Belt-alternator starter systems are an increasingly popular technology that delivers significant “bang,” in terms of incremental vehicle efficiency, for comparatively moderate “bucks.” Also known as “mild” or P1 hybrids (due to their “first” position on the front of the engine), these systems comprise what is essentially an oversized starter motor that serves double duty as a generator to provide assist to the vehicle’s combustion engine, while allowing it to be shut off whenever the car is coasting, braking, and stopped, with a rapid and seamless restart.
Experts claim systems cost of P1 hybrid setups are thousands less than for single motor/two-clutch P2 systems, and many more thousands less than two-motor input-powersplit systems similar to those used by Toyota and Ford.
The latest take on the belt-driven micro-hybrid system is called SpeedStart, developed by U.K.-based CPT and being shown at the 2012 SAE World Congress in Detroit April 24-26. The Integrated Starter Generator (B-ISG) system features a liquid-cooled switched-reluctance (SR) type electric machine, and all control and power electronics are packaged in a compact single housing. The system uses the standard 12-V vehicle architecture.
CPT claims power output up to 205 A, and what it calls “outstanding Driver Change of Mind” performance. This means sub-10-ms response times to get 90% of the current into the motor windings, without pre-flux delays or waiting for the flywheel speed to slow sufficiently before the pinion can be engaged. The company credits this to the SR machine, another benefit of which is it doesn’t use rare-earth magnets (unlike permanent-magnet motors).
Liquid cooling provides more stable thermal control of the power electronics (and a more stable overall thermal environment) than a ducted air-cooled system, claims the company. For full operation, the system temperature should not exceed 105°C (221°F). There is less chance for foreign matter entry into the system, and the liquid cooling also provides lower noise operation, according to CPT.
The company is targeting a 5% CO2 reduction (on the NEDC cycle) from SpeedStart’s stop-start function alone, with an additional reduction of up to 5% from optimized high-power regeneration during decelerations. The system offers a 1% CO2 reduction due to higher alternator efficiency, compared to current standard alternators.
SpeedStart uses existing belt-and-tensioner technology to transmit torque to the crankshaft. It also uses existing lead-acid battery technology, battery management systems, and CAN communication systems.