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Development and present situation of motor vehicle detection technology
/Source: Link News Visits: 2476 Release Time: 20111-28 QC Testing Instrument Network.
Labels: endoscope, internal micrometer, inspection instrument, ultrasonic flaw detector, Richter hardness tester, metallographic microscope, nondestructive testing, alloy analyzer, eddy current flaw detector, universal testing machine.
Xiang Zhen, Institute of Optical Engineering, School of Information, Zhejiang University, Wu Yong, Ying Zhou
I. Overview
While cars provide convenience for people, they also bring a series of problems such as air pollution, noise and traffic safety. With the increase of mileage and the continuation of service time, its technical condition will continue to deteriorate. Therefore, on the one hand, it is necessary to continuously develop cars with excellent performance; On the other hand, it needs maintenance and repair to restore its technical condition. Automobile comprehensive performance testing is a technology to test and check the technical condition of automobile in the process of automobile use, maintenance and repair. In recent years, the number of motor vehicles in China has increased sharply, and the problem of motor vehicle operation safety has become more and more prominent. Strengthening motor vehicle management and attaching importance to motor vehicle detection have become the urgent requirements of the whole society, which also provides a good opportunity for the development of motor vehicle detection instruments in China.
With the development of automobile industry, manufacturers of relevant testing equipment have increased their efforts to develop new equipment, constantly improving and increasing testing equipment to make it more suitable for actual needs. Single detection equipment is more and more advanced, all sensors have changed from mechanical to electronic, and the control mode has changed from relay control to computer control. Both data acquisition and processing use computers.
Second, the development of automobile testing technology
Automobile detection technology is developing with the development of automobile technology. In the early days of automobile development, people mainly found automobile faults through experienced maintenance personnel and carried out targeted maintenance. With the progress of modern science and technology, automobile inspection technology has also developed rapidly. At present, people can rely on all kinds of advanced instruments and equipment to test cars safely, quickly and reliably.
1. Development Status of Foreign Automobile Testing Technology
Automobile inspection technology has developed from scratch and gradually. As early as 1950s, some industrialized countries formed single detection technology and production single detection equipment focusing on fault diagnosis and performance debugging. In the early 1960s, the automobile inspection and test equipment that entered China included American engine analyzer, British engine ignition system fault diagnosis instrument, automobile road test speed analyzer, etc., all of which were developed earlier abroad. In the late 1960s, foreign automobile inspection and diagnosis technology developed rapidly, and a large number of photoelectric, physical and chemical and mechanical integrated inspection technologies were applied. Since 1970s, with the development of computer technology, there have been automobile performance testing instruments and equipment with the functions of automobile detection and diagnosis, data acquisition and processing automation, and direct printing of test results. On this basis, in order to strengthen automobile management, various industrialized countries have successively established automobile inspection stations and inspection lines to institutionalize automobile inspection.
Generally speaking, the automobile inspection management in industrialized countries has been institutionalized; The basic technology testing has been standardized; Detection technology is developing in the direction of "intelligent and automatic detection".
2. Overview of domestic automobile inspection technology development.
China began to study automobile inspection technology in 1960s.
In the 1970s, China vigorously developed automobile inspection technology, and automobile non-disassembly inspection technology and equipment were listed as the development and application projects of the State Science and Technology Commission. The reaction automobile brake test-bed was developed with the support of the Ministry of Communications. Inertia automobile brake test bench: engine comprehensive detector: automobile performance comprehensive test platform (with brake detection, chassis dynamometer, speed test and other functions. ).
In 1980s, with the development of national economy, various fields of science and technology developed rapidly, and so did automobile detection and diagnosis technology. How to ensure that vehicles are fast, economical and flexible, and do not cause public hazards as much as possible, has gradually been put on the agenda of relevant government departments, thus promoting the development of automobile diagnosis and testing technology.
On the basis of the successful development of a single testing equipment, in order to ensure the good technical condition of automobiles, strengthen the technical management of automobiles in use, and give full play to the use function of automobile testing equipment, the Ministry of Communications began to plan to build automobile testing stations in the national highway transportation and vehicle management system (which was in charge of automobile supervision at that time) on 1980, and the testing content was mainly automobile safety testing.
