Semiconductor lamp and method for its manufacture

Abstract

Semiconductor lamp (1; 21), comprising - a translucent bulb (2) with a tubular basic shape, which has contact areas (5) at the end, - at least one substrate (3) accommodated in the bulb (2), on which at least one semiconductor light source (4) is arranged, - end caps (7; 22) for closing the end of the piston (2) and - constant volume adhesive (6) for the material connection of a respective pair of an end cap (7; 22) and a contact area (5), wherein - the contact areas (5) taper towards a respective end (9) of the piston (2), wherein the piston (2) has continuously tapered end areas which provide the contact areas (5), wherein - the end cap (22) has a base body (23, 7a) with an end wall (7a) and a circumferential side wall (23) attached thereto on the piston side, - at least a part of an inner surface of the side wall (23) is designed as a contact counter-region (24) which is placed on a respective contact region (5) of the piston (2), and - the contact counter region (24) of the end cap (7) is widened in the direction of the piston (2), wherein an angle of inclination (α2) of the contact counter region (24) and an angle of inclination (α1) of the contact region (5) of the piston (2) differ by 1° to 2°.

Description

[0001] The invention relates to a semiconductor lamp comprising a translucent bulb with a tubular basic shape, at least one substrate accommodated in the bulb, which bulb has contact areas extending around its end, as well as end caps for closing the end of the bulb and a constant-volume adhesive for at least firmly bonding a respective pair of end caps and contact areas. The invention also relates to a method for producing a semiconductor lamp. The invention is particularly applicable to replacement lamps or retrofit lamps for replacing conventional fluorescent lamps or linear lamps.

[0002] As so-called “LED retrofit lamps” 101 are, as in Fig. As indicated in Figure 4, tubular LED lamps are known, which are used as replacements for conventional fluorescent lamps. Such LED retrofit lamps 101 are essentially composed of a translucent tubular bulb 102 (with a longitudinal axis A), a circuit board 103 accommodated in the bulb 102 with LEDs 104 arranged thereon, electronic components 105, and end caps 106 for both lamp ends. The electronic components 105 form a driver circuit, which is integrated as a separate component into an end cap 106.

[0003] In conventional fluorescent lamps, the end caps are attached to a bulb using putty. The putty is applied to a cylindrical cross-sectional constriction or rolled portion at the end of a glass bulb. A cylindrical, open-ended end cap in the form of a metal base is then pushed over the rolled portion, so that the putty is located in a hollow cylindrical annular gap between the rolled portion and the metal base. The putty foams, creating a firm bond between the bulb and metal base in the annular gap. After curing at high temperatures (typically in an oven at over 200°C), the putty is hard and the connection is stable and rigid. A slight inclination or tilting of the bulb and metal base is not critical for sealing the bulb due to the foaming properties of the putty.

[0004] Returning again to Fig. 4, however, this type of connection is not suitable for the end cap 106 and the bulb 102 of the LED retrofit lamp 101, since the curing temperatures of the cement in an annular gap 107 between a rolled portion 108 and the end cap 106 are above damage temperatures of typical components of a retrofit lamp 101, e.g., the LEDs 104 and the electronic components 105. Therefore, in the case of LED retrofit lamps 101, an adhesive 109 in the form of epoxy resin or silicone is typically used instead of the cement to prevent curing at high temperatures. The epoxy resin or silicone does not foam, so the annular gap 107 between the rolled portion 108 and the end cap 106 must be particularly narrow (typically with a gap width or gap height Rh in a range of 0.2 mm to 1.0 mm) to ensure a tight seal.Since the annular gap 107 should be equally wide throughout the circumference, this small gap height Rh significantly increases the requirement for precise positioning and thus also the manufacturing costs. To ensure sufficient sealing of the piston 102, the adhesive 109 must also be pressed onto the corresponding bonding surfaces, which further increases the joining requirements, particularly with regard to the inclination or tilting of the piston 102 and the end cap 106.

