0 Introduction. With the advancement of automobiles towards electrification and intelligence, pure electric vehicles will become the most important means of transportation for people to travel in the future. As an extremely important component of the interior system, the seat structure and function have a direct impact on the ride comfort and safety of the driver and passengers. Based on the requirements of ergonomics and human sitting comfort, the car seat should make the human body have a good body pressure distribution to ensure the riding comfort of the driver and passengers. When designing the seat, under the condition of ensuring safety, strength, rigidity, energy saving and environmental protection, it is also necessary to consider factors such as seat comfort and aesthetics. Seat is one of the auto parts with the largest contact area and longest contact time between people and the automotive interior system, and its aesthetics and comfort have also become important considerations for consumers to choose a car. With the application of AI intelligent technology in car seats, in order to meet the driving comfort needs of drivers and passengers of different heights and sizes, pure electric vehicle seats not only need to have a variety of conventional functions such as height adjustment, front and rear adjustment, seat cushion and backrest angle adjustment, but also need to have the advantages of lighter, safer, comfortable and intelligent. Compared with fuel vehicles, the body structure of pure electric vehicles is different, and the engine and its auxiliary systems are canceled and the power battery is added, and the seat boundary environment is quite different, so it is necessary to study the seat structure and parameters, material selection and development trend of pure electric vehicles, so as to provide guidance for future car seat design.
1. The main structure and parameters of the seat.
Seat comfort is an important basis for consumers to choose a car, which mainly involves several aspects such as static comfort, dynamic comfort, and convenience of operation. Seat structural parameters are the basis for seat design and comfort studies, so they need to be continuously adjusted and optimized according to the results of seat evaluation.
1.1 Seat cushion.
Seat cushion length: The length of the seat cushion has an extremely important impact on the riding comfort of the driver and passengers, the seat cushion length is too short will lead to insufficient leg support of the driver and passengers, the seat cushion length is too long will affect the activity space of the driver and the passenger's calf, and even more so, the front edge of the seat cushion interferes with the occupant's calf, affecting the riding comfort. Generally speaking, the length of the seat cushion can be controlled between 460mm and 510mm depending on the vehicle level and the cabin space. For car seats with additional leg rests, the relationship between the length of the seat cushion and the leg rest and the rotation mechanism should be balanced in combination with ergonomics and the force on the human legs.
Seat cushion width: In order to improve the riding comfort of drivers and passengers, combined with ergonomics and pressure distribution of the human femur, the seat cushion width can be controlled between 490mm and 530mm.
Seat cushion angle: The seat cushion angle has an important impact on the riding comfort of the driver and passengers, generally speaking, if the seat cushion angle is too large, the hip angle will be reduced, and the leg pressure of the driver and passengers will be increased, and the riding comfort will be reduced. If the angle of the seat cushion is too small, the seat cushion does not support the legs enough, and the driver and passengers are prone to fatigue during long-term driving. The seat cushion angle can generally be controlled at 12° to 16°.
Seat cushion thickness: Since most of the weight of the driver and passengers is concentrated near the seat H point, the seat cushion foam on the underside of the seat H point should have sufficient thickness to support it. If the seat cushion is too thin, it will affect the ride comfort, and if the seat cushion is too thick, it will increase the manufacturing cost of the seat. Basically, the foam thickness of the front seat cushion can be controlled at more than 60mm, and the rear seat can be controlled at more than 90mm.
Seat cushion depression: If the depression is too small, the driver and passengers will feel that the seat is stiff when sitting in the seat, which will affect the comfort. If the amount of depression is too large, the driver and passengers will feel that the seat is soft and people will be trapped in the seat, and it is easy to get tired when riding for a long time. The amount of hip depression in the conventional design can be controlled at 20mm 60mm, and the amount of leg depression can be controlled at 20mm and 50mm. When the rear seat is limited by the influence of the vehicle space factor (such as the rear wheel cover), and the backrest angle cannot be greater than 90 °, in order to ensure the comfort of the seat, the depression of the rear seat cushion can be slightly greater than the depression of the front seat cushion, and the depression of the rear seat cushion can be controlled at 35mm 70mm.
