Gear pump with cover and bearing on both sides

Abstract

A gear pump, in particular for pumping liquid fuel in a fuel-operated heating appliance, comprises a pumping chamber (22) in a pump housing (20), a housing cover (40) which at least partially closes off the pumping chamber (22), a pumping gear (24) rotatable in the pumping chamber (22) about an axis of rotation (D), a drive shaft (26) coupled to the pumping gear (24) for common rotation about the axis of rotation (D), a first bearing unit (28) for supporting the drive shaft (26) on a first axial side of the pumping gear (24) and a second bearing unit (44) for supporting the drive shaft (26) on a second axial side of the pumping gear (24).

Description

[0001] The present invention relates to a gear pump according to the preamble of claim 1, which can be used, for example, for pumping liquid fuel in a fuel-operated heating appliance. Such fuel-operated heating appliances can be used in stationary applications, for example, as building heating systems, or can be used, for example, as auxiliary heaters or parking heaters in vehicles, for example, to heat the air to be introduced into a vehicle interior.

[0002] A gear pump of this type, known from US 2013 / 0052058 A1, according to the preamble of claim 1, has two conveying gears arranged meshing in a conveying chamber. To drive the two conveying gears to rotate and thereby convey liquid medium present in the conveying chamber, one of these conveying gears is supported on a drive shaft which can be driven to rotate by an electric motor. The drive shaft, arranged in a pump housing which also provides the conveying chamber, is rotatably mounted axially between the drive and the conveying gear coupled to it for common rotation relative to the pump housing by means of a ball bearing. On an axial side of the conveying gear coupled to the drive shaft for common rotation, facing away from the drive, the drive shaft is supported by means of a plain bearing on a housing cover fixed to the pump housing and closing off the conveying chamber.

[0003] From US patent 2006 / 0292025 A1, a gear pump is known in which a drive shaft, coupled to a conveying gear for common rotation and capable of driving a drive, is rotatably mounted on a ball bearing on an axial side of the drive facing away from the conveying gear. On an axial side of the conveying gear, coupled to the drive shaft for common rotation and facing away from the drive, the drive shaft is rotatably mounted on a housing cover by means of a ball bearing.

[0004] From CN201593500U a gear pump is known which, although it has bearings and seals on both sides, has a different basic design with regard to the arrangement of the drive and the housing cover.

[0005] The object of the present invention is to design such a gear pump in such a way that excessive wear, particularly in the area of ​​a conveying gear mounted on a drive shaft, is avoided when pumping non-lubricating media, such as non-lubricating fuels. According to the invention, this object is achieved by a gear pump according to claim 1, in particular for pumping liquid fuel in a fuel-operated heating appliance, comprising: a conveying chamber in a pump housing, a housing cover that at least partially closes off the conveying chamber, a conveying gear rotatable about an axis of rotation in the conveying chamber, a drive shaft coupled to the conveying gear for common rotation about the axis of rotation and driven by a drive to rotate about the axis of rotation, a first bearing unit for supporting the drive shaft on a first axial side of the conveying gear in an area axially between the drive and the conveying gear; a second bearing unit for supporting the drive shaft on a second axial side of the conveying gear with respect to the housing cover.

[0006] The second bearing unit comprises a second rolling element bearing. To shield this rolling element bearing from the liquid medium being conveyed, the second bearing unit includes a second shaft seal, for example a shaft seal ring, axially positioned between the second rolling element bearing and the conveying gear, providing a fluid-tight connection between the drive shaft and the housing cover.

[0007] By supporting the drive shaft on both axial sides of the conveying gear coupled to it for common rotation, transverse loads on the drive shaft, induced by the comparatively high pressure of the conveyed liquid medium during operation, can be avoided. These loads could cause the conveying gear to come into contact with the walls of the pump housing that define the conveying chamber when moving perpendicular to the axis of rotation. Excessive wear of the conveying gear, particularly in the area of ​​its teeth, can thus be prevented.

[0008] The drive shaft can be supported by means of the first bearing unit relative to the pump housing.

[0009] To achieve the simplest and most cost-effective design possible, the drive shaft can be cantilevered between the first and second bearing units. By supporting the drive gear axially at only two bearing points on both sides, reliable support of the drive shaft, and thus also of the conveyor gear, against lateral movement is ensured.

[0010] To avoid such lateral deflection movements in the area of ​​the conveyor gear, it is particularly advantageous if the axial distance of the second bearing unit from the conveyor gear is smaller than the axial distance of the first bearing unit from the conveyor gear.

[0011] To ensure a long service life, it is proposed that the first bearing unit include a first rolling element bearing. For example, the first rolling element bearing could be a ball bearing.

[0012] To shield this rolling element bearing from the liquid medium to be conveyed, it is proposed that the first bearing unit axially between the first rolling element bearing and the conveying gear includes a first shaft seal, for example a shaft seal ring, which provides a fluid-tight connection of the drive shaft to the pump housing.

[0013] The second bearing unit can, for example, include a ball bearing.

