Abstract:
A filter device for treating fluids, in particular for filtering fluids such as fuel, oil, or water, has a housing ( 56 ) with a housing pot ( 58 ), a housing cover ( 60 ), at least one inlet ( 88 ) for the fluid to be treated, and at least one outlet ( 82 ) for the treated fluid. A connecting head ( 12 ) has at least one feed ( 16 ) for the fluid to be treated and connectable to the at least one inlet ( 88 ), and/or at least one discharge ( 18 ). The connecting head ( 12 ) and the treatment element ( 14 ) can be connected to each other by means of a releasable bayonet-type connecting device ( 34 ) through the execution of a rotational/plug-in movement about a connecting axis ( 20 ) of the treatment device ( 10 ).

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a treatment device, in particular a filter device for treating fluids, in particular for filtering fluids, in particular liquid fluids, in particular fuel, oil, or water, in particular of an internal combustion engine, in particular of a motor vehicle, the treatment device comprising a treatment element which has a housing comprising a housing pot, a housing cover, at least one inlet for the fluid to be treated, and at least one outlet for the treated fluid, as well as a connecting head having at least one feed for the fluid to be treated, said feed being connectable to the at least one inlet, and/or at least one discharge for the treated fluid, said discharge being connectable to the at least one outlet, wherein the connecting head and the treatment element can be connected to each other by means of a releasable bayonet-type connecting device through the execution of a rotational/plug-in movement about a connecting axis of the treatment device, and the connecting device has at least one housing connecting part on the side of the housing and at least one head connecting part on the side of the connecting head, said connecting parts being able to interact with each other in order to connect the connecting device. 
         [0002]    The invention also relates to a treatment element of a treatment device, in particular a treatment device according to the invention, in particular, a filter device for treating fluids, in particular for filtering fluids, in particular liquid fluids, in particular fuel, oil, or water, in particular of an internal combustion engine, in particular of a motor vehicle, the treatment element having a housing comprising a housing pot, a housing cover, at least one inlet for the fluid to be treated, and at least one outlet for the treated fluid, wherein the treatment element can be connected to a connecting head of the treatment device by means of a releasable bayonet-type connecting device through the execution of a rotational/plug-in movement about a connecting axis of the treatment device, and the connecting device has at least one housing connecting part on the side of the housing that can interact with at least one head connecting part on the side of the connecting head for the purpose of connecting the connecting device, wherein the at least one inlet can be connected to at least one feed of the connecting head for the fluid to be treated and/or the at least one outlet can be connected to at least one discharge of the connecting head for the fluid to be treated. 
       BACKGROUND 
       [0003]    DE 10 2010 035 465 A1 discloses a filter for filtering fluids, in particular liquid fluids, in particular fuel or oil, in particular of an internal combustion engine, the filter comprising a filter pot in which a filter element is arranged, and a filter head having an inlet and/or an outlet for the fluid. The filter head and the filter pot are connected to one another by means of a releasable bayonet-type rotational/plug-in connector. The rotational/plug-in connector comprises at least two interacting catch components, one of which is connected to the filter pot and the other of which is connected to the filter head. 
       SUMMARY 
       [0004]    The invention addresses the problem of providing a treatment device and a replaceable filter of a filter device of the aforementioned type, with which it is possible to facilitate the connection of the treatment element, in particular of the replaceable filter to the connecting head and facilitate separation from the connecting head. The invention is also intended to reduce the space required, in particular for the connecting device, in particular in the axial direction with respect to the connecting axis. 
         [0005]    This problem is solved according to the invention in that: at least one first one of the connecting parts has a respective functional surface on faces lying axially opposite one another with respect to the connecting axis; at least one second one of the connecting parts has at least one counter functional surface which engages behind one of the functional surfaces of the at least one first connecting part for interaction purposes; at least one guiding element is arranged on faces of the at least one second connecting part, said guiding element delimiting at least one insert gap together with the at least one counter functional surface, the axial extension of the insert gap with respect to the connecting axis being at least as large as the maximum axial distance between the two axially opposing functional surfaces of the at least one first connecting part; and the at least one first connecting part can be guided in the insert gap when the connecting device is being opened/closed, one of the functional surfaces of the at least one first connecting part being guided along the counter functional surface, and the other functional surface being guided along the at least one guiding element. 
         [0006]    Provided according to the invention is at least one guiding element, in particular a guide peg, with the aid of which the at least one first connecting part can be guided on the side lying axially opposite to the counter functional surface. The at least one connecting part can thus be guided between the at least one guiding element and the corresponding counter functional surface of the at least one second connecting part. In this manner, a precise rotational/plug-in movement can be executed. It is furthermore possible to reduce the risk of the treatment element being tilted relative to the connecting axis when being installed/dismantled. With the aid of the at least one insert gap, the at least one first connecting part can be easily and accurately positioned relative to at least one second connecting part when the treatment element is being installed. 
