Page 209 - Mechatronics with Experiments

MECHANISMS FOR MOTION TRANSMISSION 195
C
P/R/N/D F , F 2,...... 1......
1
B 1...... u
Gear selection N Clutch/Brake look Clutch Bi
w eng Brake
Algorithm up table
1
w xmn R , R 2 Pressure control u Ci
P
P Bi
P Ci
(a)
Vehicle speed
(Transmission
output speed)
100 mph
3 4
75 mph
4 3
2 3
50 mph
3 2
1 2
25 mph
2 1
Engine
speed
25% 50% 75% 100%
(b)
Torque
Start
Clutch/ Grear shift
brake
on
Time
Fill period Modulation period (ms)
Clutch/ 200 ms 500 ms
brake
off

Time (ms)
(c)
FIGURE 3.32: Automatic transmission control algorithm: (a) different logical components of
an automatic transmission control algorithm, (b) gear selection logic, (c) controlled pressure as
a function of time in engaged and disengaged clutch/brakes.

and disengagement takes between 300–700 ms. Notice that a clutch/brake engagement is
performed in two phases:
1. fill phase (up to 200 ms), and
2. modulation phase (up to 500 ms).
During part of the gear shift process, engine torque is not transmitted from the transmission
input shaft to the output shaft. As a result, the lower powertrain (components between the
transmission output shaft and wheels) does not get power from the engine during part of
the gear shift time period. That is why it is important that the gear shift happens smoothly
without too much time delay so that the vehicle does not lose noticeable speed. On the
other hand, if the shift happens too fast there will be too much variation in the speed