Automobile Inspection Technology

Chapter 31 Vehicle Inspection Technology (7)
The dynamic characteristics of the vehicle are usually characterized by the frequency characteristics of the yaw rate of the vehicle.Therefore, the measurement of frequency characteristics becomes an important experiment.This test is to determine the amplitude ratio and phase difference between the output (vehicle yaw rate) and the input when the sine angle input is given to the steering wheel.It is very difficult to measure the frequency characteristics of the car by directly inputting the sinusoidal angular displacement of the steering wheel, because on the one hand, it is difficult to obtain an accurate sinusoidal input, and it is necessary to give the steering wheel a sinusoidal input of different frequencies at several fixed speeds. People are also time consuming.Therefore, the steering wheel angular displacement pulse test is often used to determine the frequency characteristics of the car.When carrying out this kind of test, input a steering wheel angular displacement pulse to a vehicle running at a constant speed, and record the input angular pulse and the output vehicle yaw angular velocity, see Figure 5-40.By obtaining the Fourier transform of input and output, the frequency characteristics can be determined.

1. Experiment method
During the test, the car runs in a (approximately) sinusoidal snaking at a speed of 100km/h, the period of the sinusoidal motion is 5s, and the maximum lateral acceleration is 0.2g.The test was carried out on a windless, level road section.The tested car is equipped with sensors such as steering wheel angle, steering wheel torque, vehicle speed and yaw rate.According to the product of the yaw rate and the vehicle speed, the vehicle can be obtained
The value of the vehicle's lateral acceleration.Figure 5-42 is the original data curve measured in the test.

2. Evaluation of steering wheel force input

index
According to the original data of the test, 5 power curves can be drawn, and 12 evaluation indicators of three aspects, such as steering wheel input, steering wheel force input and steering work, can be obtained from the curves on the graph.The following only introduces five evaluation indexes in terms of force input, which are obtained from the steering wheel torque-vehicle lateral acceleration curve, see Figure 5-5.The steering wheel torque-vehicle lateral acceleration curve is equivalent to the steering wheel force characteristic given by Motorfan magazine.

(1) The lateral acceleration of the vehicle when the steering wheel torque is 0
It characterizes the return performance of the car.In order to understand the meaning of this indicator, it can be imagined that the steering wheel of the car is moving in a curve before it finally returns to the straight-line driving position. If the steering wheel is released, the steering wheel will not return to the straight-line driving position and will be "stuck" somewhere.Obviously, the torque of the steering wheel is 0 at this time, but the car is still moving in a large radius curve, and the car has a certain lateral acceleration. The smaller the acceleration, the better the car's returning performance.The lateral acceleration when the torque is zero obtained in the center position test of the steering wheel is similar to this, but it is also affected by system damping and vehicle response lag.This evaluation indicator should not be too large or too small.

(2) The steering wheel torque at 0g represents the Coulomb dry friction in the steering system, but it is also affected by hydraulic damping and vehicle phase lag.

(3) Steering wheel torque gradient at 0g

It is the rate of change of the steering wheel torque at 0g with the lateral acceleration of the vehicle, which characterizes the "road feel". It is mainly affected by the geometric parameters of the kingpin and the total transmission ratio of the steering system.On cars with power steering, the stiffness of the torsion bar in the steering valve, the design of the rotary valve, and the friction in the steering system all affect its value.

(4) Steering wheel torque at 0.1g

It represents the size of the steering wheel force.

(5) Steering wheel torque gradient at 0.1g

It is the rate of change of the steering wheel torque at 0.1g with the lateral acceleration of the car, which characterizes the "road feel" when you just leave the straight-line driving situation.For cars equipped with power steering gear, the steering wheel torque and torque gradient at 0.1g are much smaller than those of ordinary (manual) steering gear.

See Table 5-17 for the evaluation index values ​​of vehicle input.

(Section [-]) Detection of Vehicle Emission Pollutants

As the number of automobiles in our country continues to increase, the environmental pollution caused by automobiles is becoming more and more serious.Detecting and controlling pollutants and noise levels emitted by automobiles is of great significance for protecting the living environment of human beings.At the same time, the composition and concentration of pollutants discharged from automobile engines are closely related to the technical status of the engine, so the technical status of the engine can be evaluated by detecting the exhaust pollutants of the engine, especially the technical status of the fuel supply system and ignition system .

