Page 197 - Mechatronics with Experiments

MECHANISMS FOR MOTION TRANSMISSION 183
Impeller
Turbine Stator C1 C2 B1 B2 B3 B4 B5
C- Clutch B - Brake
C1 C2 B1 B2 B3 B4 B5
Reverse 1 (a) (a)
Reverse 2 (a) (a)
Neutral N (b)
(L)
Neutral N (b)
(H)
Forward 1 (a) (a)
Forward 2 (a) (a)
D Forward 3 (a) (a)
C B
SE4212 SE4213 A Forward 4 (a) (a)
SE4202 SE4214
Forward 5 (a) (a)
SE4203
A - hydraulic control lines Forward 6 (a) (a)
B - pump, C- torque convertor,
D - retarder (hydraulic brake) (a) - Activated, (b) Activated with low pressure
FIGURE 3.27: Automatic transmission used in heavy equipment applications showing the use
of planetary gears, controlled clutches, and brakes to select gear ratios. The torque converter
provides a variable hydrodynamic coupling (variable gear ratio) between the engine input shaft
and gear reducer section of the transmission. The table on the right shown which clutch/brake
combination must be engaged to select a particular gear (Reproduced with permission from
Volvo Trucks).

ring gear is fixed to the vehicle frame, and the output shaft is the planetary carrier which is
connected to the tire-wheel assembly (Figure 3.34).
In transmission applications, multiple stages of such planetary gears are stacked in
series (Figure 3.27). Then, using electrically (or electro-hydraulically) controlled multi
disc clutches and brakes, we can decide in real-time which component to fix and which
component to rotate in each planetary stage. Through controlled clutches and brakes, we
can change from one gear ratio to another, for example from N 21 to N 31 by disconnecting
the motion of the gear 2, and then connecting the motion of gear 3 to the output shaft by dis-
engaging and engaging the clutches and brakes for the respective gears. For a good smooth
transition, the transient dynamics of this clutch/brake disengagement/engagement motion
must be carefully controlled. For instance, simple ON/OFF control of the clutch/brake
disengagement/engagement would result in very rough and unacceptable response (i.e.,
similar to a beginner driver’s gear shift on a manual shift transmission).
The multi stage planetary gear mechanism, shown in Figure 3.27, provides ten dif-
ferent gear ratios, as shown on the table on the right: six gear ratios for forward motion,
two gear ratios for reverse motion, and two gear ratios for the neutral condition. This type
of automatic transmission is used in articulated trucks and similar mobile and construction
equipment applications. A common design characteristic of multi stage planetary gears is
that adjacent stages share a component with each other. For instance, the stage 1 ring gear,
stage 2 carrier (Figure 3.28), and the stage 3 ring gear are all rigidly connected to each other
as one component. Similarly, the stage 3 planetary carrier is connected to stage 4 ring gear,
which is then rigidly connected to the stage 5 ring gear. The stage 4 carrier is connected to
the sun gear of stage 5. Notice that the sun gear of stage 5 is the output shaft of this multi
stage planetary gear mechanism (Figure 3.28).
The electro-hydraulically controlled multi disc brakes (B1 through B5) and clutches
(C1 and C2) are engaged or disengaged, as shown in the table, to select the desired gear
ratio. It is important to note that the transition of the state of a clutch or brake from engaged