The invention relates to an internal combustion engine with a fuel system, wherein the fuel system comprises a fuel valve, wherein the fuel valve has a housing in which a fuel chamber is formed. The fuel system comprises a fuel pump that conveys fuel from the fuel tank into the fuel chamber. The fuel system has a conveying pump for forced conveyance of fuel into the fuel system.
It is known to provide a conveying pump in fuel systems that operate with a carburetor, wherein the conveying pump is operated manually and primes the fuel system before starting the internal combustion engine, for example, after a longer shutdown period of the internal combustion engine. Such systems operate usually by suction. In such a system, the fuel is sucked in through the control chamber of the carburetor by the conveying pump that is arranged downstream of the carburetor. Such a system is disclosed, for example, in U.S. Pat. No. 6,938,884.
In fuel systems that comprise a fuel valve, it can be provided also that the fuel system is primed prior to starting the engine. Such a fuel system is disclosed in U.S. Pat. No. 7,743,751. In this fuel system, by means of a conveying pump fuel is forced through a portion of the fuel system back into the fuel tank. In this way, the fuel system is primed. The fuel system disclosed in U.S. Pat. No. 7,743,751 has a high-pressure pump that conveys the fuel to the injection valve. The part of the fuel system in which the high-pressure pump is arranged is not primed by the conveying pump.
The invention has the object to provide an internal combustion engine with a fuel system of the aforementioned kind in which excellent starting behavior of the internal combustion engine is achieved.
In accordance with the present invention, this is achieved in that the internal combustion engine with the fuel system is provided with a conveying pump that is arranged in a feed line to the fuel chamber of the fuel valve and conveys fuel into the fuel chamber and in that the fuel chamber is connected to a relief line in which a first valve is arranged.
It has been found that in fuel systems with a fuel valve, vapor bubble formation in the fuel system and in the injection valve makes it very difficult to start the internal combustion engine, or even prevents starting the engine. The vapor bubble formation is a problem primarily in fuel systems that operate at minimal pressure, for example, a pressure of only one or several tenth of a bar, or a few bar, above ambient pressure. The pressure in such a fuel system can be, for example, approximately 100 mbar above ambient pressure. When the fuel valve heats up too much, vapor bubbles can form in the fuel valve. The vapor bubble formation is in particular also a problem when the internal combustion engine is shut off and after-heating occurs because no cooling air is conveyed anymore.
In order to flush out vapor bubbles that are formed within the fuel system, it is provided that the conveying pump is arranged in a feed line into the fuel chamber of the fuel valve and conveys the fuel into the fuel chamber of the fuel valve. The fuel chamber is connected with a relief line in which a first valve is arranged. Since the fuel chamber of the fuel valve is flushed or primed, it is ensured that vapor bubbles in the fuel system are flushed out. At the same time, by priming the fuel valve with fuel, an effective cooling action of the fuel valve is achieved in a simple way and this prevents new vapor bubbles from being formed. By means of the first valve that is arranged in the relief line, the desired pressure in the fuel system can be maintained in operation. Depending on the control action and configuration of the first valve, priming of the fuel chamber in the injection valve can be done at a pressure significantly higher than operating pressure in the fuel system. In this way, an effective priming action and removal of gas or vapor bubbles, possibly contained in the fuel chamber, is enabled and this prevents new vapor bubbles from being formed.
A simple configuration results when the feed line in which the conveying pump is arranged is positioned in the flow path from a pump chamber of the fuel pump into the fuel chamber. The conveying pump can therefore be arranged in a feed line of the fuel system that is existing anyway. Advantageously, a pressure regulator is arranged downstream of the fuel pump. The feed line in which the conveying pump is arranged connects a control chamber of the pressure regulator with the fuel chamber. Since the conveying pump is arranged downstream of the pressure regulator, the pressure regulator does not act to limit the pressure that is supplied by the conveying pump for priming the fuel valve so that by means of the conveying pump a fuel pressure can be generated in the fuel system that is significantly higher than the fuel pressure that is conventionally existing in operation. However, it can also be provided that the feed line is a bypass line bypassing the fuel pump and connecting the fuel tank with the fuel chamber. As a result of the arrangement of the fuel pump in a bypass line bypassing the fuel pump, the spatial arrangement of the conveying pump relative to the fuel pump and the internal combustion engine can be substantially freely selected.
