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CPT developing 48-volt electric supercharger for micro-mild hybrids

Controlled Power Technologies (CPT) is developing a 48-volt version of its 12 volt electric supercharger based on its variable torque enhancement system known as VTES. (Earlier post.) The higher-voltage variant will support moves by European vehicle manufacturers announced earlier this year to introduce 48 volt passenger vehicle power networks to help meet the requirement for lower fuel consumption and CO2 emissions.

At 48 volts, a VTES electric supercharger will transform 7kW of battery power into a highly boosted charge of air for downsized gasoline and diesel engines. Unlike crankshaft-driven superchargers and exhaust-gas-driven turbochargers, an electric supercharger is mechanically decoupled from the engine, meaning it can deliver the air almost instantaneously into the engine—spinning up to 70,000 rpm in less than a third of a second.

Even with the higher transmission gearing adopted by manufacturers to reduce CO2 emissions and particularly at the lowest engine revs, the instant additional torque when the driver needs to accelerate these smaller powertrains from low engine speeds is already very beneficial at 12 volts.

Electric supercharging at 48 volts extends that envelope of torque enhancement. It’s an efficient way of using 7kW of stored electrical power to deliver not less than six times that at the crankshaft. In other words adding a useful 42kW boost for low speed overtaking and hill climbs. Depending on the turbocharged engine system optimisation the boost could be as much as much as 70kW or 10 times the instantaneous power extracted from the batteries or supercapacitors.

The torque response of these future VTES equipped vehicles will be equivalent to the best mass market vehicles on the road today. There will be no torque deficit or other tradeoffs from essential engine downsizing and higher gearing, which now dominates the development of internal combustion engines. If anything their low speed performance will be even better, while still delivering very significant fuel economy benefits and CO2 reduction.

—Guy Morris, CPT’s engineering director and chief technical officer

Micro-mild hybrids. CPT argues that currently the most cost-effective solution for reducing CO2 emissions is modular micro-mild (MM) hybrid technology, based on highly boosted and radically downsized gasoline and diesel powertrains. For further CO2 reduction and economies of scale the automotive industry should also press ahead with the standardization and implementation of the proposed 48 volt vehicle power network being championed by some European vehicle manufacturers.

CPT foresees a new generation of MM hybrid vehicles with radically downsized engines featuring transient electric boosting as a more effective hybrid alternative to the mechanical supercharging and/or twin turbo-charging systems in use today.

For a 15-25 percent reduction in CO2 emissions using micro-mild hybrid technologies we have established an incremental cost to the manufacturer of between €750 and €1500. This compares favorably with the 8-20 percent typical of CO2 emissions benefit offered by mild hybrids, full hybrids and plug-in hybrids, at a much higher manufacturing on-cost of between €1,600 and €10,000.

Our modular technology is very scalable and also well suited to higher voltages, but currently the most customer benefit is delivered through the optimisation of micro-mild systems. CO2 reduction across a manufacturer’s entire vehicle range requires a comprehensive strategy, and this means delivering customer value in all segments of the car market.

—Guy Morris

LC Super Hybrid technology demonstrator. CPT’s production-ready VTES technology has already been incorporated as a 12 volt system in its LC Super Hybrid technology demonstrator. The company has commissioned AVL to build the demonstrator, which is currently undergoing final shake-down trials in Austria in readiness for evaluation by vehicle manufacturers. Following this initial assessment by carmakers, the vehicle will then be re-built with a 48 volt electrical system. The project is being supported and funded by the Advanced Lead Acid Battery Consortium (ALABC).

The demonstrator will improve significantly on the energy efficiency of a gasoline-engine variant of the VW Passat. With performance similar to that of the 1.8 TSI and 2.0 TDI models, but even lower CO2 emissions and fuel consumption than the current production 1.4l TSI BlueMotion model, the CPT/ALABC demonstrator will provide carmakers with real world confirmation of the potential for this new class of MM hybrid vehicle, according to CPT.

