Lockup torque converter q&a
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Lockup torque converter q&a
Hey all
Was talking to my dad (my truck has a 46re,his a 42re) and had some questions I figured some of the more knowledgeable people on here could answer as far as the lockup torque converter and "using" it properly. Assuming of course it works properly. These really are more generic questions instead of focused on our trucks.
First, he keeps talking about the torque multiplication functionality of an automatic transmission. Can someone explain this in layman's terms?
Second, I read on here that the converter being unlocked creates more heat - but dad's telling me even though it's unlocked, and generating more heat, it has more "pulling power" due to the torque multiplication he mentioned earlier. Assuming this is true, is the consensus to tow unlocked and live with the heat, or trade off the power for better longevity?
Third - our transmission has the od off button. Is this supposed to simultaneously lock in drive (or specifically, out of od) and also force the torque converter to lock? My dad's and I seem to behave differently in this regard. If I hit the od off button, it's forced in drive with tc locked. It will stay locked until I hit the button again - it will then stay in third (assuming the load is enough it needs to stay in third) but the TC will unlock. Dad's will lock and unlock the TC even with the od off button engaged. Assuming they "should" act the same but don't seem to.
Long story short, I'm just trying to glean a little bit more about best practices. I understand towing with od off. But to getting the next step deeper, trying to understand fundamentals of the auto. And yes, I still wish everyday I had my five speed with 4.10s back and big enough factory axles the little 360 couldn't hope to break anything... Damn kids.
Was talking to my dad (my truck has a 46re,his a 42re) and had some questions I figured some of the more knowledgeable people on here could answer as far as the lockup torque converter and "using" it properly. Assuming of course it works properly. These really are more generic questions instead of focused on our trucks.
First, he keeps talking about the torque multiplication functionality of an automatic transmission. Can someone explain this in layman's terms?
Second, I read on here that the converter being unlocked creates more heat - but dad's telling me even though it's unlocked, and generating more heat, it has more "pulling power" due to the torque multiplication he mentioned earlier. Assuming this is true, is the consensus to tow unlocked and live with the heat, or trade off the power for better longevity?
Third - our transmission has the od off button. Is this supposed to simultaneously lock in drive (or specifically, out of od) and also force the torque converter to lock? My dad's and I seem to behave differently in this regard. If I hit the od off button, it's forced in drive with tc locked. It will stay locked until I hit the button again - it will then stay in third (assuming the load is enough it needs to stay in third) but the TC will unlock. Dad's will lock and unlock the TC even with the od off button engaged. Assuming they "should" act the same but don't seem to.
Long story short, I'm just trying to glean a little bit more about best practices. I understand towing with od off. But to getting the next step deeper, trying to understand fundamentals of the auto. And yes, I still wish everyday I had my five speed with 4.10s back and big enough factory axles the little 360 couldn't hope to break anything... Damn kids.
Legend
Joined: Nov 2014
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Yes, they do multiply torque: initially. The stator is the key.
From TCI's website
Stator --- the stator can be described as the "brain" of the torque converter, although the stator is by no means the sole determiner of converter function and characteristics. The stator, which changes fluid flow between the turbine and pump, is what makes a torque converter a torque converter (multiplier) and not a fluid coupler.
With the stator removed, however, it will retain none of its torque multiplying effect. In order for the stator to function properly the sprag must work as designed: (1) It must hold the stator perfectly still (locked in place) while the converter is still in stall mode (slow relative turbine speed to the impeller pump speed) and (2) allow the stator to spin with the rest of the converter after the turbine speed approaches the pump speed. This allows for more efficient and less restrictive fluid flow.
