FRONT SUSPENSION DESCRIPTION
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King-pin Axis Configuration
• The king-pin axis, depending on the type of front suspension, is as follows:
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- In the strut type front suspension, wheels rotate around the king-pin axis going from the point where the shock absorber is attached to the body (point A) to the ball joint (point B).
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- In the high-mount double wishbone type front suspension (with double-pivoted lower arm(s)), wheels rotate around the king-pin axis going from the upper arm ball joint (point C) to the imaginary pivot line (point D) extended from the lower arm(s).
• The intersection of king-pin axis and the road surface (point E) is offset in the vehicle from the wheel setting center point of on the road (point W), producing a king-pin offset.
• Compared to the strut front suspension, the high-mount double wishbone front suspension (with double-pivoted lower arm(s) has the following technical advantages:
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- The moment of inertia around the king-pin axis is reduced due to the short king-pin to wheel-center offset. This feature reduces undesirable vehicle behaviour such as steering pull and judder when breaking, smooth steering obstruction due to road conditions, and the influence of steering torque due to road undulation.
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- The king-pin offset value (negative king-pin offset) is optimized. Due to this, the influence of the axis weight is not felt and steering control is lightened. Also, straight driving stability is improved because the toe-in moment from the braking effort the wheels counteracts the yaw moment caused by road surface conditions and/or the difference of right and left wheel braking effort.
Suspension system comparison
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1
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King-pin axis
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2
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King-pin inclination
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3
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King-pin offset
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4
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King-pin to wheel-center offset
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5
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Wheel center
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6
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Imaginary pivot
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7
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High-mount double wishbone front suspension
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8
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Strut front suspension (reference)
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9
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View from horizontal axis of the vehicle
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10
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View from vertical axis of the vehicle
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11
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Front
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Camber Control
• The camber change during a front suspension stroke is properly controlled by optimizing the ratio of the front upper arm and the front lower arm(s) lengths.
Camber control characteristic comparison
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1
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Rebound stroke area
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2
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Bump stroke area
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3
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Camber angle (°)
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4
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Wheel stroke (mm)
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5
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Vehicle roll angle (°)
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6
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Strut front suspension (reference)
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7
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High-mount double wishbone front suspension
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Vehicle Roll Center Height Setting
• The front roll center height is set lower than the rear. Straight- ahead driving handling is improved by setting the rolling axis at a slightly forward angle.
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1
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Front roll center height
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2
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Rear roll center height
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3
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Rolling axis
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4
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Extended line (parallel to the ground) from front roll center height
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Low-friction Ball Joint
• A low-friction ball joint is used on the knuckle side of the front upper arm and lower arm(s) to improve steering response and to smoothness.
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1
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Front upper arm
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2
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Low-friction ball joint (for front upper arm)
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3
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Front lower arm (rear)
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4
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Knuckle
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5
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Low-friction ball joint (for front lower arm (rear))
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6
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Low-friction ball joint (for front lower arm (front))
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7
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Front lower arm (front)
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8
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Cross-sectional view
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Front Lower Arm (Rear)
• An oil-filled bushing is used with the front lower arm (rear) to reduce vibrations such as shimmy, judder, and road noise.
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1
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RH front lower arm (rear)
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2
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Vertical view
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3
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Horizontal view
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4
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Front
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5
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Cross-section A-A
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6
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Oil-filled bushing
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7
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Oil
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