09-08-2012, 01:12 PM
The Kinematic Design of Automatic Gear Transmissions for Bicycles
The Kinematic Design.pdf (Size: 769.85 KB / Downloads: 317)
Abstract
Recently, bicycles are used as exercising
machines and traffic vehicles. Planetary gear trains can
be used as the transmission systems for bicycles. The
purpose of this work is to propose a design methodology
for the kinematic design of automatic gear transmissions
with planetary gear trains for bicycles. First, applying
the check list method (combining and extending methods),
the design concepts are proposed. Then, based on the the
design concepts proposed and train value equation of
planetary gear train, we derive the gear ratio equations of
automatic three-speed gear transmissions for each
invention. Three automatic three-speed gear
transmissions are designed to illustrate the design
methodology. Based on the proposed methodology, all
automatic gear transmissions with planetary gear trains
can be synthesized.
Introduction
The bicycle is invented so far more than 200 years.
Early bicycles are mankind's main tool to ride instead of
walk. In recent years, because of having the advantages
of light weight, cheap and pollution-free, Bicycles become
the most popular traffic vehicles. They can be used as
exercise machines and traffic vehicles.
The characteristics of the transmission systems are
the important factors for bicycles. The transmission
systems of the bicycles can be the external or internal
multi-speed gear systems. The internal multi-speed gear
system is also called as multi-speed gear hub. The
multi-speed transmission system of a bicycle includes
multi-speed gear unit, control device of changing speed,
and operating device for steering control device to change
speed. Figure 1 shows the multi-speed transmission
system of a bicycle.
Planetary Gear Train
A planetary gear train is a gear train contains at least
one gear (planet) which is required to rotate above its own
axis and another axis. A simple sun gear is a sun gear if it
is adjacent to one planet only, and a simple carrier is a
carrier if it is adjacent to one planet only or several serial
planets.If all sun gears and all carriers are simple sun
gears and simple carriers, the planetary gear train is called
non-coupled planetary gear train; otherwise, it is called
coupled planetary gear train. Figures 2(a) and 2(b) show
the non-coupled planetary gear train and coupled
planetary gear train, respectively.
Centrifugal Clutch and One-Way Clutch
Generally speaking, the automatic speed changer
includes the shifting control devices (centrifugal clutches),
planetary gear train, clutches (including one way clutch),
brakes, and so on. The centrifugal clutch can be roughly
divided into two categories: (1) radial motion centrifugal
clutch, shown in Figure 5, (2) axial motion centrifugal
clutch, respectively shown in Figure 6. The radial
motion centrifugal clutch plays the role of engaging or
divorcing by using the centrifugal block to make the radial
motion, respectively shown in figures 5(b) and 5©. The
axial motion centrifugal clutch makes use of axial
displacement caused by the additional weight movement,
as shown in Figures 6(b) and 6©. Due to speed change,
the centrifugal clutch draws or pushes the shifting control
device to realize the purpose of automatic shift.
One-way clutch which is consist of outer ring, rollers,
inner ring, and spring (not shown). Figure 7(a) shows
the structure when engaging separating, figure 7(b) and ©
are the reprentations of these two states.
Automatic speed changer
The automatic speed changer can be divided into
step speed changer and continuously variable speed
changer. In turn the step speed changer can be divided
into the fixed-axle gear type and the planetary gear type
according to the gear train mechanism used in it. The
automatic step speed changer uses the centrifugal clutch
inducting the engine (motor) speed to change the gear
position. The automatic speed changer is composed of
several clutches, brakes and shifting control device and its
whole operating process uses the clutch (or brake) to
automatically change the reduction ratio. Thus provide
the bicycle (motorcycle) with better maneuvering.
Innovation Design
In this paper, we make use of the planetary gear
trains now available so as to pick out the better planetary
gear trains design concepts. Also, combine with the
one-way clutch and the centrifugal clutch and by apply the
check list method, to conceive the creative concepts of
automatic three-speed gear transmissions.
Design Concepts
There are numerous design concepts of planetary
gear trains, from which this paper has chosen the
non-coupled planetary gear train to act as the reference
basis for our design of the automatic three-speed gear
transmissions for bicycles. According to the design
concept of planetary gear trains conceived by Hsieh &
Yan [30-33], the five planetary gear trains shown in Figure
9 are chosen. Figures 9(a) and 9(b) are five-bar planetary
gear trains with two degrees of freedom, and figure 9©,
9(d), and 9(e) are six-bar planetary gear trains with two
degrees of freedom.
Conclusion
In this paper, we propose a design methodology for
the kinematic design of automatic gear transmissions with
planetary gear trains for bicycles. First, applying the
check list method (combining and extending methods), the
design concepts are proposed. Then, based on the design
concepts proposed and train value equation of planetary
gear train, we derive the gear ratio equations of automatic
three-speed gear transmissions for each invention. Three
automatic three-speed gear transmissions are designed to
illustrate the design methodology. Based on the proposed
methodology, all automatic gear transmissions with
planetary gear trains can be synthesized. The design
approach can also be used to design the more than three
speed gear transmissions for bicycle.