Power pack for an electromechanical steering system for a motor vehicle

Abstract

The invention relates to a power pack (15) for an electromechanical steering system (1) for a motor vehicle, having a controller (14) enclosed by a housing (16) and having an electric motor (10), wherein the controller (14) comprises a multipart circuit board (19) that has at least two parts (20, 21) that are located parallel to one another and connected to one another, and wherein fastening elements (31) are present and connect the housing (16) to the multipart circuit board (19) and the electric motor (10), wherein the fastening elements (31) are press-in fasteners having two ends, with a joining region (33, 36) being present on each of said two ends, and wherein the press-in fasteners penetrate at least one of the parts of the circuit board (20, 21) that are located parallel to one another and are pressed into recesses (32) in the electric motor (10) and / or recesses (37) in the housing (16) by way of a corresponding joining region (33, 36) so as to establish a connection.

Description

[0001] Power pack for an electromechanical steering system of a motor vehicle

[0002] The present invention relates to a power pack for an electromechanical steering system of a motor vehicle having the features of the preamble of claim 1 as well as to an electromechanical steering system of a motor vehicle having such a power pack and to a method for assembling a power pack.

[0003] Electromechanical automotive power steering systems feature servo units that can be mounted on a pinion or rack of the steering gear as a power assistance device. The servo unit includes an electronic control unit for calculating the steering assistance.

[0004] A distinction is made between solutions in which the control unit (ECU) required for the electric motor is supplied together with the electric motor and attached to the steering system as a unit, the so-called power pack, and those in which the motor and ECU are supplied separately and are connected to each other with cables directly or via plugs.

[0005] In the Power Pack solutions, the motor housing is firmly connected to the control unit housing and provides an additional cooling surface for the control unit.

[0006] It is desirable to design the power pack to be particularly space-saving and to further simplify production.

[0007] It is therefore an object of the present invention to provide a power pack for an electromechanical steering system of a motor vehicle that is compact and easy to manufacture.

[0008] This object is achieved by a power pack having the features of claim 1, by an electromechanical steering system of a motor vehicle having such a power pack and by a method for assembling a power pack having the features of claim 15.

[0009] Accordingly, a power pack for an electromechanical steering system of a motor vehicle is provided, comprising a control unit enclosed by a housing and an electric motor. The control unit comprises a multi-part printed circuit board having at least two parallel parts that are connected to one another, and fastening elements that connect the housing to the multi-part printed circuit board and the electric motor. The fastening elements are press-in fasteners having two ends, each with a joining area. The press-in fasteners penetrate at least one of the parallel parts of the printed circuit board and are pressed into receptacles in the electric motor and / or receptacles in the housing with a corresponding joining area to establish a connection. The use of press-in fasteners makes the connection significantly simpler than conventionally used screws.Self-clinching fasteners preferably form a force-locking and form-locking connection. Furthermore, the layout of the power pack can be simpler and more compact. The electric motor mounts are preferably formed in a motor bearing plate, particularly the outer side of the B-side motor bearing plate.

[0010] Preferably, the housing has a connector plate arranged on the front side, in which the receptacles of the housing are formed on the inside.

[0011] In a first embodiment, the fastening elements can be provided to penetrate both parallel parts of the circuit board and to be pressed into a receptacle of the electric motor in a first joining area and into a receptacle of the housing in a second joining area. The first and second joining areas are preferably each located at one end of the fastening elements. Preferably, a total of four fastening elements are provided.

[0012] In another embodiment, the fastening elements may comprise first fastening elements and second fastening elements, wherein the first fastening elements are pressed into corresponding receptacles of the electric motor and, in the respective other joining region, into first receptacles of a spacer. The spacer is arranged between the two parallel parts of the circuit board, and wherein the second fastening elements are pressed into corresponding receptacles of the housing and, in the respective other joining region, into second receptacles of the spacer. Preferably, a total of 8 fastening elements are provided.

[0013] It is advantageous if the two parallel parts of the circuit board are rigid and connected by at least one flexible part of the circuit board, with the spacer being designed to align the circuit board parts with each other. The spacer can also be made of a material with high thermal conductivity and form an additional cooling surface.

[0014] Preferably, the fastening elements have a substantially constant outer diameter over their entire length, except for at least one area in which a type of disc is formed, which serves as a support surface. The fastening elements preferably have undercuts, for example, in the form of a fir-tree-like structure.

[0015] It is particularly cost-effective if the circuit board is manufactured in one piece and the circuit board has the rigid and flexible parts.

