Road and Track magazine recently ran an article about the Abacus Transmission, a new development that was described as the first new rotary transmission since the 1960s.
The idea came about whilst engineers were looking for a better and cheaper solution to providing a transmission that suits modern electric motors – i.e. a transmission to help an electric car perform better.
Electric motors work best at high revolutions however they can produce lower torque than a classic internal combustion engine. To make the motors work efficiently in a car, the drive train needs to reverse the speed/torque equation such that the speed is lower and the torque is higher.
A senior engineer at SRI International in the US has created the Abacus Drive, so called because the rollers are supposed to look like an Abacus counting machine. It actually looks like an oversized roller bearing because that is pretty much what it is – with some mechanical smarts.
The Abacus uses beads that look like the tips of bullets and they roll inside a groove with a variable diameter. Because both the bead and the groove have variable diameters, it is possible to take the higher speeds of the electric motor, slow it down and create more torque. It is a similar concept to a cycloidal drive (which has been around for decades).
So the Abacus can flip the speed/torque equation however it also does it more efficiently than many other transmissions. As it is a rolling transmission, it produces less friction, less friction means less power needed to rotate the gears and therefore more power can be delivered to the wheel. In addition, less friction means less heat and therefore less wear. SRI claims a 90% efficiency, compared to 50% from a conventional transmission.
But there’s more …. due to the simplicity of the design, it is expected to be cheaper to manufacture and with less parts to wear out, should last longer. The design is currently in “lifetime” testing prior to going into production, possibly some time later this year if all goes to plan.
SRI International are a specialised research company that develops technology that gets licensed to manufacturers. They have many offices across the US and their only two international offices are in Japan and Greenland. They are developing some pretty amazing technology!