WO2021175526A1

WO2021175526A1 - Water pump bearing unit having blocking fluid lubricant and water pump equipped therewith

Info

Publication number: WO2021175526A1
Application number: PCT/EP2021/052490
Authority: WO
Inventors: Franz Pawellek; Marcel BERNER
Original assignee: Nidec Gpm Gmbh
Priority date: 2020-03-04
Filing date: 2021-02-03
Publication date: 2021-09-10
Also published as: DE102020105771A1

Abstract

The invention relates to a water pump bearing unit having a seal arrangement which comprises a filling of a blocking fluid lubricant in order to prevent a vapor leakage. The water pump bearing unit (1) having a sealing arrangement (2) is characterized in particular in that a filling having a blocking fluid lubricant (22) is received in the water pump bearing unit (1) for sealing and lubricating; wherein the filling of the blocking fluid lubricant (22) occupies a bearing gap (10) of the slide bearing bush (11) and at least one free space (21), elevated radially relative to the bearing gap (10), between the wet-side shaft seal (24) and the dry-side shaft seal (25); wherein the blocking fluid lubricant (22) is hydrophobic; and a density of the blocking fluid lubricant (22) is at least 30% higher or lower than the density of water.

Description

description

Water pump bearing unit with barrier fluid lubricant and water pump equipped with it

The present invention relates to a water pump bearing unit with a sealing arrangement which includes a filling of a barrier fluid to prevent steam leakage, as well as a water pump for a coolant circuit in a vehicle, in which a corresponding water pump bearing unit is arranged.

When using shaft bearings in a water pump, the shaft bearing must be protected from the ingress of a coolant leak from the flow of the water pump. Rolling element bearings are generally sensitive to moisture penetration, since the materials used, in particular suitable steels for the rolling elements and raceways, are not sufficiently corrosion-resistant for use in moisture. The occurrence of a coolant leakage leads to a reduction in the surface quality of the rolling elements and raceways due to corrosion. In addition, even the smallest amounts of coolant in the lubricant cause the lubricating film to break through as a result of the typically high contact pressure in rolling heads. Higher friction on the rolling elements can lead to bearing damage due to the corresponding heat generation, which results in a defect in the water pump. In addition, water pumps are increasingly being driven electrically, with an electric motor of the dry-running type often being used on the drive side. Just like the shaft bearing, the electric motor must also be protected from the ingress of a coolant leak from the flow of the water pump.

In the technical field of pumps and turbomachines, structural measures are known in the prior art which serve to seal a drive shaft between a conveying medium guided in a pump chamber from a drive side. For example, in the construction of a pump housing between a shaft seal on a pump chamber and a shaft bearing located behind a leakage chamber. A slight leak, which the shaft seal on the pump chamber overcomes, is caught by the leakage chamber and evaporates through a drain at an operating temperature. This prevents the leakage from reaching the shaft bearing located behind it or from exposing an electric motor located behind it to moisture. This measure for sealing a shaft against a leakage flow requires a considerable amount of installation space. A shaft seal is per se subject to frictional wear and tear

Embrittlement due to pressure and temperature fluctuations. It often represents the limiting factor in the service life of a pump. Thus, a long-lasting liquid seal between the delivery flow in a pump chamber and the shaft bearing and the drive-side area of a pump housing behind it is of great importance with regard to the operational reliability of a vehicle.

As a rule, conventional shaft bearings, such as roller bearings, are sealed by radial sealing seals, i.e. sealing washers, which are integrated in the shaft bearing. Furthermore, separate sealing arrangements for a shaft bearing are known from the prior art, whereby an individual adaptation of the sealing property to application-specific pressures and dimensions as well as greater freedom in the selection of bearing types is made possible. In addition, the service life of shaft seals depends heavily on the

Lubrication conditions on the sealing lip. A dry-running sealing lip or a sealing lip that is only lubricated by a coolant leak has a shorter service life than sealing lips in the vicinity of a system carrying lubricating oil due to the coefficient of friction of the lack of a lubricating film or a phenomenon explained below. When sealing lips were lubricated by a coolant, the phenomenon of deposit formation under the dynamic sealing surface of the sealing lip, which had a lasting effect on the sealing function, was observed. The cause lies in that leakage drops of a coolant evaporate after passing the sealing point and leave behind crystalline components from the coolant, which form a coating on the shaft. Accordingly, there is especially for compact pump structures, such as

For coolant pumps in the automotive sector, there is a need for long-lasting sealing solutions between a pump chamber and a drive. More precisely, there is a need for a unit comprising a compact bearing, i.e. a suitable bearing for the sole bearing of the shaft, and an integrated sealing arrangement in order to combine the function of the shaft bearing and the function of the desired seal in a small installation space.

