THE MOTOR TRAIN

Evening Post, Volume XCI, Issue 107, 6 May 1916, Page 9

THE MOTOR TRAIN

NEW VEHICLE ON TRIAL

SUCCESSFUL IN PULL AND SPEED

THE THOMAS TRANSMISSION.

Railway vehicles propelled by internal combustion engines (or "motors" of the kind used in automobiles) are not novel, but they are infrequent. The New Zealand Railways Department has already one motor train, which runs on the Johnsonville line; and another, of much larger size and higher power, is now almost complete. This second vehicle is of a new and particularly interesting type } it is fitted with the Thomas 'transmission system

The new motor-carriage was, except for the body, built in England by Thomas Transmission Limited, and it has been reassembled at the Petone workshops at a speed which has been greatly reduced by tlie interference of the war with the despatch of various parts from England. The whole outfit, including a substan-tially-built body, has now been completed to the point where full working tests are possible, and an unofficial trial of the machine has been. made.

The vehicle is of striking appearance. Its length is - greater than that of any passenger carriage, and .at each end there is a driving cab, with a V-shaped wind-shield, carrying on its front a big radiator, with expanded wings to direct a strong air-current through its pipes. At each end of the car proper is a passenger compartment for' about thirty people, and between these the engineroom. Apart from the stream-line cabs and the radiators and the great length of the vehicle, the most noticeable feature is that the steel under-framing is unusually high; and this naturally reduces the height of the body work, and incidentally the amount of headroom within by several inches.

200 HORSE-POWER ENGINE,

The power-unit is a massive and, to the' engineer's eye,' very fine-looking Vtype 8-cylinder petrol engine of about 200. horse-power, set low down between the main frames. It is dropped so low that the tops of the cylinders are barely above the general floor-line of the vehicle, and the power-shafting runs horizontally to' the final transmission gear on the axles of the wheels. This engine, which, during the trial ran smoothly and without giving any trouble, is powerful enough to drive, and' actually did drive, a total load of 80 tons on the level at a speed of over 36 miles per hour. This 'load consisted of the motor-car itself, two heavy Red Cross cars, and a brake van. With one "trailer" the motor has done 40 miles an hour; and alone its speed is 45 miles an hour. During the. run the motor-car-alone was taken up tho hill between Upper Hutt and Kaitoke; and notwithstanding the abrupt curves, climbed the gradient at a speed varying between 13 and 15 miles an hour, which was regarded by the railwaymen on board as a very creditable performance. Mr. K. J. Thomson, who ,is the company's representative in charge of the job, states that dra.wing a trailer the motor takes the hill at practically the same speed. Tlie special feature of the vehicle is not, however, its ability to make speed or climb .■ hills (though that, of course, is vital) because such ability depends upon engine power. Tlie novelty is in the transmission, or transfer of tlie engine's power to the wheels. THE DRAWBACK OF THE MOTOR. Every designer of motor-vehicles is faced by the fact that, while internal combustion engines are splendidly adapted- for driving a vehicle at a given speed, they are remarkably ill adapted, by themselves, for.giving a wide range of speeds, and for starting a big load. They deliver most power when they are running fast, and their driving force falls off regularly as their speed diminishes. In this way they are the converse of steam-engines, which can exert a great starting effort, as anyone who has! watched a heavy team pull out of a station knows. A petrol engine has to be run up to speed before its effort is really useful, and there arises the difficulty, which is in the case of big powers very formidable, of enabling its great driving force to be gradually applied to the load with the best effect, and without such a shock as will neither smash the machinery, shake the passengers out of their seats, nor stop the engine altogether. In motor-cars the gear-box and clutch are used for this purpose; and it is within motoring experience that with them^-and they are admittedly a mechanical compromise— any of the three nasty events named may happen. ELECTRICAL DRIVES—AND LOSSES. In the case of an engine 'powerful enough to draw a train, a gear-box and clutch are almost out of the question. Moreover, for. their successful operation, engines .are usually made more powerful than is really justified by the load, in order to minimise the amount of gearchanging required upon gradients. To secure the required "flexibility" of drive from an almost "inflexible", engine, an electrical drive suggests itself. The engine, running .always at full speed,' may drive a dynamo, the current from which is sent through a controller like that of a tram-car-to an electromotor geared to the wheels. In this case there-are, however, serious losses of power. Bart of the engine power is lost by the dynamo; part of the dynamo's output is dissipated by losses in . the electro-motor;. and then there is a further loss in the gearing by which the motor drives the wheels of the car. Tlie, Thomas system aims at securing the flexibility of tho electrical drive and the convenience of the electrical control, and at the same time cutting down the electrical losses. They are reduced by the method of transmission; and when the vehicle is running at full speed, on top gear, they do not exist at all, because the drive is then purely mechanical, and involves only tho mechanical losses, which in the case of a bevel-gear drive can bo kept on. the right side of. 10 per cent. A CLEVER SYSTEM. Anything like a [nil description of the working of this ingenious system would be too technical and elaborate for a newspaper; but the principle is so interesting that its broad lines can be stated hi plain terms with advantage. The engine shaft drives a casing containing a set of "planetary" gears, and from this casing emergen a driving shaft geared to the planetary Hyateni and con- I nected with the main driving axles. Tho j gearing is so arranged that when the vehicle is stationary and the driving! shaft is also still, and tho engine running, a third shaft revolves freely in an opposite direction to that of the engine. But if by some means the third shaft is checked or stopped,, tho driving shaft will begin to rotate in the same direction as the engine, and at a speed increasing as the third shaft slows down, and greatest when it 6tops. The gears in the casing are arranged so that the driving shaft, in these circumstances, runs at about half the speed of the engine. Then, if the third shaft be forced, after stopping, to revolve the other way (i.e., in the same direction as , the engine) the -dxiving_ shaft __U run

