Patent Application
20060193736
The invention is based on a fuel injection apparatus for an internal combustion engine as generically defined by the preamble to claim 1.
A fuel injection apparatus of this kind is known from WO 01/40656 A. This fuel injection apparatus has a high-pressure pump that delivers fuel into a reservoir from which fuel is drawn for injection into the engine. In addition, a fuel-supply pump is provided, which supplies fuel to the high-pressure pump from a fuel tank. The high-pressure pump has a housing and at least one pump element that is driven by a drive unit disposed in an internal chamber of the housing. The pump element has a pump piston, which is set into a stroke motion by the drive unit and delimits a pump working chamber. During an intake stroke of the pump piston, it draws fuel into the pump working chamber via an inlet and during a delivery stroke of the pump piston, it displaces fuel from the pump working chamber via an outlet. The pump piston moves into the internal chamber of the housing during its intake stroke and moves out from the internal chamber during its delivery stroke. The fuel-supply pump can be electrically or mechanically driven. In order to be able to generate a sufficiently high pressure, the fuel-supply pump requires a high-output, correspondingly costly drive unit. Alternatively, it is also possible for a fuel-supply pump with a low-output electric drive unit to be combined with an additional fuel-supply pump with a mechanical drive unit, but this is also costly.
The fuel injection apparatus according to the invention, with the characterizing features of claim 1, has the advantage over the prior art that the high-pressure pump simultaneously constitutes a fuel-supply pump that delivers the fuel that is to be taken in during its intake strokes. The fuel-supply pump that delivers fuel from the fuel tank to the internal chamber of the housing of the high-pressure pump can therefore be embodied with a low output and therefore be inexpensively designed.
Advantageous embodiments and modifications of the fuel injection apparatus according to the invention are disclosed in the dependent claims. The embodiment according to claim 2 permits a continuous operation of the fuel-supply pump by allowing fuel that it delivers while the check valve is closed to flow out into the discharge region. The embodiment according to claim 6 permits a delivery quantity that is greater than the required intake quantity of the pump element and consequently also an overflow quantity that can be used to lubricate and cool the drive unit in the internal chamber of the housing.
An exemplary embodiment of the invention is shown in the drawings and will be explained in detail in the subsequent description.
A fuel-supply pump 22 supplies fuel from a fuel tank 24 to the high-pressure pump 10. The fuel-supply pump 22 preferably has an electric drive unit, but can also be mechanically driven. Between the fuel-supply pump 22 and the high-pressure pump 10, a filter 26 is provided in order to filter the fuel delivered by the high-pressure pump 10.
The high-pressure pump 10 has a housing 30 with an internal chamber 31 in which a drive shaft 32 is supported so that it can rotate around an axis 33. For example, the engine drives the drive shaft 32. Inside the internal chamber 31, the drive shaft 32 has at least one cam 34; in the exemplary embodiment shown, a dual cam is provided, which has two cam protrusions disposed diametrically opposite from each other. The high-pressure pump 10 has at least one pump element 36 disposed in the housing 30; in the exemplary embodiment shown, two pump elements 36 are provided, which are disposed diametrically opposite from each other. Each pump element 36 has a pump piston 38 which is guided in a sealed fashion inside a cylinder bore 40 extending at least approximately radial to the rotation axis 33 of the drive shaft 32 and delimits a pump working chamber 42 in this cylinder bore 40 with its outward facing end surface. The cylinder bore 40 can be provided directly in the housing or in an insert piece that is inserted into the housing 30. With its end oriented radially inward, the pump piston 38 protrudes from the cylinder bore 40 and rests with a tappet 44 against the cam 34 of the drive shaft 30. The tappet 44 is guided in a sealed fashion in a bore 46 in the housing 30 and preferably has a larger diameter than the pump piston 38 in the region in which it is guided in the pump working chamber 42. The pump piston 38 has a larger diameter at its piston base 39 with which it rests against the tappet 44 than it does in its region that delimits the pump working chamber 42 and has a diameter approximately equal to that of the tappet 44. A prestressed spring 48, for example in the form of a helical compression spring, is clamped between the housing 30 and the piston base 39 and holds the pump piston 38 and, via its piston base 39, the tappet 44 in contact with the cam 34 of the drive shaft 32. A cylindrical roller 50 that rolls against the cam 34 is inserted into the end of the tappet 44 oriented toward the cam 34. The part of the tappet 44 that is oriented away from the pump piston 38 and protrudes from the bore 46 delimits the internal chamber 31 of the housing 30. The tappet 44 can also be omitted; in this case, the piston base 38 of the pump piston 38, which can, for example, have a roller 50 integrated into it, rests directly against the cam 34.
