It’s been almost 14 years since Mike Dale wrote about the use of higher voltages in vehicle electrical systems in the No-vember 2001 issue of Motor. Back then, the fi rst-generation

Prius had only recently been offered for sale in the U.S. for the fi rst time. Predictions were that the fi rst 42V sys-tems would be available on nonhybrid vehicles as early as 2004 to 2006, and 2010 for full-bore mass production. Dual-voltage setups with both 12V and 36V batteries would come first; true 42V systems would come later in the program.

Just like the flying cars and per-sonal jetpacks we were also promised

many years ago, things didn’t exactly work out as predicted. The fi rst thing you may have noticed is that we were talking about 42V electrical systems back then. That fi gure was arrived at by multiplying a conventional electri-cal system’s nominal charging rate of 14V by a factor of three.

Today, 48V has replaced 42V as the new higher voltage standard. This is still below the 50V threshold that’s sup-posed to represent a signifi cant electri-cal shock risk. Perhaps the increase to 48V is a byproduct of infl ation. Regard-less, the main reasons for making the change have remained the same.

As vehicles have incorporated a growing number of electrical systems,

the demand for power has also grown. Things like electric power steering motors draw large amounts of current when they’re in operation. It was orig-inally believed that the conventional 12V system wouldn’t be capable of producing enough current to power these larger consumers, along with all of the other electronics on board. Even if a big enough alternator could be constructed to keep everything happy, extra large wiring would also be needed to assure an adequate supply of current to the big consumers.

Heavier wires in the wiring harness mean greater cost—anathema to au-tomakers. Increasing the operating voltage offers a simple solution. By

30 August 2015

NUMBERS GAME:48V SYSTEMS SHOW POTENTIAL

BY KARL SEYFERT

Once seen as a remedy for tapped-out 12V vehicle electrical systems, 48V systems have shown great potential

in new applications that boost engine performance, while reducing fuel

consumption and emissions.

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tripling the voltage, the relationship between voltage and current for a con-stant power dictates that the current falls to one-third the previous value. Wire gauges needed for automotive harnesses are chosen mostly on the basis of the current they must carry. Going to 48V makes it possible to re-duce the size, weight and expense of the harness and connector assemblies, and to increase the use of ribbon ca-ble assemblies, which are smaller and easier to produce than conventional wiring harnesses.

The design and manufacture of more efficient electric motors have allowed the automakers to forestall the transi-tion to higher electrical system voltages, which is why things haven’t followed the predictions of the previous decade. But change is still on its way; it’s just go-ing to arrive in a different guise.

As fuel economy standards contin-ue to rise, automakers must look for every possible way to make a gallon of gasoline go even a tiny bit further. One of the techniques being em-ployed is to convert systems that were previously driven by the engine to electric power. That way, the engine can concentrate on moving the vehicle forward, while electric systems handle everything else.

Think about some of the ener-gy-wasters that were previously, and in many cases still are, driven by the engine. These include the belt-driven water pump, power steering pump and air conditioning compressor. In the days before fuel injection, even the fuel pump was driven by the engine. Inside the engine, the oil pump also saps some energy from the engine.

All of these devices have at least one thing in common: Even though their functions are normally needed only on an intermittent basis, they’re powered by the engine on a full-time basis. In some cases, engine efficien-cy could actually be improved by not running them. The water pump, for example, not only adds no value on cold start-up, it actually slows engine warm-up and consumes power from an idling engine.

Electrifying the front-end accesso-ry drive (FEAD) loads on the engine eliminates the need for drive belts, which offers vehicle manufacturers additional advantages in terms of

31August 2015

engine and body packaging. Electri-fication means FEAD loads can be mounted anywhere there’s available space. For example, an electric a/c compressor could just as easily be lo-cated in the trunk or under the dash. Electric power steering eliminates the need for a pump and hoses, as the electric motor can be mounted direct-ly to the steering rack.

Even at a higher operating voltage, it takes engine power to run the spe-cial alternator to generate the elec-tricity required to operate these elec-trically powered devices. It wouldn’t make sense to make the change, and end up losing efficiency instead of gaining it. The primary savings are due to the reduced amount of time the electrically powered pumps and ac-cessories actually operate. Additional savings come from the improvement in efficiency of new integrated starter/alternator designs.

Where Are We Now?We already know that things haven’t worked out exactly as planned in regard to high-voltage electrical systems. That’s why we thought it would be interesting to get a better understanding of where we are today, and where we’re likely to be in the future. Several vehicle manufacturers and suppliers have developed systems that rely on higher voltages for their operation. We’ll devote the remainder of this article to describing these systems.

