Abstract: The invention is directed to an ignition circuit for an internal combustion engine in a portable handheld work apparatus wherein a work tool is driven via a clutch. The ignition circuit includes an ignition time point control which connects a spark plug via a switch to a voltage source in order to trigger an ignition spark. The spark plug is mounted in the combustion chamber of the engine. This connection takes place in dependence upon the crankshaft angle and the rpm of the engine. In order to prevent damage to the clutch because of a blocked work tool, a test value counter driven via a rpm gate circuit is provided. The test value counter increments its value in the pregiven rpm window of the gate circuit with each rotation of the crankshaft and the content of the test value counter is compared to a pregiven limit value by a comparator. The output of the comparator activates a rpm-reducing protective circuit and the output of the comparator indicates reaching or exceeding the limit value.

Abstract: The invention is directed to a fuel pump for an internal combustion engine such as a two-stroke engine in a portable handheld work apparatus such as a motor-driven chain saw or the like. A pump chamber is connected via a suction valve to a fuel feed and via a pressure valve to a pressure line. A pump membrane delimits the pump chamber and is driven by the fluctuating crankcase pressure of the engine which is present in the work chamber. Pump operation free of disturbances over a wide rpm range is attained with the suction valve to the pump chamber being configured essentially as a valve having the shape of a part circle, The pressure valve is disposed approximately at the center of the suction valve and delimits the pump chamber in the stroke direction of the pump membrane.

Abstract: The invention is directed to a fuel-injection arrangement for a two-stroke engine in a portable handheld work apparatus such as a motor-driven chain saw or the like. Fuel is drawn by suction from a fuel tank by a fuel-feed pump and is made available at the suction connection of an injection pump. The injection pump has a pressure connection which is connected to an injection line through which the engine is supplied with fuel. A rapid start of a two-stroke engine provided with this fuel-injection arrangement is achieved by providing a bypass line which conducts fuel and bypasses the injection pump. A switchable flow valve is mounted in the bypass line. The bypass line opens directly into the intake channel conducting combustion air to the engine so that even without the pump action of the injection pump, adequate fuel is made available to the engine for starting the same.

Abstract: The invention is directed to a fuel-injection arrangement for a two-stroke engine in a motor-driven chain saw. An injection pump is mounted in a base housing with the injection pump including a pump piston axially displaceable in a pump cylinder. The pump piston delimits a pump chamber. The pump chamber is connected via a suction valve to a fuel tank. The fuel drawn by suction is pumped by the pump piston via a pressure valve, an injection line and an injection valve to the engine. For driving the pump piston, the latter is connected at one end to a membrane via a membrane plate. The membrane delimits a work chamber charged with fluctuating crankcase pressure. A simple assembly is provided by arranging the pump chamber, the suction valve and the pressure valve in a common valve housing which, in turn, is seated in the base housing of the injection pump in a seal-tight manner. The injection line is connected directly to the valve housing.

Abstract: The invention is directed to a pump for pumping a viscous fluid. The pump includes a stator body and a rotor body rotatably mounted in the stator body so as to be coaxial therewith. The stator body has a wall structure having a spiral slot formed therein which communicates with a suction connection formed in the stator body for conducting the viscous fluid to be pumped into the slot. A pressure connection is formed in the stator body for conducting the viscous fluid out of the slot. The suction connection and the pressure connection open into respective peripheral annular slots which are formed between a total of at least three sealing rings on the outer surface of the stator body. The channels for liquids provided in a housing can be disposed in any rotational position relative to the stator. This affords the advantage that the pump stator can be seated with any rotational position in a receiving cylinder of the housing.

Abstract: The invention relates to an operating-mode position selector arrangement for an internal combustion engine in a portable handheld tool such as a motor-driven chain saw. The engine includes an electrical ignition system and is supplied with a fuel mixture by a carburetor. In a start position of the operating-mode position selector, the position selector holds the choke flap and the throttle flap of the carburetor in pregiven start positions. In an operating position of the operating-mode position selector, the throttle flap is released for actuation via a throttle lever and the choke flap is fully opened. In a stop position of the operating-mode position selector, an electric contact is closed between a terminal of the electric ignition system and ground. The different positions of the operating-mode position selector are detected electrically.

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 a handle for a pull-rope starter. The handle includes a T-shaped base body having an elongated part extending in the direction of the pull rope and a handle part extending transversely to the elongated part. The elongated part has a receptacle for accommodating an elastic expansion element which is connected at one end thereof to the pull rope. The expansion element is supported at its other end on the base body. The expansion element is as long as possible and has the longest possible expansion path. This is achieved in that the expansion element is supported at its upper end on the base body with the upper end facing away from the pull rope. In this way, the expansion element is stretched thereby providing a longer expansion path.

