DE102020105771A1 - WATER PUMP BEARING UNIT WITH BARRIER FLUID LUBRICANT AND WATER PUMP EQUIPPED WITH IT - Google Patents

Abstract

A water pump bearing unit with a sealing arrangement is proposed which includes a filling of a barrier fluid lubricant to prevent steam leakage. The water pump bearing unit (1) with sealing arrangement (2) is particularly characterized in that the water pump bearing unit (1) has a filling with a barrier fluid lubricant (22) for sealing and lubrication; wherein the filling of the barrier fluid lubricant (22) has a bearing gap (10) of the plain bearing bushing (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.

Description

The present invention relates to a water pump bearing unit with a sealing arrangement that includes a filling of a barrier fluid lubricant to prevent steam leakage, and 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 coolant leakage 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 lead to the breakdown of the lubricating film due to the typically high contact pressure in rolling elements. 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 structure of a pump housing, a leakage chamber is arranged between a shaft seal on a pump chamber and a shaft bearing located behind it. 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 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 reason for this is that leakage droplets 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 a need for long-lasting sealing solutions between a pump chamber and a drive, particularly for pump structures of compact design, such as coolant pumps in the automotive sector. 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 pumped 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 by a belt water pump is known, in which a shaft connected to a pump impeller via a Sintered plain bearing is stored. 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 10 2018 104 015 A1 by the same applicant describes a storage 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 entering moisture. More precisely, a non-critical moisture balance is achieved under the operating conditions. 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 not yet published on the filing date of this patent application DE 10 2018 123 901.7 by the same applicant 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 not yet published on the filing date of this patent application DE 10 2019 126 968.7 the same applicant relates to a shaft bearing with a sealing arrangement against steam leaks which 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 a temperature-dependent volume fluctuation of 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 water pumps, which is not lubricated by a pumped medium, but rather carries a separate lubricant that serves as a barrier fluid for separating steam leaks in the bearing gap and in the free spaces of the water pump bearing unit.

In contrast to rolling bearings or ball bearings, which always require a seal to protect the rolling elements, the previously published state of the art only uses plain bearings in water pumps that 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 properties, 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 film of lubricant, 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 deviating from the standard provided, which relates to frost protection and, in particular, also to a lubricating property affects 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 leakage 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 into the water pump bearing unit as water vapor in gaseous form 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, moisture ingress occurs on electronic components and an electric motor, which the invention is intended to prevent.

In the case of a cooling circuit for an internal combustion engine, a cooling water can assume an operating temperature of up to 110 ° C. in accordance with standards in automobile construction, and under special load cases it can even be higher for a short time. 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 suitable as a barrier fluid, 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 an evaporation temperature which 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 evaporation point of the aqueous leakage, also above the operating temperatures.

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, together with the at least one free space and the shaft seals, is 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 driving 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, i. 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 matter 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 conveying medium, the more effectively the separation and containment of the steam leakage in the free space takes place. If the barrier fluid lubricant has a higher density than water, a condensed vapor leak will be forced and confined in an upper portion of the clearance. 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. In addition, 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 than the barrier fluid lubricant. A corresponding 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 within the water pump bearing unit caused by a rise in temperature. An internal pressure or a pressure difference between the filling of the barrier fluid lubricant and an outside can thus 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 regulating 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 becoming almost incompressible, or the enclosed gas from escaping into the lubricant and being present in an uncontrolled manner in the lubricant depot.

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. In the idle state, a pressure difference of 1 bar with respect to the internal pressure to atmospheric pressure, that is to say to approximately 2 bar, can preferably be set.

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 manufactured from 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 lubricating 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 as well as a service life of the lubrication for the bearings 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. Thus becomes one Pressure difference between the wet side and the dry side counteracted.

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 are more efficient due to the smaller air gap between rotor and stator and the omission of a containment shell in between. 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.

• 1 einen Querschnitt durch einen Aufbau mit einem Wasserpumpenlager und einer Dichtungsanordnung nach einem Konzept aus dem Stand der Technik; und
• 2 einen Querschnitt von einer Wasserpumpenlagereinheit mit Dichtungsanordnung gemäß einer Ausführungsform der Erfindung.

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

• 1 a cross section through a structure with a water pump bearing and a sealing arrangement according to a concept from the prior art; and
• 2 a cross section of a water pump bearing unit with sealing arrangement according to an embodiment of the invention.

1 shows a concept known from the prior art of a pump structure for a water pump bearing with rolling elements and a sealing arrangement. For sealing the shaft bearing and a drive side located behind it, the concept known from the prior art is shown in FIG 1 three seals and a structural measure in the form of a leakage chamber in a pump housing. 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 from exposing an electric motor behind it to moisture. This measure for sealing a shaft against leakage requires a considerable amount of installation space.

