Passive smoking too!
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Passive smoking too!


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Passive smoking too! Smoking can kill. To the attention of hoteliers, restaurant keepers, office managers and allergy sufferers.
  • copiers with the help of a special particle filter
  • area around deep fryers
  • deep breath of clean air
  • indoor air
  • sophisticated multi-stage filter system
  • particle distribution
  • fine dust
  • appliance
  • uc



Publié par
Nombre de lectures 15
Langue English


Continuously Variable Transmission Systems
Stephen Geller, Aaron Phinney
University of Maine, Mechanical Engineering
December 17, 2004

snowmobiles overcome this dilemma and deliver ABSTRACT
uninterrupted engine power to the ground. Furthermore,
the two and four-stoke engines common to snowmobiles CVTs, or continuously-variable transmissions or
have a smaller range of deliverable power than those clutches, are an essential component of a snowmobile
used in geared transmissions, so use of a CVT allows drive train. By gaining a thorough knowledge of how
for the engine to operate at a constant speed, namely CVTs operate and how this translates to snowmobile
that speed which produces the maximum power. performance, one is able to adapt a particular
snowmobile and clutch setup to achieve a range of
HOW DOES A CVT WORK? – A CVT operates on performance. Snowmobiles are used in a variety of
dynamic principles which are based on three main applications, each with different performance goals. To
mechanical components – flyweights or cams, springs, maximize any of these goals, such as acceleration while
and ramps. Essentially, these three component-types drag racing or fuel economy while touring, a clutch must
work in conjunction to transmit engine power and torque be properly tuned. Generally the clutch is the last piece
to the ground, while maintaining a constant engine of the puzzle in tuning the entire snowmobile for a
speed. There are certain mechanical feedback systems, specific performance. This is due to the fact that the
created by the CVT components, which govern how the clutch’s performance is dependent on many other
transmission behaves, and ultimately how the components in the system. For example, engine power
snowmobile performs. modifications, such as a different engine altogether or
changes made to the exhaust line, may affect the power
or torque peaks of the engine, and in turn the
unchanged CVT will have a different response. It is not
OBJECTIVE helpful to tune the CVT until all these other modifications
have been made first, since the CVT’s objective may
change dramatically. The clutching team’s primary ADJUSTMENT MATRIX – An adjustment matrix,
goals for the SAE Clean Snowmobile Challenge are to provided in the Appendix, was created for use in tuning
find a compromise between the 500 ft. drag race and the a CVT for specific performance goals. It is a quick-
100 mile fuel-economy event, a compromise which will reference guide for use by anyone to qualitatively
maximize the total points earned from both categories. change performance characteristics of the CVT and
The emphasis will be on fuel economy, however, since it ultimately, the snowmobile as a whole. For quantitative
carries a higher percentage of the total competition tuning, a performance goal must first be specified, and
points. can then be tested and iterated until the goal is met. For
the scope of the SAE Clean Snowmobile Challenge,
these performance goals are a trade-off between the
100 mile endurance test (emphasizing fuel efficiency),
INTRODUCTION and the 500 ft. drag race (emphasizing acceleration).
TESTING – The objective of testing is for feedback of WHY USE A CVT? – A CVT is an ideal power
any tuning adjustments made. Testing plays a crucial transmission device for a snowmobile for one main
role in tuning, in that all adjustments must be tested to reason – it allows power from the engine to be
make sure that they are producing the desired effects. transmitted continuously to the ground. In contrast, a
Of course, testing is also the stepping stone for the standard gear-box transmission takes time to shift
design process which is necessitated by the SAE Clean gears, time in which the engine and wheels are
Snowmobile Challenge. Tests will range from laboratory disconnected, and results in a loss of momentum.
and dynamometer readings to qualitative ride Because of the terrain that snowmobiles often encounter
characteristics (bogging down, backshift feel, etc.). (snow, and specifically unbroken snow), it is not practical
to experience a loss of momentum while operating a
TOOL BOX – The objective of the tool box is to have snowmobile. The time spent in changing gears would
quick-access to any tool(s) necessary for any allow the high drag properties of deep snow to overcome
