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Petrol-Electric Transmission for Road Vehicles.

7th March 1907, Page 3
7th March 1907
Page 3
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Page 3, 7th March 1907 — Petrol-Electric Transmission for Road Vehicles.
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Which of the following most accurately describes the problem?

Reply to the Discussion on Messrs. Hart 81 Durtnall's paper.

(Continued from page 544.1

We agree with Mr Parker, that Mr. Hoppa has very ably criticised our paper. The last part of our reply to Mr. Hopps' criticism will also answer that of Mr. Parker.

It was quite interesting to hear Mr. R. G. I.. Markham state that there had been failure of the direct-current motors on the tramways that evening. In reply to his enquiry as to whether our system is applicable in connection with internal-eombustien engines, or steam turbines, for marine purposes, we have plea. sure in informing him that we have a special arrangement for marine purposes for such uses: the prime mover is coupled direct with the propellers, when speed has been attained, and, for manoeuvring, acceleration, or low speeds, our electrical equipment, without commutators or brush gear, is very suitable : it will be appreciated, we feel certain, by marine ergineers. As regards the steam turbine, our device provides that the steam turbine can be run at the highest and, as regards steam consumption, most economical speed, for, by our electromagnetic, gear reduction, 0, suitable and economical speed is given to the propellers. It will, perhaps, interest you to know, that we are, already, engaged on designs for a steam yacht, which will be fitted with three turbines and six propellers. Dr. E. Lehwess asked for particulars of our system. We think, if Dr. Lehwess will consult his memory, that this system was thoroughly explained to him, in November, 1905: but, perhaps, if he has listened to the replies to the other critics, he will have learnt more about, and become more acquainted with, our simple method of electrical power transmission.

Mr. Shrapnell Smith proposed a vote of thanks to Messrs. Hart end Durtnall for their reply. They had given those gentlemen a .vote of thanks for their paper, at the previous meeting. He had listened to a good many replies, but he thought he had never heard one more racily put than Mr. DurtnalPs. His a-ides were most entertaining. (Hear, hear.) Messrs. Hart and Durtnall had saved up for them a most interesting point,

namely, that their voltage never exceeded eighty. lie, the e1-esker, understood from Mr. Durtriall before, that it sometimes reached ninety. If Mr. Durtaall, upon leading over the notes of the evening's discussion, found any points to which he had not replied, he hoped be would communicate his reply to them through the Secretary. He thought that, amongst other things, this system must have an important' bearing upon the developmerit of the submarine.

The vote was carried with acclamation.

Conclusion of Reply.* We are glad to hear the opinions of so experienced an engineer as Mr. P. Frost Smith, and we hope, with him, that petrolelectric transmission will, owing to the diminution in the cost of maintenance, he the saving of the motorbus movement commercially. The absence of mechanical friction-clutches with their withdrawal rods, levers, joints, pins, etc., is a considerable advantage in construction, and, as petrol-electric transmission becomes more popular, and is more used, much less attention should be required to be paid to the maintenance of the buses, especially if fitted with polyphase alternating-current apparatus. The Hart.Durtnall electrical transmission is Eng fish in every respect, :ad is not a copy of any foreign design. and we can assure Mr. Frost Smith that the Hart-Durtnall apparatus will always embody the very best of mechanical and electrical engineering. We thank him for his practical anpreelation of, the good features in our system, in which ther are no humming gears, rattling chains, or noisy final gear drive. It will be quite in the range of possibility to bring old buses in line with new ones, as regards noiseless working, and we believe that a large part of our future work will be the conversion of existing gear transmissions on motorbuses, etc. We appreciate Mr. Frost Smith's statement that it takes much time to get a noisy bus back to the pitch of perfection required by the police, and, probably, it is that work that runs away with a lot of money, which would, otherwise, be available for dividends. With the Hart-Durtnall system the whole set of machinery can be dropped down, from the main chassis, thoroughly and minutely inspected, and any necessary adjustment made under the best possible conditions, though even this advisable performance should not be required very often in connection with our equipment owing to the very robust character of the constructional details. There is no reason why the transmission should not be just as reliable and quiet, at the end of. say, ten years' working, as on the first day it started. It is possible to make our electric transmission suitable for a 28h.p. Milnes-Daimler engine, and we might mention that we have in hand, at the Luton works, the conversion to our alternatingcurrent system of touring cars ranging from an 8h.p. De Dion, to a 70h.p. Richard-Brasier.

Reference has been made to the possibility of burning out the rotor of our induction motor, and we would, therefore, like to state that the proportion of the quantity of material to the engine power is so arranged that it is not possible to burn out the rotor, as the engine could not provide sufficient power to make that interesting performance possible. Our magnetic clutch is the result of considerable experiment, made in order to get the best design and quality of material, and at the same time the greatest efficiency; with 450 watts excitation, our clutch can easily transmit fifila.h.p. The fool-proof control in our system should not fail to commend itself to all practical and experienced engineers, and difficulties in the driver question should be greatly reduced.

