CROSS-REFERENCE TO RELATED APPLICATIONS

This utility patent application is a U.S. National Stage filing under 35 U.S.C. § 371 of application Ser. No. PCT/EP2018/086658, filed Dec. 21, 2018, which is an international patent application claiming priority of/to German Pat. Appl. Nos. 10 2018 100 647.0 and 20 2018 100 161.2, each filed Jan. 12, 2018, the disclosures of which are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The invention relates to a fastening unit for connecting thermally stressed components to each other. Moreover, the invention also relates to the fastening units in combination with a thermally stressed component, and to a method for connecting two thermally stressed components.

BACKGROUND

A generic fastening unit for connecting thermally stressed components to each other, in particular for connecting a heat-generating body to a heat sink, comprises a retaining pin and a retaining element. The retaining pin is connected to a retaining head. The retaining pin passes through the retaining element. The retaining head rests against the retaining element. The retaining element engages the body or the heat sink, retaining it in a fastening direction of the retaining pin. In the mounting position, the retaining head connected to the retaining pin holds the retaining element in place, which latter in turn holds the body or the heat sink in place. The retaining pin is anchored in a hole in a component, for example a heat sink, if a power module generating thermal energy is to be retained.

DE 103 06 227 A1 discloses a power module as a thermally stressed body, which comprises at least one circuit board and heat generating components. In addition, a heat sink is provided which is designed as a hollow body and through which a cooling medium flows for heat dissipation. The heat-generating components are arranged on cooling surfaces on the outside of the heat sink and are connected to these in a heat conducting manner. The heat sink is symmetrical in design and has several cooling surfaces that are arranged at an angle around a longitudinal axis of the heat sink. In the centrally arranged longitudinal axis of the heat sink, a fastening screw with a screw head is provided which connects the heat sink to the circuit board via a spider-shaped clamping spring. The clamping spring presses the heat-generating components onto the cooling surfaces of the heat sink and also serves to dissipate heat. Such a design is very complex as it requires a retaining element in the form of the spider-shaped clamping spring to be provided for each heat sink shape.

DE 196 30 173 C2 discloses a power module with semiconductor components and a circuit board on which several chip-shaped power semiconductor components and contact pads are arranged. A housing with pressure contacts is arranged on the board in order to switch the board accordingly. A pressure piece is fixed to the housing using a centrally arranged fastening screw, and the printed circuit board is firmly connected to the pressure piece. The pressure piece is made of an electrically insulating material. In order to insulate the fastening element from the housing of the circuit board, a sleeve is provided in the housing which surrounds the fastening screw. The problem with this design is that the interconnected components—circuit board, housing and pressure piece—which are made of different materials and will thus undergo different expansion when exposed to the temperature generated during operation, are not able to move relative to each other. This leads to stresses and premature material failure.

SUMMARY OF THE INVENTION(S)

It is the object of the invention to improve on a fastening unit of the type specified in the preamble of claim1in such a way that it will prevent stresses due to the thermal expansion of thermally stressed bodies and further bodies in a simple manner, while avoiding the above mentioned disadvantages.

This object is accomplished by the characterizing features in combination with the features specified in the preamble.

The dependent claims relate to advantageous embodiments of the invention.

According to the invention, the retaining element is designed for lateral engagement with the heat-generating body or the heat sink, in that the retaining element is provided with a retaining groove, on its side facing the heat-generating body or the heat sink, which groove extends in a longitudinal direction perpendicular to the fastening direction, with at least some areas of at least one groove surface coming into contact with the heat-generating body or the heat sink at least in the mounted state. This is a simple way to enable relative movement in the event of thermal expansion of the heat sink or the heat-generating body if mounted appropriately.

According to an advantageous further development of the invention, the retaining groove is formed in a V-shape by two groove surfaces, of which one groove surface is oriented parallel to the longitudinal axis of the fastening or retaining pin and the other groove surface is inclined with respect thereto, the groove surfaces being in particular arranged at an acute angle or an obtuse angle relative to each other. This V-shaped retaining groove allows different edge areas of heat sinks to be held in place in a simple manner without restricting movement along the retaining groove. Depending on the design of the edge area of the heat-generating body or the heat sink, or on the thermal stress to be expected, an acute angle or an obtuse angle is useful. This will result in a linear or flat contact of at least one groove surface of the retaining groove with the heat-generating body or the heat sink to be held in place.

