate the shift control valve55. The valve driving circuit15supplies a current according to a signal input from the control unit40to a solenoid valve constituting the clamp force control valve56to thereby activate the clamp force control valve56.

Note that, in this example, the control device10preferably includes an engine control device12connected thereto via a bus. The engine control device12as well is supplied with an output signal from the throttle sensor25b, the engine rotation speed sensor23b, and so forth, via a signal line (not shown). The engine control device12controls an ignition time for the ignition plug29and the amount of fuel to be injected by the fuel supply device26, based on these data.

FIG. 3is a block diagram showing functions of the control unit40of the transmission control device14. As shown in the diagram, the control unit40preferably includes a speed reduction ratio control unit41and a clamp force control unit42. The speed reduction ratio control unit41actuates the shift control valve55to change a clamp force (a force with which the movable sheave31aand the stationary sheave31bsandwich the belt33) of the primary pulley31to thereby control the speed reduction ratio. The clamp force control unit42actuates the clamp force control valve56to generate an oil pressure in the first oil passage59aand the secondary oil chamber52that is enough to prevent slip of the belt33. The control unit40preferably includes an actual speed reduction ratio calculating unit43, a secondary clamp force calculating unit44, a front wheel rotation speed obtaining unit47, and a rear wheel rotation speed obtaining unit48.

The actual speed reduction ratio calculating unit43calculates a speed reduction ratio of the continuously variable transmission30. In this example, the actual speed reduction ratio calculating unit43calculates a speed reduction ratio of the continuously variable transmission30, based on a secondary rotation speed determined by the secondary rotation speed sensor34a(hereinafter referred to as a secondary rotation speed Sspd) and a primary rotation speed determined by the primary rotation speed sensor36a(hereinafter referred to as an actual primary rotation speed Pspd).

The secondary clamp force calculating unit44calculates a clamp force of the secondary pulley32(hereinafter referred to as a secondary clamp force Fs). Specifically, as the secondary clamp force Fs includes a clamp force generated according to a secondary pressure and a clamp force generated due to a centrifugal force of the hydraulic oil in the secondary oil chamber52, the secondary clamp force calculating unit44calculates the secondary clamp force Fs, based on, e.g., the oil pressure determined by the oil pressure sensor81(hereinafter referred to as an actual secondary pressure Ps) and the secondary rotation speed Sspd.

The stand position obtaining unit46determines whether or not the center stand9is at the support position A. A determination method will be described later in detail. Here, when the center stand9is not at the support position A, that is, when the rear wheel3is in contact with the ground, the speed reduction ratio control unit41and the clamp force control unit42carry out a normal process to be described below. Meanwhile, when the center stand9is at the support position A, that is, when the rear wheel3is not in contact with but floating above the ground, the speed reduction ratio control unit41and the clamp force control unit42carry out an add-at-support-position process and a speed reduction ratio change reducing process to be described later.

The clamp force control unit42in normal processing controls the oil pressure of the first oil passage59aand that of the secondary oil chamber52, based on a torque output from the engine (hereinafter referred to as an engine torque T) and a speed reduction ratio (hereinafter referred to as an actual speed reduction ratio Rt) calculated by the actual speed reduction ratio calculating unit43. This process by the clamp force control unit42is carried out as follows, for example.

That is, initially, the clamp force control unit42calculates the engine torque T, based on a throttle opening (hereinafter referred to as a throttle opening Th) determined by the throttle sensor25band an engine rotation speed (hereinafter referred to as an engine rotation speed Espd) determined by the engine rotation speed sensor23b. Then, the clamp force control unit42calculates a target clamp force of the secondary pulley32(hereinafter referred to as a target secondary clamp force Fs-tg), based on the engine torque T and the actual speed reduction ratio Rt. Specifically, for example, with reference to a map and a relational expression stored in the memory unit49, the clamp force control unit42calculates a target secondary clamp force Fs-tg corresponding to the engine torque T and the actual speed reduction ratio Rt. Then, the clamp force control unit42calculates a target secondary pressure Ps-tg, based on the target secondary clamp force Fs-tg calculated as described above. Further, the clamp force control unit42supplies a current from the valve driving circuit15to a solenoid constituting the clamp force control valve56such that the actual secondary pressure Ps becomes equal to the target secondary pressure Ps-tg. The clamp force control unit42repetitively carries out the process described above in a predetermined cycle after activation of the transmission control device14. Consequently, the secondary pressure and the oil pressure of the first oil passage59agradually changes according to changes in the throttle opening Th and the actual speed reduction ratio Rt.

