An interdisciplinary team of students is needed to tackle the multi-physics nature of the problem and also assess purchase decision making behavior and criteria and the barriers to and potential of market adoption. This emphasizes the need for science and business students as well as those with background or interest in manufacturing, in addition to students from various fields of engineering. Initial design work of a segmented rotor lamination and compaction dies will be carried out using finite element analysis and CAD. A series of basic segmented rotor structures and DC field winding compaction dies will be designed by the team so that they can be machined in the IIT machine shop. The team will also be involved in the design of test fixture, hands on testing, and prototyping basic manufacturing jigs.
The Department of Energy has set the following very aggressive technical and economic performance goals for electric vehicle traction motors: $4.7/kW, 1.6 kW/kg, and 5.7 kW/l (Source: https://www1.eere.energy.gov/vehiclesandfuels/pdfs/program/eett_roadmap_june2013.pdf). In particular the cost per kilowatt target will be very difficult to meet since current estimates of electric vehicle traction motor costs are greater than $10/kW using mature electric machine designs and production technologies. Two approaches that are being investigated to meet the cost per kilowatt target are reduction of the electrical steel scrap generated during stamping and enhancement of power density by increasing winding fill factor (ratio of copper to area available for conductors) which potentially allows the substitution of copper wire with aluminum wire for substantial cost reduction.
There are many technological approaches to reduce the traction electric motor cost while maintaining high power density. One promising approach uses segmented laminations to reduce the amount of scrap generated during the lamination stamping process. Currently, approximately 40 percent of the incoming electrical steel is scrapped in non-segmented designs. Segmentation of the laminations, ideally both stator and rotor, potentially allows for stamping die layouts which minimize the scrap. Historically, segmented laminations have not been used for electric vehicle traction motors because of concerns of losses at high speeds due to higher order space harmonics. Recently, new low space harmonic fractional slot concentrated winding layouts have been developed which may accommodate segmented laminations in electric vehicle traction motors. Very little public information, however, is available about the impact of segmentation on structural, electromagnetic, and thermal properties of the machine and their associated manufacturing issues which are critical for adoption by automotive Original Equipment Manufacturers (OEMs).
Additionally, the use of segmented stator and rotor structures potentially allows the use of compacted wire bundles for the windings to increase the winding fill factor. Typically in hand wound or even standard winding equipment the fill factor is around 45 percent. Using a compaction die to preform coils allows slot fills of ~70 percent, significantly reducing ohmic losses in electric machines and the Ampere turns that can be applied. Wound field synchronous machine rotors are an ideal machine topology to leverage both low scrap segmented construction and compacted windings. An example segmented design that would be amenable for use with a compacted rotor winding is shown in the figure below.
The goal of this IPRO project is to develop low-scrap segmented lamination and coil winding compaction technology, for both stators and rotors, with minimum impact or, ideally, enhancement of the power conversion properties of the electric vehicle traction motors. The team will investigate the impact of reduced scrap segmented lamination designs, including structural and electromagnetic behavior, to determine the potential tradeoff between power conversion properties and cost reduction. The team will also design and prototype winding compaction dies. The team will also investigate and design prototype scale manufacturing jigs and test fixtures to determine technical feasibility and viability of the low-scrap segmented motor technology for widespread adoption by the automotive industry. Basic costing and economic studies will also be carried out to assess market viability.