Three pillars on the car body
The body welded by various skeleton parts and plates is also commonly known as "body in white" in the industry. Every part of it has a related name. No matter in a car factory, a repair shop or an accessory shop, people will know which part of the car it belongs to and where it is installed as long as they hear a name. (see photo)
Main components of car body structure diagram:
1, hood 2, front fender 3, front cowl 4, front cowl 5, roof 6, front pillar 7, upper side member 8, roof side panel 9, rear cowl 10, trunk lid 1 1, rear pillar 12 and rear pillar. Door 16, lower side member 17, bottom plate 18, front fender 19, front longitudinal beam 20, front cross member 2 1, front apron 22, radiator frame 23, and hood front support plate.
The skeleton and plates of the car body are mostly stamped with steel plates, and the special steel plates for the car body have the characteristics of delayed deep drawing and are not easy to crack. Depending on the position of the car body, some parts are rusted with zinc steel plates, such as fenders and roofs. High-strength steel plates are used in some places with high stress, such as radiator support beams and upper side beams. The thickness of steel plate commonly used in car body structure is 0.6 ~ 3 mm, and the thickness of most parts is 0.8 ~1.0 mm.
In the body structure, the position of some important parts is related to the overall layout, safety and ride comfort of the vehicle, such as the column.
Generally, a car body has three pillars, namely, front pillar (A pillar), middle pillar (B pillar) and rear pillar (C pillar) from front to back. For an automobile, the column not only plays a supporting role, but also plays the role of a door frame.
When designers consider the geometric scheme of the front column, they must also consider the angle at which the front column blocks the driver's sight. Under normal circumstances, when the driver passes through the front column line of sight, the binocular overlap angle is 5 ~ 6 degrees. From the driver's comfort, the smaller the overlap angle, the better. However, this involves the rigidity of the front column. It is a contradiction to have a certain geometric size to maintain the high rigidity of the front column and to reduce the influence of the driver's line of sight occlusion. Designers must strive to balance the two to achieve the best results. At the North American International Auto Show 200 1, Volvo of Sweden introduced the latest concept car SCC, which changed the front column into a transparent form and inlaid with transparent glass, so that drivers can observe the outside world through the column and minimize the blind area of vision (see Volvo SCC, "Car Shell Picking" on this website for details).
The center pillar not only supports the roof, but also supports the front and rear doors. Some accessories, such as seat belts in front seats, are installed on the center pillar, which sometimes wears wires and harnesses. Therefore, most central columns have convex radius to ensure good force transmission performance. The cross-sectional shape of the center pillar of modern automobile is complex, which is welded by several stamped steel plates. With the development of automobile manufacturing technology, the closed cross-section center pillar has appeared without welding. Its rigidity is greatly improved and its weight is greatly reduced, which is beneficial to the lightweight of modern cars. However, some designers simply canceled the center pillar from the convenience of passengers getting on and off. The most typical car is French Citroen C3 car. The center pillar on the left and right sides of the car body is cancelled, and the front and rear doors are opposite, so passengers can get on and off completely without obstacles. Of course, if the center pillar is cancelled, the front and rear pillars should be strengthened accordingly, and the body structure must be in a new form and the material selection is different.
The difference between the rear column, the front column and the middle column is that there are no problems such as line-of-sight occlusion and obstacles to getting on and off, so it is no problem to have a larger structural size. The key is that the seal between the rear pillar and the car body should be reliable.
Stiffness is an index of automobile body design. Stiffness refers to the ability of the body not to deform easily when an ordinary external force is applied that will not damage the body, that is, the elastic deformation ability to restore the original shape. When a car is driven by various external forces, it will deform. A small degree of deformation means good rigidity. Generally speaking, good rigidity means good strength. Cars with poor rigidity are prone to creak when driving on uneven roads. The stiffness of the column determines the overall stiffness of the car body to a great extent, so the column is the key part of the whole car body structure and should have high stiffness.
Two pairs of contradictions in body design
Modern automobile pursues comfort, good power and safety performance, which constitute the contradiction of body modeling design.
