Dear Laurel,
a pre selective gearbox is a mechanical gearbox with a mechanical clutch.
The difference is, that you don't have a big gearshift lever. You only=20
have a little (most electrical) switch. To shift the gears they don't use
your muscle power, they use electric power or air pressure or vacuum.
If you drive a vehicle with pre-selective gearbox and you want to shift
the gear, you move the little switch. At first nothing happens. You only
have pre-selected the new gear, but not yet shiftet. Now (or later) you
can push down the clutch pedal. If you have done this, the gearbox will
shift to the selected gear. After this you can release the clutch pedal.
Such a gearbox is used in all modern Mercedes-Benz trucks. They call it
"EPS" which means "Electronic Power Shift". The driver has only a little
gearshift lever, like a computer joystick. Pushing it forwards shifts up,
pulling it back shifts down.=20
If you want to change gear, you move the "joystick". A digital display=20
shows the pre-selected gear postion. If you now push down the clutch pedal
completely, it shifts to the new gear. The power to switch the gears=20
comes from pneumatic cylinders on the gearbox.
Pre-selective gearboxes were also used in London double deck busses (WILSON=
)
and in the big German halftrack tractors and some tanks.
Regards
Andreas
-Likes to drive Mercedes-Benz trucks with EPS-
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