Possibilities for further development of the driver's seat in the case of a non-conventional seating positions

Abstract

The seat significantly contributes to driving safety. Ergonomic seats prevent physical strain and fatigue, so attention and concentration do not drop so quickly, which helps to avoid accidents. The article generally presents the development of seats used in cars and the current areas of use of rotatable seats. Furthermore, it gives an overview of the possible seating positions for fully autonomous vehicles. The article leads the reader through the crash test simulation focusing on the model used. Subsequently, the article presents the research results so far and the possibilities for further development of the driver's seat. The article highlights the change in the driver's movement kinematics as a crucial observation. This change significantly increases the risk of serious injury. In frontal collisions, the modified seat consistently demonstrates results below the specified limit. It is important to note that there are injury values that increase, but these are not a problem because they remain below the limit. In the case of a side collision, the aim was less to reduce injury values and more to better coordinate the kinematics of the passenger's movement during the accident. It can be concluded that this is achievable with the modified seat, as the passenger's movements are notably more predictable and coordinated under these circumstances.

1. Introduction

It was a long way to the car seat as we know it today. Early motorists lacked individual adjustment options for their seats. It took many decades until comfort and safety features such as headrests or easy-to-use longitudinal adjustments found their way into series production. Nowadays there are a lot of high-tech car seats, up to twelve percent of the production costs of a vehicle are in the seats. Initially, the body and seats are more reminiscent of a carriage than a car.

The seating position is extremely upright and high. Of course, there are no adjustment options and despite the noble leather upholstery, the driver is sitting on a soft board. Anyone who had to drive this vehicle for more than half an hour definitely got off with back pain. As time progressed, the seats continued to consist of a solidly fixed bench, but the seating position shifted significantly. In early rudimentary cars, occupants sat on chairs with feet placed directly on the floor, whereas in cars from the 1930s, the seats were fixed, resembling the configuration seen in modern vehicles today. However, there are still no adjustment options, and we searched in vain for the thigh support.

Cars from the 50s already offer a more comfortable seating position. Now the seats can also be adjusted lengthwise. Of course, this method is rudimentary and complicated, but it works. This construction allows drivers and passengers of larger and smaller sizes to travel comfortably. In addition, it is also possible to fold the backrests of the front seats forward, facilitating easier access for rear-seat passengers. But there is no sign of a headrest or side support here, and comfort takes its toll because the adjustable seat frame must be considered quite critically when it comes to occupant safety.

By the end of the 70s, thanks to the extendable telescopic rod, the height of the seats could be adjusted with relatively low effort. Furthermore, during this period, an optional headrest is already being used, the first sign that safety is becoming a development criterion alongside comfort. By the 90s, the length, height and angle of the seats were adjustable in all directions. They offer good lateral support, sufficient thigh support and, of course, the headrest which is nowadays legally required.

Today, a driver's seat with multiple options weighs 35–40 kg and is a complex system consisting of a metal frame, upholstery, covers, various hydraulic shock absorbers, electric motors, heating filaments, fans, cables, and connectors. A modern seat consists of a total of around 500 parts. After the drivetrain, the driver's seat is one of the most expensive components in the vehicle. Manufacturers usually offer their cars to their customers with basic seats, which can be upgraded with options such as massage or heating and ventilating functions.

Seats are important for safe driving. Ergonomic seats play a key role in minimizing physical strain and fatigue, thereby supporting sustained attention and concentration. This helps prevent rapid decreases in focus, consequently aiding in accident prevention. In modern vehicles, an airbag is installed on the side of the backrest towards the body, the purpose of which is to reduce side collisions. The far-side airbag is a novelty in vehicle development. This airbag is designed to prevent the driver and front passenger from colliding in the event of a side impact by deploying from the seat and inflating towards the headliner. This new type of airbag protects those in front rows from injuries due to interaction between passengers. These brand-new concepts can prevent about one-third of serious injuries related to the side collision. In 2020, the first series featuring the utilization of far-side airbags in a passenger car was observed.

