Power transmission device

Abstract

A power transmission device for transmitting power of an internal combustion engine of a motorcycle. By improving the arrangement of a continuously variable transmission, a balancer shaft and a drive pulley and a driven pulley of the continuously variable transmission, a lateral width and longitudinal length of a power unit are decreased thus making the power unit more compact. A continuously variable transmission is arranged behind a crankshaft, and a balancer is arranged between the continuously variable transmission and the crankshaft in a state wherein the balancer does not overlap the continuously variable transmission. A drive force of the crankshaft is transmitted to a drive pulley shaft of the continuously variable transmission by way of a gear of a balancer shaft. The approximate center of the crankshaft, the balancer and the respective pulleys of the continuously variable transmission are arranged on a vertical plane of a vehicle body center line.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 is a side view of a motorcycle on which a power unit is mounted according to embodiments of the present invention;

FIG. 2 is a right side view of the power unit according to a first embodiment of the present invention;

FIG. 3 is a left side view of the above-mentioned power unit;

FIG. 4 is a cross-sectional developed view taken along a line IV-IV in FIG. 2;

FIG. 5 is a right side view of a power unit according to a second embodiment of the present invention;

FIG. 6 is a left side view of a power unit according to a third embodiment of the present invention;

FIG. 7 is a cross-sectional developed view of a power unit according to a fourth embodiment of the present invention which includes respective rotational shafts; and

FIG. 8 is a plan view showing the positional relationship between a vehicle body and the power unit according to the embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a side view of a motorcycle 140 having a power unit 1 according to the present invention mounted thereon. A vehicle structure body of the motorcycle 140 is configured such that a main frame (not shown in the drawing) extends rearwardly from a head pipe 141 mounted on a front end of the motorcycle 140 and, at the same time, a rear frame 143 which extends obliquely and downwardly from a rear portion of the main frame is connected to the main frame, and a down frame 144 extends downwardly and rearwardly from the head pipe 141. A rear end portion of the down frame 144 is bent upwardly and is connected to the rear frame 143. A fuel tank 145 is formed in a state that the fuel tank 145 strides over the main frame (not shown in the drawing). Between the main frame, the rear frame 143 and the down frame 144, a power unit 1 which is integrally formed of an internal combustion engine 2 and a transmission 3 is mounted. A front fork 146 is rotatably supported on the head pipe 141, a steering handle 147 is mounted on an upper end of the front fork 146, and a front wheel 148 is pivotally supported on a lower end of the front fork 146. Front ends of a pair of rear forks 149 are pivotally supported on a rear portion of the down frame 144 in a state wherein the rear forks 149 are tiltable in the vertical direction. A rear shock absorber 150 is provided between a rear portion of the rear fork 149 and a rear end portion of the rear frame 143. A rear wheel 151 is pivotally supported on a rear end of the rear fork 149.

The above-mentioned internal combustion engine 2 is a water-cooled V-shaped double-cylinder internal combustion engine in which cylinders are arranged to form a V-shape in the longitudinal direction of the vehicle body. A throttle body 23 having an electronic throttle valve is arranged in a space defined between both cylinders which forms a V-bank and is connected to intake ports of the front and rear cylinders via a manifold. A crankshaft of the internal combustion engine 2 is arranged orthogonal to the vehicle advancing direction and is arranged horizontally in the lateral direction of the vehicle. A transmission shaft of the transmission 3 is arranged in parallel to the above-mentioned crankshaft 16 (FIG. 2). An extension shaft for driving the rear wheel (not shown in the drawing) is connected to a connection shaft 43 (FIG. 2) arranged orthogonal to an output shaft of the transmission, extends toward a rear portion of the vehicle, and arrives at a rotary shaft of the rear wheel 151 thus driving the rear wheel 151. A seat 152 is mounted on a rear portion of the fuel tank 145.

