Patent Application
20080006247
Preferred embodiments of the present invention will now be described with reference to the drawings.
A fuel tank 1 is connected to a strainer 3 through a fuel supply passage 2, and the strainer 3 is connected to a gear pump 5 through a fuel supply passage 4. The gear pump 5 is configured in one body together with a high-pressure pump 6, and the fuel sucked up by the gear pump 5 is supplied to the high-pressure pump 6 and pressurized. The gear pump 5 and the high-pressure pump 6 are driven by the above-mentioned engine.
The high-pressure pump 6 is provided with a discharge amount control valve 7, and the fuel which passes the discharge amount control valve 7 is supplied to a common-rail 10 through a high-pressure passage 9, and is retained. The high-pressure pump 6 is further connected to the fuel tank 1 through a return passage 8, and the fuel which overflows from the high-pressure pump 6 is returned to the fuel tank 1 through the return passage 8.
The common-rail 10 is provided with a relief valve 11. The relief valve 11 opens when a fuel pressure PF in the common-rail 10 exceeds a predetermined upper limit pressure PFMAX (e.g., 185 MPa). Once the relief valve 11 opens, the relief valve 11 keeps the open state until the fuel pressure PF becomes lower than a predetermined lower limit pressure PFMIN (e.g., 12 MPa), and closes when the fuel pressure PF becomes lower than the predetermined lower limit pressure PFMIN. The relief valve 11 is connected to the return passage 8 through a return passage 12. The fuel, which flows out when the relief valve 11 opens, is returned to the fuel tank 1 through the return passages 12 and 8. The common-rail 10 is provided with a fuel pressure sensor 21 for detecting the fuel pressure PF, and a detection signal is supplied to an electronic control unit (hereinafter referred to as “ECU”) 20.
The fuel injection valve 14 is connected to the common-rail 10 through a fuel passage 13. Further, the fuel injection valve 14 is electrically connected to the ECU 20, and opening and closing of the fuel injection valve 14 is controlled by the ECU 20. The fuel injection valve 14 is connected to the return passage 12 at a connecting portion 15, and fuel overflowing from the fuel injection valve 14 is returned to the fuel tank 1 through the return passage 12. The connecting portions 15 corresponding to the other three engine cylinders are shown in
An accelerator sensor 22 for detecting an operation amount AP of an accelerator of the vehicle driven by the engine and an engine rotational speed sensor 23 for detecting a rotational speed NE of the above-described engine are connected to the ECU 20 and the detection signals of these sensors are supplied to the ECU 20.
The ECU 20 calculates a target fuel pressure PFCMD according to the accelerator operation amount AP and the engine rotational speed NE, and controls the discharge amount control valve 7 so that the detected fuel pressure PF coincides with the target fuel pressure PFCMD.
The ECU 20 includes an input circuit, a central processing unit (hereinafter referred to as “CPU”), a memory circuit, and an output circuit. The input circuit performs various functions, including shaping the waveform from of input signals from above-described sensors and other sensors not shown, correcting the voltage levels of the input signals to a predetermined level, and converting analog signal values into digital values. The memory circuit preliminarily stores various operation programs to be executed by the CPU and stores the results of computations or the like by the CPU. The output circuit supplies control signals to the discharge amount control valve 7, the fuel injection valve 14, and the like.
The module shown in
The subtraction amount calculation block 32 calculates a subtraction amount ΔPFCMD according to the detected fuel pressure PF. Specifically, the subtraction amount ΔPFCMD is set to “0” when the fuel pressure PF is lower than a predetermined fuel pressure PFTH, and the subtraction amount ΔPFCMD is set to a predetermined value DPF0 (e.g., 150 MPa) when the fuel pressure PF is equal to or greater than the predetermined fuel pressure PFTH. The predetermined fuel pressure PFTH is set to a value (e.g., 167 MPa) which is slightly higher than the above-described target fuel pressure upper limit value PFCMDH and lower than the predetermined upper limit pressure PFMAX.
The first subtracting block 33 subtracts the subtraction amount ΔPFCMD from the basic target fuel pressure PFMAP, to calculate the target fuel pressure PFCMD. Therefore, when the subtraction amount ΔPFCMD is equal to “0”, the target fuel pressure PFCMD coincides with the basic target fuel pressure PFMAP. When the subtraction amount ΔPFCMD is set to the predetermined value DPF0, the target fuel pressure PFCMD is modified to a value less than the basic target fuel pressure PFMAP by the predetermined value DPF0.
The second subtracting block 34 subtracts the detected fuel pressure PF from the target fuel pressure PFCMD, to calculate a difference ΔPF. The discharge amount command value calculation block 35 calculates the discharge amount command value FR with the PID (proportional, integral, and differential) control method so that the difference ΔPF becomes “0”.
The ECU 20 supplies a drive signal according to the discharge amount command value FR to the discharge amount control valve 7, and controls the discharge amount of the high-pressure pump 6.
As described above, in this embodiment, when the detected fuel pressure PF becomes equal to or greater than the predetermined fuel pressure PFTH, the target fuel pressure PFCMD is reduced by the predetermined value DPF0, thereby reducing the fuel pressure PF. Accordingly, an abnormal rise in the fuel pressure that causes opening of the relief valve 11 can be certainly prevented, to maintain good operating performance of the engine.
In this embodiment, the high-pressure pump 6 corresponds to the fuel pump, the common-rail 10 corresponds to the pressure accumulating means, the relief valve 11 corresponds to the relief means, the fuel injection valve 14 corresponds to the injection means, and the fuel pressure sensor 21 corresponds to the fuel pressure detecting means. Further, the discharge amount control valve 7 and the ECU 20 correspond to the fuel pressure control means.
In the embodiment described above, the subtraction amount ΔPFCMD is set to a value as shown by the dashed line in
The present invention can be applied also to a fuel supply apparatus for internal combustion engine with more than four engine cylinders, for example, internal combustion engines with five engine cylinders, six engine cylinders, eight engine cylinders, twelve engine cylinders and the like. Further, the present invention is also applicable to a fuel supply apparatus for, a watercraft propulsion engine such as an outboard engine having a vertically extending crankshaft.
The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are, therefore, to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2006-184478 | Jul 2006 | JP | national |
