BND TechSource
Tire Envelope Swept VolumeUsingCATIA V5 DMU Kinematics
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
To create the correct tire clearanceenvelope, there needs to be
anunderstanding of basic suspensiongeometry.This example will touch
upon areas suchas Ackermann Steering, Front/Rear
Steer,Jounce/Rebound, Clearance Zones andTurning Radius.The result
will be a swept volume usingCATIA DMU Kinematics.Prepared by: Bill
Harbin Technical Director 1-Jun-09
BND TechSource
Certain parameters were set in this particulardesign.
Track: Front/Rear = 1490/1510mmWheelbase = 2489.2mmTire Size:
(http://www.csgnetwork.com/tireinfo4calc.html)
Front = P245/45ZR-17(Tire Radius = 326.15mm)Rear =
P275/40ZR-18(Tire Radius = 338.60mm)
Wheel Size:
Front = 17 x 8.5 in, Offset = 56mmRear = 18 x 9.5 in, Offset =
63mmPrepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
Parameters (contd).
Scrub Radius = +10mmoSteering Axis Inclination = 8.8oCaster
Angle = 6.5SLA Ratio = 1.43:1Brake Rotor Offset (Hub face to Rear
Rotorface) = 38mmAckermann Steering = 82.5%Shock
Extension/Compression = 48.7/48.7mm
All of these parameters affect Tire ClearanceEnvelope.
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
Ackermann Steering Principle.
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
Rear Steer is used with Recirculating BallSteering
Gear.(Projected Steering Axis)
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
Front Steer is used with Rack & PinionSteering
Gear.(Projected Steering Axis)
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
Ackermann angles set up the Tie Rod Ends.
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
100% Ackermann angles and the resultantTurning Angles.
Curb-to-curbturning radiusset at 17.5 ft.
100% Ackermann willconverge at the samepoint along the rear
axlecenterline.
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
82.5% Ackermann angles and theresultant Turning Angles.
Notice the divergencefrom the true center ofthe Turning
Radius.This will cause scrubbingof the inner tire as thevehicle
makes the turn.
Curb-to-curbturning radiusset at 17.5 ft.
Center ofturning radius
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
Less than 100% Ackermann is a normalcompromise in todays
passenger vehicles.Due to packagingconstraints, 100%Ackermann is
notalways achievable.
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
The worst condition is at full jounce and fullturning
angles.
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
The jounce (full up) and rebound (full down)must be
determined.
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
Measure the jounce (full up) and rebound(full down).
Jounce = 63.8mm
Rebound = 65.8mmPrepared by: Bill Harbin Technical Director
1-Jun-09
BND TechSource
Another parameter is the clearance zonerequired around the
tire.
The clearance zone seton this one-off sports caris 19 mm.A mass
produced vehiclewould need to consideradditional clearance dueto
tire chains.
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
Now there is enoughinformation to get an accurateSwept Volume
representing theTire Clearance Envelope.
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
Step 1: Create a Rigid Joint for the Tire ClearanceZone in the
current Kinematic Mechanism.
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
Step 2: Create a Simulation in DMU Kinematics.
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
Step 3: Compile the Simulation in DMU Kinematics.
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
Step 4: Generate the Swept Volume in DMUKinematics.
Prepared by: Bill Harbin Technical Director 1-Jun-09
BND TechSource
Step 5: Add the Swept Volume into the Product.
Prepared by: Bill Harbin Technical Director 1-Jun-09
