With the continuous growth of people's demand for personalized automotive products, the design and production of automobiles and their internal components have also shown diversified functional characteristics. Comfort is one of the core goals of car seat design optimization. At present, the design of car seats not only needs to follow the laws of ergonomics and ensure reasonable structure, but also take into account the relief of driving fatigue and the promotion of human health, and continuously enrich and enhance the functional value of seats. The introduction of graphene materials has a significant positive impact on improving the heating performance of car seats.

 

1 Analysis of the development trend of car seats

As a car product component that directly contacts the human body, car seats need to have good safety, comfort and environmental protection. With the continuous improvement of the personalized needs of the automobile user group, giving play to the role of intelligent technology and meeting users' requirements for car seat heating, massage, ventilation, etc. has gradually become the main direction and trend of current car seat product research and development design.

 

2 Overview of graphene materials

2.1 Features Graphene material is a honeycomb structure composed of carbon hexagonal materials. It is an emerging lightweight material with good functional characteristics in recent years. Graphene atoms have the characteristics of consistent structural distribution and present stable and firm properties. Since graphene materials are characterized by a single-layer structure and are both thin, light and flexible, they have good application advantages at both the physical and chemical levels and have high application value. From the perspective of conductivity, the electrons inside graphene will not be disturbed too much by external environmental factors during movement, and the conductivity is good. The thermal conductivity is similar to that of carbon materials. It can be used as a new experimental material and applied in multiple industries and fields.

 

2.2 Advantages

(1) Ultra-thinness. In the process of preparing graphene materials by chemical vapor deposition and redox methods, by optimizing the performance of the prepared graphene materials, the prepared graphene sheets can show a significant light, thin and light-transmitting effect.

(2) Toughness. Graphene materials have good toughness and elasticity. In the experiment, the stretched size of graphene materials can reach about 20% of their actual size.

(3) Conductivity. Affected by the single-layer atomic structure of graphene materials, the movement of electrons is confined to this layer of plane, thus giving graphene unique electrical properties. The study found that the combination of graphene materials with electronic components and equipment can significantly improve the power storage capacity of electronic products.

 

3 Comparison of heating performance of graphene and resistance wire

Based on the excellent performance of graphene materials, this paper mainly studies the application of graphene materials in seat heating performance. The study compares the traditional resistance wire heating method with the heating technology using graphene materials to evaluate their application effects.

 

3.1 Power comparison The comparative experiment of heating performance of graphene materials and resistance wire materials adopts the following steps.

(1) Heating pads are made of graphene materials and resistance wire materials respectively, and they are installed on two car seats.

(2) Temperature sensors are arranged at key positions on the seat surface to monitor temperature changes.

(3) The car seat equipped with the heating pad is placed in a high and low temperature test chamber, and the test chamber temperature is set to -10 ℃. After the temperature of each part of the seat is stabilized at -10 ℃, the indicators related to heating performance are tested, including heating efficiency, heating speed and temperature distribution uniformity.

 

The power of the heating pads using the two materials was compared. According to the standard of every 1 minute, the change of the current value after the heating pad was started was measured, and the corresponding power value was calculated to obtain the power change curve of the heating pads of the two materials. After obtaining the comparison results, it was found that the average power of the graphene heating pad was maintained at 55.8 W in the first 7 minutes, and dropped to 40 W after 7 minutes. In the subsequent detection process, its power has been maintained at 40 W. The average power of the resistance wire heating pad was maintained at 73 W in the first 13 minutes, and it dropped to 50 W after 14 minutes. It can be seen that the power used by the heating pad mainly based on graphene material is significantly less than that of the resistance wire heating pad.

 

3.2 Comparison of heating speed From the analysis of the heating speed of the heating pads using the two materials, in the actual test, the programmable linear DC power supply provides power supply for the two heating pads, and the voltage of 13.5 V is connected to the two samples respectively, and the change of the surface temperature of the car seat is detected and recorded. The test found that the temperature of the graphene heating pad can reach 40 ℃ when heated for 6 minutes and maintain around this temperature value. The temperature of the resistance wire heating pad only reached 40 ℃ when heated for 13 minutes. From the perspective of the temperature change range, within 2 minutes of starting heating, the surface temperature of the car seat equipped with the graphene heating pad can rise from -10 ℃ to 21 ℃, while the surface temperature of the car seat equipped with the resistance wire heating pad can only rise from -10 ℃ to 11 ℃. The test results confirm that the graphene material has a better heating performance than the resistance wire.

