Automobile Inspection Technology

Chapter 26 Vehicle Inspection Technology (2)
In the centralized control system, the analog and switch I/o function boards that the host communicates with the field are generally not directly inserted into the expansion slot of the host itself, but another special expansion box to reduce I/O channel pairings. The possible interference of the host system improves the reliability of the host system, and the host uses an industrial computer.In this kind of control system, the input of vehicle data is completed by the inspection machine and sent to the host, and the switching request signals of each station on the site are directly sent to the host, and the host controls the controlled detection equipment to perform parameter detection according to the preset program. The detected analog signal is sent to the host after being amplified and A/D converted.A single testing device can be displayed by an instrument or not, and the measurement result can be directly displayed by the host.The data acquisition, processing and judgment, display, printing, storage and process control of the entire detection system are all completed by the host computer.

The centralized control system is characterized by simple structure and low price, but has the following disadvantages.

① A large number of signal cables are required to send the analog signal from the detection device to the main control computer for digital processing.Analog signals have different properties, including weak current signals, voltage signals, pulse and switching signals, plus environmental interference, so the measurement accuracy is not high.In order to avoid interference in the long-distance transmission of analog quantities, high-quality connecting cables must be used and anti-interference measures must be taken, which increases the difficulty of system anti-interference design and implementation.

②Because the main control computer needs to control all the detection equipment, and also collects sensor signals for data processing, and is also responsible for the management and printing of vehicle information and detection data.The task of the main control machine is too heavy, and it is easy to cause a crash.Once the master computer fails, the entire system will be paralyzed.For inspection stations with relatively busy inspection tasks, it is necessary to back up the software and hardware of the main control system to prevent the entire line from being shut down due to failure of the main control system.

③ The investment in control and management software is relatively large, and the stability of the software is required to be high.Of course, the performance requirements of the main control computer are relatively high.

④ Difficulties in system expansion, upgrade, improvement and station exchange.The core of the design idea of ​​the centralized control system is to use the master computer to perform station division and time-sharing processing through software logic, so as to achieve the purpose of multi-station simultaneous detection and scheduling, thereby reducing hardware links, reducing costs, reducing failure points, and improving system quality. reliability.

(2) Hierarchical distributed control system

Generally, distributed schemes have various structural forms. For systems such as automobile automatic detection lines, hierarchical distribution should be adopted.The hierarchical distributed control system is a structural control system in which a master computer is connected with several slave computers, and generally adopts a two-level or three-level control method.

In the two-level distributed control system (Figure 5-6), the first level is the station control level, which is completed by the station computers distributed on each station. The station computers are mainly responsible for data collection, processing, display, and communication. , on-site monitoring, diagnosis and judgment tasks.The second level is the supervision and management level, with a powerful computer as the host computer, which has the functions of arranging testing procedures, information analysis, system command, full-line scheduling, comprehensive judgment of testing results, centralized printing of testing results and database management.

The working condition of the system control is: when the vehicle needs to be inspected online, the operator inputs the vehicle information such as the license plate number, vehicle unit, and chassis number on the keyboard of the inspection machine at the entrance of the inspection line.When declaring the inspection items, the inspection machine notifies the host computer or related station computers through serial communication, and the host computer generates inspection commands and sends them to each station computer according to the transmitted information, and the station computers automatically schedule inspections according to the commands. , through the photoelectric switch to know whether the car is in place, and the driver operates through the indication information on the indication screen.After the detection is completed, the station computer will transmit the detection results of this station to the host, and the host will analyze and judge the data of each station, give the overall result, and print the report.

The hierarchical distributed control system can effectively improve the reliability, accuracy and ease of use of the detection system due to the adoption of distributed control, stand-alone display, multi-level management, and data communication measures.When the main engine fails, each station can complete the detection control, display and printing work of each station, which can prevent the detection system from being completely paralyzed.Since the distributed control station is close to the detection equipment, there are relatively few interference signal strings, and the signal transmission between the station and the host uses data communication, which can avoid the inconsistency between the display of the station and the print data of the host, thus improving the detection accuracy. high.Since each workstation has a single task, it is more convenient for equipment calibration and maintenance, and it is also easy to establish a backup machine to improve the effectiveness of the system.

