ELECTRIC GEAR PUMP

The present invention relates to an electric gear pump. In particular the present invention relates to an electric gear pump of the gerotor type.

Furthermore, the present invention relates to a pump assembly comprising in series:

- a low-pressure pump (the aforementioned electric gear pump of the gerotor type), for drawing fuel, preferably diesel fuel, and for a first compression thereof; and

- a high-pressure pump, preferably of the pumping piston type, for a further compression of the fuel and for feeding the high-pressure fuel to an internal combustion engine.

Nowadays it is known to use systems for feeding fuel, in particular diesel fuel, to an internal combustion engine comprising a high-pressure pump, for feeding the internal combustion engine, and a low-pressure pump for feeding fuel to the high- pressure pump. The high-pressure pump comprises at least one pumping piston moved by a shaft and housed inside a cylinder fed with low-pressure fuel. At present there exist at least two different types of low-pressure pump for these systems.

The first type comprises a gear pump driven by the same shaft for driving the pistons of the high-pressure pump. In particular, this gear pump may be a "gerotor" pump. As is known, the gerotor pump comprises an externally toothed rotor rotated by the shaft and housed inside an internally toothed rotor. During rotation, the teeth of the externally toothed rotor engage with the teeth of the internally toothed rotor which has one more tooth than the externally toothed rotor. The two rotors, which rotate both in an absolute sense and relatively or one with respect to the other one, pump fuel from an inlet, which is connected to the tank, towards an outlet, which is connected to the high-pressure pump.

The second type of gear pump comprises gear pumps which are not driven by the shaft driving the pumping pistons, but pumps driven electrically or electromagnetically. According to this type of pump, at present in gerotor pumps at least one of the internally toothed rotor and the externally toothed rotor supports magnetic modules, such as stacks of iron laminations, which interact electromagnetically with a stator arranged on the outside of the internally toothed rotor and comprising electrical windings. When current is supplied to these windings electromagnetic conditions are created such that the gerotor starts to rotate performing the desired pumping action between the tank and the high- pressure pump.

In this type of gerotor electric gear pump, the stator provided with electrical windings, which may also be defined "electric motor" since it induces the movement of the gerotor, is situated on the same level as the gerotor in order to increase the electromagnetic interaction. This concentric arrangement of gerotor and stator today requires the presence of a bearing arranged between the outer wall of the internally toothed rotor of the gerotor and the stator. Since metallic materials present between stator and gerotor could result in the loss of efficiency in the electromagnetic interaction, at present the aforementioned bearing is made of plastic material, for example peek (polyethylene ether ketone). The steps for assembly of this peek bearing involve firstly mounting it by means of interference, or at least by means of superficial force-fitting, inside the stator, and then machining it to ensure correct rotational supporting of the gerotor. In this coupled arrangement, therefore, the external surface of the internally toothed rotor is a moving surface which is displaced with respect to the bearing fixed to the stator. Owing to this moving surface connection the magnets associated with the gerotor cannot be mounted on the outer surface of the internally toothed rotor, but must be housed inside seats formed inside this rotor, for example seats formed during production of the component by means of sintering.

The aforementioned type of gerotor electric gear pumps, namely with a plastic bearing mounted on the stator and magnets embedded in the rotor, has a number of drawbacks.

A first drawback consists in the fact that the operations for assembling the bearing on the stator and the subsequent surface-machining operation once the bearing has been assembled are very complex and costly.

A second drawback consists in the fact that the steps for forming the seats for the magnets in the rotor close to the moving surface and for fixing the magnets in their seats are very complex and costly.

Based on this known technology one object of the present invention is to provide an alternative gear pump, preferably an alternative gerotor electric gear pump. In particular, it is an object of the present invention to provide a gerotor electric gear pump which is able to overcome the drawbacks of the prior art mentioned above in a simple and low-cost manner from both a functional and a constructional point of view.

