Talk:Steering rack

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Client Comments on Report 1

We received your report, and we have some comments and questions. Some sections appear to be incomplete, and the missing executive summary makes your big-picture conclusions and recommendations difficult to assess. Please respond point by point to the items below. We are looking forward to seeing your ideas in Report 2.

  • Executive Summary: Missing - please provide.
  • Stakeholder Needs: Good identification of stakeholders and nice list. Please list out needs as a bullet list - for example, if "easy to integrate into design" and "flexible" are different needs, list them as such - each need is of the type "the product should..." - listing this way will help with next phases. It seems that there are quite a few missing needs like reliability, resistance to wear, corrosion, dirt, avoidance of pinch points or grease to contact driver, gear ratio to provide low enough force on driver and also avoid need for large angles of motion and switching hands while turning, low weight, low cost, etc.
  • Use: Clear description. For phase 2 you should observe the car being driven by members not on your team, and interview them.
  • Assembly: Clear diagram, but it is not clear how the extensions are secured to the rack. An exploded view would help.
  • Mechanical Function: Clear. A picture of the tie rod connection with the wheel suspension would be helpful. What component provides the stop if the user attempts to turn the wheel too far, and how is the rack mounted to the frame?
  • Mechanical Analysis: You seem to be doing two useful analyses but please explain further what design implications they have and what you can conclude from your analyses.
    • On your graph, please label both of the axes, make the text larger for readability, and instead of having a legend you could provide a figure caption that explains what we are looking at, since there is only one line.
    • How do you interpret this graph? The relationship looks essentially linear, but you mention that it is nonlinear in what might be an important way - is the nonlinearity significant?
    • In your second analysis, please provide a clearer free body diagram. It is somewhat ambiguous how the parts that you have drawn fit together, and whether some of the drawings are the same part shown from different angles. You might be able to clarify by showing an exploded view of the assembly and/or orthographic projections of one or more of the parts, but please label clearly which part is which in the drawing(s). Also, please show the equations you are using and define your notation before plugging in the numbers. What is your conclusion from this analysis?
  • Bill of Materials: Good list. Why is a steel pinion matched with an aluminum rack? It is okay that a few sub-assemblies were not fully dissected to avoid destruction, but please identify every individual component in your bill of materials (how many bushings in sub assembly 001, and are they all identical? What material and manufacturing process, and what assembly process? Is the rear pinion bushing identical to the front?)
  • DFMA: Good observations - since this product is manufactured at low volume, optimizing the process, particularly assembly, is less critical.
  • FMEA: The FMEA appears to be only a table. What are your conclusions and recommendations? What are the failure modes associated with the increased slop in the system that you noted in the user study?
  • DFE: Nice analysis breaking down production into components. How did you estimate the cost of each grouping? The assessment of difference between primary and secondary aluminum is insightful, since this is the largest impact. However, you didn't comment on the implication of a CO2 tax. Also, use phase emissions would include those associated with additional gasoline consumption to carry the weight. While this may dominate production emissions for mass produced vehicles driven daily, it is likely small in your application, but you should state this assumption. Please replace your figure number placeholders with actual numbers.
  • If any of your images, figures, or text were taken from another source, please be certain to provide proper attribution.

Response To Client Comments

  • The Executive Summary: added per request
  • Stakeholder Needs: list has been updated as a bullet list. More needs were added for clarification.
  • Use: N/A
  • Assembly:
  • Mechanical Function: Pictures of tie rod connection to wheel suspension and rack mounting points have been added to the report. The stop is provided by a bushing mounted to the chassis. The clevis, which is attached to the extensions, is stopped by this axial bushing on either side of the footbox to create the wheel stop. The rack is mounted to the frame at the center by 2 3/8" bolts and to the outboard ends by two axially constrained bushing housings.
  • Mechanical Analysis: From our analysis we determined that the steering rack is not in danger of failure. Also we determine how the input rotation of the steering wheel affects the output rotation of the wheel uprights.
    • Graph is updated
    • The graph shows a rather linear ratio between input and output angles for the system. Depending on geometry, the non linearity of this relationship can be significant. Because of the setup of this specific system, the relationship can be considered effectively linear and a constant gear ratio.
    • Free Body Diagram has been updated. Second image showing components and interactions added. Equations were updated
  • Bill of Materials: Most steering racks produced by this company have a steel rack and a steel pinion. It is hypothesized that a steel pinion was used to keep the steel pinion gear constant amoung all racks of the same gear ratio. Additionally, the stress put on each tooth of the gear may be too much for an aluminum pinion and the spline on the rear end of the pinion gear could not have been machined with aluminum.
    • Bill Of materials has been updated to include components in sub assemblies
  • DFMA: N/A
  • FMEA: The most critical failure modes, as determined by RPN value, are: abrasive wear on the spur rack, thread stripping on the rack extensions, and overload of the bushings resulting in binding. It is therefore preferable to design a system which mitigates these factors, by such means as protective coatings, fastener reduction, and re-specification of bearings, respectively. Slop is associated with Abrasive wear of the Spur Rack.
  • DFE: The cost of each grouping was estimated with respect to raw material cost, machining complexity, manufacturing process, and relative cost to the whole steering rack. Implied CO2 tax has been added. It is $8.29 for a primary aluminum produced rack and $6.06 for secondary aluminum. Usage has been added to analysis. Also, figure numbers have been updated to a chronological order.
  • No images, figures, or text were taken from other sources
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