The industry’s race to deploy 48-V hybrid systems has begun. Renault is the latest OEM to announce incorporation of the “mild” low-voltage hybrid technology, developed and supplied by Continental, in its new 2017 Scenic MPV entering production next month. The news follows Audi’s earlier production announcement of a Valeo-supplied 48-V system in the 2017 SQ7 (http://articles.sae.org/14662 ). Mercedes also recently announced its new inline-six and four-cylinder engine families will include 48-V subsystems.
Conti’s 48-V system will be standard equipment on both gasoline and diesel versions of the Scenic Hybrid Assist model. The system features a liquid-cooled induction motor with inverter integrated into the motor housing comprising the integrated starter-generator (ISG) unit. It is fitted in the so-called “P0 [zero]” position on the combustion engine’s front-end accessory drive, coupled to the crankshaft via a reinforced belt. The system includes a .5 kW·h lithium-ion battery. Total system mass including battery is 15 kg (33 lb), said Juergen Wiesenberger, head of HEV engineering at Continental North America.
The Renault business is the tip of the iceberg for Continental’s 48-V program, Wiesenberger told Automotive Engineering. The company has 48-V production programs in the pipeline for both gasoline and diesel vehicles in North America, Europe and China over the next few years. His colleague Rudolf Stark, executive VP of Conti’s hybrid-electric business unit, forecast about 20% of new vehicles worldwide will be equipped with a 48-V system by 2025, about 4 million of them by 2020.
Stark considers 48-V systems to be a “bridge technology” between current mild HEVs and full EVs, providing 6 to 20 kW to meet the increased power demands of a variety of new vehicle-efficiency and customer-pleasing features including electrically-heated windshields, adaptive suspension systems and electric turbochargers. By comparison, a full hybrid system typically offers 20-40-kW and a plug-in hybrid, 50-90 kW.
Stark echoed other propulsion-system engineers that 48-V systems “provide about 70% of the benefit of higher-power systems for about 30% of the cost.” He and Wiesenberger claim Conti’s latest 48-V production systems have demonstrated up to 20% greater fuel economy in real-world driving, compared with non-hybridized powertrains in similar weight-class vehicles.
Continental is among a number of Tier 1 suppliers that are lining up production contracts for both ISG and P2 (e-motor fitted in the “second” position between the ICE and transmission) types. They are expected to launch within the 2017-2020 timeframe in conjunction with tightening CO2 regulations in the major regions.
Wiesenberger claims that Continental’s liquid-cooled 48-V ISG can, depending on specification, continuously provide 6 kW and 60 N·m (44 lb·ft) roughly within the package space of a 12-V starter alternator. Variants of the ISG are rated up to 150 N·m (110 lb·ft). Conti’s 48-V system is a modular design using a MOSFET (metal-oxide-semiconductor field-effect transistor)-based inverter.
Conti’s 48-V system starts the ICE within 0.2 s—about twice as fast as a 12-V stop-start system, Wiesenberger said. He added that when part of a diesel-hybrid propulsion system, 48-V has demonstrated reduced NOx emissions at lower rpm by up to 10% due to the supplemental torque generated by the e-motor.
P2-type 48-V systems enable independent operation of the combustion engine. According to Wiesenberger, Conti’s P2 system co-developed with Schaeffler allows all-electric driving at up to 31 mph (50 km/h) with a claimed fuel savings of up to 25% greater fuel efficiency than a non-hybridized model.