Petrol-Electric Transmission for Road Vehicles.
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Opening of the Discussion on Messrs. Hart and Durtnall's Paper.
One hundred members and associates of the Society of Motor Omnibus Engineers were present, at the Hotel Cecil, to hear the delivery of the paper by Messrs. E. W. Hart and William P. Durtnall. MR. E. SHRAPNELL SMITH, the Honorary Vice-President of the Society, occupied the chair.
Ties; CHAIRMAN said that the subject for their consideration that evening was of considerable interest, and, as the paper to be read by Messrs. Hart and Durtnall was a rather long one he would proceed with the business at once. He wished to announce, first of all, that he had received a telegram from Mr. Coventry, who was attending an inquest at Penzance, stating that he would not be able to return to London in time to attend the meeting. The question of change-speed gears in motor mnibtees was giving a certain amount of trouble to everybody at the present time, and it was a subject which was, unquestionably, occupying a lot of attention. Some people thought there would be a choice, ultimately, between hydraulic transmission and purely electric transmission, and others thought that the step gear would continue to be used. He was sure that all those present would give very close attention to the paper on this important subject. He was pleased to say that the HartDurtnall system of transmission was not like a good many other systems, which existed only on paper, because a vehicle driven by this system had been on the road during the last eight or nine days, and he was able to say, from personal knowledge, that it had behaved itself admirably. This vehicle had been tested in the country under a good load, and had fully borne out the tests made on the bench.
Ma. Haler then proceeded to read the paper, and MR. Dt7RTNALL explained the diagrams and pictures, which were depicted on a large screen by the aid of a powerful lantern.
[The paper, as read, was printed in last week's issue.]
THE CHAIRMAN moved a vote of thanks to Messrs. Hart and Durtnall for their interesting paper. He did so with every sincerity, because all must have been surprised at the celerity with which they had got through a long paper, in the course of which they had exhibited 55 lantern slides. In view of the fact that the paper had been despatched so quickly, it might not be necessary to adjourn the discussion, and, therefore, he wished to warn Messrs. Hart and Durtnall, that they had better be ready with their paper and pencils. He had heard it stated that the paper did not give half as much information as those present intended to secure before the discussion, and reply, was over. He noticed that the continuous-current motor, which had been so freely condemned by Messrs. Hart and Durtnall, was retained as a fundamental portion of this new system. It was, of course, a very different thing to have a continuous-current dynamo, for an output of 1,300 watts, compared with a continuous-current motor for, perhaps, 27,000 watts. Mr. Durtnall was, no doubt, prepared to satisfy his critics in regard to the retention of his continuous-current exciter, which, if it were to fail on the road, would hang the vehicle up hopelessly. He did not propose to go over the ground covered by the paper, but, in moving this vote of thanks, he wished to state that he had been very much struck by the simplicity of control in practice. One lever on the steering wheel effected all that was necessary for the ordinary driving of this omnibus, and in an amazingly facile manner. He had travelled upon it, over give and take roads with heavy surfaces, and he had never been upon an omnibus before which was so easily controlled : it was, indeed, a revelation to him to see how well it worked.
MR. T. F. CARTER (engineer to the Associated Omnibus Company) said he had great pleasure in seconding the vote of thanks. He was glad to say that he had had the opportunity of a run on Messrs. Hart and Durtnall's machine, and, taking it all round, he thought it was very satisfactory indeed. He was, mainly, struck with the ease with which it was manipulated, especialy going down hill. They could, actually, run down hill, as slowly as they liked, without any brakes, and that was a wonderful thing for a bus. (Hear, hear.) The machine could be managed as easily as possible, and he had never seen anything like it. He was very pleased with his run in Messrs. Hart and Durtnel's vehicle, and he thought they would see the system introduced in London before long.
MR. THOMAS CLARKSON congratulated Messrs. Hart and Dortnall upon the lucid manner in which they had placed before them this descriptive, historical review of petrol-electric transmission in comparison with purely mechanical systems. So far, the authors had not given them any figures, although the title of the paper indicated that it was to be a comparison with purey mechanical systems. Before they could make a fair comparison,
they would have to compare the efficiency of transmission with other systems. There would have to be a comparison as to their relative weights and prices, and, also, as to the first cost and cost of maintenance. Until they had these statistics, he did not see how they could make a fair comparison, or one which would be sufficient to satisfy anybody who proposed to go closely into the matter. The devices in the system were extremely ingenious, and appeared to him to be very clever attempts to obtain from the petrol motor the flexibility of a steam motor. (Oh, oh !) He looked with great interest upon the future development of this system. If he might venture to make a criticism upon one point, it would be as to the lack of quantitive results. The invention, possibly, was only in its early stages, and the system might not have been in use long enough to obtain the necessary figures. They should recognise, also, that this system of transmission which they were now considering was not an attempt to deal with the fuel question, which was limited by the use of the petrol motor.
