EP3755907A1

EP3755907A1 - Coolant pump having an optimized bearing assembly and improved heat balance

Info

Publication number: EP3755907A1
Application number: EP18808277.0A
Authority: EP
Inventors: Franz Pawellek
Original assignee: Nidec GPM GmbH
Current assignee: Nidec GPM GmbH
Priority date: 2018-02-22
Filing date: 2018-11-21
Publication date: 2020-12-30
Anticipated expiration: 2038-11-21
Also published as: CN111601971B; DE102018104015A1; EP3755907B1; BR112020014776A2; US20210079920A1; WO2019161950A1; US11306723B2; CN111601971A

Abstract

The invention relates to an electrical coolant pump, preferably for use as an additional water pump in a vehicle, which electrical coolant pump is characterized in that radial support of the shaft (4) is provided by means of a coolant-lubricated radial sintered plain bearing (41) having a defined porosity, which is arranged between the pump impeller (2) and the rotor (32), and a shaft seal (5) is arranged between the radial plain bearing (41) and the motor chamber (13). In the sintered plain bearing (41), in the axial direction, at least one coolant flow channel (14) having a predefined depth proceeding from the end of the sintered plain bearing (41) on the side of the pump chamber (10) is provided.

Description

Coolant pump with optimized bearing arrangement and improved

heat balance

The present invention relates to an electric coolant pump whose structure is optimized by a combination of storage, sealing and electric motor in terms of cost, space and life on the application of a make-up water pump, and which is an optimized bearing in consideration of this application storage arrangement and an improved heat balance having.

Such auxiliary electric water pumps are used to circulate subregions of a vehicle's coolant-carrying thermal management system equipped with a combustion engine and a main water pump to supply so-called hotspots to components of auxiliary equipment such as an exhaust gas recirculation on a turbocharger a charge air cooling or the like to cool more flexible. Due to the redundancy of the main water pump and the increased number of pipes and junctions, the type of such make-up water pumps is subject to high price pressure and high requirements for 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, among other things due to the easier sealing in the relatively small pump structure, wet rotor electric motors of the internal rotor type are used. The use of wet-rotor electric motors, in which typically the stator is dry-sealed by a canned or the like relative to the rotor and the rotor and a bearing are designed for operation in the pumped medium, represent a known measure to the problem of a leakage at a Shaft seal and a defect of a wave bearing to counter. Wet runners, however, have a lower efficiency, since the gap between the stator and the rotor for receiving a split tube fails larger and thereby acting on the rotor field strength is weakened by this. In addition, fluid friction occurs on the rotor, which further reduces the efficiency, especially in the relatively small-sized pump drives of additional water pumps. In addition, wet-running problems occur at low temperatures, such as ice formation in the gap between the stator and the rotor.

On larger pumps such as the electric main water pumps and dry-running electric motors are used due to the better efficiency. For the storage of pump shafts, which are driven by a dry-running electric motor, mainly roller bearing, such as, for example, are used. Ball bearings are used, which support both axial and radial loads and achieve low coefficients of friction.

However, rolling element bearings are generally sensitive to moisture penetration since the materials used, particularly suitable steels of 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 a higher friction of the bearing and corresponding heat development and further consequential damage to bearings and seals. As a result, the already costly roller bearing in pumps on both ends must be provided with even more costly seals that ensure a low-friction and reliable seal against the operating pressures occurring in the pump chamber.

In addition to the cost disadvantage, corresponding seals always cause a slight leakage and often represent the limiting factor of the service life of a pump, since they per se are subject to frictional wear and embrittlement due to pressure and temperature fluctuations.

From the patent application DE 196 39 928 Al a mechanically driven water pump is also known, in which one with a Pumpenlauffad connected shaft is mounted on a sintered bearing and the bearing gap is lubricated by a part of the pumped medium. The disclosed water pump is used as the main water pump and externally driven by a belt. In comparison, water pumps used as make-up water pumps place increased demands on variable control of the delivery volume of the pump, so that a belt drive appears inappropriate in this connection. Due to the use of the belt drive prevail in this known water pump in comparison to electric water pumps with an integrated electric motor also fundamentally different thermal conditions, since the introduced by integrated electric motors amount of heat lost. This amount of heat is particularly important when using dry-running electric motors, since the heat generated in this case can not be dissipated by a pumping medium flowing around the electric motor.

