« НазадПродовжити »
mitigating factors are eliminated in the V type eight cylinder motor, as it consists of two blocks of four cylinders each, so arranged that one set or block is at an angle of forty-five degrees from the vertical center line of the motor, or at an angle of ninety degrees with the other set. This arrangement of cylinders produces a motor that is no longer than a four cylinder engine of half the power would be.
Q. Is the eight cylinder V engine a new or untried type?
any means, although it is not generally known to automobilists. It has been a standard power plant for aeroplanes for many years, leading exponents being the Antoinette, the Woolsley, the E. N. V. in Europe and the Curtiss in the United States. Messrs. De DionBouton, a leading French automobile manufacturer, is credited with being the first to produce an eight cylinder motor as a commercial proposition. Many racing cars have been built with eight cylinder motors, notably the Rolls-Royce, the Darracq and Winton. The eight cylinder V type has also been widely used in racing motor boats and gasoline propelled railway coacles. It was not a surprise, therefore, to those who were familiar with internal combustion engineering when the eight cylinder engine was applied for automobile propulsion.
Q. What are the real advantages of the eight cylinder engine?
A. Apparently there is considerable misconception as to the advantage of the two extra cylinders of the eight as compared with the six cylinder. It should be borne in mind that the mul.
00 120 150 100 210 240 270 300 350 360 30 600 90 1200 150" 180° 210 240* 270 300 350 360 Comparative torque dlagrams of four, slx and elght-cylinder motor, showing Increase in uniformity with added cylindera
Fig. 331.—Curves Showing Torque of Various Engine Types Demon
strate Graphically Marked Advantage of the Eight Cylinder Type.
tiplication in the number of cylinders noticed since the early days of automobile development has not been solely for increasing the power of the engine, but to secure a more even turning movement, greater flexibility and to eliminate destructive vibration. The ideal internal combustion motor would be that which more nearly conforms to the steady running produced by a steam turbine or electric motor. The advocates of the eight cylinder engine bring up the item of uniform torque as one of the most important advantages of the eight cylinder design. A number of torque diagrams are shown at Fig. 331. While these appear to be deeply technical, they may be very easily followed when their purpose is explained. At the top is shown the torque diagram of a single cylinder motor of the four cycle type. The high point in the line represents the period of greatest torque or power generation, and it will be evident that this occurs early in the first revolution of the crank shaft. Below this diagram is shown a similar curve except that
Fig. 332.—Front View of the King Eight Cylinder V Engine with
Cover Removed from Timing Gear Case to Show Use of Silent
it is produced by a four cylinder engine. Inspection will show that the turning moment is much more uniform than in the single cylinder; similarly, the six cylinder diagram is an improvement over the four, and the eight cylinder diagram is an improvement over the six cylinder.
Q. Why is better torque obtained with an eight cylinder engine than with a four or six?
A. The reason that practically continuous torque is obtained
in an eight cylinder engine is that one cylinder fires every ninety degrees of crank shaft rotation, and as each impulse lasts nearly seventy-five per cent. of the stroke, one can easily appreciate that an engine that will give four explosions per revolution of the crank shaft will run more uniform than one that gives but three explosions per revolution, as the six cylinder does, and will be twice as smooth running as a four cylinder, in which but two explosions occur per revolution of the crank shaft. The comparison is so clearly shown in graphical diagrams that further description is unnecessary.
Q. How does an eight cylinder engine differ mechanically from a four or six?
A. The front view of a typical eight cylinder engine with the cover removed from the timing gear case is outlined at Fig. 332. In this engine the cylinders are cast in blocks of four and are of the L head type, the valves being on the inside of the cylinder block facing those of the other cylinders. This makes it possible to operate the valves by one cam shaft, driven by silent chain gearing from the pinion on the crank shaft. There is ample space between the two cylinder blocks to mount the carburetor, ignition distributor and other parts. The method of installing the eight cylinder motor in the Cadillac automobile frame is clearly shown at Fig. 333. The only point in which an eight cylinder motor differs from a four cylinder is in the arrangement of the connecting rod, as in many designs it is necessary to have two rods working from the same crank pin. This difficulty is easily overcome in some designs by staggering the cylinders and having the two connecting rod big ends of conventional form side by side on a common crank pin. In other designs one rod is a forked form and works on the outside of a rod of the regular pattern. Still another method is to have a boss just above the main bearing on one connecting rod to which the lower portion of the connecting rod in the opposite cylinder is hinged.
As the eight cylinder engine may actually be made lighter than the six cylinder of equal power, it is possible to use smaller reciprocating parts, such as pistons, connecting rods and valve gear, and obtain higher engine speed with practically no vibration. The firing order in nearly every case is the same as in a four cylinder except that the explosions occur alternately in each set of cylinders. In prevailing practice the sequence is 1-3-4-2. The firing order of an eight cylinder motor is apt to be confusing to the motorist, especially if one considers that there are eight possible sequences. The majority of engineers favor the alternate firing