University of California, Berkeley

Super Mileage Vehicle Team

Electronic Fuel Injection


This webpage will catalogue a custom electronic fuel injection system that I made for the Cal Super Mileage Vehicle team (Cal SMV) in the Fall 2008 semester .  I did this project as my class project for ME 230 - Real Time Applications of Mini and Micro Computers.


The project is divided pretty cleanly into three categories: hardware, software/electronics, and engine theory.  While I do not claim to know very much about this field that has roots over 150 years ago, I will try to present a complete solution that has worked for me.  I will also try to explain the relevant theory in an introductory format, as I understand it.  I do not claim to be an authoritative source on anything covered in this project, but I hope that my experience can serve as a helpful starting point for the beginner.  Fiddling with parts on your car based solely on information found on this web page is a bad idea.  I will not be liable for any incorrect information or its consequences.  Please wear safety glasses at all times and keep a fire extinguisher near by when running an engine or handling gasoline.


Abstract

 

A working fuel injection system was built from the ground up around a Honda GX25 25 cubic centimeter four-stroke gasoline engine and successfully demonstrated.  Parts specially assembled or fabricated include a pressurized fuel system, throttle body with working throttle, sensors and actuators.  The system is controlled by a Luminary Micro LM3S8962 evaluation board, with an ARM 7 processor at the center.  The goal is to maximize fuel efficiency.  The starting point is to inject gasoline every time the hall effect sensor indicates that the cam is in the correct position, which allows operation of the engine under electronic control.  The software includes two additional key features that will allow the entire system to be tuned to a high level of performance: a 2D fuel map and a closed loop operation mode.  The closed loop mode uses an oxygen sensor to adjust the injection timing until the mixture is neither too rich or too lean.  The 2D fuel map uses RPM and throttle position to estimate load on the engine.  Several issues in the performance of the Luminary Board were discovered, primarily the difficulty of operating on a sub millisecond clock.  Development of the code incorporating C nodes into the LabView program is ongoing.

Hardware

Electronics

Software

Theory

Motivation: 

I am a member of the UC Berkeley Super Mileage Vehicle Team.  More information on the team is available on the team website.  We compete at the annual Shell Eco-Marathon Americas competition in Fontana, California.  The goal of this competition is to get the best possible mileage in a custom made car with a prize of $10,000 for first place.  The car must safely carry a single passenger at an average speed of at least 15 miles per hour on an approximately 9 mile track.  Gasoline must be the sole energy source.


Last year's (April 2008) winner at the competitio
n was Mater Dei High School with 2800 miles per gallon.  Cal SMV has never had a strong showing at this competition in the two years for which it has been running.

We employ several strategies to maximize our fuel efficiency including super lightweight materials and construction, good aerodynamics, efficient transmission/tires/bearings, and, probably most importantly, a well made and well run engine.

An important feature of a highly efficient engine is the proper air to fuel ratio.  Achieving this requires the injection of the precise amount of gasoline called for by the conditions.  This level of performance can only be accomplished using electronics.

Electronic fuel injection systems became ubiquitous on passenger cars in the 1970s and 1980s following the Clean Air Act and several similar laws passed by the US Federal and State governments in response to huge pollution problems.  Today there are several hobbyist level fuel injection kits with fairly sophisticated software available, some as low as $200-$300.  Unfortunately for us, none of these kits are made to handle Super Mileage Vehicle applications.  Our engines are smaller than anything these kits are built to handle, and our application different enough from standard driving that pre built fuel injection systems are unsuitable for us.

The team has been around for about 10 years now, and previously it competed exclusively in a competition held by the Society of Automotive Engineers in Michigan.  This competition was more restrictive, requiring that all contestants use a 150 cc Briggs and Stratton engine, an old technology that meant extensive modifications to the engine itself had to be made to increase efficiency.  One of our best recent showings at this competition was a bit over 1000 mpg with a carbureted engine.  This shows just how good the team is at building the rest of the car, and demonstrates that we have probably gone as far as we can go without increasing engine efficiency.

Thus, we see the motivation for building a completely custom fuel injection system, including custom software implemented on a generic microprocessor.