Torque Convertors: A Physics Puzzle

  • Context: Automotive 
  • Thread starter Thread starter Rx7man
  • Start date Start date
  • Tags Tags
    Torque
Click For Summary

Discussion Overview

The discussion revolves around the functioning of torque converters, particularly their ability to amplify torque and the mechanics behind their operation. Participants explore the principles of torque, power conservation, and the role of various components within the torque converter system.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how torque converters can increase torque without a stationary element to apply force, suggesting they only serve as a fluid coupling.
  • Another participant states that a torque converter cannot amplify power, asserting that torque and RPM must conserve energy according to the equation TORQUE1*RPM1=TORQUE2*RPM2.
  • A different participant explains the role of the stator in the torque converter, noting that it redirects flow and is stationary during certain conditions, which can amplify torque at the expense of speed.
  • One participant expresses confusion about the stator's function, emphasizing that torque on the input and output shafts must be equal, leading to the belief that the engine must produce the output torque.
  • Several participants discuss the presence of splined shafts and their implications for torque transfer, with some noting discrepancies in their understanding of the number of shafts involved.
  • Another participant mentions that in an automobile transmission, there are multiple outputs, including one for the oil pump, which complicates the torque dynamics.
  • One participant reflects on their previous experiences with automatic transmissions, agreeing that input torque equals output torque but noting the necessity of a reaction torque for any difference.
  • Another participant acknowledges the existence of multiple splined shafts in older transmission models, which clarifies their earlier confusion about torque dynamics.

Areas of Agreement / Disagreement

Participants express a mix of agreement and disagreement regarding the mechanics of torque converters. While some acknowledge the role of the stator and the necessity of additional components for torque amplification, others maintain that input and output torque must be equal without a third member to provide reaction torque. The discussion remains unresolved with competing views on the mechanics involved.

Contextual Notes

Participants reference specific components and configurations of torque converters, indicating that their understanding may depend on the particular models being discussed. There are unresolved questions about the efficiency and operational principles of torque converters, as well as variations in design across different transmission types.

Rx7man
Messages
425
Reaction score
189
I have a question about torque convertors... They just aren't making any sense to me because they don't seem to follow laws of physics.

I don't see how they can increase torque AT ALL without having something stationary somewhere against which to apply force.. I can only see them as a fluid coupling that allows the engine to rev to a point where it's in it's torque band, but in no instance can the torque out be more than the engine is capable of producing.

The outer part of the torque convertor rotates with the engine, and the outer output sleeve drives the oil pump in the transmission..
The inner part is acted on by the fluid and is where your power is taken from.. Without something stationary somewhere, can you somehow get more torque from the output shaft than the engine produces? Am I missing something? Even if the output shaft turns at a lower speed than the engine it doesn't make sense.
 
Engineering news on Phys.org
A torque converter can't amplify power (torque*RPM).

If it conserves power, then TORQUE1*RPM1=TORQUE2*RPM2 or TORQUE2=TORQUE1*RPM1/RPM2.

Even if it is only 50% efficient, and 50% of the power is turned to heating the fluid, TORQUE2=-0.5*TORQUE1*RPM1/RPM2.
 
A torque converter has a stator that redirects the flow. This is the stationary element in the circuit.
The stator is housed on a one way clutch so it only reacts when there is a speed differential between the pump and the turbine.

It amplifies torque at the expense of speed.

Maximum torque ratio occurs at stall. (input rotating output stationary).
At slip reduces the torque ratio reduces.
When output = input speed torque ratio = 1 (ie no torque advantage)http://www.volkspage.net/technik/ma..._fundamentalsselectiondesignandaplication.pdf
See chapter 10
 
  • Like
Likes   Reactions: Rx7man
That's a really excellent read, definitely saving it for future reference as well for the other chapters!

