Delivery device with bellows and cooling means

Abstract

Conveying device, in particular in the form of a compressor, consisting of at least one housing (10) and a partition element which is arranged movably in the housing (10) and separates two fluid regions (14, 16) in the housing (10) from each other, wherein the partition element is formed of a partition bellows (18) with individual bellows folds (20), wherein a mechanical actuation device for controlling a movement of the partition bellows (18) is provided, and wherein the heat generated by means of the actuation device via the movement of the partition bellows (18) can be at least partially removed from the housing (10) by means of a cooling device.

Description

[0001] The invention relates to a conveying device, in particular in the form of a compressor, having the features in the preamble of claim 1.

[0002] WO 2013 / 079222 A2 discloses a delivery device for improving energy efficiency in hydraulic systems, comprising an actuator that operates as a consumer of hydraulic energy in one operating state and as a generator of hydraulic energy in another operating state, and comprising a hydraulic accumulator that can be charged by the actuator to store energy in one operating state and discharged to deliver energy to the actuator in the other operating state. The hydraulic accumulator is a continuously adjustable hydropneumatic piston accumulator in which several pressure chambers are formed that border on different sized active surfaces on the fluid side of the accumulator piston. Furthermore, an actuating arrangement is provided that connects a selected pressure chamber or several selected pressure chambers of the piston accumulator to the actuator depending on the respective pressure levels prevailing on the gas side of the piston accumulator and at the actuator.

[0003] This makes it possible to transfer energy regardless of the pre-charge pressure on the gas side of the accumulator and regardless of the respective load pressure, because by selecting an appropriately sized effective area, the desired pressure level at the accumulator can be used for charging or discharging. This enables optimal energy conversion under all operating conditions. The familiar multi-piston arrangement for the piston accumulator requires seals such as metallic piston rings or rubber-elastic plastic seals to seal the individual piston chambers from one another. Due to the high forces and pressures that occur during operation, the additional use of lubricants is usually necessary to keep the frictional forces as low as possible, thus reducing wear and creating a seal that is as leak-free as possible.Nevertheless, leaks cannot be avoided and the friction causes wear on both the individual pistons and the associated sealing material. These wear particles, although usually small, nevertheless lead to contamination of the gases or liquids being conveyed, some of which may even be extremely pure. This in turn can only be removed by very complex filtering measures in the fluid flow. If heat is introduced through friction on the gas side of the conveying device with a predefined amount of trapped gas during operation of the conveying device, the excess heat can be dissipated from the housing of the conveying device via the amounts of liquid passing through on the fluid side, thus preventing additional damaging effects from unwanted heat input into the conveying device.

[0004] EP 3 578 820 A1 describes a conveying device, in particular in the form of a compressor, with the features in the preamble of claim 1, consisting of at least one housing and a separating element which is movably arranged in the housing and separates two fluid regions in the housing from one another, wherein the separating element is formed from a separating bellows with individual bellows folds, wherein a mechanical actuating device is provided for controlling a movement of the separating bellows, and wherein the heat generated by means of the actuating device via the movement of the separating bellows can be at least partially dissipated from the housing by means of a cooling device.

[0005] Further conveyor systems are described in CN 110 761 989 A, DE 10 2018 001 523 A1, US 2019 / 0383280 A1, WO 2015 / 078487 A1 and EP 3 078 856 A1.

[0006] WO 2013 / 079222 A2 discloses a piston accumulator.

[0007] Based on this prior art, the invention is based on the object of improving the known solution in such a way that a leak-free conveying device is created which also enables compressor operation with gases, such as hydrogen gas.

[0008] This object is achieved by a conveyor device having the features of patent claim 1 in its entirety.

[0009] According to the characterizing part of claim 1, the housing has parts of the cooling device on its outer circumference or these are an integral part of the housing, and the cooling device has a cooling chamber through which a cooling medium flows and which, in a concentric arrangement, at least partially encloses the housing on its outer circumference. The parts of the cooling device essentially consist of a fluid guide for the coolant or a receptacle for such a coolant on the circumference of the housing of the conveying device. Thus, the mentioned parts of the cooling device can consist of a cooling coil that is placed around the outer circumference of the housing and through which cold coolant originating from a central cooling supply is introduced at the inlet side for cooling, and the coolant heated by the operation of the conveying device can be discharged at the outlet side to the central cooling supply point.

