Automobile Inspection Technology

Chapter 27 Vehicle Inspection Technology (3)
Select the equivalent moment of inertia of the chassis dynamometer test bench that is suitable for the curb weight of the tested vehicle.When the moment of inertia of each level of the moment of inertia simulation system (flywheel) equipped on the chassis dynamometer test bench cannot accurately meet the requirements of the equivalent moment of inertia of the test vehicle, the moment of inertia level closest to the curb weight of the test vehicle should be selected.

① Overtaking acceleration time detection.Put the driving wheel of the test car on the roller of the chassis dynamometer test bench. After starting the car, gradually accelerate and shift gears until the direct gear is reached. Accelerate to 30% of the maximum speed of the model, record the required acceleration time, test twice, and take the average value.

② Car starting acceleration time detection.After the car is started on the test bench, start from the initial speed of 0km/h, continuously shift gears at the best time, and accelerate to 100km/h with full force, record the required acceleration time, test twice, and take the average value.

(4) Determination of sliding distance and time
The tire pressure of the tested car should meet the specified value, and the lubricating oil temperature of the transmission system should not be lower than 50V.Select the corresponding moment of inertia of the chassis dynamometer test bench according to the quality of the test car, when the moment of inertia of each level of the moment of inertia simulation system (flywheel) equipped with the chassis dynamometer test bench cannot accurately meet the requirements of the equivalent moment of inertia of the test car , the moment of inertia level closest to the curb weight of the test vehicle should be selected.

Put the driving wheel of the test vehicle on the roller of the dynamometer test bench, start the car, accelerate to 30km/h higher than the specified initial speed of taxiing according to the guidance system prompts, put the transmission in neutral, and use the kinetic energy stored in the coefficient of the car dynamometer test bench , make it run until the wheels stop moving.Record the sliding distance and compare it with the reference value in Table 5-4 to judge whether the sliding distance of the car meets the requirements.

[-]. Automobile dynamic road test detection

1. Test conditions
(1) Loading quality
The loading quality of the test vehicle shall be the maximum loading quality specified by the factory; the loading shall be evenly distributed and fixed firmly, and shall not be shaken or tilted during the test; the mass of the occupants and the distribution of substitute weights shall comply with the provisions in Table 5-5.

(2) Tire pressure
During the test, the inflation pressure of the tire in a cold state should meet the requirements of the technical conditions of the vehicle, and the error should not exceed ±10kPa (±0.1kg/cm2).

(3) Fuel, lubricating oil (grease) and brake fluid
The grades and specifications of the fuel, lubricating oil (grease) and brake fluid used in the vehicle test shall be strictly in accordance with the technical conditions of the vehicle.The same batch of fuel, lubricating oil (grease) and brake fluid must be used for the same test.

(4) Meteorological conditions
The test should be carried out under fine weather conditions, the relative humidity is less than 95%, the temperature is 0-40°C, and the wind speed is not greater than 3m/s.

(5) Test track

All performance tests should be carried out on a clean, dry, flat straight road paved with asphalt or concrete.The length of the road is not less than 2-3km, the width is not less than 8m, and the longitudinal slope is not more than 0.1%.

(6) Test instruments and equipment

All test instruments and equipment must be verified by metrology, and within the validity period, they should ensure normal function and meet the requirements of accuracy.If the speedometer and odometer that comes with the car are used in the test, it is necessary to check whether the speedometer and odometer are accurate, and perform necessary error correction.

(7) Preparation of test vehicle

Before the test, it is necessary to record the name of the manufacturer, brand, model, engine number, chassis number, main assembly numbers and date of manufacture of the test sample vehicle.

Before the road test, first check the completeness of the vehicle equipment and the assembly adjustment, which should meet the technical conditions for the assembly adjustment of the vehicle and the relevant provisions of the national standard. , In accordance with the provisions of the vehicle manual before running-in.During the test, the vehicle should be warmed up to make the engine, drive train and other parts reach the specified water temperature and oil temperature.

2. Test equipment
The odometer and speedometer on the car's dashboard can be used when measuring the distance and speed of a vehicle during a road test, but they are not accurate.Because they are driven by the car's drive train, the rolling radius of the vehicle's drive wheels is affected by factors such as driving torque, tangential reaction force of the ground to the tire, axle load, tire air pressure and its degree of wear.

And the precision of vehicle odometer and speedometer itself is also low.In order to eliminate the influence of these factors on the measurement accuracy, a wheel called a pentameter for measurement is attached to the side or rear of the vehicle.This wheel is a driven wheel, and there is no slippage during driving, so the distance can be accurately measured on a flat road.This equipment is often used in acceleration, coasting, braking and other tests, and can accurately measure the distance, time and speed of the vehicle.

(1) Contact five-wheel instrument
The domestic AM-2020 vehicle dynamic performance tester is a commonly used five-wheel instrument, and its composition is shown in Figure 5-11.

The five-wheel instrument mainly consists of a wheel 1, a magnetoelectric sensor 9, a mounting plate 7, a display 5, an afterburner spring 8, a foot switch 6, and the like.The ring gear 2 and the wheel 1 are fixed together, and when the wheel rotates, it drives the ring gear to rotate synchronously; the magnetoelectric sensor 9 is fixed on the connecting arm 3, and the gap between its head and the tooth top of the ring gear is 0.5-1mm; the sensor The signal line is connected with the display, and the effect of the force spring is to press the wheel tightly on the ground through the connecting arm, so as to keep in contact with the ground all the time during the test.The quintameter is installed on the special bracket at the rear or side of the vehicle through the mounting plate, and the foot pedal switch is used to send out signals when tests such as acceleration performance and braking performance start.The function of the display is to receive the pulse signal, calculate and display the test results, set the relevant parameters of the test initial conditions, etc.

(2) Non-contact five-wheel instrument

When the road condition is not good, the contact five-wheel instrument will sometimes slip or jump off the ground, and the tire pressure of the five-wheel instrument will reduce the test accuracy; the contact five-wheel instrument is not suitable for 180km due to its structural limitations /h above high-speed test.The non-contact speedometer adopts photoelectric filter technology, which is the replacement product of the contact five-wheel meter.The test range can reach 1.5-250km/h.It is only fixed on the rear or side of the vehicle body under test with vacuum suction cups without special fixtures.Its key component is the SF series spatial filter, which is a very special sensor that can extract the Specific reflection patterns (color spots, convex and concave spots, etc.) and make spatial (ground) reflection information processing.Figure 5-12 is a schematic diagram of the non-contact five-wheel instrument.

3. Road test detection

(1) Detection of sliding distance

The level of vehicle transmission efficiency affects the sliding distance of the vehicle.If the driving resistance is small and the transmission efficiency is high, the sliding distance will be long and the power of the car will be good.On the contrary, if the driving resistance is large, the transmission efficiency is low, and the power loss of the car is large, the gliding distance will be short and the dynamic performance will be poor.It can be seen that this test can be used to check the technical condition of the chassis part of the car.When detecting the sliding distance, the initial driving speed of the car is 50km/h.This test is applicable to all types of vehicles.The length of the car's gliding distance will also affect the fuel economy of the car. The longer the car's gliding distance, the better the fuel economy of the car.

Close the doors and windows of the car during the test, and use a five-wheel meter and other vehicle speed and travel recording devices for measuring instruments.

①Test method:
a. Set up benchmarks at both ends of the test road section with a length of about 1000m as the sliding test detection section.

b. Before the car enters the sliding detection section, the speed of the car is slightly higher than 50km/h. At this time, the driver puts the transmission gear in neutral and the car starts to slide.When the vehicle speed drops to 50km/h, the vehicle should enter the sliding inspection section, use the foot switch to send a signal, and the five-wheel instrument will record until the vehicle stops completely.Record the taxiing distance at the initial speed of taxiing (should be about 50km/h ± 0.3km/h).During the sliding distance detection process, the driver does not turn the steering wheel and keeps the car in a straight-line driving state.

c. Test at least one round-trip for each slide, and the round-trip sections overlap as much as possible to reduce the impact of the road on the test results.

②Test data processing.In the test, it is difficult to accurately ensure that the initial sliding speed is the standard 50km/h, so the sliding distance with the standard speed of 50km/h should be calculated according to the actual test results, that is, correction should be made.

Glide distance is the corrected average for both directions, round trip.

(2) Determination of rolling resistance coefficient f and air resistance coefficient C D
Rolling resistance coefficient f and air resistance coefficient C can be detected by road test method, and the test conditions are the same as those for measuring instruments and glide distance.

The test method is that the car slides in neutral, and the time and distance of the slide are measured.During taxiing, the car should be kept running in a straight line, and it is not allowed to turn the steering wheel and use the brakes.

