ORIGINAL ARTICLE
POSTURAL COMFORT OF DRIVER WORKS SPACE IN VEHICLE PACKAGE DESIGN GEOMETRY: A PILOT STUDY ON MALAYSIAN DRIVERS IN SEDAN CAR AND MPV
1Zuli’zam R, 1Nooh AB, 2Raja Ariffin RG
1Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Skudai, Johor, Malaysia
2Centre for Product Design and Manufacturing, Faculty of Engineering, University of Malaya, 50603 Lembah Pantai, Kuala Lumpur, Malaysia
ABSTRACT
The study of driver posture and comfort in driver workspace is important in vehicle package design especially in two different type of vehicle, sedan and Multi-Purpose Vehicle (MPV). Due to different seat position in the driver workspace, investigation of driver accommodation in relations to driver anthropometry is essential to ensure its meet the ergonomic quality. Therefore, this research is to investigate the preferred driving posture of Malaysian driver in both sedan and MPV type of car. Sixty two subjects (32 males and 30 females) aged between 17–60 years old were selected to simulate the comfortable driving posture using mock-ups of sedan car and MPV. Measurements based on SAE J1100 vehicle package design geometry were carried out for each subject. Result shows slight differences in the range of posture angle between the two types of vehicles, the posture joint angle in MPV is slightly smaller as compared to those of sedan car. The range postural angles for Malaysian driver population also is slightly smaller compare to Caucasian people especially on lower body portion such as knee angle, hip angle and ankle angle. These angles are due to the body stature and body segment length in which the population of Malaysia have shorter thighs and legs than those in Europe and America.
Keywords: Comfort, posture, driver work space, body segment
INTRODUCTION
Driver comfort is considered an important feature of the automobile1. The comfort and spaciousness of the environment in an ergonomically well-designed car contributes significantly to the reduction in driver fatigue. A key components influencing driver fatigue is the design and configuration of the driver seat. The automobile seating represent a workspace which needs to be, acceptable to the comfort of the driver, that provides the occupier adequate positioning for the required driving task and other necessary activities such as safety2. Although there are many factors when dealing with automotive driver seating or accommodation, the two primary considerations are the anthropometrical and postural condition.
These are important towards analysing the reach ability and postural comfort of the driver3,4. Posture may be defined as the relative orientation of body parts in space. The purpose of seating is to achieve satisfactory comfort over a period of time and to stabilize the appropriate body postures related to the on-going task and activity. To maintain such postural orientation over the time period, the muscles would be used to counteract any external forces, such as gravity, that act upon the body, thus creating the feeling of comfort or discomfort. Driving posture emerges from a chain of interrelationships between man and several elements of the system5, so it is important to carefully consider the design of driver package from an ergonomics perspective, in order to meet the comfortable driving posture of the user.
In the development of the automobile package design, vehicle designers often refers to the SAE (Society of Automotive Engineers) Standards, which is a two dimensional accommodation guideline and tools to determine vehicle design parameter such as seat position, reach envelopes, head contours and eye ellipse6. Examples of SAE recommended Standards which are of relevance to this study are the SAE J1517 (Driver Selected Seat Position) and SAE J826 (Devices for Use in Defining and Measuring Vehicle Seating Accommodation). Although these guidelines are globally referred to by many automobile makers, it is important to note that these standards were developed based on the U.S Army population7. Several researches have concluded that the differences between population anthropometry would greatly influence the occupant packaging design8-10,13. Hence, the driving comfort and performance for a particular population would be affected if the seating designs do not accommodate them.
Adopting the data from other population in designing the seating package may aggravate driving and posture discomfort.
Therefore, the aim of this research is to investigate the postural comfort of Malaysian driver in two different car models which are the sedan and Multi Purposes Vehicle (MPV) in an attempt towards improving the driver package design.