The following is an embodiment of the water pump bearing unit according to the invention 1 with sealing arrangement 2 described.

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

The water pump bearing unit 1 is of the sintered plain bearing type and has a plain bearing bush 11 as well as a wave 3 on. The plain bearing bush 11 is made of a porous sintered metal alloy. An internal sliding surface 13th the plain bearing bush 11 is in sliding contact with a peripheral surface 31 the rotating shaft 3 and takes radial forces from the shaft 3 between a pump impeller and the electric motor. For the sliding contact between the sliding surface 13th and the peripheral surface 31 is a radial bearing gap 10 of less than 21 µm, preferably 3.5 to 15 µm. A sliding property between the shaft 3 and the plain bearing bush 11 is also achieved by filling a barrier fluid lubricant as described below 22nd supports.

The water pump bearing unit 1 with sealing arrangement 2 is designed to the shaft 3 to be sealed in such a way that even at higher operating temperatures in the pump chamber on the wet side 4th , no steam leakage through the water pump bearing unit 1 axially through into a cavity for the electric motor on the dry side 5 entry. The water pump bearing unit is used for this 1 with a sealing arrangement 2 fitted. The sealing arrangement 2 includes a shaft seal on the wet side 24 and a dry-side shaft seal 25th also a volume of fat 20th , a free space 21 , a sealing filling of the barrier fluid lubricant 22nd as well as a volume compensator 23 .

The wet-side shaft seal 24 is a radial shaft seal that forms one side of the plain bearing bush 11 in the bearing housing section of the pump housing 6th to the wave 3 concludes. The wet-side shaft seal 24 has an outer collar to the pump housing 6th and an inner sealing lip on the peripheral surface 31 the wave 3 each on the wet side 4th , so point outwards. Also the shaft seal on the dry side 25th is a radial shaft seal that forms one side of the plain bearing bush 11 in the bearing housing section of the pump housing 6th to the wave 3 concludes. The dry side shaft seal 25th has an outer collar to the pump housing 6th and an inner sealing lip on the peripheral surface 31 the wave 3 each on the wet side 4th , so point inwards. The two shaft seals 24 , 25th 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 fat can optionally be added 20th are used 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 is limited or included.

Between the plain bearing bush 11 and the dry side shaft seal 25th there is a gap, which is a free space 21 for taking up a volume of the filling of the barrier fluid lubricant 22nd provides. The free space 21 serves to separate and contain steam leaks as well as to connect the barrier fluid lubricant 22nd on 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 who is also in the free space 21 is arranged.

The free space 21 , the bearing gap 10 , a reservoir 12th and any other remaining free interior space of the water pump bearing unit 1 , which is located in the axial direction between the wet-side shaft seal 24 and the dry side shaft seal 25th is located by a volume of the filling of the barrier fluid lubricant 22nd taken.

The filling of the barrier fluid lubricant 22nd offsets the plain bearing bush 11 in a lubrication bath, with rotation and loading of the shaft 3 a hydrodynamic lubricating film is created. The hydrodynamic lubricating film forms under surface pressure between the circumferential surface 31 the wave 3 and the sliding surface 13th the plain bearing bush 11 the end. The hydrodynamic lubricating film creates a cycle that runs through the bearing gap 10 axially outwards, 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 leads. Thus, with the small bearing play, the shaft has good sliding friction properties 3 achieved. The circuit also lubricates the sealing lips of the two shaft seals 24 , 25th .

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

The filling of the barrier fluid lubricant 22nd 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 torque is set.

In the free space 21 is a volume compensator 23 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 ring-shaped.

During operation, the filling of the barrier fluid lubricant heats up 22nd . This is accompanied by an increase in volume or a rise in pressure in the filling of the barrier fluid lubricant 22nd in the water pump bearing unit 1 . Due to an internal pressure, an excess part of the expanded filling of the barrier fluid lubricant could 22nd under the wet-side shaft seal 24 step out. A lack of volume of the previously leaked barrier fluid lubricant could in turn cause a negative pressure during cooling, through which a leakage of the pumped medium under the wet-side shaft seal 24 or ambient air from the air-side shaft seal 25th into the water pump bearing unit 1 entry.

