Exploring Leaf Springs: The Backbone of Automobile Suspension（二）

三. Structural characteristics of leaf springs

 

1. Classification

(1) Multi-leaf springs: Multi-leaf springs are made up of multiple steel sheets of different lengths and the same width. The number of steel sheets is closely related to the weight of the supported bus. Generally, the heavier the bus, the more steel sheets are required, and the thicker and shorter the steel sheets are, the greater the spring rigidity. However, after a period of use, the multi-leaf springs will produce noise due to mutual sliding friction between the leaves. At the same time, this relative friction will also cause the spring to deform, resulting in uneven driving. The steel sheets of the multi-leaf spring are superimposed into an inverted triangle shape, with the uppermost steel sheet being the longest and the lowermost steel sheet being the shortest. At present, multi-leaf springs are widely used in medium and large trucks.

 

(2) Less-leaf springs: Less-leaf springs are made up of steel sheets that are thin at both ends and thick in the middle, with equal width and length. The cross-section of the steel sheets varies greatly, and the rolling process is relatively complex, which also makes the price of less-leaf springs more expensive than that of multi-leaf springs. Under the condition of the same stiffness, the leaf spring with fewer leaves is about 50% lighter than the leaf spring with more leaves. This advantage reduces fuel consumption and increases ride smoothness. In addition, the leaf spring with fewer leaves is in point contact with each other, which reduces relative friction and vibration, thereby increasing ride comfort. The leaf spring with fewer leaves has the characteristics of equal stress and small friction between leaves, which meets the trend of lightweight vehicles, improves the smoothness of the whole vehicle and the comfort of the driver, and can also reduce noise.

 

2. Working principle

The leaf spring is installed in the automobile suspension. When the vertical load is positive, each spring leaf is deformed by force and shows a tendency to bend upward. At this time, the axle and the frame are close to each other. When the axle and the frame are far away from each other, the positive vertical load and deformation of the leaf spring gradually decrease, and sometimes even reverse. In order to improve the stress of the main leaf ear, the end of the second leaf is often bent into an ear and wrapped outside the main leaf ear, which is called a wrap ear. In order to allow the leaves to slide relative to each other during elastic deformation, a large gap is left between the main leaf ear and the second leaf ear. The leaf springs in some suspensions are not made into ears at both ends, but other supporting connection methods such as rubber support pads are used. The flat rectangular steel plate is curved, one end is installed on the hanger with a pin, and the other end is connected to the beam with a hanging ear, so that the spring can be extended and retracted.

 

3. Structural advantages

The leaf spring has the advantages of simple structure, firmness and reliability. Under heavy load requirements, the load can be increased by increasing the number of steel plates. The friction between multiple steel plates can form damping, which is equivalent to a small "shock absorber". This damping effect can provide sufficient adhesion, suppress roll and provide oversteering dynamic characteristics, and can also reduce the interference between the rear axle and the wheel. In addition, the leaf spring is both an elastic element and a guide device of the suspension. One end of it is hinged to the frame, which can transmit various forces and torques and determine the jumping trajectory of the wheel. At the same time, it also has a certain friction shock absorption effect. During the driving process of the car, it can gradually disperse and absorb the impact force through the deformation and friction of the spring leaf, which has a buffering effect. Although leaf springs have disadvantages such as heavy weight, high rigidity, poor comfort, long longitudinal dimensions, and the leaf spring pins at the connection with the frame are easy to wear, they are still widely used on various cars. In order to improve the performance of leaf springs, reduce weight and increase life, variable-section leaf springs and single-leaf springs have appeared.

 

四. Advantages and Disadvantages of Leaf Springs

1. Advantages

Leaf springs have many advantages, which are mainly reflected in the following aspects:

· Simple structure and reliable operation: It is composed of a number of alloy spring leaves. This structural design is relatively simple and easy to manufacture and install. During the driving of the car, it can stably exert its elastic effect and reliably bear various loads.

· Low cost and easy maintenance: Due to its relatively simple structure, the manufacturing cost is low. At the same time, when a fault occurs, it is also convenient to repair, and no complicated maintenance tools and techniques are required.

· It is both an elastic element of the suspension and a guide device: on the one hand, it can provide elastic support to alleviate the vibration during the driving of the vehicle; on the other hand, it can also determine the jumping trajectory of the wheel and guide the wheel to travel in the correct direction.

·Can transmit various forces and torques: One end of it is hinged to the frame, which can transmit various forces and torques generated during the vehicle's driving to the frame to ensure the stability and safety of the vehicle.

·It has a certain friction and shock absorption effect: The friction between the spring leaves can convert part of the impact force into heat energy, thereby playing a certain shock absorption effect.

 

2. Disadvantages

However, leaf springs also have some disadvantages:

·Can only be used for non-independent suspension: This limits its scope of application and cannot meet the needs of some vehicles with high requirements for suspension performance.

·Heavy weight: Compared with other types of suspension elastic elements, leaf springs are heavier, which increases the overall weight of the vehicle, thereby affecting the fuel economy of the vehicle.

·High stiffness and poor comfort: Due to the high stiffness, the bumps and vibrations of the road are transmitted more obviously during driving, reducing the comfort of the driver and passengers.

·Long longitudinal dimensions: It is not conducive to shortening the front and rear overhangs of the car, affecting the overall layout and appearance design of the vehicle.

·The leaf spring pin at the connection with the frame is prone to wear: During long-term use, the leaf spring pin is prone to friction and impact, resulting in increased wear and tear, which requires regular inspection and replacement.

