Abstract: The invention is directed to a fuel injection pump for a two-stroke engine which is especially for portable handheld tools such as motor-driven chain saws or the like. A pneumatic drive chamber is provided in the pump housing which is partitioned by a membrane into a pulse chamber charged by the crankcase pressure and a return chamber. A membrane plate holds the membrane and charges a pump piston which plunges into a pump cylinder for injecting fuel when a pulse is present in the pulse chamber. The pump piston draws fuel in by suction during a return stroke of the membrane plate into a start position determined by a stop. The stop is configured so as to be displaceable in the direction of the stroke of the piston in dependence upon temperature in order to obtain an adaptation of the injected quantity of fuel to the operating temperature of the engine. In this way, the stroke of the pump piston can be varied and therefore also the quantity of fuel supplied by the pump.

Abstract: The invention is directed to an ignition circuit for an internal combustion engine such as a two-stroke engine of a handheld, portable tool such as a motor-driven chain saw or the like. The engine has a cylinder and a piston conjointly defining a combustion chamber and a crankshaft connected to the piston. The ignition circuit includes a spark plug mounted in the cylinder and voltage source. A switch is actuable between an on-condition wherein the voltage source is connected to the spark plug for initiating a spark in the chamber and an off-condition wherein the voltage source is disconnected from the spark plug. An electronic control circuit actuates the switch between the two conditions in dependence upon the angular position of the crankshaft and other operating parameters of the engine such as the engine speed. The electronic control circuit includes a high-speed control circuit and an idle-speed control circuit for determining the firing time in the control range of the idle speed.

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: A centrifugal clutch for use especially in a motor-driven chain saw. The clutch includes a carrier which is provided for attachment to a drive shaft and on which radially moveable centrifugal weights are mounted. The weights can move radially outwardly under centrifugal force and counter to spring force and come into contact engagement with the drum which is the output end of the clutch. A restraining device is provided between each centrifugal weight 2 and carrier 1 so that the engagement of the clutch does not occur until after an elevated speed has been reached. Disengagement of the clutch occurs as in known clutches somewhat above the idling speed. The restraining device is configured so that it does not clear the outward path of the centrifugal weight until a certain minimum centrifugal force has been exceeded. This has the effect that the clutch engages suddenly at mid range speeds and can transmit a very high initial torque to the output tool driven through the clutch.

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: An automatic starting arrangement for a hand-started internal combustion engine is disclosed. Internal combustion engines of this type have a choke flap and a throttle flap positioned one behind the other in the air-intake channel. In order to ensure a reliable starting of the engine independently of manual positioning activities, the invention provides that in the starting operation, the choke flap initially moves independently of the throttle flap. The throttle flap is held in a half-throttle position between the full-throttle position and the idle position. Before the choke flap is brought into its at-rest no-choke position, a movable holding mechanism is actuated and the throttle flap is released.

Abstract: The invention is directed to an ignition arrangement for an internal combustion engine of a handheld portable tool such as a chain saw or the like. The engine has a crankshaft and a fan wheel is seated on the crankshaft for rotation therewith. The ignition arrangement includes a permanent magnet. The magnet has two pole shoes and an exciter coil is mounted on the permanent magnet. The permanent magnet equipped in this way is fixedly mounted on the tool to save weight. A relatively light self-supporting annular member with projections is mounted in the fan wheel. The projections of the annular member and the permanent magnet with its pole shoes conjointly define a magnetic circuit. As the projections pass the pole shoes at a minimal spacing therefrom during operation of the engine, the projections alternately open and close the magnetic circuit thereby causing changes in the flux of this circuit.

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.

Abstract: A two-stroke engine is disclosed which is controlled by a carburetor throttle valve and has a crankcase subjected to continuously alternating overpressure and underpressure. A pneumatic control member responsive to a signal dependent on the rotational speed of the engine is in pressure communication with the inner chamber of the crankcase via a valve. The output member of the pneumatic control member is connected with the throttle flap of the carburetor. The valve provided between the crankcase and the pneumatic control member is responsive to a signal for controlling the pressure in the pneumatic control member. This valve can be configured as a resonance control valve fixedly mounted to the housing of the engine.