In parallel to this, water pumps with a plain bearing that is lubricated by a required coolant are known. These water pumps are driven mechanically or by a wet-running electric motor.

From the patent application DE 196 39 928 A1 a mechanically driven water pump via a belt is known, in which a shaft connected to a pump impeller is supported via a sintered plain bearing. The bearing gap is lubricated by the pumped medium.

Leakages in shaft seals are also a problem on slide bearings, especially if a moisture-sensitive assembly such as an electric motor is arranged behind the shaft bearing.

A patent application DE 102018 104 015 A1 by the same applicant describes a mounting and sealing of a water pump with a dry-running electric motor by means of a coolant-lubricated sintered bearing. The concept of this storage and sealing provides measures for the removal of an unavoidable minor coolant leakage in order to protect the electric motor and control electronics from damage caused by the ingress of moisture. To be more precise, a non-critical moisture balance is achieved under the operating conditions achieved. Removal of the leakage droplets leads to evaporation due to the rotation and waste heat of the engine, which escapes to the atmosphere via a membrane.

A patent application DE 102018 123 901.7 by the same applicant, which was not yet published on the filing date of this patent application, relates to a slide bearing with an integrated sealing arrangement for water pumps that are driven by a dry-running electric motor. In the plain bearing, a so-called solid oil is provided as a lubricant depot, which, in addition to the lubricating function, also fulfills a sealing function between a wet and a dry side.

Another patent application DE 102019 126968.7 by the same applicant, which was not yet published on the filing date of this patent application, relates to a shaft bearing with a sealing arrangement against steam leaks that can occur in the event of temperature fluctuations or pressure fluctuations between a liquid medium on the one hand and a gaseous medium on the other hand of the compact bearing. Two lubricants with different viscosities are accommodated in the shaft bearing. For this purpose, a grease chamber surrounding the circumference of the shaft is arranged on a wet side of a rotary bearing, and an oil chamber is arranged on a dry side. In addition, a volume compensator is provided to compensate for temperature-dependent volume fluctuations in the lubricants.

It is an object of the present invention to provide an alternative construction of a compact bearing with an integrated sealing arrangement which ensures a low-friction bearing of a shaft and a seal against steam leakage between a wet pump side and a dry drive side in a water pump.

The object is achieved by a water pump bearing unit with a sealing arrangement according to the features of claim 1 and by a water pump with the features according to claim 16. The water pump bearing unit with a sealing arrangement is particularly characterized in that the water pump bearing unit contains a filling with a barrier fluid lubricant for sealing and lubrication; wherein the filling of the barrier fluid lubricant occupies a bearing gap of the plain bearing bushing as well as at least one free space which rises radially towards the bearing gap between the wet-side shaft seal and the dry-side shaft seal; wherein the barrier fluid lubricant is hydrophobic; and a density of the barrier fluid lubricant is at least 30% higher or lower than the density of water. The invention provides for the first time a plain bearing suitable as a compact bearing for

Before water pumps, which is not lubricated by a pumping medium, but rather carries a separate lubricant that serves as a barrier fluid to separate steam leaks in the bearing gap and in the free spaces of the water pump bearing unit. In contrast to roller bearings or ball bearings, which always have a seal to the

Require protection of the rolling elements, in the previously published state of the art only plain bearings are used in water pumps, which are lubricated by the pumped medium. Compared to a slide bearing that is lubricated by a coolant, the inventive provision of the filling of the separate barrier fluid lubricant with specific viscosity and lubrication property, friction of the slide bearing and the shaft seals can be reduced.

A dynamic sealing surface of the shaft seal on the wet side is always wetted with a lubricating film, so that the formation of deposits on the shaft due to coolant residues is suppressed. The opposite shaft seal is also supplied on the dry side from the filling of the barrier fluid lubricant, so that the corresponding dynamic sealing surface with a lubricating film slides on the shaft. The shaft seals lubricated with lubricant achieve a considerably longer service life compared to a shaft seal lubricated with coolant. Furthermore, the coolant can contain impurities such as metallic particles, which lead to increased wear on the plain bearing. Likewise, after unprofessional maintenance, the coolant can have a composition that deviates from the standard provided and that has an effect on frost protection and, in particular, on a lubricating property on sliding surfaces. As a result of the separate provision of a lubricant according to the invention, the air-side sealing lip and the slide bearing are protected from such impairments.

