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Freewheel and Overlap Shifts

Freewheel and Overlap Shifts. Nonsynchronous and Synchronous Shifts. Shifts. Shifts occur when one control device is applied as another is either released or becomes ineffective. Overlap Shifts.

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Freewheel and Overlap Shifts

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  1. Freewheel and Overlap Shifts Nonsynchronous and Synchronous Shifts Tom Birch, 8/06

  2. Shifts Shifts occur when one control device is applied as another is either released or becomes ineffective. Tom Birch, 8/06

  3. Overlap Shifts Overlap shifts occur when one device is applied as another is released. This power transfer must be carefully synchronized. Overlap shifts are also called synchronous shifts. Shift timing, the amount of time to complete a shift, is affected by fluid temperature and viscosity. Cold fluid is thicker, and shifts take longer. Electronically-controlled transmissions can compensate for these temperature changes. Tom Birch, 8/06

  4. Overlap Shifts, 2-3 Shift 2nd Gear: 1.5:1 Ratio 3rd Gear: 1:1 Ratio Sun Gear, shell, and clutch drum are stationary. Sun Gear, shell, and clutch drum are rotating at engine speed. Band Applied Clutch Applied Band Released Tom Birch, 8/06

  5. Apply/Release Time A clutch or band applies quickly. It’s first movement will take up the clearance. Then there is a short slip zone followed by complete engagement Applied Released Tom Birch, 8/06

  6. Clutch Apply This graph illustrates a typical clutch apply. Tom Birch, 8/06

  7. Normal Band to Clutch Shift Band completely applied Clutch completely applied This graph illustrates a smooth shift with a band release and a clutch apply. Band completely released Clutch completely released Tom Birch, 8/06

  8. Shift Flare, Early Band Release If the band releases too quickly, both the band and the clutch will be partially released. This will cause the engine rpm to flare during the shift. Tom Birch, 8/06

  9. Early Clutch Apply, Shift Bump If the clutch applies too quickly, both the clutch and band will be partially applied at the same time. The band will try to slow both the engine and vehicle and cause a bump during the shift. Tom Birch, 8/06

  10. Electronic Control Many electronic transmissions monitor the input and output shaft speeds during a shift to determine shift duration. If a shift occurs too slowly or quickly, the shift will be adjusted electronically. Tom Birch, 8/06

  11. Freewheel Shift A freewheel shift has a one-way clutch that overruns as another drive or reaction member is applied. A freewheel shift also called a nonsynchronous shift. The additional components required for freewheel shifts create a more complex transmission. Tom Birch, 8/06

  12. Freewheel Shift, Components Intermediate Clutch Intermediate One-Way Plates Clutch Direct Clutch Drum Intermediate Band Race The THM 350 uses an intermediate multiplate clutch, a one-way clutch, and an intermediate band to hold the sun gear in 2nd gear. Tom Birch, 8/06

  13. Freewheel Shift, 2nd Gear Intermediate 1-way Clutch Intermediate Band Intermediate Clutch Forward Clutch In 2nd gear, the sun gear is held from rotating by the intermediate clutch holding the outer race of the intermediate one-way clutch. Tom Birch, 8/06

  14. Freewheel Shift, 3rd Gear Direct Clutch Applied Intermediate 1-way clutch overruns The intermediate clutch stays applied as the direct clutch applies for 3rd gear. The intermediate 1-way clutch overruns to allow the sun gear to be driven. Tom Birch, 8/06

  15. Shift Timing? The upshift will occur as soon as the direct clutch applies to drive the sun gear. The intermediate 1-way clutch will automatically freewheel. Tom Birch, 8/06

  16. Freewheel Shift, M2 Intermediate 1-way Clutch Intermediate Band Intermediate Clutch Forward Clutch The intermediate band is applied in Manual 2nd. It prevents the 1-way clutch from overruning during deceleration. Tom Birch, 8/06

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