C. ontinuous
V. ariable
T. ransmissions
Alexander Hernandez-Osorio
1
What is a Continuous Variable Transmission?
A continuously variable transmission (CVT) is a type of transmission that uses a
pulley and belt system instead of traditional fixed gear ratios. Unlike conventional
gear transmissions that shift between set gear levels, a CVT provides seamless
acceleration by continuously adjusting the gear ratio. This is achieved using two
variable-diameter pulleys—an input (drive) pulley and an output (driven)
pulley—connected by either a rubber V-belt or a metal chain link. A rubber V-belt
is lighter and quieter, making it ideal for smaller vehicles, but it wears faster under
high loads. Metal chains are stronger and more durable, better suited for
high-torque applications, though they are heavier, costlier, and can be noisier.
Comparisons
Variant
Efficiency
Materials
Production
Failure rate
Maintenance
Consumer
Cost
Metal Belt
+95:+98%
Metal
Elements:
Steel and
aluminum
alloys
Stamping,
Cold forming,
Welding/
Brazing
Lower failure
rate
High
maintenance
Reliable and
durable
Rubber Belt
-20%:-50%
Rubber
Composites:
Kevlar
Calendering
Molding
Vulcanization
Higher failure
rate
Low
maintenance
Typically
higher
depending
on car make
Compare and Contrast: Efficiency/Materials
Metal Chains:
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Reached higher efficiency levels of 95-98%
Due to the materials they are made of they can resist and experience higher loads and torque
Higher material quality means higher life expectancy
Rubber Belts:
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Higher loads and stress create a dip in efficiency
When compared to classic Gear transmissions they saw up to 50% loss of power
Rubber tends to degrade faster when experiencing heat fluctuations due to friction
Advantages and Disadvantages
Item
Metal Chain
Rubber V Belt
Advantage
Disadvantage
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Robust / Durable
Handles higher loads
Higher material quality
More responsive
More efficient
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●
●
●
●
●
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Consumer friendly
Lower production cost
Lower repair costs
Less maintenance
Less responsive
●
●
●
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●
Higher overall cost
Higher maintenance
Metal shaves into the
transmission pan/fluid
Higher production cost
Less reliable
Cant handle high loads/torques
Wear and tear due to friction
Materials can be lacking in
quality
slippage
Key Comparisons: Production Methods
Metal Chains:
●
●
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Stamping/Cold Forming: Using a Die and a press the metal sheets are formed into precise die shapes
Welding: Different methods of welding are used to join each component together Offering a higher resistance
to torque and stress
○
Electron beam welding
○
Laser Welding
○
Resistance Welding
Brazing: Used to join dissimilar metals together, brazing provides a strong, permanent bond with good
durability and corrosion resistance
Rubber V Belts:
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Calendering: the rubber is passed through rollers and pressed flat, up to four times, to form continuous sheets
Molding: injection molding can also be used as an alternative method to form belts and other components
Vulcanization: Involves heating the rubber with sulfur and other chemicals. This process significantly improves the
rubbers strength elasticity and thermal resistance
Manufacturing Methods
Item
Metal Chain
Key Component
●
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Link plates
Rocker
pins/blocks
Carrier chains
Materials
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Rubber V belt
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Rubber body
Tensile cord
Fabric wrap
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Manufacturing
method
Method Relevant
Specifics
Case hardened
steels
Martensitic
stainless steel
Powder
metallurgy steel
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Stamping
Welding
brazing
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Neoprene
EPDM
Natural rubber
Fabric
●
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Calendering
molding
●
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Electron beam
welding
Laser welding
Resistance
welding
vulcanization
Common Pitfalls
Overall, both the Metal chain and Rubber belt have their pros and cons, areas in where they scale and
compare to one another. The main reason as to why they both fail and an ongoing issue in general when it
comes to the automotive industry, is friction. Both of these pulley systems use friction as their main method
of movement, The higher the friction on the contact point, the more power gets transferred from engine to
drive train. Friction comes at a price, and a hefty one at that. When it comes to to metal chains, friction
causes the metal to chip and shave, over time resulting in a degradation of material. In the case of the
rubber belt, friction can cause warping and slippage, lowering the efficiency of of the transfer of power. The
main culprit for these pitfalls is heat. Friction creates heat and heat affects how the metal and Rubber
function.
Improvements
Many improvements have been made to limit or prevent the effects of friction. Some include lubricating the
pulley to reduce the buildup of friction. This works but also limits the amount of of time and force the
belt/chain is in contact with the pulley. A few methods I would recommend would be to:
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Improve the material used
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○
○
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Maraging steels are extremely strong and do not degrade with age, they can be surface treated for extra
protection.
Advanced elastomers like HNBR can be used since they offer great heat resistance.
Reinforcing rubber components with fiber cords or steel cores. A hybrid of the two could offer the reliability of
strong alloys as well as the low costs of rubber.
Coating the surface of the pulley itself with compounds that can reduce slippage as well as not retain
the heat caused by friction.
Improvements
Item
Disadvantage
Metal chain
Metal shaves into the
transmission pan
Improvements
1.
2.
Rubber V belts
Prone to wear and tear
due to heat fluctuations
1.
2.
Implementation
Potential
downside
Apply advanced
surface coatings
Improve
lubrication
systems
Add a coating step during
manufacturing or post
heat treatment
Redesign the CVT fluid
system or use higher
grade oil
1.
Use advanced
elastomers
(HNBR)
Improve air intake
to offset the heat
buildup
When making the rubber
compounds use HNBR
instead
Modify the air ducts
around the transmission
1.
2.
2.
Will increase
production cost
Makes the
system as a
whole a lot more
complex
increasing
maintenance
costs
Will increase
material costs
Will complicate
engine bay
designs
Conclusion
Overall, both metal and rubber V-belts have their own advantages and can be reliable depending on the
application. Metal chains offer superior durability, higher torque capacity, and longevity, making them
ideal for demanding, high-performance systems—though they come with a higher cost and require more
consistent maintenance. On the other hand, rubber V-belts are the better economic option. They are more
prone to wear and tear and may not handle high torque as efficiently, but they are lightweight, quieter,
and easier to replace. One thing I would focus on would be reducing the amount of friction buildup,
friction can never be completely eliminated, but some things can be done to reduce it. I would suggest
changing the connection of the multi radial pulley connecting the pulley itself. Reducing the resistive
forces acting on the pulley itself would make it easier for the belts/chains to do what they were intended
to do. Since both variants are heavily affected by friction, reducing friction or almost negating friction can
improve both in this instance.
Sources
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History of a CVT
CVT functions
What is a CVT
Gear Teeth ratios.
Composition of a rubber Belt.
Rubber belt efficiency.
Metal CVT.
Electron beam Welding.
Automotive Welding.
Rubber belt experimental improvements.