Expansion tank for a motor vehicle fluid circuit

Abstract

The invention relates to an expansion tank (1) for a fluid circuit of a motor vehicle, comprising a tank wall (2) enclosing an interior (3) of the expansion tank (1) and a filling opening (4) provided in the tank wall (2) and closable with a lid (5) for filling the expansion tank (1) with a fluid, wherein the filling opening (4) is located on a filling nozzle (6) extending from a base body (7) of the expansion tank (1).The provision includes a filling nozzle (6) having a longitudinal center axis and circumferentially encompassing a screw collar (8) with respect to the longitudinal center axis, the screw collar having a thread (9) on its side facing the filling nozzle (6) in a radial direction with respect to the longitudinal center axis for interaction with a mating thread (19) of the cover (5), wherein a locking pin (14) is displaceably mounted on a side of the screw collar (8) facing away from the filling nozzle (6) in a radial direction with respect to the longitudinal center axis, the locking pin being arranged at a distance from the cover (5) in a release position and engaging the cover (5) in a form-fitting manner in a locking position other than the release position and securing it circumferentially.

Description

[0001] The invention relates to an expansion tank for a fluid circuit of a motor vehicle, comprising a tank wall enclosing an interior of the expansion tank and a filling opening formed in the tank wall and closable with a lid for filling the expansion tank with a fluid, wherein the filling opening is located on a filling nozzle extending from a base body of the expansion tank.

[0002] For example, German patent application DE 102 46 590 A1 is known from the prior art. This document describes a container with an opening, a lid for closing the opening, and at least one locking device for preventing the lid from opening in the event of overpressure inside the container. The locking device is designed to lock the lid by means of a positive fit. For this purpose, the locking device has at least one slidably mounted locking pin located on the container, which can be inserted into a recess in the lid.

[0003] The locking pin can be moved into a locked position by means of a piston / cylinder unit and into a released position by means of spring force, with the actuation of the clamping device being controlled by the pressure present inside the container. Specifically, it is provided that the lid can be screwed, in particular screwed, onto a nozzle having an opening, and has a closing element that projects into the nozzle when screwed on, the recess being provided on the circumference of the closing element or extending in the direction of the longitudinal extent of the nozzle.

[0004] Furthermore, German patent DE 101 64 669 A1 discloses a screw-on locking device for a cap that can be mounted on a stationary nozzle of a container, in particular a motor vehicle radiator. The cap has an outer part with a handle and a locking element that can be connected to a counter-locking element of the nozzle, and an inner part with a valve arrangement, preferably configured as a positive / negative pressure combination. An anti-rotation device acts between the outer part of the cap and the nozzle. The anti-rotation device is actuated by a drive unit controlled by the operating data in the container or by a motor. This drive unit is housed in a casing located inside or outside the container near the outer part of the cap.

[0005] Publication JP S62 - 159 721 A concerns a cap for a motor vehicle radiator, designed for the removable closure of a fluid filler opening located at the top of a radiator. To prevent scalding from splashes of hot coolant, a locking mechanism is proposed that engages at high temperatures within the cap.

[0006] Further documents known from the state of the art include US 3 587 912 A, US 2005 / 0 211 709 A1 and WO 2005 / 073 532 A1.

[0007] The object of the invention is to propose an expansion tank for a fluid circuit of a motor vehicle which has advantages over known expansion tanks, in particular enabling particularly safe handling by a user of the motor vehicle.

[0008] This is achieved according to the invention with a reservoir for a fluid circuit of a motor vehicle with the features of claim 1. It is provided that the filling nozzle has a longitudinal center axis and is circumferentially encompassed with respect to the longitudinal center axis by a screw collar, which has a thread on its side facing the filling nozzle in the radial direction with respect to the longitudinal center axis for interaction with a mating thread of the lid, wherein a locking pin is displaceably mounted on a side of the screw collar facing away from the filling nozzle in the radial direction with respect to the longitudinal center axis, which is arranged at a distance from the lid in a release position and engages the lid in a form-fitting manner in a locking position other than the release position and secures it in the circumferential direction.

[0009] Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims. It should be noted that the exemplary embodiments described in the description are not limiting; rather, any variations of the features disclosed in the description, the claims, and the figures are possible.