[0005] The document DE 10 2012 222 103 A1 describes a lighting device with a first part and a second part attached to the first part by means of a potting compound. The document DE 197 34 687 C1 describes a method and a device for separating metal bases connected to glass bodies for the purpose of recycling. The document US 2002 / 0 070 666 A1 describes a device and a method for producing a fluorescent lamp with a glass discharge vessel with a tubular end section. The document WO 2014 / 001 474 A1 describes a lighting device with a housing and with an externally operable electronic assembly accommodated in the housing. The document WO 2012 / 127387 A1 describes an LED lamp with a number of LEDs and with a tubular housing, wherein the LED lamp comprises an auxiliary light source for illuminating a supply area with driver components.US 2013 / 0182425 A1 describes a lamp with a straight tube and two light-shielding units, each with a straight end section. JP 2010 / 140843 A describes an LED lamp with multiple LEDs in the light-emitting area and driver components in a separate area, housed together in a tubular housing.

[0006] It is the object of the present invention to at least partially overcome the disadvantages of the prior art and in particular to provide a possibility for simplified joining of an end cap to a bulb of a semiconductor lamp, in particular a retrofit lamp.

[0007] This object is achieved according to the features of the independent claims. Preferred embodiments can be found in particular in the dependent claims.

[0008] The object is achieved by a semiconductor lamp comprising (i) a translucent bulb with a tubular basic shape, which bulb has contact areas extending around its ends, (ii) at least one substrate accommodated in the bulb, on which at least one semiconductor light source is arranged, (iii) end caps for closing the end of the bulb, and (iv) a constant-volume adhesive for firmly bonding the end caps to a respective contact area. The contact areas taper toward a respective end of the bulb.

[0009] The piston has continuously tapered end regions that provide the contact regions. The end cap has a base body with an end wall and a circumferential side wall attached thereto on the piston side. At least part of an inner surface of the side wall is designed as a counter contact region that is placed on a respective contact region of the piston. The counter contact region of the end cap is widened in the direction of the piston, wherein an angle of inclination (α2) of the counter contact region and an angle of inclination (α1) of the contact region of the piston differ by 1° to 2°.

[0010] The tapered contact areas significantly facilitate the joining of the end cap and piston. In particular, the impact of tilting between the end cap and piston on the seal is significantly reduced. Furthermore, the gap height continuously decreases as the end cap is pushed on, making it easy to ensure that the adhesive is sufficiently compressed around the entire circumference to achieve the required seal at the contact area.

[0011] The bulb may be completely or partially translucent.

[0012] Since the piston accommodates at least one substrate, and thus encloses the substrate, the piston can also be considered a casing. Since the piston also directly or indirectly holds or supports the at least one substrate, the piston can also be considered a carrier body.

[0013] In particular, if the piston is a straight piston, it may have an imaginary straight longitudinal axis. However, the piston may also be curved at least in sections, e.g., be U-shaped, and then have a correspondingly shaped longitudinal extension.

[0014] In particular, the at least one semiconductor light source comprises at least one light-emitting diode. If there are multiple light-emitting diodes, they can shine in the same color or in different colors. A color can be monochrome (e.g., red, green, blue, etc.) or multichrome (e.g., white). The light emitted by the at least one light-emitting diode can also be infrared light (IR LED) or ultraviolet light (UV LED). Multiple light-emitting diodes can generate a mixed light, e.g., a white mixed light. The at least one light-emitting diode can contain at least one wavelength-converting phosphor (conversion LED). Alternatively or additionally, the phosphor can be arranged remotely from the light-emitting diode (“remote phosphor”), e.g., on the bulb. The at least one light-emitting diode can be in the form of at least one individually housed light-emitting diode or in the form of at least one LED chip. Multiple LED chips can be mounted on a common submount.The at least one light-emitting diode can be equipped with at least one separate and / or shared optical system for beam guidance, e.g., at least one Fresnel lens, collimator, etc. Instead of or in addition to inorganic light-emitting diodes, e.g., based on InGaN or AlInGaP, organic LEDs (OLEDs, e.g., polymer OLEDs) can also generally be used. Alternatively, the at least one semiconductor light source can comprise, for example, at least one diode laser.

[0015] The substrate may, in particular, be a printed circuit board equipped with the at least one semiconductor light source. The printed circuit board may be a strip-shaped printed circuit board. It may be equipped with at least one semiconductor light source on one or both sides. It may be rigid or flexible. The substrate is also referred to below, without restriction of generality, as the "light source substrate."

[0016] In particular, both end caps are designed for mechanically securing the lamp in a socket, e.g., a conventional socket. At least one of the end caps also serves to electrically contact the lamp, e.g., for feeding in an electrical supply signal. Such an end cap may, for example, have two metal pins on its front end that are connected to a driver. In particular, if the end cap is designed for both mechanical and electrical connection, it may be referred to as a "base."