 

3.3 Comparison of thermal uniformity Taking thermal uniformity as the main content of the test, the thermal imaging of the surface of the car seat is mainly collected by infrared thermal imager. The test found that the surface temperature of the car seat with the graphene heating pad is more uniform, and the temperature of the car seat near the resistance wire with the resistance wire heating pad is significantly higher than other areas. It can be concluded that the graphene heating pad has better thermal uniformity.

 

4　Analysis of the application of graphene heating pads in car seats After verifying the superiority of graphene heating pads in car seats, combined with the actual application environment of car seats and the personalized needs of users, the combination of graphene heating pads and the functions of car seats themselves can better play the role of graphene heating pads.

 

4.1　Ventilation From the perspective of the heating function of car seats, the current car seats are mainly covered with heating pads with fabric or leather materials. Although the application of these materials can save the production cost of car seats, most of the materials have high density and are difficult to ventilate. Under the relatively closed and narrow space restrictions inside the car, the heating function of the heating pad can easily have a negative impact on the ventilation function of the car and the use effect of the car seat. To address this issue, the ventilation system of the seat must be carefully considered to ensure that the installation position of the graphene heating pad will not hinder the suction or blowing function, so as to play its heating role without sacrificing the ventilation effect.

 

4.2　Heating The application of graphene heating pads in car seats mainly heats the back, buttocks and other positions of the driver and passengers, helping the human body to relieve fatigue and improve the comfort of the car environment. The resistance wire heating pad used in the past only has a single heating function and is prone to uneven heating. The graphene heating pad can provide three-speed temperature control adjustment modes of high, medium and low by combining temperature sensors and heating controllers, effectively avoiding the problems of single heating function and uneven heating. In the design and production process, the power size and specifications of the heating pad must be fully considered to match the adaptability of the car seat to the selected heating pad type and the size and shape of the seat, so as to avoid the risk of fire caused by short circuit faults due to mismatch of model specifications. Therefore, when designing and producing heating pads, the specifications of car seats circulating in the market should be used as a reference to ensure that the specifications and types of the heating pads are compatible with the seats, and to ensure the quality and safety of the heating pad application.

 

4.3 Physiotherapy The application of graphene heating pads in car seat physiotherapy mainly starts from the massage function of car seats. After the graphene heating pad is powered on, the wavelength of the far-infrared waves generated by the graphene heating is concentrated between 6 and 14 µm. The far-infrared waves in this range are very close to the wavelength of the far-infrared waves generated by the human body itself, so in actual heating, the phenomenon of same-frequency resonance can be produced. In this case, the far infrared waves generated by graphene are more easily absorbed by the human body, thereby effectively improving human blood circulation, enhancing metabolism, and improving human immunity. Based on this effect, the use of graphene heating pads for car seat design can conform to the concept of healthy seats and play an important role in improving the functional value of car seats.

 

5 Design and Verification

In order to further play the role and value of the application of graphene heating pads in car seats, combined with the actual product structure of car seats, this paper designs and analyzes the graphene heating pads used for car seats to ensure that the advantages and characteristics of graphene can play a role in helping to improve the functions of car seats. The design and effect verification of graphene heating pads are mainly achieved from the following aspects.

 

5.1 Heating pad design When designing a heating pad based on graphene materials, it is required to combine the basic structure of car seats and traditional resistance wire heating pads, and determine that the graphene heating pad is mainly composed of breathable non-woven fabrics, breathable foam, base film, current collector, heating coating, and hot melt adhesive covering film. On the premise of clarifying the shape and size standards of conventional foam for car seats, the graphene heating pad is designed mainly with a curved structure, fillets are applied to the corners of the heating pad structure, flat cables are applied to the transition part, and circular riveting is used to connect the connection interface. In order to manually adjust and control the temperature of the heating pad, a temperature sensor needs to be installed at the head of the heating pad to collect the temperature. In order to give full play to the thermal conductivity of graphene materials, the breathable sponge is used as the main carrier of the heating pad, the heating pad is fixed on the breathable sponge, and then the combined device is fixed on the foam of the car seat.