[0010] The expansion tank is preferably part of the vehicle's fluid circuit, but can of course also be separate from it, particularly until the expansion tank is installed in or on the fluid circuit and / or the vehicle. The fluid circuit is, for example, a coolant circuit in which the fluid, in the form of a coolant, is circulated at least temporarily to regulate the temperature of a device requiring temperature control. In addition to the expansion tank, the coolant circuit therefore includes at least the device requiring temperature control, but preferably also a coolant radiator and a coolant pump. The coolant radiator serves to cool the coolant, and the coolant pump serves to circulate the coolant. For example, the coolant is supplied by the coolant pump to the device requiring temperature control, where the coolant absorbs heat.The coolant is then routed to the radiator, where it releases the absorbed heat, primarily to the cooling medium. Ambient air is preferably used as the cooling medium; the radiator is, for example, the main radiator of a motor vehicle.

[0011] The expansion tank has an interior space in which the fluid, for example, the fluid used to operate the fluid circuit, is stored, at least temporarily. This interior space is enclosed by the tank wall, which has at least one opening through which, for example, fluid connections of the expansion tank are fluidically connected to the interior space. In particular, one of the fluid connections is an inlet connection and another is an outlet connection, through which further sections of the fluid circuit are fluidically connected to the expansion tank or its interior space. Preferably, an opening connected to the inlet connection is geodetically positioned above an opening connected to the outlet connection. This ensures reliable fluid extraction from the expansion tank.

[0012] Furthermore, the container wall features a filler opening, closable with a lid, through which fluid can be introduced into the interior of the expansion tank. This filler opening serves to fill the expansion tank and / or the fluid circuit with fluid. For filling, the lid is positioned to open the filler opening, specifically at a distance from it, and the fluid is introduced into the expansion tank through the filler opening. After filling, the expansion tank is closed by placing the lid over the filler opening. Specifically, the lid is placed on the expansion tank and screwed to it, ensuring a complete and fluid-tight seal.

[0013] To attach the cap to the base of the expansion tank, the filler neck is enclosed by the screw collar. The screw collar features a threaded section that engages with the cap's mating thread to secure the cap. In other words, the cap's mating thread is screwed onto the thread of the screw collar. By screwing the cap onto the screw collar, it creates a tight seal around the filler neck or opening. Specifically, once screwed onto the screw collar, the cap forms a fluid-tight seal around the filler neck, completely and continuously in the circumferential direction with respect to the filler neck's longitudinal axis, and fully overlaps the filling opening.

[0014] The thread is machined into the screw collar on the side facing the filler neck. Both the filler neck and the screw collar have a rib-like design, thus projecting beyond the base of the expansion tank. A ring-shaped recess is formed between them, into which the cap engages with its mating thread. This ensures that when the filler opening is opened, i.e., when the cap is removed from the filler neck, any fluid that might escape through the filler opening cannot escape radially outwards, but is instead directed by the cap into the ring-shaped recess. This creates a type of labyrinth seal, significantly improving the safety when operating the expansion tank.

[0015] The expansion tank is also equipped with a locking device that only allows the lid to be removed from the filler neck temporarily, and conversely, prevents it from being removed temporarily. For this purpose, the locking pin is mounted so that it can be moved relative to the base of the expansion tank. The locking pin can be arranged in different positions, namely at least in the release position and in the locking position. In the release position, the locking pin is positioned at a distance from the lid, allowing the lid to be moved, in particular rotated around its longitudinal center axis. Accordingly, when the locking pin is in the release position, the lid can be unscrewed from the screw collar without hindrance to open the filler neck.

[0016] If, however, the locking pin is in the locked position, it engages positively with the lid, thus securing the lid circumferentially with respect to its longitudinal center axis. Ultimately, when in the locked position, the locking pin prevents the lid from being unscrewed from the screw collar to release the filling opening. Preferably, the position of the locking pin is selected based on the internal pressure of the expansion tank, such that, for example, the locking pin is in the release position when the internal pressure is less than a pressure threshold and in the locked position when the internal pressure is greater than or equal to the pressure threshold. Additionally or alternatively, the position of the locking pin is selected based on the fluid temperature of the fluid in the expansion tank.

[0017] To ensure reliable operation of the lid at all times, the locking pin is located on the side of the screw collar facing away from the filling port in a radial direction. This also means that the locking pin is situated on the side of the screw collar facing away from the thread. This arrangement reliably prevents the locking pin from shifting due to deformation of the lid when screwing the screw onto the mating thread. Furthermore, it ensures that the locking pin does not come into contact with the fluid, or at least not to an excessive extent.

