EP3755907B1 - Coolant pump having an optimized bearing assembly and improved heat balance - Google Patents

Description

The present invention relates to an electric coolant pump, the structure of which is optimized by a combination of a bearing, seal and electric motor in terms of costs, installation space and service life for the field of application of an additional water pump, and which has a bearing arrangement optimized taking this field of application into account and an improved heat balance .

Such electric auxiliary water pumps are used to circulate sub-areas of a coolant-carrying thermal management system of a vehicle that is equipped with an internal combustion engine and a main water pump, in order to cool so-called hotspots on components of auxiliary devices, such as exhaust gas recirculation, a turbocharger, charge air cooling or the like, more flexibly . Due to the redundancy to the main water pump and the increased number of lines and junctions, there is high price pressure for this type of auxiliary water pump and high demands on a compact design with small dimensions for integration in a complex packaging of modern thermal management systems.

In previously established products of electric auxiliary water pumps, wet-running electric motors of the internal rotor type are used, among other things because of the simpler sealing in the relatively small pump structure. The use of wet-running electric motors, on which the stator is typically dry-encapsulated from the rotor by a can or the like and the rotor and bearings are designed for operation in the pumped medium, is a known measure to solve the problem of a leak in a Counter shaft seal and a defect in a shaft bearing.

However, wet rotors have a poorer efficiency, since the gap between the stator and the rotor for accommodating a can is larger and a field strength acting on the rotor is weakened as a result. In addition, fluid friction occurs on the rotor, as a result of which the efficiency further decreases, particularly in the case of the relatively small pump drives of auxiliary water pumps. In addition, problems with wet rotors occur at low temperatures, such as ice formation in the gap between the stator and the rotor.

Dry-running electric motors are also used on larger pumps such as the electric main water pumps due to their better efficiency. To support pump shafts that are driven by a dry-running electric motor, rolling element bearings such as ball bearings are mainly used, which absorb both axial and radial loads and achieve low coefficients of friction.

However, rolling element bearings are generally sensitive to the ingress of moisture, since the materials used, in particular suitable steels for rolling elements, are not sufficiently corrosion-resistant for use in moisture. The ingress of moisture leads to a reduction in the surface quality of the rolling elements and raceways due to corrosion, which results in higher friction in the bearing and corresponding heat generation and further consequential damage to the bearings and seals. As a result, the rolling element bearings in pumps, which are expensive anyway, have to be provided with even more expensive seals on both end faces, which ensure low-friction and reliable sealing against the working pressures occurring in the pump chamber.

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

From the patent application DE 196 39 928 A1 is also a mechanically driven water pump known, in which one with a pump impeller connected shaft is supported by a sintered bearing and the bearing gap is lubricated by part of the pumped medium. The disclosed water pump is used as the main water pump and is externally driven via a belt. In comparison, water pumps used as auxiliary water pumps make greater demands with regard to variable control of the delivery volume of the pump, so that a belt drive appears unsuitable in this context. Due to the use of the belt drive, there are also fundamentally different thermal conditions in this known water pump compared to electric water pumps with an integrated electric motor, since the amount of heat introduced by the integrated electric motors is eliminated. This amount of heat is particularly significant when dry-running electric motors are used, since in this case the heat generated cannot be dissipated by a conveying medium flowing around the electric motor. An electric coolant pump is also disclosed DE 100 12 662 A1 .

Thus, with conventional coolant pumps, operating states can occur in which the plain bearing itself and also heat-generating elements, such as a control unit or circuit board or the stator of the electric motor, are not sufficiently cooled.

In conventional coolant pumps with wet-running electric motors, the bearing clearances in the plain bearing of the shaft are also set to be quite large in a range of 0.1 to 0.2 mm in order to prevent impurities (particles) in the pumped medium from causing jamming effects in the plain bearing and/or the damage the shaft seal. Due to radial displacements of the shaft, these increased bearing clearances also lead to increased noise emissions from the pump.

In addition, plain bearings made of technical carbon or high-quality polymers are often used in known coolant pumps, and these materials are comparatively expensive.

