THE COMMERCIAL MOTOR OF THE NEAR FUTURE.
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A Survey of the Practical Improvements That Experience and Presentday Knowledge Show to be Capable of Being Immediately Adopted.
IN opening up the subject of the improvements Ithat might be introduced into the commercial motor of the near future, I do not propose to consider those improvements which are entirely in the clouds, no matter how desirable the results that should be obtained from such devices may be. I feel that there are certain things known, and more or less proved, which if embodied in a new• model would place it above those in existence to-day. My desire is to avoid freaks and fads, and to keep to such alterations as would make a vehicle more serviceable, less costly to maintain and more profitable to run, as it would be on the road for more days in the year than the present types and thus have a larger earning capacity.
It will, doubtless, be said by some that the suggested improvements will increase first cost. This may be so, but is it not a fact that all machinery that is efficient is more costly in the first place than that of the less efficient type'? The fetish of low first cost may appeal to the shortsighted user, audit may appeal to the firm of motor manufacturers who have only 'a poorly developed selling organization, but, taking a lesson from engineering ' generally, I cannot think of an instance where the
sale of really efficient machinery has been rendered impossible simply because there is a cheaper and less efficient type on the market.
I am quite aware that certain manufacturers of commercial motors may say : " Let others beat the bush, and we will catch the hare." In practice' however, this plaa does not always work out well. If progress in other countries could be held back, this plan might satisfy some, but progress cannot he held back in other countries ; consequently there is the possibility of our waking up one day to find that we are very much behind in the design and manufac ture of commercial motors. We are, to-day, undoubtedly ahead in this industry, bus the foreigner will not stand still ; so it is our duty to considewhat improvements, without suggesting freaks, could be introduced into the commercial motoof the near future.
I do not intend these remarks to apply to the lighter types of commercial vehicle, which are fast becoming more like pleasure cars, but to apply to lorries carrying three tons and over, also to the larger types of passenger-carrying vehicle.
In actual use a good engine will often gives less trouble to maintain than almost any other part of a lorry. Taking into consideration the very high speed at which these engines usually run, and the rough conditions mostly prevailing in lorry work, this speaks well for the design of this part. There are, howeeer, several points worthy of consideration. The number of bearings a crankshaft should have is a matter that has never been finally settled, some considering that five bearings are required, while others think that as few as two are sufficient.
After an exceptional opportunity of examining the' effect of wear on thousands of crankshafts of all kinds I have come to the conclusion that three bearings are the best for lorry work. The bearing that 'usually suffers most in a three-bearing shaft is the centre one, and if measured with great care the position of the wear shows that it is mainly due to centrifugal force arising from the fact that the web on each side sets up a pull both in the same direction,
as in Fig. 1. if these webs -,7ere fitted with
counterbalance weights this wear would be considerably reduced.
In my opinion, the centre bearing and that at the timing gear end would be both improved by being made of greater length. The bearing near the flywheel seldom shows any sign of wear—this would seem to be due to the fact. that it is usually of greater length than the other bearings.
With regard to the bearings of the big-ends, these are usually as long as circumstances will permit. No possible room' however, should be wasted, as the longer these bearings are, without increasing the total length of the engine, the better the wearing of the engine. Attempts have been made to increase the length of these bearings by offsetting the connecting rods, but this is a method that should be avoided, as it sets up all sorts of troubles elsewhere.
The holes drilled for lubrication in a crankshaft are often the starting places of fractures. Too small a radius is also a fruitful cause of breakage, as is also the termination of a radius in a sharp shoulder, as shown in Fig. 2. The examination of the very large numbers of broken cranks referred to has convinced me that if the three defects of design mentioned above are avoided, a broken crank would be almost unknown.
All reciprocating parts should receive attention, with a, view to reducing weight to a minimum. In
many cases fhe weight of a connecting rod could e considerably reduced by greater care in the design, without in any way reducing its strength. Aluminium pistons have by now sufficiently demonstrated their suitability for use in lorries to become a standard. The bronze shells of the big-end bearings are often unnecessarily heavy. With regard to the general construction of the engine, I am in favour of certain features, but cannot say that these are absolutely essential in the design of a good-working engine. I consider that cylinders in pairs are preferable for lorry work to those east en bloc, for many reasons. They are cheaper to renew in the case of accident or cracks through frost, and they are easier to lift off when attention is necessary to internal parts. With regard to unit construction, that is to say, engine and gearbox in one unit, I consider that it is unsuitable for lorry work, and feel that those who have to keep fleets of lorries on the road will, in the majority of cases, agree with me.
. Such features as detachable heads to cylinders, overhead valves, overhead camshafts, etc., have hardly convinced me that these departures from practice which we know to have worked well can be recommended as real improvements. There are many good engines without any of these.