However, it hasn't clarified anything for me.. can anyone draw a free body diagram or anything that might help me? There's an element called a stator, but it's not fixed.. There's only and input shaft and an output shaft (if you ignore the oil pump drive).. torque on one must be equal to the torque on the other, so in any case, the engine has to produce that torque.
 
It'd be a bit silly to call it a stator if it never operated in a fixed stated.

It sits on a one way clutch that is grounded to the transmisson case via a splined sleeve.
 
I must have missed seeing the two splined shafts.. if that's the case, then it all makes sense again.
 
The last time I pulled an automatic transmission, there was one splined shaft. The torque converter was bolted to the flexplate. The transmission input shaft was inserted into the torque converter. The transmission input shaft had a bearing pilot at the tip, then splines to engage the torque converter. No other connections. One input, one output.

And I agree completely with the OP. Input torque equals output torque, but the RPM's can be different. In order for output torque to be different from input torque, there must be a reaction torque through a third member. The sum of moments must equal zero.
 
  • Like
Likes   Reactions: Rx7man
upload_2018-6-20_18-4-9.png


It's all in the book chaps.
 

Attachments

  • upload_2018-6-20_18-4-9.png
    upload_2018-6-20_18-4-9.png
    43.4 KB · Views: 565
jrmichler said:
The last time I pulled an automatic transmission, there was one splined shaft. The torque converter was bolted to the flexplate. The transmission input shaft was inserted into the torque converter. The transmission input shaft had a bearing pilot at the tip, then splines to engage the torque converter. No other connections. One input, one output.

And I agree completely with the OP. Input torque equals output torque, but the RPM's can be different. In order for output torque to be different from input torque, there must be a reaction torque through a third member. The sum of moments must equal zero.
That's what I always saw, though looking at pictures of newer transmissions it seems like they do have another splined shaft, which would then make it possible
 
  • #10
In an automobile transmission there is more than one output. Something needs to drive the oil pump. It may appear to be just one output but on the convertors that I last had my hands on there is a notched sleeve around the splined shaft. The sleeve is solid to the outer housing of the convertor, which then engages inside the transmission.
 
  • #11
yes.. and I just looked at an old 727 chrysler tranny, and indeed it does have two splined shafts, plus the notched sleeve for the oil pump, so that can work, there's something against which to put force against!.. Don't know if I was blind now or my memory is failing.. thought I saw some with only one splined shaft, hence my confusion.

I'm reading the other chapters of that book now.
 
  • #12
I didn't recall more than one splined shaft so I didn't mention it, but I thought there had to be something else. Thanks for looking.
 
  • #13

That's an excellent explanation of the components and operation of a modern torque converter. One video is worth a thousand words?
 
  • Like
Likes   Reactions: jrmichler

Similar threads

Automotive Does vehicle weight have an effect on torque capacity of the gearbox?
  • · Replies 5 ·
Replies
5
Views
5K
Automotive How to plot a power and torque graph for an engine?
  • · Replies 18 ·
Replies
18
Views
7K
Selecting hydraulic motors and a pump for hydrostatic transmission
  • · Replies 58 ·
2
Replies
58
Views
8K
Automotive Driveshaft Material for Extreme Torque Applications?
  • · Replies 21 ·
Replies
21
Views
4K
Koenigsegg Regera - acceleration
  • · Replies 4 ·
Replies
4
Views
3K
Undergrad A Question About the Physical Explanation Behind Torque
  • · Replies 8 ·
Replies
8
Views
2K
Torque Transmission - Slippage at Press Fit Connection
  • · Replies 11 ·
Replies
11
Views
19K
Gear Ratios and Constant Power/Torque: find max velocity?
  • · Replies 3 ·
Replies
3
Views
4K
Automotive Can a High RPM Gas Engine Move a Heavy Load Like a Low RPM Diesel?
  • · Replies 120 ·
5
Replies
120
Views
25K
Torque & Gearbox: Understanding Force, Torque & Ratio
  • · Replies 8 ·
Replies
8
Views
13K