Internal-combustion engines – Charge forming device – Fuel flow regulation between the pump and the charge-forming...
Reexamination Certificate
1999-07-13
2001-05-08
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel flow regulation between the pump and the charge-forming...
C261S036200
Reexamination Certificate
active
06227176
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a pressure equalization system for a fuel tank of an internal combustion engine, in particular for handheld portable tools such as cutoff machines, chain saws and the like.
BACKGROUND OF THE INVENTION
A carburetor for an internal combustion engine in a tool, namely a chain saw, is known from EP 0 688 948 A2. The air required for combustion is inducted from the ambient air through an intake channel via an intake air filter while the fuel to be mixed with the air is supplied from a fuel tank via a carburetor. The carburetor has a control chamber which is delimited by a membrane and filled with fuel. On one hand, the membrane controls an inlet valve in the control chamber and, on the other hand, delimits a compensation chamber which lies on the dry side of the control membrane. A fuel pump is provided in the carburetor housing to move the fuel to the control chamber. From the control chamber, the fuel passes to nozzles through which the fuel enters the intake channel.
In addition, a start-assist device for the internal combustion engine is also provided in the known arrangement. This start-assist device removes the vapor bubbles which develop in the carburetor while the engine is at standstill. The vapor bubbles would otherwise prevent the internal combustion engine from starting at a subsequent attempt. This start-assist device, which is connected between the control chamber and the fuel tank, serves to flood the fuel system. Subsequent start attempts are then made with a filled fuel system which ensures that the internal combustion engine will start quickly with few attempts.
In such tools, the fuel tank is hermetically sealed in order to avoid leaks whatever the work position of the tool. The consumption of fuel due to the operation of the internal combustion engine leads to the formation of underpressure in the fuel tank. This can lead to a strong decrease in fuel volume such that malfunctions occur in the carburetor to be fed or in the internal combustion engine supplied by the carburetor.
A device is known from U.S. Pat. No. 5,526,843 which enables aeration, with the aeration valve being located at an additional opening provided in the fuel tank. A venting valve can also be arranged on the fuel tank to reduce any overpressure developed by heat. Such devices, in which the aeration and venting valves are in direct connection with the atmosphere, are known as “open systems”.
A “closed system” for the aeration and venting of a fuel tank is described in U.S. Pat. No. 5,743,240. This system is based on the arrangement of a pressure equalization line together with an aeration and a venting valve between the intake channel and an equalizing vessel connected to the fuel tank itself. The connection of the pressure equalization line to the intake channel or a compensation channel connected to the compensation chamber, forms a closed system. If the tool is used correctly, this system largely prevents the escape of any fuel into the atmosphere.
SUMMARY OF THE INVENTION
The invention is based on the object to provide a pressure equalization system with which an undesired pressure level in the fuel tank can be prevented at minimal effort and cost.
The pressure equalization system of the invention is for a fuel tank of an internal combustion engine for a portable handheld work tool such as a cutoff machine, motor-driven chain saw, brushcutter and the like. The pressure equalization system includes: a carburetor for supplying an air/fuel mixture to the engine; an intake air filter having a clean air side; the carburetor including a control membrane delimiting a control chamber filled with fuel and an intake channel into which fuel from the control chamber is drawn by suction; the intake channel being connected to the clean air side of the intake air filter; a fuel tank; a feed valve controlled by the control membrane for supplying fuel from the fuel tank to the control chamber; and, a start-assist device for flooding the control chamber before starting the engine; a suction line connecting the start-assist device to the control chamber; a return line connecting the start-assist device to the fuel tank; a pressure equalization valve connected to the return line; and, the pressure equalization valve being operatively connected to the intake channel.
The start-assist device includes, preferably, a starter pump with a combination valve which is connected to the control chamber via the suction line and to the fuel tank via the return line. The manual or automated actuation of the starter pump when the internal combustion engine is started circulates fuel together with the vapor bubbles or trapped air which form in the fuel while the internal combustion engine is at standstill. This fluid mixture of fuel, vapor bubbles and/or air is pumped through the suction line and the return line to the fuel tank. This forces the flooding of the control chamber with liquid fuel and guarantees a sufficient volume of fuel to start the internal combustion engine via idle nozzles. The arrangement of a pressure equalization valve connected to the return line between the start-assist device and the fuel tank avoids the need for an additional connection to the tank. The pressure equalization valve preferably comprises a duckbill valve for aeration and a mushroom-shaped valve head with a flexible sealing edge lying on a valve seat for venting.
When the engine is running, an underpressure builds up in the fuel tank due to the withdrawal of fuel therefrom. Since the pressure equalization valve is configured for aeration, for example, in the form of a duckbill valve, an underpressure can be avoided by means of inflowing air. This air is taken in from the clean air side of the air filter via the pressure equalization line, thus ensuring that no dirt can enter the fuel.
In a further embodiment of the invention, the pressure equalization valve is also designed to vent air from the fuel tank. If an overpressure builds up in the fuel tank, the pressure lifts the sealing edge from the valve seat and the fuel-enriched vapors can be fed directly to the clean air side of the intake air filter via the pressure equalization line. Since the venting opening is not cleared by the sealing edge until a certain threshold value in the fuel tank is exceeded, no fuel flows out of the control chamber through the aeration system while the start-assist device is pumping since the pressure built up during this phase lies below the threshold value. However, the pressure equalization valve does allow the escape of air, with fuel vapors where present, at a predetermined pressure increase in the tank. Even if a small volume of fuel escapes through the equalization valve into the pressure equalization line during the process, there is no disadvantageous effect on the operating performance since, when the fuel enters the intake channel and the air filter box, it is absorbed by inflowing combustion air and carried through the carburetor venturi to the internal combustion engine.
There is no need for a further connection to the fuel tank because an existing line is used as a connection for the aeration and venting system of the fuel tank. In this way, the tank ventilation system can be positioned in a protected position well adapted to the tool. This makes a space-saving position near the diaphragm carburetor and the fuel tank possible and also results in lower manufacturing costs.
REFERENCES:
patent: 3610221 (1971-10-01), Stoltman
patent: 4824613 (1989-04-01), Scott et al.
patent: 5063891 (1991-11-01), Noisier
patent: 5429776 (1995-07-01), Edlund
patent: 5526843 (1996-06-01), Wolf et al.
patent: 5676115 (1997-10-01), Linsbauer et al.
patent: 5743240 (1998-04-01), Zerrer et al.
patent: 0688948 (1995-12-01), None
patent: 2310007 (1997-08-01), None
Andreas Stihl AG & Co.
Gimie Mahmoud M
Ottesen Walter
Yuen Henry C.
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