Patent Application
20050188958
The invention relates to an arrangement for supplying fuel to the fuel injectors mounted onto the cylinder heads of an internal combustion engine wherein fuel is supplied to the injectors by a pumping device through a pressure line under a static pressure.
Methods and fuel supply arrangements are known wherein fuel is pumped by a pump arrangement, which comprises at least one fuel pump, from a fuel tank through a pressure line under a certain pressure to the injectors of an internal combustion engine so as to be available for injection into the combustion chambers of the engine. A device for increasing the fuel injection pressure may be provided for improving the mixture formation by improving the atomization of the fuel spray during fuel injection. Particularly during the startup period of the internal combustion engine, a controllably dosed fuel amount can be provided for the first combustions in order to avoid fuel film depositions on the walls and to form a homogeneous fuel mixture, which can burn with relatively little emissions whereby the overall exhaust gas emissions from the engine can be reduced.
DE 101 27 516 A1 discloses a method, wherein, for the start-up period of the internal combustion engine, the fuel is supplied with a pressure of 45 bar to 55 bar. To this end, a fuel supply arrangement is provided wherein an engine-driven fuel pump generates a static injection pressure in a fuel line to which the injectors of the internal combustion engine are connected. Since during shut-down of the internal combustion engine, the high fuel pressure in the fuel supply line is disadvantageous, the pressure is released. In order to rapidly establish operating pressure upon engine startup thereby to improve the exhaust gas emissions, in the known fuel supply system, an additional electrically operated fuel pump is provided, which supplies fuel directly into the main fuel line and which is switched on during the engine start up procedure for providing the increased fuel pressure. DE 101 27 516 A1 proposes an arrangement with two serially arranged fuel pumps of different performance, wherein the fuel pumped by the first pump is fed by a high pressure pump into the fuel supply line. In this known arrangement, the mechanical drive of the fuel pumps can be disconnected from the engine drive by a switchable clutch and can be coupled to an electric drive in order to be able to utilize the high pressure pump for increasing the fuel pressure during the engine startup phase. This known arrangement requires substantial expenses in order to connect a device for increasing the fuel injection pressure since either a pump must be provided exclusively for the startup phase or in a staged pressure generation by means of a low-pressure and a high pressure pump, an expensive clutch or coupling arrangement must be provided for increasing the fuel injection pressure.
DE 100 05 589 A1 discloses a fuel supply arrangement wherein a pressure controller adjusts the injection pressure as needed by the internal combustion engine selectively to different pressure levels. Herein, in order to facilitate a safe hot start up of the internal combustion engine, the fuel pressure is increased for a short period in order to counteract vapor formation in the warm fuel. The arrangement provides for a fuel pressure of 3.5 bar for high fuel requirements and an increased pressure of 6 bar for hot startup operations which is generated by two serially arranged fuel pumps, each of which generates a pressure of 3 bar and which can be arranged in parallel or in series.
DE 199 39 051 A1 discloses a method using an additional fuel pump for generating the required high fuel pressure during the engine startup phase. The additional fuel pump is electrically operated and electrically switchable and supplies fuel directly into the pressure line, so that, during the startup phase in which the mechanically operated pump cannot yet supply the required high pressure level in the pressure line, an essentially higher pressure is available. The additional electric pump is arranged in parallel with the mechanical pump and is also operated during normal engine operation so as to contribute to providing a high fuel pressure.
DE 195 39 885 A1 discloses a method of operating an internal combustion engine and a fuel supply arrangement wherein a first electrically operated displacement pump supplies fuel to a mechanical engine-driven high pressure pump. The displacement pump in this case is to pump more fuel than is required and excess fuel is returned to the tank via a return line. The supply pressure generated is further increased by the high pressure pump so as to provide in the pressure line the required injection pressure. In order to counter the problem of the vapor formation in the fuel lines when, with the internal combustion engine shut down, the pressure in the fuel line drops, the known arrangement interrupts in the startup phase of the engine the return flow of the electric low pressure pump so that the electric displacement pump generates an increased pressure by which the fuel lines are flushed and any steam bubbles are pushed out of the lines. The arrangement does not provide for an increase of the fuel pressure when needed for improved atomizing of the injected fuel jet under certain operating conditions beyond the normal operating level.
