Part 5 (1/2)

[Illustration]

[Illustration: FIG 39--Showing the four strokes that the piston of a gas-engineone ”cycle”]

ACTION OF THE ENGINE

The gas-engine, the oil-engine, and the eneral principles The cylinder has, instead of a slide-valve, two, or sometimes three, ”mushroom” valves, which may be described as ses, mounted on the ends of short rods, called stems These valves open into the cylinder, upwards, doards, or horizontally, as the casefroine For the present ill confine our attention to the series of operations which causes the engine to work This series is called the Beau de Rochas, or Otto, cycle, and includes four39 will show exactly what happens in a gas-engine--(1) The piston ht, and just as the as) and A (air) open to admit the explosive mixture By the time that P has reached the end of its travel these valves have closed again (2) The piston returns to the left, co the mixture, which has no way of escape open to it At the end of the stroke the charge is ignited by an incandescent tube I (in ines by an electric spark), and (3) the piston flies out again on the ”explosion”

stroke Before it reaches the limit position, valve E (exhaust) opens, and (4) the piston flies back under the h the still open E The ”cycle” is now conition), combustion, and exhaustion It is evident that a heavy fly-wheel y of one stroke (the explosion) has to serve for the whole cycle; in other words, for two coine develops an impulse every half-turn--that is, four ti effect, ht cylinders Four-cylinder engines are at present the most popular type for powerful cars

THE MOTOR CAR

[Illustration: FIG 40--Plan of the chassis of a motor car]

We will now proceed to an examination of the motor car, which, in addition to mechanical apparatus for the trans-wheels, includes all the funda 40 is a bird's-eye view of the _chassis_ (or ”works” and wheels) of a car, fro at the left, we have the handle for setting the engine in ine (a two-cylinder in this case); the fly-wheel, inside which is the clutch; the gear-box, containing the cogs for altering the speed of revolution of the driving-wheels relatively to that of the engine; the propeller shaft; the silencer, for deadening the noise of the exhaust; and the bevel-gear, for turning the driving-wheels In the particular type of car here considered you will notice that a ”direct,” or shaft, drive is used The shaft has at each end a flexible, or ”universal,” joint, which allows the shaft to turn freely, even though it ear-box It ear-box are s, so that when the car bumps up and down, the shaft describes part of a circle, of which the gear-box end is the centre

An alternativeis by ) wheels on the ends of a shaft crossing the fraer sprockets attached to the hubs of the driving-wheels In such a case the axles of the driving-wheel are fixed to the springs, and the wheels revolve round them Where a Cardan (shaft) drive is used the axles are attached rigidly to the wheels at one end, and extend, through tubes fixed to the springs, to bevel-wheels in a central coear box (of which more presently)

Several parts--the carburetter, tanks, governor, and pueneral plan These will be referred to in the more detailed account that follows

THE STARTING-HANDLE

[Illustration: FIG 41--The starting-handle]

Fig 41 gives the starting-handle in part section The handle H is attached to a tube which ter keeps C norine shaft When the driver wishes to start the engine he presses the handle towards the right, brings the clutches together, and turns the handle in a clockwise direction As soon as the engine begins to fire, the faces of the clutches slip over one another

THE ENGINE

[Illustration: FIG 42--End and cross sections of a two-cylinder42) Each cylinder is surrounded by a water-jacket, through which water is circulated by a pureat that the walls of the cylinder would soon become red-hot unless some of the heat were quickly carried away The pistons are of ”trunk” foruides and absorb the oblique thrust of the piston rods Three orin slots (not shown) prevent the escape of gas past the piston It is interesting to notice that the efficiency of an internal-coood fit of these s ood firm will turn out standard parts which are ithin 1/5000 of an inch of perfect truth It is also a wonderful testimony to the quality of the ine which has made many millions of revolutions, at the rate of 1,000 to 2,000 per ns of wear In one particular test an engine was run _continuously for several months_, and at the end of the trial was in absolutely perfect condition

The cranks revolve in an oil-tight case (generally made of aluminium), and dip in oil, which they splash up into the cylinder to keep the piston well lubricated The plate, P P, through a slot in which the piston rod works, prevents an excess of oil being flung up Channels are provided for leading oil into the bearings The cranks are 180 apart

While one piston is being driven out by an explosion, the other is conition, so that the one action deadens the other Therefore two explosions occur in one revolution of the cranks, and none during the next revolution If both cranks were in line, the pistons wouldone explosion each revolution

[Illustration: FIG 43--Showing how the water which cools the cylinders is circulated]

The valve seats, and the inlet and exhaust pipes, are seen in section

The inlet valve here works autoines--on all powerful engines--the inlet, like the exhaust valve, is lifted by a caularly Three dotted circles show A, a cog on the crank shaft; B, a ”lay” cog, which trans the ca twice as many teeth as A, revolves at half its rate This ensures that the valve shall be lifted only once in two revolutions of the crank shaft to which it is geared

The cogs are tiins to lift the valve when the piston has hths of its explosion stroke, and closes the valve at the end of the exhaust stroke

THE CARBURETTER

A enerally uses petrol as its fuel Petrol is one of the ravity of about 680--that is, voluht is to that of water in the proportion of 680 to 1,000 It is extreas at ordinary temperatures Benzine, which we use to clean clothes, is practically the same as petrol, and should be treated with equal care The function of a _carburetter_ is to reduce petrol to a very fine spray and mix it with a due quantity of air The device consists of two44)--the _float chamber_ and the _jet cha the petrol supply A float--a cork, or air-tight ed to move freely up and down the stem of a needle-valve, which closes the inlet from the tank At the bottom of the chamber are two pivoted levers, W W, which, when the float rests on them, tip up and lift the valve Petrol flows in and raises the float This allows the valve to sink and cut off the supply If the valve is a good fit and the float is of the correct weight, the petrol will never rise higher than the tip of the jet G