We tend to take it for granted that cars just get steadily greener, consuming less fuel and emitting lower pollutant levels with each new generation. But engineers haven’t got magic wands. How do they keep making improvements, year after year?
In a short series of articles, I’ll look at the technical challenges associated with catalysts, stop-start systems, engine downsizing and other CO2 reduction measures.
Downsized engines are not just smaller engines replacing big ones. They’re smaller engines delivering the same performance as big ones but more efficiently, so they use less fuel. There are some pretty big engineering challenges in downsizing: the two biggest are matching the durability of a bigger, less highly strung engine, and matching the driving pleasure provided by the bigger engine.
Why is a bigger engine more satisfying for the driver? Because when you press the accelerator, it responds. Immediately. Smaller engines generate less torque, so they are boosted by turbocharging or supercharging to make up the deficit. Turbocharging is the more popular choice among manufacturers, but at lower engine speeds, such as when joining a roundabout, turbo lag often causes a small but disconcerting delay between pressing the accelerator and the engine responding.
Much of the engineering effort in downsizing has gone into making the low speed response as immediate as possible, pushing the boundaries of turbocharger design and achieving some success judging by the market’s response to Ford’s 1.0 Ecoboost models (Engine of the Year, 2012 and 2013).
Why isn’t supercharging more popular? Though it avoids the turbo lag issue, it’s very difficult to engineer a supercharger installation that delivers the necessary power boost at high engine speeds as well as providing instant response at low speeds. Several new technologies are being developed to allow large speed variations between the engine and the supercharger to address this issue. Electric drives, planetary gearsets and toroidal variators all have the potential to keep a supercharger spinning at the appropriate speed, regardless of engine speed.
The VW 1.4 Twincharger (Engine of the Year in 2009 and 2010) actually uses both a supercharger and a turbocharger in order to harness the benefits of both technologies but, ironically, is rumoured by Autocar to be phased out due to its complexity.
The second area of challenge is to make downsized engines as durable as their predecessors. The high output (both power and torque) achieved through boosting results in greater thermal and mechanical loads than would normally arise in an engine of smaller displacement. The search for efficiency also leads manufacturers to use smaller bearings and thinner oils, both drag reduction measures that reduce the margin of safety under extreme load.
The unsung heroes that save the day are the suppliers of specialist components, such as pistons and rings, cylinder liners, valve seats and bearing shells. Better design techniques, improved materials and coatings, and new manufacturing processes enable each new generation of components to withstand higher temperatures and heavier loads than their predecessors.
It’s always the finished car that grabs the headlines, but those impressive CO2 figures would not be possible without the steady progress made by the component suppliers; neither would the extended service intervals or the long operating life of today’s engines. As your mileage clicks past 100,000, or 150,000, you might just spare a thought for the backroom boys (and girls) who made it all possible.