DE3752040T2 - Compact double filament with use of the slope for bending control - Google Patents

Description

FIELD OF INVENTION

The present invention is directed to a unique dual filament and supports therefor which is particularly advantageous in a European version of Sylvania's Capsylite lamps. Both the PAR and A-line versions of these lamps are commercially available in the United States. The US versions of these lamps are characterized by a low power tungsten-halogen tempered glass light source capsule mounted within a heavy outer envelope. See, for example, patent US-A-4 598 225. EP-A-0 241 911 (which falls under the provisions of Article 54(3) EPC) and GB-A-1 147 140 disclose filaments according to the first part of present claim 1.

BACKGROUND OF THE INVENTION

The use of lamps with a parabolic aluminized reflector (PAR), an elliptical reflector (ER) or a reflector (R) for general spot, down and/or flood lighting purposes is well established. In particular, the R, PAR and ER type lamps have been accepted as the lamps of choice for short to medium throw outdoor applications as well as for exhibition, decorative, highlight and examination lighting applications in indoor areas.

Traditionally, PAR-type bulbs, in particular Sylvania’s PAR38, used a filament mounted transversely in the reflector, i.e. perpendicular to its axis of symmetry, as this was the easiest arrangement to manufacture.

The result of this arrangement is an asymmetric beam shape and the propagation of stray light outside the usable beam. In addition, the need to maintain the appropriate atmosphere in the outer envelope required the lamp to be hermetically sealed, with the lens flame-sealed to the reflector.

With the introduction of Sylvania's Capsylite PAR lamps, which use a halogen capsule as the light source, lamps appeared with axially mounted filaments, giving a more symmetrical beam shape and more efficient collection of light by the reflector into a usable beam.

Part of this improvement in optical efficiency is due to the fact that Capsylite lamps use a compact filament that more closely approximates the theoretically ideal "point" light source.

In Capsylite lamps operating under United States-type electrical systems (i.e., 120-130 V; 60 Hertz), such compact filaments are made possible by the use of a half-wave rectifier diode, which effectively reduces the capsule voltage from 120 V to about 84 V. Furthermore, since the atmosphere in the outer envelope is no longer critical because of the capsule, the lamp does not need to be hermetically sealed and focused-beam lamps have appeared.

PAR lamps for the European mains voltage, typically 220 to 250 V, did not use halogen capsules due to the extremely fine wire required at this high voltage.

Low power (<150W) mains voltage filaments tend to be long, loose, prone to sagging and require numerous supports which reduce efficiency. Voltage reducing diodes cannot be used as they cause unacceptable filament flickering when operating at 50Hz AC, which is standard in Europe.

"Folded" filaments tend to have damaging interactions between adjacent sections of the filament, shortening their lifespan.

Coiled filaments are known, see for example US-A-1,180,159; 1,247,068; 2,142,865; 2,306,925; 2,774,918; 4,208,609; and 4,316,116. However, none of these coiled filaments provide the unique properties of the filament of the present invention.

Filament mounts typically cause shadowing and scattering of light. Examples of typical filament mounts can be found in US-A-4,359,665; 4,208,606; 3,780,333; 3,736,455; 3,678,319; 3,634,722; 3,335,312; and 3,173,051.

Although quartz-halogen capsules have been manufactured for the 220-250 V range, they are generally inefficient and complicated affairs with "zig-zag" filaments and numerous spiral mounts.

Therefore, standard quartz capsules are not well suited for use in PAR lamps as they lack both luminous efficiency and optical efficiency. They are also more expensive to manufacture than tempered glass capsules due to the high cost of the materials and the processes involved, as well as the labor required.

-The present invention overcomes the above-mentioned difficulties with the European type PAR and A-line lamps by providing a unique filament and non-interfering supports for the same.

The present invention is directed to a low power (< 150 W) and high voltage (220-250 V) halogen filament that is particularly well suited for use in European type PAR and A-line lamps.