The MM hybrid concept, which was first proposed at the AVL conference a year ago, combines CPT’s modular VTES electric supercharger and SpeedStart stop-start technologies in a state-of-the-art yet affordable family sized vehicle. The LC Super Hybrid validates that concept and will demonstrate significantly reduced CO2 emissions combined with excellent performance at relatively low cost compared to full hybrid and range-extended or plug-in HEVs. ALABC carbon-enhanced lead-acid battery designs complement the low voltage technology helping to maximise energy recuperation during deceleration, fully realizing the potential in our stop-start and engine boosting technologies by enabling high power generation and electrical energy recovery as well as outstanding torque response.

—Guy Morris



Weight and cost are another big factor in 48 volt electrical systems; the required wire cross-section is 1/16 of that of a 12-volt system carrying the same power. Harnesses get smaller and more flexible.

Standby power demands are another issue. Most 12-volt modules use linear regulators to power their electronics' key-off functions. At 48 volts, both the power demands on the battery and the heat dissipation in the regulators skyrocket. This is going to require switching regulators, and perhaps one or more buses just for keep-alive power. It would be an opportunity for the standby systems to go down to 5 volts or even 3 volts for these functions.

As for electric supercharging, add a TIGERS on the exhaust and the compressor demand is more than supplied. The engine can even be back-fed with excess power from the turbine through a motor-generator.


I've always been a big fan of this concept.

"Harnesses get smaller and more flexible"

I'd imagine people working in vehicle design, assembly, and maintenance are huge fans of this. Vehicle wiring is a quiet crisis.


I couldn't agree with you more. Whatever electrical losses such a system would incur would be more than offset (IMO) by reduced pumping losses when the engine as at a low load (which is most of the time), reduced crankshaft drag from removing the alternator, and improved packaging.


Does this replace or step up part of the 12V starting/accessories system? The electronics may be cheaper than a present high temperature turbo back end.

Anyway, driving on a small car on an economical 60 hp ICE engine, but instantly having another 60 hp for merging/passing/fun sounds good.


A light, very high efficiency, low cost DC to DC controller could easily supply all the various voltages required for on-board gadgets and ancillaries. Eventually, all gadgets/ancilaries, with the exception of the main e-drive motor could operate with 48 VDC directly from the battery.


I agree that it would be nice to make all ancillaries electric, including AC compressor, as you often propose, provided they don't cost too much.
I did a search to find what power is needed for an AC compressor, and found this, in a study of a DOE agency (from year 2000):
" The peak air-conditioning load of 3000 W of electric power (in addition to the base electrical load of 500 W) reduces EV range over SC03 drive cycle by 36%. An electrical air-conditioning load of 1000 W, which might meet steady-state air-conditioning requirements for a small sedan, reduces SC03 range by 16%. Peak air-conditioning load, 3000 W of electric power, increases SC03 HEV fuel use by 57%. An electrical air-conditioning load of 1000 W, which might meet steady-state air-conditioning requirements for a small HEV sedan, increases SC03 fuel use by 16%."

Look at the values of 1 kW and 3 kW. It would require separate e-motor, which would need to use perm. magnets to be compact and integrated inside compressor.
The issue is COST, especially for small cars, econoboxes. If belt driven, e-motor is not needed, just a clutch. Also those compressors would probably break down more often (extra motor and inverter).


If I can ask this:
To avoid electric AC compressor in hybrid cars, would it be possible to have a somewhat larger container/radiator, well thermically isolated, using some deeply cooled liquid, so that it could, when cooled enough, provide enough "cooling energy" to cool the car cabin space for a period of 5-10 min, while engine is shut down. How big would it need to be?
It may require a bit larger compressor, belt driven, not electric, and would often help engine to work at higher load, ie more efficiently.
Even cars equipped with stop-start system could use a variation of this, perhaps it's already being used, I don't know.


Why would you want to avoid an electric A/C compressor? The engine-mounted compressor requires leaky flexible hoses and creates headaches with e.g. performance at low and high engine speeds. Even GM's BAS II system can supply 15 kW, more than enough to run a 3 kW compressor on top of everything else in the car.

The idea of a "cold battery" is interesting. It's quite feasible to freeze water, but supplying, say, 6 kW of cooling power for 10 minutes would require almost 11 kg of ice. That's a significant bump in the vehicle weight, plus around 13 liters of volume for the ice and its enclosures. Using that weight budget for more battery might be a better deal; I haven't crunched the numbers, so I can't say for certain.