FIGS. 2 to 4 are views showing the power unit according to a first embodiment of the present invention. FIG. 2 is a right side view of the power unit 1. The drawing shows a state of the power unit in which a right-side power unit case is removed and illustrates a cross-section of the cylinder. The power unit 1 is constructed of the internal combustion engine 2 and the transmission 3. An arrow F indicates a front side of the power unit 1 when the power unit 1 is mounted on the vehicle (the same applies for other drawings). The internal combustion engine 2 is a water-cooled V-shaped double-cylinder internal combustion engine, and the cylinders are arranged to form a V-shape in the longitudinal direction. The crankshaft 16 of the above-mentioned internal combustion engine 2 is arranged orthogonal to the vehicle advancing direction and is arranged horizontally in the lateral direction of the vehicle. A front balancer shaft 39A and a rear balancer shaft 39B are arranged in front of and behind the crankshaft 16 respectively, and the transmission 3 is arranged behind the rear balancer shaft 39B. A front balancer 62A and a rear balancer 62B are mounted on the front balancer shaft 39A and the rear balancer shaft 39B respectively (FIG. 2). The balancers 62A, 62B are primary balancers and are rotated at the same rotational speed as the crankshaft 16.

FIG. 3 is a left side view of the power unit 1. The drawing shows a state wherein the power unit is illustrated in which a portion of a left-side unit cover is removed and a cross-section of the rear cylinder.

FIG. 4 is a cross-sectional developed view taken along a line IV-IV in FIG. 2. The view shows the power transmission device 4 from the crankshaft 16 to the connection shaft 43 arranged on a rear end of the power transmission device 4. The following explanation is made alternately referring to the above-mentioned respective views.

A main outer shell of the power unit 1 includes a left power unit case 6, a right power unit case 7, a left unit cover 8, a right unit cover 9, a right outer protecting cover 13 shown in FIG. 4, and cylinder blocks 10, cylinder heads 11 and cylinder head covers 12 which are respectively mounted on a front cylinder 5F and a rear cylinder 5R shown in FIG. 2 and FIG. 3. A power unit case which covers a crank chamber 66 and a transmission chamber 67 is constituted of the left power unit case 6, the right power unit case 7, the left unit cover 8, the right unit cover 9 and the right outer protecting cover 13. Here, a front half portion of the power unit case forms a crank case, and a rear half portion of the power unit case forms a transmission case.

In FIG. 4, the crankshaft 16 is rotatably supported on a left journal bearing 14 and a right journal bearing 15 which are held by the left and right power unit cases 6, 7. A connecting rod 17F of the front (left) cylinder and a connecting rod 17R of the rear (right) cylinder are connected to a crank pin 16a of the crankshaft 16 in a state wherein the connecting rods 17F, 17R are arranged close to each other. As shown in FIGS. 2 and 3, a piston 18 is joined to each connecting rod 17, and the piston 18 is slidably held in a cylinder bore formed in the cylinder block 10. A combustion chamber 19 is formed in a portion of the cylinder head 11 which faces the piston 18 in an opposed manner, and an ignition plug (not shown in the drawing) which penetrates a wall body of the cylinder head 11, allows a distal end thereof to face the combustion chamber 19, and allows a rear end thereof to be exposed to the outside is provided.

In FIGS. 2 and 3, an exhaust port 21 and the intake port 22 are connected to be in communication with the combustion chamber 19. The exhaust port 21 extends to the front in the front cylinder 5F and extends rearwardly in the rear cylinder 5R. The intake port 22 of either one of cylinders extends into a space between both cylinders formed in a V bank and is connected to a throttle body 23 having the electronic throttle valve. Thus, fuel and air are supplied to the intake port 22. An exhaust valve 24 is formed in the exhaust port 21 and an intake valve 25 is formed in the intake port 22. Further, a cam shaft 26 is arranged in the inside of the cylinder head cover 12, an exhaust rocker arm shaft 27 and an intake rocker arm shaft 28 are arranged above the cam shaft 26. An exhaust rocker arm 29 and an intake rocker arm 30, which are mounted on these arm shafts, are driven by an exhaust cam and an intake cam of the cam shaft 26 thus pushing the stem top portions of the above-mentioned exhaust valve 24 and intake valve 25 so as to open or close the respective valves. In FIG. 2, the cam shaft 26 is rotatably driven at a rotational speed which is ½ of a rotational speed of the crankshaft 16 using a cam shaft drive chain 35 which extends between and is wound around a cam shaft driven sprocket wheel 33 which is mounted on an end portion of the cam shaft 26. A cam shaft drive sprocket wheel 34 is mounted on the crankshaft 16. In FIG. 2, a cam chain chamber 36 is illustrated.