Advantageously, the first valve is actuated as a function of a pressure, i.e. is opened or closed by pressure control. The actuating pressure at which, when it is surpassed, the first valve opens is advantageously higher than the operating pressure of the fuel system. Accordingly, by means of the conveying pump a limited overpressure can be generated in the fuel system relative to normal operating pressure. In this way, it is prevented that new vapor bubbles can form in the fuel valve of the fuel system. The valve can open in particular as a function of the pressure in the fuel chamber or as a function of the pressure difference between fuel chamber and fuel tank. As an alternative or in addition, it can be provided that the valve is actuated as a function of temperature. The actuating temperature can be, for example, the temperature of the fuel valve or of the internal combustion engine. It can also be provided that the valve opens and closes as a function of the engine speed of the internal combustion engine. In this context, it is in particular provided that the valve is closed above a predetermined actuating engine speed so that the first valve in usual operation is closed and is open only during the starting process. It can also be provided that the first valve is closed once the first combustion cycle has been detected. The first combustion cycle can be, for example, detected based on the engine speed of the internal combustion engine. The actuating engine speed at which the valve is closed can be an engine speed that is reached as soon as the internal combustion engine has started and that is, however, below the idle speed of the internal combustion engine. As an alternative or in addition, it can be provided that the valve is actuated by time control. The first valve closes in this connection advantageously after lapse of a predetermined time span, for example, the time for one or several pull strokes for starting the engine. In this way, the fuel system is primed during the starting procedure. The different parameters for actuating the first valve can be combined in a suitable way.
A simple configuration results when the valve is a pressure retention valve that opens in the relief direction. The pressure retention valve operates mechanically so that for control of the pressure retention valve no additional devices are required. Since the first valve opens only in the relief direction, opening in the direction opposite to the relief direction, i.e., in the flow direction from the fuel tank to the fuel chamber, is prevented, for example, when in the fuel tank a higher pressure exists than in the fuel chamber. This is the case in particular in fuel systems in which the fuel tank is loaded with pressure. Advantageously, the first valve is an electrically actuated valve. The internal combustion engine has in particular an electronic control unit that actuates the first valve. In this way, an advantageous control of the first valve can be achieved that in particular takes into consideration several parameters.
It can be provided that a second valve is arranged in a bypass line bypassing the first valve. Advantageously, the second valve is a pressure retention valve while the first valve is an electrically actuated valve. By means of the pressure retention valve that is arranged in the bypass line, independent of the parameters that are used for actuating the first valve, it can be ensured that pressure in the fuel system does not rise impermissibly.
The conveying pump can be driven manually, mechanically, electrically or pneumatically. The mechanical drive is realized advantageously by means of a component of the internal combustion engine. The pneumatic drive is advantageously done by means of the fluctuating pressure in the internal combustion engine, in particular in the crankcase of the internal combustion engine.
On the crankcase 14 a holder 24 is attached that has a receptacle 25 for the fuel valve 26 illustrated in
When the piston 21 is in the area of bottom dead center, the crankcase interior 31 communicates by means of a transfer passage 19 with the combustion chamber 22. In the illustrated embodiment, a single transfer passage 19 is provided that branches into several branch passages and opens with several transfer ports 20 into the combustion chamber 22. The transfer ports 20 are piston-controlled by the piston 21 and open when the piston 21 is at bottom dead center. An outlet 18 that is also controlled by the piston 21 extends away from the combustion chamber 22.
In operation, through the intake passage 30 combustion air is supplied into the crankcase interior 31. Fuel is metered into the crankcase interior 31 by means of fuel valve 26 (
As shown in
As also shown in
The internal combustion engine 12 has an electronic control unit 78 that controls the fuel valve 26, i.e., the fuel quantity that is to be supplied and the point in time when the fuel quantity is to be supplied. The electronic control unit 78 controls also the ignition timing. Also, further electrical components of the cut-off machine 1 can be controlled by the electronic control unit 78.