It is the object of the present invention to provide, with the least possible expenditure, a fuel supply arrangement with which, without limitations for the normal operation, the fuel injection pressure can be increased during the start-up phase of the internal combustion engine and the fuel injection volume can be accurately controlled.
In a fuel supply arrangement for supplying fuel from a fuel tank to the fuel injectors of an internal combustion engine by an electrically operated fuel pump, a first fuel pressure level adequate for normal engine operation is provided by the fuel pump and means are provided for increasing the fuel injection pressure provided by the pump for supplying fuel at a higher pressure level to the fuel injectors during an engine start-up or warm-up phase.
With this arrangement, only a limited performance for this high pressure electrical pump is required to obtain a sufficiently high fuel pressure for a good atomization of the fuel in the combustion chamber. Depending on certain conditions, the startup phase is then terminated and the fuel pressure is lowered to a level of about 3 bar to 5 bar.
In one embodiment, the fuel supply arrangement includes a low pressure fuel pump with a high pressure pump arranged in series therewith which can selectively be switched on for increasing the fuel injection pressure. In a section of the high pressure line downstream of the high pressure pump a relief line is connected to the pressure line and is connected at its other end to a low pressure section of the fuel line upstream of the high pressure pump. The relief line includes a switchable relief valve structure so that, by closing the relief valve, the pressure level is increased by activating the high pressure pump. In this way, with simple means, an arrangement is provided in which, with a simple valve structure, the high pressure pump can be switched in and by opening the valve structure the low pressure level of the upstream fuel pump can be provided. The valve structure may be a magnetic valve, which, under normal operation is de-energized, that is open and, for activating the high pressure pump for increasing the fuel pressure, is closed. Expediently, the high pressure pump is operated electrically and therefore can immediately provide the high fuel pressure level in the pressure line of the injectors upon start-up of the engine.
If the high pressure pump is provided with a by-pass line which includes a check valve, with a shut down of the electric high pressure pump, fuel injection is still ensured for an emerging operation if the magnetic valve fails.
In an alternative embodiment of the fuel supply arrangement, a pressure storage device may be provided so as to be connectable, by way of a connecting line with a valve, to the suction side of the fuel pump in the fuel supply line upstream of the fuel pump, whereby, with an opening of the connecting line, an increased pressure level can be instantly established. Such a fuel supply arrangement may be quite compact by supplying fuel to the pressurized fuel storage device from a fuel supply line which is connected to the fuel pressure line downstream of a pressure control device arranged in the pressure line. The relief line of the pressure controller which is adapted to the low pressure level is closed, whereby the fuel pump generates a pressure level beyond normal pressure when the engine consumes a relatively small amount of fuel. For controlling the injection pressure in the operating phase with an increased injection pressure in the operating phase an advance control by a variable throttle in the connecting line of the pressure storage device is expedient.
The pressure storage device can preferably be controlled by means of a control unit which also controls the injectors, the control unit being in communication with pressure sensors at the pressure storage device and in the pressure line. With a possible drop of the preliminary pressure of the pressure storage device or, respectively, a drop of the high pressure to the low normal pressure, the injection times of the injectors are adapted to the available injection pressure for an optimal injection result using stored performance graph data. In a preferred embodiment of the invention, a controllable fuel pump is provided which is controlled by the control unit taking into consideration the pressure available from the pressure storage device, so that the fuel injection process can be accurately adjusted.
In a very compact fuel supply arrangement, the pumping device for supplying the fuel under a certain pressure and an increased pressure when needed is a pump which is controllable on the basis of the desired injection pressure, since additional equipment for increasing the fuel injection pressure is then not needed. It is in this connection expedient if a controllable pressure control valve is arranged in the pressure line in order to obtain the desired pressure level. A rapid pressure drop during switch-over from high pressure operation to low pressure operation is possible if a vent line extends from the pressure line which can be opened by a valve.