In the early 1980s, the Ministry of Communications established the first domestic automobile inspection station in Dalian. Technically, it is proposed to install all kinds of single testing equipment online to form a fully functional automobile testing line, and its testing scheme is 30 thousand vehicles/year.
In order to cooperate with automobile testing, China has issued and implemented more than 100 national standards, industry standards and metrological verification regulations. From the establishment of automobile comprehensive performance testing station to the specific testing items of automobile testing, there are basically laws to follow.
3. The development direction of China's automobile comprehensive performance testing technology.
In order to catch up with the advanced level in the world, China's automobile inspection technology should be developed in the aspects of automobile inspection technology foundation, intelligent automobile inspection equipment and networked automobile inspection management.
A. Standardization of automobile testing technology foundation
B. Intelligent automobile detection equipment
C. networking of automobile inspection management
According to the requirements of automobile safety and performance testing, this paper discusses some road testing methods in the rapidly developing networking technology, emission testing, four-wheel positioning, lighting testing and braking performance testing.
Third, equipment networking.
At present, some automobile comprehensive performance testing stations in China have realized computer management system testing. Although the computer management system adopts computer measurement and control, the computer measurement and control methods of each station are very different. Even if the computer network system technology is adopted, only one station can realize networking. With the progress of technology and management, automobile inspection will realize real networking (local area network) in the future, so as to enjoy information resources, hardware resources and software resources. On this basis, the information expressway is used to connect the national automobile comprehensive performance testing station into a wide area network, so that the traffic management department at a higher level can know the vehicle situation in each area in real time. Under this structure, the automobile comprehensive performance testing station can not only undertake the testing of vehicle power, economy, reliability, safety and environmental management, but also undertake the testing of vehicle maintenance quality and technical status, as well as the performance testing and parameter testing of scientific research and teaching. The inspection items are wide and deep, which can provide reliable technical basis for departments such as automobile use, maintenance, scientific research, teaching, design and manufacturing.
At present, these devices are mainly interconnected through serial port and Ethernet protocol. With the development of communication technology, it provides a more convenient choice. For example, short message platform can be used to facilitate data exchange, and wireless Ethernet protocol based on 802. 1 can also be used. Bluetooth technology is also a standard open interconnection protocol. With the development of optical communication, optical network can be used as the transmission medium of signals in complex large-scale networks.
Fourthly, the emission test of motor vehicles.
With the increase of car ownership (the annual growth rate is above 10%), the pollution of automobile exhaust pollutants to the environment will become more and more serious. At present, air pollution has gradually developed into a worldwide problem. The purpose of measuring the concentration of waste gas pollutants by exhaust gas analyzer and smoke meter is to control the diffusion of waste gas pollutants and limit them within the allowable range to protect the ecological environment and the ecological balance of nature.
The main pollutants emitted by automobiles are carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (nitrogen oxides), sulfur oxides (mainly sulfur dioxide) and particulate matter (composed of heavy metal oxides such as soot and lead oxide and smoke dust). Compared with gasoline engines, the carbon monoxide emissions of diesel engines are much smaller. In addition, diesel engines emit less HC, but the emissions of nitrogen oxides are similar to those of gasoline engines, and they will emit annoying black smoke.
In order to control the harm of automobile exhaust pollutants to the ecological environment, governments all over the world have successively formulated the limit standards of automobile exhaust pollutants.
4. 1 Detection of pollutant emission from gasoline vehicles
The evolution of pollutant emission detection methods for gasoline vehicles is divided into two parts, one is the change of gas concentration detection method, and the other is the working state of the vehicle itself during the test. This problem is discussed in two parts.
4. 1. 1 Classification of gas concentration detection methods
The selected infrared wavelength range is 3-5um. In order to ensure the measurement accuracy and distance of the instrument, the requirements for infrared radiation sources are: the spectral components of radiation should be stable. Because the absorption of infrared rays by various gases is selective, if the emitted spectral components (wavelength and energy) are unstable, the absorbed energy will be different for gases with the same concentration, which will inevitably lead to measurement errors.
