Planetary gear transmission systems or components – With means to vary drive ratio or disconnect drive – Gear shiftable axially to disconnect or vary ratio
Reexamination Certificate
2000-03-17
2001-07-31
Estremsky, Sherry (Department: 3681)
Planetary gear transmission systems or components
With means to vary drive ratio or disconnect drive
Gear shiftable axially to disconnect or vary ratio
C475S299000
Reexamination Certificate
active
06267704
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention pertains to the use of a servo principle for a three-speed hub to shift between three speeds regardless of the load through the transmission and with negligible effort to actuate the shift. The invention uses a sloped, periodic camming action to force the shifts in both the upshifting direction and in the downshifting direction.
BACKGROUND OF THE INVENTION
In conventional three speed internal hub transmissions used on bicycles, the load path and therefore the gear ratio is controlled by the position of an element called the “clutch wheel” or “claw clutch”. The clutch wheel moves axially along the axle between three axial positions. In conventional designs which are currently in use in the marketplace, the axial position of the clutch wheel is controlled in one direction by a pull chain, cable, or pushrod/bell crank mechanism and in the other direction by a return spring.
When the transmission is transmitting a load, the splines at each end of the clutch wheel are loaded circumferentially and the resulting friction prevents easy axial movement. In order to make the transmission shift under more than zero load, the preload in the return spring is increased. In order to make the transmission shift under more load than this, the preload must be increased proportionally to the load through the transmission. This increase in preload of the return spring must ultimately be overcome by effort at the hand actuator on the handlebar. The preload needed to make the conventional design shift under load makes this effort excessive.
It is therefore desirable to find another source of axial force or forces to move the clutch wheel in both the up and down shifting directions. Ideally it would also be desirable to find a source of axial force that is always proportional to the load through the transmission and is therefore always great enough to overcome the frictional forces that oppose this movement.
European Patent Application 876953 discloses a mechanism which uses a servo principle to move the clutch wheel. As shown in
FIGS. 1-4
, this mechanism upshifts in a conventional manner using no servo effect to “force” the upshift. Movement of the clutch wheel in the upshifting direction is effected by a displacement of the control cable
73
b
toward the handlebar actuator. This rotates a bellcrank
71
which pushes on pushrod assembly
69
and
68
(FIG.
2
). A preloaded spring
60
is therefore compressed below its installed length and transfers the force to control element assembly
66
and
49
. The axial force is then transferred to a clutch wheel
45
by means of a snap ring
63
(FIG.
3
). The force to move the clutch wheel
45
in the upshifting axial direction is the result of the energy put into the hand actuator on the handlebar minus the inefficiencies of all the interactions between the handlebar actuator and the clutch wheel. The control elements
69
,
68
,
60
,
66
and
49
must move axially to displace the clutch wheel
45
the same axial distance.
The mechanism downshifts in a servo manner. To initiate a downshift, the cable
73
b
and the bell crank
71
release the control elements
69
,
68
,
60
,
66
, and
49
so that another preloaded spring
61
can apply an unopposed force on an element
49
. When the cam lobes on the inside diameter of the clutch wheel permit it, element
49
moves into a valley
47
a
between the cam lobes. Element
49
simultaneously slides along helical slot
21
b
in the axle. The angles between the helical slot
21
in the axle and the helical cam inside the clutch wheel cooperate in such a way that the control element
49
becomes axially fixed and therefore the rotation of the clutch wheel is converted to axial displacement as control element
49
slides up helical cam ramp
47
c
. As in the case of the upshifting sequence, elements
69
,
68
,
60
,
66
, and
49
move axially to accomplish a displacement of the clutch wheel the same axial distance.
One feature that distinguishes the present invention from the device disclosed in EP 876953 is that the helical camming servo effect works in one direction only in the aforementioned prior art. Furthermore, in this prior art construction, to be fully enabled to both up and down shift, the device must use both the helical camming servo effect and the conventional simple non-servo pushing method.
The use of an axially moving control element also has certain drawbacks. In a three-speed hub, it must protrude out of the end of the axle at least as much as the combined stroke of two shifts. This is a very vulnerable place to put a delicate, protruding control element. It is also awkward to convert cable displacement into control element displacement because of the 90-degree difference in orientation. The axially moving control element is also awkward to control with a gear motor since a gear motor in its simplest form is most suitable to deliver rotation, not sliding, axial movement. Also, as a general engineering principle, rotation is preferable to sliding because it is less susceptible to cocking and jamming.
SUMMARY OF THE INVENTION
The present invention answers these deficiencies because it employs a helical camming servo effect for moving the clutch wheel in both the up and down shifting directions and completely eliminates the need for the conventional control element to push the clutch wheel by moving axially itself. The present invention also uses a control element which is simply rotates.
A multiple-speed planetary hub mechanism according to the invention comprises a rotatable control cam having a plurality of axially noncylindrical camming surfaces. A clutch wheel is located about the control cam, and a plurality of ball sets are located between the clutch wheel and the control cam. As the control cam rotates, the ball sets engage selectively are radially urged outwardly by the control cam camming surface and selectively interact with camming surfaces on the clutch wheel. The movement of the ball sets against the camming surfaces produces an axial movement of the clutch wheel. The change of axial position of the clutch wheel alters the transmission load path through the hub assembly.
REFERENCES:
patent: 5855530 (1999-01-01), Huang et al.
patent: 6120409 (2000-09-01), Hawkins
patent: 411192992 (1999-07-01), None
Patterson Sam H.
Steuer Werner
Estremsky Sherry
Lewis Tisha D.
Perkins, Esq. Jefferson
Piper Marbury Rudnick & Wolfe
SRAM Corporation
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