In one aspect, the present invention provides a filament having a double coil of refractory metal wire having a diameter d, wherein the primary coil diameter D₁ and the secondary coil diameter D₂ of the filament are defined by the following equations:

D1 = d(A+2);

D₂ = D�1(B+2);

1.40 ≤ A ≤ 3.00; and

3.0 ≤ B ≤ 10.0,

where d is equal to the filament diameter, characterized in that the inner pitch IP of the double filament satisfies the condition

1.08 ≤ IP ≤ 1.35

is fulfilled, whereby the inner pitch IP of this double filament is defined as follows:

IP = (48 + 1) * PP / (48 + A + 2)

where PP is equal to the pitch of the primary helix; and that the secondary pitch is in the range of 1.40 to 1.60.

In a further aspect, the present invention provides a method for producing a double filament, consisting of the following steps:

Winding a filament with a diameter d around a primary winding core with a diameter M₁ to produce a primary coil with a primary winding diameter D₁, and winding the primary coil around a secondary winding core with a diameter M₂ to produce a double coil with a secondary winding diameter D₂, which satisfies the following equations:

D1 = d(A+2)

D₂ = D�1(B+2);

1.40 ≤ A ≤ 3.00; and

3.0 ≤ B ≤ 10.0,

where d is equal to the filament diameter, characterized in that the inner pitch IP of the double filament satisfies the condition

1.08 ≤ IP ≤ 1.35

Fulfills,

where IP is defined as follows:

IP = (48 + 1) * PP / (48 + A + 2)

where PP is equal to the pitch of the primary helix; and that the secondary pitch is in the range of 1.40 to 1.60.

Such filaments can be used in incandescent lamps, especially those with a halogen or halide gas filling.

Accordingly, at least in the preferred embodiments, an improved halogen incandescent lamp is provided, the improvements comprising a compact, high-output filament axially mounted in a single-ended tempered glass capsule with a unique support system sufficient to

to prevent significant sagging of the coil during its useful life.

The parameters of the filament according to the present invention are novel. A filament manufactured according to these parameters exhibits improved compactness and structural rigidity, which together with the unique complementary supports for the same provides a suitable light source for lamps operating under European electrical systems (220-250 volts and 50 hertz).

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an embodiment of an incandescent lamp, in particular the tungsten-halogen variant, which was manufactured according to the teachings of the present invention.

Figure 2 shows a filament wound to produce a double filament.

Figure 3 shows a filament wound to produce a double filament.

Figure 4 shows a filament wound around a primary winding core to form a primary coil.

Figure 5 shows a primary coil wound around a secondary winding core to produce the double filament.

Figure 6 shows the various parameters associated with determining the outer diameter of a double filament of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention relates to a multi-coiled filament and a support system. The filament consists of a coreless double filament made of a single filament wire for an incandescent lamp. The supports make it possible to design a simple, inexpensive and efficient filament.

Figure 1 illustrates an example of an incandescent lamp 10 made in accordance with the teachings of this invention, which in this embodiment is a tungsten-halogen variant.

As shown, the lamp 10 includes a tubular envelope 12 made of a suitable light-transmissive material, such as aluminosilicate glass. A pair of lead wires 14 and 16, portions of which serve as support members, are crimp sealed into the envelope 12 at the crimp seal 18.

The lead wires 14 and 16 may be formed of any suitable material, such as molybdenum, which forms a relatively distortion-free hermetic seal with the glass envelope 12. A refractory metal, such as tungsten, is used to form the double filament 20 in accordance with the teachings of this invention. The double filament 20 is provided with webs 21 at each of its ends during its manufacture.

In this embodiment, the envelope 12 is filled with a fill gas comprising an inert gas and a suitable halogen or halide. Preferred examples of fill gases useful herein include the inert gases argon, krypton, xenon and/or nitrogen plus the halogen or halide.

Figures 2 and 3 show enlarged views of the preferred tungsten filament of the present invention and its coiled and double coiled stages, respectively. Each stage has a pitch or percent pitch equal to the center-to-center distance S of the turns divided by the diameter d of the wire or coil, multiplied by 100.