[0017] The end caps in particular have contact mating areas which are intended to contact the contact areas of the piston.

[0018] In a further development, the contact areas of the piston and the contact mating areas of the end caps are circumferential areas to achieve a particularly secure seal for the piston. The contact mating areas of the end caps can be placed circumferentially on a respective contact area of ​​the piston to close the piston.

[0019] A contact area of ​​the piston is understood, in particular, to be an area or surface intended to contact the mating contact area of ​​the end cap. The maximum contact areas and mating contact areas intended for contact may, in particular, be larger than the actual contact area or mating contact area where the piston actually comes into contact with the end cap (directly or indirectly via the adhesive).

[0020] The fact that the contact areas of the piston are surfaces that taper towards the respective end may in particular include the fact that they have a smaller radial distance to the longitudinal axis in each circumferential direction with decreasing longitudinal distance to a next end of the piston (e.g. towards its end face).

[0021] A constant-volume adhesive may be understood in particular as an adhesive, for example an adhesive, that does not significantly change its volume after application, in particular does not foam. The adhesive may be an organic adhesive, in particular an adhesive. The adhesive may be epoxy resin or silicone.

[0022] In one embodiment, the piston has continuously tapered end regions which provide the respective contact region of the piston. In other words, the end regions can be designed as continuously tapered contact regions. This enables a particularly compact and material-saving design. A continuously tapered end region may in particular be understood to mean a terminal region or section of the piston which tapers from a certain distance from its nearest end face until it reaches the end face and, for example, after a taper has no non-tapered sections arranged closer to the end face, e.g. no partial sections with a constant profile and / or no widenings.

[0023] Another embodiment provides for the contact areas of the piston to have a truncated cone-shaped outer contour. This is particularly easy to implement and offers high manufacturing tolerance. The conical outer contour has a rectilinear shape in a longitudinal section. In particular, the wall thickness of the piston is at least substantially constant in the end region or contact area.

[0024] An alternative development is for the end areas, and thus also the contact areas, of the piston to have a curved outer contour in longitudinal section. This expands the contact design options, for example, with regard to adapting to a desired contact force profile.

[0025] In a further embodiment, an inclination or angle of inclination α of a contact area of ​​the piston relative to a longitudinal axis of the piston is at least 2° and a maximum of 10°, in particular in a range between 3° and 6°, in particular in a range between 4° and 6°. These inclination areas are so shallow that they advantageously enable a long bonding area and contact area as well as a long attachment path of the end cap(s), and are so large that they allow for a high manufacturing tolerance.

[0026] Another embodiment is for the end cap to have a base body with a front wall and a circumferential side wall attached to it on the piston side, wherein at least a portion of the side wall, in particular an inner surface thereof, represents a contact counter area that can be placed onto a respective contact area of ​​the piston. Thus, the end cap can be placed, in particular slidably, onto the tapered contact area of ​​the piston with its inner side, which provides a contact counter area.

[0027] In a further development, the circumferential side wall of the end cap or its inner surface may be shaped like a hollow cylinder, with the end wall covering one end surface of the side wall facing away from the piston. The other end surface of the side wall is open. The end cap may therefore be in the form of a hollow cylinder open on one side.

[0028] To enable a particularly large contact area between the end cap and the piston, and thus a particularly strong and tight bond, it is advantageous to have the contact area of ​​the end cap widened toward the piston. This also allows for particularly favorable centering of the end cap and distribution of the adhesive. The inclination direction of the contact area of ​​the piston and the inclination direction of the contact area of ​​the end cap are thus identical.

[0029] The contact area of ​​the end cap may, in particular, have a basic shape that is at least similar to the contact area of ​​the piston. A further development is that the side wall of the end cap has a frustoconical basic shape, at least in sections.

[0030] In yet another embodiment, the angle of inclination of the contact area of ​​the end cap, in particular relative to a longitudinal axis, is in a range between 2° and 10°, in particular in a range between 3° and 7°, in particular in a range between 5° and 7°. This allows for particularly good handling and a particularly secure and tight fit of the end cap on the piston.

