In my time, I also owned a 1955 GM PD4104 highway coach. It was powered by a Detroit Diesel 6-71 (426 cu. in.) 2 cycle supercharged engine. Detroit Diesels have been discontinued, supposedly because newer engines have beter fuel economy. Cynics say Mercedes bought them out and shut them down.
It was also of a basic monocoque construction with lots of aluminum and a stiffening robust plywood floor. Air suspension was very smooth - surprisingly so on rough gravel roads. Our farm was surrounded by the worse gravel roads.
GM put a full belly pan on this bus, right to the rear bumper. While the body had the aerodynamics of a brick, it got remarkable fuel mileage, which I attribute to the full belly pan. The log book showed that through its 680,000 mile life, at which time I purchased it, it never got less than 10 mpg. At 27,000lbs., that translates to 135 miles per gallon per ton! I can honestly say that I rarely had a problem keeping up with traffic.
So U.S. engineers could achieve 135miles per gallon per ton 60 years ago back in 1955, but today it's a dream for the distant future.
Citroen introduced its DS model in 1954. This car introduced radial ply tires, disk brakes and a central hydraulic system for suspension, steering and brakes. It had front wheel drive with inboard disk brakes for minimum unsprung weight and did its braking through it CV driveshafts. For many years its rugged transaxle and driveshafts were used in formula 1 cars. It had a very efficient aerodynamic design with particular attention to its smooth under-belly. After all most of the drag is between the bottom of the car and the road as that is where the maximum air shear occurs. It seems current automotive engineers don't realize this. Citroen uses a wind tunnel with a conveyor belt floor for its drag measurements.
The DS had amazing interior room. At 6'4" I could wear a hat in the front and back seats. With the front seat back for my long legs, I still had room in the back seat to cross my legs. It's hydro-pneumatic suspension was the ultimate in smoothness and the handling even over the roughest gravel roads was spellbinding. I got much better mileage than a WV beetle of the day.
The thing that amazes me the most though is its weight at 2700 lbs in the Pallas version. To put that in perspective, a current Fiat 500 weighs in at 2600 lbs. My current Buick Lucerne, with aluminum hood, aluminum suspension, engine, transaxle and all the other "lightweight technology" of today weighs in at 4035lbs. The Buick Lucerne doesn't have the inside room of the Citroen DS and GM's magnetic ride, though the best available these days, is not as smooth.
It still amazes me how a 60 year old design can put "modern" designs to shame in so many ways.
Thanks, j-allen, I tend to agree. Although the steel guys have come out with several AHSS alternatives. Many of the larger auto lightweighting efforts are focused on figuring out which material best goes where, and how they can all--or many of them--play together.
I wish it were true that it was simply a matter of stylists taking over that shifted automotive design towards so much standardization, but that's a secondary effect. The main reason for that change was because of the need to keep volumes high and therefore individual car prices down, while continuing to include new technology with new models.
It is gratifying that auto makers no longer see steel as the solution to virtually every one of the hundreds of structrual problems in automobiles. Such thinking, however, is not new. I have restored and worked on cars from the 1920s. These used a light of light strong materials including aluminum wood, and fabrics. For example, the doors used thin aluminum over a hardwood frame to give a lignt strong structure. Similarly widnow posts were thin steel fromed around softwoods which prevented the hollow struicture from buckling.
On the fancier cars, the engine block was aluminum with iron cylinder sleeves.
Before stylists took over, engineers were able to pick the best designs and materials for each component. It is time to get back to that, especially with the new range of materials now available.
Lou, I agree. My headline was a bit tongue in cheek, since there are other groups working on this general problem. I thought it was interesting, though, that so many formed within a short period of time, and that these seem to be more tightly focused than some of the larger efforts. Like you, I also found the software angle very interesting. The material information databases are clearly a key part of redesigning from heavier structures to lighter ones, whether that's metal-to-plastic, or heavier metals to lighter metals.
Ann, it is good to see the automotive industry finally go on a diet. The initiatives you detail are very interesting and important. After becoming lighter and more aerodynamic, personal automobiles became blockier and heavier with the popularity of SUVs. It looks like now technology is providing the solution.
I also find it interesting that the simulation and CAD information is a major part of these efforts. That's a testament to the current importantce of CAE.
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