In addition, according to the invention, the lubricant suitable as a barrier fluid also serves to seal against steam leaks between a wet and a dry side of the water pump bearing unit.

Steam leaks can occur in particular in the sealing gap of a shaft seal. Leakage droplets can get from the wet side on the shaft circumference under the sealing lip of the wet side shaft seal. Due to the friction at the seal contact, higher temperatures prevail in the sealing gap. In practice, a temperature difference can be around 20 ° C, for example. If a delivery flow of the water pump, such as cooling water in particular, has heated up to more than 80 ° C, leakage droplets can evaporate in the sealing gap under the wet-side shaft seal. A steam leakage created in this way first penetrates the water pump bearing unit as gaseous water vapor from the sealing gap of the wet-side shaft seal. If a temperature in the water pump bearing unit should be lower, the steam leakage condenses. When a temperature in the water pump bearing unit rises above 100 ° C, the steam leakage becomes or remains gaseous. The gaseous steam leakage can then e.g. pass axially through a bearing gap or free spaces through the water pump bearing unit and reach the drive side under the dry-side shaft seal. In this case there is an entry of moisture on electronic components and an electric motor, which is to be prevented by the invention.

In the case of a cooling circuit for an internal combustion engine, a cooling water can have an operating temperature of up to 110 ° C according to standards in automobile construction, may even be higher for a short time under special stress cases. Up to now, steam leaks at elevated operating temperatures, especially above 100 ° C, have regularly been a problem with regard to moisture entry and the service life of an electric drive for water pumps.

In its most general form, the invention provides a lubricant which is suitable as a barrier fluid and which brings about a separation of aqueous vapor or condensate in a free space in the water pump bearing unit. Such a steam leakage trapped in the free space is forced by the barrier fluid into an upper or lower section of the free space due to a density difference and is thereby kept away from the circumferential surface of the shaft. This means that steam leaks cannot escape under the sealing lip of the shaft seal on the dry side and enter moisture into electrical components on the drive side. The lubricant serving as a barrier fluid generally has a

Evaporation temperature that is higher than water and is not reached within the operating temperatures of the water pump, for example 200 ° C or higher. In addition, an increase in pressure in the water pump bearing unit shifts the

The evaporation point of the aqueous leakage is also above the operating temperature.

The invention is based on the knowledge that the barrier fluid or the lubricant must be hydrophobic in order to achieve effective separation and local binding of a vapor leak and must have a significantly different density than water. The greater the difference in density, the more effective is the separation and confinement of the vapor leak in the free space in order to prevent it from escaping under the dry-side shaft seal. A filling of such a barrier fluid lubricant is, together with the at least one free space and the shaft seals, part of the sealing arrangement of the water pump bearing unit. According to the invention, a cascade-like or multi-stage and multi-functional seal for water pumps is created in the manner described, which provides high safety reserves at increased operating temperatures of the delivery flow.

In addition to the mentioned advantage of sealing against gaseous steam leaks, a low-friction bearing and seal and a longer service life of the water pump are also achieved. As a result, a higher efficiency and operational reliability of the pump and, in particular, a lower probability of failure of a ferry operation of a vehicle can be ensured.

Furthermore, the sealing arrangement takes up little space within the water pump bearing unit according to the invention. Accordingly, the water pump bearing unit according to the invention is suitable for use as a compact bearing, d. H. as the only unit for bearing and sealing a pump shaft. In comparison to constructions with a leakage container, a construction of the housing can be simplified despite reliable sealing, and a more compact overall dimensions of a pump can be achieved by saving installation space. In addition, the water pump bearing unit according to the invention is based on a comparatively simple structure, which is reflected in the cost advantages of series production including assembly.

Advantageous further developments of the water pump bearing unit according to the invention with a sealing arrangement are the subject of the dependent claims.

According to one aspect of the invention, a density of the barrier fluid lubricant can be at least 50% higher than the density of water. The higher the difference in density between the barrier fluid lubricant and the water-based delivery medium, the more effective the separation and containment of the vapor leakage in the free space. If the barrier fluid lubricant has a higher density than water, a condensed vapor leak will be forced into an upper portion of the clearance and limited. Thus, even if the condensate begins to evaporate, the steam leakage remains locally bound in the same upper section of the free space.