[0018] In particular, the mating thread is located on a threaded projection of the lid. In addition to this threaded projection, the lid has a sealing projection that extends radially from the threaded projection, spaced along the longitudinal center axis, thus creating an annular recess between the threaded projection and the sealing projection. The mating thread is formed on the outside of the threaded projection, i.e., on the side of the threaded projection facing away from the sealing projection.

[0019] The sealing projection is adapted to the filling opening or filling nozzle in terms of its shape and dimensions. When the cover is arranged as intended to close the filling opening, the sealing projection preferably engages through the filling opening into the filling nozzle and rests with an outer circumferential surface facing the threaded projection against an inner circumferential surface of the filling nozzle that radially defines the filling opening and / or rests against an edge of the filling nozzle that defines the filling opening.

[0020] A further projection is formed on the lid, spaced apart from the threaded projection. An annular gap for receiving the screw collar is provided between the threaded projection and this further projection. When the lid is correctly positioned to close the filling opening and the locking pin is in its locked position, the locking pin engages this further projection, i.e., radially spaced from the threaded projection. This ensures reliable locking and unlocking of the lid by means of the locking pin at all times.

[0021] A further development of the invention provides that the locking pin is arranged in an annular recess, which is positioned radially with respect to the longitudinal center axis between the screw collar and a support collar, wherein the support collar surrounds the screw collar circumferentially with respect to the longitudinal center axis. In addition to the filling nozzle and the screw collar, the support collar thus extends from the base body of the expansion tank. This support collar surrounds the screw collar circumferentially with respect to the longitudinal center axis, at least partially, but in particular completely and continuously. It is arranged radially spaced from the screw collar, so that the annular recess is formed between the screw collar and the support collar.

[0022] Accordingly, the expansion tank, or rather its base, features several annular recesses: a first annular recess in the radial direction between the filling port and the screw collar, and a second annular recess in the radial direction between the screw collar and the support collar. When a cap is fitted to close the filling port, the annular recesses are preferably fluidically separated from one another, particularly by the interaction of the thread with the mating thread. The radial placement of the locking pin between the screw collar and the support collar provides further protection for the locking pin, especially against external influences. Overall, this ensures extremely reliable operation of the expansion tank by the user.

[0023] A further development of the invention provides that the cover 2 has two annular ribs, of which, when the cover is arranged as intended, a first rib is located adjacent to the screw collar when viewed radially with respect to the longitudinal center axis, and a second rib is in overlap with the support collar, wherein a locking device of the cover, which interacts positively with the locking pin in its locking position, is arranged radially with respect to the longitudinal center axis between the annular ribs. The annular ribs are distinct from the threaded projection and the sealing projection; in particular, they are arranged further outwards on the cover in the radial direction than these.

[0024] For example, the two ring ribs extend from the aforementioned projection of the lid. When the lid is positioned to close the filling opening, the first ring rib is located adjacent to the screw collar, specifically on its side facing away from the thread. Preferably, the first ring rib rests radially against the outside of the screw collar. The second support collar, on the other hand, overlaps the first support collar radially, so that in the axial direction, at most a small gap remains between them when the lid closes the filling opening. This ensures reliable protection of the locking pin from environmental influences.

[0025] A further development of the invention provides that the locking pin is movably mounted in an insert part which is inserted into a recess in the base body. The insert part is understood to be a component of the expansion tank that is manufactured separately from the base body. The recess is present in the base body or is manufactured there. During assembly of the expansion tank, the insert part is inserted into the recess, particularly from the interior of the expansion tank.

[0026] The use of the insert allows for particularly flexible manufacturing of the expansion tank. For example, it may be possible to equip a first expansion tank with the insert during manufacturing, i.e., to insert it into the recess of the base body. For a second expansion tank, however, the recess may be closed with a different type of closure. The second expansion tank, therefore, does not have the locking pin. Accordingly, a modular system for the expansion tank is implemented, in which at least one expansion tank is equipped with the insert, while at least one second expansion tank is not. In any case, the aforementioned advantages are reliably achieved.

[0027] A further development of the invention provides that the insert part has a guide projection designed and configured for the movable mounting of the locking pin, which extends through the recess of the base body and penetrates the annular recess in the axial direction with respect to the longitudinal center axis to at least 50%, at least 75%, or at least 90%. The guide projection serves to mount the locking pin; in this respect, the locking pin is received in the guide projection.