The speed reduction ratio control unit41in normal processing sets a target speed reduction ratio (hereinafter referred to as a target speed reduction ratio Rt-tg), based on an operating condition, including the throttle opening Th, the secondary rotation speed Sspd, and so forth, and controls the speed reduction ratio such that the actual speed reduction ratio Rt becomes equal to the target speed reduction ratio Rt-tg. As shown inFIG. 3, the speed reduction ratio control unit41preferably includes a target speed reduction ratio calculating unit41a, a target primary pressure calculating unit41b, and a valve actuating process unit41c.

The target speed reduction ratio calculating unit41acalculates the target speed reduction ratio Rt-tg, based on the throttle opening Th, the secondary rotation speed Sspd, and a vehicle speed (hereinafter referred to as a vehicle speed V) calculated based on an output signal from the secondary rotation speed sensor34a. Specifically, for example, with reference to a relational expression and a map (hereinafter referred to as a shift control map) correlating a throttle opening, a vehicle speed, and a primary rotation speed, the target speed reduction ratio calculating unit41acalculates a target primary rotation speed Pspd-tg corresponding to the throttle opening Th and the vehicle speed V, and then divides the target primary rotation speed Pspd-tg by the secondary rotation speed Sspd to thereby calculate the target speed reduction ratio Rt-tg.

The target primary pressure calculating unit41bcalculates a target primary pressure (hereinafter referred to as a target primary pressure Pp-tg), based on the actual speed reduction ratio Rt and the target speed reduction ratio Rt-tg. This process by the target primary pressure calculating unit41bwill be carried out as described below, for example.

That is, the target primary pressure calculating unit41binitially calculates a speed with respect to which a speed reduction ratio should be changed (hereinafter referred to as a shift speed Drt), based on the difference between the actual speed reduction ratio Rt and the target speed reduction ratio Rt-tg. For example, with reference to a relational expression and a map (hereinafter referred to as a shift speed map) correlating the difference between the actual speed reduction ratio and the target speed reduction ratio and a shift speed, the target primary pressure calculating unit41bcalculates a shift speed Drt corresponding to the difference between the actual speed reduction ratio Rt calculated by the actual speed reduction ratio calculating unit43and the target speed reduction ratio Rt-tg calculated by the target speed reduction ratio calculating unit41a. Then, the target primary pressure calculating unit41badds or subtracts a force in accordance with the shift speed Drt with respect to the clamp force of the primary pulley31that is necessary to maintain the current speed reduction ratio to determine a resultant value as a target clamp force (hereinafter referred to as a target primary clamp force Fp-tg) of the primary pulley31.

For example, the target primary pressure calculating unit41bcalculates the target primary clamp force Fp-tg, using the expression (1) below.
Fp-tg=Fpk−Drt/k·Pspd(1)
wherein Fpk refers to a clamp force of the primary pulley31that is necessary to maintain the current speed reduction ratio. Fpk is, e.g., a product (Fs×Rf) of the ratio between the above described clamp force of the secondary pulley32and that of the primary pulley31(hereinafter referred to as a thrust force ratio Rf). Referring to the map and relational expression, the target primary pressure calculating unit41bcalculates a thrust force ratio Rf corresponding to the actual speed reduction ratio Rt calculated by the actual speed reduction ratio calculating unit43. Then, the target primary pressure calculating unit41bcalculates the target primary clamp force Fp-tg, based on the thrust force ratio Rf and the secondary clamp force Fs, or a clamp force calculated by the secondary clamp force calculating unit44. Where k is a coefficient determined according to the speed reduction ratio and the primary rotation speed, the target primary pressure calculating unit41bcalculates a coefficient k corresponding to the actual speed reduction ratio Rt and the primary rotation speed Pspd, referring to the map, wherein Pspd is a primary rotation speed determined by the primary rotation speed sensor36a, as described above.

Based on the target primary clamp force Fp-tg calculated as described above, the target primary pressure calculating unit41bcalculates a target primary pressure Pp-tg. For example, as a clamp force of the primary pulley31includes a centrifugal force generated due to rotation of the hydraulic oil in the primary oil chamber51, the target primary pressure calculating unit41bcalculates the target primary pressure Pp-tg, based on the primary rotation speed Pspd and the pressure receiving area of the primary pulley31(the area of a portion of the movable sheave31athat receives the oil pressure).

