The Design of Commercial Motors.
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Mr. T. B. Browne's paper on The Design of Petrol Motor Vans," which was read before the members of the Institution of Automobile Engineers, on the 9th February, at a meeting held at the Institution of Mechanical Engineers, Storey's Gate, S.W., proved to have the desired effect—the discussion of many details in the design of commercial motors. Our readers will remember that, in our issue of the 10th ult., we reprinted some of the costs which were given in an appendix to Mr_ Browne's paper, and the essential parallels of other casts which were included in that appendix were communicated to the Editor, in a letter from Mr. Leycester Barwell, some months previously, and were published in this journal on the 9th December last. Mr. Browne, of course, obtained his later costs direct from Mr. %swell. The text of Mr. Browne's paper has not been reprinted in THE COMMERCIAL MOTOR, but the omission has been partly due to pressing demands on our space, and partly to the fact that the pa-per was obviously written for the purpose of stimulating a thorough discussion of the questions raised by the author. We now give a resume of the chief portions of the discussion, which, by the way, occupied the greater part of two evenings. Dr. H. S. Hele-Shaw, F.R.S.. the President of the Institution, occupied the chair during both the meetings.
Mr. F. C. A. COVENTRY, who opened the discussion, gave the results of his experience with vehicles owned by the Great Western Railway Co., and stated that : " The most expensive parts about the car I should put down as engine castings, such as cylinders and crankcases. This will be rather a surprise to the private-car people, who practically never see a broken crankcase." He was very severe on designers for their having introduced so many pin joints on cha.s.sis; such joints, he added, are very expensive to maintain. So far as clutches are converned, he favoured the coned type, faced either with chrome leather or " Ferodo." Speaking of gearboxes. Mr. Coventry declared that, with a careful driver in charge of a vehicle, 50.000 miles of running without any repairs was not difficult of attainment. "The final drive." he added, " should be anything but chains, the cost of which is quite prohibitive." Mr. Coventry was, later. asked the extent of his experience with chain-driven vehicles: most of the G.W.R.'s vehicles are of the Milnes• Daimler gear-driven type. He advocated the employment of the system of lubrication in which a scoop on each big-end dips into a shallow trough of oil—each trough is kept full to overflowing by the aid of a gear pump ; he had known engines, which, with forced lubrication, could only run 40 miles on one gallon of oil, when converted to the trough system, ran well over 320 miles for the same quantity of oil. He had found, too, that th tire question was not nearly such a serious one at the present time -jet was; • say, seven years ago; for buses, he placed the average mileage cost for tires between 10. and lid. This speaker thought that " The best way to train men was to start them as conductors at about the age of 17, and to let them travel on the cars for some years ; they thus got the spirit of the whole thing into them, and saw the driver at work. Then, after they have had about two years of cleaning, and have been in the repair shops. they become really satisfactory men." Such a course of training may be practicable for some parts of the country, but there would be few motors on the road were it necessary to spend so much time and money on the training of drivers. We are inclined to support the arguments of other men, in respect of town and urban work, that the old horse-driver makes the best man for a motor, at any rate, for vans. Mr. Coventry supported the contention, first advanced in the pages of this journal, that depreciation should be assessed on a mileage basis, and he placed the life of a motorbus at 200,000 miles. He expressed the opinion that there is a large field for vans of 1.5-eat. capacity, with wheels shod with solid tires ; further, he thought that the 6 cwt. tri-ear type of machine, such as the "Auto-carrier " (handled by F. B. Goodchild and Co., Ltd.), will find favour with small users. According to Mr. Coventry, the most-common causes of failure are as set out in the following list:— Petrol or pressure pipes broken or choked, 28; magneto (due to poor mechanical, rather than to electrical design), 23; sparking plugs, 1.3; carburetter, 13; clutch and clutch gear, 13: big-ends, 12; water pump and pipes, 10; differential shafts and castings, 9; steering gear, 8: engine gear, 7: springs, 7; frost. 7: cardan shaft, 4; governor, 2; cylinders, 2; crankshaft, 2; gearbox shafts, and (listings, 2; differential gear, 2; camshafts, 1; tires, 1; gearbox gears. 1.
Mr. CHAS. WHEELER, who followed Mr. Coventry, spoke of the necessity of keeping correct and detailed or-counts of the running of motor vehicles, and he accepted the invitation of the President to send in a short description of the system which he advocated. He criti• cieed many of the costs given in the appendix. He supported Mr. Browne's suggestion that tire makers should take speed into consideration when settling the size of a set of tires for a given vehicle; a speed limit, he argued, is as important to the life of a tire as the clue consideration of its load-carrying capacity. He also agreed with the author that the position he had selected for the driver—by the side of the engine— was a good one, because it enabled the overall length of the chassis to be kept down to a minimum.
Mr. D. H. SIMPSON, of Manchester, was very emphatic in his condemnation of the trussed frame, and we entirely agree with his statement that " Any tie bars and struts underneath the main longitudinal channels can only assist the latter when the vehicle is stationary, and the structure can be considered as a bridge." We have known the top fleece of a channel frame to become cracked right through, as a result of the " hogging " action which is caused by the tie bars and struts when the vehicle is driven over rough ground with a light load. Pin joints, he agreed, were costly to maintain, and the number of them should be kept down to a minimum, and, further, the wear should be limited to one part of the joint by the prevention of any movement in the other part.