 

On the basis of clarifying the basic structure of the graphene heating pad, the basic functions of the graphene heating pad also need to be considered. Combined with the analysis of the application of graphene heating pads in car seats, the graphene heating pad should have the functions of ventilation, massage and heating at the same time. The ventilation and heating functions are clearly introduced in the previous article. The massage function mainly emphasizes that when installing the graphene heating pad, the massage air cushions are arranged in groups at the position of the seat back, so that the graphene heating pad corresponds to the area where the massage air cushion is set. To achieve this goal, the graphene heating pad should be in the form of a flexible strip structure with an arc structure at the corner to cooperate with the movement of the massage airbag. In this way, the massage air cushion will not be damaged due to the deformation of the heating pad, and the massage function of the car seat can be effectively realized.

 

5.2 Heating pad verification In order to verify the application effect of the graphene heating pad in the car seat, the use function and performance of the graphene heating pad are verified in combination with the production quality standard requirements of automobile products. According to the current technical requirements and test methods for automobile seat heating pads in my country's automobile industry standard documents, the quality performance and application effect of the graphene heating pad are verified, mainly involving the four basic indicators of the graphene heating pad in terms of heating function, kneeling endurance, load capacity and ventilation capacity.

 

(1) The heating function test is specifically divided into two aspects: heating uniformity and temperature rise test. Referring to the test principles of 3.2 and 3.3 of this article, it is clear that in the test of heating function, the temperature difference between each temperature measuring point on the surface of the car seat and the set temperature value is within 1.5℃ as the standard for the inspection of heating uniformity; the temperature rise test requires that the temperature rise rate of multiple temperature measuring points on the surface of the car seat meets the requirements of relevant verification standards.

 

(2) The kneeling endurance test includes two aspects: sitting simulation test and swing and bounce test. The sitting simulation test requires the mechanical device of the heating pad to rotate outward and return at an angle of α along the Z axis. Under a load pressure of 900 N, 12,000 cycles are required for each angle. The swing and bounce test mainly simulates the impact of the human body on the backrest of the car seat when the car rotates and slides. According to the general human force standard, a force of 450 N is applied to the backrest of the car seat. Under the action of the force, the heating pad rotates 5° left and right with the x-axis as the center. After four repetitions, the downward sliding distance along the Z axis is based on 150 mm. The test is required to be repeated 50,000 times.

 

(3) The load capacity test is mainly based on the kneeling test. In the actual test, it is necessary to apply 0 N, 1,000 N, and 0 N test forces at the selected test points in turn, and the loading process cycle of this force is controlled to be about 4 s. Then the power of the graphene heating pad is turned on for 3 minutes and then turned off for 7 minutes. According to this operation, each test point was tested 7,500 times.

 

(4) The ventilation capacity verification is mainly carried out by ventilation test. Under normal air density, a 70 kg dummy is used to simulate the actual load of the car seat. This process requires the measured air volume to be above 130 L/min. According to the above test standards and methods, the performance and application effect of the graphene heating pad are tested. The results show that the application of this type of heating pad meets the relevant functional requirements of the car seat and can play an important role in improving the quality of car seat products.

 

The application experiment of the graphene heating pad proves that it has better performance than the traditional resistance wire heating pad, can meet the optimization design requirements of the car seat, and has good application and development prospects. As a new type of nanomaterial, the application of graphene heating pads must also consider the issue of production cost. In the future development of the automotive industry, we should further strengthen the optimization and development of graphene materials and production process technology, reduce costs, and let the graphene heating pad play a role in car seats, so as to effectively improve the overall quality of automotive products.

 

6 Conclusion

Applying graphene heating pads to the optimization design of car seats can effectively improve the comfort of car seats, enhance the overall value of car seats, and promote the improvement of the overall quality of automobile products. Car seat design based on graphene materials should combine the heating function of graphene heating pads with the functions of car seats themselves on the basis of clarifying the properties of graphene materials themselves. Verification results show that graphene heating pads can effectively improve the design level of car seats.

Foaming is an extremely important process in the design and manufacturing of automobile seats. During the operation, raw materials such as polyether and isocyanate need to be mixed together to promote chemical reactions under certain pressure and temperature conditions, and finally complete the shaping and manufacturing of the seat. In recent years, my country's automobile consumer market has expanded significantly. How to improve the foaming performance of automobile seats and how to strengthen the anti-collapse design of automobile seats have become the focus of many automobile design and manufacturing companies.