Since the performance of the hierarchical distributed control system is much better than that of the centralized control system, the automatic detection lines of automobile inspection stations widely adopt the hierarchical distributed computer control method, but due to the low cost of the centralized control system, some automatic detection lines Still choose centralized control mode.

(Section [-]) Automobile dynamic testing

Vehicle dynamic testing is divided into bench testing and road test testing.Some indicators that reflect the dynamic performance of the car can be tested separately, such as the output power of the driving wheel, driving force, sliding distance, maximum speed, acceleration ability, climbing ability, transmission system efficiency, etc.

[-]. Automobile dynamic test bench

Automobile output power detection, also known as chassis dynamometer, refers to the detection of the output power of the driving wheel of the automobile.The chassis dynamometer is carried out on a drum-type chassis dynamometer test bench, which is usually called a chassis dynamometer test bench or a chassis dynamometer, which is a comprehensive performance diagnostic device for automobile chassis.

1. Structural principle of chassis dynamometer test bench
Chassis dynamometer test bench generally consists of four parts: roller device, power absorbing device (ie loading device), measuring device and auxiliary device.Figure 5-7 shows the structure of the mechanical part of the domestic DCG-10C automobile chassis dynamometer test bench

picture.The test bench is a kind of single-chip microcomputer produced by American Intel Corporation as the control core of the system, which is suitable for the drum type test bench with the shaft mass not greater than 10t and the output power of the driving wheel not greater than 150kW.

(1) Drum device
The roller is equivalent to a continuously moving road surface on which the wheels of the inspected car roll.The drum can be divided into single drum and double drum, as shown in Figure 5-8.

(a) Single wheel and single drum type (c) Single wheel and double drum type
①Single roller test bench.The rollers supporting the driving wheels on both sides of the car are each a single test stand, called a single-roller test stand.The diameter of the roller of the single-roller test bench is generally larger, and the contact between the wheel and the roller is closer to the actual situation of its contact with the road surface, so that the slip rate between the tire and the roller is small, and the rolling resistance is small, so the test accuracy is high.However, the manufacture, installation and testing of this kind of test bench are relatively complicated, and the cost is high, so it is not suitable for productive tests such as automobile maintenance enterprises and automobile inspection stations.

②Double roller test bench.The rollers that support the driving wheels on both sides of the car are two test stands, called double-roller test stands.The roller diameter of the double-roller test bench is small, and the contact between the wheel and the roller is different from that on the road surface, resulting in an increase in the slip rate.
Large, the rolling resistance increases, the rolling loss increases, so the test accuracy is low.However, this kind of test bench has simple structure, convenient installation and use, and low cost, so it is suitable for automobile manufacturing units, maintenance companies and traffic management departments, especially the single-wheel double-drum test bench is more widely used.

The shape of the roller surface is different, and there are various forms of smooth rollers, knurled rollers, grooved rollers and coated rollers.The smooth roller is currently the most widely used. For the smooth roller with double rollers, due to the increase in the specific pressure of the wheel to the roller, although the adhesion coefficient is low, the adhesion between the wheel and the smooth roller can generate sufficient traction.The coated roller is made by coating the surface of the smooth roller with a friction layer material that is close to the actual road conditions, which can increase the adhesion and is a form with broad application prospects.Knurled rollers and grooved rollers are rarely used because the slip rate cannot be kept constant during use.

(2) Power absorption device
When the car is tested on the chassis test bench, the power absorbing device on the test bench is used to simulate various resistances that the vehicle suffers when driving on the road, so that the force of the car on the test bench is basically the same as that on the road.The power absorption device is used to absorb and measure the power and traction force transmitted from the car engine to the drive wheel through the transmission system. Commonly used power absorption devices include hydraulic dynamometers, DC generator electric dynamometers and eddy current dynamometers.

① Hydraulic dynamometer.Water is used as the braking medium, and the water acts as a link between the rotor and the stator of the dynamometer to form a braking torque.By adjusting the amount of water entering and leaving, different braking powers can be obtained.When the water flow rate is constant, the braking torque of the dynamometer increases with the increase of the rotor speed.This dynamometer has low precision.

