The Value of "Through" Driving.
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Mr. W. P. DURTNALL, who spoke first, said that the paper had evidently been prepared with a good deal of care, but in certain essentials he was absolutely at variance with some of the conclusions which had been expressed. ,As most of those present were aware he had, in conjunction with Mr, E. W. Hart, been investigating this interesting problem for some years, and they claimed to have solved it in the system with which their names were associated. He agreed with the authors of the paper that the only thing for the heavy vehicles was the adoption of the petrol-electric system of power transmission and speed regulation, but he was certain that no system using the purely-electrical drive continuously would really be commercially successful in competition wlith the petrol-electric system that only used the main electrical plant for starting, and accelerating the vehicle, and used direct mechanical drive for the majority of the time the vehicle was on the road. Electrical transmission of power, for long distances, had been proved by extensive practical experience to have no successful competitor commercially, but, when it came to the continuous transmission of the power of a motor.emnibus engine to the back axle, from a commercial point of view it was quite another matter, and, indeed, explained why the Hart-Durtnall system was so economical as regarded petrol consumption per ton-mile, when compared with other petrol. electricsystems. The right thing to do was to start the vehicle electrically, and then magnetically to clutch the engine direct through to the back axle, and so to save all the electrical losses which took place when the electrical plant was working all the time that the vehicle was running on the road. The Hart-Durtnall system, as applied to the motor-omnileus, was that, coupled direct to the engine, there was a polyphase, alternating-current generator, and series-wound exciter combined. This ran at the engine speed. At the other end of the generator was a magnetic clutch, which, with the revolving field of the alternator, formed the flywheel of the engine. Coupled to the propeller shaft was an induction motor, wound for two speeds, which equalled the vehicle speeds of about 3 and 6 miles per hour respectively. On the end of the motor shaft, nearest the engine, or generator, was mounted the armature side of the magnetic clutch, and the whole was mounted up in line on one supporting frame self-contained. Twelve m.p.h. was obtained on direct drive.
A Criticism of Details.
Mr. GUY BEAUMONT called attention to the fact that the "Hanford" omnibus only used a 30h.p. engine, which was a lower-powered engine than that used with some petrol. electric systems. It appeared to him that the omnibus laboured under a certain disadvantage in regard to hill-climbing. Mr. Frost-Smith made reference in the paper to the disadvantage of night work, and that seemed to him to be an important point. A petrol-electric transmission gear could he continuously employed without serious attention, whereas it was frequently necessary to do work at .night in connection with mechanical transmission gears. He took it that the costs referred to the. heavy mileage which Mr. Feast-Smith obtained from his motor omnibuses, and he might say that that mileage entitled Mr. Frost-Smith to be considered the most effecting task-master as far as the motor omnibus was concerned. It would be interesting to consider if these expenses would not be reduced if the Mileage were less. With regard to traction accumulators, the author stated that there had been no improverneat in the accumulator, and even if that were true, he would point out that there had been an improvement in the conditions of use of the accumulator. At present, any attempt to obtain a direct drive with electric transmission gear involved the use of other parts, and involved fresh difficulties, but, if the direct drive could be used for the higher speeds in the vehicle referred to, then he thought better results. would certainly be obtained. He agreed with Mr. Durtnall that it was desirable, if possible, to obtain a direct drive, and to cut out the electrical transmission, which must involve losses in
the system, and lead to higher running costs. The main difference between the Hart-Durtnall and the "S. B. and S." systems was that in the former it has been found necessary to use a 40h.p. engine, whereas with the latter a 30h.p. engine was found to do the work.
Mr. DURTNALL here interposed to say that a 30h.p. engine would be running immediately on one of his vehicles, and that" it was not necessary to have a 4-0h.p. engine. Mr. BEAUMONT rather questioned the reversibility of the worm driving-gear. It seemed to him that, where one had a ten to one reduction, the question of irreversibility began to crop up. He had doubts, too, concerning the design of the back axle, as it seemed to him there was some difficulty in applying the worm drive in the position shown, and, of course, trouble was bound to arise if the lubrication was not perfect. He would, therefore, like to know if any trouble had been experienced with leakage. With regard to the sparking, he had seen the omnibus in operation, and the commutators showed no sign of sparking whatever. From the point of view of vibration, the omnibus was running under fairly satisfactory conditions, as compared with tramway and railway motors. One of the chief difficulties was to construct a motor which would stand the possible overloading, without failure, and yet would not be too heavy. "
The Future of the Electric Bus.