Based on the problems discussed in the prior art, an object of the invention is a simple, inexpensive, durable and to create a compact pump structure for a glanded electric motor with improved noise emissions and improved cooling.

The object is achieved according to the invention by an electric coolant pump according to claim 1.

The electric coolant pump is characterized in particular by the fact that a radial bearing of the shaft is provided by means of a coolant-lubricated (not soaked or impregnated with lubricant) radial sintered plain bearing with a defined porosity, which is arranged between the pump impeller and the rotor, and that a shaft seal between the radial slide bearing and the motor chamber, wherein in the sintered slide bearing in the axial direction at least one coolant flow passage is provided with a predetermined depth from the end of the sintered slide bearing on the pump chamber side.

The invention in its most general form is based on the finding that the selection, combination and arrangement of the individual components of the pump according to the invention result in a simplified and long-lasting bearing of the shaft and effective heat dissipation from the plain bearing itself and from other elements arranged in the motor chamber, such as the electric motor, can be achieved in the pumping medium, which also provides the corresponding advantages of a constructive and economic nature for the task at hand.

The invention provides for the first time providing a coolant-lubricated, non-lubricant radial sintered plain bearing with a defined porosity and an axial coolant flow channel in an electric coolant pump. The use of a porous sintered bearing lubricated by the pumped medium is cost-effective on the one hand, since there is no need for a soaking process or subsequent soaking of the sintered bearing, and on the other hand the predetermined porosity of the sintered bearing in cooperation with the coolant flow channel enables a defined flow of coolant through the plain bearing and filtering of the Pumped medium through the plain bearing itself. In this context, the axial Portion of the porous sintered plain bearing, in which the coolant flow passage is not provided, as a filter element for the pumping medium and no separate filter element needs to be provided. The defined flow of coolant allows heat to be better dissipated from the plain bearing itself and the elements of the pump connected to it, such as the stator or the control unit, and also the shaft seal, into the pumped medium, thus improving the heat balance of the coolant pump. In addition, the use of the sintered plain bearing enables small bearing clearances to be set, since the thermal expansion of the sintered bearing and the shaft can be suitably adjusted with the appropriate material selection.

Advantageous developments of the auxiliary water pump are the subject matter of the dependent claims.

According to an aspect of the invention, the coolant flow passage may extend in the axial direction from the end of the sintered plain bearing on the side of the pump chamber over about 90% of the component depth of the sintered plain bearing.

As a result, the conveyed medium can be distributed very quickly and evenly over the entire axial length of the porous sintered plain bearing and can penetrate into it, as a result of which the lubrication of the bearing point can be ensured. In addition, the remaining axial end section of the porous sintered plain bearing that is not provided with the coolant flow channel on the side opposite to the pump chamber, which occupies about 10% of the component depth of the sintered plain bearing in the axial direction, can ensure sufficient filtering of the pumped medium. In addition, this configuration allows the defined coolant flow to be set more reliably in the axial direction through the porous plain bearing and then through the bearing gap of the plain bearing back to the pump chamber.

According to a further aspect of the invention, the bearing play in the sintered plain bearing of the shaft can be set to less than 10 μm.

Similar thermal expansion of the sintered plain bearing and the shaft with the appropriate choice of material (e.g. sintered iron/sintered bronze, steel shaft) allows a very small bearing clearance to be set, which means that radial displacements of the rotor shaft can be restricted and the noise emissions of the pump reduced. In addition, the small bearing clearance prevents impurities (particles) in the pumped medium from penetrating the bearing gap and causing jamming effects in the plain bearing.

According to a further aspect of the invention, the porosity of the sintered plain bearing can be set to over 40%.

As a result, the conveyed medium can be distributed quickly and evenly in the porous sintered plain bearing, which ensures reliable lubrication of the plain bearing. In addition, due to the high pore content, the flow of the pumped medium inside the plain bearing and thus the heat transport from the plain bearing to the pumped medium can be promoted.