[0016] In a preferred embodiment, the circuit board has a third rigid part arranged between two flexible parts and offset by 90° from the two parallel parts of the circuit board. The third rigid part is located between the other two rigid parts and is intended to support the bending process.

[0017] Preferably, power modules are arranged on a first part of the two parallel parts of the circuit board, which is closest to the electric motor, and there is a connection to the phases of the electric motor. Furthermore, the modules primarily responsible for signal processing and control tasks are arranged on a second part of the two parallel parts of the circuit board.

[0018] It may be advantageous to have an additional circuit board carrying components that serve as filters for electromagnetic compatibility, with this additional circuit board also being penetrated by the fastening elements. Furthermore, an electromechanical steering system of a motor vehicle with a power pack as described above is provided.

[0019] Furthermore, a method for assembling a power pack for an electromechanical steering system of a motor vehicle with a control unit enclosed by a housing and an electric motor is disclosed, wherein the control unit comprises a multi-part printed circuit board having at least two parallel parts which are connected to one another and wherein fastening elements are provided which connect the housing to the multi-part printed circuit board and the electric motor, wherein the fastening elements are press-in fasteners having two ends, each of which has a joining region, and the following steps are provided:

[0020] - Pressing a first joining area into corresponding receptacles of the electric motor and creating a force-locking and form-locking connection,

[0021] - Passing the press-in fasteners through a hole in at least one of the parallel parts of the circuit board, and

[0022] - Pressing a second joining area into corresponding receptacles of the housing or corresponding receptacles of a spacer arranged between the at least two parts of the circuit board lying parallel to one another and producing a force-fitting and form-fitting connection.

[0023] This results in the above-mentioned advantages over conventional screw connections.

[0024] Two embodiments of the invention are explained in more detail below with reference to the drawings. Identical or functionally identical components are provided with the same reference numerals in the figures.

[0025] The figures show:

[0026] Fig. 1 : a schematic representation of an electromechanical steering system, Fig. 2: a spatial view of a power pack of an electromechanical

[0027] steering system,

[0028] Fig. 3: a spatial view of the power pack of Figure 3 without the housing part,

[0029] Fig. 4: an exploded view of the power pack of Figure 3,

[0030] Fig. 5A: a longitudinal section through the power pack of Figure 3,

[0031] Fig. 5B: a top view of the power pack and representation of the section of Fig. 5A, as well as

[0032] Fig. 6: an exploded view of a power pack of another

[0033] Embodiment.

[0034] Figure 1 schematically shows an electromechanical motor vehicle power steering system 1 with a steering wheel 2 that is rotationally fixedly coupled to an upper steering shaft 3. The driver applies a corresponding torque as a steering command to the steering shaft 3 via the steering wheel 2. The torque is then transmitted via the upper steering shaft 3 and lower steering shaft 4 to a steering gear shaft 5 and a steering pinion 6. The pinion 6 meshes in a known manner with a toothed segment of a rack 7. The rack 7 is mounted in a steering housing so that it can be displaced along its longitudinal axis. At its free end, the rack 7 is connected to tie rods 8 via ball joints (not shown). The tie rods 8 themselves are each connected in a known manner to a steered wheel 9 of the motor vehicle via steering knuckles.A rotation of the steering wheel 2, via the connection of the steering shaft 3 and the pinion 6, leads to a longitudinal displacement of the rack 7 and thus to a pivoting of the steered wheels 9. The steered wheels 9 experience a reaction via a roadway 900 that counteracts the steering movement. Therefore, pivoting the wheels 9 requires a force that necessitates a corresponding torque on the steering wheel 2. An electric motor 10 of a servo unit 11 is provided to assist the driver in this steering movement.

[0035] The servo unit 11 can be coupled as a power assist device 11, 100, 101 either to a steering shaft 3, the steering pinion 6, or the rack 7. The respective power assist device 11, 100, 101 applies an auxiliary power torque to the steering shaft 3, the steering pinion 6, and / or the rack 7, thereby assisting the driver in steering. The three different power assist devices 11, 100, 101 shown in Figure 1 show alternative positions for their arrangement. Typically, only one of the positions shown is occupied by a power assist device.

[0036] As shown in Figures 2 to 4, the power assist system includes the electric motor 10. Typically, the electric motor and the control and power electronics required to operate the electric motor are manufactured as a single mechatronic assembly. They are thus interchangeable according to the modular principle and are only connected to the actual steering gear during final assembly of the steering system. This assembly is referred to in the relevant technical community as a power pack.

