Note: Descriptions are shown in the official language in which they were submitted.
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MULTI-SPEED BEVEL-PLANETARY HUB TRANSMISSION
Field of the Invention
The invention relates to the field of hub transmissions, specifically bicycle
hub transmissions,
also known as internal gear hubs. The scope includes all bicycle and tricycle
types, extending
to all types of human-powered vehicles. The hub may be chain-driven, as in a
conventional
bicycle rear wheel, or directly driven, as in a front wheel of a direct-drive
recumbent bicycle.
The hub may also be mounted entirely outside of a wheel to form another part
of a bicycle's
overall gear train system. For example, it may be directly driven as a bottom
bracket gear hub
with a chainring as the output element. Due to a potential for higher torque
capacity, the hub
transmission is also well suited for use in conjunction with electric assist,
such as in pedelecs,
e-bikes, electrically assisted tricycles, or other electrically assisted human-
powered vehicles.
Background of the Invention
.. Bicycle internal gear hubs are well known and have been in production for
over a century.
Most of these hubs operate by means of a planetary gear train, composed of the
following basic
elements: a central sun gear; a planet gear carrier which positions several
planet gears around
the sun gear; and a ring gear externally surrounding these planet gears.
Different gear ratios
are available by simply preventing the rotation of one of these elements and
choosing the
remaining two elements as either the input or output of the transmission.
United States patent US9139254 B2 to the present inventor discloses a
planetary bicycle hub
transmission, having multiple speeds, and employing bevel gears and roller
teeth.
The bevel gear system of US9139254 B2 permits much larger planet gears than
conventional
planetary systems because the bevel gear configuration allows the size of each
planet gear to
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be independent of the gear ratio. The gear ratio is instead provided by the
axial height of the
planet gear cluster, or the angle of mounting of the planet gear. The planet
gear size is therefore
constrained only by the width of the hub. These larger planet gears permit a
larger tooth pitch,
resulting in a greater torque capacity for the transmission; and the larger
tooth pitch provides
the space for friction reducing elements such as rollers. The rollers and
meshing sprockets
transfer torque like a roller cam mechanism, reducing meshing friction by
replacing sliding
contact with rolling contact throughout all angles of tooth engagement. In
contrast, the teeth of
two regular spur gears have rolling contact only at the instantaneous point
where the pitch
circles of the two gears intersect. Furthermore, the use of bevel planet gears
allows the hub
transmission to achieve higher gear ratios than conventional hubs. The higher
ratios are
particularly well suited to direct-drive, which has no chain-drive to give an
intermediate step-
up ratio. Still further, the use of bevel gears increases the minimum contact
ratio in the gear
train, improving the smoothness of the meshing or allowing less gear teeth
with the same
smoothness of meshing.
However, the number of speeds (gear ratios) available in US9139254 B2 is
somewhat limited.
In the first embodiment of US9139254 B2, if more that four speeds are desired,
the planet gear
cluster becomes increasingly tall, increasing the overall outer diameter of
the hub. In the second
embodiment of U59139254 B2, there is little circumferential space on the
planet gear carrier
for more than four speeds.
Since there is strong demand in the marketplace for more than four speeds, it
would be
advantageous to provide a hub with the advantages of US9139254 B2, but with
more speeds ¨
preferably 8 to 16 speeds. It would also be advantageous to provide these
extra speeds without
multiple planetary units connected in series, and, even more preferably, to
achieve these extra
speeds without the need for many more planet gears or ring gears.
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Summary of the Invention
Therefore, it is an object of the present invention to provide a low-friction,
high-torque capacity
bicycle hub transmission with 8 speeds or more, having a single planetary gear
stage and a
minimum number of planet gears. It is a further object to provide a simplified
gear shifting
configuration, particularly a simplified means of engaging and disengaging
gear elements that
are rotating. It is a still further object to provide a hub where the
manufacturing of the bevel
gear elements is simplified.
