Electric machine for a motor vehicle

Abstract

The invention relates to an electric machine for a motor vehicle, comprising an electric motor (24), a metal motor housing (20), and motor electronics (32) for actuating the electric motor (24), the motor electronics (32) being arranged on the motor housing (20), the motor electronics (32) having a circuit board arrangement (34) with a zero-potential conductor path (40) and an electronic component (38), the surface of the circuit board assembly (34) is substantially completely covered by an electrically non-conductive protective layer (48) except for the zero-potential conductor path (40), and the zero-potential conductor path (40) is arranged on the circuit board assembly (34) such that a discharge arc can be formed between the motor housing (20) and the zero-potential conductor path (40) in the event of electrostatic accumulation of the motor housing (20).

Description

TECHNICAL FIELD

[0001] The present application relates to an electric machine for a motor vehicle, having an electric motor and a metallic motor housing and motor electronics for controlling the electric motor. BACKGROUND

[0002] In modern motor vehicles, electric motors are used in a variety of ways as drives for different adjusting elements. Electric motors can be used, for example, as window lifter drives, sunroof drives or seat adjustment drives, steering drives (EPS, Electrical Power Steering), cooling fan drives, transmission actuators or brake boosters. Such electric motors must have a comparatively high torque density or power density and can be operated safely even at high temperatures.

[0003] Electric motors, in particular brushless electric motors, as (rotating current) electric machines generally have a stator with field windings or stator windings, which is arranged coaxially with a rotor with one or more permanent magnets. The rotor and the stator are, for example, constructed as a lamination stack, wherein the stator teeth carry the coils of the field windings in the stator slots between them.

[0004] In brushless electric motors, the alternating current provided for energizing the stator windings is generally generated by a current converter (inverter). In smaller electric motors, the current converter is generally accommodated together with the associated motor electronics (control electronics) in an electronics compartment integrated into the motor housing.

[0005] The motor electronics generally have a circuit board assembly (PCBA) equipped with electronic components (sensors, controllers, transistors, etc.). In order to center and / or hold the circuit board assembly in the electronics compartment, the circuit board assembly can have a recess by which the circuit board assembly is placed, for example, form-fittingly onto a protruding protrusion of the motor housing or the electronics compartment bottom.

[0006] During production and handling of the electric motor, which has not yet been installed, it can happen that the metallic motor housing is electrostatically charged. Thereby, there is a risk of an electrostatic discharge (ESD) in the form of an electric arc from the motor housing to the circuit board assembly. Such an electric arc can damage or completely destroy the electronic components arranged on the circuit board assembly before the electric motor is installed in the motor vehicle. SUMMARY

[0007] It is the task of the present application to specify an electric machine which is particularly suitable. In particular, a simple design and a safe operation should be achieved without the risk of static charge accumulation damaging the electronic components of the circuit board assembly.

[0008] According to the application, this task is solved with the features of claim 1. Advantageous design solutions and refinements are the subject of the dependent claims.

[0009] The electric machine according to the application is provided for and suitable and intended for a motor vehicle. The electric machine has an electric motor and a metallic motor housing. The electric machine also has motor electronics (control electronics) for controlling the electric motor.

[0010] The motor electronics is embodied in particular as an electronic control unit which is arranged on the motor housing. For example, the motor electronics is arranged directly on a housing end side of the motor housing. The motor electronics has a circuit board assembly, i.e. a circuit board or printed circuit board (English: Printed Circuit Board, PCB), which has electronic components for implementing the control functions. The circuit board assembly also has conductor tracks for electrically contacting and interconnecting these electronic components and a zero-potential conductor track (English: Ground guidance bar) or a zero-potential plane, i.e. a conductor track or a plane which is electrically conductive and connected to ground (English: Ground, GND) or zero potential.