According to one aspect of the invention, the barrier fluid lubricant can be a perfluoropolyether or PFPE. PFPE is a liquid fluoropolymer that has a relatively high density of 1.83 g / cm3 and suitable lubricating properties. Furthermore, PFPE is very inert because the ends of the molecular chains are occupied by carbon-fluorine bonds. This means that PFPE is not subject to normal aging due to oxidation like conventional lubricating oils or greases.

According to one aspect of the invention, the at least one free space can be arranged between the plain bearing bush and a sealing lip of the shaft seal on the dry side. With this arrangement, a trapped steam leakage can be reliably prevented from being kept away from a level of the shaft circumferential surface, i.e. from the sealing lip of the dry-side shaft seal sliding thereon.

According to one aspect of the invention, the at least one free space can be designed as an annular chamber open to the bearing gap and can have a radial extension which corresponds to that of the plain bearing bush. On the one hand, this configuration can be implemented relatively easily by spacing the corresponding shaft seal away from an axial end of the plain bearing bush in a bore of a bearing seat or in a bearing housing. On the other hand, compared to the sealing lip on the shaft circumference, a maximum radial dimension, which is provided for the bearing, is used to separate and limit the captured steam leakage.

According to one aspect of the invention, a volume of grease can be accommodated in the water pump bearing unit between the plain bearing bush and a sealing lip of the wet-side shaft seal. Likewise, the fat volume can only be kept available in a sealing area below the sealing lip. The grease generally has a higher viscosity than the water-based delivery medium of the water pump and possibly also as the barrier fluid lubricant. A corresponding one Volume of grease, in addition to the sealing lip, serves as a viscous cushion surrounding the circumference of the shaft, which effectively separates the media between the pumped medium on the wet side and the filling of the barrier fluid lubricant. On the one hand, this effect helps to prevent leakages of the pumped medium from penetrating. On the other hand, the fat volume counteracts a long-term loss of the filling of the barrier fluid lubricant to the wet side under temperature and pressure fluctuations.

According to one aspect of the invention, a volume compensator for compensating for a temperature-dependent volume fluctuation of the filling of the barrier fluid lubricant can be provided, which includes an enclosed gas volume.

The volume compensator compensates for an increase in volume of the filling of the barrier fluid lubricant inside the water pump bearing unit due to a rise in temperature. In this way, an internal pressure or a pressure difference between the filling of the barrier fluid lubricant and an outside can be set. The provision of the volume compensator counteracts a loss of barrier fluid lubricant at high operating temperatures and a possible entry of a leak from the wet side due to a lost volume of the barrier fluid lubricant during cooling. Accordingly, the total volume of the filling of the barrier fluid lubricant remains longer.

The design of the volume compensator by means of a gas cushion can be implemented, for example, by means of one or more elastically enclosed gas volumes or gas volumes, preferably a non-oxidative gas such as nitrogen.

According to one aspect of the invention, a volume compensator for compensating for a temperature-dependent volume fluctuation of the filling of the barrier fluid lubricant can be provided, which comprises a material with a viscoelastic compressibility. This alternative embodiment of the volume compensator can be implemented in a simple manner by means of one or more bodies made of a viscoelastic material, and offers a reliable and inexpensive provision of the desired function. By designing the viscoelastic behavior of the material, a pressure-dependent function of the volume compensation can be easily predetermined and optimized for the operating conditions of the application without the need for regulation and control means. In addition, the volume compensator can be integrated in a compact design.

According to one aspect of the invention, the volume compensator can be formed from a cellular rubber with a closed-cell structure. A cellular rubber, such as a foamed elastomer, comprises a plurality of entrapped gas bubbles and has a suitable viscoelastic compressibility to be compressed under thermal expansion in contact with the filling of the barrier fluid lubricant. In addition, foamed elastomers are available inexpensively in various degrees of hardness. The closed-cell structure prevents the elastomer from becoming saturated with the lubricant like a sponge and consequently from becoming almost incompressible, or the enclosed gas escaping into the lubricant and being present in the lubricant depot in an uncontrolled manner.

According to one aspect of the invention, the volume compensator can be designed in the shape of a ring and can be arranged in the at least one free space. In this embodiment, it is possible in a simple manner to establish direct, large surface contact between the volume of the filling of the barrier fluid lubricant and the volume compensator. Furthermore, a radial installation space for the volume compensator and a compensation volume of the same can be used to the maximum.

According to one aspect of the invention, the volume compensator can be elastically pretensioned so that an internal pressure is higher than an external pressure on the wet side and on the dry side. A pressure difference can preferably be achieved in the idle state from 1 bar with respect to the internal pressure to the atmospheric pressure, i.e. to about 2 bar.

