There are many different ways to produce a multispeed automatic transmission, and we’ll delve into some of the more innovative solutions in this article. When loads are light, the transmission may skip one or more gears during upshifts, until the most efficient gear has been selected. When more power and/ or acceleration are needed, the transmission drops down one or more gears to accommodate. Multispeed transmissions make that possible. But to operate most effi ciently and deliver much better fuel economy, while keeping emissions to a minimum, they’re happiest when running within a relatively narrow rpm range. These smaller engines develop more horsepower per cubic inch than their predecessors. On average, today’s internal combustion engine (ICE) displacements are much smaller than the big iron lumps that were the norm during the second half of the previous century. But the reason is actually much simpler than that, and it comes down to just one word: efficiency. It might seem like vehicle manufacturers are engaged in an international automatic transmission arms race, with each trying to outdo the others by adding yet another gear to its automatic transmissions. Today, automatic transmissions with eight, nine and even ten forward speeds have become commonplace. Things got only slightly more complicated when the three-speed Turbo-Hydramatic was introduced by GM some years later, and automatic transmissions have been adding forward gears ever since. That era’s large-displacement, low-revaving engines produced enough torque to get relatively heavy vehicles moving off the line in low gear, and high gear provided a comfortable engine rpm for cruising at the speed limit. If you’re old enough to remember GM’s Powerglide automatic transmission, you’ll know that just two forward gears were deemed sufficient for many of the vehicles of the day.
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