Quoting "John G. Napoli" <john@xxxxxxxxx>:
> Correct, there is no lockup clutch. However, the nature of a fluid
> coupling
> (as opposed to a torque converter) permits it to effectively lock up
> once it
> reaches a certain rpm. At that point, the entire fluid mass is
> rotating
> around and 'locking' the driven disk to the driver. Fluid couplings
> have
> straight vanes, and just a driver and driven member. Torque converters
> have
> curved vanes and three elements. This is an oversimplification that
> perhaps
> someone can expound upon, but the fluid coupling does act as if it is
> locked
> up.
>
John. Even the fluid coupling will have some slippage. Usually, fluid
couplings have a bit less slippage than torque converters (especially at low
rpm) as you said, but in order to transmit the torque through the fluid, some
slippage is necessary. Zero slippage, zero torque (unless there is a lockup
clutch). The higher the rpm, the less the slippage required for a given
torque. The 3rd element of the torque converter that you are discussing is
responsible for the multiplication. There is a sprag clutch between this 3rd
element and the engine side of the converter, and when the speed is low and
slippage high, the clutch engages, and this element (don't remember its name)
redirects the fluid flow at a sharper angle against the impeller blades of the
transmission side of the converter (I think that's called "turbine") and thus
you get the multiplication. Of course, there is a price to pay, and that is
the higher slippage. At higher speeds, this spag clutch will disengage, and
the converter will act as a normal fluid coupling. A low stall converter will
still have almost negligible slippage (of the order of 1-2%) at high speeds
(say over 3000), even at high load. However, due to the multiplication
feature, it will have to rev faster to get to this low level of slippage. So,
effectively, it generates more heat than the older fluid coupling.
D^2 w/ a lockup converter in his 68 LeBaron and a non-lockup converter in his
68 Sedan.
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