Arvid Jedlicka wrote:
> Tim,
>
> Thanks. We agree on how it works with just an input pump and various
> scenarios of the engine running, not running, in a gear, not in a
> gear, etc. But the original statement from John ...
> implies that there was only a pump on the output side - otherwise
> there would not have been a qualifier about "both input and output"
> ... which is why I was asking how that particular scenario worked.
>
> Your thoughts?
It's part of a major misunderstanding of how torque converters and
automatic transmissions work. To start with, not a single automatic
transmission made has an input shaft. Not a single automatic
transmission made has a hydraulic pump driven from a non-existant input
shaft. They have torque converters. The hydraulic pumps are driven by
the outer casing of the torque converter. This is directly bolted to
the engine crankshaft, and slotted into the hydraulic pump. If the
engine is turning, the hydraulic pump is turning. This hydraulic pump
cannot, and does not, turn the engine when the engine is turned off.
The hydraulic pump is absolutely incapable of doing this.
Power is transferred to the transmission via the output shaft of the
torque converter. This is hydraulically driven by the spinning blades
of the engine connected casing pushing against the blades of the output
shaft. This system is very directional, as the engine turns one way
only. It is all but incapable of producing any appreciable force in the
other direction. That is why it cannot turn the engine over.
Lock up torque converters are capable of keeping the engine turning over
if the torque converter stays locked. I know of none that are designed
to stay locked when the power to the engine is turned off.
Some automatic transmissions are designed intentionally or incidentally
to be able to be towed. This is by some method of providing lubrication
to the moving parts, usually a seperate lubrication pump on the output
shaft of the transmission (or transaxle). This setup does not power up
the transmission, or produce hydraulic pressure in the actuation system,
that is a function of the engine driven hydraulic pump. It simply keeps
lubrication flowing around the parts that rotate when the car is being
towed.
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