Does 'Lubrication:Spoil Leaf . Springs . ?
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WE were delighted to read the letter from W. I,.
" Woodward, in your issue dated December 2, wherein he questions the wisdom of using any form of lubricant upon laminated leaf springs.
We have long held the opinion that to oil or grease leaf springs is to act in direct contradiction to the sole raison d'être for using this type of suspension, as we believe that internal friction between the leaves provides far more shock absorption than the mere tendency of the metal leaves to return to their original contours.
Older readers will, no doubt, recall a period when one accessory manufacturer was marketing ball-bearing intesleaves, presumably with the object of reducing internal friction, Whilst a famous car maker was supplying his vehicles fitted with zinc interleaves, which were said to prevent squeaking and so obviate the need for the use of lubricants.
This problem seems to have a parallel in the motorcycle industry,
• where meticulous care is taken to avoid the tiniest friction in the steering head by The use of beautiful roller or ball bearings, then the whole process, is promptly nullified by the fitment of a large-diameter damper provided with Ferodo interleaves. What are we to think? Just that these are further examples of the many things in our industry about which far too little is known, and in which very serious wrong practice has become almost habitual.
Preston, Lancs. H. R. HOULDING,
(For Bert Houlding and Sons.) PRAISE AND CRITICISM FOR THE "MIDLAND RED" agree with P. L. Robbins, of Gloucester, when he says in your issue dated December 23 that Midland Red passenger vehicles are comfortable for travelling. They are, and I have spent a good many hours on them over a period covering many years. The suspension on the vehicles is good, and this adds greatly to the comfort of the passengers. One fault prevents Midland Red doubledeck buses being the best. There are too many of them with front entrances, and this makes them anything but comfortable at all times except when the weather is warm.
Bristol. L. M. MaRsllati,, BRAKING AND CONTROL OF BATTERY-ELECTRIC VEHICLES IN your issue dated December 23, under the title of I
"Reducing First Cost of the Battery-electric," you gave details of figures quoted by H. W. Heyman to the Industrial Transport Association. Whilst agreeing with much of this article, the comments on worm-driven axles, straight-series (rheostatic) control gear, and brakefacing wear would be most misleading to an operator without practical experience with battery-electrics.
A brake-facing life of only 1,500 miles appears incredible. On reading this we contacted the users of the first' vehicle made by this company over 13 years ago, and found that the original brake facings were replaced only eight months ago, the original shoes being
retained. The total mileage could not be quoted definitely owing to speedometer ,changes, but assuming the very low mileage of 100 per week, this would give 67,600 miles in 13 years. The same user has R fleet of our vehicles, and assures us that the minimum brake-facing life is 41 years. The answer to this point is not so much development in brake-facing material as the fitting of appropriate brakes for the considerable gross weight of a battery-electric vehicle with its battery and load.
We have used worm-driven axles exclusively until the past year, and still use them with few exceptions. We have obviously not found this type of final drive "entirely unsuitable" for door-to-door work.
In theory, the efficiency of series-parallel control gear is greater than that of rheostatic control. In practice, however; the advantages are usually outweighed by the comparatively complicated control gear involved. Incidentally, in nearly every type of series-parallel control a resistance is still used in the initial stage or stages. The resistance is in circuit for only Such a short period with either type that the difference in current consumption under average working conditions is negligible.
In 1938 we discontinued series parallel control in favour of rheostatic control, except on special models, as we found no recordable difference in
current consumption in service. For certain specialized work series-parallel control holds definite advantages and is nearly, always used. There is no doubt that a large majority of electric vehicles employs resistance control, and we have yet to find a case where, on equal work, they are fitted with batteries of 25 per cent. greater capacity. It would be possible to quote instances which prove the reverse, but it would not necessarily prove that the control gear was responsible.
Leamington Spa. A. D. JONES, Sales Manager.
(For Midland Vehicles, Ltd.) THE REAL FUNCTION OF THE SHOCK ABSORBER
AS your correspondent II. C. Barty says in your issue of December 2, 1949, the shock absorber is getting more work to do as a result of some modern developments in suspension. The coil-spring and torsion-bar types in particular eliminate the sliding friction which is inevitably a feature of leaf springs.
Rubber does give a considerable amount of damping, but the compounds in use at present do not relieve the shock absorber of more than a quarter of its load under normal conditions. Even if a material were available that had four times as much damping, it would not make a good suspension. The blow-off valve of the modern hydraulic shock absorber is essential in order that the very minimum of resistance shall be offered to the initial displacement of the spring following a severe bump. In fact, the shock absorber is not what its name implies. Its function is to damp down the rhythmic movement .which normally follows a road shock and to interfere as little as possible with shock absorption.
Rubber gives comparatively less damping for large movements than for small movements, and is, therefore, particularly suitable for vehicle springing, but there is no hope of cutting out the shock absorbers or of relieving them of more than a small part of their work, unless new types of rubber conipound can be evolved.
Leicester. A. J. HIRST,
Chief Technical Engineer. (For Metalastik, Ltd.)