[0011] According to the application, the surface of the circuit board assembly is essentially completely covered by an electrically non-conductive or electrically insulating protective layer, with the exception of the zero-potential conductor track. In other words, the surface of the circuit board assembly is essentially completely covered by the protective layer, with the exception of the zero-potential conductor track, which is bare (uncoated, uncovered). "Essentially completely covered or covered" is understood here and in the following, in particular, as meaning that the circuit board and the electronic components arranged thereon and the contact points are covered by the protective layer, wherein, for example, only the individual test points of the circuit board assembly are bare. Here, preferably, all electrically conductive surfaces are covered, which is not necessarily achieved by means of soldering points, thermal connections or thermal contacts.

[0012] A "test point" is understood here and in the following, in particular, as a defined contact point on a circuit board (English: printed circuit board, PCB), which is provided for electrical checking and diagnosis. The contact point enables an electrical measurement to be carried out during production or in operation in order to check the functionality and integrity of the motor electronics. For example, the test point is embodied as a metal surface or a pin, which can be simply contacted with a measuring instrument (for example an oscilloscope, a multimeter or a special test device).

[0013] According to the application, a bare zero-potential conductor track is arranged on the circuit board assembly or on the circuit board such that, in the event of electrostatic build-up on the motor housing, an electrical discharge arc can be formed between the motor housing and the zero-potential conductor track. For example, the spacing between the zero-potential conductor track and the motor housing is less than 5 mm, in particular less than 2 mm. A particularly suitable electric machine is thereby achieved, which is particularly safe and reliable in terms of electrostatic discharge.

[0014] According to the application, the impedance of the arc path (discharge path) to the circuit board assembly is increased by means of the electrically non-conductive protective layer, and the impedance of the robust discharge path from the motor housing to the zero potential is reduced by means of the bare zero-potential conductor track. The likelihood of an arc being formed against the zero-potential conductor track is thereby increased, thus protecting the electronic components of the circuit board assembly. In other words, a safe discharge path for electrostatic discharge of the motor housing is provided, and at the same time the sensitive electronic components of the motor electronics are protected from the effects of an arc discharge.

[0015] The coating of the electronic components by means of the protective layer further improves the electromagnetic compatibility (EMV) of the motor electronics and thus of the electric machine.

[0016] For example, the electric machine is implemented as a brake module, in particular as a so-called "integrated power brake" (IPB), in which the functions of brake boost and brake regulation are integrated in a single module. Such a brake module thus, for example, implements the functions of a conventional brake booster, an anti-lock braking system (English: Anti-lock Braking System, ABS) and further electronic brake assistance systems.

[0017] The electric motor is at least partially arranged in the motor housing. The electric motor has a stationary or housing-fixed stator, in which a rotor which is fixed relative to the motor shaft is arranged in a rotatable manner. The rotor here, for example, drives a transmission unit which converts the rotational movement of the rotor or motor shaft into a translatory piston movement of a hydraulic unit for generating brake pressure. The motor electronics are arranged on the housing end side of the motor housing, in particular on the B side of the motor shaft.

[0018] "Axial" or "axial direction" is understood here and in the following, in particular, as a direction parallel to (coaxial to) the rotational axis of the electric motor, i.e. perpendicular to the housing end side of the motor housing. Correspondingly, "radial" or "radial direction" is understood here and in the following, in particular, as a direction along the radius of the electric motor, oriented perpendicular to (transverse to) the rotational axis of the electric motor. "Tangential" or "tangential direction" is understood here and in the following, in particular, as a direction along the circumference of the motor housing or electric motor (circumferential direction, direction angle direction), i.e. perpendicular to the axial direction and the radial direction.

[0019] In conceivable embodiments, the circuit board assembly has an opening which is penetrated by a protrusion of the motor housing. The protrusion here projects, for example, axially from the housing end side, wherein the circuit board assembly is preferably placed radially and / or tangentially form-locked onto the protrusion. Thereby, a simplified orientation and / or positioning of the circuit board assembly can be achieved during the installation of the electric machine.

[0020] Here and in the following, the conjunction "and / or" is to be understood as the features associated with this conjunction can not only be jointly constituted, but also constituted alternatively to each other.