(3) Detection of the minimum stable speed of the vehicle

The minimum stable speed of the car will affect the acceleration and passing ability of the car, the lower the minimum stable speed, the better the performance.Cars running on the road are generally measured at the lowest stable speed when the car is in direct gear.Off-road vehicles usually need to determine the lowest stable speed when the car is running in the lowest gear and the lowest stable speed when the car is running in direct gear.

The idling condition of the engine of the test vehicle should be good, and the test instruments are five-wheel meter or other speed and travel recording devices, steel tapes and benchmarks, etc.

①Measurement method:
a. On the test road, select a 50m-long test road section, and insert a pole at each end.

b. Put the transmission (and transfer case) of the test car in the required gear (first gear or direct gear), keep the car running at a low and stable speed and enter the test road section, when the car leaves the test road section , Immediately step on the accelerator pedal quickly. At this time, there should be no engine flameout and drive train vibration, and the car can accelerate smoothly.In case of undesired phenomena (engine flameout, drive train vibration), appropriately increase the lower stable speed of the car, and then repeat the test until the lowest stable speed that meets the above conditions is found.During the test, use a pentameter or other speed and travel recording devices to observe the speed and time of the vehicle, and measure the actual average speed of the vehicle when it passes the test road section.During the test, it is not allowed to cut off the clutch or half-link the clutch in order to keep the vehicle running stably.

c. The test should go back and forth at least 3 times each (6 times in total).

②Test data processing.The arithmetic mean of the measured vehicle speed is taken as the minimum stable vehicle speed for the test results.

(4) Detection of the maximum speed of the vehicle

The top speed of the car is the maximum speed that the car can reach on a good level road when it is fully loaded.The higher the maximum speed of the car, the higher the average speed of the car, and the higher the transportation efficiency of the car.

Before the test, check the steering mechanism of the car, the fastening condition of each fastener and the working condition of the braking system to ensure the safety of the test.The doors and windows of the vehicle should be closed during the test.

The test instruments are timers (minimum reading is 0.01s), steel tapes, benchmarks, etc.

① Detection method:
a. On a horizontal, straight, dry asphalt or cement test road, select the middle section of 200m as the test road section, and mark it with a benchmark.

b. Select a sufficiently long acceleration section so that the car can reach the highest stable speed before driving on the measurement section.

c. In the acceleration section, the test car should shift gears and accelerate to the highest stable speed in the best acceleration state (that is, keep the transmission at the corresponding gear of the highest design speed of the car before measuring the road section, and fully depress the accelerator pedal), let the car run at the highest speed. The steady speed of the vehicle passes the measurement section.Determine the time for the car to pass the speed measurement section at the highest stable speed.

d. The test goes back and forth once each time.

②Test data processing.According to the test results, the maximum speed of the car is calculated according to the average value of the speed measurement distance and the time of passing through the speed measurement road section.

(5) Detection of vehicle acceleration performance

The acceleration performance of a car has a great influence on the average speed of the car, and is an important indicator for evaluating the dynamic performance of a car.Especially important for cars.Acceleration time is usually used to evaluate the acceleration performance of a car.The acceleration time can be divided into the acceleration time of the car starting in situ and the acceleration time of overtaking.The acceleration time of a car starting in situ refers to the time required for the car to start with the first gear or the second gear, and after shifting gears to the highest gear at the best timing to obtain the maximum acceleration, it accelerates to a predetermined distance or vehicle speed. time.Overtaking acceleration time refers to the time required for a car to accelerate from a predetermined lower speed to a predetermined distance or a higher speed (target high speed) with the highest gear or the second highest gear.The overtaking acceleration test usually adopts the direct gear, so the overtaking acceleration performance is generally called the direct gear acceleration performance.The overtaking acceleration performance is good, and the parallel stroke of the car is short, which can ensure driving safety.

Before the test, the throttle valve and choke valve of the gasoline engine should be checked to ensure that they can be fully opened, and the rack stroke of the fuel injection pump of the diesel engine should be able to reach the maximum fuel supply position.The measuring instruments are five-wheel instruments and digital printers.

