Coolant pump with application-optimised design

Abstract

An electric coolant pump is used as an auxiliary water pump in a vehicle. The pump includes radial mounting of the shaft (4) is provided by means of a coolant-lubricated radial sliding bearing (41) arranged between the pump impeller (2) and the 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 between the radial sliding bearing (41) and the motor chamber (13). The rotor (32) is bell-shaped with an inner surface facing the shaft seal (5) and being fixed to the shaft seal (5) to axially overlap with the shaft (4). The motor chamber (13) has an opening to the atmosphere, which is closed by a liquid-tight pressure equalization membrane (6) that is permeable to vapor.

Claims

1. An electrical coolant pump for conveying coolant in a vehicle, comprising: a pump housing with a pump chamber in which a pump impeller is rotatably received, an inlet and an outlet which are connected to the pump chamber; a shaft rotatably mounted on the pump housing, wherein the pump impeller is fixed to the shaft; a coolant-lubricated radial sliding bearing disposed between the pump impeller and a radially outer rotor providing a radial support of the shaft; a dry-running electric motor with a radially inner stator and the radially outer rotor is received in a motor chamber, the motor chamber being separated from the pump chamber; a shaft seal disposed between the radial sliding bearing and the motor chamber; wherein the rotor is formed in a bell shape, the inner surface of the rotor faces the shaft seal and is fixed with the shaft seal in an axially overlapping manner on the shaft; and the motor chamber has an opening toward atmosphere which is closed by a liquid-tight and vapour-permeable pressure equalisation membrane.

2. The electrical coolant pump according to claim 1, wherein an axial support of the shaft is provided by an axial sliding bearing disposed upstream of the pump impeller in a flow direction of the coolant.

3. The electrical coolant pump according to claim 1, wherein an axial sliding bearing is formed by a free end of the shaft and by a run-up surface on the pump housing, on a pump cover.

4. The electrical coolant pump according to claim 1, wherein the shaft seal has at least two sealing lips for dynamic sealing on the shaft circumference which are oriented in a sealing manner toward at least one axial side.

5. The electrical coolant pump according to claim 1, wherein the pump housing has at least one lubrication channel which connects the pump chamber to a rear end of the radial sliding bearing opposite from the pump chamber.

6. The electrical coolant pump according to claim 5, wherein the at least one lubrication channel includes at least one filter.

7. The electrical coolant pump according to claim 1, wherein the stator of the electric motor is disposed to axially overlap the at least one lubrication channel.

8. A method of operating an electrical coolant pump according to claim 1, comprising operating the electrical coolant pump as an auxiliary water pump in a coolant-carrying system in a vehicle with an internal combustion engine and a main water pump.

Description

DESCRIPTION OF THE DRAWING

(1) The invention is described below based on an exemplary embodiment with reference to the drawing of FIG. 1.

(2) As may be seen in the axial sectional views in FIG. 1, a pump housing 1 includes an intake socket 16 and a pressure socket 17 illustrated on the left side, which lead into the pump chamber 10. The intake socket 16 serves as a pump inlet which is put on an open, axial end of the pump housing 10 in the shape of a separate pump cover 11 and which leads toward an end face of a pump impeller 2 fixed on a shaft 4. The circumference of the pump chamber 10 is surrounded by a spiral housing leading tangentially to a pressure socket 17 that forms a pump outlet.

(3) The pump impeller 2 is a known radial pump impeller with a central opening adjacent to the intake socket. The delivery flow impinging on the pump impeller 2 through the intake socket 16 is accelerated by the inner vanes in a radially outward direction into the spiral housing of the pump chamber 10 and carried off.

(4) At a side shown on the right, the pump housing 1 includes a cavity referred to as a motor chamber 13 which is separated by a partition 12 of the pump housing 1 from the pump chamber 10 and in which a brushless electric motor 3 with an external rotor is accommodated. A stator 31 with field coils of the electric motor 3 is fixed around a cylindrical section of the partition 12 of the pump housing 1 inside the motor chamber 13. The rotor 32 with permanent magnetic rotor poles is fixed rotatably around the stator 31 on the shaft 4.

(5) An axially open end of the motor chamber 13 is closed by a motor cap of the pump housing 1, in which an electronic control unit or ECU of the pump including power-control electronics of the electric motor 3 is embedded in a manner open to the motor chamber 13. A cable bushing leading supply lines to the field coils past the rotor 32 is arranged between the power-control electronics and the stator 31 at a lower surface of the pump housing 1.

(6) The electric motor 3 is a dry runner of which the field coils are unenclosed or open at the air gap to the rotor 32 to the motor chamber 13. The rotor 32 has a bell shape typical for an external rotor, which is seated on the free end of the shaft 4, shown on the right, and which carries the permanent magnetic rotor poles in the axial area of the stator 31. Uncharacteristically for a rotor body, the rotor 32 preferably includes no through-holes in a radially extending section, as is usually the case in order to decrease the accelerated mass at rotating carrying bodies. The bell-shaped rotor 32 thus preferably forms a closed inner side open only at the left side for receiving the stator 31.

(7) The shaft 4 extending between the pump chamber 10 and the motor chamber 13 is radially mounted by a radial sliding bearing 41 in the cylindrical section of the division 12 of the pump housing 1. The sliding surfaces at the shaft circumference and at the bearing seat of the sliding bearing 41 are lubricated by the coolant conveyed by the auxiliary water pump, said coolant penetrating into the bearing gap between the sliding surfaces, as will be described later.