[0037] A motor shaft 13 of the electric motor 10 protrudes from one end of the motor housing 12 and is intended to be connected to a steering gear for transmitting torque. A control unit 14 is connected to the opposite end of the motor housing 12. The control unit 14 and the electric motor 10 share housing components and form a power pack 15. The housing of the power pack 15, shown in Figure 2, is closed at the end by a connector plate 16. The connector plate 16 is preferably a plastic cover with formed connector housings 17, each of which forms part of an electrical connector. The electrical contacts 18 to be contacted are each located in a connector housing 17, as can be seen in Figures 4 and 5A. The vehicle signals are transmitted from the CAN bus or FlexRay bus to the control unit via a connector and a correspondingly manufactured plug connection.The torque sensor's signals are transmitted to the control unit via a connector. Power is also supplied via two connectors between a battery and the control unit.

[0038] As can be seen from Figures 4 and 5A, the control unit 14 comprises a multilayer circuit board 19 consisting of three rigid and two flexible parts. The circuit board 19 is bent so that two of the rigid parts are aligned parallel to each other. A first circuit board layer 20 is closest to the electric motor 10. It contains power modules, such as the power switches (MOSFETs) or 3-phase bridges with bridge shunts, bridge drivers, FET drivers, connecting capacitors, and connections to the phases of the electric motor. Furthermore, a position sensor is mounted on the first circuit board layer 20, which provides information about the actual position angle of the motor shaft of the electric motor.

[0039] A second circuit board layer 21, arranged parallel to the first, contains the modules primarily responsible for signal processing and control tasks. These include a main microcontroller, a flash interface for the microcontroller, an interface for the torque sensor, a vehicle interface (CAN, FlexRay), a power supply for the components on this board, and a signal measurement module for processing various sensor signals (temperature, angle, voltage). The signal connections of the connectors are also located on the second circuit board layer 21, which is reinforced with the connector plate 16 for the connections. An additional circuit board with electromagnetic compatibility (EMC) filters 22 can be arranged inside the connector plate 16, as shown.The connector plate 16 has an opening through which lead frames 23 extend, which can transmit current directly to the first circuit board layer 20 without the second circuit board layer.

[0040] 21. The lead frames 23 are thus located outside the second circuit board 21 in the radial direction to a longitudinal axis of the power pack.

[0041] The third PCB layer 24 is located between the two flexible parts 25, 26 of the PCB 19. Its main function is to ensure the precise positioning of the remaining parts during the bending of the PCB 19. The third PCB layer 24 has no mounted electronic components and is rotated 90° compared to the first and second PCB layers 20, 21.

[0042] When assembling the control unit 14, as can be seen from Figure 4, first the second circuit board layer 21 is attached and soldered to the B-side motor bearing plate 27 and then the third circuit board layer is attached with the aid of a spacer 28

[0043] 22 is brought into contact with a support geometry 29 of the spacer 28, and the second circuit board layer 21 is bent 180° relative to the first circuit board layer 20, so that the two circuit board layers 20, 21 are parallel to one another. The support geometry 29 helps to correctly form the correct bending radius and other related geometries. The support geometry 29 has a guide for the flexible circuit board parts 25, 26, and a groove 30 is provided for the precise positioning of the third circuit board layer 24, into which the third circuit board layer 24 is placed during assembly. It is also conceivable that special tools are used in which the spacer has additional functions, such as aligning and holding the various assembly components before final fixation.

[0044] Depending on the desired design, the spacer 28 can be made of plastic or aluminum, depending on whether an additional cooling surface is required for the first circuit board layer 20. The spacer 28 can thus have additional cooling structures. It is important to achieve the smallest possible distance between the aluminum of the spacer 28 and the flexible circuit board parts 25, 26 in order to reduce the thermal stacking distance and the thermal resistance. A highly thermally conductive material is introduced between the flexible area and the rigid area. A thermal interface material (TIM) is conceivable, for example in the form of a gap filler, grease, a thermally conductive adhesive, or the like.

[0045] The use of flexible printed circuit board parts 25, 26 allows the design of the control unit 14 to be adapted to customer requirements. For example, the angle between the first printed circuit board layer 20 and the second printed circuit board layer 21 can be selected. This can be 45°, 90°, or even 270°, depending on the desired connector arrangement.

[0046] The printed circuit board 19 is manufactured in one piece. At the beginning of the manufacturing process, the flexible printed circuit board parts 25, 26 have the same properties as the rigid printed circuit board layers 20, 21, 24, since the entire printed circuit board 19 is made from a single base material. The final printed circuit board layout is a multilayer printed circuit board 19 with rigid and flexible areas, and the manufacturing process includes the following steps:

[0047] - The base material consists of a carrier material and copper material. The carrier material preferably has high thermal conductivity.