2. Current and possible future use of rotatable seats

2.1. Current use of rotatable seats

According to the road licensing policy, the driver's seat must be placed so that the vehicle can be safely driven when the seat belt is fastened or another passenger safety system. The legislator currently excludes the use of rotating seats while driving. As a result, existing rotating seats can only be used in a stationary vehicle.

Rotate seats have two areas of use. On the one hand, there are rotating or swivel seats, which aid the driver or passenger in entering the vehicle more easily. These make people with reduced mobility easier they enter the car. They can be used in the front row, but they can often be found in minivans where it is used in the second or third rows of seats. Many people with disabilities find it difficult to sit in the driver's seat and turn forward. The swivel seat is designed specifically for this purpose to help people with motion problems landing and landing. It can be installed either as a driver's or passenger's seat in the vehicle, enabling a 90-degree rotation. The swive seat is a superb alternative for wheelchair-accessible vehicles. Rotating seats are commonly used to replace the original seat of a vehicle. For safety reasons, all rotated seats must be securely fixed to the original seat fixation. The most basic type of swivel seat consists of a hand-operated arm that is typically attached to the side of the seat. When released, the seat turns 90° in the same direction as the clockwise arrival. This facilitates the transfer between the wheelchair and the car seat for the driver. Advanced electronic systems are available that allow the swivel seat to be electronically controlled at the touch of a button, enabling the seat to turn towards the driver. There are various electronic rotating seats available on the market, with more sophisticated models designed to assist the user in exiting the vehicle by adjusting the bending movement to match the vehicle's exact specifications. The seat can be adjusted to facilitate standing up or sitting in a wheelchair. This seat variant extends from the vehicle to facilitate easy passenger seating (see Fig. 1). Controlled via a control pad, the seat then reverts to its standard position within the vehicle.

Fig. 1.

Mechanical and electrical version of swivel seats for disabled people [1].

In addition to the above, there are rotatable seat consoles, which are often used in campers and vans to increase comfort. Space in campers or vans is usually very limited, prompting meticulous utilization of every millimeter to maximize functionality and efficiency. With the right seat and rotating consoles, the space of the caravan can be used optimally. The rotatable seat allows the driver and front passenger seats to be rotated 360° (see Fig. 2). This quickly creates a comfortable seating area for several people. An essential point is that the rotatable driver's seat offers more space and at the same time high seating comfort. For this reason, manufacturers are increasingly installing rotatable consoles so that vehicle occupants can make the most of the available space. Most seats and rotatable consoles can be rotated 360° in the middle. With the right camper interior, such as tables or benches, they create comfortable seating. The height-adjustable rotatable seats in the driver's cab provide a comfortable seat while driving and camping. Installation of rotatable brackets in a camper is usually simple. It is just a matter of loosening a few screws on the slide rail, then lifting the seat and fitting and screwing up the bracket accordingly.

Fig. 2.

Example of using a rotatable seat in a camper and one type of rotatable bracket [1].

Existing research consistently demonstrates that integrating swivel seats into fully autonomous vehicles poses a challenge to conventional safety systems [2]. Occupant restraint systems underwent testing across multiple seating arrangements employing a model featuring a seat belt integrated with the seat due to rotational considerations. Throughout the tests, the seat orientation varied between −45° and 45°, incrementally adjusted at 15° intervals. The results underscored the importance of integrating seat belts with seat orientation to control occupant kinematics [3]. Additionally, the protective efficacy of a restraint system might vary across different seating configurations. Hence, the integration of fully self-driving technologies is poised to revolutionize vehicle interior designs and seating configurations, ultimately enhancing passengers' comfort and overall experience. Extensive development and rigorous testing remain imperative to ensure the safety of these systems. Ongoing research aims to ascertain the occupant's kinematic threshold during the pre-crash phase, considering varied seating orientations and diverse seat belt configurations [4].