According to a further aspect of the invention, the rotor can be designed in a pot shape, the inner surface of which faces the shaft seal and is fixed on the shaft in an axially overlapping manner with it.

As a result, 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 before they can reach a motor chamber with electronics. The leakage droplets are vaporized by the operating temperature of the electric motor and by turbulent turbulence in the air gap. The resulting water vapor only then enters the motor chamber and escapes through a membrane into the atmosphere. As a result, encapsulation of the stator and the associated disadvantages in terms of the efficiency of an electric motor of the wet-running type can be dispensed with.

According to a further aspect of the invention, an axial bearing of the shaft can be provided by an axial slide bearing, which is formed by a free end of the shaft and a contact surface on the pump housing, preferably a pump cover.

During operation, the pump impeller generates a thrust towards the suction port or inlet of the pump. A particularly simple but sufficient axial bearing without the need for axial fixing in the opposite direction is provided by a sliding surface on the end face of the shaft and a corresponding contact surface on the housing. As a result, the construction and assembly can be further simplified.

According to a further aspect of the invention, the shaft seal can have at least two sealing lips for dynamic sealing on the shaft circumference, which are aligned at least on one axial side to provide a seal.

A double-lipped shaft seal provides cheap and adequate protection against leakage behind the axial plain bearing, which achieves a significantly better seal than mechanical seals and only allows a small accumulation of leakage drops to pass. A seal in the opposite direction, as in a pump design with a dry roller bearing, can be omitted due to the wet-running plain bearing.

According to a further aspect of the invention, the stator of the electric motor can be arranged in axial overlap with the at least one coolant flow channel.

By arranging one or in particular several coolant flow channels distributed in the circumferential direction of the plain bearing in the plain bearing adjacent to the stator of the electric motor, during operation a power loss of the field coils of the stator is transferred to the conveying means circulating in the coolant flow channels of the plain bearing and discharged to the flow in the pump chamber. This advantageous effect can also be used with small temperature differences between a high coolant temperature and an ever higher temperature of the coil windings.

According to a further aspect of the invention, a control unit can be provided, which is arranged in the motor chamber in the axial direction between the separating element and the stator.

As a result, the control unit can be cooled by dissipating heat via the conveying medium flowing in the porous sintered plain bearing. Due to the spatial proximity between the control unit and the stator, the contacting or wiring between the control unit and the stator is also simplified and robust wiring can be provided.

According to a further aspect of the invention, the motor chamber may have an opening to the atmosphere which is closed by a liquid-tight and vapor-permeable pressure-equalizing membrane.

As a result, water vapor produced by leaking drops in the motor chamber can be effectively discharged into the atmosphere.

The invention is described below using an exemplary embodiment with reference to the drawing 1 described.

As the axial sectional view in 1 As can be seen, a pump housing 1 comprises, on a side shown on the right, an intake connection 16 and a pressure connection, not shown, 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 on an open axial end of the pump housing 10 and leads to an end face of a pump impeller 2 that is fixed on a shaft 4 . The perimeter of the pump chamber 10 is surrounded by a volute which transitions tangentially into a discharge port forming a pump outlet.

The pump impeller 2 is a known radial pump impeller with a central opening adjacent to the intake port. The delivery flow, which flows against the pump impeller 2 through the intake port 16, is accelerated radially outwards by the internal vanes into the spiral housing of the pump chamber 10 and discharged.

On a side shown on the left, the pump housing 1 includes a cavity referred to as the motor chamber 13 , which is separated from the pump chamber 10 by a separating element designed as a support flange 12 .

The support flange 12 is made of a material with a high thermal conductivity, such as metal, to enable good heat transfer between the motor chamber 13 and the pump chamber 10 and good heat dissipation from the motor chamber 13 to the pumped medium in the pump chamber 10. At the in 1 shown embodiment, the support flange 12 is made of an aluminum alloy. The support flange 12 has a partition portion 12a providing the partition between the motor chamber 13 and the pump chamber 10, and a boss portion 12b on which the stator 31 is fixed.