Col. Caciereoe said he had watched the progress of petrol. electric systems with great interest, and he should be sorry to say which of them was going to survive. Some of the features involved in the design before them were exceedingly interesting, both mechanically and electrically. He personally was very keen on the worm drive. On the general question, although he was the last man to say anything detrimental to the electric motor, he would point out that it was an exceedingly complicated piece of mechanism, and, in the. case of machinery going out to the Colonies, and some of the parts being missing, it would call for the services of a good electrical and mechanical engineer to meet the difficulty. He mentioned this because it appeared to him that in the future, unless these things were thought of, there would be a good deal of trouble in connection with the Colonial trade, which was going to be a big branch. The employment of mechanism of this sort called for a highlytrained class of workmen and drivers, and it was going to take a very long time before the industry was properly equipped in this respect. That was the main criticism he had at present to offer on these petrol-electric systems—that they were somewhat complicated. No doubt, the electric vehicle was theoretically the proper vehicle to have, and he did not propose to criticise the paper beyond what he had said, because it was a good paper, full of good ideas which had been very modestly stated, and he believed that the system would meet with a certain measure of success.
He would like to say that he believed a great mistake was being made if it were thought that the accumulator bus had not come to stop. It had to be remembered that the accumulator omnibus, with its ability to take its charge in the off hours of a' supply station, would always get its supply of energy at lower prices than anybody else. Moreover, the cost of maintenance was going down rapidly, and he believed it was only a question of organisation for the accumulator omnibus to be put on a satisfactory commercial basis, and to pay its 'shareholders well. There was certain to be an enormous demand for energy for accumulators. New York was far ahead of England in this respect, and had used accumulators with considerable success for heavy lorry work in traffic to and from the docks, a branch of enterprise which had not yet been initiated on this side. It was not necessary to wait for a new battery; he believed that the same old accumulator we were familiar with would do the work. The electric accumulator had made its appearance in connection with the London omnibus, and through its use it had been found out for the first time that it only took about 10h.p. to run an omnibus instead of the 20h.p. which had always been considered neces sary, so that the motor-omnibus engineer now knew something definite about his gearing losses, and the general inefficiency of the present system of driving.
Recent Types of Steamers Show Good Results.
Mr. F. SEARLE (London General Omnibus Company) agreed with Col. Crompton as to the danger of putting inexperienced men in charge of intricate machinery, such as was installed in the petrol-electric and petrol vehicles. He was rather surprised, seeing the number of gear-driven vehicles that Mr. Frost-Smith was employing, to hear that gentleman crying " stinking fish." He had had experience lately of an omnibus of which Mr, Flexman French was associated (the Ryknield), which had run nearly 11,000 miles, and the total expenditure for maintenance and repairs had been no more than £4 15s. Whilst accepting Mr. Frost-Smith's figures in respect to maintenance and other charges, as applying to the past three years, he believed that his figures were much lower recently, and would like to know what his costs were for the last six months.
Mr. Frost-Smith dismissed the steam omnibus with a statement that steamers did not appeal to him for London traffic and motorbus work, and that Clarkson could not claim to have been successful. In reply to that, he would say that he had his Clarkson omnibuses working very satisfactorily, with a lost mileage of no more than 2 per cent. Mr. Clarkson had given a great deal of attention to his boiler, and his latest type was working quite successfully. His company knew little or nothing of the petrol-electric vehicle, but to talk of costs, as Mr. Frost-Smith did, after running about 6,000 miles, seemed to him to be somewhat previous. The only petrol-electric vehicle with which he had had experience lost 20 per cent. of its mileage, and only on one occasion was that the result of mechanical failure. He did not think the petrol-electric system would be of any use as far as London was concerned. If an electric vehicle was to be employed, he preferred an electric vehicle, but not a combination of the electric system and the petrol engine, which was only substituting for the present system of transmission two motors and a dynamo and other complications. He was certain that the ordinary gear box would never give anything like the trouble that would he experienced with the petrol-electric system.
