For the longest time we’ve known the most common method of forced induction to be either supercharging or turbocharging. Supercharging uses a compressor that’s powered by the engine crank while a turbocharger uses the kinetic energy harvested from the flow of exhaust gas to do the same thing.
A company called Controlled Power Technologies is offering something new called a VTES, or Variable Torque Enhancement System. It’s basically an electric supercharger. There are alot of people who try to install fans in the middle of the car’s intake tract and try to call it a supercharger, but this is a proper compressor that can spin independently of crank speed at rotational speeds of up to 70,000rpm.
CPT has installed it on various test systems including a 1.2 litre turbocharged engine. The VTES electric supercharger is meant to complement the existing turbo. CPT reported an increase of over 50% in torque at engine speeds below 3,000rpm. I guess what it does is compensate for any turbo lag there is at low engine RPMs, allowing the turbocharger to be larger than it normally would have needed to be to spool up that quickly.
VTES electric supercharger on an AVL demo engine
One way that VTES has been positioned by CPT is an alternative to mild hybrid systems, like the units installed in the Honda Civic Hybrid and the Kia Forte LPI Hybrid. According to CPT senior engineering manager Mark Criddle, one method that car makers have been using to boost performance of downsized engines is integrating an electric motor between the engine and transmission to create a mild hybrid, but this is a costly exercise and can be difficult to package within a small car’s front wheel drive engine bay.
The VTES system can provide a viable low cost micro-hybrid solution, significantly increasing an engine’s air charge density over the critical first 10 combustion cycles of a low speed transient. The supercharger’s speed can increase from zero up to 70,000rpm in less than 1/3 of a second. Adding 25kW at the crank at low engine speeds via VTES costs significantly less than a 25kW assist electric motor. It uses standard 12V power.
Left: 1.2L turbo inline-3 direct injection engine
Right: 2.0 litre turbo inline-4 direct injection engine
It will be featured in the HyBoost system, a project led by Ricardo and supported by the UK government’s Technology Strategy Board. It will also be used in an engine project by AVL. AVL is an Austrian-based independent engine developer. The 1.6 litre engine that you can find in the Chery Tiggo here in Malaysia was developed by AVL and they are actually pretty good. Some time ago there was news that Fiat was interested in using Chery’s AVL-designed ACTECO family engines in Fiat cars in China.
AVL previously showcased a demonostrator engine using CPT’s electric supercharger. A 2.0 litre inline-4 direct injection engine was equipped with a regular single-scroll wastegated turbocharger, and CPT’s VTES electric supercharger. It resulted in 200 PS and 400Nm of peak torque. The engine also has auto stop-start and smart alternator control. They installed it into a Volkswagen Passat and the resulting CO2 emissions were 159g/km. Comparatively, the Passat’s original 200 PS 2.0 TSI petrol and 170 PS 2.0 TDI diesel engines gave out 194 g/km and 165g/km respectively.