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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

Motor Flywheel
Clutch Case

Clutch Release

[graphic]

Spring

Lever

Driven Plates

Driving 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.

[graphic]

Fig. 150.-Sectional View of Multiple Disc Clutch Designed to Run

in Oil.

Q. What is the multiple disc clutch?

A. Multiple disc clutches, one of which is shown in section at Fig. 150 and another form with all parts disconnected to show the arrangement at Fig. 151, is a plate clutch in which small diameter discs are employed instead of the larger diameter plates used in the three and five plate forms. In general principle of operation the multiple disc is similar to the other plate forms and the reduction in diameter is compensated for by using a larger number of surfaces in contact. A series of driving plates are carried by and turn with a casing member attached to the flywheel, while a slightly smaller number of driven plates are carried by a central member which is independent of the flywheel when the clutch is released and which joined to the gearset drive shaft. The discs are kept in contact

by pressure of a coil spring against a pressure plate, which presses against the outer driving plate and holds the entire disc assembly into firm engagement. Obviously as long as the discs are held together the engine power must be transmitted from the clutch case attached to the flywheel through the disc assembly to the central member carrying the driven plate and attached to the gearset drive shaft. To release the multiple disc clutch the spring is compressed enough to allow the driven plates to turn freely between the driving plates.

[graphic]

Fig. 151.-Multiple Disc Clutch Parts Shown in the Order They are Removed from Flywheel in Taking Down Assembly.

Q. How many types of multiple disc clutch are used.

A. Multiple disc clutches may be of the all metal disc type, which are designed to run in a bath of lubricant, or of the dry plate pattern where one set of plates, usually the driven members, are faced with some material designed to have greater frictional qualities than metal surfaces when run without lubrication. One form of multiple disc clutch, that shown at Fig. 152, differs from the conventional form in that the clutch discs are stamped out so the surfaces in contact are in the form of a cone. In general construction this clutch follows conventional design.

[graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed]

Fig. 152.-Sectional View of Hele-Shaw Multiple Disc Clutch and Efficient English Design.

Q. Describe advantages of multiple disc clutches.

A. The most important advantage of a multiple disc clutch is that it is small and compact, and its construction such that very gradual engagement is attained: Cwing to the large number of friction surfaces and the presence of a film of oil between each pair of surfaces it is practically impossible for a clutch of this pattern to engage harshly, as the spring pressure must first squeeze out the film of oil between each pair of plates before the friction adhesion is great enough to drive positively. Owing to the small size and relatively light weight of the driven plate assembly this is not liable to spin as is the heavier cone or three plate clutches, but to offset this advantage there is a liability of dragging, due to the adhesive properties of the oil film present between the plates.

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