Patent Application
20050235962
This is a Continuation-In-Part Application of International Application PCT/EP03/13069 filed Nov. 21, 2003 and claiming the priority of German application 102 60 775.3 filed Dec. 23, 2002.
The invention relates to a fuel supply system for an internal combustion engine with direct fuel injection including a fuel supply pump and downstream thereof a high pressure pump for supplying the fuel to a plurality of injectors and, parallel to the high pressure pump, a hydraulic transmission for providing in the start up phase an increased fuel pressure.
Internal combustion engine with direct fuel injection require already during startup high fuel injection pressures in order to achieve a mixture of the fuel with the combustion air sufficient for ignition of the mixture. The minimum pressure of the fuel for gasoline engines with direct fuel injection is about 50 bar and for diesel engines with direct fuel injection it is about 120 bar.
The fuel supply pumps known from the state of the art cannot provide the necessary fuel injection pressure. The necessary pressure is generally provided by a high pressure pump mounted to the camshaft and is available after about one turn of the camshaft that is two turns of the crankshaft.
Before reaching the above minimum fuel pressure, engines with direct fuel injection cannot start properly. This results in relatively long start up times and detrimentally affects particularly start/stop operation of the engine. In order to provide the minimum fuel pressure early on, the use of pressurized fuel storage arrangements or electrically operated high pressure pumps is known in the art.
DE 38 33 430 A1, for example, discloses a fuel supply system for internal combustion engines with a fuel pump driven by the internal combustion engine and a fuel supply pump in the form of a hydraulic pump which is operated by fuel returned from the engine-driven fuel pump. In the lines interconnecting the fuel pump and the hydraulic pump a pressure storage device with a compensation chamber is arranged. The fuel supply from the hydraulic pump to the pressure storage device is controlled by a valve which is opened when the compensation chamber of the pressure storage device is empty and remains open as long as fuel can flow into the pressure storage device. The fuel returned by way of the pressure line is directed into a chamber of the pressure storage device disposed between the valve and the hydraulic pump or, respectively, the pressure line.
However, with this arrangement, the formation of gas bubbles in the suction line of the hydraulic fuel pump (HDP) cannot safely be avoided. Also, the use of an electric fuel supply or high pressure pump has the disadvantage that these pumps are very expensive and subject to failure, that, in order to provide the necessary fuel pressure, they must be relatively large and that such pumps generate certain noises.
DE 199 52 782 A1 discloses a system for reducing the aerosol contained in the liquid fuel in a fuel storage device. An internal combustion engine operating with the common rail fuel injection principle includes—besides the rail and a plurality of injectors—a fuel storage unit which is connected, via a communication line, to a fuel filter, a fuel supply pump and a high pressure pump.
WO 99/28620 discloses a fuel supply system for internal combustion engines with direct fuel injection including a fuel supply pump and a downstream high pressure pump for supplying fuel via a pipe system from a fuel tank to a plurality of injectors or injection nozzles disposed downstream of the high pressure pump wherein between the fuel supply pump and the plurality of injectors or injection nozzles a hydraulic transmission is provided in parallel with the high pressure pump. The hydraulic transmission is designed for the generation and maintenance of a high fuel pressure in the startup and shut down phases of the internal combustion engine. The fuel supply pump is connected at its inlet side to the fuel tank and with its outlet to the hydraulic transmission and the supply pump is connected by way of a branch line to the high pressure pump.
It is the object of the present invention to provide a fuel supply system for internal combustion engines with direct fuel injection with which a fuel pressure as required for fuel injection can be maintained in the startup and shutdown phases of the internal combustion engine in a particularly simple manner.
In a fuel supply system for an internal combustion engine with direct fuel injection including a fuel supply pump and, downstream thereof, a high pressure pump for supplying high pressure fuel to a plurality of injectors and, parallel to the high pressure fuel pump, a hydraulic transmission operated by the low pressure fuel of the fuel supply pump for generating initially high pressure fuel to the fuel injectors so as to permit instant engine startup upon actuation of a valve disposed in the fuel supply line from the fuel supply pump to the hydraulic transmission.
With the system according to the invention, an electrically controllable high pressure pump is not needed in order to provide a high fuel injection peak pressure early on. The pumping volume of the supply pump also called EFP (electrical fuel pump) is so designed that sufficient fuel is supplied to the internal combustion engine at full engine load and high engine speed. Since at startup only a fraction of the pumped fuel volume is needed, the fuel pressure needed during startup can be generated by a normal fuel supply pump and a pressure increase stage which will be called below a hydraulic transmission. After the engine has started, the high pressure pump (HPP) provides for the high pressure needed at engine start-up. It is advantageous in this connection that there is no problem with gas bubbles in the suction line nor with a non-uniform fuel supply to the engine cylinders.
Furthermore, the whole system can be provided at relatively low costs when compared with conventional systems. With the method according to the invention, which does not require an electrical high pressure fuel pump, a higher energetic overall efficiency can be achieved than with the use of an electric high pressure fuel pump.
