Electric automotive auxiliary device

The invention refers to an electric automotive auxiliary device with an electronically commutated electric motor.

An electric automotive auxiliary device is not the traction engine but is a secondary electric device, for example an electric pump, and electric actuator etc. Automotive devices generally are extremely weight- and cost- optimised. Therefore, electric automotive auxiliary devices are often provided with a metal motor housing part housing the motor stator and the motor rotor and with a separate light plastic electronics housing part housing the motor electronics. The motor electronics comprises the commutation electronics and power semiconductors for energizing the stator coils of the motor stator.

The motor electronics housing part is fixed to the motor housing part, for example, by screw or snap connections. Alternatively, a section of the metal body of the motor housing is moulded into the plastic body of the electronics housing to provide a form-fit and fluid-tight connection so that no atmospheric humidity can flow into the electronics chamber defined by the motor housing part. However, the process of overmoulding a section of the relatively massive metal motor housing part in the plastic electronics housing part is cumbersome because the massive motor housing part needs to be heated before the overmoulding process.

It is an object of the invention to provide a light and low-cost electric automotive auxiliary device.

This object is solved with an electric automotive auxiliary device with the features of main claim 1. The electric automotive auxiliary device according to the invention is provided with an electronically commutated electric motor comprising a motor electronics for providing the commutation and for energizing the stator coils of the motor stator, and comprising a permanently magnetized motor rotor. The electric automotive auxiliary device can be an automotive device of any kind but is not the electric traction engine. The electric automotive auxiliary device can be any kind of an actuator or can be, for example, an electric liquid pump or gas pump.

The electric automotive auxiliary device is provided with a metal motor housing part radially surrounding the motor stator and the motor rotor and is provided with a plastic electronics housing part circumferentially surrounding the motor electronics. The electronics housing part is provided, seen in axial direction, adjacent to the metal motor housing part. The electronics housing part is indirectly mechanically mounted to the motor housing part via a separate metal adapter part. The separate metal adapter part is preferably a sheet-like part which is relatively thin and light in weight. The metal body of the adapter part is provided with a form-fit section which is directly moulded in the plastic body of the electronics housing part to thereby define a positive form-fit connection which preferably defines a fluid-tight connection. The form-fit connection can be of very simple nature which provides a sufficient axial fixation. The adapter part is also provided with a blank metal section being directly connected to a metal body of the motor housing part by a positive substance joint.

The positive substance joint is preferably a welded joint which can be provided point- wise or as a closed welding seam defining a fluid tight connection between the adapter part and the motor housing part.

The motor housing part can be made of a suitable steel or aluminium, and can be produced by deep-drawing, cold-forging or by die-casting. The adapter part generally is a relatively fine-structured body with a relatively low total mass so that the adapter part can be relatively easily directly moulded in the plastic body of the electronics housing part before the adapter part is welded to the motor housing part. The moulding defines a robust positive form-fit connection between them which preferably is also a fluid-tight connection. The adapter part can be produced by stamping or by deep-drawing, and can be made of a suitable steel or aluminum. The total mass of the adapter part is less than 20% of the total mass of the motor housing part.

The assembled combination of the electronics housing part and the adapter part can be mounted to the metal motor housing part after the motor stator, the motor rotor and the motor electronics have already been mounted to the motor housing part.

Preferably, the adapter part is substantially cylindrical in shape as well as the corresponding section of the electronics housing part plastic body and the corresponding section of the metal motor housing part is cylindrical in shape. Preferably, the said adapter part and the connected housing sections are provided coaxially with the rotational axis of the motor rotor.

Preferably, the electronics housing part plastic body is made of a thermoplastic material and is produced by injection moulding. Preferably, the adapter part metal body has a thermal expansion coefficient being similar to the thermal expansion coefficient of the motor part metal body. A similar thermal expansion coefficient in the context of the present electric automotive auxiliary device is a thermal expansion similarity that guarantees an acceptable total expansion difference resulting and acceptable temperature-caused tensions within a temperature range of, for example -40° to +150°C which is a typical temperature range for automotive applications. More preferably, the metal motor housing part is of the same material as the metal adapter part. Preferably, the electronics housing part is pot-like in shape and has a coaxial and substantially cylindrical housing wall and has a distal end wall substantially lying in a transversal plane. No separate cover lid element is necessary to close the distal end of the electronics chamber, but could be provided in addition.

