Re: TA Design

Posted by K.B.-826 on January 23, 2005 at 18:56:34 from (209.163.30.68):

In Reply to: TA Design posted by PAULIH300 on January 23, 2005 at 10:43:13:

Here's how the TA works-

The Mechanical TA used in the smaller IH's is a planetary unit. It is made up of an input shaft, a 7" clutch, a planetary carrier, the planetary unit, the overrunning clutch- known as the ramp and rollers, and the output shaft. Power enters the unit through the input shaft from the engine clutch. When the lever is ahead, (DD), the 7" TA clutch locks the input shaft to the planetary carrier, and the whole assembly rotates as a unit, resulting in no reduction of speed. When the lever is pulled back, the TA clutch disengages, allowing the power from the input shaft to enter the primary sun gear in the center of the planetary unit. The primary sun gear turns the primary planet gears, which are attached to the secondary planet gears, which turn the secondary sun gear, which is splined to the output shaft, resulting in the gear reduction. If the planetary carrier wasn't held still with the lever back, it would just freewheel around the sun gears, and the tractor would not move. This is why the overrunning (one-way) clutch, or ramp and rollers, is used. It is located between the output shaft and the planet carrier, and locks up whenever the planet carrier tries to turn faster than the output shaft. If it goes bad, the planet carrier will just freewheel. One more thing about the ramp and rollers- since it is a one-way clutch, it will lock up whenever the planet carrier tries to turn faster than the output shaft. However, if the output shaft tries to turn faster than the input (traveling downhill in TA) the ramp and rollers will overrun, causing the tractor to freewheel right down the hill. That is why you never go downhill in TA.

To answer your question-

The ramp and rollers do not need to ratchet (overrun), but it was the only way avalible in 1954 to hold the carrier still. Hydraulic clutch and brake packs and the seals needed to make them work realiable enough for farm equipment hadn't been developed yet. The ramp and rollers provided a low-tech way to automaticly hold the carrier still, but the disatvantage was that it would overrun if the output shaft tries to turn faster than the input shaft. If you welded the ramp and rollers engaged, you would basically be welding the output shaft to the planet carrier.

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