Abstract: The invention relates to a motor-driven chain saw having a motor mounted in a housing for driving a saw chain on a guide bar. The guide bar extends forwardly in the longitudinal direction of the chain saw from a forward housing end face. The housing is held by a grab handle for holding and guiding the chain saw. The handle has an upper segment projecting over the housing transversely to the longitudinal center axis of the guide bar. The upper segment extends at one end with a transition segment into a lateral segment lying approximately parallel to the plane of the guide bar and next to the housing. The cross section of the upper segment and the cross section of the lateral segment are configured in a shape which departs from the circular shape and are approximately the same. This affords an ergonomically advantageous hold and increases the operational safety.

Abstract: The invention is directed to a starter arrangement for an internal combustion engine wherein a manual starter device is combined with an electrical starter. Handheld portable tools such as motor-driven chain saws, brushcutters and the like are driven by two-stroke engines which can be started with a suitable manual starter device such as a pull-rope starter. Pull-rope starters require a forceful yank on the pull rope which is difficult for persons having inadequate physical strength. For this reason, electrical starters are provided to facilitate starting such handheld portable tools. The invention combines an electric starter and a manual starter device wherein the overrun clutch of the manual starter device includes a latching device and a drive member and is combined with a further latching device which coacts with a drive member driven by the electric starter.

Abstract: The invention relates to a handheld portable tool driven by a two-stroke engine equipped with a pneumatically actuated injection pump. Injection pumps for two-stroke engines are generally rigidly connected to the engine so that the injection line can be rigid and as short as possible. This, however, leads to operational disturbances in the injection pump. To eliminate these disturbances, the injection pump is mounted in a thermally insulated handle housing portion of the tool which is damped with respect to the vibrations of the engine and is connected to the latter via flexible connecting lines.

Abstract: The invention is directed to a pump for use as a lubricating oil pump in internal combustion engines of handheld portable tools such as motor-driven chain saws or the like. The pump includes a body forming the stator and a body forming the rotor. These bodies lie coaxial with respect to each other and have respective surfaces which lie seal-tight against each other. A screw-shaped spiral slot is formed in one of these surfaces and has an input end connected to a suction connection and an output end connected with a pressure connection. According to a feature of the invention, at least the screw-shaped wall structure is made of an elastomer. This wall structure defines the spiral slot and lies against the smooth surface lying opposite thereto. An absolutely seal-tight contact engagement of the wall structure defining the spiral slot against the opposite-lying surface is assured by the elasticity of the elastomer. The service life of the pump is increased and its production and assembly simplified.

Abstract: Fuel injection arrangements having pneumatically driven injection pumps utilize the fluctuating crankcase pressure whereby the injection time point is fixed by the system. The injection time point can be fixed so as to depart from the course of the pressure in the crankcase if the crankcase pressure is applied to the injection pump via an opening controlled by the piston and if the pressure drop is directed to the combustion chamber via a relief opening. However, it has been shown that this kind of control produces considerable problems with respect to fast-running two-stroke engines. Accordingly, it is a feature of the invention to provide a check valve in the connection between the relief opening and the injection pump and to position this check valve so that it opens in the flow direction toward the combustion chamber.

Abstract: The invention relates to a two-stroke engine having an overflow channel through which an air/fuel mixture is supplied. The overflow channel is provided with a vaporization chamber having a hot wall against which fuel is injected and vaporized. The vaporized fuel is stored in the vaporization chamber and is carried into the combustion chamber of the engine by fresh air flowing in from the crankcase when the overflow channel is opened. Even at high rotational speed, a good mixture preparation is asssured.

Abstract: A pneumatically operated fuel injection pump has a work chamber which is partitioned by a membrane into a pulse chamber and a return chamber. The pulse chamber is charged with crankcase pressure from a two-stroke engine while a counterforce is built up in the return chamber which varies with rotational speed. A counterforce is developed by means of a precise pressure control in the return chamber which makes possible a highly precise injection adapted to rotational speed. For this purpose, the return chamber is connected with an adjusting volume via a throttled flow path. In addition, a leaf spring is mounted in the return chamber and is utilized as a return spring for the membrane.

Abstract: The invention relates to a fuel injection arrangement wherein the pump piston of the fuel pump is driven by the pressure in the crankcase of the engine. The fuel injection arrangement includes an opening for tapping the crankcase pressure for actuating a diaphragm in the fuel pump. This opening is controlled by a moving part of the engine such as a crank web or the piston. The moving part closes the opening at least for a portion of the time during which injection occurs thereby delaying the onset of injection to permit a complete combustion during the previous combustion cycle.

Abstract: The invention is directed to a fuel injection arrangement for two-stroke engines for portable tools such as motor-driven saws. In known fuel-injecting arrangements, the injection pump is driven by the pressure of the crankcase. The crankcase pressure increases up to a maximum value which remains constant starting with a predetermined rotational speed up to and including the maximum rotational speed. When the peak pressure of the crankcase is constant, the stroke of the pump piston of the injection pump is also constant and so is the quantity of fuel which is pumped. However, at higher speeds where the speed is increasing because of throttling in the air intake channel, the air charge of the cylinder reduces and an overrich mixture is formed. The fuel injection arrangement of the invention provides for an automatic reduction in the quantity of fuel injected at high and at the highest speeds.

Abstract: The invention is directed to a method of fuel injection for two-stroke engines, especially for hand-operated tools such as motor-driven saws and the like. The fuel-injection pump is charged with pressure present in the crankcase thereby causing fuel to be pumped for injection and combustion in the engine. The injection operation is triggered and the onset of injection into the combustion chamber is effected when the crankcase pressure rises. The pressure conducted from the crankcase to the injection pump can be automatically regulated as a function of the rotational speed and/or load conditions of the engine.