Automobile suspension is the general name of all force transmission connection devices between the frame and the axle, which can ensure the normal driving of the vehicle, make the wheels have ideal motion characteristics in the motion state of uneven road surface and load changes, ensure the handling stability of the car, and enable the car to obtain the ability to drive at high speed. Automotive suspensions are being upgraded from passive to active suspensions. As an active suspension structure, air suspension is more complex, but with the gradual increase of consumers' requirements for car driving comfort and handling, and the rapid improvement of automobile electrification and intelligence, the air suspension market space will also be further improved.
1. Introduction to automobile air suspension
Vehicle suspension is a general term for all force transmission connection devices between the frame (or load-bearing body) and the axle (or wheel) of the car, which is used to transmit the force and moment acting between the wheel and the frame, and buffer the impact force transmitted by the road surface to the frame or body, and reduce the vibration caused by it, so as to ensure the smoothness of the car.
The suspension is generally composed of elastic elements, guiding mechanisms, and shock absorbers. Elastic elements are used to support vertical loads and act as a buffer and dampene for vibrations and shocks caused by uneven road surfaces. The elastic elements on the automobile suspension can usually be divided into: leaf springs, coil springs, torsion bar springs, oil and gas springs, air springs and other 5 kinds, passenger car suspensions mostly use coil springs and torsion bar springs, air springs are generally used in high-end family cars. The function of the shock absorber is to quickly attenuate the vibration of the car, improve the driving smoothness of the car, and enhance the adhesion between the wheels and the ground. The role of the guiding mechanism is to transmit force and torque, and at the same time play a guiding role, in the process of driving, can control the movement trajectory of the wheels.
1.1 Active suspension takes into account comfort and handling stability
According to the different structural forms, the suspension can be divided into independent suspension and non-independent suspension. Independent suspension is where each side of the wheel is individually hung under the body or frame by means of an elastic element, while in a non-independent suspension the two sides of the wheel are connected by a single axle. When one side of the wheel encounters a protruding road surface, the independent suspension will only jump when it encounters the protruding road surface, and the other side of the wheel will not be affected; When a non-independent suspension encounters a protrusion, the wheel on the other side will jump. In order to ensure ride comfort, passenger cars generally adopt independent suspension, which is divided into MacPherson, double wishbones, multi-link and other forms.
Suspension types can be divided into passive suspension, semi-active suspension and active suspension according to different working principles. The main difference between the three types of suspension is whether the stiffness of the elastic elements and the damping of the shock absorbers can be actively optimally controlled and adjusted according to external inputs.
1) Passive suspension: the stiffness and damping coefficient are set at the factory, which is not adjustable, and the ride comfort is poor. The advantage is that the structure is simple and the cost is low, and it is often used in economic cars.
2) Semi-active suspension: one of the spring rate and shock absorber damping is adjustable.
3) Active suspension: the spring rate and shock absorber damping can be adjusted, generally the air spring + electromagnetic shock absorber structure. The active suspension system is equipped with acceleration, displacement, height sensors and other measuring elements and control elements, and the vehicle can automatically adjust the suspension stiffness and damping force through the control unit according to external conditions such as load, driving speed, road surface conditions, etc., so that the car has good ride comfort, handling stability and passability.
Conventional suspension springs struggle to balance handling with comfort. Automobile suspension should not only meet the requirements of vehicle comfort, but also meet the requirements of vehicle handling stability, and comfort and control are one and the other, in order to achieve good comfort, need to buffer the vibration of the car, so that the spring should be designed to be softer, but the spring design is too soft to cause the vehicle to brake "nodding", accelerating "head up" and the bad experience of serious left and right rolling, thereby affecting the vehicle steering, resulting in unstable car handling, etc.
The use of air springs solves the dilemma caused by traditional suspension springs. The biggest difference between air suspension and traditional suspension is the upgrade of elastic elements, that is, the softness and hardness of the springs can be automatically adjusted according to demand, and the addition of electronic control systems and air pumps and other components give the suspension intelligent adjustment function. For example, the suspension can be stiffened at high speeds to improve body stability, and the suspension can be softened for longer periods of time at low speeds or over bumpy roads to improve shock absorption comfort.