As in 1 is shown, the pump housing 1 has a pot-shaped motor housing 17 which forms the motor chamber 13 . The support flange 12 and the pump cover 11 are accommodated in the motor housing 17 on an axially open side of the latter, the support flange 12 abuts against a stop surface provided on the motor housing 17 and the pump cover 11 is fixed to the motor housing 17 in this position. A sealing element, such as an O-ring, is arranged between the support flange 12 and the pump housing in order to prevent leakage of the pumped medium in the pump chamber 10 . As in 1 As shown, the sealing member is disposed on an outer peripheral surface of the partition portion 12a of the support flange 12 in the present embodiment, but the sealing member may be disposed on the side surface of the partition portion 12a facing the pump cover 11 in the axial direction, for example. The above The configuration described allows easy and accurate positioning of the support flange 12 and the pump cover 11 in the radial direction.

In the motor chamber 13, an outer rotor type brushless electric motor 3 is accommodated. A stator 31 having field coils of the electric motor 3 is fixed around the boss portion 12a of the support flange 12 having, for example, a cylindrical shape so that the stator 31 is in contact with the boss portion 12a. This ensures very good heat dissipation from the stator 31 in the motor chamber 13 via the carrier flange 12 to the pumped medium in the pump chamber 10 . A rotor 32 with permanent magnet rotor poles is rotatably fixed on the shaft 4 around the stator 31

one inside 1 The control unit or printed circuit board 18 of the pump shown including power electronics of the electric motor 3 is arranged in the axial direction between the separating section 12a of the support flange 12 and the stator 31 . Due to the spatial proximity between the circuit board 18 and the carrier flange 12 on the one hand and the stator 31 and the circuit board 18 on the other hand, good heat dissipation from the circuit board 18 via the carrier flange 12 to the pumped medium can be made possible in this case and good conditions are created for a simple and robust contact or wiring between the circuit board 18 and the electric motor 3 created.

A filling material 19, such as a gap filler, with a high thermal conductivity can be arranged in the air gap between the separating section 12a and the circuit board 18, so that the heat transfer from the circuit board 18 to the pumped medium in the pump chamber 10 can be further improved.

However, the circuit board 18 of the pump can also be arranged elsewhere in the motor chamber 13, such as on the bottom section of the motor housing 17 facing the axial end of the electric motor. In addition, the circuit board 18 of the pump can also be arranged outside of the motor chamber 13 .

The electric motor 3 is a dry-running type, the field coils of which are unencapsulated or open at the air gap between the rotor 32 and the motor chamber 13 . The rotor 32 has a pot shape that is typical of an external rotor, which sits on the free end of the shaft 4 shown on the left and carries the permanent-magnetic rotor poles in the axial region of the stator 31 .

The shaft 4, which extends between the pump chamber 10 and the motor chamber 13, is mounted radially in the carrier flange 12 by a radial sintered plain bearing 41. In addition, the shaft 4 is mounted axially at the right free end. The axial plain bearing comes about through a sliding surface pairing between the end face of the shaft 4 and a contact surface, which is provided by a projection or a strut in the intake port 16 in front of the pump impeller 2 and positioned accordingly on the pump cover 11 . In operation, the pump impeller 2 pushes the shaft 4 by a suction effect in the direction of the intake port 16 against the contact surface, so that an axial load bearing of the shaft bearing is sufficient in this one direction. Since a bearing gap between the sliding surfaces is surrounded by the delivery flow, the axial plain bearing is also lubricated with coolant, at least in the form of an initial wetting of the sliding surfaces by the coolant, which occurs again under vibration or turbulence.

The coolant-lubricated plain bearing 41 is designed as a sintered bearing with a defined porosity of over 40%, for which, for example, known standard materials for sintered plain bearings, such as sintered iron and sintered bronze, can be used. By selecting such sintered materials, a very small bearing play of less than 10 μm can be set when using a steel shaft due to the similar thermal expansion of sintered bearings and steel shafts. Thus, radial displacements of the rotor shaft can be largely suppressed and the noise emission of the pump can be reduced. In addition, the porous sintered material quickly fills with the pumped medium and therefore enables the heat generated in the plain bearing itself and the heat transferred from other pump elements to the plain bearing to be efficiently absorbed and dissipated into the pumped medium.