2.2. Possible seating positions for full self-driving cars

Cars that are highly automated and therefore capable of self-driving have the advantage, among other things, of freeing up time for the driver, as they no longer must drive. The driver therefore becomes a passenger and can take any seat position [5]. In contrast to what was presented earlier, here it will be possible to rotate the seats even during the movement of the vehicle. To adapt vehicle safety systems to this new possibility, it is necessary to understand how users want to sit in highly automated self-driving cars. The subsequent section presents a study conducted in Sweden involving participants aged between 10 and 65 years old. The participants took part in the study alone. The duration of each test session varied between ten and 20 min. Before each study, participants were informed.

During the study, the participants could choose from five sitting positions (see Fig. 3) [6]. The normal forward-facing position (A), a conversation position with the front seats turned inward (B) and three lounge positions where all seats are located facing each other (C, D, E).

Fig. 3.

Top view of the five possible sitting positions [5,6].

The test showed that the most preferred seating position was C, where the front seats were turned 180°. This was followed by living room positions E, D and B. Only very few participants chose the traditional forward-facing sitting position indicated by A. The new seating positions for fully self-driving cars raise several safety issues. The airbags and seat belts are designed in such a way that they can only provide maximum protection in the forward-facing position. They are not able to provide adequate protection in different positions. In a living room situation where the passengers are facing each other, the interaction between the occupants can be a hazard in an accident.

3. Simulation system

3.1. Description of the crash simulations

With the first development of vehicles for passenger transport, the need for a safety design arose relatively quickly, since the first accidents, including fatal ones, soon occurred. In the further course of development, the first crash tests of vehicles were also carried out. With the development of computers and their increasing capacity and computing power, the first algorithms were developed to be able to deal with the problems of a crash simulation. Due to the still extremely high costs, the first uses were found in the field of military design. At this time, the first scientific applications of the crash algorithms were found, since the costs were still too high for industrial use. It should be made clear that at the beginning of the crash simulations, only very small problems could be dealt with in a meaningful way.

When a crash simulation of an accident involving a military aircraft flying into a nuclear power plant was presented at a meeting of the Association of German Engineers in 1978, there was great interest in the potential of these simulations [7]. The first complete vehicle crash simulation was carried out in 1986. It was a frontal crash of a VW Polo against a rigid wall (see Fig. 4). At that time, it was evident that there existed a relatively good correlation between the deformations observed in the simulation and those seen in the actual test.

Fig. 4.

First full model of a crash simulation, initial structure and structure after crash in simulation and test [7].

With the progressive use of these methods and the ever-improving results, the area of application also expanded, so that soon the first side crashes could also be simulated. Since then, there has been rapid development of the models, especially about the number of elements and the material models used. The integration of dummies and various restraint systems, such as seatbelts and airbags, leads to the ever-increasing reliability of the results of the simulations carried out. Crash simulations are neither simple calculations nor static problems [8]. This involves conducting a time-dependent calculation that incorporates numerous nonlinearities in the process. All sorts of non-linearities occur in a crash simulation: material non-linearities, large deformations and a lot of contact. To be able to cope with this very complex problem in a reasonable time and with not too much computing power, simplification assumptions have been made since the beginning of these simulations.

Crash test dummies are highly complex, life-size puppets that simulate people in a crash test. They essentially help to find out how human bodies behave in accidents and what loads they are exposed to. In addition, these dolls are used in experimental tests, since the risk of injury to a person cannot be ruled out. The anthropometric test dummies realistically depict the human body both in terms of resilience and in terms of kinematics their movement behaviour [9]. To realize this, the correct size of the dummy and the correct mass of a real person are crucial.

The dummies mainly consist of a metal or plastic skeleton, with the body parts being connected in an articulated manner. The muscles and soft tissues are designed as plastic foam and covered with a removable plastic skin that represents the body's surface [10]. Furthermore, the dummies are equipped with various measuring instruments and sensors, which enable the registration of the different loads on certain parts of the body.