-In particular, Figure 2 shows the primary pitch of a filament 20A having a center-to-center distance S₁, a wire diameter d₁, and an outside diameter D₁. In the present invention, the primary pitch P₁ is equal to S₁/d₁ and the secondary pitch P₂ is equal to S₂/d₂. Note: d₂ = D₁. Pj has a value not exceeding 1.70 (or 170%).

In Figure 3, S2 is the center-to-center distance of the double filament, d2 (d2 = D1) is the primary filament diameter, and BL is the body length of the double filament (or secondary) filament. The secondary pitch of the filament is in the range of 1.40 to 1.60.

The process for manufacturing the double filament of the present invention is shown in Figures 4-6.

Referring to Figure 4, the present method includes the steps of (1) providing a strand of filamentary filament 19 having a specific length L and diameter d (for a specific power, voltage and efficiency) and (2) winding the filament 19 around a primary winding core 30 having a diameter M1 to produce a primary coil 20A.

Referring to Figure 5, the method of the present invention additionally includes the step (3) of winding the primary coil 20A around a secondary winding core 40 having a secondary winding core diameter M2 to produce a double coil filament shape, where B ≥ A.

As shown in Figures 4 and 5 respectively, the primary winding diameter D�1 and the secondary winding diameter D�2 of the filament are:

D₁ = d(A+2) and D₂ = D₁(B+2), where d is the filament diameter and 1.40 ≤ A ≤ 3.00 and 3.0 ≤ B ≤ 10.0,

such that the filament exhibits an increase in compactness and maintains or exhibits an increase in structural stiffness.

Surprisingly, it was discovered that B can range from about 3.0 to about 10.0 (if A satisfies the equation 1.40 ≤ A ≤ 3.0), and if the primary slope is reduced so that the inner slope (IP) satisfies the condition 1.08 ≤ IP ≤ 1.35, and where:

IP = (4B + 1) * PP / (4B + A + 2)

and wherein the winding is further improved by reducing the primary pitch PP from about 155% to as low as about 125% and by selecting the value of B such that IP is as close as possible to the center of the region, which is given by the equation 1.08 ≤ IP ≤ 1.35.

The method of the present invention additionally includes the step (4) of removing substantially all of the core of the double filament 20, except for the core in the webs 21. The core in the webs 21 is preferably left untouched in order to preserve the structural integrity of the filament 20 when it is assembled within the envelope and crimped or secured to a fastener through the webs.

Figure 6 shows the outer diameter D2 of the filament winding shown in Figure 5, where the primary winding core diameter M1 is larger than the diameter of the filament 19 and the secondary winding core diameter M2 is larger than the diameter of the primary filament 20A.

The most preferred coil shape is centered in the piston (CC8 configuration) to equalize the piston wall temperature. At the higher power ratings, this allows the piston wall stress to be minimized. At the lower power ratings, this allows the minimum piston wall temperature (required for the tungsten-halogen cycle to function) to be achieved without cold spots.

Centering the coil in the bulb is also important for filaments located at the focal point of reflectors, as this compensates for the scattering of light around the central axis of the reflector.

The following is an example of a filament improved by the present invention: 35 WATTS/84 VOLTS

where BL / D₂ = (L/D) / (factor) and BL - Body length; D₂ - Outside diameter; P₂ - Secondary slope (1.50)

For the sample winding, where the winding core ratios are low, the resulting body length is about 14 mm. The improved windings #1, 2 and 3 show length reductions of about 39%, 57% and 67% respectively, compared to the sample filament.

As for lamps, reflector-type lamps for operation at high voltages, particularly for overseas operation at 225 and 245 volts, such lamps typically require commissioning with extremely long filaments.

In addition, filaments designed to operate at a line voltage such as 120 or 130 volts also require starting from a long filament. The improved method of reducing focus loss and improving collection efficiency will allow for winding a filament into a compact coil that is particularly advantageous for these applications and may result in improved operation at high voltages, as typical winding methods have resulted in extremely long filaments requiring larger envelopes, more complex support devices and greater scattering of the light.

