The idea was to challenge undergraduate university students to develop highperformance, electric powered race cars. Under the auspices of Centerior Energy Co., Independence, Ohio, in cooperation with the Solar and Electric Racing Association, (SERA) Formula Electric Racing was born. Now, in the second of a fouryear racing schedule, 11 universities across the country compete in the Formula Lightning program (see box, “Who’s racing”).

To focus attention on the electrical powerplant and its performance, all Formula Lightning racers have a standard chassis, disc brakes, coil-over-shock suspension, and rack and pinion steering. The open-wheel, Indy-style racers are all 163-in. long, 77-in. wide, and weigh 975 lb — not including drivetrain and batteries. These racing cars are designed for speeds up to 160 mph.

Although the sleek Formula Lightning racers may look like Indy cars, they certainly don’t sound the same. The deafening high-pitched whine of an internalcombustion engine at 10,000 rpm is replaced by a nearly inaudible swoosh as the electric racers streak past at speeds approaching 100 mph.

The Electric Falcon

At Bowling Green State University (BGSU), Bowling Green, Ohio, the starting point for the Electric Falcon design team was a review of a SERA prototype Formula Lightning car initially powered by a dc motor rated at 29.84 kW and drawing more than 400 A. Although this prototype reached almost 90 mph, it could not sustain this speed for long without depleting its batteries.

Motor and control design. The BGSU design team knew that the existing power-drive combination needed improvement. To develop and integrate components into a winning system, students, faculty, and marketing partners used concurrent engineering and rapid prototyping.

The BGSU design team set out to develop an ac induction motor rated at 60 kW at 8,000 rpm with a peak output torque of 80 lb-ft. The final motor design evolved from a C-TAC 3-phase, ac motor rated at 3.7 kW at 1,750 rpm manufactured by Lincoln Electric Inc., Cleveland.

The motor design team determined that, by operating the motor at 10,000 rpm, the basic motor produced approximately 30 kW. By rewinding the stator, the final power doubled to achieve the targeted output of 60 kW.

To achieve the 60 kW rating, the students, using reverse engineering, modified the mechanical design of the motor through lighter material selection and increased structural integrity. The bell housing design was entered into a MasterCAM software program using a coordinate measuring machine (CMM). A finite- element analysis of the design indicated that the new motor housings needed reinforcement to handle the higher torque and speed ratings. The final bell-housing design was then cast and machined.

Cooling system. Upgrading motor performance produced more heat than the original air cooling system could dissipate. So, the design team devised a system of spraying an oil mist on the rotor and the motor bearings. This system cools the rotor to acceptable levels and, in the process, recovers much of the generated heat. By cooling the oil in radiators placed in front of the battery packs, the batteries are warmed, boosting their efficiency on cool days. The students calculate that by cooling and lubricating the rotor and bearings in this manner, bearing life will increase up to 50%.

The new oil-spray cooling system was simulated and modeled using AutoCAD and became part of the concurrent engineering process.

Controller configuration. The final controller went through several phases. Originally, an ac vector drive unit designed exclusively for use in electric vehicles was used. Although the racer could achieve speeds of 74.6 mph, it only delivered half of the desired 300 A to the motor, thus limiting acceleration and maximum power.

The design team then adapted a 350-A, peak, EMS Model 2055 high-speed inverter by bypassing its rectifier section and accessing the inverter section. Bench testing showed this new design capable of much greater power than the first drive, but it was too large to fit in the Electric Falcon. Again, the design team was innovative and turned this problem into an advantage.

The controller, originally packaged in a 9.8 in. x 18.9 in. x 31.9 in. steel housing, was disassembled into five units. Each of these was repackaged in aluminum and polycarbonate containers and strategically placed in the car so the weight distribution would enhance vehicle performance. In addition, elimination of the steel housing, diode-bridge rectifier and cooling fans reduced the weight by more than 70 lb. This system has been updated to a vector drive to achieve the desired results.

Braking system. Braking involves standard hydraulic disk brakes and regenerative torque through reversing circuits. Both systems are controlled by brake pedal movement. Above 10 mph, gradual depression of the brake pedal actuates a rheostat to control regenerative energy to slow the vehicle and recover nearly 80% of the braking energy. Heavy pedal pressure adds hydraulic braking and slows the car quickly. Below 10 mph, braking is all hydraulic.

Batteries. After investigating various commercially available designs, the Falcon team found that lead acid Optima batteries provided superior power-toweight and dollar ratios, and they could be mounted in any position (facing up, down, or sideways) — a decided advantage for adjusting car ballast, Figure 1. The battery chemistry uses starved electrolyte so, in the case of an accident, the risk of a sulfuric-acid hazard is reduced.

The Electric Falcon is powered by 312 Vdc and requires 26, 12-V batteries. A total of 104 batteries — four complete sets — were purchased, tested, and grouped according to their ability to hold power. Each of the four sets was grouped into eight packs — six with three batteries each, and two packs with four.

The battery packs are modular and fit into any available space within the car. Ballast is adjustable by swapping a fourpack with a three-pack, and vice versa, in any appropriate area of the car.

The safety committee requires that the batteries be completely enclosed so, in case of an accident, all components stay within the packs. The design team chose to use a polycarbonate insulator for the battery pack enclosures rather than the aluminum the safety committee recommended. Because of aluminum’s high conductivity, the team felt there may be a problem if, in case of an accident, the batteries break open inside the pack and energize the case with live voltage.

The team paid special attention to the connections inside the battery packs, because every joint and standard batterypost connector has some resistance causing I²R (power) losses. One-piece couplers are used on about half of the internal pack connections. These couplers allow the positive and negative terminals to butt together to minimize these power losses.

Electric-car battery technology is advancing rapidly with ideas promising both lighter weight and longer run-time between charges. The BGSU team is evaluating several advanced battery designs such as lithium-metal hydride, zinc-bromide, lithium-metal sulfide, and metal air.

Power train. The drivetrain concept evolved from a direct drive through hypoid gearing to a differential, Figure 2. This meant, with no transmission, the car had only one gear. Several different power-train approaches, including transmissions and torque converters, were investigated. A Supercharger Systems Inc. cog-belt system provides the highest efficiency and lightest weight. It also enables overall ratios at the track to match racing conditions.

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