The valve actuating process unit41ccontrols a current supplied from the valve driving circuit13to the shift control valve55such that the oil pressure of the primary oil chamber51to be determined by the oil pressure sensor82(hereinafter referred to as an actual primary pressure Pp) becomes equal to the target primary pressure Pp-tg. Specifically, the valve actuating process unit41ccalculates an instruction value, based on the difference between the target primary pressure Pp-tg and the actual primary pressure Pp, and outputs the instruction value to the valve driving circuit13. In return, the valve driving circuit13supplies a current of a value according to the instruction value to the shift control valve55. As a result of this process by the valve actuating process unit41c, the difference between the target primary pressure Pp-tg and the actual primary pressure Pp is eliminated, and the actual speed reduction ratio Rt becomes closer to the target speed reduction ratio Rt-tg.

The target primary pressure calculating unit41brepetitively carries out the above described process during shifting to thereby sequentially update the target primary pressure Pp-tg. That is, every time the actual speed reduction ratio Rt is changed toward the target speed reduction ratio Rt-tg, the target primary pressure calculating unit41bnewly calculates the target primary pressure Pp-tg, based on the difference between the changed actual speed reduction ratio Rt and the target speed reduction ratio Rt-tg. Then, the valve actuating process unit41coutputs an instruction value calculated based on the difference between the newly calculated target primary pressure Pp-tg and the actual primary pressure Pp to the valve driving circuit13. Consequently, the actual speed reduction ratio Rt becomes much closer to the target speed reduction ratio Rt-tg.

With the difference eliminated between the actual speed reduction ratio Rt and the target speed reduction ratio Rt-tg, the shift speed Drt calculated based on the difference between the actual speed reduction ratio Rt and the target speed reduction ratio Rt-tg becomes zero. As a result, the target primary pressure calculating unit41bcalculates an oil pressure corresponding to the clamp force Fpk of the primary pulley31that is necessary to maintain the speed reduction ratio as the target primary pressure Pp-tg. Consequently, the actual speed reduction ratio Rt is maintained at the target speed reduction ratio Rt-tg.

In the following, a process to be carried out when the center stand9is at the support position A will be described. As shown inFIG. 1, when the center stand9is at the support position A, the rear wheel3is floating above the ground. If a passenger operates the acceleration grip of the handle6in such a condition, torque from the engine20is transmitted via the clutch61and the continuously variable transmission30to the rear wheel3, which will resultantly spin. When the support by the center stand9is then released and the rear wheel3accordingly lands while spinning, an abrupt change is caused to the torque in the torque transmission path to the rear wheel3, and the belt33may thus possibly slip relative to the primary pulley31and the secondary pulley32in the continuously variable transmission30. In view of the above, when the center stand9is at the support position A, an add-at-support-position unit42iof the clamp force control unit42carries out an add-at-support-position process to enhance the clamp force of the secondary pulley32to thereby prevent the belt33from slipping. Further, the speed reduction ratio change reducing unit41iof the speed reduction ratio control unit41carries out a speed reduction ratio change reducing process to thereby prevent changes in the speed reduction ratio of the continuously variable transmission30.FIG. 4is a flowchart of an example process carried out by the control unit40.

Initially, the stand position obtaining unit46determines whether or not the engine20is carrying out ignition control (S1). Information concerning whether or not the engine20is carrying out ignition control is obtained from the engine control device12. Thereafter, the stand position obtaining unit46determines whether or not the center stand9is at the support position A (S2). In this preferred embodiment, whether or not the center stand9is at the support position A is determined based on whether or not the rear wheel3is spinning. That is, because the rear wheel3spins when the center stand9is at the support position A and the rear wheel3is thus floating above the ground, determination as to whether or not the rear wheel3is spinning is utilized in determination as to whether or not the center stand9is at the support position A in this preferred embodiment. Further, determination as to whether or not the rear wheel3is spinning is made by determining, based on the front wheel rotation speed obtained by the front wheel rotation speed obtaining unit47and the rear wheel rotation speed obtained by the rear wheel rotation speed obtaining unit48, whether or not a first condition that the front wheel rotation speed is close to zero and a second condition that the difference between the rear wheel rotation speed and the front wheel rotation speed is equal to or larger than a predetermined value (positive value) are both satisfied. That is, because the front wheel2usually remains stopped when the rear wheel3spins, a determination as to whether or not the rear wheel3is spinning is made based on these two conditions. In detail, a determination as to whether or not the first condition is satisfied is made based on whether or not the front wheel rotation speed is smaller than a threshold that is slightly larger than zero. Alternatively, a determination as to whether or not the rear wheel3is spinning may be made based on the second condition alone. Note that the above described manners are not limiting, and determination as to whether or not the center stand9is at the support position A may be made, for example, with a stand sensor being provided to output a sensing signal in accordance with the position of the center stand9, based on a sensing signal output from the stand sensor.

