U.S. patent application number 13/147948 was filed with the patent office on 2012-01-12 for bicycle transmission systems.
Invention is credited to Frank Moeller.
Application Number | 20120010036 13/147948 |
Document ID | / |
Family ID | 40548103 |
Filed Date | 2012-01-12 |
United States Patent
Application |
20120010036 |
Kind Code |
A1 |
Moeller; Frank |
January 12, 2012 |
Bicycle Transmission Systems
Abstract
A bicycle transmission system includes an input (2) constituted
by a bicycle crankshaft, which is connected, in use, to the pedals
(4) of a bicycle, and an output (32), which is connected, in use,
to a bicycle sprocket wheel (34). The input (2) and output (32) are
connected to respective shafts of a three branch epicyclic gearset
including a sun gear (18), which is in mesh with a plurality of
planet gears (16), which are rotatably carried by a common planet
carrier (12) and are in mesh with an annulus gear (20). The rotors
of first and second electric motor/generators (22, 24) are
connected to respective shafts of the gearset via respective
step-up gearing (26, 18; 28, 20) with step-up ratios of at least 5
and at least 8, respectively. The electrical connections of the
stators of the motor/generators are connected together via a
controller (30) arranged to selectively control the electrical
power transmitted to or from an electrical energy store (31) to the
motor/generators or between them. The R.sub.o ratio of the gearset,
that is to say the ratio of the speed of the annulus gear (20) to
the speed of the sun gear (18) when the planet carrier (12) is held
stationary, is between -2 and -4.
Inventors: |
Moeller; Frank; (Stafford,
GB) |
Family ID: |
40548103 |
Appl. No.: |
13/147948 |
Filed: |
February 9, 2010 |
PCT Filed: |
February 9, 2010 |
PCT NO: |
PCT/GB2010/000223 |
371 Date: |
September 22, 2011 |
Current U.S.
Class: |
475/149 |
Current CPC
Class: |
B62M 6/55 20130101; B62M
11/145 20130101; Y02T 10/64 20130101; H02K 7/116 20130101; B60L
2240/421 20130101; B62M 11/14 20130101; B60L 2240/486 20130101;
B62M 6/45 20130101; Y02T 10/641 20130101; B60L 2220/42 20130101;
B60L 50/20 20190201; B62M 6/65 20130101; Y02T 10/646 20130101; B60L
2200/12 20130101 |
Class at
Publication: |
475/149 |
International
Class: |
B62M 11/14 20060101
B62M011/14; B62M 6/45 20100101 B62M006/45; B62M 6/55 20100101
B62M006/55 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 2009 |
GB |
0902356.5 |
Claims
1. A bicycle transmission system including an input constituted by
a bicycle crankshaft, which is connected, in use, to the pedals of
a bicycle, and an output, which is connected, in use, to a bicycle
sprocket wheel, the input and output being connected to respective
shafts of a three branch epicyclic gearset including a sun gear
which is in mesh with a plurality of planet gears, which are
rotatably carried by a common planet carrier and are in mesh with
an annulus gear, and first and second electric motor/generators,
the rotors of which are connected to respective shafts of the
gearset via respective step-up gearing with step-up ratios of at
least 5 and at least 8, respectively, and the electrical
connections of the stators of which are connected together via a
controller arranged to selectively control the electrical power
transmitted to or from an electrical energy store to the
motor/generators or between them, the R.sub.o ratio of the gearset,
that is to say the ratio of the speed of the annulus gear to the
speed of the sun gear when the planet carrier is held stationary,
being between -2 and -4, in which the input is connected to the
planet carrier and the sun gear is rotatable with respect to the
input and is connected to the first motor/generator via step-up
gearing with a step-up ratio of at least 5 and the annulus gear is
connected to the second motor/generator via step-up gearing with a
step-up ratio of at least 8.
2. (canceled)
3. A transmission system as claimed in claim 1 in which splines are
integrally formed on the bicycle crankshaft, which splines are in
mesh with splines on the planet carrier.
4. A transmission system as claimed in claim 1 in which connected
to the rotor of the first and second motor/generator is a
respective pinion gear in mesh with gear teeth on the sun gear and
annulus gear, respectively.