         [0007]    The at least one counter functional surface engages behind at least one of the functional surfaces of the at least one connecting part. In this manner, between the at least one counter functional surface and the corresponding functional surface, a tension connection can be realized axially to the connecting axis. 
         [0008]    Advantageously for the realization of the bayonet-type connection, the at least one counter functional surface may extend circumferentially with respect to the connecting axis. 
         [0009]    Advantageously, the circumferential extension of the regions of the bayonet-type connecting device in which the at least one counter functional surface interacts with the corresponding at least one functional surface in the closed state of the connecting device may be at least 50%, preferably more than 60% of the circumference of the treatment element. In this manner, a correspondingly larger region that can act in a force-transmitting manner can be realized. In addition, the forces between the treatment element and the connecting head can act circumferentially better and more uniformly. It is also possible, then, to transmit greater forces overall. Thus, the stability of the connection to the connecting device can be improved. The mechanical load of the connecting device can thus be reduced. This can positively affect the service life. 
         [0010]    In an advantageous embodiment, the at least one counter functional surface and the at least one functional surface interacting therewith may each comprise at least one latch element, in particular a latching projection or a latch section of at least one catch lock, which latch one behind the other or with or into one another in the closed position of the at least one connecting device. The catch lock makes it possible to reduce the risk of the connecting device being released through an undesired rotation of the treatment element about the connecting axis. In order to close and release the at least one catch lock, the corresponding latch elements can be separated from one another or guided past one another by the corresponding rotation of the treatment element. So doing may require overcoming corresponding latching forces. The presence of the treatment element at the correct position thereof can also be easily detected at such an increased expenditure of force in the installation. 
         [0011]    In another advantageous embodiment, the connecting device may comprise at least one biasing element for realizing a mechanical bias with which the at least one counter functional surface can be pressed against the at least one functional surface. In this manner, the connecting device can be kept under a mechanical stress. Operational vibrations can thus be dampened. It is also possible to reduce operational noise. In particular, any rattling that might occur can be prevented. Moreover, it is possible to generate or increase any latching force that must be overcome in order to close or open the latching. 
         [0012]    The at least one biasing element may advantageously be arranged on the connecting head. In this manner, the biasing element can be configured as a lifetime component. The biasing element need not be replaced together with the treatment element. Alternatively or additionally, at least one biasing element may be arranged on the housing. The biasing element then can be replaced together with the treatment element. 
         [0013]    The at least one biasing element may advantageously be elastic. The at least one biasing element may be elastic due to the shape thereof and/or the material composition thereof. Advantageously, the at least one biasing element may comprise or be made of plastic, in particular elastomer. Advantageously, the at least one biasing element may be or comprise a spring element, in particular a leaf spring. The spring element may advantageously be made of an elastic metal. 
         [0014]    The at least one biasing element may additionally have a sealing function. The at least one biasing element may be combined with a seal or a sealing unit, or vice versa. Additionally or alternatively, the at least one biasing element may be realized with a non-return diaphragm of the treatment element, or vice versa. The non-return diaphragm makes it advantageously possible to lock a passage for the fluid through the housing, preferably the at least one inlet, in one direction of flow. In this manner, the fluid can be prevented from returning. 
         [0015]    Optionally, a seal may be arranged between a pre-filtration side and a post-filtration side of the treatment element, in particular of a filter element. 
         [0016]    The at least one first connecting part and/or the at least one second connecting part may each be realized with a low material thickness in comparison to the radial and circumferential extension thereof with respect to the connecting axis. The material thicknesses of the at least one first connecting part and the at least one second connecting part may be of similar size. 
         [0017]    In another advantageous embodiment, the material thickness of the at least one first connecting part and/or the at least one second connecting part may advantageously be at most 3 mm, preferably between 1 and 2 mm. 
         [0018]    In another advantageous embodiment, the axial extension of the at least one insert gap may be at most 3 mm, preferably between 1 and 2 mm. 
         [0019]    The connecting parts may be shaped—in particular, bent, folded, kinked, cut, punched, or the like—accordingly out of semi-finished products or molded parts. The corresponding latch sections and (counter) guiding sections may optionally be realized in this manner. 
         [0020]    Advantageously, at least a part of the semi-finished product or molded parts may be provided radially inside the first connecting parts, which are shaped—in particular, bent, folded, kinked, cut, punched, or the like—out of semi-finished products or molded parts. Advantageously, the part of the semi-finished product or the molded parts that is arranged radially within the first connecting parts is closed in the circumferential direction. This makes it possible to improve the stability of the connecting device and thus the rigidity and durability of the connection between the connecting devices. 
