Page 122 - Handbook of Biomechatronics

118 Naser Mehrabi and John McPhee

Fig. 9 ISO double lane change (DLC) constraint and vehicle desired trajectory.

(Forkenbrock and Elsasser, 2005) at a speed of 10m/s, where the maximum
max
assist torque (T m ) is assumed to be 50Nm, and a value of 1Nm is selected
for the no-assist zone (T d0 ) to avoid the off-center steering feel.
The muscular effort [G(a)], defined according to a physiological cost
function (Forster et al., 2004) and shown in Eq. (33), was selected to repre-
sent the driver’s physical strength. The symbol a i represents the extensor and
flexor muscle activations, and the exponent p is chosen to be 2 in the
simulations:

2
p
X
G aðÞ ¼ a i ðÞ (33)
i¼1
The road feel criterion was used to quantify the intensity of feedback infor-
mation (feel) from the road to the driver. To consider the nonlinearity
induced by the steering system and the EPS characteristic curve for a specific
maneuver, the road feel was defined in the time domain as the relationship
between the resistive steering torque (SAT) to the driver torque (T d ) as fol-
lows (Zaremba and Davis, 1995):
8
|T d tðÞ|
1 < if SAT 6¼ 0
F rf ¼ ¼ |SAT tðÞ| (34)
F rf :
0 otherwise

3.4 Simulation Results
In this section, the sensitivity of characteristic curves to different muscle
parameters is studied. Then, the muscle parameters are set to values for