vehicle space requirement

Mueller, User-centered vehicle layout conception

*Corresponding author. Email: [email protected] 1

User-centered layout conception as an integral part of the vehicle development A. Mueller*, D. Holder and T. Maier

Institute for Engineering Design and Industrial Design Research and Teaching Department Industrial Design Engineering, Universitaet Stuttgart, Pfaffenwaldring 9, 70569 Stuttgart, Germany

Abstract This paper gives an answer to the question how a significant improvement in the individual-related vehicle design, specifically targeted on the vehicle users can be systematically achieved by means of a newly developed vehicle layout conception. In order to optimize the vehicles ergonomic characteristics, the occupants static basic postures as well as certain and critical vision and movement scenarios are considered (e.g. traffic light observation, e.g. seat belt handling movement, e.g. cornering). Exemplarily, vehicle layout concepts of two vehicles with conventional and alternative drive designs were configured using the described methodology. In this connection newly incurred degrees of freedom, especially associated with the usage of alternative drive designs are utilized in order to improve the vehicles ergonomic characteristics for the first time and in the best possible way. The results show that the application of the presented methodology is generally accomplishable.

Keywords: Ergonomics, Digital human modeling, Occupant packaging, Vehicle layout conception, Vehicle packaging

1. Introduction and method of resolution 1.1. Introduction

Today, development processes of modern vehicles are complex. The continuously increasing complexity and the associated raising number of involved disciplines have a major effect on the vehicle layout conception already in the concept phase. As a result, the ergonomic dimensioning of the vehicle has been displaced from its dominant role within the current vehicle development process.

In practice, it can be observed that the anthropometric characteristics of the vehicle users are often only represented by 2-dimensional man models (e.g. SAEJ826 template (SAE J826), e.g. Kieler Puppe) during the vehicle layout conception. However, technical function units are mainly 3-dimensional and configurable. This circumstance generally leads to an imbalance within the vehicle layout conception.

All disciplines which are involved in the vehicle layout conception are illustrated in Figure 1. Hence, the vehicle layout conception applied in practice occurs in a matter that is usually not systematic and hardly describable.

Figure 1: Centripetal vehicle layout conception.

The consequences of the applied vehicle layout conception become apparent when the general development of certain functional vehicle characteristics is taken into consideration (e.g. development of window surfaces, dimensional development of the vehicle interior and the vehicle body openings) (Mueller et al. 2009).

Moreover, new findings in the field of alternative drive engineering recently lead to the fact that vehicles with alternative drive concepts start to be mass-produced. Common examples are electric vehicles, hybrid vehicles as well as fuel cell vehicles, which also use electric drivetrain technologies. The addition of new components or


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changed geometrical dimensions of selected assemblies contribute to an increasing complexity. In fact, today alternative drive units are most often arranged in vehicle bodies that were designed for conventional drive units! This so-called conversion design produces disagreeable sequels (Wallentowitz et al 2010).

In terms of the conception of vehicles with alternative drive engineering, a promising approach called purpose design changes the complete vehicle architecture (Wallentowitz et al 2010). Using this strategy the positions and orientations of occupants as well as technical function units have to be reconsidered. In connection with the determination of the technical function units, the most important alternative drive components with direct influence on the dimensions of the occupant cabin have to be considered. These are:

Drive / Drivetrain Energy storage

Figure 2 shows principles for structuring electric drivetrain components. In this connection the position and the orientation of the electric motor itself are decisive and have a major effect on the geometry of the occupant cabin.

Figure 2: Axle concepts for an electrified drivetrain.

Concerning the energy storage, it becomes apparent that the location of the energy storage has a crucial influence on the vehicle architecture and with that on the ergonomic aspects (cp. Figure 3).

Since a holistic development methodology for the systematic generation of a vehicle layout concept, which is centrally based on the user, has not been propagated in teaching and has not entered the relevant literature in an appropriate manner, the question about a systematically generated vehicle layout concept arises. This especially applies, when novel vehicles with alternative function units are designed. Generally, such a development

methodology should be centrally based on the vehicle users.

Figure 3: Different possibilities to arrange the Energy Storage in relationship to a determined axial distance.

1.2. Method of resolution In order to solve best the primary transport task, which can be described as the transport of occupants with their luggage, vehicles should be configured centrifugally in a user-centered manner (cp. Figure 4).

Figure 4: Centrifugal vehicle layout conception.

This implies that vehicle development already starts in the concept phase with a systematic vehicle layout conception that is centrally based on the vehicle users. As a basis, the 3-dimensional man model RAMSIS (Seidl 1994) is combined systematically with SAE J1100 (SAE J1100). The presentation of such a vehicle layout conception is the objective of the presented paper.

2. Methods 2.1. Main requirements

The compilation of a complete list of requirements for the development of an automobile is very extensive and not reasonable in order to define a vehicle layout concept. Requirements that have a major influence on the vehicle layout conception are stated as main requirements and described in the following.