One thing is for certain: if you have an electric A/C and the car is plugged into the grid while parked, the car can be pre-cooled without burning any fuel to do it.


The reason I would want to avoid an electric A/C compressor is the extra cost of electric drive (2-3 kW). Perhaps I was wrong. Actually Honda Civic Hybrid/Accord (IMA) use(d) hybrid AC system, so there should be some reason for not being 100% electric.

An internal electric motor is added to the air-conditioner, so it can be powered by either the engine, an electric motor, or both. At a stop, the compressor powered by the battery keeps the cabin cool. An additional compressor that is powered by the petrol engine also engages if rapid cooling is required. When the interior temperature is stable, air conditioning is provided by the battery solely.
In the first Civic hybrid, if the air conditioning was on and the econ button was not engaged, the engine wouldn't shut down. This latest hybrid solves that problem by adding an electric-motor-driven portion to the A/C compressor. So, at a stop, the electric compressor keeps the cabin cool.


2005 Honda Accord Hybrid Sedan hybrid air conditioning system, which uses air compressors powered by both the gasoline engine's drive belt and IMA electric motor
..and provides power to the dual scroll hybrid A/C compressor used in the Accord's dual zone hybrid automatic air conditioning system...


I was in the industry when the first 42-volt electrical system proposals were going around, and one of the explicit goals of the changeover was to convert engine-driven accessories such as power steering and A/C over to electric drive. It's expensive, but has big advantages. If it's going to be done to run electric supercharging, the rest follows naturally.

Electric A/C means that both the flexible hoses and the compressor shaft seal can go away. Those are two major avenues for refrigerant loss. This doesn't directly benefit either fuel economy or cost, but there are regulatory benefits. If it allows the A/C system to be converted to isobutane a whole pile of things get cheaper and easier too. A system containing a few ounces of isobutane is no fire threat compared to the liquid fuel supply, and isobutane is chemically tractable and dirt cheap.

Begin to see how these changes cascade?


I believe the freon has to be replaced in either the Volt or the Leaf every 100k miles or 10 years.. and both use electric compressors.. must be a special refrigerant. Not sure if the Leaf still uses rubber hoses..


"This is going to require switching regulators,"

added to the electric motors and you have such an RFI nightmare...I hope they use very good error correction and noise suppression techniques when communicating between sensors and the ECU.

Stand a good chance of making police/ambulance/fire truck two-way radios have poor performance with all the noise. Hope they design such things so that the fundamental frequency, harmonics, and products are well away from the communications VHF and UHF bands. Hate to have the receivers desensed when they have an emergency call trying to come in.

They'll need to do more than just comply with part 15 for is atypical to design around radio systems and since the power would be low relative to a purpose built transmitter the receive problems may not be realized immediately until someone actually puts a spectrum analyzer in the cab of a vehicle to see what is going on when some of these systems activate (if problems arise).

And no, cellular phones are not the answer.


Resistance is futile.

BEVs already have all electric ancillaries including AC and heating. Well designed ultra high efficiency (SEER 26+) inverter type heat pumps would use a lot less than 1KW (continuous) to keep a 105 cu. ft. cab at 22C to 25C year round. The price of those units are well under $1000 and probably less the current mechanically driven AC units.

Many Asian factories could turn them out for less than $500 for orders over 1,000,000/year.

Being able to remotely control the on-board heat pump and get a head start on the vehicle cab comfort level would be appreciated by many, specially on very hot or very cold days. A roof top high efficiency solar cell could supply the energy required.


By some reason roof solar panels for automobile are inadequately expensive - factor 10x in comparison with household solar roof . Initialy I assumed that there no need of expensive power grid integration therefore automobile solar roofs should be cheaper. It seems to be oposit result. May be it should be standard then it gets cheaper.


Yes Darius, if all future HEVs, PHEVs and BEVs were equipped with standard 2/M2 to 4/M2 thin high efficiency solar cells, the cost should quickly go down by at least 4 to 5 folds. As many/most of the cars used to go to work are parked in the sun all day, it should be possible to get interesting free recharge, more than enough to cool or heat the cab a few minutes before leaving.

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