5. A transmission system as claimed in claim 1 in which the
controller is programmed selectively to direct electrical power
from an electric battery to at least one of the motor/generators to
cause it to operate as a motor.
6. A transmission system as claimed in claim 1 in which the
controller is programmed selectively to direct electrical power
from that motor/generator which is operating as a generator to an
electric battery to recharge it.
7. A transmission system as claimed in claim 1 in situ on a
bicycle, the crankshaft being connected to the pedals of the
bicycle to be rotated thereby, the output being connected to a
bicycle sprocket wheel and the controller being connected to an
electric power storage medium.
Description
[0001] The present invention relates to bicycle transmission
systems of variable transmission ratio. Bicycle transmission
systems conventionally include a sprocket wheel connected to rotate
with the bicycle pedals, a further sprocket wheel connected to
rotate with the rear wheel and a continuous chain passing around
both sprocket wheels for transmitting the propulsive force exerted
on the pedals to the rear wheel.
[0002] Many bicycle transmission systems of variable transmission
ratio are known and the most widely used are so-called hub gears
and derailleur gears. Hub gears are essentially a gearset
accommodated within the hub of the rear wheel with an input
connected to the rear sprocket wheel and an output connected to the
rear wheel. Such transmission systems are selectively switchable to
provide three or more different transmission ratios. Derailleur
gears include two or more sprocket wheels of different size
connected to the rear wheel and/or to the pedal cranks and a
mechanism arranged to selectively move the bicycle chain laterally
from one sprocket wheel to another. The known transmission systems
do not provide an infinitely variable transmission ratio but a
finite number of fixed transmission ratios.
[0003] A bicycle transmission of infinitely variable transmission
ratio is available from a company by the name of Fallbrook
Technologies under the name of NuVinci. This includes input and
output discs in rolling contact with large balls which may be
tilted, thereby altering the effective radius of the points of
contact between the balls and the discs and thus also altering the
transmission ratio between the two discs. This transmission is
complex and bulky and also does not inherently permit the
additional introduction of power produced by a motor and the
combination of that power with the power generated by the user.
[0004] Motor vehicle transmission systems are also known of the
type comprising an epicyclic gearset, of which two shafts
constitute the input and output and are thus connected, in use, to
the crankshaft of the vehicle engine and to the wheels of the
vehicle, respectively, and two shafts are connected to the rotors
of respective electrical machines constituting motor/generators.
The stator connections of the two electrical machines are connected
together via a controller arranged to control the electrical power
transmitted between them and to and from an electric storage
medium, such as a battery. In use, one of the electrical machines
acts as a generator and the power it generates is transmitted to
the other machine, which operates as a motor. Power is thus
transmitted through such transmission systems both mechanically and
electrically and variation in the proportion of the power that is
transmitted electrically will result in progressive variation in
the transmission ratio. Such transmission systems, which are
sometimes referred to as power split transmissions, are therefore
of infinitely variable transmission ratio.
[0005] However, whilst power split transmissions have been widely
used on motor vehicles, they have not been used on bicycles and it
is believed that there are two primary reasons for this. Thus
firstly it was believed that such transmission systems would be too
bulky and heavy for use on a bicycle. Secondly, it was believed
that the electric machines would be largely ineffective because
such machines are inherently not capable of generating/absorbing
any significant torque at the lower speeds which are inherent in a
bicycle transmission.
[0006] It is the object of the invention to provide a bicycle
transmission system which is of infinitely variable transmission
ratio and which will therefore permit the transmission ratio at any
one time to be at or much closer to the ratio which is the optimum
in the light of the road conditions and strength and fitness of the
user than is possible with a transmission system providing only a
relatively small number of discrete transmission ratio. It is a
further object of the invention to provide a bicycle transmission
system which readily enables mechanical power to be generated by a
motor and directed into the driveline to permit the bicycle to be
at least partially motor driven at selected times, e.g. when the
user is tired or when climbing a hill, and enables the power
produced by the motor to be combined in a simple manner with the
power applied to the bicycle pedals by the user.