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In the first place, the so-called simple ergonomic requirements and the extended ergonomic requirements are among these main requirements. On the one hand, the simple ergonomic requirements are defined by the occupants who consist of drivers and passengers. On the other hand, the luggage is considered. Both together form the basis of the transport problem. In terms of the description of the occupants, the consideration of the ergonomic key dimensions (length, corpulence and proportion) is particularly important. Since the usage of a vehicle is not a static problem, critical vision and movement scenarios should additionally be considered within the vehicle layout conception. These requirements are described by the extended ergonomic requirements. Other requirements describe the intended use, the vehicle classification and the technical requirements that specify the technical function units.

2.2. User-centered vehicle layout conception

The systematic and user-centered vehicle layout conception consists of the nine main steps listed below:

1. Definition of the main reference point. 2. Definition of the main reference planes. 3. Modeling of the drivers (includes drivers'

vision as well as statically and dynamically required space).

4. Modeling of the passengers (includes statically and dynamically required space).

5. Definition of the vehicle interior. 6. Modeling of the luggage volume and

modeling trunk loading and unloading. 7. Picturing the technical function units. 8. Definition of the vehicle exterior. 9. Picturing grid planes.

The systematic and user-centered vehicle layout conception begins with the definition of an appropriate reference point (AHP).

Secondly, the main reference planes are defined.

In the third design step, the drivers workplace is designed. Especially the definition of the SgRP (SAE J1516; SAE J1517) is regarded as critical. As a function of the SgRP location the basic body posture of a certain person defined as a reference driver (e.g. 95%M) can be determined using the posture model implemented in RAMSIS. Of particular importance is in this connection also the determination of an ideal steering wheel position. In the following all further persons defined as drivers (e.g. 5%F) are positioned relatively to the reference driver. For this purpose an appropriate sitting model has to be selected. Today a variety of these sitting models are known (e.g. Burand 1978, Bubb 1995,

Bubb and Mergel 2006, Mueller et al. 2011). Consequently, the seat travel of the driver seat results by considering the SgRP as well the hip points of all persons defined as drivers (e.g. 95%M, 5%F).

In order to meet the extended ergonomic requirements, critical vision scenarios have to be considered (Haslegrave 1993; Mueller and Maier 2009 B). This can be achieved by orienting the sight line of all drivers towards critical objects (e.g. traffic light). On this basis vision cones can be derived. Furthermore, the functional derivation of interior space that is associated with the consideration of critical movement scenarios (e.g. cornering and seat belt handling) have a major effect on the systematic and user-centered vehicle layout conception (Bubb and Hudelmaier 2001; Monnier 2004; Mueller and Maier 2008 A; Mueller and Maier 2008 B). Especially the critical and complex ingress and egress movement tasks (Riegl 2005; Cherednichenko 2008) have an influence on the systematic and user-centered vehicle layout conception (Mueller and Maier 2009 A). All critical movement sequences were modeled by defining supporting geometries that served as a basis for the derivation of decisive supporting body postures. These geometries were mostly determined on basis of conducted experiments. For instance, the modeling of the mentioned critical vision scenarios depends on the position of critical objects (e.g. traffic light). These positions were determined on basis of experiments that were conducted on a test track.

The second seat row passengers are modeled in the fourth work step with special regard to the effective leg room and knee clearance. This means that a certain reference person possessing anthropometric dimensions considered as critical (e.g. critical upper leg length, critical body height) is positioned in the best possible way. Then, the whole collective of the 2nd seat row passengers is modeled as a function of the posture of the reference person. After picturing the basic body postures, the dynamically required space has to be determined in the same manner as described for the drivers workplace.

In the fifth design step the vehicle interior is defined by considering the basic body postures as well as the dynamically required space. For the drivers workspace and for the passengers the elbow widths, the shoulder spaces and the effective head spaces are decisive.

Trunk loading and unloading corresponds to the 6th work step of the user-centered vehicle layout conception and has a major effect on the users value of a vehicle (Karwowski 1993, Divivier 2008). In this connection, the definition of the


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luggage volume forms the basis for modeling these movement sequences (Mueller and Maier 2010). Lately, a study that investigated various sized people during loading and unloading different vehicle types was conducted (Spitzbart 2010). The findings were implemented in a data based software application in order to picture movement sequences of occupants with different anthropometric dimensions and with regard to different vehicle characteristics (e.g. variation of ground to trunk floor height).

The seventh work step deals with the definition of the technical function units that have a major influence on the vehicle layout conception (cp. Figure 5).

Figure 5: Primary technical function units influencing the user-centered vehicle layout conception.

Depending on the static body postures and the dynamically required space of the vehicle users in different use cases the technical function units are positioned and oriented in the best possible way.

The user-centered vehicle layout conception considers the vehicle exterior definition not before the 8th work step. Aspects of particular importance are:

Definition of the overall body shape, Definition of the window surfaces, Definition of the vehicle body openings.

The functional derivation of all window surfaces succeeds by taking into account the predefined vision cones of all drivers. All relevant vehicle body openings are functionally determined on basis of the dynamically required space associated with the ingress/egress as well as with the loading/unloading movement task.