1.2 Seat frame.
Seat frame, including backrest frame and seat cushion frame. Among them, the seat cushion skeleton mainly provides support for the buttocks and thighs of the driver and passengers, so that they can maintain a comfortable sitting position, avoid the body swaying from side to side during driving, and provide protection in the event of a car collision. The seat frame is often bent with 20mm 25mm outer diameter and 1mm 2mm thick steel pipe or welded with steel pipe and steel plate, and can also be rolled or stamped with 1mm 3mm thick steel plate. A recliner or other backrest angle adjustment device is generally arranged between the backrest frame and the seat cushion frame, which is used to connect the backrest frame and the seat cushion frame and adjust the seat backrest angle.
When the driver and passenger sit on the seat and lean on the back of the seat, in order to prevent the back from touching hard objects and affecting the riding comfort, the human body needs to keep a certain distance between the backrest frame, which can generally be controlled at more than 35mm.
The forward adjustment angle of the front seat can be determined according to the position of the 95th percentile human body R point and combined with the slide rail stroke, instrument panel and other structures.
In order to ensure the riding comfort of the rear occupants, the angle between the center line of the thigh and the torso line of the occupants should be greater than 90°, generally 90° 115°. The seat adjustable backrest angle (the angle between the plumb line over the seat H point and the trunk line corresponding to the seat backrest) can be controlled at 0° 30°. For three-row seats, the maximum adjustable angle of the second-row seats can be determined when the second-row seats slide to the front position and the angle of the seat backrest is adjusted to touch the rear wheel cover trim.
1.3 Seat headrests.
The seat headrest is used to support the cervical spine of the driver and passenger, which can effectively relieve neck fatigue and protect the person from injury in the event of emergency braking or collision of the car. The height of the headrest in the vertical direction should be controlled at the height of the center of mass of the human head, and the vertical distance between the highest position of the headrest and the H point of the seat should be controlled at more than 720mm, so as to effectively support the head of the driver and passenger.
1.4 Seat slide and slide rail travel.
1.4.1 seat rail.
In order to meet the requirements of the driver and passengers for control and riding comfort, the seat should have the function of adjusting the front and rear directions, which needs to be realized with the help of the seat slide rail.
At present, almost all models are equipped with seat slides for the front seats, and some high-end five-seater models and three-row six- or seven-seater models are also equipped with slide rails in the rear row to realize the front and rear adjustment of the rear seats. The seat slide rail is fixed with the body floor by bolts, the upper slide rail is connected with the seat frame, and there are rollers and balls between the upper and lower slide rails. The seat and the upper slide rail are driven to move along the axis of the slide rail by manual or electronic control, so as to realize the front and rear adjustment of the seat. The commonly used slide rail types mainly include T-type, W-type, C-type, H-type, etc., and the H-shaped slide rail is used in some six-seater SUV models and MPV models, which can realize the adjustment of the left and right directions of the second-row seats. At present, the front and second row seat rails of most models are separated, as shown in Figure 1. Because the pure electric vehicle cancels the fuel tank and adds the power battery, and the power battery is mostly flat arranged under the body floor between the front and rear subframes, it creates conditions for the seat to adopt the structural type of the long slide rail. Fig. 2 is a partial schematic diagram of the front and rear seats using a long slide rail, but the front and rear seats should be balanced with the relationship between the front and rear seats and their peripheral parts such as wheel covers and trim plates.
1.4.2. Determination of the stroke of the seat slide.
The travel of the front seat slide should be determined in combination with the 95th percentile ergonomics, ride comfort and safety collision factors. Generally, if the front seat is equipped with a short slide rail, the slide rail travel should be controlled at more than 240mm, and the length of the slide rail of some mainstream or high-end models is controlled at 260mm or more. If the front and rear seats are equipped with long slides, the slide travel is more flexible.
