In order to improve the braking performance of the vehicle, most cars are equipped with a pressure limiting valve and a proportional valve to control the braking force distribution on the front and rear axles to prevent the rear wheels from locking up during braking and causing serious side slips. As safety standards and regulations become more and more stringent, anti-lock brake system oil is increasingly used in modern cars as a standard configuration. In addition, many cars also have four-wheel drive. Therefore, when assessing the safety of a vehicle, the role of these relevant parts should be included. Moreover, modern cars have high speeds, and the axle load transfer is large when the vehicle is running and braking, and the entire vehicle mass is transferred to the front axle in an instant.
The sum of the braking force of the left and right wheels of the front axle is often greater than the static axle load of the front axle, while the sum of the braking forces of the left and right wheels of the rear axle is often less than the static axle load of the rear axle. Wheel braking becomes the main braking part. Therefore, the detection under dynamic conditions is very important to determine the braking performance of the car in actual driving. Modern automobile braking performance detection methods must adapt to the development and changes of automobile technology.
Disadvantages of testing under static conditions of the roller brake test bench. Testing the braking performance of the car on the roller brake test bench can be understood as the car is stationary and the road is rolling under the wheels, that is, the car is at a standstill, so this method is analogous . The force situation at this time is very different from that when the car is braking on the road, and it cannot reflect the axle load transfer of the car during the braking process.
Because the pressure limiting valve and proportional valve of the car do not work, it cannot reflect the difference in the braking force growth process of the front and rear axles. For four-wheel drive vehicles, only one axle can be tested on a brake test bench equipped with two pairs of rollers. The measured braking force on the front and rear axles is not the same as the braking effect on the road.
The relative speed of the vehicle during the test is only at this speed, the system does not work, so the braking performance of the vehicle with the system cannot be tested. The results of this test only reflect the braking function of the wheel brakes, while other factors that have a dynamic impact on the braking performance, such as axle load distribution pressure limiting valves and proportional valves, suspension wheels and tires, have no effect. Be taken into consideration.
Such an abnormal phenomenon often occurs in the practice of testing the braking performance of automobiles with the drum brake test bench. The more high-end cars with good performance are often equipped with systems, the test results are unqualified.
This is due to the structure of the roller brake test bench and the static state of the car. Due to the limitation of the adhesion coefficient between the roller and the tires, the maximum braking force of the front axle cannot be measured, and thus the true maximum braking force of the entire vehicle cannot be measured. power.
In addition, it takes a long time to test with a roller brake test bench, and it takes at least one to complete the service brake and parking brake test. For vehicles with spoilers or low suspension, there are also collisions with the rollers. danger. The installation of the drum brake test bench is also more complicated, requiring a special concrete foundation and power supply and other equipment.
Advantages of detection under dynamic conditions of the plate brake test bench Due to the limitation of electronic technology in the early plate brake test bench, the sensor and sampling system are difficult to meet the detection requirements.
In recent years, with the rapid development of electronic technology, especially computer technology, flat brake test benches have adopted electronic technology and computer control technology. Therefore, all aspects of the performance of the new generation of flat brake test benches have a qualitative leap.
Plate brake test bench uses the actual emergency braking process of the vehicle on the test plate to determine the braking force of the front and rear axles of the car, that is, the test is performed under the braking state of the car, so it is a dynamic test.
The flat brake test bench and its dynamic detection technology rely on the electronic computer to process the detection data to ensure that all the details of the dynamic braking process of the car are obtained. When the test is performed, the car drives onto the test bench at an ingenious speed to make the car close to the road In the emergency braking state, the real brake detection results of the car can be obtained.
The horizontal braking force of the car The vertical load of each wheel and the change of the vertical load during braking can be measured by the tension sensor and pressure sensor and sent to the data acquisition and analysis system. The detection result is the comprehensive actual performance of the vehicle’s braking performance. Therefore, it is possible to test the braking performance of cars including the system.
In addition, as mentioned above, the front axle braking force of modern cars accounts for a large proportion of the entire vehicle braking force. The flat-plate brake test bench can simultaneously perform dynamic detection on each wheel of the car, and the detection results are consistent with the actual situation.
In addition to testing the braking performance of the car, the flat brake test rig produced abroad can also detect the side slip of the axle mass and the performance of the shock absorber in the suspension in the process of detecting the braking force.
The flat-plate brake test bench uses the visual color images to detect the difference between the braking force of each wheel and the braking force of the left and right wheels. The large-screen color display shows the key parameters with numerical values, supplemented by diagnostic conclusions.
Through the analysis of the fluctuation of the front and rear wheel vertical force during braking, the attenuation of the car body vibration can be obtained, and the technical status of the car suspension system can be judged. The flat brake test bench does not require auxiliary equipment, and does not require a special use site, and can be directly installed on a level ground.
Although the flat brake test rig still has disadvantages such as the inability to separate the braking force of the center and rear axle when detecting dual-rear axle driving cars, and the inconvenience of detecting semi-trailers and full trailers, it can detect under dynamic conditions. The advantages of braking performance are mainly obvious. With the development of automobile technology and the increasingly strict automobile safety regulations, the flat brake test bench should gradually replace the drum brake test bench and be widely used.
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