There is no doubt that the electrification of our transportation system is coming. What is problematic is how quickly consumers will accept fully electric battery-powered vehicles. The step between today’s reliance on fossil fuels and gasoline engines and full electrification is the hybrid. But it can be costly to build hybrids, which must carry both a gasoline-fueled powerplant and a battery and electric motor. The answer, at least in the short term, is the 48 Volt mild hybrid system.
Two in One
All hybrids have two separate powerplants that can work separately or together to propel the vehicle. Most have a gasoline internal combustion engine (ICE) as their main source of power and an electric motor placed between the ICE and the transmission. Under normal driving, the gasoline engine both charges the hybrid battery and moves the car. Under some conditions, the motor will shut off and allow the electric motor to take over drive duties. When braking, the electric motor acts as a generator, putting energy back into the hybrid battery. The energy from this regenerative braking can then be sent back to the electric motor for limited electric drive or used to assist the ICE when accelerating. Hybrids can provide a 20% improvement in fuel economy in urban and city driving.
The problem with a full-on hybrid is cost. Equipping a vehicle with both an electric and gasoline drivetrain is expensive. That’s where the 48 Volt mild hybrid comes in. In this case, a powerful 48 Volt starter/alternator replaces the normal 12 Volt alternator driven by the accessory belt at the front of the engine.
|The 48 Volt mild hybrid uses a belt driven starter/alternator to provide an entry level of electrification. (Image source: Valeo)|
Bang for the Buck
The device has several roles. Under normal driving, the 48 Volt system acts as an alternator and charges a small 48 Volt lithium ion battery. It is also used to charge the normal 12 Volt battery, working through a DC to DC converter that steps the 48 Volts down to 12 Volts. The system allows energy to be recaptured through regenerative braking as well. This energy can be used to aid in acceleration by being sent back through the system, which then acts like a motor. Or it can be used as a starting motor to restart the engine when it has been shut down while the vehicle is stopped.
“We tend to work on what we call the cost-benefit ratio, which is the dollars to grams of CO2,” Matti Vint, engineering R&D director for the auto supplier Valeo, told Design News. “We are expecting the 48 Volt belt drive system to be a little more than half the cost benefit of a high voltage solution. You get a bigger bang for the buck with a 48 Volt system.”
Anything over 60 Volts is considered high-voltage (HV). These systems (which can go up to several hundred Volts) require specialized orange color-coded cables and specific connectors and special relays (called contactors) to connect the battery pack to the vehicle. Because 48 Volt is below the HV threshold, the components used can be much less expensive. The 48 Volt pack is also much smaller and can be standardized across a range of vehicles. Hybrids with HV systems need to have their battery packs designed for each individual vehicle, adding cost and complexity.
The reduction in CO2 and improvement in fuel economy that comes from using a 48 Volt belt-driven system is significant. “With a belt-driven system, you are looking at around 8% savings,” Vint told Design News. But belt-driven systems are just the beginning. “There is a move to go from belt driven to machines that are attached to say the gearbox, or to the axle assembly, and even providing some level of EV function. Those would be expected to see higher savings—sort of 15% to 18%. It really depends upon the platform,” said Vint.
More Than Economy
The advantage of a 48 Volt system is that it can go beyond the fuel savings it provides as a mild hybrid. Because power is equal to voltage multiplied by the current, a 48 Volt system can provide the necessary electrical energy for a variety of functions that are not practical or possible with a 12 Volt vehicle electrical system. Electric power steering, air-conditioning compressors, and engine cooling water pumps have been developed, taking advantage of the extra power available with 48 Volts. Such systems can improve fuel economy by reducing drag on the ICE by only operating when they are required.
The 48 Volt system can be used to improve functionality and comfort. Seat heaters, cabin air blower motors, and window defrosting can be improved by using the higher power available from 48 Volts. The vehicle suspension can be actively controlled through electric actuators that take advantage of the extra power. In the short-term, with belt driven systems, the 12 Volt battery and traditional starter will be retained to operate the normal vehicle electrical systems and to aid in starting on cold mornings.
Vehicle performance can be enhanced through a system like an electrically powered supercharger. “You are looking at technology that customers are willing to buy,” said Vint. “Customers aren’t always willing to pay for fuel economy benefits in the USA market,” he said. The Audi SQ7 SUV, for example, has a 48 Volt electric supercharger that was developed by Valeo.
|Valeo predicts that 48 Volt mild hybrid systems wil capture 20% of the US new car market by 2030. (Image source: Valeo)|
Europe and Asia are expected to lead the way in the rollout of 48 Volt systems. The Porsche Cayenne and Bentley Bentayga SUVs already are using 48 Volts to power roll-control systems that keep the vehicles level while cornering. Volkswagen recently announced that versions of the popular Golf model will be equipped with 48 Volts to improve fuel economy. In the US, Fiat Chrysler will offer belt-driven 48 Volt systems in 2019 Ram Pickups and the Jeep Wrangler.
Valeo’s Matti Vint explained the expectations for 48 Volts to Design News (see the graph). “Based upon our own market projections, by 2030, we are anticipating about 20% of the market in North America will have 48 Volts. This compares to about 40% for high-voltage—20% for full-hybrids and 20% for plug-in hybrids. In the global markets, we are looking at much higher penetration for 48 Volts—30% instead of 20%.”
Dr. Matti Vint from Valeo will be presenting a talk titled, “Do 48v Powertrains Make Sense for the North American Market?,” at The Electric and Hybrid Vehicle Expo in Novi, Michigan on September 11-13.
Senior Editor Kevin Clemens has been writing about energy, automotive, and transportation topics for more than 30 years. He has masters degrees in Materials Engineering and Environmental Education and a doctorate degree in Mechanical Engineering, specializing in aerodynamics. He has set several world land speed records on electric motorcycles that he built in his workshop.
|The EV & HV Info You Need Now. Join our in-depth conference program to learn about topics from new developments in electric motor design to regulations and rollout timelines. The Electric & Hybrid Vehicle Technology Expo. Sept. 11-13, 2018, in Novi, MI. Get registration info for the event, hosted by Design News’ parent company UBM.|