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Q: Describe action of gearset when on high speed.
A. The highest speed is usually a direct drive obtained by locking the two members comprising the main shaft assembly together by a positive jaw clutch J carried on the face of the gear I. To engage this clutch it is necessary to push the hand lever into the extreme forward notch on the segment which moves the bell crank so that teeth J fit into the corresponding depressions on the face of gear A. As the main shaft is practically one-piece the drive is direct from the clutch cone to the universal joint.
Q. Outline method of obtaining reverse motion.
A. In order to turn the universal joint at the driving end in a reverse direction to that of the clutch cone it is necessary to push gear K to the extreme back end of the gearset where it meshes with an intermediate pinion H carried by a stud on the gear case instead of directly with member G on the countershaft. The motion of the countershaft D is always reversed to that of the main driving member A though the motion is again reversed on any of the forward speed ratios so that the squared portion of the main shaft turns in the same direction as the gear A though at a slower speed. By the interposition of the intermediate pinion H which meshes with the countershaft gear G the motion of the main shaft is made to correspond to that of the countershaft if the gear K is pushed into engagement with the intermediate pinion H and thus the universal joint is turned in a direction opposite to that of the engine
Q. What is a selective gearset?
A. The selective form of gearset, as outlined at Fig. 162 and 164, is practically the same in general principles of operation as the progressive system except that two or more shifting members, each operated by an independent rod, are employed instead of the one shifting member of the progressive gearset. One gear shift lever is employed for both shifting members and this works in a gate form of segment so the lever may be moved in or out to engage either shifting member as desired. As the shifting member may be picked out by merely pushing the gear shift lever into the proper slot in the gate plate this system is called the selective system.
Fig. 164.—Defining Arrangement of Parts and Method of Operating
Sliding Members of Three-Speed Selective Gearset. Q. What are the main advantages of a selective gearset?
A. An important advantage of the selective system of gear shifting is that a more compact construction is possible than in the progressive system and gears can be engaged more easily. When the gearshift lever is in neutral position, one can go directly into any desired speed ratio without passing through any of the others if desired. This enables the driver to select the speed he desires at once. For example, if the gearshift lever was in a position at the back end of the inside slot, as shown at Fig. 164, the low and reverse shift member would be engaged with the reverse idler gear. If it is desired to pass directly into the high speed position this
could be accomplished by a simple movement of the gear shift lever to the front end of the outside slot which would engage the direct drive clutch. With a progressive gearset it would be necessary to pass through low and intermediate ratios before the high speed clutch could be engaged. This would not only require an appreciable interval of time but would also produce more wear on the gears comprising the shifting member which would be often moved through one or more speed ratios when this would not be necessary with the ordinary selective system.
Q. How many speed changes are provided in the usual selective gearset?
A. Selective change speed gearing used on light and medium weight cars, such as depicted in halftone at Fig. 165 and in engineering drawing at Fig. 166, provide for three forward speeds and a reverse motion. As a rule the highest speed is obtained by locking both members comprising the main shaft assembly together. On heavier, more powerful cars, a gearset such as shown at Fig. 167 and providing four forward speeds and a reverse motion is often supplied. Four speed gearsets may be of two patterns, the form outlined having the highest or fourth speed on the direct drive while other forms have the direct drive on the third speed.
Q. In a four speed gearset with direct drive on the third speed how is the highest or fourth speed obtained?
A. Where the direct drive lock is utilized for the third speed of a four speed gearset the highest ratio is usually through gearing arranged in such a way that when the fourth speed is engaged the driving end of the gearset will turn at a higher speed than the engine end.
Q. What are the advantages of the geared-up fourth speed?
A. In a four speed gear box having direct drive on the third ratio it is intended that all normal driving will be on the third speed which provides maximum efficiency. When exceptionally favor able conditions are present and it is desired to drive the car at a high rate of speed, the geared-up fourth speed may be brought into action for the short time it is possible to maintain the high speed. The direct drive position permits of utilizing a lower ratio of drive