The invention will become more readily apparent from the following description thereof on the basis of the accompanying drawings.
a to 1c show schematically flow circuits for a fuel supply arrangement with two fuel pumps,
a-2c show schematically flow circuits with two fuel pumps and a pressure relief line connected to a pressure controller,
a, 3b show schematically circuit arrangements for fuel supply arrangements with a pressure storage device which can be connected to the circuit for increasing the pressure,
a, 4b show fuel supply arrangements with two pressure generating units arranged in parallel, and
a, 5b show fuel supply arrangements with a controllable fuel pump serving as pressure generating unit.
a-1c show a fuel supply arrangement 1 for supplying fuel to the injectors 2 extending into the combustion chamber 36 of an internal combustion engine. The fuel supply arrangement 1 comprises a pumping device which, by way of a supply line 7, provides fuel from a fuel tank 3 to a pressure line 8 under a certain pressure for the injection of the fuel into the combustion chamber. The pressure line 8 is connected to injectors 2 for supplying the fuel thereto, wherein the end of the pressure line 8 is in the form of a common rail via which all the injectors 2 are supplied with fuel. The pump arrangement comprises an electric fuel pump 4 whose input is connected to the supply line 7 extending from the fuel tank 3. The fuel pump 4 is designed for an injection pressure as needed for normal engine operation which in the present embodiment is 3.8 bar. The pumping arrangement furthermore includes a device 6 for increasing the pressure which is connectable for increasing the operating pressure in the pressure line as supplied by the fuel pump 4 when needed.
The switchable device 6 includes as means for increasing the pressure an electrically operated fuel pump 5, which is designed for a higher operating pressure than the fuel pump 4 and which is arranged in series with, and downstream of, the fuel pump 4. The increased pressure of the high pressure pump 5 is in the range of about 10 bar to 15 bar, in the present case 14 bar. The increased operating pressure is controllable by a pressure release line 13 with a switchable magnetic valve 10. The release line 13 branches off the pressure line 8 upstream of the high pressure pump 5 and leads to a low pressure section of the fuel supply line. The magnetic valve 10 is open under normal operating conditions and holds the injection pressure of the fuel in the pressure line to the injectors at the operating pressure of the low pressure line of about 3 bar to 5 bar, in the present example at 3.8 bar. In order to provide the fuel with the increased pressure, the magnetic valves 10 and consequently the release line 13 are closed and, at the same time, the high pressure pump 5 is switched on so that the high pressure pump 5 instantly increases the fuel pressure in the pressure line 8.
The low pressure pump 4 as well as the high pressure pump 5 are each provided with a pressure controller 11, 12 arranged downstream of the respective pump and a return line 14 is connected to the pressure controller for the lower pressure pump 4 for returning fuel to the tank 3. From the pressure controller 12 for the high pressure pump 5, a return line 15 extends to the section of the pressure line 8 between the fuel pumps 4 and 5. Between the fuel pumps 4 and 5 and the respective downstream pressure controllers 11, 12 check valves 16 are arranged which prevent backflow of the pressurized fuel.
In the fuel supply arrangement according to
The fuel supply arrangement in accordance with
In the embodiments of the fuel supply arrangement according to the invention as shown in
With the serial arrangement according to
The fuel supply system according to
a and 3b show a fuel supply arrangement 1 for supplying fuel to the injectors 2 of an internal combustion engine wherein an electric fuel pump 4 is provided in the pressure line 8 for generating the pressure level for normal operation. For increasing the pressure level, a connectable pressure storage device 25 is provided which is connected in the circuit to the supply line 7 via a connecting line 24 and a valve 28 upstream of the fuel pump 4. The arrangement for connecting the pressure storage device 25 may include a check valve 16 in the supply line 7 which prevents backflow of fuel into the pressureless tank 3 when the pressure storage device 25 is connected by the valve 28 to the connecting line 24 for supplying fuel under pressure to the fuel pump 4. The valve for connecting the fuel storage device 25 is preferably a 3/2 way valve whose symbol is shown at the right of the reference numeral 27.
