STIHL provides professional users with the ideal outdoor power equipment solution, offering all the benefits of two-stroke and four-stroke engine technologies combined.
Like the four-stroke and two-stroke engines, the STIHL 4-MIX™ engine is an internal combustion engine. Energy is released during combustion of the fuel-air mixture in the cylinder, which is converted into motion via the piston and crankshaft. The carburetor supplies the correct mixture of air and fuel. The spark plug initiates combustion by producing an ignition spark at the exact predetermined point.
THE FOUR STROKES OF THE 4-MIX™ ENGINE ARE:
Unlike other four-stroke engines, the 4-MIX™ engine is lubricated by the gasoline-oil mixture. As such, it must be run on a mixture of gasoline and engine oil. This allows a compact construction without a separate oil reservoir, oil pump and oil filter.
Like the time-proven STIHL two-stroke engines, the STIHL 4-MIX™ engine operates reliably at any angle, even upside down. It is therefore very suitable for applications in STIHL portable power tools. The 4-MIX™ engine is relatively quiet in operation and, like STIHL two-stroke engines, complies with the strict exhaust emission standards.
As the 4-MIX™ engine makes use of the gasoline-oil mixture for lubrication, it combines the benefits of two-stroke and four-stroke engines.
- Familiar fuel mixture ratio (50:1)
- Operates in all positions
- Cleaner - reduced emissions
- More power - high torque
- Good acceleration - quick starts
- Low fuel consumption
- Favourable power-to-weight ratio
- Compact construction - attractive design
- Fewer vibrations
- Low noise level
The crankshaft (5) rotates. The piston (4) moves down the cylinder. The inlet valve (3) is opened by the cam (not illustrated). Fresh fuel mixture flows through the inlet port (2) into the combustion chamber (6) until the inlet valve is closed again by the cam.
Unlike most other four-stroke engines, the valve gear (10) and crankcase (12) on the STIHL 4-MIX™ engine are connected to the inlet port (2) via a bypass bore (9). This way, part of the fuel mixture constantly flows around all the moving parts (valve gear, crankshaft, cam, piston). This ensures lubrication of the 4-MIX™ engine without a separate supply of engine oil.
The transfer of the fuel/engine oil and air mixture is controlled by the upward and downward movements of the piston (4).
Over-pressure is created in the crankcase (12) when the piston moves down the cylinder. This over-pressure forces mixture out of the crankcase (12) through the cam housing (not shown in the illustration), via the pushrod passages (11) and the valve gear (10), through the bypass bore (9) and inlet port (2) to the combustion chamber (6). All lubricating points are wetted in this process.
Both valves are closed. The piston (4) moves up the cylinder again and compresses the mixture. A depression is created in the crankcase (12) as the piston moves upwards. This depression sucks in the gasoline-oil mixture: it flows from the carburetor through the inlet port (2), via the bypass bore (9) to the valve gear (10) and the pushrod passages (11), through the cam housing to the crankcase (12). All lubricating points are wetted in this process.
Compression of the mixture is greatest when the piston (4) reaches its highest point in the cylinder (top dead centre or T.D.C.). The spark plug (1) initiates combustion of the mixture by producing an ignition spark. The piston is forced down the cylinder and produces power.
Note: To improve efficiency, the mixture is ignited just before T.D.C.
As the piston (4) moves down the cylinder the mixture is again forced out of the crankcase (12) through the cam housing, via the pushrod passages (11) and the valve gear (10) to the inlet port (2) (as on the induction stroke).
The cam opens the exhaust valve (7) before the piston (4) reaches its lowest position (bottom dead centre). During the following upward movement of the piston the spent gases are forced out of the combustion chamber (6) through the exhaust port (8). The cylinder is now clear and ready for the next induction stroke.
A depression is created in the crankcase (12) at the same time which sucks in the fuel/oil and air mixture so that it reaches all lubricating points (as on the induction stroke).
HERE ARE SOME STIHL OUTDOOR POWER TOOLS THAT CONTAIN THE STIHL 4-MIX™ TECHNOLOGY:
- FS 91 / FS 91 R
- FS 111 / FS 111 R / FS 111 RX
- FS 131 / FS 131 R
- BR 500 / BR 600 / BR 700 / BR 800 C-E / BR 800 X