Lamp having a cap in clamping fit engagement with the bulb

FIELD OF THE INVENTION

The invention relates to a lamp comprising a cap of substantially insulating material and a transparent bulb having a pinch portion provided with two lead-in wires extending outwards beyond said pinch portion, the cap comprising two electric contact members for contacting respective electric contacts of a lamp holder, while each lead-in wire is connected to a contact member of the cap and clamping means are attached to the cap, which clamping means engage the pinch portion of the lamp bulb.

BACKGROUND OF THE INVENTION A lamp of this type may be a filament lamp such as a halogen lamp or any other type of lamp comprising a bulb and a cap; in particular, the lamp may be a high- pressure discharge lamp. The bulb envelopes the light source of the lamp and may be made of quartz glass or another transparent material. The bulb has a pinch portion embedding the lead-in wires for guiding electric current to the light source. Also other parts may be embedded in the pinch portion, such as molybdenum foil members connecting the lead-in wires to electrode rods of the lamp. Moreover, a third lead-in conductor can be embedded, which may be the case in certain types of lamps.

The pinch portion of the bulb is a flat portion, where the material of the bulb is pressed together during its manufacture. The pinch portion has two sides bordered by two longitudinal edges, both extending parallel to the longitudinal axis of the lamp. The pinch portion has a relatively small thickness, measured perpendicularly to the plane of the flat pinch portion, hereinafter referred to as the X-direction. The Y-direction extends in the plane of the flat pinch portion and perpendicularly to the longitudinal axis of the lamp. The pinch portion may have the same thickness throughout its surface, but it is often larger near its longitudinally directed edges. The pinch portion may then have an I-shaped cross-section.

The cap of the lamp is substantially made of an insulating material, such as a ceramic material which may be enveloped in a metal shell. The two electric contact members may be metal tubes both extending outwardly in the longitudinal direction of the lamp, wherein the lead-in wires reach through the tubes and are connected to the outward ends of

the tubes by means of a welding operation. The tubes may have a flange near their outward ends, which flanges are engaged by the lamp holder when the lamp is attached thereto.

Apart from the clamping fit or connection between the bulb and the cap, the bulb is attached to the cap by means of the two lead-in wires which are partly embedded in the pinch portion of the bulb, and each lead-in wire is connected at its other end to a corresponding contact member of the cap. This connection between the cap and the bulb of the lamp prevents the bulb from moving with respect to the cap in the longitudinal direction (Z-direction) of the lamp. However, this connection neither prevents movements between the cap and the bulb in the X and Y-directions, nor rotation about the longitudinal axis of the lamp. Such movements should be prevented or limited by the clamping means.

An embodiment of a lamp as described above is disclosed in WO-A- 2004/1120087. According to this publication, the lamp cap is provided with two metal elements which are attached to protrusions of the cap in such a way that the pinch portion of the lamp bulb can be pushed between the two metal elements. The pinch portion is thus clamped between the two metal elements, so that it is fixed to the cap of the lamp. With such a connection, the bulb is prevented from moving in the X-direction with respect to the cap, but it may move in the Y-direction, and after this movement it may be clamped in a position other than its original position. Furthermore, the two metal elements will not resist a rotational force between the bulb and the cap, which force may occur when the lamp is fixed to its lamp holder by means of a twist-and-lock connection (e.g. bayonet connection, screw connection, etc). Another disadvantage is the quite complicated attachment of the metal elements to the protrusions of the cap.

OBJECT AND SUMMARY OF THE INVENTION It is an object of the invention to realize a connection between the cap and the bulb of the lamp by clamping means, so that movement of the bulb with respect to the cap in the X-direction as well as in the Y-direction is limited or prevented.

It is another object of the invention to realize a connection between the cap and the bulb of the lamp by clamping means, so that a rotational movement of the bulb with respect to the cap is limited or prevented.

It is a further object of the invention to realize a connection between the cap and the bulb of the lamp by clamping means, so that the lamp bulb will return to its original position with respect to the cap after a mutual displacement has taken place (i.e. elastic system behavior).

To accomplish one or more of these objects, the clamping means comprise a metal spring member engaging the pinch portion of the bulb at two opposite sides and at a longitudinal edge of the pinch portion. Consequently, the spring member engages the pinch portion of the bulb at least at three locations. The spring member surrounds an edge of the pinch portion, engaging the outer side of this edge, so that also the movement of the bulb with respect to the cap in the Y-direction is limited or prevented.