Most of the radiation energy should be concentrated in the characteristic absorption band of the device to be tested, and the beam divergence angle of the transmission system should be small to ensure that the optical signal energy is strong enough after long-distance transmission, thus increasing the energy that can be absorbed by the device to be tested. The approximately parallel infrared beam emitted by the infrared light source passes through the automobile exhaust area and is reflected by the corner reflector placed on the opposite side of the two-lane highway. The light beam returns to the receiving part of the instrument, passes through the gas calibration cell, the infrared focusing lens, the chopper and the rotating filter wheel in turn, and finally focuses on the infrared detector.
2. Tunable infrared laser differential absorption vehicle exhaust roadside monitoring system.
Recently, a laser with tunable output wavelength was introduced from abroad, which can scan in a certain wavelength range, measure the peak value of the actual absorption spectrum of the corresponding gas, and determine the concentration value of various gases by using the shape of the peak value, so as to realize the automatic monitoring of pollutants such as CO, CO2, NO and HC in the exhaust gas emitted by motor vehicles during driving. Because the wavelength of the laser output beam is smaller than the wavelength of the filter, the possibility of spectrum overlap of various gases is smaller and the test results are more accurate.
The traditional exhaust gas detection method needs to sample the automobile exhaust pipe first, and then analyze it with conventional instruments under laboratory conditions, which is time-consuming, laborious, costly and difficult to operate. Four workers can only detect about 1000 vehicles a day, while the exhaust roadside monitoring technology can realize real-time online telemetry, monitor the pollution status of automobile exhaust in real time, and detect more than1000 vehicles in one hour. It can reflect the real emission of vehicles in real time.
4. 1.2 emission detection adopts different vehicle working conditions.
As mentioned above, with the difference of engine working conditions and actual load, even the actual emission effect of the same vehicle is very different, which is also the biggest problem in emission measurement at present. The purpose of emission measurement is to better understand the pollutant emission of vehicles in actual use, so as to achieve the purpose of pollution control. If the measurement state is different from the actual use state, the measurement result has no good reference value. With the development of technology and the improvement of requirements, the exhaust measurement methods of gasoline vehicles are divided into working condition method, constant speed working condition method and idle speed method. Idle methods include single idle method and double idle method.
A. Detection of idle pollutant emission of gasoline vehicles
The single idle speed method is mainly used to measure the exhaust pollutants of gasoline vehicles at inspection stations. In fact, the idling method can not reflect the actual situation of vehicles, but it has been widely used in inspection stations because of its simple operation and few restrictions.
B, detecting pollutant emission by using a gasoline vehicle working condition method.
ASM (Steady-state Loading Condition of Acceleration Simulation Mode) requires chassis dynamometer to simulate the steady-state load in motor vehicle operation according to the reference mass of motor vehicle, and the detected motor vehicle runs at a constant speed under this load. When the vehicle speed is 24km/h, it is in BASM5024 working condition. When the vehicle speed is 40km/h, it is in BASM2540 working condition. During the test, the vehicle to be tested is tested under BASM5024 working condition, and if the emission exceeds the standard, it is tested under BASM2540 working condition.
The steady-state working condition detection system can more truly reflect the actual emission of automobiles, but it is a measurement of automobile exhaust concentration. The concentration measurement of automobile exhaust components can not completely measure the pollution degree of automobile to the atmosphere, because the actual weight of pollutants can not be measured without the total mass of automobile exhaust. For the above reasons, the European standard emission standard is in grams/km, because it takes both concentration and quality into account.
The advanced Vmas system used now can test the actual discharge gas flow, calculate the total mass of discharged pollutants, ensure that the measurement results are compatible with the prevailing Euro II or Euro III standards, and truly achieve the purpose of controlling the total discharge of pollutants.
