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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 wiihout 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 er.tire 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 ca led 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 shaft. 'Gear A is keyed to the same sleeve to which the drive sprocket A-1 is attached, while gear F is keyed to a sleeve to which the reverse drum is fastened. Suitable clutch plates serve to establish connection between the high speed clutch plate carrier which is keyed to the engine shaft and the reverse drum to which gear F is secured. Brake bands are provided, capable of arresting motion of either the low speed drum which also acts as the gear casing or the reverse drum to which the driven direct drive clutch plates are attached. These bands are not shown in the illustration.

To obtain a low speed the slow speed drum is kept from revolving by clutching it and the drive is from the gear D to the planet gears C which turn in the opposite direction and from the gear B of the planet gear assembly to the gear A which is keyed to and must turn with the drive sprocket A-1. As there is a difference in size between gears D and C, gear C turns slower than gear D, and as gear B has but half the number of teeth of the gear A the sprocket A-1 is turned at half the speed of gear B and a little less than half the speed of gear D and in the same direction. If the reverse drum is kept from rotating the gear F attached to it is also held stationary. The result is that the gear D drives the gear C just as when the slow speed drum was held, but as gear E cannot turn without running around the fixed gear F the motion of gear A which is attached to the sprocket A-1 is reverse to that of the central shaft.

If the two brakes or clutches are held out of contact with the slow speed and reverse drums and the high speed clutch plates are pushed together by the action of the clutch dogs and toggle the reverse drum is firmly locked to shaft K. As gear D cannot produce movement of the planetary gear assembly B, C and E without causing the reverse drum to rotate the entire assembly is locked together as a unit and the sprocket A-1 turns at the same speed as the shaft K and in the same direction.

Obviously, only one clutch can be engaged at a time. When the slow speed drum is held from rotation, the reverse drum must be free to turn and vice versa. When the high speed clutch is engaged both slow speed and reverse drums must be capable of turning. Another form of planetary gearset has received some application in which internal spur gears are used and a separate set of pinions employed for low or reverse ratios.

Q. How many speeds are provided in the usual form of planetary gear?

A. Planetary gears, as a rule, have two forward speeds and a reverse. It is possible to make a planetary gear that will provide three forward speeds but these are usually so complicated and require so much gearing that they are not as practical as the less costly sliding gear forms.

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Fig. 159.—Outlining Action of Planetary Gearing When Internal Gear

is Employed.

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Q. Describe action of slow speed gearing when an internal gear is used in the planetary system.

A. In order to show clearly the method of operation of the other form of planetary gearing a section through the slow speed gearset is shown at Fig. 159. In this the main driving gear A is keyed to the engine shaft extension E and must turn with it. The planetary pinions C are carried on studs attached to the plate D, which is

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