As regards engine lubrication two basic methods came into use, the circulating-splash and the force-feed or "drilled-crankshaft" system, as well as combinations of the two. Both systems were employed on early cars, but the force-feed system came into much more extensive use with the development of the high-speed engine.
Fig. 4. Cut-away view of Stewart vacuum tank (fuel feed system).
Fig. 5. Thermostatic valve for control of engine temperature.
The problem of engine lubrication was rendered much more difficult by the change in the character of the fuel used. A good deal of the fuel entered the cylinder in the unvaporized state, and some of it leaked past the pistons into the crankcase, where it diluted the lubricating oil. In 1920 it was a common experience to find a fresh supply of lubricating oil lose much of its viscosity, and hence of its lubricating value, during the first 100 m. of running. Heating of the crankcase oil also reduces its viscosity, and to reduce this heating many British engines were cast with cooling flanges on the bottom of the oil sump.
One of the greatest advances in motor-car practice was the development of electric starting and lighting systems. The first such system on a car in regular production was on the Cadillac in 1912, and was the design of C. F. Kettering. Electric lighting alone had been used on petrol cars for some years previously, in fact ever since the advent of the tungsten filament bulb. At first the lamps were supplied with current from a storage battery only, which had to be recharged periodically from electric mains; later they were fed with current from a generator and storage-battery installation. The adaptation of an electric generator to storage-battery charging on a motor-car presented considerable difficulties, for the reason that the petrol motor runs at widely varying speeds, and that the voltage of the generator, therefore, tends to vary within wide limits, whereas a substantially constant voltage is needed for charging. Many systems of regulation were used with more or less success, but finally the socalled third brush system was adopted by a majority of the manufacturers of electrical equipment. In this system the generator field was provided with a winding similar to a shunt field winding, but instead of being connected between the positive and negative commutator brushes it was connected between one of these brushes and an auxiliary brush, so that only a fraction of the voltage generated in the armature was applied to the field coils. This system of control did not give a constant generator voltage, but with a storage battery connected to the generator it kept both the voltage and the charging current within permissible limits of variation. In connexion with the electric starter the main problem was that of the drive to the engine crankshaft. After trying various devices nearly all manufacturers in the United States and a good many in Europe settled upon the use
Fig. 6. Bendix drive for electric starters.
of the Bendix drive (fig. 6), invented by Vincent Bendix of Chicago. On an extension of the starter armature shaft was loosely mounted a sleeve, which was placed in driving connexion with the shaft through a coiled spring. The spring had a coarse, square thread cut on its outside, and on this was mounted the driving pinion, the hub of which was cut with a corresponding female thread. When current was applied to the starting motor, which was always of the series wound type, the armature started to revolve at great speed, carrying along the threaded sleeve on its shaft. Owing to its inertia the pinion lagged behind, and was screwed along the shaft and thus shifted into mesh with a gear-ring on the flywheel rim. Upon abutting against a collar it became fast upon the sleeve, and the starter then cranked the engine, the shock being relieved by the coiled spring. As soon as the engine began to pick up its cycle the flywheel ran ahead of the driving pinion, and the latter was automatically thrown out of mesh by being forced along the screw. Fig. 7, illustrating the Fiat motorcar engine, shows one method of mounting the generator and starter. A necessary part of practically all motor-car electric equipments was a battery cut-out, which automatically disconnected the battery from the generator when the engine speed dropped so low that the generator voltage was less than the battery voltage, and connected it on increasing engine speed when the generator voltage surpassed the battery voltage. Ground return wiring was very much used, all electric appliances having one insulated and one grounded connection. The standard voltage for motor-car electric systems in the United States was six volts, while in Europe a pressure of 12 volts was much used.
Unit-power-plant construction, that is, the combination of the engine, clutch and change-speed gear in a single unit, became very popular, and in the United States was the almost universal practice for passenger cars. A new type of clutch, the dry-disk, largely replaced the multiple-disk-in-oil type and also partly the cone clutch (fig. 8). It was very similar to the lubricated type of disk clutch in construction, but one set of the metal disks was faced with disks of