②Power dynamometer.The electric dynamometer is also called a balance generator. When it is used as a load, it absorbs power, and its function is equivalent to a DC generator; but the electric dynamometer can also be used to drive machinery. At this time, it outputs power, and its power is equivalent to DC generator.The driving resistance and inertial force of the car can be well simulated by using the electronically controlled electric dynamometer.Thus, it greatly expands the usefulness of the chassis dynamometer test bench.The manufacturing cost of electric dynamometer is relatively high, and it is often used by general scientific research institutes.

③ Eddy current dynamometer.The drum-type chassis dynamometer test benches used by automobile inspection stations and automobile maintenance enterprises mostly use eddy current dynamometers, as shown in Figure 5-9.The eddy current dynamometer has the advantages of high measurement accuracy, small vibration, simple structure and easy regulation, and has a wide range of speed and power.

The stator of the eddy current dynamometer has an excitation coil and an eddy current ring arranged along the circumference inside, and the rotor rotates in the excitation coil and the eddy current ring.The outer circle of the rotor is processed or inlaid with evenly distributed teeth and grooves similar to the cylindrical gear, and there is a certain air gap between the tooth top and the vortex ring.

When the excitation coil is supplied with direct current, a magnetic field is formed around it, and the magnetic field lines generated by the magnetic field pass through the rotor, air gap, flow ring and stator to form a closed magnetic circuit.Since the teeth and slots on the outer circle of the rotor are evenly distributed, the air gaps around the rotor are also uniformly distributed in alternate sizes, and the passing magnetic force lines are also alternately dense.When the rotor rotates, these lines of magnetic force that alternate with density also rotate synchronously.

Since the magnetic flux passing through any point on the eddy current ring changes periodically, an eddy current is induced on the eddy current ring.This eddy current interacts with the magnetic field that generates it to create a braking torque on the rotor, whereby the dynamometer absorbs the output power that drives the wheels.As long as the magnitude of the excitation current is adjusted, the range of the braking torque (that is, the absorbed power) can be changed.The eddy current dynamometer converts the eddy current generated by the absorbed power into heat energy, so the temperature of the eddy current ring is high and needs to be cooled, so the eddy current dynamometer is divided into air-cooled and water-cooled according to the cooling method Two categories.

(3) Measuring device
Because the dynamometer cannot directly measure the output power value of the driving wheel of the car, it needs to measure the rotational speed and torque during rotary motion, or the speed and traction force during linear motion, and then convert it into its power value.Therefore, the chassis dynamometer test bench must be equipped with a force measuring device and a speed measuring device.

① force measuring device.The device measures the drive force generated by the drive wheels.The torque formed by the driving force exerted by the driving wheel on the drum is transmitted to the swingable stator by the braking action between the stator and the rotor of the dynamometer, and the stator is transmitted through a force measuring lever 2 of a certain length (Fig. 5-7). To the force measuring device, and then displayed by the indicating device.

There are three types of force measuring devices: mechanical, hydraulic and electric measuring. At present, the electric measuring type is more widely used.The electric force measuring device generally installs a force sensor 3 (Fig. 5-7) at the outer end of the force measuring lever, and converts the force transmitted by the force measuring lever into an electrical signal, which is processed and then sent to the indicating device for display.

② Speed ​​measuring device.The chassis dynamometer test bench needs to test the speed of the vehicle when performing tests such as dynamometer, acceleration, constant speed, coasting and fuel economy, so it must be equipped with a speed measuring device.Most of the speed measuring devices are electric measuring type, generally composed of a speed sensor 6 (Figure 5-7), an intermediate processing device and an indicating device.Common speed sensors include magnetoelectric, photosensitive, and tachometer generators. They are installed at one end of the driven drum and rotate with the drum to convert the rotation of the drum into electrical signals.The indicating device matched with the tachogenerator is a voltmeter, and the dial of the voltmeter is calibrated with "km/h".

③ Power indicating device.If the force measuring device is an electric measuring type, the indicating device can directly indicate the output power of the driving wheel.Especially in the computer-controlled chassis dynamometer test bench, the electrical signals output by the load cell and the speed sensor are sent to people for calculation and processing, and the output power of the driving wheel can be directly displayed on the indicating device.

The force measuring device is a mechanical and hydraulic test bench, and its indicating device can only indicate the driving force of the driving wheel. The output power Pfe of the driving wheel should be based on the relationship between the measured driving force and the corresponding test vehicle speed:
k is (kW) where F is the driving force of the driving wheel (N); v is the test vehicle speed (km/h).