[0014] The invention further relates to a fuel-operated vehicle heater comprising a burner section supplied with combustion air by means of a blower and with liquid fuel by means of a gear pump constructed according to the invention. The burner section preferably has a atomizing burner in which a mixture of fuel and combustion air is generated by injecting fuel via an atomizing nozzle.

[0015] The present invention is described in detail below with reference to the accompanying figures. These show: Fig. 1 a partial sectional view of a gear pump not constructed according to the principles of the present invention; Fig. 2 one of the Fig. 1 corresponding view of a gear pump according to the invention; Fig. 3 A schematic representation of a fuel-powered vehicle heater.

[0016] Before proceeding with reference to the Fig. 1 and 2 The detailed description of the construction of a gear pump is made with reference to the Fig. 3 The basic structure of a fuel-operated vehicle heater, generally designated as 10, is explained, in which such a gear pump 12 can be used to pump liquid fuel as a liquid medium.

[0017] The vehicle heater 10 comprises a burner section 14 and a heat exchanger section 16. Combustion air L is supplied to the burner section 14 by means of a combustion air blower 17. Liquid fuel B is also supplied to the burner section 14 by means of the gear pump 12 and is injected through a spray nozzle to create a fuel / combustion air mixture. In a combustion chamber 18 of the burner section 14, the combustion air L is mixed with the fuel B, which has been vaporized, for example, by a porous vaporizing medium, so that a combustible mixture of combustion air L and fuel B is formed. The combustion gases A produced during combustion flow into the heat exchanger section 16 before being expelled to the environment. In the heat exchanger section 16, the heat transported in the combustion gas A is transferred to a medium M to be heated.The medium M to be heated can, for example, be the air introduced into a vehicle interior. However, the medium M can also be a liquid, such as the liquid coolant present in the coolant circuit of a vehicle's internal combustion engine.

[0018] The in Fig. 1 The gear pump 12, which is not constructed according to the principles of the present invention, comprises a pump housing generally designated 20. A conveying gear 24, designed as a spur gear, is arranged on one side of the pump housing in a conveying chamber generally designated 22. The conveying gear 24 is rigidly supported on a drive shaft 26 extending substantially within the pump housing 20, such that the drive shaft 26 and the conveying gear 24 rotate together about an axis of rotation D when the drive shaft 26 is driven by a Fig. 2 a drive not shown, for example an electric motor, is set in rotation.

[0019] In Fig. 1 Not visible is another conveying gear, which, like the conveying gear 24, is arranged in the conveying chamber 22 and lies laterally next to the conveying gear 24 with respect to the axis of rotation D, such that it meshes with the conveying gear 24. When the conveying gear 24 rotates about the axis of rotation D, this gear is also engaged. Fig. 1 An unseen further conveying gear is driven to rotate, thereby displacing a liquid medium to be conveyed from the conveying chamber 22 and thus ejecting it in the direction of a system area to be fed, for example the combustion chamber 18.

[0020] In an extension area located inside the pump housing 20, the drive shaft 26 is supported by a first bearing unit 28. The first bearing unit 28 is arranged in a radially extended area 30 of a shaft opening 32 of the pump housing 20, which accommodates the drive shaft 26. The first bearing unit 28 comprises a first rolling element bearing 34, for example designed as a ball bearing, which rotatably supports the drive shaft 26 radially with respect to the pump housing 20. In order to shield this first rolling element bearing 34 from the medium to be pumped and, in particular, to prevent the medium to be pumped from escaping through the shaft opening 32, the first bearing unit 28 includes a shaft seal 36, for example designed as a shaft seal ring, axially between the pump gear 24 and the first rolling element bearing 34.This is located both on the outer circumference of the drive shaft 26 and on the inner circumference of the radially extended area 30 of the shaft opening 32, thus creating a liquid-tight connection of the drive shaft 26, which is rotatable about the axis of rotation D, to the pump housing 20.

[0021] A housing cover 40 is arranged on an end face 38 of the pump housing 20, to which the pumping chamber 22 is also generally open, and is firmly connected to the pump housing 20 in such a way that the pumping chamber 22 is closed off in the direction of the axis of rotation D by the housing cover 40.

[0022] The drive shaft 26 extends axially beyond the conveyor gear 24 into a recess 42 formed in the housing cover 40. In this recess 42, the drive shaft 26 is rotatably mounted relative to the housing cover 42 by means of a second bearing unit 44. In the Fig. 1 In the illustrated embodiment, the second bearing unit 44 comprises a plain bearing bushing 46. The plain bearing bushing 46 is constructed of a material particularly suitable for use in non-lubricating or dry-running environments. For example, the plain bearing bushing 46 can be constructed or coated with a polymer material, at least in its surface area that radially supports the drive shaft 26. The use of composite materials, at least in the surface area that radially supports the drive shaft 26, is also possible. Such composite materials can, for example, comprise a carrier body or a carrier layer in which solid lubricant particles are embedded. Such a carrier material can be, for example, lead or copper, and the solid lubricant particles embedded in this carrier material can be made of PTFE material.Such plain bearing bushings, particularly suitable for use with gear pumps, are marketed, for example, by GGB Heilbronn GmbH under the brand name DU-Buchse. These plain bearing bushings consist of a steel base body. A porous sintered bronze interlayer is applied to this steel base body, and this interlayer is covered on its bearing surface with a running surface mixture of PTFE and lead.