In FIG. 2, in the power unit 1, the front balancer shaft 39A and the rear balancer shaft 39B are arranged in front of and behind the crankshaft 16, respectively. Three transmission shafts, that is, a CVT drive shaft 40, a CVT driven shaft 41 and a transmission output shaft 42 are arranged in parallel to the crankshaft and are arranged behind the rear balancer shaft 39B. Further, a connection shaft 43, which is connected to the extension shaft for driving the rear wheel (not shown in the drawing), is arranged rearwardly and orthogonal to the transmission output shaft 42.

In FIG. 4, the left unit cover 8 is arranged outside the left power unit case 6, and a power generator 45 is constructed of a stator 45S which is fixed to an inner surface of the left unit cover 8 and a rotor 45R which is fixed to a left end of the crankshaft 16 and surrounds the stator 45S. A gear 48 shown in FIG. 4 which is arranged close to the power generator 45 is a starter driven gear 48 (FIGS. 3 and 4) for the crankshaft 16 which receives a rotational drive force from a starter motor 46 (FIGS. 2 and 3) by way of a gear train 47 (FIG. 3).

A crankshaft output gear 50 which is formed on a right end portion of the crankshaft 16 is a gear which functions in combination with a neighboring cam-type torque damper 51, and is meshed with respective balancer shaft input gears 61A, 61B (FIG. 2) which are mounted on the front balancer shaft 39A and the rear balancer shaft 39B so as to perform the power transmission at a rotational speed of 1:1.

The crankshaft output gear 50 and the cam-type torque damper 51 are mounted on a collar 52 which is engaged with the crankshaft 16 by spline fitting. The crankshaft output gear 50 is rotatably fitted on the collar 52, and a concave cam 53 having an arcuate concave surface is formed on a side surface of the crankshaft output gear 50. A lifter 54 is fitted on a spline formed on an outer periphery of the collar 52 in a state wherein the lifter 54 is movable in the axial direction. A convex cam 55 having an arcuate convex surface is formed on an end surface of the lifter 54, and the convex cam 55 is fitted in the concave cam 53. A spring holder 56 is fixed to an end portion of the collar 52 using the spline and a retainer ring. A coned disc spring 57 is provided between a spring holder 56 and the lifter 54 so as to bias the convex cam 55 to the concave cam 53 by the coned disc spring 57. Torque of the crankshaft 16 is transmitted to the crankshaft output gear 50 in following order of the collar 52, the lifter 54, the convex cam 55, the concave cam 53 and the crankshaft output gear 50. When an impact torque of the internal combustion engine is transmitted to the crankshaft 16, the convex cam 55 slips on a cam surface of the concave cam 53 in the circumferential direction and, at the same time, gets over an inclined surface of the concave cam 53, moves in the axial direction against a biasing force of the coned disc spring 57 and absorbs the impact torque. Thus, the torque with the attenuated impact is transmitted to the balancer shafts 39A, 39B (FIG. 2) via the crankshaft output gear 50.

In FIG. 4, the rear balancer shaft 39B is rotatably supported on the left power unit case 6 and the right unit cover 9 via ball bearings 59, 60. A rear balancer shaft input gear 61B is mounted by spline fitting between the right power unit case 7 and the right unit cover 9. A rear balancer 62B is engaged with the rear balancer shaft 39B by spline fitting in a state wherein the rear balancer 62B is sandwiched between a pair of crank webs of the crankshaft 16 and is rotated at the same speed as the crankshaft 16. A balancer shaft output gear 63 having a small diameter is fixed to a boss portion of the rear balancer shaft input gear 61B by press fitting and is meshed with a transmission input gear 78 having a large diameter which is fixed to a transmission input clutch 75 of the CVT drive shaft 40. Thus, the rotation is transmitted with the reduction of the rotational speed.

