Automatic transmission for motorcycles

An automatic transmission for motorcycles includes a planetary gear train. The power input is applied to a ring gear of the train by a fixed speed ratio transmission and to a sun gear by a variable speed ratio transmission so that the sun gear rotates in a direction opposite to that of the ring gear. The power is output from the planetary gear carrier. The power output is zero when the pitch line velocity of the ring gear is equal to that of the sun gear. A centrifugal clutch is mounted on the input shaft for engaging fixed speed ratio transmission when the rotational speed of the input shaft reaches a predetermined value. Furthermore, another shaft is disposed parallelly near the input shaft and connected to the input shaft by means of two interengaging gears which are respectively mounted on the two shafts so as to act as a balancing shaft for the crank shaft of the engine.

BACKGROUND OF THE INVENTION 
The invention relates to a infinitely variable transmission, particularly 
to one for motorcycle. 
Currently, some motorcycles include a clutch, a gearing and a set of 
stepless V-belt pulleys. The rotation of the wheels of such motorcycles 
must be initiated by the progressive frictional connection of the clutch. 
This causes power loss and limited accelerating ability and gradeability 
of the motorcycle. 
Planetary gear systems associated with belt pulleys have been used in 
automobiles, for example, as disclosed in the U.S. Pat. Nos. 3,152,490, 
3,670,594 and 4,406,178. These planetary gear systems are useful for 
automobiles; however, they are unsuitable for motorcycles because of their 
large volume. 
Additionally, as the vibration of motorcycle is a common problem, reduction 
of the vibration of the crank of motorcycle engines is therefore desired. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide an automatic 
transmission including a planetary gear system, which is suitable for 
motorcycles. 
Another object of the invention is to provide an automatic transmission for 
motorcycles, the output shaft of which is capable of starting from zero 
rotational speed so as to generate relatively large torque and to obviate 
the need for progressive frictional connection of a clutch which causes 
power loss. 
Another object of the invention is to provide an automatic transmission for 
motorcycles, which can reduce the vibration of the crank of the motorcycle 
engine. 
Still another object of the invention is to provide an automatic 
transmission for motorcycles which possesses a high reduction ratio in 
starting to increase the accelerating ability and gradeability of the 
motorcycles. 
According to the invention, an automatic transmission for motorcycles 
includes a first shaft, driven by a crank of an engine; a first 
transmission wheel mounted on the first shaft; a centrifugal clutch 
mounted on the first shaft and connected to the first transmission wheel 
for engaging a fixed speed ratio transmission with the first shaft when 
the rotational speed of the first shaft reaches a predetermined value; a 
second shaft disposed parallelly near the first shaft; a transmission 
mechanism disposed between the first and second shafts for driving the 
second shaft to rotate in a direction opposite to that of the first shaft; 
a compression spring mounted on the second shaft; a first variable V-belt 
pulley mounted on the second shaft and operated by the compression spring; 
a third shaft parallel to the second shaft; a centrifugal weight mounted 
on the third shaft; a second variable V-belt pulley mounted on the third 
shaft and operated by the centrifugal weight; a V-belt connecting the 
second variable V-belt pulley to the first variable V-belt pulley for 
variable speed ratio transmission; a power output shaft coaxial with the 
third shaft; a planetary gear train, including a sun gear fixed to the 
third shaft so as to be driven by the two V-belt pulleys to rotate, a ring 
gear, a planetary gear carrier fixed to the power output shaft, and a 
plurality of pinion gears meshed between the sun gear and the ring gear, 
each of the pinion gears having an axle mounted on the planetary gear 
carrier; a second transmission wheel fixed to the ring gear; and a fixed 
speed ratio transmission member connecting the second transmission wheel 
to the first transmission wheel for driving the ring gear to rotate with 
the first shaft; whereby, the ring gear always rotates in a direction 
opposite to that of the sun gear so that when the pitch line velocity of 
the sun gear is equal to that the ring gear, the power output is zero; 
subsequently, when the rotational speed of the first shaft surpasses the 
limit of its idle speed, the power is output immediately.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a pinion gear P meshs between a sun gear s and a ring 
gear r at points A & B respectively. The pinion gear P has an axis C, 
which is supported by a planetary gear carrier c which itself rotates 
about a point O. The sun gear s is driven to rotate in a first direction 
with a pitch line velocity Va and acts as a first input member. Ring gear 
r is driven to rotate in an opposite second direction with a pitch line 
velocity Vb, and acts as a second input member. Thus, the planetary gear 
carrier c will rotate in either the first or second directions with a 
velocity Vc at axis C determined by an equation, Vc=1/2(Vb-Va) and acts as 
an output member, i.e. when Vb=Va, Vc=0; when Vb&gt;Va, Vc&gt;0; and when Vb&lt;Va, 
Vc&lt;0. 
Given that Ra, Rb & Rc and Na, Nb & Nc respectively represent the rotating 
radii and angular velocities of the sun gear s, ring gear r and planetary 
gear carrier c, then, Nc=(NbRb-NaRa) /2Rc. Accordingly, as Ra, Rb and Rc 
is designed to be fixed, Nc is varied as desired when Na or Nb varies by 
design. 
