Torque Converter

[ever_green]

symptoms of UNLOCKED TC:
- Increasing RPM without (or very little) increase in vehicle speed
- Slipping RPMs with throttle (rpm rises and falls smoothly yet quickly just like a CVT transmission)
- Engine speed rises by ~500 rpm
- can be induced by increasing change in throttle position (rate of change in throttle position)
- Depending on the vehicle, Torque Converter is usually unlocked below 30-50mph under any throttle

symptoms of LOCKED TC:
- vehicle speed increases along with RPM (relative)
- adding more throttle doesn't seem to affect RPMs much but engine load increases substantially (specially at higher gears and low engine speeds)
- engine speed slowly decreases by ~500rpm
- can be induced by decreasing change in throttle position (rate of change in throttle position)
- Depending on the vehicle, Torque Converter may lock up above 30-50mph under light throttle
- Depending on the vehicle, Torque Converter is never locked in first few gears (usually gears 1&2)

symptoms of GEAR CHANGES:
- engine speed suddenly changes abruptly and quickly, in excess of ~1000rpm specially at higher engine speeds
- This can often be felt, like a jolt
- Shifts can induce Ignition Timing dips, lean AFRs. TC lock/unlock doesn't.
- Gear shifts are Not usually induced by throttle 'changes', rather by vehicle speed and throttle 'position'

[Christ]

A locked TC will not prevent the transmission from shifting. In fact, the TC has nothing to do with transmission shifts at all. All that changes when the TC locks are the relationship between the engine and input shaft, and the passage to teh trans cooler closes. The transmission will still shift at it's set points because that is based on fluid pressure, which increases with engine and vehicle speed.

[vlad]

Originally Posted by Christ

A locked TC will not prevent the transmission from shifting. In fact, the TC has nothing to do with transmission shifts at all. All that changes when the TC locks are the relationship between the engine and input shaft, and the passage to teh trans cooler closes. The transmission will still shift at it's set points because that is based on fluid pressure, which increases with engine and vehicle speed.

If TC was not needed for transmission operation it could be replaced with centrifugal clutch which would be locked at 10-15 km/h. When did you see something like this in car? TC is not usually locked in 1-3 gears. This helps transmission to shift. If I lock my TC at 40km/h I can feel vibrations from engine working near Idle and trying to pull the truck. This is why I set lock point @ 65 km/h.

Also I do need to turn lock off manually sometimes. Here is scenario: I slow down to 60 km/h TC is locked and will be locked until 59 km/h. Suddenly I need to speed up for whatever reason (light changes etc) if I floor my throttle the engine is at low rpm range about 1000 rpm it needs to rev-up to get more power but TC holds it. In this case I just flip the manual switch which is near by.

[Cobb]

Its a cvt, once its locked it varies the pulley diameters for ratios.

Originally Posted by vlad

I have never heard about locking TC at such a low speed. It defeats the purpose. How you transmission will shift right from 1 gear?

[vlad]

Originally Posted by Cobb

Its a cvt, once its locked it varies the pulley diameters for ratios.

CVT is a variator. It doesn't have gears at all. You only need to engage it when start moving. It can variate any gear ratio in it's range this is like TC + auto transmission. TC is smoothing auto gear operation.

If you lock TC right away and start shifting auto transmission will operate very rough, overloading engine and transmission itself.

[Cobb]

I wouldnt say there are NO GEARS in a cvt, there is a few, but the connection between the input and output shaft is by a steel belt.

As for a conventional automatic you can lock up the tc while its shifting, but the harmonics and stresses are a great way to break the input shaft.

I knew of guys at one time who use to rig up switches to lock the tc for performance. Sometimes you got away with it, other times it wore out the lock up clutch and with bigger engines it broke the engine.

Originally Posted by vlad

CVT is a variator. It doesn't have gears at all. You only need to engage it when start moving. It can variate any gear ratio in it's range this is like TC + auto transmission. TC is smoothing auto gear operation.

If you lock TC right away and start shifting auto transmission will operate very rough, overloading engine and transmission itself.

[vlad]

Originally Posted by Cobb

I wouldnt say there are NO GEARS in a cvt, there is a few, but the connection between the input and output shaft is by a steel belt.

As for a conventional automatic you can lock up the tc while its shifting, but the harmonics and stresses are a great way to break the input shaft.

I knew of guys at one time who use to rig up switches to lock the tc for performance. Sometimes you got away with it, other times it wore out the lock up clutch and with bigger engines it broke the engine.

In CVT there are positions where pulleys stop to "create" gears. Our brain is just to used to gears this is why engineers don't want to reinvent the wheel. They can program cvt to use different positions to kinda mimic gear shifting.

As I said right at the beginning I use this "smart switch" for low power low speed conditions only. This is why I posted it here where people are trying to squeeze extra mile from a gallon of fuel. Locking TC at low speeds will improve your gas mileage. Your auto transmission will be like manual. Auto transmission leads to higher fuel consumption because of slippage in TC.

[Cobb]

Plan b would be to upgrade the stall stator to a lower rpm one in the tc. This way it hits the rpm range sooner for max transfer minus a direct connection. Typically you want the stall speed at your peak torque or power band.

I had a van with a sticky lock up clutch. To stop without stalling the engine was to almost coast to a stop and feather the brakes til I felt a bump like. Then I knew I could stop harder without stallout out. If I just jam on the brakes to a stop like a fast light or someone coming out in front of me it stalled out. In all it still got me 9mpg.

Yeah the cvt in the honda is more fluid in drive where it has predefined ratios in sport mode. Kind of like how the newer prius 3 where you start to floor it you hear the engine rev up to different preset rpms and holds it til you lift.

[Christ]

Originally Posted by vlad

If TC was not needed for transmission operation it could be replaced with centrifugal clutch which would be locked at 10-15 km/h. When did you see something like this in car? TC is not usually locked in 1-3 gears. This helps transmission to shift. If I lock my TC at 40km/h I can feel vibrations from engine working near Idle and trying to pull the truck. This is why I set lock point @ 65 km/h.

Also I do need to turn lock off manually sometimes. Here is scenario: I slow down to 60 km/h TC is locked and will be locked until 59 km/h. Suddenly I need to speed up for whatever reason (light changes etc) if I floor my throttle the engine is at low rpm range about 1000 rpm it needs to rev-up to get more power but TC holds it. In this case I just flip the manual switch which is near by.

It /can/ be replaced with a centrifugal clutch, actually. You don't see them because they wouldn't perform the same function that a torque converter does.

A torque converter acts like a clutch in a manual car, allowing slip when necessary to increase engine speed and transmit more power than a locked gear ratio would allow.

That TC's don't typically lock until they're in the final gear is an NVH issue, nothing else. The locking torque converter that comes in the Ford Aspire actually has a centrifugal clutch in it, it locks based on RPM, not vehicle speed. There's nothing electronic about it.

[Cobb]

No one has mentioned it, but I was lead to believe by physics that the tc offers a 2 to 1 gear reduction and increase in twisting force/reduction in rpms for when the going gets tough?