Pump

Abstract

The invention relates to a pump having a pump casing, in which a pump chamber is formed, having an inlet leading to it and an outlet leading away from it. In the pump chamber there is a pump impeller, which is secured to a drive shaft, which can be driven in rotation and is mounted rotatably in bearings in the pump casing. Surfaces of the pump chamber which bear against the surfaces of the pump impeller and surfaces of the pump impeller which bear against the surfaces of the pump chamber have a coating of low thickness and high hardness which is applied by physical vapor deposition.

Description

CLAIM FOR PRIORITY

[0001] This application claims priority to Application No. 10201405.1 which was filed in the German language on Jan. 15, 2002.

TECHNICAL FIELD OF THE INVENTION

[0002] The invention relates to a pump, and in particular, to a fuel pump.

BACKGROUND OF THE INVENTION

[0003] For pumps which deliver aggressive liquids, such as fuels, it is known to provide the inner parts of the pumps with a layer of anodized metal to protect against corrosion.

[0004] Currently, fuels increasingly include contaminants, which lead to wear between the parts of the pumps which move relative to one another and damage the layer of anodized metal. Fuels contaminated by water or substances which undergo similar chemical reactions and a very wide range of additives in the fuels can then lead to further damage to the pump parts.

[0005] In the case of pump components made from aluminum, fuels with a high alcohol content lead to oxidation and therefore to blooming and ultimately to the pump impeller becoming blocked. A blockage of this type may also result from the contamination.

[0006] However, very small gaps are required between the moving and stationary pump parts, so that it is possible to build up sufficient pressure, in particular, in the case of a pump which is constructed as a flow pump.

[0007] Further drawbacks of the layer of anodized metal are the high cost of this layer, its environmental incompatibility and its considerable thickness of approximately 30 &mgr;m, which leads to wide tolerances. These wide tolerances in turn do not allow a satisfactory build-up of pressure in the pump.

[0008] To mount and guide the drive shaft, bearings, for example in the form of carbon bushes, are arranged in bearing bores in the pump casing. This involves a high level of outlay in terms of assembly and components.

SUMMARY OF THE INVENTION

[0009] The invention relates to a pump, in particular a fuel pump, having a pump casing, in which a pump chamber is formed, which has an inlet leading to it and an outlet leading away from it, having a pump impeller which is arranged in the pump chamber and is secured to a drive shaft, which can be driven in rotation and is mounted rotatably in bearings in the pump casing.

[0010] The invention provides a pump of the type described in the introduction which is of simple structure and low-wear design and permanently ensures a high build-up of pressure.

[0011] According to one embodiment of the invention, surfaces of the pump chamber which bear against surfaces of the pump impeller and/or surfaces of the pump impeller which bear against surfaces of the pump chamber have a coating of low thickness and high hardness which is applied by physical vapor deposition.

[0012] The thin coating can be applied with an exactly uniform thickness and thereby makes it possible to maintain low tolerances, so that a good build-up of pressure in the pump is ensured.

[0013] The fact that the coating is built up with a uniform layer growth of dense structure and smooth surface also contributes to this, and furthermore leads to good protection against corrosion and allows the pump to be used for a very wide range of fuel grades and other delivery media.

[0014] The high hardness protects the coating from wear and ensures that the pump has a long service life. This hardness may preferably lie in a range from 2500 HV to 3500 HV (Vickers hardness), but may also lie above or below this range.

[0015] Since low process temperatures are required to produce the coating, there is no distortion of the coated components or changes in the material, for example the microstructure, at these components.

[0016] Since, furthermore, the coating can be applied to a very wide range of materials, it is in each case possible to use the optimum materials and material pairings for pump casing and pump impeller.

[0017] The layer is applied in a manner which does not pollute the environment.

[0018] In another embodiment, the drive shaft is mounted rotatably in bearing bores in the pump casing, the bearing bores and/or the drive shaft having a coating of low thickness and high hardness which is applied by physical vapor deposition.

[0019] In addition to the features of pump casing and pump impeller, the very hard and smooth surface of the coating of bearing bore and/or drive shaft and the tight tolerances means that these parts will transfer the positive properties of a carbon bush as a bearing directly to the simple bearing bore. In this way, it is possible to eliminate separate bearings and the machining of these bearings. If the pump is a flow pump, the tight tolerances of the components which are inevitably required in flow pumps in order to build up pressure and therefore the small gaps between the components which move relative to one another can be minimized.

