free to rotate around the shaft E. The internal gear B is in mesh with the planetary pinions C. This form of gear assembly can be used for either low or reverse speed depending upon whether the plate D or the internal gear B is kept from rotating. If the internal gear B is kept from turning the drive is taken from the plate D. If the plate D is kept from turning the driving sprocket is attached to internal gear B.

Considering first the action of this assembly to provide a slow speed ratio, let us assume that the internal gear B is provided with a brake band to hold it stationary and the plate D is in rigid connection with the drive sprocket or shaft which turns the rear wheels. If the engine shaft E is turning in the direction of the arrow, gear A must turn in the same direction. If the internal gear B is kept from rotating the planetary pinions C must not only turn around on their supporting stud in a direction opposite to that of the drive gear A but they must roll around the internal periphery of the gear B and carry the disc or plate D forward at a slower speed than driving shaft A but in the same direction as indicated by arrow F. As the drive sprocket is attached to plate B it turns at a slower speed than the engine shaft E.

Q. Describe action of reverse gearing.

A. In order to obtain a reverse motion it is necessary to provide a brake band for plate D and attach the driving sprocket to internal gear B. When the plate D is kept from rotating the planetary pinions C turn around on their studs and rotate the internal gear B in a direction opposite to engine rotation, as indicated by the arrow H, and at a slower speed than that of the drive gear A. Q. How is direct drive obtained?

A. Direct drive is obtained with any form of planetary gearset by some form of friction clutch which is adapted to lock all parts of the transmission into one rigid unit.

Q. How does the gearset act when on direct drive?

A. When all parts of the planetary gear assembly are locked together the gears are still in mesh but are not turning and the revolving mass acts as a flywheel member.

Q. What is the operating principle of the individual clutch gearset with master clutch?

A. In this form of change speed gearing two shafts are provided, one being a main shaft and the other a countershaft. Suitable gears are attached to and turn with the countershaft, these meshing with corresponding members on the main shaft which are normally free to turn unless clutched to the main shaft by some form of positive clutch. A typical individual clutch gearset is shown at Fig. 160 with all parts clearly outlined.

Q. What types of clutches are used in the gear box?

A. The clutches employed to secure the loose gears to the main shaft are of the positive jaw type, one member having projecting teeth designed to engage with the depressions in female member of the clutch. The master clutch is of the friction type and usually is carried with the flywheel. Any form of friction clutch previously described may be used as a master clutch.

Q. Why is the master clutch needed?

A. The positive types of clutches are obviously harsh in action, i. e., they will transmit power as soon as engaged and if these were used alone there would be considerable strain imposed on the mechanism owing to the sudden starting of the car and the clutches themselves would become damaged if they fail to engage promptly. When a master clutch is used in the flywheel, this is released before the positive clutches are shifted and is re-engaged and the power applied to the gearset gradually after the positive clutch has been shifted.

Q. How many speeds can be obtained from individual clutch gearset?

A. Any reasonable number of speeds may be provided in a gearset of the individual clutch type though those commonly constructed provide either three or four forward speeds and a reverse ratio.

Q. Describe construction of typical individual clutch gearset and name important parts.

A. In the individual clutch change speed gearing shown at Fig. 160 the important parts are the casing, the main shaft, which carries

two double end clutches and two loosely revolving members, and the countershaft to which four gears are secured. Both of these shafts are carried on suitable ball-bearings, and the driving end of the main shaft is provided with a bevel drive pinion which engages with a driven gear which forms part of a countershaft carried as part of the gearset. The main shaft is made in two pieces, one end telescoping into the other. The power of the engine is applied to the short portion of the main shaft or sleeve into which the end of the longer shaft telescopes. One of the constant mesh gears is an integral part of the sleeve. This gear is in mesh with a larger member carried by the countershaft.

To obtain a high speed or direct drive, the high and intermediate speed sliding clutch is pushed forward until it engages with the projecting teeth of the constant mesh drive gear. This serves to lock the two portions of the main shaft together and power is transmitted directly from the constant mesh drive gear sleeve which is turned by the engine to the bevel drive pinion. If, however, the high and intermediate sliding clutch is moved toward the back of the gearset in such a way that it locks the intermediate gear C to the shaft, then the engine power is transmitted from constant mesh gear H to countershaft gear B and from intermediate drive gear D to the driven gear on the main shaft with which gear D meshes. To obtain low or reverse speed the other sliding clutch is moved so that low speed driven gear F is locked to the main shaft for the slow speed and reverse gear H is locked to the main shaft for reverse motion.

The countershaft turns slower than the drive sleeve of which the constant mesh drive gear A forms a part on account of the difference in size between gears A and B. When the intermediate ratio is desired, practically the only reduction in speed between the engine and the drive pinion is obtained by the difference in size between gears A and B because gears C and D are practically the same diaameter. On low speed and reverse motion there is a reduction in speed because gear E is smaller than gear F and gear G is smaller than gear H. On the direct drive, the speed of the bevel drive pinion and the engine crankshaft is the same. On the intermediate ratio there is one reduction in speed at the constant mesh

gear. On the low and reverse speed, there are two reductions in speed, one at the constant mesh gears and the other between the driving gear on the countershaft and the driven gear on the main shaft. When both clutches are in a neutral position the master clutch may be engaged without driving the transmission main shaft. Before either sliding clutch member is engaged it is necessary to interrupt the engine drive by means of the master clutch.

Fig. 161.-Sectional View of Coventry Silent Chain Individual Gear Box With Chains Removed from Gearing to Show Arrangement of Parts.

Q. Are gears the only speed reducing members used in gearsets of this character?

A. Forms of individual clutch gear boxes have been devised abroad where silent chains are used to connect the main shaft and countershaft instead of having gears in mesh. A gear box of this character with the chains removed is shown at Fig. 161. The various speeds are obtained by sliding clutches, just as in the previously described outfit, the only exception being the method of obtaining the reverse ratio.