In accordance with these objects the present invention relates to an electric gear pump comprising:

- a gerotor comprising an externally toothed rotor rotatable about an axis of rotation A and an internally toothed rotor arranged on the outside of the externally toothed rotor;

- a stator provided with electrical windings;

- a shaft arranged along the axis of rotation A and connected to the externally toothed rotor;

- at least one magnet or ferromagnetic structure configured so as to cause the shaft to rotate when the electrical windings of the stator are supplied with current. Advantageously in this way there is no longer the need for complex or costly machining in order to form the seats for the magnet or the ferromagnetic structure in the rotors of the gerotor and the subsequent operations for fixing the magnets in these seats. In fact the rotation of the gerotor according to the invention is performed by causing rotation not of the rotors, but of the shaft, which rotationally drives the gerotor, in particular the externally toothed rotor, in cascade.

According to a preferred embodiment of the invention, the electric gear pump further comprises a cup-shaped structure associated with the shaft and forming a seat for housing the gerotor. According to this example, advantageously, the ferromagnetic structure or the magnet may be joined externally to the cup-shaped structure without interference during production of the gerotor.

Preferably, the cup-shaped structure comprises a base and a side wall. According to this example, the ferromagnetic structure or the magnet is joined to the outer surface of the side wall of the cup-shaped structure. Advantageously, in this way the ferromagnetic structure or the magnet is situated directly facing the windings of the stator, making the electromagnetic interaction more efficient. Preferably, the cup-shaped structure is formed as one piece with the shaft. Advantageously, in this way the transfer of the movement from the side wall of the cup-shaped structure, which is stressed by the rotating magnet, to the shaft, occurs more efficiently.

Preferably, the electric gear pump further comprises a first bearing arranged between the gerotor, namely the outer surface of the internally toothed rotor, and the inner surface of the side wall of the cup-shaped structure. In particular, this first bearing may be made of metallic material since it is not arranged between the magnet associated with the cup-shaped structure and the winding of the stator. Owing to this arrangement, the aforementioned first bearing may be made in an extremely more simple and low-cost manner compared to the plastic bearings used in the electric gear pumps known nowadays.

Preferably, the electric gear pump further comprises a seal arranged between the shaft and a portion of the first bearing situated underneath the gerotor. Advantageously, in this way the seeping of the fuel along the shaft underneath the gerotor is avoided.

In particular, the electric gear pump comprises a support base and a closing cover which comprises channels for feeding and delivery of the fuel relative to the gerotor. According to this example, the first bearing is connected to the cover preferably by means of screws. Advantageously, in this way the positioning of the first bearing is performed by means of a very simple and rapid procedure.

Preferably, the electric gear pump comprises a second bearing housed in the support base for the shaft. Advantageously, in this way the rotation of the shaft is guided stably along the axis A of the gerotor.

Finally, the present invention also relates to a pump assembly for feeding fuel from a tank to an internal combustion engine. This pump assembly comprises:

- a low-pressure electric gear pump;

- a high-pressure pump;

- a low-pressure intake duct for feeding the fuel from the tank to the electric gear pump;

- a low-pressure delivery duct for feeding the fuel from the electric gear pump to the high-pressure pump; - at least one high-pressure delivery duct for feeding the fuel from the high- pressure pump to the internal combustion engine;

wherein the electric gear pump is designed according to any one of the embodiments described above.

Further characteristic features and advantages of the present invention will become clear from the description below of a non-limiting example of embodiment thereof, with reference to the figures of the attached drawings, in which:

- Figure 1 is a schematic view of an example of a pump assembly for feeding fuel, preferably diesel fuel, from a tank to an internal combustion engine, in which a low-pressure gear pump and a high-pressure pumping piston pump are arranged in series;

- Figure 2 shows a schematic view of a gerotor low-pressure gear pump;

- Figure 3 shows a cross-sectional view of an example of embodiment of a gerotor low-pressure electric gear pump according to the present invention.