[0023] By supporting the drive shaft 26 on both axial sides of the conveyor gear 24, and especially by positioning the second bearing unit 44 axially much closer to the conveyor gear 24 than the first bearing unit 28, lateral displacement of the drive shaft 26, and thus of the conveyor gear 24, in the axial area where the conveyor gear 24 is supported on the drive shaft 26 is essentially completely eliminated. The risk of the conveyor gear 24 shifting in its radially outer and in Fig. 1 The possibility of the gear tooth striking a wall of the pump housing 20, which defines the conveying chamber 24, within the area enclosed by line I, and thus causing excessive wear of the conveying gear 24, can be ruled out. This makes the gear pump 12 particularly suitable for use with non-lubricating media or fuels, such as kerosene, gasoline, or the like. Therefore, the addition of lubricating additives is unnecessary. Because the drive shaft 26 is supported on both axial sides of the conveying gear 24 by the two bearing units 28, 44, additional bearing measures, such as another bearing unit between the first bearing unit 28 and the conveying gear 24, or another bearing unit between the first bearing unit 28 and the drive (not shown in the figures), are unnecessary.

[0024] One embodiment of such a gear pump 12 according to the invention, particularly for use in conjunction with non-lubricating media to be pumped, is described in Fig. 2 depicted. In the Fig. 2 In the illustrated embodiment, the second bearing unit 44 is constructed with a second rolling element bearing 48, by which the drive shaft 26 is radially supported on the housing cover 40. A second shaft seal 50, for example again in the form of a shaft seal ring, is arranged axially between the second rolling element bearing 48, which is again designed as a ball bearing, and the conveying gear 24, in order to shield the second rolling element bearing 48 from the medium to be conveyed.

[0025] In this design, lateral deflection movements of the conveyor gear 24 are essentially completely excluded, so that excessive wear of the conveyor gear 24, especially in the area of ​​its radially outer teeth, can be ruled out.

[0026] With the gear pump constructed according to the invention, the service life of such a gear pump can be significantly increased, particularly when it is used, for example, in a fuel-operated vehicle heater in conjunction with non-lubricating or poorly lubricating fuels to pump them into a combustion chamber, due to the avoidance of unlubricated contact between a conveying gear carried on a drive shaft and a wall surrounding a conveying chamber, without requiring comparatively complex structural measures or the introduction of a radial gap between the teeth of a conveying gear and a wall of a pump housing surrounding the conveying chamber, which would impair the conveying efficiency.

Claims

1. A gear pump, in particular for conveying liquid fuel in a fuel-operated heating apparatus, comprising: - a conveying chamber (22) in a pump housing (20), - a housing cover (40) which closes the conveying chamber (22) at least in regions, - a conveying gear wheel (24) which in the conveying chamber (22) is rotatable about a rotation axis (D), - a drive shaft (26) which for co-rotation about the rotation axis (D) is coupled to the conveying gear wheel (24), and which can be driven by a drive for rotation about the rotation axis (D), - a first bearing unit (28) for mounting the drive shaft (26) on a first axial side of the conveying gear wheel (24) in a region axially between the drive and the conveying gear wheel (24), - a second bearing unit (44) for mounting the drive shaft (26) on a second axial side of the conveying gear wheel (24) in relation to the housing cover (40), characterized in that the second bearing unit (44) comprises a second rolling-element bearing (48), and in that the second bearing unit (44), axially between the second rolling-element bearing (48) and the conveying gear wheel (24), comprises a second shaft seal (50) providing a fluid-tight connection between the drive shaft (26) and the housing cover (40).

2. The gear pump as claimed in claim 1, characterized in that the drive shaft (26) by means of the first bearing unit (28) is mounted relative to the pump housing (20).

3. The gear pump as claimed in claim 1 or 2, characterized in that the drive shaft (26) is self-supporting between the first bearing unit (28) and the second bearing unit (44).

4. The gear pump as claimed in one of claims 1 to 3, characterized in that an axial spacing of the second bearing unit (44) from the conveying gear wheel (24) is smaller than an axial spacing of the first bearing unit (28) from the conveying gear wheel (24).

5. The gear pump as claimed in one of claims 1 to 4, characterized in that the first bearing unit (28) comprises a first rolling-element bearing (34).

6. The gear pump as claimed in claim 5, characterized in that the first rolling-element bearing (34) comprises a ball bearing.

7. The gear pump as claimed in claim 5 or 6, if referring back to claim 2, characterized in that the first bearing unit (28), axially between the first rolling-element bearing (34) and the conveying gear wheel (24), comprises a first shaft seal (36) providing a fluid-tight connection between the drive shaft (26) and the pump housing (20).

8. The gear pump as claimed in one of claims 1 to 7, characterized in that the second rolling-element bearing (48) comprises a ball bearing.

9. A fuel-operated vehicle heating apparatus, comprising a burner region (14) which is to be supplied with combustion air (L) by means of a fan (17), and with liquid fuel by means of a gear pump (12) as claimed in one of claims 1 to 8.

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