The Extroid CVT is a unique form of Continuously Variable Transmission developed to handle higher torque than conventional belt- or chain-driven CVTs. Instead of using a flexible belt, the Extroid uses two pairs of solid rollers to vary the transmission ratio. This design was inspired by early friction-based drive systems developed between 1860 and 1905.
The concept dates back to 1877, when Charles Hunt secured the first patent for a toroidal CVT in industrial use. The principle was sound, but early models faced challenges with wear caused by the extreme friction between rollers and discs.
Modern interest in this system grew in the 1960s and 70s, with attempts by Curtis Wright Corp. and Excellamatic Inc. to bring toroidal CVTs into automotive use. However, those projects were short-lived due to limitations in materials and durability.
In 1978, NSK began serious development of a toroidal CVT for vehicles. After years of testing and refinement, they partnered with Nissan to produce a version capable of managing significant torque. The result was the Extroid CVT — a transmission that offers both performance and strength, and is now featured in select models such as the Nissan Cedric, Gloria, and Skyline 350GT-8.
In contrast, a Continuously Variable Transmission (CVT) replaces these fixed gears with a more adaptable system. Instead of switching between a set number of gears, a CVT uses a single pair of durable pulleys connected by a high-strength belt, allowing the transmission to change seamlessly across an infinite range of ratios.
Unlike traditional CVTs that rely on belts or chains, the Extroid CVT transmits power through friction rollers placed between two discs. One disc is connected to the engine’s crankshaft (input), while the other is connected to the driveshaft (output).
By adjusting the tilt angle of the rollers, the system alters the point of contact on each disc. When the rollers are positioned closer to the centre of the input disc and further out on the output disc, the result is a lower gear ratio. This means the output disc rotates more slowly, providing the torque needed for acceleration or low-speed driving. Reversing the contact points increases the gear ratio for higher-speed cruising.
The Extroid CVT offers a wide transmission ratio range of 4.4:1, which supports both responsive performance and efficient operation. Its solid roller design is better suited to high torque applications than traditional belt-based systems, making it more durable under load.
Because the input and output discs are positioned along the same axis, the Extroid CVT is compact enough to fit in a longitudinal gearbox, making it ideal for rear-wheel-drive vehicles.
Bringing the Extroid CVT to market took decades of development, not only in mechanical design but also in materials science. NSK had to engineer a process for producing ultra-pure metal components capable of withstanding the intense pressure and heat generated within the system.
Equally important was the development of a specialised oil that could perform under these extreme conditions. The lubricant used in the Extroid CVT plays a vital role in maintaining grip between the rollers and discs, while also reducing wear and cooling the internal components. Without it, the system would fail rapidly under stress.
These breakthroughs in metallurgy and lubrication were essential in making the Extroid CVT a viable and durable solution for real-world driving.
This design has been tested extensively and is capable of handling high torque loads. It has proven to be extremely reliable and durable, even under demanding driving conditions.
In contrast, a Continuously Variable Transmission (CVT) replaces these fixed gears with a more adaptable system. Instead of switching between a set number of gears, a CVT uses a single pair of durable pulleys connected by a high-strength belt, allowing the transmission to change seamlessly across an infinite range of ratios.