 

1 Types of automobile seat foaming technology

 

1.1 Composite foaming of cover The emergence of composite foaming of cover is mainly to solve the defects of traditional process. In the traditional mode, the seat cover and the foam body are designed and manufactured separately. After the foam body is cured, the two are connected to form a whole by means of Hog Ring or Velcro. This coating scheme has a relatively large workload, and the coating operation tolerance is difficult to control. The skin may wrinkle, affecting the appearance. With the development and improvement of automobile seat foaming technology, the PIP method has entered the seat design and manufacturing link. The mold is fixed to the cover, and the pouring and curing are completed at one time, which can effectively avoid the wrinkle problem. However, the PIP method also has certain limitations. It is difficult to fix the mold, which may lead to an increase in the scrap rate. Therefore, at this stage, many automobile manufacturers have begun to decompose the entire structural layer of the seat from top to bottom and analyze the foaming materials in the structural layer. The foaming layer is located within the leather composite layer, which can better solve the wrinkle problem on the seat surface, reduce the scrap rate, and improve the comfort and aesthetics of seat manufacturing.

 

1.2 Comfortable foaming Comfortable foaming is a manufacturing process that fits the foaming surface of the seat. Audi's cut foam is a representative type of this process. Its seats use a multi-layer foaming method, and the hysteresis loss rate close to the surface layer is low. Different characteristics are related to different perception directions of comfort. During operation, it is necessary to mix polyurethane and foaming agent according to the ratio, and add a certain amount of catalyst and stabilizer to make the mixture react and expand quickly and fit the inner wall of the mold. The main component of the seat filling layer obtained under this process is polyurethane foam sponge, which has a relatively high-quality pore structure, low density, light texture, and ideal softness and elasticity. It can achieve shock absorption and buffering effects and conform to ergonomic principles. Therefore, it is also called "memory sponge layer". In addition, the durability and wear resistance of this material attached to the foam surface of the seat are also relatively outstanding. Even in a long service life, it can ensure a good user experience, improve riding comfort while extending the service life, and delay the deformation and aging speed of the car seat.

 

1.3 Foaming body According to different foaming reaction conditions, the foaming body can be subdivided into hot foaming and cold foaming. Among them, hot foaming is more commonly used in the European automobile manufacturing industry. During operation, the mixture needs to be poured into the mold and cured at 220~250℃ to form a flexible cured foaming structure. After demoulding, the surface layer is well connected to make a finished seat that can be used. The seat made of hot foaming has good heat resistance and a slow aging speed in a high temperature environment, but the energy consumption is relatively large. Cold foaming is a common method in my country's automobile manufacturing process, and the existing production line system is relatively complete. When applied, the mold needs to be heated first, and then the PU mixture is poured for demoulding. Compared with hot foaming technology, this technology has a relatively low energy consumption level and more considerable economic benefits, but the production line needs to add mold temperature controllers, bubble breakers, etc., and the equipment system is relatively complex.

 

2 The relationship between the collapse of automobile seats and foaming performance

 

2.1 The permanent deformation rate under different foaming performances In order to verify the relationship between the collapse degree of automobile seats and foaming performance, a special research test was designed. In the permanent deformation rate test, four groups were mainly set up to simulate different working environments of automobile seats. Group A simulates a hot and humid environment, with a test temperature of 50 ℃ and a humidity of 95%; Group B simulates a dry and hot environment, with a test temperature of 70 ℃ and a humidity of 50%; Group C simulates a normal temperature environment, with a test temperature of 23 ℃ and a humidity of 50%; Group D simulates a low temperature environment, with a test temperature of -30 ℃ and a humidity of 50%. The samples are numbered from 1# to 4#, where 1# uses low-hardness foaming, and the density of the foaming material is controlled at 45 kg/m 3; 2# uses high-hardness foaming, and the density is also 45 kg/m 3; 3# uses low-hardness foaming, and the density is controlled at 70 kg/m 3; 4# uses high-hardness foaming, and the density is 70 kg/m 3. The dimensions of the four groups of samples are 100 cm×100 cm×50 cm, and the height of the samples is measured uniformly before the test. Then the samples are compressed to 75% and placed in different temperature and humidity environments for testing. After 24 hours of storage, they are taken out, the height is re-measured, and the permanent deformation rate is calculated. The calculation method is (initial height-height after deformation)/initial thickness×100%. The specific test results are shown in Table 1.

