Environmental Engineering Reference
In-Depth Information
example. For a very light load of 500W regen, the vehicle speed versus time and
deceleration are shown here.
Notice that after 169 s of deceleration at this light load, the vehicle speed, once
it reaches just under 5m/s, collapses very quickly. The briskness of vehicle speed
deceleration near 165 s is evident in the plot of V_Dot. Since mechanical 'jerk' is
defined as the rate of acceleration or deceleration change, the fast upsweep in
V_Dot for the Camry Hybrid case noted in Figure 3.8 is apparent. When the vehicle
kinetic energy can no longer sustain the demanded constant power, its rate of
deceleration, or jerk, becomes very large. All hybrid powertrains must release the
demand for brake energy recovery before this threshold, and most will relax brake
recuperation power as vehicle speed drops below 10mph and disengage completely
at 5mph.
Vehicle speed (m/s)
V_dot (m /s
2
)
35.00
5.00
30.00
4.00
25.00
3.00
20.00
15.00
2.00
10.00
1.00
5.00
0
0
0
25.00
50.00
75.00
100.00
125.00
150.00
175.00
0
25.00
50.00
75.00
100.00
125.00
150.00
175.00
t
t
Figure 3.8 Camry Hybrid deceleration characteristics for P
v
= 500 W
Example 4:
A Camry Hybrid described in Example 3 with NiMH energy storage
pack rated 25 kW will use series regen braking to slow from an initial vehicle speed
of 65mph (29.06m/s). Determine to what vehicle speed it can sustain a battery
charging power of 25 kW before the onset of vehicle jerk.
Solution:
The numerical integration shown in Figure 3.7 is used. In ANSYS/Ansoft
the numerical integration routine is an adaptive trapezoidal method and is used to
solve this example. The following results for vehicle speed,
V
, and deceleration,
V_Dot, are found:
V_dot (m/s
2
)
Vehicle speed (m/s)
35.00
10.00
30.00
8.00
25.00
6.00
20.00
15.00
4.00
10.00
2.00
5.00
0
0
0
5.00
10.00
15.00
20.00
25.00
0
5.00
10.00
15.00
20.00
25.00
t
t
At
T
f
= 21 s the vehicle jerk becomes very excessive and
V
~ 2.5 m/s (5.5mph).
