Academic competition leads the way to a new electric car
University of Ontario Institute of Technology
NX helps engineering students transform Saturn Vue to clean and green
The University of Ontario Institute of Technology (UOIT) is one of 17 North American Universities participating in EcoCAR: The NeXt Challenge, a three-year engineering competition established by the United States Department of Energy and General Motors, and managed by Argonne National Laboratory. The competition challenges the participants to reduce the environmental impact of vehicles by minimizing fuel consumption and reducing emissions while retaining the vehicle’s performance, safety and consumer appeal. Students use a real-world engineering process to design and integrate their advanced technology solutions into a 2009 Saturn Vue.
UOIT’s EcoCAR team is turning the gasoline-powered Vue into a full-function electric vehicle. Such a dramatic transformation posed a number of engineering challenges for the students, including designing and integrating a fairly large onboard energy storage system (ESS) into the competition vehicle. To qualify for the project and receive an actual vehicle, the team had to demonstrate the validity of its concept through virtual simulations. GM supplied a digital model of the Vue and the UOIT team used the NX™ digital product development solution from Siemens PLM Software on three main areas of the ESS: wiring layout, thermal management and structural component design and mounting. The team created a unique battery mounting approach that incorporates wiring looms, chassis mounts and a thermal management system. The students also proved the validity of their design by conducting finite element analyses using NX Nastran. This enabled them to avoid any potential performance failures and the need to test physical prototypes.
Wiring made easy
The proposed ESS required high-voltage wiring running the length of the battery tray to connect the batteries, as well as wiring to connect the motor with the battery management system. The limited amount of space in the existing vehicle made wire routing a challenge. “It would have been difficult if not impossible to do this work using 2D routing diagrams and engineering drawings,” says Nicholas Shopian, an automotive engineering student at UOIT and an EcoCAR team member.
“A three-dimensional digital model and the NX quick connect tool provided a rapid way to set up several points and generate a wiring path,” Shopian continues. “This made it relatively simple to see the high voltage lines laid out inside the ESS module. With the wiring laid out, it also allowed for several necessary changes to be seen, enabling the wire routing to safely clear all obstructions. The electrical routing tool proved invaluable when generating a wiring design. Using the routing tool and with all of the other systems in their place, it was possible to ensure any one system would not overlap and that the proper clearances were maintained.”
To maintain the ESS at the correct operating temperature, the team had to find a way to extract internal heat build up and also to supply heat to the system if necessary. The proposed thermal management system encloses all the batteries with small Teflon or nylon cooling tubes. A system of this nature was very hard to visualize on such a large scale. Determining the quantity of material necessary for construction was another problem.
The students used NX to design the thermal management system around a central supply line and one main return. With these laid out, routing software was used to construct the individual battery cooling system. This was done with the NX mechanical routing application using mostly the quick path tools. The mechanical routing application allowed for easy layout of the main path, and then for several iterations to be made based upon the number of batteries in each stack to generate the entire system. After all of the individual pipes were made, they were then linked into the main tees and the main line.
One very helpful feature was the volume calculation tool, which was used to determine the amount of material needed for construction. The use of NX was also helpful for seeing how the various systems fit together and if there was any interference.
Perhaps the biggest challenge encountered over the course of the preliminary design related to packaging the ESS module and feasibility of the proposed support structure. To achieve the desired range and vehicle performance, it was determined that 88 to 90 battery cells were required. With an individual cell weight of five kilograms (approximately 11 pounds) this capacity translates to a significant amount of additional mass.
Using the digital model of the existing vehicle, students used NX to take measurements and then design components. This process was crucial in testing overall fit and design feasibility to ensure that the ESS module integration would in fact be possible. The team performed structural analyses of the proposed design using NX Nastran to ensure that displacements and stresses were within acceptable limits for individual components and assemblies.
NX makes it possible
“A competition of this magnitude would not be possible in the context of an academic setting without software such as NX,” says the co-leader of UOIT’s EcoCAR team, Mike Maduro. “We wouldn’t have the time or the resources. We are basically redesigning a vehicle. It would be extremely expensive to do packaging studies by putting rapid prototypes together, and it would probably take six months to a year. That would put us out of the running. Using NX, we are doing packaging studies in weeks, even days.” Dr. Greg Rohrauer, the team’s faculty advisor, notes, “The complete vehicle model supplied by GM is very large, constituting over 10 gigabytes spread across thousands of parts. However, with our $3,000 (i7-920 based) workstation running NX, we can open the entire model at once and navigate to any area nearly as fast as one can drag the mouse. My students habitually section across the entire vehicle to refine on our very tight packaging constraints.”
Another area where the NX suite of tools has been especially helpful is for quickly making design modifications, such as those required in response to contest rule changes. One recent change involving ground clearance could have been disastrous for the UOIT team, whose battery pack fits below the vehicle. “We had to basically move everything up an inch,” says Maduro. “Without the ability to easily modify an assembly in NX, that would have been impossible.”
NX is the only CAD solution being used by UOIT’s 20-person EcoCAR team, which consists of electrical, industrial, mechanical and software engineers. Maduro notes that the students are doing amazing things with NX, pointing out, “They are modeling shapes I would have thought required a 3D scanner to create.”
In subsequent years of the three-year EcoCAR competition, the team plans to use NX to conduct flow and crash analyses.