PatrickR
Well-Known Member
- First Name
- Patrick
- Joined
- Jan 8, 2020
- Threads
- 4
- Messages
- 159
- Reaction score
- 136
- Location
- North Carolina
- Vehicle(s)
- 2018 JLU
You are mistaken, I never said torque multiplication happens at all speeds. And yes, torque converters are rated with a given stall speed, with modern converters approaching 1:1 at the stall speed before locking. There is a range of ratios that the torque converter operates in, with lock-up being 1:1. Anything not 1:1 results in some amount of torque multiplication, which is constantly changing. My example was that even with a miniscule amount of torque multiplication, the apparent gearing is greater than the manual's first gear ratio. Even with pumping/efficiency losses, the automatic's first gear would provide greater force than the manual.
Since I guessing you didn't like Wikipedia as a source, here's another "Typical stall torque multiplication ratios range from 1.8:1 to 2.5:1", and another "Torque multiplication rapidly decreases until it reaches a ratio of 1:1 (no torque increase over crankshaft torque.) A typical torque converter will have a torque multiplication ratio in the area of 2.5:1"
You missed it in the original post, so I'll say it again: regarding the graph, it's probably best to ignore first gear. I said this because there's no way that I know of to quantify when lock-up happens. True, the rest of the chart didn't take into account any losses (which I noted), please see this post for one that does. Neither chart is factoring in any torque multiplication at any point. They are both based off of the published gear ratios, tire height, and engine torque from here. The second graph has the engine output at 95% on the automatic, to simulate the automatic's lower efficiency.
Also according to Wikipedia (and a dead link to ZF's website) the ZF8HP70 (which is stronger than the Jeep's auto) weighs 192 pounds. I can assume the Jeep's 8HP50 is not any heavier, which is way lighter than I expected. This doesn't include the transmission cooler/lines/fluid, but I'm not sure the auto's weight penalty is as much as we expected.
Your chart shows torque multiplication going on in all gears at all RPM. It's literally just the gearing multiplied by a scalar for torque multiplication.....
Also, Stall speed is not where they go 1:1, stall speed is max multiplication. They go to 1:1 fairly shortly thereafter.
Edit: You do understand that torque multiplication and an effective gearing change would be the same thing, right?
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