Automobile Inspection Technology

Chapter 34 Vehicle Inspection Technology (10)
在检验前照灯远光光束及远光单光束照射位置时，根据检测标准，其光束中心应位于高度为Hi、Hi-0.1H的两条水平线和距垂直线距离为S/2+170mm、S/2-350mm(对左灯)或S/2-170mm、S/2+350mm(对右灯）的两条垂直线所围成的矩形内。

The screen method is simple and easy, but it can only detect the beam irradiation position; at the same time, the screen needs to be replaced frequently to adapt to different models, and it takes up a lot of space.Therefore, according to the provisions of GB7258-2004 "Technical Conditions for Motor Vehicle Operation Safety" (Appendix D), when conducting motor vehicle safety technical inspections at automobile inspection stations, headlight detectors are widely used to detect automobile headlights.

2. Use a detector to detect the luminous intensity and beam irradiation of the headlight
位置
There are many types of headlight detectors, but the basic detection principle is similar. Generally, photocells that can convert the absorbed light energy into current are used as sensors, and the size and ratio of the current generated when the headlight beam shines on it are generally used. , to detect the luminous intensity and beam deflection of the headlamp.

(1) Principle of luminous intensity detection

The luminous intensity detection circuit shown in Figure 5-63 is composed of a photometer, a photocell and a variable resistor. When the headlight irradiates the photocell at a specified distance, the photocell will generate a current proportional to the intensity of the received light, and the pointer of the photometer will deflect. After calibration, the deflection of the pointer can reflect the luminous intensity of the headlight.The variable resistor in the circuit is used to adjust the zero position of the photometer pointer.The main type of commonly used photovoltaic cells is the photocell. When exposed to light, the left and right ends of the metal film and the amorphous film generate an electromotive force, the backlight side is positively charged, and the light-receiving side is negatively charged.Therefore, if a lead-out line is installed on the metal film and the iron base plate, and it is connected to the ammeter with a wire, the current will flow through the ammeter to make the pointer of the ammeter swing, as shown in Figure 5-64.

Figure 5-64 Structure and working principle of selenium photocell Figure 5-65 Detection principle of beam center deflection

1一电流表；2-引线；3-金属薄膜；1一左右偏斜指示计；一光电池；3-上下偏斜指示计

4-Amorphous crystal; 5-Crystalline; 6-Iron soleplate

(2) Principle of beam center deflection detection

The beam center deflection detection circuit shown in Figure 5-65 is composed of two pairs of photocells. The left and right pair of photocells S, left and S are connected with left and right deflection indicators, which are used to detect the left and right deflection of the beam center. ; The upper and lower pairs of photocells Sj: St are connected with an up and down deflection indicator, which is used to detect the up and down deflection of the beam center.When the photocells are irradiated by the headlights, each photocell generates current respectively. If the center of the beam of the headlights is deflected, the illuminance received by the four photocells is not equal, so the currents generated are also not equal.The difference between the currents generated by the photocells S, S, and S, and the right causes the pointer of the left and right deflection indicators to swing; The amount of deflection from the center of the headlamp beam.If the position of the light irradiating the photocells is adjusted through an appropriate adjustment mechanism, so that the illuminance of each pair of photocells on the left, right, and upper and lower sides of S is the same, at this time, the output current of each pair of photocells is equal, and the pointers of the two deflection indicators are in the same direction. Pointing to the zero position, its adjustment reflects the deflection of the center of the beam.

[-]. Brief introduction of commonly used headlight detectors

1. Concentrating headlamp tester
The spotlight headlamp tester uses a condenser lens to aggregate the scattered light beams of the headlamp and direct them to the light surface of the photocell, and detect the luminous intensity and optical axis deviation of the headlamp according to the irradiation intensity of the photocell. displacement.

The spotlight headlamp tester consists of a bracket, a running part, an instrument box, an instrument lifting adjustment device and an aligner.When testing, the detector is located 1m in front of the headlight.The driving part is equipped with three grooved wheels, which can walk on the guide rail and align quickly; the instrument box is the main part of the detector, and the center of the instrument box can be aligned with the base of the headlight of the vehicle under test by turning the lifting handwheel.
准中心高度保持一致；仪器箱顶部的对正器观察仪器与被测车辆的相互位置是否对正；检测仪的光度指示装置由电源开关、电源欠压指示、光度表和三个按键开关及三个相应调零按钮组成；远光I号键可测0-40000cd的发光强度，远光n号键可测0-20000cd的发光强度，近光按键可测0-1000cd的发光强度，调零按钮用于调零。图5-66为聚光式前照灯检测仪的外形图，其光度指示装置如图5-67所示。

There are three detection methods for spotlight headlamp detectors:

(1) Moving mirror detection method
The light of the headlight irradiates the light on the photocell through the condenser lens and the reflector, as shown in Figure 5-68.Turning the optical axis scale can change the installation angle of the reflector.When the reflector is adjusted so that the pointer of the optical axis deflection indicator points to zero, the deflection of the optical axis can be read from the optical axis dial, and the photometer also indicates the luminous intensity at the same time.