Sparking plugs undoubtedly work better if surrounded with water-jacketed parts. Three-point suspension of engine in the frame has proved itself to be essential. As to lubrication of the engine, I have seen far more trouble caused through forcedfeed through a drilled crankshaft than I have ever seen where properly designed troughs and dippers are employed. The extreme simplicity of the trough-and-dipper system renders it particularly suitable for lorry work. There should be some simple tell-tale, visible by night as well as day, and there should also be some simple means of ascertaining the amount of oil in the sump.
Pumps or hustlers for the "water circulation do not seem to me to be a necessity, as some of the lorries which give best service are without them. Anything in the nature of a gland round a revolving shaft is always likely to give trouble by leaking, and in some places a loss of water is a serious thing, as it is not always easy to get a fresh supply. There is no direct economy in dispensing with a pump, as water pipes and radiators have to be larger, but there is undoubtedly a saving in small troubles.
Clutch construction is still a controversial point. The cone clutch, if properly dressed, will give fairly good results, but the question is, will it be properly dressed and attended to My experience of lorry maintenance is that it is usually sadly neglected. There is nothing worse for the general welfare of all parts of a lorry than a fierce clutch. The dry-plate clutch is one that will stand more of this neglect—and gross neglect is what we may generally expect, and what we generally findSo far, there does not seem to have been an ideal clutch invented. As I have pledged myself notto advocate things that are not already procurable, I will only say that we may hope some day to see a clutch that will admit of any degree of slipping for an hour at a time. Such a clutch would undoubtedly cost more than the present imperfect type, but I think the money would be well spent.
The fan, although apparently a simple thing. is responsible for a good deal of delay and trouble. -Unless a fan be running at its correct speed it is not efficient, and much trouble through boiling is due to a fan which, although apparently running at its right speed, has its belt slipping, and so the current of air is reduced. The belt is undoubtedly a nuisance, but I am not sure that we shall ever be able entirely to dispense with it. If this be the position, the only thing to do is to make the best of a bad job, by choosing the best form of belt.
Special leather is procurable, so treated that it is not affected to any great extent by oil or hot water. Belts made of this material, and in an endless form, can be relied upon to give very little trouble. Provision should be made between the jaws of the starter dog so that an endless belt can he fitted with B30 out taking any part of the engine down, as shown in Fig. 3. A knurled nut is preferable to one turned by a spanner for the purpose of tightening the belt, as drivers are apt unduly to stretch a belt by tightening it up too much. Apart from this, a belt which is kept at too high a tension not only wears rapidly itself, but also causes excessive wear on the bearings of the fan and pulley, and in the case of the latter this is often accentuated by overhang. Before leaving the subject of the engine of the future, I would like to say that it would not sur prise inc to see the six-eylindered engine become more popular for the larger powers. I am fully prepared for the usual objections, namely, extra cost, more details to keep in order, etc., but I feel sure that all these would be counterbalanced by the advantages obtained by the more even torque from a six-cylindered engine.
One of the greatest troubles that a driver has to contend with in the larger types of engine is the difficulty of starting on a cold morning. Should a man not be very strong, the effort necessary is likely to strain him beyond his powers of endurance. The plan of making a starting handle of extra strength, and having a detachable tube of extra length which can be slipped over the ordinary hand tube, as shown in Fig. 4, so that two men can crank the engine together, for the first time of starting in the morning, is worth considering.
SOme improvement is badly needed • in the starting arrangement of heavy lorries.
In use, much inconvenience and delay is experienced through leaks which develop in radiators, some times by external damage and sometimes by internal
defects. The removal of the headers of the usual type of radiator is not a difficult job, but, owing to
the multiplicity of bolts and nuts, it is a long job and may hold up a lorry from earning money for an appreciable part of a day. The sectional radiators as used on some agricultural tractors might be applied to ordinary lorries with advantage, as a spare section can quickly be inserted. Another plan which may he worth consideration is to locate the header by means of steady pins on to the perforated plate and to provide sections of channel steel fitted with setscrews, as shown in Fig. 5. These can be removed by simply loosening the setscrews by the use of a tube spanner. By this means, cleaning or repairing operations would be rendered easier. The ordinary alloys of aluminium are hardly suitable for the headers of radiators, as, in some districts, they are badly affected by ingredients in the water: There are more suitable alloys now being produced which would give better results. Our manufacturers should take up this matter and carry out exhaustive trials with the new alloys now on the market.
A radiator should be demountable without the need for breaking away the rubber hose front its pipe, as, in an emergency, it is easy to make a gasket, whereas a new piece of rubber hose may not always be procurable.
A. simple indicator to show whether there is water in the radiator would save many a cracked cylinder. ENGINEER-DesioNER.
(To be continued.)