NerraTrac CVT

Votes: 3
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The NerraTrac continuously variable transmission (CVT) utilizes a traction drive in a traction fluid (high viscosity lubricant) that ‘solidifies’ momentarily between two hardened metal surfaces under high contact pressure, thus providing a traction force. It employs the same elasto-hydrodynamic lubrication principle used by all current automotive CVT transmissions.

The NerraTrac CVT uses a commercially available traction fluid, such as Santotrac, from Santolubes. Refer:

A 1985 NASA paper on the Design of Traction Drives provides a credible reference on the technology principles. Refer to: Well established and proven technology principles.

The NerraTrac CVT enables features such as:

  • Automated ratio control
  • Geared regeneration
  • Full CVT capability under all load conditions
  • 91-94% efficiency (MATLAB Simscape simulation, 374% ratio)
  • Shaft driven, fully enclosed system; practically zero maintenance
  • Simple, durable, lightweight design (2.3kg or 5.0lbs without external casing)
  • 370% ratio range (198mm diameter disk)
  • 510% ratio range (248mm diameter disk)

Benefits include:

  • multiplication of motor torque
  • motor down-sizing (optimization)
  • maximising motor efficiency
  • maximum current reduction
  • high speed capability
  • extended range
  • limited to zero maintenance
  • no cooling issues
  • silent operation


  • 9.2 kW (current ebike CVT design):
    If the input power is 25 Nm, it will be suitable for an 9.2 kW ICE or an electric motor at 3,500 rpm.
    Power (Watt) = 0.105 x Nm x rpm, therefore, this will result in Hertz contact stresses of around 1.35 GPa, thus, it can be manufactured using relatively low cost EN36B steel (case hardened to 60 HRC).
  • 15.8 kW:
    As per above example but at 6,000 rpm input, will result in 15.8kW
  • 34.6 kW:
    As per the first example, but using special steel* for the disk and rollers that can handle 2.7 GPa (55 Nm) at a high duty cycle. * Note: an example of suitable steel is KUJ7 manufactured by Koyo.
    This will result in 20.2 kW at 3,500 rpm and 34.6 kW at 6,000 rpm.
  • Further scaling (bespoke):
    The NerraTrac CVT can be further scaled by increasing input rpm above 6,000 ≤ 21,000rpm.
    Secondly, by applying the variations on the design space & relationships e.g. larger rollers, a larger disk etc, according to the requirements of specific applications.

The NerraTrac CVT represents an adaptable platform technology

Suitable a transmission for light electric vehicles and ICE vehicles such as:

  • motorcycle scooters, mopeds, three wheelers
  • ‘pod’, microcars, LEVs, autonomous delivery vehicles (ADVs)
  • UTVs & ATVs
  • ebikes, ecargo bikes
  • golf carts, lawnmowers etc
  • and all rubber belt CVT applications

Also suitable be for industrial applications including:

  • Pumps
  • Compressors
  • HVAC
  • Geared motor drives
  • Conveyors
  • Appliances such as washing machines
  • As a Variable Speed Drive (VSD) alternative
  • Artificial lift (oil & gas)

CVT vs VSD advantages include:

  • multiplication of motor torque
  • speed control
  • motor optimization
  • motor size reduction
  • system start-up control
  • energy/electricity optimization and start-up current spike reduction


Voting is closed!


  • Name:
    Bruce Thompson
  • Type of entry:
  • Software used for this entry:
    MATLAB Simscape
  • Patent status: