Automobile Inspection Technology

Chapter 28 Vehicle Inspection Technology (4)
b. The loading quality of the test vehicle is the rated loading quality.
.
Record the odometer indication, time, and fuel flow meter reading at the start and end of the ramp test.

d. When climbing a slope, the car should use the highest gear as much as possible to maintain a higher driving speed, record the temperature value every 1km, and record the number of times and time (or mileage) of each gear used during the entire test. , pay attention to observe whether there is any abnormal phenomenon in the engine and transmission system.

If the engine boils (cooling water boils), the engine oil temperature exceeds 105°C, the fuel system produces air resistance, the engine detonates strongly, the transmission system is out of gear, etc., which affect normal driving, the vehicle should be stopped.Do a good job of recording the mileage, driving time and temperature values ​​of each part of the parking point, and record the failure situation in detail.

(Section III) Vehicle Economy Test

There are two ways to test the fuel economy of automobiles, one is indoor bench test, and the other is road test.car inspection station

Due to site conditions, road test methods cannot be used to test the fuel economy of vehicles. Therefore, the fuel economy of vehicles is often tested by simulating road test methods on the chassis dynamometer with reference to relevant regulations.

[-]. Bench testing of automobile economic performance

In addition to the chassis dynamometer, the bench test equipment for automobile fuel economy also needs a fuel consumption meter (or a fuel flow tester).

1. The working principle of commonly used fuel consumption meters
The fuel consumption of the car is measured by the fuel consumption meter.There are many types of fuel consumption meters, which can be divided into volumetric fuel consumption meters, mass fuel consumption meters, flow rate fuel consumption meters and flow rate fuel consumption meters according to test methods.The fuel consumption meter consists of a fuel consumption sensor and a display device.The following mainly introduces the volumetric and mass fuel consumption meters.

(1) Volumetric fuel consumption meter
The working principle of the volumetric fuel consumption meter is to make the measured fluid fill a measuring chamber with a certain capacity. The total amount of the measured fluid can be obtained through the number of times the measuring chamber is filled, and then divided by the measuring time interval or driving mileage to get the average value. fuel consumption.

Figure 5-13 is a working principle diagram of the flow conversion mechanism of the planetary piston type fuel consumption sensor.This device consists of four pistons arranged in a cruciform configuration and a rotating crankshaft for converting a volumetric flow of fuel into rotation of the crankshaft.

Under the action of pump oil pressure, the fuel pushes the pistons to reciprocate, and each of the four pistons reciprocates once, and the crankshaft rotates one revolution to complete an oil intake and discharge cycle.The piston is in the oil inlet stroke or the oil discharge stroke in the cylinder, depending on the position of the piston relative to the oil inlet and outlet.Figure 4-5 shows that the piston 13 is in the oil intake stroke, and the fuel from the sensor crankcase is pushed by P1

Move it down and make the axis rotate clockwise.At this time, the piston 2 is at the end of the oil discharge stroke, the piston 4 is at the oil discharge stroke, the fuel is discharged from the upper part of the piston 4 through the oil discharge port, and the piston 5 is at the end of the oil intake stroke; when the positions of the piston and the crankshaft are as shown in Figure 5- At 13(b), piston 1 is at the end of the fuel intake stroke, piston 2 is at the fuel intake stroke, channel P4 is turned on, piston 4 is at the end of the oil discharge stroke, piston 5 is at the end of the oil discharge stroke, and fuel flows from channel P2 through the oil discharge port E2 discharge.Figure 5-13 and Figure 5-13(d) show the state of oil intake and discharge and the direction of rotation of the crankshaft as shown by the arrows in the figure.In such a cycle, every time the crankshaft rotates once, each cylinder pumps oil once, thereby having the effect of continuously pumping oil with a fixed capacity.The amount of oil pumped for one revolution of the crankshaft is:

It can be seen that, after the conversion by the above-mentioned flow conversion mechanism, the fuel consumption is converted into the number of rotations of the crankshaft of the flow conversion mechanism.Then by the signal conversion device installed at one end of the crankshaft. (Generally, a photoelectric measuring device is used) to convert the signal, and convert the number of rotations of the crankshaft into an electrical pulse signal.

The signal conversion device is composed of active magnets, driven magnets, rotating shafts, gratings, light emitting diodes and photosensitive tubes.The active magnet is installed at the end of the crankshaft, and the driven magnet is installed at the end of the rotating shaft. The two magnets are installed opposite to each other but there is a gap between the magnets. Its function is to form a magnetic coupling; the grating is fixed on the fixed rotating shaft and driven by the rotating shaft to rotate; Light-emitting diodes and photosensitive tubes are fixed on opposite sides of the grating. The photosensitive tube is used to receive the light emitted by the light-emitting diodes. The grating is located between the two, and its function is to convert the continuous light emitted by the light-emitting diodes into light pulses.When the crankshaft rotates, the magnetic coupling drives the rotating shaft and the grating to rotate, and the grating rotates between the light-emitting diode and the photosensitive tube to make the photosensitive tube receive light pulses.Due to the photoelectric effect of the photosensitive tube, the light pulse is converted into calculation processing, and the fuel consumption is displayed on the display device.

The structure and oil circuit of the fuel flow sensor are shown in Figure 5-14.

The weighing pan of the weighing device is equipped with an oil cup 1, and the fuel is added to the oil cup through the solenoid valve 3.The opening and closing of the solenoid valve is controlled by the stroke limiter 8 mounted on the balance weight and toggles two miniature limit switches 6 and 7.The photoelectric sensor is composed of two photodiodes 5, 10 and a light source 9 mounted on a rhombic pointer, and is used to give fuel consumption starting point and end point signals.The photodiode 5 is fixed, and the photodiode 10 is mounted on a movable slider, which moves through a rack and pinion mechanism, and the gear shaft is connected with the drum 12, and the metered fuel is read from the dial by rotating the drum 12.When the metering starts, the light velocity of the light source 9 shoots on the photodiode 5, and the photodiode sends a signal to make the counter 13 start counting, and along with the consumption of fuel in the oil cup, the pointer moves.When the light beam hits the photodiode 10, the photodiode 10 sends a signal to make the counter stop counting.Indicates that the fuel in the oil cup is exhausted.There are two semiconductor counters with digital display on the recorder, one is used to calculate the crankshaft speed of the engine; the other counter records the time.

2. Bench test of vehicle fuel economy
The vehicle fuel economy bench test is completed by using the chassis dynamometer and the fuel consumption meter together.The chassis dynamometer is used to provide active road surfaces and simulate various resistances when the car is running on the road, and the fuel consumption meter is used to measure fuel consumption.Therefore, the accuracy of the fuel economy test results is not only related to the measurement accuracy of the fuel consumption meter, but also depends on whether the chassis dynamometer simulates the driving resistance of the vehicle accurately.

Installation of fuel consumption sensor in fuel pipeline

①The connection of the fuel consumption sensor in the fuel supply pipeline For gasoline vehicles without oil return pipelines, the sensor can be connected in series between the gasoline pump and the carburetor, so that the mouth of the sensor is connected to the outlet of the gasoline pump, and the outlet of the sensor is connected to the outlet of the gasoline pump. carburetor man

The mouth is connected.See Figure 5-16.

There are many oil return pipes on the car. The fuel supply of this kind of automobile gasoline pump is much larger than that of the carburetor, and the excess fuel flows back to the fuel tank through the oil return pipe.At this time, the sensor should be installed to avoid redundant counts caused by oil return.For example: the Santana car returns oil from the oil storage tank, and the sensor should be installed between the oil storage tank and the carburetor.

In the oil supply system of a diesel vehicle, oil return pipelines are all installed, and the oil supply volume of the fuel delivery pump is 3-4 times more than the oil output volume of the fuel injection pump.In order to maintain a certain pressure in the oil chamber of the fuel injection pump, a relief valve is generally installed at the low-pressure oil outlet of the fuel injection pump. A small amount of fuel leaked from the working gap of the injector also flows back to the fuel tank through the oil return pipe.Figure 5-17 shows the connection method of the fuel consumption sensor in the fuel supply pipeline of a diesel vehicle. The fuel consumption sensor is connected to the oil pipeline between the fuel tank and the high-pressure fuel pump, and the oil return pipeline is connected to the oil outlet pipe of the fuel consumption sensor with a tee on the road to prevent fuel from being double-metered by the fuel consumption sensor.

②Elimination of air bubbles in the oil circuit.In order to ensure the accuracy of fuel oil measurement results, after the sensor is connected to the oil supply pipeline, care must be taken to check and remove the air entering the pipeline.Because the air does not exclude the sensor, the volume occupied by the air bubbles will be regarded as the volume of the consumed fuel to calculate the fuel consumption, so that the detection results will be inaccurate.

When removing air bubbles, the sensor can be placed at a lower position, and the oil can be manually pumped, and at the same time, the carburetor oil pipe joint is removed, and the oil is pumped continuously until the pumped oil does not contain air bubbles.If there is an air release screw on the sensor housing, the screw can be loosened to discharge the air in the sensor body.