We agree with Mr. Parker, that Mr. Hopps made a very good defence for the continuous-current motor and dynamo system but it will want a good champion against the superior qualities of the polyphase, induction-motor system for high-speed bus work, as the cost of maintenance cannot possibly be so low a.; with the latter system. As regards the formula used by us in deciding the horse-power of our engine, it may interest Mr. Parker to know that we find that the moat satisfactory method is by means of a water-cooled drum and loaded brake; we, also, have used a series-wound, continuous-current dynamo for this purpose, and our calculations are based on results so given, and which, we maintain, are correct. We use a mechanical gear reduction of eight to one to our live axle, and this ratio, we find, is the most efficient one, when taking the varying nature of the load into consideration. As regards maximum speed, we do not consider that 'any double-deck motorbus should be allowed to run at more than 12 miles per hour, and, as soon as

our bus exceeds that speed, a tappet valve will open between the carburetter and the engine, allowing the engine to thaw in air only, and thus to brake itself. This mechanism will save fuel, and it. is independent of the driver. We have already given the weight and tests of our apparatus, and we can assure Mr. Parker that a commercial efficiency of practically 70 per cent. is very good for the electrical transmission of power. Mr. Parker's figures for a 14h.p. transmission are Interesting, but we would draw his attention to the fact that, when transmitting the power from a 10b.h.p. engine, the efficiency is much higher if the transmission is by means of polyphase, alternating-current apparatus, and by means of a direct, electro-magnetic, mechanical drive. The commercial efficiency of the complete vehicle is raised to the level, at least, of the best types of buses that are fitted with mechanical transmission, but without the noise, wear

and tear, etc. It has, we think, nothing to fear from any hydraulic-power transmission system, as Mr. Parker suggests, especially if that system consists of rotary or reciprocating, rilunger-type pumps, etc.; Mr. Parker's figure of 4,2001b. as the et e ndard weight for a 40b.h.p. alternator, exciter, and motor are no doubt, right as regards heavy stationary machinery, such as it t. sed in coal mines and in other applications where weight is

,onsideration. Our set is about 25 per cent. of that figure.

We are glad to see our paper has come under the notice of Mr. Douglas Mackenzie, and to have his very interesting remarks, which we value more especially because of his connection with the earlier types of petrol-electric systems. Cost, as he says, is one of the most important matters in reference to the possible adoption of electrical transmission of power on motor vehicles: the Hatt-Durtnall system, owing to its simple construction and detail, is by far the cheapest, as well as the most robust, electrical combination yet ready for the market. Owing to some improvements we are making in the method of gas and ignition control, which will, in our opinion, make a considerable economy in petrol consumption, we have net yet made efficial tests of the petrol consumption. We have taken rough measurements, and the consumption per mile is about .19 gallon tor iie miles per gallon). We quite agree with him that there must be economy in petrol consumption, or electrical transmission is not much improvement. We hope to be able to show a large reduction, when our official fuel-consumption tests have been carried out. We are glad to hear that he approves of our design of live axle, and we can assure him that there is nobody more ready to support the use of proper ball bearings than we. In reply to Mr. Wyatt, we are sure that those systems in which continuous-current apparatus is used, and, especially those utilising two motors, are not commercial : they do away with that very simple and reliable piece of mechanical gear, the differential, but two series-wound motors, owing to their low general efficiency, well not be able to compete, either as regards running conditions or first cost. We agree with him that the gear box should be abolished, but we cannot agree with him that a smaller engine than 30b.h.p., ought to be used for London traffic. We use a 40b.h.p. engine for carrying out our various experiments with this, our first, chassis, but, as previously explained, the system can be fitted successfully to almost any type of chassis—to even a steam bus fitted with a turbine. The loss, when on direct drive, is very small, and, by cutting off the gas, the engine-speed can be lowered to about 200r.p.m (three miles per hour) by means of the exciter and the magnetic cluteh, and, also, because, at the low speed stated, it is possible practically to double the number of ampere-turns on the magnetic field of the exciter, which, thus, holds itself up, at the lower speeds, to supply about 80 to 100 watts. To climb an ordinary hill, we keep on direct drive, and, when going at 12m.p.h. (800r.p.m. of the engine, with full gas), we transmit the full 401).h.p. with about 97 per cent. efficiency. A 40h.p. bus fitted with a dynamo and two series-wound motors would not be nearly so efficient, for the reason that the mechanical power has to he transformed into electrical power, split up between two motors, and transformed into a certain amount of mechanical power, again, at high speed, and that power, at high epeed, has to be transformed into a still lower power, at lower speed, for the road wheels. We have tried the above continuous-current method of transmission (with the very best-designed apparatus. end we find that an average efficiency of about 35 per cent, is all that can be obtained, taking a day's run through. This materially affects the petrol consumption and, although the combination works very well, it is absolutely no good rommercially, and there are, also, other troubles, with which we have previously dealt. Mr. Wyatt must remember that the electric: dynamo and motor are not always working at the most efficient part of their characteristic curve, and that for the major part of the time they are working at about one.third of full load, and even the best types of electrical power transmission app.ratue are not efficient at " under " full load. At full load, when climbing a steep hill, the efficiency of the centintems-current system, without differential gear, is not more than, and is, peseibly, less thae, 50 per cent. : the rest goes in heat, etc., and all the troubles which we have experienced will be repeated, with all the lose soldered joints, and quite a pyrotechnic display.

