OPINION
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S and QUERIES
Controversy on Metal Bodies. The Vital Need for Efficient Braking Systems on Lorries and Trailers
THE PROS AND CONS OF GOVERNING VEHICLE SPEEDS.
The Editor, THE COMMERCIAL MOTOR.
[4338] Sir,—Under this heading in your issue dated June 22 you state that a governor may actually constitute a direct cause of accidents owing to .a driver not having at his command a certain reserve of speed in order to enable him to get out of "tight corners." You also suggest that this is of rather greater importance in the case of comparatively speedy machines.
It is admitted that this idea is quite common amongst drivers who, naturally, do not wish to have governors fitted, also amongst engineers and others who have had no personal experience of handling governed vehicles or whose experience with governors ceased with wartime models.
The opinions stated by you are in direct opposition to modern practice, and I venture to ask if you will allow the courtesy of a little space on this matter, which is of considerable interest to-day. Without a governor at all every vehicle has a maximum speed for the particular load and road conditions under which it is operating, and even if this maximum speed be 50 m.p.h. it could still be argued that a reserve of speed (say, to 55 m.p.h.) would be desirable to enable the driver to get out of " tight corners." In other words, it does not matter what the maximum speed is a vehicle can never have sufficient road speed to enable it to get out of all tight corners, as the higher the road speed the " tighter " the corners. Experience shows that with a vehicle governed to a reasonable maximum the necessity of escaping danger by means of excessive speed does not arise.
The principle of escaping danger by the use of speed is wrong and directly opposed to the public safety and the interests of the vehicle owner.
The real reason why governing at the legal speed limit is sometimes impossible is that when the engine speed is governed to give the maximum permissible road speed in top gear the engine output is reduced if this governed speed be below the peak horse-power speed. This is not, however, noticeable to the extent which would be expected, except with the high-speed type of engine in which governing to a low road speed may govern Vie engine r.p.m. to a point substantially below the speed at which the maximum torque is produced.
This is generally more noticeable in the case of vehicles with a 20 m.p.h. limit, and in most instances a maximum speed of about 25-28 m.p.h. is preferable B36 for this type. On the other hand, there are large numbers of lighter vehicles operating in this country governed at or very slightly above the legal maximum of 30 m.p.h. As mentioned by a well-known engineer in your. columns some few weeks ago, the solution lies, of course, in the selection of suitable gear ratios and rear tyre sizes, and there is already a tendency to revise existing ratios in this direction.
It would appear to be advisable to stress the difference between governing from the point of view of engine protection and economy and governing with the idea of limiting the vehicle speed to the legal maximum. As indicated above, it is frequently possible to govern satisfactorily filling both requirements, but in general -the modern idea of governing is solely from the point of view 'of reducing maintenance costs and improving the petrol, oil, tyre and brake-facing consumption figures. This principle has been extensively adopted by many of the largest fleet owners in the country, and it would be unfortunate if your comments conveyed the suggestion that the principle was conducive to dangerous conditions when, in fact, it is exactly the reverse.
It is my experience that practically all commercial vehicle manufacturers approve and strongly recommend the fitting of governors to commercial vehicles, whilst oil-engined vehicles are almost invariably equipped with a maximum-speed governor. Surely this must disprove the fallacy of governors being "a direct cause of accidents"? The Associated Equipment Co. has governed every goods-carrying vehicle for more than three years, whilst Albion, Leyland, Thornycioft and others have fitted governors as standard to one or more models for a very long time, and still continue to do so.
More attention is being given to governing commercial vehicle engines than at any time during the history of the internal-combustion engine, and I hope that this explanation may prove of guidance to your readers, most of whom must be interested in the subject.
R. BEDFORD, A . . A E. , . S. A . E.
Beckenham.
[As this matter is of some considerable interest we would welcome further views from drivers of governed vehicles and from technicians who have studied the use of such governors.—En.}
ALUMINIUM-ALLOY TIPPING BODIES.