First of all, comfortable driving requires enough interior space, and to get spacious space, it is necessary to increase the size of the car appearance. The increase of the overall size, especially the cross-sectional size, will inevitably increase the windward area of the car and directly affect the drag coefficient of the car. In this way, comfort and motivation constitute a pair of contradictions. This has little effect on the contradiction when the vehicle speed is relatively low. Early cars were basically box-type, and the appearance of cars was completely designed according to internal needs.
With the development of automobile technology, the speed of automobile is getting higher and higher, and the contradiction of wind resistance is becoming more and more prominent. Research shows that with the increase of vehicle speed, the road resistance increases slightly, but the wind resistance increases greatly. Generally, when the speed of boxcar is below 30 kilometers per hour, the power consumed by road resistance is greater than that consumed by overcoming wind resistance. Beyond this speed, the power consumed by wind resistance increases sharply. At a speed of about 70 kilometers per hour, the power required to overcome wind resistance will exceed the road resistance. If the speed exceeds 100 km per hour, most of the power will be spent on overcoming wind resistance.
There are two main factors of wind resistance, one is windward area, and the other is eddy current. The main measure to reduce the windward area is to reduce the height of the carriage. Although reducing the width of the carriage can also reduce the cross-sectional area, the effect is generally not as significant as reducing the height. In order to keep enough space in the car and ensure comfortable riding space, the cross section of the car should not be reduced at will. In order to further reduce the wind resistance, it is necessary to start with reducing the eddy current generated during the driving of the car.
In the street, we often see some big trucks passing by, and dust and scraps of paper flying all over the sky. This is a vortex formed by the air stirred by the car driving. Vortex will be generated on the front windshield, roof, side and back of the car. The most effective way to study eddy current is wind tunnel test. The car model is still in the tunnel space, surrounded by high-speed flowing air to simulate the conditions of high-speed driving of the car. The flow of air is measured by sensing devices installed in various parts of the car body. So as to understand the motion of the eddy current. The research shows that the car with streamlined body has the best anti-vortex performance.
The longitudinal section of a streamlined car body is similar to the shape of an airplane wing, which will generate lift at high speed and have a negative impact on driving stability. This leads to the second contradiction, namely, the contradiction between power and safety. In order to increase the stability, modern automobile body modeling has been continuously improved on the basis of streamlining, with the center of gravity moving forward, the front is low and the rear is high, the relative area of the longitudinal section of the tail is increased, and the spoiler is added.
Comfort and power, power and stability, how to solve these two contradictions constitute the mainstream topic in the history of body design. The car body has developed from box type and beetle type to ship type, wedge type and now dripping type, and many variants based on these shapes, and its internal driving force is the balance process of these two pairs of contradictions. The design workflow of automobile body has also developed from simple inside to outside to the combination of inside and outside.
Five components of automobile wind resistance
Car body modeling design is a great knowledge, and the important content is wind resistance.
Wind resistance usually refers to the resistance caused by the interaction between the outside of the car and the airflow. In fact, the airflow in the car also has resistance to the driving of the car. The research shows that the resistance acting on the car consists of five parts.
1. External resistance refers to the resistance formed by the difference between the positive pressure at the front of the car and the negative pressure at the back of the car body, accounting for about 58% of the total air resistance;
Second, the interference resistance refers to the resistance caused by airflow interference caused by the protruding parts of the automobile surface, such as bumper, rearview mirror, front license plate, drainage trough and chassis transmission mechanism, which accounts for about14% of the total air resistance;
3. Internal resistance refers to the resistance caused by the ventilation airflow inside the automobile and the airflow cooling the engine, accounting for about12% of the total air resistance;
Fourthly, the resistance caused by the lift generated by high-speed driving accounts for about 7% of the total air resistance;
5. The friction of air relative to car body flow accounts for about 9% of the total air resistance;
In view of the first and second kinds of resistance, the car body should be designed as streamlined as possible, and the cross-sectional area should not be too large. All parts of the car body should be transitioned with appropriate arcs to minimize the accessories protruding from the car body. The front face, hood and windshield should be properly tilted backwards, and the length and inclination angle of the rear window and roof should be properly designed. In addition, baffles or spoilers can be installed at appropriate positions. Through the research on the law of air flow outside the car, we can not only design a more reasonable car body structure, but also skillfully turn the air flow, properly use the scouring effect of local air flow, and reduce the deposition of dust on the car body.