To meet these objects, the present invention improves on the transmission of
US9139254 B2
by replacing the single output bevel gear with multiple output bevel gears,
each selectively
engageable to drive the hub by means of an associated engageable freewheel.
This will increase
the number of speeds from four to eight with the addition of only two more
output bevel gears,
or from five speeds to eleven, with the addition of only three more output
bevel gears.
The engageable freewheels are preferably controlled wirelessly to eliminate
the complex
mechanical linkages that otherwise would be needed to reach the rotating
parts.
When engaged, the selected output bevel gear drives the hub, but the hub may
still overrun it
if the hub is moving faster. When disengaged, the output bevel gear is free to
move in either
direction relative to the hub and therefore no drive is transmitted to the
hub. In this way, the
freewheel and gear shift elements are combined, simplifying the design.
Engageable freewheels are also provided to hold the bevel ring gears
stationary.
The use of engageable freewheels prevents the transmission from jamming if the
shift control
system fails and several bevel ring gears are held stationary at the same
time. Rather than
jamming, the engaged freewheels associated with the faster moving elements
will simply
overrun, avoiding internal damage to the hub.
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Engageable freewheels are known in the art of bicycle hub transmissions, for
example in
US6048287 to Rohloff. However, it is not known to apply engageable freewheels
to a multi-
speed bevel planetary bicycle hub transmission in such a way as to achieve the
particular
benefits here disclosed.
Other advantages and variations to the design will be evident from the
detailed description and
referenced drawings.
Brief Description of the Drawings
Figure 1 depicts an exemplary embodiment of the transmission hub according to
the invention,
configured for chain-drive.
Figure 2 illustrates the transmission hub of figure 1 with the cover and first
gear freewheel
removed.
Figure 3 is an exploded view showing the mounting of the planet clusters on
the drive shaft
unit.
Figure 4 is detailed view of a planet gear cluster.
Figure 5 depicts the meshing of the bevel planet gears with the bevel output
gears.
Figure 6 is a plan view of the bevel output gears.
Figure 7 shows the engageable freewheel of the smallest bevel output gear.
Figure 8 illustrates the engageable freewheel configuration of figure 7 in
more detail.
Figure 9 depicts the meshing of the bevel planet gears with the bevel reaction
gears.
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Figure 10 is a plan view of the bevel reaction gears.
Figure 11 show the first gear freewheel configuration.
Figure 12 illustrates the wireless control system for the engageable
freewheels of the bevel
output gears.
Figure 13 illustrates a means for controlling the engageable freewheels by
linear actuators.
Figure 14 illustrates the wireless control system for the engageable
freewheels of the bevel
reaction gears.
Figure 15 depicts an exemplary wireless shifter unit configuration.
Figure 16 shows the ratios attainable for an 8-speed example of the
transmission hub.
Figure 17 shows the ratios attainable for an 11-speed example of the
transmission hub.
Figure 18 shows the transmission hub configured for direct-drive.
Figure 19 depicts the transmission hub configured for bottom bracket mounting.
Figure 20 illustrates an alternative control of the engageable freewheels
using a cam ring and
electric motor.
Figure 21 is a schematic of an alternate wired control system for shifting
gears.
Figure 22 illustrates a means of attaining mechanical control of the rotating
engageable
freewheels of the bevel output gears.
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Detailed Description of the Invention
Figure 1 shows an overall view of an example embodiment of the hub
transmission (100) of
the present invention. Figure 2 depicts the hub transmission (100) with a
cover portion (101)
removed. Input torque to the hub transmission (100) is transmitted by a drive
shaft (102) which
rotates about a drive shaft axis (104). The drive shaft (102) is directly
connected to a planet
gear axle (106) consisting of a stub axle (108) and an identical, but
oppositely directed, stub
axle (108). The stub axles (108) share a common planet gear axis (110). The
planet gear axis
(110) intersects the drive shaft axis (104) at 90 degrees. The drive shaft
(102) combined with
the stub axles (108) form a drive shaft unit (111).
