frag me if you will: what is a torque converter?
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D(irecto)r Pepper
Joined: Nov 2001
Posts: 1,952
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From: Houston Raceway Park...in TEXAS.
Re: frag me if you will: what is a torque converter? <img src="http://xs-fx.com/raughammer/UltraThruster.jpg" alt=" - " />
Now read this ....
http://xs-fx.com/raughammer/CONVERTER.HTM
or here is a quick break down, though the same info and a LOT more are on my web page WITH pictures:
A torque converter consists of the standard fluid coupling components and a stator. The impeller is actually attached to the housing, which is bolted to the engine flywheel. The turbine is connected to the drive shaft which extends back through the center of the impeller. In between the turbine and the impeller rests the stator, which is grounded and attached to a shaft which encases (but is independent of) the drive shaft. To emphasize, the stator remains stationary with respect to the rotating impeller/turbine combination at all times.1 If this sounds confusing, refer to the torque converter take apart file (keep in mind that the impeller and turbine seem to "face" the wrong direction).
The Stator, or How This Thing Actually Works
The stator, as its name implies, is a stationary disk located in between the impeller and the turbine and “grounded” independently of both the input and output shafts. The stator accomplishes several things. It allows the blades on the turbine and impeller to be angled so that the fluid must reverse its direction of flow when moving from the impeller to the turbine by reversing that flow yet again before the fluid is sucked back into the impeller (and thus preventing the flow of the turbine from hindering that of the impeller), and it causes a “reaction force” to transmit more torque to the turbine than would otherwise be available. It’s actually these reversals in fluid flow that allow the torque converter to transmit torque. To be clear: the blades of the impeller and the turbine are cut in opposite directions, forcing the fluid which flows from the impeller to the turbine to reverse rotational direction (it does not affect vortex flow). This reversal would impede the motion of the driving impeller when the fluid returned at its base if it weren't for the stator, which has blades cut in such a way that it forces the fluid to reverse direction yet again, matching the rotational direction of the impeller. These forced flow reversals generate torque because the stator provides a necessary reaction force. Now that you're thoroughly confused, we'll go into the details.
The stator accomplishes both of these tasks (which are really inseparable, interrelated functions) because of its dramatically angled blades, placed in opposition to the direction of flow within the turbine.
Without the stator, the fluid from the turbine would rush back into the vacuum at the center of the impeller in an opposing direction. This would impede the rotation of the impeller and dramatically decrease the efficiency of the coupling; lots of power would be dissipated in the resultant turbulent flow. And since it’s the reversal of fluid flow that allows power to be redistributed (i.e., speed converted into torque) a mechanism is needed to correct this inefficiency.
The real function of the stator, however, is to provide a reaction force. Recall the complicated flow pattern of a normal fluid coupling from the previous section – there was circular movement along the circumference of the disks as well as vortex flow. In the torque converter, there are two separate flow patterns, identical to each other but opposite in rotational direction.
Remember that the presence of the stator allows the blades in the turbine to be angled so that they force the fluid to reverse direction as it passes through the turbine. The result is this complicated, parallel and opposite flow within one housing. Consequently, the fluid must reverse rotational direction (clockwise to counter-clockwise, for example) as it passes through the stator.
This means that fluid with an instantaneous velocity in one direction must de-accelerate until it reverses direction within the very small space of the stator blades. Anything which de-accelerates (or accelerates; same thing) must do so in response to a force (Newton’s 2nd) and for each and every force there is an equal and opposite, or reaction, force (Newton’s 3rd – he proves very useful). Since the mass of the liquid is conserved, this force is directly proportional to the change in fluid velocity. This means that the more aggressively you cut the blades on your stator – the more you force the liquid to change direction as it passes through those stator blades – the greater the resultant reaction force.