METHODS
A random selection of Sixty two subjects (32 males and 30 females) aged between 17–60 years old were selected for the driving posture data collection. In this study two types of car from the same manufacturer a sedan car and an MPV (Multi Purposes Vehicle) were used as the test vehicle. These two car body types were chosen since they are the most popular types in Malaysia. The sample size was chosen based on sampling convenience. 3D photogrammetric method was used to capture and measure the driving postures of each subject. Two groups of measurements were carried out the posture joint angles. The measurements are defined by Society of Automotive Engineers (SAE) Recommended Practice J1100 and related practices. The five angle measurements consisting of the torso angle, thigh angle, hip angle, knee angle and the ankle angle were chosen for determining the driver postural measurements. These areas are chosen since they are the most prone areas for disorders or discomfort during driving.
Massaccesiet al.8 mentioned that most researchers would measure only four or five angles. The five angle measurements, as shown in Figure 1(a) and 1(b), are A40: Torso angle, A57: Thigh angle, A42: Hip angle, A44: Knee angle and A46: Ankle angle. Prior to capturing the image, each subject is given 5 minutes to adjust the positioning of the car seat to be at the most comfortable configuration for them to sit in. The initial configuration of the seat was set to the minimum range, as shown in Figure 2. The subjects were able to adjust the seating positions within the range of the allowable design specification. The adjustable seating position enables the accommodation for a wide range of subjects in various driving postures (extended, flexed). Upon completion of the image capture session for the measurement data collection, the participants were given a subjective body comfort questionnaire to obtain their responses. This is used later to be compared with the quantitative results.
Figure1 (a)- Angle measurement points
Figure1(b)- Angle measurement points
Figure 2- Definition of postural angles, design specification and the measurement of SgRPx, AHP, L6, H30 and A27 following a Society of Automotive Engineers (SAE) nomenclature RESULTS& DISCUSSION
Joint Angle Postural Measurement Results Table 1 tabulates the first and third quartile range of box plot analysis of the various joint angles for both the sedan type and MPV driver works space. Table 2 shows that the values for comfortable range of postural angles in the MPV which were generally smaller as compared to those of the Sedan, in particular, the torso angle, knee angle, ankle angle and seat angle.
This is probably due to the higher and more upright driving position in the MPV as compared to the driving position in the Sedan car.
Table 1- Preferred posture angle in Sedan and MPV
Table 2 Comparison comfort range of postural angle for Sedan and MPV
Subjective body comfort survey results
A subjective survey was conducted to obtain respondent’s feedback on seating posture in the sedan and MPV-types vehicles. A descriptive analysis was carried out on the data obtained from the survey to evaluate the body mapping postures in both types of cars. Table 3 and 4 shows the percentages of comfort and discomfort of the subjects for both the sedan and MPV driver workspace.
Although most of the subjects found that most their body segments are comfortable in their preferred posture but there still subjects which found there are body segments that they feel at least some discomfort even though they have set the seat positioning dimensions to their preferred
Table 3 Percentage comparison of body mapping on Comfort and Discomfort in Sedan car
Drivermost comfortable posture. This might indicate that in some subjects the seat configuration design may not sufficiently accommodate them to be comfortable. From the table below it is found that the body segment Left buttock has scored the highest feeling of discomfort at 37% followed by the Right and Left foot & ankle (33.3%). Other body segments showing high discomfort scores are the Right buttock, Left knee and Right calf, both at 31.5%.
This could indicate the possibility that the driver workspace design dimension that affects these lower body segments may not be accommodative to some subjects. Similar trends is also observed for the MPV driver workspace where the body segment of the Right buttock has scored the highest feeling of discomfort at 36.4% followed by Right foot & ankle, (34.5%), and the Right thigh, Left & Right knee, Left and Right Calf, all at 32.7 %. Table 5 summarizes the comfort and discomfort body segments observed from the survey.
Table 4 Percentage comparison of body mapping on Comfort and Discomfort in MPV driver workspace.
