Do Automatic Trans Torque Converters really "amplify-multiply" torque

[outrun]

Sorry,

This is sort of a continuation of the previous controversial thread.

A recent reading I did said the torque converter amplifies the engines torque.

If that is the case how come on a 200hp+ engine (lets say) you do not detect 400hp at the wheels or so? In fact you likely see a 20% driveline loss over the initial number.

Can someone explain the principal of torque multiplication. The reading states that this also happens at the differential.

Again I am puzzled.

 

[VaderSS]

At high slippage rates, T/Cs do indeed multiply torque, but at the RPMs that you run on a chassis dyno, slippage is relatively low. Even so, sometime you will see a torque spike though at the very bottom (RPMwise) of the dyno run.

The differential and transmission also multiply torque. The transmision in the lower gears, at their rate, and the differential by nature it's ratio, in my case, the driveshaft turns 3.08 times for one turn of the tire. So it multiplies the torque 3.08 times minus losses, of course.

By the same token, overdrive reduces torque.

In all of these cases, power input is always the same, and so is the output, minus losses. You can't multiply power without adding power. With a reduction gear, you are losing power to friction, and though the torque is multiplied, the RPM is divided by the same rate, so the net power remains the same, minus losses.

 

[Rick in PA]

I didn't see the previous thread, so I may "step in something" here.

"Amplifies" is not an appropriate word to use here.

Power is the result of torque times RPMs (there may be a squared in there and a conversion factor, but that is the fundamental relationship).

The torque converter, transmission and differential are capable of:
taking in power at high RPMs / low torque,
then
outputing power at lower RPMs / higher torque.

The power (excepting losses) remains constant.

The thing that's special about a torque converter is that it provides a fluid coupling between the motor and the transmission, performing the functions of a clutch (but a clutch cannot "convert torque"). The torque converter contains turbine like elements that not only provide the fluid coupling but also "convert torque" as above.

 

[FordManVT]

No, they do NOT. However, they do allow the engine to rev higher where it will create more torque. Think of it like slipping the clutch on a manual.

The key is the stall speed of the TC, which is determined by both the TC size, internal construction, and engine power.

from a dead stop, and all other things being equal, which will put more torque to the rear wheels, a manual leaving at 1000rpms with 15% losses, or an auto leaving at 3000rpms with 20% losses? The Auto.

Beware of a high stall TC, you can go too high, and the higher the stall, the more heat that will be generated.

Vader is correct about gears.

[ March 29, 2003, 10:24 PM: Message edited by: FordManVT ]

 

[S2000driver]

The torque converter is something like an electrical tranformer.

You will never get more power out of a transformer than was put in, because of the laws of conservation of energy, and the fact that a transformer can never really be ideal (there are losses).

Same with a torque converter. Torque is not the same as horsepower. You cannot get more HP out of a torque converter than you put into it.

A transformer can step up voltage though. Remember, there is the law that Power = voltage * current, so if you get more voltage on the output of the transformer, it's at the "expense" of current, because the output power cannot be more than the input power.

So the same is for a torque converter. You are not magically creating more power. In fact, the torque converter lockup is intended to make power-out as close to power-in as possible.

Without getting into all the math, just remember that when the torque converter is not locked up, it allows the engine to spin faster and produce more power, which gets transfered to the rear axle as more power than when the torque converter was locked up, preventing the engine speed from increasing. However, the transmission is not as efficient when the torque converter is "converting".

The torque converter allows an automatic transmission to "get by" with less gears than an equivalent manual transmission, because the torque converter extends the range of each gear.

[ March 29, 2003, 10:45 PM: Message edited by: S2000driver ]

 

[VaderSS]

A T/C does not fuction like the "slipping of a clutch." It's function, when at high slippage rate, and I'm not talking high stall converters here, is more akin to the gears, than slipping of the clutch to allow the engine to get to a higher rpm.

Say the car is at a standstill, and the engine is at 1800 RPM, a perfectly normal stock stall, the torque converter can actually multiply the torque 2 or more times. So say the engine is producing 100 Lb-Ft, the torque at the output side of the T/C will be around 200 Lb-ft. There will, of course, be tremendous power losses present, represented by the heat generated at this point, but the torque is still there to help motivate the car.

As the slippage rates are reduced, so to does the torque multiple, until it is virtually gone.

The torque mutiplying benefit of the T/C is due to the stator. The earlier fluid couplings lacked this, and could be properly called "fluid clutches" because they did not multiply torque. The torque multiplying feature is why a fluid coupling with a stator is called a, "Torque Converter."

 

[FordManVT]

quote:

---

Originally posted by VaderSS:
As the slippage rates are reduced, so to does the torque multiple, until it is virtually gone.

---

Exactly, and after you have reached the stall speed, any good transmission will lock the TC, reducing losses, giving maximum power to the wheels.

 

[Steve S]

The torque converter has 3 parts input ,stator ,output. When the output and input are at different rpms the fluid flow in the torque converter causes the stator to not turn which routes the fluid which causes the torque to multiply as the rpms match the stator starts turning which changes how the fluid flows in the torque convertor and then the torque converter acts as a fluid coupling . The stator is mounted on a 1 way clutch so it can lock or spin depending on the difference of the torque converter rpms. yes it multiplys torque drive a car where the stator clutch is not working the car will be a dog while accelerating .Like wise if the stator is locked up all the time top end will be changed . A fluid coupling would be a torque convetor with out a stator . This is basic ASE test question.

