Vertical Dynamics - ## 전산설계자동화 실험실 ## 방문해 주셔서...

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Vertical Dynamics

Vehicle Dynamics (Lecture 5)

2

Vertical Vehicle Performance

Vertical Dynamics and its applications

3

Vehicle Ride Performance Model

Vertical Dynamics and ride evaluation

승차감을 객관적 지수로 평가할 수 있는 방법 활용을 위한 수직 동역학 모델

4

Vertical Vehicle Dynamics

Ride evaluation• ISO 2631 (인체 진동 노출 평가 기준, 1974년 제정)• 노출한계 범위: 안전이나 건강에 치명적인 영향을 줄 수 있는 범위• 피로 및 작업능률 저하 범위: 운전 등과 같은 작업능률 저하 범위• 안락감 감소 범위: 차안에서의 독서 식사 등의 행동에서 안락감이 감소되는

범위

• 앉은자세, 선 자세 4-8Hz z방향 가속도에 민감• 누운자세 1-2 Hz에서 민감

5

Road roughness


G: 거칠기 계수-거칠기 정도를 나타내는 거칠기 진폭W: 파동정도를 나타내는 파동계수 - 스펙트럼 밀도함수의 기울기

스펙트럼 밀도 함수

6

Road roughness


스펙트럼 밀도 함수는 일정속도 v 로 차량이주행할 때 주파수 f 의 식으로 표시 가능

동일한 도로면을 달릴때도 속도에 따라서 가진입력이 달라지는 것을 알수 있음.

7

Road roughness


8

Quarter Car Model


• Single DOF model Assumptions

- Single car body

- No wheel mass

- Tire stiffness is relatively small

compared with suspension stiffness

- Voigt-Kelvin model is used for

suspension spring and damper

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Quarter Car Model


• Single DOF model

10

Quarter Car Model



Quarter Car Model



Quarter Car Model


• Single DOF model 현가 설계시 스프링 K 조건

• 구동력이 바퀴에 전달될 수 있도록 접지력 확보• 인체의 걷는 주파수 1-1.3 Hz 로 조정 (motion

sickness), 4-8Hz (유해한 주파수 (0.1-0.5Hz human fatigue)) 회피 설계

••

고려한 설계



Quarter Car Model


Quarter Car Model (1 DOF)



• Forced vibration – sinusoidal road input

assume


Quarter Car Model (1 DOF)• Forced vibration – sinusoidal road input


• 차체진동이 도로가진 보다 낮게 되기위해서는

고유진동수를 아래의 P점 이상 되는 방진구역에 위치

D 의 크기도 작게 (보통 D= 0.25-0.5)

•

을 높이기 위해서는 주어진 w 에 대해서 고유진동수 wo 값이

작을 수록, 일정 질량의 차량에 대해서는k 값이 작을 수록 유리 ( 3-5)



Car body acceleration vs road vibration도로 부가력


Quarter Car Model (2 DOF model)


Sprung mass

Un-sprung mass



Free vibration

assume

Characteristic equation

No damping case:

Undamped frequency vs. damped frequency = 5% difference

Un-sprung mass vs. sprung mass = 10% neglect un-sprung mass


No damping case:

Undamped frequency vs. dampled frequency = 5% difference

Un-sprung mass vs. sprung mass = 10% neglect un-sprung mass

Primary ride frequency for the sprung mass Damping ratio for the sprung mass


Secondary ride frequency for the un-sprung mass Damping ratio for the un-sprung mass


Primary ride frequency for the sprung mass Damping ratio for the sprung mass


Secondary ride frequency for the un-sprung mass Damping ratio for the un-sprung mass

Dynamic wheel force



Forced vibration - Sinusoidal road profile input

assume and

Frequency response function for the sprung mass

Frequency response function for the un-sprung mass


Frequency response function for the sprung mass Frequency response function for the un-sprung mass

Kb soft, ride comfort increase


Sprung mass FRF Un-sprung mass FRF

Cb hard, ride comfort increase



Forced vibration - Ramdom road profile input



Mb increase, ride comfort increase

Mb does not affect to dynamic axle force much

• Sprung mass variation simulation



• Mt does not affect to ride comfort and dynamic axle force in near the natural

frequency of the sprung mass

• Mt does affect to ride comfort and dynamic axle force in near the natural

frequency of the un-sprung mass

• Mt decrease, Ride comfort increase, dynamic force decrease

• Un-sprung mass variation simulation



• Suspension stiffness variation simulation

• Kb decrease, Ride comfort increase, But handling (Roll, pitch) problem



• Suspension damper variation simulation

• Cb hard, Accel decrease in near 1.25 Hz

• Cb soft, Accel decrease in near 1- 10 Hz

Need variable damper control according to frequency

• Cb hard, dynamic force decrease in near 10 Hz (natural

frequency of un-sprung mass) Wheel hop motion decrease



• Tire stiffness variation simulation

• Softer tire Natural frequency of unsprung mass decrease,

• Softer tire amp. of unsprung mass decrease

Thus, Softer tire increase ride comfort and handling. However, softer tire increase

rolling resistance and tire deformation in high speed.


One track Half-Car Model (4 DOF model)


One track Half-Car Model (4 DOF model)• EQM for sprung mass for vertical motion

• EQM for sprung mass for pitch motion

• EQM for front un-sprung mass for vertical motion

• EQM for rear un-sprung mass for vertical motion

Vertical Dynamics - ## 전산설계자동화 실험실 ## 방문해 주셔서...

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