there is a tendency for the cone to continue to rotate when released from driving engagement with the flywheel. The rim of even the lightest cone and its leather facing have appreciable weight, and while this is not much it is carried at a sufficiently large radius from the center so the cone has considerable momentum and acts, to some extent, as a flywheel. This continued rotation is called "spinning" and is objectionable, because it makes gear shifting difficult.

A.

Continued rotation of the clutch cone is easily prevented by applying some form of braking member which will come in contact with the revolving cone after it has been pulled clear of the flywheel. A simple clutch brake is shown at Fig. 146. The friction pad A is carried by the clutch shifter yoke B in such a way that it comes in contact with the clutch cone only when this has been withdrawn a certain distance by the yoke F and the rolls G, as previously described. Suitable adjustments are provided at C, D, and E, so

the friction pad may be brought into engagement with the cone at any time that is desirable and in order to compensate for wear or other depreciation of the friction pad A.

Q. Describe three plate clutch and explain its action.

A. Two forms of three plate clutches are in general use; that outlined at Fig. 147 uses a large number of small springs to produce the pressure required to keep the parts in contact, while the form

Fig. 147.-Principal Parts of Knox Three-Plate Clutch.

depicted at Fig. 148 utilizes one main spring. A three plate clutch is so called because the central driven member serving to drive the clutch shaft connected to the gearset is sandwiched in between driving plates carried by the flywheel. In the Knox clutch shown at Fig. 147 the clamping pressure to keep the driving plates in firm contact with the driven plate is obtained from a series of clutch springs carried near the flywheel rim. As the total pressure exerted by these springs is somewhere in the neighborhood of a thousand

Fig. 148.-Showing Construction of Three-Plate Clutch in Which Spring Pressure is Augmented by Levers to Increase Adhesion Between Clutch Members.

pounds it is necessary to provide some form of leverage so the inner and outer driving plátes may be separated without undue exertion on the part of the operator. As will be evident in the clutch shown at Fig. 147 any pressure exerted against the long arms of the levers

will be multiplied many times and comparatively little effort is needed on the part of the operator to push the levers in toward the flywheel and transfer the multiplied pressure through the pins which extend through the outer driving plate and into the inner driving plate to compress the springs and thus relieve the driven plate from contact with either of the driving plates between which it is normally held.

In the clutch outlined at Fig. 148 the spring pressure is made light enough so that it may be compressed without difficulty by the operator but its effective pressure or that brought to bear against the outer driving plate is multiplied about six times. In this clutch the flywheel web is faced off to serve as one driving surface and a clutch brake is provided so spinning of the driven plate may be prevented when the clutch release collar is pushed back against the revolving disc keyed to the clutch shaft. Whereas the average spring pressure of a cone clutch is seldom over three hundred pounds that of a three plate form is much higher as greater pressure is needed to hold flat surfaces in engagement than is required to drive through a male and female cone combination. The three plate clutch has an important advantage in that it releases positively and will engage gradually. Its main defect is that it requires a large diameter driven plate which brings up the same objection offered against the cone clutch, that of spinning, which however can be taken care of in the same manner.

Q. What materials are used in three plate clutches?

A. The two driving plates which are carried by the flywheel are either of steel or cast iron with smoothly finished surfaces while the driven member may be either of cast iron or bronze studded with a large number of cork inserts, which increase the frictional adhesion and make for smooth engagement. Either of the three

plate clutches described may be run in an oil bath as the entire clutch mechanism is fully protected by the casing formed in the flywheel interior by the application of a suitable cover bolted to the flywheel rim. In the Knox clutch the flywheel cover serves as one of the driving members but in that at Fig. 148 the cover is a separate member serving only to enclose the clutch parts. The inset at A, Fig. 148, shows a method of insuring prompt release of the driven

plates, by means of small coil springs which are placed between the two driving plates and which serve to push these out of engagement with the driven plate as soon as the main spring pressure is released.

Q. What is a five plate clutch?

A. A typical five plate clutch is outlined at Fig. 149. This is

Driven Plates

Crank Shaft

Fig. 149.-Simple Form of Five-Plate Clutch.

practically the same in construction and operation as the three plate pattern shown at Fig. 148 with the exception that two driven plates and three driving plates are used. A five plate clutch offers more surface than a three plate type and may be made somewhat smaller in diameter and use less spring pressure if employed to transmit the same power.