2008-7-25 9:35:22

Why do cars do four-wheel alignment is a problem that everyone is very concerned about.

The function of four-wheel alignment is to keep the car running smoothly in a straight line and turn lightly, and reduce the wear of tires and steering parts when the car is running. Due to the different original design and manufacture of four-wheel alignment by various automobile manufacturers, the various inclination angles and beam values of each wheel are also different, including adjustable parts and non-adjustable parts. Four-wheel alignment is to detect whether the inclination angle and toe-in value of each wheel of the tested vehicle meet the original factory standard through a four-wheel alignment instrument, and if not, it can be adjusted randomly.

In other words, when the driver feels that the steering wheel is heavy, trembling, off-course, incorrect and does not automatically reset, or finds abnormal tire wear such as unilateral wear, wavy wear, block wear and eccentric wear, as well as abnormal driving feelings such as floating, jerking and swaying during driving, when the steering wheel is incorrect or the driving direction is off-course, four-wheel alignment should be considered.

Four-wheel alignment related factors: caster angle, caster angle, camber angle, toe angle, containment angle, propulsion angle and friction radius.

1. camber: when viewed from the front of the car, the included angle between the geometric center line of the tire and the vertical line on the ground is called camber. The upper edge of the tire is offset inward (near the engine) or outward (away from the engine).

When the tire centerline coincides with the vertical line, it is called zero camber angle, which is used to prevent uneven tire wear.

The included angle when the tire centerline is out of the vertical line is called positive camber, which is mainly used to reduce the load acting on the steering knuckle, prevent the wheel from slipping, prevent unnecessary camber due to the load, and reduce the steering control force.

The included angle when the tire center line is inside the vertical line is called negative camber, which can make the rolling radius of the inner and outer sides approximately equal, make the tire wear evenly, and improve the lateral stability of the car body.

The adjustment method of camber is different according to different models. The main adjustment methods are: adjusting gasket, beam groove, eccentric cam, eccentric ball head, adjusting upper control arm, adjusting lower control arm, etc.

2. Toe: The toe-in of the front wheel is measured from the front of the vehicle at the same height on both axles, and the difference between the front and rear ends of the left and right tire center lines is called the total toe-in.

The function of toe-in is to eliminate tire sideslip caused by camber.

When the toe-in is too large, the outer wear of the tire will appear a wear state formed by excessive positive camber, and the tread wear form is feathery. When you touch the tread pattern from the inside out, the outer edge of the tread pattern has a sharp tingling sensation.

When the negative toe-in is too large, there will be a wear pattern formed by the excessive negative camber on the inner side of the tire, and the tread wear pattern is feathery. When touching from the outside to the inside with hands, the outer edge of the tread pattern has a sharp tingling sensation.

Adjustment method of front wheel toe-in: adjust the adjustable pull rod. Before adjustment, loosen the stop bolts of the left and right ball joint pins and clamp the center position of the steering wheel. Then make synchronous adjustment according to the data provided by the computer. If the original steering wheel is in the middle position, adjusting the toe-in steering wheel at the same time may not change. Until it is adjusted to the standard value, then try to see if there is any change, and if there is any change, it must be adjusted.

3. caster angle: viewed from the side of the vehicle, the connecting line between the upper ball head or the top of the strut and the lower ball head (assuming the steering shaft) inclines forward or backward, that is, the included angle between the steering shaft and the vertical line on the ground. The caster angle includes positive caster angle, negative caster angle and zero caster angle.

The caster angle of the kingpin is used to reset the wheels and improve the stability of straight driving. The generated righting moment enables the automobile to automatically righting the steering wheel when encountering external force during driving, so as to set the caster angle of the kingpin.

The main function of caster angle is to keep the vehicle running in a straight line. The angle of the caster will not affect the wheel mill. It is used to stabilize the direction of the vehicle and automatically return to the right when turning.

For the adjustment of the caster angle, we should first analyze and judge according to different models, and then make adjustments. The adjustment method is as follows: gasket, eccentric camshaft, eccentric ball head, beam groove, balance bar, etc.

4. Inclination angle: the angle formed by the steering shaft and the vertical line on the ground when viewed from the front of the car.

The function of internal inclination angle is to reduce steering control force, rebound and deviation, and improve the stability of vehicle driving in a straight line.

The definition and function of each angle in four-wheel alignment are well understood. However, when it is applied to four-wheel alignment and chassis maintenance, it is often impossible to apply the theory encountered to solve the problem. The reason is that due to the structure of the chassis of the car body, all the four-wheel positioning angles are connected with each other through the chassis through mechanical structure. For example:

⑴ Changing toe angle will change camber: Because the wheels will rotate along the steering shaft when changing toe angle, camber will change. The greater the caster angle, the greater the change of camber angle.

⑵ Adjusting the caster angle of the kingpin will change the wheel deflection angle: when the caster angle of the kingpin increases or decreases, the fulcrum on the steering shaft can move forward or backward. The other movable part is the lowest fulcrum of the steering shaft, which is the tire. Therefore, the adjustment of increasing or decreasing the caster angle will make the front wheel slide forward or backward, and the turntable used must also be able to slide forward and backward.

⑶ Changing camber can change camber at the same time, and changing camber will change camber. Different suspension structures have different camber adjustment methods. If you move the upper bracket point or the lower bracket point left and right, not only the camber angle changes, but also the camber angle changes. Therefore, even if the camber is adjusted, the garage will not be smooth because of the change of camber. Solved a problem, and at the same time produced another problem.

⑷ The change of the toe angle of the rear wheel will affect the toe angle of the front wheel single wheel: the toe angle of the rear wheel determines the angle of the rear wheel propulsion line. Modern four-wheel alignment uses the propulsion line positioning method to determine the toe-in of the front wheel. Therefore, the toe angle of the rear wheel is changed, resulting in the change of the propulsion line. Although the toe-in has not changed, the baseline (propulsion line) of the single-wheel toe-in has changed, so will the single-wheel toe-in, and the total toe-in of the front wheel has not changed.