4.2 Detection of Free Accelerated Smoke of Diesel Vehicles
A. the principle of filter paper smoke meter
Smoke meter is mainly used to measure the exhaust smoke of diesel engine. The sampler is a spring pump with a sampling probe at the front end. It is inserted in the center of the exhaust pipe to absorb a certain volume of exhaust gas and make it pass through a white filter paper with a certain area. The soot in the exhaust gas accumulates on the surface of the filter paper, which pollutes the filter paper. Measure the pollution degree of filter paper with a detector. The pollution degree is defined as filter paper smoke, and the unit is FSN. It is stipulated that the FSM value of all-white filter paper is 0, and the FSM value of all-black filter paper is 10, which is uniformly graded from 0- 10.
The filter paper method is reliable for measuring smoke under steady-state working conditions, but when it is used for continuous measurement of soot under variable working conditions, the accuracy of the measurement results is affected by the quality of filter paper, and blue smoke and white smoke cannot be measured. From the above indicators, the measurement accuracy of this instrument is not high.
B. Principle of opaque opacimeter
The opaque opacimeter adopts the principle of opaque optics, so that the incident light with a certain luminous flux passes through a certain length of smoke column to be measured, and the emission degree of visible pollutants is evaluated by the intensity of transmitted light received by the optical receiver.
Because the accuracy of the measurement results of filter paper smoke meter is affected by the quality of filter paper; Opaque smoke meter can not only measure continuously, but also measure moisture and smoke in waste gas. Therefore, in order to make China's emission regulations in line with international standards, the concept of opacity has been introduced into the emission standards implemented since 2000. ventilator
Measuring principle of opaque smoke meter
The higher the concentration of smoke and steam in the waste gas, the greater the attenuation of light energy when light passes through the measuring chamber, and the weaker the electrical signal converted by the photoelectric converter.
C, measuring the concentration and average particle size of smoke and dust by scattering method.
Opaque opacimeter uses the principle of opaque optics to measure the total smoke density in diesel engine emissions. In fact, the energy received by the detector is not only related to the concentration of particles discharged, but also related to the average particle size.
Five, automobile positioning detection technology and its development
Due to the increase of vehicle speed, the influence of handling stability on vehicle safety is becoming more and more important. Vehicle handling stability is mainly determined by vehicle positioning parameters. Automobile positioning parameters include: front wheel positioning parameters (toe-in, caster, caster, front axle caster, steering angle, etc.). ) and rear wheel positioning parameters (toe-in, caster angle, rear axle retreat angle, propulsion angle, etc. ). Cars not only have front wheel alignment parameters, but also some luxury cars and luxury cars have rear wheel alignment parameters. The error of these positioning parameters will seriously affect the handling performance of the car. For example, if the caster angle of the kingpin is too large and the steering is heavy, and the caster angle of the kingpin is too small, it will easily cause the front wheel to shimmy, the steering wheel will be unstable, and the automatic righting ability of the steering wheel will become worse. When the caster angle deviation of the left and right kingpins is too large, it will cause driving deviation, and when the toe-in of the rear wheel is incorrect, it will not only cause driving deviation, but also cause abnormal tire wear.
1, classification of locators
Locator is a kind of equipment for measuring automobile positioning parameters. The equipment for detecting front wheel alignment parameters is called front wheel alignment instrument. The handling performance of the car is not only related to the front wheel, but also related to the positioning parameters of the rear wheel. The equipment for detecting the alignment parameters of the front and rear wheels is called a four-wheel alignment instrument.
With the development of electronic technology, the measurement mode, data processing and data transmission mode of four-wheel alignment instrument are constantly changing, but their basic measurement principles are basically the same.
1. 1 according to the order of appearance.
A. toe-in ruler;
B. optical level;
C. stay wire locator;
D. computer four-wheel locator for cable drawing
E. optical computer four-wheel locator
1.2 according to the measurement data transmission technology
Wired Locator: The sensor transmits the measured data to the host through cable, which is characterized by reliable transmission and low cost. Infrared wireless locator: transmit the sensor measurement data to the host computer by infrared communication technology. Compared with wired mode, its main feature is more convenient operation. However, due to the directionality of infrared transmission, special care should be taken during installation and use.