According to one aspect of the invention, the volume compensator can ensure compensation for a temperature-dependent volume fluctuation of the lubricants. The volume compensator can be biased relative to the air pressure at room temperature.

According to one aspect of the invention, the plain bearing bush can be made of a porous material with an open-pore structure through which the barrier fluid lubricant can circulate. The use of a plain bearing bush saturated with a lubricant enables the use of very little running play on the shaft. A correspondingly small running clearance of such a radial slide bearing reduces a deflection of the sealing lips and a pumping effect arising therefrom between two axial sides. Furthermore, the small running play in the bearing gap to the shaft at the same time produces a sealing gap between two axial sides that is advantageous for the desired sealing effect.

The open-pore body and the surfaces of the plain bearing bushing create a circulation that supplies a hydrodynamic lubricating film in the plain bearing gap. The hydrodynamic lubricating film is created under the rotational movement and surface pressure from loads on the shaft in the sliding bearing gap. A pumping action of the hydrodynamic lubricating film on the one hand pushes the barrier fluid lubricant out of the axial ends of the plain bearing, while on the other hand it flows back radially inward through the body of the plain bearing bush via the free space and through an open-pored end face or is drawn in again radially to the hydrodynamic lubricant film will.

The circuit described also promotes transport and the deposition according to the invention of a vapor leak in the free space. According to one aspect of the invention, the plain bearing bush can be made from a porous sintered metal. A sintered metal alloy is suitable for setting a defined porosity and has sufficient strength for manufacturing the plain bearing bush.

According to one aspect of the invention, a reservoir for increasing the filling of the barrier fluid lubricant can be provided, which reservoir is formed in the plain bearing bush in relation to the sliding surface. The increase in the volume of the filling of the barrier fluid lubricant increases the service life of the mode of operation according to the invention for separating and delimiting steam leaks and a service life of the lubrication for the bearing and the seals. The design of a corresponding reservoir as a recess in the middle of the plain bearing gap enables the avoidance of a structural overdetermination of bearing points of the shaft along the plain bearing gap and simplifies assembly and dimensional accuracy.

According to one aspect of the invention, the sealing lip of the dry-side shaft seal and the sealing lip of the wet-side shaft seal, which rest on the circumferential surface of the shaft, can face the wet side. This counteracts a pressure difference between the wet side and the dry side.

According to one aspect of the invention, a water pump bearing unit with a sealing arrangement can be arranged between a pump impeller and an electric motor in a water pump. Such a pump type benefits from a compact pump structure with only one shaft bearing and a reliable seal between the pump chamber and a drive side, which is made possible by the water pump bearing unit according to the invention.

According to one aspect of the invention, the electric motor can be of the dry running type, in which both a stator and a rotor connected to the shaft are arranged on the dry side of the housing. The seal according to the invention enables moisture-sensitive assemblies, such as, in particular, an electric motor of the dry-running type or electronics. Dry runners show due to a smaller air gap between rotor and stator and the omission of an intermediate containment shell, a higher efficiency. In contrast to wet runners, dry runners can be obtained more cheaply as a standardized unit regardless of a type-specific geometry or a containment can of a pump.

According to one aspect of the invention, a sliding surface for axially mounting the shaft can be provided on the housing of the water pump, against which a face of a free end of the shaft runs. This provides a simple and inexpensive design for absorbing axial forces of the pump shaft.

The invention is described below on the basis of two exemplary embodiments with reference to the drawing. In this show:

1 shows a cross section through a structure with a water pump bearing and a sealing arrangement according to a concept from the prior art; and

Fig. 2 shows a cross section of a water pump bearing unit

Sealing arrangement according to one embodiment of the invention.

1 shows a concept of a known from the prior art

Pump structure for a water pump bearing with rolling elements and a sealing arrangement. The concept known from the prior art in FIG. 1 provides three seals and a structural measure in the form of a leakage chamber in a pump housing for sealing the shaft bearing and a drive side lying behind it. The leakage chamber is arranged between a first shaft seal to a pump chamber and a shaft bearing located behind it, which is sealed by two further shaft seals or bearing seals. A slight leak that the first shaft seal overcomes is caught by the leakage chamber and drained through a leakage hole. At operating temperature, the captured leakage can also evaporate through a ventilation hole. This prevents the leakage from reaching the shaft bearing or one behind it Electric motor is exposed to moisture. This measure for sealing a shaft against leakage requires a considerable amount of installation space.

