Combination of radar sensor and trim component for a motor vehicle

Abstract

A combination of a radar sensor and a trim component, which are to be mounted on a motor vehicle so that the trim component is penetrated by microwaves of the radar sensor, the trim component including at least one layer, which reflects a portion of the microwaves, the trim component including an additional layer, which is configured based on thickness and dielectric constant to reduce the reflection.

Claims

1. A system, comprising: a combination of a radar sensor and an external trim component, which are mountable on a motor vehicle so that the external trim component is penetrate-able by microwaves of the radar sensor, the external trim component including at least one layer on an outer surface of a base body of the external trim component, the outer surface facing away from the radar sensor, the at least one layer reflecting a portion of the microwaves; wherein the external trim component includes an additional layer on an inner surface of the base body of the external trim component, the inner surface facing the radar sensor, and wherein the additional layer is configured based on a thickness and a dielectric constant to reduce the reflecting of the portion of the microwaves.

2. The system of claim 1, wherein the external trim component is a bumper.

3. The system of claim 1, wherein the reflecting layer and the additional layer are situated on opposite sides of a base body of the external trim component.

4. The system of claim 1, wherein the additional layer contains at least one ply of film.

5. The system of claim 4, wherein the additional layer contains multiple plies of the film.

6. A motor vehicle system, comprising: a motor vehicle; and a combination of a radar sensor and an external trim component, which are mountable on a motor vehicle so that the external trim component is penetrate-able by microwaves of the radar sensor, the external trim component including at least one layer on an outer surface of a base body of the external trim component, the outer surface facing away from the radar sensor, the at least one layer reflecting a portion of the microwaves; wherein the external trim component includes an additional layer on an inner surface of the base body of the external trim component, the inner surface facing the radar sensor, and wherein the additional layer is configured based on a thickness and a dielectric constant to reduce the reflecting of the portion of the microwaves.

7. A method for manufacturing an external trim component for a motor vehicle for use in combination with a radar sensor, which is situated on the motor vehicle so that microwaves of the radar sensor are able to penetrate the external trim component, the method comprising: providing a base body of the external trim component, the base body having at least one layer on an outer surface of the base body of the external trim component, the outer surface facing away from the radar sensor, the at least one layer being configured to reflect a portion of the microwaves, the base body and each layer of the at least one layer having a certain thickness and a certain dielectric constant; ascertaining a reflection coefficient curve for the external trim component, which is formed by the base body, the at least one layer, and an additional layer as a function of at least one independent variable, which indicates the thickness of the additional layer; determining an optimum thickness of the additional layer based on the reflection coefficient curve; and applying the additional layer having the optimum thickness.

8. The system of claim 1, wherein the base body is plastic, and wherein the at least one layer includes a primer layer, a layer of a base coat of varnish, and a layer of a clear coat of varnish.

9. The system of claim 1, wherein the additional layer includes at least one ply of a polyvinyl chloride (PVC) film.

10. The system of claim 9, wherein the at least one ply of the polyvinyl chloride (PVC) film has a dielectric constant of about 8 and a thickness of about 200 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows a view of a radar sensor in combination with a trim component, of which only one wall section is depicted in cross section.

(2) FIG. 2 shows a diagram which indicates the reflection coefficient for different thicknesses of an additional layer of the trim component shown in FIG. 1 as a function of the dielectric constant of a coat of varnish of this trim component.

(3) FIG. 3 shows an error diagram, which indicates the angle error for angle measurements with the radar sensor according to FIG. 1 in combination with a conventional bumper with no additional layer as a function of the location angle.

(4) FIG. 4 shows an error diagram for the radar sensor in combination with a bumper according to the present invention.

DETAILED DESCRIPTION

(5) FIG. 1 schematically shows a radar sensor 10, which is situated a certain distance behind a trim component 12, namely, a bumper of a motor vehicle, so that microwaves 14 emitted from radar sensor 10 are forced to penetrate bumper 12. Radar sensor 10 is, for example, a 77 GHz radar, so that the wavelength of microwaves 14 lies approximately in the range of 4 mm.

(6) Trim component 12 has a layer structure which is not represented to scale in the drawing, and includes a base body a made of plastic having a typical thickness d.sub.a of 2.8 mm, to which, in order, a primer layer b having a thickness of typically approximately 10 μm, a base coat of varnish c having a thickness d.sub.c of typically approximately 20 μm, and finally a clear coat of varnish d having a thickness d.sub.d of typically approximately 30 μm are applied to the side facing away from radar sensor 10.

(7) The dielectric constant (relative dielectric constant) ∈r.sub.a of the plastic material of the base body a is typically between 2 and 4. Primer layer b typically has a dielectric constant ∈r.sub.b of 8, and clear coat of varnish d typically has a dielectric constant ∈r.sub.d of 3.5. Dielectric constant ∈r.sub.c of base coat of varnish c may assume values of up to 120. The level of this dielectric constant ∈r.sub.c is dependent on the desired visual properties and assumes very high values, particularly in the case of varnishes having a metallic effect.

(8) For microwaves 14, any boundary surface on which the dielectric constant and, therefore, the optical density of the medium changes, represents, in principle, a reflecting surface on which a portion of the incident radiation is reflected. In the layer structure shown herein, base coat of varnish c in particular, acts as a reflecting surface due to its high dielectric constant, i.e., particularly strong reflections occur at the boundary surfaces, which this layer forms with primer layer b and clear coat of varnish d. The microwaves which are reflected at the various boundary surfaces of the bumper overlap one another and may interfere with one another constructively or destructively, depending on the thickness of the layers and pairing of the dielectric constants at the boundary surfaces. These interference effects ultimately determine the reflection coefficient, which trim component 12 as a whole exhibits for microwaves 14.

