A new kind of continuously variable transmission (CVT) started showing up at agricultural trade shows in recent years. This CVT outperforms all others due to its greater efficiency. Among other advantages, it uses a toroidal variator system to optimize vehicle speed. This saves fuel and, because it’s so easy to use, increases operator productivity.
It took more than 15 years of research and development to perfect this transmission, which is mainly intended for compact and utility tractors in the 70 to 180 HP range. However, the group is also working on higher power transmissions. Because the mechatronic system delivers more power to the wheels, a smaller engine can be used to operate farm machinery while improving overall performance by roughly 20% to 30%.
The toroidal variator
Unlike other CVTs, the one developed by CVTCORP does not have toothed gears that fit together so that the right ratio is associated with the right torque (when gears are changed).
In the system housing, two input flanges at each end and an output flange in the central position are aligned on the same shaft to form two cavities. In each cavity, three rollers on a fixed pivot rotate vertically between the output flange and the input flange on either side. This assembly is the heart of the toroidal variator.
The input and output flanges transmit power to the rollers, causing them to change angles based on their position. The speed variation happens when the rollers are horizontal, inclined or on a more or less wide diameter of the output flange.
“At both ends of the system,” explains Daniel Girard, President and Founder of CVTCORP, “the input and output flanges are working together. They’re sending power to the rollers through a film of traction fluid, getting the rollers to change angles depending on their position. The speed variation occurs when the rollers become horizontal, inclined or on a more or less wide diameter of the output flange. The rollers can complete a full range in less than a second.”
For example, for a given farm job, the transmission will find the optimal ratio to maximize tractor speed. So if you have 100 acres to mow, you’ll be done faster.
“A certain level of compression needs to be exerted on the system to solidify the film of traction fluid between roller and flange. This is done using a cam, a single part that continuously adjusts the compression force exerted on the rolling elements over the entire speed and torque range, which optimizes the transmission’s efficiency and prevents any slip.” – Daniel Girard, President and Founder of CVTCORP
The mobile rollers are pressed between the input and output flanges, and the quality of the materials and surfaces of these rolling elements is part of the designer’s expertise.
“To operate,” explains Mr. Girard, “a certain level of compression needs to be exerted on the system in order to solidify the film of traction fluid between roller and flange. This is done using a cam, a single part that continuously adjusts the compression force exerted on the rolling elements over the entire speed and torque range, which optimizes the transmission’s efficiency and prevents any slip.”
“There’s no metal-to-metal contact,” continues the President of CVTCORP, “because the specially formulated traction fluid used in the transmission is trapped at each point of contact between the surfaces of the rolling elements. The pressure at the contact points induces a phase change in the fluid, which momentarily becomes solid. This transfers the torque without slip.”
Roller position is oriented by rotating the outer control ring with a simple, low-power actuator.
Becoming the new standard
The simple yet heavy-duty design of this transmission gives it a long service life with minimal maintenance.
“It replaces everything on the market today,” concludes Daniel Girard. “Although priced similarly to a power-shift transmission, it’s more efficient than a hydrostatic transmission. We’re convinced that the top equipment manufacturers will be adopting it in the next few years.”
The company is looking for partners to market its transmission in the agricultural sector. Several license agreements are in process, and the organization plans to continue manufacturing five key components, the electronic controls and the software.