Dynamic performance test of the hottest car

2022-09-22
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Automobile dynamic performance test

I. automobile dynamic performance evaluation index

automobile dynamic performance is the maximum speed, maximum acceleration ability and maximum climbing ability that the automobile can achieve during driving. It is the basic use performance of the automobile. Automobile is an efficient means of transportation, and the level of transportation efficiency depends on the power of automobile to a great extent. This is because the higher the average technical speed of the car, the higher the transportation productivity of the car. The most important factor affecting the average technical speed is the vehicle power

with the increase of the mileage of high-grade highways in China, the output results of highway 5. The improvement of road conditions and vehicle performance, the driving speed of vehicles is getting higher and higher, but the dynamic performance of vehicles in use will gradually decline with the continuation of service time, and they cannot meet the requirements of high-speed driving, which not only reduces the transportation efficiency of vehicles and the traffic capacity of highways, but also becomes a traffic accident Potential factors of traffic jam. Therefore, in order No. 13 issued by the Ministry of transport in 1990, it is particularly required to regularly test the dynamic performance of vehicles. Passing the dynamic test is an important technical condition for operating vehicles to run on the road. 199 in order to improve the technical performance of in-service vehicles, the Ministry of Communications issued jt/t "standards for the evaluation of automotive technical grades" after using electronic traction machines for five years, and evaluated the power performance as the first major performance. In addition, as early as 1983, the minimum requirements for the acceleration performance of vehicles after overhaul were stipulated in item 2.6 of gb3798 "technical conditions for completion and delivery of vehicle overhaul", which shows that the state attaches importance to the power performance of vehicles in use

automobile inspection departments generally use the maximum speed, acceleration capacity, maximum climbing gradient, maximum output power of engine and maximum driving power output of chassis as dynamic performance evaluation indicators

1. The maximum speed Amax (km/h)

the maximum speed refers to the maximum stable driving speed that the vehicle can achieve on a dry, clean and flat concrete or asphalt pavement under the factory determined maximum total mass state and the wind speed of 3m/s

2. Acceleration ability t (s)

vehicle acceleration ability refers to the ability of the vehicle to rapidly increase the driving speed during driving. It is usually evaluated by the acceleration time of the car. Acceleration time refers to the time required for the vehicle to accelerate from a low speed to a high speed on a dry, clean and flat concrete or asphalt pavement under the factory determined maximum total mass state and the wind speed of 3m/s

(1) the acceleration time of starting in place, also known as the acceleration time of starting and shifting, refers to the time required to start with the specified low gear, gradually change to the highest gear with the maximum acceleration (including selecting the appropriate shift timing), and accelerate to a specified speed. The specified speed varies from country to country, such as km/h, which is commonly used for cars, km/h, km/h, or start with the specified low gear, The most important purpose is to increase the time required to reach a certain distance after the equipment is gradually changed to the highest gear with high acceleration due to wear. The specified distance is generally m, m, OM. The shorter the starting acceleration time is, the better the power is

(2) overtaking acceleration time, also known as direct gear acceleration time, refers to the time required to fully accelerate to a high speed from a predetermined speed with the highest gear or secondary gear. The shorter the overtaking acceleration time, the better the high-gear acceleration performance

China has no clear regulations on the overtaking acceleration performance of vehicles, but it is stipulated in GB "technical conditions for the completion and delivery of automobile overhaul" that the acceleration time of vehicles with speed limiting device after overhaul from 20km/h to 40km/h should comply with the provisions of Table 1 when they drive in direct gear without load

Table 1 direct gear acceleration time

3 Maximum climbing gradient IMAX (%)

maximum climbing gradient refers to the maximum gradient that the car can climb with the lowest forward gear on a ramp with a good concrete or asphalt pavement when the car is fully loaded. Due to the limitation of road ramp conditions, the vehicle comprehensive performance testing station usually does not do the vehicle climbing test

4. The maximum output power of the engine pmax

the maximum output power of the engine refers to the power output when the engine is under full load with only accessories necessary for maintaining operation, also known as the total power. At this time, the tested engine generally does not have air filter, cooling fan and other accessories. The maximum output power of the newly delivered engine generally refers to the rated power of the engine. The rated power is the total power specified by the manufacturer under the full load condition and the specified rated speed according to the specific purpose of the engine. In some foreign manufacturers, the so-called rated power refers to the net power output of the engine at the rated speed. It is often marked with the word "net" after the rated power to show the difference. Net power refers to the power output of the engine with a full set of accessories under full load. The maximum output power of automobile engine is the basic parameter of automobile power performance. After the vehicle is used for a certain period of time, the technical condition changes, and the maximum output power of the engine becomes smaller, so the smaller difference is used to evaluate the degree of decline in the technical condition of the engine. For example, China's jt/t "automobile technical grade evaluation standard" defines the technical condition of the vehicle as grade III when the maximum output power of the engine in use is less than 75% of the rated power. Therefore, the maximum output power of the engine is reasonable as an evaluation index of the dynamic performance of a vehicle before and after use and before and after maintenance, but it should be noted that the engine power measured by the no load dynamometer or chassis dynamometer in the vehicle comprehensive performance testing station must be converted into the total power before it can be compared with the rated power. 5. Maximum driving power output of chassis dpmax

maximum driving power output of chassis refers to the maximum driving power output by the driving wheel when the vehicle is driving in direct gear (the corresponding speed is near the rated speed of the engine)

the maximum driving power output of the chassis is generally referred to as the maximum power output of the chassis, which is the maximum ability to actually overcome driving resistance and an important index for the evaluation of vehicle dynamics. During the use of the vehicle, the technical conditions of the engine itself, engine accessories and transmission system will decline, and the maximum power output of its chassis will be reduced