In addition, the filament shape mentioned above can also lead to operation without voltage reducing or rectifying elements (e.g. a diode), which eliminates the modulation of light and power fluctuations resulting from the use of such rectifying elements. The elimination of the rectifying elements is particularly important in the range of 225 to 245 Volt, since the small filament mass leads to greater thermal fluctuations, and advantageous where small reflector lamp models are sought, because of the heat generated by the lamp capsule to which the rectifier is exposed.

The resulting more compact coil also results in a smaller capsule size, which provides the following previously unattainable advantages:

1. Enables operation of lower power tungsten-halogen capsules at higher voltages as the stress on the bulb wall is reduced;

2. Enables the use of high pressure tungsten-halogen capsules, which in turn results in lower capsule energy and consequently improved containment during lamp arc breakdown in the event of lamp failure; and

3. Enables lower overall material costs for lamp parts such as glass, fill gas and outer envelope.

Claims (12)

1. Incandescent lamp with a double coil (20) made of fire-resistant metal wire (19) with a diameter d, the primary winding diameter D₁ and the secondary winding diameter D₂ of the filament (20) being defined by the following equations: D1 = d(A+2); D₂ =D�1(B+2); 1.40 ≤ A ≤ 3.00; and 3.0 ≤ B ≤ 10.0, where d is equal to the filament diameter, characterized in that the inner pitch IP of the double-coil filament (20) satisfies the condition 1.08 ≤ IP ≤ 1.35 where the inner pitch IP of this double-coil filament (20) is defined as follows: IP = (4B + 1) * PP / (4B + A + 2) where PP is equal to the pitch of the primary helix (20A); and that the secondary pitch is in the range of 1.40 to 1.60. 2. Filament according to claim 1, wherein the primary pitch PP is in the range of 1.55 to 1.25. 3. Filament according to claim 1 or 2, wherein the refractory metal wire (19) comprises tungsten. 4. An incandescent lamp having a filament as claimed in any of the preceding claims. 5. A lamp according to claim 4, which is a tungsten-halogen lamp with a halogen or a halide as part of the fill gas. 6. Lamp according to claim 4 or 5, wherein the filament shape (20) is centered in the bulb. 7. A lamp according to any one of claims 4 to 6, comprising a pair of lead wires (14, 16) crimp sealed in and extending from the envelope (12). 8. Lamp according to any one of claims 4 to 7, which additionally comprises a reflector. 9. A lamp according to claim 7 or 8, additionally comprising rectifying or other voltage reducing elements electrically coupled in series with the filament (20) to one of the lead wires (14, 16) and to a voltage source, whereby the voltage applied to the filament (20) is reduced. 10. A lamp according to any one of claims 4 to 9, wherein the envelope (12) has an infrared reflective coating such that infrared light is reflected back onto the filament (20). 11. A method for producing a double-coil filament, consisting of the following steps: Winding a filament (19) with a diameter d around a primary winding core (30) with a diameter M₁ to produce a primary coil (20A) with a primary winding diameter D₁ and winding the primary coil (20A) around a secondary winding core with a Dutch knife M to produce a double coil filament (20) with a secondary winding diameter D₂, which satisfies the following equations: D1 = d(A+2); D2; = D1 = D1(B+2); 1.40 ≤ A 3.00; and 3.0 ≤ B ≤ 10.0, where d is equal to the filament diameter, characterized in that the inner pitch IP of the double-coil filament (20) satisfies the condition 1.08 ≤ IP ≤ 1.35 Fulfills, where IP is defined as follows: IP = (4B + 1) * PP / (4B + A + 2) where PP is equal to the pitch of the primary helix (20A); and that the secondary pitch is in the range of 1.40 to 1.60. 12. The method of claim 11, additionally comprising the step of removing substantially the entire core of the coiled filament (20), except at the webs (21) thereof.