Continuously variable transmission
**Types of CVTs:**
V-Belt CVT:
– Most common type with two variable-diameter pulleys.
– Pulleys consist of two cone-shaped halves that move together and apart.
– Belt needs to be stiff in the axial direction for short radial movements.
– Steel-reinforced V-belts used in low-mass applications like utility vehicles.
– Offers approximately 88% efficiency.
Toroidal CVT:
– Consists of discs, rollers, and can withstand higher torque loads.
– Discs arranged almost conically, with rollers varying the drive ratio.
– Can reverse the direction of thrust within the CVT.
– Eliminates the need for an external reverse gear.
– Can achieve a 1:1 drive ratio.
Ratcheting CVT:
– Uses one-way clutches or ratchets to rectify and sum forward motion.
– Drive ratio adjusted by changing linkage geometry within oscillating elements.
– Can transfer substantial torque and has high efficiency.
– Design principle dates back to before the 1930s.
– Still in production for low-speed electric motors.
Hydrostatic/Hydraulic CVT:
– Uses an engine-driven, positive-displacement pump to deliver oil under pressure.
– Oil under pressure delivered to one or more hydraulic motors.
– Creates torque applied to the vehicle’s driving wheel(s).
– Differentiates from other transmissions by incorporating hydraulic motors.
**Specific Types of CVTs:**
Hydrostatic CVT:
– Gear ratio determined by pumps displacement and motors displacement.
– Advantages include capacity scalability, flexibility, smoothness, and slow crawl speeds.
– Disadvantages include reduced efficiency, higher cost, and greater weight.
– Commonly used in various agricultural and industrial equipment.
Cone CVT:
– Varies drive ratio by moving a wheel along conical rollers.
– Simple design for continuously variable transmission.
– Patented in 1903 by William Evans and Paul Knauf.
Epicyclic CVT:
– Gear ratio shifted by tilting axes of spherical rollers.
– Utilizes planetary gearset principle.
– Provides variable contact radii for different drive ratios.
– Includes production versions like the NuVinci CVT.
Other Types of CVTs:
– Friction-disk transmissions used in early 20th-century vehicles.
– Magnetic CVT in development using non-contact magnetic coupling.
– Claims 3 to 5 percent fuel consumption reduction.
**Applications and History of CVTs:**
History:
– Invented in 1879 by Milton Reeves for sawmilling.
– Used in early cars like the 1913–1923 David, 1923 Clyno, and 1926 Constantinesco.
Applications:
– Mass production in the 1958 DAF 600.
– Adoption by various manufacturers like Nissan, Fiat, and Ford in the late 1980s.
– Various uses in racing cars, small vehicles, farm equipment, power generation systems, and other machinery.
**Advantages and Disadvantages of CVT:**
Advantages:
– Smooth acceleration.
– Improved fuel efficiency.
– Constant power delivery.
– Simplified design.
– Enhanced driving experience.
Disadvantages:
– Limited towing capacity.
– Overheating concerns.
– Noise under heavy load.
– Reduced durability in high torque applications.
– Maintenance costs.
**Innovations in CVT Technology:**
Toroidal CVTs.
Full-Toroidal Traction Drive Infinitely & Continuously Variable Transmissions.
Magnetic Continuously Variable Transmission.
Double CVT for high-torque applications.
PIV Vertical Drives.