Electric coolant pump

The invention is directed to an electric coolant pump and a manufacturing method thereof, in particular an automotive electric coolant pump for providing an automotive coolant circuit with liquid coolant.

Electric coolant pumps become more and more common in a cooling circuit of an internal combustion engine. The volumetric flow rate of the electric coolant pump can be controlled independently of the rotational speed of the internal combustion engine, so that the electric coolant pump is controlled depending on the engine requirements and not on the engine speed.

Alternatively, electric coolant pumps are used, for example, for cooling the accumulators as part of a drive system of an electric vehicle or a hybrid electric vehicle.

This high-performance electric coolant pumps generate a lot of heat, especially the power electronics of the brushless electric motor driving such an electric coolant pump generate large heat amounts within the pump housing.

EP 3 232 543 Al discloses a drive system arrangement of an electronic coolant pump with a pump motor being provided with a separating can for separating a wet zone from a dry zone. The brushless coolant pump is provided with commutator and power electronic components at a printed circuit board. The printed circuit board lies in a cross plane with a small distance to a bottom wall of the separating can. The separating can bottom wall surface transfers heat to the circulating coolant at the wet side of the separating can. The printed circuit board is axially supported by static supporting means within the pump housing. The axial gap between the printed circuit board and the uneven separating can bottom wall is filled with a heat conductive paste to improve the heat transfer between the printed circuit board and the separating can. The different layer thicknesses of the heat conductive paste dehomogenize the heat transfer between the printed circuit board and the separating can bottom wall.

The separating can and the supporting structure of the printed circuit board are subject to production-related dimensional variations, so that in every manufactured pump the height of the axial gap is differing.

It is an object of the invention to provide a cost-effective electric coolant pump with an effective heat dissipation and a method for manufacturing the electric coolant pump.

This object is achieved by an electric coolant pump with the features of claim 1 and with a method with the features of claim 10.

An electric coolant pump according to the invention comprises an electric motor for driving the electric coolant pump, a pump housing with a pump housing body, and a separating can with a substantially plane separating can bottom wall and a substantially cylindrical separating can shell. The separating can flu id ically separates a wet zone from a dry zone within the pump housing. A substantially plane separating can bottom wall is a separating can bottom wall surface of which the major part is defined by one plane surface. However, the separating can bottom wall can be defined by two or more substantially parallel surfaces lying at different planes, for example for reinforcing the separating can bottom wall. Alternatively, a substantially plane separating can bottom wall can be provided with reinforcement ribs. The electric motor comprises a motor rotor and a motor stator, wherein the motor rotor and the motor stator are separated by the separating can. The motor rotor is arranged within the wet zone at the inside of the separating can shell directly driving, for example, a rotor shaft with an impeller wheel. The motor stator is arranged concentrically to the motor rotor at the outside of the separating can shell, so that the motor rotor in the wet zone is electromagnetically driven by the motor stator in the dry zone. Accordingly, the electric motor is brushless and therefore electronically commutated.

The electric coolant pump further comprises a substantially plane printed circuit board, which is equipped with electronic components, for example, with electronic power semiconductors for electrically exciting the stator coils of the motor stator. The electronic components generate heat during the operation of the electric motor. The generated heat is transferred to the coolant circulating in the wet zone of the coolant pump and is thereby dissipated from the pump housing. As a result, the electric coolant pump does not require a separate cooling circuit for cooling the electronic components.

The printed circuit board is arranged substantially parallel to the liquid-cooled separating can bottom wall to create a heat sink allowing a heat transfer between the printed circuit board and the circulating coolant via the separating can. The printed circuit board is not in direct contact with the separating can bottom wall. Thus, a small axial gap is defined between the separating can bottom wall and the printed circuit board, which is filled with a heat conductive means, for example, with a heat conductive paste. The heat conductive means is most effective, if it is applicated with a relatively small and substantially constant layer thickness, so that a height-constant axial gap with a defined nominal gap height is required. The printed circuit board is supported by at least three height-adjusted supporting means, which are preferably defined by a plastic supporting means body each. With at least three supporting means the printed circuit board is supported in axial orientation. A distant arrangement of three separate supporting surfaces at the supporting means ends defines a statically determined system. The number of supporting means can alternatively be smaller or larger than three, thereby accepting a statically indetermined system with a less precise spatial orientation of the printed circuit board.

Because of production-related dimensional variations of the separating can or the pump housing body, the axial position of the separating can bottom wall is slightly differing in every manufactured pump. The nominal gap height is defined by the axial support of the printed circuit board at the permanently height-adjusted supporting means. The distal tip of every supporting means has been trimmed to a specific height before the assembly of the pump. As a result, the nominal gap height can be individually adjusted to any type of deviation of the axial position of the separating can bottom wall from its nominal axial position.