[0031] Another design feature is that the angle of inclination of the contact area is greater or smaller than the angle of inclination of the contact surface of the piston. By varying the opening or inclination angle between the piston and the end cap, the flow direction of the adhesive can be influenced and thus the longitudinal end at which excess adhesive escapes can be determined. A difference in the angle of inclination between 1° and 2° is particularly advantageous for this purpose.

[0032] Another embodiment is for the base body of the end cap to be made of plastic. For an end cap serving only as a mechanical mount, it may be made entirely of plastic. For mechanical and electrical contact, the end cap may additionally have at least one electrically conductive element (e.g., at least one contact pin), which can serve, in particular, as an electrical connection element between a socket and a driver.

[0033] The driver may comprise one or more electrical and / or electronic components. The driver may, in particular, be driver electronics. The driver components may be arranged entirely or partially on a separate printed circuit board (hereinafter referred to, without limitation of generality, as the "driver board"). The driver components may be arranged entirely or partially on the light source substrate. The driver components may, in particular, be arranged partly on the separate driver board and partly on the light source substrate. If a driver board is present, it may, in particular, be arranged in or on an end cap.

[0034] It is also possible for the bulb to be a glass bulb. A glass bulb is, among other things, particularly mechanically, chemically, and thermally resistant. The present invention is particularly effective for a combination of a glass bulb with an end cap (or its base body) made of plastic, since plastic exhibits a noticeably higher thermal expansion than glass.

[0035] A further development is that the piston is made of plastic. This type of piston is particularly lightweight and inexpensive to manufacture.

[0036] Another design feature is that the end caps or their contact surfaces only touch the contact areas of the piston via the adhesive, meaning the end caps do not directly or immediately contact the piston. This ensures a particularly reliable seal for the adhesive connection. This design can be implemented, for example, by applying a predetermined maximum force when applying the end cap.

[0037] However, it is also possible for the end caps to at least partially directly contact the contact areas of the piston, e.g., an inner edge of the end cap rests on a contact area of ​​the piston. This design can be implemented, for example, by sliding an end cap all the way to the stop at a comparatively high maximum force.

[0038] It is also an embodiment that a gap width or gap height of an adhesive gap filled by the adhesive between the contact area of ​​the piston and the end cap, in particular its contact counter area, lies in a range between 0.2 mm and 1 mm.

[0039] Another embodiment is for the semiconductor lamp to be a retrofit lamp. In particular, it may have the form factor of a fluorescent lamp, e.g., a T5 or T8 type, or a linear lamp. At least one end cap of the retrofit lamp may be shaped similarly to a G5 or G13 type base.

[0040] The object is achieved by a method for producing a semiconductor lamp, the method comprising at least the following steps: (a) providing a light-transmitting bulb with a tubular basic shape, the circumferential contact regions of which taper towards the respective end; (b) providing end caps; (c) applying a volume-constant adhesive to the contact regions of the bulb and / or to contact mating regions of the end caps; and (d) placing the end caps on the contact regions such that they press onto the adhesive.

[0041] The process can be designed analogously to the lamp described above and has the same advantages.

[0042] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in conjunction with the following schematic description of an exemplary embodiment, which is explained in more detail in conjunction with the drawings. For clarity, identical or equivalent elements may be provided with identical reference numerals. Fig. 1 shows a sectional side view of a section at an end region of a semiconductor lamp according to a first embodiment; Fig. 2 shows a further enlarged section of the end region of the semiconductor lamp according to the first embodiment; and Fig. 3 shows an enlarged section of an end region of a semiconductor lamp according to a first embodiment analogous to Fig. 2.

[0043] Fig. Figure 1 shows a semiconductor lamp in the form of a fluorescent tube retrofit lamp 1, e.g., for replacing conventional fluorescent lamps of the T5 or T8 type. The retrofit lamp 1 has a translucent bulb 2 with a tubular basic shape, which is made of, for example, plastic or glass. A light source substrate in the form of a strip-shaped circuit board 3 is housed in the bulb 2, which is equipped with several semiconductor light sources in the form of LED chips 4.

[0044] The piston 2 has as its end regions a circumferential contact area 5, which is coated with an adhesive 6, as described in more detail in Fig. 2 shown. In Fig. 2, the light source substrate 3 and the LED chips 4 are not shown. A cylindrical end cap 7, open toward the bulb 2, is placed on a respective contact area 5. The end cap 7 has a base body 15, which consists of at least one end wall 7a with a circular cylindrical basic shape and a circumferential side wall 7b with a hollow cylindrical basic shape attached to the bulb side.