[0048] Unwanted copper material is chemically removed to create the desired

[0049] To obtain circuits on the substrate. This is done individually for each layer of the final product.

[0050] - The PCB layers are then stacked on top of each other, using pre-impregnated material between the PCB layers,

[0051] - The base material and the pre-impregnated material are removed by depth-controlled milling to create the flexible parts of the circuit board. The flexible parts still have a thin layer of material over the conductive copper material, and the copper is not milled during the process. Copper is required so that the flexible parts of the circuit board can also carry high currents. In such a high-current application, the spacer is made of metal and serves as a heat sink on the flexible part of the circuit board. A thermally conductive material is also applied between the heat sink (spacer) and the flexible part of the circuit board (see above).

[0052] In its final state, the circuit board 19 has a thick and equally wide copper layer (preferably 2 oz as is state of the art) in the rigid circuit board layers 20, 21, 24, with a specially shaped heat sink. This allows for a reduction in parasitic resistance.

[0053] In order to simplify the assembly of the control unit 14 of the power pack 15 and to make the power pack 15 as compact as possible, special fastening elements 31 are used for the assembly of the power pack components.

[0054] The fastening elements 31 are shown in Figure 4 and Figure 5A. A total of four fastening elements 31 are provided, which are designed as self-clinching fasteners. Self-clinching fasteners are pressed into a receiving hole. There, the self-clinching fastener displaces the material in the area of ​​the hole. This material flows through cold forming into an undercut in the shaft area of ​​the fastener. The self-clinching fastener has two ends, each of which is used for a joining process and for establishing a connection. The joining areas can, for example, be designed in the shape of a Christmas tree. For a first connection, the electric motor 10 has receptacles 32 on its front side, which protrude from the top side and extend parallel to the longitudinal axis of the motor. In the embodiment shown, the receptacles 32 are located in the B-side

[0055] Motor position plate 27 is formed and is distributed approximately evenly along the circumference of the electric motor or lies on the edges of an imaginary right-angled quadrilateral. The receptacles 32 are located as far apart as possible. The self-clinching fasteners are pressed into the receptacles 32 with a first joining area 33 located at the first end, and a permanent connection to the electric motor is established. The self-clinching fasteners have an area 34 adjacent to the first joining area 33 in which the outer diameter is enlarged, forming a type of disk. The disk lies on the receptacles 32 of the electric motor, limits the press-in depth, and serves to precisely define the position. The circuit board 19 has corresponding holes 35 in the rigid circuit board layers 20, 21 lying parallel to one another, through which the self-clinching fasteners protrude.The press-in fasteners are dimensioned such that, when mounted, they protrude beyond the circuit board 19, leaving the second end exposed. This second end has a second joining area 36, ​​which is pressed into corresponding receptacles 37 formed on the underside of the connector plate 16.

[0056] The described fastening method using self-clinching fasteners saves a significant amount of space for the power pack and the entire electronics assembly. Multiple subcomponents are connected together using a single connection point / assembly process. Furthermore, the self-clinching fastener can connect different types of raw materials, such as plastic and aluminum. Compared to a screw, the self-clinching fastener has the advantage that the manufacturing of the fastener itself can be simpler, and the connection process is also simpler and faster.

[0057] As shown in Figure 6, it can also be provided that a total of 8 fastening elements 31 in the form of press-in fasteners are used. In this exemplary embodiment, the first four press-in fasteners are fastened in the first joining area 33 in the receptacles 32 of the B-side motor bearing plate 27 and in a second joining area 36 in corresponding receptacles 38 of the spacer 28. The second four press-in fasteners are pressed in a first joining area 33 into corresponding receptacles 38 of the spacer 28, which are located on the opposite side of the spacer as the receptacles for the first four press-in fasteners, and in a second joining area 36 into the receptacles 37 of the connector plate 16. The second four press-in fasteners penetrate the respective holes 35 of the second circuit board layer 21 of the circuit board 19 and the first four

[0058] Press-in fasteners the respective holes 35 of the first circuit board layer 20. The press-in fasteners are not pressed into the circuit boards.

