Abstract: A four-stroke reciprocating piston internal combustion engine with an intake valve an exhaust valve and a valve drive assembly (18) driven by the crankshaft (4) for actuating the intake valve (8) and the exhaust valve (10) A mixture-preparation device (15) supplies an air/fuel-lubricant mixture to the crankcase, which together with the piston functions as a pump for the mixture charge. A valve drive assembly housing (19, 20, 21, 22) comprising one or more sections (19, 20, 21, 22) and the intake channel (16) is supplied with a connecting duct (17) communicating with the crankcase volume (12) either by being connected to the crankcase or the cylinder, or by being connected to the valve drive assembly housing (19, 20, 21, 22), which communicates with the crankcase volume (12), and the communication from the intake channel (16) to the crankcase volume is arranged through at least one valve.

Abstract: A four-stroke reciprocating piston internal combustion engine with an intake valve an exhaust valve and a valve drive assembly (18) driven by the crankshaft (4) for actuating the intake valve (8) and the exhaust valve (10). A mixture-preparation device (15) supplies an air/fuel-lubricant mixture to the crankcase, which together with the piston functions as a pump for the mixture charge. A valve drive assembly housing (19, 20, 21, 22) comprising one or more sections (19, 20, 21, 22) and the intake channel (16) is supplied with a connecting duct (17) communicating with the crankcase volume (12) either by being connected to the crankcase or the cylinder, or by being connected to the valve drive assembly housing (19, 20, 21, 22), which communicates with the crankcase volume (12), and the communication from the intake channel (16) to the crankcase volume is arranged through at least one valve.

Abstract: This disclosure relates to a two-stroke engine comprising an engine frame forming a cylinder, and a piston mounted for reciprocating movement in the cylinder. The engine frame further includes a crankcase chamber and inlet flow passages for fresh mixture, which form a crankcase compression arrangement. The cylinder includes a cylinder wall having an intake port and an exhaust port. The piston is movable in compression and combustion strokes between a top-dead-center (TDC) position and a bottom-dead-center (BDC) position in the cylinder, and the piston includes a piston skirt. Movement of the piston toward the BDC position opens the intake port and the exhaust port, and fresh mixture flows from the crankcase chamber into the cylinder and scavenges the burned gases through the exhaust port. When the piston moves toward the TDC position, the inlet flow passage is opened which allows fresh mixture to flow into the crankcase chamber.

Abstract: A portable power tool includes a manually actuable safety lever and an inertial safety system for activating a brake of the tool to provide a more effective safety arrangement. A first spring applies the brake when the safety lever contacts the hand, wrist or arm of an operator during "kick-back" or like violent movement of the tool. A second spring is operable independently of the safety lever for also releasing the first spring. An inertia mass is displaceable effectively independently of the safety lever when the brake is in the inoperative condition. This inertia mass releases the second spring, so releasing the first spring and applying the brake, upon occurrence of "kick-back" or the like. Preferably, the second spring operates a hammer release mechanism for striking a locking lever releasably retaining the safety lever. A band brake of a chain saw or circular saw may particularly be operated in this manner.