 

 

From the test results, the average permanent deformation rate of the seats in Group D is the lowest among the four groups, indicating that the deformation and aging speed of the seats is relatively slow in low temperature environments, while the average permanent deformation rate of the foam material in Group B's dry heat environment is the highest. This may be because the high temperature environment destroys the original stable structure of the foam material, causing the water in it to be lost, reducing the material's resilience, and causing the permanent deformation rate to increase. From the perspective of material manufacturing technology, in the wet and hot environment of Group A, the 1# low-hardness, low-density foaming method has the highest permanent deformation rate, and the 4# high-hardness, high-density foaming method has the lowest permanent deformation rate. Analysis found that this may be because the internal structure of the 1# material is looser under the same size, and its own resilience after compression is weaker. Coupled with the influence of the wet and hot environment, the curing ability of the sample is insufficient, and some materials even stick together, resulting in an increase in the permanent deformation rate. In the dry heat environment of group B, the permanent deformation rates of samples 1# and 3# are relatively high, both exceeding 65%, while the permanent deformation rate of sample 4# is the lowest, because the internal structure of the material is more compact under the high hardness and high density foaming method, the internal rebound expansion stress is higher after compression, and the height loss will be reduced accordingly, followed by the 2# high hardness foaming method. Although its density is low, the addition of foaming agents, catalysts, etc. will increase the adhesion and connection between microscopic molecules, and enhance its ability to resist loads and prevent deformation. The permanent deformation rates of samples 1# to 4# in groups C and D are basically maintained at around 1%, and the overall difference is not large. These test data show that under high temperature (50 ℃+) and high humidity (70+) environments, the permanent deformation rate of long-term compressed foaming will increase, and the seat will collapse, while under low temperature and room temperature environments, the permanent deformation of the seat is relatively small. In addition, high hardness and high density have a certain optimization effect on foam deformation after wet heat; other parameters are not strongly correlated with foam collapse after durability. When the foaming process is applied to automobile seats, the foaming hardness and density can be appropriately increased to optimize durability. Considering that high-hardness foaming may damage comfort, the process plan can also be optimized and adjusted, using low-hardness foaming in the seating area and high-hardness foaming in the support area, setting a material separation groove in the middle, adding embedded parts, etc., while reducing the permanent deformation rate, improving the durability of the seat.

 

2.2 Test results of seat cushions and backrest springs under different foaming conditions

In addition to the permanent deformation rate test, this study also conducted performance tests on seat cushions and backrest springs. The main test instruments are seat static load testers, laser marking instruments, rotating platforms, and angle meters. The main test materials are Φ50 mm indenters and seat cushion samples with a size of 250 mm×350 mm×5 mm. The samples use 4 different foaming methods, and the specific parameters are the same as 2.1. The main purpose of the test is to simulate the human body's sitting position and load action scenarios, and objectively evaluate the deformation performance of seat cushions and backrests under different foaming conditions. To achieve this goal, the load application point and data measurement point must be accurately calculated and marked before the test begins to provide support for subsequent measurement operations.

 

First, fix the seat frame on the positioning fixture, and refer to the design plan to adjust the seat to a suitable reference state. The test data is mainly collected by the laser line marker, so the instrument cross cursor should be aligned with the center of the seat REC test to facilitate the instrument to identify the target and collect data. Then, according to the human body's riding habits, find the intersection of the torso line and the thigh line, that is, the H.P point, readjust the state of the laser line marker, and align it with the H.P point by shaking the handle. With the help of the laser line marker, project the red line, find the intersection between the red line and the center axis of the seat, mark it as point b, and move it up 35 mm to mark point a. Fix the seat on the rotating platform and adjust the seat angle based on point b until point b is in a horizontal state.