Claims

Patent claims 1. Power pack (15) for an electromechanical steering system (1) of a motor vehicle, comprising a control unit (14) surrounded by a housing (16) and an electric motor (10), wherein the control unit (14) comprises a multi-part printed circuit board (19) having at least two mutually parallel parts (20, 21) which are connected to one another, and wherein fastening elements (31) are provided which connect the housing (16) to the multi-part printed circuit board (19) and the electric motor (10), characterized in that the fastening elements (31) are press-in fasteners having two ends, at each of which a joining region (33, 36) is provided, wherein the press-in fasteners pass through at least one of the mutually parallel parts of the printed circuit board (20, 21) and are inserted into receptacles (32) of the electric motor (10) and / or receptacles (37) of the housing (16) having a corresponding joining region (33, 36) for are pressed in to create a connection.

2. Power pack (15) according to claim 1, characterized in that the receptacles (32) of the electric motor (10) are formed in a motor bearing plate (27).

3. Power pack (15) according to claim 1 or 2, characterized in that the housing comprises a plug plate (16) arranged on the front side, in which the receptacles (37) of the housing are formed.

4. Power pack (15) according to one of the preceding claims, characterized in that the fastening elements (31) pass through both parts (20, 21) of the printed circuit board which are parallel to one another and are pressed into a receptacle (32) of the electric motor (10) in a first joining area (33) and into a receptacle (37) of the housing (16) in a second joining area (36).

5. Power Pack (15) according to one of the preceding claims, characterized in that a total of four fastening elements (31) are present are.

6. Power pack (15) according to one of claims 1 to 3, characterized in that the fastening elements (31) comprise first fastening elements and second fastening elements, wherein the first fastening elements are pressed into corresponding receptacles (32) of the electric motor (10) and, in the respective other joining region, into first receptacles (38) of a spacer (28), wherein the spacer (28) is arranged between the two parts (20, 21) of the printed circuit board (19) lying parallel to one another, and wherein the second fastening elements are pressed into corresponding receptacles (37) of the housing (16) and, in the respective other joining region, into second receptacles (38) of the spacer (28).

7. Power pack (15) according to claim 6, characterized in that the two parallel parts (20, 21) of the printed circuit board are rigid and are connected by means of at least one flexible part (25, 26) of the printed circuit board (19), wherein the spacer (28) is designed to align the printed circuit board parts (20, 21) with each other.

8. Power pack (15) according to one of the preceding claims, characterized in that the fastening elements (31) have a substantially constant outer diameter over the entire length except for at least one region in which a type of disc (34) is formed which serves as a support surface.

9. Power pack (15) according to one of the preceding claims, characterized in that the circuit board (19) is manufactured in one piece.

10. Power pack (15) according to one of the preceding claims, characterized in that the printed circuit board (19) has a third rigid part (24) which is arranged between two flexible parts (25, 26) and which is arranged offset by 90° to the two parts (20, 21) of the printed circuit board (19) which are parallel to one another.

11. Power Pack (15) according to one of the preceding claims, characterized in that on a first part (20) of the two parallel Power modules are arranged on the parts of the printed circuit board (19) that are closest to the electric motor (10) and that there is a connection to the phases of the electric motor, and that the modules that are mainly responsible for signal processing and control tasks are arranged on a second part (21) of the two parts of the printed circuit board (19) that are parallel to one another.

12. Power pack (15) according to one of the preceding claims, characterized in that an additional circuit board (22) is provided which carries components which serve as filters for electromagnetic compatibility, said additional circuit board (22) also being penetrated by the fastening elements (31).

13. Power pack (15) according to one of claims 7 to 12, characterized in that the spacer (28) is formed from a material with a high thermal conductivity and forms a cooling surface.

14. Electromechanical steering system (1) of a motor vehicle with a power pack (15) according to one of the preceding claims.

15. A method for assembling a power pack (15) for an electromechanical steering system (1) of a motor vehicle with a control unit (14) surrounded by a housing (16) and an electric motor (10), wherein the control unit (14) comprises a multi-part printed circuit board (19) having at least two parallel parts (20, 21) which are connected to one another, and wherein fastening elements (31) are provided which connect the housing (16) to the multi-part printed circuit board (19) and the electric motor (10), wherein the fastening elements (31) are press-in fasteners which have two ends, each of which has a joining region (33, 36), and the following steps are provided: - pressing a first joining area (33) into corresponding receptacles (32) of the electric motor (10) and producing a force-locking and form-locking connection, Passing the press-in fasteners through a bore (35) of at least one of the parallel parts (20, 21) of the printed circuit board (19), and - pressing a second joining region (36) into corresponding receptacles (37) of the housing (16) or corresponding receptacles of a spacer (28) arranged between the at least two mutually parallel parts (20, 21) of the printed circuit board (19) and Creating a force-locking and form-locking connection.

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