1.2 The working principle and advantages of air suspension for passenger cars
The air suspension can automatically adjust the elasticity coefficient of the spring and the damping coefficient of the shock absorber according to the driving conditions, maintain the vehicle height, improve the passability, handling and stability of the vehicle, and equip the automotive intelligent suspension system to help electric vehicles be more energy-saving and comfortable. This configuration has become a new selling point for consumers to buy passenger cars, which is not only an important configuration for vehicle consumption upgrading, but also in line with the development direction of automotive intelligence.
The air suspension is mainly composed of front air springs, rear air springs, controllers, air pumps and distribution valve assemblies, body height sensors, main and auxiliary air reservoirs, pipelines, etc. The height sensor is fixed to the frame and the other end is fixed to the suspension swingarm. In the process of jumping up or down the wheel, the swing arm is driven, resulting in the relative angle change of one end and the other end of the sensor, so that the height sensor generates signal height difference information, and the body status signal (speed, acceleration, road impact, etc.) is transmitted to the electronic control unit, and the electronic control unit issues instructions according to a series of established algorithms, such as when the height of the vehicle needs to be adjusted, the controller issues instructions, and the corresponding valve of the distribution valve is opened. When the height of the vehicle needs to be reduced, the air vent valve and the air spring distribution valve are opened to reduce the body height, so that the body height can be manually adjusted, the body height can be dynamically adjusted with speed, the body is leveled, and the function of convenient getting on and off the car can be realized.
1) The air suspension can flexibly adjust the height of the vehicle, thereby reducing wind resistance, improving energy consumption, improving operational stability, and making it convenient for people and goods to get on and off the vehicle. The weight of new energy vehicles is higher than that of fuel vehicles of the same level (electric passenger cars are 0 heavier than fuel vehicles of the same level and size6-1 ton), when driving at high speed, in order to combat wind resistance, the energy consumption of electric vehicles is higher, and the electric vehicles equipped with air suspension can automatically lower the body and reduce wind resistance in the high-speed driving state, thereby reducing the energy consumption of the vehicle in the high-speed driving state.
2) By adjusting the volume of the air chamber of the air spring, the suspension stiffness is automatically adjusted. The spring mass of electric vehicles is heavier than that of gasoline vehicles, which is equivalent to compressing the travel of the coil spring, and the traditional coil spring stroke becomes smaller, and the undulations of the road surface are more easily transmitted to the cockpit. The air spring relies on air as the medium, and the stiffness can be made very small, and the natural frequency of the mass on the spring of the automobile suspension is adjusted to about 1Hz, so as to improve the driving comfort; And when the vehicle load changes (unloaded and fully loaded), different initial stiffness can be matched to ensure the comfort of driving and riding at all times.
3) Adjust the damping force of the suspension through the damping continuously adjustable shock absorber, improve the ride comfort in different road conditions, and control the vehicle more conveniently when starting, cornering, and braking.
Taking the Li L9 as an example, as the flagship SUV of Li Auto, the L9 has undergone more technological innovations in the chassis suspension. The minimum ground clearance for no-load in the Ideal L9 standard attitude is 176 mm, and through the self-developed air spring control system, the chassis can be automatically lowered in sports mode or high-speed scenarios to achieve better energy consumption and high-speed stability performance.
When the number of passengers and position change, the Ideal L9 will monitor the sensor value of each suspension in real time and make dynamic adjustments, so that whether it is a 1-person or 6-person ride, the suspension comfort experience is consistent.
Taking advantage of the adjustable height of the air spring, the Ideal L9 is also designed with other intelligent convenience functions, such as when the car is parked in P-gear, the "convenient boarding and getting on and off function" will be automatically activated, the chassis height will be lowered by 40 mm to facilitate passengers to get on and off the car, and when the speed exceeds 5 km h, the convenient boarding and boarding function will be automatically turned off. In addition, the rear axle can be lowered by 50 mm in trunk loading mode for daily loading and unloading of trunk items, a function that can be manually activated in the trunk. The Ideal L9's smart gas spring can also be iteratively upgraded via OTA.
Second, the development process of air suspension and the development trend of undeveloped
Gas springs were invented in the early twentieth century, and at first, they were used for vibration isolation in mechanical equipment, especially some precision instruments. Due to the general large volume of air springs at that time, they were well used in passenger cars that were not sensitive to space, which greatly improved the riding comfort of passengers; Air springs are also used in rear heavy-duty trucks and trailers, which can improve the bearing capacity of the vehicle on the one hand, reduce the impact of road bumps on the goods, reduce the vibration frequency, and protect the safety of goods, especially dangerous goods. In China's high-speed rail trains, a large number of air springs are also used.