The Audi RS 5 TDI competition concept is based on a technical con-cept car presented in summer 2014 on the 25th anniversary of the TDI en-

gine. The car’s 3.0 TDI biturbo is pow-er-boosted to 435 hp. Its maximum torque rose to 590.0 ft.-lbs. A core in-novation with this biturbo V6 TDI is that, in addition to its two exhaust-gas driven turbochargers, it also utilizes an electrically driven compressor.

The electrically driven compressor utilizes a 48V electrical subsystem as its energy supply source. This auxiliary subsystem is a key component of the Audi electrification strategy. It enables rapid transfer of large amounts of elec-trical energy, and so it’s well suited for use with the electrically driven com-pressor. Both of these technologies will soon go into series production.

The electric compressor ensures faster buildup of charge pressure at low engine speeds and significantly improves engine response as well as sprint performance. It utilizes a small electric motor with 7kW of power that drives a turbine to a speed of up to 72,000 revolutions per minute within 250 milliseconds; this means that it builds up its charge pressure inde-pendent of the energy available in the exhaust gases.

This technology reacts very quick-ly; a typical exhaust-gas-driven tur-bocharger takes two to three times longer to reach a comparable turbine wheel speed. Thanks to its electrically driven compressor technology, high charge pressure is available quickly in any driving situation.

Valeo is supplying the electric com-pressor to Audi. The company refers to it as an electric supercharger, al-though the effect is the same. It en-ables the downsizing of combustion

By Karl Seyfert

Once seen as a remedy for tapped-out 12V vehicle electrical systems, 48V systems have shown great potential

in new applications that boost engine performance, while reducing fuel

consumption and emissions.

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The Audi RS 5 TDI combines two conventional turbochargers with a 48V electric compres-sor. At 12V, the compressor would not be powerful or efficient enough to make a differ-ence, but at 48V, it provides nearly instantaneous response, eliminating turbo lag.

Charge Air Path Without the Use of the Electric Compressor

Charge Air Path With the Use of the Electric Compressor

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32 August 2015

Numbers Game: 48V Systems Show Potential

engines, an important factor in reduc-ing fuel consumption. In a 12V archi-tecture, fuel savings of 8% to 10% are reachable. When coupled with a Valeo energy recovery system, the electric supercharger has the energy required to function while reducing the vehicle’s fuel consumption (by 15% to 20% in the standard European Drive Cycle).

Ricardo’s ADEPT project was launched in 2013 to demonstrate the potential for 48V-based intelligent elec-trification in delivering full hybrid-scale fuel efficiency from a highly cost-ef-fective package. Based on a Ford Fo-cus, the ADEPT prototype incorpo-rates a 48V electrical architecture, a SpeedStart 10kW belt integrated start-er-generator (later to be upgraded to 12.5kW) and a turbine integrated ex-haust gas energy recovery system (TI-GERS), both switched reluctance ma-chines supplied by Controlled Power Technologies (CPT) and an advanced lead-carbon battery pack provided by the European Advanced Lead Acid Battery Consortium (EALABC). The supporting systems for electrical and vehicle integration include a 12V to 48V DC-to-DC converter and a Ricar-do hybrid supervisory controller.

Engine downsizing through charge boosting is a well-recognized means of improving internal combustion engine fuel efficiency, by increasing the pro-portion of the drive cycle at which the powertrain operates within or close to

the region of peak fuel efficiency of its operating map. An effective limitation on downsizing, however, is the deliv-ery of acceptable driveability charac-teristics and launch performance. In the earlier “HyBoost” project based on a similarly sized gasoline vehicle, Ricardo and its partners demonstrated fuel economy benefits equivalent to a full hybrid—but at a projected cost premium of less than a diesel. With the ADEPT project, the research team aims to demonstrate a powertrain with uncompromised performance and less than 70g/km CO2 emissions as mea-sured over the European Drive Cycle, but at a projected production cost sig-nificantly lower than a comparable full hybrid electric vehicle.

The ADEPT concept features in-

telligent electrification to deliver a very low CO2 mild-hybrid diesel C-segment vehicle. In addition to the 12.5kW 48V starter-generator, AD-EPT also incorporates a 48V low-cost advanced lead-acid battery, 48V elec-tric coolant pump and 48V electric oil pump. Like the system on the Audi RS 5 TDI, a 48V electric turbine is lo-cated downstream of a standard turbo-charger to capture exhaust waste heat for reapplication as crankshaft torque. Regenerative braking energy is cap-tured for further fuel savings.

Valeo’s Hybrid4All combines a con-ventional combustion engine with a low-power electric engine, generat-ing up to 15% reductions in fuel con-sumption and halving the cost per gram of CO2 saved compared to a hybrid on the market today. It deliv-ers system functions including brak-ing energy recovery, electric motor boost and extended start-stop, and it’s suitable for all types of vehicles, par-ticularly those in the entry-level and midrange segments.