① Overtaking acceleration performance test method:

a. On a horizontal, straight, dry asphalt or cement test road, select a road section of appropriate length as the test road section, and set up marks at both ends.

b.汽车使用变速器预定的挡位(最高挡或次高挡），以选定的初速度（稍高于该挡的最低稳定车速)等速行驶。选定的初速度一般在20km/h、25km/h、30km/h、35km/h、40km/h中选择，20km/h常取作为直接挡试验初速度。当五轮仪监督初速度在选定的初速度稳定行驶并驶人试验路段时，急速将油门踏板踩到底，使汽车以最大加速性能加速到该挡最大车速的80%以上。对于轿车应加速到100km/h以上。用五轮仪记录汽车的加速度、由初速度加速到目标高速的加速时间和加速行驶的全过程。
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The test is carried out once each round trip, and the test sections should overlap.

②Test method for acceleration performance of continuous shifting at start:

a. The test road section is the same as the overtaking acceleration test road section.

b. The car is parked at the starting point of the acceleration test section, the transmission is put into the starting gear of the car, start quickly to obtain the best gear shifting time for maximum acceleration, and then shift to the highest gear, and accelerate to more than 80% of the maximum speed (the car should be Accelerate to more than 100km/h).Use a pentameter to record the whole process of acceleration.

c. The test shall be carried out once each round trip, and the test sections shall overlap.

(6) Detection of vehicle climbing ability

The climbing ability of the car is divided into the steep climbing ability and the long slope climbing ability of the car.The car's ability to climb steep slopes is the maximum slope that can be overcome when the car is fully loaded with 1 gear on a good road.Usually the maximum climb is indicated by imax.

Trucks running on various grounds in various regions require sufficient climbing ability, generally around 30% of iax.When off-road vehicles drive on bad roads and roadless areas, the maximum climbing ability is very important, and generally iax is around 60%.Cars usually drive on better roads, and generally do not emphasize its climbing ability. However, due to the high maximum speed of the car, the engine equipped with it has large power, large torque, and strong acceleration ability. Therefore, the maximum climbing ability of the car is Also pretty good.

The car's long-slope climbing ability is to assess the car's power, starting and thermal state of the drive train when the car is driving on a long slope.
conditions, gear usage and fuel consumption, etc.

During the test, the technical condition and climatic conditions of the vehicle shall comply with the relevant regulations, and the technical conditions of the engine, transmission system, steering system and brake system (including parking brake) shall be checked.

Test instruments include stopwatch, steel tape measure, benchmark, tachometer, inclinometer, thermometer, fuel flow meter, gear use times and time (or mileage) recording device, etc.

① Detection of the maximum climbing ability of the vehicle:
a. Select a test ramp whose slope is close to the maximum climbing gradient of the test vehicle, the length of the ramp is greater than 25m, and there should be a straight section of 8-10m before the ramp.The road surface with a slope of not less than 30% should be paved with cement, and the road with a slope of less than 30% can be paved with cement or asphalt.Set a 10m speed measuring section in the middle of the ramp.It is allowed to replace it with a natural slope with a flat, solid surface and a uniform slope.For the sake of safety, when the slope is greater than 40%, a safety device must be installed.

b. Use the lowest gear for the transmission, and do not shift gears during climbing.

c. After warming up, the car is parked on the straight road before the ramp.Start and drive to the front of the slope, press the accelerator pedal to the bottom, climb the slope with all your strength, record the time when the car passes the speed measurement area and the engine speed, and monitor the working conditions of the water temperature gauge, oil pressure gauge and other instruments.When the car climbs to the top of the slope, stop and check whether there is any abnormality in each part of the car.

If you cannot climb uphill, measure the distance from the bottom of the slope to the grounding center of the rear wheel at the parking point, and analyze the reason why you cannot climb uphill.If you can't climb up for the first time, you can do it for the second time, but no more than 2 times.

d. If the slope is inappropriate (too large or too small), you can increase or decrease the loading mass or use the higher gear of the transmission (such as 2nd gear) to conduct the test, and convert the test results to the maximum total mass specified by the automobile factory. Maximum gradeability when the transmission is in the lowest gear.

e. For off-road vehicles, the transfer box should be placed in the first gear, all-wheel drive, in addition to testing according to the above regulations, when the vehicle reaches the middle of the ramp, stop the vehicle, put it in neutral, brake with the parking brake, and turn off the engine After 1 minutes, restart the engine, and then start to climb to the top of the slope.

② Detection of the ability of vehicles to climb long slopes:
a. The test section is a flat, hard, dry continuous long ramp with a slope length of 8-10km; the uphill section accounts for more than 90% of the total length of the ramp, and the maximum slope is not less than 8%.

(End of this chapter)