Figure 3 illustrates an exploded view of the drive shaft unit (111). A planet
gear cluster (112)
is mounted on each stub axle (108) and rotates about the planet gear axis
(110). Each one of
the two planet gear clusters (112) is identical and comprises three axially-
spaced bevel planet
gears (114, 116, 118). The axial spacing between successive bevel planet gears
(114, 116, 118)
in the planet gear cluster (112) may differ ¨ as shown. The diameter of each
bevel planet gear
(114, 116, 118) may also differ, as illustrated. The bevel planet gears (114,
116, 118) are
integrally formed with the planet gear cluster (112) and therefore rotate
together as a unit. Each
one of the bevel planet gears (114, 116, 118) is equipped with roller teeth
(115), which rotate
on supporting pins (117) about roller tooth axes (119). Figure 4 shows a
planet gear cluster
(112) in more detail.
As shown in figure 5, the bevel planet gears (114, 116, 118) of each planet
gear cluster (112)
mesh with corresponding bevel output gears (120, 122, 124) ¨ more clearly
shown in face view
in figure 6. The bevel output gears (120, 122, 124) are rotatably mounted on
an inside of an
output gear carrier (126), to which the cover portion (101 ¨ figure 1) is
attached, together
forming a hub shell (127). As the name implies, the bevel output gears (120,
122, 124) provide
output torque to a hub shell (127). The bevel output gears (120, 122, 124)
have an axis of
rotation that is concentric with the drive shaft axis (104). The hub shell
(127) also has an axis
of rotation that is concentric with the drive shaft axis (104).
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As shown in figure 6, each bevel output gear (120, 122, 124) has a
corresponding engageable
freewheel (128, 130, 132) positioned between the corresponding bevel output
gear (120, 122,
124) and the hub shell (127). The term "engageable freewheel" is defined as a
freewheel that,
relative to its mounting surface, allows rotation in one direction only when
the freewheel is
engaged and allows rotation in both directions when the freewheel is
disengaged.
Figures 7 and 8 show the engageable freewheel (128) for the smallest bevel
output gear (120)
in more detail. A ratchet wheel (134) is integrally formed on a reverse side
of the bevel output
gear (120). Pawls (136) are rotatably mounted on the hub shell (127) and, in a
manner well
known in the art, the pawls (136) are spring-loaded to engage with a surface
of the ratchet
wheel (134). Therefore, when the engageable freewheel (128) is engaged, the
pawls (136)
transmit power to the hub shell in a clockwise direction (when viewed facing
the hub right
side) while allowing the hub to freewheel if it is turning faster than the
bevel output gear (120).
To disengage the engageable freewheel (128), the pawls (136) are lifted clear
of the surface of
the ratchet wheel (134) against their spring loading, and thus no power is
transmitted to the
hub shell (127) in either direction by the bevel output gear (120). A similar
configuration of
engageable pawls and corresponding ratchet wheels is employed in the
engageable freewheels
(130, 132) of the two larger bevel output gears (122, 124).
As illustrated in figure 9, on the left side of the hub transmission (100) the
bevel planet gears
(114, 116, 118) of each planet cluster (112) mesh with three corresponding
bevel reaction gears
(140, 142, 144) ¨ more clearly shown in face view in figure 10. These gears
are called "bevel
reaction gears" because they provide the necessary reaction force for the
bevel planet gears
(114, 116, 118) to drive the corresponding bevel output gears (120, 122, 124)
on the opposite
side of the hub. The three bevel reaction gears (140, 142, 144) are rotatably
mounted on a
reaction gear carrier (146) and each bevel reaction gear (140, 142, 144) has
an axis of rotation
that is concentric with the drive shaft axis (104). The reaction gear carrier
(146) is prevented
from rotating by being fixed relative to the bicycle frame or fork.
