GB2027188A

GB2027188A - Adhesive jointed reflector-lens in vehicle headlamps

Info

Publication number: GB2027188A
Application number: GB7926621A
Authority: GB
Original assignee: Cibie Projecteurs SA
Current assignee: Cibie Projecteurs SA
Priority date: 1978-08-03
Filing date: 1979-07-31
Publication date: 1980-02-13
Also published as: DE2931480C3; RO76836A2; JPS6231761B2; YU181979A; IT1122690B; YU41344B; FR2432676B1; GB2027188B; DE2931480B2; JPS5522595A; FR2432676A1; BR7904962A; ES483823A1; DE2931480A1; IT7924878A0

Abstract

A light unit for a motor vehicle headlamp consists of a reflector (10) and a lens (20) connected by a bead (30) of epoxy resin adhesive. The reflector has a lip (11) which surrounds a rim (21) on the lens, with a substantial radial clearance, which is filled by the adhesive. The reflector (10) also has lugs (16) which co- operate with complementary recesses (26) in the lens to centre the reflector relative to the lens, so that the radial clearance is uniform, before the adhesive sets. The presence of a generous thickness of adhesive helps to avoid troubles arising from differential thermal expansion. <IMAGE>

Description

SPECIFICATION Light units for vehicle headlamps This invention relates to light units for headlamps, especially motor vehicle headlamps.

The term 'light unit', as used herein, denotes an inseparable assembly of a reflector and a lens.The reflector receives one or more lamps, whose rays are reflected by the reflector to form a beam, which may then be modified by the lens to have the required characteristics.

According to one aspect of the present invention, a light unit for a vehicle headlamp comprises a reflector made of a plastics material, and a front lens which closes a front opening of the reflector, the lens being connected to the reflector by a bead of adhesive cement received between respective connecting portions of the lens and the reflector, one of the said connecting portions lying radially outwards of the other connecting portion with respect to the reflector front opening, in a region extending at least partially around the periphery of the front opening, with a substantial radial clearance between the two connecting portions in the said region, which radial clearance is filled by the said adhesive cement, and the light unit also includes centring means provided on at least one of the reflector and the lens, which centring means is adapted, when the adhesive is in an unsolidified condition, to center the reflector relative to the lens, and thereby to fix the said radial clearance.

The invention may be of assistance in making it possible to use a plastics reflector instead of a metal reflector, while largely avoiding defects resulting from differential thermal expansion. It will be realised that the coefficients of thermal expansion of a glass lens (glass is the usual lens material) and a metallic reflector would be reasonably compatible, so that they could be connected by an adhesive, such as an epoxy resin cement, without encountering troubles from differential thermal expansion. However, if a plastics reflector were to be made in more or less the same design as a deep-drawn sheet metal reflector, there would be a possibility of defects arising.In particular, plastics reflectors have been found in some cases to develop cracks and fractures, so that the lens and the reflector no longer form a sealed unit, and in other cases the connecting joint between the two elements shows imperfections. While the incidence of such defects might not be very high, any incidence of such defects would be undesirable in mass production.

The invention provides a generous thickness of adhesive between the reflector and the lens, and the resilience of this adhesive can absorb movements resulting from differential thermal expansion.Such differential expansions may arise either from changes in the ambient temperature to which the light unit is subjected, or when, during operation, the light unit is subjected to the heating of the associated lamp, which results in a varying temperature rise in the different zones of the reflector.

The invention also provides, according to a second aspect, a vehicle headlamp incorporating a light unit according to the first aspect The invention also extends methods of assembling light units according to the first aspect. In one method, the lens and the reflector are brought together, with the centring means locating the reflector relative to the lens, and the adhesive cement is then introduced between the connecting portions of the lens and reflector, and allowed to set. In an alternative method the adhesive cement is applied to one or both of the connecting portions, the lens and the reflector are brought together, with the centring means locating the reflector relative to the lens, and the adhesive cement is allowed to set.

The invention may be carried into practice in various ways, but one specific embodiment will now be described by way of example, with reference to the accompanying drawings, of which: Figure 1 is a front view of an assembled prefocus light unit embodying the invention; Figure 2 is a section of part of the light unit, on the line Il-Il in Figure 1; and Figure 3 is a perspective showing how the light unit is assembled.

The pre-focus light unit comprises a reflector 10 made from a plastics material, and a glass lens 20. For its connection to the lens, the reflector 10 has a rim 11 of generally L-shaped cross-section; one limb 1 la of the L-shaped cross-section extends outwards from the reflector 10, in a plane generally parallel to the front opening of the reflector, while the other limb 11b extends forwards from the outer edge of the limb 1 a. The lens 20 has a rim 21 which lies within the wall 1 a of the rim 1 with a radial clearance between the rim 21 and the wall 11 a.The difference between the outer diameter of the rim 21 and the inner diameter of the wall 1 a, which gives rise to this clearance, may for example be between 0.5mum and 3mm.