[0028] The locking pin, at least when in its locked position, projects beyond the guide projection on the inside to engage positively with the cover. The guide projection extends axially through a significant portion of the annular recess, in particular at least 50%, at least 75%, or at least 90%. This ensures that fluid present in the annular recess does not enter the insert along the locking pin and impair its function. Consequently, particularly reliable operation of the expansion tank is achieved.

[0029] A further development of the invention provides that a guide chamber is formed in the insert part, in which a piston, connected to the locking pin via a drive mechanism, is arranged to be displaceable in the axial direction with respect to the longitudinal center axis. The guide chamber serves to guide the piston in the axial direction. The guide chamber can also be referred to as a cylinder, or is contained within one; in particular, the guide chamber is cylindrical, preferably circular.

[0030] The guide chamber is bounded radially outwards by a wall, which can also be referred to as the cylinder wall. The cylinder wall rests tightly against the piston in the circumferential direction, or vice versa, so that the piston divides the guide chamber into two sub-chambers. Preferably, one sub-chamber is penetrated by the locking pin. For example, the locking pin is integrally formed with the piston and made of the same material. Preferably, the locking pin is arranged symmetrically with respect to the piston; in particular, it merges into the piston at its center.

[0031] The guide chamber is bounded axially by walls that form end stops for the piston. In a first position, for example the release position, the piston rests against one of the walls, and in the locking position against a second wall. This design of the reservoir ensures sufficient guidance of the piston and thus of the locking pin.

[0032] A further development of the invention provides that the guide chamber is fluidically connected on one side to the interior of the expansion tank and on the other side to the external environment of the expansion tank. As already explained, the piston divides the guide chamber into two sub-chambers. One of the sub-chambers is fluidically connected to the interior, and the second sub-chamber to the external environment. Accordingly, a pressure difference between the pressure present in the interior and the pressure present in the external environment exerts an actuating force on the piston. Depending on the actuating force, the piston, and thus also the locking pin, is displaced.

[0033] The fluid-dynamic connection of the guide chamber or sub-chambers to the interior and the external environment is designed such that, in the event of overpressure in the interior relative to the external environment, the locking pin is forced towards its locked position. This ensures that opening the expansion tank by removing the cap from the filler neck is reliably prevented if the pressure in the expansion tank becomes too high. Thus, the escape of gaseous fluid, which may also carry liquid fluid with it, to the external environment is reliably prevented. This ensures a high level of operational safety for the user.

[0034] A further development of the invention provides that the insert protrudes into the interior of the expansion tank, wherein the guide chamber is closed by a bottom wall attached to the insert and is fluidically connected to the interior via a pressure equalization opening formed in the bottom wall. The insert and the bottom wall are manufactured separately. After being arranged on the insert, the bottom wall at least partially closes the guide chamber; at the very least, it forms one of the walls that limit the axial movement of the piston.

[0035] The pressure equalization opening is located in the bottom wall, through which the guide chamber is fluidically connected to the interior. Preferably, when manufacturing the expansion tank, the piston, together with the locking pin, is first inserted into the guide chamber, and then the guide chamber, with the piston located within it, is closed by attaching the bottom wall to the insert. This results in simple and cost-effective manufacturing.

[0036] A further development of the invention provides that the locking pin is subjected to a spring force by means of a spring element, which pushes the locking pin towards the release position, or that the locking pin is pushed towards the release position solely by a weight force acting upon it. The compensating reservoir can be configured in two variants in this respect. According to a first variant, the spring element is present, which exerts the spring force on the locking pin. Preferably, the spring element is arranged together with the piston in the guide chamber. In particular, it is supported on one side by one of the walls of the guide chamber and on the other side by the piston. The spring force is directed such that it pushes the locking pin towards its release position.This ensures that the lid is always reliably released by the locking pin, provided that the pressure difference between the bridge in the interior and the external environment is sufficiently small.

[0037] In a second variant, the spring element is omitted. The displacement of the piston, and consequently the locking pin, occurs solely due to the actuating force generated by the pressure differential and the force of gravity acting on the locking pin and piston. This force of gravity results from the influence of gravity on the locking pin and piston when the reservoir is properly positioned. Specifically, the locking pin and piston are arranged on the reservoir or its base in such a way that the force of gravity pushes the locking pin towards the release position. The aforementioned advantages are achieved with this design as well.