With the integration of air springs, the reduction of volume and the development of sensors and other technologies, high-end passenger cars have also begun to use air springs instead of coil springs, the penetration rate of new energy vehicles is gradually increasing and the new forces have driven the application of air suspension in China for the sake of creating vehicle highlights, which is mainly due to the fact that the curb weight of new energy vehicles is higher than that of fuel vehicles of the same level. Air suspension can effectively balance the requirements of high load carrying and comfort, and air suspension can reduce wind resistance and thus energy consumption by adjusting the chassis height at the right time.
Significant sinking of air suspension supporting models: due to the air suspension structure and control system are more complex than other suspensions, the research and development of core components such as shock absorbers and air compressors is difficult, and the manufacturing process of air springs is complex, resulting in high air suspension research and development and production costs, which have only been configured in luxury models for a long time, and the market scale is small. The small scale leads to the high cost of independent development of car companies, and the air suspension is provided by overseas first-class manufacturers such as Continental and Vibrator, with deep software and hardware binding and high unit price. In order to build a high-end brand image, China's new car-making forces have improved product competitiveness and customer satisfaction by configuring air suspension systems to improve product competitiveness and customer satisfaction, making the configuration of air suspension, a luxury car with a configuration of more than 6 or 700,000 yuan, sink to 300,000+ models, accelerating the air suspension configuration to the mainstream. The first model to be equipped with an electronically controlled suspension system assembly for a local passenger car is the VOYAH FREE (starting at 33.).360,000).
Combination of air suspension and intelligent perception to provide more intelligent active adjustment function: with the development of automatic driving technology, the vehicle has an environmental perception system can be combined with air suspension, the air suspension system can call the camera, radar and other sensors that the vehicle has been equipped with to achieve more accurate and timely identification of road conditions, through the preset algorithm, to achieve a more intelligent active adjustment function of the air suspension system, and further improve the driving comfort of the vehicle.
For example, the domain controller self-developed by Li Auto L9 is responsible for the integrated control of the entire suspension system of Ideal L9, in addition to controlling the chassis system, the domain controller is also responsible for the extended range electric system, air conditioning system and seat control system. The L9's CDC damper control algorithm adjusts the damping of the shock absorber in real time based on the signals of more than 15 sensors, including wheel end acceleration sensors, steering wheel rotation angle, throttle status, and ABS status, so as to control the pitch of the vehicle and stably control the body attitude fluctuations during driving, so as to ensure the comfort of drivers and passengers. For example, the pitch control algorithm can solve the problem of motion sickness caused by the vehicle's acceleration and braking nodding; The roll control algorithm can reduce the lateral sway of the vehicle; The heave control algorithm allows the Ideal L9 to keep its body stable when navigating undulating roads.
Another example is that in addition to the front double wishbone + rear five-link + air suspension, the VOYAH Dreamer introduces the "magic carpet" function into the MPV, and actively changes the damping of a single CDC shock absorber according to needs, which can effectively improve the roll balance when cornering and ensure handling stability. When accelerating or braking, the combination of traditional coil springs + ordinary shock absorbers may cause the MPV with higher dead weight to accelerate and look up or brake nodding, etc., and the Dreamer "Magic Carpet" function can change the damping force of the front and rear axle shock absorbers in milliseconds, greatly improving this situation. Even when emergency braking and electronic stability systems are triggered, the Dreamer is equipped with the "magic carpet" function, which can control the body attitude, shorten the braking distance and improve the transient stability of the vehicle thanks to the real-time adjustment of the suspension damping.
In addition to demand-side drives, the air suspension business model is also changing. Car companies represented by the new forces tend to choose the air suspension procurement model of software and hardware decoupling, that is, self-developed air suspension algorithm and integrated in the chassis domain controller or domain controller, and other air suspension hardware is split and purchased, which is for the vehicle brand, the chassis components can be flexibly defined through software to ensure the scope and timeliness of the follow-up OTA. business ushered in large-scale industrialization opportunities.