An embodiment of the water pump bearing unit 1 according to the invention with a sealing arrangement 2 is described below.

2 shows the water pump bearing unit 1 with a sealing arrangement 2 in a bearing housing section of a pump housing 6, more precisely between a pump chamber on the left side and an electric motor on the right side of a water pump (not shown further). To the left of the water pump bearing unit 1, a wet side 4 is therefore shown, which is formed by a conveying medium guided in the pump chamber, and to the right of the water pump bearing unit 1, a dry drive side 5 is shown, on which the electric motor is accommodated.

The water pump bearing unit 1 is of the sintered plain bearing type and has a plain bearing bush 11 and a shaft 3. The plain bearing bush 11 is made of a porous sintered metal alloy. An inner sliding surface 13 of the plain bearing bush 11 is in sliding contact with a peripheral surface 31 of the rotating shaft 3 and absorbs radial forces of the shaft 3 between a pump impeller and the electric motor. For the sliding contact between the sliding surface 13 and the circumferential surface 31, a radial bearing gap 10 of less than 21 μm, preferably 3.5 to 15 μm, is set. A sliding property between the shaft 3 and the plain bearing bush 11 is further supported by a filling of a barrier fluid lubricant 22, which is described below.

The water pump bearing unit 1 with sealing arrangement 2 is designed to seal the shaft 3 in such a way that even at higher operating temperatures in the pump chamber on the wet side 4, no steam leakage through the water pump bearing unit 1 axially into a cavity for the electric motor on the dry side 5 entry. The water pump bearing unit 1 is equipped with a sealing arrangement 2 for this purpose. In addition to a wet-side shaft seal 24 and a dry-side shaft seal 25, the seal arrangement 2 also comprises a Grease volume 20, a free space 21, a sealing-effective filling of the barrier fluid lubricant 22 and a volume compensator 23.

The wet-side shaft seal 24 is a radial shaft sealing ring which closes off one side of the plain bearing bush 11 in the bearing housing section of the pump housing 6 with respect to the shaft 3. The wet-side shaft seal 24 has an outer collar facing the pump housing 6 and an inner sealing lip on the circumferential surface 31 of the shaft 3, each of which faces the wet side 4, that is to say outward. The shaft seal 25 on the dry side is also a radial shaft seal ring which closes off one side of the plain bearing bushing 11 in the bearing housing section of the pump housing 6 with respect to the shaft 3. The dry-side shaft seal 25 has an outer collar facing the pump housing 6 and an inner sealing lip on the circumferential surface 31 of the shaft 3, which likewise each point towards the wet side 4, that is to say inward. The two shaft seals 24, 25 consist, for example, of Teflon or PTFE or an elastomer such as HNBR or fluororubber FKM.

To increase the sealing effect, a locally bound volume of grease 20 can optionally be used, which is delimited or received in an annular cavity, surrounding the shaft circumference, between the sealing lip of the wet-side shaft seal 24 and the plain bearing bush 11.

Between the plain bearing bush 11 and the shaft seal 25 on the dry side there is a spacing which provides a free space 21 for receiving a volume of the filling of the barrier fluid lubricant 22. The free space 21 serves both to separate and limit steam leaks and to connect the barrier fluid lubricant 22 to an open-pored surface of the plain bearing bush 11 to supply the same for a hydrodynamic lubricating film, and also to establish contact with an annular volume compensator 23 , which is also arranged in the free space 21.

The free space 21, the bearing gap 10, a reservoir 12 and another remaining free interior space of the water pump bearing unit 1, which is located in the axial direction Direction between the wet-side shaft seal 24 and the dry-side shaft seal 25 is occupied by a volume of the filling of the barrier fluid lubricant 22. The filling of the barrier fluid lubricant 22 sets the plain bearing bush 11 in a

Lubrication bath, whereby a hydrodynamic lubricating film is created under rotation and loading of the shaft 3. The hydrodynamic lubricating film is formed under surface pressure between the circumferential surface 31 of the shaft 3 and the sliding surface 13 of the plain bearing bush 11. The hydrodynamic lubricating film causes a cycle that leads axially outward through the bearing gap 10, over the free space 21 and back again through the porous structure of the sintered metal of the plain bearing bush 11 to the lubricating film in the bearing gap 10. In this way, good sliding friction properties with respect to the shaft 3 are achieved with the small bearing play. The circuit also lubricates the sealing lips of the two shaft seals 24, 25.