[0007] According to the present invention, a bicycle transmission
system includes an input constituted by a bicycle crankshaft, which
is connected, in use, to the pedals of a bicycle, and an output,
which is connected, in use, to a bicycle sprocket wheel, the input
and output being connected to respective shafts of a three branch
epicyclic gearset including a sun gear which is in mesh with a
plurality of planet gears, which are rotatably carried by a common
planet carrier and are in mesh with an annulus gear, and first and
second electric motor/generators, the rotors of which are connected
to respective shafts of the gearset via respective step-up gearing
with step-up ratios of at least 5 and at least 8 and preferably at
least 10, respectively, and the electrical connections of the
stators of which are connected together via a controller arranged
to selectively control the electrical power transmitted between
them, the R.sub.o ratio of the gearset, that is to say the ratio of
the speed of the annulus gear to the speed of the sun gear when the
planet carrier is held stationary, being between -2 and -4.
[0008] Thus the transmission system in accordance with the present
invention is of split power type but it is found surprisingly that
it is not only extremely effective but also that it may be small
enough and light enough to be readily accommodated on a bicycle.
The small size of the transmission system is made possible by the
fact that the R.sub.o ratio of the gearset is between -2 and -4 and
it is found in practice that R.sub.o values greater than -4 result
in the gearset being unacceptably large. It has been appreciated
also that the problem of the motor/generators being essentially
ineffective at the low speeds associated with bicycle transmission
systems may be overcome by the use of step-up gearing so that
whilst the elements of the epicyclic gearset rotate at low speed,
the motor/generators rotate very much faster, that is to say at
speeds at which they can operate effectively. The transmission
system in accordance with the invention thus inherently includes
two motor/generators and this means that it is therefore very
simple for a bicycle to which the transmission system is fitted to
be motor-assisted. Thus the two motor/generators may be connected
via the controller to an electric storage medium, such as a battery
which may be arranged to selectively direct electrical power from
the battery to one or even both motor/generators to cause them to
operate as motors and thus to provide some or even all of the
propulsive power needed to drive the bicycle. It is therefore
proposed that the controller is programmed selectively to direct
electrical power from an electric battery to at least one of the
motor/generators to cause it to operate as a motor. The presence of
the motor/generators and an electric battery also opens up the
possibility to use regenerative braking, that is to say of braking
the bicycle, at least in part, electrically rather than
mechanically and using the kinetic energy of the bicycle and rider
which must be dissipated to generate electrical power, which is
then used to recharge the battery. It is therefore preferred that
the controller is also programmed selectively to direct electrical
power from that motor/generator which is operating as a generator
to an electric battery to recharge it.
[0009] In normal operation of the bicycle, one of the
motor/generators will normally operate as a generator and the power
which it produces is directed by the controller to the other
motor/generator, which operates as a motor. The amount of
electrical power transferred between the two motor/generators will
be controlled by the user, e.g. by means of an infinitely variable
gear lever on the bicycle handlebars, and this will result in the
transmission ratio changing progressively to the instantaneously
desired value. Alternatively or additionally, the change in
transmission ratio may be effected automatically by the controller,
e.g. in dependence on the effort exerted by the user, which may be
sensed by a torque sensor associated with the bicycle crankshaft.
The transmission ratio is therefore infinitely variable and may be
set at whatever value the user requires and is not limited to one
of the relatively small number of discrete values available with
the known bicycle transmission systems.
[0010] In the preferred embodiment, the input is connected to the
planet carrier and the sun gear is rotatable with respect to the
input and is connected to the first motor/generator via step-up
gearing with a step-up ratio of at least 5 and the annulus gear is
connected to the second motor/generator via step-up gearing with a
step-up ratio of at least 8. It is preferred further that gear
teeth are integrally formed on the input, that is to say on the
bicycle crankshaft, which teeth are in mesh with gear teeth on the
planet carrier.
[0011] It is preferred that the rotors of the first and second
motor/generator are connected to a respective pinion gear in mesh
with gear teeth on the sun gear and annulus gear, respectively.
