Magnesense Small Engines

Magnesense Small Engines

Why Small Engines?

In 2002, Magnesense identified an opportunity in the small engine market. Improved control technologies for the automotive scale could be developed in a less demanding small-engine environment. The simpler context would permit quicker commercialization, yielding payback and providing a stepping stone toward the large automotive market. Simplifications specific to small engines could lead to an affordable solution for a much cleaner, quieter, easier-starting, more powerful and efficient power plant for lawnmowers, small tractors, jet skis, skimobiles, ATVs, generators, and eventually on the smaller scale of leaf blowers, power washers, chain saws, etc. This effort received a boost from an Environmental Protection Agency Phase I SBIR grant, which was completed with reviews ranging from good to excellent. The EPA relationship heightened our awareness of emerging emission standards that will challenge the industry and can be met with Magnesense innovations.

We Can Improve Small Engines:

We can make major, needed reductions in the abysmal pollution of small engines;
We can get significantly more power and more torque from a quieter small engine;
Inexpensive digital control will improve every aspect of operation (spark, etc.), not just valves;
Electric valve control leads to very easy pull start for small (no battery) engines;

Small Engines Provide a Manageable Development Environment:

Uncrowded one- and two-cylinder heads are easy to work with;
Low maximum-RPM requirements for many small engines simplify the engineering;
Valves need last only for the modest number of actuation cycles in a small engine lifetime;
A "forgiving" initial market environment provides income while we develop the very high reliability required in automotive applications;
We can do it cheaply enough to meet market requirements for quality lawnmowers.

The last item comes out of the others. Multiple factors come together to make a small engine electric valve system much cheaper and easier than an automotive application. Many innovations and patents, particularly in control technology, have value in both small engine and automotive fields.

The Magnesense Small Engine System

Departing from the predominant linear solenoid approach, Magnesense has developed a magnetic valve rocker intended to replace a cam rocker. Its features include:

Rocking armature laminations line up to combine high strength with minimum eddy currents;
Very low power to latch, open or closed;
12 volt electronics with low power demand;
Control with an inexpensive DSP;
Fast-running fixed-point software;
Sensorless servo control;
Demonstrated soft landing;
“Drop in” replacement of conventional cam rocker mechanism.

We need to take maximum advantage of these simplifications, because the price needs to be much lower in the small engine setting. Whether or not a 42-volt standard might be on the way for cars, we need to design for a 12-volt power supply in the small engine field. We need to make do with a very inexpensive microprocessor or DSP. After a few false starts, we settled on the Motorola 56800 DSP family.

After examining the valve rockers in a Honda generator engine (left), we decided to depart from the traditional in-line solenoid structure and develop a magnetic rocker design that would functionally replace the cam-driven valve rockers seen below on the left. The result was the solenoid on the right, using a vertical armature rocking between two e-core yokes. Note the solid model illustrated below the engine photo, showing holes drilled in the valve rockers for bolting on the clamp shown on the right. This clamp holds down the bottom horizontal segment of the L-shaped rocker and also captures one end of a folded torsion spring. The rocker itself consists of L-shaped laminations, this time stacked in the same plane as the E-core yokes on either side.

The valve rocker employs yet another non-standard spring design: a folded torsion spring making a U-shape in a horizontal plane with the ends of the “U” bent up. The same aluminum piece that clamps down the armature “L” also receives one of the upward-bent ends of the spring. The other end of that same spring is fixed, screwed down adjustably to the front surface of the valve and solenoid enclosure, where the recessed screw holes are seen facing the viewer in the image above on the right. The action of the torsion springs is seen in the view below on the right, with the rocking clamp and valve rocker removed, leaving only the rocker pivot pins and the set screws that hold the moving ends of the springs. The lash adjustment screws pressing down on the valve ends are threaded through the valve rockers, which are removed from view. The action of the torsion springs is readily seen.

The valves and actuators are seen in the context of the cylinder and piston below. An animation of the valves and piston head is provided in low and high bandwidths.

Now that we have the illustrated valve rocker design operating on an instrumented lab bench, we understand how to make it smaller easier to fabricate, and especially how to facilitate its assembly and alignment. Its power consumption is extremely low, and design tradeoffs could reduce the size while maintaining acceptably low power consumption.

Magnesense LLC Gorham,ME (207) 839-8637