 

[VaderSS]

quote:

---

Exactly, and after you have reached the stall speed, any good transmission will lock the TC, reducing losses, giving maximum power to the wheels.

---

I'm not sure if you are just saying it wrong, but actually, the only time the T/C locks, is in low throttle, cruising situations, such as on the highway. If it were to try to lock at a high slippage rate, near stall, it would destroy a stock converter. The lock-up portion of an OEM T/C is only designed to handle a small portion of the power of the engine, say 25% or less, and is not designed to slip. Slipping would destroy it in short order.

There are aftermarket converters that are designed to lock up under high load situations, but the PCM would have to be programmed for that.

 

[Ken2]

Let me see if I understand this...

A torque converter serve two purposes
a) fluid coupling or clutch
b) torque multiplication

When there's a heavy drivetrain load there's a big difference between the transmission input rpm and output rpm, the torque is multiplied at the expense of output rpm and the creation of heat. As the vehicle gets going, the slippage between the two halves decreases, torque multiplication is reduced, and efficiency increases. Eventually, when slippage between the tc input and output are very low, another part of the transmission activates a device to lock the two halves of the tc together for max efficiency.

The transmission also has its four or five gears doing their job, again torque multiplication at the expense of rpm, but not smooth and stepless like a torque converter, plus you still need a clutch (fluid coupling)...and that's another article about the gears and shifting.

I'm old enough to remember the old Chryslers with the manual clutch and automatic gear box (but not old enough to have driven one). I do remember the GM Hydamatic transmissions with the fluid coupling and four speed gearbox which was replaced a few years later with the Hydramatic with the torque converter and three speed gears. Now we still have somewhat the same transmission, plus locking torque converter, plus the addition of an overdrive of about 0.7:1 as the 4th gear in the name of economy...and 5 speeds in some vehicles, six speeds coming, and a few continuously variable transmissions on the road.

Is this an accurate, simple summary of a torque converter?


Ken

 

[outrun]

Thanks for the enlightening follow-ups.

Can you give me your definition of Slippage on these lines. Then I can fuily make sense of this string.

 

[Steve S]

Ken2 you the man !!!

 

[VaderSS]

Some other interims and offshoots were;

Pre-Selector transmissions; manual transmissions with electrical or vacuum gear actuation via a small low effort selector. Shifts were selected before you pushed in the clutch, and the gear change was actuated after the clutch was pressed in.

Fluid-Drive transmissions that were nothing more than a direct drive transmission(no gears) and a T/C, plus a reverse.

Semi-Automatic transmissions that had automatic clutch, ala VW. Put your hand on the shifter, and the clutch automatically dis-engaged, make your shift and release the shifter, clutch automatically engages.

2 speed transmissions such as the PowerGlide. Very popular in drag racing now for high horsepower, light weight applications.

3 speed transmissions with a lock-up converter but no overdrive, still in production today, but getting pretty rare.

And my favorite, the gasoline-electric drive, much like the diesel electric drive seen in trains. Very rare in the past(only one car I've ever heard of, and I can't remember what it was), but making a comeback now.

 

[Jimbo]

Ah, the VW auto-stick, my ex-wife had one of those. What a steaming pile! It also had a torque converter and they left out first gear. With no oil cooler the t/c fluid would overheat. At least there was a warning light.

 

[MolaKule]

Man, I still love the PowerGlide. Simple yet reliable.

 

[VaderSS]

Good link;
http://www.howstuffworks.com/torque-converter.htm

 

[dickwells]

Molakule: If you like the power glide they you should really like the Dynaflow, let me tell you, with a 425 Buick engine in front those things would smoke the tires.

When I was a kid one of my buddies dads had an old Chrysler that had a three speed manual transmission, manual clutch, and Torque convertor. You could put it in any gear and start out without the clutch but needed the clutch to shift up. Of course we used to shift without the clutch by matching rpm in regular manual cars, but thats another story.

 

[Oldswagon]

I have an old Chevrolet repair and maintenance manual covering model years 1929 to 1950. This book actually gives quite the in depth description of the operation of the first version of the powerglide and its torque converter. In the description it claims that the powerglide with its torque converter has almost as much torque multiplication as the conventional three speed manual in first gear. It's quite an interesting read. I had one of these tranny's in my '72 Chevelle with a 250 six.

 

[MolaKule]

Dickwells,

Yeah, dad had a 54 buick with a Dynaflow and a big block in it (don't recall the displacement). Built like a tank and had the power to match. I don't ever recall him having to have the tranny rebuilt in 195,000 miles.

Braking was a problem though. We went through quite a few brake linings and drums.

He sold me his '62 Impala (283 V8) and his '67 Impala SS and both had PG's. The '67 had the 327 and could take anything on the street.

[ April 02, 2003, 11:00 PM: Message edited by: MolaKule ]

 

[Oldswagon]

The Dynaflow had two speeds as well as the variable pitch converter. The Dynaflow shift pattern was different than conventional autos of today. It was as follows: N-D-L-R

There were many changes made to the Dynaflow throughout its production years. The triple turbine, or flight pitch, came out in 1958. I am not 100% sure, but I believe it was only made for '58 and '59. The Dynaflow was produced until 1963 when it was then replaced by the more modern ST300 and ST400. The ST400 was just a TH400 with a switch pitch convertor. The ST300 was an aluminium two-speed tranny used in Buick, Olds and Pontiac A-bodies, as well as some smaller displacment fullsizers.