In view of the fourth resistance, the lift should be reduced as much as possible during driving, including measures such as making the front of the chord low and then high, raising the tail of the bottom plate appropriately, and installing deflector and spoiler.
Introducing part of the external airflow into the interior of the automobile may reduce the resistance of the external airflow to the automobile to a certain extent, but the airflow will also produce friction and eddy current loss when it flows through the internal airway. Studying the air flow law inside the automobile can reduce the internal air resistance as much as possible and effectively cool and ventilate. Using the valve distribution law, the air inlet of the engine can be skillfully arranged in the high-pressure area to improve the air intake efficiency and reduce the vortex near the high-pressure area. At the same time, the air outlet can be arranged in the low-pressure area to make the exhaust smoother.
Careful readers may have noticed that the above discussion uses many non-limiting words, such as "five times". Some readers may want to use some exact figures to express it, such as the backward angle, fillet radius and so on. This involves the overall concept of body design. Wind resistance is a concept based on the overall structure of an automobile. The optimal geometric parameters of a car are not suitable for other models. A small change will often have a huge impact on the whole, as the saying goes. The data in the technical book are all the results of testing a specific range of cars under strict test conditions. Without these preconditions, the data is absurd.
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Main body part
In the article "Three Pillars on the Car Body", there is a car body structure diagram, which lists the positions and names of various parts of the car body. This paper introduces the front column, middle column and rear column, and continues to introduce other main components.
engine cover
Hood (also known as hood) is the most striking body part, and it is also one of the parts that car buyers often look at. The main requirements for the hood are heat insulation, sound insulation, light weight and strong rigidity.
The engine hood is generally composed of an outer panel and an inner panel, with heat insulation material sandwiched between them. The inner plate plays a role in enhancing rigidity, and its geometric shape is selected by the manufacturer, basically in the form of skeleton. Generally, the engine hood is turned backwards and a small part is turned forwards. The hood turned backward should be opened to a predetermined angle, and should not contact with the windshield, with a minimum spacing of about10 mm. To prevent it from opening automatically due to vibration during driving, the front end of the hood should be provided with a safety hook locking device, and the switch of the locking device should be set under the dashboard of the carriage. When the door is locked, the hood should also be locked.
Roof cover
The roof is the cover plate at the top of the carriage. The roof is not a very important part of the overall rigidity of the car body, which is why the skylight is allowed to open on the roof cover. From the design point of view, it is important how to make a smooth transition with the front and rear window frames and columns to obtain the best visual sense and minimum air resistance. Of course, in order to ensure the safety of the car roof, there must be some strength and rigidity. Generally, a certain number of reinforcing beams are added under the roof, and thermal insulation gasket materials are laid on the inner layer of the roof to prevent the conduction of external temperature and reduce the transmission of noise during vibration.
Trunk lid
The trunk lid requires good rigidity, basically the same as the engine lid in structure, and also has an outer panel and an inner panel, and the inner panel has ribs. Some cars called "hatchback and half" have trunks extending upwards, including the rear windshield, which increases the opening area and forms a door, so it is also called the back door, which not only keeps the shape of the sedan car, but also facilitates the storage of articles. If the back door is used, the rafter sealing strip should be embedded on the inner panel side of the back door, and the surrounding area should be waterproof and dustproof. Hook hinges and four-bar hinges are usually used as supporting members for opening the trunk lid. The hinge is equipped with a balance spring, which is convenient for the trunk lid to open and close, and can be automatically fixed in the open position for easy access.
