Final Selection and Design Specifications Page
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| Author: Jon Evans | Team: Solar Car |
Final Selection
After modeling the two different design alternatives, it was necessary to select the final design of the interface equipment. This was done using another QFD decision matrix. After discussing this design problem with other members of the Solar Vehicle Design team, we determined that the metrics used in the previous QFD were still valid. These were reused for this QFD matrix. The two designs were again compared. Figure 1 shows the decision matrix used. From this matrix and examining the designs, it was determined that the direct mounting design was the best choice.
Figure 1: QFD Decision Matrix
Reasoning
As shown in the QFD matrix, the direct mounting design was equal or superior in almost every category.
- Mass
- Because the direct mounting design could be smaller, it also had less mass.
- Ease of Manufacture
- The wheel well design would require large amounts of sheet metal shaping or casting to get its shape. The direct mounting design could be made from mostly COTS materials.
- Ease of Repair/Replacement
- Because the direct mounting design does not have to interact with the steering and suspension, accessing it for removal or repair would be easier.
- Parts Cost
- As with ease of manufacture, the parts for the direct mounting design could be standard, COTS parts, while many of the wheel well components would need to be custom built. This makes the direct mounting design more cost effective.
Technical Drawing/Parts List
Figure 2 shows an assembly drawing of the direct mounting ventilation interface hardware. Included in the drawing is a Bill of Materials (BOM) Table which lists the components. Those components that are purchased include a manufacturer’s part number.
Figure 2: Technical Drawing (Click the picture to see a full sized image)
Design Description and Specifications
This design mounts directly to the shell of the vehicle, mating with a hole cut into the shell. Machine Screws secure the base plate in place. A Y-type flow splitting tube is clamped into the base plate using a sealing bracket. The seal is made airtight using a gasket. The air flow into the Y-splitting tube, which in turn directs the air into the ducts leading to the battery boxes and driver compartment. This design meets all of the design requirements:
- Batteries must be ventilated at a minimum of 280 L/min
- This design allows the use of fans which profide 22.94 cubic ft. per minute (or 646.8 liters per minute) of airflow. (See Appendix for fan specifications)
- Must be active whenever battery system is electrically connected to the rest of the car.
- The fans will turn on automatically, and even if there is a problem with the fans, at normal speeds, this inlet will provide enough airflow to meet the requirements. (See Appendix for air flow calculations)
- Outside air must be provided for the driver.
- The Y-splitter directs separate airflows to the driver and battery boxes.
- Shell interface must not significantly compromise aerodynamics.
- The design’s advantages outweigh any aerodynamic losses experienced.
- Shell interface must be lightweight.
- It was the lightest of the design alternatives.
- Shell interface must be easy to manufacture and include Commercial Off The Shelf (COTS) parts.
- It includes COTS parts which will be combined with easy to manufacture components.
- Shell interface must connect with COTS ducting equipment.
- The Y-slpitter connects with the standard ducting.
- Shell interface must not be overly expensive.
- This design was the most cost effective solution considered.
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