still faster, ultimately reaching fhe_ same speed of rotation as the engine it-' self. Up to the stage of bringing the third shaft to a standstill, the process described could be effected by means of a brake upon the shaft, and this would, within its limits, give a variable drive ; but it would waste power (putting on a brake always wastes power), and the final top speed drive would be through the planetary gearing', which would involve a constant loss of power THE ELECTRIC SPEED CONTROL. The Thomas system gets over both difficulties. The third shaft, instead of being braked, is coupled to a dynamo, which, during its period of rotation, gives current that is used to drive an ! electro-motor coupled to one pair of the ear-wheels, at the end opposite to those driven by the mechanically-driven shaft. The control of the. drive is done wholly upon the current between these two electrical machines, although it really represents /at most much less than half 'the total power, and is, at times practically a vanishing quantity Until the car is started, no current passes; but as the driver moves the controller round, more and more work is put upon the dynamo, ,which moves more and more slowly ; and this slowing down of the dvnamo, which is. coupled- to the third shaft of the planetary gear, compels the driving shaft to revolve, and the car moves off at an increasing speed. Ultimately, the dynamo becomes so checked by its labour that it almost stops; and then an ingenious change in the electrical connections is effected. The major part of tlie engine's power is already being transmitted through the planetarygearing to the driving shaft, and the erstwhile motor that has done its share of driving is reversed in function. Itbecomes a dynamo (motors and dynamos being thus reversible in action), and supplies current to the machine that hitherto acted as dynamo. The latter is gradually speeded up in a direction opposite to its original rotation and now similar to that of the engine, and presently comes to an equal speed. A clutch comes into operation as the next stage, and the engine shaft and the third shaft, now moving together, are firmly coupled. The whole electrical circuit which has operated in the transmission becomes inert, and the drive is a direct mechanical one from the engine through the clutch to the driving shaft and the wheels of the car.

■ There is a subsidiary -, electrical arrangement. One of the 'dynamos can now be used for generating current for charging a storage battery. The current thus "bottled" is used for three purposes: Starting the engine (a task too big for hands), operating the clutches (which are magnetic), and lighting the car. There is no arrangement for using the batteries for driving the vehicle,although in case of a breakdown the battery could be made to shift the car a, few miles at a low speed.

SIMPLE TO DRIVE.

The process described is not simple, and the macliinery to carry it out is elaborate. But it is wonderfully easy to control, and only one man is needed to drive the vehicle—the engine is left severely to itself. The driver merely rotates the controller, operates the brakes (Westinghouse and hand) and controls the speed of the engine by means of a throttle worked by a pedal. He and a guard form the whole crew of the car or train as the case may be.

It is rather. astonishing at first glance that this remarkable equipment of electrical and mechanical devices is in operation during only a very small portion of the running time. At each start it is probably only about twenty seconds in use and only operates during a run on steep gradients. But its value is in the fact that it enables the car to be propelled in all circumstances by a.n engine only powerful enough to give speed on a level track; it is a highly efficient " lever," and does the hard work at a lower speed witb the minimum of losses. The cutting of losses is due to the direct mechanical drive at full speed, and to the fact that at all speeds the greater part of the power is sent through the mechanical gearing,' and not through the more wasteful electrical power-cirexut.