How a torque converter works

[The_Handier_Man1]

From: leftyizme  (Original Message)
Sent: 8/4/2003 1:11 AM

O.K., There still seems to be some confusion on how a torque converter works and what it does for your transmission so I thought I would take a minute to try and break it down for you. The torque converter is a fluid filled cyl. attached onto the front of the transmission,and fastened to the engine via a flexible plate (flex-plate), inside there are two sets of fan shaped vanes facing each other.as fluid is spun along the outer edge inside by centrifigal force it causes the vanes on the other fan to also try and turn. the simplest example of what I mean can be illustrated by taking two electric fans and setting them facing each other as close as possible on a table,plug one fan in and leave the other fan unplugged.when the powered fan is turned on, the ailflow pushing against the other fans blades will also cause it to spin.In an ideal condition both fans would reach the same rpm. however you lose energy having to overcome the drag of other parts inside the non-powered fan, and also it is impossible to harness 100% of the airflow,so the non-powered fan never reaches quite the same speed as the powered fan. A torque converter is the same way. Some slippage occurs because of the distance required to keep the fans from hitting each other,and also to overcome the other moving parts inside the transmission.A lockup converter uses an electric clutch similer to one on an A/C compressor to physically lock the two together after they have achieved as close a speed as possible to eliminate the slippage normal to a standard converter.The converters slippage reduces as vehicle speed increases from a standing start similer to one "feathering" the clutch on a manual transmission. This effectivly reduces the gear ratio to a level the engine can handle.The ratios inside the transmission are fixed and do not vary.If the converter slippage is at a 50% level this would effectivly increase the drive ratio by two. A good converter starts at 95% slip at idle(thats why vehicles creep forward at idle without your foot on the brakes) and progressivly reduce as engine speed(and hense the cintrifigual force inside the converter) increases until the maximum stall speed is reached(usually around 2,000-2,500rpms).where it stabalizes around 5%-10% slip.A lockup unit only engages after the vehicle is in high gear and is running a steady speed.it unlocks automatically as needed when vehicle load exceeds the holding power of it's clutch. It can reduce fuel consumption and transmission heat developed by the slippage of  a standard converter.That's why they are so popular with todays vehicles. But I don't know how they would handle the torque requirements of a rig weighing as much as mine(14,500lbs GVRW),as most are designed for light duty vehicles.As a side note; I haven't seen anyone mentioning using a two-speed rear end similer to those found in heavy trucks.I am sure that one could be found that would fit a "Winnie" with minor modifications, that would double the gear ratios available and could provide good starting power and a better cruising gear ratio at the same time.--lefty



From: leftyizme
Sent: 8/4/2003 1:15 AM

Boy did I ever misspell a lot of words in that post!!lol, sorry about that, I hope you all can still read it--lefty



From: chip
Sent: 8/4/2003 7:46 AM

lefty, well done. however, we can "split" gears [and hairs]and, in theory, use a continuously variable transmission but still the final drive ratio is about 1:1 to the ring and pinion and the o.d. of the tires.
each engine design has a limited range where it is most efficient and, unless we change something radically in the powerplant the results are negligible- and sometimes negative[i.e. less mpg].
Lefty, you didn't sound preachy at all. in fact, you are a real knowledgable gentleman in this discussion. After too many years of teaching I hold the rights to being pedantic!



From: Jhoffa_
Sent: 3/20/2004 5:28 PM

".A lockup converter uses an electric clutch similer to one on an A/C compressor to physically lock the two together..."

It's actually a hydraulic clutch. Very similar to what's in the rest of the clutch drums in the transmission. There's an electronic solenoid (They are usually HPWM now, so they are modulated on for a smooth apply.) in the transmission that handles engagement/disengagement as required by the vechile computer. 



From: Jhoffa_
Sent: 3/20/2004 5:31 PM

PS: Torque converters actually multiply engine torque.. As opposed to a simple fluid coupler, which will not. As in the "two fan" example.