The present invention relates to a common rail type fuel injecting device.
Recently, a common rail type fuel injecting device is focussed on in a diesel engine technology. The common rail type fuel injecting device is designed such that high pressure operation fluid charged in a common rail is transmitted therefrom to an injector to thereby activate the injector with the operation fluid.
As the injector, the following types have been proposed. One type is a pressure charging type that injects a fuel which has been pressure-increased to a predetermined pressure preliminarily, and another type is a pressure increasing type which injects a fuel while increasing the pressure thereof during injection. For example, the pressure charging type injector is disclosed in Japanese Patent Application Laid-open No.10-18934, and the pressure increasing type injector is disclosed in Japanese Patent Application Laid-open NO.10-110658.
The pressure charging type injector disclosed in Japanese Patent Application Laid-open No.10-18934 preliminarily increases the pressure of the fuel, and therefore, as shown in FIG. 8, the injection ratio is abruptly increased at the start of the fuel injection, and is abruptly lowered at the end of injection since the pressure of the pressure-increased fuel can be utilized.
The pressure increasing type injector disclosed in Japanese Patent Application Laid-open No.10-110658 is designed to control together two valves, i.e. a pin spool valve and an intensifier valve, using one electromagnetic solenoid. The pressure increasing type injector increases the pressure at the time of injection, and accordingly, as shown in FIG. 9, the increase in ratio of fuel injection at the start of the fuel injection is gentle, and since the pressure of the pressure increased fuel can not be used at the end of the injection, and an injection valve is closed only by a spring force of a return spring provided to the injection valve, so that the injection ratio is gently lowered.
These pressure charging type and pressure increasing type fuel injecting devices, however, suffer from a problem in that these devices can not put exhausted gas into an appropriate state, or the like.
In more detail, in view of engine characteristics, the fuel injection ratio is preferably increased gently rather than abruptly at the start of the fuel injection in order to suppress generation of nitrogen oxide, combustion noise and vibration, whereas the fuel injection ratio is preferably increased abruptly rather than gently at the end of the fuel injection in order to suppress generation of incompletely combusted fuel and particulate.
However, the pressure charging type increases the fuel injection ratio too abruptly at the start of the injection, and the pressure increasing type decreases the fuel injection ratio too gently at the end of the injection.
As described above, the pressure charging type and the pressure increasing type in the related art encounter the problems at either one of the start and end of the fuel injection.
For this reason, a fuel injection device has been required, which has characteristics of gently increasing the injection ratio at the start of the injection similarly to the pressure increasing type and abruptly decreasing the injection ratio at the end of the injection similarly to the pressure charging type, as shown in FIG. 10.
The present invention was made in view of the aforementioned problem. An object of the present invention is to provide a common rail type fuel injecting device, which can gently increase the injection ratio at the start of the fuel injection and abruptly decrease the injection ratio at the end of the fuel injection.
The present invention is directed to a common rail type fuel injecting device for an internal combustion engine, comprising: a common rail receiving operation fluid; and an injector having a pressure application chamber and a fuel pressure increasing chamber at both ends of a pressure increasing piston, in which at a start of fuel injection, the operation fluid charged in the common rail flows therefrom into the pressure application chamber to bias the pressure increasing piston and pressurize fuel within the fuel pressure increasing chamber, thereby injecting the fuel, whereas at an end of the fuel injection, the operation fluid within the pressure application chamber flows out therefrom to end pressure application to the fuel within the fuel pressure increasing chamber using the pressure increasing piston, thereby ending the fuel injection, said injector being provided with a passage through which the fuel within the fuel pressure increasing chamber flows out externally and switching means for interrupting communication of the passage at the start of the injection, and establishing the communication of the passage at the end of the injection.