[0045] The contact area 5 has a frustoconical shape, in particular an outer contour, which continuously tapers towards an end or end face 9 and is a continuation of a cylindrical central area 8 of the piston 2. An angle of inclination α1 against a longitudinal axis A is between 5° and 7°, in particular 6° to 7°.

[0046] A layer of constant-volume adhesive 6 in the form of silicone or epoxy resin is applied to the outside or outer contour of contact area 5. End caps 7 are placed on piston 2 in such a way that their free edge area presses against adhesive 6, thus forming a material-to-material contact. The free edge area, serving as the counter contact area and contact surface 11 of end cap 7, and the associated opposite contact surface 12 of contact area 5 are separated from each other by an adhesive gap 13 filled with adhesive 6, having a gap width or gap height H between 0.2 mm and 1 mm. The inclination of contact area 5 also makes it easy to ensure that adhesive 6 is compressed all the way around the longitudinal axis A, particularly in the area of ​​contact surfaces 11 and 12, as indicated by a front bead 14 of adhesive 6.Thus, the adhesive 6 can securely seal the piston 2 and the end cap 7 with a high tolerance to positioning inaccuracies, e.g., inclination errors, of the piston 2 and the end cap 7. An inner side of the contact surface 11 may be chamfered (not shown), e.g., with the inclination angle α1.

[0047] An inner diameter dI of the end cap 7 is, in particular, smaller than a widest edge of the contact area 5, which here corresponds to the outer diameter dK of the central area 8 of the piston 2 (corresponding to dK > dI). This ensures that the end cap 7 cannot be pushed beyond the contact area 5 onto the central area 8. Furthermore, an outer diameter dS of the piston 2 at the end face 9 is smaller than the inner diameter dI of the end cap 7 (corresponding to dI > dS).

[0048] The base body 15, 7a, 7b of the end cap 7 is made of plastic, in which the electrical and / or electronic components 105 of the driver circuit are housed on a common driver board 16. The components 105 are connected to the light source substrate 3 via electrical lines 17 (not shown). Fig. 2). The components 105 are also connected via electrical lines 18 to electrically conductive contact pins 19 guided through the base body 15. The end caps 7 can thus be designed, in particular, as bi-pin sockets, e.g., of the G5 or G13 type. Electrical supply signals can be fed in via the contact pins 19, which are converted by the components 105 or the driver circuit into operating signals for operating the LED chips 4.

[0049] Fig. 3 shows in a Fig.2 shows a semiconductor lamp in the form of a fluorescent tube retrofit lamp 21, which can also be used, for example, to replace conventional fluorescent lamps of the T5 or T8 type. In contrast to the retrofit lamp 1, the retrofit lamp 21 has an end cap 22 whose circumferential side wall 23 is widened in the direction of the bulb 2, specifically in a truncated cone shape with an angle of inclination α2 relative to a longitudinal axis A. The angle of inclination α2 of the side wall 23 here is 4° to 6°, in particular 4° to 5°, and is in particular 1° to 2° less than the angle of inclination α1 of the contact area 5.

[0050] At least a portion of an inner surface of the side wall 23 is formed as a contact mating area 24 that can be placed on the contact area 5 of the bulb 2. The contact mating area 24 of the end cap 22 corresponds at least approximately to the actual contact area 25. The generally usable contact mating area 24 is thus practically completely used as the contact area 25. The actual contact area 11 of the contact area 5 is considerably larger than in the retrofit lamp 1 and is consequently more sealed and secure.

[0051] Although the invention has been illustrated and described in detail by the embodiment shown, the invention is not limited thereto and other variations can be derived therefrom by a person skilled in the art without departing from the scope of the invention.

[0052] In general, “a”, “an”, etc. can be understood as a singular or a plural, in particular in the sense of “at least one” or “one or more”, etc., unless this is explicitly excluded, e.g. by the expression “exactly one”, etc.

