When it comes to comfortable car seats, many people first think of the wide, soft "big sofa" type, and it seems that this kind of seat that makes people find a home feeling in the car is the most perfect. But in fact, the big sofa does not have the three core elements that a comfortable car seat should have! Let me take you to understand what a really good car seat should look like!
Excitation table test
When it comes to car shock absorption, everyone usually only associates the shock absorption effect with the shock absorber, and it seems that little attention is paid to the dimension of the seat. But don't forget, people sit directly on the seat, and the seat is directly mounted on the floor of the car. The seat will not only receive residual vibrations that the shock absorbers cannot fully filter, but also vibrations generated when the car's powertrain is running. Speaking of this, it is estimated that many friends think that I am going to start talking about the impact of seat material and structure on the shock absorption effect. But in fact, before reducing the vibration, there is a more fatal thing to solve, that is, by avoiding the frequency of the road surface + powertrain vibration, to avoid the seat resonance!
Resonance caused by sound radiation
You know, any structure will have its own natural frequency, and the human body is no exception. When its own natural frequency coincides with the vibration frequency from the outside world, it will begin to resonate. As shown in the figure above, if the left and right tuning forks are the same, the sound radiation generated by tapping the left tuning fork will spread through the air, driving the right tuning fork of the same frequency to vibrate. If you change its own frequency by changing the length of the right tuning fork, then when the left tuning fork is struck, the right tuning fork will not resonate with it.
Don't underestimate the power of resonance, the following real accident should be heard: in the middle of the 18th century, on a bridge in the French city of Angers, a group of soldiers was preparing to pass a 102-meter-long bridge. It is reasonable to say that the weight of this pedestrian is far less than the load of the bridge design, but when they began to cross the bridge with a neat step, the bridge collapsed before they could go far, and the accident killed a total of 226 officers and soldiers and pedestrians. An after-the-fact investigation revealed that the cause of the accident was precisely because the frequency of the soldiers' steps coincided with the natural frequency of the bridge, and eventually the resonance of the two caused the bridge to break. It can be seen that the power of resonance is so great that even the engineering structures such as bridges and car bodies cannot withstand it, not to mention the fragile internal organs of human beings.
Seat travel resonance
Therefore, if the frequency of the seat is consistent with the frequency of human organs, then the human body will resonate, which feels like sitting on an old-fashioned bus, obviously the car is not driving fast, but the stomach is always turning over the river... If the vehicle's seat overlaps with the frequency of the tire and engine, then as shown in the figure above, the back of the vehicle will produce a visible sway.
Seat frame
In terms of vibration frequency, the natural frequency of human organs and heads is 3-12 Hz, the vibration frequency of engine idling is 23-26 Hz, and the vibration frequency generated by tire rolling is 3-18 Hz. So the first thing a qualified seat has to do is to completely avoid the above vibration bands. The vibration frequency of a seat depends on the three parts of the seat frame, the dragnet (the basket circle area above), and the backrest angle adjuster (the yellow circle area in the upper picture), and does not depend on the filling of the seat.
After avoiding resonance, the next step to consider is how to give the seat a good shock absorption effect, this task is mainly responsible for the seat cushion, cushion and dragnet. Among them, the thicker and softer the cushions and cushions, the better the shock absorption effect of the seat. The less rigid the pullnet, the better the shock absorption effect.
However, it should be noted that in the process of vehicle driving, the car seat is not an independent individual, it needs to match the chassis and steering characteristics of the vehicle. Because the cushion, cushion, and dragnet are equivalent to the suspension of the seat, and the vibration of the seat is an important way for the driver to perceive the road surface and obtain a sense of the road, if it is a model that is biased towards sports, the cushion and cushion must not be too soft, otherwise the splitting feeling caused by the driver's body and body dynamics and steering control will make people more uncomfortable. This means that when we evaluate the comfort of a seat, we cannot judge it solely by the size and softness of the seat, but to consider whether the seat can meet the design orientation of the car.
Subjective simulation test of the seat
For example, when BMW develops seats, it will conduct a lot of simulation tests. The engineer will collect the driving status data of a car in the enclosed field in advance, and then bring this data into the seat simulation equipment to test the state of the car with different seats, and invite people of different sizes to actually experience, and finally the engineer will improve the seat according to the subjective evaluation of the experiencer.
