By on December 23, 2014


Ford 10 speed transmission cross section design pieced together from various patent disclosures

Ford 10 speed transmission cross section design pieced together from various patent disclosures

If a transmission has 5 clutches and for the realization of a gear ratio 3 out of the 5 clutches have to be engaged, there are a total of 10 possible combinations. The ZF 8HP and GM 8L transmission families have 5 clutches of which 3 are engaged for any gear state, but only have 9 out of these 10 states are present and accounted for (8 forward gear ratios along with 1 reverse gear ratio). The 10th combination leads to a situation where the transmission would want to turn in forward and reverse direction at the same time, i.e. the transmission would lock up the output shaft and potentially self destruct.  The Ford 10R transmission design has 6 clutches and 4 are engaged for any given gear ratio. This gives us 6C4 or 15 possible combinations, 11 of which are used to yield 10 forward gear ratios and 1 reverse gear ratio. The 4 other combinations do not yield a functional transmission gear state or put the transmission in Neutral.

In the last article on the Ford 10 speed transmission we looked at some of the design details of the Ford 10 speed RWD automatic transmission without going into the details of the actual power flow for the various gears. In this article, a detailed analysis of the power flow is presented along with the gear ratio calculations and shifting operation of the transmission. Just like the last article on the subject, the information is based on invention disclosures by Ford. The most relevant patent for the purpose of understanding the power flow is US Patent #8545362.

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