This application claims priority from Federal Republic of Germany application 200 20 655.9, and the entire contents of same are incorporated herein by reference.
The invention relates to a two-stroke motor with a fresh-gas supply, preferably with oil-in-gasoline lubrication. The invention relates to a two-stroke motor with a fresh-gas supply (preferably with oil-in-gasoline lubrication), with a motor housing in which a crank chamber with an inlet opening and a cylinder chamber with an outlet opening are formed, with a crank drive in the crank chamber and with a piston in the cylinder chamber that are connected to one another by a connecting rod, with at least one overflow conduit, with a carburetor comprising a carburetor chamber with a fresh-air entrance opening, a fuel entrance opening and a mixture exit opening as well as comprising a throttle flap that can move in a regulatable manner, with an inlet conduit in order to connect the mixed outlet opening of the carburetor chamber to the inlet opening of the crank chamber, and with a fresh-gas conduit that empties through an opening into the overflow conduit in order to supply fresh gas to the overflow conduit. The invention also entails a flange for a two-stroke motor with fresh-gas supply, especially for a two-stroke motor with oil-in-gasoline lubrication.
Two-stroke motors are known. The operating principle of a two-stroke motor with a fresh-air supply is described in the MTZ Motortechnischen Zeitschrift 74 (1972) 12, p. 475. The fresh-air supply causes the loss of the noxious air-fuel mixture through the outlet opening of the cylinder chamber, which in turn causes the hydrocarbon emissions of the two-stroke motor to be low. Since only a small part of the air-fuel mixture is expelled unburned out of the cylinder chamber, the two-stroke motor with the fresh-air supply is not only environmentally friendly but saves fuel at the same time. However, the realization of the fresh-air supply has the disadvantage that the design of the two-stroke motor with a fresh-air supply is expensive. Furthermore, the fresh air supplied adversely affects the synchronization property of the two-stroke motor, especially at low speeds.
EP 0 997 623 A1 discloses a two-stroke motor with mixed scavenging and with a suction device that comprises a carburetor and by means of which suction device cold fresh gas from the carburetor is placed at a slight interval from a mouth of an overflow conduit into a cylinder chamber. The fresh gas serves to cool the inner cylinder wall and the piston bottom. The disclosed two-stroke motor has the significant disadvantage that the placed fresh gas comprises an air-fuel mixture. The two-stroke motor therefore puts hydrocarbon compounds into the environment.
EP 0 997 621 A1 discloses a two-stroke motor with mixed scavenging in which a carburetor is arranged between an air filter and an inlet conduit to a crank chamber. A mixture conduit and a fresh-air conduit are formed in the carburetor that is connected to the inlet conduit and to an overflow conduit. A first throttle flap for controlling the mixture volume flowing through is fixed in the mixture conduit; a second throttle flap for controlling the volume of fresh air flowing through is fixed in the fresh-air conduit. The mixture volume flowing through and the fresh-air volume flowing through are controlled independently of one another in the disclosed two-stroke motor. However, the design of the carburetor of the two-stroke motor requires many components and is very expensive; furthermore, the control of the mixture volume flowing through and the control of the fresh-air volume flowing through must be coordinated with one another, which necessitates an additional operating expense.
U.S. Pat. No. 6,101,991 discloses a two-stroke motor with mixed scavenging and with a cylinder chamber and a crankcase. The two-stroke motor comprises an inlet conduit in order to supply an air-fuel mixture to the crankcase. A throttle flap is provided in order to throttle the air flow through the inlet conduit and a carburetor is provided for delivering fuel into the inlet conduit. The interior of the crankcase is subdivided into at least two crankcase volumes separate from one another: A rich volume and a lean volume. Each crankcase volume communicates with the cylinder chamber through an associated opening in the cylinder wall. Furthermore, a lateral opening between an outlet opening and a rear overflow opening is formed in the cylinder wall in such a manner that it is freed before the outlet opening is closed. This lateral opening communicates with the lean volume by means of a lateral overflow conduit. The rear opening communicates with the rich volume. A section of the inlet conduit is subdivided into two inlet lines: A rich line and a lean line that communicate with the rich volume and the lean volume. The carburetor and the throttle flap are designed and arranged in such a manner that upon a high load substantially the entire fuel delivered from the carburetor passes into the rich line. Upon a small load the fuel delivered by from the carburetor passes into both lines, into the rich line as well as into the lean line. This known two-stroke motor has the disadvantage that in the crankcase the separation of the rich volume from the lean volume can only be achieved in an expensive and incomplete manner if, e.g., only a disk-shaped flywheel functions as a separating wall. The flywheel increases the weight of the two-stroke motor and as a result of the device into which the two-stroke motor is installed. Furthermore, the flywheel causes an especially large angular momentum whose change of adjustment requires an especially large amount of force upon a corresponding movement of the two-stroke motor. If a hand-held device is involved, the operating of the hand-held device therefore becomes particularly difficult.
EP 1 006 267 A1 discloses a two-stroke motor with mixed scavenging that comprises overflow conduits, each of which communicates with a fresh-air conduit. The mouths of the overflow conduits into the cylinder chamber are arranged in such a manner that the reduction of pressure in the crank chamber after an upward movement of a piston makes it possible to draw air out of the lateral fresh-air conduits into the overflow conduit. If the piston is at top dead center the mouths are located below the piston in free communication with the crank chamber. This construction prevents mixture from being located in the mouth area of the overflow conduits at the start of a scavenging process which mixture is expelled through the outlet opening. However, this construction also has the disadvantage that the fresh air is not supplied in a manner independent of the speed.
The invention has the task of creating a two-stroke motor of the initially described type that avoids the cited disadvantages, in particular has the simplest possible design and emits as few pollutants as possible during operation.
The invention solves this problem with a two-stroke motor with a fresh-gas supply, especially with a two-stroke motor with oil-in-gasoline lubrication, with a motor housing in which a crank chamber with an inlet opening and a cylinder chamber with an outlet opening are formed, with a crank drive in the crank chamber and with a piston in the cylinder chamber that are connected to one another by a connecting rod, with at least one overflow conduit, with a carburetor comprising a carburetor chamber with a fresh-air entrance opening, a fuel entrance opening and a mixture exit opening as well as comprising a throttle flap that can move in a regulatable manner, with an inlet conduit in order to connect the mixed outlet opening of the carburetor chamber to the inlet opening of the crank chamber, and with a fresh-gas conduit that empties through an opening into the overflow conduit in order to supply fresh gas directly to the overflow conduit, characterized in that the fresh-gas conduit and the carburetor chamber communicate with one another in such a manner that the throttle flap acts in a regulatable manner on the direct supply of fresh gas to the overflow conduit.
The invention creates a two-stroke motor with a regulatable fresh-gas supply with an especially simple design. In particular, a fuel component of the fresh-gas supply can be regulated. In the two-stroke motor of the invention the regulating of the fresh-gas supply takes place in a speed-dependent manner. In this way the performance of the two-stroke motor can be optimized as a function of the speed. The fuel consumption and the emitting of pollutants of the two-stroke motor with optimized performance are particularly low. The two-stroke motor of the invention can be operated in an especially environmentally friendly manner.