Thus, in conventional coolant pumps operating conditions may occur in which the plain bearing itself and further heat-generating elements, such as a control board or the stator of the electric motor, are not sufficiently cooled.

In conventional coolant pumps with wet-rotor electric motors, the bearing clearances in the plain bearing of the shaft in a range of 0.1 to 0.2 mm are also set quite large in order to prevent impurities (particles) in the fluid to cause clamping effects in the plain bearing and / or damage the shaft seal. These increased bearing games lead due to radial displacements of the shaft beyond to increased noise emission of the pump.

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

Based on the problems of the discussed prior art, it is an object of the invention to provide a simple, inexpensive, durable and compact pump design for a dry-running electric motor with improved noise emission and improved cooling.

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

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

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 results in a simplified and long-lasting bearing of the shaft and effective heat dissipation from the slide bearing itself and from further elements arranged in the motor chamber , as the electric motor, are achieved in the medium, which also provides the tasks corresponding advantages of a constructive and economic nature.

For the first time, the invention provides for a coolant-lubricated radial sintered plain bearing with a defined porosity and an axial coolant flow channel not impregnated with lubricant in the case of an electric coolant pump. The use of a lubricated by the fluid medium porous sintered bearing is on the one hand cost, since a Tränk process or a Nachtränken the sintered bearing can be omitted, on the other hand allows the predetermined porosity of the sintered bearing in cooperation with the coolant flow channel a defined flow of coolant through the sliding bearing and a filtering of the fluid through the slide bearing itself. In this context, the axial Portion of the porous sintered plain bearing, in which the coolant flow channel is not provided, as a filter element for the pumped medium and no separate filter element must be provided. By the defined flow of coolant heat from the slide bearing itself and connected to this elements of the pump, such as the stator or the control unit, and the shaft seal better dissipated in the fluid and thus the heat balance of the coolant pump can be improved. In addition, the use of the sintered plain bearing allows the setting of small bearing clearances, since the thermal expansion of the sintered bearing and the shaft can be suitably adapted with appropriate choice of material.

Advantageous developments of the additional water pump are the subject of the dependent claims.

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

As a result, the fluid can spread very quickly and evenly over the entire axial length of the porous sintered plain bearing and penetrate into this, whereby the lubrication of the bearing can be ensured. In addition, the remaining, not provided with the coolant flow channel axial end portion of the porous sintered sliding bearing 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, ensure sufficient filtering of the pumped medium. In addition, by this configuration, the defined coolant flow in the axial direction through the porous sliding bearing and then through the bearing gap of the sliding bearing back to the pump chamber can be set more reliable.

According to a further aspect of the invention, the bearing clearance in the sintered plain bearing of the shaft can be set below 10 μm. By a similar thermal expansion of the sintered plain bearing and the shaft with appropriate material selection (for example, sintered iron / sintered bronze, steel shaft), a very small bearing clearance can be set, thereby limiting radial displacements of the rotor shaft and thus reducing the noise emission of the pump. In addition, the small clearance prevents impurities (particles) in the pumped medium from penetrating into the bearing gap and causing clamping effects in the slide bearing.

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

As a result, the fluid can be distributed quickly and evenly in the porous sintered sliding bearing, whereby a reliable lubrication of the sliding bearing can be ensured. In addition, due to the high pore content, the flow of the pumped medium in the interior of the slide bearing and thus the W transport from the slide bearing are promoted in the fluid.

According to a further aspect of the invention, the rotor may be formed in a cup shape, whose inner surface facing the shaft seal and is fixed axially overlapping with this on the shaft.

As a result, liquid droplets of leakage past 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 pass into a motor chamber with electronics. The leakage drops are vaporized by the operating temperature of the electric motor and by a turbulent turbulence in the air gap. The resulting water vapor then enters the motor chamber and escapes through a membrane into the atmosphere. As a result, encapsulation of the stator and the associated disadvantages of the efficiency of an electric motor of the wet rotor 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 sliding 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 force in the direction of the suction port or inlet of the pump. By a front-side sliding surface of the shaft and a corresponding housing-side contact surface, a particularly simple but sufficient thrust bearing is provided without necessary axial fixation in the opposite direction. Thereby, the structure and the assembly can be further simplified.