Thereafter, when the center stand9is at the support position A (S2: YES), the add-at-support-position unit42iof the clamp force control unit42starts an add-at-support-position process to enhance the clamp force of the secondary pulley32(S3).FIG. 5is a functional block diagram of the clamp force control unit42. The add-at-support-position unit42icalculates the target secondary pressure Ps-tg similar to the above described normal processing, and adds a predetermined value (a positive value) to the target secondary pressure Ps-tg to thereby correct the target secondary pressure Ps-tg (hereinafter referred to as a corrected target secondary pressure Ps-tg#). Thereafter, the clamp force control unit42supplies a current from the valve driving circuit15to the solenoid of the clamp force control valve56such that the actual secondary pressure Ps becomes equal to the corrected target secondary pressure Ps-tg#. With the above, the clamp force of the secondary pulley32increases more in the above described normal processing. Note that although a predetermined value is preferably added to the target secondary pressure Ps-tg in this preferred embodiment, this is not limiting, and a predetermined value may be added to the target secondary clamp force Fs-tg instead. As described above, the target primary pressure calculating unit41bof the speed reduction ratio control unit41calculates the target primary clamp force Fp-tg, based on the secondary clamp force Fs calculated by the secondary clamp force calculating unit44, and further calculates the target primary pressure Pp-tg. Therefore, the clamp force of the primary pulley31will increase more in normal processing as the clamp force of the secondary pulley32increases. As clamp forces of the primary pulley31and the secondary pulley32both increase in this manner, the belt33can be prevented from slipping.

Specifically, the add-at-support-position unit42ihas an inertia torque corresponding value output unit421iand a weight corresponding value output unit423i, wherein the inertia torque corresponding value output unit421ioutputs a predetermined value to be added to the target secondary pressure Ps-tg. The inertia torque corresponding value output unit421ioutputs a predetermined value in accordance with the inertia torque in the torque transmission path (hereinafter referred to as an upstream transmission path) from the engine20to the primary pulley31of the continuously variable transmission30. That is, when the rear wheel3lands while spinning, torque in the opposite direction is applied to the torque transmission path from the secondary pulley32of the continuously variable transmission30to the rear wheel3(hereinafter referred to as a downstream transmission path), while torque in the forward direction remains in the upstream transmission path. Therefore, the inertia torque in the upstream transmission path is applied to the belt33of the continuously variable transmission30when the rear wheel3lands while spinning. In view of the above, the inertia torque corresponding value output unit421iadds a value that compensates for slip of the belt33due to such an inertia torque to the target secondary pressure Ps-tg, to thereby prevent the belt33from slipping.

Further, the weight corresponding value output unit423ioutputs a value in accordance with the weight applied to the rear wheel3. That is, when the rear wheel3lands while spinning, a torque in magnitude in accordance with the weight applied to the rear wheel and in the opposite direction is applied to the downstream transmission path. The torque in the opposite direction can prevent the belt33from slipping. In this view, the weight corresponding value output unit423iadds a value to compensate for slip of the belt33due to such a torque to the target secondary pressure Ps-tg to thereby prevent the belt33from slipping. Note that the weight applied to the rear wheel3corresponds to the total of the weight of the vehicle body itself and the weight applied to the vehicle body (a load weight), such as the weight of a passenger. Such a load weight may be, e.g., a fixed value or obtained, based on a sensing signal from a load sensor (load cell) provided to the rear cushion (not shown) of the two-wheeled motor vehicle1to output a sensing signal according to the weight applied to the vehicle body (a function of a load obtaining unit).