[0010] The fact that the separating element is formed from a separating bellows with individual bellows folds, a mechanical actuating device is provided to control the movement of the separating bellows, and the heat generated by the actuating device via the movement of the separating bellows can be at least partially dissipated from the housing by means of a cooling device, ensures that no further leaks can occur. The separating bellows with its individual bellows folds creates a media-tight, and in particular gas-tight, separation between the two fluid areas in the housing, so that any particles that may enter cannot be accidentally exchanged between the fluid areas. The separating bellows can therefore be described as media-tight, meaning that the conveying device can also be used as a compressor for gases such as hydrogen gas.

[0011] If the separating or bellows is extended, the volume of one fluid area increases and the fluid to be pumped flows into one fluid area, whereas the volume of the other fluid area necessarily decreases at the same time. Conversely, when the separating bellows contracts, the volume of the other fluid area increases while one fluid area decreases and the pumped volume previously taken up in this one fluid area during the intake stroke is expelled from the pumping device in a single pumping stroke under the pressure of the contracting separating bellows. The separating bellows is preferably extended by the pumped volume flowing in on the inlet side of the housing at a predefined pressure from a fluid supply circuit to which the pumping device is connected in a fluid-carrying manner.

[0012] The contraction of the separating bellows, however, occurs under the influence of a mechanical actuating device which controls the separating bellows in such a way that the previously absorbed fluid volume in one fluid area is ejected under pressure from the housing into the fluidic supply circuit, whereby the supply of subsequent fluid in the direction of one fluid area is prevented.

[0013] However, it is also possible to couple the separating bellows to the mechanical actuating device in such a way that it exclusively or at least predominantly initiates both the extension and contraction movements of the separating bellows. Due to the mechanical actuating device, movement processes can be initiated on the separating bellows in rapid succession; this is unlike the prior art, in which more or less large quantities of liquid always have to control a piston drive for fluid delivery, which, with regard to the housing, always have to be introduced or removed first with the movable pistons. In this way, the conveying device according to the invention can be used for the transport of flowable fluids in associated supply circuits. In addition to pure liquids, the transport of gases or gas-liquid mixtures is also possible.

[0014] The use of hydrogen as an energy carrier has recently become increasingly important. To keep the volume of hydrogen to be pumped low, it may be advisable not only to pump the hydrogen in a connected supply circuit, but also to compress or densify it to higher pressure levels during a pumping step. This allows the volume to be pumped to be reduced and hydrogen to be made available at high pressure for the intended later use.

[0015] However, when hydrogen is compressed, as with other gases, there is a significant increase in temperature, which, on the one hand, counteracts the desired compression due to the resulting expansion of the gas. On the other hand, this unwanted heat input can impair the function of the mechanical components of the conveying system or even damage them, which may also include any remaining, necessary sealing systems.

[0016] In any case, the separating bellows, preferably made of stainless steel, serves as a reliable media separation device, preventing any particulate contamination, particularly from the mechanical actuation device, from accidentally reaching the gas side of the conveying device. Especially when hydrogen is used in fuel cell operation, no particulate contamination whatsoever must be present in the gas stream. Furthermore, the separating bellows in stainless steel design is suitable for effectively counteracting any embrittlement caused by the potentially very cold hydrogen gas. This has no equivalent in the state of the art.

[0017] In a preferred embodiment of the conveying device according to the invention, the actuating device comprises a drivable actuating rod that extends at least partially through the housing and can be brought into contact with a bellows base of the separating bellows to control movement of the separating bellows. The actuating rod of the actuating device can be actuated hydraulically, for example, using a hydraulic working cylinder or, if necessary, by engaging a suitable intermediate gear, by means of an electric motor operable in both directions. The actuating rod can be made solid and is capable of transmitting high actuating forces to the separating bellows to be moved.

[0018] In a further preferred embodiment of the conveying device according to the invention, the bellows base of the separating bellows, on its side opposite the actuating rod, is controllable by a fluid pressure which, penetrating into one fluid region, leads to an extension of the separating bellows and to the retraction of the actuating rod, which is held at least partially free of force in this respect. In this way, the separating bellows can be controlled for an extension or filling process by the pressure medium to be conveyed, whereas the actuating rod acting under pressure on the opposite side causes the bellows to contract in a volume-reducing manner for a delivery stroke, reducing the volume in one fluid region of the housing. These actuating processes take place in an alternating manner in time, whereby the separating bellows can be brought from the intake stroke to the delivery stroke and back again in rapid succession.In particular, when transporting a working gas such as hydrogen gas, high compression ratios can be achieved via the conveying device by means of the separating bellows, so that the conveying device can also operate as a compressor with conveying function.