After installing the fuel consumption sensor in the oil circuit of the diesel vehicle, a manual pump must also be used to pump oil to remove air bubbles in the oil circuit.One of the differences between diesel vehicles and gasoline vehicles is that gasoline vehicles can remove air bubbles after the engine is started, while diesel vehicles must remove air bubbles before starting; Air bubbles, while diesel vehicles still need to remove the air bubbles just generated in the oil circuit after removing the sensor and restoring the oil circuit.

(2) Constant speed [-]km fuel consumption test simulated loading test

中华人民共和国交通行业标准JT/T199一1995《汽车技术等级评定的检测办法》规定了用底盘测功机检测汽车的等速百公里油耗时的测试条件为：汽车的为正常热状态；变速器挂直接挡或最高挡；加载至限定条件并使汽车稳定在试验车速。GB/T12545-1990《汽车燃料消耗量试验方法》规定限定条件下试验车速为：轿车（60士2)km/h，铰接式客车（35士2)km/h，其他车辆(50士2)km/h。

When testing the fuel consumption of a car at a constant speed of [-] kilometers on the bench, it is extremely important to reasonably determine the load of the dynamometer to simulate the resistance that the car will encounter when it is running at a specified speed on a straight road above m level.At this time, the driving wheel power consumed by the car to overcome rolling resistance and air resistance is:

Use this as the module load of the dynamometer.During the test, drive the driving wheel of the car into the roller device of the chassis dynamometer, connect the fuel consumption sensor to the fuel pipeline of the car; set the test speed, start the engine, and put the transmission in direct gear; The power value indicated by the engine is equal to the calculated value and stabilized. At this time, press the fuel consumption measurement button, and when the driving wheels drive a distance of not less than 500m on the roller, the constant speed of the car can be read from the display device. fuel consumption per kilometer.In order to eliminate the influence of accidental factors, the test should be repeated three times, and the average value should be taken as the fuel consumption value per [-] kilometers of the tested car under the given test conditions.

With reference to the relevant provisions of GB/T12545-1990 "Automotive Fuel Consumption Test Method", the constant speed 20 km fuel consumption test of the vehicle can be carried out at different test speeds, and the constant speed 10 km fuel consumption characteristic curve of the vehicle can be drawn.During the test, the car uses the usual gears, the test speed starts from 90km/h, and the test speed is evenly selected with the whole number of 5km/h until it reaches [-]% of the maximum speed.Measure at least [-] test vehicle speeds.

When the fuel consumption within 500m is measured in milliliters, the following formula can be used to convert it into fuel consumption per [-] kilometers.

In the formula, Q——fuel consumption per 100 kilometers (L/[-]km);

Fuel consumption (ml) of y-500m.

Obviously, under different test speeds, the loading power corresponding to the chassis dynamometer is different.Under different test speeds and corresponding loading power conditions, each test speed is tested three times, and the average value of the test values ​​(after conversion by the above formula) is taken as the fuel consumption per 5 kilometers of the tested vehicle at a given test speed.After the 18-kilometer fuel consumption at each specified speed is measured, the [-]-kilometer fuel consumption characteristic curve of the vehicle can be drawn in a plane Cartesian coordinate system with the vehicle speed as the horizontal axis and the [-]-kilometer fuel consumption as the vertical axis.As shown in Figure [-]-[-].

(3) Test environment conditions
Ambient temperature: 0-40°C;

Environmental relative humidity: less than 85%;

Atmospheric pressure: 80-110kPa.

(4) Precautions
In order to make the vehicle fuel economy test results accurate and reliable, the following points should be noted:
①The engine coolant temperature should be within the range of 80-90C,
When the temperature is too high, use a cooling fan to cool down; the tire pressure should meet the regulations, the error should not exceed ±0.01MPa, and the pattern of the left and right tires should be the same; the chassis temperature of the tested vehicle should be strictly controlled with the room temperature. Should be controlled above 10C.

②The accuracy of the test instrument should meet the requirements, the vehicle speed measuring instrument and the fuel flow meter: the accuracy is 0.5%; the timer: the minimum reading is 0.3s.

③Correctly connect the sensor of the fuel consumption meter, and pay attention to eliminate the air bubbles in the oil circuit.

④ In order to ensure the safety of the fuel economy of the bench test, the following points should be paid attention to:
a. A fire extinguisher with good performance must be equipped next to the vehicle under test.

b. The oil pipe used for the fuel consumption sensor should be transparent, oil-resistant, and pressure-resistant. The oil pipe joint should use a qualified ring clamp, and must not be wound with lead wire, and ensure that there is no leakage.

c. When disassembling the fuel pipe, it is necessary to use a sand table to catch the oil. It is not allowed to use cotton yarn or other flammable objects to catch the oil, and the fuel is not allowed to flow to the engine exhaust pipe.

d. During the test, the engine cover should be opened to observe whether there is any leakage. After the test is completed, install the original pipeline and start the engine. Only when there is no leakage can the engine cover be closed.