II. Automobile power testing items and relevant standards

automobile power testing items mainly include: acceleration performance testing, maximum speed testing, sliding performance testing, engine output power testing, automobile chassis output power testing

the standards that can be used for dynamic performance testing are:

JT/t198-95 "automobile technical grade evaluation standard"

GB/T15746. Standard for inspection and evaluation of automobile repair quality -- engine overhaul

gb technical conditions for completion and delivery of automobile overhaul

jt/t vehicle maintenance process specification

III. vehicle power bench test method

the indoor bench test of vehicle power is mainly to use the no-load dynamometer to detect the engine power, and the chassis dynamometer to detect the maximum output power, maximum speed and acceleration capacity of the vehicle. The indoor bench test is not affected by the objective conditions such as climate and driving technology, but only by the test accuracy of the tester itself, and the test conditions are easy to control, so the vehicle dynamic indoor bench test method is widely used in the vehicle inspection station. In order to obtain accurate measurement results, the manufacturer of the chassis dynamometer should give the power consumed by the mechanical friction of the chassis dynamometer with the change of speed in the test process in the manual. For the air-cooled dynamometer, it is also necessary to give the power consumed by the cooling fan with the change of speed. In addition, due to the different structure of the chassis dynamometer, the rolling resistance of the vehicle when simulating road driving on the roller is also different. The rolling resistance coefficient values of wheels of different sizes at different speeds should also be given in the manual. 1. Detection method of automobile chassis output power

the maximum chassis driving power of the vehicle is detected by the chassis dynamometer to evaluate the technical condition level of the vehicle

(1) before the dynamic performance test, the preparation before the test must be carried out according to the provisions of the specification of the chassis dynamometer. The platform lifter should be in the lifting state, and the roller without lifter must be locked; There shall be no small stones or hard objects on the surface of the wheel and tire

(2) the vehicle chassis dynamometer control system, road simulation system, guidance system, safety assurance system, etc. must work normally

(3) during the dynamic test, the control mode is in constant speed control. When the vehicle speed reaches the set speed (error 2km/h) and stabilizes for 5S (the time is too short, and the repeatability of the test results is poor), the computer can read the vehicle speed and driving force values and calculate the output power of the vehicle chassis

(4) output the test results

2. The detection method of engine power

the engine dynamometer is detected by the engine no load detector. The engine dynamometer is also classified by the largest force value applicable to the structure and samples of a universal experimental machine. According to the machine power, it is convenient to use and fast to detect. On the premise of standardized operation, it can provide an effective basis for the detection and management of engine power. It can also be used to compare the power of the same engine before and after debugging and maintenance, so it is also widely used

(1) start the engine and preheat it to the normal state. At the same time, connect the power supply of the dynamometer without external load and connect the sensor

(2) operate according to the instrument instruction

(3) read (or calculate) the power value of the engine from the dynamometer

3. Data processing

(1) detected data processing

at present, the values displayed by the chassis dynamometer are some values of the absorbed power of the power absorption device, and some values of the maximum chassis output power output by the driving wheel. For displaying the value of the power absorbed by the power absorption device, the power consumed by the rolling resistance of the car on the drum, the power consumed by the mechanical resistance of the bench and the power consumed by the fan of the air-cooled power absorption device must be increased during the data processing of the test results, The calculation formula should be:

maximum output power of automobile chassis = power consumed by power absorption device + power consumed by rolling resistance

+ power consumed by bench mechanical resistance

+ power consumed by cooling fan of air-cooled power absorption device

(2) data processing of detecting maximum output power of engine

according to the provisions of jt/t automobile technical grade evaluation standard, The measured maximum output power of the engine shall be compared with the rated power of the engine. Therefore, the calculation formula of the maximum output power of the engine should be:

the maximum output power of the engine pmax= accessory consumption power P1 + transmission consumption power P2 + chassis maximum output power dpmax

therefore, after the maximum output power of the chassis is measured, the transmission consumption power P2 and accessory consumption power P1 should be increased to determine the maximum output power Pmax of the engine. If the rated power of the automobile engine is net power, Excluding the power P1 consumed by engine accessories, the maximum output power Pmax of the engine after treatment is pmax=p2+dpmax

the engine power P measured by the engine dynamometer without external load is the net power. If the rated power of the automobile engine is the total power rather than the net power, the measured power P should be added to the consumed power P1 of the engine accessories before it can be compared with the rated power

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