WO2003003022A1

WO2003003022A1 - Method for producing a housing for an electrical component comprising an acceleration sensor

Info

Publication number: WO2003003022A1
Application number: PCT/EP2002/006601
Authority: WO
Inventors: Josef Bärenweiler; Richard Baur; Günter Fendt; Markus Krakowitzer; Hermann Küblbeck; Alfons Wöhrl; Engelbert Wörle
Original assignee: Conti Temic Microelectronic Gmbh
Priority date: 2001-06-29
Filing date: 2002-06-14
Publication date: 2003-01-09
Also published as: DE10292875D2; DE10131424A1

Abstract

The invention relates to a method for producing a housing for an electrical component comprising an acceleration sensor and a corresponding housing. According to said method, useful frequency fractions of the acceleration signal can be retransmitted to the acceleration sensors, the retransmission of disturbing frequency fractions being damped, however. To this end, construction means, especially damping elements consisting of a plastic material which is different to that of the housing, are incorporated into the material of the housing itself. The damping properties of the damping element can vary not only in terms of the choice of the material, but also due to inner cavities in the damping element. Furthermore, a series of supplementary measures enables the vibration behaviour to be optimised in a frequency-selective manner.

Description

Method for producing a housing for an electrical assembly with a

accelerometer

The invention relates to a method for producing a housing for an electrical assembly with an acceleration sensor.

Electrical assemblies with accelerometers are used in motor vehicles to trigger safety devices, such as airbags, in the event of an accident. For this purpose, the accelerations that occur in an accident must be transmitted to the sensor as precisely as possible, which is usually to be achieved in the prior art by connecting the electrical sensor module to the housing as rigidly as possible. For example, EP 0 675 363 A2 provides a housing for a sensor assembly which is stiffened to such an extent by a lead frame molded around by the plastic housing that the natural frequency of the housing is extremely high (> 4 kHz) and the frequency range of interest is transmitted as unadulterated as possible. In particular, for further stiffening, the connection pieces of the lead frame are shaped by

Ribs thickened (col. 10, lines 10 ff., Fig. 1). However, this rigid connection leads to an equally strong forwarding of interference accelerations, such as those caused by bumps in the road, curbs or

Stone or hammer blows can be caused.

In addition to stiffening, EP 0 675 363 A2 also wants to do this by additionally gluing the sensor with a special, elastic adhesive and at a distance defined by a spacer from that formed from the leadframe

Avoid the back plate (column 8, lines 40-54). In addition, the filling of the space around the sensor with an elastic medium is considered in order to protect the sensor against external influences, such as temperature, mechanical tension, UV radiation, as is also the case in US Pat. No. 5,548,999, EP 0 566 758 A1 or EP 0 557 917 A1. Damping holders for the sensor can be found in DE 44 06 499 C2, which are intended to protect the sensor from destruction.

EP 0 540 071 A1 presents a sensor module which, according to the application, should in turn be constructed in such a way that the influences of mechanical stresses and resonance vibrations on the sensor are minimized, particularly in the case of

Vehicle applications, uneven road, vehicle vibrations, etc. Only the part of the acting forces that is required for the evaluation is detected (column 2, lines 7 ff.) A recess is provided in a rigid lower housing in a floor spaced apart from the carrier body , in which the sensor is arranged in a separately enclosed unit. The rigidity is chosen so that vibrations of 3 kHz and more are none

Cause more interference (column 5 line 1 ff.) The sensor unit is separated from the circuit board with the evaluation circuit and is only electrically connected by means of bond wires, so that vibrations are not transmitted. (Column 6, line 40 ff.) The sensor unit is fixed at a defined distance (spacer 36) to the bottom of the recess of the lower housing part with an adhesive (primerless silicone adhesive material) (column 5, line 37 ff.)

The interior of the housing around the sensor unit is largely filled with a gel (column 7, lines 30-50).

US Pat. No. 5,548,999, DE 39 30 314 A1 and DE 42 42 789 C2 dampen the vibrations of the part that can be deflected by acceleration forces by means of a resilient mounting.

