Our team felt that the best place to start generating our design concepts was the morphological chart that we had created in the first part of the project.  However, a morphological chart alone will generate an extremely large number of design concepts; too many to effectively evaluate by hand.  In order to reduce the number of design concepts that we would have to consider, we went through our morphological chart and eliminated certain solutions to the sub functions on the chart that our group thought was impractical.  The items that were eliminated from our design concepts and the reasons are as follows:

1.)  Standard automotive batteries were not considered as a viable method of storing energy because we could not store enough energy within the space of the battery case to make it worth while.  Using the same logic, kinetic methods of storing energy (gyros and flywheels) were also ruled out.

2.) Liquid cooling was ruled out because it would take up more room and weigh more than an air cooling system.  Space within the battery case is already very tight, and we would need all the room we can spare to hold the batteries.  Also, weight is a major customer concern, so we are taking all steps possible to lighten the battery pack.

3.) Some form of a shock absorber as the only method of absorbing impact on the battery case was ruled out because it is somewhat impractical.  If the case is hit, there will still be a large amount of local shock to the case.  Shock absorbers would not reduce this to acceptable levels in our opinion.  In addition, shock absorbers would change how rigidly the case is mounted to the frame of the vehicle.

4.) A case coating and sacrificial material are chemical resistance solutions that were ruled out by the group.  A coating would allow us to use stronger case materials, such as steel, but if the coating was chipped or even cracked it is possible that battery acid could come in contact with the base case material.  So, if the case material itself is not resistant to the battery acid there is a safety concern.  Sacrificial material works well in marine environments, but battery acid spills would probably be too localized to certain areas of the case to make them an effective chemical resistance solution.

5.)  Sliding trays would be an interesting way to access the batteries in the case, but they were ruled out due to conditions in which the battery case will be used and serviced.  It would not be wise to allow the bottom of the case to slide down while the battery pack was attached to the car, due to safety issues.  Since there is no room for battery trays to slide to the side of the case while it is attached to the vehicle, the case must be removed from the vehicle for service anyway.  At which point, a sliding tray would provide only a marginal advantage over a top case lid at the cost of greatly reducing the internal case space available for batteries.

6.)  Base clamps (found in many automobiles) and a pressure fit for securing the batteries in the case were eliminated from the design considerations for the following reasons.  Base clamps are difficult and cumbersome to deal with, based on the battery changing experience of the group members.  Why would we include a design feature that we do not like ourselves?  The pressure fit was ruled out simply because the batteries could come loose due to shock and vibration.

7.) Of the four types of battery connectors that were considered by the group, we ruled out all but one.  Alligator clips and press-fits are fast and easy, but they do not hold onto battery leads well enough for elongated amounts of time.  Hardwiring the batteries is great in terms of keeping the connections between the batteries, but it makes maintenance much harder.  One of the major goals of this design is to make user maintenance of the battery pack as easy as possible.  The team felt hardwired batteries would detract too much from "ease of maintenance."

8.) Many different wire metals were considered, but in the end we selected copper.  The other options were either too expensive (silver and gold) or too low quality to handle the current the battery pack would generate (lead based).

A morphological chart with all of the ruled out sub function solutions highlighted in red can be found here.

Pugh's Selection

After we made the initial concept eliminations, we created a list of all the possible design concepts (all the possible combinations of sub function solutions from the morphological chart that were not ruled out).  We then used Pugh's concept selection method to narrow our choices down to two different design concepts.  All of the concepts that we generated from our morphological chart were compared to the current battery pack as an evaluation baseline.  The team determined whether each of our design concepts was better, the same, or worse than the stock battery to the best of our engineering judgment.  The questions that we used to evaluate the designs and our Pugh's selection chart (the two best design concepts are highlighted) can be found here. 

The ways that the two different design concepts fullfill the subfunctions of the battery case can be seen in the picture below.  The only difference between the two designs is where the over charge protection will be done, from a computer system in the battery pack or by the batteries themselves.

Pictures of design concepts 1 and 2 can be seen below.  Again the only difference is the extra computer module (highlited in blue) that is found inside the case of design concept 2.

Concept 1

Concept 2

Continue to Task 11