The fuel pressure damper 36 as well as the fuel valve 26 are arranged in the holder 24. The fuel pressure damper 36 has a damper membrane 54 that delimits the damper chamber 53. At the side of the damper membrane 54 that is facing away from the damper chamber 53 a back chamber 56 is provided where a spring 55 is arranged. The spring 55 tensions the damper membrane 54 into the desired position. Instead of the spring 55 the damper membrane 54 can also be maintained in the desired position by its inherent elasticity. The back chamber 56 is loaded through opening 57 with reference pressure. The reference pressure is advantageously ambient pressure. The feed line 50 extends through the pressure damper 36 up to the fuel valve 26.
The fuel valve 26 is connected by a relief line 58 with the fuel tank 32. In the relief line 58 a first valve 73 is arranged that, in the embodiment, is designed as a mechanically acting pressure limit valve. The first valve 73 has a valve member that is loaded by a spring. When the pressure upstream of the first valve 73 surpasses a predetermined actuating pressure, the first valve 73 will open. In this connection, the first valve 73 will open when an actuating pressure difference between fuel valve 26 and fuel tank 32 surpasses a constructively predetermined value that is defined by the spring of the first valve 73. When the pressure in the fuel tank 32 is greater than the pressure in the fuel valve 26, the first valve 73 remains closed. This can be the case when the fuel tank 32 is loaded with pressure. The first valve 73 blocks therefore a flow in the flow direction from the fuel tank 32 to the fuel valve 26. Flow of fuel from the fuel tank 32 to the fuel valve 26 is therefore prevented.
The fuel system has a conveying pump 69 which is arranged in the feed line 50 downstream of the control chamber 43 and upstream of the fuel pressure damper 36. The terms upstream and downstream relate in this context to the flow direction of the fuel in the fuel system. The conveying pump 69 is to be actuated manually by the operator. For this purpose, the conveying pump 69 has a pump bellows 77 that is also shown in
The fuel valve 26 has a housing 67 in which a fuel chamber 62 is formed. The fuel chamber 62 has a metering opening 87 that is opened and closed by the fuel valve 26 embodied as an electromagnetic valve (solenoid valve) and that connects the fuel chamber 62 with the fuel passage 61 in the holder 24; the fuel opening 61 opens into the crankcase interior 31. As also shown in
Before starting the internal combustion engine 12, advantageously the conveying pump 69 is actuated by the operator by compressing the pump bellows 77 several times. Accordingly, the conveying pump 69 forces fuel through the feed line 50 into the fuel chamber 62 of the fuel valve 26. As soon as the actuating pressure difference is reached that is constructively predetermined by the first valve 73 upstream and downstream of the valve 73, i.e., between fuel chamber 62 and fuel tank 32, valve 73 opens and fuel flows through relief line 58 back into the fuel tank 32. The conveying pump 69 sucks in fuel through control chamber 43 of the pressure regulator 35 and through the fuel pump 34 from the fuel tank 32. The fuel that is conveyed by the conveying pump 69 primes the fuel system. Since the fuel is conveyed under pressure to the fuel valve 26, the function of the conveying pump 69 is not impaired by vapor bubbles that are possibly existing in the fuel chamber 62. The fuel pump 34 and the pressure regulator 35, as shown in
In the embodiment according to
In the embodiment according to
In the embodiment according to
In the embodiment according to
In the embodiment according to
In the embodiment according to
In the illustrated embodiments, different combinations of conveying pumps and valves in the relief line are shown. The illustrated combinations are to be understood only as examples and are not limiting. All illustrated conveying pumps can be combined in any combination with any of the illustrated arrangements of the conveying pump and with any of the illustrated valve arrangements.
The pressure in the fuel system downstream of the fuel pump is advantageously minimal in all embodiments and is only a few bar or only one or several tenths of a bar above the ambient pressure. Advantageously, the pressure is in the magnitude of approximately 100 mbar above ambient pressure.
The specification incorporates by reference the entire disclosure of German priority document 10 2011 120 465.6 having a filing date of Dec. 7, 2011.
While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.
Number | Date | Country | Kind |
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10 2011 120 465 | Dec 2011 | DE | national |
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