Land vehicles – Wheeled – Occupant propelled type
Reexamination Certificate
2000-12-29
2002-08-13
Hurley, Kevin (Department: 3619)
Land vehicles
Wheeled
Occupant propelled type
C474S162000
Reexamination Certificate
active
06431573
ABSTRACT:
BACKGROUND
This invention relates to human powered vehicles in general, and to automatic transmissions therefor, in particular.
Human powered cycles, such as bicycles, and some tricycles, often have a variable speed transmission. With known bicycles, such as shown in
FIG. 1
, there are various types of variable transmission. Internal rear hub transmissions, typically 3 speed, are known. With such transmissions, the rider rotates pedals
10
that are connected to a chain ring
12
through a crank
11
, which, in turn, through a chain
14
, is connected to a rear wheel sprocket
16
. The sprocket is connected through a variable internal hub transmission (not shown) to the wheel
18
. (
FIG. 1
is a composite, showing aspects of various, different types of prior art transmissions. It does not show the internal hub transmission or a cable thereto, but, rather, shows a type of rear wheel transmission that is described below. Since the internal hub type transmission is well known, and not germane to the invention, it is not shown specifically.
FIG. 1
is used herein only to show where such known, internal hub transmissions reside.) The internal workings of the hub change according to controls manually manipulated by the user, such as through a handlebar-mounted lever that connects to the hub through a cable.
Another popular type of known transmission, such as shown with reference to
FIG. 1
, employs a multi-sprocket rear cartridge
18
, for instance mounted on the rear hub
16
, having several, typically between three and eight variable diameter sprockets
20
. A rear derailleur
22
engages the chain
14
, as described above, and, again under manual control of the operator, typically through a cable
24
, moves the chain from engagement with one of the sprockets to another. By changing the active sprocket to one with a different diameter, the gear ratio of the operable transmission elements is changed. A larger rear sprocket
20
reduces the effort required to rotate the rear wheel
26
against a load, and is typically referred to as a “lower gear.” A smaller rear sprocket
20
increases the effort required to rotate the rear wheel against a load, but also increases the circumferential distance covered by the rear wheel for a single rotation of the pedals
10
, and is referred to as a “higher gear.” Typically, the cable moves the derailleur such that it directs the chain from a higher to a lower gear while a spring within the derailleur returns the chain from a lower to a higher gear when the user relaxes the tension on the cable by moving a lever.
A similar type of transmission also employs a set of sprockets having different diameters, but, rather than being mounted on the rear hub, such varying diameter sprockets
28
are coupled directly to the pedal assembly, so that one rotation of the pedals causes one full rotation of the front sprockets
28
. The sprockets are typically referred to as chain ring sets. A front derailleur
30
engages the chain
14
, and, again under manual control of the operator, typically through a cable (not shown), moves the chain
14
from engagement with one of the chain rings
32
to another
34
. By changing the active chain ring to one with a different diameter, the gear ratio of the operable transmission elements is changed. A larger
32
front chain ring
28
increases the effort required to rotate the rear wheel
26
against a load, and is typically referred to as a “higher gear.” A smaller
34
front chain ring
28
decreases the effort required to rotate the rear wheel against a load, but also decreases the circumferential distance covered by the rear wheel for a single rotation of the pedals
14
, and is referred to as a “lower gear.” Typically, the cable moves the derailleur such that it directs the chain from a lower to a higher gear while a spring within the derailleur returns the chain from a higher to a lower gear when the user relaxes the tension on the cable by moving a lever.
Thus, a higher gear is obtained by engaging a smaller rear sprocket
18
or a larger front chain ring
28
. A lower gear is obtained by engaging a larger rear sprocket or a smaller front chain ring.
Often, bicycles use both a front and rear derailleur type transmission, thereby obtaining a large number of effective gear ratios, equal to the product of the number of rear sprockets
18
times the number of front chain rings
28
. However, often, some of the gear ratio combinations are very nearly equal to others of the combinations, and often the extreme combinations, such as the largest rear sprocket and the largest front chain ring (which would result in an intermediate gear ratio) are not comfortably obtained without the chain rubbing excessively on the chain ring and sprocket. Thus, a nominally eighteen speed transmission (six rear sprockets and three front chain rings) might have only eight to ten significantly different gear ratios.
There are other types of transmissions also, which are known to the art.
All of the above mentioned transmissions are typically available in a manual embodiment, in which the user decides when to change gears (“shift gears”) and does so by manually moving some element of the transmission system. Typically, the movable element is a lever near the front of the bicycle. Over the years, many different types of levers have been used. (For purposes of illustration, only, several types are shown in FIG.
1
. Only one type would be present for any actual bicycle.) A popular three speed-internal hub transmission used a single handle mounted lever (not shown). Other cartridge and chain ring models use levers
40
mounted on the handle bars, or
42
on the down tube and
44
at the ends of the handle bar tubes (both lever and rotary types). A relatively recent configuration incorporates the gear shift levers into handles
46
that are also part of the braking assembly. With some models, a unitary lever actuates both a brake and a gear shift, while in others, tandem, nested levers are used, one for braking and one for shifting. Some shifting lever mechanisms use one lever for shifting from a lower gear to a higher gear, and another for the reverse direction.
A problem with all of the conventional transmissions that use a rear cartridge
18
or/and a front set of chain rings
28
, is that shifting the chain from one toothed gear wheel to another, when shifting from a higher to a lower gear, such as when climbing a hill, typically occurs at a time when the user wants to be applying power to the transmission. However, if power is applied at the wrong moment, as the chain is intermediate between one ring and another, the next chain ring does not pick up the chain, and the shifting mechanism malfunctions. The result is grinding and wear of all of the components, as well as loss of power and momentum, which often necessitates shifting to an even lower gear. There are some semi-automated shifting mechanisms which delay the actual shifting until the components are aligned properly to avoid missing.
One reason that gear missing occurs is that the chain is being moved adjacent the gear wheels, right at the circumferential location around the gear wheel where the chain engages the gear wheel, and where power is transmitted from the gear wheel to the chain (front gear wheels), or vice versa (rear gear wheels). In other words, the chain is removed from the first gear wheel within the driving zone, and is deposited onto the next gear wheel within the driving zone. As shown in
FIG. 1
, the “driving zone” is roughly the forward half of the chain ring (for a front chain ring), indicated between the arrows D
z
. (For a rear chain ring sprocket, the driving zone is roughly the rearward half.)
Force is generated between the chain and the chain ring in part due to the torque applied by the user pushing on the pedals, and in part by the tension in the chain, which is established by a spring in the rear derailleur
22
. Thus, as the chain is moving over toward the chain ring, torque is being applied by the pedals to the chain ring. If there is no engagement be
Lerman Harry H.
Lerman Victor S.
Otten David M.
Hurley Kevin
Massachusetts Institute of Technology
Weissburg Steven J.
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