[0053] A numerical value may also include the exact number stated as well as a usual tolerance range, as long as this is not explicitly excluded. Reference symbol 1 fluorescent tube retrofit lamp 2 pistons 3 circuit board 4 LED 5 Contact area 6 Adhesives 7 End cap 7a front wall 7b side wall 8 Central area 9 Frontal surface 11 Contact surface of the end cap 12 Contact surface 13 Adhesive gap 14 front bulge 15 basic bodies 16 Driver board 17 Electrical cable 18 Electrical cable 19 contact pin 21 fluorescent tube retrofit lamp 22 End cap 23 Side wall 24 Contact area 25 contact surface 101 LED retrofit lamp 102 pistons 103 circuit board 104 LED 105 Electronic component 106 End cap 107 Annular gap 108 Roll-up 109 Adhesives A Longitudinal axis dI inner diameter dK outer diameter of the central area dS outer diameter of the piston face H gap height Rh gap height α1 inclination angle α2 inclination angle

Claims

[1] Semiconductor lamp (1; 21), comprising - a translucent bulb (2) with a tubular basic shape, which has contact areas (5) at the end, - at least one substrate (3) accommodated in the bulb (2), on which at least one semiconductor light source (4) is arranged, - end caps (7; 22) for closing the end of the piston (2) and - constant volume adhesive (6) for the material connection of a respective pair of an end cap (7; 22) and a contact area (5), wherein - the contact areas (5) taper towards a respective end (9) of the piston (2), wherein the piston (2) has continuously tapered end areas which provide the contact areas (5), wherein - the end cap (22) has a base body (23, 7a) with an end wall (7a) and a circumferential side wall (23) attached thereto on the piston side, - at least a part of an inner surface of the side wall (23) is designed as a contact counter-region (24) which is placed on a respective contact region (5) of the piston (2), and - the contact counter region (24) of the end cap (7) is widened in the direction of the piston (2), wherein an angle of inclination (α2) of the contact counter region (24) and an angle of inclination (α1) of the contact region (5) of the piston (2) differ by 1° to 2°. [2] Semiconductor lamp (1; 21) according to claim 1, wherein the contact regions (5) have a frustoconical outer contour. [3] Semiconductor lamp (1; 21) according to one of the preceding claims, wherein an angle of inclination (α1) of the contact regions (5) of the bulb (2) against a longitudinal axis (A) of the bulb (2) is in a range between 2° and 10°, in particular in a range between 3° and 6°, in particular in a range between 4° and 6°. [4] Semiconductor lamp (21) according to claim 1, wherein an angle of inclination (α2) of the contact counter-region (24) of the end cap (22) against a longitudinal axis (A) is in a range between 2° and 10°, in particular in a range between 3° and 7°, in particular in a range between 5° and 7°. [5] Semiconductor lamp (1; 21) according to one of claims 1 to 4, wherein the base body (15; 22, 7a) consists of plastic. [6] Semiconductor lamp (1; 21) according to one of the preceding claims, wherein the volume-constant adhesive (6) comprises or is silicone or epoxy resin. [7] Semiconductor lamp (1; 21) according to one of the preceding claims, wherein the bulb (2) is a glass bulb. [8] Semiconductor lamp (1; 21) according to one of the preceding claims, wherein the end caps (7; 22) contact the contact areas (5) of the bulb (2) only via the adhesive (6). [9] Semiconductor lamp (1; 21) according to claim 8, wherein a gap height (H) of an adhesive gap (13) filled by the adhesive (6) between the contact region (5) and the end cap (7; 22) is between 0.2 mm and 1 mm. [10] Semiconductor lamp (1; 21) according to one of the preceding claims, wherein the semiconductor lamp (1) is a retrofit lamp. [11] Method for producing a semiconductor lamp (1; 21), the method comprising at least the following steps: - Providing a translucent bulb (2) with a tubular basic shape, the circumferential contact areas (5) of which taper towards the respective end (9); - Providing end caps (7; 22); - applying a volume-constant adhesive (6) to the contact areas (5) and / or to contact mating areas (11; 24) of the end caps (7; 22); and - placing the end caps (7; 22) on the contact areas (5) so that they press on the adhesive (6), wherein the piston (2) has continuously tapered end areas which provide the contact areas (5), wherein - the end cap (22) has a base body (23, 7a) with an end wall (7a) and a circumferential side wall (23) attached thereto on the piston side, - at least a part of an inner surface of the side wall (23) is designed as a contact counter-region (24) which is placed on a respective contact region (5) of the piston (2) and - the contact counter region (24) of the end cap (7) is widened in the direction of the piston (2), wherein an angle of inclination (α2) of the contact counter region (24) and an angle of inclination (α1) of the contact region (5) of the piston (2) differ by 1° to 2°.

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