The recent Navigant Research report Automotive Fuel Efficiency Technologies concluded that one of the main approaches to delivering better fuel economy for cars is to downsize existing engines but coax more power out of them. The principle of increasing air pressure at an internal combustion engine intake to produce extra power is well-established and is known generically as forced induction. The two main mechanical types of forced induction are usually defined as:
• Turbocharging, where the compressor is driven by exhaust gases; and
• Supercharging, where the compressor is driven directly off the engine crankshaft
Turbochargers are well known for being a relatively simple way to get more power from a small engine, but also have the disadvantage of lag because the maximum boost is not available until the engine speed is high. Superchargers can be set up to provide boost at low engine speeds, but they also use power when they are not needed, and so they can adversely affect fuel economy under normal driving conditions.
A third variant, electric turbochargers, now looks set to hit the market. An electric turbocharger offers an engine boost on demand without the lag of an exhaust-driven component or the physical drag that a supercharger places on the engine. The technology operates from electrical energy that is recovered by regenerative braking, and takes advantage of the fact that electric motors develop their maximum torque immediately from a stationary position.
The concept has been under development for some years, and the biggest challenge so far is to get enough usable power from a 12V electric motor. However, with the imminent rollout of 48V electrical subsystems for advanced stop-start systems (as discussed in detail in the Navigant Research report 48-Volt Systems for Automotive Applications), it will become practical to implement an electric turbocharger for the first time. Audi is the only manufacturer to announce a planned launch so far, but most other manufacturers are thought to be working on similar concepts.
French Tier One supplier Valeo is one of the first to offer a production-ready electric turbocharger. The company acquired the switched reluctance motor technology from U.K.-based Controlled Power Technologies in 2011. The motor is liquid-cooled and the 48V system needs additional power electronics and a bigger battery than normal, so there are additional costs to consider. Benefits include improved performance as well as better fuel economy, so manufacturers are expected to be able to charge a premium.
Conventional turbocharger suppliers are also developing electric products. BorgWarner offers electric turbocharging in its eBOOSTER system, which has been tested on both gasoline and diesel engines. Honeywell is another well-established supplier of conventional turbochargers, and is thought to be developing an electric version for introduction in a couple of years’ time. As is often the case, emerging technology stimulates innovation from brand new companies as well as established suppliers; one example is U.K.-based Aeristech.
Fuel efficiency is a key focus for automotive manufacturers that want to avoid financial penalties for missing emissions targets in the coming years in many countries around the world. Incremental improvements of 1%–2% may not be enough, so investing in technology that has the potential to deliver significant fuel economy increases without sacrificing performance or drivability may be money well spent. Electric turbocharging looks likely to be the first application that will launch 48V systems into series production, a shift brings with it many other benefits of electrification that will challenge hybrid technology at a much lower price point.
Tags: Advanced Transportation Technologies, Electric Vehicles, Emissions Regulations, Transportation Efficiencies
| No Comments »