[0019] In a further preferred embodiment of the conveying device according to the invention, it is provided that the fluid volume enclosed in the other fluid region remains the same or substantially the same when the separating bellows is pulled out by moving the actuating rod back out of this other fluid region, in order to avoid disruptions in operation when the bellows is pulled out. When the bellows is pulled out, a volume of air in the other fluid region is displaced, wherein the actuating rod moves back to the extent that the bellows is pulled out and partially extends out of the housing of the conveying device, so that additional free volume is created in the other fluid region into which the separating bellows can displace air, thus enabling unhindered operation despite the amount of air enclosed in the further fluid region of the conveying device.

[0020] In a further preferred embodiment of the conveyor device according to the invention, it is provided that a bellows receptacle is arranged within the housing in such a way that, when the bellows base rests against the bellows receptacle, the bellows folds are stacked, preferably lying one against the other, in a receiving space between the bellows receptacle and the housing. Since the separating bellows with its bellows folds is sensitive to buckling and buckling stresses, secure fold guidance is achieved via the receiving space and, in particular, it is ensured that when the separating bellows is contracted, the individual folds cannot buckle or bulge until they lie one against the other. Furthermore, a space-saving receptacle for the bellows folds in the housing of the conveyor device is achieved in this way.If the separating bellows with its bellows folds is completely stacked in the receiving space, the bellows base rests flat on the bellows receptacle at least on the inside and facing the bellows receptacle at least in a circular edge area, so that a secure, dent-resistant support is achieved in this respect, and the free, changing fluid volume for the one fluid area of ​​the conveying device is zero or almost zero at maximum conveying stroke.

[0021] If the separating bellows extends during a suction stroke, the bellows base can be supported on one of its free front sides on the free front end of the actuating rod, which ensures that the bellows folds cannot be accidentally overstretched, which could otherwise render the bellows unusable.

[0022] Preferably, at least one fluid line is arranged in the bellows receptacle, which opens into one of the fluid regions. The intake stroke for the fluid volume to be conveyed, as well as the discharge or delivery stroke for this volume from one of the fluid regions of the conveying device, takes place via the respective fluid line.

[0023] To monitor the position of the separating bellows, a proximity sensor, for example in the form of a proximity switch, is preferably provided in the bellows holder, which, when actuated, can control the extension movement of the actuating rod so that the separating bellows, controlled by fluid, again performs an extension movement.

[0024] Advantageously, the cooling chamber is defined by the housing and an additional housing part, which together with the housing forms a tradable unit. Alternatively, several individual cooling chambers can be arranged on the outer circumference of the housing of the conveying device, or the housing can be provided with cooling fins, which are preferably blown onto from the outside by a fan device for the purpose of dissipating heat from the housing. Furthermore, to implement a cooling device, it is also possible to install cooling channels directly in the housing of the conveying device, through which a coolant can flow from the coolant supply.

[0025] The conveyor device according to the invention is described in more detail below with the aid of drawings. These drawings are schematic and not to scale. Fig. 1 in the form of a longitudinal section along the line XX in Fig. 2 the essential components of the conveyor system; Fig. 2 a front view in the direction of arrow Y of the conveyor system after Fig. 1 ; and Fig. 3 the essential components of a cooling supply for cooling the conveyor device according to the Fig. 1 and 2 .

[0026] The Fig. 1 The conveying device shown has a pot-shaped housing 10 with a housing base 12. In the preferably hollow-cylindrical housing 10, a separating bellows 18 is arranged as a separating element that separates two fluid regions 14, 16 from each other in the housing 10. The separating bellows 18 has, in the usual way, a plurality of individual, connected bellows folds 20, which, according to the illustration according to the Fig. 1 driven on a block in succession one after the other. Such separating bellows systems are known in particular from bellows accumulators as a subgroup of hydraulic accumulators, as shown by way of example in DE 10 2009 060 852 A1. The last bellows fold 20 in the stacking sequence on a free end face is welded to a retaining ring 22 and the opposite other bellows fold 20 is welded to a bellows base 24 on the further, free end face. The bellows base 24 is designed as a flat end plate and has an annular groove 26 on the outer circumference for receiving a sealing and / or guide ring (not shown in detail), via which the bellows base 24 is guided so as to be longitudinally movable along the inner circumference 28 of the housing 10.

