CHAIN TRANSMISSION VERSUS SHAFT DRIVE.
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"Chain Enthusiast" Replies to "Worm-drive Enthusiast."
''NVORM-DRIVE ENTHUSIAST," who contributed an essay on the alleged superiority of the worm to all other forms of transmission in the issue of The Commercial Motor for May 19th, will, no doubt, be disappointed if his effort does not evoke a reply from me. To his opening paragraph I would answer that abuse, however polite, is no argument, and pass on to the substance.
"Worm-drive Enthusiast" complains of the limits I set to the range of vehicles employing chain drive; he wishes to extend it so that it will include internal-combustion locomotives. I am quite willing to do this, and would refer him to the issue of The Engineer for April 17th last, wherein he will find illustrations and a description of a chain-driven locomotive.
"Worm-drive Enthusiast" appears to resent the inclusion of cycles and motorcycles in my range. Why? Shaft drive has been tried on both of these.
For the small mercies contained in the next paragraph I should, I suppose, be grateful. The value of the chain as a transmission for cycles is conceded, and we are informed that there are chain-driven light cars ; but why drag in the poor inoffensive Ford car in order to bolster up a claim for worm transmission when it has not even got one in the steering gear?
"Worm-drive Enthusiast" is apparently a poor seeker, since he has sought in vain for heavier cars propelled by chain. May I refer him to the 300 h.n. chain-driven Fiat, which has annexed many world's records in the capable hands of Mr.. Eldridge?
According to "Worm-drive Enthusiast," there is a hiatus extending over the central -portion of my range which I discreetly, passed over. Very well, let us examine this hiatus. "Worm-drive Enthusiast " appeals to American statistics. I will do likewise.
There lies before me a table giving particulars of 110 American passenger-car chassis. Are any of these cars worm-driven? Not a solitary one I With two exceptions, one of which is "Worm-drive Enthusiast's" friend, the Ford, they all use the spiral bevel. My memory may be at fault. but I seem to recollect that a prominent manufacturer of worm gearing has lately been advertising spiral bevels also.
The use of a second reduction after the worm, although, in the case referred to, it is made by spur gearing, finds favour with "Worm-drive Enthusiast" because, in his own words, "the high speed . . drive gives a light and well-mounted differential." Precisely. I am glad that we see eye to eye on one matter at least.
This admission on the part of " Worm-drive Enthusiast" really nullifies a good deal of his following argument, and thus saves me the trouble of replying to him ; one portion, however, must not be allowed to pass, and that is the little balance sheet which concludes with the artless reference to "two simple universal joints." No, sir ! rather put it that the cost of your shaft-drive transmission is the price you have to pay for very substantial universal joints ; an extremely costly, cumbersome, would-be-rigid axle easing; a differential which is not according to your own prescription given above, and a pair of heavily loaded final drive gears which, together with the differential aforesaid, are bumped and banged about on an unsprung portion of the chassis, and are still, according to some people, supposed to have an efficiency of 97.31 per cent. !
The next paragraph did, I admit, give me a momentary shock. Those horrid accelerations and deceleriations ! I visualized a chain-driven vehicle proceeding along a road in a succession of leaps and bounds ; but then I reflected, does it? Is this a practical argument? Or is it a product of sonic: highbrow application of dv/dt? And.I was comforted.
"Worm-drive Enthusiast's" reply on the subject of efficiency does not sound convincing ; he says "there is very little reason to suppose that the efficiency is seriously affected by practical working conditions." One gathers that he, like many others, has hitherto thought in terms of laboratory efficiency only, and that the practical aspect of the question finds him rather out of his depth.
However, let not "Worm-drive Enthusiast" be discouraged ; there is plenty of room for the worm, but the rear axle of a heavy lorry intended to traverse bad or unmade surfaces is most emphatically not the place for it. Placed farther forward, on the sprung Chassis, it will operate under conditions more suitable for obtaining the best results from it ; furthermore, the "light and well-mounted differential" which "Worm-drive Enthusiast" praises can then be used also.