L'effet Ackermann
Publié : 16 nov. 2013 08:39
Avez-vous déjà conduit une voiture dont le train avant rippe en manoeuvres avec de forts angles de braquage ? Ma 550 le fait depuis le début, la 991 du Dahu le faisait aussi l'autre soir.
Et bien cela a un nom: l'effet Ackermann. C'est la raison pour laquelle la plupart des voitures ont une épure de direction qui donne plus d'angle (carrossage positif) à la route intérieure. ANE en donne une très bonne explication.
Et bien cela a un nom: l'effet Ackermann. C'est la raison pour laquelle la plupart des voitures ont une épure de direction qui donne plus d'angle (carrossage positif) à la route intérieure. ANE en donne une très bonne explication.
Chances are you have never heard of Georg Lankensperger, a 19th-century German wooden-wheel maker. He solved a problem nearly 200 years ago that Corvette engineers chose to live with in the redesigned 2014 Stingray. Take a Stingray for a low-speed spin around a parking lot, turn the steering wheel at a sharp angle, and you'll feel a bumping-jumping-rubbing noise, as if a tire is skipping over the pavement. This sensation is called the Ackermann Effect, named for Rudolph Ackermann, who patented Lankensperger's steering system in Great Britain in 1818.
Lankensperger figured out how to make a pair of wheels turn smoothly in two separate arcs. You see, when you turn the steering wheel of your car all the way to the right, for example, the left or outer wheel travels in a larger circle than the right or inner wheel. Lankensperger figured out that if the inside wheel is turned at a greater angle than the outside wheel, it won't skip over the pavement and make that thumping noise that's prevalent in the 2014 Corvette.
Corvette engineers decided the Stingray's tight turning radius is more important than eliminating the Ackermann Effect, said Chevrolet spokesman Monte Doran. It comes into play only at parking-lot speeds. The Corvette's firm 18-inch front tires and cold weather also aggravate the problem. It's so noticeable that when a 2014 Stingray landed in the Automotive News test fleet recently, some who drove the flashy sports car thought it had a major defect. Some were hesitant to take the car home for the evening.
"It does no damage to the car," Doran said.
Corvette drivers also had to deal with the Ackermann Effect in the last generation, which ended production with the 2013 model. Doran said the problem could be fixed by limiting the turning radius. But that might not sit well with Corvette customers who like agile, sharp turns. The 450-hp 2014 Chevrolet Corvette is a mean-looking, well-made sports car ready to take on the world. It delivers a nearly unbeatable combination of performance, fuel economy, style and value. But the Ackermann Effect is a wart on an otherwise very pretty nose.