The volume compensator 23 Compensates with its compressibility a temperature-dependent volume change in the filling of the barrier fluid lubricant 22nd and limits a corresponding fluctuation in internal pressure in the water pump bearing unit 1 . A viscoelastic compressibility of the material is preferably set in such a way that the temperature-dependent internal pressure in the water pump bearing unit 1 is at least greater than a temperature-dependent vapor pressure of the delivery medium in operation. A pressure difference between the higher internal pressure in the water pump bearing unit 1 opposite the wet side 4th is preferably set to up to 2.6 bar for a steam leak-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 achieved by the wet-side shaft seal 24 and dry-side shaft seal 25th be included in the long term.

By compensating for an increase in volume, leakage of the barrier fluid lubricant or long-term loss of the same is prevented. On the other hand, there is a positive pressure difference between the filling of the barrier fluid lubricant 22nd in the water pump bearing unit 1 and the wet side 4th is applied, it occurs when the wet-side shaft sealing lip is properly designed 24 to prevent leakage of the pumped medium into the water pump bearing unit 1 . In addition, the pressure leads to the filling of the barrier fluid lubricant 22nd in the water pump bearing unit 1 for an optimized supply of lubricant to the sealing lips of both shaft seals 24 and 25th , which run almost wear-free.

In an axially central area of the plain bearing bush 11 can also have one in the sliding surface 13th radially recessed reservoir 12th be trained. The reservoir 12th is on both sides of the plain bearing bush 11 by axial sections of the sliding surface 13th limited. The optional reservoir 12th stands with the bearing gap in both axial directions 10 in connection and enlarges one in the water pump bearing unit 1 the volume of the filling of the barrier fluid lubricant that can be provided 22nd .

The sealing arrangement 2 the water pump bearing unit 1 puts together through the shaft seals 24 , 25th , the fat volume 20th and the filling of the barrier fluid lubricant 22nd that with the volume compensator 23 and the space 21 cooperates, a cascade of several sealing stages, which offers an effective protection against axial penetration of steam leaks even at higher operating temperatures above the evaporation point of a water-based pumping medium.

List of reference symbols

1

Water pump bearing unit

2

Sealing arrangement

3

wave

4th

wet side

5

dry side

6th

Pump housing

10

Bearing gap

11

Plain bearing bush

12th

reservoir

13th

Sliding surface

20th

Fat volume

21

free space

22nd

Filling of a barrier fluid lubricant

23

Volume compensator

24

wet side shaft seal

25th

shaft seal on the dry side

31

Circumferential surface

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 19639928 A1 [0009]
• DE 102018104015 A1 [0011]
• DE 102018123901 [0012]
• DE 102019126968 [0013]

Claims (18)

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. 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. Water pump bearing unit (1) with sealing arrangement (2) according to Claim 1 or 2 , wherein the barrier fluid lubricant (22) is a perfluoropolyether or PFPE. 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). 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 designed as an annular chamber open to the bearing gap (10) and has a radial extension which corresponds to that of the plain bearing bush (11). Water pump bearing unit (1) with sealing arrangement (2) according to one of the preceding claims, a volume of grease (20) being accommodated in the water pump bearing unit (1) between the plain bearing bush (11) and a sealing lip of the wet-side shaft seal (24). Water pump bearing unit (1) with sealing arrangement (2) according to one of the preceding claims, wherein a volume compensator (23) is provided to compensate for a temperature-dependent volume fluctuation of the filling of the barrier fluid lubricant (22), which comprises an enclosed gas volume. Water pump bearing unit (1) with sealing arrangement (2) according to one of the Claims 1 until 6th wherein a volume compensator (23) for compensating for a temperature-dependent volume fluctuation of the filling of the barrier fluid lubricant (22) is provided, which comprises a material with a viscoelastic compressibility. Water 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. Water pump bearing unit (1) with sealing arrangement (2) according to one of the Claims 7 until 9 , wherein the volume compensator (23) is annular, and in which at least one free space (21) is arranged. Water pump bearing unit (1) with sealing arrangement (2) according to one of the Claims 7 until 10 , wherein the volume compensator (23) is elastically biased so that an internal pressure is higher than an external pressure on the wet side (4) and on the dry side (5). 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-pored structure through which the barrier fluid lubricant (22) can circulate. Water 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. Water pump bearing unit (1) with sealing arrangement (2) according to one of the preceding claims, wherein a reservoir (12) is provided for increasing the filling of the barrier fluid lubricant (22), which in relation to the sliding surface (13) in the sliding bearing bushing (11) is trained. Water 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), to the wet side (4). 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 the Claims 1 until 15th ; set up for mounting and sealing a shaft (3) in a housing (6) between a pump impeller and an electric motor. Water pump after 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). Water pump after Claim 16 or 17th wherein a sliding surface for the axial mounting of the shaft (3) is provided on the housing (6), against which a face of a free end of the shaft (3) runs.

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