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

A double-lip shaft seal provides favorable and sufficient leakage protection behind the axial slide bearing, which achieves a significantly better seal compared to mechanical seals and allows only a small accumulation of leakage drops to pass. A seal in the opposite direction, as in a pump assembly with a dry rolling 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 may be arranged in axial overlap with the at least one coolant flow channel.

By arranging one or in particular a plurality of distributed in the circumferential direction of the sliding bearing coolant flow channels in the sliding bearing adjacent to the stator of the electric motor, a power loss of the field coils of the stator by a W poor transition in the projecting portion of the separating element is transferred to the circulating in the coolant flow passages of the sliding bearing conveyor and discharged to the flow in the pump chamber. This advantageous effect is even at low T emperaturdifferenzen between a high coolant temperature and a still higher temperature of the coil windings usable.

According to a further aspect of the invention, a control unit may 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 heat removal via the conveying medium flowing in the porous sintered sliding bearing. In addition, due to the physical proximity between the control unit and the stator, the wiring between the control unit and the stator is simplified, and a 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, a water vapor arising in the motor chamber due to leakage drops can be efficiently discharged into the atmosphere.

The invention will be described below with reference to an embodiment with reference to the drawing in Fig. 1.

As can be seen from the axial sectional view in FIG. 1, a pump housing 1 comprises, on a side shown on the right, an intake pipe 16 and a pressure pipe, not shown, which open into a pump chamber 10. The intake manifold 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 runner 2, which is fixed on a shaft 4. The circumference of the pumping chamber 10 is surrounded by a volute which passes tangentially into a discharge nozzle forming a pump outlet. The impeller 2 is a known radial impeller with a central opening adjacent to the intake manifold. The delivery flow, which flows against the pump impeller 2 through the intake manifold 16, is accelerated and discharged by the inner vanes radially outward into the volute casing of the pumping chamber 10.

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

The support flange 12 is made of a material with a high thermal conductivity, such as metal, in order to allow a good heat transfer between the motor chamber 13 and the pump chamber 10 or a good heat dissipation from the motor chamber 13 to the pumped medium in the pump chamber 10 , In the embodiment shown in Fig. 1, the support flange 12 is made of an aluminum alloy. The support flange 12 has a partition portion 12a, which provides the partition between the motor chamber 13 and the pump chamber 10, and a projection or projection portion 12b on which the stator 31 is mounted.

As shown in FIG. 1, 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 received on an axially open side of the motor housing 17 in this, the support flange 12 abuts against a provided at the motor housing 17 stop surface and the pump cover 11 is fixed in this position on the motor housing 17. Between the support flange 12 and the pump housing, a sealing element, such as an O-ring, arranged to prevent leakage of the fluid in the pump chamber 10. As shown in FIG. 1, in the present embodiment, the seal member is disposed on an outer peripheral surface of the partition portion 12a of the support flange 12, but the seal member may be disposed, for example, on the side surface of the partition portion 12a facing the pump cover 11 in the axial direction. The above described configuration allows easy and accurate positioning of the support flange 12 and the pump cover 11 in the radial direction.

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

A control unit or circuit board 18 of the pump shown in FIG. 1, including power electronics of the electric motor 3, is arranged in the axial direction between the separating section 12a of the carrier flange 12 and the stator 31. Due to the spatial proximity between the board 18 and the support flange 12 on the one hand and the stator 31 and the board 18 on the other hand, in this case a good W ärmeableitung be made possible from the board 18 via the support flange 12 to the medium and there are good V oraussetzungen for a simple and robust contacting or wiring between the board 18 and the electric motor 3 created.