Body segment parameter Comfort ( 1 - 3 ) Discomfort ( 5 - 7 )
n Percentage (%) n Percentage (%)
1. Neck 20 37.0 13 24.0
2. Upper back 26 48.0 11 20.4
3 Middle back 19 35.0 12 22.2
4 Mediumer back 17 31.5 14 25.9
5 Left buttock 20 37.0 20 37.0
6 Right buttock 19 35.2 17 31.5
7 Left thigh 18 33.3 13 24.1
8 Right thigh 17 31.5 13 24.1
9 Left knee 19 35.0 17 31.5
10 Right knee 21 38.8 15 27.7
11 Left shoulder 22 40.7 9 16.6
12 Right shoulder 25 46.3 9 16.6
13 Chest 21 38.8 12 22.2
14 Left arm 22 40.7 10 18.5
15 Right arm 19 35.2 10 18.5
16 Stomach 20 37.0 12 22.2
17 Left calf 19 35.2 15 27.7
18 Right calf 20 37.0 17 31.5
19 Right foot & ankle 19 35.0 18 33.3
20 Left foot & ankle 17 31.5 18 33.3
Body segment parameter Comfort ( 1 - 3 ) Discomfort ( 5 - 7 )
n Percentage
(%)
n Percentage (%)
1. Neck 13 23.6 15 27.3
2. Upper back 18 32.7 19 34.5
3 Middle back 14 25.4 13 23.6
4 Mediumer back 17 30.9 14 25.4
5 Left buttock 19 34.5 17 30.9
6 Right buttock 17 30.9 20 36.4
7 Left thigh 15 27.2 17 30.9
8 Right thigh 14 25.4 18 32.7
9 Left knee 17 30.9 18 32.7
10 Right knee 17 30.9 18 32.7
11 Left shoulder 17 30.9 12 21.8
12 Right shoulder 19 34.5 15 27.2
13 Chest 21 38.2 10 18.2
14 Left arm 22 40.0 13
23.6
15 Right arm 22 40.0 16 29.1
16 Stomach 17 30.9 13 23.6
17 Left calf 22 40.0 18 32.7
18 Right calf 23 41.8 18 32.7
19 Right foot & ankle 19 34.5 19 34.5
20 Left foot & ankle 20 36.4 18 32.7
From this study it could be observed that the body postures which experienced the most discomfort for both types of vehicles were mostly located below the hip segment such as the buttock, foot ankle, knee, calf of hip and thigh. The discomfort may have been influenced by dimensional mismatches in the driver seat configuration to the posture of lower body segments of the Malaysian population.
As discussed in Zuli’zam Rashid9, the Malaysian population tend to have shorter posture of body segment on hip and lower body parts, therefore there is a possibility that having followed US based standard may not be accommodative to the Malaysian driver population. This study also found some differences in terms of the driving posture of Malaysia driving population as compare to other published studies. Table 6 shows a comparison of the postural joint angle ranges between the Malaysian population and other region and also the different postural angles in the sedan, MPV and SUV.
This current research in comparing the sedan and MPV have shown some slight differences in the range of posture angle between the two types of vehicles, which is similar to the findings of Lee at al.4. In general, the posture joint angle in MPV is slightly smaller as compared to those of the sedan. For example, the Torso angle range in the sedan is 17o - 26o whereas for the MPV it is in the range of 16o - 24o, a difference of 7o ~ 8o. This is due to higher seat position in the MPV is more higher and up-right as compared to the sedan car, as shown in Figure 3 and Figure 4.
Nevertheless, the difference is small as compared to the finding of Kyung and Nussbaum10 where difference of posture angle between the sedan and SUV is about ranged 24o ~ 27o.
Generally, the range postural angles for the Malaysian driver population is slightly smaller as compared to Caucasian people especially on lower body portion such as the knee angle, hip angle and ankle angle.
These angles are due to the body stature and body segment lengths in which the population of Malaysia have shorter thighs and legs than those in Europe and America. This factor may explain why Malaysian drivers tend to seat closer to the steering wheel to comfortably reach the pedal positions9,11. It was also found that there is no significant difference between the left and the right side of the bodies for comfort/discomfort issues as compared to previous studies on other populations10,12.
Table 5 Comparison on data from the respondents on the most Discomfort and Comfort seating with reference to main body posture and seat parameters for Sedan and MPV driver workspace
Comfort Car Type
Body Posture
Sedan Car MPV
Most Discomfort
1. Left buttock 2. Right & Left
foot ankle 3.Right buttock 4. Left knee 5. Right calf
1. Right buttock 2. Right foot & ankle 3. Right thigh 4. Left & Right knee 5. Left & Right calf
Most Comfort
1. Upper Back 2. Right shoulder 3. Left Arm
1. Right calf
2. Left arm & Right arm 3. Chest
4.Left foot & ankle 5. Right shoulder.