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As shown in figure 10, each bevel reaction gear (140, 142, 144) has a
corresponding
engageable freewheel (148, 150, 152) positioned between a corresponding bevel
reaction gear
(140, 142, 144) and the reaction gear carrier (146). The engageable freewheels
(148, 150, 152)
operate similarly to the engageable freewheels (128, 130, 132) of the output
gears (120, 122,
124). Since the reaction gear carrier (146) is fixed relative to the mounting
structure of the
bicycle, when the engageable freewheels (148, 150, 152) are engaged, the
corresponding bevel
reaction gear (140, 142, 144) is prevented from rotating in a clockwise
direction when viewed
facing the right side of the hub. This provides the necessary reaction force
for the
corresponding bevel planet gear to drive the engaged bevel output gear and so
drive the hub
shell (127).
The bevel output gears (120, 122, 124) do not transmit any torque to the hub
shell (127) when
all their associated engageable freewheels (128, 130, 132) are disengaged.
Similarly, the bevel
output gears (120, 122, 124) do not transmit any torque to the hub shell (127)
when all the
engageable freewheels (148, 150, 152) of the bevel reaction gears (140, 142,
144) are
disengaged. When either, or both, of these cases are true, the hub is designed
to revert to a 1:1
ratio (first gear) by means of a first gear freewheel (154). As illustrated in
figure 11, the first
gear freewheel (154) consists of a pawl holder (156) located at a distal end
of each stub axle
(108), a spring-loaded first gear pawl (158) installed in in each pawl holder
(156), and first
gear ratchet ring (160) fixed to the inside of the cover portion (101) of the
hub shell (127) in a
cover portion protrusion (103) - figure 1.
Figure 12 illustrates the transmission hub (100) with a side cover (105 -
figure 1) removed
showing the control elements for the engageable freewheels (128, 130, 132) of
the bevel output
gears (120, 122, 124). Each engageable freewheel (128, 130, 132) of each bevel
output gear
(120, 122, 124) is controlled by an actuation system comprising a pair of
linear actuators (162,
164, 166) respectively. Each pair of linear actuators (162, 164, 166)
disengages each of the
respective engageable freewheels (128, 130, 132) by lifting the associated
pawls clear of
ratchet wheel surface, and engages the freewheel by retracting, allowing the
pawls to return to
the ratchet wheel surface under spring load. A typical arrangement is shown in
figure 13 for
the smallest bevel output gear (120) - the linear actuators (162) lift the
pawls (136) from the
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surface of the ratchet wheel (134) to disengage engageable freewheel (128).
The pairs of linear
actuators (162, 164, 166) of the engageable freewheels (128, 130, 132) of the
bevel output
gears (120, 122, 124) are wirelessly controlled by an output gear controller
(168), output gear
receiver (170), and output gear power source (four rechargeable batteries 172 -
figure 12). The
output gear receiver (170) receives an incoming wireless signal that is
subsequently processed
by the output gear controller (168) to operate the linear actuators (162, 164,
166) according to
the selected gear. In this way, complex mechanical linkages between the
rotating hub shell
(127) and the bicycle frame or fork are avoided, as well as shifter cables.
Referring to figure 14, a similar control system is applied to the engageable
freewheels (148,
150, 152) of the bevel reaction gears (140, 142, 144) on the left side of the
hub. In a manner
similar to figure 13, pairs of linear actuators (184, 186, 188) disengage the
associated
engageable freewheel (148, 150, 152) by moving the respective freewheel pawls
clear of the
ratchet wheel surface, and engage the associated engageable freewheel by
retracting, allowing
the pawls to return to the ratchet wheel surface under spring load. The pairs
of linear actuators
(184, 186, 188) of the engageable freewheels (148, 150, 152) of the bevel
reaction gears (140,
142, 144) are also wirelessly controlled. A reaction gear controller (190), a
reaction gear
receiver (192), and reaction gear power sources (four rechargeable batteries
172) are mounted
on the reaction gear carrier (146) on the left side of the hub. Although a
mechanical linkage is
simpler on the left side of the hub than on the right side because the left
side is stationary, the
exemplary wireless control is preferable for compatibility with the right-side
control system,
and to avoid shifter cables.
