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Suspension design

TTR9 懸吊系統設計方向

[name=撰寫人:吳汶桓/底盤組/7~9代][color=#d904ed] 以下內容根據TTR7、TTR8懸吊系統調整與TTR9懸吊系統設計經驗。 前情提要：這邊來說一下TTR9的設計理念 可以參考一下可悲專題(數值應該是錯的(因為後來有大聰明給我設計變更...)，如果有說到相同的東西以這邊為準)，主要會著重在補充後半段的設計，也就是專題沒寫到的

前言： 在進入具體設計流程前，需先釐清本年度設計變更的核心邏輯。本隊屬於成熟的持續開發型（Iterative Development）車隊，設計方向通常依據前代車輛的實測數據、賽道表現及調校反饋進行優化。然而，受限於過去幾年疫情導致的技術交接斷層，第 6 至 8 代的懸吊設計幾乎處於停滯狀態。 與此同時，隨著賽事趨勢從內燃機（IC）轉向電動車（EV），為了建構穩定的動力平台，車輛的整備重量與軸距均大幅增加，這使我們在車輛動態條件上處於先天劣勢。面對交接斷層與架構巨變的雙重挑戰，本年度的懸吊系統採取了「歸零重構」的策略，雖在各項參數上力求嚴謹，但仍不免有待完善之處，目標在於為新一代電車架構奠定穩固的基礎。

Issues Observed in Last Year's Suspension and Vehicle Dynamics

1. Inside Rear Wheel Lift During Trail Braking

  • The inside rear wheel was observed to lift off the ground during trail braking.

  • Root cause:

    • The center of gravity (CG) was positioned too far forward.
    • During trail braking, load transfers forward and laterally to the outside wheel.
    • This resulted in insufficient normal force on the inside rear wheel, causing wheel lift.

2. Poor Vehicle Dynamics Predictability

  • Root causes:

    • Suspension data calculations were incomplete and lacked a solid analytical foundation.

    • Suspension parameters deviated from typical ranges without supporting validation data.

    • Suspension geometry designed for a different tire size was reused.

      • This caused excessive roll center (RC) movement during body roll.
      • Leading to nonlinear roll moment generation, reducing predictability.

3. Front Wing Ground Contact Under Heavy Braking

  • Under heavy braking, the front wing made contact with the ground.

  • Root cause:

    • Significant forward load transfer caused excessive front suspension compression.
    • The resulting ride height dropped below the front wing clearance.

Design Objectives and Rationale for This Year

1. Optimization of Center of Gravity (CG)

Design Direction

  • Shift CG rearward and lower

Objectives

Maximize Total Tire Grip

  • Lower CG reduces load transfer:

    • Allows more even load distribution across all four tires
    • Utilizes the nonlinear tire load sensitivity more effectively

  • Helps eliminate rear wheel lift during braking

Improve Stability and Control

  • Lower CG reduces:

    • Brake dive
    • Acceleration squat

  • Mass centralization reduces:

    • Roll inertia
    • Pitch inertia

  • Result:

    • More responsive handling
    • Improved recovery near the limit

2. Establish a Robust Suspension Data Calculation Process

  • Predictable vehicle dynamics must be built on:

    • A solid theoretical foundation
    • A systematic calculation workflow

  • To avoid repeating previous design issues:

    • A new suspension calculation methodology was developed from scratch

3. Reasonable Suspension Parameter Selection

  • Due to time constraints, advanced simulations were not conducted for the 9th generation car

  • Therefore:

    • Suspension parameters were selected based on typical benchmark values
    • Ensuring baseline reliability and feasibility

4. Optimization of Suspension Kinematic Behavior

A predictable vehicle requires not only good parameter selection but also well-designed suspension kinematics.