If you look carefully at the flow diagram to see where this direction change takes place, you should see that the force-reaction force pair must always act tangentially to the circular rotation about the drive train axis. A force tangential to a rotating body can be described as a torque with reference to the axis of that rotating body; this is why the torque converter produces torque. In other words, any force that causes a reversal in rotational direction is a torque, and the torque that causes this reversal in direction has a corresponding torque in the direction of the initial rotation. It should also be clear that this torque is the result of a de-acceleration, or loss of speed, preserving the familiar principle of power conservation.
This “reaction force” might seem sort of mysterious, or at least abstract. We can try to demystify it, however, by explaining how it acts on the turbine as a torque. The reaction force produced by the force exerted when the fluid rushes against the opposed stator blades acts on the turbine through the fluid medium itself. This may seem non-intuitive, but it makes sense if you think of it as a rippling effect: the disturbance in the fluid flow created by the presence of the stator causes alterations in the fluid path preceding the disturbance; or, the disturbance reverberates through out the fluid medium, transmitting the reaction force as a torque to the inner walls of the turbine.
The physics of the torque converter can also be analyzed in the context of momentum (p).1 Recall that momentum is mass times velocity and that momentum is conserved within a closed system (as we can consider our torque converter to be for a small change in time, i.e., dt). Since momentum is conserved, as is mass, the change in momentum caused by the change in fluid velocity must be compensated by some equal and opposite change in momentum elsewhere within the closed system. Since the space and time within which the fluid must de-accelerate - the area between the stator blades - is so small the rate of change of momentum must be very large.
Efficiency Issues
The torque converter is interesting in that it appears to exhibit continuously adaptive behavior, or adjusts continuously to changing operating conditions. Even though the degree of driver control of this adaptation is negligible, torque converters can be engineered in order to optimize this adaptive behavior.
What does “adaptive behavior” mean? It’s just a vague term that we’re using to refer to the torque converter’s characteristic efficiency curves. Examining these curves reveals that just after time t = 0 the torque conversion is very high while the efficiency of speed transfer is very low. In other words, there is a large difference between the speeds of the turbine and the impeller or a high degree of “slip,” and the direction of the fluid flow is such that its opposition to the angle of the stator blades is maximized. Since the fluid opposes the stator, it transmits quite a bit of torque but very little rotation. It turns out at high speeds, however – when the turbine speed begins to approach the impeller speed, or at about 40 mph for most standard lock-up converters – the direction of fluid flow exiting the turbine changes. Exactly how this happens is beyond the scope of this course (think 2.005, 2.006), but trust that as the speed of the turbine increases the direction of fluid flow changes, slowly righting itself so that it starts to flow against the back side of the stator blades.
This change in direction produces a change in the direction of the resultant reaction force, and thus the torque produced by the presence of the stator actually hinders the rotation of the impeller and substantially decreases the efficiency of power transfer. This process begins at the “lock up” point, where the torque on the stator falls to 0, and continues as the torque becomes negative and actually reverses direction: as more and more energy is consumed in the turbulent and contrary fluid flow within the converter the parabolic efficiency curve of the torque converter begins to fall off at an increasing rate. While the details are complicated, you can see how this change in flow direction corresponds to the familiar torque-speed relationship: when the fluid flow is parallel to the stator blades - as it must be at some point in the process of reversing direction - slip is minimized, so speed/rotational transfer is maximized while there is no torque transfer, and when flow direction is opposing, torque (regardless of whether it can be harnessed by the converter due to direction) is maximized and speed is sacrificed.
Since it would be really unfortunate if your car hated to go above 40 mph, manufacturers use a “lock up” torque converter in passenger vehicles with automatic transmissions. The industry standard is the Trilok Converter, and it essentially consists of a torque converter with a one-way clutch on the stator. This means that the stator can free-wheel in one direction but is held fast in the other, and avoids the energy loss associated with torque converters at high RPM while preserving the advantages of torque conversion during low speed accelerations etc. So while the relative speeds of the turbine and impeller are such that the torque produced is transmitted back to the turbine the stator is held fixed, but as soon as the fluid flow reverses direction the stator begins to rotate with the fluid. This prevents the energy-draining reaction forces associated with the stator at this stage, and the torque converter operates as a simple fluid coupling.