The mattress was too soft
In addition to the seat to conform to the tonality of the model, if you want to create a comfortable seat, it is not simply by making the cushions and backrest soft. This is just like the mattress, when we experience it in the mall, the too soft mattress can indeed bring a soft, comfortable feeling, but once we buy the overly soft mattress home and sleep all night, the feeling of back pain is far from the word "comfortable". So what kind of seats can reduce the fatigue caused by people riding for a long time?
We've all seen that if you put a spoon flat on the tabletop, the spoon can't be in full contact with the tabletop anyway. If this spoon is conscious, the head and handle of the spoon that bears its own pressure must have been numbed long ago
Like spoons, if viewed from the side, any person's body is composed of multiple curved surfaces, so when we sit on the flat and vertical metal or wooden dining chair at home, the body is doomed to fail to fit the straight back and chair surface, which will cause our hips, waist, and back pressure to be concentrated on a small area in contact with the seat, which will cause back pain. So in order to create a car seat that allows passengers to sit more comfortably, engineers have proposed two hard indicators for "good seats" based on ergonomics: the first is to allow the occupants' physical pressure to be distributed in a large area on the cushions and backrests; the second is that the passengers will not be allowed to have excessive pressure distribution at a certain point in the seat.
Seeing this, some friends will think that it is a good seat to distribute body pressure evenly throughout the seat. But this is not the case. Because in biology, there are some places in the human body that are inherently more suitable for stress, such as the human pelvis. And there are some places in the human body that are inherently unsuitable for weight bearing, such as the thighs that concentrate a large number of blood vessels and nervous systems, and a little more pressure will affect the body's blood circulation system and nerve conduction function, and eventually cause discomfort. This means that the best pressure distribution of the seat cushion should be that the pressure is evenly distributed from the pelvis from the largest to the smallest to the thigh.
So far, we have figured out the pressure distribution characteristics that a "good seat" should have, so what method should the engineer do to achieve it?
Pressure test with a pressure pad
In order to objectively and accurately judge the pressure distribution of the seat and the fit of the seat, the engineers designed a pressure pad that can accurately display the contact area of the human body and the value of the pressure distribution. Simply lay it on the seat and the pressure exerted on the cushions and backrests after the passenger is seated can be converted into data. This allows the passenger-seat junction area and pressure distribution to be clear at a glance. Once the verification method is in place, the next step is for engineers to start optimizing the seat's filler.
The softness and stiffness of the seat filling will directly affect the pressure distribution of the passenger's body. Among them, the harder the filling, the more concentrated the pressure on the body, just as a hard seat will cause people to feel uncomfortable sitting on a stone; and the softer the filling, the easier the pressure on the body will be dispersed, just like the palm pressed into a soft sponge. However, if the padding is too soft and the seat cannot provide the necessary and uniform support for the muscles and bones of the human body, then when the driver hits the direction, presses the accelerator/brake pedal, or copes with body postures such as over-bending and bumps, the body needs to complete the action and maintain balance through additional force. In addition, coupled with the fact that the muscles and bones deviate from the normal physiological posture, it is easy to have low back pain when driving long distances.
Seat pressure
Therefore, a good seat will not pursue softness too much, but will design the softness and hardness of the filling according to the characteristics of the human body. On the side of automobile manufacturers, the indicator of "pressure subsidence" is usually used to evaluate the softness and hardness of the seat. Under the same force weight, the softer the seat, the greater the pressure recess, and the harder the seat, the smaller the resupposition. When passengers are seated, because the hips will bear a larger body weight, a larger amount of pressure filler is needed to disperse the pressure. The waist, back, and shoulders are small in weight and require certain support, so the amount of pressure on the backrest is smaller than that of the cushion. In general, the pressure retraction of the seat cushion ranges from 35-60mm, while the backrest is 25-40mm.
However, we also said above that although the softer filling can give people a comfortable first impression, due to insufficient support, it will be more likely to fatigue after a long time. The harder filler will directly attract scolding because of the poor pressure distribution. So is there a way to make a good chair that is both soft and supportive? In fact, you only need to match the soft and hard of the filling to achieve ~
Multi-hardness seat foam
When designing the seat, in addition to the soft combination of the middle of the cushion and the hard and soft wings on both sides, in fact, the same area can also be soft and hard. For example, in the cushion part, you can use a double-layer hardness filler with soft surface and hard underneath. In this way, when passengers are seated, a soft cushioning sensation is instantly generated, while the harder padding of the lower layer can also ensure good support to reduce fatigue during long-distance driving.