As shown schematically in figure 15, the output gear receiver (170) and the
reaction gear
receiver (192) receive wireless signals (193) from a transmitter (174) forming
part of a shifter
unit (176) mounted on the handlebars (177) of the bicycle. The shifter unit
(176) comprises a
gear selector (178), a shifter unit controller (180), the transmitter (174),
and a shifter unit power
source (182).
All the linear actuators (162, 164, 166, 184, 186, 188) are preferably
latching solenoids.
Latching solenoids hold their retracted and extended position without any
power input,
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requiring electrical power only when moving. They are therefore much more
efficient than
conventional solenoids. The linear actuators may alternatively be lead screw
actuators, which
encompass a small electric motor and lead screw to give the linear motion.
Operation
The hub transmission operates as follows. For the lowest gear (having a ratio
of 1:1), all the
engageable freewheels (128, 130, 132, 148, 150, 152) are disengaged, allowing
the bevel
reaction gears (140, 142, 144) and bevel output gears (120, 122, 124) to
rotate freely with the
no torque transmitted through them to the hub shell (127). As a result, the
torque is instead
transmitted to the hub shell (127) through the first gear freewheel (154),
giving the 1:1 ratio.
Higher gears are obtained by engaging one engageable freewheel (148, 150, 152)
corresponding to one of the bevel reaction gears (140, 142, 144) and one
engageable freewheel
(128, 130, 132) corresponding to one of the bevel output gears (120, 122,
124). Since this will
always result in a ratio greater than 1:1, the first gear freewheel (154) will
overrun, and the
ratio will be determined by the engaged freewheels alone. Since there are
three bevel output
gears (120, 122, 124) and three bevel reaction gears (140, 142, 144),
theoretically a total of
nine extra gear ratio combinations should be available. However, three of
these ratios will be
the same (1:2) giving two redundant ratios and thus seven extra ratios
available. This means
that the example hub transmission (100) has a total of eight speeds (including
the 1:1 first gear).
Expressed generally, where n is the number bevel planet gears per planet gear
cluster, the total
number of ratios (N) available will be:
N = n2 ¨ n + 2
The ratios are determined by the following equation:
R = 1 + (Dp,, (DR
U3pR) U30)
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Where,
R is the ratio
Dpo is the pitch diameter of the bevel planet gear than meshes with the
engaged bevel
output gear
DpR is the pitch diameter of the bevel planet gear than meshes with the
engaged bevel
reaction gear
DR is the pitch diameter of the engaged bevel reaction gear
Do is the pitch diameter of the engaged bevel output gear
Example hub dimensions and ratios for the illustrated embodiment (8-speed)
Table 1 presents the dimensions for the example hub transmission (100)
described above and
shown in figures 1-15. The gear module is 2.7.
Table 2 presents the gear ratios and control combinations for each ratio,
where an engaged
freewheel is represented by "x" and a disengaged freewheel is represented by
"0".
Table 1: 8-speed example bevel gear dimensions
Gear element Number of teeth
Pitch diameter [mm]
Bevel planet gear (114) 24 64.8
Bevel planet gear (116) 20 54.0
Bevel planet gear (118) 18 48.6
Bevel output gear (120) 18 48.6
Bevel output gear (122) 30 81.0
Bevel output gear (124) 38 102.6
Bevel reaction gear (140) 18 48.6
Bevel reaction gear (142) 30 81.0
Bevel reaction gear (144) 38 102.6
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Table 2: 8-speed engageable freewheel control combinations and resulting ratio
Engageable freewheels
Bevel reaction gear freewheels Bevel output gear freewheels
Gear Ratio Pt (148) 2nd (150) 3rd (152) 1st (128) 2nd (130) 3rd
(132)
1 1.00 0 0 0 0 0 0
2 1.36 x 0 0 0 0 x
3 1.50 x 0 0 0 x 0
4 1.71 0 x 0 0 0 x
2.00 0 x 0 0 x 0
6 2.41 0 0 x 0 x 0
7 3.00 0 x 0 x 0 0
8 3.81 0 0 x x 0 0
A graph of the resulting ratios is presented in figure 16 including a
comparison to the
5 theoretical best ratios (ratios having a constant percentage increment).
