More Design Pointers for Makers
Page 19
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THE 15 points for the manufacturer put forward by Mr. H. M. Lawrence in your issue dated January 7 have my full approval. I would like to add the following to his list:—
All commercial-vehicle engines to have inserted valve
seats, those up to diameter to have a minimum depth ofl in and above that a minimum of tin Main bearings to have a minimum width of 66i per cent. of diameter and big-end bearings a minimum of 75 per cent, of diameter Pistons to have a length-bore ratio of at least 3 to 2.
Where vacuum is available, an Autovac to be fitted in preference to a lift pump. All fuel or petrol piping to be of steel in lieu of copper or brass.
No gears or shafts to be used as bearing anti-friction bearings. No circliplocated anti-friction bearings to be used, particularly in aluminium housings. Tapered shaft and key to be employed in place of splines for propeller-shaft flanges and eight-bolt fitting for these flanges in preference to the four-bolt arrangement. The overall length of the rear propeller shaft not to exceed 6 ft.
J. L. G. BREWSTER.
(For J. Brewster and Co. (Transport Engineers), Ltd.) Newcastle-upon-Tyne, 4.
WHY NOT SEALED HEAD LAMPS?
ALTHOALTHOUGH on new vehicles modern types of head UGH give improved lighting, their design still is such that they are not weatherproof. Water or damp air can invade them and will ultimately destroy the fine polish on the reflectors. Even in the case of companies which replace these reflectors frequently, they seem unable to prevent their electricians from renewing bulbs without correctly focusing them.
As a result, we drivers find ourselves with lamps which do not permit us to meet approaching traffic with confidence, and yet our lamps often dazzle the drivers of oncoming vehicles. Incidentally, in the case of my company (the third largest bus operator in the country), the single pass-lamp system is used.
I would suggest to manufacturers the advisability of employing sealed head lamps, as used for some years in the U.S.A. In these, the reflectors do not deteriorate, whilst the bulbs cannot be wrongly adjusted by maintenance men who are ignorant of the effects of careless
fitting. N. M. KELLY. Wrexham.
TWO-SPEED AXLES v. AUXILIARY GEARBOXES I HAVE read with great interest the article, "The Link Between Power and Its Use," in your issue dated January 14.
In it you express an opinion in favour of an auxiliary gearbox, on account of the extra unsprung weight of a two-speed axle. You state, however, that it "must, of necessity, be appreciably heavier," and, as this is an exaggeration, I trust that you will correct the impression your article may create in the minds of potential operators.
The additional parts used in an Eaton two-speed rear axle are comparatively small, and a glance will readily show that the pinion and differential assembly is only slightly larger. I would say, too, that the increase in weight of the Eaton two-speed axle is less than that of a corresponding auxiliary gearbox.
There are numerous advantages in the use of a twospeed axle which obviously cannot be mentioned within the limits of an article such as you have written, but I confine my remarks to answering the disadvantages which you allege.
(1) Although you commend the auxiliary gearbox because " it adds nothing to the unsprung weight," you do not say that with a two-speed axle it is unnecessary to increase the • size and, therefore, the weight of the transmission.
(2) It is true
that in America the two-speed axle has attained considerable popularity, but it is also very popular all over the world, as over 1,000,000 have been produced. There is also much evidence that British trucks will have to be equipped with two-speed axles to satisfy overseas demands. Conditions in Britain are very favourable to the use of two-speed axles, as are any conditions where plenty of gear changing is necessary.
(3) There is many a component on the conventional British truck which started as an "alternative extra." It is noticeable that with few exceptions the vehicle manufacturers in this country have Eaton two-speed axles, and some of the more important have already included them in their truck production.
(4) The means for operating the Eaton axle requires much less finesse than a normal gear change, thus encouraging a driver to use the axle change instead of his main gearbox. This is precisely what is recommended, and is due not only to the ease of a finger-tip control but also to the changing being effected at much slower speeds in the axle (by virtue of the final-drive reduction) than in an auxiliary gearbox.
T. R. BEADY, M.I.Mech.E., M.S.A.E., M.I.M.I. (For Eaton Axles. Ltd.) London, S.W.1.
PAle cannot agree that the comments In the article referred to would be likely to influence operators adversely It may well be that, in due time, two-speed axles will form part of the standard specification of British-built vehicles, but as the article was based on current practice, we feel that the views expressed in it were fair and reasonable—En.] • PAINT-BRUSH INDICATOR FOR BRAKE TESTING I HAVE noted with interest the brake-testing apparatus described in "The commercial Motor" dated January 21 and produced by Mr. W. L. Russell, of Stockton-on-Tees passenger transport department. I thought it might be of interest to point out that we have used a similar device for nearly 20 years in our chassis-testing department.
The advantages of the paint-brush method are simplicity and practicable accuracy. If the arrangement be correctly adjusted with the brush near to the road, the time lag is negligible.
F. J. HUGHES, Service Manager.
Maidstone. (For Tilling-Stevens, Ltd.)