Abstract: In a method of controlling the point of ignition and/or air-fuel mixture of an i. c. engine, a signal circuit is used for emitting a signal indicating abnormal combustion or disturbance, and the first derivative of the spark current is used for the detection. According to the invention, the average peak value of the first derivative of the spark current is a reference value of the detection, and the actual signal of the derivative of the spark current is compared via a voltage divider and a comparator circuit with said average peak value, whereby detection is obtained when the signal from the voltage divider exceeds said average peak value.

Abstract: For adjusting the air/fuel ratio (A/F) of an i. c. engine having an electrically adjustable carburetor, an electronic detector and control unit is used to which current is supplied by an ignition magnet or generator and which comprises a tachometer, data processing means, an electronic memory, and a control unit for adjusting said ratio. The first derivative of the speed of revolution of the engine is used as a parameter for the adjustment. According to the invention, the adjustment is made after a period of time during which the speed of the engine has been generally constant. Generally constant speed is detected by calculating the average value of said derivative, such that the speed of revolution of the engine is considered to be generally constant when said average value is approximately zero.

Abstract: An arrangement for limiting the temperature in a carburetor etc. of an engine prevents evaporation of fuel at a temporary stop in the operation of the engine. A receptacle (30) integrated with the carburetor contains a material (31), e.g. paraffin, with a melting point over the normal operating temperature. At a temperature above this melting point the material absorbs melting heat from the environment causing a limitation of the temperature. In this limited temperature the fuel evaporates much slower and a direct start with the remaining fuel after the operating stop is quite possible.

Abstract: A motor saw wherein combustion air is drawn via a port tangentially located at the fan wheel in the fan housing of the motor saw. The combustion air is taken from an air stream in circulation from an air inlet at the top surface of the motor saw body where the concentration of pollutants is low. Pollutants are separated by the centrifugal effect of the fan before the air gets into the port. The cooling capacity of the air stream is completed with further cooling air from a second inlet. The combustion air can be pre-heated in a heating loop.

Abstract: A magnetic ignition system with an ignition coil primary circuit having an ignition switch is controlled by a control switch to break at a given ignition time so that an ignition voltage is induced in the secondary circuit. A signal is delivered by a control circuit between the voltage supply and earth via resistors to a control switch at the ignition time. The control circuit serves the functions of voltage limiting and prevention of double spark (retriggering).

Abstract: The invention relates to an indicator controlled by the ignition system of an i.c. engine, so that the indicator, e.g. an LED, makes an indication when the engine is adjusted to an appropriate idle r.p.m. or race r.p.m. As the carburetor is calibrated against such selected and adjusted r.p.m. the said adjustment will bring about a minimum of exhaust gases.

Abstract: Upon a kick-back of a motor saw, energy is transferred from the rotating parts of the engine into energy which generates the kick-back. This causes a tremendous decrease of the r.p.m. of the engine. In the saw there is an electronic control comprising a timer which measures the r.p.m. of the engine. During certain intervals the difference in r.p.m. is computed with respect to previous intervals and if the r.p.m. has decreased more than a predetermined value, a sensor in the electronic control emits a signal which releases an electrically controlled chain brake for stopping the chain.

Abstract: An electro-mechanical brake in a motor saw requires electric energy for the operation of the brake. This energy can, according to the invention, be surplus energy in the ignition system of the saw. Surplus energy exists usually only when the r.p.m. exceeds a certain value. A capacitor is charged by current from the system and is prepared to discharge through a coil to actuate the brake on a signal from a kickback sensor.

Abstract: A capacitor ignition system of magnet type comprises a charging winding (10), a trigger winding (11), an ignition coil (13) and an ignition switch (14) with electronic control means, in this case a micro-processor (16). For practical, economical reasons the voltage of the charging winding cannot be used for current supply to the electronic control means as this voltage is several hundred volts. In the trigger winding the chosen voltage can be a few volts which is a proper voltage for the control means. The trigger winding of the invention has double functions: to generate a reference voltage for spark release (triggering) and to be an energy source for the electronic control means.