The precisely adjusted and height-constant axial gap allows a reliable heat dissipation by directly and constantly conducting the heat via the constant-layered heat conductive means to the separating can bottom wall. The heat is convectively transferred from the bottom wall to the circulating coolant contacting the wet side of the separating can bottom wall and is thereby transported away from the pump housing. The adjusted axial gap allows rougher manufacturing tolerances of the separating can and the supporting means, because the distance between the supporting surface and the separating can bottom wall, which defines the axial gap height, is individually adapted and thereby normalized for every manufactured pump. This results in a cost reduction of the manufactured electric coolant pump.

In a preferred embodiment of the electric coolant pump according to the invention, the pump housing body is made of a plastic material and the supporting means body is an integral part of the pump housing body. The supporting means body can, for example, be moulded or be casted in the plastic pump housing body. The effective heat dissipation within the pump housing, which prevents the pump housing from heat accumulations and thereby from an overheating allows to provide the application of a plastic pump housing body. As a result, the use of plastic for the pump housing body significantly reduces the production costs of the pump compared to a pump with a casted metal pump housing. Further, the total weight of the pump is reduced by the plastic pump housing.

In a preferred embodiment of the invention, the lateral position of the printed circuit board is defined by at least one, preferably by at least two separate positioning pins. Each positioning pin is reaching through a corresponding hole in the printed circuit board, so that a lateral movement of the printed circuit board is avoided. With the positioning pins, the printed circuit board is radially positioned, so that a maximum overlapping of the heat transfer surfaces of both the separating can bottom wall and the printed circuit board is guaranteed and a large heat transfer to the coolant is ensured.

Preferably, the head of each positioning pin reaching through the printed circuit board is deformed, for example by a thermal riveting process to axially fix the printed circuit board in the axial direction opposite to the direction being supported by the supporting means, so that the printed circuit board is completely fixed within the pump housing.

In a preferred embodiment of the electric coolant pump according to the invention, the positioning pin is arranged substantially centrically between two supporting means. The two supporting means are arranged adjacent and substantially equidistantly to the positioning pin. Accordingly, the printed circuit board is supported on two supporting means in the first axial direction and is fixed in the second axial direction by the deformed head of the positioning pin. As a result, the supporting means and the positioning pin define a supporting and fixing arrangement as an integral part of the pump housing body.

In a preferred embodiment of the invention the supporting means body is wedge-shaped or conical, so that the cross-sectional area of the supporting means body is distally tapering. As a result, the supporting surface of the supporting means body is relatively small, but the supporting means body is structurally relatively strong.

Preferably, the nominal gap height of the axial gap between the separating can bottom wall and the printed circuit board is less than 1.0 mm. In a more preferred embodiment, the axial gap is less than 0.8 mm. A small axial gap between the separating can bottom wall and the printed circuit board reduces the layer thickness of the heat conductive means filling the axial gap. This results in a minimal application volume of the heat conductive means and thereby results in reduced material costs. Additionally, the reduced layer thickness of the heat conductive means results in a small total wall thickness, so that the total thermal resistance of the different material layers is reduced and the heat transition is improved. In a preferred embodiment of the electric coolant pump according to the invention, the supporting means is surrounded by a collecting groove. The collecting groove collects melting material, in particular if the distal tip of the supporting means body is trimmed by a thermal process.

A method for manufacturing an electric coolant pump according to the invention comprises at least three essential process steps:

In a first manufacturing step, the electric coolant pump is in a pre-assembled state, in which the printed circuit board is not mounted. In this pre-assembled state, the pump housing body and the separating can are already mounted together. The axial position of the separating can bottom wall is measured with respect to a reference point at the pump housing body, for example, with respect to each raw supporting means body.

In a second manufacturing step, each raw supporting means body is trimmed to a defined trimming height in relation to the measured axial position of the separating can bottom wall. After all supporting means bodies have been trimmed accordingly, the distance between the axial supporting surfaces of each supporting means body and the separating can bottom wall is substantially equal.

In a third manufacturing step, the printed circuit board is assembled to the trimmed supporting means body. Due to the individual trimming of the supporting means, the axial gap is substantially constant and the opposing heat transfer surfaces of both the printed circuit board and the separating can bottom wall are substantially parallel. Preferably, an additional manufacturing step is provided before the assembly step: Before inserting the printed circuit board into the pump housing, the separating can bottom wall or the printed circuit board is provided with a heat conductive means. The applicated heat conductive means, for example a heat conductive paste, fills the axial gap between the printed circuit board and the separating can bottom wall after the printed circuit board has been mounted onto the supporting means. The heat transfer between the printed circuit board and the separating can bottom wall is thereby increased.

Preferably, the supporting means is trimmed by machining the raw supporting means body. The supporting means body is thereby mechanically trimmed, for example by milling or by ultrasound-cutting, which causes a relatively low heat input to the supporting means.

Alternatively, the supporting means is trimmed by thermally processing the raw supporting means body. For example, the supporting surface of the supporting means body is hot-formed. Thereby the material is melted and is preferably collected by the surrounding groove, so that no cutting chips are produced during the trimming method step.

In a preferred manufacturing method of the electric coolant pump according to the invention, the material removal during the trimming method step of every supporting means body is at least 0.1 mm. As a result, the distal end of every supporting means body is provided with a substantially plane supporting surface at a defined distance to the separating can bottom wall to ensure a constant axial gap between the printed circuit board and the separating can bottom wall.

