A New High-Performance Four-Stroke Engine for All-Position Use in Hand-Held Power Tools

This paper reviews the current and new mini-four-stroke engine technologies that are suitable to be implemented in light-weight outdoor power equipment. A new mixture lubrication setup has been developed for a very compact mini-four-stroke engine.

Special emphasis is laid on the design of the combustion chamber and the valve train. The paper derives how to systematically translate the user demands of a light weight engine to the new mini-four-stroke engine. The new STIHL 4-MIX-engine features an integral one-component cylinder including the cylinder head, two valves and a very simple drive train consisting of a plastic cam including a decompression mechanism. The valve train stands speeds in excess of 12000 rpm and it is also lubricated by the new mixture lubrication setup. The piston is used as an oil-mist pump. The engine has an output of 1.0 kW out of 31.4 cm³. Pressure indication work is used in order to optimize the combustion process.

The development effort and process of this new mini-four-stroke technology are very important and to a certain extent pioneering for the use of mini-four-stroke engines in all-position hand-held outdoor power equipment.