[0027] The bellows base 24 spans according to the illustration after the Fig. 1 a bellows receptacle 30, which is designed as a screw-in part and is screwed flush into the free end of the housing pot, which is open on one side. On the opposite side of the bellows base 24 and held at an axial distance, there is an actuating rod 32 as part of a mechanical actuating device. The actuating rod 32 can be moved back and forth over a predeterminable distance via an actuator device (not shown in detail), for example in the form of a hydraulic working cylinder. Furthermore, the actuating rod 32 extends concentrically to the longitudinal axis 34 of the housing 10 through the otherwise closed housing base 12. A further annular groove 36 is introduced into the housing base 12 for the purpose of receiving a guide and / or sealing device (not shown) in order to seal the interior of the housing 10, in the form of the further fluid region 16, from the environment in every travel position of the actuating rod 32.This further fluid region 16 is preferably filled with air; however, another filling gas, such as nitrogen gas, can also be introduced if necessary. Furthermore, parts 38 of a cooling device (designated as a whole by 40) are arranged on the outer circumference of the housing 10. Fig. 3 ), which will be discussed in more detail below.

[0028] As can be seen from the Fig. 1 As can be seen, the bellows receptacle 30 is penetrated by a channel-like fluid line 42, which opens with one free end into one fluid region 14 and is connected with its other free end via a corresponding connection point to a conventional fluid supply circuit 44, which should correspond to the usual state of the art. Two check valves 46, 48, preferably of the same design, are connected to the relevant circuit 44, which, if necessary, can also be held in their shown closed position by spring loading. The check valve 46 is assigned to a fluid inlet 50 and the check valve 48 to a fluid outlet 52. Both the inlet 50 and the outlet 52 are part of a T-shaped connecting piece that opens into the fluid line 42 in the bellows receptacle 30.

[0029] As the representation after the Fig. 2 shows, several, in the present case three, fluid lines 42 can be arranged in the bellows receptacle 30, so that both during the inflow and outflow of fluid via the one fluid region 14, the bellows base 24 is pressurized uniformly on its inside, for example during an inflow or outflow process. In this respect, too, the other two fluid lines 42 are to be connected to the supply circuit 44 via a corresponding line guide. In an embodiment not shown in detail, however, it is also possible to separate the inlet 50 with check valve 46, which opens in the direction of the one fluid region 14, from the outlet 52 via an independent fluid line 42 in the bellows receptacle 30, wherein the corresponding check valve 48 opens opposite to the check valve 46 as in the present case.In this way, one fluid region 14 is provided with a separate inlet and a separate outlet via independent fluid paths. The fluids in the . Fig. 3 The third fluid line 42 indicated can then be omitted accordingly. However, in each case, for space-saving accommodation, the respective fluid lines 42 are preferably grouped at the same distance around the longitudinal axis 34 of the housing 10, and furthermore, the individual fluid lines 42 occupy the same radial distance from one another ( Fig. 2 ).

[0030] If fluid under pressure is now introduced into one of the fluid areas 14 via the inlet 50 and the associated fluid line 42 shown with the check valve 46 open, the bellows base 24 is pressurized and performs a pulling movement in which the individual bellows folds 20 are pulled apart. In this respect, the bellows base 24 moves in the direction of the Fig. 1 viewed from right to left and, after a predeterminable travel path, comes into contact with the free end face of the actuating rod 32. The actuating rod 32 can then be locked and in this way form a stop for the bellows base 24; however, it is also possible for the actuating rod 32 to be carried to the left by the bellows base 24, whereby the actuating rod 32 is pushed out of the further fluid region 16 of the housing 10 with as little force as possible. However, it is also possible (not shown) for the actuating rod 32 to rest against the bellows base 24 from the outset and, together with it, to carry out the travel movement to the left during the extension movement of the separating bellows 18. During this suction stroke, the check valve 48 in the outlet 52 remains closed so that fluid that has already been pumped cannot inadvertently flow back from the supply circuit 44.