Due to the constraints of seat rails, rear wheel bags, wheel covers, and manufacturing costs, the rear seats of many models only retain the folding function and do not have the function of seat adjustment. When driving a car, if the body posture remains unchanged for a long time, it is easy to cause problems such as lumbar spine and back discomfort. As shown in Figure 3, in the three-row seat model, the front row seats are moved to the last position, and when the third row of human bodies is guaranteed to be more comfortable sitting posture and good head space, the head space of the second-row human body is more spacious, and the rear seats are provided with the possibility of increasing the seat frame, and also create conditions for the realization of functions such as seat multi-directional adjustment, massage, ventilation and heating. At present, more and more models of pure electric vehicles have added adjustment functions to the rear seats, especially in some high-end five- and three-row seats.
When determining the adjustable travel of the front and rear of the second-row seats, when the front row of seats slides to the front limit position, when the legs of the second-row 95th percentile human body touch the backrest of the front seat, it is the front limit position of the second-row seats X1. When the backrest of the second-row seats touches the rear wheel cover trim, it is the theoretical position of the rear limit of the second-row seats x2, and the ultimate position of the seat also needs to be comprehensively determined by considering the gap between the seat and functional parts and the rear wheel cover trim plate and the arrangement space of the seat slide rail on the body floor. The distance between x1 and x2 is the effective travel of the second row of seat rails.
2 Seat Materials.
Pure electric vehicles have eliminated the engine and its ancillary systems in the combustion engine vehicle, and added the motor and power battery. The power battery structure is large in size and weighs up to several hundred kilograms. As one of the components with large structural size and weight in the interior system, the material selection, lightweight design and manufacturing process of the skeleton structure are of great significance to achieve the goal of vehicle weight reduction.
2.1 High-strength steel.
High-strength steel is used in the car seat frame due to its high yield strength and tensile strength, which can significantly reduce the weight of the seat. Because most of the raw materials of high-strength steel need to be imported, the cost is relatively high, and the problems of poor cold forming ability and low ductility of high-strength steel restrict its application in seat frames.
2.2 Aluminum alloy.
As a lightweight material, aluminum alloy has the advantages of low density, light weight, impact absorption ability and thermal conductivity, and has been used in body-in-white and wheel parts for a long time [8]. However, due to the high cost of aluminum alloy raw materials, poor welding performance, molding process and other limitations, its application in aircraft and high-speed rail seat frames is relatively mature, and its application in automobile seat frames is low, which can be used as the direction of car seat material selection.
2.3 Magnesium alloys.
Compared with high-strength steel and aluminum alloys, magnesium alloy has lower density, lighter weight, higher strength, stiffness, stability, better thermal conductivity and vibration absorption and easy forming. In addition, magnesium alloy die-casting molds have two to three times the service life of aluminum alloys, and the process cost is lower than aluminum alloys, and there are successful precedents for applying magnesium alloys for lightweight design in seat frames. However, in the die casting process, magnesium alloys are prone to microscopic defects and have low fatigue strength, and galvanic corrosion problems occur when they are connected to steel. The above are the problems that need to be solved urgently in the application of magnesium alloy for seat lightweight design.
2.4 Composites.
Composite materials made by mixing plastic materials such as PP and PA6 with high-strength materials such as carbon fiber and glass fiber are also one of the directions for the lightweight design and selection of pure electric vehicle seats in the future. The use of plastic and fiber composites for the seat frame reduces the weight of the seat by about 40% and can reduce production costs. Plastic materials can also be combined with metal inlays to form composite materials, and injection molding processes are used to form seat frame structures, which can also reduce weight and costs. In addition, the seat frame made of carbon fiber prepreg and wood fiber composite material can effectively improve the NVH performance of the vehicle by reducing the weight of the seat and CO2 emissions, while also improving the sound absorption function. The connection between the seat frame made of composite materials and metal parts such as seat rails and recliners is a major problem to be solved for the lightweight design of the skeleton.
