Coolant pump with application-optimized design

Abstract

Electric coolant pump for pumping coolant in a vehicle, comprising: a pump housing (1) with a pump chamber (10) in which a pump impeller (2) is rotatably mounted, an inlet (16) and an outlet (17) which are connected to the pump chamber (10); a shaft (4) which is rotatably mounted on the pump housing (1) and on which the pump impeller (2) is fixed; a radial support of the shaft (4) is provided by means of a coolant-lubricated radial sliding bearing (41) which is arranged between the pump impeller (2) and a rotor (32); a dry-running electric motor (3) with a radially inner stator (31) and a radially outer rotor (32) is accommodated in a motor chamber (13) separated from the pump chamber (10); a shaft seal (5) is arranged between the radial sliding bearing (41) and the motor chamber (13); the rotor (32) is designed in a bell shape, the inner surface of which faces the shaft seal (5) and is fixed axially overlapping with it on the shaft (4); characterized by the fact that the motor chamber (13) has an opening to the atmosphere which is closed by a liquid-tight and vapor-permeable pressure equalization membrane (6), wherein an axial sliding bearing (42) is formed by a free end of the shaft (4) and a running surface on the pump housing (1).

Description

[0001] The present invention relates to a coolant pump whose design is optimized for the application area of ​​an auxiliary water pump in terms of cost, installation space and service life by a combination of a bearing, seal and electric motor.

[0002] Such electric auxiliary water pumps are used to circulate sub-areas of a coolant-carrying thermal management system of a vehicle equipped with a combustion engine and a main water pump. This allows for more flexible cooling of so-called hot spots on components of auxiliary systems, such as exhaust gas recirculation, a turbocharger, an intercooler, or similar systems. Due to the redundancy to the main water pump and the increased number of lines and nodes, this type of auxiliary water pump is subject to significant price pressure and high demands for a compact design with small dimensions for integration into the complex packaging of modern thermal management systems.

[0003] In established electric auxiliary water pump products, internal rotor wet-running electric motors are used, partly due to the simpler sealing in the relatively small pump design. The use of wet-running electric motors, in which the stator is typically dry-encapsulated from the rotor by a can or similar, and the rotor and bearings are designed for operation in the pumped medium, represents a well-known measure for addressing the problems of shaft seal leakage and shaft bearing failure.

[0004] However, wet-running pumps are less efficient because the gap between the stator and the rotor is larger to accommodate a can, thus weakening the field strength acting on the rotor. In addition, fluid friction occurs at the rotor, which further reduces efficiency, especially in the relatively small pump drives of auxiliary water pumps. Furthermore, wet-running pumps are prone to problems at low temperatures, such as ice formation in the gap between the stator and the rotor.

[0005] For larger pumps, such as electric main water pumps, dry-running electric motors are also used due to their higher efficiency. Rolling element bearings, such as ball bearings, are predominantly used for the support of pump shafts driven by dry-running electric motors. These bearings absorb both axial and radial loads and achieve low friction values.

[0006] However, rolling element bearings are generally sensitive to moisture penetration because the materials used, especially suitable rolling element steels, are not sufficiently corrosion-resistant for use in humid conditions. The ingress of moisture leads to corrosion, reducing the surface quality of the rolling elements and raceways, resulting in increased friction in the bearing and corresponding heat generation and further consequential damage to bearings and seals. As a result, the already costly rolling element bearings in pumps must be fitted with even more costly seals on both ends to ensure low-friction and reliable sealing against the operating pressures occurring in the pump chamber.

[0007] In addition to the cost disadvantage, corresponding seals always cause a small amount of leakage and often represent the limiting factor in the service life of a pump, as they are inherently subject to frictional wear and embrittlement due to pressure and temperature fluctuations.

