The year 2009 was relatively quiet for the simplest type of electric-drive vehicles, known as mild hybrids. Sexier battery electric vehicles, various flavours of plug-in hybrids, and even conventional full hybrids have lately gotten far more media attention, writes John Voelcker.

The sole new entry in the mild hybrid game was the 2010 Honda Insight, the company’s first dedicated hybrid since the demise of the original 1999-2006 Insight two-seater. This Prius-shaped five-door B-segment hatchback arrived to high hopes, but fell flat in its largest expected market, North America. The consensus was that in its quest to offer the world’s least expensive hybrid, Honda had cut too many corners, producing a cramped car with unimpressive dynamic qualities that paled in comparison to the less expensive, more flexible Fit model next to it on showroom floors.

Honda is by far the global leader in mild hybrids, and the Insight is the first of three new global models based on the latest evolution of its IMA system. Next year, however, General Motors will roll out a revised, second-generation version of its Belt-Alternator-Starter system that uses a lithium-ion battery pack and provides much greater capability than its frankly unsuccessful first-generation model. It plans to spread this system across a wide range of vehicles globally. Hyundai last year launched a low-volume mild hybrid system on a LPG-fuelled vehicle in its home market, which it is expected to extend to petrol-engine cars this year or next.

Other recent entrants include Mercedes-Benz and BMW, who collaborated on the first mild hybrid system based on a lithium-ion battery pack for their respective full-size luxury sedans. The two German makers took different tacks in exploiting the technology, however. Daimler paired its mild hybrid with a downsized engine, producing impressive fuel efficiency in a full-size S-Class saloon, while BMW opted for minor improvements in fuel efficiency but used its hybrid to boost performance above comparable petrol-engine models. Subsequent iterations of this system are expected to elevate it into ‘full hybrid’ territory by adding the capability of pure electric running.

So are mild hybrids the sleeping giant in the hybrid world, or a not-quite-good-enough side road along the highway of hybrid technology? With regulations tightening on carbon emissions and fuel consumption around the world, both cases can be made. The challenges facing mild hybrid systems lie in cost competitiveness and consumer perceptions.

A mild hybrid offers one way to downsize a petrol engine while maintaining acceptable performance under peak power demands, but direct injection and turbocharging (à la Ford’s ‘EcoBoost’ engine programme) is another. The two tactics are likely to compete among vehicle makers placing their bets for the powertrains they offer through 2015 or so.

Mild hybrids are defined by a small high voltage battery pack (0.1-1.0kWh), and the ability to complement engine torque with electric power. But crucially, unlike the ‘full hybrid’ variant, their motors (at 10-15kW) are too small to power the vehicle on electric power alone.

Despite that limitation, mild hybrids still incur the cost of the battery pack, an electric motor, the power electronics to deal with high voltage electricity, and the associated control systems to manage integration with the engine and transmission controllers. The incremental costs of that equipment are substantial.

Mild hybrids must thus compete favourably on cost against downsized, high-output, direct injected and/or turbocharged diesel and petrol engines that achieve close to the same consumption. Beyond 2012, mild hybrid systems may be harder to cost-justify as production volume ramps up substantially and – incremental costs fall with volume – for boosted DI small engines.

On the other end, mild hybrids will be pressed by cheaper full hybrid systems. And the costs of those systems can be amortised over their plug-in variants as well, whereas mild hybrids are not powerful enough to be fitted with larger battery packs that can be plugged in. In this sense, they are a technology that is ‘stuck in the middle’ and searching for a long-term niche.

Beyond sheer cost, for consumers, the big question is whether full hybrids offer special ‘hybrid’ capabilities that are more appealing. Because it cannot run electrically, a mild hybrid vehicle ‘feels’ like a slightly underpowered petrol car with a stop-start system, rather than a ‘real hybrid’. Ford’s Nancy Gioia told just-auto that in its surveys, the vehicle maker sees consumers increasingly expecting all-electric running from any vehicle carrying a ‘hybrid’ label.

As consumers gradually grow comfortable with the notion of vehicles that plug in, and start to learn about battery electric vehicles from major manufacturers, OEM sources and industry analysts alike feel that electric running will increase in importance as a selling point for any electric-drive vehicle.

It is a fact that Honda and GM are the sole major vehicle makers focusing on mild hybrid systems today. Honda virtually invented the mild hybrid, but even it has said that it is now working on full hybrid systems for its larger vehicles. GM has always had parallel mild and full hybrid tracks. And Daimler and BMW are evolving their modular systems beyond mild hybrid abilities into full electric running.

Together, all these facts indicate that the industry as a whole considers electric running and the greater efficiencies of a full hybrid system to offer the best payback on the investment in electric machinery. Virtually every major vehicle maker is working on a full hybrid system; few are pursuing mild hybrid systems.

This hardly means that mild hybrids will vanish overnight. But while mild hybrid production volume is likely to increase to as much as 1m per year by 2015, we expect full hybrids to be at volumes three times that or more at that same point. That volume puts mild hybrids at less than 2% of total global production of, say, 70m vehicles. And mild hybrid production volume could even plateau in the middle of the decade, when the incremental cost for a (non-plug-in) full hybrid system will likely have fallen to no more than that of a mild hybrid system today, and then begin to decline.

Mild hybrid technology has earned its place in the evolution of electric-drive vehicles. But we see mild hybrid vehicles as neither fish nor fowl, with costs high enough to face serious challenge from more efficient boosted DI petrol engines, but with motors too small to provide the all-electric running that we believe consumers will come to expect of ‘hybrid’ vehicles.

John Voelcker

Global market review of mild hybrid vehicles – forecasts to 2017 (download)