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Is This Your Electric Supercharger?

Peak boost in one-third of a second!

by Julian Edgar

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At a glance...

  • Serious engineering
  • Currently marketed at Original Equipment manufacturers
  • Massive increases in bottom-end torque
  • Can be used to spool-up an existing turbo
  • Petrol and diesel applications
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They’ve been talked about for years but the reality has never hit the showroom floor – but here, finally, is perhaps your new electric supercharger.

Called Variable Torque Enhancement System (VTES) and developed by UK company Controlled Power Technologies working in conjunction with AVL, the electric supercharger has real-world specs a million miles from the pretend units we’ve seen touted over the years.

It’s being aimed initially at Original Equipment suppliers and has specs that include:

  • 12V operation

  • Maximum boost of 6.6 psi

  • Maximum shaft speed – 70,000 rpm

  • Maximum mass airflow – 100 kg/hour

  • Time to reach maximum shaft speed – 0.35 seconds

  • Current draw – idle 1.5 amps, acceleration – 350 amps, steady state – 220 amps

  • Operating temps – minus 40 degrees C to plus 125 degrees C

Anatomy

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The electric supercharger uses a centrifugal compressor and a switched reluctance electric motor optimised for automotive applications.

The electric motor is brushless and uses electronic switching of the field windings. Most of the heat is generated in the stationary field windings - this allows straightforward cooling and provides a long bearing life. Should one phase fail, the multi-phase design also allows for limp-home capability. Finally, this design of motor has accurately known relationships between speed, torque and current (allowing intelligent driving) and can be operated across a wide range of speeds.

The control electronics uses switching MOSFETs with very low ‘on’ resistances, allowing smaller packaging and reduced need for heatsinking. The control of the unit is via a microprocessor, allowing easy calibration for a wide range of applications.

Click for larger image

The electric supercharger can accelerate very rapidly – at a rate as high as 400,000 rpm per second. However, perhaps more indicative of its on-road performance potential is its ability to accelerate from idle (which appears to be about 5,000 rpm) to 70,000 rpm in just over 1/3rd of a second!

Although working on a standard 12V bus, it appears that the supercharger requires a Valve Regulated Lead Acid (VRLA) battery to power it. However, this battery is likely to replace the original car battery.

Applications

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Because of the wide-ranging control strategies that can be implemented, the VTES electric supercharger can be used on a variety of engines.

On a small, naturally aspirated petrol engine of around 1.6 litres, Controlled Power Technologies (CPT) suggest a 40 per cent torque increase with no CO2 penalty (probably equating to no increase in fuel consumption) on the NEDC standard European test cycle.

But what about when the unit is fitted to a tiny performance engine? The sample 3-cylinder, 1.2 litre turbo engine developed 120kW at 6000 rpm. Then the VTES electric supercharger was added. The result was a 59 per cent increase in torque output at low revs, a 25kW power increase below 3000 rpm, and a potential decrease in NEDC driving cycle CO2 of 20 per cent.

The 0-100 km/h time dropped from 13.0 to 10.9 seconds and, showing the vastly increased flexibility, 70 – 100 km/h in sixth gear plummeted from 18 seconds to 11 seconds!

The graph for the 1.2 litre turbo + electric supercharger tells the story better than any words.

Click for larger image

Below 3000 rpm the fitting of VTES massively boosted the lower-rpm torque curve.

And on turbo diesels? As the graphs (below) show, CPC says the electric supercharger gives a torque increase and improvement in response better than moving from a single turbo to a twin turbo system!

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This is the bottom-end torque diesel engine comparison between the VTES electric supercharger plus one turbo, a twin turbo system, and a single conventional variable geometry turbo.

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The responsiveness to a sudden torque request (that is, when the driver mashes down their right foot) is even more impressive for the VTES electric supercharger working with a single turbo – the VTES providing stabilised torque literally seconds earlier.

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CPC also suggests that the quicker response of the electric supercharger to driver requirements can reduce the transient black smoke output that still afflicts many diesels. (One reason that diesels often seem sluggish in coming onto boost is the reduced fuelling needed to control smoke emissions. If the boost can be provided by the electric supercharger, the engine can be made more responsive without the smoke.)

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Finally with diesels, VTES can be used to pump clean and cooled exhaust gases, allowing greater use of Exhaust Gas Recirculation.

Current Draw

But what about the huge current draw of VTES – up to 350 amps? Apart from specifying the use of a Valve Regulated Lead Acid battery and also describing some potential breakthroughs that integrate super capacitors with lead-acid batteries, CPC isn’t clear as to where this massive power will come from. However, a clue can be found in a tech paper by the company that suggests VTES typically operates for periods of less than 2 seconds.

Remember, the company’s name for the product is Variable Torque Enhancement System (rather than “electric supercharger”) and for short-term use to bring a conventional turbo up to boost, or to cover a low-rpm torque hole, it seems reasonable that most on-road usage would be for less than 2 seconds.

That makes the current draw able to be satisfied by a largely conventional 12V system, especially one that uses a more powerful alternator.

When will see it?

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CPC has developed VTES as one of a suite of technologies to improve engine efficiencies. Another of the company’s products is an advanced Belt - Integrated Starter Generator (B-ISG - pictured here) that allows some hybrid capability to be added underbonnet to existing drivelines (and would also boost battery recharge current sufficient to easily run VTES).

By...

- downsizing the engine capacity

- adding VTES to boost low-speed torque

- using the B-ISG to add rapid engine restarting after automatic switch-off and provide regenerative braking capacity and give electric assist

...CPC expects to reduce CO2 outputs by about 25 per cent without altering real-world driving performance.

But from a clean and green performance driving perspective, increasing bottom-end torque by 50 per cent and at the same time rapidly spinning-up a conventional turbo could result in stunningly useable performance from very small and efficient engines.

Bring it on!

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