48V system achieves near full-hybrid characteristics

November 03, 2015 // By Christoph Hammerschmidt
Significant fuel savings without sacrificing driving performance are typically expected from hybrid vehicles with high voltage electric motors. British engineering company Controlled Power Technologies (CPT) has demonstrated that it is also possible with motors running at just 48V.

The application by Controlled Power Technologies (CPT) of a switched-reluctance motor-generator deep into the driveline, as well as being applied directly to a petrol or diesel engine, will enable the technology developer to deliver to carmakers and tier 1 driveline system developers an almost full-hybrid functional capability. The combination of two low voltage SR machines promises to significantly reduce vehicle fuel consumption and exhaust emissions, whilst avoiding the cost and complexity of a high voltage plug-in hybrid.

“Computer simulations based on our LC Super Hybrid technology demonstrator indicate an impressive 26 per cent improvement in fuel economy for a large family saloon when the rear axle is boosted with low voltage electrical power,” says Nick Pascoe chief executive CPT.

The significant reduction in fuel consumption and exhaust emissions results from the electric boosting and regenerative braking of CPT’s engine mounted SpeedStart unit combined with its new axle mounted SpeedTorq unit. This combination is further enhanced by driveline down-speeding without compromising vehicle drivability - made possible by the electric boosting capability of two low voltage SR machines acting in tandem.

The SpeedTorq unit is a recent addition to CPT’s portfolio of SR machines. Unlike its engine cranking and generating focused, belt-integrated SpeedStart unit, which replaces an engine alternator, the SpeedTorq unit has the ‘four quadrant’ contra-rotational functionality essential for integration with a gearbox or axle, requiring the machine to provide its motoring and generating capability in both forward and reverse rotations.

“In this proposed dual-motor mild hybrid configuration, the e-motoring is only effected by the SpeedTorq unit,” says Dr Andreas Hubert, technical business development manager CPT. “The 48V e-motor installed on the final drive, results in additional efficiency benefits, because there is no drive through the combustion engine and transmission – and hence minimal parasitic losses. SpeedStart, mounted on the engine in place of the alternator, meanwhile, is focused on providing an extended start-stop capability, while both units are used for energy recuperation.”

“This relatively simple combination of low voltage electrical machines represents a cost-effective intermediate step between conventional vehicles powered solely by internal combustion engines and expensive plug-in hybrids with their larger traction motors and expensive high voltage battery systems,” says Paul Bloore, product validation and functional safety manager for the company’s hybrid product group. “The use of smaller switched reluctance machines that operate at 48 volts supported by a modest 1-2kWh battery pack, will enable vehicle OEMs to fully realise the benefits of mild hybridisation.”