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底盘系统设计chassis_system_design_methodology.pdf

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底盘 系统 设计 CHASSIS_SYSTEM_DESIGN_METHODOLOGY
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August 5, 20051 Table of Contents 1.1 Chassis System Synthesis Process..............................................................................................................3 1.1.1 Assumptions and Limitations for Synthesis Approach..........................................................................3 1.1.2 The Synthesis Method..................................................................................................................................4 1.1.3 The Ride Mode...............................................................................................................................................6 1.1.4 The Roll Mode................................................................................................................................................9 1.1.5 The Lateral Dynamic Mode.......................................................................................................................12 1.2 Suspension Kinematics Properties .............................................................................................................19 1.2.1 Toe ..................................................................................................................................................................19 1.2.2 Camber ..........................................................................................................................................................22 1.2.3 Scrub Radius ................................................................................................................................................26 1.2.4 Spindle Offset...............................................................................................................................................28 1.2.5 Roll Center and Roll Axis...........................................................................................................................28 1.2.6 Relationship of Camber Pattern, Roll Center and Scuff.....................................................................30 1.2.7 Braking and Acceleration Pitch Control..................................................................................................30 1.2.8 Turn Circle and Ackermann ......................................................................................................................33 1.2.9 Caster Trail ...................................................................................................................................................34 1.2.10 Steering Axis Inclination ........................................................................................................................36 1.2.11 Hierarchy of Parameters .......................................................................................................................36 1.3 Suspension Compliance Properties ............................................................................................................37 1.3.1 Rate and Compliance.................................................................................................................................37 1.3.2 Overview of Compliance vs. Lateral Forces .........................................................................................40 1.3.3 Ride Frequency and Rate..........................................................................................................................46 1.3.4 Vehicle Roll Rate.........................................................................................................................................48 1.4 Typical Vehicle Parameters for Vehicle Dynamics Analyses ................................................................49 1.4.1 Vehicle Sample............................................................................................................................................49 1.4.2 Mass and Inertia Properties......................................................................................................................49 1.4.3 Suspension Geometry and Compliance Properties ............................................................................53 1.5 Design Layout Procedure for Suspensions ...............................................................................................56 Step 1: Front View Grid Lines ...................................................................................................................................56 Step 2: Spindle Centerline .........................................................................................................................................56 Step 3: LBJ Center ......................................................................................................................................................57 Step 4: Spring & Strut Mount Clearances ..............................................................................................................57 Step 5: Upper Strut Mount Pivot Center.................................................................................................................57 Step 6: Kingpin Axis ....................................................................................................................................................57 Step 7: Strut Length.....................................................................................................................................................59 Step 8: LCA Pivot Axis Height...................................................................................................................................59 Step 9: Sideview and Plan View...............................................................................................................................60 Step 10: Plan View Spindle Centerline...................................................................................................................60 Step 11: Frame Attachment.......................................................................................................................................60 Step 12: LCA Attachment ..........................................................................................................................................61 Step 13: Point A ...........................................................................................................................................................61 Step 14: Steering System..........................................................................................................................................62 Step 15: Steering Gear Fore/Aft Location..............................................................................................................63 Step 16: Pinion Angle..................................................................................................................................................64 Step 17: Outer Tie Rod Ball ......................................................................................................................................64 Step 18: High Gear Position......................................................................................................................................65 Step 19: Adjust Outer Tie Rod Ball..........................................................................................................................65 