Thereafter, the speed reduction ratio change reducing unit41iof the speed reduction ratio control unit41starts a speed reduction ratio change reducing process (S4). That is, although the transmission ratio of the continuously variable transmission30under normal control is changed from the low side (the maximum speed reduction ratio) to the top side (the minimum speed reduction ratio) when the rear wheel3spins, the transmission ratio of the continuously variable transmission30in this preferred embodiment is maintained on the low side due to the function of the speed reduction ratio change reducing unit41i. Specifically, the speed reduction ratio change reducing unit41ifixes the target speed reduction ratio Rt-tg calculated by the above described target speed reduction ratio calculating unit41ato a predetermined value on the low side or is maintained such that the target speed reduction ration Rt-tg will not be changed from a predetermined value on the low side to the top side. With the above, the transmission ratio of the continuously variable transmission30is kept on the low side during the add-at-support-position process. As described above, with the transmission ratio of the continuously variable transmission30kept on the low side, the vehicle can start moving smoothly when the rear wheel3lands while spinning. Further, as the movable sheave32aof the secondary pulley32is located relatively close to the stationary sheave32bwhen the transmission ratio of the continuously variable transmission30is kept on the low side, the belt33remains in contact with the secondary pulley32by a relatively long distance. This can better prevent the belt33from slipping.

While the add-at-support-position process and the speed reduction ratio change reducing process are being carried out, the stand position obtaining unit46determines whether or not the support by the center stand9is released (S5). Whether or not the support by the center stand9is released is determined based on whether or not a condition that the front wheel rotation speed is larger than about zero (a condition opposite in meaning from the above described first condition) and another condition that the difference between the rear wheel rotation speed and the front wheel rotation speed is equal to or smaller than a predetermined value (a condition opposite in meaning from the second condition) are both satisfied. That is, it is determined that the support by the center stand9is released when the front wheel2and the rear wheel3are both rotating. When these conditions are satisfied (S5: YES) and a predetermined period of time thereafter elapses (S6), the add-at-support-position unit42iand the speed reduction ratio change reduction unit41iterminate the add-at-support-position process and the speed reduction ratio change reducing process (S7and S8), whereby a series of processes are terminated.

The above described two-wheeled motor vehicle1includes a hydraulic continuously variable transmission30that transmits torque via the belt33. The control device10includes the stand position obtaining unit46that obtains position information of the center stand9and the add-at-support-position unit42ithat increases the oil pressure to be generated in the primary oil chamber51and the secondary oil chamber52by a predetermined amount when the center stand9is at the support position A. With this arrangement, it is possible to prevent the belt33from slipping in the continuously variable transmission30even when the support by the center stand9is released and the rear wheel3thus lands while spinning.

The stand position obtaining unit46determines that the center stand9is at the support position A when the condition that the difference between the rear wheel rotation speed and the front wheel rotation speed is equal to or larger than a predetermined value is satisfied. A condition that the front wheel rotation speed is equal to or smaller than a predetermined value may additionally be taken into consideration. This makes it possible to determine whether or not the center stand9is at the support position A without providing a determination unit to directly determine the position of the center stand9. Further, it is possible to detect spinning of the rear wheel3, which may cause slip of the belt33of the continuously variable transmission30.

Note that the above described arrangement is not limiting, and a stand sensor95that outputs a sensing signal in accordance with the position of the center stand9may be provided to the two-wheeled motor vehicle1, as shown inFIG. 6.FIG. 6is a schematic diagram showing a modified example of a preferred embodiment of the present invention, in which a structure identical to that described in the above described preferred embodiment is given an identical numeral and a description thereof is omitted. In this modified example, a sensing signal from the stand sensor95is input to the control unit40, and the stand position obtaining unit46(seeFIG. 3) in the control unit40determines whether or not the center stand9is at the support position A, based on the sensing signal. This makes it possible to directly determine the position of the center stand9.

The control unit40further preferably includes a speed reduction ratio change reducing unit41ithat reduces changes in the speed reduction ratio of the continuously variable transmission30when the center stand9is at the support position A. The speed reduction ratio change reducing unit41imay keep the speed reduction ratio of the continuously variable transmission30lower than what is predetermined. With the above, the belt30remains in contact with the secondary pulley32by a relatively long distance in the continuously variable transmission30, as described above, so that the belt33can be better prevented from slipping.

The add-at-support-position unit42iof the clamp force control unit42may increase the oil pressure generated in the primary oil chamber51and the secondary oil chamber52by an amount in accordance with the load applied to the vehicle body when the center stand9is at the support position A. This can facilitate adjustment of the clamp forces of the primary pulley31and the secondary pulley32so as to have a necessary magnitude.