Abstract: In engine-powered machines (motor cutting saw, motor chain saw) with a centrifugal clutch a wearing on the clutch and belt takes place by a high load at an r.p.m. around or above the skidding r.p.m. of the centrifugal clutch. A step for reducing the said wearing can--according to the invention--be taken by limiting the driving torque of the engine in the above-said r.p.m. interval. The invention means that the cutting machine/motor saw is provided with electronic equipment counting r.p.m. and then controlling the ignition system so that the torque of the engine is lowered in a predetermined interval. In a cutting machine ignition is allowed in, for example, every third revolution within the interval 3000-6000 r.p.m. The working mode can also be widened so that the time difference between several revolutions is detected.

Abstract: A system for the automatic recommencing of the ignition function of an i.c. engine with a computer controlled ignition system. The system includes an oscillator which occasionally can stop working. An RC-circuit is charged by ignition pulses supplied by the micro-computer and is discharged by possible failure of these pulses. A sensing circuit influenced by the RC-circuit thereby supplies a reset pulse to the computer which then recommences the supply of ignition pulses.

Abstract: Actuator for the release of automatic emergency brakes of hand-operated, powered tools, such as chain saws, having a driving shaft for the tool. Such emergency brakes are constituted of a brake mechanism released by means of stored energy. The actuator is constituted of a rotatable and balanced body with a small amount of friction on a shaft situated essentially parallel to the driving shaft. The actuator is fabricated of a permeable material, and has a mass having an essential inertia against rotation on the shaft. The actuator cooperates firstly with a magnet retaining the actuator with a predetermined magnetic force against rotation in an angular position of the actuator, and then with a sensor which is so arranged that an impulse for releasing the brake mechanism is given as soon as the actuator comes out of said angular position.

Abstract: A microcomputer is used in the invention for the control of the ignition function of an ignition system of an i.c. engine. The limitation of r.p.m. of the engine at high r.p.m. is brought about by an acurately developed procedure of delayed ignition in two steps. The control of ignition timing is carried out by counting timer pulses between reference points, whereby the number of pulses between such points constitutes an address of a position in the ROM of the computer, where a reference number of the ignition time is stored. In manufacturing of a great assortment of engines several demands for limitation of maximum r.p.m. can be fulfilled in that the microcomputer has a spacing for storing several characteristics. The selection of a particular characteristic for a sort of engine is made by establishing permanent connections (or disconnections) in separate inputs of the computer which reads the combination and choses the corresponding characteristic.

Abstract: An electronic circuit device for ignition pulses for an i.c. engine having a two- or three pole magnetic system generating positive and negative pulses. One of the pulses is used for ignition energy and the other for power supply of electronic equipment. As a reference point for ignition advance calculation is the peak of said power supplying pulses used. An oscillator (36) supplies a pulse frequency many times higher than the r.p.m. of the engine. A peak detector (14) and said oscillator are connected to a pulse counter (39) which after a predetermined number of pulses from the reference point releases a trigger pulse for the ignition energy. A logic unit (12) sets the counter on the predetermined number in dependence of the r.p.m. of the engine.

Abstract: A microcomputer is used in the invention for control of the ignition functions of an ignition system of an i.c. engine. A switch (17) in an operating handle or the like is connected via a transistor to a digital input of the computer. This reads the status of the switch once every revolution of the engine and as long as the switch is closed the ignition is delayed at an r.p.m. above a predetermined, programmed value (e.g. 3000 r.p.m.) and the r.p.m. of the engine is restricted. When the engine shall work the switch is opened and the ignition is normal. The restriction is used at start in order to avoid speeding during the start procedure. As a complement to said switch a parallel switch (27) can be connected and operated by a brake device of the engine. During braking the r.p.m. of the engine is thereby restricted to the same value as the r.p.m. during the start.

Abstract: An ignition circuit according to the present invention has the properties of trigging, i.e. releasing the spark at a predetermined point behind the top of the primary voltage (the ignition generator voltage). During the ascending primary voltage the ignition switch (12) is conducting while a capacitor voltage (U.sub.K) is developed. When the primary voltage has passed its top value a potential difference to the capacitor voltage (U.sub.K) is created, which is used for the control of the switch to make it break. By the interruption of the primary current an ignition voltage is induced at duty r.p.m. in an ignition coil (11). At an extremely high r.p.m. the ignition is delayed behind the voltage top whereby the induced voltage will be too low for ignition. Too high an r.p.m. is thereby avoided.