What has changed in automotive transmission technology that has allowed manufacturers to be able to make 10 speed transmissions today?

Question

When I first started driving in the 90s it seemed like the 4 and 5 speed transmission was the best, modern transmission you could get. They were relatively reliable, and had enough gears to make acceleration, and fuel economy good in my Honda CRX.

Today, I can buy a Honda Odyssey with a 9-speed automatic transmission standard, and 10-speed on the high end model.

**What has changed in transmission engineering, materials science, and technology to allow more gears in the gearbox?**

What are the potential downsides? E.g. is the typical 10-speed as reliable as the old standard 5-speed gearbox?

Edit: To be more clear, this is an ENGINEERING, MATERIALS SCIENCE, and TECHNOLOGY question. I understand the benefits of having more gears for ride quality, and fuel efficiency.

In: Engineering

Answer 1

The thing that changed was mostly the fuel economy requirements.

They have been using 15 and 30 speed transmissions in semi trucks for decades because they needed that range to be able to haul the loads they had.

For passenger cars 3-4 was good enough for a long time, then customers started wanting smoother accel and better fuel economy and were willing to pay the extra couple hundred dollars versus a simpler transmission. Now we are up to 10 gears because the marginal cost of adding a bunch of extra gears is small enough that most people consider the fuel economy gains and improvements in power band to be worth it.

Also we have got to a point where new car buyers almost never request a manual transmission, so having a really silly number of gears to shift through isn’t considered to be a major drawback the way it would have been back when manual transmissions were more typical.

And as far as reliability goes, there is no reason that a 5 or 10 would be inherently more or less reliable. It really just comes down to the manufacturer. The kinds of things that used to break on 5 speed autos still exist in a 10, and aside from transmissions used in heavy vehicles doing towing or drag cars the actual load being on put on the individual gears was never really a limiting factor, it mostly comes down to how well manufactured they are.