Preferably, the retaining element has a rectangular base area. As a result, it is easy to manufacture but can also be easily aligned with the body to be held in place during assembly. In particular, the retaining element has a greater length in the longitudinal direction of the retaining groove than perpendicular to the longitudinal direction of the retaining groove.

According to a further embodiment of the invention, the retaining element is symmetrically formed and has two retaining grooves so that the retaining element can come to rest against different adjacent heat-generating bodies or heat sinks at the same time. This extends its range of application and increases the flexibility of the fastening unit.

In order to protect in particular the retaining element against rotation relative to the heat-generating body or the heat sink to be retained, it has proved advantageous for the retaining element to have, at its center, to the side of the retaining pin, an elongated projection that extends perpendicular to the retaining pin, which projection in turn has a further groove on its side remote from the retaining head. This groove engages in particular with a strip. This results in a positive engagement in the direction of rotation, but which will not impair movement relative to the retaining groove due to thermal expansion. This thus prevents twisting of the retaining element, while still allowing thermal expansion in the longitudinal direction of the groove and the retaining groove arranged parallel to it.

Preferably, the other groove is also V-shaped. This is a simple way of obtaining linear contact as well as planar contact, depending on the design of the contact surface of the heat-generating body or the heat sink to be held in place that is located opposite the groove.

To prevent the fastening unit from being too high, the retaining head engages in a recess in the retaining element and rests against it there.

In particular, the retaining head and the recess of the retaining element are of a cylindrical design, with one end face of the retaining head resting against the end face of the recess, thus allowing a relative compensating movement about the cylinder axis. During assembly, this is important for the purpose of aligning the retaining element relative to the body or the heat sink to be held in place. In addition, in certain designs of the bodies and heat sinks, this can also be advantageous for compensating for stresses.

As an alternative, however, the side of the retaining head facing the recess can also be at least partially spherical, with the recess being of a partially spherical shape to match the retaining head, so that the spherical surfaces facing each other enable a compensating movement relative to each other in the manner of a ball joint. This ensures that any thermal expansion of the heat-generating body and the heat sink that are connected to each other will not result in stresses due to torques.

The retaining pin may have a thread provided on its end remote from the retaining head, which thread is adapted to engage a thread in a hole in the heat sink or the heat-generating body. This allows the fastening unit and thus the heat-generating body and the heat sink to be screwed together via the fastening unit.

Alternatively, the retaining pin can have at least one detent means at its end remote from the retaining head, which is adapted to engage an undercut in a bore in the heat sink or the heat-generating body. The retaining pin is slotted at its end remote from the retaining head. Using a latching connection, the heat-generating body and the heat sink can be connected to each other via the fastening unit. This simplifies mounting.

Preferably, the heat-generating body is constituted by a power semiconductor. Power semiconductors generate a lot of heat and thus must be cooled by means of heat sinks. The fastening units according to the invention are particularly suitable for this, as the heat sinks will undergo expansion.

The heat sink can be an air heat sink and/or a liquid heat sink.

According to one embodiment of the invention, the retaining head of the fastening unit consists of a thermally and/or electrically insulating material, or of an electrically conductive material.

According to another aspect thereof, the invention is characterized by at least two fastening units of the above mentioned type for connecting a heat sink and a heat-generating body to each other, in which two fastening units are mounted on the heat-generating body or the heat sink diametrically opposed from each other and form a floating bearing with the heat-generating body or the heat sink. This is an easy way to allow a relative movement to take place between the heat-generating body and the heat sink along the retaining grooves of the retaining elements of the fastening units.

When mounted, the retaining grooves of the fastening units are in particular aligned parallel to each other.

According to another aspect, the invention is generally characterized by a method for connecting two thermally stressed components to each other, in particular a heat sink and a heat-generating body, by means of a floating bearing which will allow movement of the one component relative to the other component at least along one axis, in particular using a fastening unit of the aforementioned type.

Additional advantages, features and possible applications of the present invention may be gathered from the description which follows, in which reference is made to the embodiments illustrated in the drawings.