A steam leakage, which can arise through friction under the wet-side shaft seal 24 and penetrate into the water pump bearing unit 1, is absorbed by the circuit in the filling of the barrier fluid lubricant 22 and transported in the direction of the free space 21. Due to a large difference in density between the heavier barrier fluid lubricant and the lighter condensate of the steam leak, this is separated from the hydrophobic barrier fluid lubricant in an upper section of the free space 21 in the sense of an air trap, or in the present case serving as a water trap. The steam leakage captured in this way cannot then reach the shaft circumference and escape under the shaft seal 25 on the dry side.

The filling of the barrier fluid lubricant 22 consists of a PFPE lubricant of high density, which is, for example, 30% to 80%, in particular 50% heavier than water, and its viscosity on a circulation through the porosity of the sintered metal of the plain bearing bush 11 and the permissible internal Frictional torques is set. In the free space 21 a volume compensator 23 is arranged, which consists of a flexible, non-sorbent material such as a foamed, closed-cell elastomer, for example a cellular rubber or a foam rubber with a closed surface. In the present embodiment, the volume compensator 23 is annular.

During operation, the filling of the barrier fluid lubricant 22 is heated. This is accompanied by an increase in volume or a pressure increase in the filling of the barrier fluid lubricant 22 in the water pump bearing unit 1. Due to an internal pressure, an excess part of the extensive filling of the barrier fluid could be - Lubricant 22 emerge from under the shaft seal 24 on the wet side. A lack of volume of the previously leaked barrier fluid lubricant could in turn cause a negative pressure during cooling, through which leakage of the pumped medium under the wet-side shaft seal 24 or ambient air from the air-side shaft seal 25 into the water pump bearing unit 1.

The volume compensator 23 compensates with its compressibility a temperature-dependent volume change in the filling of the barrier fluid lubricant 22 and limits a corresponding fluctuation in the internal pressure in the water pump bearing unit 1. Preferably, a viscoelastic compressibility of the material is set such that the temperature-dependent internal pressure in the water pump bearing unit 1 at least is greater than a temperature-dependent vapor pressure of the pumped medium during operation. A pressure difference between the higher internal pressure in the water pump bearing unit 1 compared to the wet side 4 is preferably set to up to 2.6 bar for a vapor leakage-free seal. An internal pressure difference of 1 bar in the idle state represents a good compromise between service life and maximum high operating temperature; such a range of pressure differences can be absorbed in the long term by the wet-side shaft seal 24 and dry-side shaft seal 25.

By compensating for an increase in volume, leakage of the barrier fluid or long-term loss of the same is prevented. There On the other hand, if there is a positive pressure difference between the filling of the barrier fluid lubricant 22 in the water pump bearing unit 1 and the wet side 4, if the wet-side shaft sealing lip 24 is properly designed, there is no excitation of leakages of the pumping medium into the water pump bearing unit 1 the pressure of the filling of the barrier fluid lubricant 22 in the water pump bearing unit 1 results in an optimized supply of lubricant to the sealing lips of both shaft seals 24 and 25, which run almost free of wear.

In an axially central region of the plain bearing bush 11, a reservoir 12 which is radially recessed in the sliding surface 13 can also be formed. The reservoir 12 is delimited on both sides of the plain bearing bush 11 by axial sections of the sliding surface 13. The optional reservoir 12 is connected to the bearing gap 10 in both axial directions and increases a volume of the filling of the barrier fluid lubricant 22 that can be provided in the water pump bearing unit 1.

The sealing arrangement 2 of the water pump bearing unit 1 together with the shaft seals 24, 25, the grease volume 20 and the filling of the barrier fluid lubricant 22, which interacts with the volume compensator 23 and the free space 21, represents a cascade of several sealing stages, which also at higher operating temperatures above the evaporation point of a water-based pumped medium, offers effective protection against the axial passage of steam leaks.

List of reference symbols:

1 water pump bearing unit

2 seal arrangement

3 wave

4 wet side 5 dry side

6 pump housing

10 bearing gap Plain bearing bush

reservoir

Sliding surface

Fat volume

free space

Filling of a barrier fluid lubricant Volume compensator, wet-side shaft seal, dry-side shaft seal, circumferential surface

