A POWER ASSEMBLY. A UNIT COMPRISING SUCH POWER ASSEMBLY AND A METHOD OF ASSEMBLING SUCH UNIT

FIELD OF INVENTION The present invention relates generally to power assemblies and more particularly to a power assembly comprising spacers.

BACKGROUND

Power assemblies typically comprise one or more printed circuit boards arranged in parallel. In order to conduct high currents to and/or between the printed circuit boards and their surroundings, electrically conductive spacers are arranged between or adjacent to the circuit boards .

As power assemblies are assembled, the spacers are arranged with their contact surfaces in contact with the printed circuit boards. Due to the high currents that are being transferred through the spacers it is of utmost importance that the contact between the spacer and the printed circuit boards is very good without any distance or impurity. Such a distance or an impurity may cause an increased resistance leading to an increased heating which can destroy the assembly.

Typically, power assemblies have a support structure plate with support structures that are made of plastic, then one or more electrically conducting plates with isolation in between them may be mounted on top of the support structure plate and then spacers are mounted on top mechanically securing the power assembly so that it can easily be mounted in any orientation together with the boards, heat sinks and power connectors. When the

spacer is mounted onto the support structure there is a risk of the spacer scraping the plastic support structure causing small particles of plastic to come off and fall between the contact surface of the spacer and the printed circuit board, i.e. abrasion damages. This would lead to increased resistance, causing increased heating and could possibly also to destroy the assembly.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a power assembly, which is easy to assemble while minimizing the risk of abrasion damages to the parts comprised in the assembly.

The invention is based on the realization that a spacer can be mounted to a support structure by providing the support structure and the spacer with cross sectional shapes with varying radiuses.

According to the invention there is provided a power assembly as defined in appended claim 1.

There is also provided a unit comprising a power assembly according to the invention and a method of assembling a power unit.

As the power assembly is assembled with the spacers mechanically securing the power assembly, the assembly forms a unit or element that can be easily handled and turned upside down when mounting it in a bigger assembly. It is often the case that the power assembly needs to be put into a bigger and heavier structure such as a big cooler with e.g. an IMS-substrate.

In a preferred embodiment, the inner radius of the hollow spacer has at least two steps arranged so that from a first step the inner radius is of a first inner radius VaIUe ₁ and continuously increases as the rotation angle increases up to the next step where the inner radius returns to the first inner radius value.

In yet a preferred embodiment, the hollow spacer is made from an electrically conductive material, thereby acting as current conductors in the power assembly.

Further preferred embodiments are defined by the dependent claims.

BRIEF DESCRIPTION OF DRAWINGS

The invention is now described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is an overall exploded view of a power assembly according to the invention;

Fig. 2 is an overall view of an assembled power assembly of Fig. 1;

Figs. 3a and 3b are perspective and end views, respectively, of a spacer comprised in the power assembly of Figs. 1 and 2;

Fig. 4 is a detailed view of a support structure comprised in the power assembly of Figs . 1 and 2 ; and

Figs. 5a and 5b are plan views of support structure and spacer before and after assembly, respectively.

DETAILED DESCRIPTION OF THE INVENTION

In the following a detailed description of preferred embodiments of the present invention will be given.

In Fig. 1, an overall exploded view of a power assembly is shown. This arrangement includes a bottom support plate 10 which preferably is made of an electrically non-conductive material such as plastic . On the support plate 10, a plurality of support structures 12, which preferably are shaped as knobs, are arranged which are also preferably made of plastic. The support structures 12 have a longitudinal axis and a cross sectional shape with varying outer radius. On the support plate 10, using the support structures 12, different elements are first mounted. Typically, at least one brick 14 is attached having one hole 14a adapted to be mounted over the support structure and another hole 14b used to connect to an electrically powered device such as an engine or a motor. The at least one brick is made out of an electrically conductive material. There could be other such bricks mounted upon the support structures connected to a battery with a positive pole and a negative pole. As can be seen in figure 1, at least one board 16, 20 can be mounted upon the support plate. These boards are made of an electrically conductive material. If at least two boards are assembled on top of the support structure, an electrically isolating plate 18 is mounted in between. On top of the upper board 20, hollow spacers 22 are mounted to the support structure. The spacers 22 have a cross sectional shape with an inner radius r _± which varies with the rotation angle so as to be mounted with no friction on the support

structures 12 in a first angular position between the support structures and the spacers wherein there is a gap or space between the support structures 12 and the spacers 22 and wherein by turning the spacers 22 into a second angular position between the support structure and the spacers 22, there is frictional contact between the support structures and the spacers. The spacers 22 are made of an electrically conductive material such as metal. In the second angular position in which there is frictional contact between the support structures 12 and the spacers 22, the spacers have full contact with the top board so that the spacers can therefore conduct electricity from the top plate.

