PH Origins: Diesel-electric hybrids

It's easy to understand the justification for marrying internal combustion engines and electric motors in one powertrain. The engine grants you significant range and freedom from charging points, while the electric motor typically permits silent, smooth running and myriad efficiency benefits.

The concept, after all, is well proven - with the technology's origins dating back to the late 1800s. The development of petrol-electric hybrids continued apace from then on, with several small companies offering new systems as technology advanced.

As air pollution became a significant problem in cities, however, major manufacturers took more interest in the concept and began work on systems designed for mass production. Diesel engines were typically overlooked for automotive hybrid applications, though; in many markets diesel was expensive, and the engines themselves often proved heavier, costlier and less refined than their petrol counterparts.

As emissions and economy became increasingly prominent points of discussion, and with engine technology improving, Volkswagen reconsidered the frugal diesel option. Its studies resulted in the 1987 Golf 'Elektro Hybrid' concept, which featured a 1.6-litre diesel engine and an electric motor coupled to a semi-automatic transmission. Some 20 Elektro Hybrids were used in trials, according to VW, but high costs and a lack of demand seemingly quelled further developments.

The VW Group's subsidiary, Audi, took a similar interest in hybrid development - as it foresaw a time when conventional cars might be banned from city centres. The company, in particular, was keen to find a way to tackle excessive hydrocarbon and nitrogen oxide emissions and, in 1989, it introduced a prototype petrol-electric hybrid 100 Avant, called the 'Duo'. Its weight and cost again proved prohibitive but, as pollution continued to increase in urban areas, work on the concept persisted.

Audi revealed its third Duo concept, based on an A4 Avant and dubbed 'Audi Duo', at the Berlin motor show in October 1996. A 90hp 1.9-litre diesel drove the front wheels through a manual gearbox, while a 30hp electric motor drove the back axle - an arrangement later called 'through the road'. Audi claimed a 0-62mph time of 15.6 seconds, an all-electric range of 31 miles and an average economy of 79.4mpg.

Field trials started in April 1997 and Audi decided to test the market by unveiling a production version at the Frankfurt motor show in September of that year. It was aimed at commercial and government operators and could only be leased, according to reports from that era, with rates ranging from £180 to £550 per month - equivalent to £310 to £950 today. Audi, however, did state that the cost of each Duo was approximately twice that of a standard diesel A4 at the time.

The third-generation Duo was, in any case, Audi's first production hybrid and the world's first production diesel-electric hybrid car. Its onboard battery could also be recharged from the mains, making it the first production plug-in hybrid - some 14 years before the Volvo V60 Plug-in Hybrid was touted as trail blazing.

Audi envisioned 500 Duos being produced each year but several months later only 60 had been made. Cost was cited as the reason for a lack of commercial success, but feedback from real-world trials also proved underwhelming.

The European Commission's 'Electric Vehicle City Distribution' report, for example, stated: "While the Audi Duos are well accepted and acclaimed for their overall performance, their potential for saving primary energy is, at best, moderate - due mainly to the 400 additional kg over an identical Audi A4 TDI."

Other reports were similarly damning; when the Duo was unveiled in September, Toyota was also previewing its petrol-electric Prius. Its hybrid powertrain was reportedly more mature and, according to the Institute of Electrical and Electronics Engineers, likely to 'represent the defining hybrid configuration'. Interestingly, the report suggests that the Duo was available before the Prius, which was certainly the case in Europe, although the Toyota was unquestionably the first mass-produced hybrid.

Audi, finding no success with its expensive Duo, quietly dropped the concept. It wasn't until 2010 that it ventured back into the production hybrid field - and it took until 2012 for the next production diesel-electric hybrid to arrive, in the form of Peugeot's 3008 HYbrid4.

Peugeot's diesel-electric hybrid was predictably marketed as 'a first' but, in any case, it served to draw the technology back into the limelight. Many manufacturers, striving to meet ever-tightening regulations and demand, jumped onto the bandwagon - but, unbeknownst to them and despite technological advances, most were merely repeating what Audi had already encountered and achieved years before.

Lewis Kingston

P.H. O'meter

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Comments (23) Join the discussion on the forum

  • simon-tigjs 08 Jan 2018

    Can anyone explain to me why an alternative diesel electric hybrid has not worked ? My logic is this. A diesel engine that just generates electricity and powers and charges a battery , thus then only 2 wheels are then driven by electric motors. Diesel are highly economic and don't waste power creating spark thus all it has to do is drive a generator. add in kinetic re generation on braking ...surely it would go for miles on very little pollution and wouldn't need tons of batteries.. i would love to know why not ? its a bit like an i3 but using a diesel for more economy is it not ??

  • TooMany2cvs 08 Jan 2018

    simon-tigjs said:
    Can anyone explain to me why an alternative diesel electric hybrid has not worked ?
    Because hybrids came out of the Japanese and US markets, primarily, neither of which are big on diesels - so they've been developed with petrol engines, because that's where the global sales are.

  • 99dndd 08 Jan 2018

    and I suppose 'dieselgate' has killed this off already.

  • havoc 08 Jan 2018

    TooMany2cvs said:
    simon-tigjs said:
    Can anyone explain to me why an alternative diesel electric hybrid has not worked ?
    Because hybrids came out of the Japanese and US markets, primarily, neither of which are big on diesels - so they've been developed with petrol engines, because that's where the global sales are.
    Also because the majority of a (turbo) diesel's economy/emissions benefits come at lower rpms and therefore non-motorway speeds. Which is exactly where hybridisation offers the most benefits (i.e. why combine two power sources both optimised for low-medium speed use).

    Conversely n/a petrol doesn't lose anywhere near as much economy at m-way speeds, so 'complements' hybridisation better. So combining n/a petrol with hybridisation gives almost all of the benefits with significantly less risk/complexity (modern TD engine is notably more complex and more likely to fail at some point than a n/a petrol).

  • simon-tigjs 08 Jan 2018

    Excuse me for being comments thank you but my point is this. What has motorway speeds or turbos got to do with it. all a diesel engine will do is provide a recharge via an efficient generator. All the power drive etc is electric. it might have to play catch up but its a powerful constant. Surely that all the range extender on an i3 does only it has a tiny tank and petrol, thus the same size diesel tank would last longer and a chugging diesel is efficient as it only runs the generator not anything else like spark plugs coil etc Seems too simple so something must be wrong. Have we just re invented the wheel for obviousness ??

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