In recent years, EPP (Expanded Polypropylene), a plastic foam material with more weight reduction potential, has emerged, which is light in weight, has good stability, heat resistance, low temperature characteristics and energy absorption, etc., because of its own lack of strength, it needs to be matched with the steel skeleton to meet the strength requirements. Due to the high cost of raw materials, the core technology of EPP material is still shallow in China, but it has excellent performance, and it is also one of the key directions for the selection of lightweight design materials for seats in the future.
In addition to the above-mentioned materials, more environmentally friendly and energy-saving materials such as recycled rattan wood, bio-based materials, etc., are also the research direction of lightweight seat design materials in the future because of their low raw material cost, strong processability, light weight and degradability.
3 Future Seat Development Trends.
As one of the interior parts that are sensitive to user perception, the structure and function of the seat are also increasing day by day. With the continuous improvement of consumers' requirements for car ride comfort, the seats of some models launched by various OEMs have appeared in the seats of eight-way adjustment, ventilation and heating system, electric lumbar support, leg rest, foot rest, electric massage, charging, multi-functional headrest and other functional configurations, and even in some high-end models have become standard. Car seats are developing in the direction of intelligent networking, human-computer interaction and more entertainment and comfort.
3.1 Intelligent networking.
At present, the multi-directional position adjustment of car seats is mostly controlled by buttons or knobs, and the buttons or knobs of some seats are arranged more hidden, which is not easy to find and also occupies space. In the future, seats are bound to be equipped with more and more AI intelligent technology, and seat adjustment buttons or knobs may disappear and be replaced by a touch display, which can display the seat position and backrest angle in real time, as well as the temperature of the seat cushion and backrest, and be equipped with Bluetooth or intelligent voice system and can be interconnected with mobile terminals such as mobile phones, and the seat position and temperature can be adjusted through voice or mobile terminals. The seat is equipped with a memory function, when the driver and passengers sit in the seat, the seat position and backrest angle can be automatically adjusted according to their settings, and the seat heating or ventilation system can be automatically turned on through the seat cushion temperature, humidity and other signals monitored by the sensor.
In addition, the seat can also be equipped with an intelligent human physiological information collection device and a customized medical diagnosis terminal, which collects physiological information such as body temperature, respiratory rate and heart rate of the driver and passengers through various sensors arranged on the seat and inputs them to the medical diagnosis terminal, so as to realize routine health monitoring and early warning of personnel.
3.2. Human-computer interaction.
At present, the welcome function has been configured in some high-end models, that is, when the driver and passengers get on and off the car, the seat automatically slides back to a certain preset distance and rotates outward at a certain preset angle to facilitate personnel to get on and off the car. With the successive introduction of three-row seats and the continuous improvement of consumers' requirements for vehicle space and cabin flexibility, the rear seats of future models will also be equipped with welcome functions. In the three-row six-seater model, the front and rear seats can be equipped with long slides and lateral slides, so that the front and rear seats can slide horizontally and vertically simultaneously, making the use of space in the cabin more flexible.
In addition, the front and rear seats can be equipped with swivel discs and small tables according to the boundary conditions of the vehicle to achieve 360° rotation. Combined with the configuration of the sliding sub-instrument panel, it can realize multiple scene modes such as welcome, meeting and parent-child of the seat.
When the driver and occupants are seated, the seat memory function automatically adjusts the seat position and backrest angle. In the process of riding, when the sitting posture of the person changes greatly for a long time, the seat can automatically adjust the angle of footrest, leg rest, lumbar support, seat cushion and backrest according to the angle information of the feet, legs, torso and the force of the human spine collected and calculated by the sensor, and can automatically trigger the electric massage function according to the user's customization, which has stronger human-computer interaction.
3.3 Entertainment comfort.
3.3.1. Entertainment.
Traditional in-vehicle entertainment audio-visual and navigation systems are mostly realized through the central control screen to control multiple high-woofer speakers arranged in the instrument panel, door guards and other positions. In the future, the structure and appearance of the seat will largely break the original seat design, and more new elements and new ideas will be added to the seat structure. Some of the more high-end models now have swivel or fold-out displays behind the seat backrests to allow rear passengers** and control the entertainment system.