In the air gap between the separation section 12a and the circuit board 18, a filling material 19, such as a gap filler, with a high Wärmmeleitfahigkeit be arranged so that the heat transfer from the 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, as on the axial end of the electric motor facing bottom portion of the motor housing 17. In addition, the circuit board 18 of the pump can also be arranged outside the motor chamber 13. The electric motor 3 is a dry-runner type whose field coils lie unencapsulated or open at the air gap to the rotor 32 to the motor chamber 13. The rotor 32 has a typical for an external rotor cup shape, 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 radially supported by a radial sintered sliding bearing 41 in the support flange 12. In addition, the shaft 4 is axially supported at the right free end. The axial sliding bearing is achieved by a pair of sliding surfaces between the end face of the shaft 4 and a contact surface, which is provided by a projection or a strut in the intake manifold 16 in front of the pump impeller 2, correspondingly positioned 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 manifold 16 against the contact surface, so that an axial load bearing of the shaft bearing sufficient in one direction. Since a bearing gap between the sliding surfaces is surrounded by the delivery flow, the axial sliding bearing is also lubricated with coolant, at least in the form of an initial wetting of the sliding surfaces by the coolant under vibrations or turbulences.

The coolant lubricated sliding bearing 41 is formed 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 clearance of less than 10 μm can be set when using a steel shaft due to the similar thermal expansion of the sintered bearing and the steel shaft. 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 fills quickly with the fluid and therefore allows efficient absorption and dissipation of the heat generated in the sliding bearing itself and the heat transferred from other pump elements to the sliding bearing heat into the fluid. The sintered sliding bearing 41 shown in FIG. 1 also has two axial coolant flow channels 14 having a predetermined depth 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 in a defined flow direction starting from the radially outer region of the pump chamber 10 at high pressures, the pumped fluid may flow across the pump chamber 10 between the pump impeller 2 and the support flange 12 with radially inwardly decreasing pressures , through the coolant flow channels 14 and the axial end portion of the sliding bearing 41 on the side opposite to the pump impeller 2 without coolant flow channel 14 (filter section) toward the space between the sintered plain bearing 41 and the shaft seal 5, through the bearing gap of the sliding bearing 41 and finally towards the radially inner region of the pump chamber 10 are returned to even lower pressures. The axial circulation of the coolant in the bearing gap 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 having a low friction property, such as a glycol, silicate or the like. At the same time, particles are transported away from abrasion of the sliding surface pairing to the pump chamber and into the delivery flow.

Although two coolant flow channels 14 are shown in FIG. 1, 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 may be provided. In the example shown in FIG. 1, the coolant flow channels 14 are formed as grooves on the outer circumference of the sintered plain bearing 41. However, the coolant flow channels 14 may also be provided as axially extending blind holes in the sintered sliding bearing 41. Furthermore, the at least one coolant flow channel formed as a groove 14 may be formed spirally around the circumference of the sintered sliding bearing 41.

By the above-defined defined flow of coolant, the sliding surfaces on the shaft circumference and the bearing seat of the sliding bearing 41 by that of the Lubricated additional water pump required coolant that penetrates into the bearing gap between the sliding surfaces. In this context, the porous sintered sliding bearing 41 also serves as a filter element for the flowing through the conveying medium, so that only filtered coolant passes in front of the shaft sealing ring and into the bearing gap. A separate filter element for the pumped medium is thus not required.

Between the radial sintered sliding bearing 41 and the motor chamber 13, a shaft seal 5 is arranged, which seals an open end of the protruding portion 12 b of the support flange 12 to the shaft 4. The shaft seal 5 is a double-lip seal, which is pressed into the v jump portion l2b of the support flange 12, and two successive, directed towards the radial slide bearing 41 sealing lips (not shown) for unilateral dynamic sealing on the shaft circumference. The small unavoidable leakage resulting from the circulation of the coolant

Shaft seal 5 happens dropwise over time, but does not come directly to the field coils or possibly arranged in the motor chamber 13 engine electronics in contact. In operation, the leakage drops reach behind the shaft seal 5 to the inner surface of the rotating rotor 32 and are carried by the centrifugal force radially outward. As a result of turbulences at the rotor poles or permanent magnets and due to the operating temperature resulting from the power loss at the field coils, the leakage drops vaporize in the air gap between the stator 31 and the rotor 32 without wetting in the liquid phase on the radially inward stator 32. ie to be able to exert a corrosive action.

Due to the pot shape of the rotor 32, the leakage drops can not get directly into the engine compartment 13 in the axial direction, but are collected on the inner surface of the rotor 32 and fed to the air gap for evaporation. In order to keep a volume of the air gap small, this is complementary to the enclosure of the stator 32. The passage of leakage drops from the liquid to the gaseous phase is accompanied by a V olumenzunahme, 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 would arise due to T perperature fluctuations between operation and standstill of the pump.