[0031] The bellows folds 20, which are susceptible to bending and denting, are, as shown, Fig. 1 received in an annular receiving space 54, which is delimited on the inside by an annular shoulder 56 of the bellows receptacle 30 and on the outside by the inner circumferential side 28 or inner wall of the housing 10. Since the bellows base 24 is also guided on the inner circumferential side 28 of the housing 10, there is no unwanted bulging or buckling of the bellows folds 20 when the bellows is extended, which folds are still guided in a stabilizing manner in the receiving space 54 in the area of ​​the retaining ring 22 on the base side even when the separating bellows 18 is fully extended. The retaining ring 22 is supported with one free end on the annular shoulder 56 in the bellows receptacle 30 and with its other free end on the outer circumference side on a projection 58 on the inner circumferential side 28 of the housing 10.In this way, the separating bellows 18 with its retaining ring 22 can be loosely placed on the shoulder 56 of the bellows receptacle 30 for assembly and, together with the latter, can be brought into position on the projection 58 of the housing 10 during a screwing-in process via the threaded section 60. Between the bearing of the retaining ring 22 and the threaded section 60, a further third annular groove 62 is provided for receiving a sealing ring (not shown in detail) for sealing one fluid region 14 from the surroundings of the housing 10.

[0032] To move the separating bellows 18 back into its Fig. 1 shown initial or basic position with a minimum fluid volume in one fluid area 14, the actuating rod 32 is in contact with the bellows base 24 and has moved it back to its shown initial position by force actuating it. During this force actuated movement of the bellows base 24 from left to right, the fluid volume previously stored in one fluid area 14 during the intake stroke is discharged via the outlet 52 and thus under pressure from the conveying device, with the check valve 46 closing and the check valve 48 open. If the conveying volume is a gas, such as hydrogen gas, it is compressed to a higher pressure level during the conveying stroke movement. For example, it is conceivable that, as part of a gradual pressure increase, three of the conveying devices after the Fig. 1 in sequential order, form a 3-stage overall compressor with which it is easily possible to raise hydrogen gas with an inlet pressure of 15 bar on the last compressor stage to a pressure level of 500 to 600 bar for further use.

[0033] In an embodiment not shown, it is also possible to firmly connect the actuating rod 32 directly to the bellows base 24 and to have both the suction stroke and the discharge stroke carried out by the actuating rod 32 as a component of the mechanical actuating device. Fig. 1 As further shown, a proximity sensor in the form of a proximity switch 64 is arranged centrally in the bellows receptacle 30, concentrically to the longitudinal axis 34 of the housing 10, which can monitor the position of the bellows base 24 and, associated therewith, the functional state of the separating bellows 18. This position monitoring is necessary so that the actuating rod 32 can be effectively controlled by a central control device (not shown in detail), in particular for carrying out the conveying stroke.The inner side of the bellows base 24 is supported in the outer circumferential edge region 66 on an associated projecting annular surface of the bellows receptacle 30, wherein within this annular support surface, a small trough-like depression 68 is introduced on the front side of the bellows receptacle 30, in which residual fluid remains, so that during the extraction movement of the separating bellows 18, no vacuum can arise between the associated wall parts of the bellows base 24 and the bellows receptacle 30, which could impair the extraction process.

[0034] The outer wall of the cylindrical housing has a circumferential wall recess 70, which is overlapped on the outer circumference by a thin-walled cylindrical housing part 72, which is a component of a housing pot, which is screwed to the housing base 12 at the bottom by means of a screw connection 74. Furthermore, the housing part 72 projects beyond the wall recess 70 on both sides, and in the area of ​​this projection, a further fourth recess 76 is provided in the wall of the housing 10, which serves to accommodate a ring seal (not shown) and which then seals off a cooling chamber 78 from the environment, which is delimited by the housing 10 and the housing part 72. This cooling chamber 78 is a component of a cooling unit designated as a whole by 40, as described in more detail in the Fig. 3 is shown.