[-]. Vehicle economic performance road test detection

The road test of vehicle fuel consumption includes three types: uncontrolled road test, controlled road test and cycle road test.

The uncontrolled road test refers to the road test method without any control on various factors such as the test driving road, traffic conditions, driving habits and surrounding environment.In this test method, various factors vary greatly at random, the test data has a large dispersion, the number of test vehicles is large, and the test journey is long.Because the test is extremely expensive and takes a long time, it is rarely used.

Controlled road test means that the test has specific requirements for one or several of the above factors, that is to say, the test data is valid only when the test conditions meet the requirements. This method is called controlled road test.

Cyclic road test means that the car is tested completely according to the specified speed-time specification.When to shift gears, when to brake, as well as driving speed, acceleration, deceleration, etc. are all specified in the specification.This test method is also often referred to as "multi-condition test"

The controlled road test is introduced below, that is, fuel consumption at full throttle acceleration with full throttle, fuel consumption at constant speed, average fuel consumption under limited conditions, and fuel consumption under multiple operating conditions.

1. Basic conditions for fuel economy road test
Before the test, the test vehicle should be run-in; during the test, the test vehicle must be warmed up to run, so that the engine, transmission system and other parts are preheated to the specified temperature state.The inflation pressure of tires should meet the requirements of the technical conditions of the vehicle, and the error should not exceed 10kPa.Unless there are special regulations, the passenger car should be half of the specified number of passengers (integer); the city bus should be 65% of the total mass; other vehicles should be fully loaded, and the load should be evenly distributed and fixed firmly. Shaking and bumping should not be allowed during the test. Its quality should not be changed due to changes in conditions such as moisture and loss, so as to ensure that the size and distribution of the loaded quality remain unchanged.The test vehicle must be clean, the windows and cab vents must be closed, the air flow controlled by the thermostat must be in a normal adjustment state, and the vehicle engine should not be adjusted when doing various fuel consumption tests.

The test road should be a clean, dry, flat straight road paved with asphalt or concrete, with a length of 2-3km, a width of not less than 8m, and a longitudinal gradient within 0.1%.

The accuracy of the vehicle speed measuring instrument and the fuel flow meter is 0.5%; the minimum reading of the timer is 0.1s.The volumetric type is commonly used in the test fuel consumption meter.

2. Test items and procedures

(1) Fuel consumption test for direct block full throttle acceleration
The length of the test section is 500m. During the test, the car is in gear (the highest gear is available if there is no direct gear), and at an initial speed of (30±1) km/h, it passes through the 50m preparation section stably, and starts at the starting point of the test section. Fully open the throttle, accelerate through the test section, measure and record the acceleration time, fuel consumption and the speed when the car reaches the end of the test section.

The test was carried out twice, and the relative error of the acceleration time in the same direction was measured to be no more than 5%.Take the arithmetic mean value of the four acceleration time test results as the measured value, and it must meet the requirements of the technical conditions of the vehicle.

(2) Isokinetic fuel consumption test
The length of the test section is 500m. The car uses common gears and drives at a constant speed. It passes the 500m test section and measures the time and fuel consumption of the section.

The test vehicle speed starts from 20km/h (when the minimum stable vehicle speed is higher than 20km/h, it starts from 30km/h), and the vehicle speed is uniformly selected every 10km/h until 90% of the maximum vehicle speed, and at least 5 test vehicle speeds are measured. Two round trips are performed each.

Taking the vehicle speed as the horizontal axis and the fuel consumption as the vertical axis, draw a constant-speed fuel consumption scatter diagram, and draw a constant-speed fuel consumption characteristic curve according to the scatter diagram.

(3) Average fuel consumption test under limited conditions
The test road section should be set on the plain arterial road above grade 50, and its length should not be less than [-]km. Under normal traffic conditions, the speed of the train should be lower than that of the train, and the speed should be kept as uniform as possible.

轿车，车速为（60±2)km/h；铰接客车，车速为（35±2)km/h；其他车辆，车速为（50士2)km/h。

The passenger car should stop every 10km/h, start again after idling for 1min, and record the number of braking times, the number of times each gear is used, the time and the journey.Measure the fuel consumption per 50km one-way, go back and forth for each test once, and take the arithmetic mean of the two measurement results as the measured value of the average fuel consumption under limited conditions.

(4) Multi-condition fuel consumption test
(End of this chapter)