[0008] Patent application DE 10 2015 114 783 B3 by the same applicant discloses an electric coolant pump designed for use as a main water pump, in which the pump shaft is supported by a single so-called water pump bearing with two rows of rolling elements between the pump impeller and the electric motor. To counteract the problem of leakage entering the bearing and the electronic components behind it of a dry-running electric motor, a leakage chamber is provided in the pump housing between a shaft seal and the water pump bearing, in which leakage can be collected and discharged without coming into contact with the water pump bearing. A leakage seal located behind it, in turn, prevents any collected, discharged leakage from entering a housing section in which the motor components and electronics are housed.If a leak from the leakage chamber were to reach the housing section of the engine directly, the operating temperature of the engine would cause water vapor from the housing section to penetrate in the opposite direction on the unsealed, unprotected side of the water pump bearing into the bearing and permanently destroy it.

[0009] The provision of such a leakage space between the pump chamber and the drive entails the disadvantage of additional installation space, which increases the axial dimension of the pump structure.

[0010] Furthermore, the use and installation of the shaft seal and leak seal are associated with costs that would not be acceptable for auxiliary water pump products. To minimize the risk of damage to the water pump bearing due to water vapor penetration, the use and installation of an additional bearing seal on the unprotected side of the water pump bearing would be necessary.

[0011] A circulation pump for heating systems is also known from patent application WO 2015 / 011268 A1, which is driven by a wet-running electric motor. The pump shaft is supported by a radial plain bearing and a thrust bearing arranged behind it with a shaft seal. The plain bearing is lubricated with the pumped medium through a supply line within the pump shaft. A rotor chamber located axially behind it is separated from a stator receiving chamber by a diaphragm with a static sealing function.

[0012] The problem of leakage at the shaft seal is not addressed in the disclosure. However, a critical case is mentioned as a loop through the diaphragm, which leads to fluid ingress into the electrical section of the housing, and which should be prevented by a filter in the lubrication supply.

[0013] A generic coolant pump is known from the document DE 100 12 662 B4.

[0014] It is known from WO 2015 / 121 052 A1 that in coolant pumps with external rotor motors the motor chamber has an opening to the atmosphere, which is closed by a liquid-tight and vapor-permeable pressure compensation membrane.

[0015] Based on the problems of the discussed prior art, one object of the invention is to create a simple, cost-effective and compact pump structure for a dry-running electric motor.

[0016] A further aspect of the invention is to provide a pump structure in which a leakage space between a shaft seal and the dry-running electric motor can be eliminated in favor of a shorter axial structure of the pump.

[0017] Another aspect of the invention is to provide a cost-effective and durable alternative with regard to the bearing and sealing of a shaft.

[0018] The objects are achieved according to the invention by an electric coolant pump according to claim 1.

[0019] The electric coolant pump is characterized in particular in that a radial bearing of the shaft is provided by means of a coolant-lubricated radial plain bearing which is arranged between the pump impeller and a rotor of a dry-running electric motor; the electric motor with a radially inner stator and a radially outer rotor is accommodated in a motor chamber separated from the pump chamber; a shaft seal is arranged between the radial plain bearing and the motor chamber; the rotor is designed in a bell shape, the inner surface of which faces the shaft seal and is fixed on the shaft in an axially overlapping manner; and the motor chamber has an opening to the atmosphere which is closed by a liquid-tight and vapor-permeable pressure compensation membrane.Furthermore, an axial bearing of the shaft (4) is provided by an axial plain bearing (42) which is formed by a free end of the shaft (4) and a contact surface on the pump housing (1).

[0020] The invention in its most general form is based on the knowledge that through the inventive selection, combination and arrangement of the individual components of the pump, a complementary chain of effects consisting of a pressure reduction to limit a leakage at a shaft seal, an optimal evaporation of a leakage and a removal of an evaporated leakage is achieved by utilizing operating conditions in the pump, which also provides the advantages of a constructive and economic nature corresponding to the tasks.

