"B.H.P." AND HOW IT IS FOUND

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” B•H.P. AND HOW IT IS FOUND TYPICAL EQUIPMENT OF THE TEST SHOP

IN the complicated and intricate process of automobile production there is, perhaps, no more interesting or essential branch than that of engine testing. When a designer, after prolonged thought and careful calculation, has ultimately placed his plans on paper, and when the multitudinous operations have been carried through so that from the raw material the completed article 11.t, been evolved, the success or failure of his ideas is soon revealed in the test depart ment. Naturally, the acid test is found in the conditions met with on the road, or better still in racing, but without the aid of the ” bench” no manufacturer

could hope to obtain the all-round efficiency which the exacting conditions of present-day needs demand. In by-gone days when the motor car engine was a stolid worker of moderate revs., the designer had a relatively easy task, but to-day the high-speed engine, which is now universally used, calls for intense accuracy and the working to fine

limits, and this precision has to be carried through to the very last stage, which is reached in the test shop. The work in this department consists in the main of checking the power output of engines, though it is obviously also concerned with fuel and oil consumption, stamina, balance, running-in and so forth. But the chief job, in dealing with standard-built engines, is to see that the power

and revs, are there. This is done by the aid of a dynamometer, known more familiarly as ” the brake.” The dynamometer, like the engines for which it has been evolved to test, has progressed considerably in recent years, and bears but scant resemblance to the apparatus of long ago. The hydraulic brake type of dynamometer, which is the one most generally

in use, consists primarily of a turbine or rotor running within a casing ; the former is provided with vanes facing forward in the direction of rotation, and corresponding with similar vanes cast on the inner surface of the casing. The casing vanes, however, are formed so as to face backwards, against the direction of rotation. Situated between the two vanes (those on the casing and those on the rotor) are a series of movable sluice plates, which can be adjusted by means of a hand wheel. The outer casing is supported on ball

bearing trunnions, and attached to it is lever arm which extends horizontally, and which is coupled at its extremity to a weighing machine. The shaft of the rotor is coupled to the engine under test by a suitable universal joint, and when in action the water, which is fed to the interior of the dynamometer, is forced very rapidly from the moving vanes to the casing vanes and vice versa, with the result that whatever force is exerted to turn the rotor, tends with precisely equal force to move the casing on its mounting. It will be obvious that this movement is then transmitted Via the horizontal arm to the weighing machine, which being suitably graduated, at once shows the Brake Horse Power (B.H.P.) which is being produced by the engine. The object of the adjustable sluice plates is to reduce the power absorbed by the dynamometer and this is done by moving them so that they cut off a portion of the effective area of the annualar channels formed between the blades. In this way the power may be reduced from the maximum down to about one-thirtieth of that amount. A further development of the brake is found in the Heenan and Fronde Electrodynamometer, which in addition to serving as an indicator of an engine’s power output at various speeds, also motors the engine during the running-in process. The usual practice at one time in driving or motoring a new or repaired engine was to use an ordinary electric motor, but owing to the fact that the torque is uncontrolled, and any stiffness or tightening up in the engine consequently overcome with some violence, damage to the wearing surfaces often resulted. With the Heenan and. Froude appliance this running-in

-work is done at first at a low speed, and at a torque which adjusts itself automatically according to the freeness or otherwise of the engine. As the bearings settle down, and the engine becomes less stiff, the Electrodynamometer increases its speed to complete the process, and when a predetermined state of freeness has been reached and the engine is ready to run under its ovrn power, the moment is indicated by a signal.

During the whole period of running-in, a dial shows the exact degree of internal stiffness of the power unit, and thus the operator can tell at once how it is shaping.

As soon as the running-in process has been completed, the engine is allowed to work on its own account ; at first it is set to run light only, in order to allow the pistons and rings to accommodate themselves to the resulting expansion. Later the throttle is gradually opened and the endurance and power tests begun. While this operation is going on the Electrodynamometer converts the power given off by the engine into electric current which can be either dissipated through a series of resistances, or switched over into the factory’s main electrical supply.

As with the water brake, the torque of the engine is visually indicated on the dial of the weighing device throughout the whole period of the test, and the engine revolutions are shown by the usual tachometer.

The electrical brake has much to commend itself, since it is clean, simple and has a high degree of elasticity, but this apparatus of Messrs. Heenan and Froude is remarkable on account of the fact that the whole work from the time the runningin process is begun till the engine has completed its power tests is carried out practically automatically.

NEW MOTOR REGULATIONS CLAUSES WHICH NOW TAKE EFFECT.

THE Automobile Association draws attention to the following new Regulations affecting motorists and which come into force to-day, 1st January.

Mirrors.—Every motor vehicle (motor cycles excepted) must be fitted with a reflecting mirror so that the driver may be acquainted with the proximity of vehicles about to overtake. Vehicles drawing trailers are exempted if the attendant on the trailer has an uninterrupted view to the rear and, is able to communicate with the driver. Windscreens.—All glass fitted to windscreens or windows facing to the front on the outside of any motor vehicle, except

glass fitted to the upper deck of a double decked vehicle, must be safety glass. Vehicles registered before 1932 are exempt until 1937, but, meantime, the glass fitted (safety or otherwise) must be maintained in a condition which does not obscure driver’s vision.” Safety glass “is defined as glass which, if fractured, does not fly into fragments capable of causing severe cuts. Springs.—Motor vehicles (except motor cycles or mobile cranes) registered after 1st January, 1932, and any trailer constructed after 1st June, 1931, must be equipped with suitable and sufficient springs between each wheel and the frame of the vehicle. Tractorsznot in excess of

4 tons unladen weight are exempt if unsprung wheels are fitted with pneumatic tyres.

Taxation.—Motor cycles, the cylinder capacity of the engines of which. do not exceed 150 c.c. will pay the reduced annual tax of 15s.

The Motorist’s Legal Guide, available free of charge to A.A. members, deals with these points and many others of prime importance to motor owners. Any motorist who is in doubt as to the effect of the new Regulations should communicate with the A.A. Legal Department, Fanum House, New Coventry Street, London, W.I.