In accordance with the invention, the connecting line between the outlet of the fuel supply pump and the hydraulic transmission is provided upstream of the branch-off line with a first control valve. The hydraulic transmission is arranged between the fuel supply pump and the plurality of injectors or injection nozzles in parallel with the high pressure fuel pump and is capable of generating the high fuel pressure required for the injection during start-up of the internal combustion engine. By the method according to the invention, for the start-up of internal combustion engines with direct fuel injection, the high fuel pressure required can be generated or maintained in the standstill or start up phase of the engine. This advantageously results in a reduction of the startup time required for the engine. The invention therefore provides for an extremely advantageous rapid or instant start of the internal combustion engine.
The procedural step required therefor will be described below in greater detail with reference to the accompanying drawings.
The fuel supply system 1 shown in
The connecting line 3b between the outlet of the fuel supply pump 4 and the hydraulic transmission 9 includes downstream of the branch-off of the branch line 5a, a first control valve 8. A second control valve 15 arranged in a branch line 14a, 14b which extends between a chamber 9b of the hydraulic transmission 9 and the connecting line 3b between the fuel supply pump 4 and the hydraulic transmission 9. A third control valve 17 is provided in a return line 16a, 16b extending from the chamber 9b of the hydraulic transmission 9 and the fuel tank 2.
The fuel flow between the fuel supply pump 4 and the hydraulic transmission 9 is controlled by the first control valve 8. By way of the line 14a, 14b and the second control valve 15, fuel can be supplied from the outlet side of the fuel supply pump 4 to the chamber 9b. Furthermore, fuel can be returned from the chamber 9b of the hydraulic transmission 9 to the fuel tank 2 via the return line 16a, 16b and the third control valve 17.
Immediately before the start of the internal combustion engine, the fuel injection pressure p2 required for the startup of the engine is generated by way of the hydraulic transmission 9. To this end, the first and the third control valve 8, 17 are opened and the second control valve 15 is closed. The fuel supply pump 4 supplies fuel via the open valve 8 to the operating chamber 9a of the hydraulic transmission 9. The fuel pressure p1 generated by the fuel supply pump 4 is effective on the piston K1 of the hydraulic transmission 9, which piston delimits the low pressure chamber 9a with a certain piston surface area A1 and moves the piston K1 from the position I to the position II. The pressure force generated on the piston K1 acts on a second piston K2 which is connected to the first piston K1 and which delimits the high pressure chamber 9c with a certain piston surface area A2. The pressure p2 then generated by the piston K2 is increased over the pressure p1 by the ratio A1/A2. In this startup phase, the high pressure pump 6 is not yet in operation. The high pressure chamber 9c is in communication with the high pressure rail 11 by a high pressure connecting line 10. When the fuel pressure needed for ignition is generated in this way, the engine can be started instantly. During the startup phase, in which the fuel supply pump 4 continues to operate, the high pressure pump 6 which is driven by the camshaft of the engine and which therefore is driven mechanically generates a fuel pressure p3. The pressure p3 developing at the outlet side of the high pressure pump 6 is transmitted to the high pressure rail 11 and, via the connecting line 10 to the high pressure chamber 9c. when the pressure p3 generated by the high pressure pump 6 exceeds the hydraulic pressure p2 generated by the hydraulic transmission 9, the piston K1 is moved back from the position II to the position I, that is, to its original position while the third control valve 17 is closed and the first and second control valves 8, 15 are opened.
During normal operation of the internal combustion engine, wherein the fuel pumps 4 and 6 provide for the fuel supply to the engine all three control valves 8, 15, 17 are closed.
The transmission ratio of the hydraulic transmission is so selected that, during normal operation of the internal combustion engine, the piston K1, K2 is always returned from the position II to the position I, that is, during operation the pressure p3 after the high pressure pump 6 is higher than the pressure p2 generated by the hydraulic transmission wherein p2=p1x (hydraulic transmission ratio). In order to prevent that during the return movement of the piston K1, K2 a pressure drop occurs in the high pressure rail 11 which would result in a drop in the engine power output the return movement of the piston can be adapted to the requirements of the internal combustion engine by means of a throttle 20, which slows the return movement of the piston K1, K2.
The same effect however could be achieved by the control valve 8. In the startup phase, the control valve 8 is opened, so that the piston K1, K2 is moved from the position I to the position II. When the engine is operating the pressure p3, which is generated by the high pressure pump 6 is higher than the pressure p2 which is generated by the hydraulic transmission so that the piston K1, K2 is moved from the position II to the position I. In order to prevent a pressure drop at the high pressure rail 11, the control valve 8 is then closed. Also, in this case, the procedure can be slowed down by the throttle 20.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102 60 775.3 | Dec 2002 | DE | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP03/13069 | Nov 2003 | US |
| Child | 11159090 | Jun 2005 | US |
