But why does mainstream media snub the quietly radical interim solution – the 48-volt mild hybrid system?
It was hard to miss Volvo’s recent pronouncement that it will ditch traditional gasoline and diesel engines by 2019. But that didn’t mean Volvo was about to launch a fully battery-electric line of XC90s, V90s, S90s and so on. What the Swedish carmaker really meant was that they were developing two new chassis architecture for 48-volt mild hybrids, plug-in hybrids, plus a full battery-electric system. And they’re just one of many automakers to hop aboard the 48-volt bandwagon. Audi, Mercedes, Renault, Volkswagen also getting into the 48-volt game, as well as auto parts makers Delphi, Bosch, Continental, and Valeo.
What’s so special about 48 volt systems? How are they different from a regular hybrid system? For starters, 48-volt technology is cheaper but can still increase the fuel efficiency of a car with an internal combustion system. It’s also less complicated than a full hybrid system, which requires special CVTs, planetary gear sets, complex drivetrains, etc.
Some of the advantages of 48 volt systems include capturing energy lost while braking, providing torque in the low rpm range, and improving the stop-start function, seriously reducing NOx emissions.
Since they work with existing ICE systems, 48 volt systems are relatively inexpensive for OEMs to produce, from $650 to $1,000 more per light commercial vehicle. Retail costs are estimated to be anywhere from $800 to $2,000 more per vehicle. Fleet managers will appreciate the efficiencies, estimated at 10 to 15 percent increased mileage.
Even though they aren’t sexy enough to make the headlines, 48-volt hybrids are catching on. In fact, 48-volt hybrids are expected to make up more than half of electric vehicles sold in 2025, according to Global Insight IHS. One out of every 10 cars sold globally in 2025 predicted to be a 48-volt mild hybrid. When you do the math, that’s 11 million 48 volt mild hybrid vehicles, which would reduce oil consumption by four billion gallons. According to the U. S. Department of Energy, the impact of not burning that much fuel would equal carbon sequestration of a forest the size of New York State or all of Iceland. In other words, 48-volt mild hybrids are a pretty respectable stepping stone on the way to full vehicle electrification.
It also means carmakers can breathe a little easier as they scramble to meet fuel economy deadlines. A group of angst-ridden OEMs recently sent a letter to China pleading for mercy in electric and hybrid car sales quotas. China is eyeing regulations for automakers to sell enough electric or plug-in hybrid vehicles to generate “credits” equivalent to eight percent of sales by 2018, 10 percent by 2019 and 12 percent by 2020. The letter states such quotas would be impossible to meet and would “severely disrupt their business.” It was signed by the American Automotive Policy Council, European Automotive Manufacturers Association, Japan Automobile Manufacturers Association and Korea Automobile Manufacturers Association. But by adopting 48 volt systems, carmakers might actually be able to meet these quotas.
What’s in the not-so-secret mild hybrid sauce?
A 48-volt system simply adds a few components to an ICE and 12-volt battery system. The most common set-up usually consists of three components – a belt alternator starter unit (BAS) or a motor generator unit (MGU) or belt-driven starter generator, a DC to DC converter, and a higher voltage 48-volt lithium ion battery pack (usually in the trunk).
Why 48 volts? Because anything above 50 volts is considered potentially lethal! Getting zapped by 48 volts is no picnic, but it won’t kill you. Also, although a higher voltage battery could offer more capability, it would require expensive shielding, conduits and connectors. So a lower voltage arrangement keeps costs down.
According to Mary Gustanski, Delphi vice president of engineering, a 48-volt battery can provide four times the onboard juice of a 12-volt battery, to power electrical accessories like fans, pumps, electric power steering racks and compressors. It can also help with increasingly pervasive stop-start systems, by using the alternator as a starter. The wire harnesses on these designs are lighter and smaller, for further efficiencies.
Drivers will appreciate that there’s no sacrifice in power. The Delphi E-charged Honda Civic provides up to 25 percent low-end torque and 30 percent better acceleration. A typical four cylinder car with a turbocharger, traditionally driven by exhaust gas, has the performance of a V6 without a turbo. Drivers complain about “turbo lag,” that gap when turbo spools to up 1000,000 to 200,000 rpm to force more air into the engine. But the E charger is driven by an engine-powered belt, so there’s no lag.
Why hasn’t this been done before?
In 2007, General Motors launched a 42 volt Belted Alternator Starter mild hybrid system on the Saturn Vue Green Line, as well as the Chevrolet Malibu. This system
recovered energy during braking and acceleration, but wasn’t efficient enough to justify the extra cost, especially as brawnier six-speed transmissions came along.
Even as far back as 1990, German automakers wanted to triple electrical systems to 36 volts, to accommodate more powerful electrical accessories and lighter wiring harnesses. But this would have meant complicated and costly engineering, especially with lighting, and ultimately failed.
However, none of this means that the 12-volt system or internal combustion engine is DOA, as The Economist suggests. That’s because the 12-volt battery and the ICE is part of the 48-volt design. Let’s not forget that the industry standard life cycle of any car is seven years, and it takes 20 years to turn a fleet over. Fortunately, the 48-volt mild hybrid system will ultimately make the transition to electrification much easier.