A partition wall 65 is formed on a portion where the left power unit case 6 and the right power unit case 7 abut each other thus forming a transmission chamber 67 partitioned from a crank chamber 66. “Transmission” is a general term for a plurality of devices inside of the transmission chamber 67. A continuously variable transmission (CVT) 85 is housed inside of the transmission chamber 67. The continuously variable transmission 85 is constructed of a CVT drive pulley 86, a CVT driven pulley 92 and an endless metal belt 99. Three transmission shafts, that is, the CVT drive shaft 40, the CVT driven shaft 41 and the transmission output shaft 42 are arranged in the transmission chamber 67. The CVT drive shaft 40 is rotatably supported on the left power unit case 6 and the right power unit case 7 via ball bearings 68 (not shown in the drawing), 69. The CVT driven shaft 41 is rotatably supported on the left power unit case 6 and the right power unit case 7 via ball bearings 70, 71. The transmission output shaft 42 is rotatably supported on the left power unit case 6 and the right power unit case 7 via ball bearings 72, 73.

The transmission input clutch 75 is mounted on a right end portion of the CVT drive shaft 40 which is sandwiched between the right power unit case 7 and the right unit cover 9. The transmission input clutch 75 is a hydraulic-driven-type multiple disc clutch which transmits power applied to the CVT drive shaft 40 from the rear balancer shaft 39B at the time of starting the engine. A clutch outer 76 of the transmission input clutch 75 is fixed to a right end portion of the CVT drive shaft 40 by spline fitting. A clutch inner 77 of the transmission input clutch 75 is fitted in a boss portion of the clutch outer 76 in a relatively rotatable manner. A transmission input gear 78 is fixed to a boss portion of the clutch inner 77 and is rotated together with the clutch inner 77. The transmission input gear 78 is meshed with the balancer shaft output gear 63 of the rear balancer shaft 39B. A plurality of drive friction discs are mounted on the clutch inner 77 in a state wherein the drive friction discs are non-rotatable relative to the clutch inner 77 and are movable in the axial direction. A plurality of driven friction discs are mounted on the clutch outer 76 in a state that the driven friction discs are non-rotatable relative to the clutch outer 76 and are movable in the axial direction. The clutch inner 77 and the clutch outer 76 alternately overlap with each other to form a group of friction discs 79. A pressure receiving plate 81 is fixed to an opening side of the clutch outer 76 in a state wherein the pressure receiving plate 81 is brought into contact with the group of friction discs 79, and a pressurizing plate 82 which is movable in the axial direction pushes another side of the group of friction discs 79. A transmission input clutch oil chamber 83 is formed between the clutch outer 76 and the pressurizing plate 82. A coil spring 84 is arranged close to the oil chamber 83 and pushes the pressurizing plate 82 in the direction to constantly disengage the clutch. When the internal combustion engine arrives at a predetermined rotational speed, due to a control of the transmission-input-clutch-use solenoid valve 135, low-pressure engine oil is supplied to a transmission-input-clutch oil chamber 83. Thus, the pressurizing plate 82 is pushed against a biasing force of the coil spring 84 whereby the transmission input clutch 75 is engaged.

A CVT drive pulley 86 is arranged at a portion of the CVT drive shaft 40 sandwiched between the left and right power unit cases 6, 7. The drive pulley 86 is constructed of a drive pulley fixed half body 87 and a drive pulley movable half body 88. The fixed half body 87 is integrally formed with the CVT drive shaft 40. Thus, the fixed half body 87 is not movable in the axial direction and is not rotatable relative to the CVT drive shaft 40. The drive pulley movable half body 88 is mounted on a right side of the drive pulley fixed half body 87. The movable half body 88 is mounted on the CVT drive shaft 40 using a key 89 in a state wherein the movable half body 88 is not rotatable relative to the CVT drive shaft 40 but is movable in the axial direction. A CVT drive pulley oil chamber 91 is formed between the movable half body 88 and the partition plate 90. Oil pressure of oil for continuously variable transmission is configured to be applied to the oil chamber 91. A distance between the fixed half body 87 and the movable half body 88 is controlled by adjusting the oil pressure of the oil for continuously variable transmission applied to the oil chamber 91 by way of a hydraulic control valve unit 136. When the pressure in the oil chamber 91 becomes high, the drive pulley movable half body 88 is pushed in the direction to make the drive pulley movable half body 88 approach the drive pulley fixed half body 87.