[0021] Here, the zero-potential conductor track is arranged on an edge of the circuit board assembly which surrounds the opening. For example, the circuit board assembly is implemented approximately ring-shaped, wherein the opening forms a ring-shaped opening, and wherein the zero-potential conductor track is arranged along the outer periphery of the opening. Thus, in particular, the zero-potential conductor track is arranged between the protrusion and the electronic components and / or test points, so that it is ensured that the shortest discharge path extends from the motor housing or the protrusion to the zero-potential conductor track.

[0022] In a preferred design, the protective layer is implemented as a solder mask. In other words, a solder mask or solder mask material is applied to the circuit board assembly as an (arc) protective layer. Thus, in this design, the surface of the circuit board assembly is essentially completely covered by the solder mask, except for the zero-potential conductor track. Thus, a particularly simple and inexpensive protective layer is achieved.

[0023] A "solder mask" or "solder mask layer" here and in the following is understood in particular as a protective layer on a circuit board, which is provided and designed to prevent undesired solder adhesion on specific points of the circuit board.

[0024] For example, such a solder mask is made of a polymer material and covers all areas of the circuit board in a conventional manner, except for those areas which are provided for soldering. The solder mask protects the conductor tracks and pads from oxidation and short circuits and makes the application of solder only at the desired contact points simple.

[0025] Thus, in this design, such a solder mask serves as a protective layer which essentially covers all metal surfaces and components. Here, the solder mask applied as a protective layer is applied, in particular, after the soldering process, so that the solder mask also covers the contact points formed with solder on the circuit board assembly.

[0026] For example, a two-component alkaline liquid photoimageable (English: Liquid Photoimageable, LPI) solder resist, i.e. an LPI solder resist (also referred to as solder resist lacquer), is used as the solder resist. Here, the solder resist material is applied to the circuit board in liquid form and is subsequently cured to a solid protective layer by irradiation with ultraviolet light and subsequent development. The solder resist is applied to the circuit board assembly, for example, in a flow-and-drain and / or spray application process.

[0027] The protective layer is designed with a layer thickness that is sufficiently large in order to sufficiently reduce the possibility of a discharge from the motor housing to the circuit board assembly. Here, first of all, which possibility is considered to be sufficient here and how large a possibility is specific. This depends, for example, on the protective layer material used, the distance of the circuit board assembly to the motor housing and the distance of the zero-potential conductor track to the motor housing. A suitable protective layer thickness can be learned from past machine data or corresponding tests or attempts, for example, during testability measurements. Testability measurements are carried out, for example, in the context of a design or product validation against electrostatic discharges, in particular by means of a DVE SD (Design Validation Electrostatic Discharge) test or a PVE SD (Product Validation Electrostatic Discharge) test. Different layer thicknesses can result for different electrical machines, layer materials, operating and environmental conditions or application scenarios.

[0028] In a suitable design, the protective layer has a layer thickness of more than 15 pm (micrometers). The protective layer preferably has a layer thickness of between 20 pm and 25 pm. In other words, the protective layer has a minimum layer thickness of 15 pm, in particular between 20 pm and 25 pm.

[0029] In a possible embodiment, the protective layer or the solder resist has a breakdown strength of 120 kV / mm (kilo-volt per millimeter) and at least 10 pm for 500 V (volt). Thus, with a layer thickness of 25 pm, an ESD breakdown strength of 3000 V is obtained.

[0030] The distance between the exposed zero-potential conductor track and the motor housing or the protrusion is designed to be as small as possible, so that the impedance of the discharge path to the zero-potential conductor track is as small as possible. The discharge possibility of an arc to the zero-potential conductor track is thereby advantageously increased. The distance is essentially given by the (radial) air gap formed between the motor housing (or the protrusion) and the zero-potential conductor track. In a suitable embodiment, the air gap is designed here to be less than 2 mm, in particular between 0.9 mm and 1.5 mm. BRIEF DESCRIPTION OF DRAWINGS

[0031] The embodiments of the present invention will then be described in detail with reference to the accompanying drawings. Hereinafter:

[0032] Figure 1 A schematic diagram illustrates an electric motor in the form of a braking module.

[0033] Figure 2 The electric drive of the electric machinery is shown in a schematic fragment, and

[0034] Figure 3 The electric drive is shown in perspective image segments.