In the ninth and final work step the grid planes are pictured according to SAE J182 (SAE J182).

In case of geometrical interferences during the described methodology, iteration loops can be conducted any time in order to improve the vehicle layout concept.

2.3. Generation of a designing framework Another main focus of the present paper deals with the generation of a designing framework which supports the user of the systematic and user-centered vehicle layout conception by defining dimensions. On the one hand, the determination of a designing framework and with that the definition of dimensions and dimensional ranges succeeds by the individual definition of competing vehicle layout collectives. On the other hand, the definition of dimensions and dimensional ranges succeeds by applying ergonomic and different specifications (e.g. specifications of upper and lower critical sight lines that define the so-called primary sight cone). This designing framework and also the results of the digital human modeling (definition of the occupants' basic body postures, the vision cones of all critical vision scenarios, the dynamically required space of all critical movement scenarios) serves as a basis for the systematic and user-centered vehicle layout conception.

From the described methodology that is based on main requirements, the vehicle layout concept can be derived by considering vehicle dimensions as well as ergonomic and different specifications. The vehicle layout concept is regarded as the groundwork of the vehicle interior and exterior design (cp. Figure 6).

Figure 6: The systematic and user-centered vehicle layout conception as a basis of the vehicle interior- and exterior design


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3. Implementation In the following paragraph a user-centered vehicle layout concept, which was generated using the described methodology is presented.

Figure 7: The systematic and user-centered vehicle layout conception as a basis of the vehicle interior- and exterior design

Initially, the described main requirements were defined. In this context, a 95%M and a 5%F were selected as drivers and a 95%M was defined as second seat row passenger. Furthermore, a luggage volume of 350 L and two suitcases serving as transport goods were chosen. The generation of a compact car primary serving for the transport of people was phrased as the primary objective. Considering these requirements the primary

technical function units as well as their position and orientation were selected as follows:

4 Cylinder front transverse engine, Front wheel drive, Fuel tank (55 L) Chassis (McPherson strut, multi-link

suspension) including wheels

Figure 7 shows the results of the user-centered vehicle layout conception as a function of the work steps described above.

Figure 8 shows an application of the presented methodology to a vehicle with alternative drive units in side view. As shown in the figure, the driver has an upright basic body posture. This fact results from the limited horizontal AHP - H-Point distance. However, the effective leg room is larger for the 2nd seat row passenger.

Figure 8: Axle concepts for an electrified drivetrain.

The dimensions for energy storage and electric motors are the results of realistic assumptions. Typically, the energy density for lithium ion accumulator is 120 Wh/kg (Gerschler and Sauer 2010). A generic data for energy consumption for an electric vehicle is 15 kWh/kg (Lunz and Sauer 2010) To reach a range of about 200 km the application of an energy storage with the mass of 200 kg is necessary. In the present case, it was possible to integrate the energy storage under the rear occupants. Other technical function units of importance are the electric motors. The concept uses a tandem axle as drive unit. As previously described, these two functional units particularly have a great influence on the vehicle layout concept of an E-Car (Mueller et al. 2011).

The experience gained from the repeated application of the presented methodology shows that the systematic and user-centered vehicle layout conception is generally feasible and reasonable.

4. Evaluation

The systematic and user-centered vehicle layout conception described was evaluated in a double-


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stage process. A general evaluation was conducted by means of a survey conducted with 18 specialists each possessing industrial experience during the RAMSIS User-Conference 2009 (Mueller et al. 2009). A specific evaluation was carried out afterwards. Therefore, successful vehicle concepts of three different vehicle manufacturers were considered using the systematic and user centered vehicle layout conception. The developed methodology presented on the basis of these layout concepts was then discussed with the vehicle manufacturers.

A consolidated view indicates that the systematic and user-centered characteristic of the presented methodology, which offers the opportunity to create and visualize vehicle versions rapidly, was approved. However, the user-centered vehicle layout conception was also judged to be only a partial, human factors oriented approach, which does not sufficiently consider restrictions originating from primary technical function units.

5. Conclusion Various vehicle layout concepts can be generated rapidly and efficiently by the application of the systematic and user-centered vehicle layout conception. This can be specifically demonstrated when the methodology is implemented into an interactive software application (Mueller et al. 2009). The ergonomist can greatly benefit from the application of such a development methodology since rapidly generated vehicle layout concepts which can also consider alternative function units can serve as an argumentation aid in the interdisciplinary vehicle development process. Hence, the application of the vehicle layout conception contributes to an improvement of the vehicles user value.

It became apparent that systematically generated and user-centered vehicle layout concepts have not necessarily larger exterior dimensions compared to vehicle concepts currently distributed on the market. This especially applies for vehicles of the middle-sized and the luxury class.

A promising field of application is especially evolving from the utilization of primary technical function units associated with alternative drive technologies. Especially the new degrees of freedom connected with the lack of conventional technical function units can be used in the best possible way in order to improve the occupants ergonomics. (e.g. visibility conditions can be improved due to the lack of an internal combustion engine (Mueller et al. 2011)).

References

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