(9) In FIG. 2 a dash-lined curve f0 shows the reflection coefficient of a trim component made up only of layers a, b, c, and d in FIG. 1 as a function of dielectric constant ∈r.sub.c of base coat of varnish c. It apparent that the reflection coefficient increases sharply with increasing dielectric constant of the base coat of varnish and may even amount to more than 90% in the case of dielectric constants greater than 100.

(10) The reflections are mitigated as a result of an additional layer e included in trim component 12 shown in FIG. 1 on the side of the base body a facing radar sensor 10, which forms additional reflection surfaces, and thereby alters the interference pattern. In the example shown in FIG. 1, additional layer e is made up of two plies of a film 16, for example, a PVC film having dielectric constant ∈r.sub.e=8 and a thickness of 200 μm. The overall thickness d.sub.e of additional layer e is therefore 400 μm.

(11) The reflection coefficient, which results in the presence of this additional layer e, is depicted as curve f2 in FIG. 2. It is apparent that at approximately ∈r.sub.c=30, this curve has a distinct minimum, so that the reflection on the trim component is almost completely suppressed when the base coat of varnish c has a dielectric constant close to 30.

(12) Varying the number of plies of film in additional layer e (in which the thickness and dielectric constant of individual film 16 is unchanged) allows the reflection behavior for different dielectric constants ∈r.sub.c to be adapted to base coat of varnish 10, as is illustrated by the other curves in FIG. 2. In the case of just one ply of film 16, a reflection coefficient results, which is indicated by curve f1. This curve does not have such a distinct minimum, but it is very flat and thus remains below 60%, even in the case of high values of ∈r.sub.c. This additional layer is, therefore, a good choice in conjunction with base coats of varnish which have very high dielectric constants.

(13) In the case of an additional layer e having three plies of film 16, a reflection coefficient is obtained, whose curve f3 resembles the curve for f2, but which has a minimum of approximately ∈r.sub.c=5. In the case of four plies, the reflection coefficient is described by a curve f4, which is also comparatively flat, but exhibits no distinct minimum. Curve f5 indicates the reflection coefficients for five plies and has a minimum of between 40 and 50, and curve f6 indicates the reflection coefficient for six plies and has a minimum of between 10 and 20.

(14) In this way, for each given dielectric constant ∈r.sub.c of base coat of varnish c, the number of plies of film 16 may be selected in such a way that a minimizing of the reflection coefficient is achieved by additional layer e. It should be noted here, however, that because of the periodic nature of the microwaves, there is no simple relationship between dielectric constant ∈r.sub.c of the base coat of varnish and optimum thickness d.sub.e of additional layer e, so that the optimum thickness of the additional layer must be calculated or empirically ascertained in individual cases.

(15) To a certain extent, the diagram shown in FIG. 2 is also affected by the thicknesses and electric constants of layers a, b and d, so that a different diagram is obtained for each combination of parameters d.sub.a, d.sub.b, d.sub.d, ∈r.sub.a, ∈r.sub.b and ∈r.sub.d. The effect of layers b and d, however, will be negligible in many cases, so that the number of parameters to be taken into account is correspondingly reduced.

(16) Of course, dielectric constant ∈r.sub.e of film 16 also affects the appearance of the diagram in FIG. 2. Thus, instead of varying thickness d.sub.e of additional layer e, it is also possible, given a constant thickness, to vary the material of this layer and, therefore, dielectric constant ∈r.sub.e, and then, based on the diagram, to select the dielectric constant ∈r.sub.e, which shows the smallest reaction coefficient for given base coat of varnish c.

(17) Of course, it is also possible in additional layer e to combine films with one another, which have a different thickness and/or different dielectric constants.

(18) To manufacture a trim component optimized for use in conjunction with radar sensor 10, it is possible in general to proceed as follows.

(19) For a trim component having n layers (including additional layer e), a set of 2n variables is obtained, namely, the layer thicknesses and the dielectric constants of these layers. In principle, all of these variables may be varied independently of one another. For a radar sensor having a given operating frequency and, accordingly, microwaves of a given wavelength, the reflection coefficient may then be calculated or, if necessary, empirically ascertained, as a function of the 2n independent variables. The function thus obtained will, in general, have multiple local minimums. For some of the independent variables, certain limitations will apply. This applies, in particular, to thickness d.sub.a of the base body and, if a particular color of varnish is desired, to dielectric constant ∈r.sub.c of the base coat of varnish. Taking these limitations into account, the lowest local medium may then be sought and a trim component with the corresponding layer structure may be manufactured.

(20) The complexity may be significantly reduced by treating some of the 2n variables as fixed parameters, for example, the layer thicknesses and the dielectric constants of layers a, b and d and, if necessary, also layer thickness d.sub.c of the base coat of varnish, as well as dielectric constant ∈r.sub.e of additional layer e, so that the task is reduced to seeking the minimum of a function in two variables (∈r.sub.c and d.sub.e).

(21) By minimizing the reflection coefficient, it is possible, in particular, in the case of an angle-resolving radar sensor 10, to improve the accuracy of the angle measurement. This is illustrated by the diagrams shown in FIGS. 3 and 4.

(22) In FIG. 3, a curve 18 indicates the error occurring in the angle measurement of an individual object as a function of the angle for the case in which trim component 12 has the layer structure shown in FIG. 1 without additional layer e. Also depicted in FIG. 3 is an admissible tolerance range 20. It is apparent that the error often clearly exceeds the admissible tolerances.

(23) In FIG. 4, a curve 22 shows the corresponding results for the case in which trim component 12 includes additional layer e. The angle error is reduced considerably as a result and lies largely within tolerance range 20.