The sprag is a one-way mechanical clutch mounted on races and fits inside the stator while the inner race splines onto the stator support of the transmission. The torque multiplier effect means that a vehicle equipped with an automatic transmission and torque converter will output more torque to the drive wheels than the engine is actually producing. This occurs while the converter is in its "stall mode" (when the turbine is spinning considerably slower than the pump) and during vehicle acceleration. 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. The main point to remember is that all properly functioning torque converters do indeed multiply torque during initial acceleration. The more drastic the change in fluid path caused by the stator from its "natural" return path, the higher the torque multiplication ratio a given converter will have. Torque multiplication does not occur with a manual transmission clutch and pressure plate; hence the need for heavy flywheels, very high numerical gear ratios, and high launch rpm. A more detailed discussion of torque multiplication can get very confusing to the layman as high multiplication ratios can be easily considered the best choice when in fact more variables must be included in the decision. Remember, the ratio is still a factor of the engine torque in the relevant range of the torque converter stall speed, i.e.: a converter with a multiplication ratio of 2.5:1 that stalls 3000 rpm will produce 500 ft.-lbs. of torque at the instance of full throttle acceleration if its coupled to an engine producing 200 ft.-lbs. of torque at 3000 rpm. However, if this same engine produces 300 ft.-lbs. of torque at 4000 rpm, we would be better off with a converter that stalled 4000 rpm with only a 2.0:1 torque multiplication ratio, i.e.: 300 x 2.0 = 600 ft.-lbs. at initial acceleration. Of course it would be better yet to have a 2.5:1 ratio with the 4000 rpm in this example (provided his combination still allows the suspension to work and the tires don't spin.) This is just a brief overview as the actual scenarios are endless.
Here is the link on TCI's website to more good info:
http://www.tciauto.com/tech_info/tor..._explained.htm
As for when O/D off is pressed both transmissions will still engage TCC. They are essentially the same transmission just one is more "heavy duty." The stock axles handle the 360 very well. The reason for towing with O/D off is to save the transmission
From TCI's website
Stator --- the stator can be described as the "brain" of the torque converter, although the stator is by no means the sole determiner of converter function and characteristics. The stator, which changes fluid flow between the turbine and pump, is what makes a torque converter a torque converter (multiplier) and not a fluid coupler.
With the stator removed, however, it will retain none of its torque multiplying effect. In order for the stator to function properly the sprag must work as designed: (1) It must hold the stator perfectly still (locked in place) while the converter is still in stall mode (slow relative turbine speed to the impeller pump speed) and (2) allow the stator to spin with the rest of the converter after the turbine speed approaches the pump speed. This allows for more efficient and less restrictive fluid flow.
The sprag is a one-way mechanical clutch mounted on races and fits inside the stator while the inner race splines onto the stator support of the transmission. The torque multiplier effect means that a vehicle equipped with an automatic transmission and torque converter will output more torque to the drive wheels than the engine is actually producing. This occurs while the converter is in its "stall mode" (when the turbine is spinning considerably slower than the pump) and during vehicle acceleration. 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. The main point to remember is that all properly functioning torque converters do indeed multiply torque during initial acceleration. The more drastic the change in fluid path caused by the stator from its "natural" return path, the higher the torque multiplication ratio a given converter will have. Torque multiplication does not occur with a manual transmission clutch and pressure plate; hence the need for heavy flywheels, very high numerical gear ratios, and high launch rpm. A more detailed discussion of torque multiplication can get very confusing to the layman as high multiplication ratios can be easily considered the best choice when in fact more variables must be included in the decision. Remember, the ratio is still a factor of the engine torque in the relevant range of the torque converter stall speed, i.e.: a converter with a multiplication ratio of 2.5:1 that stalls 3000 rpm will produce 500 ft.-lbs. of torque at the instance of full throttle acceleration if its coupled to an engine producing 200 ft.-lbs. of torque at 3000 rpm. However, if this same engine produces 300 ft.-lbs. of torque at 4000 rpm, we would be better off with a converter that stalled 4000 rpm with only a 2.0:1 torque multiplication ratio, i.e.: 300 x 2.0 = 600 ft.-lbs. at initial acceleration. Of course it would be better yet to have a 2.5:1 ratio with the 4000 rpm in this example (provided his combination still allows the suspension to work and the tires don't spin.) This is just a brief overview as the actual scenarios are endless.
