CVT technology set for key role in Volvo flywheel evaluation

Torotrak’s continuously variable transmission (CVT) technology will form part of the Volvo Car Corporation’s (VCC’s) evaluation of flywheel technology this autumn.

Volvo’s project, part-funded with a grant worth SEK6.57m (£648,210) from the Swedish Energy Agency, will bring together Torotrak’s variable drive technology and Flybrid Systems (UK) flywheel technology, working with SKF and Volvo Powertrain.

‘Our aim is to develop a complete system for kinetic energy recovery,’ said Derek Crabb, vice-president at VCC Powertrain Engineering. ‘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 per cent. What is more, it gives the driver an extra horsepower boost, giving a four-cylinder engine acceleration like a six-cylinder unit.’

Volvo said in a statement that it will test Flywheel KERS (Kinetic Energy Recovery System), which is fitted to the rear axle. During slowing, the braking energy causes the flywheel to spin at up to 60,000rev/min. When the car starts moving off again, the flywheel’s rotation is transferred to the rear wheels via a specially designed transmission.

The combustion engine that drives the front wheels is switched off as soon as the braking begins. The energy in the flywheel can be used to accelerate the vehicle when it is time to move off once again, or to power the vehicle once it reaches cruising speed.

Since the flywheel is activated by braking, and the duration of the energy storage — the length of time the flywheel spins — is limited, the technology is at its most effective during driving featuring repeated stops and starts.

Torotrak says its compact CVT has emerged as an effective transmission solution in flywheel-based mechanical hybrid systems.

Compared with conventional electric hybrid systems, mechanical flywheel hybrids reduce the number of inefficient conversions during the recovery and reuse of braking energy.

Instead of converting kinetic energy into electricity to be stored in a battery pack, energy is stored in a high-speed flywheel with power transfer controlled by a compact CVT.

‘If the tests and technical development go as planned, we expect cars with flywheel technology to reach showrooms within a few years,’ said Crabb.

Super fly: Derived from F1, flywheel systems will offer energy-efficiency benefits for road-ready hybrids. Click here to read more.