The most used test dummy is a 50% dummy, which means 50% of the male population is smaller than the dummy. The 50% dummy simulates the average male driver, it is weight is 78 kg and it is height is 175 cm. In addition to child dummies of different ages, there is a 5% female dummy (152 cm, 54 kg) for small and a 95% male dummy (188 cm, 101 kg) for very large inmates. For a variety of front crash load cases, Humanetics ATD Hybrid III test dummies are used. Fig. 5 illustrates the configuration of the Hybrid III dummy with its measuring points.

Fig. 5.

Structure of the Hybrid III dummy [9].

Recently, the Hybrid III dummy has been replaced by the so-called Test Device for Human Occupant Restraint (THOR) dummy [11]. The THOR dummy was already successfully tested by the Euro-NCAP working group in 2016, and according to the information of the 2020 Roadmap, it was included in the test protocol. Unlike the Hybrid III dummy, the THOR dummy has greater biofidelity and is equipped with additional sensors [12]. In this research, the THOR dummy is used for all calculations. Regarding human kinematics, the following developments were made. In the neck area, better imaging through better deformation, in the chest and shoulder areas, improved restraint and the spine, flexible joints in the thoracic and lumbar spine. In the pelvic area, less contact with thigh movements and thighs, enhancing biofidelity to absorb axial forces. In addition to improving human kinematics, the THOR dummy offers new measurement functions compared to the Hybrid III [13]. Three-dimensional measurement of chest cavity, abdomen three-dimensional compression measurement at two points and a force sensor in the acetabulum (see Fig. 6).

Fig. 6.

Structure and measuring points of the THOR dummy (Source: Author's plot) [9].

3.2. The applied model and methods

During the research ANSA preprocessor from BETA CAE Systems was employed. Once boundary conditions and the model were transferred, the solver determined and solved the differential equations, storing them in an output file for each time step. Simulations were conducted using the LS-Dyna solver from Livermore Software Technology Corporation for FE model calculations [14]. Subsequently, the postprocessor Animator 4 from GNS GmbH, coupled with ANSA META, was utilized to assess and present the results graphically. ANSA META serves as a dedicated postprocessor for ANSA. Evaluation of analysis outcomes encompasses the visualization of deformations, movements over time, as well as stress distributions and natural frequencies.

This research involves crash simulations incorporating occupant models. Non-linear dynamic processes with short durations are typical in crash simulations, hence the use of explicit time discretization [15]. Stress is not the primary source of information during vehicle collisions; instead, the focus lies on plastic strains and the absorbed deformation energy (internal energy). During deformation, elements can reduce in size, affecting the critical time step, thus increasing computational demands. However, this issue can be largely mitigated through “mass scaling,” which involves scaling density and consequently mass. This adjustment decreases the speed of sound (dependent on density), effectively maintaining the time step. While this approach introduces some computational errors, they are generally negligible within a specific scope.

Crash simulations involve multi-body systems comprised of numerous components and bodies, forming the basis of the calculations. Contacts are crucial for optimal simulation performance. Each component necessitates self-contact to realistically reflect its kinematics, enabling contact with itself. Defining contacts between different components is essential for mutual influence, otherwise, these components can move freely, resulting in visible penetrations. Within these contacts, every node on the contact surface (master) is checked during each calculation step to establish contact with an element on the target surface (slave). To resolve convergence issues, crash simulations employ the penalty formulation algorithm, allowing a certain overlap of contact surfaces. Consequently, nodes in contact experience a spring force based on contact stiffness, known as the penalty force. Different types of contact can be defined based on stress type and the specific problem at hand. Simultaneously defining multiple components with a corresponding number of contacts is necessary and beneficial, especially in complex occupant simulations.

