As the main vehicle on the land, the automobile death caused by the automobile traffic accident accounted for the first place in the death toll of various accidents. Therefore, the issue of vehicle crash safety has attracted more and more attention. In the process of car collisions, the highest probability of collision is the collision of the front of the car. Firstly, it involves the collision of the front SUV bumper, and the impact characteristics of the car bumper are studied. The energy absorption characteristics in the collision process are of great significance for improving the collision safety of automobiles. Due to the importance of bumpers in low-speed collisions, countries around the world have formulated specific regulations and test requirements for crashworthiness of bumpers.
SUV bumper
1. Introduction to the bumper
The bumper is one of the larger covers on the car. As an independent assembly, it is installed on the car. It has a great influence on the safety protection, styling effect and aerodynamic characteristics of the vehicle. The bumper is installed at the forefront and rear end of the car and plays a crucial role in the vehicle's styling style. A good bumper can not only protect passengers from injury and damage to the car, but also make the user Feel pleasing and enjoy the beauty. In addition, when a collision occurs, the bumper as a safety protection device is an important part of the modern automobile structure, and it is also an indispensable part, which can effectively reduce the degree of casualties and damage to the car.
1.1 The function of the bumper
(1) Protection function: When a car collides longitudinally, the bumper should absorb some energy to protect the car body. In this regard, all countries have strict laws and regulations, generally require the bumper can absorb the impact energy equivalent to 8km/h speed, and after the impact, the body and body function protection and the permanent deformation of the bumper are made strictly Provisions.
(2) Device function: On the bumper, fixtures, license plates, license plates and other objects can be installed, and sufficient space and device conditions must be provided.
(3) Landscaping function.
(4) Improve aerodynamic characteristics: The frontal windage area of the bumper is large, which has a great influence on the aerodynamic characteristics of the vehicle, which affects the economical efficiency and dynamic performance of the automobile. Therefore, the optimum design of the front bumper should reduce the positive effect. The wind resistance coefficient (CD) and lift coefficient (CL) have obvious effects.
Because the bumper system plays a decisive role in both "low-speed collision" and "pedestrian protection", it is a key research content in the field of passive safety at home and abroad.
1.2 Main categories of car bumper systems
The car bumper can be divided into a front bumper and a rear bumper by location.
According to the materials used, it can be divided into metal bumpers and non-metallic bumpers. Metal bumpers are generally stamped with high-strength steel sheets. This kind of steel sheet has both high strength and good stamping performance. Compared with general hot-rolled steel sheets, the thickness of the steel sheet can be reduced, thereby reducing material consumption and quality. If using phosphorus-containing high-strength stamping steel plate, compared with ordinary steel plate, the strength is increased by about 15% to 30%, and the thickness is reduced by about 10%. Metal bumpers are generally used for passenger cars and trucks. Non-metallic bumpers use molded plastic sheets, modified PP materials, and glass fiber reinforced plastics. The mechanical properties of these materials are similar to those of cold-rolled steel sheets. The density is only 1/5 of that of steel. Non-metallic bumpers are generally used in cars. .
According to the function of the bumper, it can be divided into non-absorbing bumper and energy absorbing bumper. In addition, airbag bumpers are now being researched abroad for the protection of pedestrians.
1.2.1 Non-absorbing bumper
Non-absorbing bumpers are the simplest form of construction. Since there is no inner lining, the stent does not absorb energy, so the buffer energy absorption capacity is poor, basically only play a decorative role, can not afford protection. In the event of a rear-end and front-end collision, this type of plastic bumper does not have sufficient strength and rigidity to withstand strong collisions and does not protect it. This will cause cracks in the car fenders and serious damage to radiators and lamps. In terms of lightness, the front wall is damaged, the windshield is damaged, and the steering wheel and instrument panel are severely deformed, even causing injury to the driver. Some of the light buses in China's market use non-absorbable bumpers, which pose a great threat to the safety of cars and occupants.
1.2.2 Energy Absorbing Bumper
Energy-absorbing bumpers can be roughly divided into three types according to different ways of buffering energy absorption: self-energy absorbing type, hydraulic buffering energy absorbing type and air-entraining type.
(1) Ordinary (self-absorbing type) bumper (Conventional Bumper System)
Its characteristic is that the structure is relatively simple, mainly through the deformation of the bracket and the liner to absorb the collision energy. Since the bracket needs a certain strength, metal materials are generally used, and the lining materials include foamed metal materials, various plastics, honeycomb materials, and resin composite materials. Most cars use this type of bumper. Its buffer capacity is generally determined by its buffer material.
(2) Hydraulic Bumper System (Hydraulic Bumper System)
The inside reinforcement of the bar is connected with the piston rod of the hydraulic buffer shock absorber through a rubber pad. The piston rod is a hollow structure and is internally provided with a floating piston. The piston separates it into left and right chambers, and the left chamber is filled with nitrogen gas. Right The chamber is filled with mechanical oil, and the outer cylindrical surface of the piston rod is slidably fitted with the cylindrical surface of the buffer cylinder. The mechanical oil in the buffer hydraulic cylinder communicates with the right chamber of the piston rod.
The buffer tank is usually fixed on the frame or body reinforcement. When a car crashes, the impact force on the bumper is transmitted to the piston rod. The end of the piston rod moves to the right, and the hydraulic oil is squeezed to flow through the throttle hole to the right chamber of the piston rod to push the floating piston to the left and make Nitrogen is compressed. In this way, the impact energy is absorbed by the hydraulic oil through the viscosity of the orifice, and the energy absorption efficiency can be as high as 80%. This type of oil-hydraulic spring type buffer shock absorber effectively utilizes the working principle of gas buffering and liquid throttling vibration damping, and its working characteristics are relatively stable. After the impact, the recovery power is generated by nitrogen and the bumper is reset. This kind of bumper is expensive, and is usually used on high-end cars.