[0038] A further development of the invention provides that a wall bounding the guide chamber and / or the piston and / or the locking pin are provided with a sliding coating. Such a design is particularly advantageous if the locking pin is to be forced into the release position solely by gravity. In this case, smooth movement of the locking pin and the piston relative to the insert is necessary. For this reason, the sliding coating is provided with which the guide chamber, the piston, and / or the locking pin are at least partially coated. In particular, a side surface of the piston bearing against a cylinder wall of the guide chamber is coated with the sliding coating. The sliding coating consists, for example, of polytetrafluoroethylene (PTFE).With this design of the expansion tank, the spring element can be dispensed with, thus ensuring reliable operation throughout its entire service life.

[0039] The features and combinations of features described in the description, in particular those described in the following figure description and / or shown in the figures, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention, in particular the scope of the claims. Thus, embodiments that are not explicitly shown or explained in the description and / or the figures, but which emerge from or can be derived from the explained embodiments, particularly within the scope of the claims, are also to be considered as encompassed by the invention.

[0040] The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing, without limiting the invention. The drawing shows: Fig. 1 a schematic representation of an expansion tank for a fluid circuit of a motor vehicle with a locking pin displaceably mounted in an insert part, as well as Fig. 2 a schematic sectional view of the expansion tank in the area of ​​the locking pin, with a lid of the expansion tank also shown.

[0041] The Fig. Figure 1 shows a schematic representation of an expansion tank 1 for a motor vehicle fluid circuit. The expansion tank 1 has a tank wall 2 that encloses an interior space 3. A filling opening 4 is provided in the tank wall 2, which can be closed by means of a cover 5 (not shown). The filling opening 4 is located on a filling nozzle 6, which projects beyond a base 7 of the expansion tank 1. The filling nozzle 6 is surrounded by a screw collar 8, which is provided with a thread 9, namely an internal thread, for screwing the cover 5 to the screw collar 8 to close the filling opening 4. The screw collar 8 is in turn surrounded by a support collar 10. For example, it is provided that the cover 5, when screwed to the expansion tank 1, rests against an end face of the support collar 10.

[0042] The expansion tank 1 has several annular recesses 11 and 12. The annular recess 11 is arranged radially between the filling nozzle 6 and the screw collar 8 with respect to a longitudinal center axis of the filling nozzle 6, and the annular recess 12 is arranged radially between the screw collar 8 and the support collar 10. Preferably, the dimensions of the annular recess 11 are larger in the radial direction than the dimensions of the annular recess 12. It can be seen that the thread 9 is produced on one side of the screw collar 8 facing the annular recess 11.

[0043] A locking arrangement 13 for temporarily locking the cover 5 is arranged in the annular recess 12. Specifically, a locking pin 14 of the locking arrangement 13 is located in the annular recess 12. The locking pin 14 is movably mounted in a guide projection 15 of an insert 16 of the locking arrangement 13. The guide projection 15 extends predominantly, for example to at least 50%, through the annular recess 12 in the axial direction with respect to the longitudinal center axis. A cylinder 17 adjoins the guide projection 15 and projects at least partially into the interior 3.

[0044] The Fig.Figure 2 shows a schematic sectional view of the expansion tank 1. It can be seen that the cover 5 has a threaded projection 18 with a mating thread 19. The mating thread 19 interacts with the thread 9 to hold the cover 5 on the screw collar 8, such that the cover 5 seals the filling opening 4 in a fluid-tight manner. Furthermore, the cover 5 has a sealing projection 20, which preferably, when the cover 5 is arranged as intended, interacts sealingly with the filling nozzle 6. Radially on the outside, the cover 5 has another projection 21, from which two annular webs 22 and 23 extend. Viewed radially, the annular web 22 rests against the screw collar 8 from the outside, whereas, viewed radially, the annular web 23 is arranged in overlap with the support collar 10.

[0045] In the insert 16, or cylinder 17, a guide chamber 24 is formed, which is divided into two sub-chambers by a piston 25, namely the sub-chambers located on the one hand and on the other hand of the piston 25. One of the sub-chambers is fluidically connected to the interior 3 of the pressure equalization reservoir 1 via a pressure equalization opening 26. Due to a pressure difference between the pressures present in the sub-chambers, an actuating force is exerted on the piston 25 and thus on the locking pin 14, which moves the locking pin 14 between different positions.