The default penalty values are calculated from the material properties of the underlying slave and master surfaces, including factors like mass density and sound speed. These default values may not be optimal for all load cases, potentially leading to excessive penetrations or suboptimal convergence performance due to being either too stiff or too soft. If adaptive penalty is defined, the maximum value of the ratio $\frac{p}{T}$ will be computed at the end of each increment, where $p$ is the penetration value at the active contact pair and $T$ is the contact thickness at the same pair. If the maximum penetration to thickness ratio is larger than 20%, a new penalty number will be computed, and the increment will be re-computed with this new number. For one slave node/master element pair, if its $\frac{p}{T}$ ratio has the maximum value compared to other contact pairs on the interface, the corresponding penetration and thickness are noted as $p_m$ and $T_m$, respectively.

At a slave node $i$, the normal contact force is computed as:

$$f_{n_i}=a\cdot \epsilon \cdot A_i\cdot \left(1+\left(b‐1\right)\cdot \frac{p^2}{T^2}\right)\cdot p\text{,}$$ (1)

where $a$ is the penalty factor defined in the input file, $\epsilon$ is the calculated uniform penalty number, $A_i$ is the slave nodal area, $b$ is the nonlinear factor defined in the input file. Assuming the new penalty number will generate the same contact force, we will have

$${\epsilon }_{new}={\epsilon }_{old}\frac{\left(1+\left(\mathrm{b}‐1\right)\cdot \frac{p_m^2}{T_m^2}\right)\cdot p_m}{\left(1+\left(\mathrm{b}‐1\right)\cdot \frac{p_t^2}{T_m^2}\right)\cdot p_t}\text{,}$$ (2)

where the target penetration $p_t$ is defined as a percentage of the contact thickness [16].

The simulations are based on the 2008 model of the Honda Accord. This is a complete vehicle model that includes all the necessary parts (see Fig. 7). This is a conventional vehicle model, so any modifications necessary to model a fully self-driving car must be made, these modifications were made at an earlier stage of the research [17]. The main changes were justified by the rotation of the seats. In addition, the chassis of the vehicle model was adapted to the boundary conditions so that the driver's seat could be turned to the correct rotational position. Compared to the original model, a notable alteration has been made in securing the seat belt. Typically fastened on the B-pillar due to the substantial force required, the driver's seat cannot rotate using this belt fastening method to prevent strain on the passenger's neck. Consequently, the seat belt holder has been incorporated into the seat itself. This modification necessitates consideration of a shift in the force distribution and an added load on the seat. As documented in the literature, the belt has been integrated into the seat design to address these concerns.

Fig. 7.

Relevant components to occupant safety used during the research (Source: Author's plot) [15].

3.3. The research carried out so far and its results

Fig. 8 shows the positions investigated in the current phase of the research. As observed in Chapter 3, it is imperative to limit the potential scenarios when investigating rotated seating positions. During the research, in addition to the traditional sitting position, the 30°, 60°, 90°, 135° and 180° rotated seating positions were examined. These therefore include all the possible positions listed in Chapter 3. The examined spectrum therefore extends from 0° to the 180° position, in which the driver's view is directed backwards [18]. During the rotation, the geometric center of the seat forms the center of the rotation.

Fig. 8.

Representation of the examined angles of rotation (Source: Author's plot) [17].

Before evaluating the simulations, it was necessary to validate the simulation model. The validation was based on the results of an available real crash test. During the research, first was confirmed the validity of the vehicle model in its original, unmodified state. After the initial validation, essential modifications were made to the previously validated simulation model. Subsequently, the updated model was used to evaluate the effects of rotated seating positions. Based on the simulations carried out, certain trends can be established for certain properties of the rotation angle. During the research, two main load cases were examined, the first is the frontal crash where a rigid wall is placed in front of the vehicle model and the car collides at a speed of 50 km/h with 100% overlap. The second load case is the side crash where the test vehicle collides with a 254 mm diameter pole at an angle of 75° to the longitudinal axis of the vehicle at a speed of 32 km/h. In the following, the obtained results are briefly summarized. Table 1 shows the results obtained during the frontal impact test. The study investigated injury outcomes for frontal collisions across seat positions rotated at 0°/30°/60°/90°/135°/180°.

Table 1.

Results overview frontal crash (yellow = maximum value) [19].