1.2.3 Gastube Bumper System
The difference between this type of bumper and the first type of bumper is shown in Figure 3. The air chamber is generally installed between the outer cover and the bar, which is equivalent to the inner liner. When a collision occurs, the air chamber is compressed, affecting the deformation modes of the outer wrapping components, thereby improving the energy absorption effect. If the air pressure and the number of air chambers are properly designed and the strength of the air chamber components is ensured, the bumper can reduce the deceleration of the 15 km/h, 40% offset collision by 20% compared with the first type bumper. 50%.
2. Relevant regulatory requirements and standards for car bumpers
Due to the importance of bumpers in low-speed collisions, bumpers around the world have specific regulations and test specifications. For example, CFRpart 581, comsumertest and IIHS-Test in the United States, CFVSS 215 in Canada, AZT-Crash-Reparatur-Test in Germany, and ECE-R42 in Europe. In accordance with European ECE-R42 regulations, China also promulgated the standard GB17354-1998 for front and rear car protection devices.
Standards related to bumper design:
The automobile industry standards related to bumper design are IS02985 "External Protection of Road Vehicles and a Saloon", European Standard ECENo42 "Unified Regulations on the Certification of Vehicles and Front/Rear Protective Devices (Bumper, etc.)", American Standard PART 581 "Auto Bumper Standards, Japanese Standard JASOB 102-87 "Higher Bumper Heights," etc. These standards should be implemented in product design.
The national standard “Pre- and Rear-end Protective Devices for Passenger Cars” (revised draft) stipulates that the reference height of the bumper is 455mm, and the reference height is the height of the horizontal plane that passes through the baseline of the impactor; whether the vehicle is in the “whole vehicle equipment quality” or When it comes to "loading the quality of the test vehicle," the bumper should have an effective protective effect. The Japan Standard (JASO 8102-87) “Bumper Height” provides clear regulations on the areas of effective front and rear bumpers for various types of automobiles, and stipulates that more than 70% of the total vehicle width should be continuously blocked at the front and rear ends, among which the sedan Bumper, minimum height at the upper end ≥ 480mm, maximum height at the lower end ≤ 470mm, and the maximum height at the lower end of a large vehicle and the minimum height at the upper end of a small vehicle shall be specified so as to protect the external device of the vehicle from minor collisions during low speed driving. . In the specific product design process, the bumper should be raised as much as possible for small vehicles under the condition of meeting high standards. For large vehicles, the bumper should be as low as possible to make different types of car bumper heights possible. Close to.
3. Application of Bumper in Pedestrian Protection
In the case of serious injury to the leg and knee joints, the pedestrian is mainly hit by the bumper. Although the injury to the human leg and knee joint is generally not life-threatening, it often leads to life-long disability or incapacity. In addition to protecting the car and the occupants, the bumper also needs to consider pedestrians when designing.
The airbag bumper is a bumper designed specifically to protect pedestrians. It is a passive safety device that allows pedestrians to avoid harm or reduce injuries in an emergency in which a car and a pedestrian are in a frontal collision. The device is composed of sensors, air pump and airbag, and is integrated into the bumper, which is equivalent to the airbag in the re-bump. Immediately after the pedestrian hits the bumper, the bumper has a built-in push plate that quickly falls and stops the pedestrian from being knocked under the car. At the same time, the sensor mounted on the bumper is triggered, the ignition circuit is turned on, the spark sparks, and the pilot charge The solid fuel in the gas generator of the pump, the combustion of fuel releases a large amount of nitrogen, and reaches a high temperature of about 1000°C; after the gas is cooled down through the cooler layer, it enters the filter, and the filtered cleaning gas is quickly filled into the built-in wedge shape. The airbag is opened forward to lift the impacted pedestrians. At the same time, the wing-shaped airbags on both sides of the bumper are inflated and lifted on both sides to prevent pedestrians from rolling onto the road and control the automobile to implement emergency braking. . The dummy simulation test abroad has measured the response time of the sensor detecting pedestrian crash signal as 20ms, the ignition time is 2ms, the gas emission time is 3ms, the airbag inflation time is 30ms, and the accumulated time is 55ms. The whole process is very short. During the time completed, the crashed party is almost invisible (the human reaction time is about 0.2s). When people understand that a crash has occurred, the crash is over. It is impossible for people to instinctively protect themselves from a collision accident and rely on this new type of passive safety device to reduce injuries. This type of bumper can effectively ensure the safety of the person hit by the crash, but it is still in the research and experimental stage.
In addition, improving the shape of the bumper can also improve pedestrian protection. Taking Audi as an example, the bumper of the old model will cause great harm to the pedestrian's leg when it bumps into a pedestrian. And because the collision point is low, it is easy to hit pedestrians and make the pedestrian's head hit the hood to cause more damage. The new Audi uses a “big mouth” front face design to integrate the bumper into the entire front center. This not only makes the appearance look more rounded but also helps increase the level of pedestrian protection. Tests have proved that this design is very beneficial to reduce the damage to pedestrians.
4, summary
The design of car bumpers should not only meet the requirements of automotive performance and aesthetics, but also reflect the people-oriented principle. With the development of automotive technology, new materials technology and computer simulation technology, car bumpers should be more secure and beautiful. The direction design, through the reasonable selection of cushioning materials, reasonable design of the buffer structure, effectively improve the crashworthiness of the bumper system, thereby improving the car's crash performance, improve the safety of car occupants and pedestrians.