1 / 42

Ride Quality Factors in Design

Spring Centers. Longitudinal Axis Spring Centers. The spring center of a vehicle is defined as the location, along the longitudinal axis of the vehicle, through which an applied vertical load will result in a pure vertical displacement of the sprung mass. An applied vertical load at any other loca

sunila
Download Presentation

Ride Quality Factors in Design

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

    1. Ride Quality Factors in Design Dr. Richard Hathaway, P.E. Professor Mechanical and Aeronautical Engineering

    2. Spring Centers

    3. Longitudinal Axis Spring Centers The spring center of a vehicle is defined as the location, along the longitudinal axis of the vehicle, through which an applied vertical load will result in a pure vertical displacement of the sprung mass. An applied vertical load at any other location along the axis of the vehicle will introduce a pitch angle into the sprung mass. An offset (c) of the spring center from the center of gravity (CG) is desirable as vertical accelerations of the sprung mass will introduce pitching motions. The offset and resulting "coupled behavior" between pitch and bounce is desirable in a passenger vehicle to aid in reducing ride harshness.

    4. The spring center can be determined if the front (Kf) and rear (Kr) spring rates are known, as shown below. From the definition of the spring center, the deflection at the front (?f) and the deflection at the rear (?r) are equal when a vertical force is applied at the spring center (X). Longitudinal Axis Spring Centers

    5. The distance between the spring center and the center of gravity (c) can be determined from equations 2.1 - 2.5. Then : Longitudinal Axis Spring Centers

    6. From which the distance between the spring center and the cg {c} is derived. The vertical spring rate for the sprung mass, at the spring center, is. Longitudinal Axis Spring Centers

    7. The vertical spring rate for the sprung mass, at the spring center, is as shown below. The vertical rate, for the sprung mass, at the center of gravity is Longitudinal Axis Spring Centers

    8. The torsional stiffness in pitch, or the pitch stiffness about the spring center, is also easily determined from the above. The torque about the pitch center (Tp) is shown to be: therefore: The above Equation represents the stiffness to angular motions about an axis passing through the spring center at 90o to the longitudinal axis of the vehicle. Longitudinal Axis Spring Centers

    9. Lateral Spring Center Position

    10. The Spring Center to Cg distance (x) at either end of the vehicle is important. Lateral Spring Center Position

    11. Then from The spring center to cg distance (x) is positive (to right of cg) if Lateral Spring Center Position

    12. The location of the Cg from the inside wheel centerline, distance ll, at each axle can be found from the scale weights at each wheel location. Then by substitution yields equation 6 indicating the distance between the spring center (sc) and the center of gravity (cg). Lateral Spring Center Position

    13. Two Degree of Freedom Ride Model

    14. 2-DOF Ride Model Sprung Mass Behavior

    15. 2-DOF Ride Model -- Jounce Sprung Mass Behavior

    16. 2-DOF Ride Model -- Pitch Sprung Mass Behavior

    17. 2-DOF Ride Model Sprung Mass Behavior

    18. 2-DOF Ride Model Sprung Mass Behavior

    19. 2-DOF Ride Model Sprung Mass Behavior

    20. 2-DOF Ride Model Sprung Mass Behavior

    21. 2-DOF Ride Model Sprung Mass Behavior

    22. 2-DOF Ride Model Sprung Mass Behavior

    23. 2-DOF Ride Model Sprung Mass Behavior

    24. 2-DOF Ride Model Sprung Mass Behavior

    25. 2-DOF Ride Model Sprung Mass Behavior

    26. 2-DOF Ride Model Sprung Mass Behavior

    27. 2-DOF Ride Model Sprung Mass Behavior

    28. 2-DOF Ride Model Sprung Mass Behavior

    29. 2-DOF Ride Model Sprung Mass Behavior

    30. 2-DOF Ride Model Sprung Mass Behavior

    31. From either the Bounce or Pitch equations the amplitude ratios of bounce to pitch can be determined. Sprung Mass Behavior

    32. The Pitch node will always be inside the wheel base, the bounce node will always be at or outside of the axle locations (at only if an infinite spring rate exists). Sprung Mass Behavior

    33. The coupled natural frequencies always lie outside the uncoupled natural frequencies. Sprung Mass Behavior

    34. Dynamic Index. The dynamic index is the relationship that exists, in the vehicle design that relates the radius of gyration and the center of gravity. Sprung Mass Behavior

    35. Ride Model Example Vehicle Specifications M = 1600 kg c = 6% L = 0.15 m L = 2.5 m k2/(lf lr) = DI = 0.9 Wf/W = 0.6 fnF = 1.2 hz

    36. Ride Model Example From the above specifications

    37. Ride Model Example Coefficients continued

    38. Ride Model Example Sprung mass uncoupled frequencies

    39. Ride Model Example Sprung mass coupled pitch & bounce frequencies

    40. Ride Model Example Sprung mass pitch & bounce centers

    41. Ride Model Example The following ride variables have now been obtained

    42. The end! Thank You

More Related