Taşıt koltuklarının titreşim konforu açısından değerlendirilmesi
Evaluation of vehicle seats for the vibration comfort
Yazar: AKİF YAVUZ
Danışman: PROF. DR. İSMAİL AHMET GÜNEY
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Otomotiv Bilim Dalı
Derece: Yüksek Lisans, 2017
Konu: Makine Mühendisliği = Mechanical Engineering
Dizin: Mekanik titreşim = Mechanical vibration ; Zorlanmış titreşim = Forced vibration

Özet:
Titreşim konforu, insan sağlığı ve konforu açısından oldukça önemlidir. Günümüzde
çeşitli otomotiv firmalarının bu konudaki amacı uzun süren sürüş sonrası insanlarda
meydana gelen yorgunluk hissini ve taşıtın insanlarda hissettirdiği konforsuzluğu
minimum düzeye indirmek yönündedir. Koltuk konforu ile ilgili yapılan çalışmalar,
koltuktan düşey yönde gelen titreşimlerin oldukça önemli olduğunu anlatmaktadır.
Taşıt koltukları yaklaşık olarak 4 Hz bölgesinde rezonansa sahiptirler. Düşey koltuk
titreşimleri bu frekans değeri ve bu frekans değerinin çevresindeki değerlerin etrafinda
güçlenmektedir. Taşıt koltuklarında rastlanan titreşim geçirgenliginin çeşitliligi, taşıt
koltuk seçiminin, taşıt koltuk titreşimlerine maruz kalmayı kontrol edebilecek
faktörlerin başında gelmesini sağlayabilir.
Taşıt koltuklarını, taşıta düşey yönden gelen titreşimler açısından değerlendirmek için
yaygın olarak ISO 2631-1 standardı kullanılmaktadır. Tez kapsamında yapılan
çalışmada ISO 2631-1 standartındaki kriterler ve dönüşümler dikkate alınmıştır. ISO
2631-1 Standardı, taşıt titreşimlerini değerlendirmek için, taşıttan ölçülen rms ivme
değerlerinin kullanılmasını ifade etmiştir. İnsan vücudunun tüm vücut titreşimlerine
olan hassasiyeti frekans değerlerine göre değişiklik göstermektedir. Farklı frekans
değerleri vücut kısımları üzerinde farklı etkiler yapabilir. Bundan dolayı ISO 2631-1
Standardı kapsamında frekans başına verilen frekans ağırlıklandırma eğrileri
kullanılır. Yapılan çalışma kapsamında sadece düşey yöndeki frekans ağırlıklandırma
eğrileri kullanılmıştır. Kullanılan bu eğriler, elde edilen rms ivme değerleriyle
çarpılarak taşıt konforunu belirler.
Bu çalışmamda geliştirdiğim ara yüz sayesinde giriş parametreleri bilinen aracın
koltuk konforu, tekerlek ve koltuk yay yolu, rms ivme değeri hesaplamaları ve
grafiklerinin çıktıları alınabilmektedir. ISO 2631-1 Standardı'na göre sadece koltuk
düşey yöndeki titreşimler incelenmiştir. Arayüzden elde edilen değerlere göre mevcut
taşıtın konfor analizleri ve değişik yol, hız durumlarında karşılaştırılmalar yapılmıştır.
Elde edilen verilere göre mevcut araçla ne kadar süre konforsuzluğa maruz kalmadan
seyahat edilebileceği ISO 2631-1 Standardı'ndaki sağlık uyarı bölgeleri temel alınarak
hesaplanmıştır. Farklı yol pürüzlülüklerinde ve farklı hızlarda, aracı konforlu şekilde
sürebileceğimiz sürelerin farklı olduğu gösterilmiştir. Bu tezde elde edilen çalışma
sayesinde, seçilen bir taşıtın giriş parametreleri arayüze tanımlandığında konfor ile
ilgili birçok bilgiye sahip olabileceğimiz değerler elde edilebilmektedir.

Abstract:
Comfort is the word usually defined as a state of being away from the discomfort and people feel good himself. To better understand the relationship between vibration and comfort, systematic empirical studies have attempted to determine the variation of the judgments of people with respect to the types of vibrations. However, there is no internationally recognized methodology for assessing comfort. The fact that Comfort does not have an internationally accepted methodology has led every vehicle manufacturer to make and evaluate its own tests to measure and evaluate the comfort of its vehicles.
Vibration comfort is a considerably important issue in terms of human health and comfort. Nowadays, the goal of many automotive companies is to minimize the tiredness and driver's discomfort feeling in long journeys. Studies about the vibration comfort show that the vibrations coming from the seat, which are in normal direction, have a lot of importance.