High-frequency wireless locator: transmit the sensor measurement data to the host computer through high-frequency radio communication technology. It has the advantages of non-directional transmission, long distance and little influence by obstacles, and its main disadvantage is high cost.
2. The development history of four-wheel alignment.
The early positioning measuring tools were composed of toe-in, camber and caster measuring devices. The toe-in meter measures the toe-in by measuring the front-rear distance difference between the left and right front wheels. Only the total toe-in value expressed in length unit can be measured, but the parameters such as single-wheel toe-in, retraction angle and propulsion angle cannot be measured, so the measurement accuracy is limited. With the continuous development of automobile technology, its measurement function and accuracy are far from meeting the positioning requirements.
A. an optical level for measuring toe-in by laser technology.
The laser transmitter is installed on two front wheels and two rear wheels of the vehicle to be tested, and the toe-in is measured by reading the position of the laser beam irradiated on the scale. When the current beam is 0, the laser beam irradiates the 0 position of the scale, and when the current beam is not 0, the laser irradiation position moves. This deviation represents the toe-in value of the measured wheel.
B. Pulling wire four-wheel locator
Using pull wire instead of laser to measure toe-in further strengthens the measurement function of the device, and improves the automation of measurement because of the control of microcomputer such as single chip microcomputer. The display screen adopts LED, which is more intuitive and convenient. Some of them are controlled and displayed by computer, and the positioning data of various models are stored in the computer and compared with the measured results. The core of the cable locator toe-in measurement principle is the rotary potentiometer for measuring the rotation angle (some use Hall sensor or photoelectric encoder or resolver to measure the rotation position), which is used to measure the deflection angle of the cable.
The early cable locator only had two heads, and it was necessary to measure four wheels of the whole vehicle twice. Measure the two front wheels first, and then measure the two rear wheels. Later, there were four pan/tilt platforms, which could measure the positioning parameters of four wheels at the same time. The main disadvantages of cable locator are complicated operation and low measurement accuracy.
C. optical computer four-wheel locator.
Whether it is a laser four-wheel locator or an infrared four-wheel locator, although their measuring sensors are different, the final measurement object is the deflection angle of light (laser infrared). The computer laser four-wheel locator calculates the deflection angle of the laser by measuring the position information of the laser on the sensor receiver, so as to obtain the toe-in measurement data, and the CCD infrared sensor calculates and measures the horizontal coordinates of the infrared light source in the CCD field of view by measuring the imaging information of the area CCD, so as to calculate the deflection angle of the infrared light.
With the continuous development of electronic technology and the continuous decline of personal computer price, a computer four-wheel locator is developed by combining computer technology and optical measurement technology. The invention greatly enriches the functions of the four-wheel locator and simplifies the operation of the four-wheel locator. The computer four-wheel aligner stores the positioning data of various vehicles, compares the measured data with the technical specifications, guides the operators to adjust the vehicles, and helps the operators to use, store and print the measured data. At present, there are many kinds of computer four-wheel aligners on the market, but the performance and quality are very different, and the prices are also very different. The key lies in the type and quality of sensor elements and sensor data processing technology, which have an important influence on the measurement accuracy, response speed, reliability and stability of four-wheel positioning equipment. Some high-end four-wheel aligners have adopted DSP technology.
3. Data transmission technology of computer four-wheel alignment instrument.
The measured data of the sensor head need to be transmitted to the upper computer for processing and display. At present, the main methods are as follows:
A. wired mode
The measured data of the sensor is transmitted to the host computer through the cable. There are many technologies that can be used for wired data transmission, and which technology is adopted mainly depends on factors such as cost performance.
B. Infrared wireless transmission technology
Infrared wireless transmission technology is to modulate the data to be transmitted and send it out through infrared carrier. The infrared receiver will demodulate the modulated infrared signal and recover the transmitted data. Because infrared ray is directional, so is its propagation, which has some disadvantages, such as being unstoppable and not far away. Its main features are simple process and low cost.