[0020] This is advantageous in particular if the flow pump is a peripheral impeller or side channel pump.

[0021] Over and above those surfaces of pump impeller and pump chamber which bear against one another, it is also possible for the entire surface of the pump chamber to be provided with a coating which is applied by physical vapor deposition, with the surfaces of the fuel-carrying parts of the pump preferably also being provided with a coating which is applied by physical vapor deposition. As a result, it is possible for the pump to deliver even aggressive media without any damage.

[0022] The fact that the coating has a thickness of approximately 2 &mgr;m to approximately 5 &mgr;m makes it possible to ensure that the tight production tolerances are met. A layer thickness of 2 &mgr;m is entirely sufficient to protect against wear, while 5 &mgr;m is preferred if the layer is to protect against corrosion.

[0023] Particularly when the pump is used as a fuel pump, the coating is preferably a chromium nitride layer.

[0024] The pump casing and/or pump impeller may include metal or a metal alloy, in particular of aluminum or aluminum alloy, which are made wear-resistant and corrosion-resistant by the coating but are still easy to produce and lightweight.

[0025] In one alternative, the pump casing and/or pump impeller includes a plastic, in particular a phenolic resin. Parts of this type, which can easily be produced as injection moldings and have a low weight, are also made wear-resistant and able to withstand aggressive delivery media by the coating.

[0026] A particularly favorable material pairing consists in the pump casing including coated aluminum and the pump impeller including phenolic resin. The pump impeller consisting of phenolic resin may be coated or uncoated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] An exemplary embodiment of the invention is illustrated in the drawing and is described in more detail below.

[0028] FIG. 1 shows a fuel pump with flow pumps as pump stages.

DETAILED DESCRIPTION OF THE INVENTION

[0029] The pump illustrated in FIG. 1 is a two-stage fuel pump. An electric motor arranged in the closed motor casing 1 illustrated can be used to drive a drive shaft 2 in rotation, a first pump impeller 3 of a peripheral impeller pump 14 being arranged in a rotationally fixed manner on the right-hand end region of this drive shaft 2. The radially encircling region of the first pump impeller 3 is formed with a first ring of vanes, which is largely surrounded by an annular passage. A first pump chamber 5 is formed as a pot-shaped recess 31 in one end side of a cover 6 which is part of the pump casing 7.

[0030] In the pump cover 7 there is an inlet 8, via which the peripheral impeller pump can suck in fuel. Furthermore, a ball 9 is arranged centrally in a receptacle on the side of the first pump impeller 3 in the cover 6, against which ball the drive shaft 2 is supported at the end side and which ball forms an axial bearing of the drive shaft 2.

[0031] The first pump chamber 5 is closed off by a partition 10 which bears against the opening in the pot-shaped recess 31 in the cover 6 and through which the drive shaft is guided. The drive shaft 2 is guided through a bearing bore 11 in the partition 10, which likewise forms a part of the pump casing 7, and is rotatably mounted directly in this bearing bore 11.

[0032] In a plane which cannot be seen, the first pump chamber 5 is connected to a radially encircling annular passage 12 on that side in the partition 10 which faces the peripheral impeller pump 14, a connection 13 leading from this annular passage 12 to that side of the partition 10 which is remote from the peripheral impeller pump 14 and opening out into a first side passage 15, which is formed in the shape of a ring at that location, of a side channel pump 16.

[0033] On the side of the first side channel 15, the partition 10 is likewise designed with a pot-shaped recess 17, which forms a second pump chamber and in which a second pump impeller 18 of the side channel pump 16 is arranged, this second pump impeller likewise being seated in a rotationally fixed manner on the drive shaft 2.

[0034] In one of its side faces, the second pump impeller 18 has a second ring of vanes 19 which is aligned with the first side channel 16 and is connected, via axial apertures 20, to a third ring of vanes 21 on the other side face of the pump impeller 18.

[0035] The third ring of vanes 21 is covered by an annular second side channel 22, which is formed in a partition 23, closes off the pot-shaped opening 14, forms part of the pump casing 7 and is guided through a drive shaft 2.

