ECO Running

abstract

Development of electric vehicles is essential to reducing pollutants and additionally beneficial to reducing transportation costs. Part of the Shell Eco-Marathon was to design the electric systems of such a vehicle, and our goal was to optimize efficiency of the vehicle’s battery usage. To achieve this we programmed a motor control system to improve acceleration efficiency for the SAE-NAU urban concept vehicle. All  components were chosen to work together in order to optimize efficiency and reliability based on statistical data gathered about the motor, potentially increasing battery life up to several hours in an urban driving environment.  Making electric vehicles more efficient is a key improvement to the world’s economy and environment.

 

 

project overview

The EE Team is responsible for all electrical features for the vehicle. The two major electrical aspects of this project are the critical drive train system and accessories required to make the vehicle viable and efficient. There will be a 12V accessory battery that will power two headlights, two front turn signals, two rear brake lights, windshield wipers, two cooling fans, two rear running lights that will have integral blinkers, and a horn.  In addition to the accessories, a crucial part in designing our Shell Eco-Marathon competition vehicle is electrical power control and distribution, Figure 1, specifically, the behaviors of various electrical components. Efficient power usage of the electric subsystems is a key performance criteria of an electric vehicle, and our motor controller will be programmed to reflect this.

schematics

The Block diagram in Figure 2 shows the basic layout of the electric subsystems in the vehicle. Power to the accessories from the accessory battery is regulated by switches in the dashboard interface, which also sends signals to the programmable controller, along with the throttle and brake switches. This information, in combination with encoder feedback from the motors is used to regulate efficient power usage by the individual motor controllers

torque efficiency model

The graph shown in Figure 3 below shows the power consumption (color) of the motor for an applied torque at a given speed.  This information was used to program efficient drive cycles to be implemented by the programmable microcontroller in competition.

development

For the future on this project, there are plans to implement real time efficiency mapping of the torque curve in Figure 3. This differs from the current auto-acceleration setup in that it is reactive to the drivers input rather that pre-programmed. There is also the potential for construction of a solar charging station for the battery. This would serve as a better model of efficiency for future electric vehicles, and serve as an education research project in energy generation for the vehicle, as well as also serve as a showcase with the vehicle.

requirements & Specifications

Marketing Requirements	Engineering Requirements	Justification
Vehicle must have running lights, turn signals, reverse lights, brake lights, headlights, internal lighting, and displays.	All of these lights will be LED’s, and not exceed the amount of the 12V accessory battery.	The instructive lighting is required by the competition, and the displays are for making the vehicle realistic as specified by Dr. Tester.
In an emergency there must be a way to kill the battery connection to the motor, for the safety of the driver or someone outside the vehicle.	Vehicle must have one internal and two external kill switches.	The kill switch is to shut off the motor in the event of an emergency and must be accessible to the driver and/or emergency track personnel.
Must be a battery electric vehicle.	50V battery power supply for the motors. 12V battery power supply for the accessories.	The battery is limited by the Shell Eco-Marathon rules. Dr. Tester specified the maximum voltage for the motors as well as the max for the accessories.
Must have a mechanism for visibility in rain, a horn, and air conditioning.	A fan will be installed for air conditioning. A wind shield wiper will be installed for visibility in rain.	Specified by Dr. Tester, these requirements make the vehicle realistic.
Interface with accessories, (lights, wipers, etc.) will be done via switches.	6 switches will be necessary.	Makes the vehicle realistic and easy to use.
Interface with vehicle will be done via accelerator pedal.		Makes the vehicle similar to marketed cars.
The vehicle must survive the competition, and be in working order through the end of the spring semester.	Parts will be durable.	Specified with Dr. Tester, the vehicle will be a trophy to promote SAE and NAU.
The power usage must be handled as efficiently as possible.	All accessories will be within the accessory range. The motor controller will be provided so the team hopes it is efficiently using the motor battery.	This is the goal when designing any green technology, and if set forth by the client, but also the motivation to promote cleaner technology.