The available ratios vary
within 12% of the theoretical best ratios.
Increasing the number of planet gears per cluster to four (11-speed example)
Table 3 presents example dimensions for an embodiment of the transmission hub
having four
bevel planet gears per planet gear cluster. The gear module is 2.7.
Table 4 presents the gear ratios and control combinations for each ratio,
where an engaged
freewheel is represented by an "x" and a disengaged freewheel is represented
by a "0".
Although fourteen gears are available, several of these gears are very close
in ratio resulting in
eleven useful ratios, as shown in the table.
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Table 3: 11-speed example bevel gear dimensions
Gear element Number of teeth Pitch
diameter [mm]
1st bevel planet gear 21 56.7
21 bevel planet gear 20 54.0
3rd bevel planet gear 19 51.3
4th bevel planet gear 18 48.6
1st bevel output gear 18 48.6
21 bevel output gear 28 75.6
3rd bevel output gear 44 118.8
4th bevel output gear 54 145.8
1' bevel reaction gear 18 48.6
2nd bevel reaction gear 28 75.6
3rd bevel reaction gear 44 118.8
4th bevel reaction gear 54 145.8
Table 4: 11-speed engageable freewheel control combinations and resulting
ratio
Engageable freewheels
Bevel reaction gear freewheels Bevel
output gear freewheels
Gear Ratio 1st 2nd 3rd 4th 1st 2nd 3rd 4th
1 1.00 0 0 0 0 0 0 0 0
2 1.29 x 0 0 0 0 0 0 x
3 1.47 0 x 0 0 0 0 0 x
4 1.61 x 0 0 0 0 x 0 0
1.77 0 0 x 0 0 0 x 0
6 2.00 0 0 x 0 0 0 x 0
7 2.30 0 0 0 x 0 0 x 0
8 2.63 0 x 0 0 x 0 0 0
9 3.14 0 0 0 x 0 x 0 0
3.70 0 0 x 0 x 0 0 0
11 4.50 0 0 0 x x 0 0 0
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A graph of the resulting ratios is presented in figure 17 including a
comparison to the
theoretical best ratios (ratios having a constant percentage increment). The
ratios are within
11% of the theoretical best ratios.
Mounting and drive options
The hub transmission (100) is designed to be mounted for chain-drive, as in a
regular bicycle,
but it can also be mounted for direct-drive, where the hub is driven directly
by the pedal cranks.
This allows the hub to be used in a direct-drive recumbent bicycle which is
front-wheel drive
and has no chain. Other direct-drive wheel mountings are also possible. The
direct-drive
configuration also allows the hub to be mounted in the bicycle frame as a
bottom bracket gear.
For standard chain-drive, as shown in figure 1, an axle (194) is rotatably
mounted in a drive
shaft bore (196 ¨ figure 2) in the drive shaft (102), allowing the drive shaft
(102) to rotate
freely relative to the axle (194) around the drive shaft axis (104). The axle
is fixed to the bicycle
frame in a manner well-known in the art. A sprocket (198) is fixed to the
outer diameter of the
drive shaft (102) on the right side. A chain drives the sprocket (198) to
provide driving torque
to the drive shaft (102). Toothed belt drive, or shaft drive, may be used
rather than chain drive.