In 2025, the scale of China's air suspension market is expected to reach 2 million to 3 million sets. In 2022, the air suspension penetration rate of passenger cars in China will be about 1%, and the shipment volume will be about 280,000 sets (+142%), and the shipment will be 19 in the first five months of 2023560,000 sets, a year-on-year increase of 2229%。We expect that 300,000+ passenger cars will have a higher air suspension penetration rate, and it is expected that the proportion of 300,000+ models will rise to 15% in 2025, assuming that the air suspension penetration rate of 300,000+ passenger cars exceeds 50%, the air suspension market size will be about 2 million units in 2025, assuming that a single set of air suspension **8,000 yuan, the corresponding amount will be 16 billion. On this basis, it is further optimistic that the air suspension configuration will continue to sink to 20-300,000 ** bands, and the air suspension market size will be 3 million units in 2025, corresponding to 24 billion sales (assuming that 20-300,000 ** with passenger cars accounts for 18.).5%, and the air suspension permeability is about 30%).
3. Air suspension industry chain
3.1 Air suspension industry chain
The links of this industrial chain include:
Upstream – Air suspension components, including air springs, air supply units, variable damping shock absorbers, air suspension system ECUs.
Midstream - air suspension system assembly.
Downstream - downstream passenger car OEMs. Air suspension is mainly used in fuel vehicles, such as Mercedes-Benz, BMW, etc. Domestic new energy vehicles are trying to use air suspension, and the models used are gradually extending to the middle and low end, representing companies such as Geely Automobile, Weilai, and Li Auto.
The structure of the air suspension system is complex, mainly including air springs, air supply units (air compressors, air storage tanks, distribution valves, etc.), ECU controllers, sensors (vehicle height sensors, acceleration sensors, etc.), etc., and air springs are generally used with variable damping shock absorbers.
Among them, the components with the highest value and the highest technical barriers are air compressors and air springs.
According to Gaogong Intelligent Automobile, in 2022, the share of China's passenger car air suspension system front-loading manufacturers will be ranked as: Vibrator (4455%), Kong Hui Technology (18.).
3.2 Introduction of key business providers
The hot sales of benchmark models such as the Ideal L series, Denza N7, and ZEEKR 009 are expected to drive the willingness of subsequent competing products, and the demand for air suspension is broad. China's local first-class enterprises are mainly concentrated in the upstream parts manufacturing field, and a large number of new energy OEMs have been added to the downstream of the industry. From the perspective of the comprehensive air suspension industry chain, local first-class manufacturers have achieved multi-point breakthroughs in the upstream, and core components such as air springs and air compressors have been localized, and have significant advantages in cost, which is 25%-30% lower than similar imported parts. In the downstream of the industry, traditional air suspension car companies are used in European and American luxury brands such as BBA, Porsche, Land Rover, etc., and the main manufacturers are still Continental and Vibrator.
3.2.1 Zhongding Co., Ltd. - a wholly-owned subsidiary, AMK, is the global leader in air supply units with a high market share
Zhongding Co., Ltd. is a leading enterprise of non-tire rubber parts in China, with a revenue of 14.9 billion yuan and a net profit of 9 in 2022600 million, of which 6800 million (domestic income 1.)400 million), accounting for 46%, gross margin of 214%。
Since 2008, Zhongding has mastered the technology of high-end rubber parts through a number of overseas mergers and acquisitions, and has entered the global supporting system of high-end luxury brands. Combined with the dividends of local engineers and overseas advanced rubber parts technology, the local implementation of Zhongding's overseas M&A projects has achieved remarkable results.
In 2016, AMK acquired by Zhongding Co., Ltd. is a leading air compressor company, the core component of the global air suspension system, with a global market share of more than 60%. AMK entered the field of drive and control technology in 1964 and in the field of automotive components in 1998 with the introduction of air compressors with tire sealants. Since entering the field of air suspension system, AMK has continuously improved its product assembly technology, and has been deeply involved in the industry for more than 20 years, supporting the world's top OEMs such as Jaguar Land Rover, Volvo, Audi, Mercedes-Benz, and BMW. The structure of the air supply unit of the air suspension is precise and complex, and there are requirements for reliability, heat generation, noise control, and inflation efficiency.
