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Taşıtların seyir konforu

The ride comfort

  1. Tez No: 66404
  2. Yazar: İBRAHİM HİLMİ ÇAĞIL
  3. Danışmanlar: PROF. DR. YAŞAR ÖZDEMİR
  4. Tez Türü: Doktora
  5. Konular: Makine Mühendisliği, Mechanical Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1997
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Otomotiv Ana Bilim Dalı
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 145

Özet

ÖZET Taşıt titreşimleri ortaya çıkardıkları yük salınımları ile irdelenen seyir dinamiği ve emniyetle ilgili etkilerinin yanında ivme salınımları ile de sürücü ve yolcuların konforunu etkilemektedir. Taşıtın tabi olduğu dinamik yük uyarılarının ve bu uyarıların etkilerinin objektif yöntemlerle incelenmesi mümkündür. Ancak ivme değişmelerinin insan üzerine olan etkilerinin incelenmesi sübjektif değerlendirmelere göre yapılabilmektedir. Bu güne kadar yapılan çalışmalarda, titreşimlerin insana ve insan sağlığına etkisi incelenmiş kurulan matematik modellerde koltuk baş vurma yayı alınmamış, koltuk arkalığının koltuk oturağına rijit bağlı olduğu varsayılmıştır. Çözüm işlemleri sırasında hareket denklemleri sürekli durum uzayında birinci dereceden bir diferansiyel denklem takımına dönüştürülmüş ve daha sonra ayrık durum uzayına taşıt dinamiğinde daha önce kullanılmamış bir yöntemle geçilmiştir. Diferansiyel denklem takımının çözümü sırasında matlab dilinin 4.üncü jenerasyon özellikleri kullanılmıştır. Parametrik incelemeler için her seferinde alınan örnek taşıt datalarından biri değiştirilerek konfor sayısını veren çözümler elde edilmiştir. Bu çözümler değerlendirilerek taşıt tasarımı için yol gösterici sonuçlara varılmıştır. Çözüm işlemleri için frekans boyunca genlik incelemelerine geçilirken değişik frekanslarda sinus uyarı fonksiyonları kullanılmış, elde edilen genlik değerleri ile yol pürüzlülüğü yol fonksiyonundan alınarak yol kalitesine bağlı gerçek uyarı genlikleri ile gövde ağırlık merkezine, koltuk ağırlık merkezine, ellere ve ayaklara ulaşan düşey ve baş vurma titreşim ivmelerinin genlikleri bu frekanslar için bulunmuştur. Parametrelerin seçiminde elde edilen sonuçlara dayanılarak aşağıdaki tavsiyelerde bulunmak mümkündür: Yay katsayıları maksimum konfor değerlerinin yanısıra çökme miktarlarının değerlendirilmesi ile seçilmelidir. Sönüm katsayıları minimum konfor sayısını yani maksimum konforu sağlayacak şekilde seçilmelidir. Düşük hızda taşıt kullanımı konforlu taşıt kullanabilme süresini artırmaktadır. Sürücü koltuğunun ağırlık merkezi taşıt ağırlık merkezinden bir miktar geride olması sürücü konforunu artırmaktadır. Başvurma yay sertliğinin çok sert olduğu bir koltukta bile başvurma konfor sayısı toplam konfor sayısının yaklaşık %35 lik payını tek başına etkilemektedir. Örnek taşıtta, koltuk başvurma yay sertliğinin 20000 - 60000 Nm/rad olması halinde ise baş vurma konfor sayısı çok yüksek olmakta ve bu husus taşıtın konforsuzluğunda büyük rol oynamaktadır. Bu nedenle koltuk yaslanma yayının sert yapılması istenir. Bu da incelememde koltuk baş vurma yay sertliğinin ele alınmasının önemini gösteren bir sonuçtur. XV111

Özet (Çeviri)

