MacGuffin,
As the owner of several mechanical/automatic watches I at least understand why I buy them. I would argue that complexity is all in how you look at it. A semiconductor certainly seems more complex to me. We may mass produce them but it still is a complex bit compared to even a mechanical chronograph. Of course when it comes to watches remember that around the late 70s and early 80s the mechanical watch was near dead because the holy grail of what made one watch better than the other, accuracy was achieved with quartz timing. Rolex could no longer claim their watch was better than the next due to being more accurate. Part of why mechanical watches are valued is due to a dedicated marketing effort that convinced people that mechanical is some how better and should command a premium over the more reliable and accurate quartz watches. It worked as I paid a lot extra to get an automatic movement in my watch
As for the leaf springs, again several European companies have used them. Volvo used them on the 960 for packaging reasons. VW used them on a 100 km/L prototype because they are very light. Mercedes uses them on the front axle of at least some Sprinter vans (used with McPherson struts). Smart used them on the first generation Smart cars. Ford and Honda have filed patents (recent ones at that) regarding the use of the springs but I don?t think they have used the technology.
There are a few disadvantages to the leaf spring but not many. The big one is cost. Even in high end cars there are cost benefit trade offs. If one type of spring costs more than another it better have some advantages. I suspect in most cases the transverse composite spring doesn?t fair well in a cost benefit analysis due to the high cost.
Based on what GM has said in both an SAE paper and in ?All Corvettes are Red? the leaf spring was one of three suspension types GM considered for the C5 Corvette. They also considered conventional coil overs and a bell crank system where the shocks would be articulated via a pushrod. The design constrains for the C5 were a low hood line in front as well as saving space for the V8. In back they wanted to retain a decent sized trunk. In the Corvette specifically GM decided the leaf spring was the packaging concept that worked best so they paid the extra money for the springs. The reduction in weight (springs and anti-roll bar) were likely secondary benefits.
It is worth noting that when designing the C5 a dollar value was assigned to each pound of a component. For each pound over a component came in over a target weight the price had to be reduced by say $5. For each pound under a target weight the price could be increased by that same $5. This system allows the engineers to get an idea when it is worth paying extra for lightness or when it is OK to save money with a heavier part. I suspect the leaf spring failed to meet this price/weight trade off. It was likely much more expensive than its weight savings.
So the Corvette used the springs primarily for packaging (but they lighter weight didn?t hurt). What about Volvo. Well when they updated the 940 into the 960 they used a leaf spring in back as well. I believe the 940 had a live axle out back. The 960 was given IRS. Given that the 960 was based on the 940 it is possible that the IRS was designed to fit into the same space as the live axle on the old car. True or not, Volvo stated that they used the leaf spring because it packaged better than the coils and allowed for a larger cargo area.
I don?t know why Mercedes and Smart chose the transverse leaf spring for the front of the Sprinter and Smart. Again I suspect it was packaging. Mercedes might have chosen them due to their good service life. I am purely speculating at this point but they VERY good cycle life of the springs might be important in a delivery vehicle which will likely run up many more mileage per year and more miles over it?s life than many cars. The Sprinter vans do use fiberglass leaf springs in a conventional leaf spring, solid axle layout in back. Again, service life and compared to a steal leaf spring a BIG reduction in weight are likely the reason.
Some heavy trucks and trailers use the composite leaf springs in a conventional layout because they are MUCH lighter than conventional leaf springs. So while the weight savings over a coil spring isn?t really enough to justify their use on most cars, the weight savings compared to a leaf spring is enough to justify their use on commercial trucks.
VW chose the leaf for performance reasons alone. Given their car was a technology demonstration vehicle cost wasn?t a big concern. Weight however, was a big concern. Well the fiberglass springs can store more energy per lb than any metal spring and when used with two mounting points it can serve as an anti-roll bar (the Corvette uses the supplemental roll bar because the leaf spring alone doesn?t provide enough roll stiffness for a sports car).
As for actual performance advantages over coils, I think the benefits are small if we don?t include packaging. Yes, there is a weight advantage but springs aren?t a great percentage of a total vehicle?s mass. While they do have better self damping characteristics than a coil the difference is just not that big of a deal in a road car. In short, unless your packaging situation demands their use, their high costs outweighs their benefit. A search of the patent literature shows that quite a number of automakers have looked into using them and recognize their advantages but the cost of the parts is really what keeps them out of a car. If an automaker can save a few dollars on the springs and put that money back into the dampers or somewhere else, then why over spend on the springs.
Ignoring costs, the Corvette is not handicapped at all by the springs and they certainly are ?higher tech? than conventional coils attached to double wishbones (another GM invention BTW). However, it seems their cost disadvantage almost always negates their use. If the cost of manufacture were to drop to the point of being similar in cost to coils I suspect we would see many more cars use them. Caroll Smith had talked about the virtues of just this sort of suspension in Engineer to Win
If I were involved in the design of a new passenger vehicle, however, I would give serious consideration to the use of a transverse composite single leaf spring of unidirectional glass or carbon filament in an epoxy matrix. This would be the lightest practical spring configuration and, although space constraints would seem to limit its use in racing, it should be perfectly feasible on road-going vehicles, from large trucks to small commuter cars. (Since I wrote this paragraph the new-generation Corvette has come out with just such a spring to control its independent suspension systems-at both end of the car.)
BTW, I wouldn?t say Porsche, Ferrari etc always use the latest and greatest either. Ferrari was still using tube frames long after even a Corolla was a full unibody chassis. Porsche still uses a rear engine layout which is not exactly ideal. They use what they use for many reasons. Some are performance, some are cost, some are because a small volume maker can afford to put more money into each component but can?t afford to pay large up front tooling costs. When it comes to springs, I have a lot of experience ordering them for non-automotive applications. We would pay $500 to set up a spring machine then $x per spring in quantities of 1 or 1 million. The fiberglass spring requires a mold. That means the $500 is more likely to be $50,000+ . That?s hard for say Ferrari to swallow. BMW?s M cars and the AMG cars are all based on production road cars. That means they share a basic suspension design with the lower line modes. It the leaf spring doesn?t work for cost reasons on the low line car you don?t add it to the high end car. Also, most sedans wouldn?t have the particular suspension packaging constrains that GM was working around. If the constraints don?t exist, don?t spend the extra cash on the higher dollar spring.
