Further, if you shift the driven wheel across the center of the driving wheel from one side to the other the direction of rotation of the driven wheel will be reversed. This is the kind of a power trans mission device that is installed in the Metz motor car for connecting the propeller shaft with the crank shaft of the engine, and by means of it the usual clutch arrangement and transmission gears are done away with and a variable change of speed is gained.
Finally, you can bevel the driven wheel, as shown at .D, and in this way change its angle of rotation in relation to the rotation of the crankshaft, and make it revolve at whatever angle it may suit your pur pose the best.
But setting another wheel on the opposite side of the driven pulley, as shown at E, with its face parallel with the face of the driving wheel and with its shaft in a line with the crankshaft, then the latter Will rotate in the reverse direction to that of the driving wheel.
How Friction Clutches friction wheels, as you have seen, both elements, as the driv ing and the driven wheels are called, rotate and it is the friction at their points of contact which prevents them from slipping.
Now, friction clutches differ from friction wheels in that after the driven cone or disk, which is fixed to the machine, is brought up to a speed as high as that of the driving cone or disk the former is forced hard against the latter, and they revolve in the same direction together, exactly as if they were a solid line of shafting.
Clutches for Mobile mobile engines such as are used on motor cars the friction clutch in one form or another is held in high favor among engineers as an easy and effective means for con necting and the drive shaft with and from the crankshaft of the engine.
In fact, with the exception of the Metz car, which has the friction wheel drive described above, and the Owen car, which employs a magnetic clutch, to be described presently, all motor cars are provided with friction clutches.
There are two kinds of friction clutches designed especially for motor cars and these are (1) cone clutches and (2) disk clutches.
The Cone Clutch.—The cone clutch is formed of a leather-covered cone fixed to the end of the drive shaft and this is made to fit into a conical recessed member, that is, a cone-shaped hole in a piece of steel—usually the flywheel—and this is keyed to the crankshaft of the engine.
A strong, steel spiral spring forces and keeps the cone in the recessed member all the time except when it is pushed out by a lever worked by the foot of the c\ CLUTCH.
driver who is running the car. The whole scheme is shown at A and B in Fig. 7Z The Disk Friction this type of clutch a number of thick, sheet steel disks, called the driven disks, are fixed on the drive shaft, and these inter leave with an equal number of circular rings called the driving disks, which are mounted on the crank shaft of the engine.
A stiff, spiral spring holds the driven disks in close contact with the driving disks except when they are pushed out by the clutch pedal. Disk friction clutches for motor cars usually run in oil to keep them from wearing, but this does not prevent them from biting enough to make them hold rigidly to gether.
The Magnetic Clutch.—In this type of clutch magnetism is used instead of friction to grip the driving and driven shafts. The principle of the magnetic clutch will be understood from the draw ing Fig. 7.4. Let a horseshoe magnet be mounted on the driving shaft and a round, soft iron core, or at-mature, as it is called, be mounted on the driven shaft so that they are free to revolve independently of each other.
Now if the soft iron core is placed between the poles of the magnet and the latter is rotated the iron. core will be attracted to and pulled around with it in virtue of the magnetic lines of force that flow through them. To engage and disengage a magnetic clutch an electromagnet energized by a battery is used instead of the permanent one and the magnetic pull exerted by it on the iron core can be varied from 0 to a pull between them which is without slippage.
Clutches for Stationary Engines.—Two kinds of clutches are used for coupling up stationary engines to machinery and these are (1) friction clutches and (2) magnetic clutches.
Friction Clutches.—Clutches of this type can be divided broadly into two classes namely (1) solid clutches and (2) split clutches. These classes can be further divided into those (a) in which the pres sure necessary to set up the friction is applied by hand, and (b) in which it is set up by the running of the engine.