Some seat manufacturers have begun to study the configuration of headrest audio and interactive microphones in the seats, so that the sound can be transmitted directly from the seat to the human ear, so as to avoid affecting the driver and ensure driving safety. Drivers and passengers can also directly control the navigation system through the microphone, making travel more convenient and faster, creating a more intelligent and human-computer interactive immersive cockpit.
3.3.2. Comfort.
A model that has entered the market has canceled the glove box on the right side of the instrument panel due to the use of a central air conditioning system, and the passenger side is provided with a seat long slide rail, which has created conditions for its configuration of the queen's co-pilot, adding leg rests, foot rests and other functions. The Queen's co-pilot can make the co-pilot occupant nearly lie flat, providing the occupants with more flexible riding space. In the future, the seat will be equipped with a fully wrapped airbag, which will be integrated with the seat to provide more comprehensive safety protection for the occupants. 、
In order to reduce the vibration of the cockpit and personnel caused by uneven road surface, rapid acceleration, rapid deceleration and other reasons, the seat cushion and backrest of the car seat will be equipped with a shock absorbing device with better performance in the future. For example, the seat backrest can automatically move according to the movement of the driver's spine, and always keep the angle of the human torso within the most comfortable range, effectively improving the riding comfort of the driver and passengers.
At present, zero-gravity seats that combine ergonomics and zero-gravity technology have appeared, and the modeling surface of zero-gravity seats is more in line with ergonomics and the natural curve of the human spine, and can optimize the pressure distribution between the human body and the seat, so that the human body pressure distribution is more uniform. The seat fabric is made of high-quality leather fabric, which can make the seat feel softer and more delicate, and some high-end models use Nappa leather as the seat fabric, which can bring more extreme riding comfort to the occupants. Therefore, zero-gravity seats will also be one of the directions for the development of seats in the future.
It is foreseeable that smart seats with lighter structures and shapes and equipped with AI technology will continue to appear in new models launched in the future. When buying a car, consumers can freely choose seats with different functions and configurations, and can also customize the seats according to their actual needs, so as to truly realize the integration of people and vehicles.
4 Concluding remarks.
As an important component affecting the ride comfort of pure electric vehicles, the seat will be more diversified in terms of structural types and shapes, more flexible structural parameters, and lighter, energy-saving and environmentally friendly materials. The integration of AI technology will make the seats of future pure electric vehicles more intelligent, making them move towards intelligent networking, human-computer interaction, and entertainment comfort, so as to build the car into a safer, more comfortable, and intelligent mobile home.
Author: Kong Lingyang.
*: Research and Applications
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CIAIE2024 The 18th Shanghai International Automotive Seat Innovation and Application Technology Exhibition
When: August 2-4, 2024
Address: Shanghai New International Expo Center (No. 2345 Longyang Road).
1200+ exhibitors
20+ concurrent events.
At the same time, the exhibition was jointly sponsored by the Society of Automotive Engineers of China, the Society of Automotive Engineers of Shanghai, the China Association of Automotive Engineers, the Guangdong Automobile Industry Association, and the Yingfo Conference and Exhibition (Shanghai)**, the "China Automobile Chain Innovation Achievement Exchange and Shanghai Whole Zero Matchmaking Conference", with the theme of "innovation, empowerment and development", the "exhibition" and "meeting" were deeply combined, and the theme forum and the whole zero promotion matchmaking meeting were set up at the professional exhibition site. Experts and scholars and other industry elites attended. While displaying the most cutting-edge scientific and technological innovation products, exchange development hotspots, analyze development pain points, develop difficulties, gather wisdom, and discuss together, so as to provide a one-to-one communication platform for the whole zero enterprise, covering the upstream and downstream of the entire automotive industry chain, stabilizing the chain and strengthening the chain control chain, integrating industry forces, and promoting China's automobile chain to become bigger and stronger.