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The Amazing Advances In Automobile Technology—The Effect Of Transmissions On Economy.
The Astounding Developments in Motorcar Technology-- The effect of Transmissions on Fuel Economy.
{Overview:}
In the previous decade one had the notion that motor cars had reached the highest point of its development. The call for cleaner exhaust emissions and finite oil resources of which less and less are being discovered, compelled engineers to make cars more efficient.
Advances in engine efficiency the last few years has been quite mind boggling. How is it possible that manufacturers such as VW/Audi, BMW and Mercedes can claim decreases in gas consumption in the order of 20%, 25% and even 30% over their outgoing models? This is mind boggling that such advances in efficiency can still be attained.
New transmission designs were some of the ways in which this was achieved.
Improved transmission efficiency was a constant goal of engineers and recently there have been some new innovations in this regard. Manually operated gear shifts used to be much more efficient than automatic transmissions.
Two speed automatic transmissions have receded into history due to their legendary inefficiency though they might have been very smooth. With up to eight ratios automatic gearboxes can reach the efficiency of manual gearboxes.
Friction and hydraulic losses are prevented with modern locking torque convertors in contemporary automatics. With two or three speeds, old type automatics had the torque convertor do the job of spreading the ratios.
The double clutch automatic systems that function like manually operated transmissions, were pioneered by the Germans and are rapidly gaining ground, by doing away with the torque convertors. The gears are similar to a normal manual gearbox, but with two clutches, which open and close alternatively and not simultaneously. Volkswagen and Porsche are the major proponents of this.
The principle was known for many years but CV (constantly variable) transmissions have only lately been used more often. A very simple principle where one pulley contracts and the other pulley, which is connected by a chain or band , expands, thus varying the ratios infinitely.
This system with rubber belts was used by DKW on its Hobby scooter in the 1950's and later by the Dutch firm of DAF for a small car and is used these days in a more advanced form by most manufacturers.
However people do not like the resulting flat drone of an engine running at a constant speed while the car accellerates. The transmission is designed to change gears in steps like a normal transmission,which is electronically controlled to prevent this irritation. This makes the car feel more like one with a normal transmission.
The days of three speed manual transmissions have long gone. In the days of long ago it was considered to be an inferior automobile if you had to change gears often and was thus avoided whenever possible Low traffic, low gearing and tractor like pulling power of the engines of old motor cars allowed them to be put into top gear soon after setting off on a trip and leaving the car in top gear.
The best fuel efficiency is guaranteed by high gearing, within certain limits. That makes frequent gear changing necessary and requires a multitude of gear ratios to fill the gap and that is why modern motor cars have such a number of gears, whether manual or automatic. Today's manual gearboxes have synchromesh on all gears and are properly designed to make gear changing more of a delight than a chore.
Automatics are becoming the preferred choice because of even the best manual transmission can be a nuisance in heavy traffic, especially if this is the daily routine.
The efficiency of automatics is approaching and even equalling that of manual transmissions and the double clutch boxes can even improve on that. In stead of gear sets meshing automatics use planetary gear sets where changing gears is done by braking certain band clutches and releasing others.
Gearchanges on double clutch transmissions are done by paddles on the steering wheel, one for upchanges and one for downchanges, similar to those on formula one racing cars but can also do it automatically. The changes will however also work automatically. These gearboxes rival and even exceed the efficiency of manual transmissions.
In another article I will discuss the upcoming diesel engine use in cars. In Europe a high percentage of cars use diesel engines because of their economy and other characteristics.
Author: Dieter Hoffmann a car, nut if ever there was one. My website is not about cars but about another of my interests i.e. woodworking. The name of the website is http://www.toolsforcarpentry.com where you can find information about woodworking tools plus plans for making just about any woodworking project as well as boats .
RepRap using Synchromesh cable instead of belts
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