This in 1 The sintered plain bearing 41 shown also has two axial coolant flow channels 14 with a predetermined depth starting from the end of the sintered plain bearing 41 on the pump chamber 10 side. Thus, during pump operation, due to the prevailing pressure conditions in the pump, the pumped medium can flow in a defined direction of flow, starting from the radially outer area of the pump chamber 10 with high pressures via the area of the pump chamber 10 between the pump impeller 2 and the support flange 12 with pressures decreasing radially inwards , through the coolant flow passages 14 and the axial end portion of the plain bearing 41 on the side opposite to the pump impeller 2 without a coolant flow passage 14 (filter portion), to the space between the sintered plain bearing 41 and the shaft seal 5, through the bearing gap of the plain bearing 41, and finally to the be recycled radially inner region of the pump chamber 10 with even lower pressures. The axial circulation of the coolant in the bearing gap in combination with the rotational movement between the sliding surfaces ensures an even distribution and lubrication of the bearing gap with the coolant. The coolant contains an antifreeze additive with a friction-reducing property, such as a glycol, silicate or the like. At the same time, particles from abrasion of the sliding surface pairing are transported away to the pump chamber and into the flow.

Although in 1 two coolant flow channels 14 are shown, it is sufficient according to the invention if at least one such coolant flow channel 14 is provided. In addition, more than two coolant flow channels 14 can also be provided. At the in 1 In the example shown, the coolant flow channels 14 are designed as grooves on the outer circumference of the plain sintered bearing 41 . However, the coolant flow channels 14 can also be provided as axially extending blind holes in the plain sintered bearing 41 . Furthermore, the at least one coolant flow channel 14 embodied as a groove can be embodied in a spiral shape around the circumference of the sintered plain bearing 41 .

By the coolant flow defined above, the sliding surfaces on the shaft circumference and on the bearing seat of the plain bearing 41 by the Auxiliary water pump promoted coolant lubricated, which penetrates into the bearing gap between the sliding surfaces. In this context, the porous sintered plain bearing 41 also serves as a filter element for the conveyed medium flowing through, so that only filtered coolant reaches the shaft sealing ring and the bearing gap. A separate filter element for the pumped medium is therefore not required.

A shaft seal 5 is arranged between the radial sintered slide bearing 41 and the motor chamber 13 and seals an open end of the projection section 12b of the carrier flange 12 to the shaft 4 . The shaft seal 5 is a double-lip seal that is pressed into the projection section 12b of the carrier flange 12 and has two sealing lips (not shown) one behind the other, directed in the direction of the radial plain bearing 41, for one-sided dynamic sealing on the shaft circumference.

The small, unavoidable leakage that occurs drop by drop over the course of time through the shaft seal 5 from the circulation of the coolant, however, does not come into direct contact with the field coils or any motor electronics that may be arranged in the motor chamber 13 . During operation, the leakage droplets reach the inner surface of the rotating rotor 32 behind the shaft seal 5 and are carried radially outwards by the 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 droplets evaporate in the air gap between the stator 31 and the rotor 32 without wetting the radially inner stator 32 in the liquid phase, i. to exert a corrosive effect.

Due to the pot shape of the rotor 32, the leakage droplets cannot reach the engine compartment 13 directly in the axial direction, but are caught on the inner surface of the rotor 32 and fed to the air gap for evaporation. In order to keep the volume of the air gap small, it is designed to complement the circumferences of the stator 32 .

