1. Kingpin caster
The kingpin is installed on the front axle, and its rear upper part is slightly tilted backward, which is called kingpin caster. The function of the kingpin caster is to maintain the stability of the car in a straight line and to enable the car to automatically return to alignment after turning. Simply put, the greater the caster angle, the higher the vehicle speed and the greater the stability of the wheel. However, excessive caster angle will cause heavy steering, so the caster angle should not be too large, generally 2°~3°.
In order to increase the driving speed, modern cars generally use flat, low-pressure tires. Increased tire deformation causes increased stability, so the caster angle can be reduced or even close to zero, and some are even more negative.
2. Kingpin inclination
The kingpin is installed on the front axle, and its rear upper part is slightly tilted inward, which is called kingpin inclination. The function of the kingpin inclination is to turn the wheel. It can automatically return to the right position and is easy to operate. The inclination angle is generally 5°~8°.
Both kingpin caster and kingpin inclination have the function of automatically returning the car to a straight line after steering and keeping the car running straight. The main difference between the two is that the backing function of the kingpin caster is related to the vehicle speed. The centering effect of the kingpin inclination has nothing to do with the vehicle speed. At high speeds, the back-aligning effect of the rear tilt is large, and at low speeds, the back-aligning effect of the inward tilt is mainly relied on. When the wheel occasionally encounters an impact and deflects when traveling in a straight line, it mainly relies on the inward tilting of the kingpin to return to the correct position.
3. Front wheel camber
The front wheel's rotation plane is slightly tilted outward, which is called front wheel camber. The function is to improve the lightness of steering control and the safety of wheel driving. The combination of front wheel camber and kingpin inclination can make the car turn easily. The front camber angle is generally 1°. The camber angle should not be too large, otherwise it will cause uneven tire wear.
4. Front wheel toe
Looking down at the wheels, the rotation planes of the two front wheels of the car are not completely parallel, but at a slight angle. This phenomenon is called Front wheel toe-in. The function of front wheel toe-in is to eliminate the "rolling cone effect" of the front wheel caused by wheel camber.
As the name suggests, four-wheel alignment requires not only the alignment of the front wheels, but also the alignment of the rear wheels.
1. Rear wheel camber angle
Like the front wheel camber angle, the rear wheel camber angle also affects tire wear and handling. The ideal state is that the camber angles of all four wheels are zero, so that the tires and the road surface are in good contact, thereby obtaining the best traction performance and handling performance.
In order to compensate for the load caused by the suspension sinking after the vehicle is loaded, most vehicles with independent rear suspension often have a small positive rear wheel camber angle.
2. Rear wheel toe-in
Like front wheel toe-in, rear wheel toe-in is also an important item for rear wheel positioning. If the toe-in is improper, the rear tires will also be scratched, which will lead to unstable steering and reduced braking efficiency (this should be avoided for anti-lock braking systems)
For front For a wheel-drive vehicle, the front-wheel drive should have toe-in, and the rear driven wheel should have toe-in; for a rear-wheel drive vehicle, the opposite is true, and the front wheel should have toe-in. The rear drive wheels of independent suspension should be toe-in as far as possible.
If the rear wheel toe does not meet the technical requirements, it will increase tire wear and affect steering stability to the same extent as the front wheel toe.
3. Line of action of driving force
If the two rear wheels are parallel to each other and parallel to the vehicle, then the line of action of driving force will be perpendicular to the rear axle and coincide with the longitudinal axis of the vehicle. However, if the front section of one or both rear wheels is biased in or out, or one wheel is slightly retracted relative to the other, the line of action of the driving force will deviate from the center line, thus producing a driving force deviation angle and causing the vehicle to move toward the deviation angle. Deviation in the opposite direction.
When the line of action of the driving force deviates to the right, the car deviates to the left. The occurrence of the driving force deviation angle makes the vehicle's directional stability worse on ice, snow or slippery roads. It sometimes causes the vehicle to wander when braking or accelerating sharply. The front wheels used for steering control have to overcome this effect of the rear wheels, thereby increasing wear.
Only eliminating the driving force deviation angle can solve the appeal problem. By resetting the rear wheel toe, the drive line of action can be centered. On most front-wheel drive vehicles, this is easy to do. You can use the toe adjustment method provided by the manufacturer, or you can place a toe camber spacer between the wheel steering knuckle and the rear axle, or use an eccentric shaft. Set. Rear-wheel drive vehicles have an integral rear axle, and adjustment of the rear wheel toe is not easy to achieve. Therefore, the front wheel positioning is generally adjusted based on the line of action of the rear axle driving force rather than the longitudinal axis of the vehicle.
The vibration problem is caused by the independent suspension