(2) Mobile photocell detection method
Turn the optical axis dial to move the photocell up and down and left and right until the pointers of the left and right deflection indicators and the up and down deflection indicators point to zero, as shown in Figure 5-69.At this time, the deflection of the optical axis can be read from the optical axis dial, and at the same time, the output current of the photocell indicates the luminous intensity through the photometer.

(3) Moving lens detection method
Adjust the orientation of the condenser lens by moving the optical axis detection lever, so that the light passing through the condenser lens to the photocell is the strongest, as shown in Figure 5-70.At this time, the pointer indication value of the optical axis deflection indicator is zero.The power output by the photocell is used to indicate the intensity of light emitted by the photometer, and the optical axis dial is linked with the optical axis detection lever to indicate the amount of deflection of the optical axis.

2. Screen-type headlight tester The screen-type headlight tester uses the light beam of the car headlight to irradiate the screen to detect its luminous intensity and optical axis deflection. Usually the test distance is 3m0
As shown in Figure 5-71, the screen-type headlamp tester is equipped with a movable screen that can move left and right on the fixed screen, and a light receiver with a photocell inside that can move up and down is installed on the movable screen.When testing, adjust the relative position of the vehicle, headlights and detector through the finder, move the light receiver and the movable screen, so that the indication value of the photometer is the largest, the indication value is the luminous intensity, and this position is the main optical axis For the irradiation position, the optical axis deviation can be read from the two optical axis scales installed on the screen.

3. Projection headlamp tester
The projection headlamp tester maps the beam of the headlamp onto the projection screen to detect its luminous intensity and optical axis deflection. The test distance is generally 3m.

Figure 5-72 shows the projected headlamp tester, and the internal structure of its light receiving box is shown in Figure 5-73.When testing, first use the alignment sight to find out the relative position between the vehicle and the instrument, the beam of the inspected headlight is converged by the lens and then enters the light receiving box, and the beam is reflected to the projection screen by the reflector.Five photocells are arranged symmetrically on the projection screen. Photocells m and F detect the light distribution in the horizontal direction, and photocells I and n detect the light distribution in the vertical direction. The balanced output of each pair of photocells

(a) Front of detector
They are respectively connected to the left, right and top and bottom optical axis balance meters; the V photocell detects the luminous intensity, and its output is connected to the luminous intensity indicating table.Rotating the left and right or up and down optical axis dials can change the angle of the reflector, so that the indication of each optical axis balance indicator is zero.At this time, the value indicated by the optical axis dial is the optical axis deflection of the headlight, and the value indicated by the luminous intensity meter is the luminous intensity of the headlamp.Some projection headlamp testers are marked with a scale line indicating the amount of deflection of the optical axis. According to the position of the beam image of the headlamp on the projection screen, the amount of deflection of the optical axis can be directly read.

4. Automatic tracking optical axis type headlight detector
The automatic tracking optical axis type headlamp detector adopts the method of automatically tracking the optical axis by the light receiver to detect the luminous intensity and optical axis deviation of the automobile headlamp, and the general detection distance is 3m.

Figure 5-74 shows the automatic optical axis tracking type headlamp tester, and the structure of its light receiver is shown in Figure 5-75.There are four photocells on the top, bottom and left and right of the condenser lens of the light receiver, and four photocells are also installed inside the light receiver, which respectively constitute the main and auxiliary light receivers. The central part of the lens is equipped with a central photocell.Its test principle is the same as that of the beam center deflection described in Figure 5-65, the difference is that the displacement of the detector stand and the light receiver is driven by a motor.The current difference generated by each pair of photocells due to uneven light reception is not only used to deflect the pointer of the optical axis offset indicator, but also used to control the operation of the driving motor to move the detector platform along the guide rail and make the photoreceiver up and down. move.During detection, the main light receiver is used to track the optical axis. If the upper and lower photocells on the main light receiver and the left and right photocells receive uneven light, the resulting current difference will control the operation of the drive motor, so that the detector platform moves laterally along the guide rail and makes The light receiver moves up and down until each pair of photocells receives the same light intensity and the output current is equal; at the same time, the headlight beam shines on the sub-light receiver photocell and the central photocell through the condenser lens. If the headlight beam is deflected, the sub-light receiver The intensity of light received by the upper and lower photocells and the left and right photocells is also different, thereby generating a corresponding current to control the position of the sub-receiver or condenser lens to move until the beam deflection of the sub-lamp is indicated by the optical axis deflection indicator.At this time, the intensity of light received on the central photocell is the strongest, and its output current reflects the luminous intensity of the headlight and is indicated by a photometer.

[-]. Precautions for using the headlight tester
There are many types of automotive headlight detectors, and their specific usage methods are different. Therefore, when using a detector to detect the luminous intensity and optical axis deflection of a car headlight, you should carefully read the instruction manual of the detector used. , master the correct method of use, so that the test results are accurate and reliable.Generally, the following issues should be paid attention to:

(1) Preparation of the car to be tested
①Remove the dirt on the headlight.

②The tire pressure meets the regulations.

③The battery is fully charged.

(2) Precautions for using the detector
① Install the equipment correctly according to the instructions (such as site requirements, detection distance requirements, parallelism requirements, verticality requirements, height requirements, etc.).

(End of this chapter)