Since the triggering of the safety devices must occur very early in the course of an accident, this requires a correspondingly low triggering threshold, which, however, further increases the risk of incorrect triggering due to disturbance acceleration forces. Post-processing of the sensor signal obtained by analog or digital

Filtering, as can already be seen, for example, from DE 26 55 604, also leads to limited success.

The object of the invention is therefore to provide a method for producing a housing, by means of which the transmission of the useful frequency components to the acceleration sensors in the housing is made possible in a particularly simple manner

Forwarding of the interference frequency components is attenuated.

While additional construction means were previously provided in the exterior or interior of the housing to achieve the damping effect, the housing material itself is now to be used alternatively or additionally as a frequency-selective construction means are used and thus the coupling is optimized through the targeted design of the housing, so that accelerations over a defined temperature range are transmitted as unfiltered as possible within a trigger-relevant useful frequency range, while interference frequency components outside this frequency range are damped.

In particular, a plastic housing is proposed in which a damping element made of a second plastic material, different from a first plastic of the other housing, is inserted between the mounting surfaces for fastening the housing to the carrier body and locking points for the electrical assembly, in particular by two-component

Injection molding is introduced.

A frequency characteristic of the housing can be achieved by utilizing the material properties that can be variably set in the plastic, in particular the elasticity and the damping due to internal friction in the plastic. Through the cross section of the housing material and the damping element, but in particular also through the

The formation of cavities in the damping element can further vary the frequency characteristic and thus optimize it.

As an alternative to two-component injection molding, particles made of a material with different damping properties or stiffness, if necessary also locally limited, can be introduced into the plastic base material of the housing and the stiffness of the plastic base material can be influenced in a targeted manner by process parameters during the injection process.

The invention will be explained in more detail below on the basis of exemplary embodiments and figures. Brief description of the figures: Figure 1 Detailed view of a damping element in the housing

Figure 2 section through a mounting surface of a housing with

damping element

3 shows a further sectional view with a damping element with cavities which are formed vertically on both sides. FIG. 4 shows a detailed view with a taper of the housing and insertion of the

Damping element in the area of the taper

Figure 5 additional additional damping element in the area of the

Molded locking point Figure 6 Influencing the material rigidity during the injection process

Figure 7 Manufacture of the housing from a plastic base material with locally limited admixture of additional materials

FIG. 1 shows a detailed view of a damping element 2 in a housing, in particular a plastic housing 1.

The damping element 2 consists of a second plastic material that differs from a first plastic of the other housing 1, in particular of an elastomeric material mixture, for example SEB 5, whose elastomeric phases, bswp. based on ethylene butylene, integrated as a soft component in thermoplastic materials and a Shore hardness of approx. 65 to 95 Shore A is selected.

The choice of a suitable plastic material of the damping element 2 is predetermined in accordance with the desired damping characteristic of the damping element 2, this permitting a particularly large adjustment range for plastic materials due to their high variability. By adding fillers, for example small balls of higher rigidity, the damping properties of the damping element 2 can be additionally influenced. The damping effect is mainly due to internal friction. The plastic material of the other housing 1 consists, for example, of thermoplastic two-component (2-component) injection molding material, for example PBT GF 30, a polyethylene terephthalate with glass fiber reinforcement. The damping elements 2 are in the housing 1 in the path from the support body to

Module 3 arranged with the one or more acceleration sensors. The housing 1 has mounting surfaces 11 for attachment to the carrier body and locking points 4 inside the housing (see FIG. 5) for the electrical assembly 3 with the acceleration sensor. A damping element 2 is inserted in each case in the housing 1 in the area between the mounting surfaces 11 and the support points 4.

The housing 1 is fastened to the carrier body, for example a body frame of a motor vehicle, for example by a screw, not shown, with the mounting surface 11, the mounting surface 11 in this example having a metal insert 15 for stiffening the mounting area.

