Quote from earlier message:
"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."
OK, I've been trying to stay out of this thread, but if this is true,
how is it the engine can slow the car down when the driver lets off the
throttle? To get engine braking the transmission must be pushing
against the engine and the engine must be resisting the force through
the torque converter. This is true without regard to whether a modern,
lock-up converters is being used or not. Torque converters must be
capable of transmitting torque in both directions or there would be no
engine braking effect. There may a difference in efficiency between the
two directions, but its clearly not 100% one way and 0% the other.
Ben....
Ben Zwissler
bjzwissler@gmail.com
Columbus, IN
1966 Triumph TR4A
1973 MG Midget
1980 Triumph TR8
2007 Mazda RX8
2002 Yamaha FZ1
2003 Honda ST1300
On 2/5/2010 2:48 PM, Nolan wrote:
> 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.
>
> 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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