MR. BERNARD IIOPPS thought they all agreed with the authors that this was an interesting subject ; it was, in fact, a most important and far-reaching subject, and one to which both manufacturers and users alike must, if they would consider their best interests, give their earnest attention. The most serious defect of the present-day motorbus was the question of noise, which had been the chief cause of police "stop notices," and the refusal to license new buses on account of their unsuitablity in this respect. It would be interesting to know the figures that would represent the financial loss, to operating companies and manufacturers, due to the attitude taken by the police authoritiss on the standard of noise. The petrol-electric system offered a solution to this problem, as all the speed reductions necessary might be confined to worm gears. Such a system, also, afforded a considerable saving in the time required to train drivers, owing to the suppression of the change-speed gear, and the substitution of a perfectly simple and fiexib'e control. A further point, which must be noted, especially by operating engineers, was the saving that could be effected in maintenance, both on the engine and transmission and on the tires, by adopting a petrol-electric drive; these economies were, chiefly, due to the absence of all shocks, or snatch, at starting. The motorbus problem was similar, in some respects, to that of electric railroads and tramways, as, in both cases, frequent stoppages and restarts were necessary. It was under such service conditions that rapid and srnosth acceleration was of great importance, in order that the fastest schedule might be maintained without exceeding a safe maximum speed. The question of acceleration had, as yet, not received sufficient attention from operating engineers, who had had their time occupied in overcoming numerous troubles inseparab'e from a new industry, but, as the motorbus was developed, rapid and smooth acceleration would be looked
upon as a sine qua non; and here, again, the petrol-electric system offered a great aavantatie, tor, not only could this be obtained, but the acceleration could he rendered entirely automatic, and not dependable in the least degree on the skill of the driver, as was the case, at present, with the use of a change-speed gear and clutch. He had mentioned only a few of the advantages of a petrol-electric drive, which had not been touched upon by the authors in their paper. Referring to the paper itself, and, particularly, to the description of the authors' system, the arguments advanced were, chiefly, in support of the use of the alternating-current system, and condemnation of the direct-current system : this was, apparently, solely On account of commutation troubles, attributed to the latter. Whilst he did not stand there to champion the direct current system to the exclusion of the alternating-current system, he felt it due to the former to say that the commutation troubles, which the authors stated having experienced in their experiments, might, safely, be attributed to unsuitably designed machines. He was prepared to admit that the design of a satisfactory, automobile, direct-current motor was a difficult problem, and was one which demanded as extensive experience, and as costly manufacturing facilities, as was required in the manufacture of railroad and tramway motors ; but it was an established fact that a satisfactory direct-current motor, suitable for severe bus ser vice, could be produced. The design and method of manufacture of these special motors, was, like those of the petrol engine
itself, evolved more from experience than from following rules which applied to every-day stationary machines. The chief advantage which direct current had over alternating current, was, the higher torque per ampere that could be obtained front directcurrent motors. In order to reduce the current input, and to increase the torque, of an induction motor, it was necessary to sacrifice the efficiency ; otherwise, the increased current required to produce the necessary torque, at starting and climbing grades, would cause destructive overheating of the windings. It was a well-recognised fact, that it was not possible to approach, with an induction motor, the torque, range, and efficiency of a serieswound direct-current motor, of a similar weight, and with the same heating characteristics. A further point that must be recognised, was the fact that a series-wound, direct-current motor had a far greater maximum torque limit per lb. of weight than had an induction motor, even although the latter were wound for two speeds. This would mean that, assuming there were two vehicles, one fitted with an alternating-current motor, and the other with a direct-current motor of equal weight, and assuming the same engine power and gear ratios, the vehicle with the direct-cur-rent motor would be able to ascend a grade that the alternating-current motor would be unable to negotiate. In order to increase the torque limit of the induction motor, it was necessary to increase the weight. As a proof of these statements, he would call their attention to the general adoption of direct-current motors for electric traction. Efforts had been made to utilise the induction motor for this work, but, owing to its having a characteristic similar to a direct-current, shunt-wound motor, no commercial success had, so far, been obtained. In cases where alternating current had been applied to electric traction, the alternating-current motors, generally, had commutators which rendered their characteristics similar to the series-wound, direct-current motors. The general • adoption of direct-current motors, for traction purposes, was a proof of the absence of the commutation troubles referred to by the authors, and he ventured to say that, if they questioned an electric tramway engineer, he would tell them that one of the least of his troubles was due to commutators, although tramway motors were, owing to the higher voltage necessary, working tinder more severe conditions than those used for motorbuses. On studying the diagram of the stator of the induction motor of the authors' system, he noticed that two separate three-phase windings were shown, presumably one for each speed ; this would indicate that one complete winding was always idle. The authors were, no doubt, aware that the same result could be obtained by using one winding which was always active. The use of two independent windings must, necessarily, involve greater space and a heavier machine. In the authors' system, he noticed, too, that the field excitation on the alternator was increased by hand regulation. Was it not possible, for an inexperienced driver, at starting, to increase the excitation too suddenly, and, thereby, throw a heavy load on the engine, suffinient to stop it? He should be glad to know if there were any means taken to prevent such an occurrence. He noted, also, that, by applying the brake, the field of the exciter was shortcircuited, and the magnetic clutch was released ; if, now, the vehicle stopped, and, if the driver released his brake without first returning the field-control lever to contact No. 9, he would throw the clutch in with the vehicle stationary, and would, thereby, tend to stop the engine suddenly. No mention was made as to engine control. It would be interesting to know if the engine was governed, and, if so, at what speed. Lastly, he was sure they would all be interested to know the weight of
the complete electrical equipment, including alternator, motor, exciter, controller, and field switch.