Figure 1 is a schematic view of an example of a pump assembly for feeding fuel, preferably diesel fuel, from a tank to an internal combustion engine, in which a low-pressure pump and a high-pressure pump are arranged in series. In particular, Figure 1 shows a pump assembly 1 comprising:

- a low-pressure electric gear pump 4;

- a high-pressure pump 5;

- a low-pressure intake duct 6 for feeding the fuel from the tank 2 to the electric gear pump 4;

- a low-pressure delivery duct 7 for feeding the fuel from the electric gear pump 4 to the high-pressure pump 5;

- high-pressure delivery ducts 8 for feeding the fuel from the high-pressure pump 5 to the internal combustion engine 3.

In this example the internal combustion engine 3 is shown only in schematic form and comprises a common header 17 fed by the high-pressure delivery ducts 8 and a plurality of injectors 18 configured to atomize and inject the high-pressure fuel into the cylinders of the internal combustion engine 3 (not shown). In Figure 1 the high-pressure pump 5 is shown only in schematic form and comprises two pumping pistons 11 fed with the low-pressure fuel at feed valves 12 and connected to delivery valves 13 for feeding the high-pressure fuel to the engine 3. Figure 1 further shows a filter 10 arranged downstream of the low-pressure pump 4, a fuel metering device 14 downstream of the filter 10, an overflow valve 15 between the filter 10 and the fuel metering device 14, a pressure limiting valve 26 connected to the header 17 and a delivery valve 27 connected to the tank 2. The arrows shown in Figure 1 indicate the flow path of the fuel within the pump assembly 1.

Figure 2 shows an enlarged detail of the low-pressure pump 4, in particular a gerotor gear pump 9. As can be seen in Figure 2, this gerotor 9 comprises an internally toothed rotor 20 inside which an externally toothed rotor 21 is housed. In a known manner the gerotor 9 comprises an inlet 22, connected to the low- pressure feed duct 6, and an outlet 23 connected to the high-pressure delivery duct 7. Figure 2 shows in schematic form the chambers inside the gerotor 9 for performing feeding, at the inlet 22, and delivery, at the outlet 23. The mode of operation of a gerotor electric gear pump is known and involves rotational driving of the gerotor relative to a stator as a result of the electromagnet interaction between these parts. In Figure 2, for greater clarity, the stator with the electrical windings arranged on the outside of the gerotor 9 and the magnets associated with the same gerotor 9 have not been shown.

Figure 3 shows a preferred embodiment of an electric gear pump 4 according to the invention.

In accordance with this example, the electric gear pump 4 comprises:

- a gerotor 9 comprising an externally toothed rotor 21 rotatable about an axis of rotation A and an internally toothed rotor 22 arranged on the outside of the externally toothed rotor 21;

- a stator 29 provided with electrical windings 30 and arranged on the outside of and on the same level as the gerotor 9.

In particular, the externally toothed rotor 21 is keyed onto, or rigidly coupled together with, a rotational shaft 32 which, rotating about its axis, causes rotation of the externally toothed rotor 21 along the axis A thus driving the gerotor 9.

During its rotation, the gerotor 9 in a known manner compresses the fuel fed from the feed duct 6 and discharges the compressed fuel along a delivery duct 7. In the example shown in Figure 3, these ducts, i.e. feed duct 6 and delivery duct 7, are formed in a cover 27 which, when fastened to an associated base 28, serves to contain the gerotor 9 and the stator 29. According to the embodiment shown in Figure 3, the shaft 32 is formed as one piece with a cup-shaped structure 37 which is open towards the cover 27 and comprises a base 38 and a side wall 39. This cup-shaped structure 37 forms a housing for the gerotor 9. In particular, the outer surface of the side wall 39 of the cup-shaped structure 37 supports a magnetic structure 31 directly facing the windings 30 of the stator 29. The outer surface of the side wall 39 instead faces a first bearing 34, or radial bearing, which supports the rotation of the internally toothed rotor 22. As can be seen, this first bearing 34 may be fixed to the cover 27 by means of simple screws 36 and may have seats for housing a seal 35 around the shaft 32. The bearing is preferably made of metallic material.

Finally it is clear that the invention described here may be subject to

modifications and variations without departing from the scope of the

accompanying claims.