[0021] The invention, for the first time, provides a pressure-reduced area for a shaft seal in front of a pumped medium for a dry-running electric motor. This reduced-pressure area is formed axially behind a plain bearing lubricated by the pumped medium. Due to the lower pressure of the pumped medium compared to a corresponding sealing surface within the pump chamber, leakage at the shaft seal is reduced.

[0022] Furthermore, the invention provides for the first time the use of a dry-running electric motor of the external rotor type with a rotor bell behind the shaft seal, the preferably closed inner surface of which faces the shaft seal. Thus, liquid droplets from a leak behind the shaft seal are forced through the air gap of the dry rotor between the open field coils of the stator and the magnetic poles of the rotor by radial acceleration on the inner surface of the rotor bell before they can reach a motor chamber containing electronics. The leakage droplets are evaporated by the operating temperature of the electric motor and by turbulent swirling in the air gap. The resulting water vapor only then enters the motor chamber and escapes through a membrane into the atmosphere. This eliminates the need for encapsulation of the stator and the associated disadvantages in terms of efficiency of a wet-running electric motor.

[0023] Furthermore, the use of a dry rotor provides an alternative to the use of cost-intensive rolling element bearings and their sealing on both sides.

[0024] As a result, the disadvantage of a limited service life of each bearing seal, which is always present even with complex seal types, is eliminated, so that a longer service life of the auxiliary water pump can be expected without a defect in the shaft bearing.

[0025] At the same time, the elimination of shaft seals and motor seals or a containment shell enables the invention to construct a pump with fewer components and inexpensive plain bearings.

[0026] Finally, according to the invention, a compact pump design with small axial dimensions is achieved in which, despite the elimination of a leakage chamber, a permanently safe operating environment for a dry rotor in the pump housing is provided.

[0027] During operation, the pump impeller generates a thrust force toward the pump's suction port or inlet. A sliding surface on the shaft end and a corresponding thrust surface on the housing side provide a particularly simple yet sufficient axial bearing without the need for axial fixation in the opposite direction. This further simplifies design and assembly.

[0028] Advantageous further developments of the additional water pump are the subject of the dependent claims.

[0029] According to one aspect of the invention, the axial support of the shaft can be provided by the axial plain bearing, which is arranged in front of the pump impeller in a flow direction of the coolant.

[0030] As a result, an axial load on the shaft is also absorbed by a plain bearing, whereby, in accordance with the object of the invention, a simple, cost-effective shaft bearing is provided which consists exclusively of two plain bearings lubricated by the coolant.

[0031] According to one aspect of the invention, the axial plain bearing can be formed by a free end of the shaft and a thrust surface on a pump cover.

[0032] According to one aspect of the invention, the shaft seal can have at least two sealing lips for dynamic sealing on the shaft circumference, which are aligned in a sealingly effective manner at least to one axial side.

[0033] A double-lipped shaft seal provides cost-effective and sufficient leakage protection behind the axial plain bearing. Compared to mechanical seals, it achieves significantly better sealing and allows only a small accumulation of leakage droplets to pass through. Sealing in the opposite direction, as in a pump design with a dry rolling bearing, is unnecessary due to the wet-running plain bearing.

[0034] According to one aspect of the invention, the pump housing may have at least one lubrication channel connecting the pump chamber to a rear end of the radial plain bearing opposite the pump chamber.

[0035] Through one or more connections from the front and rear axial ends of the plain bearing to the pump chamber, not only a one-sided static application of fluid until the bearing gap is saturated, but also a continuous circulation of fluid within the bearing gap can be provided for lubrication of the plain bearing. This achieves a more even pressure distribution of the fluid within the bearing gap and the removal of particles caused by wear on the bearing surfaces, resulting in better lubrication and reduced friction.

[0036] According to one aspect of the invention, at least one filter can be associated with the at least one lubrication channel.