fender
The fender is the exterior panel of the car body that covers the wheels. It is named after the shape and position of this part of the old car body like the wings of a bird. According to the installation position, it is divided into front fender and rear fender. The front fender is installed at the front wheel, which needs to ensure the maximum limit space when the front wheel rotates and jumps. Therefore, the designer will use the "Wheel Runout Diagram" to verify the design size of the fender according to the selected tire model size. The rear fender has no problem of wheels rubbing on the ground, but due to aerodynamic considerations, the rear fender is slightly arched outward. Now some car fenders have been integrated with the car body in one go. However, there are also fenders of cars that are independent, especially the front fenders. Because there are many collision opportunities, it is easy to replace the whole piece by independent assembly. The front fenders of some cars are made of elastic plastic materials (such as plastic). Plastic cushioning, relatively safe.
Front wall plate
The front panel refers to the partition between the engine compartment and the carriage, which is connected with the floor and the front column and installed under the front panel. There are many openings in the front wall panel for cables, tie rods, pipes and wire bundles to pass through, and it is also necessary to match the installation positions of pedals, machine columns and other components. In order to prevent exhaust gas, high temperature and noise from entering the engine compartment, sealing measures and heat insulation devices should be provided on the front panel. In the event of an accident, it should have sufficient strength and rigidity. Compared with other parts of the body, the most important technology for assembling the front panel is sealing and heat insulation, and its advantages and disadvantages often reflect the running quality of the vehicle.
Roof cover
Car roofs are usually divided into two types: fixed roofs and convertible roofs. Fixed roof is a common form of automobile roof, which belongs to large-scale covering parts and is a part of the overall structure of the car body. Strong rigidity and good safety, which can protect passengers when the car rolls over. The disadvantage is that it is fixed, there is no ventilation, and you can't enjoy the sunshine and ride.
Convertible tops are generally used for high-end cars or sports cars. By moving part or all of the roof through electric and mechanical transmission, you can fully enjoy the sunshine and air and experience the pleasure of driving. The disadvantage is that the mechanism is complex and the safety and sealing are poor. There are two forms of convertible top cover, one is called "hard top", and the movable top cover is made of light metal or resin material. The other is called "soft top", and the top cover is made of tarpaulin.
At present, most of the new convertibles are in the form of hard tops, such as the famous Peugeot 206CC sports car. Press the button to open the rear luggage compartment cover backwards, and the top cover will automatically fold and move backwards with the swing of the column (rear column), move to the luggage compartment, descend into the luggage compartment, and then close the luggage compartment cover. At this time, the whole car will become a convertible. The parts of the hardtop convertible are very precise, and the whole electronic control mechanism is complicated. However, due to the use of hard materials, the sealing performance of the restored roof is better. A soft-top convertible consists of a tarpaulin and a support frame, and the tarpaulin and the support frame are folded backwards to obtain a convertible carriage. Because the tarpaulin is soft and compact to fold, the whole mechanism is simple, but the sealing and durability are poor.
Fixed roof and convertible top have their own advantages and disadvantages. Can we get rid of the shortcomings and keep the advantages? The designer came up with a compromise, that is, opening a window on the fixed roof, that is, a "skylight", which can not only maintain the advantages of the fixed roof, but also obtain the effect of a convertible to a certain extent, giving consideration to increasing the light in the carriage. This way is welcomed by automobile consumers. After the 1980s, cars with skylights became popular rapidly.
Generally speaking, the skylight is mainly composed of glass window, sealing strip and transmission mechanism. Opening forms are generally divided into outer slide plate type, inner slide plate type and inclined type. The outer slide glass window slides on the top cover; The inner sliding plate glass window slides between the lower surface of the top cover and the inner decorative lining of the roof; The front end or rear end of the inclined glass window inclines upward to an open state; At present, the latter two forms are mostly used.
The sliding plate type driving mechanism consists of a bracket guide rail, a driving motor, a gear reducer, a clutch, a wire rope belt, a position sensor and a limit switch. The whole driving mechanism is installed in front of the roof, and the glass window is driven by steel cable to move on the guide rail. When the driving mechanism works, the limit switch can detect the status of the glass window, such as full opening, full closing and upward inclination. In order to prevent the motor from overloading when the glass window moves, an overload protection clutch is also set.
