Environmental Engineering Reference
In-Depth Information
the brakes and aerodynamic losses. The driveline losses are negligible since there is
no power flow upstream in the vehicle driveline when the foundation brakes are
engaged, regen is disabled, ABS is active and all braking energy is dissipated in the
wheel hub brake assembly. For this case (3.6) is written as follows at the level of
force components:
MV
dV
dx
¼
F
b
þ
C
a
V
2
ð
3
:
8
Þ
Since all four wheels are engaged in braking, the total braking force at the
wheel tyre patches can be very high. In general, the braking force
F
b
=
m
gM
and
(3.8) can be integrated in closed form as
SD
¼
M
ð
0
V
0
VdV
MVdV
¼ð
F
b
þ
C
a
V
2
Þ
dx
;
ð
3
:
9
Þ
ð
F
b
þ
C
a
V
2
Þ
Example 5:
Solving (3.9) compute the stopping distance, SD, for the Camry
Hybrid with four passengers on level terrain from an initial speed,
V
0
= 29.06 m/s,
when tyre coefficient of friction
m
= 0.85.
Solution:
SD
¼
2
C
a
ln
ð
F
b
þ
C
a
V
0
Þ
M
F
b
16
;
462
þ
0
:
392
ð
29
:
06
2
¼
ð
1
;
673
þ
4
75
:
5
Þ
2
ð
0
:
392
Þ
Þ
ln
¼
50
:
15m
16
;
462
and
F
b
= (0.85)(9.8066)(1,975) = 16,462 N.
The Camry Hybrid will therefore stop at 50.15 m (165 ft) from 65mph on level
ground.
3.3.4 RBS interaction with IVD/VSC/ESP
The previous sections have described how RBS, a necessity for hybrid function-
ality, reacts with the vehicle's longitudinal stability functions (i.e. ABS) during
extreme manoeuvres. Also, the introduction of EHB hardware into the vehicle
platform brings with it additional stability features. In both CVs and HVs having
EHB (in the future EMB), it is possible to further enhance overall stability during
vehicle handling manoeuvres.
This author has test driven EHB and EMB equipped test cars on a handling
course to more fully appreciate the benefits of dynamic stability programmes.
In this series of tests [2], vehicles equipped with outriggers are driven at speeds of
50-60mph on a marked course that forces a brisk lane change manoeuvre on wet
pavement. The active stability programmes (IVD, ESP or VSC algorithm) initiate
appropriate control of vehicle throttle and brakes (independent control is possible)
so that manoeuvre induced yaw motion is damped. An EHB or EMB system