Criteria	Limit	Unit	0°	30°	60°
Head (HIC15)	700	[−]	487	1159	964
Head (a3ms)	80	[g]	55,1	91,3	93,1
Head (BrIC)	1,05	[−]	0,57	0,93	0,95
Neck (Nij)	0,85	[−]	0,43	0,59	0,48
Chest (Compress.)	60	[mm]	41,4	50,6	54,9
Abdomen (Compress.)	88	[mm]	68,1	113,4	103,5
Femur (Force)	7,56	[kN]	6,88	4,39	6,11
Criteria	Limit	Unit	90°	135°	180°
Head (HIC15)	700	[−]	833	803	731
Head (a3ms)	80	[g]	83,3	75,3	72,9
Head (BrIC)	1,05	[−]	1,74	1,43	1,18
Neck (Nij)	0,85	[−]	0,57	0,63	0,61
Chest (Compress.)	60	[mm]	48,3	46,1	56,7
Abdomen (Compress.)	88	[mm]	91,4	78,6	71,4
Femur (Force)	7,56	[kN]	6,32	8,17	7,26

The results indicated a significant alteration in the driver's movement dynamics, attributed to the altered seating positions. Regrettably, conventional passive protection systems no longer offer sufficient safety measures, which is indicated by a significant decrease in their effectiveness. This is expressed firstly in the fact that in the case of rotated seating positions, the chance of fatal injuries increases significantly. This primarily applies to injuries to the head and neck area, but injuries to the chest and the extent of leg injuries also become more serious. It was observed that in the simulation model, the maximum HIC15 value is already reached at a seat rotation angle of 30°, so head injuries are highest here. As a result, there was a risk of head injuries because the impact point of the head changes. Nevertheless, the decline in the efficacy of conventional passive occupant protection systems is evident also in the considerable alteration of the driver's movement kinetics, ultimately leading to impaired coordination.

The protective effect of the airbag is reduced, as the shape and size of the airbag were optimized for the traditional seating position. Despite obtaining lower head injury values in the 60° version, it's crucial to note that at maximum forward movement, the head comes into direct contact with the steering wheel, therefore this rotation angle is the most dangerous. The seat position rotated at an angle of 60° is the worst for the airbag and the highest damage values occur here, therefore, it is necessary to investigate this scenario in the case of a side impact. Moving on from the 60° rotation position, a slow decrease in the injury values can be observed. This is primarily due to the damping effect of the driver's seat. As the rotation angle increases, so does the damping effect of the driver's seat, resulting in a positive impact on injury values. The current research was motivated by the recognition of this effect.

Table 2 shows the results obtained during the side impact test. In the event of a side crash, our simulations and evaluations focused on scrutinizing the most critical seat position rotated by 60° in frontal crashes. Afterwards, the injury results obtained in this position were compared with those observed in the traditional sitting position. Even in the case of a side crash, it can be said that the kinematics of the driver's movement change radically because of the rotated seat position. However, in contrast to frontal crash, injury values in side crash show a radical decrease, except for injuries to the chest and abdomen. The decrease in injuries can be attributed to the damping effect of the driver's seat. This effect is more pronounced in a side crash due to the lower impact speed, whereas in a frontal crash, characterized by higher deceleration, this effect is comparatively smaller. Based on the results obtained, although in the case of a side crash, it can be said that the damage values only partially increase, it is still necessary to expand the passive safety system. With the obtained results, the next goal of my research is to create a protection system that can provide protection even when the seat is rotated at any angle and can properly coordinate the passenger. It is therefore necessary to provide sufficient protection in both frontal and side crashes. To achieve this goal, the possibilities of further development of the driver's seat were examined in the current research. The seat must be able to coordinate the movements of the occupants in case of loads coming from any direction and, if possible, should be involved in preventing serious injuries and absorbing large deformations.

Table 2.

Results overview side crash [20].

