De Dion tube

de Dion suspension characteristics: Camber change on one sided bumps, none on rebound. de Dion tube is shown in blue. The differential (yellow) is connected directly to the chassis (orange).

A de Dion tube is an automobile suspension technology. It is a sophisticated form of non-independent suspension and is a considerable improvement over the swing axle, Hotchkiss drive, or live axle. Because it plays no part in transmitting power to the drive wheels, it is sometimes called a "dead axle".

De Dion suspension uses universal joints at both the wheel hubs and differential, and uses a solid tubular beam to hold the opposite wheels in parallel. Unlike an anti-roll bar, a de Dion tube is not directly connected to the chassis nor is it intended to flex. In suspension geometry it is close to the trailing beam suspension seen on many front wheel drive cars, but without the torsional flexibility of that suspension.

History

The de Dion tube was named after Comte Jules-Albert de Dion, founder of French automobile manufacturer De Dion-Bouton. The tube, however, was invented around 1894 by co-founder Charles Trépardoux for use on the company's steam tricycles.

Advantages and disadvantages

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The benefits of a de Dion suspension include:

1. Reduced unsprung weight compared to the Hotchkiss drive, since the differential and half-shafts are connected to the chassis.
2. Unlike most fully independent suspension there are no camber changes on axle loading and unloading (or rebound). Fixing the camber of both wheels at 0° assists in obtaining good traction from wide tires and also tends to reduce wheel hop under high power operations compared to an independent suspension.
3. Total unsprung weight is lower than a live axle, and is comparable to independent suspension.
4. The choice of shock absorbers and springs is made easier.

There are costs, however:

1. A pair of CV or universal joints are required for each wheel, adding complexity and weight.
2. If coil springs are used then a lateral location link (usually either a Panhard rod or Watt's linkage), plus additional torque links on each side (five link suspension) or a combination of lower trailing links and an upper transverse wishbone are required. None of these additional links are required if leaf springs are used, but ride can be compromised due to the leaves having to do double duty as both locating links and springs.
3. Sympathetic camber changes on opposite wheels are seen on single-wheel suspension compression, just as in a Hotchkiss drive or live axle. This is not important for operation on improved surfaces but is more critical for rough road or off road use.
4. Cost is greater than a comparable live axle.
5. Spring base (distance between left and right springs, where they contact the axle) is commonly narrower than the track (tread), so springing must be stiffer. (It need not be; Bristol prototyped a design with spring base wider than track.)

Use in production cars

de Dion tube used in a 1998 Ford Ranger EV

Older cars

In addition the original Mazda Cosmo, Alfa Romeo Alfetta, GTV6, Giulietta, Alfa 6, 90, 75/Milano, Lancia Aurelia (fourth series onwards), first and second generation Prince Gloria, Lancia Flaminia, Volvo 300-series, Rover P6 and Dodge Caravan & Grand Caravan (all wheel drive version from 1991–2004), DAF 46, DAF 66, are examples of production vehicles using this suspension. All Iso Rivolta cars GT, Grifo, Fidia, Lele and early Bizzarrini 5300's. Some of the largest Opels, such as the Opel Diplomat "B" of 1969, all Aston Martins from 1967 to 1989, Ferrari 375 and 250TR, Maserati Quattroporte, Bugatti 251, Mercedes-Benz W125 and W154 as well as Auto Union Type D also used this suspension.

Recent cars

The Smart Fortwo and Smart Roadster micro-compact cars produced by Daimler AG, Mitsubishi i kei car produced by Mitsubishi Motors and the Caterham 7 (a development of the Lotus Seven after Lotus sold the design rights to Caterham Cars), are the only cars currently in production that utilize this arrangement, as well as the products of some kit car companies. A recent vehicle to use this suspension coupled with leaf springs was the Ford Ranger EV. The American built MV-1 van by VPG also uses this suspension in the rear with leaf springs and was starting production in spring 2010. 4WD variants of the Honda Fit use a De Dion style suspension in lieu of a torsion bar.

See also

• List of car brands

Sources

• G.N. Georgano (1990). Cars: Early and Vintage, 1886-1930. London: Grange-Universal.  (reprints AB Nordbok 1985 edition).
• Setright, L. J. K. "De Dion axle: The First Step to Independence", in Ward, Ian, executive editor. World of Automobiles, Volume 5, pp. 515–516. London: Orbis, 1974.