Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
1999-05-19
2001-06-05
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S447000
Reexamination Certificate
active
06240901
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a fuel feeding system for a multi-cylinder engine, especially a large diesel engine, in which the fuel is fed from a fuel tank by means of a high pressure pump into a pressure supply, from which it is fed further by means of injectors into the cylinders of the engine. Large diesel engines refer here to such engines that are applicable for instance for main propulsion engines or auxiliary engines for ships or for power plants for production of heat and/or electricity.
In a modern diesel engine, fuel is injected by means of fuel injecting valves or injectors directly into the cylinders of the engine. Since the injection occurs at a relatively late phase at the end part of the compression stroke, a sufficiently high pressure is correspondingly necessary for the injection. In a conventional fuel feeding system each cylinder is provided with an injection pump of its own which pumps fuel through an injection valve and an injection nozzle into the combustion chamber of the cylinder. The arrangement is expensive since it includes many separate components. In addition the pressure in the injection pumps may vary, whereby the injection into the different cylinders may correspondingly take place under different pressures and provide different amounts of fuel.
A newer solution is a so-called common rail or common pressure injection, in which the generation of pressure and the injection of fuel are functionally separated from each other. Fuel is fed by means of a high pressure pump into a common pressure supply, from which it is led through separate pipes to the respective injectors of the several cylinders. In practice the operation of an injector is electronically controlled for instance by means of a solenoid valve in order to obtain a sufficiently short and precise injection.
Especially in large engines the common rail system is attended by certain drawbacks as a consequence of the length of the common fuel rail serving as a pressure supply, since depending of the type of engine the length may be 3 m or even more. If the common fuel rail is long and narrow, severe pressure waves or pressure pulses moving back and forth appear easily in it. These affect correspondingly the amount of fuel injected into the several cylinders. In addition due to the high pressures involved the strength of a long fuel rail and thus the security of the system may become a problem. On the other hand if the common fuel rail is long and has a relatively large diameter so as to prevent the pressure waves mentioned above and the fuel rail is cooled, reheating of the fuel to its operating temperature takes longer than in the case of a narrow fuel rail. This may be a problem especially when heavy fuel oils are utilized.
SUMMARY OF THE INVENTION
The aim of the invention is to provide a new and improved fuel feeding system, which is applicable especially to large diesel engines and from which the problems evident in the known solutions, as mentioned above, are eliminated. The aim of the invention is to provide a fuel feeding system which enables the fuel pressure to be maintained more constant than before and which is as a whole more secure and reliable than before and yet advantageous as to its costs.
In accordance with the invention the pressure chambers of the pressure accumulator units are continuously in connection with each other. In addition one of the pressure accumulator units is provided with an auxiliary valve by means of which the pressure chamber of that pressure accumulator unit, and at the same time the pressure chambers of the other pressure accumulator units connected thereto, can be connected to the fuel tank. This enables circulation of fuel for instance for heating thereof before starting of the engine, which is of importance especially when heavy fuel oil is utilized. By means of a solution according to the invention it is possible to avoid utilization of a long common fuel rail, and yet the solution makes it possible to effectively balance the possible pressure differences among the separate pressure accumulator units. The strength of the construction is no problem either in this case so the system is more reliable and secure than before.
The system includes with advantage a low pressure pump for feeding fuel from the fuel tank to the high pressure pumps which in turn feed fuel to the pressure accumulator units. The fuel feeding system is divided into a low pressure feeding circuit to which fuel is fed by the low pressure pump and a high pressure circuit to which fuel is fed by the high pressure pumps. The feeding circuit may be provided with a throttle means, a constant pressure valve or the like for maintaining a uniform feeding pressure. In practice the pressure in the feeding circuit may with advantage be 5-10 bar. Since part of the fuel feeding system is under low pressure, the part that is under high pressure (the high pressure circuit) can to a large degree be limited, which improves the reliability of the system and decreases costs, since the components for the low pressure part are simpler and less expensive.
Each high pressure pump is with advantage provided with a control valve, by means of which the volume flow provided by the high pressure pump is controlled and by means of which the connection between the high pressure pump and the low pressure pump can additionally be closed. In addition by opening and closing the control valves it is possible to ensure that the fuel flow takes place through all the pressure accumulator units even if there is a blockage somewhere in the system. Consequently, when heating the fuel it is possible to ensure that all the fuel in the pressure accumulator units is heated and that there are no dead spaces containing unheated fuel.
The auxiliary valve may with advantage serve also as a constant pressure valve and it may be utilized in order to unpressurize the pressure accumulator units when necessary.
The fuel pressure in a pressure accumulator unit is about 800-1600 bar, preferably 1000-1400 bar. When a pressure accumulator unit is connected to at least two injectors the volume of its pressure chamber can with advantage be defined on the basis of the formula:
S=Vtot
/(
Vinj*Ncyl
)
in which
Vtot=the common volume of all the pressure accumulator units of the engine;
Vinj=the amount (volume) of fuel injected by one injector for one combustion occurrence of a cylinder, under full (100%) engine load;
Ncyl=the number of cylinders in the engine;
so that the value of S is in the range of 50-100.
The pressure accumulator units are connected to each other by means of a pipe or a duct connected from one unit to another and the diameter of which is then with advantage 4.5-5.0 mm, preferably about 4.7 mm. These dimensioning parameters can affect the extent of vibrations and pressure waves possibly occurring in the system and they are dependent on the construction of the system in each case. The diameter of the connecting pipe is in practice a compromise whereby different features and properties such as dampening of pressure waves and the need to circulate fuel before starting the engine should be taken account of.
The high pressure pump is driven by a cam included in a cam shaft of the engine. The cam may have multiple lobes.
REFERENCES:
patent: 3827409 (1974-08-01), O'Neill
patent: 4784101 (1988-11-01), Iwanaga et al.
patent: 4884545 (1989-12-01), Mathis
patent: 5183019 (1993-02-01), Suhara
patent: 5230613 (1993-07-01), Hilsbos et al.
patent: 5433182 (1995-07-01), Augustin et al.
Gimie Mahmoud M
Smith-Hill John
Smith-Hill and Bedell
Wartsila NSD OY AB
Yuen Henry C.
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