through the webs and crank-pins, whence it feeds the connecting-rod
bearings, enough squirting out to splash on to the cylinder
walls. Sometimes, a shallow trough is placed under each connecting-rod
end, to hold oil to a certain depth and no more, and
a scoop on the big end collects enough oil to effect the lubrication
of the connecting-rod bearings and cylinder walls. The aim has
been to secure definite lubrication of all moving parts, and, at
the same time, to prevent oil being present on the cylinder walls
in such quantities as will permit the piston to carry it up into
the combustion chamber. Any oil present in the combustion
chamber is burnt during the explosion, but, its combustion being
imperfect, smokiness of the exhaust is the result. By reducing
the oil on the cylinder walls to the minimum necessary for
lubrication, smoking has been abolished, whilst clogging, or
carbonizing, of the valves has been materially reduced.
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| The 40–50 h.p. Six-cylinder Rolls-Royce Engine (valve side, showing also position of magneto). |
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| Fig. 4.—The 40–50 h.p. Six-cylinder Rolls-Royce Engine (carburettor side, showing also high-tension distributor, and position of centrifugal water pump). |
Methods of carburation have also undergone improvement, so that the carburation shall not materially vary with varying engine speed. The only other feature in the engine that calls for mention is the method of cooling. With the introduction of the honeycomb type of radiator, by which the water is made to flow through canals an eighth or a sixteenth of an inch wide, the efficiency of the cooling system has been doubled because of the large amount of surface, in a given size of radiator, for dissipating the heat. A fan is generally employed, either situated behind the radiator and driven by the engine, or the flywheel is vaned so as to induce a current of air through the radiator. To deal now with the transmission mechanism, the drive is taken through a clutch and gear-box as in the earliest days, but, for the final drive, chain transmission to the road wheels running on a fixed axle has largely given place to propeller drive on to a live axle. The leather-faced conical clutch, although still employed, has in many cases given way to the multiple-disk clutch in which a number of disks bearing against each other, either flat in section, or (as in the Hele-Shaw clutch) having annular tapered grooves, are contained in an oil-tight box. These plates are capable of being separated laterally from each other when “out of gear,” or brought into frictional contact with each other when it is desired to start the car. Metal-to-metal cone clutches expanding metal shoe clutches, single metal plate clutches and coil spring clutches have all at some time found favour with designers wishing to avoid a leather clutch. Hydraulic and electro-magnetic clutches have also been tried, but these have not gained any vogue. In the matter of the gear-box, the sliding into mesh of the gear-wheels as employed by Levassor is still the standard practice although that pioneer himself regarded the method as barbarous, and looked upon it as a mere temporary expedient. But details of the gear-box have materially improved. A single lever is usually employed for engaging any of the forward gears or the reverse, so that the mistake of simultaneously engaging a reverse and a forward gear is not possible. The spur-wheels are generally mounted in pairs on two sleeves, so that, by means of a selector mechanism that compels one sleeve to be brought to the neutral position before the other can be moved, no two gears can ever be engaged together. By means of “dog clutches,” the clutch shaft can generally be coupled direct with the bevel-wheel driving the back axle the “drive” on the highest gear being thus transmitted without passing through any spur-wheels. This reduces noise and frictional losses. Except for cars of great weight, chain transmission is fast dying out, the power being generally transmitted through a propeller shaft (with universal joints at one or both ends) to a bevel-drive on the back axle; such axle being divided into two revolving or live axles carrying the differential gear between them. The bevel-wheels, differential gear and live axles are enclosed and run in a lubricant.
Wire suspension wheels are growing considerably in favour, a saving in weight being thus effected. The liability of the pneumatic tire to deflation, through a puncture or burst,