 

五. The development of leaf springs

 

1. Historical origin

As early as the Roman Empire, leaf springs appeared as a primitive form of suspension for chariots and other two-wheeled vehicles. At that time, the savvy Romans did not use steel, but used elastic sticks. It was not until 1804 that a young inventor named Obadiah Elliott designed a steel version of the leaf spring, which was made of two stacked steel plates, which helped to ride the carriage smoothly. Before that, carriages without suspension systems were very bumpy to ride.

 

2. Modern development

With the rise of the automobile industry, leaf springs have gradually developed from simple original designs. In terms of structure, it has developed from the initial simple stacking to a complex multi-piece combination to meet the high requirements of modern vehicles for suspension performance.

Today, leaf springs are widely used in the automotive industry. According to market research data, the current market size exceeds XX billion US dollars and is expected to maintain steady growth in the next few years. Its growth is mainly due to the following aspects:

 

On the one hand, with the continuous development of the automobile industry and the continuous innovation of suspension system technology, customers' requirements for automobile safety and comfort are constantly increasing, which has prompted leaf springs to continuously improve their performance. For example, the domestic leaf spring industry has made certain progress in materials, processes, and designs, and has developed new high-strength, lightweight, and fatigue-resistant steel plate materials, optimized heat treatment, shot peening and other processes, and improved the strength and corrosion resistance of leaf springs. At the same time, advanced sensors and control systems are introduced to achieve intelligent manufacturing and improve production efficiency and product quality.

 

On the other hand, with the rapid growth of the new energy vehicle market, the demand for suspension system leaf springs is also increasing. Enterprises are actively developing high-performance suspension system leaf spring products suitable for new energy vehicles to meet market demand.

 

In addition, with the improvement of global environmental awareness, governments of various countries will strengthen environmental protection regulations on the automobile industry. The suspension system leaf spring industry needs to pay attention to changes in relevant regulations and actively respond. For example, adopt new materials, improve production processes, and reduce pollution emissions to meet environmental protection requirements.

 

In short, leaf springs continue to develop in the modern automobile industry, adapting to market demand and technological progress, and will continue to play an important role in the automobile industry in the future.

 

六. Application fields of leaf springs

 

1. Traditional applications

Leaf springs are widely used in traditional fields, mainly in commercial vehicles, buses, light vehicles and various special vehicles.

In the field of commercial vehicles, leaf springs are an important component of the suspension system, which can withstand large loads and ensure the stability and safety of the vehicle during driving. Its good elasticity and load-bearing capacity enable commercial vehicles to cope with various road conditions when transporting goods and reduce damage to goods.

 

In terms of buses, leaf springs provide passengers with a more comfortable riding experience. It can effectively absorb bumps and vibrations on the road and ensure the stability of the bus. At the same time, leaf springs also play a role in supporting the body of the bus in the suspension system to ensure the structural stability of the vehicle.

 

In light vehicles, although leaf springs face competition from some other types of suspension systems, they are still widely used due to their low cost and easy maintenance. Especially in some light commercial vehicles and pickup trucks with strict cost control, the advantages of leaf springs are more obvious.

 

Special vehicles, such as engineering rescue vehicles and fire trucks, have extremely high requirements for the reliability and load-bearing capacity of the suspension system. Leaf springs can meet the operating needs of these special vehicles under complex road conditions and provide strong support and shock absorption functions for the vehicles.

 

In addition, leaf springs are also used in seats, brake systems and other parts. In seats, leaf springs can provide certain elastic support and increase riding comfort. In brake systems, leaf springs may serve as elastic elements of certain components to play a role in buffering and stabilization.

 

2. Emerging fields

With the continuous advancement of science and technology and the development of emerging industries, the application scope of leaf springs continues to expand.

 

The demand for high-performance leaf springs in the field of new energy vehicles continues to grow. Due to their own characteristics, new energy vehicles have more stringent requirements for suspension systems. On the one hand, the battery pack of new energy vehicles increases the weight of the vehicle and requires a more powerful suspension system to support it. Leaf springs can meet this demand of new energy vehicles with their high load-bearing capacity. On the other hand, new energy vehicles also have high requirements for driving stability and comfort. High-performance leaf springs can reduce noise and vibration and improve riding comfort by optimizing design and material selection.

 

In the field of industrial automation, leaf springs also have certain application potential. In some automated production equipment, elastic elements are needed to buffer vibration and absorb impact. The high strength and good elastic properties of leaf springs enable them to play a role in industrial automation equipment, protect key components of equipment, and improve the stability and reliability of equipment.

 

In the field of robotics, although the application of leaf springs is relatively small at present, with the continuous development of robotics technology, the demand for high-performance elastic elements is also increasing. Leaf springs can be used as elastic support elements for robot joints, or play a role in shock absorption and buffering in the mobile mechanism of robots.

 

In the field of medical equipment, leaf springs can be used in some medical equipment that requires elastic support and shock absorption, such as beds, operating tables, etc. Its good elasticity and stability can provide patients with a more comfortable treatment environment, while also protecting key components of medical equipment and extending the service life of the equipment.

 

In the field of home appliances, some high-end home appliances have also begun to use leaf springs as elastic elements. For example, some high-end washing machines use leaf springs in the shock absorption system, which can effectively reduce the vibration and noise of the washing machine during operation and improve the user experience.

 

In the field of electronic products, although the application of leaf springs is still relatively limited, there are also potential application prospects in some electronic products that require shock absorption and protection, such as laptops and tablets. Leaf springs can be used as internal support elements of these electronic products to protect key components from external impact.