FREE WHEELS

Timaru Herald, Volume CXXXIV, Issue 18849, 11 April 1931, Page 14

FREE WHEELS

ENGINEERS’ EXPERIMENTS. After being pioneered for five year? or more by a few British concerns, the | free wheel was adopted by a wellknown American organisation some time ago. and created widespread interest throughout America. So great an attraction did the free wheel prove to the buying public that several other concerns have since taken it up. and at the New* York show r cars which can coast w r ere exhibited by no few-er than five well-known manufacturers. At the same time (says an article in a recent issue of ‘ The Motor") the engineers of various concerns have been actively engaged upon research work with tw’o aims in view; first, to ascertain the precise advantages which a free wheel confers, and. secondly, to study the various mechanisms available from the viewpoints of performance and durability. Some of the results of these investigations were conveyed to the Society of Automotive Engineers in a paper recently read before the New’ York branch by Messrs. D. G. Roos and W. S. James. The authors commenced their paper by discussing various free-wheel mechanisms such as the De Lavaud, Millam, Humfrey-Sandbarg, and Constantinesco. They also gave a technical analysis of the special type of free wheel used on cars of the organisation that first adopted the idea. This is a roller-cam device w'hich fits into a sliding sleeve in the gearbox, and is so arranged as to be operative w*hen either top gear or second speed are in use. By pressing a button the driver can. however, move the gear lever through a bigger range, and this enables the free wheel to be locked at will. The following test was adopted to ascertain the durability of the free wheel, using only three rollers out of the twelve which are ordinarily employed. The rear wheels of a car w*ere placed upon loaded dynamometer drums and, with second 6peed engaged, were caused to drive them at a rate corresponding to 30 m.p.h. on the road. An automatic device then closed the throttle, allowing the car to free-wheel until the speed dropped to 20 m.p.h. The throttle was then again opened until 30 m.p.h. was regained. This cycle w r as repeated 50,000 times without any appreciable signs of wear. Many comparative tests were made on the road in order to ascertain the degree of economy obtainable in fuel and oil consumption. Two cars wjere employed in eacTi case, these being identical but for the fact that one was fitted with a free wheel, whereas the other had a conventional drive. According to conditions it was found that the free wheel reduced the petrol consumption by amounts varying from 16 to 23 per cent. The figures for oil consumption varied still more widely, but in most cases showed an economy greater than 30 per cent. Effect Upon the Brakes. Next, a research was undertaken to ascertain the effect of free-wheeling upon the use of brakes. Two cars were once again employed, and it was found that under the worst conditions the increase in the use of the brakes is not very great, whilst In towns the number of brake applications was actually fewer on the free-wheel car than on the other. Stopping distances were also investigated. and it was found that in emergencies a given pedal pressure gave better results when coasting than when running with a fixed transmission. At more moderate rates of deceleration conditions are reversed, but even so. only a slight increase in pedal pressure is needed on the free-wheel car as compared with the other. The investigators do not appear to have tested the rate of wear of brake linings, but to judge from their figures it seems unlikely that the addition of a free wheel would reduce the life of the linings by more than 10 per cent. A very important point which is given full attention in the paper is the way In which a free wheel safeguards the gearbox, back axle, and engine from the wear and tear which they usually experience through over-running and reversals of stress. They point out. incidentally, that the dynamo of a free-wheel car should be made to provide a higher charging rate. Needless to say, free-wheel cars were submitted to State officials and private motorists for trial before it was decided to place them on the market. According to the authors of the paper, there people gave the new transmission . unanimous and enthusiastic approval.” Many well-known American engineers took part in the dlucussion which followed the reading of the paper. number of interesting questions were asked an danswered, such

as the following:— Is It not a fact that an Intermittent or fluctuating noise is more noticeable than a continuous noise? The contmst in noise encourages the driver to make increased use of freewheeling. There is a noticeable lapse of time between pressing the accelerator and the instant at which the engine begins to drive the car. Do motorists object to this? There is no shock when the engine i takes up the drive, and owners have I not raised any objection to the short I time lag. I Does free-wheeling affect the tenI dency to skid? | No difference has been detected even j when travelling over icy roads. In a tight place—for example, on a I railway crossing—has the driver equal- ! ly good control with a free-wheel car : as with a normal car? He has better control because he can j change gear without even udng the | clutch; this enables him to engage i second speed while coasting up to the | crossing, so that he has rapid aeceleraI tion at command. I What happens when a foolish driver | suddenly wishes to obtain a positive drive when coasting down a hill? | Conditions are much better than i when the driver of a normal car wishes j to change down from top gear in cimii lar circumstances.