An embodiment of the invention is described with reference to the enclosed drawings, wherein figure 1 shows an embodiment of an electric coolant pump with a height-adjusted supporting means according to the invention in a schematic cross-sectional view, figure 2 shows an enlarged section of figure 1, and figure 3 shows an embodiment of a raw supporting means in a schematic perspective view.

An embodiment of the electric coolant pump 10 is shown in figure 1. The electric coolant pump 10 comprises a static pump housing 30 defined by a plastic pump housing body 32, a volute-shaped pump cover 35 and a motor cover 38. The electric coolant pump 10 further comprises a metallic pot-type separating can 20 with a plane and disc-shaped separating can bottom wall 25, a cylindrical separating can shell 28 and a ring-shaped separating can flange 26. The separating can 20 flu idically separates a wet zone 12 from a dry zone 14 within the pump housing 30 of the electric coolant pump 10.

The electric coolant pump 10 is driven by a brushless electric motor 50 with a cylindrical motor rotor 52 being concentrically arranged to the cylindrical separating can shell 28 in the wet zone 12 at the radial inside of the separating can 20. The motor rotor 52 is co-rotatably connected to an impeller wheel 62 via a rotatable rotor shaft 60. The rotor shaft 60 is rotationally supported by bearings (not shown). The electric motor 50 comprises a substantially cylindrical motor stator 54, which is concentrically arranged to the cylindrical separating can shell 28 in the dry zone 14 at the radial outside of the separating can 20, and thereby surrounds the separating can shell 28 and the motor rotor 52 in the wet zone 12. The motor stator 54 in the dry zone 14 electromagnetically drives the motor rotor 52 in the wet zone 12 by exciting the stator coils (not shown) and electronically commutates the magnetic field of the stator coils.

For electronically driving the brushless electric motor 50, the electric coolant pump 10 further comprises a disc-shaped printed circuit board 40, which is arranged concentrically and in parallel to the separating can bottom wall 25. The printed circuit board 40 is axially supported by a number of axially extending height-adjusted supporting means 70, shown in figure 1 and figure 2. Each supporting means 70 is defined by an arc-shaped supporting means body 72 with an axial distal tip 71 and a collecting groove 74 surrounding the supporting means body 72. The arc of the arc-shaped supporting means body 72 is concentrically arranged to the separating can shell 28 and supports the printed circuit board 40 in its edge region. The supporting means body 72 is formed as an integral part of the plastic pump housing body 32. The supporting means body 72 is wedge-shaped, so that it distally tapers in axial direction. A plane supporting surface 76 is defined by trimming the distal tip 71 of the supporting means body 72 before mounting to axially support the printed circuit board 40.

Due to the trimming height of the supporting means body 72, a height-constant axial gap 75 is defined between the separating can bottom wall 25 and the printed circuit board 40 with a nominal axial gap height h. The nominal gap height h is preferably less than 1.0 mm and is particularly preferred less than 0.8 mm. The ideal nominal gap height h in this embodiment of the electric coolant pump 10 is 0.5 mm. The axial gap 75 is completely filled with a heat conductive paste 78 to improve the heat transition between the printed circuit board 40 and the separating can bottom wall 25. The printed circuit board 40 is provided with power electronic components 45. The power electronic components 45 are arranged within the application zone of the heat conductive means at the opposite side of the printed circuit board 40 to allow a relatively high heat flow rate transferring heat directly from the power electronic components 45 to the circulating coolant in the wet zone 12.

The electric coolant pump 10 comprises cylindrical positioning pins 80, for fixing the printed circuit board 40 in radial direction and in opposite axial direction of the supporting means 70. Each positioning pin 80 extends in axial direction and has a positioning pin head 81 at its distal end. The cylindrical positioning pins 80 reach through corresponding holes in the printed circuit board 40, so that the position of the printed circuit board 40 is thereby radially fixed. After mounting the printed circuit board 40 to the positioning pins 80, the positioning pin heads 81 are thermally deformed, so that the riveted positioning pin head 81' axially fixes the printed circuit board 40 in opposite axial direction of the supporting means 70.

Figure 3 shows an embodiment of the supporting means 70 in a raw state before the distal tip 71 of the arc-shaped supporting means body 72 is trimmed. In this embodiment two supporting means 72 are arranged as pairs at both sides of a centric and cylindrical positioning pin 80 with a conical positioning pin head 81. The two supporting means 70 are adjacent and equidistantly arranged to the centric positioning pin 80. Thereby the supporting means 70 and the positioning pin 80 define an integrally moulded mounting unit 90, which is an integral part of the plastic pump housing body 32. The mounting unit 90 is arranged concentrically to the separating can shell 28 in an arc-shaped arrangement to support and fix the printed circuit board 40 in the edge region of the printed circuit board 40. The supporting means body 72 is wedge-shaped and is surrounded by a collecting groove 74 for collecting melted material produced by thermally processing the distal tip 71 of the supporting means body 72.