 

After the adjustment preparation is completed, the simulation test can be carried out. Adjust the static load tester pressure head to ensure that its center point is aligned with the marked pressure point a, then place the sample to be tested, adjust the static load parameter value to 350 N, and control the loading speed to 200 mm/min for testing. To ensure that the test instrument is in good operating condition, the initial load parameter of 5 N can be used for pre-pressing during operation. No data needs to be recorded during the period. After unloading, formal test is carried out and relevant test results are recorded. After completion, change the load to 200 N and record the deflection at points a and b. When testing the backrest, the seat fixing adjustment method is the same, but it is necessary to use the H.P point as the center, vertically paste the masking tape along the Torsoline direction, and mark multiple measurement points at intervals of 50 mm to complete the data collection.

 

The results show that the collapse of the 4# cushion is the slightest, followed by the 2# cushion, and the 1# and 3# cushions are the most serious. The collapse depth is 2~3mm, and the collapse amount at the center of the test point is the largest and gradually decreases outward. In the backrest spring test, the foaming structure of the 1# backrest was damaged and some springs were exposed. This may be because the internal structure support capacity is insufficient under the low-density and low-hardness foaming method. The structure was damaged during compression, resulting in exposure. The hardness of the 3# sample is relatively small and the deformation is relatively large, but due to sufficient density, there is no spring exposure. The 4# backrest collapsed the least, but excessive hardness may reduce comfort. The 2# backrest has high hardness but relatively low density, and only a slight collapse occurred.

 

3 Methods for preventing automobile seat collapse and foaming performance optimization methods

 

3.1 Methods for preventing seat collapse From the above analysis, it can be found that the application of high-hardness foaming can improve the performance of automobile seat materials to a certain extent, reduce its permanent deformation rate, and extend the service life of seats, backrests, etc. However, excessive hardness of foaming materials will lead to reduced riding comfort. Therefore, while improving the foaming technology, it is also necessary to explore practical and feasible methods for preventing seat collapse. Research can be carried out from the following two aspects.

 

(1) Seat spring optimization design. The main reason for the collapse of the seat cushion is fatigue and bumping. During the bumpy driving of the vehicle, the impact force generated can reach more than 3 times the body weight of the human body. This can be used as a reference value when designing the spring to optimize the selection of spring materials and adjust the diameter of the spring wire to ensure that the spring can withstand a load of more than 2,250 N (assuming the weight of the passenger is 75 kg).

 

 (2) Optimization design of the seat wire structure. The unreasonable connection between the wire structure and the frame is also an important reason for the collapse of the seat. After the connection part slips, the seat loses support locally, which can easily lead to collapse. Therefore, when designing and manufacturing, it is necessary to reasonably select the material and length of the connection material to improve the fixing performance of the wire structure and reduce the risk of seat collapse.

 

3.2 Foaming formula/performance optimization The foaming formula will also affect the performance and durability of the car seat. Therefore, the anti-collapse design also needs to actively optimize the formula and raw materials to promote the improvement of foaming performance. The common foaming raw materials are mainly polyurethanes, among which the polyols have strong flexibility and can improve the rebound rate of the foaming material. The specific types include polyether polyols, polyester polyols, etc. Isocyanate is the key component involved in the foaming reaction. The options include TDI and MDI. The types and proportions should be adjusted according to the actual situation. At the same time, the chain extenders used in different polyurethane raw materials are also different. This substance can effectively extend the length of the molecular chain and improve the uniformity and stability of the foam. The optional types include ethylene glycol, propylene glycol, etc.

 

Foaming agents and catalysts will also directly participate in the foaming of car seats, which can promote the expansion of raw materials and shorten the foaming time. In the actual design and manufacturing process of car seats, it is necessary to scientifically grasp the properties and characteristics of different components, determine the best ratio through the design of parallel tests and comparative tests, ensure the improvement of car seat comfort and safety, and ensure the extension of seat service life.

 

4 Conclusion

 

The foaming process directly affects the user experience of car passengers, and it must be given full attention in practice. Automobile companies should deeply study and grasp the characteristics, advantages and disadvantages of different foaming technologies, and choose appropriate types of foaming processes in combination with automobile brand positioning, audience needs and economic costs. Experiments show that there is a correlation between the collapse of car seats and foaming performance. Therefore, we should understand the permanent deformation rate of the seat, the performance of the seat cushion and backrest springs under different foaming conditions, and design the seat springs and seat wire structure on the premise of fully mastering the quantitative data. We should scientifically adjust the foaming formula and proportion to lay a solid foundation for improving the quality of car seats.