Table 6 Comparison comfort range of postural angle
Figure 3 95%Tile Male Malaysia in driving position
MPV Sedan Car
CONCLUSION
For both types of vehicles, it was generally found that the Malaysian driver experiences discomfort in the lower body segments from the hip area to the ankle, with the most discomfort being felt at the buttock, knees and ankles. This may indicates that both of sedan and MPV models used in this study, which was designed based on SAE’s US population based standards, may have issues in accommodating the Malaysian driver population. The problem may have arisen due to the anthropometric differences as mention by Zuli’zam Rashid9 and the posture adoption. It this study it is found that Malaysian driver has smaller comfort postural range angle compare to Caucasian people especially on knee angle, ankle angle and hip angle which might suggest the observed discomfort in roughly 30% of the subjects. Malaysian drivers in this study are observed to tend to seat closer to the steering wheel which they perceive as most comfortable to them. This situation might a case of the human following the workspace where due to design of the workspace the driver has to adopt a posture which may allow them to perform better but with less comfort. Therefore a further study into the development of new design models and standards may need to be carried out to further increase the level of comfort to accommodate drivers of Malaysian population.
REFERENCES
1. Ebe, K., Griffin, M.J. Factors affecting
static seat cushion
comfort.Ergonomics2001;44(10): 901- 921.
2. Kolich, M. Predicting automobile seat
comfort using a neural
network.International Journal of Industrial Ergonomics2004;33(4): 285- 293.
3. Park, S. J., Lee, Y. S., Nahm, Y. E., Lee, J. W., & Kim, J. S. Seating physical characteristics and subjective Driving Posture: design considerations. SAE Publication SP-1358. Human Factors in Driving Vehicle Seating and Rear Vision, (SAE Technical Paper 980653); 1998.
4. Lee, J.H., B. K. Kwon, Kyung, G. and Nussbaum, M.A. Predicting Driving Postures and Seated Positions in SUVs using a 3D Digital Human Modelling Tool (No. 2008-01-1856). SAE Technical Paper 2008.
5. Da Silvaa, L. Bortolottib, S.L.V., Campo, I.C.M. & Merinoa, E.A.D. Comfort model for automobile seat.Work2012;41: 295- 302.
6. Roe, R.W. Occupant packaging. In B.
Peacock and W.
Karwowski(eds.),Automotive
ErgonomicsLondon: Taylor and Francis,1993.
7. Gordon,C.C,Churchil,T.,Clausr,C.E.,Bradt Miller,B.,McConville,J.T.,Tebbetts,I.
Anthropometric survey of US Army personnel: Methods and summary statistic. Final report (NATICK/TR- 891027). Natick, M.A. US Army Natick Research Development and Engineering Center,1989.
8. Massaccesi, M., Pagnotta, A., Soccetti, A., Masali, M., Masiero, C. & Greco, F.
Investigation of work-related disorders in truck drivers using RULA method. Applied Ergonomics 2003;34(4):
303-307.
9. Zuli’zam Rashid, Nooh Abu Bakar and Raja Ariffin Raja Ghazilla. Comparison of Malaysian and SAE J833 anthropometric proportions for vehicle package design, Advanced Engineering Forum2013;10:
336-344.
10. Kyung, G., Nussbaum, M.A. Specifying comfortable driving postures for ergonomic design and evaluation of driver workspace using digital human model,Ergonomics2009;52(8): 939-953.
11. Mohamad, D., Deros, B.M., Wahab, D.A., Daruis, D.D.I. & Ismail, A.R. Integration of Comfort into a Driver’s Car Seat Design Using Image Analysis, American Journal of Applied Sciences2010;7(7):
937.
12. Hanson, L., Sperling, L., Akselsson, R.
Preferred car driving posture using 3-D information. Int. J. Vehicle Des.2006; 42 (1/2):154-169
13. Robert T.Bove, Jr.,Jacob L. Fisher, Lauren Ciccarelli, Robert S. Cargill ll and Tara L.A. Moore. The Effect of Anthropometry on Driver Position and Clearance Measures (No. 2006-01-0454), SAE Technical Paper 2006.