[-]. Composition and hazards of pollutants emitted by automobiles
The pollutants emitted by automobiles mainly include: CO (carbon dioxide), HC (hydrocarbons), Ni (nitrogen oxides), particulates (composed of soot, lead oxides and other metal oxides and soot) and sulfide things etc.The pollutants are discharged through the exhaust pipe of the automobile engine, the crankcase and the fuel supply system, which are respectively called exhaust pollutants, crankcase pollutants and fuel evaporation pollutants.

1. Carbon monoxide C0
CO is the product of incomplete combustion of fuel. When the engine mixture is too rich or the combustion quality is poor, CO is easily generated and discharged from the engine exhaust pipe.Especially when the engine is idling, the mixed gas supply is relatively rich, the gas pressure and temperature in the engine working cycle are not high, the combustion speed slows down, and the concentration of CO generated by incomplete combustion increases; the engine supplies a richer mixed gas during acceleration , or when the supplementary combustion increases due to excessive ignition delay, the emission of C0 will increase.

2. Hydrocarbon HC
HC in the exhaust gas is a gas produced by the decomposition of unburned fuel in the engine.Among the pollutants emitted by automobiles, 20%-25% of HC comes from blow-by gas in the crankcase; 20% comes from the evaporation of fuel in the carburetor and fuel tank; the rest is discharged from the engine exhaust pipe.The HC content in the exhaust gas from the engine will increase when the engine is cold started or the mixture is rich under idling conditions, and the combustion temperature is too low or the atomization of the carburetor is poor.

3. Nitrogen oxides N0i
N01是空气中的N2与02在高温高压条件下反应而成的。汽车发动机所排出废气的N01主要由N0(-氧化氮）和N02(二氧化氮）构成。汽油机排出的氮氧化物中，N0占99%，而柴油机排出的氮氧化物中N02的比例稍大。发动机的负荷和压缩比越高，发动机的燃烧温度越高，燃烧终了汽缸内的压力越高，生成N0i的条件越充分。

4. Particulate matter

The floating particles discharged from the gasoline engine mainly include: lead compounds, sulfates, and low molecular substances.When a gasoline engine uses leaded gasoline, lead compounds in the combustion exhaust gas will be discharged from the exhaust pipe in the form of particles; diesel engines emit 30-60 times more particles than gasoline engines, mainly carbonaceous substances (soot) and high molecular weight organic matter (Oxidation and cracking products of lubricating oils).Soot is a product of incomplete combustion of diesel engines, mainly composed of porous carbon particles with a diameter of 0.1-1.0m.When the car starts, accelerates, and goes uphill, the carbon smoke emission increases because the mixture is too thick; or when the diesel spray quality is not high and the atomization is poor, the carbon smoke emission will also increase.

5. Chemicals

The sulfur compounds emitted by the engine are mainly S02 (sulfur dioxide), which is formed by the reaction of the sulfur contained in the fuel used and the oxygen in the air.

[-]. Standards and testing of exhaust pollutants from gasoline vehicles

1. Testing Standards for Exhaust Pollutants from Gasoline Vehicles

my country promulgated the Environmental Protection Law in 1979, and in 1984 implemented the national standards for vehicle pollutant emission standards and measurement methods.Afterwards, several national emission standards were formulated successively, and the above-mentioned emission standards were revised in 1993, strictly regulating the limits of diagnostic parameters and measurement methods.

国家标准GB14761-2001《汽车排放污染物限值及测试方法》等效采用了联合国欧洲经济委员会(ECE)1995年7月2日生效的ECER83/02《按发动机对燃料的要求类别就污染排放物对车辆认证的规则》的全部技术内容，采用了国际通用的试验方法，在控制力度上达到欧洲20世纪90年代初的水平。

The national standard GB18285-2000 "Limits and Test Methods of Exhaust Pollutants of Exhaust Vehicles in Use" has accelerated simulation test limits and test methods, which refer to the US Environmental Protection Agency standard EPA-AA-PSPD-IM-96-2 "Technical Guidelines for Accelerated Simulated Working Conditions Test Procedures, Emission Standards, Quality Control Requirements, and Equipment Technical Requirements" (July 1996), which stipulates that vehicles equipped with spark-ignited engines must conduct idle speed tests, dual- The idling speed test and the acceleration simulation (ASM) test, the provisions of this standard make my country's control of the exhaust pollution of in-use vehicles embark on a more stringent road.