2022 is the first year of AMK's landing in China, and the volume period of orders in hand
The domestic air suspension market is in its infancy, and AMK China has been accelerating the improvement of the first-chain system for optimizing the performance and cost of air suspension systems in the Chinese passenger car market. At the beginning of 2021, AMK's industrial business was divested and moved lightly, focusing on the strategic goal of "localization promotion, technology iteration and upgrading, and industrial reinforcement and completion". 2022 is the first year of AMK China's landing, the revenue volume is still small, and the orders in hand are in the volume period, and it has obtained orders from a number of domestic new car-making forces and traditional independent brand leading enterprises, and AMK China has disclosed a total order output value of 73$1.4 billion.
While assembling air supply unit products and launching production lines, AMK China continues to promote the implementation of other self-produced air suspension hardware projects such as air springs and gas storage tanks, and the company's passenger car air spring project has completed sample production. The core barrier of air springs lies in the manufacture of leather bags, the manufacture of leather bags requires rubber parts to ensure sufficient strength, and its durability largely determines the service life of air suspension. It is expected to provide OEMs with better cost solutions.
The company's air suspension business revenue is expected to reach 4.5 billion yuan in the medium term
At present, AMK has few competitors in the field of domestic air compressors, and is expected to occupy the vast majority of the share of air compressors for air suspension, and in the medium term, AMK's air supply unit is expected to occupy about 70% of the domestic market share (more than 60% of the global market share). At present, the gas spring is expected to make a breakthrough from a single cavity to a double cavity, and the unit price has increased, and the value of the gas spring is expected to be 2500 yuan in steady state. Assuming that AMK obtains 30% of the domestic market share of air springs (the current competitors are Baolong Technology, Konghui Technology, and Tuopu Group), and assuming that the number of passenger cars equipped with air suspension in China reaches 2 million, the revenue volume of AMK China's air supply unit (excluding air storage tank) + air spring is expected to reach 4 billion, and with overseas revenue, the revenue of Zhongding's air suspension business is expected to reach about 4.5 billion.
3.2.2 Baolong Technology - high self-made rate of air springs and outstanding leading advantages
Baolong Technology was founded in 1997 and went public in 2017. At present, the company's main products are automotive tire pressure monitoring system (TPMS), automotive sensors (pressure, light and rainfall, speed, position, acceleration and current), ADAS (advanced driver assistance system), automotive metal pipe fittings (lightweight chassis and body structural parts, exhaust system pipe fittings and EGR pipe fittings), valve and balance weights, air suspension parts, etc.
In 2022, the company achieved revenue of 47800 million, net profit 2100 million. According to the investor interactive platform, in 2022, more than 460,000 sets, 1Q23 The company's average monthly shipment of air springs is 8,000 sets.
The company started the development of air spring products in 2012, and began to set up a research and development team in 2018 to research and develop the integration of electronically controlled air suspension systems. Before 2022, the company's air suspension system products were mainly shipped with commercial vehicle air springs, and 125 commercial vehicle air springs were sold in 2021 and 202239/50.880,000 pieces, a single ** close to 40 yuan, commercial vehicle air spring customers include ZF, Changchun Fuwei Adient, Beijing Guanghua Rongchang, Shanghai Koman, China Road Vehicle Machinery *** Guangzhou Huajin and Saifu Hualand, etc. In 2020, the company's front air spring damping assembly and rear air spring products were exclusively designated for NIO's ET7 model, and in 2022, more than 460,000 sets, according to the information of the investor interactive platform, at present, Baolong Technology's air suspension business has more than 10 billion orders in hand, and its customers cover Li Auto, BYD, Xiaopeng Motors, Weilai Automobile, Chery, Hongqi, etc., and Baolong Technology has achieved mass production of 8 model projects. In addition to air springs, the company is also involved in air suspension gas reservoirs, air suspension ECUs and other fields, and Baolong Technology's air suspension controller products are expected to start mass production and shipment in October 2023.
The construction of production capacity has accelerated. In the face of the rapid growth of orders, Baolong Technology built a new plant in Ningguo, Anhui Province, and at the same time launched the second phase of the construction of Hefei Park, replicating the already built automation, informatization and intelligent benchmark factories, and planning new production capacity to meet the rapidly growing order demand. It is expected that by the end of 2023, 5-7 fully automatic production lines for air springs will be built, achieving the goal of supporting 500,000 vehicles.
In 2022, the company's air suspension business achieved revenue of 2600 million, assuming that the domestic air suspension system loading volume is 2 million sets in 2025, Baolong Technology's air spring market share is expected to be 30%+, plus gas storage tanks, air suspension ECUs, sensors and other components, the company's air suspension business revenue is expected to exceed 3 billion.
