Copyright © 2012 Ford Motor Company of Southern Africa.
9
TechnicAL
Combination of light feel at low-to-mid speeds and stability at high speeds
When the yaw gain (the force that turns a vehicle) is set at a high level to enhance the car’s nimbleness at the low-to-mid speeds, it tends to become excessive at high speeds, producing an oversensitive response in the car’s
movements. To resolve this issue, we re-examined the geometry of the rear
suspension. First of all, to ensure smooth movement at high speeds, we optimized the suspension links, and increased the grip of the rear wheels in response to impact (reducing the yaw gain).
Next, to ensure nimbleness of movement at low-to-mid speeds, we adopted
a higher steering gear ratio (increasing yaw gain). By doing so, we simultaneously increased yaw gain at low-mid speeds and reduced yaw gain at high
speeds, achieving improved nimbleness at the low-mid speed range and
greater stability at the high-speed range.
The next challenge was to deliver agility at low-to-mid speeds at the same
time as maintaining stability at high speeds, in terms of both vehicle movement and the steering force required. In other words, this refers to ensuring
that the steering feel varies according to the speed of the vehicle. First of all,
to ensure firm steering at high speeds, the front suspension caster angle and
caster trail were increased to enhance self-aligning torque. Next, to ensure
light and smooth steering at low-mid speeds, electric power steering controls
were used to increase the power assistance at low-mid speeds, thus making
the steering lighter. In this way we have created a steering feel that conveys
security and a sense of oneness between car and driver, while also matching
the car’s movements.
Balance of ride comfort with agility at low-mid range
The next aim was ride comfort, the balance of agility with comfort. We revised the structure of the suspension to improve handling without making the
springs and dampers stiff. First of all, to enhance the operational efficiency of
the dampers, the mounts were set at a position that enables a greater lever
ratio. By implementing this change, damping force and the rigidity of the top
mount rubber could be reinforced, reducing the impact on ride comfort.
Caster angle
Caster trail