A CVT driven pulley 92 is formed on a portion of the CVT driven shaft 41 sandwiched between the left and right power unit cases 6, 7. The driven pulley 92 is constructed of a driven pulley fixed half body 93 and a driven pulley movable half body 94. The fixed half body 93 is integrally formed with the CVT driven shaft 41. Accordingly, the fixed half body 93 is not movable in the axial direction and is not rotatable relative to the CVT driven shaft 41. The driven pulley movable half body 94 is mounted on the left side of the driven pulley fixed half body 93. The movable half body 94 is mounted on the CVT driven shaft 41 using a key 95 (not shown in the drawing) in a state wherein the movable half body 94 is not rotatable relative to the CVT driven shaft 41 but is movable in the axial direction. A CVT driven pulley oil chamber 97 is formed between the movable half body 94 and a fixed end plate 96. The oil pressure of oil for the continuously variable transmission is configured to be applied to the oil chamber 97. A distance between the fixed half body 93 and the movable half body 94 is controlled by adjusting the oil pressure of the oil for the continuously variable transmission applied to the oil chamber 97 by way of the hydraulic control valve unit 136. A coil spring 98 is arranged in the oil chamber 97 and constantly pushes the driven pulley movable half body 94 in the direction which makes the driven pulley movable half body 94 approach the driven pulley fixed half body 93. When the pressure in the oil chamber 97 becomes high, the driven pulley movable half body 94 is pushed in the direction which makes the driven pulley movable half body 94 further approach the driven pulley fixed half body 93.

An endless metal belt 99 extends between the CVT drive pulley 86 and the CVT driven pulley 92 so as to transmit the rotation of the CVT drive pulley 86 to the CVT driven pulley 92. When a distance between the movable half body and the fixed half body is large, a winding radius of the endless metal belt 99 becomes small, while when the movable half body approaches the fixed half body, the winding radius of the endless metal belt 99 becomes large. When a winding radius of the endless metal belt 99 on the drive-pulley-86 side is small and the winding radius of the endless metal belt 99 on the driven-pulley-92 side is large, the rotational speed is decreased, while when the winding radius of the endless metal belt 99 on the drive-pulley-86 side is large and the winding radius of the endless metal belt 99 on the driven-pulley-92 side is small, the rotational speed is increased.

A start clutch 101 is formed on a right side of the CVT driven pulley 92. The start clutch 101 is provided for disconnecting the power transmission from the CVT driven shaft 41 to the transmission output shaft 42. A clutch outer 102 of the start clutch 101 is fixed to the CVT driven shaft 41, and in the inside of the clutch outer 102, a clutch inner 103 is mounted on the CVT driven shaft 41 by way of a ball bearing 104 and a needle bearing 105 in a state wherein the clutch inner 103 is rotatable relative to the CVT driven shaft 41. A plurality of drive friction discs are mounted on the clutch outer 102 in a state wherein the drive friction discs are not rotatable relative to the clutch outer 102 but is movable in the axial direction, while a plurality of driven friction discs are mounted on the clutch inner 103 in a state wherein the driven friction discs are not rotatable relative to the clutch inner 103 but is movable in the axial direction. The drive friction discs and the driven friction discs alternately overlap each other to form a group of friction discs 106. A pressure receiving plate 108 is fixed to an opening end of the clutch outer 102 in a state wherein the pressure receiving plate 108 is brought into contact with the group of friction discs 106, and a pressurizing plate 109 which is movable in the axial direction pushes another side of the group of friction discs. A start clutch oil chamber 110 is formed between the clutch outer 102 and the pressurizing plate 109 and an oil pressure of the oil for continuously variable transmission is configured to be applied to the start clutch oil chamber 110. A coil spring 111 is arranged close to the start clutch oil chamber 110 and pushes the pressurizing plate 109 in the direction to constantly disconnect the clutch. When the oil pressure of the oil for continuously variable transmission is applied to the pressurizing plate 109 by way of the hydraulic control valve unit 136, the pressurizing plate 109 is pushed against the biasing force of the coil spring 111 thus engaging the start clutch 101.