Other Speakers.
Mr. H. KERR THOMAS thought that in the Hart-Durtnall system, with the direct drive, some of the advantages to be gained were given up in comparison with the vehicle which was driven continuously through the electric gear. In the system employed by Mr. Frost-Smith, the arrangements certainly made for simplicity, and he was in a position to say that, given perfect lubrication, the worm drive was absolutely reversible.
Mr. WYATT referred to possible trouble from sparking. If the motor were entirely sprung from the back axle, there should be little or no trouble in this respect, experience having shown tivt there was really very little trouble with sparking, even when the motor was only half sprung, or not sprung at all. With regard to what had been said as to the accumulator. driven vehicle, the costs of maintenance of the accumulator had come down very considerably, and seemed like reaching a still lower point, but, in employing a system of that sort, a large number of vehicles must be in service; otherwise the maintenance costs would still be too heavy. He believed, however, that with a sufficiently large fleet of omnibuses, maintenance could be reduced to a point to make the electric bus commercially possible. Mr. FLEXMAN FRENCH said that his experience of the HartDurtnall system was that it took the hills as well as any petroldriven bus, and he thought the petrol.electric system was a step in the right direction.
Authors Reply on Discussion.
Mr. FROST-SMITH replying on the discussion, said that, when considering the question of employing a petrol-electric vehicle, he noted that it appeared to call for the employment of a big engine, although Mr. Dui-troll now said that this was not necessary. He had been led to adopt the arrangement referred to, as the result of his own experience. He agreed that on steep gradients the petrol-electric bus was rather at a disadvantage as compared with the petrol vehicle, but there were no steep gradients in London, and their experience was that in London the " Hanford," with its " S.B. and S." equipment, took the hills as weli as any gear-driven omnibus.
He had had experience with accumulators in connection with the Birmingham Central Tramways, and it yet remained to be proved if a dividend could be paid working with accumulators pure and simple. No doubt energy could be obtained cheaply, but it was a question of wear and tear, although the charges in this respect were coming down. He was watching the present experiments being made with electric omnibuses with much interest, and would be glad if the companies at present running accumulator buses in London were able to do so successfully. The worm gear proved itself perfectly reversible, and they had had no trouble over the lubrication in respect to leakage. It took 4 lb. of grease per week per worm to run the omnibus. Some criticism had been made with regard to the position of the worm, but it had been impossible owing to certain features of the design, to place it in any other position. He did not think that Mr. Searle should condemn the petrolelectric system because of his own unfortunate experience with a particular vehicle, and, if he might suggest it, Mr. Searle had formed his opinion without any real experience. His positive condemnation was no argument, and was far from conclusive.
Mr. W. A. STEVENS pointed out that in London working the omnibus was continually accelerating and stopping, and he could not agree that the Hart-Durtnall was the ideal system under such conditions. The efficiency of the electric drive was at its maximum just at the point where Mr. Durtnall would cut it out altogether. They were now using thicker yokes, which gave greater permeability, and they thus obtained the full benefit of the field windings. In the original form, they were obliged to couple up the motors in series, but they were now able to join them in parallel, and the resistance fell one-fourth, and, therefore, the drop of the potential was only one-fourth, of what it was in the earlier type of vehicle. The result was that the omnibus would climb hills in London as well as any gear-driven vehicle. With regard to the consumption of petrol, the petrol-electric vehicle was the most economical on the road, and the efficiency worked out at from 85 to 92 per cent., whilst, on all ordinary roads, such as were met with in London, the efficiency of the electric motors was more than 90 per cent., and the total efficiency was 70 per cent., with a gear ratio of 12 to one, on a hill of one in 12.