formulaRACINGU

CD

INTRODUCTIONThe Formula Racing Team at UC Davis competes in the Formula SAE Student Design Competition every year and is building a new vehicle to compete in this year’s Electric Series. This project’s goals were to design and fabricate the electric drivetrain for the team’s 2014 vehicle.

The drivetrain was designed to be compatible with a torque vectoring system that independently drives each rear wheel. The entire system includes two inboard electric motors and their mounting, an eccentric chain tensioning design, and a unique axle assembly.

DESIGN SPECIFICATIONS AND CRITERIA• Conform to all 2014 Formula SAE rules• Free movement between two halves of the rear axle for independent wheel drive

• Minimum of 250 ft-lb of torque at each wheel• Maintain 6000 RPM at motor side• Maximum speed of at least 70 mph• 0-60 mph in about 3 seconds• System must safely endure 30 minutes of continuous race operation• Design for strength and reliability through fatigue and strength analysis

FINAL DRIVE RATIOBased on weighted design metrics, a dual chain reduction drive was chosen. Through analysis in MATLAB, a final drive ratio was set by varying the sprocket sizes to attain top speed and acceleration goals. The graph below shows the motor’s RPM and the vehicle’s estimated speed versus time. The table shows ideal vehicle performance specifications.

MANUFACTURING PROCESSES AND MATERIALS SELECTION• Axle parts CNC machined on a Mori Seiki NMV5000• Axle supports and motor mounts waterjet cut• Remaining custom parts fabricated in Engineering Fabrication Laboratory• Aluminum used on majority of parts due to ideal strength to weight ratio

• Carbon Steel used on high fatigue and critically stressed members

SYSTEM ARCHITECTURE

Important components were determined based on their impact on the design criteria. Analysis showed that the highest priority items were the gear ratio and axle assembly. The internal components of the rear axle allow each wheel to operate independently and keep them axially constrained. The center axle is bolted to the left spindle and is constrained by a pair of internal bearings on the right, allowing each spindle to rotate independently. The stub axles hold constant velocity joints which transmit torque from the axle through the half shaft to the wheels.

The figures to the left show the eccentric chain tensioning system in its foremost and rearmost positions.

Calculated  Vehicle  Performance  Specifica6ons  Final  Drive  Ra6o   4.54  

Small  Sprocket  Teeth   ANSI  40:  13.00  Large  Sprocket  Teeth   ANSI  40:  59.00  

Es6mated  Vehicle  Weight   550.0  lb  Driver  Weight   180.0  lb  

Top  Speed  (Gear  Limited)   80.71  mph  (6000  RPM)  0  -­‐  60  Time   2.84  s  

Total  Distance  Covered   89.52  m  0  -­‐  60  Distance   39.74  m  

Accelera6on  Time  (75m)   3.99  s  Accelera6on  Final  Speed   76.4  mph  

Max  Accelera6on   1.01  g  

AxleBearing

Spindles

FINITE ELEMENT ANALYSISCritical components were analyzed under worst case scenarios to refine the design using Solidworks Simulation. Visual results for the sprocket, motor mounts, and motor brackets are shown below. All components had a safety factor of at least 2.5

CONCLUSIONThrough the course of use, it is important to routinely check the condition of the bearings, sprockets, and chains.

The final design meets all specifications while conforming to FSAE rules. Strength and fatigue analyses confirm the system will endure the extreme conditions of automotive racing for many seasons.

ACKNOWLEDGEMENTSWe would like to thank Dr. Steven Velinsky, Dr. Roland Williams, Dr. Jae Wan Park, Dr. Mike Hill, Alexander Hashimoto, Randy Floresca, David Robinson, Henry Herndon, and the EFL Staff for their guidance, critiques, and manufacturing assistance.

Motor Mounts

Axle Support

ANSI 40 Sprocket

FORMULA ELECTRIC DRIVETRAIN

Bryce Yee, Jonathan Hromalik, Michael Brown, Nicholas Hori, Zachary March FACULTY ADVISOR: Steven Velinsky

PROJECT SPONSOR: Formula Racing Team at UC Davis