Preferably, the electric automotive auxiliary device is a fluid pump, and the motor housing part is pot-like in shape so that the motor housing part defines a fluid separation wall substantially lying in a transversal plane and fluidically separating a dry electronics chamber from a wet motor rotor chamber. More preferably, the power semiconductors of the motor electronics are in direct thermal contact with the fluid separation wall fluidically separating the dry electronics chamber from the wet motor rotor chamber. The power semiconductors are thereby cooled by the pumped fluid which is preferably a liquid, for example a cooling liquid or a lubrication liquid. One embodiment of the invention is described with reference to the enclosed drawings, wherein figure 1 schematically shows a longitudinal cross-section of an electric automotive auxiliary device with a metal motor housing part, a metal adapter part and a plastic electronics housing part, and figure 2 shows a detail II of the assembly of the motor housing part, the adapter part and the electronics housing part of figure 1.

The figures show an electric automotive auxiliary device 10, which is, in the present embodiment, a liquid pump for pumping a liquid coolant for cooling another primary or a secondary automotive device. The electric automotive auxiliary device 10 is provided with an electronically commutated electric motor 14 which is substantially defined by a motor stator 50 and a permanently magnetized internal motor rotor 72. The motor stator 50 comprises a stacked stator body 52 and several stator coils 54 which are electrically energized by a motor electronics 28 comprising a printed circuit board 28' with several power semiconductors 29 at the proximal surface of the printed circuit board 28' lying in a transversal plane YZ. Alternatively, the power semiconductors could be provided only at the distal surface of the printed circuit board, so that the printed circuit board is in direct contact with a separation wall 44.

The rotor rotates around a rotor axis 11 and comprises a rotatable rotor shaft 70 co-rotatably supporting the motor rotor 72 and a pump rotor 12, which is, in the present embodiment, an impeller.

The electric motor 14 has, seen in axial direction X, an electronics section 18 with the motor electronics 28 and an adjacent electromagnetic section 16 with the motor stator 50 and the motor rotor 72. The housing arrangement of the electric automotive auxiliary device 10 comprises a substantially cylindrical and pot-like motor housing part 40 , a substantially cylindrical metal adapter part 30 and a substantially cylindrical and pot-like electronics housing part 20 defining an electronics chamber 22 housing the motor electronics 28. The pump-sided end of the housing arrangement is closed by a bearing shield 80 supporting a bearing 88 for rotationally supporting the rotor shaft 70.

The metal motor housing part 30 is pot -like in shape and defines a substantially cylindrical housing wall 42 and a fluid separation wall 44 substantially lying in a transversal plane YZ. The fluid separation wall 44 and a separate separating cylinder 82 filling the cylindrical gap between the motor stator 50 and the motor rotor 72 provide a fluidic separation of the wet motor rotor 72 at one side and the dry motor stator 50 as well as the dry motor electronics 28 arranged in a dry motor electronics chamber 22 at the other side.

The electronics housing part 20 is defined by a pot-like electronics housing part plastic body 20' made of a suitable thermoplastic material and defining a substantially cylindrical housing wall 23 radially surrounding the motor electronics 28 and a distal end wall 24 lying in a transversal plane YZ. Before the pump assembly, a form-fit section 32 of the cylindrical metal sheet body 30' of the adapter part 30 is directly moulded into the plastic body 20' to thereby define a form-fit connection 34. The form-fit section 32 is substantially defined by several openings 33 in the thin metal sheet body 30' of the adapter part 30.

A blank metal section 31 of the adapter part 30 is directly connected to the metal body 40' of the motor housing part by a positive substance joint 39 which is, in the present embodiment, a welded circumferential joint 39' defining a closed and fluid tight welding seam.

A circumferential elastic sealing ring 25 is provided axially between the distal front end of the metal motor housing part 40 and a proximal front end of the plastic electronics housing part 20. The elastic sealing ring 25 is lying in a sealing groove 26 defined at the proximal front end of the plastic electronics housing part 20 and provides a reliable fluid-tight sealing so that no atmospheric humidity can infiltrate into the motor electronics chamber 22.

The motor housing part metal body 40' and the adapter part metal body 30' are made of the same steel and therefore both have a substantially identical thermal expansion coefficient.

The power semiconductors 29 are in direct thermal contact with the fluid separation wall 44 which means in the present context that no air gap is provided between the power semiconductors 29 and the fluid separation wall 44.