The swing arm is usually located between the wheel and the body, and it is a safety component related to the driver that transmits force, weakens vibration transmission, and controls the direction.
The swing arm is usually located between the wheel and the body, and it is a safety component related to the driver that transmits force, reduces vibration transmission, and controls the direction. This article introduces the common structural design of the swing arm on the market, and compares and analyzes the influence of different structures on the process, quality and price.
Car chassis suspension is roughly divided into front suspension and rear suspension. Both front and rear suspensions have swing arms to connect the wheels and the body. The swing arms are usually located between the wheels and the body.
The role of the guide swing arm is to connect the wheel and the frame, transmit force, reduce vibration transmission, and control the direction. It is a safety component involving the driver. There are force-transmitting structural parts in the suspension system, so that the wheels move relative to the body according to a certain trajectory. The structural parts transmit the load, and the entire suspension system bears the handling performance of the car.
Common functions and structure design of car swing arm
1. To meet the requirements of load transfer, swing arm structure design and technology
Most modern cars use independent suspension systems. According to different structural forms, independent suspension systems can be divided into wishbone type, trailing arm type, multi-link type, candle type and McPherson type. The cross arm and the trailing arm are a two-force structure for a single arm in the multi-link, with two connection points. Two two-force rods are assembled on the universal joint at a certain angle, and the connecting lines of the connecting points form a triangular structure. The MacPherson front suspension lower arm is a typical three-point swing arm with three connection points. The line connecting the three connection points is a stable triangular structure that can withstand loads in multiple directions.
The structure of the two-force swing arm is simple, and the structural design is often determined according to the different professional expertise and processing convenience of each company. For example, the stamped sheet metal structure (see Figure 1), the design structure is a single steel plate without welding, and the structural cavity is mostly in the shape of "I"; the sheet metal welded structure (see Figure 2), the design structure is a welded steel plate, and the structural cavity is more It is in the shape of "口"; or local reinforcement plates are used to weld and strengthen the dangerous position; the steel forging machine processing structure, the structural cavity is solid, and the shape is mostly adjusted according to the chassis layout requirements; the aluminum forging machine processing structure (see Figure 3), the structure The cavity is solid, and the shape requirements are similar to steel forging; the steel pipe structure is simple in structure, and the structural cavity is circular.
The structure of the three-point swing arm is complicated, and the structural design is often determined according to the requirements of the OEM. In the motion simulation analysis, the swing arm cannot interfere with other parts, and most of them have minimum distance requirements. For example, the stamped sheet metal structure is mostly used at the same time as the sheet metal welded structure, the sensor harness hole or the stabilizer bar connecting rod connection bracket, etc. will change the design structure of the swing arm; the structural cavity is still in the shape of a "mouth", and the swing arm cavity will A closed structure is better than an unclosed structure. Forging machined structure, the structural cavity is mostly "I" shape, which has the traditional characteristics of torsion and bending resistance; casting machined structure, shape and structural cavity are mostly equipped with reinforcing ribs and weight-reducing holes according to the characteristics of casting; sheet metal welding The combined structure with the forging, due to the layout space requirements of the vehicle chassis, the ball joint is integrated in the forging, and the forging is connected with the sheet metal; the cast-forged aluminum machining structure provides better material utilization and productivity than forging, and has It is superior to the material strength of castings, which is the application of new technology.
2. Reduce the transmission of vibration to the body, and the structural design of the elastic element at the connection point of the swing arm
Since the road surface on which the car is driving cannot be absolutely flat, the vertical reaction force of the road surface acting on the wheels is often impactful, especially when driving at high speed on a bad road surface, this impact force also causes the driver to feel uncomfortable. , elastic elements are installed in the suspension system, and the rigid connection is converted into elastic connection. After the elastic element is impacted, it generates vibration, and the continuous vibration makes the driver feel uncomfortable, so the suspension system needs damping elements to reduce the vibration amplitude rapidly.
The connection points in the structural design of the swing arm are elastic element connection and ball joint connection. The elastic elements provide vibration damping and a small number of rotational and oscillating degrees of freedom. Rubber bushings are often used as elastic components in cars, and hydraulic bushings and cross hinges are also used.
Figure 2 Sheet metal welding swing arm
The structure of the rubber bushing is mostly a steel pipe with rubber outside, or a sandwich structure of steel pipe-rubber-steel pipe. The inner steel pipe requires pressure resistance and diameter requirements, and anti-skid serrations are common at both ends. The rubber layer adjusts the material formula and design structure according to different rigidity requirements.
The outermost steel ring often has a lead-in angle requirement, which is conducive to press-fitting.