[0037] If the design of the flow paths provides a circulation direction in which the pumped medium first flows through a lubrication channel and then through the bearing gap, a filter in each lubrication channel or a filter for all lubrication channels prevents particulate contaminants from entering the bearing gap or reaching the shaft seal. The filter's composition and thickness allow for a suitable pressure drop to be set, resulting in a pressure-reduced area compared to the pump chamber, which relieves the shaft seal while still ensuring sufficient circulation through the bearing gap.

[0038] According to one aspect of the invention, the stator of the electric motor can be arranged in axial overlap with the at least one lubrication channel.

[0039] By arranging one or, in particular, several radially distributed lubrication channels adjacent to the stator of the electric motor, the power loss of the stator's field coils during operation is transferred through heat transfer in the pump housing to the fluid circulating in the lubrication channels and dissipated to the flow in the pump chamber. This advantageous effect is also usable with small temperature differences between a high coolant temperature and an ever-higher temperature of the coil windings.

[0040] The invention will be explained below using an embodiment with reference to the drawing in Fig. 1 described.

[0041] As the axial section views in Fig.1, a pump housing 1 comprises, on a side shown on the left, an intake port 16 and a discharge port 17 which open into a pump chamber 10. The intake port 16 serves as a pump inlet, which is placed in the form of a separate pump cover 11 onto an open axial end of the pump housing 1 and leads to an end face of a pump impeller 2 which is fixed on a shaft 4. The circumference of the pump chamber 10 is surrounded by a spiral casing which leads tangentially into a discharge port 17 which forms a pump outlet.

[0042] The pump impeller 2 is a conventional radial pump impeller with a central opening adjacent to the intake port. The flow approaching the pump impeller 2 through the intake port 16 is accelerated radially outward by the inner vanes into the spiral casing of the pump chamber 10 and discharged.

[0043] On a side shown on the right, the pump housing 1 comprises a cavity designated as the motor chamber 13, which is separated from the pump chamber 10 by a partition 12 of the pump housing 1 and in which a brushless external rotor electric motor 3 is housed. A stator 31 with field coils of the electric motor 3 is fixed in the motor chamber 13 around a cylindrical portion of the partition 12 of the pump housing 1. A rotor 32 with permanent magnet rotor poles is fixed on the shaft 4 so as to be rotatable about the stator 31.

[0044] An axially open end of the motor chamber 13 is closed by a motor cover of the pump housing 1, in which a control unit or ECU of the pump, including power electronics of the electric motor 3, is embedded open to the motor chamber 13. A cable bushing is arranged between the power electronics and the stator 31 on an underside of the pump housing 1, which guides the supply lines to the field coils past the rotor 32.

[0045] The electric motor 3 is a dry-running type whose field coils are unencapsulated or open at the air gap to the rotor 32, exposed to the motor chamber 13. The rotor 32 has a bell shape typical of an external rotor, which sits on the free end of the shaft 4 shown on the right and supports the permanent-magnet rotor poles in the axial region of the stator 31. Atypical for a rotor body, however, the rotor 32 preferably does not contain any openings in a radially extending section, as is conventionally done to reduce the accelerated mass of rotating support bodies. Thus, the bell-shaped rotor 32 preferably forms a closed interior, which is only open on the left side to accommodate the stator 31.

[0046] The shaft 4, which extends between the pump chamber 10 and the motor chamber 13, is radially supported by a radial plain bearing 41 in the cylindrical portion of the boundary 12 of the pump housing 1. The sliding surfaces on the shaft circumference and on the bearing seat of the plain bearing 41 are lubricated by the coolant pumped by the auxiliary water pump, which penetrates the bearing gap between the sliding surfaces, as described later.

[0047] In addition, the shaft 4 is axially mounted at the left-hand free end. The axial plain bearing 42 is created by a sliding surface pairing between the end face of the shaft 4 and a thrust surface, which is provided on the pump cover 11 by a projection or strut in the intake port 16 in front of the pump impeller 2, appropriately positioned. During operation, the pump impeller 2 pushes the shaft 4 towards the intake port 16 against the thrust surface by means of a suction effect, so that axial load absorption of the shaft bearing in this one direction is sufficient. Since a bearing gap between the sliding surfaces is surrounded by the flow, the axial plain bearing 42 is also lubricated with coolant, at least in the form of an initial wetting of the sliding surfaces by the coolant and then, under vibrations or turbulence, re-wetting of the sliding surfaces.

