Over the last five years, it has become clear to carmakers and consumers alike that the slow progress in battery technology still plagues EVs, which therefore suffer a multitude of practical limitations. The battery pack’s size, weight, comparatively low driving range on a full charge and high manufacturing cost are the major challenges, but the most serious constraint is the battery’s inability to recharge in the same time it takes to refill a petrol or diesel car’s empty fuel tank. The few road going EVs currently available need to be plugged-in for several hours to get a complete “refill” and hit the road again. Compare that with the 10 to 15 minutes you spend at a service station – that includes paying at the cashier and, if it’s not too crowded, browsing a few magazines and buying some groceries.
So, the battle between internal combustion and electric power is far from over. In fact, it hasn’t really begun, with petrol/diesel engines still dominating the automotive industry through and through. While motorists await the elusive breakthrough in EV battery performance, user convenience and cost-effectiveness, “old-school” mechanical engineers beaver away in their laboratories, testing hightech internal combustion engines that bank on forced induction to deliver the goods. At the heart of internal combustion is, well, combustion, and optimising this complex thermodynamic process is key to increasing efficiency. Supercharging (i.e. Forcing in more air than the pistons can otherwise “ingest”) has the most profound effect on torque output. This has given engineers a golden opportunity to resize cylinder volumes and even downsize cylinder count.
A perfect example of this is BMW’snew-generation 1.5-litre 3-cylinder. It is essentially the automaker’s well-known3-litre inline 6-cylinder “cut” into half, with a single-scroll turbocharger boosting torque at all crankshaft speeds. Ready to be signed off, this prototype power plant has been fitted in a 1 Series hatchback for evaluation.
Tuned to deliver 178bhp and about200Nm, the test mule accelerated strongly, revved smoothly and sounded uncannily like BMW’s famed straight-6. Production versions of the 1.5-litre turbo 3-pot will offer between 121bhp/180Nm and 221bhp/270Nm, compared to 170bhp/250Nm from the 1.6-litre turbo 4-pot in the current118i. The upcoming 3-cylinder also has fewer moving parts, which means lower frictional losses and consequently higher operating efficiency. It will no doubt boast sparkling fuel economy and CO2 figures. This interesting new engine will go into the 1 Series, 3 Series and the company’s transverse front-drive models, i.e. the next Mini, coming soon.
Over in the Audi camp, there is another intriguing 3-cylinder in the works. Also displacing 1.5 litres, this experimental powertrain housed in an A1 supermini comprises two electric motors and a singlespeed transmission. An 116bhp/250Nmtraction motor is the default drive unit up to a speed of 130km/h. Thereafter, the petrol engine takes over, and because there is no conventional gearbox, the power delivery is perfectly seamless. So far, this setup sounds just like any hybrid today, but Audi calls it a Dual-Mode Hybrid for a reason.
The smaller 68bhp/210Nm electric motor functions primarily as the starter generator, powered by the engine whenever the battery charge is depleted. Electrical energy thus produced is supplied to the battery (to replenish it) and the traction motor to drive the A1. But the smaller motor can also assist the engine to boost performance.
On the road, the Dual-Mode Hybrid felt more like an EV than a typical hybrid, because the car runs on electricity most of the time. When the engine cut in, it did so without any noticeable change in driving behaviour, except for a slight increase in noise from the 3-cylinder. The whole system is rated at 174bhp, but the big news is the consumption and exhaust emissions claimed by Audi – 100 kilometres per litre and merely 23 grams per km.
Audi’s engineers have something else up their (lab coat) sleeves – an electric compressor for supercharging. This neat little device, incorporated with the intake plumbing, works by building up pressure immediately at low speeds, particularly during the lag period between engine idle and full turbo boost. The thing looks like half a turbocharger, since there is no exhaust gasdriven turbine coupled to it, with its function taken over by an electric motor that spins to maximum speed the instant it is switched on by the engine control unit.
It works remarkably well, at least in the prototype we drove. It’s a 3-litre turbo diesel, 313bhp/650Nm V6 A6, which is already a very quick saloon. A consolemounted switch allows the clever electric boost system to be deactivated, so we could experience the difference between “on “and “off”. In standing-start acceleration, the difference was significant, with the compressor totally eliminating initial lag and giving the A6 a clear advantage in the first few seconds of take-off. Apparently, within three seconds from a standstill, the electric-boosted A6 would be at least two car-lengths ahead of one without.
“Closing up” the traditional turbo lag-zone in this manner makes plenty of sense. Less sensible perhaps is to call it an Electric Bi turbo (cutaway below), which is what Audi has decided even though it is actually a combination of a single turbocharger and a single electric compressor. In any case, the installation requires few additional parts and the assembly appears to be elegantly simple.
The Electric Bi turbo could be easily applied to any turbocharged engine, for the purpose of boosting low-speed induction pressure and hence available torque just beyond idle speed. In fact, with the current generation of compact and reliable powertrains, the electric compressor could function on its own as a low-pressure, on-demand supercharger to raise the engine’s overall torque. And it would be far less costly than a belt driven “kompressor”.
Toying with new-age motors might be enjoyable for the technically inclined, but as Audi and BMW have demonstrated, it is also serious business
This article was written by Shreejit Changaroth, freelance writer for Torque.