Low voltage motor-generators ease range anxiety

The fuel consumption and greenhouse gas emissions of vehicles could be cut by over a quarter without the need for costly high voltage plug-in hybrid systems, according to a UK company.

Controlled Power Technologies (CPT), an Essex-based powertrain technology developer, is investigating the use of two low voltage motor-generators, mounted at different points on the vehicle, to provide a power boost to downsized engines at a much lower cost than plug-in hybrid technologies.

The two switched-reluctance motor-generators would act in tandem to provide electric boosting, according to Nick Pascoe, chief executive of CPT.

“In this way you have no range anxiety issues because you still have a base engine, but you can use the electric machine to accelerate,” he said. “That means you can retain the same vehicle architecture, and continue to use petrol or diesel to drive it, but you can make that vehicle a lot more fuel efficient than it is today, by assisting it with intelligent electrification.”

The company is exploring the use of a newly developed 10 kilowatt axle-mounted SpeedTorq unit, to be used in tandem with its existing 10 kilowatt engine-mounted SpeedStart unit, to provide energy recuperation during braking and torque assist during acceleration.

The combination of two 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 units and costly high voltage battery systems, the company said.

The car industry is considering moving from the use of 12 volt electrical systems within vehicles to a new level of 48 volts. This will increase the energy available for the growing range of vehicle control and safety systems within modern vehicles, but without the expense of moving above the 60 volt threshold, beyond which electrical systems require additional safety restrictions, said Pascoe.

“So if you want to stay beneath the 60 volt safety and cost threshold, why not put a second 48 volt machine in there?” he said.  “Keeping both motors at a low voltage keeps the cost down, and then you can add a smart control system that allows them to work in tandem with the base engine.”

Switched reluctance devices offer a number of advantages over other motor technologies, the company said. Their stator structure has simpler windings compared with a permanent magnet motor, coupled with a simple lightweight low inertia rotor.

Eliminating the use of permanent magnets also means that the price volatility and special recycling requirements associated with rare earth materials are no longer a factor.