A CVT output gear 112 having a small diameter is integrally formed with a boss portion of the clutch inner 103. The CVT output gear 112 is meshed with an output shaft gear 114 having a large diameter which is mounted on a right end of the transmission output shaft 42 by spline fitting. When the start clutch 101 is engaged, a rotational speed of the CVT driven shaft 41 is decreased and is transmitted to the transmission output shaft 42. A bevel gear 115 is integrally formed on a left end of the transmission output shaft 42. Further, a bevel gear 116 is also integrally formed on a front end of the connection shaft 43 and is meshed with the bevel gear 115 of the transmission output shaft 42. A spline 117 is formed on an end portion of the connection shaft 43 to be connected with an extension shaft for driving rear wheel (not shown in the drawing) by the spline 117. By way of these shafts, a metal belt and gears, a rotational output of the crankshaft 16 is transmitted to the rear wheel.

In FIG. 2, on a lower portion of the power unit 1, an engine-use oil pump 120 and a transmission-use oil pump 128 are mounted. The engine-use oil pump 120 is rotatably driven by a drive chain 124 extending between and wound around a drive sprocket wheel 121 which is mounted on the rear balancer shaft 39B and a driven sprocket wheel 123 which is mounted on an engine-use oil pump shaft 122. The engine-use oil pump 120 sucks up the engine oil from an oil pan 125 mounted on the lower portion of the power unit 1 by way of an oil strainer 126, and feeds the oil to the inside of the internal combustion engine 2, to a lubricating portion in the inside of the crank chamber 66 and to the transmission input clutch 75. The engine oil is fed to the transmission input clutch 75 by way of a solenoid valve 135 for the transmission input clutch when a rotational speed of the internal combustion engine exceeds a predetermined value. While the engine oil is fed to the transmission input clutch 75 for reducing friction of a metal sliding portion, the engine oil is also fed to an oil chamber 83 of the transmission input clutch 75 for driving the pressurizing plate 82.

The transmission-use oil pump 128 is rotatably driven by a drive chain 132 extending between and wound around a drive sprocket 129 which is mounted on the CVT driven shaft 41 and a driven sprocket 131 which is mounted on a transmission-use oil pump shaft 130, and the transmission-use oil pump 128 sucks up the oil for the continuously variable transmission from an oil pan (not shown in the drawing) in the lower portion by way of an oil strainer (not shown in the drawing), and feeds the oil to the CVT drive pulley movable half body 88, the driven pulley movable half body 94, the endless metal belt 99 and the start clutch 101 by way of the hydraulic control valve unit 136. The oil pans for both pumps are separately provided so that respective oils are not mixed. The oil for the continuously variable transmission is supplied to the oil chamber 91 of the drive pulley movable half body 88 and the oil chamber 97 of the driven pulley movable half body 94 and drives the respective movable half bodies. Further, the oil for continuously variable transmission is supplied to the oil chamber 110 of the start clutch 101 and is used for driving the pressurizing plate 109. The oil for the continuously variable transmission has a function of enhancing a friction force compared to the engine oil. Thus, it is possible to prevent a slippage at a contact portion between the endless metal belt 99 and the drive pulley 86 and at a contact portion between the endless metal belt 99 and the driven pulley 92. The oil for continuously variable transmission is, in addition to the above-mentioned purposes, used for lubrication of the inside of the transmission chamber.

In FIGS. 2 to 4, the hydraulic control valve unit 136 is mounted on an upper surface of a rear portion of the left power unit case 6. The oil for the continuously variable transmission which is supplied to this device is fed to the CVT drive pulley oil chamber 91, the CVT driven pulley oil chamber 97, the start clutch oil chamber 110 and the like in such a manner that timings and pressures for these parts are respectively controlled. The changeover of the oil pressures for controlling these parts is performed using solenoid valves by way of spool valves arranged inside of the hydraulic control valve unit 136.

FIG. 5 is a right side view of a power unit 1 according to a second embodiment of the present invention. In this embodiment, a hydraulic control valve unit 136 is mounted on an outer surface of a right-outer-side protection cover 13 of a rear portion of the power unit 1. Since the hydraulic control valve unit 136 is arranged close to a transmission chamber 67 in which devices to be supplied with oil are housed, such an arrangement is useful for shortening a length of an oil-passage piping.

FIG. 6 is a left side view of a power unit 1 according to a third embodiment of the present invention. In this embodiment, a hydraulic control valve unit 136 is mounted on a left-side outer surface of a rear portion of the power unit 1. Since the hydraulic control valve unit 136 is arranged close to a transmission chamber 67 in which devices to be supplied with oil are housed, such an arrangement is useful for shortening a length of an oil-passage piping.