2001年颁布了GB18352.1-2001《轻型汽车污染物排放限值及测量方法（I)》、GB18352.2-2001《轻型汽车污染物排放限值及测量方法（II)》，本标准等效采用和参照欧盟(EU)的有关最新标准。规定了轻型车辆冷启动后排气排放污染物排放限值、点燃式发动机曲轴承箱污染物排放限值、点燃式发动机燃油蒸发排放污染物排放限值及车辆排放控制装置的耐久性等要求。

按照国家标准GB18285-2000《在用汽车排气污染物限值及测试方法》的规定，对于装配点燃式四冲程发动机，最大总质量大于或等于400kg，最大设计车速大于或等于50km/h的在用汽车，排气污染物限值见表5-18、表5-19。

2. Detection of gasoline vehicle exhaust pollutants

The non-dispersive infrared analyzer (NDIR) is used for the detection of exhaust pollutants from gasoline vehicles, and the detection conditions and detection procedures are specified.

(1) Basic detection principle

Gases such as 03"0:￡工02 in automobile exhaust have the property of absorbing a certain wavelength of infrared rays, and there is a certain relationship between the degree of infrared rays absorbed and the concentration of exhaust gas, as shown in Figure 5-44. No spectroscopic The infrared analyzer method is based on this principle, which is to detect the content of various pollutants in the exhaust gas according to the change of the exhaust gas absorbing a certain wavelength of infrared energy. In the case of various gases mixed together, this detection method has the measurement value. characteristics of the impact.

The analyzer made by non-spectral infrared analysis method can be made into a single analyzer that can detect CO or HC content alone, or can be made into a comprehensive analyzer that can measure the content of these two gases.The CO concentration in the exhaust is directly measured, but the HC components in the exhaust are very complex, so the concentration of various HC components should be converted into the concentration of n-hexane (C0H0) and then used as the measured value of the CO concentration.

(2) The structure and working principle of the non-dispersive infrared gas analyzer

It is an instrument that can collect gas samples from automobile exhaust pipes and continuously measure the concentrations of CO and HC contained in them.Figure 0-5 shows the external structure of the analyzer.It consists of an exhaust gas sampling device, an exhaust gas analysis device, an exhaust gas concentration indicating device, and a calibration device.

①Exhaust gas sampling device.The exhaust gas sampling device is composed of a sampling probe, a filter, a conduit, a water separator and a pump.It collects exhaust gas from vehicle exhaust pipes through sampling probes, conduits and pumps, and then uses filters and water separators to remove carbon residue, dust and moisture in the exhaust gas, and only sends the exhaust gas to the analysis device.

②Exhaust gas analysis device.The exhaust gas analysis device is composed of an infrared light source, a gas sample chamber, a rotating fan wheel (light chopper), a measurement chamber and sensors.According to the non-spectral infrared analysis method, the device measures the concentration of CO and HC from the exhaust gas mixed with various components from the sampling device, and sends them to the exhaust gas concentration indicating device in the form of electrical signals.According to different sensor forms, exhaust gas analysis devices can be divided into different forms such as capacitor microphone type and semiconductor type.

③Exhaust gas concentration indicating device.The concentration indicating device of the comprehensive gas analyzer is mainly composed of a C0 indicating device and an HC indicating device, and there are two types of pointer meters and digital displays.From the electrical signal from the exhaust gas analysis device, the CO concentration on the CO indicator instrument is expressed in volume percent (%); on the HC indicator instrument, the HC concentration is expressed in million percent (0-0) of the normal hexane equivalent volume.

Pointer instruments, as shown in Figure 5-46, can be controlled by zero adjustment knobs 2 and 7, standard adjustment knob 1, and C0 reading shift switch 4.In addition, the flow meter designed at one end of the air flow channel can also be used to know whether there are abnormal conditions such as dirty filters in the exhaust gas channel.

④ Calibration device.The calibration device is a device to maintain the indication accuracy of the analyzer so that it can accurately indicate the measured value.In this device, there are often not only devices for calibration by adding standard gas samples, but also devices for simple calibration by mechanical means.

a. Standard gas sample calibration setting: the standard gas samples (C0 and HC) attached to the analyzer manufacturer for calibration are sent directly to the exhaust gas analysis device from the dedicated standard gas sample injection port on the analyzer, and then compared A device for calibration by means of standard gas sample concentration values ​​and instrument indication values.

b. Simple calibration device: It is usually a device that uses a shading plate to block part of the infrared rays passing through the gas sample chamber in the exhaust gas analysis device, and performs simple calibration by reducing a certain amount of infrared energy.

