Commercial vehicles.

1. Everybody is trying to develop electric vehicle drive systems and many small companies see an
   opportunity to develop alternative drive trains to retrofit to cars and commercial vehicles.
2. You work for a transmission consultancy group. A company developing a gearbox has reported
   excessive noise and vibration from some gears in service.
3. You are required to undertake a feasibility study to re-design, analyse and specify the gears and
   shafts of a simple single stage parallel axis gearbox. The gears you design will be used in a test
   gearbox to verify your design and low noise optimisation strategy.
4. A single specification will be allocated to you, as provided in the ‘Electric Vehicle Gearbox Design
   Assignment Load Cases’ document.
5. The requirement is for 14,000 hours total operation.
6. The transmission will rotate in one direction only in this test gearbox.
7. The proposed electric motors may produce a torque ripple, and the application will include varying
   loads so an application factor (kA) has been defined to account for this.
8. Drive motors and brake systems to test the gearbox are connected with spline couplings and
   assumed to exert no radial and axial loads on the shafts. You do not need to specify these
   couplings.
9. A key objective is to minimise noise and vibration by good gear design and specification.
   Specifying appropriate gear macro and micro gear geometry is critical for achieving this.
10. A rectangular gearbox casing will be machined with a precision CNC 5-axis milling machine,
    capable of machining general tolerances of ±25µm. The detailed design or analysis is not part of
    this assignment.
11. State your assumptions and justify all the decisions you make in the main report. You are
    defending your design from other designers who will criticise it.
12. Gear macro and micro geometry should be developed with Dontyne Systems GPS gear software
    which is available online, via the Windows Virtual Desktop.
13. An ISO 6336 fatigue analysis is required for the single stage gearbox. Use the GPS software for
    the gear specification and analysis.
14. Gear micro geometry (tip relief and helix crowning and/or helix correction) should be specified
    with the corrections calculated using basic hand calculations. For maximum marks, this should be
    verified with the proper use of the load analysis software (standard TCA in the GPS software)
15. Choose an acceptable bearing type for your gearbox to react the gear loads. Do not select or
    analyse specific bearings- this is a qualitative requirement only to show you have selected the
    correct bearing type and have located it appropriately.
16. Shaft deflections should be quantified using the GPS deflection calculation software properly
    applied for appropriate shaft sizes. You don’t need to calculate the shaft stresses.
17. State and justify all your assumptions.
    MEC8029 Assignment 2020-2021 V1
    Assignment report
18. Use the provided Microsoft Word ‘assignment report template’ for writing your report. This gives
    you guidance as to what should be included as a minimum, together with mandatory headings.
19. Read the guidance in the ‘assignment report template’ highlighted in yellow. This guidance can
    be deleted as you write your report.
20. The final report must be a maximum of 10 pages, not including any annexes. A report of between
    5 and 10 pages is normal. Size 11 font must be used.
21. Neat free hand drawings approximately to scale are welcome when appropriate.
22. Provide a clear cross-section drawing (sketch) of your gearbox layout, illustrating the gears,
    shafts and bearing arrangements, clearly showing how everything is mounted and constrained.

Sample Solution