Mechanical Engineering Design Assignment: Race car single blade windscreen wiper mechanism
The windscreen wiper is an important part of a vehicle safety system with the main purpose of enabling an acceptable outside visibility by wiping water or snow from the glass surfaces, even in the presence of solid contaminants such as mud, operating in all travel speeds and wind speeds and challenging weather conditions. The wiper system is a complex mechanism that must comply with a number of international regulations such as ISO and SAE.
There are detailed performance requirements from a wiper system, such as operating speeds, windscreen surface coverage (Figure 1), contact pressure (or force per length) on the blade, cleaning effectiveness, geometrical configuration, pedestrian safety, noise and vibration levels, durability, aerodynamic performance, sprayers performance etc. [1]. It is not possible to study all of these aspects of the windscreen wiper mechanism as part of the ME214 coursework, therefore your project should concentrate on the position, kinematic and dynamic analysis of a simplified car windscreen wiper mechanism consisting of a number of parts driving a single blade race car windscreen wiper, and also including an investigation into the material selection for various parts in the mechanism. The figures given below should give ideas on how to create a windscreen wiper mechanism. Figure 5, B1 design is suitable for this assignment. The B2 design is more complex and will increase the difficulty significantly. Figures 20 & 21 show possible arrangements.
In order to develop your windscreen wiper mechanism, choose a car make / model and identify the windscreen wiper mechanism. Start by creating a simple sketch of the windscreen and the wiper mechanism identifying the main dimensions and the skeleton of the mechanism. Keep your sketch so that it can be scanned and inserted in your report explaining your initial design idea.
Start modelling simplified parts using Creo 2:
- Motor with a shaft / worm / worm wheel,
- Crank arm attached to the worm wheel with a shaft,
- Linking rods from worm wheel crank arm to wiper crank arm,
- Wiper crank arm with a shaft to connect the wiper arm body,
- Wiper arm body, spring for blade down force (not defined as a part but a simple Creo Mechanism spring),
- Wiper blade (assume flat and rigid),
- Simplified shape (flat) windscreen etc.
The part dimensions will be approximate and shapes simplified but realistic. Once you have a successfully running mechanism more detail can be added to a part for enhanced realism. Worm / worm wheel can be downloaded & scaled parts, for example from: https://www.rushgears.com/
The parts will be assembled using the Creo 2 Mechanism joints as appropriate. Create simple and small sub-assemblies and check their operation before combining to a full assembly.
Your report should include the following studies:
-Measure the total surface area of your windscreen. Using a Creo Mechanism Position analysis create a motion envelope and the coverage area of the single blade. Then estimate the approximate percentage coverage of a single stroke of the wiper mechanism. Compare with basic hand calculations.
-Using a Creo Mechanism Kinematic analysis, select three operating speed levels:
- Intermittent: 45 strokes per minute speed for 5 strokes but with a gap of 1 sec between each stroke, then,
- Slow: 45 strokes per minute for 10 strokes, and finally,
- Fast: 65 strokes per minute for 10 strokes.
- Create a continuous animation of your mechanism at the three operating speeds and capture as a video file.
- Measure blade tip velocity and acceleration and obtain a graph for the duration of the above simulation.
-Using a Creo Mechanism Dynamic analysis, for the slow and fast operating speeds above, estimate the loads on mechanism connections.
- What is the force-time, and moment-time graph for the main joints (blade-arm pin joint etc.)?
- Can you estimate the motor spec. such as the torque & power requirements?
-Investigate what materials are used / selected in a wiper mechanism and provide a bill of materials in your design (BOM). Use CES Materials and Selection studies to illustrate suitability for the parts, by including the design requirements and charts used to screen and rank materials (provide at least top 3 materials). Comment on the selected material based on the supporting information.
Extension work: Can you optimize your design, achieve a lightweight mechanism, increased surface coverage etc.? Illustrate with design studies and optimization studies.
References:
1) L. Morello, Lorenzo Rosti Rossini, Giuseppe Pia, Andrea Tonoli, The Automotive Body: Volume I: Components Design, Springer, 2011.
Attachment:- Assignment.rar