Page 203 - Mechatronics with Experiments

MECHANISMS FOR MOTION TRANSMISSION 189
TABLE 3.1: Table for measurement and calculations to characterize the steady-state
input–output behavior of a torque converter: determining torque gain (N (N )) and
w
T
primary torque (T (N )) as a function of speed ratio (N w = w turb ∕w imp ).
P
w
Controlled Controlled Measure Measure Calculate Calculate
w eng = w rated w dyno T eng = T p T dyno N w = w dyno N = T dyno
T
w eng T eng
1800 rpm 0 rpm x x … …
1800 rpm 100 rpm x x … …
… … x x … …
… … x x … …
1800 rpm 1800 rpm x x … …

4. then measure the following variables in steady state: engine output shaft (impeller)
and dyno shaft (turbine) speeds as well as torques,
w imp = w eng = w rated (3.312)
w turb = w dyno (3.313)
T = T imp = T eng (3.314)
p
T turb = T dyno (3.315)
5. then calculate and plot the following data (Figure 3.29c):
N = w dyno ∕w eng = w dyno ∕w rated (3.316)
w
N = T turb ∕T imp (3.317)
T
Plot the two variables
T (N ) versus speed ratio N w

p
w
N (N ) = T dyno (N )∕T eng (N ) versus speed ratio N .

w
w
w
w
T
These two functions characterize the steady-state input–output relation of a torque
converter.
For a given torque converter, we would have the T (N ), N (N ) functions. In specific
w
w
p
T
steady-state operating conditions, if the input and output shaft speeds of the torque converter
are known (given: w imp , w turb ), then the input and output torques can be calculated as
( ) 2
w eng
T imp (N , w imp ) = T (N ) ⋅ (3.318)
p
w
w
w rated
T (N , w ) = N (N ) ⋅ T (N , w ) (3.319)
turb w imp T w imp w imp
where w = w , w are impeller and turbine speeds, T , T are torques at impeller
eng imp turb imp turb
and turbine shafts. Notice that, in the above measurements to characterize a torque converter,
the impeller (engine output shaft) speed is maintained at a constant rated speed and T (N )
p w
is obtained for a constant impeller speed as turbine speed varied from zero to the rated
speed. To obtain the impeller torque at a general operating speed of the engine, we use the
parabolic relationship as shown above. In the most general form T imp = T imp (N , w eng ).
w
When w eng = w rated , then this relationship reduces to the T imp (N ) = T (N ).
w
w
p
The magnitude of these two functions depends on the physical size of the torque
converter. The exact shape of these two functions is determined by the shape of the blades
in the impeller, turbine, and stator, which are customized differently for different machine
applications. For instance, the blade shapes in a torque converter in a truck would be