Abstract: The invention is directed to a seal arranged between two housing parts of a muffler. The seal is configured essentially as a frame and made of sheet steel and has at least two layers. The first layer is defined by the frame itself and the second layer is defined by lugs which are folded over and are configured so as to be integral with the frame.

Abstract: The invention relates to a motor chain saw having a guide bar clamped between the housing and a clamping piece. The chain saw has a drive motor arranged in a housing and the drive motor drives a saw chain running on a guide bar. The guide bar is clamped to the housing at one end between the housing and a clamping piece with the clamping being transverse to the plane of the guide bar. For tensioning the saw chain, the guide bar is displaceable in the longitudinal direction thereof by means of a chain tensioning device when the clamping piece is loosened. If high forces act on the guide bar, then the latter slips toward the sprocket wheel in the longitudinal direction notwithstanding the fact that the guide bar is clamped to the housing. Accordingly, the saw chain must be again tensioned by means of the chain tensioning device.

Abstract: An injection valve for fuel injection systems in internal combustion engines which comprises a movable valve element cooperating with a valve seat disposed in a nozzle body, with a guide bore provided downstream of the valve seat. A swirl insert is partially compressed in the guide bore and disposes open swirl channels in the direction of its circumference. The swirl channels extend in an axial direction from one end of the swirl insert to the other, are slanted toward the longitudinal shaft of the injection valve and discharge in a tangential direction into a preparation bore. The swirl channels serve simultaneously as metering channels whose throttling length is adjustable by displacing the swirl insert inside the guide bore.

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 relates to a carburetor for an internal combustion engine and especially for a portable small engine. The carburetor includes a carburetor housing defining an intake pipe and a control chamber which communicates with the intake pipe via intake channels. A fuel-feed line which is closable by an inlet valve opens into the control chamber. The inlet valve includes a valve seat formed in the fuel-feed line and a valve body mounted on a positioning lever which is connected to a membrane defining a wall of the control chamber. The positioning lever can be pivotally actuated to open the inlet valve to admit fuel into the control chamber. An actuating lever is pivotally mounted on the carburetor housing and can be pivoted from a rest position to an active position whereat the actuating lever applies a force against the membrane to displace the latter and pivotally actuate the positioning lever to immediately open the inlet valve when starting the engine.

Abstract: The invention relates to an ignition switch arrangement for an internal combustion engine having electrical ignition. Engines for handheld portable tools are for the most part equipped with magneto ignition and are switched by short circuiting the ignition coil for bringing the engine to standstill. The ignition switch arrangement of the invention includes an ignition switching unit which is switchable between an ignition-enabling position wherein the ignition is operative and an ignition-disabling position wherein the ignition is inoperative. According to the invention, a latching actuator having a latch latches the ignition switch unit in the ignition-disabling position when the latching actuator is in its latching position when the ignition switch unit is switched into the ignition-disabling position while the engine is running. The latch releases automatically when the engine coasts to standstill so that the ignition is automatically enabled for the next starting operation.

Abstract: An injection valve for fuel injection systems in internal combustion engines which comprises a movable valve element cooperating with a valve seat disposed in a nozzle body, with a guide bore provided downstream of the valve seat. A swirl insert is partially compressed in the guide bore and disposes open swirl channels in the direction of its circumference. The swirl channels extend in an axial direction from one end of the swirl insert to the other, are slanted toward the longitudinal shaft of the injection valve and discharge in a tangential direction into a preparation bore. The swirl channels serve simultaneously as metering channels whose throttling length is adjustable by displacing the swirl insert inside the guide bore.

Abstract: The invention is directed to an exhaust gas muffler for a two-cycle engine, especially for a handheld portable tool, such as a chain saw. In exhaust gas mufflers equipped with a catalyzer, the formation of flame from the fuel-containing exhaust gases exiting from the muffler must be prevented. These exhaust gases are intensely overheated because of the exothermal process in the catalyzer. The muffler according to the invention includes a catalyzer which establishes a connection between separate component chambers of the muffler housing. The muffler can be mounted directly on the motor outlet.

Abstract: The invention relates to an exhaust gas muffler for a two-stroke engine of a portable handheld tool such as a chain saw. The exhaust gas muffler includes a catalyzer wherein high exhaust gas temperatures are developed because of the exothermal reaction which takes place therein. The catalyzer is located in the forward portion of a gas-tight hollow body mounted in the housing of the muffler. The hollow body has a tapered portion which extends out of the housing in the direction of the exhaust gas flow. In this way, the surface temperature of the muffler housing is reduced.

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 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.