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Volvo Working on Mechanical(!) Regenerative Braking

… but it’s not the usual regenerative braking found on hybrid-electric vehicles. Volvo calls it KERS, and it is mechanical.

The Kinetic Energy Recovery System (KERS) developed by Volvo uses energy created during the braking of the vehicle to spin up a flywheel at speeds of up to 60,000 rpm.

With the flywheel spinning at such speeds in a vacuum, energy can be transferred back into the rear wheels when the driver needs to accelerate again, powering the vehicle until it reaches cruising speed.

The extra boost makes a four-cylinder engine feel like a six-cylinder in terms of acceleration, says Volvo, giving an extra boost of up to 80 horsepower when it’s needed the most and cutting the 0-100km/h time “significantly.”

Volvo regenerative braking flywheel design, 3/4 view
Volvo regenerative braking flywheel design, 3/4 view

From My bolds. There is also an excellent explanation at Car & Driver:

In Volvo’s system, the flywheel is mechanically coupled and decoupled from the rear axle using a continuously variable transmission. The CVT engages the flywheel as the car slows, spinning it to up to 60,000 rpm, then decouples the flywheel as the car comes to a halt, finally re-coupling the spinning flywheel to the rear wheels when the car accelerates from a stop. Volvo’s mechanical, motorless rear-axle-mounted setup is unique from Porsche’s approach to KERS, which relies on motor-generators to spin up the flywheel, recover its energy, and transfer that energy back to the car’s forward motion. (Read more about the system in the 911 GT3 R hybrid here.) Volvo claims that the flywheel’s accelerative boost not only aids fuel economy, but performance as well, with up to 80 additional horsepower available when the flywheel and engine join forces.

Volvo regenerative braking flywheel design, top view
Volvo regenerative braking flywheel design, top view

This is neat stuff. Hybrids have been doing this for over a decade, but it’s been electrical, thus the energy gets converted back into electricity and stored in the hybrid’s batteries. I’m guessing KERS will be a more efficient braking energy recovery system because it’ll not require energy to be converted back and forth to another form like hybrids’ regenerative braking systems do.

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