The position, orientation and width 26 of the damping element 2 in the housing 1 is determined beforehand in each application by means of vibration analysis and subsequently specified exactly accordingly. In particular, the Alignment of the damping element 2 can have a great effect if the direction of propagation of interference and useful signal components is different.

The damping element 2 additionally has internal cavities 21, the dimensions of which make it possible to set the vibration behavior particularly precisely. So are in particular cavities 21 in the form of vertical slots or in the form of

Crosses are provided, which either extend over the entire height 27 (see FIG. 2) of the cross section or are interrupted by webs 23, as shown in FIG. 3. The depth 28a / 28b of the slots also determines the damping characteristic. In the case of the cavities 21, too, the alignment of the slot-shaped cavities in particular is decisive if the direction of propagation of interference and useful signal components is different. The damping elements 2 with slit-shaped cavities 21 have a significantly stronger damping for vibrations with a direction of propagation parallel to the slits than vibrations impinging perpendicularly. Figure 1 also shows the mechanical attachment of the

Damping element 2, which is anchored in the housing 1 by toothing elements 12 and 22 formed in the contact area.

The damping element 2 in FIGS. 2 and 3 extends over the entire cross section of the housing 1 in the area between the mounting surfaces 11 and the locking points 4.

Alternatively, FIGS. 4 and 5 show damping elements 2 which are arranged in tapering of the housing 1, the remaining part 13 of the plastic housing being able to perform both a fastening and a protective function. The cross-section of the housing is then filled up by the damping element 2, with cavities 21 which are continuous in the damping element or are interrupted by struts 23 are also possible in this embodiment.

FIG. 5 shows an additional further damping element 25 in the area of the locking point 4 formed from the housing.

The damping characteristic of all damping elements 2 and 25 can be adjusted by changing the plastic material of the damping element

Width 26 and the cross section 27 of the damping element, the cross section of a remaining housing part 13 in a taper and the size of the cavities 21, in particular their width and depth 28 and the strength of the struts 23, 24 between these cavities 21. The vibration transmission behavior of the housing is optimized via the damping characteristic of all damping elements 2 in such a way that accelerations are transmitted as unfiltered as possible within a trigger-relevant useful frequency range, while interference frequency components outside of this frequency range are damped.

In addition, stiffening ribs or comparable construction means can be used in the housing and also arranged in this damping elements 2.

The damping elements 2 are preferably inserted directly by two-component injection molding in the manufacture of the housing 1. In addition, as an alternative, the housing can also be glued to it

Module 3 in the locking point 3 or on the housing 1, for example. A housing cover or bottom, in particular with special damping adhesive.

Instead of the two-component injection molding technology, there is also the known addition of particles made of a material that is stiffer than the plastic base material, in order to meet the frequency behavior of the housing in accordance with the requirements

To improve the damping of the interference components. For this purpose, these particles are mixed into the plastic base material of the housing, as outlined in FIGS. 6 and 7, or molded from the plastic material, that is to say, encapsulated in the housing shape by the plastic material. So most plastics can selectively particles 6, such as

Glass balls or glass fibers with dimensions which are still relatively small in relation to the housing thickness, but which are large compared to the plastic molecules, and whose concentration can also be varied within the housing 1. The addition of glass particles 6 that are stiffer than the plastic base material increases the rigidity and thus the natural resonance frequency of the housing 1

Definition of the local distribution of the particle concentration in the plastic base material, as sketchily exaggerated in Fig. 7, the frequency selectivity can be set even more precisely. Thus, the plastic base material with (10b) or without admixture (10a) of particles 6 are injected at different points of the housing shape 31. The particles to be added can be made of solid or hollow material and, within the practical limits, can be precisely aligned with the desired frequency ratios with regard to their mass and rigidity.