[0048] A shaft seal 5 is arranged between the radial plain bearing 41 and the motor chamber 13, which seals an open end of the cylindrical section of the partition 12 of the pump housing 1 to the shaft 4. The shaft seal 5 is a double-lipped seal that is pressed into the cylindrical section of the partition 12 and has two sealing lips (not shown) arranged one behind the other, directed toward the radial plain bearing 41, for one-sided dynamic sealing on the shaft circumference.

[0049] Furthermore, lubrication channels 14 are provided in the wall of the cylindrical section of the partition 12 in the pump housing 1. These channels open into the pump chamber 10 on the one hand on the rear side of the pump impeller 2 and, on the other hand, lead to an annular cavity surrounding the shaft 4 between the rear end of the radial plain bearing 41 and the shaft seal 5. During operation, coolant flows from the pump chamber 10 through the lubrication channels 14 to the shaft 4 and, delimited by the shaft seal 5, penetrates the bearing gap between the shaft circumference and the bearing seat of the radial plain bearing 41, so that it flows back in the opposite direction. The axial circulation of the coolant in combination with the rotational movement between the sliding surfaces ensures even distribution and lubrication of the bearing gap with the coolant. The coolant contains an antifreeze additive with friction-reducing properties, such asa glycol, silicate, or the like. At the same time, particles from the abrasion of the sliding surface pair are transported to the pump chamber and into the flow stream.

[0050] On the other hand, filters 15 are arranged in the area of ​​the openings of the lubrication channels 14 to the pump chamber 10. These filters prevent particulate contaminants, such as metallic abrasion or the like, from being flushed from the flow into the bearing gap of the radial plain bearing 41 or into the sealing gap of the shaft seal 5. When the coolant circulates through the lubrication channels 14 and the radial plain bearing 41, a reduced pressure acts in the annular cavity between the radial plain bearing 41 and the shaft seal 5 due to the flow resistance of the filters 15, compared to the pump chamber 10.The reduced pressure, which is adjusted not only by the nature of the filter but also by the number and flow cross-section of the lubrication channels 14, weakens the circulation through the radial plain bearing, but it also relieves the load on the shaft seal 5, resulting in a longer service life of the sealing lips due to lower friction and smaller leakage.

[0051] However, the small, unavoidable leakage that passes drop by drop through the shaft seal 5 from the circulation of the lubrication channels 14 over time does not come into direct contact with the field coils or the motor electronics in the motor chamber 13. During operation, the leakage drops reach the inner surface of the rotating rotor 32 behind the shaft seal 5 and are carried radially outward by centrifugal force. Due to turbulence at the rotor poles or permanent magnets and the operating temperature resulting from the power loss at the field coils, the leakage drops evaporate in the air gap between the stator 31 and the rotor 32 without being able to wet the radially inner stator 32 in the liquid phase, i.e., without having a corrosive effect.

[0052] Due to the closed bell shape of the rotor 32, the leakage drops cannot reach the motor compartment 13 and the electronics in the axial direction, but are collected on the inner surface of the rotor 32 and directed into the air gap for evaporation. To keep the volume of the air gap small, it is designed in a stepped shape complementary to the circumferences of the cylindrical section of the boundary 12 and the stator 32.

[0053] The transition of leakage drops from the liquid to the gaseous phase is accompanied by an increase in volume, which, in the case of a closed volume of the motor chamber 13, would lead to an increase in pressure, independent of a pressure fluctuation that would arise due to temperature fluctuations between operation and standstill of the pump.