FIG. 7 is a cross-sectional developed view of a power unit 1 which includes respective rotational shafts according to a fourth embodiment of the present invention. This embodiment differs from the first embodiment (FIG. 4) with respect to a point wherein a transmission input clutch 175 is arranged inside of a transmission chamber 67. A boss portion 176a of a clutch outer 176 and a boss portion 177a of a clutch inner 177 extends to a right side of a right power-unit case 7 through the inside of an inner lace of a ball bearing 169, and a transmission input gear 178 is fixed to the boss portion 177a of the clutch inner. Also in this embodiment, the relative positional relationship among the clutch outer 176, the clutch inner 177, a group of friction discs 179, a pressure-receiving plate 181, a pressurizing plate 182, a transmission-input-clutch oil chamber 183 and a coil spring 184 which are arranged in the inside of the transmission-input clutch 175 is the same relationship described in conjunction with the first embodiment.

By housing the transmission input clutch 175 inside of the transmission chamber 67, the actuation and the lubrication of this clutch 175 are performed using oil for the continuously variable transmission by way of a hydraulic control valve unit 137 in the same manner as other devices arranged inside of the transmission chamber 67. Accordingly, one solenoid valve is added to the hydraulic control valve unit 137. The lubrication of the transmission input gear 178 which remains outside the transmission chamber 67 is performed using engine oil in the same manner as the case explained in conjunction with the first embodiment. When the internal combustion engine reaches a predetermined rotational speed or more, high-pressure oil for the continuously variable transmission is supplied to a transmission-input-clutch oil chamber 183 by controlling the hydraulic control valve unit 137. Thus, a pressurizing plate 182 is pushed against a biasing force of a coil spring 184 thus engaging the transmission input clutch 175. Due to such an operation, it is possible to largely reduce a load in the cranking at the time of starting the engine.

FIG. 8 is a plan view showing the positional relationship between the vehicle body and the power unit of the above-mentioned embodiments. In the drawing, a vertical plane which passes a vehicle-body center line, which includes the center of the front wheel 148 and the center of the rear wheel 151, is a vertical plane 190 of the center line of the vehicle body. In the above-mentioned respective embodiments, the approximate center of the crankshaft 16, the balancers 62A, 62B, and the CVT drive pulley 86 and the CVT driven pulley 92 of the continuously variable transmission are arranged on the vertical plane 190 of the vehicle body center line. Thus, the center of gravity of the power unit and the center of the vehicle body agree with each other whereby the motion performance of the motorcycle can be enhanced.

Due to the embodiments described in detail heretofore, it is possible to obtain following advantageous effects.

When the drive pulley of the continuously variable transmission is mounted on an end portion of the crankshaft, the lateral width of the power unit is increased. In this embodiment, the continuously variable transmission is arranged behind the crankshaft, and at substantially the center in the lateral direction of the crankshaft, that is, behind a crankpin. It is also necessary to arrange the balancer behind the crankpin. According to the present invention, by arranging the balancer between the crankshaft and the continuously variable transmission such that the continuously variable transmission and the balancer do not overlap with each other in a side view, the width of the power unit can be decreased thus enabling the acquisition of a large vehicle-body bank angle.

(2) When the drive pulley of the continuously variable transmission is directly driven by the crankshaft by mounting the gear on the extension of the crankshaft, the power unit suffers from a disadvantage wherein the width of the power unit is increased. Accordingly, the rotation of the crankshaft is transmitted to the drive pulley shaft by way of the gear mounted on the balancer shaft. Due to such a construction, the width of the power unit can be decreased.

(3) When the drive pulley and the driven pulley are arranged on the vehicle in the longitudinal direction, the length of the power unit in the longitudinal direction is increased. Accordingly, by arranging the drive pulley and the driven pulley in the vertical direction, it is possible to shorten the longitudinal length of the power unit.

(4) The approximate center of the crankshaft, the balancer and the respective pulleys of the continuously variable transmission are arranged on the vertical plane of the vehicle body center line. Thus, the center of gravity of the power unit and the center vertical plane of the vehicle body agree with each other whereby the motion performance of the motorcycle can be enhanced.

