Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2002-02-11
2004-09-21
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S456000
Reexamination Certificate
active
06792919
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an accumulator type fuel injection system.
BACKGROUND OF THE INVENTION
There is an accumulator type fuel injection system (common rail system) as a fuel injection system for a diesel engine, capable of improving the engine performance in a wide operational region from a low-speed region to a high-speed region by stably supplying a high-pressure fuel accumulated in an accumulator to each cylinder of the engine. When a fuel injection rate immediately after the starting of a fuel injection operation is excessively high even in a case where such a fuel injection system is used, sudden explosion combustion is carried out in an initial stage of the combustion of the fuel, so that not only the engine noise but also the nitrogen oxide (NOx) content of an exhaust gas increases.
To eliminate such inconveniences, an accumulator type fuel injection system has been proposed which is adapted to inject a fuel at a lower fuel injection rate in an initial stage of each fuel injection cycle. The fuel injection system relating to this proposition is provided with, for example, a low-pressure accumulator adapted to store therein a low-pressure fuel, a high-pressure accumulator adapted to accumulate therein a high-pressure fuel, a change-over valve adapted to switch a fuel injection rate from one to another by communicating the low-pressure accumulator or the high-pressure accumulator selectively with an injector (fuel injection nozzle), and a switch valve adapted to control the fuel injection time by communicating and shutting off a pressure control chamber of the injector and a fuel tank with and from each other.
Regarding the formation of a fuel pressure in the accumulators, there is, for example, a fuel injection system adapted to obtain low-pressure and high-pressure fuels by using low-pressure and high-pressure fuel pumps which are driven by an engine respectively, or a fuel injection system adapted to obtain a high-pressure fuel by a high-pressure fuel pump, and a low-pressure fuel by regulating the pressure of the high-pressure fuel introduced into a low-pressure accumulator (for example, Japanese Patent Laid-Open 93936/1994).
In an accumulator type fuel injection system (for example, WO98/09068) adapted to obtain a low-pressure fuel in a low-pressure accumulator from a high-pressure fuel in a high-pressure accumulator, a fuel chamber (fuel reservoir) of an injector is filled with a low-pressure fuel with the injector kept closed by closing a fuel injection time control switch valve provided correspondingly to the injector in each cylinder, and switching a fuel injection rate change-over valve to a low-pressure side, and the injector is kept closed. When the fuel injection starting time comes, a switch valve is opened to open the injector and thereby carry out initial low-pressure injection (which will hereinafter be referred to as “low-pressure injection”) of a fuel from a nozzle. When a low-pressure injection period elapses, the change-over valve is switched to a high-pressure side, and main high-pressure injection (which will hereinafter be referred to as “high-pressure injection”) is carried out by injecting the high-pressure fuel, which is supplied from the high-pressure accumulator, from the nozzle. When the injection finishing time comes, the change-over valve is switched to the low-pressure side with the switch valve closed at the same time. Namely, the controlling of an injection waveform of the fuel is done by switching the low-pressure and high-pressure accumulators from one to the other by the change-over valve during a fuel injection operation.
In the low-pressure accumulator, a low-pressure fuel is obtained by regulating the pressure of the high-pressure fuel collected between the change-over valve and the fuel chamber of the injector after the change-over valve is closed. Namely, the fuel in the low-pressure accumulator is discharged to a fuel tank (atmosphere-opened side) by controlling a duty of a pressure control valve, which is connected to the portion of a fuel passage which is between the low-pressure accumulator and fuel tank, of the low-pressure accumulator so that the fuel pressure in the low-pressure accumulator attains a predetermined level.
A case where the change-over valve provided correspondingly to the injector in each cylinder and adapted to switch a fuel injection rate gets out of order in the accumulator type fuel injection system of the above-described construction adapted to control an injection waveform by switching the low-pressure and high-pressure accumulators from one to the other will be discussed. When the change-over valve in one cylinder out of, for example, six cylinders or four cylinders gets out of order, the fuel injection pressure and fuel injection rate in the mentioned cylinder become abnormal in comparison with those in the remaining cylinders, and a decrease in the engine output and an increase in the fluctuation of torque occur in consequence, so that the engine cannot be normally operated. When the operation of the engine continues to be carried out in such an abnormal condition, damage to the engine or the vehicle occurs in some cases due to an overload, an increase in the exhaust gas temperature and the like.
When the pressure control valve provided in the low-pressure accumulator gets out of order after the valve is closed, the fuel pressure in the low-pressure accumulator increases, and finally becomes equal to that in the high-pressure accumulator. Consequently, high-pressure injection is carried out from an initial injection period, and the fuel injection rate becomes high to cause the engine to be subjected to an overload operation. Therefore, when the engine continues to be operated in such an abnormal condition, the engine or the vehicle is damaged in some cases. Since a permissible pressure resistance (permissible pressure) of the low-pressure accumulator is set lower than that of the high-pressure accumulator, an excessive increase in the fuel pressure in the low-pressure accumulator has a possibility of occurrence of damage to the low-pressure accumulator and leakage of fuel.
When the pressure control valve gets out of order while it is opened, the execution of low-pressure injection becomes impossible, and the high-pressure injection (main injection) only is carried out. This causes a delay of ignition time, an increase in the exhaust gas temperature and shortage of torque, and exerts ill influence upon the engine. Moreover, due to a necessary operation for increasing the pressure in the low-pressure accumulator, a high-pressure fuel supply pump carries out excessive force feeding of fuel repeatedly, so that there is the possibility that the high-pressure fuel supply pump gets out of order.
When a pressure sensor for detecting the fuel pressure in the high-pressure accumulator gets out of order (for example, the breaking of wire occurs) with a signal output at a low level in the accumulator type fuel injection system of the above-described construction adapted to control an injection waveform by switching the low-pressure and high-pressure accumulators from one to the other during a fuel injection operation, the fuel pressure in the high-pressure accumulator increases due to a necessary operation for controlling the same fuel pressure so that it increases. However, a relief valve provided in the high-pressure accumulator is finally operated, and damage to the high-pressure accumulator and fuel passage can be prevented.
However, the injecting of the fuel is necessarily done at an injection pressure not lower than a maximum level in a regular mode at all times, so that an increase in the injection rate, maximum inside-cylinder pressure and noise vibration occur. Moreover, due to a necessary operation for increasing the fuel pressure in the low-pressure accumulator, the high-pressure fuel pump repeats excessive force feeding of the fuel to give rise to a possibility of the occurrence of an accident.
When the pressure sensor of the high-pressure accumulator gets out of order w
Kohketsu Susumu
Tanabe Keiki
Miller Carl S.
Mitsubishi Fuso Truck and Bus Corporation
Rossi & Associates
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