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power if this is necessary. In a gas engine the power is generated by explosions occurring directly in the cylinders and it is not possible to start an engine of this kind under full load. In order to start the engine, it should be free from the retarding influence of the car, and for this reason, it is necessary to interpose the clutch between the source of power and the point of application to enable the engine to be started independently of the vehicle it propels. Then again it would be inconvenient to be constantly stopping the motor every time one desired to stop the car, so the clutch enables one to stop the car and the motor can be kept in operation until such time it is desired to start again, when the clutch may be re-engaged and the motor power again directed to the traction members.
Q. What is the principle of clutch action?
A. Most clutches operate because of frictional adhesion of various substances under pressure. In some forms the power is transmitted by the actual mechanical interlocking of two members, one which has projecting points and the other which has depressions made to receive the projections of the opposing member. These clutches are known as positive clutches, while those which depend on frictional adhesion are termed "friction clutches." The essential parts of all clutches are the same, consisting of a driving member attached to the source of power, a driven member attached to the power transmission member and suitable means to hold this into engagement when it is desired to transmit the power and separate them when it is necessary for the engine and gearset to run independently of each other.
Q. What are the principal types of friction clutches?
A. Friction clutches may be divided into four main classes: the cone, plate, multiple-disc and band forms.
Q. Describe construction and name important parts of cone clutch.
A. A typical cone-clutch assembly with the main parts clearly indicated is outlined at Fig. 144 and an optional arrangement of parts sometimes used is depicted at Fig. 145. The driving member of the clutch is formed by the motor flywheel, while the driven member is a cone that is held in contact with the tapering inner periphery by means of a heavy spring connected in such a way that it is restrained from end movement by a suitable means of fastening to the crankshaft. As long as the spring keeps the clutch cone in contact with the flywheel and the spring is permitted to exert its full pressure, the clutch cone and flywheel are firmly locked together to form practically a rigid coupling. When it is desired to release the clutch a shifting yoke carrying clutch release rolls is
Fig. 144.—Cone Clutch Used on Pope-Hartford Motor Cars. adapted to bear against an upstanding flange attached to the clutch cone and to pull the cone out of engagement with the motor flywheel by compressing the clutch spring.
The form of cone clutch shown at Fig. 145 is known as the inverted type because the clutch cone is held in contact by a spring pushing the cone away from the flywheel and having an inverted taper so that the more the cone is pushed away from the flywheel
the greater will be its degree of frictional adhesion with the applied ring that serves as a female clutch member. To release a clutch of this type it is necessary to push the cone toward the flywheel, while in the forms shown at Fig. 144 it is necessary to pull the clutch cone away from the flywheel. Q. What is the female mem
Female Member. ber, and how is it made ?
A. The female member of a cone clutch is usually the driv
Cone. ing portion and is made of cast iron, either in the form of an
Clutch applied ring machined with an
Spring internal taper, as shown at Fig. 145, or it may be integral with the motor flywheel as is common practice. When the inverted type of clutch is used, it is necessary to bolt the female member in place to the flywheel, as shown at Fig. 145. Q. What is the cone made of?
Ball Thrust A. The clutch cone is usually a light aluminum casting or a 1 sheet steel stamping.
Q. What is the angle of the Fig. 145.-Simple Inverted Cone cone taper and why?
Clutch of Foreign Design. A. The usual angle employed for clutch cone is twelve and onehalf degrees and this is used because it is the least that can be utilized and have a clutch that will release promptly and yet not require excessive spring pressure to keep the parts in contact when transmitting power. More gradual tapers are apt to produce wedging and make it difficult to release the clutch promptly, while more abrupt tapers will cause the clutch to slip, unless the parts are held together by considerable spring pressure.
Q. Why is it desirable to make the cone as light as possible? A. The clutch cone is usually made light so that it will not spin