Housing

Details Housing Housing

1999-06-17

2001-01-30

Reichard, Dean A. (Department: 2831)

Electricity: conductors and insulators

With fluids or vacuum

Boxes and housings

C174S0170CT, C174S050500

Reexamination Certificate

active

06180875

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a housing for an electric or electronic component, in particular a motor vehicle control unit, including a one-part or multi-part container and one or more one-part or multi-part sealing devices.
Electric and electronic components, in particular electronic control units, as a rule are mounted inside a housing to protect them against environmental influences, such as mechanical effects, dust, and humidity. If the housing is used in a motor vehicle, these requirements are particularly high. Housings of this type must protect the sensitive electronic components from moisture, which can enter the housing in liquid form as water or in gaseous form as water vapor. As a rule, the housings are made at least in part of a thermoplastic synthetic material. These synthetic parts are watertight, but not gas-tight, so that water in a gaseous form can penetrate. If a multi-part housing is sealed watertight with corresponding seals, no liquid can penetrate, but gas can reach the inside of the housing. The following applies in that case:
Q
=
P
*
A
*
t
d
Q: Amount of gas penetrating in cm
3
or amount of water vapor in g
A: Surface in cm
2
t: Effective time in days
d: Wall thickness in cm
P: Permeation constant in cm
2
/t (gas) or g/(cm*t) (water vapor)
1
However, if the pressure outside of the housing differs from the pressure on the inside of the housing, which is generated above all by the temperature difference between the inside of the housing and the outside of the housing, air can reach the inside of the housing. The following applies in that case:
Q
=
P
*
A
*
t
*
δ
⁢
 
⁢
p
d
Q: Amount of gas penetrating in cm
3
or amount of water vapor in g
A: Surface in cm
2
t: Effective time in days
&dgr;p: Difference in pressure in cm mercury column
d: Wall thickness in cm
P: Permeation constant in cm
2
/t (gas) or g/(cm
2
*t) (water vapor)
However, the air also contains gaseous water vapor, which penetrates the synthetic material and enters the housing because of its smaller particle size and owing to the pressure difference. Given the following parameters, a non-negligible amount of water can accumulate in the housing in the motor vehicle region. This is true for a relative humidity level of 85% on the outside and 0% relative humidity on the inside and a temperature of 20° C. and 1 bar air pressure.
P=2.1 10
−6
g/(cm
2
t) for polybutylene terephthalate
A=32 cm
2
d=1.5 mm
t=15 years=5475 days wherein:
10% operating time (547.5 days) at 20° C.
no pressure difference
20% operating time (1095 days) at 40° C.
&dgr;p = 0.068 bar = 5.17 cm
50% operating time (2737.5 days) at 60° C.
&dgr;p = 0.137 bar = 10.41 cm
20% operating time (1095 days) at 80° C.
&dgr;p = 0.2 bar = 15.2 cm
Q
total
= Q
20° C.
+ Q
40° C.
++ Q
60° C.
+ Q
60° C.
= 0.25 g + 2.5 g + 12.8 g + 7.5 g = 23 g
It means that over the total service life of a motor vehicle, in the worst case 23 g water enter through a synthetic housing part with a surface of 32 cm
2
and a thickness of 1.5 mm. The condensed water can do considerable damage to the electronic components. For example, it changes the conductivity between the various components, which can lead to short-circuits and causes oxidation, meaning rusting, of contacts. For those reasons, housings were provided until now with so-called pressure-equalizing openings, where a pressure compensation can occur between the housing inside and the environment. To prevent water from entering at the openings in the housing, these were closed off with a watertight and breathable foil, e.g. as known under the name Goretex or Sympatex, so that the electronic circuit is protected against water damage and moisture damage. This state of the technology is reflected in the German Patent Application No. 197 08 116.9.
It is disadvantageous in this case that an additional operational step is required for closing off the pressure-compensation openings with the watertight and breathable foil. Such watertight and breathable foils are very expensive. Furthermore, it is a disadvantage of such foils that they reduce the diffusion rate as a result of the pressure compensation, to be sure, but are also water vapor permeable.
SUMMARY OF THE INVENTION
Thus, it is the object of the invention to create a housing of the aforementioned type, which does not have the previously listed disadvantages and which protects an electronic or electric component reliably against environmental influences.
This object is solved according to the invention. Closing off the container to be watertight with a movable sealing device inside or on the container to change the inside volume by permitting movement between the container and the sealing device or by having the container or the sealing device be fully or partially expendable. The basic idea behind the invention is that the inside volume of the housing is variable, depending on the pressure conditions, thus resulting in pressure compensation. Less moisture reaches the inside of the housing as a result of this pressure adaptation, which is achieved through an increase or decrease of the housing inside volume. Owing to this pressure adaptation, less water vapor can permeate the synthetic material and reach the inside of the housing. The changeable housing inside volume can be realized in two different ways. One option provides for a mutual displacement of the housing parts. The other option provides that at least a portion of the housing is expandable.
The advantages achieved with the invention are that no liquid and no gas enter this housing as a result of pressure differences. The electric and electronic components are protected reliably inside the housing against damaging environmental influences. At the same time, the life expectancy of components in such housings is increased strongly. Based on the previous calculations, only 2.5 g instead of 23 g of water would then enter the housing.
Advantageous modifications of the invention are possible. For example, a so-called pressure compensation element may be provided on one housing part. This pressure compensation element is movable and changes its size and thus the inside volume of the housing in dependence on the pressure conditions. Another advantageous modification of the invention consists in that an adhesive connection or a seal is elastic, as a result of which the housing parts can be mutually displaced and the housing volume can thus be changed. The same effect, namely a variable housing inside volume, is achieved in that a plug, which closes off the housing, is attached movably in a plug-in device in the housing, so that it can be moved back and forth.
Several exemplary embodiments of the invention are to be illustrated with the aid of
FIGS. 1
to
5
.


REFERENCES:
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patent: 44 47 513 (1996-02-01), None
patent: 197 08 116 (1998-09-01), None
patent: 0 248 181 (1987-12-01), None
patent: WO 84 01082 (1984-03-01), None

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