[0046] In an unlocked position (not shown here), the locking pin 14 is positioned at a distance from the cover 5, allowing the cover 5 to be rotated to unscrew it from the screw collar 8. In the locked position shown here, however, the locking pin 14 engages positively with the cover 5 to secure it circumferentially and thus prevent it from being unscrewed from the screw collar 8. This ensures a high level of safety for the user when using the expansion tank 1. REFERENCE MARK LIST: 1 expansion tank 2 Container wall 3 Interior 4 Filling opening 5 lids 6 filling ports 7 Basic shapes 8 screw collars 9 threads 10 support collars 11 ring recess 12 ring recess 13 Locking arrangement 14 Locking pin 15% lead 16 Insert part 17 cylinders 18 thread projection 19 counter threads 20 Density advantage 21 lead 22 Ring Bridge 23 Ring Bridge 24 Leadership Chamber 25 pistons 26 Pressure equalization opening

Claims

Expansion tank (1) for a fluid circuit of a motor vehicle, comprising a tank wall (2) enclosing an interior (3) of the expansion tank (1) and a filling opening (4) formed in the tank wall (2) and closable with a cover (5) for filling the expansion tank (1) with a fluid, wherein the filling opening (4) is located on a filling nozzle (6) extending from a base body (7) of the expansion tank (1), characterized in that the filling nozzle (6) has a longitudinal central axis and is circumferentially encompassed with respect to the longitudinal central axis by a screw collar (8) which has a thread (9) on its side facing the filling nozzle (6) in a radial direction with respect to the longitudinal central axis for interaction with a mating thread (19) of the cover (5),wherein a locking pin (14) is displaceably mounted on a side of the screw collar (8) facing away from the filling nozzle (6) in a radial direction with respect to the longitudinal center axis, which in a release position is arranged spaced apart from the cover (5) and in a locking position different from the release position engages the cover (5) in a form-fitting manner and secures it in the circumferential direction. Expansion tank according to claim 1, characterized in that the locking pin (14) is arranged in an annular recess (12) which is arranged in a radial direction with respect to the longitudinal center axis between the screw collar (8) and a support collar (10), wherein the support collar (10) surrounds the screw collar (8) in a circumferential direction with respect to the longitudinal center axis. Expansion tank according to one of the preceding claims, characterized in that the lid (5) has two annular webs (22, 23), of which, when the lid (5) is arranged as intended, a first annular web is arranged adjacent to the screw collar (8) when viewed in the radial direction with respect to the longitudinal center axis, and a second annular web is in overlap with the support collar (10), wherein a locking device of the lid (5) which interacts positively with the locking pin (14) in its locking position is arranged in the radial direction with respect to the longitudinal center axis between the annular webs (22, 23). Expansion tank according to one of the preceding claims, characterized in that the locking pin (14) is displaceably mounted in an insert part (16) inserted into a recess of the base body (7). Expansion tank according to claim 4, characterized in that the insert part (16) has a guide projection (15) provided and designed for the displaceable bearing of the locking pin (14), which extends through the recess of the base body (7) and extends through the annular recess (12) in axial direction with respect to the longitudinal center axis to at least 50%, at least 75% or at least 90%. Expansion tank according to claim 4 or 5, characterized in that a guide chamber (24) is provided in the insert part (16) in which a piston (25) connected to the locking pin (14) is arranged to be displaceable in the axial direction with respect to the longitudinal center axis. Expansion tank according to claim 6, characterized in that the guide chamber (24) is fluidically connected on the one hand to the interior (3) of the expansion tank (1) of the piston (25) and on the other hand to an external environment of the expansion tank (1). Expansion tank according to claim 7, characterized in that the insert part (16) projects into the interior (3) of the expansion tank (1), wherein the guide chamber (24) is closed with a bottom wall attached to the insert part (16) and is fluidically connected to the interior (3) via a pressure equalization opening (26) produced in the bottom wall. Expansion tank according to one of the preceding claims, characterized in that the locking pin (14) is subjected to a spring force by means of a spring element which pushes the locking pin (14) in the direction of the release position, or that the locking pin (14) is pushed in the direction of the release position exclusively by a weight force acting on it. Expansion tank according to one of claims 6 to 8, characterized in that a wall defining the guide chamber (24) and / or the piston (25) and / or the locking pin (14) are provided with a sliding coating.

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