(3) Detection method of gasoline vehicle pollutants

① Prepare the instrument, do various inspections according to the requirements of the instrument manual; connect the power supply, and preheat the gas analyzer for more than 30 minutes.

② Instrument calibration, including standard gas sample calibration and simple calibration.

a. Calibration of standard gas sample: let the analyzer inhale clean air first, adjust the pointer of the meter to zero point with the zero point adjustment knob; Adjust to the standard indicated value.Note: When filling the standard gas sample, turn off the pump switch on the analyzer.

The standard value of CO calibration is the CO concentration value marked on the standard gas sample bottle; the standard value of HC calibration, since propane is used as the standard sample, the conversion of n-hexane must be calculated as the standard value of calibration according to the following formula.

Calibrated standard value (i.e. converted from n-hexane) = standard gas sample (propane) concentration X conversion factor
In the formula, the standard gas sample (propane) concentration is the concentration value marked on the standard gas sample bottle; the conversion factor is the value given by the gas analyzer, generally 0.472-0.578.

b. Simple calibration: first turn on the simple calibration switch. For instruments with standard scale lines, use the standard adjustment knob to adjust the meter pointer to the position facing the standard scale lines; Carry out simple calibration immediately after calibration, so that the pointer of the meter coincides with the indicated value after calibration of the standard gas sample.

Install the sampling probe and sampling conduit to the analyzer. If the pointer of the meter exceeds zero, it indicates that there is more HC adsorbed on the inner wall of the conduit. It is necessary to clean the sampling probe and conduit with compressed air or cloth strips.

③Preparation of the vehicle or engine under inspection:

——The air intake system should be equipped with an air filter, and the exhaust system should be equipped with an exhaust muffler, and there must be no leakage.

——Gasoline should meet the relevant national standards.

——The temperature of engine coolant and lubricating oil should reach the thermal state stipulated in the instruction manual of the vehicle during measurement.

——Gasoline engines newly produced since July 1995, 7 shall have an idle screw limiting device.The ignition advance angle should meet the requirements of emission standards within its adjustable range.

④ Idle speed measurement procedure:
——If necessary, install test instruments such as tachometer, ignition timing instrument, coolant and lubricating oil temperature gauge on the engine. ——The engine accelerates from idling speed to 70% of rated speed, maintains it for 60s, and then drops to idling state.

After the engine drops to idle speed, insert the sampling probe into the exhaust pipe to a depth equal to 400mm, and fix it on the exhaust - first turn the CO reading gear switch of the indicating instrument to the highest range gear, and then watch the indicating instrument,
While using the reading gear changeover switch to select the range gear suitable for the exhaust gas content.The engine starts to read after idling for 15s, read the highest value and the lowest value within 30s, and the average value is the measurement result.

——If there are multiple exhaust pipes, take the arithmetic mean value of the measurement results of each exhaust pipe.

——After the measurement work, pull out the sampling probe from the exhaust pipe, let it inhale fresh air for 5 minutes, and turn off the power after the pointer of the meter returns to zero.

⑤Double idle speed measurement program: The dual idle speed measurement program is similar to the idle speed measurement program.

⑥Acceleration Simulation Condition Method (ASM): Place the vehicle on the chassis dynamometer, and load the vehicle through the dynamometer according to the vehicle's reference mass and test conditions, so that the vehicle is equivalent to 50% of the maximum acceleration.
Run at a constant speed with 25% load, and use five-gas analysis to directly sample and measure the concentration of exhaust pollutants.The operating cycle of the test specification is shown in Figure 5-47.

[-]. Standards and testing of exhaust pollutants from diesel vehicles

1. Testing standards for diesel engine exhaust pollutants

There are three types of smoke emitted by diesel vehicles: black smoke, blue smoke and white smoke. Among them, the black carbon smoke emitted by diesel engines under full load and acceleration conditions is the most common.The degree of darkness of the black smoke is indicated by the exhaust smoke, which is detected by a smoke meter.Smoke meters can be divided into filter paper type, light transmission type, mass type and other forms.

(End of this chapter)