ADAMS - Project - Hardpoint tuning to achieve pitch gradient targets using suspension “anti” characteristics
Deliverables:
- Tune hardpoints to achieve pitch gradient targets.
Acceleration pitch gradient: ~2.25 deg/g
Braking pitch gradient: ~1.60 deg/g
- Plots from Adams showing the effect of tuning.
Pitch is the front-and-rear motion of a car about an axis that extends from the left to right of a vehicle and trough the center of gravity, or transverse (side-to-side) Y-axis.
Pitch is typically taken to be positive (+) for upward movement of the vehicle nose and negative (-) for downward movement of the vehicle nose. The effects of the pitch will increase as a function of vehicle altitude. Pitch is happening in response to acceleration and deceleration forces.
The basic idea is that during acceleration or braking, the springs compress and extend. Anti is a geometry setup that uses the horizontal forces(acceleration or braking) to eliminate the spring deflection caused due to vertical load change.
Anti-dive: Reduces the compression travel in the front suspension during braking.
Anti-squat: Reduces the compression travel in the rear suspension during acceleration.
Anti-lift: Reduces the rebound travel in the front suspension during acceleration and the rebound travel in the rear suspension during braking.
Front suspension
Double wishbone suspension
Double wishbone geometry is selected for the front and vehicle parameters were modified. Spring stiffness was increased from 50N/mm to 100N/mm as per the given conditions and the assembly was simulated from 100mm in jounce to -100mm in the rebound.
Rear suspension
Multi-link suspension
The multi-link suspension was selected for the rear and the vehicle parameters were modified. Spring stiffness was increased from 50N/mm to 125N/mm as per the given conditions and the assembly was simulated from 100mm in jounce to -100mm in the rebound.
Calculation:
Total weight of the vehicle: 2000Kg
Drive ratio: 70% front
Drive ratio: 30% rear
Brake ratio: 60% front
Brake ratio: 40% rear
CG height: 530mm
Wheelbase: 2900mm
Tire radius: 350mm
Tire stiffness: 200N/mm
Front spring stiffness: 100N/mm
Rear spring stiffness: 125N/mm
Front motion ratio: 0.48
Rear motion ratio: 0.59
Front-axle static weight: 60% of 2000= 1200Kg
Rear-axle static weight: 40% of 2000= 800Kg
Front-axle static load: 1200*9.81=11772N
Rear-axle static load: 800*9.81=7848N
ΔW=2000*9.81*530/2900= 3585.72N
Wf=W+ΔW=11772+3585.72=15357.72N
Wr=W-ΔW=7848-3585.72=4262.28N
Front-wheel rate:
Kw=Ks*(MR)^2
=100*(0.48)^2
=23.04N/mm
Rear-wheel rate
=125*(0.59)^2
=43.51N/mm
Ride rate front=Ks*Kt/(Ks+Kt)
=100*200/300
=66.67N/mm
Ride rate rear=Ks*Kt/(Ks+Kt)
=125*200/325
=76.92N/mm
Front deflection under load:ΔW/(2*ride rate)
=3585.72/(2*22.89)
= 78.32mm/g
Rear deflection under load:ΔW/(2*ride rate)
=3585.72/(2*42.80)
=41.88mm/g
Pitch gradient without compensation in deg/g: ((Zf+Zr)*180)/(L*pi)
=2.37 deg/g
Front-end deflection: 73.35mm
Rear-end deflection: 37.24mm
Front IC vertical distance from the contact patch: Sin(side-view swing arm angle)*side view swing arm length
=6.24m
Front IC horizontal distance from the contact patch: cos(side-view swing arm angle)*side view swing arm length
=8.83m
Rear IC vertical distance from the contact patch: Radius of tire + Sin(side-view swing arm angle)*side view swing arm length
=5.25m
Rear IC horizontal distance from the contact patch: cos(side-view swing arm angle)*side view swing arm length
=0.76m
Anti-dive braking: 0.6*6.24/(8.83*0.18)
=2.35%
Anti-lift braking: 0.4*6.24/(8.83*0.18)
=1.57%
Anti-squat acceleration: 0.7*4.95/(0.76*0.18)
=25.32%
Anti-lift acceleration: 0.3*4.95/(0.76*0.18)
=10.85%
Adams plots:
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