Electronic Control for One-cylinder Engines

Small engine manufacturers are starting to feel pressure, from government regulatory agencies around the world, to increase the efficiency and reduce the emissions from their products. To accomplish this, the engine control system must undergo a fundamental change from mechanical to electronic control. Some lessons learned from the conversion of the automotive engine from mechanical to electronic control can be applied to the small engine. Recent circuit integration efforts have been undertaken to enable small engine manufacturers to develop electronic controls that make their products "Greener". This article outlines some of the changes that are necessary and what Freescale is doing to help make this transition simple, easy and cost effective.

INTRODUCTION

Two recent events have emerged that are causing small engine manufacturers to consider replacing their traditional mechanical engine controls with newer, more effective electronic controls.

ENVIRONMENTAL CONCERNS

The high levels of pollution in urban areas and the growing significance of "greenhouse effect" causing gas emissions from two wheel vehicles and other small engine driven products is forcing many governments to enact stricter emission regulations. These new regulations are starting to specifically target small internal combustion engines. In order to satisfy the new exhaust emission levels contained in these regulations, the manufacturers will need to replace traditional mechanical engine controls with electronic controls, but the strict target costs and size requirements for small engine control systems will require manufacturers to seek innovative design solutions to implement these electronic controls.

FUEL EFFICIENCY

The cost of a gallon of gasoline has risen from 20 cents in 1956 to a recent high point of almost 4 dollars. Instability, in the crude oil producing regions of the world, is being blamed for the price volatility of this essential commodity. The supply of crude oil, once thought to be limitless, is predicted by the oil companies, to be running out. To extend the life of this fuel supply and to reduce engine operating costs means that all engines, large or small, will need to be designed to become more fuel efficient.

2 OR 4 STROKE ENGINES

One of the primary differences between certain small engines and their larger counterparts is the number of "strokes" or times the piston travels up or down in the cylinder to complete one cycle. While it is beyond the scope of this article to discuss the various good and bad points of both kinds of engine, suffice it to say that most existing low-cost, fuel and oil burning, 2 stroke engines will have to be radically redesigned to meet the requirements contained in this new emission legislation.

MECHANICAL CONTROLS

In the traditional internal combustion engine, invented in 1876 by Nicholas Otto, the operation is dependent upon three elements: air, fuel and combustion. In the cylinder of the engine, a precisely timed spark ignites an air/fuel mixture resulting in the combustion that pushes the piston, within the cylinder, down, causing the engine crankshaft to turn. The mechanical control system in a small internal combustion engine consists of two mechanical parts and one electrical part. The first mechanical part, the carburetor, uses the vacuum created in the cylinder, as the engine is initially cranked via the starter motor, pull cord or kick starter, to draw in and atomize the fuel and mix it in the correct proportion with air. This fuel/air mixture is drawn into the cylinder, at the proper time, through the second mechanical part, the intake valve.