The Editor, THE COMMERCIAL MoroB.
(43391 Sir,—A correspondent (letter No. 4330) in the June 15 issue of The Commerciol Motor makes certanx statements which are apt to be misleading. Reference is made to " 'erent defects in high-tensile aluminium alloys which ender them less satisfactory than steel for construction work where excessive vibration takes place."
My company has supp ed a large number of lightalloy tipping bodies duriI g the past three and a half years—all these bodies I•ve been subjected to the hardest work possible, and in no case can it be suggested that inherent weakness insults show that they w I do not wish to 'labo obvious, and we all know a body in the sand an floors rust up overnight a the first few tips repolish portion of the thickness.
The point I wish to str words " inherent defects. priate to say "inherent point to differentiate bet which have a high resis have not, and furthermor and proper application utmost importance, so th certain interesting featur high-duty alloys.
The alloys we use have the strength of a good-quality mild steel, but only approximately one-third the weight —a mild-steel body of equal strength and with plate of the same gauge must, therefore, weigh nearly three times as much. have developed—in fact, far outlast the steel body. the point about rust--it is how long paintwork lasts on ballast trade. The polished d during the week-ends, and the plate at the expense of a
ss, however, is the use of the ' It would be more approharacteristics." I make this -een those high-tensile alloys nee to fatigue and those that to emphasize that the design f frame members is of the t advantage can be taken of s which are peculiar to these
In designing we do not start with the disadvantage of having to save weight by introducing light sections which do not give sufficient rigidity, and reduced thicknesses of plate.
Steel bodies are obviously less costly, but from an economic point of view the saving in weight and longer life soon enables the extra outlay to be written off.
E. L. OGLETHORPE, Managing Director,
For The Duramin Engineering Co., Ltd.
London, N.W.I0.
MORE ABOUT TRAILER BRAKING.
The Editor, THE COMMERCIAL MOTOR.
[4340] Sir,—From the interesting letters on trailer braking which have appeared in your recent issues one gathers that a considerable amount of thought has been, and is still being given, to that important question, braking efficiency. Emerging from these letters is the fact, among other considerations, that only split seconds are involved. No doubt vehicle owners (and drivers) are taking due note of this remarkable efficiency, and it is to be hoped that the powers that be are at least interested in these improvements.
Now we have—perhaps unconsciously—another 'entrant into the field of discussion involving fractions of a second, inasmuch as a recent editorial comment on an overrunning trailer brake states that it is theoretically wrong to brake the towing vehicle earlier than the trailer.
Whether it be fight or wrong in theory the fact remains that only a fraction of a second is involved. It will be apparent that immediately the driver applies the brakes to the towing vehicle comes the overrun of the trailer, which applies the brakes thereof, and these remain operative until the towing vehicle draws ahead. Not until then are the brakes released.
Still thinking in split seconds, it will be appreciated that the removal of the driver's foot from the accelerator pedal to the brake pedal occupies time (in fractions of a second), and in that time the trailer has overrun the towing vehicle, causing the brakes to operate, because the towing vehicle has decelerated, momentarily. In this respect it would appear that the theory (as well as the practice) of the overrunning type of trailer brake has a definite advantage.?
It should be remembered that such a brake readily lends itself to further advantages. For instance, it can contain a shock-absorber, eliminating jolts between the towing and the towed vehicles. It can also incorporate an emergency brake; one arranged to operate with the utmost reliability when the trailer breaks away from the towing vehicle. These advantages are more readily and less expensively incorporated in the overrun brake than they are (even if they can be) in any other type of trailer brake. F. G. CLARK.
For The Projectile and Engineering Co., Ltd. London, S.W.8.
[Mr. Clark's statement that the overrun brake is brought into operation by the moderate retardation of the towing unit when the throttle is closed, appears to corroborate the opinion we recently expressed. Incidentally 80 m.p.h. equals 14.7 yards per second.—En.)