SMART Series 451 Service Manual page 57

SN_Typ 451_us.book Seite 56 Freitag, 30. November 2007 1:56 13
Transmission control
Transmission motors 1 and 2 (M17/3 and M17/4)
Location
The transmission motors are located on the trans-
mission housing.
Task
Depending on the shift request from the automated
manual transmission control unit (N15/6), the
transmission motors adjust the selector drums via a
two-stage spur gear transmission. Actuation is
pulse-width modulated by two output stages with
four electronic switches each. Upon reaching the
specified position the transmission motor is
braked. It can, if necessary, be actuated with
opposing voltage, if an overshoot beyond the spec-
ified position is to be prevented or reversed.
Actuation of the transmission motors is monitored
by the incremental sensors, which are located on
each motor shaft. These detect the rotation angle
and rotation direction of the respective transmis-
sion motor using the integrated Hall sensors.
The transmission motors are only actuated to
execute the shift operations. Once a target position
is reached, a pin engages in the locking groove of
the selector drum to maintain the selected gear.
56 Introduction of the smart fortwo, Model Series 451
1 Transmission motor 1 selector drum
2 Transmission motor 2 selector drum
M17/3 Transmission motor 1
M17/4 Transmission motor 2
P26.60-2321-00