[0054] However, a membrane 6 is provided between the motor chamber 13 and the surrounding atmosphere, which allows pressure fluctuations from the motor chamber 13 to the atmosphere to be equalized. The membrane 6 is semi-permeable with regard to water permeability, i.e., it does not allow water in the liquid phase to pass through, whereas moisture-laden air can diffuse through up to a limit in terms of droplet size or a droplet density agglomerating on the membrane surface. Thus, upon volume expansion due to evaporation in the motor chamber 13, warm moisture-laden air can pass through the membrane 6, so that evaporated leakage droplets are effectively discharged into the atmosphere. In the opposite direction, the membrane 6, in turn, protects against the penetration of splash water or the like while the vehicle is driving.

[0055] The diaphragm 6 closes an opening in the pump housing 1, which is located above the outlet of the air gap between the stator 31 and the rotor 32. A connector for the external power supply is also located on the top of the pump housing 1.

[0056] In addition to the embodiment shown and described, the invention can also be implemented by alternative configurations with additional features or by omitting described features. As can be seen from the explanations for solving the problem, the pump can also be realized without lubrication channels 14 and filter 15, or with an axial bearing other than the plain bearing 52 in the area of ​​the intake port 16, or with a shaft seal 5 other than the one with two sealing lips. In a case in which no lubrication channels 14 are provided, at least a static lubrication of the bearing gap of the radial plain bearing 41 can be used via the bearing gap using the operating pressure from the pump chamber 10, wherein behind the radial plain bearing 41 a reduced pressure acts on the shaft seal 5 compared to the pump chamber 10.

Claims

[1] Electric coolant pump for pumping coolant in a vehicle, comprising: a pump housing (1) with a pump chamber (10) in which a pump impeller (2) is rotatably received, an inlet (16) and an outlet (17) connected to the pump chamber (10); a shaft (4) which is rotatably mounted on the pump housing (1) and on which the pump impeller (2) is fixed; a radial bearing of the shaft (4) is provided by means of a coolant-lubricated radial plain bearing (41) which is arranged between the pump impeller (2) and a rotor (32); a dry-running electric motor (3) with a radially inner stator (31) and a radially outer rotor (32) is accommodated in a motor chamber (13) separated from the pump chamber (10); a shaft seal (5) is arranged between the radial plain bearing (41) and the motor chamber (13); the rotor (32) is designed in a bell shape, the inner surface of which faces the shaft seal (5) and is fixed on the shaft (4) in an axially overlapping manner; characterized by , that the motor chamber (13) has an opening to the atmosphere which is closed by a liquid-tight and vapor-permeable pressure compensation membrane (6), wherein an axial plain bearing (42) is formed by a free end of the shaft (4) and a contact surface on the pump housing (1). [2] Electric coolant pump according to claim 1, wherein an axial bearing of the shaft (4) is provided by the axial plain bearing (42) which is arranged in a flow direction of the coolant in front of the pump impeller (2). [3] Electric coolant pump according to one of claims 1 or 2, wherein the axial plain bearing (42) is formed by the free end of the shaft (4) and the contact surface on a pump cover (11). [4] Electric coolant pump according to claims 1 to 3, wherein the shaft seal (5) has at least two sealing lips for dynamic sealing on a shaft circumference, which are aligned in a sealingly effective manner at least to one axial side. [5] Electric coolant pump according to one of claims 1 to 4, wherein the pump housing (1) has at least one lubrication channel (14) which connects the pump chamber (10) to a rear end of the radial plain bearing (41) opposite the pump chamber (10). [6] Electric coolant pump according to claim 5, wherein at least one filter (15) is associated with the at least one lubrication channel (14). [7] Electric coolant pump according to one of claims 5 or 6, wherein the stator (31) of the electric motor (3) is arranged in axial overlap with the at least one lubrication channel (14). [8] Use of an electric coolant pump according to one of claims 1 to 7 as an additional water pump in a coolant-carrying system in a vehicle with an internal combustion engine and a main water pump.

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