Chapter 6 the suspension system Kinematics of suspension 2011

Spring strut type front axle of the VW Passat (1995).
Kinematics of the semi-trailing rear axle of an Opel Omega (1996)
Purposes of the axle setting
• To ensure the required road holding and direction stability; • To prevent excessive tire wear; • To remain the wheel at the manufacturer’ setting (kingpin inclination, kingpin offset at ground, caster offset and different toe in angle);
Roll camber during cornering
During cornering camber varies. At outside, camber increases +Δεw,o, and at inside the angle decreases Δεw,i.
0 . 5 w w , o w , i
The track (b) between the two wheels of an independent wheel suspension depends on the loading.
Track alteration with load change
Track alteration with roll center position and suspension type
Calculation of track alteration of SLA suspension by drawing
W– the impression center of tire contact road U -- the out joint point of steering tie rod
Average roll camber factors
The average roll camber factors for the following axles
Long. Link axles McPherson struts SLA suspension Compound crank axles Rigid axles 1.05 0.85 0.80 0.55 0.0
Track
The tread width on passenger cars is normally: bf or r = 1210 to 1602 mm ib can be used as a ratio for the width utilization and should be as large as possible:
tread width i 0 . 84 ~ 0 . 87 b vehicle width
Influences of track alternation
the bump and rebound travel a track alteration the slip angle of tires disturbing in lateral forces, directional stability and rolling resistance deteriorate
Camber
Studies have shown that a camber of W = +5′ to 10′ leads to the most even tire wear, A ±30′ deviation is usual to enable the components of the front axle to be manufactured economically.
Camber alteration with the change of caster
Camber angles ε W,o and ε W,i, as a function of the steering angle δo (outside of bend) andδ i (inside of bend). The influence of the various caster angles can be clearly seen. Values given: σ= 6° and ε W = 0°.
Forces acted on control arms
Elasticity track alteration with the spring displacement of inner joint of upper control arm in Double wishbone suspension
Elasticity camber
McPherson susp caused by steering
Camber alteration measured and calculated as a function of the steering angle on a front-wheel drive vehicle. Due to the large kingpin inclination σ0 = 12°25′, the wheels on both the inside and outside of the bend go into positive camber.
Calculation of track alteration of McPherson suspension by drawing
W– the impression center of tire contact road U -- the out joint point of steering tie rod
McPherson suspension
Double wishbone suspension
Height hro,f of front axle roll center alteration
Vehicle Opel vauxhall Audi
Design Permissible Position axle load 40 77 15 30
Kinematic camber alteration
Camber alteration on the front suspension
Camber Alteration of Rear Wheels
Camber alteration calculation by drawing
W W 0
Honda
138
111
Track alteration with the pivot P of suspension control arm
Lowing the P, track alteration reduced.
Almost zero alteration in track requires Ro on the ground.
Measured Track alteration of one wheel on the driven rear axle
Track alteration and lateral force
the tire Lateral forces FY,W acted to the road resulting from an alteration in track A radial 175/65 R 14 82 H tire inflated to 1.9 bar under a load of 380 kg and at a speed of 80 km h–1.
Camber alteration caused by steering
Camber alteration measured on a Mercedes as a function of the steering angle. The axle settings in the design position were ε W = 0°, σ= 14°40', τ= 10°10′, r σ= –14 mm and the negative caster offset nτ = –28 mm.
Kinematics of suspension
Chapter 6 suspension system
What is kinematics suspension? And what is elasto-kinematics of suspension?
Wheel movement in 3D space
Toe-in and self-steering
The tractive / braking/roll resistance forces FX,W,a attempt to push/pull the wheels into toe-in.
Toe-in and steering angle alteration owing to wheel bump-travel kinematics
Roll camber coefficient
The mean value


dw d
kW
Influence of Dimension of Suspension on Camber
Average roll camber factors
w , 0 . 5 w , k , o w , k , i s1 s 2 d ( rad ) b f , or , r s1 s 2 53 . 7 (deg ree ) b f , or , r k , w , d w , d
Positive or negative camber
Camber , Kingpin inclination and kingpin offset at ground
Camber tolerance
• The tolerance values of camber are important. • A ±30′ deviation of camber is enable to manufacture the component economically. • The difference in kingpin inclination angle between left and right should be less than Δσ=30′ . • The measurement condition, which must relate to the kerb weight (i.e. the unoccupied vehicle), must also be added.
Toe-in and self-steering
The toe-in rΔ,t of both wheels in accordance with the DIN 70 020 is the difference in dimension b – c in mm, measured on the rim flanges at the level of the wheel centre.
Track alteration of both wheels measured on the front axle of a loaded VW Golf II GTi.
Track alteration with displacement of pivot of upper control arm