Step 20: Inner Tie Rod Ball Location.......................................................................................................................65 Step 21: Adjust Suspension Points .........................................................................................................................65 Step 22: Steering Linkage..........................................................................................................................................66 Step 23: Stabilizer Bar................................................................................................................................................66 Step 24: Recheck Clearances ..................................................................................................................................672 Chapter 1: Design Methodology for Automotive Suspensions As we know, the design of automotive suspensions is the important process in the vehicle development. There are many compromises in the overall design of a successful vehicle. As it is practically impossible to design a modern vehicle in a continuous (sequential) fashion, the design must be continually reviewed and refined in a series of stages. A balanced approach starts with the overall concept through brainstorming to ensure that nothing is overlooked, proceeds to preliminary design followed by stages of refinements and finally detailing to the required level. Parallel design concepts and iterations occur at each stage. At the preliminary design stage, usually many vehicle parameters are not available for detailed vehicle dynamics analysis, but some of the parameters can be achieved through the combination of the initial definition of the vehicle structure and chassis synthesis process. The overall design of suspension systems is mainly driven by several key factors, including handling, ride, package, cost and durability. The objective of suspension design is to satisfy the defined performance criteria and to reduce the cost as much as possible. Usually the high-level vehicle development team defines the overall suspension objective and type based upon the benchmarking analysis from the competitor vehicles. Then the suspension characteristics may be clearly defined including the kinematics and compliance. Through the synthesis process, the component or sub-system objective or parameters can be initially determined in conjunction with the layout design. The design of suspension components should be satisfied with the component design objectives. If the component designs are completed, then the front and rear suspension models can be built and used for analysis and evaluation of the suspension performance. Such analyses and evaluation include the kinematics, compliance and stress distribution. Once the suspensions are evaluated to satisfy the defined targets, the full vehicle system model can be further built to analyze and evaluate the overall vehicle performance including handling, ride and durability. It should be noted that the whole design process involves several iterations to refine the suspension components and the suspension type may be changed in some special case. If the analytical evaluation of full vehicle is completed and satisfied, a prototype vehicle should be built for more detailed evaluation. The overall design process of suspension system is illustrated in Figure 1-1. In this Chapter, the detailed synthesis process will be firstly introduced in conjunction with an example followed by the kinematics and compliance of suspension systems with the guidelines proposed. The key parameters for vehicle dynamics simulations will then be briefly introduced in order for the readers to have some reference data for their primary dynamics analysis. Finally the design layout procedure and the loading criteria will be given with examples illustrated. Figure 1-1: Overall Suspension Design Process. Definition of Suspension Characteristics Front/Rear Suspension Type Selection Suspension System Synthesis For Component Targets Suspension Layout Design Suspension Component Design Suspension Performance Analysis and Evaluation Meet Packaging, Cost, Weight and Objective Build Full Vehicle Model, Analysis and Evaluation No Yes Meet Component Weight, Cost and Objective Yes No No Meet Vehicle System Objective Build Next-Level Vehicle Check With Other Subsystem and Modify Design Yes3 1.1 Chassis System Synthesis Process Recent trends in automotive chassis design have shown the increasing use of performance targets. Use of such targets has the advantages of objectively defining the desired performance of the proposed vehicle, unifying the design effort, and identifying conflicts between the design and desired performance. Successfully meeting well chosen targets usually produces designs requiring only further optimization. But traditional methods of design and performance analysis do not lead directly to designs having the desired performance. The alternative is a design synthesis method in which the chassis design is determined from the performance targets and certain basic knowledge of the chassis. This iterative process relies on the separation of the design task into smaller parts which have a certain logical dependence on each other. Each part, or mode, can be more easily visualized and solved with certain orderly steps and graphical techniques. The solution of each mode depends, in turn, on the separation of the design variables into the three categories of performance variables, independent design variables, and dependent design variables. Values for the dependent design variables, which are consistent with the limits placed on the performance variables, are determined in the mode solution. In a basic chassis design synthesis, there are three related modes. They are associated with vehicle ride, roll, and directional control dynamics. The design of a contemporary passenger car has been studied using the synthesis process. Values for spring rates, stabilizer bar diameters, tire coefficients, and the overall steering ratio have been determined. A continuing recent trend in the design of automobiles is the use of product performance objectives in the design process. As a result, certain benefits of designing to such targets have become apparent. First, their establishment early in the design process objectively defines the vehicle’s target performance for its desired role in the marketplace. It also allows better use of computer simulation of expected performance in concert with performance testing, which can clarify communication between members of the design team and unify their efforts. Third, the existence of performance targets clearly identifies design and performance conflicts, as soon as accurate simulations or tests are run. Finally, striving to meet these targets throughout the design process tends to produce designs that require optimization, rather than complete redesign, during subsequent development. In the traditional design process, complete, or nearly complete, vehicle concepts are analyzed to see if they meet the performance targets. This approach does not lead directly to a design that will perform as desired. The alternative is to synthesize a chassis design that will meet the performance targets. Analysis and synthesis differ from one another in the parts of the problem which are unknown. Figure 1.1-1 shows this. In analysis, the physical system and input are known but the output is unknown. In synthesis, the input and output are known but the nature o
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