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Volvo KERS system   (Source: Volvo)
KERS system will propel the vehicle from a stop

In the automotive world, a lot of manpower and money is being put into research and development of systems to help boost fuel economy. The most common system today is a hybrid arrangement that uses batteries and electric motors to help propel the vehicle. Another green system is a KERS flywheel like the one used on the Porsche 918 RSR racecar.

The KERS system on the Porsche is activated with a push button to give the car added performance. Volvo is set to start testing its own version of KERS on the public roads of Sweden after receive a grant from the Swedish Energy Agency.

"Our aim is to develop a complete system for kinetic energy recovery. Tests in a Volvo car will get under way in the second half of 2011. This technology has the potential for reducing fuel consumption by up to 20 percent. What is more, it gives the driver an extra horsepower boost, giving a four-cylinder engine acceleration like a six-cylinder unit," relates Derek Crabb, Vice President VCC Powertrain Engineering.

The KERS flywheel that Volvo will use spins at up to 60,000 RPM and gets its energy for the forces created when braking. That rotational inertia is then transferred to the rear wheels via a special transmission. In the Volvo system, the combustion engine will be switched off as soon as braking starts and then the energy in the flywheel will be used to propel the vehicle from a stop and help it accelerate. 

This sort of system will be most effective in stop and go city driving. Volvo estimates that the combustion engine might be able to be turned off as much as half the time. When combined with the combustion engine the energy in the flywheel could add as much as 80hp to the vehicle and increase performance while allowing the car to be more fuel-efficient. 

The Volvo flywheel will be made from carbon fiber instead of steel for maximum efficiency. The flywheel measures a diameter of 20cm and weighs 13 pounds. It also spins in a vacuum to minimize losses. 

"We are not the first manufacturer to test flywheel technology. But nobody else has applied it to the rear axle of a car fitted with a combustion engine driving the front wheels. If the tests and technical development go as planned, we expect cars with flywheel technology to reach the showrooms within a few years," says Derek Crabb. He concludes: "The flywheel technology is relatively cheap. It can be used in a much larger volume of our cars than top-of-the-line technology such as the plug-in hybrid. This means that it has potential to play a major role in our CO2-cutting DRIVe Towards Zero strategy."

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RE: Bearing Hell
By Solandri on 5/31/2011 2:18:15 PM , Rating: 2
You can translate (move in the x, y, or z axes) a rotating mass just the same as if it weren't rotating. So a bumpy road doesn't present any difficulties. Any suspension system capable of supporting 13 pounds steady relative to its bearings would suffice.

The problem with a 60k RPM mass would be that the huge angular momentum resists rotation. I had thought any flywheel would be mounted horizontally (like most CD players) because of this. Cars mostly turn around the z-axis, so if you mount the flywheel with its angular momentum vector along the z-axis, it doesn't change the car's turning characteristics.

However, from the diagram, it looks like they're mounting it vertically. At high RPM, this will make it easier for the car to turn in one direction, harder to turn in the other. The Sopwith Camel (WWI biplane) exploited this for improved maneuverability in one direction. But it's something I would consider to be a distinct disadvantage in a car.

A possible solution is to have two counter-rotating flywheels mounted next to each other. They rotate at the same RPM, but in opposite directions. That cancels out the angular momentum, resulting in no change to turning characteristics. (OTOH, the containing structure must be twice as strong since the two flywheels will try to turn in opposite directions every time you rotate them.)

RE: Bearing Hell
By BZDTemp on 6/1/2011 5:32:41 PM , Rating: 2
I have been wondering about this as well but they do run similar systems on F1 cars and they are able to change direction like nothing else.

"Young lady, in this house we obey the laws of thermodynamics!" -- Homer Simpson
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