THE RIDE COMFORT SUMMARY Since they cause load oscillations, vehicle vibrations have a considerable effect on safety and the dynamic characteristics of motion. At the same time vehicle vibrations bring forth the vertical body acceleration oscillations that constitute a decisive factor on the ride comfort of the driver and the passengers. Dynamics' loads imposed on the vehicle and their effects can be studied by some objective methods. But the effects of the acceleration variations on the human body can only be brought to picture by some subjective considerations. A great deal of research has done on the subject. In this work we investigate the properties of vehicle vibrations in connection with the precautions to be taken to increase the comfort of the driver and as a consequence to improve the safety. The factors causing vehicle vibrations are road surface unevenness, defects of alignment in the rotating parts, engine vibrations and some dynamic effects of the motion of vehicle. Riding comfort is a concept expressing the degree the discomfort and fatigue caused by the vibrations due to the above mentioned factors. Drivers and passengers are subjected to the effects of vibrations as a result of their transmission from floor to soles, feet and legs and from steering wheel and arm rests to hands and arms. In addition to vertical direction, vibrations are being transmitted in inclined directions as rolling and pitching. When it is considered as a vibrating system, the human body can be assumed of consisting of several masses connected with springs and dampers. Therefore it is concluded that the human body is influenced by the frequencies of these masses that have different natural frequencies, rather than their amplitudes. Research showed that there is a relation between subjective perception and physical measurement data in terms of frequencies. This relation varies with the direction of the effect depending on the particular part of the body. To determine the factors effecting the riding comfort subjects sitting on a vibration plate oscillating with different amplitude and frequencies were being used. Subjects categorized various vibration conditions as noneffective, effective, discomforting etc. Experimental research concludes that in the frequency band from 1 to 4 Hz. human body sensitiveness increases with frequency, from 4 to 8 Hz. it remains constant and beyond 8 Hz. it tends to decrease. In the work that has been done on the subject until now a general mathematical formulation of the problem has not been introduced. The general mathematical formulation obtained in this work facilitates the calculations involved and is applicable to all types of vehicles. Vehicles consist of several elastic parts linked to each other with different types of connections. Setting up a mathematical model including these connections and parts with their degrees of freedom brings on many formidable calculation difficulties XIXdepending on the degrees of freedom. Just the formulation of the problem requires comprehensive manipulations. For this reason a simple mathematical model with lower degrees of freedom that is capable of representing the essential properties of the vibrating system is chosen. If the car body is assumed to be rigid then its motion can be represented by specifying a translation wand a rotation vector 0 only. In this fashion the degree of freedom of the vehicle body becomes 6. As far as the riding comfort is concerned the important displacements are uy and 0Z. Degrees of freedom that do not contribute any significant effect on these displacement components, which are the essential ones for the vibration system, may not be taken into account. For example, in case when a vehicle moves on a straight road where lateral unevenness negligibly small compared to longitudinal defects, it can be assumed that uz = 0. For the same road condition one also may write 0X = 0 and 0y = 0. By substituting uz = ©x = ©y = 0 in the mathematical model it is assumed that only the degrees of freedom in the vertical plane containing the road axis may be considered. The front and rear axles including the wheels are idealized as being rigid bodies. As it is done for the vehicle body, for each axle one translation ü and one rotation vector @ are defined. This way, in general, each axle has 6 degrees of freedom. As a result, the sum of the degrees of freedom of a vehicle body and axles are 18. The axles of the vehicle are idealized as rigid bodies, vibrating in xOy plane and executing only translatinonal modes. Considering the effects of its position and its properties on riding comfort the driver seat is idealized as a rigid body having translational and rotational degrees of freedom in xOy plane. Above mentioned rigid parts and the elastic links connecting them are represented by springs and dampers. This simplified model is shown in figure 2.3. In the model, mx and m2 indicate the masses of the front and the rear axles respectively, including the wheels. m3 represents the mass of the vehicle body except for the driver and his seat. m4 is the total mass of the driver and his seat. This way 4 rigid bodies of masses m1,m2,m3, and m4 and the springs and dampers connecting them constitute a plane model. yoi(t) and yo2(t) are the road surface roughness functions of the front and rear axle respectively. yi(t) and y2(t) represent the absolute vertical displacements of the front and rear axles respectively. y3(t) stands for the absolute vertical displacement of the center of gravity G of the car body. ©i(t) indicates the absolute rotation of the car body in the plane of motion. y4(t) is the absolute vertical displacement of the center of gravity G' of the mass consisting of the driver and his seat. @2(t) shows the absolute rotation of this total mass in the plane motion. koi (i = 1,2) and kj (i = 1,2,3) are the constants of the springs used in idealization. K is the constant of the torsional spring of the driver and his seat, coi (i = 1,2) and Cj (i = 1,2,3) are the damper constants. For the purpose of writing down the equation of motion of each part of