Abstract: An automatic starting arrangement for a hand-started internal combustion engine is disclosed. Internal combustion engines of this type have a choke flap and a throttle flap positioned one behind the other in the air-intake channel. In order to ensure a reliable starting of the engine independently of manual positioning activities, the invention provides that in the start position the choke flap is coupled with the throttle flap in a position-dependent manner and the choke flap holds the throttle flap in a position between the full-throttle position and the idle position. The choke flap is brought into an at-rest position via an actuating device which is actuable in dependence upon the operating condition of the engine. The choke flap is decoupled from the throttle flap in the at-rest position.

Abstract: A centrifugal clutch has a carrier and at least two centrifugal weights which are each connected to the carrier by means of at least one spring. These centrifugal weights are pivotally mounted on the carrier and are preloaded radially inwardly with respect to the carrier by means of the springs. In this way, the centrifugal weights have a defined pivot axis so that they can pivotally move from their rest position to the coupling position when the rotational speed exceeds a predetermined speed above no-load speed. By preloading the centrifugal weights, the latter are prevented from pivoting outwardly at speeds below no-load speed so that the centrifugal weights do not strike the clutch drum at rotational speeds beneath a predetermined value.

Abstract: A portable tool such as a motor-driven chain saw is disclosed which includes a cylinder, a piston, a connecting rod and a crankshaft. The crankshaft is rotatably journalled in crankshaft bearings and a crankcase made of plastic is provided. The bearing shells of the crankshaft bearings are releasably connected only to the cylinder and independently of the plastic crankcase. The plastic crankcase is likewise attached to the cylinder in such a manner that a housing arrangement is provided which is free of transmitted forces and is fully independent of the crankshaft bearings.

Abstract: The invention is directed to a fuel injection apparatus for two-stroke engines and is especially for small engines of high-speed tools such as motor-driven chain saws, for example. It provides for the valve-controlled input of fuel into a pressure chamber of a housing and includes a spring-loaded pump piston journalled for reciprocatory movement in a bore to supply the fuel. The pump piston is sealed by an annular seal. For fuel induction, the pump piston has a passageway opening into the pressure chamber and a valve seat. The valve seat of the pump piston cooperates with a substantially free-flying sealing body for opening and closing the valve.

Abstract: The invention is directed to a braking arrangement for a chain saw having a housing and a guide bar mounted on the housing for accommodating a saw chain thereon. The brake arrangement includes a brake drum operatively connected to the saw chain with a brake band disposed in surrounding relationship thereto. A brake member is connected to the brake band and moves between a ready position whereat the brake band is disposed in spaced relationship to the brake drum and a released position whereat the brake band is drawn tightly around the brake drum. A brake spring resiliently biases the brake member to cause the brake member to pull the brake band tightly about the brake drum when in the released position. A latch arrangement holds the brake member in the ready position against the force of the brake spring. A cam connected to the drive motor rotates through a predetermined path.

Abstract: The invention is directed to a tensioning arrangement for adjusting the tension in the saw chain of a chain saw. The cutter bar for the saw chain has an elongated opening for engaging the guiding means upon which the cutter bar is displaceably mounted and guided in the housing of the chain saw. The tensioning arrangement includes a bolt-like drive member which extends through the elongated opening of the cutter bar and acts upon an output member via a transmission. The output member is configured as a slider which entrains the cutter bar for displacing the latter to tension the saw chain. The drive member extends through the elongated opening and beyond the housing as well as the cover of the sprocket wheel to the outside so that it can be adjusted conveniently and simply from outside of the housing for tensioning the saw chain.

Abstract: A portable motor chain saw with a braking device, for stopping the saw chain during recoil, and with a release, for the braking device, which in the release position is operatively connected with a locking mechanism of the braking device. The release is an inertial mass which is freely movable along an acceleration path, with the kinetic energy of the inertial mass in the release position being greater than the resistance force of the locking mechanism. The release is held in the ready position by at least one holder, preferably a spring which extends between the saw housing and the release.

Abstract: Disclosed is a starting device for an internal combustion engine having a stationary bearing axle attached to the engine, a pulley rotatably mounted on the axle and adapted for accepting a starting rope wrapped thereabout, a recessed coupling attached to the drive shaft of the engine, coaxially surrounding the rope pulley in its recess and having a plurality of inwardly facing ratchet teeth.