BRP ski-doo MACH Z 1000 SDI, Руководство пользователя

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SECTION 06 - DRIVE SYSTEM
MMC2005-001_06A.FM
06-7
The weight of the lever arms will have a similar
effect on the shift RPM.
By adding or removing weight to or from the arms,
we can fine tune the shift RPM to the engine pow-
er peak.
If you increase the horsepower of the engine at
the same RPM, you would normally add more
weight to keep the engine pulling as hard as pos-
sible and not over rev.
If you lighten the weights on the arms, you will be
increasing the shifting RPM. However, your vehi-
cle will not
pull as hard, since less centrifugal
force is being generated.
EFFECTS OF THE RAMP PROFILE
ON THE SHIFT FORCE
The shift force is the component or part of the cen-
trifugal force that is used to actually move the slid-
ing half of the drive pulley. This force is applied to
the sliding half at the three lever arm pivot points
(following illustration item 49). The ramp profiles
are used to control the size of this shift force.
As the clutch rotates around the center line of the
crankshaft, the axis of rotation, centrifugal forces
begin building and act on the center of mass of the
lever arm, roller combination trying to pull the lever
away from the axis of rotation. The center of mass
of the lever arm assembly is the point where all
the centrifugal force acts (following illustration
item 70).
The ramp provides an angled surface for the roller
to push against and the angle of the ramp at the
point of contact with the roller determines how
much of the centrifugal force is translated into ax-
ial force. The axial force pushes the sliding half in
and the remainder of the centrifugal force is un-
used and absorbed by the integrity of the sliding
half. A steeper ramp angle gives less shift force,
while a smaller angle gives more shift force.
As you can see in following illustration, the angle
of the ramp varies constantly from start to finish.
The angle varies to achieve the proper axial force
to transmit a given amount of torque through the
drive belt at each diameter of the pulley.
As discussed before, the centrifugal force gener-
ated by the lever arm assembly increases at higher
ratios. This is why the ramp profile is much steep-
er at the high ratio end. This reduces the shift force
in order to maintain the correct load on the belt.
Remember, it is the angle of the ramp at the point
of roller contact that will help determine the shift
force at any given ratio. Think of the ramp profile
as a hill that the roller must climb. A small angle or
hill can be overcome easily thus providing a faster
shift out to a higher ratio which will lower the en-
gine RPM. If the hill is steeper (the ramp angle is
larger) the roller will not be able to climb it as quick-
ly thus staying in a lower ratio longer which will
keep the engine RPM higher.
Note that at engagement and very low ratios, many
ramp angles actually go downhill. These are gener-
ally used on engines with good low RPM power.
Engines with narrower power bands and less low
RPM power will usually have a flatter angle at en-
gagement and low speed. A ramp with a small
bump at engagement is used to raise the engage-
ment RPM. Again, the steeper the “hill” the roller
must overcome, the higher the RPM will be before
the clutch shifts out. If the spring selection cannot
give the desired engagement RPM, then use a
ramp with a bump or grind a notch at the point
where the roller sits at engagement. Of course if
the shift profile was good at higher ratios, then you
would want to use a ramp with only changes at the
low speed area.
Also, a thicker or taller ramp will provide higher
RPM than a thinner ramp with the same profile
because the lever arm assembly is tucked in fur-
ther by the taller ramp.
The TRA clutch allows you to fine tune the ramp
profile by using the adjusters provided. The adjust-
ers are cams which allow you to raise and lower
the outer end of the ramp through six different po-
sitions. Moving the ramp end toward the lever arm
makes the ramp angles steeper, thereby raising
engine speed and slowing the upshift. As the
ramp is adjusted away from the lever arm, the en-
gine speed is lowered and the upshift is faster.