E0082 Pitch Geometry Part 2 FWD Lift Anti-Geometry pitch angle Vehicle Attitude - EulSeoggy Ko

I've explained pitch geometry for front-wheel drive vehicles. Lift is the upward movement of the front end of a front-wheel drive vehicle during acceleration. This occurs because the horizontal driving force generated at the road surface acts below the center of gravity, causing the front end of the vehicle to naturally lifts and the rear end lowers. Anti-lift geometry refers to the geometric arrangement of the front suspension links to prevent the front end from lifting. The virtual reaction point is, from a kinematic perspective, the instant center of the front wheel relative to the body, or, the instant center of the body relative to the wheel. At any point on the wheel, any forces passing through the virtual reaction point, will not rotate the wheel or the sprung mass. In a front solid axle, if the virtual reaction point is behind the front wheel and above the ground, a force that reduces ride height will be generated in the suspension links when front wheel drive is applied. I explained the vehicle attitude when the front-wheel drive solid axle is driving with zero lift. Zero lift means the front spring displacement is zero, meaning the front ride height remains unchanged. With zero lift, the front spring displacement is zero, but the rear spring displacement is not zero; it decreases. I explained how to achieve a zero pitch angle. To achieve a zero pitch angle, the front ride height must be lowered to the level of the rear ride height. To achieve this, the virtual reaction point must be raised. Raising the virtual reaction point increases the downward ground reaction force in response to the suspension link force, thus reducing the front ride height. I explained how to achieve a zero pitch angle, when the front and rear suspension wheel rates are the same. Under zero lift conditions, either lower the center of gravity by half, or double the ratio of the vertical component to the horizontal component of the virtual reaction point under zero lift conditions. When driving force is applied in a front-wheel drive vehicle, the conditions for a zero pitch angle are described. As the rear ride height decreases, the front ride height must also decrease accordingly.Therefore, both front and rear ride heights must decrease by the same amount. I explained the relationship between the virtual reaction point and the pitch angle, when driving force is applied. For front-wheel drive vehicles, to achieve zero pitch angle, the virtual reaction point must be raised, lowering the front ride height. Increasing the virtual reaction point in a front-wheel drive vehicle, reduces the front ride height. For rear-wheel drive vehicles, to achieve zero pitch angle, the virtual reaction point must be raised, raising the rear ride height. Increasing the virtual reaction point in a rear-wheel drive vehicle increases the rear ride height. I explained the relationship, between the location of the virtual reaction point, and vertical load transfer. Increasing the virtual reaction point reduces the vertical dynamic load through the spring, and increases the vertical dynamic load through the suspension links. Lowering the virtual reaction point increases the vertical dynamic load through the spring, and decreases the vertical dynamic load through the suspension links. The physical principles of the virtual reaction point location are explained. If CR is defined as the ratio of the center of gravity height to the wheelbase, and SR as the ratio of the vertical length to the horizontal length of the virtual reaction point with respect to the tire-road contact center of the drive wheel, then the change in ride height can be determined from these. If SR is smaller than CR, the front ride height increases and rear ride height decreases. If SR is equal to CR, the ride height remains unchanged at the front but decreases at the rear. In this case, the lift becomes zero. If SR is smaller than 2CR but larger than CR, the ride height decreases in both the front and rear, but the reduction in the rear is greater. If SR is equal to 2CR, the ride height decreases by the same amount at both the front and rear, and the pitch angle is zero. If SR is larger than 2CR, the ride height decreases in both the front and rear, but the reduction in the front is greater. The relationship between the vertical dynamic load and the virtual reaction point is explained. The vertical dynamic load is the load transfer from the front wheels to the rear wheels. The vertical dynamic load transfer is independent of the location of the virtual reaction point. The role of the virtual reaction point is to determine the ratio of load transfer through the springs and suspension links. Once the load transfer ratio is determined, the lift and pitch angles are determined. The location of the virtual reaction point can be used to adjust the lift and pitch angles.