Here is the link on TCI's website to more good info:
http://www.tciauto.com/tech_info/tor..._explained.htm
As for when O/D off is pressed both transmissions will still engage TCC. They are essentially the same transmission just one is more "heavy duty." The stock axles handle the 360 very well. The reason for towing with O/D off is to save the transmission
Record Breaker
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The TL;DR version is that a combustion engine has a torque curve which typically has fairly low torque at low RPM. The torque curves rises up to a certain RPM and then starts to flatten out and ultimately fall again. The torque converter takes a higher RPM input with a certain torque and converts it into a lower RPM output with proportionally higher torque.
As the torque converter is essentially a fluid pump the operation generates heat, and the lock-up function reduces heat but that is not the main benefit. Lock-up reduces losses in the converter for better economy. At cruising speeds there is little to no multiplication so not much heat is generated. Climbing up a grade with transmission in lower gear generates a lot of heat, and that's when transmission often fail.
O/D off limits the transmission to 3rd/1:1 direct gear. It still allows the lock-up to engage based on operating parameters however with a heavy trailer that probably never happens.
As the torque converter is essentially a fluid pump the operation generates heat, and the lock-up function reduces heat but that is not the main benefit. Lock-up reduces losses in the converter for better economy. At cruising speeds there is little to no multiplication so not much heat is generated. Climbing up a grade with transmission in lower gear generates a lot of heat, and that's when transmission often fail.
O/D off limits the transmission to 3rd/1:1 direct gear. It still allows the lock-up to engage based on operating parameters however with a heavy trailer that probably never happens.
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Thanks for all the information. I'm going to read through it a few more times to try and understand better.
As far as towing with overdrive locked out, I'm still curious. I know that running in drive is best - but once in drive, do we want the converter locked or unlocked? Or is it minimal difference at that point?
Am I going to create more heat in drive with the converter locked at 2500 rpm, or 2nd at 4k rpm?
As far as towing with overdrive locked out, I'm still curious. I know that running in drive is best - but once in drive, do we want the converter locked or unlocked? Or is it minimal difference at that point?
Am I going to create more heat in drive with the converter locked at 2500 rpm, or 2nd at 4k rpm?
Legend
Joined: Nov 2014
Posts: 8,098
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Thanks for all the information. I'm going to read through it a few more times to try and understand better.
As far as towing with overdrive locked out, I'm still curious. I know that running in drive is best - but once in drive, do we want the converter locked or unlocked? Or is it minimal difference at that point?
Am I going to create more heat in drive with the converter locked at 2500 rpm, or 2nd at 4k rpm?
As far as towing with overdrive locked out, I'm still curious. I know that running in drive is best - but once in drive, do we want the converter locked or unlocked? Or is it minimal difference at that point?
Am I going to create more heat in drive with the converter locked at 2500 rpm, or 2nd at 4k rpm?
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So mine doesn't, it will stay locked if the od off button is engaged. I'll test again tomorrow, I'm pulling vantage with a few thousand pounds, but I'm pretty sure that's been my experience.
Administrator
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From: Clayton MI
TCC is controlled by the computer, even with O/D locked out, you should still get TCC. If you don't, it should set a code. You really want TCC working properly, especially if you tow heavy loads.
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Well, it's certainly engaging/disengaging. When I hit the od off button it really likes to stay locked, the truck will lose a lot of speed and I have to really step into the Throttle to get it to unlock. Seems ineffective if I'm trying to proactively kick it out of overdrive when I know I'll need it versus either losing speed or hammering the Throttle to get it to shift. Or maybe I'm being over sensitive and it's working fine and I shouldn't expect so much out of a 20 year old four speed. Truck just seems to struggle towing 3k pounds more than I think it should, and I'm trying to figure out potential reasons, having ruled out (I think) most things engine related.
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Hopefully I'm not showing my ignorance here, I've seen all the "don't tow in od" directives, but I kind of assume that meant "don't push it very hard in od". If I'm chugging along on flat ground with no headwind, I selectively have it od. I just feel that two quads on a utility trailer (granted steel not aluminum) shouldn't be asking that much. I've considered regearing I just don't tow heavy enough often enough to justify the cost.