Discussion on automobile four-wheel alignment

Looking at the wheel from the side, the steering kingpin (the center of rotation of the wheel when turning) leans backward, which is called kingpin caster. After the caster angle of the kingpin is set, the distance between the center line grounding point of the kingpin and the ground projection point of the wheel center (called kingpin pitch, which is the same as the principle that the front wheel fork beam of the bicycle leans backwards) is generated, so that the wheel grounding point is located at the back end of the extension line of the steering kingpin, and the wheel is pulled backwards through rolling resistance during driving, so that the wheel direction naturally faces the driving direction. Setting a large caster angle of the kingpin can improve the straight running performance, and at the same time, the pitch of the kingpin also increases. Excessive pitch of the kingpin will make the steering wheel heavy, and the front and rear bumps of the wheels will be aggravated by road interference.

Inclination angle of king pin:

When the tire is viewed from the front and rear direction of the vehicle, the kingpin axis is inclined to the inside of the vehicle body, and this angle is called kingpin inclination angle. When the wheel rotates around the kingpin, the lowest point of the wheel will fall below the road surface, but in fact, the lower edge of the wheel cannot fall below the road surface, but the steering wheel and the whole front of the car will be raised by a corresponding height, so that the gravity of the car itself will restore the steering wheel to its original middle position, so the steering wheel can be easily reset.

In addition, the inclination angle of the kingpin also reduces the distance from the intersection point between the kingpin axis and the road surface to the intersection point between the wheel center plane and the ground, thus reducing the force exerted by the driver on the steering wheel during steering, making the steering operation lighter and reducing the impact force transmitted from the steering wheel to the steering wheel. However, the inclination angle of the kingpin should not be too large, otherwise the tire wear will be accelerated.

Front wheel camber:

When looking at the wheel from the front and rear direction, the tire is not installed vertically, but slightly inclined in the shape of Zhang Kaicheng, which is called negative camber, and the one that opens in the opposite direction is called positive camber. In the heyday when diagonal tires were used, the camber angle was set to be relatively large because the tires touched the ground obliquely, which was convenient for the operation of the steering wheel. Nowadays, cars generally set the camber angle very small, close to vertical. Flat radial tires for automobiles are becoming more and more popular. Due to the characteristics of radial tire (high tread rigidity and wide tread), if camber is set, the tire will be eccentric and the tire friction will be reduced. Due to the continuous use of power steering mechanism, camber angle is also shrinking. However, setting a small camber angle can exert appropriate lateral thrust on the wheel bearings on the axle.

Foretoe:

The toes are inward, and the so-called "inner splayed feet" means that the left and right front wheels are inward respectively. The purpose of adopting this structure is to correct the outward rotation of the wheel caused by the camber angle of the front wheel. As mentioned earlier, steering wheel operation becomes easy due to camber angle. On the other hand, because the wheels are inclined, the left and right front wheels rotate outward respectively. In order to correct this problem, if the left and right wheels have inward angles, plus or MINUS zero, the left and right wheels can keep moving in a straight line and reduce tire wear.

The above four positioning values are all indicators of front wheel positioning. The rear wheel alignment value is similar to the front wheel alignment value, but the rear wheel alignment of most cars is not adjustable.

What are the requirements for four-wheel alignment?

Answer: If the data suggested in your vehicle manual is the same as that in the four-wheel locator computer, it is universal. Generally speaking, the following situations require four-wheel alignment.

1, after replacing a new tire or repairing a collision accident;

2. Unilateral eccentric wear of front and rear tires;

3. The steering wheel is too heavy or floats and shakes when driving;

4. When going straight, the car deviates to the left or right;

Although there is no such situation, for the purpose of maintenance, it is suggested that the new car should be driven for three months, once every six months or ten thousand kilometers.

Four-wheel alignment is one of the necessary work contents of automobile maintenance. Unless there are obvious related problems before four-wheel alignment, such as poor linear stability, you can feel it immediately after four-wheel alignment, otherwise it is difficult to judge whether it is good or not by feeling. At present, the quality of the auto repair industry is uneven. I suggest you try to go to a better maintenance company to ensure the quality of four-wheel alignment and traffic safety.

Its advantages are:

1. Enhance driving comfort;

2. Reduce gasoline consumption;

3. Increase the service life of tires

4. Ensure the linear stability of the vehicle;

5. Reduce the wear of chassis suspension fittings;

6. Improve driving safety

Shopping knowledge of four-wheel positioning

At present, there are many brands and types of four-wheel positioning equipment in the domestic market. Because of its relatively high technical content, many users don't know much about its technical performance and measurement principle, and they are often at a loss when purchasing equipment in the face of various and hyped product introductions from manufacturers. The following are some suggestions on the main aspects:

1, cost performance: At present, the four-wheel positioning prices of different brands vary greatly. Because the country has no relevant regulations on the production of four-wheel positioning products, domestic products are mixed. For example, although some brands of equipment are equipped with computers, the computers only use the management function of vehicle model data, and the sensors are not connected to the computers, so the data of the sensors cannot be displayed on the computers, and users make a hullabaloo about when buying. Some devices cheat users under the banner of import, and some devices cut corners; Some manufacturers use imported low-grade sensors for simple assembly, and lack of sensor maintenance technology, which leads to the failure of user equipment can not be eliminated in time and effectively: the cheapest positioning equipment can be bought for more than 20 thousand yuan, while expensive equipment (generally speaking, imported equipment) costs hundreds of thousands or even hundreds of thousands. Generally speaking, you get what you pay. However, due to the existence of tariffs, agent price increases and other factors, the price of imported equipment is relatively high. Different brands of equipment have different market selling prices because of their advanced technology, different production processes and configurations, and different costs. Technically, users can identify the technical performance of equipment from the following aspects:

1. Do you use DSP technology?

DSP (Digital Signal Processor) is a special processor for high-speed real-time processing of digital signals, and its processing speed is 10-50 times faster than the fastest CPU. Early DSP was mainly used in military products. Later, with the continuous development of large-scale integrated circuits and the continuous reduction of costs, it was gradually applied to civilian products. Due to the powerful computing power of DSP, the application of DSP in sensors not only improves the measurement speed and data accuracy, but also greatly improves the anti-interference ability of measurement. Four-wheel positioning products using DSP have the following characteristics:

1, toe-in measurement has strong anti-interference ability: infrared or laser transceiver sensors are widely used in four-wheel aligners to measure the toe-in data of vehicles by optical measurement. Because there are components with the same wavelength as the measured light in sunlight or ordinary light source, the data of optical measurement will be affected by this, thus deviating from the correct measurement results. Therefore, some positioning devices use optical filters to reduce the influence of external light, but they cannot completely eliminate the influence of external light. This is why many four-wheel aligners need to draw curtains when measuring in the sunlight environment. However, at night or in other poor light environment, it is difficult to block the outside light with curtains.

If the measuring light is modulated by DSP technology, the modulated infrared ray has different characteristics from sunlight or other light sources. When receiving, the modulated measurement light is demodulated and filtered, which can ensure that the measurement result is not interfered by other light.

The equipment cost of DSP technology is relatively high, and its price is relatively high because of its advanced technology.

B, whether to use electronic level?

In order to achieve the designed measurement accuracy, the universal four-wheel alignment instrument must ensure that the four probes are always in a horizontal state during the measurement process. The uneven state of any probe may lead to wrong measurement results. For the four-wheel locator with bubble indication, the operator must pay great attention to whether each probe is in a horizontal state, which not only distracts the operator's energy, but also inevitably prevents wrong measurement. If all four probes are equipped with electronic level meters, the horizontal state data of the sensor probes will be transmitted to the computer in time, and the computer will monitor the horizontal data of each sensor probe and prompt the operator in time when one probe is not horizontal, which not only reduces the work intensity of the operator, but also easily avoids the wrong measurement operation. Among the imported equipment, Hunter in the United States and Bossh in Germany all adopt electronic level positioning equipment, and the price is relatively expensive.

C, whether to use electronic turntable?

Among the positioning parameters, the caster angle and caster angle cannot be measured directly, but can only be measured indirectly based on the geometric relationship: the camber angle and caster angle are measured respectively when the front wheel rotates 20 degrees left and right, and then the caster angle and caster angle are calculated according to a certain functional relationship. Therefore, the measurement of caster angle and caster angle is closely related to the measurement of steering angle. Steering Angle When the steering angle is 20 degrees and 20.5 degrees, the relative error of the detected kingpin angle is 2.39%, which far exceeds the requirements of detection accuracy. It can be seen that the turntable error has a great influence on the detection results. Therefore, the forthcoming national industry standard stipulates that electronic angle codes must be adopted in the four-wheel aligner in 2005. In addition, the use of electronic dial greatly improves the automation of the measurement process and shortens the measurement time. Foreign high-grade four-wheel alignment instruments all use electronic turntable.

D. Is the data communication mode infrared or radio?

E transmission technology: the cost of radio communication equipment is higher than that of infrared transmission equipment; 8 toe-in system is higher than 6 toe-in measuring system, and electronic level is higher than bubble level.

F, measurement accuracy:

G, measurement repeatability

H, measuring the reaction speed

In addition, the stability, repeatability, failure rate and maintenance price of equipment are also very important factors, but it is difficult for users to obtain this information from manufacturers properly and objectively, and users need to obtain it from the side.

2. After-sales service:

In automobile inspection and maintenance products, the after-sales service of four-wheel alignment instrument is more important, and the after-sales service content is more abundant and complex. Because of its high price, it is necessary to provide timely maintenance service after the equipment fails. Because of its high technical content, only those manufacturers with technical development strength can provide low-cost and high-quality maintenance services. For manufacturers without technical ability, the method of replacing sensor probe and main control board is often used to repair customer equipment, which not only has high maintenance cost, but also makes users unbearable and often cannot be repaired in time.

The operation of four-wheel positioning equipment is complex, which requires manufacturers to provide high-quality operation training services. For those users who are not familiar with automobile chassis, manufacturers must also have the ability to locate automobile faults and adjust them.

In addition, due to the continuous emergence of new models, manufacturers are also required to update the vehicle positioning data in time. +