MR. WEEKS said he had not had long to look into this paper, hut he hoped that the authors would give them some idea as to how far their system was successful in altering the torque in a polyphase motor.
MR. F. C. BLAKE (Kew Gardens) said he was engaged on the Farrow car two or three years back, and he knew the actual results. The first of lr. A. E. Farrow's petrol-electric cars was fitted with one of his four-cylinder motors, giving 14 horsepower at a thousand revolutions per minute. Its weight was 208 pounds. 'The motor had no flywheel, but was coupled direct to the dynamo, the armature of which acted as a flywheel. 'the dynamo was a four-pule shunt machine, with carbon brushes, specially designed to run as dynamo, or motor, as desired. The weight of the dynamo was 336 pounds, giving, when driven as a dynamo, 86 amperes, at 100 volts, with the petrol motor running at 995 revolutions per minute. In combination with the dynamo was an accumulator battery of 40 cells, weight 900 pounds. When running on accumulators only, there was art arrangement fitted to the motor to hold open the inlet valves and to close the throttle. On the road, with a gradient of one in twenty, thc car travelled at eighteen miles an hour without taking any current from the cells. After this gradient was exceeded, the battery started discharging. On the level road, the dynamo generated about 10 amperes, at 90 volts, when the car was travelling at eighteen miles an hour. The cells, alone, when fully charged, would run the car twenty miles, on a level road, without using the petrol motor, The weight of the complete car was thirty hundredweights, and it carried seven people. The controller had nine contacts, each giving a separate speed.
MR. F. J. FIELD said that a paper like this, to be properly and intelligently dismissed, required that they should have a better opportunity for going into it. As was the case with many other members present, he had not seen this paper until it was put into his hands on entering the room. As to this system, he thought it all depended what voltage was employed. In the case of any voltage approaching 6,000, immense troubles were experienced, from short-circuiting of the stator coils. He did not knew so much about these small units. Mr. Hart did not explain what their pressures or energy consisted of, but he took iL that they must employ a fairly high voltage, which, of course, meant insulation troubles.
MR. THOMA S PARKER said he could not add very much to what Mr. Hopps had said, for he thought that he had hit the nail on the head very well. This paper had been very interesting indee:1 to him, and he should be very glad if they could have the discussion continued at some future date.
MR. R. G. 1.. MARKHAM said that he had seen an example of the failure of the direct-current motor that evening. At the bottom of Rosebery Avenue, he saw three electric tramcars hung up, and a little further on he saw seven more. They were obliged to hitch horses to the electric cars, in order to get them over the points. This was a demonstration of the advantages of the motor omnibus over the tramcars. He wished to know if this system was applicable, with the internal-combustion engine, or with the steam turbine, to marine propulsion. From a marine point of view, the speed of revolution was an important point. The petrol engine suffered, in its present form, because it was, inure or less, a high-speed engine, and this was neutralised by the loss of efficiency on the propeller. The flexibility of the motor was, of course, more essential in marine work, than in any other class. If the discussion was adjourned, he should like :Messrs. Hart and Durtnall to reply upon those points.
Dn. E. LEHWESS asked what was, the peculiarity of the system, end that the authors should define it more clearly. Was it only the use of the alternating polyphase motor?
THE CR/tram/tie said he would take the sense of the meeting as to whether they should adjourn the discussion. He agreed that it was difficult to discuss such a subject as this offhand. The authors of the paper had expressed themselves willing to attend in a fortnight's time. Mr. DurtnaIl was thirsting for more questions, so that he might come to the adjourned meeting prepared to give information on all points which required elucidation. He would, now, take the sense of the meeting as to whether the discussion should be adjourned.
The adjournment of the discussion to Monday, the 4th February, at 8 o'clock, was, unanimously, agreed. The vote of thanks having been put and carried with acclamation,
MR. HART briefly returned thanks, and said he, and Mr. Durtnall, should be pleased to meet them again in a fortnight.