C. high-frequency radio transmission technology
The data to be transmitted is modulated and sent to the surrounding space with high-frequency radio waves as carriers. It uses ordinary radio frequency bands. Compared with infrared transmission, radio transmission has the advantages of long transmission distance and weak directivity. Its main disadvantage is high cost.
4.3-dimensional locator
The measuring device of the three-dimensional image locator consists of a high-resolution CCD camera and a reflecting plate. Each wheel is equipped with a reflector with a specific reflection point. Because of the focal length of CCD, each mirror must correspond to a CCD with a corresponding focal length. An image acquisition card should be installed in the computer, and the computer should also obtain the height information of the elevator when it is used, so as to get the correct calculation results.
The computer first lifts the car to a specified height, and then gates each CCD one by one in time order to collect the image information sent by the CCD. The computer calculates each positioning angle according to the collected graphic information. Its measuring principle is to calculate the two-dimensional angular coordinates of each mirror (corresponding to toe-in and camber), the coordinates of the mirror center in CCD and the distance to the corresponding CCD. The coordinates of the four CCDs in the selected three-dimensional coordinate system are fixed and known, so that the coordinates of the center of each mirror in this coordinate system can be obtained. Thus, the relative position of each mirror can be obtained, and the parameters of each wheel of the vehicle, such as toe-in, camber, retraction angle and so on, can be obtained. The measurement of kingpin parameters is similar to that of other locators.
The measuring part of the three-dimensional image locator adopts a high-resolution area array image sensor (area array CCD or digital camera), but the original head is replaced by a mirror, and there are reflection spots arranged according to certain rules on the mirror. Observe the mirror with an image sensor, and calculate the position parameters of each wheel according to the position and size of the reflecting point. As shown in the figure, if the wheel tilts outward, the mirror rotates around the central axis of the field of view in the field of view of CCD, and the up, down, left and right positions of each reflected spot change.
When the front beam emission changes, the reflector will rotate around the Y axis by a certain angle. At this point, the original circular reflection spot in CCD camera will become oval. According to the shape change of ellipse, toe-in can be calculated.
Because the measurement distance cannot be completely equal to the focus distance before adjustment, the image is not clear and the accuracy calculation will be discounted. Therefore, this kind of positioner needs to push the vehicle back and forth slightly for a certain distance to obtain multiple measurements of different postures.
The main problem of locator is accuracy. Because the focal length of different types of CCD and the actual distance from the mirror to the CCD may be far apart, focusing becomes the biggest obstacle to the measurement accuracy. In addition, due to the high cost of this kind of CCD, designers also hope to use only one CCD on each side, and the focal length problem is more prominent. If autofocus is used, but the focused imaging object is not ideal, autofocus itself also brings measurement errors. Choosing a higher resolution CCD is also difficult to solve the fundamental problem. Therefore, this locator is not suitable for ordinary users at present.
Sixth, headlight test
Car headlights is mainly used for driving lighting at night or in dark, rainy and foggy days. Its brightness and lighting direction are very important for driving safety. At night, when all the headlights of the car are illuminated at the same time, the lamps should have the performance of enabling the driver to see clearly the traffic obstacles within the distance of 100 meters ahead, and the illumination beam should be aimed at the direction of the car, and the main optical axis direction should be low. If the luminous intensity of the headlights is insufficient or the irradiation direction is not suitable, you can't see the situation in front of the car clearly. However, if the luminous intensity is too strong or the irradiation direction is too high, the oncoming driver in the car will feel dazzled and hinder the driver from making a correct judgment. These are all important causes of traffic accidents. In order to reduce traffic accidents and ensure traffic safety, the headlights must be adjusted correctly before the car leaves the factory. Car headlights inspection must be regular and institutionalized. Therefore, the state has published the Technical Scheme for the Use and Beam Adjustment of Motor Vehicle Headlights (GB7454-87) and the Light Distribution Performance of Motor Vehicle Headlights (GB4599-84), which set clear requirements for the luminous intensity and irradiation direction of motor vehicle high beam and low beam. Especially after China's entry into WTO, this requirement will be gradually strengthened in order to be in line with international standards.