Now read this ....
http://xs-fx.com/raughammer/CONVERTER.HTM
or here is a quick break down, though the same info and a LOT more are on my web page WITH pictures:
A torque converter consists of the standard fluid coupling components and a stator. The impeller is actually attached to the housing, which is bolted to the engine flywheel. The turbine is connected to the drive shaft which extends back through the center of the impeller. In between the turbine and the impeller rests the stator, which is grounded and attached to a shaft which encases (but is independent of) the drive shaft. To emphasize, the stator remains stationary with respect to the rotating impeller/turbine combination at all times.1 If this sounds confusing, refer to the torque converter take apart file (keep in mind that the impeller and turbine seem to "face" the wrong direction).
The Stator, or How This Thing Actually Works
The stator, as its name implies, is a stationary disk located in between the impeller and the turbine and “grounded” independently of both the input and output shafts. The stator accomplishes several things. It allows the blades on the turbine and impeller to be angled so that the fluid must reverse its direction of flow when moving from the impeller to the turbine by reversing that flow yet again before the fluid is sucked back into the impeller (and thus preventing the flow of the turbine from hindering that of the impeller), and it causes a “reaction force” to transmit more torque to the turbine than would otherwise be available. It’s actually these reversals in fluid flow that allow the torque converter to transmit torque. To be clear: the blades of the impeller and the turbine are cut in opposite directions, forcing the fluid which flows from the impeller to the turbine to reverse rotational direction (it does not affect vortex flow). This reversal would impede the motion of the driving impeller when the fluid returned at its base if it weren't for the stator, which has blades cut in such a way that it forces the fluid to reverse direction yet again, matching the rotational direction of the impeller. These forced flow reversals generate torque because the stator provides a necessary reaction force. Now that you're thoroughly confused, we'll go into the details.
The stator accomplishes both of these tasks (which are really inseparable, interrelated functions) because of its dramatically angled blades, placed in opposition to the direction of flow within the turbine.
Without the stator, the fluid from the turbine would rush back into the vacuum at the center of the impeller in an opposing direction. This would impede the rotation of the impeller and dramatically decrease the efficiency of the coupling; lots of power would be dissipated in the resultant turbulent flow. And since it’s the reversal of fluid flow that allows power to be redistributed (i.e., speed converted into torque) a mechanism is needed to correct this inefficiency.
The real function of the stator, however, is to provide a reaction force. Recall the complicated flow pattern of a normal fluid coupling from the previous section – there was circular movement along the circumference of the disks as well as vortex flow. In the torque converter, there are two separate flow patterns, identical to each other but opposite in rotational direction.
Remember that the presence of the stator allows the blades in the turbine to be angled so that they force the fluid to reverse direction as it passes through the turbine. The result is this complicated, parallel and opposite flow within one housing. Consequently, the fluid must reverse rotational direction (clockwise to counter-clockwise, for example) as it passes through the stator.
This means that fluid with an instantaneous velocity in one direction must de-accelerate until it reverses direction within the very small space of the stator blades. Anything which de-accelerates (or accelerates; same thing) must do so in response to a force (Newton’s 2nd) and for each and every force there is an equal and opposite, or reaction, force (Newton’s 3rd – he proves very useful). Since the mass of the liquid is conserved, this force is directly proportional to the change in fluid velocity. This means that the more aggressively you cut the blades on your stator – the more you force the liquid to change direction as it passes through those stator blades – the greater the resultant reaction force.
If you look carefully at the flow diagram to see where this direction change takes place, you should see that the force-reaction force pair must always act tangentially to the circular rotation about the drive train axis. A force tangential to a rotating body can be described as a torque with reference to the axis of that rotating body; this is why the torque converter produces torque. In other words, any force that causes a reversal in rotational direction is a torque, and the torque that causes this reversal in direction has a corresponding torque in the direction of the initial rotation. It should also be clear that this torque is the result of a de-acceleration, or loss of speed, preserving the familiar principle of power conservation.
