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

摘要

This paper reviews the current and new mini-four-stroke engine technologies that are suitable to be implemented in lightweight 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 lightweight 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 12,000 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 cm{sup}3. 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.