Different body types and weights
While we now have a way to build the right pressure distribution seat, that doesn't mean the same seat will satisfy all Earthlings. As we said above, when a chair is designed, engineers will collect data from the experiencer to verify that the pressure distribution of the seat is reasonable and adjust it. However, due to the geographical limitations of the headquarters of car brands and seat suppliers, and the tendency to prioritize serving local consumers, the data collection experiencers they recruit are basically people from the brand's country. Because the people in different regions are tall, fat and thin, it will lead to a car seat that is recognized as a "good chair" in European countries, and Asians will feel hard after sitting on it, and the support and fit of the body are not good enough; and when Europeans sit on the seat specially developed for Asians, they will feel that the seat is soft and the flanks are tight. So, if you buy a model that doesn't have a careful localization seat design after entering China, or if you buy a European imported car, the seat ride usually doesn't feel the best. The following comparison case between domestic cars and joint venture cars is a living example.
Comparison of cushion pressure distributions
Domestic A car and joint venture B car are medium-sized SUVs, the above picture is the pressure distribution map of the driver's seats of the Chinese people riding two cars. Among them, the contact area between the A car cushion and the body is 1305c㎡(color area above), while the B car is 1279c㎡. Although the pad contact area of both A/B cars is relatively large and the fit is very good, the pressure of the seat cushion of the A car is obviously more evenly distributed (the dark red area is smaller), while the hip pressure of the B car is concentrated in a small area, and it is easy to produce numbness after a long time.
Comparison of backrest pressure distributions
From the perspective of the contact area of the backrest, the waist fit area of the joint venture B car is significantly greater than that of the domestic A car, but this does not mean that the B car will be more comfortable than the A car, this is because the waist fit area of the B car has been greater than the normal value, which is caused by the excessive sagging of the passenger's body caused by the soft backrest. At this time, because the passenger's waist can not get enough support, so the passenger's upper body will unconsciously ensure stability by curling forward when driving, as well as to ensure the convenience of rotating the steering wheel, that time is long, the shoulder that needs to be forced forward will have tightness and soreness. This can also be seen from the above figure, the lack of shoulder pressure in the passengers of Car B. It is also because of the better fit of the shoulder, so the backrest contact area of the A car reaches 1008c ㎡ (the color area in the picture above), which is greater than the 882c㎡ of the B car. Overall, the backrest of the domestic A car is not only better than the joint venture B car, but also the shoulder fit is also better.
Finally, it is time to reveal the mystery, the domestic A car that performs better in the above comparison is actually the previous generation of Trumpchi GS8, and the slightly worse performance of the B car is the previous generation Toyota Highlander. Seeing this result, it is estimated that some friends will be surprised: "How can a domestic car be better than a joint venture car?!" "In fact, the reason is very simple, this is because the domestic car seats are referred to in the development of the Chinese body shape, so the Chinese people will naturally feel more comfortable when sitting up." Although the Highlander is a Japanese car, in fact, the owner of this car is playing the American market, so the seat design will naturally refer to the body characteristics of americans.
Is that a good chair all right after solving the pressure distribution of the seat? Non-also, because although from the outside, the human body is just a lump of meat, but in fact there is a complex skeletal structure inside. More importantly, whether it is the flesh outside the human body or the internal skeletal structure, it is actually the form evolved by the human species in order to be able to walk more upright, which has nothing to do with the longest sitting posture that modern people maintain every day. Therefore, if we want to create an extremely comfortable chair, we must ensure that when the human person sits down, the posture of the body can be as stable as when standing, and the impact can be dissolved as when standing.
Humans are an evolved advanced animal, and this superiority is not only reflected in the high iq of ours, but even our bodies are a fairly advanced thing. If you don't feel it deeply, I can only say that it is because the starting point when we were born was too high, and everyone is used to it. As a most common example, when we are walking, our feet will cause the lower body to rise and fall by about 20 cm in a crossed travel. It stands to reason that under such a large ups and downs, our heads should be shaken in less than a few steps. However, after actual measurements, the upper and lower amplitude of the human head in the walk is only within 5cm, so it has not happened that it has thrown up on itself. The 15cm ups and downs that disappear from the footsteps to the head are actually dissolved by our spine.
