Suspension Preliminary Design

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Suspension Preliminary Design

• Updated ADAMS/View ADAMS/Car Models
• Plots Screen Captures

Kiumars Jalali, Kai Bode, June 20th, 2006
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Full Vehicle Model in ADAMS/View
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Front and Rear Suspension
Double Wishbone Suspension at the Front
Multi Link Suspension at the Rear
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Hardpoints Front Suspension
Reference Frame as shown, located in the middle
of the front axle, 72mm below the road
surface All values in mm.
z
y
x
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Hardpoints Rear Suspension
Reference Frame as shown, located in the middle
of the front axle, 72mm below the road
surface All values in mm.
z
y
x
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Axle Models in ADAMS/Car

• Full axle models in ADAMS/Car with same
  hardpoints
• Run of equivalent simulations, comparison,
  verification

Front Axle Model in ADAMS/Car
Rear Axle Model in ADAMS/Car
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Steering Ackermann Analysis

• To minimize the wheel scrub, the steering angle
  on the outside do has to be smaller than the
  steering angle on the inside di.
• Theoretical difference di-do is given by
  Ackermann.
• In practice, the 100 Ackermann is reduced to
  achieve a smaller turning circle and a higher
  lateral force capacity.

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Steering Ackermann Analysis
steering rack 40mm in front of axle, after toe-in
optimization
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Wheel Travel Toe-in Angles

• To increase the high speed stability during lane
  change manoeuvres, the suspension could be
  modified to implement some understeer behaviour
  both on front and rear axles.
• At front axle, the outer bumping wheel must get
  some toe-out angle and the inner wheel must be
  forced into toe-in.
• At rear axle, the opposite behaviour is required
  to implement roll understeer effect.
• On commercial cars, toe-in changes during
  vertical wheel travel are in the range of
  -0.250.5.

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Toe Angle versus Wheel Travel
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Camber Angle Effect During Cornering

• During cornering, the outside wheels will be
  pushed into positive camber angle and the inside
  wheels into negative camber angle due to the
  effect of vehicle body roll angle.
• In order to produce maximum lateral force during
  cornering on each wheel, it is important for each
  tire to stay vertical to the ground both in bump
  and rebound position.
• The suspension is designed such that the bump
  traveling wheels are getting negative camber and
  the rebounding wheels are getting positive
  camber.
• Camber angle changes should not exceed 4.

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Camber Angles versus Wheel Travel
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Track Width versus Wheel Travel
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Anti-Dive Effect During Braking

• The anti-dive mechanism reduces the amount by
  which the front end of the vehicle dips or the
  tail rises when the brakes are applied.
• By inclining the control arms at an angle in side
  view, the body pitch motion can be reduced.
• This inclined angle will cause that a part of the
  additional vertical force due to the weight
  transfer during acceleration or braking is
  carried by the A-arms, which reduces the spring
  deformation.
• Although the theoretical calculation was done to
  have an anti-dive effect of 60, the practical
  value from simulation yields only 51.

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Anti-Dive Effect
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Anti-Squat Effect during Acceleration

• The anti-squat mechanism reduces the amount of
  pitch during acceleration and acts only on the
  driven axle.
• On independent wheel suspensions, it is important
  to locate the virtual centers of rotation higher
  than the wheel center of driven axle.
• Although the theoretical calculation was done to
  have an anti-squad effect of 60, the practical
  value from simulation yields only 51.

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Anti-Squat Effect
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Concluding Remarks

• The ADAMS/View and ADAMS/Car models yield almost
  exactly the same results
• Toe, camber, caster, and kingpin angles as well
  as track changes during wheel travel are set to
  the ranges of commercial vehicles available on
  the market
• The current ADAMS/View and /Car models are good
  bases, on which further vehicle dynamics and
  control studies can be based.