Theory Of Operation - Arctic Cat Panther 1974 Manual

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THEORY OF OPERATION
General
The Drive System, as it will be referred to in this
section, is composed of a drive clutch, drive belt,
driven pulley, sprockets, chain, track drive and
track. Operating as a complete system, the
components will deliver optimum power to the
track under varying snow conditions and load
factors (resistance on the track).
The Arctic Cat Snowmobile uses a torque sensing,
sheave-type, variable ratio (3 .79:1) drive clutch
and driven pulley. This method of transmitting
power from the drive clutch by means of a belt to
the driven pulley is used to multiply engine torque
that is needed by the track to pull the snowmobile
through varying snow depths, up and down steep
hills and mountains, and across open hard-packed
areas at high speeds. The Arctic drive cLutch and
driven pulley automatically determines the proper
ratio that will enable the snowmobile to move
without hesitation from drive clutch engagement
speed to high speed operation, no matter what the
snow conditions are.
Resistance (load on the track) has an effect on the
ratio that the drive clutch and driven pulley
automatically "seeks out". As resistance increases
and when more torque is needed, the belt will
"down shift" to a larger radius on the driven
pulley. If track resistance decreases, the belt will
"up shift" to a 1: 1 ratio between the drive clutch
and driven pulley. The engine RPM is maintained
at somewhat of a constant throughout the "down
shift" and "up shift" pattern.
Snowmobile speed is then governed by the "ratio"
the belt seeks between the drive clutch and driven
pulley. If the clutch / pulley ratio is 3.79: 1 and
engine RPM is 6,000, the snowmobile should travel
at th'e slowest designed speed possible. If the ratio
changes to 1: 1 and engine RPM is 6,000, speed
should increase to fastest designed speed possible.
Th is characteristic evolves because at a 3.79: 1
ratio, the drive clutch must turn 3.79 revolutions
before the driven pulley can turn 1 revolution.
When a 1: 1 ratio exists, the drive clutch turns 1
revolution as does the driven pulley.
II
Note: Minimum and maximum MPH are af-
fected by the sprocket ratio used (see Sprock-
et/Chain Specifications, Sprocket Ratio, page V-4).
I n the paragraphs that follow, elements of the drive
clutch and driven pulley will be examined.
Knowing what influence the various elements have
on the drive clutch/driven pulley will help you to
better understand the operating characteristics.
Spring (Drive Clutch)
The drive clutch spring is manufactured from
straight, high quality spring steel wire that has
excellent spring rate retention qualities. The wire
is wound with a definite number of windings and
to a predetermined length that will provide the
desired spring rate. Once the spring rate is
established, the spring is color coded for
identification purposes (see Drive Clutch Specifi-
cations, Spring Color Code, page V-2).
II
Note: I n comparing spring rates, four factors
will affect the rate characteristic:
1. Wire Diameter
2. Number of Coils
3. Total Spring Diameter
4. Total Spring Length
Comparison - Spring will be weaker if the wire
diameter is smaller, there are more coils, larger
spring diameter or longer spring length. A stronger
spring will have larger diameter wire and less
number of coils in relation to a spring of the same
length.
The spring's primary function is to control initial
moveable sheave engagement with the drive belt
and stationary sheave. At idle speed there is no
applied belt force because the spring keeps the
stationary and moveable sheaves apart. The drive
clutch is designed so that when the sheaves are
fully apart, stationary and moveable sheaves are
sl ightly wider apart than the top th ickness of the
belt. As engine RPM increases to a predetermined
point established by the factory (see Specifica-
tions, Engagement Speed, page V -2), centrifugal
weights and rollers roll outward on ramps, Fig.
V-1, with enough force to overcome the spring
pressure. Therefore, engagement speed can be
increased or decreased by using springs with
different spring rates (see Specifications, Spring
Rate, page V-2) .
II
Note: Desired engagement speed is when the
engine delivers sufficient horsepower RPM to
pull the snowmobile from a stop without a "flat
spot" or undue hesitation.
V-5