[0036] The partition 23 separates the side channel pump 16 from the motor casing 1, the outlet 24 formed in the partition 23 opening out into the motor casing 1. The fuel which is delivered flows through the motor casing 1 and is fed via a nonreturn valve 25 to a pressure port 26 of the fuel pump, which are arranged in a closure wall 29. A plug contact 30 for supplying power to the electric motor is likewise located in the closure wall 29.

[0037] A bearing wall 27, which has a second bearing bore 28 coaxially with respect to the first bearing bore 11, is arranged in the end region of the motor casing 1 on the side of the pressure port 27, in which second bearing bore 28 the left-hand end of the drive shaft 2 is directly rotatably mounted.

[0038] The two pump impellers 3 and 18 comprise phenolic resin. The parts of the pump casing 7 are formed from aluminum. In all the regions which face the partition 10 and in the inlet 8, the cover 6 has a coating of chromium nitride. The partition 10, the separating wall 23 and the bearing wall 27 are completely provided with a coating of chromium nitride. Furthermore, the surfaces of the closure wall 29 and of the pressure port 26 around which the fuel washes are coated with chromium nitride.

[0039] The cylindrical inner walls of the first and second bearing bores 11 and 28 are also coated. In addition, the drive shaft 2 consisting of steel has a chromium nitride coating in its regions located in the bearing bores 11 and 28.

[0040] These chromium nitride coatings have been applied by physical vapor deposition and have a thickness of 5 &mgr;m and a Vickers Hardness of approximately 2500 HV.

LIST OF REFERENCE SYMBOLS FOR DRAWING FIGURE

[0041] 1 Motor casing

[0042] 2 Drive shaft

[0043] 3 First pump impeller

[0044] 4 Ring of vanes

[0045] 5 First pump chamber

[0046] 6 Cover

[0047] 7 Pump casing

[0048] 8 Inlet

[0049] 9 Ball

[0050] 10 Partition

[0051] 11 First bearing bore

[0052] 12 Annular passage

[0053] 13 Connection

[0054] 14 Peripheral impeller pump

[0055] 15 First side channel

[0056] 16 Side channel pump

[0057] 17 Pot-shaped recess

[0058] 18 Second pump impeller

[0059] 19 Second ring of vanes

[0060] 20 Axial apertures

[0061] 21 Third ring of vanes

[0062] 22 Second side channel

[0063] 23 Separating wall

[0064] 24 Outlet

[0065] 25 Nonreturn valve

[0066] 26 Pressure port

[0067] 27 Bearing wall

[0068] 28 Second bearing bore

[0069] 29 Closure wall

[0070] 30 Plug contact

[0071] 31 Pot-shaped recess

Claims

1. A pump, comprising:

a pump casing, in which a pump chamber is formed, which has an inlet leading to the casing and an outlet leading away from the casing; and

a pump impeller which is arranged in the pump chamber and is secured to a drive shaft, which can be driven in rotation and is mounted rotatably in bearings in the pump casing, wherein

surfaces of the pump chamber which bear against surfaces of the pump impeller and/or surfaces of the pump impeller which bear against surfaces of the pump chamber have a coating of low thickness and high hardness which is applied by physical vapor deposition.

2. The pump according to claim 1, wherein the drive shaft is mounted rotatably in bearing bores in the pump casing, the bearing bores and/or the drive shaft having a coating of low thickness and high hardness which is applied by physical vapor deposition.

3. The pump according to claim 1, wherein the pump is a flow pump.

4. The pump according to claim 3, wherein the flow pump is a peripheral impeller or side channel pump.

5. The pump according to claim 1, wherein the surface of the pump chamber is provided with a coating which is applied by physical vapor deposition.

6. The pump according to claim 1, wherein the surfaces of the fuel-carrying parts of the pump are provided with a coating which is applied by physical vapor deposition.

7. The pump according to claim 1, wherein the coating has a thickness of approximately 2 &mgr;m to approximately 5 &mgr;m.

8. The pump according to claim 1, wherein the coating is a chromium nitride layer.

9. The pump according to claim 1, wherein the pump casing and/or pump impeller comprises metal or a metal alloy.

10. The pump according to claim 1, wherein the pump casing and/or pump impeller comprises a plastic.

11. The pump according to claim 1, wherein the pump is a fuel pump.