the model show in figure 2.3 representing a vehicle in motion, the free body diagrams of each part are given in figure 2.4. IG and Iq being the polar inertia moments of the bodies of masses ni3 and rri4 with respect to their center of gravities G and G1 respectively, we write the equations XX[-K]x9+[lGtxn + Kxu] = 0 (12) [-(c3x6 + kjX5 )] + [-Zg(c3xI0 + ^x9 )] + [mtxs + c3xs + £3*7] = 0 (13) x,=x2 (14) x3 = x4 (15) x5 = x6 (16) x7 = xg (17) x9 = x10 (18) xu=x12 (19) The solution has been achieved by original transformation of these equations from continuous state space representation into discretized domain in the sense of application area. Furthermore acceleration values are calculated by taking appropriate time derivatives of the state variables and by using the maximum amplitudes of the oscillations in the stable region normalized amplitudes versus frequency's ranging from 0 to 20 is calculated. Magnification function of accelerations and weighting function for the parts of the body are multiplied. Square of this multiplication and the amplitude h of wavy road function are then multiplied to integrate the resulting function through frequency giving the square of riding comfort number related to the type of acceleraion which are might be a) Vertical vibration of the seat b) Pitch vibration of the seat c) Vertical vibration of hands and arms d) Vertical vibration of feet. For the numerical example the following natural frequency values are calculated: Seat natural frequency 2,90 Hz Vehicle body natural frequency 1,43 Hz Axle natural frequency 1 1,00 Hz The driver is also subjected to the pitch vibrations together with the seat. This is one of the factors that decrease the riding comfort by 35%. For this reason, the pitch vibrations are important, so that we included in the model. The evaluation of the numerical results of the calculations with various data ensures that a softly sprung system with lower accelerations offers more comfort. For a high level ride comfort the suspension system should be equipped with soft springs and damping elements. Furthermore soft seat springs and hard seat damping tend to increase the riding comfort. In addition, the position of the seat has an effect on the riding comfort too. The seat should be placed a little backwards to the center of gravity of the vehicle. XX1X1[-K]x9+[lGtxn + Kxu] = 0 (12) [-(c3x6 + kjX5 )] + [-Zg(c3xI0 + ^x9 )] + [mtxs + c3xs + £3*7] = 0 (13) x,=x2 (14) x3 = x4 (15) x5 = x6 (16) x7 = xg (17) x9 = x10 (18) xu=x12 (19) The solution has been achieved by original transformation of these equations from continuous state space representation into discretized domain in the sense of application area. Furthermore acceleration values are calculated by taking appropriate time derivatives of the state variables and by using the maximum amplitudes of the oscillations in the stable region normalized amplitudes versus frequency's ranging from 0 to 20 is calculated. Magnification function of accelerations and weighting function for the parts of the body are multiplied. Square of this multiplication and the amplitude h of wavy road function are then multiplied to integrate the resulting function through frequency giving the square of riding comfort number related to the type of acceleraion which are might be a) Vertical vibration of the seat b) Pitch vibration of the seat c) Vertical vibration of hands and arms d) Vertical vibration of feet. For the numerical example the following natural frequency values are calculated: Seat natural frequency 2,90 Hz Vehicle body natural frequency 1,43 Hz Axle natural frequency 1 1,00 Hz The driver is also subjected to the pitch vibrations together with the seat. This is one of the factors that decrease the riding comfort by 35%. For this reason, the pitch vibrations are important, so that we included in the model. The evaluation of the numerical results of the calculations with various data ensures that a softly sprung system with lower accelerations offers more comfort. For a high level ride comfort the suspension system should be equipped with soft springs and damping elements. Furthermore soft seat springs and hard seat damping tend to increase the riding comfort. In addition, the position of the seat has an effect on the riding comfort too. The seat should be placed a little backwards to the center of gravity of the vehicle. XX1X1of motion for all rigid parts and after some rearrangement we get a set of differential equations as follows: [/w, yx + (cx + cox )yx + (kx + kox )yx] + {-cxy3 - ^^3] + [-c.Z,®, - £,£,©,] \nwy2 + (c2 + c02 )y2 + (k2 + k02 )y2 ] + [-{c2y3 + k2y3 )] + [Z2 (c2Qx + k2®x )] = ^02^02 ~*~“'02^02 [m, y3 + (cx + c2+c3 )y3 + (kx + k2+k3 ) v3] + [-{cxyx + kxyx )] + \-{c2y2 + k2y2 )] +{{cxLx + c3L3 - c2L2 )0, +(Ar,Z, + k3L3 - k2L2 )©,] + [-c3y4 - k3yA] = 0 [IG&i + (Z,2c, +I2C2 + -Z3C3 )©! + (L2xkx +L22k2 + L]k3 + K)®l\ +[(Lxcx ~ Lzci + L3ci)y3+(LA ~L2k2 + L3k3)y3] +[L2c2y2 + L2k2y2] + [-Lxcxyx - Lxkxyx] + [-L3c3yA - L3k3y4] + [-£0,] = 0 (D (2) (3) [iGe2 + Ke2-K0x] = o [mj4 + c3yA + k3yA] + [-{c3y3 + k3y3)} + [-L3(c3Sx + k3Qx )] = 0 (4) (5) (6) The notations (') and (”) placed above the functions indicate the first and second order derivatives with respect to time. The vector of unknowns of the set of differential equations is: {«} = yx yi yi ©> 02 (7) It has 6 independent elements. In other words, the vibration has six degrees of freedom. In the equations the letters y and 0 represent translations and rotations respectively. The terms on the right hand sides of the equations are the forced functions representing the unevenness of the road surface. These are known functions. When riding comfort is concerned it may be necessary to calculate the velocities and accelerations and amplitudes of the functions ©2(f) and y4 (t). On the other hand knowing all the elements of the vector ü is important for design purpose. In the earlier works done on the subject of riding comfort equations of motion similar to those given above were obtained and for solution researchers in general XXI

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