(8) Additionally, the shaft 4 is axially mounted at the left free end. The axial sliding bearing 42 is formed by a pair of sliding surfaces between the end face of the shaft 4 and a run-up surface provided by a projection or a stay inside the intake socket 16 correspondingly positioned in front of the pump impeller 2 at the pump cover 11. During operation, the pump impeller 2 pushes the shaft 4 via a suction effect in the direction of the intake socket 16 against the run-up surface such that an axial load received by the shaft bearing in this one direction is sufficient. Because a bearing gap between the sliding surfaces is surrounded by the delivery flow, the axial sliding bearing 42 is also lubricated by the coolant, at least in the form of initial and, during vibrations or turbulences, renewed wetting of the sliding surfaces with the coolant.

(9) A shaft seal 5 sealing an open end of the cylindrical section of the partition 12 of the pump housing 1 against the shaft 4 is arranged between the radial sliding bearing 41 and the motor chamber 13. The shaft seal 5 is a seal with two lips which is pressed into the cylindrical section of the partition 12 and which comprises two successive sealing lips (not illustrated) directed toward the radial sliding bearing 41 for one-sided dynamic sealing on the shaft circumference.

(10) Furthermore, lubrication channels 14 are provided inside the wall of the cylindrical section of the partition 12 in the pump housing 1 which, on the one hand, open at a back surface of the pump impeller 2 into the pump chamber 10 and, on the other hand, lead to a ring-shaped cavity surrounding the shaft 4 between the rear end of the radial sliding bearing 41 and the shaft seal 5. During operation, coolant flows out of the pump chamber 10 through the lubrication channels 14 toward 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 sliding bearing 41 such that it flows back in the opposite direction. The axial circulation of the coolant, combined with the rotational motion between the sliding surfaces, ensures a regular distribution and lubrication of the bearing gap with the coolant. The coolant includes an anti-freeze agent with friction-reducing properties, e.g. a glycol, silicate or the like. At the same time, particulate caused by friction of the sliding surface pair are discharged into the pump chamber and into the delivery flow.

(11) On the other hand, filters 15 are arranged in the area of the openings of the lubrication channels 14 to the pump chamber 10, which prevent particulate impurities, such as metal abrasion or the like, from being flushed out of the delivery flow into the bearing gap of the radial sliding bearing 41 or into the sealing gap of the shaft seal 5. When the coolant circulates through the lubrication channels 14 and the radial sliding bearing 41, a reduced pressure, compared to the pump chamber 10, acts in the radial cavity between the radial sliding bearing 41 and the shaft seal 5 due to a flow resistance of the filter 15. Although the reduced pressure set by, in addition to the configuration of the filter, the number and the flow cross-section of the lubrication channels 14, weakens the circulation through the radial sliding bearing, it also relieves the shaft seal 5, which results in a longer service life of the sealing lips due to less friction and smaller leakage.

(12) The small, unavoidable leakage dripping out of the circulation of the lubrication channels 14 through the shaft seal 5 over time does not, however, come directly into contact with the field coils or the motor electronics in the motor chamber 13. During operation, the drops of leakage reach the inner surface of the rotating rotors 32 behind the shaft seal 5 and are carried out radially by centrifugal force. Due to turbulence at the rotor poles or permanent magnets and due to the operating temperature resulting from the power dissipation at the field coils, the drops of leakage vaporize in the air gap between the stator 31 and the rotor 32 without being able to moisten the radially inner stator 32 in a liquid phase, i.e., without being able to exert a corrosive effect.

(13) Due to the closed bell shape of the rotor 32, the drops of leakage may not reach the motor chamber 13 and the electronic devices in an axial direction but are instead intercepted at the inner surface of the rotor 32 and supplied to the air gap for vaporization. In order to keep a volume of the air gap low, it is shaped in a complementary manner and staggered toward the circumference of the cylindrical section of the division 12 and the stator 32.

(14) When the drops of leakage transit from the liquid phase to the gaseous phase, their volume increases, which, if the volume of the motor chamber 13 were closed, would lead to a pressure increase independent of a pressure fluctuation, which would be caused by temperature fluctuations between operation and an idle state of the pump.

(15) However, a membrane 6 is provided between the motor chamber 13 and the surrounding atmosphere, which enables compensation of pressure fluctuations from the motor chamber 13 to the atmosphere. The membrane 6 is semi-permeable with respect to a water permeability, i.e., it does not allow water in a liquid phase to pass, while air carrying moisture may diffuse through it up to a limit with respect to the size of the droplets or a density of droplets agglomerating at the membrane surface. When a volume expands due to vaporization inside the motor chamber 13, warm air carrying moisture may pass through the membrane 6 such that vaporized drops of leakage are effectively carried out into the atmosphere. In the opposite direction, the membrane 6 in turn protects against splash water or the like entering during operation of the vehicle.

(16) The membrane 6 closes an opening of the pump housing 1 which is arranged at the top in an area of an exit of the air gap between the stator 31 and the rotor 32. Furthermore, a plug for an external power supply is arranged at the top surface of the pump housing 1.

(17) In addition to the illustrated and described embodiment, the invention may also be implemented with alterative developments having additional features or omitting described features. As may be seen from the explanations regarding the solution of the problem, the pump may also be implemented without lubrication channels 14 and the filter 15, or with a different axial bearing than the sliding bearing 42 in the area of the intake socket 16, or with a different shaft seal 5 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 sliding bearing 41, which may be set via the bearing gap, may be utilized via the operating pressure from the pump chamber 10, a decreased pressure compared to the pump chamber 10 once again acting on the shaft seal 5 behind the radial sliding bearing 41.