This “reaction force” might seem sort of mysterious, or at least abstract. We can try to demystify it, however, by explaining how it acts on the turbine as a torque. The reaction force produced by the force exerted when the fluid rushes against the opposed stator blades acts on the turbine through the fluid medium itself. This may seem non-intuitive, but it makes sense if you think of it as a rippling effect: the disturbance in the fluid flow created by the presence of the stator causes alterations in the fluid path preceding the disturbance; or, the disturbance reverberates through out the fluid medium, transmitting the reaction force as a torque to the inner walls of the turbine.
The physics of the torque converter can also be analyzed in the context of momentum (p).1 Recall that momentum is mass times velocity and that momentum is conserved within a closed system (as we can consider our torque converter to be for a small change in time, i.e., dt). Since momentum is conserved, as is mass, the change in momentum caused by the change in fluid velocity must be compensated by some equal and opposite change in momentum elsewhere within the closed system. Since the space and time within which the fluid must de-accelerate - the area between the stator blades - is so small the rate of change of momentum must be very large.
Efficiency Issues
The torque converter is interesting in that it appears to exhibit continuously adaptive behavior, or adjusts continuously to changing operating conditions. Even though the degree of driver control of this adaptation is negligible, torque converters can be engineered in order to optimize this adaptive behavior.
What does “adaptive behavior” mean? It’s just a vague term that we’re using to refer to the torque converter’s characteristic efficiency curves. Examining these curves reveals that just after time t = 0 the torque conversion is very high while the efficiency of speed transfer is very low. In other words, there is a large difference between the speeds of the turbine and the impeller or a high degree of “slip,” and the direction of the fluid flow is such that its opposition to the angle of the stator blades is maximized. Since the fluid opposes the stator, it transmits quite a bit of torque but very little rotation. It turns out at high speeds, however – when the turbine speed begins to approach the impeller speed, or at about 40 mph for most standard lock-up converters – the direction of fluid flow exiting the turbine changes. Exactly how this happens is beyond the scope of this course (think 2.005, 2.006), but trust that as the speed of the turbine increases the direction of fluid flow changes, slowly righting itself so that it starts to flow against the back side of the stator blades.
This change in direction produces a change in the direction of the resultant reaction force, and thus the torque produced by the presence of the stator actually hinders the rotation of the impeller and substantially decreases the efficiency of power transfer. This process begins at the “lock up” point, where the torque on the stator falls to 0, and continues as the torque becomes negative and actually reverses direction: as more and more energy is consumed in the turbulent and contrary fluid flow within the converter the parabolic efficiency curve of the torque converter begins to fall off at an increasing rate. While the details are complicated, you can see how this change in flow direction corresponds to the familiar torque-speed relationship: when the fluid flow is parallel to the stator blades - as it must be at some point in the process of reversing direction - slip is minimized, so speed/rotational transfer is maximized while there is no torque transfer, and when flow direction is opposing, torque (regardless of whether it can be harnessed by the converter due to direction) is maximized and speed is sacrificed.
Since it would be really unfortunate if your car hated to go above 40 mph, manufacturers use a “lock up” torque converter in passenger vehicles with automatic transmissions. The industry standard is the Trilok Converter, and it essentially consists of a torque converter with a one-way clutch on the stator. This means that the stator can free-wheel in one direction but is held fast in the other, and avoids the energy loss associated with torque converters at high RPM while preserving the advantages of torque conversion during low speed accelerations etc. So while the relative speeds of the turbine and impeller are such that the torque produced is transmitted back to the turbine the stator is held fixed, but as soon as the fluid flow reverses direction the stator begins to rotate with the fluid. This prevents the energy-draining reaction forces associated with the stator at this stage, and the torque converter operates as a simple fluid coupling.