[0035] Looking towards the Fig. 3 The conveyor system is designed according to Fig. 1 and2 Top right, only schematically shown with the housing 10 and the housing part 72 arranged above it, as well as the cooling chamber 78 located therebetween, which is connected to a cooling circuit 82 of the cooling device 40 via two fluid connection points 80. The cooling device 40 forms a type of semi-closed cooling circuit 82, for which purpose a storage tank 84 is closed off from the atmosphere except for a specially designed aeration and venting device. The presence of the storage tank 84 opens up the possibility of using a submersible pump 86 as the supply pump, the pump inlet of which is immersed below the fluid level 88 of the tank 84. The aeration and venting device mentioned is provided on a ventilation filter 90 and is formed by a valve (not shown in detail), which opens outwards at a predetermined internal tank pressure and inwards at a predetermined tank negative pressure.

[0036] The submersible pump 86 is driven by an electric motor 92, and the operating submersible pump 86 conveys a coolant in the direction of the arrows within the cooling circuit 82 via a feed line to the consumer, here in the form of the cooling chamber 78 for the conveying device. Conventional coolants can be used as the coolant; in this specific case, a water-glycol mixture is used. The compression heat generated by the conveying device, particularly as part of its compression properties, is introduced via the interior of the separating bellows 18 and the housing 10 into the cooling chamber 78 with the coolant. In the process, it is heated and returned to the tank 84 via a return line 94 and a heat exchanger 96 or 98.The heat exchanger can be a plate heat exchanger 96, in which the heat exchange with the coolant takes place through a liquid cooling medium, or a finned cooler 98, which is cooled by cooling air via a motor-driven fan 100. The cooling device 40 according to the . Fig. 3 is only an example and of course other suitable cooling devices can be used here, for example those with a completely closed or open cooling circuit.

[0037] It is also within the scope of the invention to replace the cooling chamber 78 shown with a cooling coil that is guided around the outer circumference of the housing 10 of the conveying device. In this respect, the connection points 80 then form the fluid inlet and outlet of the coil for the coolant supply. The cooling chamber 78, which runs like a jacket around the housing 10, can also be divided into subsegments, or cooling channels for supplying cooling can be incorporated into the housing 10 itself (not shown).

Claims

1. Conveying device, in particular in the form of a compressor, consisting of at least one housing (10) and a separating element which is movably arranged in the housing (10) and separates two fluid regions (14, 16) in the housing (10) from each other, wherein the separating element is formed of a separating bellows (18) with individual bellows folds (20), wherein a mechanical actuating device is provided for controlling a movement of the separating bellows (18), and wherein the heat generated by means of the actuating device via the movement of the separating bellows (18) can be at least partially dissipated from the housing (10) by means of a cooling device (40), characterised in that the housing (10) has parts of the cooling device (40) on the outer circumference or these are an integral part of the housing (10), and the cooling device (40) has a cooling chamber (78) through which a cooling medium flows and which at least partially encompasses the housing (10) on the outer circumference in a concentric arrangement.

2. Conveying device according to claim 1, characterised in that the actuating device comprises a drivable actuating rod (32) which at least partially passes through the housing (10) and can be brought into contact with a bellows base (24) of the separating bellows (18) for controlling a movement of the separating bellows (18).

3. Conveying device according to claim 2, characterised in that the bellows base (24) of the separating bellows (18) can be controlled on its side opposing the actuating rod (32) by a fluid pressure which, penetrating the one fluid region (14), results in the separating bellows (18) being expanded and in the actuating rod (32), which is kept at least partially free of forces in this respect, being moved back.

4. Conveying device according to either claim 2 or claim 3, characterised in that the fluid volume enclosed in the other fluid region (16) remains the same or substantially the same when the separating bellows (18) is expanded by moving the actuating rod (32) back out of this other fluid region (16).

5. Conveying device according to any of the preceding claims, characterised in that a bellows retainer (30) is arranged inside the housing (10) in such a manner that, with the bellows base (24) bearing on the bellows retainer (30), the bellows folds (20), preferably abutting against each other, are stacked in a receiving space (54) between the bellows retainer (30) and the housing (10).

6. Conveying device according to any of the preceding claims, characterised in that at least one fluid line (42) is arranged in the bellows retainer (30), which fluid line opens into the one fluid region (14).

7. Conveying device according to any of the preceding claims, characterised in that a proximity sensor, in particular a proximity switch (64), is arranged in the bellows retainer (30) for monitoring at least one position of the separating bellows (18).

8. Conveying device according to any of the preceding claims, characterised in that the cooling chamber (78) is bounded by the housing (10) and an additional housing part (72), which, together with the housing (10), constitutes a marketable structural unit.

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