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

However, between the motor chamber 13 and the surrounding atmosphere there is an in 1 membrane, not shown, is provided, which is attached to the pot-shaped motor housing 17 in the motor chamber 13 . The membrane can, for example, at an in 1 illustrated opening 20 of the motor housing 17 may be provided at the outer periphery of the motor housing 17. The diaphragm can also be bonded at a radially central portion of an inner surface of the motor housing 17 facing the rotor in the axial direction, and enables pressure fluctuations from the motor chamber 13 to the atmosphere to be equalized. As a result, an inexpensive and large-area adhesive membrane can be used at a protected location. The motor housing 17 then has an opening or a permeable or open-pored structure in this area, which is designed in such a way that the membrane is adequately protected during high-pressure jet tests and is not damaged. The membrane is semi-permeable with regard to water permeability, ie it does not allow water to pass through in the liquid phase, whereas air laden with moisture can diffuse through up to a limit with regard to droplet size or a droplet density agglomerating on the membrane surface. Thus, in the event of a volume expansion due to evaporation in the motor chamber 13, warm air laden with moisture can pass through the membrane, so that evaporated leakage droplets are effectively discharged into the atmosphere. In the opposite direction, the membrane in turn protects against the ingress of spray water or the like when the vehicle is being driven.

Claims (11)

1. An electrical coolant pump for conveying coolant in a vehicle comprising:

   a pump housing (1) with a pump chamber (10) in which a pump impeller (2) is rotably accommodated, an inlet (16) and an outlet which are connected to the pump chamber (10);

   a shaft (4) which is rotably supported at a separating element (12) between the pump chamber (10) and a motor chamber (13) separated from the pump chamber (10), and on which the pump impeller (2) is fixed;

   a dry-running electric motor (3) with a radially inner stator (31) and a radially outer rotor (32) which is accommodated in the motor chamber (13);

   characterized in that

   a radial bearing of the shaft (4), which is arranged in an axial direction between the pump impeller (2) and the rotor (32), is provided by means of a radial sintered sliding bearing (41) having a defined porosity lubricated by coolant; and

   a shaft seal (5) is arranged between the radial sliding bearing (41) and the motor chamber (13);

   wherein at least one coolant flow channel (14) with a predetermined depth is provided in the sintered sliding bearing (41) in an axial direction extending from the end of the sintered sliding bearing (41) on the side of the pump chamber (10).
2. The electric coolant pump according to claim 1, wherein
   the coolant flow channel (14) extends in the axial direction from the end of the sintered sliding bearing on the side of the pump chamber (10) across 90 % of the component depth of the sintered sliding bearing (41).
3. The electric coolant pump according to claim 1 or 2, wherein
   the bearing play in the sintered sliding bearing (41) of the shaft (4) is set to be smaller than 10 µm.
4. The electric coolant pump according to any one of claims 1 to 3, wherein
   the porosity of the sintered sliding bearing (41) is set to more than 40 %.
5. The electric coolant pump according to any one of claims 1 to 4, wherein
   the rotor (32) is formed in a pot-shaped manner, the inner face thereof faces the shaft seal (5) and is fixed on the shaft (4) axially intersecting the same.
6. The electric coolant pump according to any one of claims 1 to 5, wherein
   an axial mounting of the shaft (4) is provided by an axial sliding bearing which is formed by a free end of the shaft (4) and a thrust surface at the pump housing (1), preferably a pump cover (11).
7. The electric coolant pump according to any one of claims 1 to 6, wherein
   the shaft seal (5) comprises at least two sealing lips for sealing dynamically on the shaft circumference which are arranged to seal effectively towards at least one axial side.
8. The electric coolant pump according to any one of claims 1 to 7,
   wherein the stator (31) of the electric motor (3) is arranged in an axially intersecting manner with the at least one coolant flow channel (14).
9. The electric coolant pump according to any one of claims 1 to 8, further comprising
   a control unit (18) which is arranged in the motor chamber (13) in an axial direction between the separating element (12) and the stator (31).
10. The electric coolant pump according to any one of claims 1 to 9, wherein
    the motor chamber (13) comprises an opening (20) to the atmosphere which is closed by a pressure equalizing membrane impermeable to liquid and permeable to vapor.
11. A use of an electric coolant pump according to any one of claims 1 to 10 as a supplementary water pump in a system carrying coolant in a vehicle with a combustion machine and a main water pump.

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