For direct-drive, as shown in figure 18, the axle (194) is removed and
replaced with splined
crank axle ends (200). The sprocket (198) is removed and replaced with a
mounting bearing
(202). A similar mounting bearing (202) is mounted on the left outer surface
of the drive shaft
(102). The hub is then mounted to the bicycle on the mounting bearings (202)
and cranks are
attached to crank axle ends (200) to provide driving torque to the drive shaft
(102).
For bottom bracket mounting, as illustrated in figure 19, the hub is
configured for direct-drive
as described above, but the hub is not built into a wheel. Instead, it is
mounted by the mounting
bearings (202) in a specially configured bottom bracket. A chainring (206) is
bolted to
chainring mounting bosses (208 ¨ figure 18) to provide drive to the chain.
When not used for
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bottom bracket mounting, the chain ring bosses (208) may be employed as a disk
brake
mounting, although this would mean a non-standard right-side disk brake
position. Separate
disk brake mounting bosses (not shown) may also be integrated into the left
side of the hub
shell (127) in a conventional manner. Similarly, a belt drive sprocket may be
attached to the
chainring mounting bosses (208) to provide drive to a toothed belt, rather
than a chain.
Instead of being adaptable between chain-drive, direct-drive, and bottom
bracket mounting (as
described above), the hub transmission may be customized for chain-drive
alone, direct-drive
alone, or bottom bracket mounting alone. For chain-drive alone, the mounting
surfaces for the
mounting bearings (202) may be excluded, as well as the chainring mounting
bosses (208). For
direct-drive alone, the crank axle ends (200) can be integral with the drive
shaft (102) and the
chainring mounting bosses (208) excluded. For a customized bottom bracket
application, the
crank axle ends (200) can be integral with the drive shaft (102) and the spoke
flanges excluded.
E-bike or pedelec options
The potential for higher torque capacity of the hub transmission (100) is well
suited for use in
conjunction with electric assist, such as in pedelecs or e-bikes. For example,
the hub
transmission may be mounted in a rear wheel for chain-drive as described
above, and the crank
axle electrically assisted as is known in the art.
Alternatively, the hub transmission may be configured for bottom bracket
mounting as
described above, and the drive shaft unit (111) electrically assisted, or the
front wheel
electrically assisted as is known in the art.
The hub transmission may also be mounted in a rear wheel for chain-drive as
described above,
and the front wheel electrically assisted as is known in the art.
Alternatively, the hub transmission may be mounted in a front wheel of a
direct-drive
recumbent bicycle as described above, and the drive shaft unit (111)
electrically assisted. Or
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the rear wheel may be electrically assisted, avoiding the traction issues with
front wheel electric
assistance.
The control of the gear shifting may include communication with the e-bike or
pedelec torque
sensor to provide automatic shifting.
Planet gear variations
The planet gear clusters may have more, or less, than the three or four bevel
planet gears
presented. Furthermore, there may be more than two stub axles mounted to the
drive shaft, so
that more than two planet gear clusters are employed, or there may be only one
stub axle and
a single planet gear cluster.
The bevel planet gears may be equally axially spaced within each planet
cluster, or they may
be differently spaced apart axially, as in the example embodiment. Similarly,
the pitch diameter
of each bevel planet gear within each planet cluster may be the same, or
different, as in the
example embodiment.
The bevel planet gears in each planet gear cluster may be separable rather
than integrally
formed, but each planet gear must be interlocked, to transmit torque
therebetween.
Roller tooth options
The roller teeth may be placed on the bevel reaction gears and bevel output
gears, rather than
on the bevel planet gears.
The roller teeth may be frustoconical in shape, whereby an imaginary apex of
the engaging
surface of each roller intersects the planet gear axis and the drive shaft
axis. This is theoretically
the best geometry. However, employing cylindrical roller teeth, as in the
example embodiment,
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simplifies the manufacturing of the rollers, and allows the teeth of the
meshing gears to be
machined using simpler tooling. The deviation from the frustoconical shape is
very small due
to the relatively small face width of bevel reaction gear teeth and bevel
output gear teeth. These
teeth can have a narrower face width due to the lower loads that result from
the larger gear
size.