Mr. Wyatt will, no doalst, realise from the above why we prefer to have our magnetic clutch arranged in connection with the series-wound exciter, with sectional magnetic field and designed for long continuous running. In reply to Mr. Carter, we may say, as regards maintenance, that we do not anticipate that our apparatus will want a great deal. When It is necessary to do a lot of mileage at anything

so low as three or four miles per hour, we accomplish this on the electric drive, but, as the work is generally, unless on a hill, very little, our machines are so calculated that very little heat, if any, is generated, even when climbing a steep hill. With regard to the possibility of dropping the whole propelling plant down from the main chassis frame for inspection or possible repairs, we were under the impression that this would appeal to operating engineers, as it will be quite possible to send a bus out again in about three hours.

Mr. F. Broadbent stated a fact when he remarked that our system is very similar to a slipping clutch, but unlike most

slipping clutches it provides an increase of torque in proportion to the slip. At half speed, the torque is double; no slipping clutch provides this, but, at the same time, such an increase in torque is absolutely essential in the operation of heavy vehicles. We quite agree with Mr. 13roadbent that a good deal of criticism has been levelled at our polyphase system of power transmission, but it has conic chiefly from the advocates of continent's-current apparatus, who recognise that, at last, they have a very interesting and serious competitor to deal with. We were glad to hear him support us in our views in reference to the small use of polyphase apparatus in tramway work. A much greater use of this type of plant would certainly he seen if it did not require two overhead lines, because the polyphase inducticn motor is so simple, and it would be regenerative when a tram descended a hill, sending current back to the lines which would be utilised by ascending trams. We emphatically endorse his remarks: "That polyphase systems can be left with safety in unskilled hands, and that this would be impossible, certainly not advisable, with the continuous-current system," and that one of the great features of the polyphase induction motor was that it could stand double and treble its normal load, without disastrous results. Concerning the rotor, which was shown, it was not, of course, our motorbus rotor, it really belonged to a lower-powered set. The rotor does not, of course, run up steep hills at top speed, but at half speed with double torque ; there is no chance of a 4011.p. engine burning it nut. We agree with Mr. E. G. E. Beaumont's point that most of the systems we described provided an easy control of speed, over a wide range, and that with the petrol-electric system quieter running can be obtained. He referred to the successful use of polyphase induction motors on electric railways, and no doubt it is very sttitable for such heavy and exacting work_ On the occasion of Mr. Shrapnell Smith's early trial of our bus, the nett weight of the chassis and load was about 5 tons, but what Mr. Shrapnel! Smith was really referring to was the very simple and complete control of the vehicle, especially when descending steep gradients. This is independent of the mechanical brakes. We have previously given the dimensions and brake-horse-power of the engine on our chassis. As regards Mr. Beeumont's remarks about possible noise coming from the magnetic reversal of the polarity of the iron used in the construction of polyphase induction motors, we can only say that noise is possible where motors are started with a fixed voltage, such as that obtained from a supply company in stationary plant, but, owing to the exciter gradually building up in voltage at starting, no such noise is experienced by us. in answer to the remarks of the chairman (Mr. F. C. A. Coventry), we may say that we are certain that our system will have a large application in connection with railway-car and tramcar propulsion, in conjunction with the internal-combustion engine. We are already working on designs for such applications, and it is quite within the range of possibility to instal our system on existing horse trams, and, thus, obviating the necessity for that expensive edifice, the central generating Station. As Mr. Coventry remarks, there is a very large field for rail-car services in connection with main trunk railways, as feeders, and the internal-combustion engine is very suitable for this class of service, because, when the car has finished itS" journey, the driver shuts off the gas, the engine stops, and the working costs with it. The car can stand, ready for immediate re-starting when occasion demands, and it will be noted that no banked fires are required as with steam rail cars. We hope that our system will one day be tried for the propulsion of trains under main line conditions, using a steam turbine as prime mover. Owing to the fart that each carriage would propel itsalf there would be very little, if any, draw-bar pull, and the rolling stock could be made considerably lighter than et present.

In conclusion, we have nothing to add, except to thank you for your attendance, and for the interesting criticisms which have been offered. We feel proud of the fact that our efforts have received so much attention from those forming a body of such importance as the Society of Motor Omnibus Engineers.


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