[0012] The present invention also embraces a transmission system of
the type referred to above in situ on a bicycle, the crankshaft
being connected to the pedals of the bicycle to be rotated thereby
and the output being connected to a bicycle sprocket wheel. In
practice, a chain will be in mesh with that sprocket wheel and with
a further sprocket wheel connected to rotate with the rear wheel of
the bicycle.
[0013] Further features and details of the invention will be
apparent from the following description of one specific embodiment
which is given by way of example with reference to the single
accompanying drawing, which is an axial sectional view of a bicycle
transmission in accordance with the invention.
[0014] The transmission system includes an input shaft 2, which
constitutes the crankshaft of a bicycle. This crankshaft is
connected, in use, to the pedals of the bicycle but only a portion
4 of the shafts of the pedals is shown. The transmission is
enclosed within an outer housing 6 and the crankshaft is mounted to
rotate with respect to that housing by means of two bearings 8.
Formed integrally with the crankshaft 2 is a circumferential array
of gear teeth 10, which are in mesh with complementary gear teeth
formed on the planet carrier of an epicyclic gearset. The planet
carrier 12 carries a number of planet shafts 14, each of which
rotatably carries a respective rotatable planet gear 16. The planet
gears 16 are in mesh with teeth formed on a sun gear 18, which is
rotatable with respect to the crankshaft 2, and with teeth formed
on an annulus gear 20.
[0015] The transmission system also includes a first
motor/generator 22 and a second motor/generator 24. The rotors of
these two motor/generators carry respective pinion gears 26, 28.
These two pinion gears are in mesh with teeth formed on the sun
gear 18 and the annulus gear 20, respectively. The two pinion gears
are of relatively small diameter compared to the sun gear and
annulus gear and the connection of the pinions therefore
constitutes step-up gearing. The step-up ratio between the sun gear
18 and the motor/generator 22 is at least 5 and is in this case 8.
The step-up ratio between the annulus gear and the pinion 28 is at
least 10 and is in this case 12. The electrical stator connections
of the two motor/generators are connected together via a controller
30, which is arranged to control the electrical power transferred
between the two motor/generators, in this case in response to the
position of a movable gear lever or transmission ratio lever
mounted on the handlebars of the bicycle. The controller is also
connected to a rechargeable electric battery 31.
[0016] The annulus gear 20 is connected to rotate with an annular
output member 32, which is connected to rotate with a bicycle
sprocket wheel 34 of conventional type. In use, a bicycle chain
(not shown) will pass over and be in mesh with both the sprocket
wheel 34 and also a further sprocket wheel (not shown) connected to
rotate with the rear wheel of the bicycle.
[0017] In use, the user rotates the pedals of the bicycle in the
usual manner and this rotational movement is transmitted to the
epicyclic gearset and the sun gear 18 and annulus gear 20 thus
rotate also and the sprocket wheel 34 rotates with the annulus gear
20. Although the sun gear 18 and annulus gear 20 necessarily rotate
relatively slowly, the step-up gearing between them and the two
motor/generators 22, 24, means that these two electrical machines
rotate relatively rapidly. One of them normally operates as a
generator and the power which it generates is directed by the
controller 30 to the other machine, which acts as a motor. The
speed of the annulus gear 20 and thus the transmission ratio of the
transmission may be varied at will by the user by controlling the
controller 30 to transmit a desired amount of electrical power from
one machine to the other. If the user should require motor
assistance, e.g. when climbing a hill, he operates the control
system to cause electrical power to be drawn from the battery 31
and directed to that electrical machine which is operating as a
motor, thereby adding mechanical power to the transmission system
resulting either in the bicycle moving more rapidly or in the
amount of effort that must be exerted by the user to maintain a
constant speed being reduced. If the user should operate the
bicycle brake, this is communicated to the controller which then
directs electrical power from that electrical machine which is
operating as a generator to the battery 31 in order to recharge it.
This is of course so-called regenerative braking and will result in
the braking effort which must be exerted by the bicycle braking
system being reduced or largely eliminated and will also result in
the frequency with which the battery 31 must be recharged by
conventional means, that is to say with the aid of a battery
charger, being reduced.
* * * * *