The spine is S-shaped
As we all know, the human spine is not as straight as a stick, but will show an S-shaped physiological bend. The three bends of the cervical spine, thoracic spine, and lumbar spine can absorb the vibration from the foot through their own compression and extension, and the effect is equivalent to adding three springs to the spine that can be cushioned, so as long as we can keep the spine S-shaped, our upper body will feel very relaxed. Conversely, if our thoracic spine cannot be bent backwards, or the lumbar spine cannot be bent forward, it will not only cause rapid soreness in the muscles of our upper body, but also our head will not be adequately buffered due to the narrowing of the S-shaped spine. Returning to car seat design, we need to create a seat that allows the driver to sit down and the spine to take on an S-shaped shape as if standing. Let me talk about the specific implementation steps.
Seat cushion considerations
When we sit down, in order to keep the spine of the upper body in an S-shape like standing, the first thing is to keep the upper body connected to the pelvis connected to the leg in the upright state when standing, because only in this way can we provide the basis for the upright state of the upper spine. As shown in the figure above, when the driver is in place, the position of the pelvis is located on the innermost side of the saddle, so in order to keep the pelvis standing, it is first necessary to avoid the problem of moving the thigh forward to prevent the pelvis from being moved forward by the thigh and then causing backward tilt. For this, we can avoid it by simply adding a suitable elevation angle to the cushion. After ensuring that the pelvis does not lose its erection due to forward sliding, the next step is to focus on the position of the cushion corresponding to the pelvis. We need to strengthen the padding of this area cushion to avoid the inability to maintain the most natural relative relationship with the spine after the pelvis is excessively sunken. After these two steps, we created a cushion that guarantees "sitting as if standing". Let's take a look at how to create a "sitting as standing" backrest.
Backrest considerations
As we have already said above, the upper part of the pelvis is connected to the lumbar spine and the lower part is connected to the thigh. If the pelvis cannot remain upright, the upper lumbar spine cannot remain upright. Conversely, if the lumbar spine does not get enough support and begins to collapse backwards, the lower pelvis will also tilt backwards, and the upright state cannot be guaranteed. Therefore, the first point in order to create a "sitting as standing" backrest is to ensure that the driver's waist is sufficiently supported. Similarly, if the driver's thoracic spine does not get enough support and begins to collapse backwards, not only can the driver's spine not maintain the most natural physiological curvature, but the driver also needs to rely on his own strength to probe forward when holding the steering wheel. Therefore, the second point of creating a "sitting as standing" backrest is to provide sufficient support for the driver's thoracic spine.
For the seat backrest, although the surface of the padding is soft and hard, the thickness will have a certain impact on the support of the back of the seat. But what is decisive for support is the metal dragnet inside the backrest. Because the human lumbar spine and thoracic spine have different needs for support, the task of support must be completed by different dragnets. As shown in the figure above, the support of the lumbar spine is done by pulling a net in the upper purple area, which includes a separate pull net codenamed Kp for the pelvis, and a separate large silver pull net in the lower part. The upper part of this large silver dragnet (the green box area pictured above) will be responsible for the support of the thoracic vertebrae. However, because the lower part of this dragnet will involve the back of the passenger, in order to avoid too strong support and cause the problem of the top back, the hardness of the two purple springs on the left and right at the code Kl in the above figure will be set to be smaller than the four green springs codenamed Kt that provide support for the thoracic spine above. Through the above methods, a seat backrest that can maintain the S shape of the passenger's spine and allow the passenger to "sit as if standing" was born.
Finally, it is the time to reveal the secret, the above set of "sitting as standing" seat design concept proposed, in fact, is the main "human and horse integration" brand - Mazda. And this kind of seat design also conveys a new concept to us, a seat can provide passengers with a comfortable riding experience for a long time, the key is no longer based on the softness and hardness of the filling can be judged, but depends on how deep the car manufacturer's understanding of the human body.
In fact, there is no seat in this world that does not make people feel tired, because fatigue is a self-protection mechanism for the human body to avoid compression damage, so sitting for a long time will definitely have uncomfortable feelings. So all a good chair can do is delay the arrival of fatigue and reduce the degree of fatigue. In addition, there is no seat in this world that can make people "comfortable" (except for massage chairs), and the comfort of sitting down on our butts comes more from releasing the fatigue of standing on our legs for a long time and distributing the weight of the body over a larger area. Therefore, the standard of a really good seat should actually be "sitting without feeling". Because of this feeling of "no feeling", it proves that all parts of the body are in the best balance.