[0035] The corresponding parts and dimensions are always labeled with the same reference numerals in all the accompanying drawings. Detailed Implementation

[0036] Figure 1 A schematic and simplified diagram of a motor vehicle's braking system 2 is shown. The braking system 2 is configured to generate hydraulic braking pressure on the wheel brake cylinders 4. The braking system 2 has a (braking) pressure generating unit as an electromechanical device 6, which can be operated by means of an operating unit 8, particularly by means of a brake pedal. When the operating unit 8 is operated, braking pressure is generated on the wheel brake cylinders by means of the electromechanical device 6 according to the driver's predetermined braking desire.

[0037] Next, the electromechanical device 6 is also referred to as the pressure generating unit 6. For example, the pressure generating unit 6 is implemented as a braking module, and more particularly as an integrated power brake (IPB).

[0038] The pressure generating unit 6 has an electric actuator 10 and a brake cylinder 12. A coupling transmission device 14 is arranged between the actuator 10 and the brake cylinder 12, which connects the motor shaft or drive shaft 16 ( Figure 2 The rotational motion of the brake cylinder 12 is converted into the translational motion of the piston 18 of the brake cylinder 12. For example, the chamber of the brake cylinder 12 is connected to a hydraulic reservoir (not shown in detail).

[0039] Next, using Figure 2 The driver 10 described in detail has a metal motor housing 20 and an electronics cover 22 disposed on its end side. An electric motor 24 is arranged within the motor housing 20, having a stator 26 fixed relative to the housing and a rotor 28 coupled to a motor shaft 16 in a manner resistant to relative rotation. The motor shaft 16 is rotatably supported within the motor housing 20. For example, the motor shaft 16 is supported on side B by means of a bearing 30, which is arranged, for example, in a bearing housing within the electronics cover 22.

[0040] An electronics compartment or electronics structure space is formed between the end side of the motor housing 20 on the B side and the electronics cover 22 placed thereon, in which motor electronics 32, in particular in the form of a control electronics or control unit (English: Electronic Control Unit, ECU), are arranged. The motor electronics 32 receive signals of the operating unit 8 and actuate the electric motor 24 depending on the desired brake pressure.

[0041] The motor electronics 32 have a circuit board assembly 34 with a circuit board 36 and a number of electronic components 38 for implementing the actuation function. In the figures, the components 38 are merely exemplarily provided with reference numerals. The motor electronics 32 also have a number of test points 39 Figure 3 ), which are merely exemplarily provided with reference numerals.

[0042] The circuit board assembly 24 also has a number of conductor tracks for electrically contacting and interconnecting the electronic components 38. At least one of these conductor tracks is implemented as a zero-potential conductor track 40, i.e. as a conductor track that is connected to ground (English: Ground, GND) or zero potential.

[0043] As can be seen in particular in Figure 3 , the circuit board 36 is implemented approximately circularly and has a central recess 42. On the housing end side of the motor housing 20, an axially protruding protrusion 44 is formed, which is preferably inserted into the recess 42 in a form-locked manner, radially and / or tangentially.

[0044] Here, the at least one zero-potential conductor track 40 is arranged on the edge of the circuit board assembly 34 that surrounds the recess 42. Here, the radial distance 46 between the zero-potential conductor track 40 and the protrusion 44 is designed to be less than 2 mm, in particular between 0.9 mm and 1.5 mm. As can be seen in particular in Figure 3 , the zero-potential conductor track 40 is thus arranged between the protrusion 44 and the electronic components 38.

[0045] Furthermore, the circuit board assembly 34 also has an applied electrically non-conductive or electrically insulating protective layer 48, which covers the surface of the circuit board assembly 34 substantially completely. The test points 39 and the at least one zero-potential conductor track 40 are here uncovered, thus not covered by the protective layer 48. The protective layer 48 covers the circuit board 36, its conductor tracks and the electronic components 38.