As shown in
The operation of the pressure storage device 25 for high pressure operation is controlled by a control unit 21, which, via signal lines 33, is in communication with a pressure sensor 22 in the pressure line 8 and a pressure sensor 22′ at the outlet of the pressure storage device 25 for sensing the fuel pressure therein. Depending on the acquired data, the control unit 21 controls the pressure in the pressure line 8 by adjusting the variable throttle 26. For controlling the formation of the fuel/air mixture, the control unit 21 is connected by control lines 35 to the injectors 2 and adapts, by a suitable variation of the injection parameters, particularly the injection time, the measured actual values of the pressure conditions to form an optimal mixture. For adapting the fuel injection times of the injectors 2, the control unit utilizes stored data of a flow performance graph. For adjusting the pressure level in the pressure line 8, in place of a variably adjustable throttle 26, a controllable fuel pump 4 may be provided which is controllable by the control unit 21.
b shows an alternative embodiment of a fuel supply arrangement 1 with a pressure storage device 25 which can be connected for increasing the fuel injection pressure level, wherein, for controlling the pressure level in the pressure line 8, two pressure controllers 11, 12 are arranged in parallel branches of the pressure line 8. The line branch, in which the pressure controller 11 for the low pressure level is arranged, includes a magnetic valve 10 for closing this branch during operation at an increased operating pressure, whereby fuel flows through the bypass line 17 and the pressure controller 12 arranged therein for supplying the fuel to the injectors 2 at the increased pressure level. The branch supplying the fuel at lower pressure during normal operation is secured by a check valve 16′.
In the embodiments with pressure storage devices, which are particularly advantageous with regard to construction expenditures, the pressure storage device 25 is so selected that, taking into consideration the fuel volume, the increased pressure level is available during the whole startup phase of the internal combustion engine. The pressure storage device is provided with a pressure sensor 22 or a pressure switch by way of which the engine can also be started at the lower pressure level if this should become necessary. During operation of the internal combustion engine, a switchover between two pressure levels for the fuel injection pressure is possible; the programming of transition functions during switchover between the pressure levels in the control unit of the internal combustion engines is not necessary.
a and 4b show fuel supply arrangements 1 with serially arranged fuel pumps 4, 5 and a second pressure generating unit parallel to the fuel pump 43, which includes a fuel pump 4′ for the lower pressure level. The second pressure generating unit 29 includes a pressure controller 11 for the lower normal pressure of the fuel injection, the relieved fuel of which is returned to the tank 3 via a return line 14. The pump arrangement with the low pressure pump 4 and the serially arranged downstream high pressure fuel pump 5 is provided with a pressure controller 12 for the higher fuel pressure level of the high pressure fuel pump 5. Downstream of the pressure controller 12, a relief line 13 is connected to the pressure line 8 so that it can be opened by a magnetic valve 10. The relief line 13 may lead to the pressure-free return line 15 to the fuel tank 3 or, as shown in
b shows a fuel supply arrangement with serially arranged fuel pumps 4, 5 and a second pumping unit 29 parallel to the fuel pumps 4, 5, wherein the pressure line 8 for supplying fuel to the injectors 2 includes a separate high pressure rail 30. The pump unit including the pumps 4, 5 for generating the high fuel pressure can be rapidly connected to the other arrangement components by rapid switches 31.
In the fuel supply arrangement as shown in
The arrangements for providing controllably a higher fuel injection pressure level permits an operation with increased fuel pressure during startup and warmup operation of the engine without detrimentally affecting normal engine operation. It also permits multiple injections for improving exhaust gas emissions. With the use of pressure storage devices, the ideal fuel pressure can be provided instantly upon startup of the engine that is already with the first ignition as high pressure fuel is instantly available. The increase of the fuel pressure level—when needed—by a switchable arrangement may also be utilized in the high load ranges of the internal combustion engine in order to supply sufficient fuel to the engine by providing an increased injection pressure during higher fuel requirements. The embodiment of the fuel supply arrangement with parallel pressure generating units also offers the possibility to operate the engine with different types of fuel.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 009 792.5 | Feb 2004 | DE | national |