However, between the motor chamber 13 and the surrounding atmosphere, a membrane, not shown in Fig. 1 is provided, which is mounted in the motor chamber 13 on the cup-shaped motor housing 17. The diaphragm may be provided at the outer periphery of the motor housing 17, for example, in an opening 20 of the motor housing 17 shown in FIG. The diaphragm can also be glued to a radially middle portion of an inner surface of the motor housing 17 facing the rotor in the axial direction and makes it possible to compensate for pressure fluctuations from the motor chamber 13 to the atmosphere. As a result, a cost-effective 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-pore structure in this area, which is designed such that the membrane is sufficiently protected during high-pressure jet tests and is not damaged. The membrane is semipermeable with respect to water permeability, i. it does not allow water to pass in the liquid phase, whereas moisture laden air can diffuse to a limit in droplet size or droplet density agglomerating at the membrane surface. Thus, at a volumetric expansion by evaporation in the motor chamber 13, a warm air laden with moisture may pass through the membrane so that vaporized leak drops are effectively discharged into the atmosphere. In the opposite direction, the membrane in turn protects against the ingress of spray water or the like in the ferry operation of the vehicle.

Claims

claims

An electric coolant pump for delivering coolant in a vehicle, comprising: a pump housing (1) having a pump chamber (10) in which a pump impeller (2) is rotatably received, an inlet (16) and an outlet connected to the pump chamber (10) are connected; a shaft (4) rotatably supported on a partition member (12) between the pump chamber (10) and a motor chamber (13) separate from the pump chamber (10) and on which the pump impeller (2) is fixed; a dry running electric motor (3) having a radially inner stator (31) and a radially outer rotor (32) received in the motor chamber (13); characterized in that a radial bearing of the shaft (4) by means of a coolant-lubricated radial Sintergleitlagers (41) is provided with a defined porosity, which is arranged in the axial direction between the pump impeller (2) and the rotor (32); and a shaft seal (5) between the radial sliding bearing (41) and the

Motor chamber (13) is arranged; wherein at least one coolant flow channel (14) having a predetermined depth from the end of the sintered plain bearing (41) on the pump chamber (10) side is provided in the sintered sliding bearing (41) in the axial direction.

2. The electric coolant pump according to claim 1, wherein the coolant flow passage (14) extends in the axial direction from the end of the sintered sliding bearing on the pump chamber (10) side over 90% of the component depth of the sintered plain bearing (41).

3. Electric coolant pump according to claim 1 or 2, wherein the bearing clearance in the sintered sliding bearing (41) of the shaft (4) is set to less than 10 pm.

4. An electric coolant pump according to one of claims 1 to 3, wherein the porosity of the sintered sliding bearing (41) is set to over 40%.

5. Electric coolant pump according to one of claims 1 to 4, wherein the rotor (32) is formed in a cup shape, whose inner surface facing the shaft seal (5) and with this axially overlapping on the shaft (4) is fixed.

6. An electric coolant pump according to one of claims 1 to 5, wherein an axial bearing of the shaft (4) is provided by an axial sliding bearing, which by a free end of the shaft (4) and a contact surface on the

Pump housing (1), preferably a pump cover (11) is formed.

7. An electric coolant pump according to one of claims 1 to 6, wherein the shaft seal (5) has at least two sealing lips for dynamic sealing on the shaft circumference, which are aligned at least on one axial side sealing effect.

8. An electric coolant pump according to one of claims 1 to 7, wherein the stator (31) of the electric motor (3) is arranged in axial overlap with the at least one coolant flow channel (14).

9. An electric coolant pump according to one of claims 1 to 8, further comprising a control unit (18) which is arranged in the motor chamber (13) in the axial direction between the separating element (12) and the stator (31).

10. An electric coolant pump according to any one of claims 1 to 9, wherein the motor chamber (13) has an opening (20) to the atmosphere, which is closed by a liquid-tight and vapor-permeable pressure equalization membrane.

11. Use of an electric coolant pump according to one of claims 1 to 10 as an additional water pump in a coolant-carrying system in a vehicle with a V erbrennungsmaschine and a main water pump.