You're right, I totally forgot the part about planetaries when I was typing that.Honda has been making their own automatic transmissions since the 1970s. The reason they use the design they use is because of patent issues with planetary geared transmissions. Long before Z1 and the upscale shift. They used Dexron in their transmissions until 2000 when they created Z1. Another decade later, they started using DW1.
The new 10-speed automatic they just released does use planetary gears like most automatics, making it Honda's first in-house planetary gear automatic transmission (they also use the ZF9 on some cars)
Of course, prior to the early 2000's, they were also 3 and 4 speed units. Probably a great bit easier to get the shift timings down on those. The 5 speed is where they really started to run into issues with shift quality, although the 99-02 I4 transmission certainly had its fair share of problems and it was only a 4 speed.
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