[0046] The protective layer 48 is embodied as a solder resist. Thus, the surface of the circuit board assembly 34 is substantially completely covered by the solder resist, except for the zero-potential conductor tracks 40. Here, the protective layer 48 is designed with a layer thickness which is sufficiently large in order to reduce the possibility of a discharge from the motor housing 20 or the protrusion 44 to the circuit board assembly 34. The protective layer 48 has, for example, a layer thickness of more than 15 pm. The protective layer 48 preferably has a layer thickness of between 20 pm and 25 pm.

[0047] Here, at least one exposed zero-potential conductor track 40 is arranged on the circuit board assembly 34 or the circuit board 36 such that, in the event of an electrostatic build-up of the motor housing 20, an electrical discharge arc can be formed between the protrusion 44 and the zero-potential conductor track 40.

[0048] Due to the small spacing 46 between the exposed zero-potential conductor track 40 and the protrusion 44, the impedance of the discharge path to the zero-potential conductor track 40 is particularly small. Furthermore, the impedance of the discharge path to the circuit board assembly 34 is increased by the protective layer 48. Thus, the possibility of an arc being formed against the zero-potential conductor track 40 is increased, thereby protecting the electronic components 38 of the circuit board assembly 34.

[0049] The application is not restricted to the embodiments described above. Rather, other variants of the application can also be derived therefrom by those skilled in the art without departing from the subject matter of the application claimed, within the scope of the claims disclosed. In particular, all individual features described in connection with the different embodiments can also be combined in other ways without departing from the subject matter of the application claimed, within the scope of the claims disclosed.

[0050] List of reference signs

[0051] 2 brake system

[0052] 4 wheel brake cylinder

[0053] 6 electric machine / pressure generating unit

[0054] 8 actuating unit

[0055] 10 drive

[0056] 12 brake cylinder

[0057] 14 coupling gear

[0058] 16 motor shaft

[0059] 18 piston

[0060] 20 motor housing

[0061] 22 electronics cover

[0062] 24 electric motor

[0063] 26 stator

[0064] 28 rotor

[0065] 30 bearing

[0066] 32 motor electronics

[0067] 34 circuit board assembly

[0068] 36 circuit board

[0069] 38 electronic components

[0070] 39 test point

[0071] 40 zero potential conductor track

[0072] 42 recess

[0073] 44 protrusion

[0074] 46 spacing

[0075] 48 protective layer

Claims

1. An electric machine (6) for a motor vehicle, having an electric motor (24) and a metallic motor housing (20) and motor electronics (32) for actuating the electric motor (24), - wherein, the motor electronics (32) being arranged on the motor housing (20), - wherein the motor electronics (32) have a circuit board assembly (34) equipped with a zero-potential conductor track (40) and electronic components (38), - wherein the surface of the circuit board assembly (34) is essentially completely covered by an electrically non-conductive protective layer (48) apart from the zero-potential conductor track (40), - wherein the zero-potential conductor track (40) is arranged on the circuit board assembly (34) such that, in the event of electrostatic build-up on the motor housing (20), a discharge arc can be formed between the motor housing (20) and the zero-potential conductor track (40).

2. The electric machine (6) as claimed in claim 1, characterized in that - the circuit board assembly (34) has a recess (42) which is penetrated by a protrusion (44) of the motor housing (20), - wherein the zero-potential conductor track (40) is arranged on an edge of the circuit board assembly (34) which surrounds the recess (42).

3. The electric machine (6) according to claim 1 or 2, characterized in that The protective layer (48) is embodied as a solder resist layer.

4. The electric machine (6) according to any one of claims 1 to 3, characterized in that The protective layer (48) has a layer thickness of more than 15 μιη.

5. The electric machine (6) according to any one of claims 1 to 4, characterized in that, The protective layer (48) has a layer thickness of between 20 μιη and 25 μιη.

6. The electric machine (6) according to any one of claims 1 to 5, characterized in that The spacing (46) between the motor housing (20) and the zero-potential conductor track (40) is less than 2 mm.

7. The electric machine (6) according to any one of claims 1 to 6, characterized in that, The spacing (46) between the motor housing (20) and the zero-potential conductor track (40) is designed to be between 0.9 mm and 1.5 mm.

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