The inspection of headlamps in China is becoming more and more strict, and the inspection requirements of high beam lamps will change to low beam lamps. Therefore, automobile inspection stations and automobile production enterprises urgently need to be equipped with instruments that can detect low beam and low beam.
Due to the gradual improvement of national laws and regulations, headlamp detector has experienced a process from high beam measurement to far and near beam measurement. In the early days, a single high beam measuring instrument made extensive use of the symmetry of the high beam and used symmetrical photovoltaic cell arrangement to measure the optical axis center of the high beam. With the national standard beginning to emphasize the importance of low beam detection, many instruments with low beam detection function have appeared at present. The main content of lighting equipment in this paper is to measure far and near light.
1. Light distribution characteristics of headlamps
Typical headlamp low beam light distribution is characterized by an obvious cut-off line, with a dark area at the upper left of the cut-off line, a bright area at the lower right of the cut-off line, and the area with the strongest light intensity at the lower right of the cut-off line.
3. Classification of headlamp measurement principle
At present, most of the testers produced by various manufacturers of headlamp testing equipment adopt five measuring methods:
(1) The method of combining CCD and photocell is adopted. Measure the high beam with photocell and the low beam with CCD. This method is improved from the original high beam measuring instrument.
(2) Full CCD is used to measure the position, angle and light intensity of the high beam.
(3) The angle of far and near light is measured with high resolution of CCD imaging, and the intensity of high beam is measured with photoelectric tube with large dynamic range.
(4) Adopt the method of full photovoltaic cell. Scan the low beam with a photocell to obtain a plane image for low beam analysis. ;
(5) Position the instrument by hand, observe the deflection angle by visual inspection, and measure the light intensity by photoelectric cell;
CCD method has advantages in angle measurement, and has high accuracy and repeatability in measuring the light type of high beam and multiple groups of symmetrical points that do not meet the standard. If the light type should be ensured in the production of lamps, its advantages are not obvious. Similarly, due to the limitation of the production process of CCD itself, the dynamic range of its devices is small. At present, the dynamic range of domestic devices is only a few hundred. In order to avoid the disadvantage of easy saturation, nonlinear correction is often carried out. If corrected, it is not competent for light intensity measurement. The dynamic range of foreign high-end products is only two or three thousand, but the price is quite expensive. Because the light intensity range of headlights changes greatly, photocell is better than CCD; In light intensity measurement;
4. The main problems of lighting detection at present.
In light detection, the biggest problem at present is that the measured data is caused by the deviation of vehicle parking direction, and the current instruments can not identify whether the measured data is caused by the deviation of vehicle lighting direction or the overall deviation of the vehicle. According to the national standard, the angle maximum permissible error is 1 ~ 2 degrees, so such a small angle is too demanding for car parking. For headlamp detector, it is urgent to solve this problem so as to make the measurement results accurate.
Seven, automobile road test detection technology
At the stage when automobile testing instruments have not been fully developed, some projects are evaluated by road test. With the development of test instruments, at this stage, measurement can usually be completed conveniently and quickly. At this time, the car is usually at rest. Some testing items are actually testing the dynamic characteristics of automobiles, such as common braking performance and emission testing. At present, the common method is to complete the testing process at a fixed station, which greatly improves the convenience of testing at the initial stage of development. With the improvement of requirements, people want to obtain real dynamic data. There are two ways.
Add artificial load to the car by simulation method, such as measuring exhaust emission by working condition method;
Develop road test equipment so that the expected data can be obtained when the car is driving.
At present, the method of simulating the running state is only an approximation in a sense, and it is difficult to achieve the same effect as the actual situation. Therefore, if conditions permit, carrying out actual road tests and mastering the real operation of motor vehicles can provide important guiding significance for the maintenance and design of measurement.
The roadside monitoring system of tunable infrared laser differential absorption automobile exhaust described in this paper.