Vibration has physiological and psychological effects, such as movement disorder, which it creates on human health, performance and comfort. Various firms and academicians have been studying for a long time to reduce these effects. Vehicle vibration models, along with the driving dynamics and safety-related effects that are examined by the load fluctuations that they emerge, as well as the rms acceleration values affect the comfort of the driver and passengers. The effects of acceleration increases or decreases on human health can be examined according to mathematical evaluations.
The vehicles in the course of the voyage vibrate mainly with warnings from the road. These vibrations are generally in the frequency range of 0 Hz to 25 Hz. The warnings that the vehicle gets from the road pass through the wheel system and the axle body through the spring and damping elements. In addition to the vertical movements, the wheels can make camber angle movements and generate lateral forces, depending on the wheel suspension systems, even when the vehicle is flat. In general, the bodies of four-wheeled vehicles make vertical, horizontal, recumbent and yaw vibrations. There is also a seat system between the occupant in the vehicle and the vehicle body, which is also considered to consist of spring and damping elements.
Vehicle seats (seats with metal or rubber springing and foam) have resonances in the region of 4 Hz. Vertical vibration is amplified this frequency and around this frequency. With a large variation in transmissibility between seats, it seems likely that the selection of a seat may be a prime factor in controlling occupational exposures to whole-body vibration.
The ISO 2631-1 standard is widely used to evaluate vehicle seats in terms of vibrations from the vertical direction of the vehicle. In the study carried out within the scope of the thesis, criteria and transformations in ISO 2631-1 standard are taken into consideration. ISO 2631-1 Standard specifies the use of vehicle measured rms acceleration values to evaluate vehicle vibrations. The sensitivity of the human body to all body vibrations varies according to the frequency values. Different frequency values can have different effects on body parts. Therefore, the frequency weighting curves given per frequency are used in accordance with ISO 2631-1 Standard. Within the scope of the study, only the frequency weighting curves in the vertical direction were used. These curves are multiplied by the obtained rms acceleration values to determine vehicle comfort.
In this study, by using of the interface that I have developed and known input parameters of a vehicle, we could obtain the seat comfort, wheel and spring way, rms acceleration calculations and the output graphs of these parameters. In to ISO 2631-1 Standard, investigated vibrations are only the normal direction ones. According to parameters obtained from the interface, the comfort of existence vehicle has been aanalyzed and comparison of differenat roads and velocities has been done. 
Regarding to obtained data, the duration of the journey by using the existent vehicle without facing discomfort, based the health notice area of ISO 2631-1 Standard, is calculated. It shows that the duration of driving the vehicle in comfort mode is different in various road roughness and velocities. In this thesis regarding to the obtained study, when the input parameters of a chosen vehicle are defined to the interface, a lot of values could be obtained about the comfort of vehicle.
It is possible to interface with the MATLAB Graphical User Interface (GUI) toolbox. This interface allows the user to enter the input parameter values of the vehicle and then take the results quickly. The interface allows us to quickly compare the results of vehicle values by iterating according to different vehicle values entered. To summarize the generated MATLAB interface briefly; Information input boxes for inputting the parameter values of the user, application buttons necessary for calculating the entered values, graphs in the middle so that the results can be displayed graphically, and information result boxes for displaying the results as numerical values.
In the study of 'Evaluation of Vehicle Seats in terms of Vibration Comfort', three-mass vehicle model was considered as the basis. A special program has been written with the aid of MATLAB computer software for the purpose of analyzing the vehicle vibration model in detail in this section, analyzing, plotting the result curves, performing optimization with different input values, and examining the obtained results in terms of health warning areas in ISO 2631-1 Standard. The results obtained from this special program are dependent on parameters such as vehicle speed, road roughness, mass, spring and damping coefficient. The input values ​​of the spring and damping coefficients are kept constant and the effects of vehicle speed and intermediate road roughness on vibrational comfort and their place in the health alert area are studied. The aim of this study is to examine the increase and decrease in the number of comforts at different vehicle speeds and road roughness spectrum intensity values, as well as to analyze the chart of the health warning zone in the ISO 2631-1 standard and then to discuss the results comparatively.
The paths to be followed in computer program calculation are as follows;
1. Creation of a three-mass vehicle vibration model,
2. Finding the accelerations on the seat by multiplying the enlarged functions by the road roughness wavelength,
3. Frequency weighting of the vibration values on the seat with frequency weights,
4. Calculation of rms acceleration values according to different road spectrum intensities of vibrations on the seat,
5. Calculation of seat comfort number,
6. Using the rms acceleration value on the seat, it is necessary to study the place in the health warning area.
This study within the scope of the thesis was established according to the above steps.
With the values emerging as a result of this study, it can be interpreted that in the current vehicle, under certain road conditions, people will be exposed to the comfort of the seat after being driven. Thanks to the MATLAB GUI interface created in the study, seat comfort, rms acceleration values and other comfort evaluation criteria of any vehicle can be obtained.