In a preferred embodiment, two metal spring members are present, while each of the two longitudinal edges of the pinch portion of the lamp bulb is surrounded by a spring member, each spring member being attached to the lamp cap. The two spring members limit, or prevent, movement of the bulb with respect to the cap in the X-direction as well as in the Y-direction. The two metal spring members are preferably identical, so that the same spring members can be applied around each of the two longitudinal edges of the pinch portion. This reduces the number of different parts and makes it easier to assemble the lamp.

In another preferred embodiment, the metal spring member engages both longitudinal edges of the pinch portion as well as each of the opposite sides of the pinch portion, preferably at two locations. The spring member surrounds the whole pinch portion, or a major part of it, while only one metal spring member has to be attached to the cap. The application of such a spring member is sufficient to limit, or prevent, movement of the bulb with respect to the cap at least in the X and Y-directions. The metal spring member preferably engages the two opposite sides at locations near a longitudinal edge of the pinch portion. When two spring members are present, each spring member may engage both sides of the pinch portion near the same longitudinal edge. When only one spring member is present, each flat side of the pinch portion may be engaged by the spring member at two locations at a distance from each other. The distance between the central longitudinal axis and the location of engagement is preferably more than 25% of the distance between the two longitudinal edges. Such an engagement at locations at a substantial distance from the central longitudinal axis of the lamp limits, or prevents, the rotational movement of the bulb with respect to the lamp cap.

In a preferred embodiment, the metal spring member engages both sides of the pinch portion by flat surfaces extending substantially parallel to the sides of the pinch portion. Such flat surfaces may contribute to reducing or preventing a tilting movement of the bulb with respect to the lamp cap. The flat surfaces preferably border on inclined portions of the spring member for guiding the pinch portion between these flat surfaces during manufacture of the lamp. This facilitates assembly of the lamp.

In a preferred embodiment, the metal spring member comprises at least two flat portions extending perpendicularly to the longitudinal axis of the lamp, which portions rest against corresponding surfaces of the lamp cap at both sides of the pinch portion of the bulb. The cooperation between said flat surfaces and the corresponding surfaces of the cap defines the position of the spring member in the longitudinal direction. Consequently, after the spring member is attached to the cap, it does not move in the longitudinal direction when the pinch portion is pushed between the engaging parts of the spring member during manufacture of the lamp.

The spring member may be made of a metal wire. The metal spring member is preferably made of a piece of flat sheet material. In an appropriate design, to be described hereinafter as an embodiment of the invention, the spring member may be made of a flat metal plate resulting in an inexpensive product.

As the bulb and the cap of the lamp are connected through the lead-in wires, the metal spring member is kept in its position between the bulb and the cap. However, in a preferred embodiment, the metal spring member comprises clamping elements for engaging the cap, so that the spring member can be firmly attached to the cap before the bulb is clamped between the engaging parts of the spring member. This facilitates manufacture of the lamp.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further elucidated by means of a description of two embodiments of a lamp comprising a cap and a bulb having a pinch portion provided with two lead-in wires, wherein clamping means engage the pinch portion of the bulb, and with reference to the drawings, in which: Fig. 1 shows a cap with clamping means in a first embodiment;

Fig. 2 shows the metal spring member;

Fig. 3 shows the cap attached to the lamp bulb; and

Fig. 4 shows a second embodiment of the lamp.

DESCRIPTION OF EMBODIMENTS

Fig. 1 is a perspective view of the lower end of the lamp bulb 1 and, at some distance, the cap 6 in a first embodiment of the invention. The bulb 1 is provided with a pinch portion 2 (main pinch) having two flat sides 3 (side pinches) and two longitudinal edges 4, which edges have a flat surface at their outer side. The pinch portion 2, perpendicular to the

longitudinal axis of the lamp, has an I-shaped cross-section , while the thickness of the pinch portion 2 at its edges 4 is about three times the thickness of the remaining part of the pinch portion 2. Two lead-in wires (not shown in Fig. 1) are embedded in the pinch portion 2.

Fig. 1 further shows the cap 6 of the first embodiment of the lamp which has a cylindrical shape and is substantially made of insulating ceramic material. Two electric contact members 7 (only one of which is visible in Fig. 1) are present at the lower side of the cap 6, which contact members 7 can be connected to corresponding electric contacts of the lamp holder (not shown) to which the lamp is to be attached. The cap 6 is provided with a recess 8 forming a slit for receiving the pinch portion 2 of the bulb 1, while the two lead-in wires are connected to the two contact members 7.