In the invention, the sun gear s and ring gear r are driven by the same 
power source through respectively a variable speed ratio transmission and 
a fixed speed ratio transmission. Thus, the rotational speed Nb of the 
ring gear r varies in a fixed ratio with the rotational speed of the power 
source, and the rotational speed Na of the sun gear s varies in a variable 
ratio with the rotational speed of the power source. When the power source 
rotates at a minimum speed, the relation between Na and Nb is designed so 
that Nc is zero. When the power source rotates at a speed below the 
minimum speed, the power is disconnected by means of a centrifugal clutch. 
When the rotational speed of the power source surpasses the minimum speed, 
the relation between Na and Nb is designed so that Nc increases gradually. 
FIG. 2 shows a preferred embodiment of the invention. It includes a first 
shaft I driven by the crank shaft XX of the motorcycle; an active gear 1 
fixed to shaft I; a second shaft II parallel to the first shaft I; a 
reactive gear 2 fixed to the second shaft II and meshed with the active 
gear 1 so that the second shaft II acts as a balancing shaft for the crank 
XX of the motorcycle; a first transmission wheel 4 fixed to the first 
shaft I; a known centrifugal clutch 3, connected to the first transmission 
wheel 4 for engaging fixed speed ratio transmission with the first shaft I 
when the rpm of the first shaft I reaches a predetermined value; a 
compression spring X mounted on the second shaft II; a first variable 
V-belt pulley 7 mounted on the second shaft II and operated by the 
compression spring X; a third shaft III parallel to the second shaft II; 
centrifugal weights W mounted on the third shaft III; a second variable 
V-belt pulley 8 mounted on the third shaft III and operated by the 
centrifugal weight W for adjusting automatically the speed variation of 
the third shaft III; a power output shaft IV coaxial with the third shaft 
III; a planetary gear carrier 9 & 9a fixed to power output shaft IV; a 
ring gear 10; a sun gear 12 fixed on the third shaft III; two pinion gears 
11 & 11a meshed between the ring gear 10 and the sun gear 12; two pinion 
axles 13 & 13a respectively mounted on the planetary gear carrier 9 & 9a; 
a V-belt 15 connecting the V-belt pulleys 7 and 8 for variable speed ratio 
transmission; a second transmission wheel 5 fixed on the ring gear 10; a 
fixed speed ratio transmission member 16, such as a belt or a chain, 
connecting the transmission wheels 4 and 5 for a fixed speed ratio 
transmission; and a starting shaft S. In idle operation, the centrifugal 
clutch 3 disengages from the first transmission wheel 4 and the motorcycle 
wheels mounted securely on the output shaft IV rests on the ground, i.e. 
the planetary gear carrier 9 & 9a is fixed. Thus, the rotation of the sun 
gear 12 will rotate the ring gear 10 which in turn, through the fixed 
speed ratio transmission member 16, will rotate first transmission wheel 
4. The first transmission wheel 4 rotates in the same direction as that of 
the clutch means in the centrifugal clutch 3. The centrifugal clutch 3 
engages with the first transmission wheel 4 without friction to rotate 
synchronously when the rpm of shaft I reaches the predetermined value, 
i.e. the limit of the idle speed. When the rpm of shaft I surpasses the 
limit of the idle speed, with the action of the centrifugal weights W 
which will increase the action radius of the first variable V-belt pulley 
8 and decrease the action radius of the V-belt pulley 7, the rpm of sun 
gear 12 will be correspondingly gradually reduced. Thus, an automatic 
differential transmission is obtained. 
It can be noted that a fixed speed ratio transmission member used in the 
present invention can be a timing belt, a chain or a gear train mounted on 
the power source and the planetary gear set. 
A set of experimental data according to the present invention is as 
follows: 
Given that: 
1. the speed ratio of the fixed speed ratio transmission wheels 4 and 5 
equals 1:1.8; 
2. the speed ratio of the variable speed ratio transmission pulleys 7 and 8 
ranges from 1.25:1 to 1:1.2 intermittently corresponding to the rpm of 
the crank shaft XX ranging from 2500 to 4500, i.e. 2500 rpm is the limit 
of idle speed of the crank shaft XX and the speed ratio of the variable 
speed ratio transmission pulleys is maintained at 1:1.2 if the rpm of the 
crank shaft XX is higher than 4500; and 
3. the tooth ratio of sun gear 12 and ring gear 10 is 4:9; 
then, the output of the power output shaft IV is gradually increased from 
zero to 577 rpm when the rpm of the crank shaft XX is increased from zero 
to 4500, i.e. the reduction ratio between the first shaft I and output 
shaft IV, ranging from infinity to 0.13, varies according to the small 
speed ratio variation of the variable speed ratio transmission pulleys 
which ranges from 1.25 to 0.83. The motorcycle incorporating with the 
present invention is easy to start because of such the high reduction 
ratio of the transmission when it starts to output. 
From the above description, the following advantages for the present 
invention can be inferred: 
1. The accelerating ability and the gradability of a motorcycle 
incorporating with the present invention are improved because of the high 
reduction ratio of the transmission. 
2. With the differential output in a planetary gear train, the speed of the 
output is certainly reduced, which eliminates the usage of reduction gear 
assemblies as needed in the conventional transmission. 
3. The a motorcycle incorporating the present invention does not cause 
power loss since the friction loss of the clutch of the conventional 
transmission is avoided. 
4. The second shaft II acts as a balancing shaft of the crank shaft XX; 
thus, the vibration of the motorcycle incorporating the invention is 
reduced to increase the comfort of the ride. 
While the present invention has been described in the preferred embodiment, 
it is to be understood that within the scope of the appended claims, the 
invention may be practiced otherwise than as described.