(4) Auxiliary device
① Flywheel device.Some chassis dynamometer test benches are also equipped with a flywheel device.The flywheel is supported on the frame of the chassis dynamometer test bench by rolling bearings, and is connected with the main drum through a clutch.The chassis dynamometer test bench with a flywheel is called an inertial chassis dynamometer test bench, which can simulate the rotational inertia of the car and conduct performance tests such as acceleration performance and sliding performance.The quality of the flywheel is generally selected according to the quality of the car under test.

②Lifting device.In order to facilitate the entry and exit of the vehicle into the chassis dynamometer test bench, a lifting device is provided between the driving and driven rollers.The lifting device consists of a lifter and a lifting plate.There are three types of lifts: pneumatic, hydraulic and electric, and pneumatic is the most common.Pneumatic lifters are divided into cylinder type and airbag type. The airbag type has simple structure, easy manufacture and low cost, and has begun to be applied on chassis dynamometer test benches.

③Control device.The control device and indicating device of the chassis dynamometer test bench are often made into one body, forming a cabinet structure and placed in the place where the mechanical part of the chassis dynamometer test bench is easy to operate and observe in front of the left.Figure 5-10 shows the panel diagram of the control cabinet of the domestic CDG-10C chassis dynamometer test bench. The buttons, display windows, knobs, function lights, alarm lights, indicator lights, etc. on the control cabinet are used to control the test process and display test results.The chassis dynamometer test bench with a printer can also print out the measured data or curves.Most chassis dynamometers are also equipped with a cold air device for cooling the engine radiator of the inspected vehicle and a longitudinal restraint device (triangular wood and steel cable chain) to prevent the inspected vehicle from driving out of the roller during the inspection.

2. Bench detection method

Before driving the car on the chassis dynamometer test bench, it must pass the road test run to the normal working temperature, then adjust the engine oil supply system and ignition system to the best working condition, check and fasten the connection of the transmission system and wheels, and check the tire pressure And make it reach the specified value of the automobile factory.

After the vehicle is ready, open the chassis dynamometer test bench. If it is a double-roller test bench, place the driving wheel of the vehicle under test between the two rollers, put down the lifter plate, and use triangular wood to test the driven wheel of the vehicle if necessary. Vertical constraints.

(1) Detection of drive wheel output power or driving force

① Under the rated power of the engine, the output power or driving force of the driving wheels.

When testing the output power and driving force of the driving wheels at the rated engine power and rated speed, put the transmission in the selected gear, then release the hand brake, gradually step on the accelerator pedal, and the engine will gradually accelerate.At the same time, load the engine by gradually increasing the excitation current of the dynamometer test bench until the engine reaches the rated speed and runs stably at this speed when the throttle is fully open.At this point, the output power or drive force of the driving wheel can be read or printed

value of .

②The output power or driving force of the driving wheels at the maximum torque speed of the engine.

After reaching the above test conditions, that is, after the throttle valve is fully opened and the engine speed reaches the rated value, keep the throttle valve fully open, and continue to increase the excitation current to load the engine, the engine speed will drop, and the speed will reach the maximum engine torque. When the operation is stable up to the corresponding speed, read or print the driving power or driving force value of the driving wheel.

It can be seen that if you want to measure the output power or driving force of the driving wheels under different gears of the transmission, you only need to put people in different gears in turn and perform detection according to the above method.When the engine emits rated power, put it in direct gear to measure the maximum output power of the driving wheels; when the engine emits the maximum torque, put it in 1st gear, and then measure the maximum driving force of the driving wheels.

③The output power or driving force of the drive wheels under full engine load and selected vehicle speed.

According to the above method, when the throttle valve is fully open, adjust the excitation current of the dynamometer to make the engine run at the speed corresponding to the selected vehicle speed.After running stably, the output power or driving force of the driving wheels at the speed can be read or printed.

④ The power or driving force of the drive wheels under partial engine load and selected vehicle speed.

The method is the same as item ③, but the throttle valve should not be fully opened, but partially opened, that is, work under partial load. After the engine runs stably at the speed corresponding to the selected vehicle speed, the load and the value can be read or printed. The output power or driving force of the drive wheels at a selected vehicle speed.

(2) Detection of transmission efficiency 0 of automobile drive train

(3) Acceleration time test method

(End of this chapter)