The rollers may rotate directly on the supporting pins as in the example
embodiment, or the
rollers may be fitted with bushings. Alternatively, the roller may be mounted
on ball bearings,
roller bearings, or needle bearings to further decrease friction. In some
cases, the exterior race
of the ball, roller, or needle bearing may form the roller body, with no
separate roller.
Other gear shifting arrangements
As an alternative to linear actuators, the engageable freewheels (128, 130,
132, 148, 150, 152)
may be engaged and disengaged by a cam ring arrangement, as shown for the
right side of the
hub in figure 20. A shifter motor (210) drives a cam ring (212) through a worm
gear (214). The
cam ring has indents (216) and raised portions (218) that interact with push
rods (220) to
engage or disengage the freewheel pawls to select the required gear. The
control system is
configured to position the cam ring (212) in the correct position for each
selected gear. A
similar configuration may be employed for the left side of the hub.
The control of the engageable freewheels may be wired, rather than wireless.
As illustrated in
figure 21, a wired shifter unit (222) mounted to the handlebars (177) provides
control and
power directly by wires (225, 227) to the transmission hub (100). Since the
engageable
freewheels (148, 150, 152) of the bevel reaction gears (140, 142, 144) are
mounted on the
reaction gear carrier (146) which is stationary, the wires (225) can enter the
hub directly. The
engageable freewheels (128, 130, 132) of the bevel output gears (120, 122,
124), however,
rotate relative to the bicycle frame with the output gear carrier (126).
Therefore slip rings (224)
are required to make the electrical connection between the wires (227) and the
rotating output
gear carrier (126). Alternatively, the engageable freewheels (148, 150, 152)
of the bevel
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reaction gears (140, 142, 144) may be wired, and the engageable freewheels
(128, 130, 132)
of the bevel output gears (120, 122, 124) may be wirelessly controlled to
avoid the need for
the slip rings (224).
To reduce freewheeling friction from the first gear freewheel (154), when the
transmission is
in a gear higher than first gear, the first gear freewheel (154) may be
wirelessly controlled to
disengage. The first gear freewheel may be located differently than shown, for
example the
first gear freewheel may be located between the drive shaft (102) of the drive
shaft unit (111)
and the output gear carrier (126) section of the hub shell (127), rather than
between the stub
axle (108) of the drive shaft unit (111) and the cover portion (101) of the
hub shell (127).
The engageable freewheels may also be mechanically controlled. For the
stationary left side of
the hub this is relatively simple. For example, the engageable freewheels
(148, 150, 152) of
the bevel reaction gears (140, 142, 144) may be controlled mechanically by a
cable that rotates
a cam ring, similar to the cam ring (212) shown in figure 20.
Transferring mechanical control to the rotating right side of the hub is much
more complex,
however. Figure 22 shows a possible means to achieve this mechanical control.
A cable ring
(226) is threaded to a stationary mounting (228) so that the cable ring (226)
moves axially in
the direction of the drive shaft axis (104) as the cable ring (226) is rotated
around the drive
shaft axis (104) by a control cable (231) in cable groove (230). By means of a
shifter bearing
(232), the cable ring (226) translates this axial motion, against the pressure
of return springs
(234), to a mechanical actuator (236) that rotates with the hub shell (127).
The mechanical
actuator (236) has axially extended arms (238) having cam surfaces (240) at
the outward facing
surfaces of each axially extending arm (238). The cam surfaces (240) interact
with mechanical
push rods (242) that are similar to push rods (220) in figure 20. The
mechanical push rods
(242) engage or disengage the freewheel pawls of the engageable freewheels
(128, 130, 132)
of the bevel output gears (120, 122, 124) to select the required gear.
The above detailed description describes a possible embodiment with design
variations. The
following claims define the full scope of the invention claimed.
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