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mitting more power than the simple face friction gearing previously described by using more discs in order to obtain a greater driving surface. The form shown at Fig. 155 utilizes two driving discs A and B driven by the engine and two driven discs A and B attached to a countershaft divided in the center and supported by a bearing so that it virtually becomes two countershafts. Driven disc A which contacts with the driving disc A only turns sprocket A while driven disc B contacts with driving disc B only and drives sprocket B. The various speed ratios are obtained by moving the driven discs simultaneously, the principle of speed reduction being the same as with simple face gearing. Reverse motion is provided by auxiliary gearing.

The friction gearing shown at Fig. 156 is a form which uses beveled driving and driven members but this method of construction does not provide an infinitely variable number of speed reductions. The form shown gives only two forward speeds and a reverse motion. Three cones are mounted on the driven shaft, which is turned by the engine, each of these being actuated by independent means so that they may be brought into action with corresponding faces of the driven wheels A and B. When the low speed cone is brought into action with the larger beveled face the greatest reduction of speed is obtained. When this is released from contact and the high speed cone is pushed into engagement with the small diameter beveled faces the highest ratio of drive is provided. The reverse cone is brought in contact with the large diameter bevel surface and driven wheels A and B reverse the direction of motion of the drive sprockets which transmit power to the wheels by chain connection. It will be observed that driven wheel A is not attached to the sprocket as is driven wheel B but that the sprocket is turned by means of a pair of spur gears which reverse the motion of driven wheel A and cause both sprockets to turn in the same direction.

Q. Has friction drive ever been applied directly to rear axle? A. A form of friction drive in which the change speed and driving mechanism has been applied directly to a rear axle is shown at Fig. 157. The driving disc A in this case is the fiber faced member and slides on the squared shaft H which is driven from the engine

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Fig. 157.-Showing One Method of Applying Friction Drive Directly to Rear Axle.

by the usual form of propeller shaft. The driven discs B and C are adapted to be brought out of engagement with the driving member A by means of the actuating collars M connected to a suitable pedal. The driven wheels B and C are normally kept in engagement with the driving member A by means of springs surrounding the axles I and J and transmitting their pressure through ball thrust bearings against the hubs of the driven wheels B and C. Wheel B is attached to axle I by means of a key and drives the spur pinion D which meshes with the spur gear E attached to the wheel hub N which rotates on the stationary axle K. The driven wheel C is attached to axle J in a similar manner and rotates the spur pinion F which meshes with an internal spur gear G attached to the hub of the wheel O. This wheel revolves on the fixed axle L. It will be noted that driven members B and C are provided with a recess at their center and when the wheel A is moved into this recess it is out of contact with the driven members and can turn without producing movement of wheels B and C and of the road wheels N and O to which they are connected. In this case the higher speed ratios are obtained when the disc or driving wheel A is nearest the center of the effective driving face of B and C. As the wheel A is moved toward the outer peripheries of the driven members the speed ratio becomes lower on account of the difference in size between the driving wheel A and the diameter of the circle on wheels B and C with which it contacts. The reason that an internal spur gear drive is used at wheel O instead of the external spur gear arrangement used to turn wheel M is that this is necessary to insure that both wheels will turn in the same direction, on account of the wheels B and C being at opposite sides of the driving member A. As is true of the simple form of face friction gearing outlined at Fig. 154 a reverse motion may be obtained by moving the disc A along the drive shaft H to the other side of center of the driven wheels B and C.

LESSON SEVENTEEN

THE INDIVIDUAL CLUTCH CHANGE SPEED GEAR

Q. What is an individual clutch change speed gear?

A. An individual clutch change speed gear is a form in which the various changes of speed are effected simultaneously with the engaging of some form of clutch that brings that gear ratio into action.

Q. What are its advantages?

A. In most forms of individual clutch gearsets the various gears through which the different speed ratios are obtained are always in mesh and the construction is such that it is not possible to injure the gear teeth when changing from one speed to another.

Q. What are the principal types of individual clutch gears? A. There are two main forms of individual clutch gears, the simplest being the planetary or epicyclic gear, the other form resembling a sliding gear transmission in general outline and arrangement of parts but having the gears always in mesh. In the planetary system the speed desired is obtained by manipulating clutch bands, a different clutch being provided for each speed. In the positive clutch type a separate jaw clutch is provided for each speed ratio but the entire gearset is controlled by a master clutch, which is common to all speed ratios, as it serves to couple the engine and gearset shaft together.

Q. What is the planetary gear and why is it so designated? A. A typical planetary gear is outlined at Fig. 158 and it is so called because the change speed gears revolve around a center gear attached to the main shaft, the motion of the gearing resembling that of the planets around the sun. In the form outlined the gear D, which is attached to the central shaft, is termed the "sun" gear

while the gear assembly comprised of members B, C and E are termed "planet" gears.

Q. Describe the construction of a typical planetary gearset.

A In the form shown at Fig. 158, the shaft K is attached to the flywheel of the engine by means of the flange machined integral with it. This serves as the main driving member for the gearset and the gear D and the high speed spider which carries the clutch plates J are keyed to this shaft so they must turn with it. The change speed gearing is contained in a casing which has bushings

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Fig. 158. Parts of All Spur Gear Two-Speed and Reverse Planetary

Gearset.

so that it can turn on the sleeves to which the sprocket A-1 and gear F are attached and these sleeves are in turn provided with an internal bearing so they may revolve independently of the driving shaft K if necessary. The planet gears, B, C, and E are joined together to form an assembly which turns on a suitable shaft parallel to the shaft and spaced on a circle whose radius is equal to the distance between the centers of the planet gear pin and the main

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