Criteria	Limit	Unit	0°	60°
Head (HIC15)	700	[−]	592	141
Head (a3ms)	80	[g]	77,6	41,7
Head (BrIC)	1,05	[−]	1,01	0,89
Neck (Nij)	0,85	[−]	0,41	0,69
Chest (Compress.)	60	[mm]	27,4	37,1
Abdomen (Compress.)	88	[mm]	53,7	61,2

3.4. Possibilities for further development of the seat

Looking at the results of the research so far, it can be said that the driver's seat can greatly reduce the measure of injuries that occur in the event of an accident if the direction of the loads is advantageous. Using this conclusion, the following seat form was created. The goal was therefore to extend the backrest geometry of the seat, thereby providing a wider spectrum of protection in the event of an accident. Due to symmetry, the backrest was only extended in one direction. The modified seat therefore has a 400 mm extension. In terms of its structure, the extension follows the original structure of the seat, so the inside is a metal structure, and the outside is a soft foam suitable for deformation. During the modifications, the dummy's seating position did not change, the seat was modified so that this was not necessary. This is important because if the seat position of the dummy were to change, the obtained results would no longer be comparable. Fig. 9 shows a three-dimensional model of the original and modified seats and a Z-section at shoulder height.

Fig. 9.

Original (orange) and extended backrest seat (turquoise) (Source: Author's plot). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Initially, the results from the frontal collision are presented. With the modified seat, only the seat position rotated by 60° was tested in the case of frontal and side crashes. Fig. 10 shows the head acceleration of the basic version and the version with the modified seat model. Here, a clear decrease in head acceleration can be recorded, as the dummy head receives a smaller load due to the increased seat size. The impact of the head occurs approximately 20 ms earlier in the case of the modified seat. There are two peaks of head acceleration to be considered, resulting from the setup. The first deflection shows the initial contact of the head with the installed headrest. Nonetheless, the rise in the curve signifies that the headrest brackets are unable to endure the load, resulting in a decrease in protective effectiveness, as denoted by the second peak. The subsequent descent results from the extension of the backrest, which has a restraining effect. The effect of the modified seat is distinctly evident in another important area, the indentation of the ribs.

Fig. 10.

Head acceleration with original and modified seat (Source: Author's plot).

Fig. 11 shows that similar to head acceleration, the settings lead to a different time when the collision takes effect. Moreover, there is a decrease of 12 mm in maximum rib deformation in the upper chest in comparison to the baseline simulation. However, there is a notable increase in mid and lower chest deflections. Raising the backrest increases the impact area. As a result, the force generated during the impact is distributed over a larger area, which reduces the maximum value of chest compression. To summarize the findings concerning head values and chest load, it can be concluded that with the modified seat, the achieved values demonstrate significant improvement.

Fig. 11.

Rib compression with original and modified seat (Source: Author's plot).

Table 3 summarizing the results, further corroborates this trend. Observing the curves, it can be asserted that the loads on the passengers have significantly diminished, which is also reflected in the injury values.

Table 3.

Results overview frontal impact with the seat position rotated by 60° for the original and modified seat (yellow = maximum value).

Criteria	Limit	Unit	0°	60° ori. seat	60° mod. seat
Head (HIC15)	700	[−]	487	964	628
Head (a3ms)	80	[g]	55,1	93,1	71,3
Head (BrIC)	1,05	[−]	0,57	0,95	0,67
Neck (Nij)	0,85	[−]	0,43	0,48	0,73
Chest (Compress.)	60	[mm]	41,4	54,9	48,4
Abdomen (Compress.)	88	[mm]	68,1	103,5	81,9
Femur (Force)	7,56	[kN]	6,88	6,11	7,22

In the event of a side impact, it can be seen a large improvement in the previously examined 60° rotated position, however, the kinematics of the driver's movement change radically. The seat deforms a lot, thereby reducing the load on the passenger, but there is a risk of the passenger slipping out of the seat. The modified driver's seat presented earlier in frontal collisions is a solution to the problem. The Z-section illustrated in Fig. 12 shows that in the case of the modified seat, the deformation of the seat is significantly reduced, thereby significantly reducing the chance of the passenger slipping out. This means that in the case of the modified seat, the acceleration value of the head increases minimally, but in return, the loads on the neck and ribs are greatly reduced.