In Fig. 2, an assembled state of the power assembly is shown. In Fig. 2, three bricks 14 have been mounted upon the support plate. In this example, the two square holes 16a, 20a, in the respective plate 16, 20 are connected to a battery with a positive pole and a negative pole or some other power source. The holes 14b in the three bricks 14 are connected to an electrically powered device such as an engine or a motor. Also at least a first electrically conductive board is mounted upon the support plate and then the assembly is secured with the spacers in a locked angle/position.

The outlines of the unit 1 in which the power assembly is provided are shown with dashed lines in Fig. 2.

In Fig. 3a and 3b, a hollow spacer 22 is shown in detail. As already stated, the spacers should be made of an electrically conductive material. Fig. 3a and 3b also show how the spacers have a cross sectional shape with

varying inner radius r^ The spacers may also preferably have at least one groove, rib or other arrangement 22a on the outer side of the spacer to enable an easier grip when turning the spacer to or from a, with the support structure, locked position. The inner radius r _± of the hollow spacers have at least two, preferably three, steps 22b arranged so that from a first step the inner radius r _± is of a first inner radius value and continuously increases up to the next step 22b where the inner radius instantly returns to the first inner radius value r _± . The steps are preferably symmetrically arranged so that in case of two steps they are on opposite sides and in case of three steps they are arranged with 120 degrees in between.

In Fig. 4, the support plate 10 with its support structures 12 are shown. The support structures have cross sectional shape with an outer radius r _u with segments of constant value and intervening protruding ribs 12a. The protruding ribs 12a are preferably arranged symmetrically so as to fit the steps 22b of the hollow spacers 22.

In another embodiment (not shown), the support structures have cross sectional shape with an outer radius which varies with the rotation angle . The outer radius of the support structures has at least two ribs arranged so that from a first rib, the outer radius is of a first outer radius value and continuously decreases down to the next rib where the outer radius r _u instantly returns to the first outer radius value. In this embodiment, the same hollow spacers 22 as in the previous embodiment may be used. It is also possible to

use hollow spacers with an inner radius r _± with segments of constant value and intervening protruding ribs.

In Fig. 5a and 5b, a support structure 12 is shown with a spacer 22 before and after assembly, respectively. Thus, Fig. 5b shows the spacer 22 after it has been turned in the direction of the arrow from the position shown in Fig. 5a.

According to the invention, as the power assembly as in Fig.l and 2 has been assembled, it can then be held upside-down and put down with the spacers first on top of a printed circuit board so that the spacers are in contact with said printed circuit board. The printed circuit board is typically made of an IMS-laminate. When assembled, the printed circuit board controls the power supply to the electric engine or motor through the power assembly.

The spacers can be made from long cylindrical units or hollow tubes with the desired outer and inner radiuses and designs and then cut in smaller pieces to be used as the spacers as herein described.

The invention also relates to a method of assembling power assemblies. On a bottom support structure plate 10 with support structures 12, at least one brick 14 may be mounted. Then one or more electrically conductive boards 16, 20 may be mounted onto the support structures 12. If more than one board is mounted onto the support structures, an electrically isolating plate 18 may be mounted in between. If three electrically conductive boards are mounted, then electrically isolating plates may be mounted in between each two boards. On top of the

upper board 20, hollow spacers 22 are mounted onto the support structures 12 to secure the power assembly by first mounting each spacer 22 in a first angular position with no frictional contact between the spacer 22 and the support structure 12 and then turning each spacer 22 until it locks with frictional contact with the support structures 12. Then it can then be held upside-down and put down with the spacers first on top of a printed circuit board so that the spacers are in contact with said printed circuit board.

Preferred embodiments of a power assembly according to the invention and a unit comprising such power assembly have been described. A person skilled in the art realizes that this could be varied within the scope of the appended claims.