(5) By arranging the continuously variable transmission behind the crankshaft of the internal combustion engine, and by arranging the approximately center of the crankshaft and respective pulleys of the continuously variable transmission on the vertical plane of the vehicle body center line, the width of the power unit which includes the internal combustion engine and the transmission can be decreased. Thus, it is possible to acquire a large bank angle of the motorcycle and, at the same time, the center plane of the vehicle body (vertical plane which passes the line which connects the centers of the front and rear tires) and the center of gravity of the power unit agree with each other whereby the motion performance of the motorcycle is enhanced.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

1. A power transmission device which transmits power of an internal combustion engine of a motorcycle, wherein a continuously variable transmission is arranged behind a crankshaft of the internal combustion engine, and a balancer is arranged between the continuously variable transmission and the crankshaft in a state wherein the balancer does not overlap the continuously variable transmission in a side view of the internal combustion engine and the continuously variable transmission.

2. The power transmission device according to claim 1, wherein a drive force of the crankshaft is transmitted to a drive pulley shaft of the continuously variable transmission by way of a gear of a balancer shaft.

3. The power transmission device according to claim 1, wherein a drive pulley and a driven pulley of the continuously variable transmission are arranged vertically.

4. The power transmission device according to claim 1, wherein the approximate center of the crankshaft, the balancer and the respective pulleys of the continuously variable transmission are arranged on a vertical plane of a vehicle body center line.

5. The power transmission device according to claim 3, wherein the drive pulley includes a fixed half body and a movable half body, the fixed half body is formed with a drive shaft and is not movable in an axial direction, the movable half body is mounted on a side of the fixed half body and is mounted relative to the drive shaft by a key wherein the movable half body is not rotatable relative to the drive shaft and is axially movable relative to the drive shaft.

6. The power transmission device according to claim 5, and further including an oil chamber operatively connected to the movable half body for selectively imparting an axial movement thereto based on an oil pressure applied to the oil chamber.

7. The power transmission device according to claim 6, and further including an oil control valve operatively connected to the oil chamber for adjusting the oil pressure therein.

8. The power transmission device according to claim 1, wherein approximate centers of the crankshaft, the balancer and the continuously variable transmission are arranged on a plane of the motorcycle for aligning the center of gravity and enhancing performance.

9. A power transmission device adapted for transmits power of an internal combustion engine comprising: a crankshaft;a continuously variable transmission is arranged behind the crankshaft of the internal combustion engine; anda balancer arranged between the continuously variable transmission and the crankshaft, wherein the balancer does not overlap the continuously variable transmission in a side view of the internal combustion engine.

10. The power transmission device according to claim 9, wherein a drive force of the crankshaft is transmitted to a drive pulley shaft of the continuously variable transmission by way of a gear of a balancer shaft.

11. The power transmission device according to claim 9, wherein a drive pulley and a driven pulley of the continuously variable transmission are arranged vertically.

12. The power transmission device according to claim 9, wherein the approximate center of the crankshaft, the balancer and the respective pulleys of the continuously variable transmission are arranged on a vertical plane of a vehicle body center line.

13. The power transmission device according to claim 11, wherein the drive pulley includes a fixed half body and a movable half body, the fixed half body is formed with a drive shaft and is not movable in an axial direction, the movable half body is mounted on a side of the fixed half body and is mounted relative to the drive shaft by a key wherein the movable half body is not rotatable relative to the drive shaft and is axially movable relative to the drive shaft.

14. The power transmission device according to claim 13, and further including an oil chamber operatively connected to the movable half body for selectively imparting an axial movement thereto based on an oil pressure applied to the oil chamber.

15. The power transmission device according to claim 14, and further including an oil control valve operatively connected to the oil chamber for adjusting the oil pressure therein.

16. The power transmission device according to claim 9, wherein approximate centers of the crankshaft, the balancer and the continuously variable transmission are arranged on a plane of a vehicle for aligning the center of gravity and enhancing performance.

17. A power transmission device for transmits power of an internal combustion engine of a motorcycle, wherein a continuously variable transmission is arranged behind a crankshaft of the internal combustion engine, and the approximate center of the crankshaft and respective pulleys of the continuously variable transmission are arranged on a vertical plane of a vehicle body center line.