Teching In
Joined: Apr 2002
Posts: 27
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From: Northeast Ohio
Re: frag me if you will: what is a torque converter? A torque converter is what makes a driver delete option car quick! Comeon guys you know I am kidding. Had I known about stalls back in 99 I wouldn't have gotten a 6 speed, but I do have a 98 Z28 with an A4 <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> . Thats going to be the quick one!
Re: frag me if you will: what is a torque converter? Raughammer has spoken! <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" /> <img border="0" title="" alt="[Cool]" src="gr_images/icons/cool.gif" /> <img border="0" alt="[Burnout]" title="" src="graemlins/burnout.gif" />
TECH Addict
Joined: Mar 2002
Posts: 2,189
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From: Glendale, CA
Re: frag me if you will: what is a torque converter? lol... i read all that... might as well be speaking chinese... damn my high school education! damn it to hell! ok my real question is.... like during launches, lets say i have a torque converter with a stal speed of 3500... does that mean i have to get the engine up to 3500 rpm before it starts moving?
Re: frag me if you will: what is a torque converter? No, the stall is the rpm the converter will flash to at WOT. You can put-put around and not break 2K rpms if you want.
<small>[ July 09, 2002, 02:28 PM: Message edited by: Kdubroc 99 SS ]</small>
<small>[ July 09, 2002, 02:28 PM: Message edited by: Kdubroc 99 SS ]</small>
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TECH Addict
Joined: Mar 2002
Posts: 2,189
Likes: 0
From: Glendale, CA
Re: frag me if you will: what is a torque converter? so you mean when im flooring it at the track, instead of the rpms dropping to 2 after a shift, theyll drop to 3500? so my street drivability wont be affected much?
TECH Addict
Joined: Mar 2002
Posts: 2,189
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From: Glendale, CA
Re: frag me if you will: what is a torque converter? ttt come on guys im serisouly considering this and im trusting you guys to gimme good info so i can go like this: <img border="0" alt="[Camaro]" title="" src="graemlins/camaro.gif" />
TECH Addict
Joined: Nov 2001
Posts: 2,003
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From: Live Oak, FL - in the woods where the creatures lurk.
Re: frag me if you will: what is a torque converter? With 2.73 gears and a Yank ST3500 my rpm drop between 1-2 shifts is to around 4700. That's 1000 rpms+ more than the stock converter shift was.
Answer your question?
Answer your question?
On The Tree
Joined: May 2002
Posts: 108
Likes: 0
From: Richmond, Virginia
Re: frag me if you will: what is a torque converter? I will try and give you a quick simple answer here. A torque converter can be thought of as a rubber band in a sling shot. Say the car is the ball you will fire. With the stock converter, you have roughly maybe 1500 RPM Stall speed, which means that depending upon the weight of the car, the converter will allow the engine under high HP conditions to freewheel basically up to 1,500 RPM. Now say that that 1,500 RPM is equivalent to pulling the rubber band back about two inches and releasing the ball or launching the car, it pops out and goes so far at a certain speed. Now say you change the converter to a 2,500 RPM Stall, you now mash the throttle to the floor and basically the engine wings up to 2,500 RPM and wham..... the car leaps off the line like a raped ape. Back to our slingshot.. the 2,500 RPM converter is like you now pull the rubber band back say 6 inches and let it go... Wham... the ball comes out harder and faster. You will find on a car that can barely break the tires loose, you chage the converter and suddenly everything is up in smoke... due to the tremendous amount of torque being released. Remember though that using a torque converter with stall speeds of 3,000 RPM and over... you better be putting in a Tranny cooler or you will overheat the trans from the extra heat being generated. Rule of thumb is that the stall speed should generally be rated at or a little above the point that the cam is designed to start working. The manufacturer of the torque converter can, if given information like the weight of the car, rear gears, tire size, size of the engine and HP, give you a pretty good idea of what stall speed your car will see with different rated torque converters. The rating given by the manufacturers is a generalized rule of thumb number... and should only be used for seeing the different sizes, but the number is by no ways implicit.