The hydraulic bushing has a complex structure, and it is a product with complex process and high added value in the bushing category. There is a cavity in the rubber, and there is oil in the cavity. The cavity structure design is carried out according to the performance requirements of the bushing. If oil leaks, the bushing is damaged. Hydraulic bushings can provide a better stiffness curve, affecting overall vehicle drivability.
The cross hinge has a complex structure and is a composite part of rubber and ball hinges. It can provide better durability than the bushing, swing angle and rotation angle, special stiffness curve, and meet the performance requirements of the whole vehicle. Damaged cross hinges will generate noise into the cab when the vehicle is in motion.
3. With the movement of the wheel, the structural design of the swing element at the connection point of the swing arm
The uneven road surface causes the wheels to jump up and down relative to the body (frame), and at the same time the wheels move, such as turning, going straight, etc., requiring the trajectory of the wheels to meet certain requirements. The swing arm and the universal joint are mostly connected by a ball hinge.
The swing arm ball hinge can provide a swing angle greater than ±18°, and can provide a rotation angle of 360°. Fully meets wheel runout and steering requirements. And the ball hinge meets the warranty requirements of 2 years or 60,000 km and 3 years or 80,000 km for the whole vehicle.
According to the different connection methods between the swing arm and the ball hinge (ball joint), it can be divided into bolt or rivet connection, the ball hinge has a flange; press-fit interference connection, the ball hinge does not have a flange; integrated, the swing arm and the ball hinge All in one. For single sheet metal structure and multi-sheet metal welded structure, the former two types of connections are more widely used; the latter type of connection such as steel forging, aluminum forging and cast iron is more widely used.
The ball hinge needs to meet the wear resistance under the load condition, due to the larger working angle than the bushing, the higher life requirement. Therefore, the ball hinge is required to be designed as a combined structure, including good lubrication of the swing and dustproof and waterproof lubrication system.
Figure 3 Aluminum forged swing arm
The impact of swing arm design on quality and price
1. Quality factor: the lighter the better
The natural frequency of the body (also known as the free vibration frequency of the vibration system) determined by the suspension stiffness and the mass supported by the suspension spring (sprung mass) is one of the important performance indicators of the suspension system that affects the ride comfort of the car. The vertical vibration frequency used by the human body is the frequency of the body moving up and down during walking, which is about 1-1.6Hz. The body natural frequency should be as close as possible to this frequency range. When the stiffness of the suspension system is constant, the smaller the sprung mass, the smaller the vertical deformation of the suspension, and the higher the natural frequency.
When the vertical load is constant, the smaller the suspension stiffness, the lower the natural frequency of the car, and the larger the space required for the wheel to jump up and down.
When the road conditions and vehicle speed are the same, the smaller the unsprung mass, the smaller the impact load on the suspension system. The unsprung mass includes wheel mass, universal joint and guide arm mass, etc.
In general, the aluminum swing arm has the lightest mass and the cast iron swing arm has the largest mass. Others are in between.
Since the mass of a set of swing arms is mostly less than 10kg, compared with a vehicle with a mass of more than 1000kg, the mass of the swing arm has little effect on fuel consumption.
2. Price factor: depends on the design plan
The more requirements, the higher the cost. On the premise that the structural strength and rigidity of the swing arm meet the requirements, the manufacturing tolerance requirements, manufacturing process difficulty, material type and availability, and surface corrosion requirements all directly affect the price. For example, anti-corrosion factors: electro-galvanized coating, through surface passivation and other treatments, can achieve about 144h; surface protection is divided into cathodic electrophoretic paint coating, which can achieve 240h corrosion resistance through adjustment of coating thickness and treatment methods; zinc-iron Or zinc-nickel coating, which can meet the anti-corrosion test requirements of more than 500h. As corrosion test requirements increase, so does the cost of the part.
The cost can be reduced by comparing the design and structure schemes of the swing arm.
As we all know, different hard point arrangements provide different driving performance. In particular, it should be pointed out that the same hard point arrangement and different connection point designs can provide different costs.
There are three types of connection between structural parts and ball joints: connection through standard parts (bolts, nuts or rivets), interference fit connection and integration. Compared with the standard connection structure, the interference fit connection structure reduces the types of parts, such as bolts, nuts, rivets and other parts. The integrated one-piece than the interference fit connection structure reduces the number of parts of the ball joint joint shell.
There are two forms of connection between the structural member and the elastic element: the front and rear elastic elements are axially parallel and axially perpendicular. Different methods determine different assembly processes. For example, the pressing direction of the bushing is in the same direction and perpendicular to the swing arm body. A single-station double-head press can be used to press-fit the front and rear bushings at the same time, saving manpower, equipment and time; If the installation direction is inconsistent (vertical), a single-station double-head press can be used to press and install the bushing successively, saving manpower and equipment; when the bushing is designed to be pressed in from the inside, two stations and two presses are required , successively press-fit the bushing.
