Development of a Rotary Valve Small Four-Stroke Engine

ETA Engineering

Wolf Burger Fritz Winter

ABSTRACT

An experimental small four-stroke engine for the application in hand held equipment was developed. The engine provides all position operations, light weight design and low cost production. The developed technology includes the following items: • Rotary valve system, which has the features as low noise, high revolution limits and low operation power losses • 360° all position operation by adopting a new 64% mixture lubrication system Compared to a two stroke engine almost the same size and weight is achieved. In addition emissions are drastically improved and fuel consumption is reduced.

INTRODUCTION 70%

Emission regulation for small hand held equipment forced the industry to develop “clean” Figure 1: Comparison with conventional engines. A numerous volume of small four stroke four-stroke engine engines is now launched for production in brushcutter applications. Still there is a need for an engine, which fits in the requirement of chainsaws and powercutters. The new BASIC DESIGN AND SPECIFICATIONS ROTAVALVE system was developed to beat the two stroke engine in this application. Compared To realize the most suitable structure for hand with standard four-stroke engines there is a held application the basic design includes the reduction in the height to 64% and of the length following items: to 70%. Figure 1 shows the comparison of a 3 3 • Uniblock cylinder with NIKASIL coating 31cm production engine to the 34cm • Cylinder design for die casting production ROTAVALVE prototype. • Mixture lubrication system, similar to a two- stroke engine • Resin gearing of the rotary valve to reduce the noise • Integrated driveshaft of the rotary valve system for optimised package • Port layout to reduce noise

29.07.2002 Table 1 shows the basic engine specification conventional two-strokes. So the integration of the ROTAVALVE engine in a chainsaw or unit brushcutter application is easy. Basic Engine Type EFCO 8350 Displacement cm3 34 Bore / Stroke mm 38 / 30 Compression Ratio 10,1:1 Power kW 1 Carburetor Walbro WT Ignition System CDI Table 1. Engine specification

ROTARY VALVE STRUCTURE

To fulfill the operational features of hand held equipment , no maintenance and high wear Figure 4: Rotary valve resistance of the valve train was requested. The rotary valve and driveshaft unit is made out of NI- RESIST, the liner of the valve is NIKASIL coated LUBRICATION SYSTEM (figure 3). NI-RESIST has almost the same thermal expansion coefficient as aluminium. The Today all chainsaws are equipped with two stroke engines. So the availability of fuel/oil mixture in this special application is much better than of standard gasoline. A lubrication system with an oil sump requests 3 different tanks for fuel, engine oil and chain oil. The new lubrication system uses a premixed fuel/oil mixture. The rotary valve and the piston is lubricated with the intake charge, conrod and main bearing by an lubrication port in the rotary valve. During the depression in the crankcase a port between intake and crankcase is opened and the engine sucks fuel/oil mixture in to the crankcase. The port opens also during the intake phase and residual oil and fuel travels back in the cylinder.

Figure 3: View on the valve liner CONCLUSION rotary valve is lubricated by the fuel/oil mixture and cooled by the fresh charge. So no additional A new experimental four-stroke engine with a sealing system is necessary. To compensate the rotary valve system was developed. Design combustion pressure, a port between the innovations to facilitate low cost production and combustion chamber and the valve chamber, assembly have been described. The pushes the valve back in the seat. Compared to performance and size of this unit is comparable a conventional two-stroke, the rotary valve / to two-stroke engines. The developed technology drivetrain unit is the only additional part. The can beat the two-stroke engine even in the weight of the complete system is approx. 100g. application of chainsaws and powercutters. The rotary valve has only one slot for the timing of intake and exhaust and is simple and cheap to produce. Figure 4 shows the rotary valve. REFERENCES

1. Muroki T., Moriyoshi Y., Sekizuka S. UNIBLOCK CYLINDER A Study of rotary Valve for a Single Cylinder Engine, SAE Paper No. 9938077 The cylinder has a uniblock design with 2. Gablish P.W, Vial A.R, and Irving P.E, integrated cylinderhead. Cylinder bore and valve Rotary Valves for a Small Four-cycle IC liner can be machined in the same axis. Intake Engine, SAE Paper No. 891793 and exhaust port are located similar to

29.07.2002 3. Schaal T. Auslegung und Konstruktion der Gaswechsel- steuerung eines 45cm3 Viertaktmotors mittels eines Walzendrehschiebers, Master Thesis 2000, University of Applied Science Saarbrücken

29.07.2002