Fibers can also be used as particles and these can be introduced into the plastic material with a predetermined orientation. In addition to a targeted choice of In the direction of the injection of the mixture of plastic base material and fiber admixture, the other injection parameters, the frequency properties of the housing can be influenced in a targeted manner. The mixture of plastic base material and particles is injected into a housing shape via an injection nozzle with a variable nozzle opening 32. The rigidity of the housing can be at least locally reduced by increasing the injection pressure and / or reducing the size of the nozzle opening 32 or 30a, 30b, 30c. These measures lead to an increase in stress, that is to say the tensions in the melt of the housing material, and thus to shortening or tearing off long plastic molecule chains as well as long fiber particles. The nozzle opening (in Fig. 7 30a, 30b, 30c) can be through a perpendicular to the. Nozzle opening movable and insertable into the nozzle opening 33, 33a, 33b or changed by a nozzle opening with a variable outer cross section 34, a narrower opening means increased stress for the melt and thus lower rigidity of the housing. In the case of fiber particles, the nozzle opening thus also affects the fiber alignment.

By constricting the wall or increasing the wall thickness on the required wall surfaces of the housing shape 31, the stress on the melt and thus the rigidity of the hardened housing 1 can also be influenced.

Claims

claims

1) Method for producing a housing (1) for an electrical assembly (3) with an acceleration sensor, with a) the assembly (3) being arranged in a carrier body, in particular a motor vehicle b) _, _ the acceleration sensor acting on the carrier body measures, c) the force impulses for a later evaluation have important useful frequency components as well as for a later evaluation disruptive interference frequency components, d) the housing consists of a plastic base material, e) the additional materials are added and molded into the plastic base material in such a way that the transmission of the useful frequency components is frequency-selective to the acceleration sensors and at the same time the forwarding of the interference frequency components is damped.

2) Method according to claim 1, wherein the housing has a low-pass attenuation characteristic with a cut-off frequency in the range of the useful frequency components.

3) Method according to one of the preceding claims, wherein a) the housing (1) mounting surfaces (11) for attachment to the support body and in the housing locking points (4) for the electrical assembly (3) with the

Acceleration sensor, b) wherein in the housing (1) in the area between the mounting surfaces (11) and the locking points (4) each have a damping element (2) made of a second plastic material that differs from a first plastic of the other housing (1).

4) Method according to claim 3, wherein the damping element (2) extends over the entire cross section (27) of the housing (1) in the region between the mounting surfaces (11) and the locking points (4). 5) Method according to claim 3, wherein the first plastic material of the housing (1) has a taper (13) in the area between the mounting surfaces and the locking points and the damping element (2) is arranged in the area of this taper.

6) Method according to one of claims 3 to 5, wherein the damping element (2) has internal cavities (21).

7) The method of claim 7, wherein the cavities (21) are aligned in the damping element so that the damping element (2) for a predetermined useful

.. signal propagation direction has a lower attenuation than for a deviating, in particular perpendicular, signal propagation direction.

8) Method according to one of the preceding claims 3 to 7, wherein the damping element (2) is anchored to the housing by means of toothing elements (12, 22) formed in the contact area.

9) Method according to one of the preceding claims 3 to 8, wherein the damping characteristic of the damping element is adjustable by:

Change the plastic material of the damping element (2) by the width (26) and the cross section (27 ^* 29) of the damping element by the size and orientation of the cavities (21), in particular their width and depth (28).

10) Method according to claim 1, wherein in the plastic base material (10) of

Housing (1) particles (6) of a material that is stiffer than the plastic base material (10) are mixed in or formed by the plastic material.

11) Method according to claim 10, wherein fibers are used as particles (6) and these are introduced with a predetermined orientation in the housing (1).

12) Method according to one of claims 10 or 11, wherein the particles (6) within the housing (1) locally with different concentration, in particular only locally limited, are introduced into the plastic base material. 13) Method according to one of claims 10 to 12, wherein the particles (6) are made of glass.

14) Method according to one of the preceding claims, wherein a mixture (10b) of plastic base material (10) and particles (6) via an injection nozzle (30) with a variable nozzle opening (32, 30a, 30b, 30c) in a housing shape (31) is injected and the rigidity of the housing (1) is at least locally reduced by a) increasing the injection pressure and / or b) reducing the size of the nozzle opening.

15) housing, produced according to the method according to any one of the preceding claims.