Volvo Builds a Different Kind of Hybrid

KERS stands for kinetic energy recovery system, and if you?re a fan of Formula 1 or LeMans series racing you know all about it. The concept is to use a highly developed flywheel to capture, store, and reuse vehicle inertia normally lost as heat during braking. Think of it as a mechanical hybrid that?s lighter and simpler than traditional battery and motor systems. Until now it?s only been used in racing, but Volvo has been hard at work adapting the idea to work in passenger cars.

Everything in the Volvo KERS system is built around the?flywheel, but it?s not just a lump of round metal. It?s a wound carbon fiber shell over a lightweight aluminum core totaling 13.2 lbs and precisely balanced. This construction is optimized to prevent the structure from stretching outward due to centripetal force?important because this thing is designed to spin up to an unfathomable 60,000 rpm.

That kind of speed can generate lots of heat, so the flywheel lives in a vacuum-sealed housing and rides on precision bearings. With no atmosphere there?s a lot less surface friction generated. It?s so well designed the flywheel takes 30 minutes to spin down from maximum speed. The trick with the whole thing is too manage the inbound and outbound flow of power. The energy that would normally be scrubbed away with mechanical brakes needs to be transferred to the flywheel. With the KERS unit situated at the rear where the spare tire normally would be, the rear wheels are driven by normal half shafts attached to a differential. The diff is connected to a clutched and hydraulically controlled continuously variable transmission (CVT). Apply the brake and the CVT shifts to direct power into the flywheel while slowing the car. Apply throttle and the CVT shifts again to pull power out of the flywheel and direct it to the wheels. Interestingly, this does give the car through-the-road all-wheel-drive while stability control and ABS are not effected at all, just tuned as it if were a normal all-wheel-drive model.

Control is done over a Bluetooth connection to an Android tablet mounted on the center console, with repurposed steering wheel button used for hard resets. The KERS has options for two different driving styles, economy and power. In economy, the car gains a claimed 25 percent fuel economy improvement in NEDC testing. Power mode adds a whopping 80 hp to the bottom line and has delivered 1.5-second 0-60 mph improvements in turbocharged five-cylinder testers and a blistering 2.5-second improvement with 4-cylinder cars. All this benefit comes in a package that?s just 132 lbs and, unlike conventional hybrid systems, doesn?t face the challenges of battery replacement, modifying the regular gas powertrain, or hefty weight penalties.

Volvo representatives gave us the opportunity to test this prototype at its Gothenburg development facility in Sweden, and it does make a compelling argument for consumer market KERS hybrids. Even at a development stage, power comes on seamlessly, feeling no different than a gear change. In economy mode the engine works far less in city driving, although there?s little benefit at highway speeds. The most interesting part is the sound. In production cars the efficient but loud straight-cut gears would probably be replaced with helical cut pieces and sound deadening would take care of the rest. In the prototype, the KERS unit sings a tune somewhere between frenetic supercharger whine jet engine. It?s not loud enough to be annoying, but it?s a bit backwards from normal cabin noises. Big sounds happen when you step on the throttle, but in this case the flywheel spins up as you brake. We say leave the sound the way it is and put it into production.

Source: http://www.popularmechanics.com/cars/news/auto-blog/Volvo-Demonstrates-KERS-system-15682389?src=rss

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