The efficiency of a 48-volt system is largely dependent on the amount of drive and recovery output available in continuous operation. As a result, Continental has chosen to employ the water-cooled induction motor that can be connected directly to the engine’s cooling circuit. This makes it possible to assemble a machine that, depending on the version, can continuously provide an output of 6 kW and torque of 60 N·m, all in the installation space of a conventional starter alternator. Using a belt drive means that up to 150 N·m can be transmitted to the crankshaft.

Within the modular system, only the length of the motor changes the power. The inverter, based on a metal-oxide-semiconductor field-effect transistor (MOSFET), is integrated in the housing lid, which saves space. The modular system from Continental also includes a DC/DC converter, which enables the 48-volt system to be connected to the vehicle’s on-board power supply. This makes it possible to use some of the energy stored in the lithium-ion battery to stabilize the on-board power supply as well.

The technology is a particularly cost-efficient solution to reduce fuel consumption and exhaust emissions.

Belt driven starter generator (48-volt electric drive) from Continental. Click to enlarge.

Simple adaptation to existing powertrain designs is a major benefit of the P0 concept that Continental has pursued. It enables the load point of the combustion engine to be shifted. The fuel savings demonstrated in test vehicles are considerable, with a figure of 13% in the New European Driving Cycle. In real-world use—especially in cities—the savings are even higher thanks to the greater share of driving spent in energy recuperation phases, and can reach up to 21%, according to Continental.

This is helped by the fact that the combustion engine can be switched off when the vehicle approaches traffic lights, starting at speeds below 20 km/h (12.4 mph). The combustion engine is always started with the 48-volt drive within just 0.2 seconds—a conventional starter needs roughly twice as much time.

When the 48-volt drive is combined with a diesel engine as in its first production application, there is an additional effect: the nitrogen oxide emissions produced during acceleration from low engine speeds fall by up to 10%, as some of the necessary torque is generated via the electric motor.

With the mild-hybrid system, Renault is aiming for combined fuel consumption of 3.5 liters of diesel per 100 km (67 mpg US). They are also aiming to reduce the new Scénic’s CO₂ emissions to 92 grams per kilometer—a new CO₂ benchmark in this vehicle class.

The 48-volt solution from Continental is relatively easy to combine with preexisting internal combustion engines, as it does not require any more room than a conventional starter generator. This is due to the high power to size ratio of the electric motor, which does not contain rare earth materials. This is achieved by water cooling of the stator and the high efficiency of the induction motor.

To save space, the inverter, which is needed to convert direct current stored in the battery into alternating current required for operation, is integrated in the housing lid of the motor. The ready-to-install 48-volt drive is manufactured at the Continental plant in Nuremberg, which already specializes in complex electronic modules, such as those used for automatic transmissions.

Since 2013, Continental engineers have been working together with Renault on a hybrid drive, which is so cost-efficient to produce that it becomes an appealing option for mid-size vehicles. To achieve this, the development partners have used low-voltage hybrid technology, which operates at 48 volts. This is in contrast with the considerably more expensive high-voltage technology, which operates at between 300 and 400 volts and is usually used in hybrid vehicles.

We are proud that we were able to secure Renault as the first customer for our innovative 48-volt drive. Other production launches for both diesel and gasoline vehicles are in the pipeline for Europe and other markets including China and North America.

—José Avila, Continental Executive Board Member responsible for the Powertrain Division

According to Continental, the market for 48-volt drives will experience significant growth in the coming years. Rudolf Stark, Head of the Hybrid Electric Vehicle Business Unit, says that in 2025, approximately one in five new vehicles across the world will be equipped with a 48-volt drive.

Even after the start of production, Continental will continue to develop the 48-volt technology. As well as optimizing all components for the P0 arrangement, the focus will be on another system configuration—a P2 arrangement, with the electric motor located between the engine and the transmission. It can therefore be operated entirely independently of the combustion engine, which means that electric driving at speeds of temporarily up to 50 km/h (31 mph) is possible with a 48-volt drive as well.

Such a solution, which enables fuel savings of up to 25% in concert with additional efficiency-boosting measures, was presented for the first time by Continental and Schaeffler at the 2016 Vienna Motor Symposium.