Claims

Expectations

1. Water pump bearing unit (1) with sealing arrangement (2), set up for radial bearing and sealing of a shaft (3) between a wet side (4) and a dry side (5) in a housing (6) of a water pump, comprising: a plain bearing bush (11) with an inner sliding surface (13) for the radial mounting of a circumferential surface (31) of the shaft (3); a dry side shaft seal (25) which is arranged between the plain bearing bush (11) and the dry side (5); a wet-side shaft seal (24) which is arranged between the plain bearing bush (11) and the wet side (4); characterized in that a filling with a barrier fluid lubricant (22) for sealing and for lubrication is accommodated in the water pump bearing unit (1); wherein the filling of the barrier fluid lubricant (22) has a bearing gap (10) of the plain bearing bush (11) and at least one free space (21) which rises radially towards the bearing gap (10) between the wet-side shaft seal (24) and the dry-side shaft seal (25) ) takes; wherein the barrier fluid lubricant (22) is hydrophobic; and a density of the barrier fluid lubricant (22) is at least 30% higher or lower than the density of water.

2. Water pump bearing unit (1) with sealing arrangement (2) according to claim 1, wherein a density of the barrier fluid lubricant (22) is at least 50% higher than the density of water.

3. W ater pump bearing unit (1) with sealing arrangement (2) according to claim 1 or 2, wherein the barrier fluid S lubricant (22) is a perfluoropolyether or PFPE.

4. Water pump bearing unit (1) with sealing arrangement (2) according to one of the preceding claims, wherein the at least one free space (21) is arranged between the plain bearing bush (11) and a sealing lip of the dry-side shaft seal (25).

5. W ater pump bearing unit (1) with sealing arrangement (2) according to one of the preceding claims, wherein the at least one free space (21) is designed as an annular chamber open to the bearing gap (10) and has a radial extension that corresponds to that of the plain bearing bush (11) is equivalent to.

6. W ater pump bearing unit (1) with sealing arrangement (2) according to one of the preceding claims, wherein a grease volume (20) is received in the water pump bearing unit (1) between the plain bearing bush (11) and a sealing lip of the wet-side shaft seal (24).

7. W ater pump bearing unit (1) with sealing arrangement (2) according to one of the preceding claims, wherein a V olumenkompensator (23) to compensate for a temperature-dependent volumetric fluctuation of the filling of the barrier fluid lubricant (22) is provided, which comprises a sealed volume of gas.

8, water pump bearing unit (1) with sealing arrangement (2) according to one of claims 1 to 6, wherein a volume compensator (23) for compensating a temperature-dependent volume fluctuation of the filling of the barrier fluid lubricant (22) is provided, which is a material with a viscoelastic compressibility includes.

9. W ater pump bearing unit (1) with sealing arrangement (2) according to claim 8, wherein the volume compensator (23) is formed from a cellular rubber with a closed-cell structure.

10. W ater pump bearing unit (1) with sealing arrangement (2) according to one of claims 7 to 9, wherein the V olumenkompensator (23) is annular, and in which at least one free space (21) is arranged.

11. Water pump bearing unit (1) with sealing arrangement (2) according to one of claims 7 to 10, wherein the V olumenkompensator (23) is elastically preloaded so that an internal pressure is higher than an external pressure on the wet side (4) and on the dry side ( 5) is.

12. Water pump bearing unit (1) with sealing arrangement (2) according to one of the preceding claims, wherein the plain bearing bush (11) is made of a porous material with an open-pore structure through which the barrier fluid S lubricant (22) can circulate.

13. W ater pump bearing unit (1) with sealing arrangement (2) according to claim 12, wherein the plain bearing bush (11) is made of a porous sintered metal.

14. W ater pump bearing unit (1) with sealing arrangement (2) according to one of the preceding claims, wherein a reservoir (12) for increasing the filling of the barrier fluid S lubricant (22) is provided, which in relation to the sliding surface (13) in the Plain bearing bush (11) is formed.

15. W ater pump bearing unit (1) with sealing arrangement (2) according to one of the preceding claims, wherein the sealing lip of the dry-side shaft seal (25) and the sealing lip of the wet-side shaft seal (24), which rest on the peripheral surface (31) of the shaft (3) , point to the wet side (4).

16. A water pump for a coolant circuit in a vehicle, comprising: a water pump bearing unit (1) with a sealing arrangement (2) according to one of claims 1 to 15; set up for mounting and sealing a shaft (3) in a housing (6) between a pump impeller and an electric motor.

17. Water pump according to claim 16, wherein the electric motor is of the dry running type, in which both a stator and a rotor connected to the shaft (3) are arranged on the dry side (5) of the housing (6).

18. Water pump according to claim 16 or 17, wherein a sliding surface for the axial mounting of the shaft (3) is provided on the housing (6), against which an end face of a free end of the shaft (3) runs.