1 bracket, 2 inner sun visor, 3 glass window, 4 driving motor, 5 operating mechanism, 6 steel cable.
The main problem of roof skylight design is water leakage. The inner side of the skylight should be provided with a sink and a frame embedded with sealing strips, and the water leaked from the gap flows out of the car through the sink and drain pipe. Mobile phone glass windows are generally brown, which can reflect sunlight, and there is a sun visor inside. When the sun visor is opened, light can enter the compartment. (
door
For large and small buses, the door is a very important part. The door of a modern car is not only a "door", but also a symbol. Take the car as an example, the door can be used as a sign of the car. Official cars have four doors, family cars have four doors, three doors and five doors (the back door is lifted), and sports cars have two doors. If it is a bus, the door can be used as a symbol to measure the level and advancement of the bus. For example, the doors of modern luxury buses are mostly flat doors, while ordinary buses are mostly folding doors.
For a car, the quality of the door is directly related to the comfort and safety of the whole car. If the door is of poor quality, rough manufacture and thin material, it will increase the noise and vibration in the car and make passengers feel uncomfortable and unsafe. Therefore, car buyers should pay great attention to the manufacturing quality of car doors in the process of car selection.
The car body is composed of various skeleton parts, plates and parts, among which the door is the most complicated part in the car body, involving parts stamping, parts welding, parts assembly, assembly and other processes, with strict dimensional fit and technological requirements. Automobile door is a moving object, and its shortcomings such as flexibility, firmness and sealing are easy to be found and difficult to be "covered up". Therefore, manufacturers attach great importance to the manufacturing quality of car doors, and the quality of car doors actually reflects the manufacturing level of manufacturers.
Automobile doors are composed of outer door panels, inner door panels, door and window frames, door glass guide grooves, door hinges, door locks and door and window accessories. The inner panel is equipped with glass lifter, door lock and other accessories. In order to assemble firmly, the inner plate needs to be strengthened locally. In order to enhance safety, the anti-collision bar is generally installed on the inner side of the outer plate. The inner plate and the outer plate are combined by flanging, bonding and roll welding. According to the different bearing capacity, it is required that the outer plate is light in weight and the inner plate is rigid and can bear large impact force.
Designers should fully consider the deformation degree when the door is closed when designing the door. Europe and the United States have corresponding regulations, standards and test methods to measure the degree of deformation when closing doors. According to the American Test Method (FMVSS), a cylinder with a diameter of 12 inch (304.8 mm) was pressed on the door fixed on the car body with a hydraulic device, and the deformation and stress of the door were observed.
The door hinge consists of a hinge seat and a hinge shaft. It should rotate flexibly, not stagnate, not make noise, and keep its function within the expected service life of the car. The door opening angle is based on 75 degrees and should not interfere with the body.
Door lock is an important safety component. The door lock consists of two parts, one is fixed on the door and the other is fixed on the car body. Doors are blocked from opening outward by latches, and they are released by simple lever movement or button pressing. The door lock must work reliably and will not fall off by itself under a certain impact.
Doors should be sealed, dustproof, waterproof and soundproof. In addition to the reasonable size of the door and the car body, it is also important to embed or paste the sealing strip on the frame and the door. Sealing strip is a kind of rubber product with hollow section. Its flexibility makes it have the function of filling different gaps. When the gap is large, fewer sealing strips are extruded, and when the gap is small, more sealing strips are extruded. The quality of the sealing strip directly affects the sealing performance of the door.
The quality of the door can be roughly judged by opening and closing the door. A good quality car door, using strict materials and manufacturing technology, is reflected in the use, and it feels heavy and heavy. There was a low "bang" sound when it was closed, as if the air in the car was compressed. If the door is thin, there is a sense of lightness, and when it is closed, it will make a crisp "bang", which is obviously different from before.