GB1221253A - Improvements relating to internal combustion engines - Google Patents

Abstract

1,221,253. I.C. engines - relieving compression during starting. TECUMSEH PRODUCTS CO. Oct.29, 1968, No.51331/68. Heading F1K. An internal combustion engine is provided with an automatic compression release mechanism for reducing cranking effort at starting, the compression release comprising a chamber arranged to communicate with the combustion chamber and with a region of lower pressure, the inlet to the chamber being controlled by a one-way valve which is arranged to be closed when the chamber pressure exceeds the combustion chamber pressure, and the outlet from the chamber being controlled by a second one-way valve, the second valve being resiliently biased to an open position but being moved to a closed position in response to sudden increase of pressure consequent upon firing of fuel-air charge in the combustion chamber. The engine shown is of the two-stroke type and comprises air inlet ports 16, transfer ports 14 and exhaust ports 12. A vent passage 40 is also formed in the cylinder wall, the passage communicating with a valve chamber 34 formed by a boss 46 formed integrally with the cylinder 42 and a cover plate 48 secured to the boss 46 by screws 50, 52. A reed valve 30 is secured by screw 60 to the boss 46 and is disposed adjacent the vent passage 40 being normally unstressed and closing the passage. An outlet passage 36 is formed in the cover plate 48 and has associated therewith a reed valve 32 secured to the cover plate by screw 66, the reed valve being normally spaced from the seating so that the chamber 34 is in communication with the outlet passage 36. The passage 36 extends through the cover plate 48 and communicates at 54 with a passage 56 formed in the cylinder block, the passage 56 in turn communicating with the exhaust duct 26 which communicates with the exhaust port 12. As the piston 11 moves upwardly in the cylinder 42 as the engine is cranked at starting the pressure above the piston is relieved through the vent passage 40, fuel-air mixture passing through the passage, past the open valve 30 into the chamber 34, thence past the still-open valve 32 and passages 36, 54, 56 to the exhaust passage 26. Such flow ceases as soon as the piston passes the vent passage 40. Thus the compression pressure is relieved during engine cranking. As soon as the engine fires however the sudden increase of pressure passed into the chamber 34 causes the valve 32 to close. The valve 30 is also closed by the pressure of gases within the valve chamber 34 so no loss of gas pressure occurs when the engine is running. The valve seating associated with the reed valve 32 is a raised circular land 70, Fig. 5 (not shown), to prevent valve sticking.