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In the first gear, the first gearset actuates on the second gearset and output shaft; the second gearset reacts and makes the sun turn in reverse, causing the first gearset to increase the reduction ratio. In first gear, the input is locked to the first ring. The first carrier is locked to the output
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Nevertheless, it is still possible to find new automatic transmissions based on the
Simpson gearset. Such transmissions are three- or four-speed, and are often electronically controlled versions of older projects. They are kept in production because they are cheap, reliable, well-known and good
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in both the low and intermediate gears, allowing for fully progressive shifting with no "overlap". Gear changing patterns in some
Simpson gearboxes, including modern 4-speed units, avoid first gear as much as they can, going up to 2nd as soon as possible, and avoiding reducing to 1st unless
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Even the latest 4-speed transmissions are not
Simpson; they have only two planetary sets, while a Simpson transmission needs three planetary sets to get four speeds, the third planetary being an integrated overdrive.
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One problem of changing from first to second gear is that two bands must actuate in synchrony: the planet carrier of the second gearset must release at the same time as the sun band is actuated.
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The third gear is always direct drive (1:1), by feeding input to both the sun drive and the first ring, both carriers are effectively locked, so input directly drives the output.
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Command of second gear is simpler, the second carrier is released and the sun drive is braked. Thus input is locked to the first ring, and output is locked to the first carrier.
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sharing a common sun gear. A Simpson gearset delivers three forward gears and one reverse, plus neutral, and is commonly employed in three and four ratio
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129:, both gearsets share a common sun gear. The planet carrier of the first gearset ("first" means closer to the input shaft) is in
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The two planetaries are interdependent via two permanent connections, that commonly but not necessarily have the same gears and
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349:"Nomographs for enumeration of clutching sequences associated with epicyclic-type automatic transmission mechanisms"
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In the 1990s and 2000s, the
Simpson gearset went out of fashion and was replaced by more complex transmissions. A
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415:, "Planetary transmission for selfpropelled vehicle", published 1956-06-12, issued 1956-06-12
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and second ring. The second carrier is locked so its ring motion causes the common sun to spin
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mitigate roughness when a shift requires a combination of bands to be released or actuated.
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InASME International
Mechanical Engineering Congress and Exposition
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with the second gearset's ring. Owing to these linkages, only two
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105:. It is one of the several designs invented by American engineer
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is a compound planetary gear train consisting of two
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298:absolutely necessary (very slow speed plus
121:Simpson Planetary Gearset Schematic Diagram
66:Learn how and when to remove this message
322:, that offers six useful forward gears.
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29:This article includes a list of general
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438:Automotive transmission technologies
141:are needed to command the gearsets.
330:enough for the target application.
293:350 and 400 transmissions utilized
35:it lacks sufficient corresponding
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145:Gearset Command Configurations
89:to a Simpson planetary gearset
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374:"SIMPSON PLANETARY GEAR UNIT"
383:. 2005-03-23. Archived from
312:Ravigneaux planetary gearset
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95:Simpson planetary gearset
347:Esmail EL (2008-01-01).
316:simple planetary gearset
103:automatic transmissions
50:more precise citations.
409:US patent 2749775A
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314:was combined with a
295:overrunning clutches
448:Epicyclical gearing
320:Lepelletier gearset
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99:planetary gearsets
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291:Turbo Hydra-Matic
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83:Turbo Hydra-Matic
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127:gear ratios
48:introducing
432:Categories
394:2007-03-05
362:: 165–174.
334:References
318:to form a
266:retrograde
31:references
131:synchrony
242:Reverse
202:Reduced
183:-receive
139:clutches
137:and two
113:Overview
85:mates a
56:May 2011
257:output
222:Direct
172:Carrier
163:Carrier
44:improve
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411:,
254:braked
228:output
208:output
205:braked
195:braked
186:output
33:, but
443:Gears
388:(PDF)
377:(PDF)
360:48784
352:(PDF)
289:GM's
251:input
231:input
225:input
211:input
192:-send
189:input
175:Ring
135:bands
180:Low
166:Ring
93:The
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169:Sun
160:Sun
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