Key Focus Areas

(1) Roll Center Movement

  • Vertical RC movement during roll should be minimized

  • Smaller RC displacement → smaller variation in CG–RC distance

  • Result:

    • More linear roll moment generation
    • Better alignment with theoretical behavior

(2) Camber Recovery

  • Objective: Maintain optimal tire contact conditions under all dynamic states

Key considerations:

  • Ideal: Outer wheel camber ≈ 0° at maximum roll

  • However:

    • Tires are not rigid bodies
    • To prevent tire rollover, slight negative camber is required

Design target:

  • Maximum camber ≈ -0.5°

Final tuning:

  • Based on real-world tire wear and contact patch observations

(3) Anti-Geometry (Anti-Dive / Anti-Squat)

  • Governs vehicle behavior in pitch dynamics

Purpose:

  • Control longitudinal load transfer effects

  • Reduce excessive pitch angle caused by:

    • Aerodynamic center of pressure (CoP)
    • Front wing ground contact

(4) Motion Ratio (Installation Ratio) Curve

Heave Motion Ratio

  • Designed as progressive (non-linear) rather than linear

  • Reason:

    • Aerodynamic downforce increases with speed

  • Benefit:

    • Maintains ride height at high speeds
    • Improves stability under high downforce
Roll Motion Ratio

  • Must be:

    • Symmetrical
    • Linear

  • Ensures:

    • Consistent suspension behavior in left and right turns

5. Optimization of Stiffness-to-Weight Ratio of Suspension Components

Importance of Structural Stiffness

  • Higher stiffness reduces deviation between:

    • Actual suspension behavior
    • Theoretical kinematics

  • Improves:

    • Vehicle dynamics predictability

Benefits of Reducing Total Vehicle Mass (Sprung + Unsprung)

Improved Power-to-Weight Ratio

  • Better acceleration and braking performance

Reduced Load Transfer

  • More even tire loading
  • Increased cornering grip

Benefits of Reducing Sprung Mass

  • Direct reduction of total vehicle weight
  • Improves overall vehicle performance

Benefits of Reducing Unsprung Mass

Improved Mechanical Grip

  • Lower inertia allows wheels to follow road surface more effectively
  • Maintains consistent normal force

Faster Dynamic Response

  • Higher natural frequency of suspension system
  • Quicker settling after disturbances
  • More responsive steering feedback

Suspension System Design Process

1.Vehicle parameter calculation and setup

I. Vehicle static parameter calculation and setup

  • Vehicle overall layout adjustment and center of gravity calculation

II. Vehicle dynamic parameter calculation and setup

  • Maximum G-forces and wheel loads during acceleration, braking, and cornering
  • Wheel loads, roll moment, and roll moment distribution during steady-state cornering at the limit

2. Suspension system parameter calculation and setup

I. Vehicle dynamic characteristics parameter

  • Total ground clearance
    • Heave motion
    • Roll motion
  • Ride rate
  • Wheel rate (Wheel center rate)
  • Sprung mass natural frequency
  • Unsprung mass natural frequency
  • Body roll angle
  • Roll gradient
  • Roll rate

II. Suspension parameter setup

  • Heave motion
    • Heave spring rate
    • Heave damping coefficient
    • Heave installation ratio (motion ratio)
  • Roll motion
    • Roll spring rate
    • Roll damping coefficient
    • Roll installation ratio (motion ratio)

3.Suspension geometry design and optimization

I. Front view

  • Scrub radius
  • King pin inclination
  • Roll camber recover
  • Roll center movement

II. Side view

  • Caster angle
  • Caster trail (mechanical trail)
  • Pitch angle
  • Pitch center height
  • Anti-geometry
    • Anti-dive
    • Anti-squat
    • Anti-lift

III. Rocker system

  • Heave installation ratio curve
  • Roll installation ratio curve

4.Suspension component design and optimization

I. FEA- Stress analysis & Fatigue analysis II. Topology- Optimized stiffness-to-weight ratio III. Component lightweighting

5.3D print functional check & prototype

I. Interference check during actuation

6.Vehicle fabrication

7.Vehicle testing and theory validation

I. Functional Check

  • Verified proper operation of steering, braking, and suspension systems
  • Checked for interference and abnormal actuation in all mechanisms

II. Static Inspection

  • Measured suspension geometry (camber, toe, ride height)
  • Verified vehicle weight and weight distribution
  • Inspected structural integrity and assembly quality

III. Dynamic Testing

  • Conducted straight-line acceleration and braking tests
  • Evaluated low-speed handling (skidpad / slalom)
  • Assessed high-speed stability and steering response

IV. Data Acquisition & Analysis

  • Collected data on vehicle speed, acceleration, steering angle, and damper travel
  • Analyzed discrepancies between vehicle behavior and design targets

V. Feedback & Iteration

  • Adjusted setup parameters (damping, weight distribution, tire pressure)
  • Performed design modifications when necessary
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