The Hybrid4All architecture is based on a low-voltage 48V integrat-ed inverter Belt Starter Generator (i-BSG). The i-BSG electrically as-sists the internal combustion engine and has three optional mounting posi-tions—on the accessory drive, behind the gearbox or between the engine and the gearbox.

This solution integrates the compa-ny’s iStARS start-stop system, which automatically shuts off the engine when the vehicle is at a standstill. It also incorporates regenerative braking and torque-assist (boost) functions,

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Ricardo’s ADEPT system combines a 1.5L diesel engine with a 48V starter-generator. A 48V water pump is combined with a 48V oil pump to reduce economy-robbing engine loads. An advanced 48V lead-acid battery pack stores regenerative brake energy and is combined with other vehicle systems to optimize fuel economy, emissions and performance.

48V Oil Pump

48V Advanced Lead-Acid

Battery Pack

48V Water Pump

Charge Air Cooler

EGR Cooler

48V, 12.5kW Belt Starter Generator

pSCRLNT cDPF

48V E-Turbine

1.5L Diesel

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The Valeo Hybrid4All system provides considerable power (up to 15kW peak) even though its size is equivalent to a conventional alternator. High torque is immediately delivered at start-up, compensating for loss of power in smaller engines when accelerating.

Powertrain Control Unit

14V BatterySensor

BSG 8-12kW/55Nm Peak With Integrated Inverter

DC/DC Converter (60V/12V, 2kW)

48V Energy Storage (200-600Kj)

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enabling combustion engine downsiz-ing and gearbox down-speeding.

Hybrid4All is compatible with die-sel and gasoline engines, and the sys-tem will enable automakers to meet the future European target of 95g of CO2 per kilometer to be introduced in 2020.

The electrification of the power-train—from fuel-saving start-stop functionality to all-electric drive—plays one of the key roles in reduc-ing fuel consumption and emissions. However, up to now, within this spec-trum of electrification possibilities, there has been a huge gap between the reasonably priced 12V start-stop systems and the more expensive hy-brid solutions with voltages from 110V.

Continental intends to close this gap with its 48V Eco Drive system. The new hybrid technology can be easily integrated into the architecture of conventional-drive vehicles, yet, at the same time, provide features that up to now have been found only in high-voltage hybrid systems—such as switching off the combustion engine while driving (“sailing,” “coasting”), ex-tremely quick and comfortable engine start-up and efficient brake energy re-covery (recuperation).

The new Continental technology will go into production with European car manufacturers for the first time in 2016. The Continental demo vehicle is a standard compact car with a 1.2L gasoline engine fitted with the 48V Eco Drive system. Under real condi-tions in a mainly urban environment, the manufacturer claims a 21% fuel savings compared to the standard ver-sion with a 12V start-stop system.

The Eco Drive system supplements the 12V supply and consists of three components—an electric motor with integrated inverter which replaces the generator, a 48V lithium-ion battery and a voltage converter (DC-to-DC converter) for exchanging energy be-tween the two on-board power sup-plies. Major intervention in the vehicle system is not necessary, since a 48V supply requires no contact protection measures. These are prescribed only with voltages from 60V upwards, ac-cording to the manufacturer.

The electric motor in the Continen-

tal demo vehicle is a belt-starter gener-ator with integrated power electronics. The electric moto—which can be built directly onto the transmission as an op-tion—supplies the 48V on-board power supply, provides electromotive support for the drive system (during e-boosting and coasting) and starts the combustion engine extremely quietly and twice as fast (in less than .2 second).

The 48V on-board power supply also offers numerous advantages in terms of further energy-saving mea-sures and new electric features. Elec-tric consumers with a larger energy re-quirement can thus be operated more efficiently at 48V. In addition, this high efficiency allows 48V consumers to be built lighter, reducing vehicle weight. And as far as larger vehicles in partic-ular are concerned, where the con-ventional 12V on-board power supply is already reaching its performance limits, new features such as an electric a/c compressor or electric rolling sta-bilization (active restriction of lateral tilting when the vehicle is cornering) are extremely difficult to achieve with-out additional voltage.

With the 48V Eco Drive system, recuperated energy is stored in the Li-ion battery and makes a key con-tribution to fuel reduction. The new 48V hybrid system also reduces fuel consumption by extending the start-stop functionality to driving mode; the combustion engine is switched off for

almost a third of the time in total. The 48V supply supports the 12V on-board power supply and ensures that all the electric features are maintained. In contrast, conventional 12V start-stop systems often have to restart the en-gine in order to operate energy-inten-sive consumers (such as the a/c unit) or do not switch the engine off at all when the vehicle is at a standstill.