Mr. G. H. BAILLIE was surprised that the author should advocate the fitting of a two-cylinder vertical engine, which type, the speaker added, is devoid of all merit; its turning moment is irregular, and it leads to more wear and tear than does the more-even torque of the four-cylinder type of motor of equal power. He asked the author why he had not fitted one of the horizontal, two-cylinder, opposed type, which were fitted to James and firowne pleasure cars; the speaker thought that a very good engine, and its balance quite satisfactory. He thought that many of the objections urged against tht use of forced lubrication, with drilled oil ducts, were due to the use of an insuffieient pressure of oil ; the pressure should be sufficient to clear away temporary obstruction in the ducts. He strongly opposed Mr. Browne's suggestion for the abolition of the usual centre bearing of a four-cylinder engine crankshaft.
Mr. DOUGLAS MACKENZIE was sarcastic about carburetters. He stated: " We have wonderful, fancy carburetters, which will give such low rates of fuel consumption as to make our mouths water, but we have no end of trouble with them on the road, so that the earl-wetter that enables us to ` get there,' even at the cost of twice the petrol we would otherwise consume, is the one we should choose." He thought that the mileage hesis was not the correct method of assessing depreciation, which charge, in his opinion, should be a definite percentage of the original cost on the outfit, because, with the present method of meintaining a machine in a state equal to new, depreciation becomes a matter of obsolescence only.
Col. CROMPTON, C.B., advocated the use of rolled channel-steel frames, in preference to those of the pressed. steel variety, but his arguments were not clearly understood by the audience. Col. Crompton is a persistent advocate for the fitting of very-large-diameter wheels.
but he agreed with Mr. Browne that motor manufacturers are rieht in continuing to use wheels of 40 in. in diameter for buses and lorries of over three tons load capacity; larger wheels would involve the raising of the loading platform—an objectionable feature. ITe. gave sonic most-in teresting data relating to ball bearings, which data go to show that no appreciable wear takes place in a modern bearing provided it be kept free from moisture and acids. Amongst other speakers who contributed to the discusShen were Messrs. Gilchrist, Knight, Martinenu, and Stermey.
Capt. It. K. BAGNALL-WILD, in a communication to the Secretary of the Institution, stoutly defended the
pressed-steel 'frame, and condemned the fitting of trusses. Regarding the sueeestion, which was made by the author, that starting handles and other similar levers should be
made detachable, in order to avoid their being damaged, Capt. Bagnall-Wild thought it would be preferable to employ a driver who was not in the habit of running into timings. He stated that he is " up against " the use of aluminium and cast-iron for crankcases and gearboxes, and thinks that the day is not far distant when we shall be using pressed-steel boxes of extremely-simple construction. We wonder what he saw going through the shops on the ocoasion of his last visit to Marienfelde?
Mr. F. STRICKLAND also sent in a letter to the Secretary, and, amongst other subjects mentioned, he thought that more attention should be paid to the " simpling " of the construction, and the reduction of the total number oi parts in a commercial vehicle.
Mr. T. B. BROWNE, in replying to the discussion, set out by making it quite clear that he did not advocate the use of any particular form of construction, or system, as being the best under all conditions. On the question of chain-driven versus gear-driven vehicles, he said the battle had been fought and won by the latter typo of drive, so fee as pleasure cars are concerned, but, for commercial vehicles, it would be a matter of the survival of the fittest. He commented .upon Mr. Coventry's remarks regarding chains, and asked if it is not a fact that nearly all of the G.W.R.'s machines are gear-driven? He quoted the results obtained by Shoolhred's, which company gets 10,000 miles of running out of every chain fitted. He agreed that the mileage basis is the correct one on which to base the charge for depreciation, and did not think that 200,000 miles is too much to expect from a machine.
Mr. Browne thought that Mr. Wheeler had been very kind to him, so far as concerned the body of the paper, although he had shown a desire to " operate " on the author's appendix ; the costs figures were given to the author by users, and he had inserted them without alteration or addition; consequently, he could not accept any responsibility for their accuracy. Mr. Wheeler had said that items were left out which ought to have been included; in the case of Shoolbred's, Mr. Browne said he
-td subsequently communicated with Mr. Barwell, and the following was an extract from his reply :--" Our yard is freehold and takes 300 horses and 200 vans. The cost of garage ' is provided with the before-mentioned accommodation. The figures were compiled by myself from our books, and I am quite satisfied that I am doing 70 per cent, more mileage for the same money as was spent before motorvans were used. Our head engineer's salary is, of course, charged to motor repairs, but other management consists of the same foreman who looks after the horse-vans. Chains and sprockets cost money, but not more than new parts for live axles; we get 10,000 miles out of a pair of chains, and do not grumble. My engineer would be horrified if I suggested live axles instead of side chains. My figures were got out to compare the cost of motor transit with cost of horse-vans, and what. ever items are missing in one are also missing in the other. Naturally, the garage of motorvans (one motorvan does the work of six horse-vans) would cost much less than stabling for horses and vans."
Answering Mr. Baillie's question about the horizontal engine, Mr. Browne said that, if the opposed type be used, the rear cylinder is buried under the platform, unless the crankshaft be arranged longitudinally on the chassis; in the latter ease, the cylinder ends and the valves and spnrking plugs are most inaccessible. Tn spite of what Mr. Baillie had stated concerning crankshafts, the author said he still held the belief that it is possible to build stweessful four-cylinder engine with only two hearings for the crankshaft. The (.rankshaft could easily be made stiff enough for the purpose, and that without greatly increasing its weight, because, if ball bearings be used, there conld he a saving of 3 in. in the distance between the two outer hearings of a four-cylinder 4 in. engine. He reminded his audience that the latest fourcylinder de Dion-Bonton engine has such a crankshaft.
Mr. Browne, in conclusion, expressed his satisfaction with the discussion winch his paper had hen the means of promoting.