3.2.3 Kong Hui Technology - leading share of air springs
Zhejiang Konghui Automobile Technology Co., Ltd. is a national high-tech enterprise and a national specialized and new "little giant" enterprise. Co-founded in 2018 by Guo Konghui, academician of the Chinese Academy of Engineering, and his son Guo Chuan, Konghui Technology became the first domestic passenger car air suspension system manufacturer in June 2021, breaking the foreign monopoly. In April 2023, the dual-cavity air spring assembly will be mass-produced and equipped on the ZEEKR 009 model, and Konghui Technology is currently the first air suspension system or air spring assembly for brands such as Li Auto, Dongfeng Lantu, and ZEEKR Automobile, and the cumulative supply volume of Konghui Technology has exceeded 120,000 sets by the end of March 2023.
According to Kong Hui Technology***, in 2023, Kong Hui Technology will mass produce and supply 7 new models (a total of 10). The supply fixed-point letter obtained by Kong Hui has involved more than 30 models from 14 car companies such as Ideal, BYD, Changan, and VOYAH, and achieved 1 in 1Q23With sales of 700 million yuan, Konghui Technology currently has a total adult production capacity of 600,000 sets of air springs, and is expected to deliver more than 500,000 units of air suspension products to customers in 2023. According to Gaogong Intelligent Vehicle, from January to May 2023, the domestic share of Konghui Technology's air springs will reach 391%, Kong Hui Technology is currently the leader in the local passenger car air suspension business.
3.2.4 Tuopu Group - Air suspension business was fixed
Ningbo Tuopu Group covers nine business modules, including automobile chassis body lightweight business, interior functional parts, shock absorbers, thermal management systems, robot actuators, and air suspension systems. In 2022, it will achieve revenue of 16 billion yuan and net profit attributable to the parent company of 1.7 billion yuan.
According to the company's announcement, the company's air suspension system has been officially designated by 7 official designations, including the R&D and manufacturing of the front air spring assembly, the rear air spring assembly, and the integrated air supply unit (air pump, valve body, and ECU integration), which is expected to be delivered in batches in Q3 of 2023. In November 2021, Tuopu Group's first air suspension system manufacturing plant was opened, which can meet the needs of 500,000 vehicles per year after the plant is fully put into operation.
The electronically controlled air suspension system independently developed by Tuopu Group adopts a closed air supply unit. In contrast to traditional open-type air supply units, it integrates air compressors, distribution valves, and ECUs, among others.
3.2.5 Tianrun Industry: Open up the second main business of air suspension, and gradually develop the passenger car market
The predecessor of Tianrun Industry, "Tianrun Crankshaft", is mainly engaged in crankshaft business, connecting rod business and casting and forging business. In 2020, it was renamed "Tianrun Industry", and jointly established Tianrun Intelligent Control System Integration with Dr. Zhang Guangshi, an expert in air suspension, Zhang Guangshi has been deeply engaged in the field of air suspension for many years and has obtained many patents. The company's main products include commercial vehicle chassis air suspension, semi-trailer air suspension, engineering vehicle rubber suspension, suspension assembly containing ECAS, etc.
As the second main business, the air suspension business benefits from the traditional business: 1) the production and processing capacity of castings and forgings, which can realize the self-production of key structural parts of the air suspension system; In addition, the company has a heavy truck customer base, and has long-term cooperative relations with customers such as Weichai, Sany Heavy Industry, and Shangchai Power. 2) Assisted by the star technical team. 3) Jinan and Shanghai R&D centers will be established one after another, and large investment in new product development will be made.
Also in the field of commercial vehicle air suspension, the company refers to the development path of Vibracoustic to gradually achieve full market coverage in different regions and at different levels.
Refer to the article. 1] The latest analysis of the air suspension industry chain at home and abroad, local manufacturers welcome development opportunities, and the frontline of the automotive industry is observed2023-08-10
2] Intelligent car series, air suspension industry chain tracking: Baolong Technology, Kaizhong shares, Zhongding shares ......(2023-September) M&A and M&A industry chain map.
3] Depth of the air suspension industry: business model, competitive landscape, industrial chain and related companies in-depth combing of hy huibo information2022-10-17
Finishing of automotive materials network.