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Synthetic oil for continuously variable transmissions

A continuously variable transmission (CVT) is a pulley system, using a belt or chain, that provides infinite gear ratios. This transmission style was popularized by vehicle manufacturers in Japan but is becoming popular in China and other markets. Constant metal-on-metal traction is required to avoid slippage in the belt-and-pulley system.

Like other types of transmission oils, CVT fluids are moving to lower viscosity to improve energy efficiency in the system – lower than 6 cSt kinematic viscosity at 100°C – despite high pump pressures that increase shear and raise temperature. Along with this challenge, formulators must meet increasing demands for longer drain intervals – from 60K to 100K KM, with some OEMs targeting fill-for-life – as well as low-temperature performance.

Striking a balance

Balance of tribological characteristics are essential for CVT fluids. Desirable metal-on-metal friction coefficient is essential for optimum performance and torque transfer for belt/chain and pulleys in transmission. Formulators also seek a balance between film thickness and low traction to ensure both wear protection and energy efficiency. Our advanced synthetic base stocks, including SpectraSyn Elite™ metallocene polyalphaolefin (mPAO), have proven their capability to achieve this critical balance, demonstrating superior performance in block-on-ring tests to competitive base stocks (see test results below).

Metal-on-metal friction coefficient  

In laboratory testing, five lubricant blends were evaluated to measure metal-on-metal friction coefficient using a block-on-ring machine (LFW-1, JASO M358). The three SpectraSyn Elite™ metallocene polyalphaolefin (mPAO) blends with Group III/II mineral base stocks demonstrated stable and high friction coefficient compared to mineral blends featuring ethylene propylene copolymer (EPC) and conventional polyalphaolefins (cPAO). This friction performance can result in smooth and high torque transfer in continuously variable transmissions. 

Gr III/II comparison at different speeds and friction coefficients


In friction coefficient measurement tests at 40°C and 80°C, SpectraSyn Elite™ 150 and 65 metallocene polyalphaolefin (mPAO) and SpectraSyn™ 40 polyalphaolefin (PAO) blends demonstrate better traction than ethylene propylene copolymer (EPC) and VI blends. This lower traction can help improve fuel economy and energy efficiency.
Traction charts by SSR at varying temperatures.

Film thickness  

To ensure adequate wear protection, lubricants must retain film thickness, even at the low viscosities today’s market demands. In comparison tests at three temperatures (40°C, 80°C and 120°C), blends using SpectraSyn Elite mPAO synthetic base stocks provide similar or better EHL film thickness than EPC, VI and reference CVTF blends.
Film thickness by viscocity.

Low temperature performance

Like other transmission lubricants, CVT fluids need performance capabilities at cold temperatures. In ASTM D2983, the standard test method for low-temperature viscosity for transmission fluids, SpectraSyn Elite mPAO and SpectraSyn™ PAO base stocks demonstrate superior low-temperature performance to EPC.

brookfield low temperature viscosity test

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