adjustment that is governed by the adjustment matrix. most of the vehicle’s momentum. By using a CVT, The tool box is an ongoing consideration which is added Flyweights - The flyweights, or cams, are housed inside
to each time a new scenario is introduced. the primary clutch and are allowed to swivel on a pin. A
typical cam is shown in Figure 3, and shown in situ in
Figure 1. For the arctic cat 660 stock clutch there are THEORY AND EQUATIONS
three cams, spaced equally around the clutch housing.
They ride against rollers attached to the spider housing. VARIABLES – The major mechanical components of the
As the primary clutch rotates directly with the engine, the CVT introduce variable parameters influencing the
cams swing outward with a force governed by their mass CVT’s behavior and the sled in general. Once installed
and a direction based on their geometry. Also factoring or implemented, these components are no longer
into this force are the radius of the cam from its axis of variable, however there is a wide range of working
rotation and the speed at which it is spinning. The latter parameters, and customizations that can be achieved
two contributors to the force are certainly not to be with just three components—flyweights, springs, and
overlooked, but are taken to be constant as they are ramps. Figure 1 illustrates the primary clutch
dependent on the engine itself and the clutch geometry. components while Figure 2 illustrates the secondary
So, once tuning becomes necessary, only the mass is clutch.
considered variable, since the other contributors are
determined before-hand. In general, the surface of the
cam which comes into contact with the spider roller has
a curved profile, creating a non-linear and complex
interaction with the spider. Essentially, from an idle
(while the clutch sheaves are held together by the spring
in the spider housing), as the primary clutch spins faster
(more engine RPM), the cams exert an increasingly
greater force outward against the spider tower. Once
the cams’ outward force overcomes the spring force, the
clutch will engage. It is easy to influence this
engagement force by adding or subtracting weight from
the cams.
Springs - The two clutch springs are located in the
primary and secondary clutch respectively. Typical
ii springs are shown in Figure 3, and shown in situ in
Figure 1. Primary Clutch Schematic
Figures 2 and 3. The primary, or pressure spring, as
mentioned above, is located with the spider housing and
works axially to hold the sheaves of the primary clutch
closed. The secondary, or torque spring works in
twisting to hold the sheaves of the secondary clutch
open. As one pair of clutch sheaves is made to open or
close, the other pair will do the opposite. Since the belt
rides between the two sets of sheaves, as they open
and close they change the radius that the belt rides
along. As a clutch opens, the belt’s riding radius
decreases and as it closes, the radius increases.
Ramps - The ramps, also known as torque sensitive
cams, are located in the secondary clutch. A typical
ramp is shown in Figure 3, and in situ in Figure 2. They
provide torque-sensing feedback from the track, and are
integral in back-shifting. The ramps consist of three
ramps which are spaced evenly around a cylinder
surface. Each ramp is a surface on which a roller acts
against. The governing parameters of the torque ramp
are the angle and radius which the ramps are set to. As
the ramp angle is decreased (becomes flatter), it creates
more side force to act on the belt at the secondary
sheaves. The side force, mathematically, is:

Figure 2. Secondary Clutch Schematic T ⋅mshift
force = ,
where T is torque, m is the CVT shift ratio, r is the TESTING -- One of the main tests needed for shift ramp
ramp radius and is the angle of the ramp measured determining the proper clutching setup is an engine
from the horizontal. This force grabs the belt and is ‘felt’ dynamometer test. This test must be done after the
at the primary clutch causing the primary sheaves to ECU has implemented any of their snowmobile
open, and thus backshift. performance modifications. Once this and all other
modifications take place, the Arctic Cat 660’s engine
power and torque curves can be determined on the
engine dynamometer. A track dynamometer will also
provide needed data for comparison of sled models that
are engine-based, in which track data is calculated.
Comparison of the calculated track data and the track
dynamometer will provide insight regarding losses along
the drive train. Other tests will include field testing of the
snowmobile as needed for data such as top speed,
iii engagement speed, or simply how the ride ‘feels’.
Figure 3. Typical cams, springs, and ramp

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