The 48V Eco Drive system switches the combustion engine off as soon as the driver takes his foot off the accel-erator pedal. This disengages the pow-ertrain from the engine, so the vehicle rolls freely. The system switches to this coasting mode not only in urban traffic, such as when approaching traf-fic lights, but also at higher speeds. During an average trip, the system is in coasting mode around 20% to 25% of the time, which alone saves up to 8% of fuel.

In sailing mode—with the com-bustion engine switched off, as in the coasting mode—the electric motor keeps the speed of the vehicle con-sistent for a brief time. And during e-boosting the electric motor supports the combustion engine during acceler-ation, which can compensate for turbo lag, for example.

Whether the combustion engine is switched off during coasting, the elec-tric motor provides support in e-boost-ing or sailing turns into coasting, the driver hardly notices anything during

34 August 2015

Numbers Game: 48V Systems Show Potential

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Continental’s 48V Eco Drive systems offers many of the advantages of a more expensive high-voltage hybrid system, at a lower cost. In addition to familiar start-stop functions when the vehicle is at a standstill, engine switch-off under certain driving conditions gives the engine a break while improving fuel savings and reducing emissions.

Electrical2.indd 4 7/21/15 9:03 AM

the transition between the driving modes. This also applies to starting the combustion engine after the switch-off phases, which takes place very quickly, quietly and with very little vibration.

The central element of the Schaef-fl er system is a compact 48V electric drive module that includes a clutch and planetary transmission, which can be placed on the front or rear ax-le. This drive module paves the way for economical hybridization. The low-voltage design reduces the costs and outlay compared to high-voltage solutions with their associated require-ments. This hybridization allows sig-nifi cant advances to be made in terms of drive effi ciency, as the 48V electric system opens up operational possibili-ties that were previously the exclusive domain of vehicles with high-voltage hybrid components.

Even with a 48V system, a signifi-cant level of energy recuperation can be achieved; i.e., a high proportion of the energy released when the vehicle decelerates can be recovered and fed back into the battery. This recovered energy can be used for the supplemen-

tary electric drive, which in turn directly reduces the vehicle’s fuel consumption. In addition to energy recovery, a gener-ator with an output of up to 12kW can also be used to drive the vehicle.

This provides options including so-called crawling—electrically pow-ered driving in dense inner-city traf-fic, as well as moving off, driving at low speeds, and parking using electric power. Electric boosting during start-ing and so-called electric sailing—a driving mode in which the electric motor ensures constant speed while the internal combustion engine is

switched off—make a positive contri-bution in terms of fuel consumption and emissions, however.

The electric drive, which has an out-put of up to 12kW, acts as the hybrid vehicle’s sole source of power when crawling, i.e., in stop & go traffi c. The electrically generated propulsion of Schaeffler’s 48V drive module is also suffi cient for driving in residential areas, parking garages and other low-speed driving situations. This is also true of the sailing mode. The electric drive as-sists the internal combustion engine by providing additional torque, e.g., when moving off from the traffic lights—a function referred to as boosting.

Battery manufacturer Johnson Controls has introduced a 48V Li-ion micro hybrid battery for use in a dual-voltage system involving a 12V starter battery and a 48V Li-ion bat-tery that enables optimization of ener-gy generation and consumption. The company claims its technology has the potential to provide up to 15% fuel savings in vehicles.

The 48V battery is designed with the capacity to quickly capture en-ergy from braking and can support higher loads such as a/c and active chassis technologies. The 12V battery will continue to provide power to the vehicle starter, interior and exterior lights and entertainment systems such as radios and DVD players.

You may have noticed that many of the systems we’ve described have seen their fi rst implementation in Eu-rope, perhaps due to more stringent fuel economy and emissions stan-dards already in place or due for im-plementation there. Manufacturers claim they could move quickly to the U.S., with mass adoption by 2020.

That’s well behind the original pre-dictions, but be assured, these systems will be coming your way. Just as you’ve grown familiar with and received training on hybrid vehicles over the past dozen or so years, you’ll need to gear up for 48V systems as well. These systems may not have the scare factor of the higher voltages found in hybrid systems, but they’ll still demand your respect and attention.

36 August 2015

Numbers Game: 48V Systems Show Potential

This article can be found online at www.motormagazine.com.

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The compact design of the Schaeffl er cylin-drical electric drive module means it can eas-ily be combined with a conventional power-train, so it can be integrated into the architec-ture of the vehicle without having to reduce the volume of the trunk or the fuel tank.

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