Further recesses are present at the upper side 9 of the cap 6 in order to accommodate portions of two identical metal spring members 10. Each spring member 10 comprises two flat portions 11 extending parallel to the surface of the upper side 9 of the cap 6, which flat portions 11 rest against corresponding surfaces at the upper side 9 in order to keep the two spring members 10 at their location near the upper side 9 of the cap 6.

Furthermore, each spring member 10 comprises three engaging parts 12,13: two engaging parts 12 for engaging both sides 3 of the pinch portion 2 and one engaging part 13 for engaging the flat outer surface of a longitudinal edge 4 of the pinch portion 2.

Fig. 2 shows the metal spring member 10 in a perspective view. The spring member 10 is made of a metal plate by means of a punching operation and a subsequent bending operation, followed by a hardening process so as to obtain the appropriate elastic property of the material. The first embodiment of the invention comprises two of these metal spring members 10 as shown in Fig. 1, both of which are attached (for example, by clicking or clamping by friction) to the cap 6 before the bulb 1 is attached thereto. The metal spring member 10 comprises two flat portions 11 which can rest against flat surfaces of the cap 6, as explained above. The spring member 10 is attached to the cap 6 by a clamping fit or connection, i.e clamping parts 14 are pressed in corresponding recesses of the cap 6 (see Fig. 1). Curved parts 15 will click in corresponding recesses of the cap 6, so that the spring member 10 is firmly fixed to the cap 6 and is maintained in a predetermined position.

The spring member 10 comprises two engaging parts 12 having flat parallel surfaces facing each other, which surfaces can abut both sides 3 of the pinch portion 2 of the bulb 1, whereby they engage the pinch portion 2 by clamping. The engaging parts 12 are provided with inclined portions 16, so that the two parts 12 flare when the pinch portion 2 is

pushed between them. Furthermore, the spring member 10 comprises engaging part 13 for engaging one of the edges 4 of the pinch portion 2, which part 13 is also provided with an inclined portion 17, so that the engaging part 13 moves to its clamping position when the pinch portion 2 is pushed to its final position in the recess 8 of the cap 6. Engaging part 13 is connected to the surrounding part 18 of the spring member 10, which part 18 surrounds the longitudinal edge 4 of the pinch portion 2.

Fig. 3 shows the cap 6 and the lower end of the bulb 1, with the pinch portion 2 being present in the recess 8 of the cap 6. The two spring members 10 are attached to the cap 6 as described above and keep the bulb 1 in its position by two engaging parts 12 at each of the sides 3 of the pinch portion 2 and by two engaging parts 13 at the longitudinal edge 4 of the pinch portion 2. The bulb 1 is further fixed to the cap 6 by means of the two lead-in wires (not shown), which are connected to the two contact members 7 of the cap 6. Fig. 3 shows the two contact members 7 in different dimensions. The electric contacts of the lamp holder have corresponding different dimensions, so that the lamp must be fixed in the lamp holder in a predetermined position.

The connection between the two lead-in wires and the contact members 7 ensures fixation of the bulb 1 in the longitudinal direction and the two engaging parts 13 ensure fixation in the Y-direction (perpendicular to the longitudinal direction and parallel to the pinch portion 6). The four engaging parts 12 ensure fixation of the bulb 1 in the X- direction (perpendicular to the longitudinal direction and the Y-direction) and both engaging parts 12, 13 limit, or prevent, a rotational movement of the bulb 1 about the longitudinal axis of the lamp.

Fig. 4 shows the cap 19 and the metal spring member 20 in a second embodiment of the invention. The cap 19 is similar to the cap 6 of the first embodiment (see Fig. 1), but comprises only one spring member 20. The spring member 20 comprises two identical spring member parts which are identical to the two spring members 10 of the first embodiment. The two spring member parts are connected by a strip 21 in order to form the spring member 20, which strip 21 is accommodated in a recess 22 of cap 19. The spring member 20 functions identically to the two spring members 10 of the first embodiment. Corresponding parts of the spring member 20 are therefore denoted by the same reference numerals as in Fig. 1 for the spring members 10.

The two embodiments described above are only examples of the lamp according to the invention; many other embodiments are possible.