ME 455 Lecture Ideas, Fall 2010

Transcription

1 ME 455 Lecture Ideas, Fall 2010 COURSE INTRODUCTION Course goal, design a vehicle (SAE Baja and Formula) Half lecture half project work Group and individual work, integrated Design - optimal solution subject to constraints VEHICLE DESIGN PROCESS OVERVIEW Problem Definition - WHAT Design tasks needed to achieve the design Critical paths what depends on what? Critical decisions design freeze Schedule Gant Chart when tasks start, end include purchase parts Conceptual Design HOW, Level 1 Decision making approach Detail Design HOW, Level 2 Design Implementation, testing, development CONSTRAINTS AND OPPORTUNITIES Overall constraints are Vehicle (Weight, space, cost) Enterprise (Space, time, money, people, administration ) Details of these 1. Selection design ordering lead times What to select, what to make Selection drives the shape of what you make Lead times for selected components - availability Selections must be early in the process Selections freeze parts of the design Therefore, selections are critical 2. Manufacturing constraints What made here, what farmed out What are our shop capabilities What are YOUR capabilities get training early Our shop schedule Outside shop schedules and lead times (see number 1 above) 3. Team skills Early designation of team resources Invest early in team mfg skills (later, you will find it always easier to do it yourself not good) 4. University constraints

2 Shop access hours Your stuff versus PU stuff storage, access Test facility access Interfaces to police, neighbors, department, BOSO, ME Dept head Tours Department public relations 5. Money constraints Spend time raising money versus doing the work yourself Managers versus doers Early, easier to do yourself, later, pressure to spend money to have it done. TEAM ORGANIZATION AND MANAGEMENT (develop as needed as tasks form) Interest and Resource assessments Chain of command flow of information decision authority - documentation How will design information be shared? How will decisions be made? Information gathering Who makes decisions? Documentation Who documents current design information? Document WHAT was decided. Document WHY the choices were made. Teams groups and subgroups Specialization needed to manage work How will integration be assured with specialization? Publish local results/progress globally Flagging information for critical integration needs (how will A know to look for new design information from B?) Leaders and followers How many levels of management? How to selecting leaders permanent or rotated? Define responsibilities of leaders and followers PROBLEM STATEMENT vs PROBLEM DEFINITION Difference between a problem statement and a problem definition Statement: It is hard to stop on inline skates that is the statement of a problem Definition: Stopping on inline skates is hard because Until you can answer the because you don t understand the problem. To answer the because you need to learn about inline skating physics, and current designs Dangerous to jump to solutions without adequate understanding of the because Definition should include engineering targets specific numbers Another example, ME 452 gearbox design Problem statement design a gear box for a hand held auger

3 Problem definition include my problem handout as the SPECIFICATION SAE Start point givens, what s known, existing team structure, past designs, what s the goal? 1. Goal student design competition 2. Go over the rules for the competition 3. Review the past vehicle designs and how well they placed in each event 4. Review how the teams have been organized in the past 5. Summarize what worked well and what didn t work well. In the designs In the team structure and organization Class activity, get a problem definition (End of week 1??) Problem statement is relatively simple place top 5 in competition? Overview of competition point system Determine overall competition strategy How have we done in the past Target what place in each category Set vehicle performance parameter targets Top speed target, braking, handling, etc. engineering targets - numbers What vehicle design choices affect these desired results? Set vehicle design parameter choices (cg, track, wheelbase, ratios, ) Draft problem definition statement and targets for each vehicle Maybe use the design specification of the ME 452 gear box as an example My handout is the problem definition Design SPECIFICATION should result includes all performance targets All performance targets speed, weight, etc. Load scenarios for strength design Factors of safety and reliability Cost and timing targets Design Process Plan should include Team organization plan Fund raising plan Schedule gant chart schedule Documentation plan (what was decided and why and by whom) Integration/coordination plan CONCEPTUAL DESIGN (whole group activity???) Overall vehicle simulations Overall vehicle parameter selections Packaging and layout Vehicle concepts (suspension, power-train, steering, braking) Vehicle dynamics Acceleration vehicle model

4 Engine model torque curve Drive train model, ratios, inertias, efficiencies Include special model of CVT for the Baja team Aero and rolling resistance models Vehicle FBD used for acceleration, braking, hill climb Braking Brake Bias coefficient, Kbf Optimum braking Braking Stability Braking efficiency non-optimum braking Brake system design getting Kbf Linkage motion ratios transmission angles Master cylinder Brake cylinders Disk Brake equations Anti-dive effects Handling Tire models SS model, Kus oversteer and understeer Transient model??? maybe just mass, damping, stiffness issues (progression) Suspension equivalent swing arm lengths Good values for Caster, Camber, toe, etc???? Bump steer Roll steer Flight dynamics (Baja) Wheel rates, motion ratios Setting stiffnesses and damping front and rear CG effects on flight dynamics Vehicle Design Targets (wheel rates, power, gear ratios, turning radius, etc.) Layout Design packaging 3D CAD DETAIL DESIGN (sub group specific assignments management integrated) Component shape and material selections Detailed analysis Integration (details may change concepts) Strength design shape design principles structural design Go over shape synthesis principles for parts and joints handout included Examples from past designs good and bad let them find these? Load scenarios for stress analysis or parts and frame Reasonable loads and factors of safety Expected failure loads and N = 1 Specific assignments to sub groups

5 Tolerancing??? For fame For uprights For brackets/mounts For joints preloads