The fuel delivered by the fuel-supply pump 22 is supplied via a line 23 to the internal chamber 31 of the housing 30 of the high-pressure pump 10. The line 23 contains a check valve 52 that opens toward the internal chamber 31, thus preventing fuel from flowing out of the internal chamber 31 and to the fuel-supply pump 22. Between the fuel-supply pump 22 and the check valve 52, a line 54 leads from the line 23 to a discharge region that can, for example, be a return 55 to the fuel tank 24. From the internal chamber 31 of the housing 30 of the high-pressure pump 10, a line 56 leads to a discharge region that can once again be the return 55 to the fuel tank 24. The line 56 contains a discharge valve 58 that only opens the connection to the return 55 when a predetermined pressure is exceeded in the internal chamber 31 and keeps the connection to the return 55 closed when the pressure is low.
The pump working chambers 42 of the pump elements 36 are each fed by an inlet 60 that contains a check valve 62, which opens into the pump working chamber 42 and serves as an inlet valve. In addition, an outlet 64 leading from the pump working chamber 42 feeds into the reservoir 12 and contains a check valve 66, which opens away from the pump working chamber 42 and toward the reservoir 12 and functions as an outlet valve. The inlet 60 of each of the pump working chambers 42 of the pump elements 36 is connected to the internal chamber 31 of the housing 30 of the high-pressure pump 10. The pump pistons 38 of the pump elements 36 deliver synchronously with one another, i.e. they execute their respective delivery strokes and intake strokes at the same time as each other. When the pump pistons 38 execute their intake strokes, then the springs 48 cause them to move radially inward in accordance with the profile of the cam 34 against which the tappets 44 rest with their rollers 50, and the tappets 44 move out from the bore 46 and into the internal chamber 31. As a result, the volume of the internal chamber 31 is reduced so that the pressure in the internal chamber 31 increases; the check valve 52 prevents fuel from being displaced into the return 55. During the intake stroke of the pump pistons 38, a lower pressure prevails in the pump working chambers 42 than in the internal chamber 31 so that when the inlet valves 62 are open, fuel is displaced from the internal chamber 31 and is fed into the pump working chambers 42. During the delivery stroke of the pump pistons 38, the inlet valves 62 close and the outlet valves 66 open when a predetermined pressure is exceeded so that fuel is fed through the outlet 64 into the reservoir 12.
During the delivery stroke of the pump pistons 38, they are actuated by the cams 34 and move radially outward counter to the force of the springs 48 and the tappets 44 move into the bores 46 so that the volume of the internal chamber 31 increases. The check valve 52 opens as a result and fuel delivered by the fuel-supply pump 22 flows into the internal chamber 31 and fills it up. The fuel-supply pump 22 continuously delivers fuel and, when the check valve 52 is closed, fuel supplied by the fuel-supply pump 22 flows into the return 55 via the line 54.
Since the tappets 44 have a larger diameter than the pump pistons 38 in their regions delimiting the respective pump working chambers 42, they displace more fuel from the internal chamber 31 during the intake stroke of the pump pistons 38 than the pump pistons 38 draw into the pump working chambers 42. When the discharge valve 58 is open, the excess fuel flows into the return 55 via the line 56. This achieves a constant emptying and refilling of the internal chamber 31 with fuel and consequently provides a good lubrication and cooling of the drive unit of the high-pressure pump 10, particularly of the drive shaft 32, as well as the tappets 44 and the rollers 50 traveling on the cam 34. The fuel-supply pump 22 therefore only requires a relatively low pressure in order to be able to fill the internal chamber 31 with fuel. During the intake stroke of the pump pistons 38, they generate a relatively high pressure in the internal chamber 31, which permits a sufficient, rapid filling of the pump working chambers 42. It is also possible for the tappets 44 to have approximately the same diameter as the pump pistons 38 in their region that delimits the pump working chambers 42 so that the tappets 44 deliver a correspondingly lower fuel quantity.
| Number | Date | Country | Kind |
|---|---|---|---|
| 103-07-877.0 | Feb 2003 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DE03/03394 | 10/13/2003 | WO | 8/24/2005 |