The reflector 10 is secured to the lens 20 by an adhesive 30, in this example an epoxy resin adhesive; which occupies the space between the rim 21 and the rim 1 To locate the reflector and the lens correctly relative to one another before the adhesive sets, the reflector 10 has centring means in the form of three integrally moulded locating lugs 1 6 on the front surface of the wall 1 lea, which lugs co-operate with three corresponding recesses 26 on the rear edge of the lens 20. The lugs 1 6 and the recesses 26 have inclined flanks, so that minor misalignments will be corrected as the reflector and the lens are brought together.Two of the lugs 1 6 are positioned at opposite ends of a horizontal diameter of the reflector 10, while the third lug is positioned at the top end of a vertical diameter of the reflector. The recesses 26 are correspondingly positioned. Thus, as well as locating the lens and the reflector to provide the radial clearance between the rim 21 and the wall 1 lea, the lugs 16 and recesses 26 ensure that the light unit cannot be assembled with one of its components inverted.

The adhesive 30 may be applied to the parts 21 and 11 either before or after the reflector and the lens are brought together. After the adhesive has set, the light unit will be able to withstand both local and overall temperature variations, because of the generous thickness of adhesive between the reflector and the lens.

Of course the invention is not limited to the embodiment described. The formations which fit one inside the other at the periphery of the lens and of the reflector may be of any type (edges, rims, grooves, and so on) and it does not matter which of the two elements has which. The same applies to the centring means.

Finally, if a prefocus light unit embodying the invention is to be fitted on a motor vehicle, by means of rods or screws engaging the periphery of the light unit from the rear, the areas where the rods or screws act will preferably be those zones of the reflector where the centring means are situated, because these centring means serve as local reinforcements for the light unit and obviously it is better to fit the light unit by fixing means operative in the strongest zones.

Claims

1. A light unit for a vehicle headlamp, comprising a reflector made of a plastics material, and a front lens which closes a front opening of the reflector, the lens being connected to the reflector by a bead of adhesive cement received between respective connecting portions of the lens and the reflector, one of the said connecting portions lying radially outwards of the other connecting portion, with respect to the reflector front opening, in a region extending at least partially around the periphery of the front opening, with a substantial radial clearance between the two connecting portions in the said region, which radial clearance is filled by the said adhesive cement, and the light unit also including centring means provided on at least one of the reflector and the lens, which centring means is adapted; when the adhesive is in an unsolidified condition, to centre the reflector relative to the lens, and thereby to fix the said radial clearance.

2. A light unit as claimed in Claim 1, in which the said other connecting portion comprises a first peripheral rim around the respective one of the reflector or lens, and the said one connecting portion comprises a second peripheral rim around the other of the reflector or lens, and encircling the first peripheral rim.

3. A light unit as claimed in Claim 1 or Claim 2, in which the centring means are disposed on two mutually perpendicular diameters of the said front opening of the said refiector.

4. A light unit as claimed in Claim 3 in which the centring means comprises three centring elements on the reflector, two of the centring elements being located at opposite ends of a diameter of the reflector opening, and three correspondingly situated centring elements on the lens, whereby the lens and the reflector can be assembled, with all the centring elements cooperating in pairs, in only one relative position.

5. A light unit as claimed in any of the preceding Claims, in which the centring means comprises raised protrusions formed on one of the reflector or lens, and complementary recesses formed on the other of the reflector or lens, the said protrusions and recesses having inclined flanks.

6. A light unit for a vehicle headlamp, the light unit being substantially as herein described; with reference to the accompanying drawings.

7. A vehicle headlamp incorporating a light unit as claimed in any of the preceding Claims.

8. A headlamp as claimed in Claim 7 when appendant to Claim 5, which is fitted to a motor vehicle by means acting on the said one of the reflector or lens in the areas of the raised protrusions, whereby the raised protrusions provide reinforcement at the supporting points for the light unit.

9. A method of assembling a light unit as claimed in any of Claims 1 to 5, in which method the lens and the reflector are brought together, with the centring means locating the reflector relative to the lens, and the adhesive cement is then introduced between the connecting portions of the lens and reflector, and allowed to set.

10. A method of assembling a light unit as claimed in any of Claims 1 to 5, in which the adhesive cement is applied to one or both of the connecting portions, the lens and the reflector are brought together, with the centring means locating the reflector relative to the lens, and the adhesive cement is allowed to set.

11. A method of assembling a light unit for a vehicle headlamp, the method being substantially as herein described, with reference to the accompanying drawings.