Fig. 12.

Seat deformation in the event of a side impact with original and modified seat (Source: Author's plot).

Fig. 13 is a section in the X direction that perfectly illustrates the difference in head movement between the original and the modified seats. Overall, it can be said that the passenger's movement is much more coordinated in the case of the modified seat.

Fig. 13.

Difference in head movement between the original and the modified seats (Source: Author's plot).

In the case of the original seat, there appears to be a lack of coordination between the movement of the upper and lower body. Specifically, the upper body, particularly the head, exhibits uncoordinated movement separate from the lower body. Table 4 summarizing the results, also confirms this tendency.

Table 4.

Results overview side impact with the seat position rotated by 60° for the original and modified seat (yellow = maximum value).

Criteria	Limit	Unit	0°	60° ori. seat	60° mod. seat
Head (HIC15)	700	[−]	592	141	268
Head (a3ms)	80	[g]	77,6	41,7	53,9
Head (BrIC)	1,05	[−]	1,01	0,89	0,93
Neck (Nij)	0,85	[−]	0,41	0,69	0,42
Chest (Compress.)	60	[mm]	27,4	37,1	29,3
Abdomen (Compress.)	88	[mm]	53,7	61,2	57,2

4. Conclusion

In this article, using the results of our ongoing research, further studies were conducted to explore possible advances in the development of the driver's seat. The article offers an overview of the evolutionary trajectory of car seats, delves into contemporary applications of rotatable seats, and explores potential seating configurations in fully autonomous vehicles. It reviews the crash test simulation methodology, the model used during the research and the dummy types used. During the investigation, a computer simulation model was used that was validated in the earlier phase of the research. The modified seat is presented, and the results obtained with it are compared with the results obtained with the original seat. Based on the results obtained in the previous research phase, the most critical seat position turned by 60° was examined in the case of frontal and side collisions. In the case of a frontal collision, the result was that, in the case of the modified seat, all previous results fall below the desired limit. It is important to note that there are injury values that increase, but these are not a problem because they remain below the limit. In the case of a side collision, the aim was less to reduce injury values and more to better coordinate the kinematics of the passenger's movement during the accident. It can be concluded that this is achievable with the modified seat, as the passenger's movements are notably more predictable and coordinated under these circumstances. The damage values in a side impact scenario present a more varied pattern compared to those in a frontal impact. Definitely can be said, that in the case of the modified seat, the upper body values demonstrate an increase while the lower body values indicate a decrease.

Summarizing the results so far, it can be said that the modified seat can meet expectations in both frontal and side collisions. However, the feasibility of this seat may be questionable due to its size. The interior designs known today do not allow the use of such seats, so in the future, a completely new interior design concept will be needed, which offers much more space for passengers. The research does not encompass the practicality and comfort facets of the proposed new seat model, including ease of boarding and disembarking. Although these aspects couldn't be evaluated using the available model, they should constitute a pivotal component of any later contingent implementation study. Consequently, creating a protection system that ensures safety regardless of the seat's rotation angle will require significant modifications. The next goal of the research is to examine the future possibilities of using airbags in fully self-driving vehicles. The future development of airbags as we know them today will be an important area in an unmanned vehicle. Our research aims to identify the challenges impacting airbags and explore potential solutions to address these issues. Possible research directions will be tests of the airbags known today in a new position, shape, and size to achieve the desired goal. The subsequent phase of the research aims to address these issues by investigating the integration of airbags into conventional seats. The objective is to potentially replicate the findings obtained in the current study using new airbag designs. This approach also offers a potential resolution to the manufacturability and comfort concerns associated with the modified seat.

Data availability

Data will be made available on request.

CRediT authorship contribution statement

Laszlo Porkolab: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Istvan Lakatos: Writing – review & editing, Validation, Supervision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.