         [0021]    The connecting parts may advantageously be arranged radially within at least one circumferential wall of the housing and/or the connecting head. In this manner, the bayonet-type connecting device is protected from the surroundings. The connecting device may advantageously be arranged in a corresponding connection space between the housing and the connecting head. 
         [0022]    Advantageously, the at least one counter functional surface may abut against the corresponding functional surface over the largest possible extension and preferably the entire extension thereof in the circumferential direction as well as in the radial direction with respect to the connecting axis. In this manner, the transmission of forces between the connecting parts can be improved. Corresponding guide contours of the at least one counter functional surface may slide along the corresponding guide contours of the corresponding functional surface when the connecting device is being opened or closed. 
         [0023]    In this manner, it is possible to axially compress any biasing element and/or a seal when the connecting device is being closed. In the case of a seal, the sealing function can thus additionally be improved. 
         [0024]    Advantageously, the at least one counter functional surface and the corresponding functional surface interacting therewith may be complementary. In this manner, said surfaces may lie flat against one another in the closed position of the connecting device. The transmission of forces can thus be improved. Loading of the components involved can thus be further reduced. The components may be dimensioned so as to be smaller in order to transmit equal forces. Adapting the shapes of the connecting parts to one another enables a corresponding reduction in the axial extensions of the connecting parts. Advantageously, the connecting parts may be mutually engaging molded parts. The contours of the at least one counter functional surface and the corresponding functional surface may slide along one another when the connecting device is being opened or closed. 
         [0025]    In another advantageous embodiment, the at least one counter functional surface and at least the functional surface interacting therewith may each travel substantially helically about the connecting axis. In this manner, the housing connecting part can be drawn toward the connecting head in the axial direction at the same time as rotation of the treatment element in the direction of closing, by means of the connecting parts. A combined rotational/plug-in movement can thus be realized. Advantageously, the pitches of the at least one counter functional surface and the at least one functional surface may be identical. 
         [0026]    Advantageously, the pitches may correspond to the pitch of a typical right-handed thread. In this manner, the connecting device can be closed by rotation of the treatment element to the right and opened by rotation of the treatment element in the opposite direction, as is typical with fuel filters or oil filters. 
         [0027]    Advantageously, a height may correspond axially to the connecting axis—which is traveled when the bayonet-type connecting device is closed—to an axial distance of a possible seal on the side of one of the connecting parts from a corresponding seal surface on the side of the other connecting part. In this manner, the corresponding seal can be positioned on the corresponding seal surface through the rotational/plug-in connection when the connecting device is being closed. 
         [0028]    In another advantageous embodiment, the treatment element—in particular a housing cover and/or an end plate of a possible filter element—and the connecting head may each comprise at least one correspondence element, in particular a connecting piece, preferably a sealing connecting piece and/or cylindrical connecting piece, which can correspond in a pairwise manner when the treatment element is mounted. Advantageously, correspondence elements—in particular, the connecting pieces—may engage pairwise with one another. In this manner, the correspondence elements may be fixed radially with respect to the connecting axis relative to one another. Alternatively, the correspondence elements may be arranged as an abutting pair, in particular with interposition of a sealing device. In this manner, radial positional tolerances can be easily compensated with respect to the connecting axis. 
         [0029]    Advantageously, at least one pair of correspondence elements may radially outwardly and/or radially inwardly delimit a fluid-conducting space. 
         [0030]    In another advantageous embodiment, at least one pair of correspondence elements may be arranged within at least one other pair of correspondence elements. In this manner, a first fluid-conducting region, in particular an outlet channel for the fluid, can be realized in the inner pair of correspondence elements. 
         [0031]    Between the inner pair of correspondence elements and the outer pair of correspondence elements, there may advantageously be realized a second fluid-conducting space, in particular an annular inlet space for the fluid. 
         [0032]    The correspondence elements, in particular the pairs of correspondence elements, may each be coaxial to the connecting axis. In this manner, the correspondence elements can be more easily positioned relative to one another. In addition, the fluid-conducting regions may then be circumferentially more uniform. 
         [0033]    At least one pair of correspondence elements, in particular a radially outer pair of correspondence elements, may advantageously circumferentially surround a plurality of fluid-conducting regions, in particular at least one inlet region and at least one outlet region for the fluid. In this manner, the corresponding fluid-conducting regions can be easily delimited from the surroundings with only one pair of correspondence elements. Here, contact regions between the correspondence elements of one pair may optionally be sealed off with only one single sealing unit. 
         [0034]    Advantageously, the connecting parts of the connecting device may be arranged radially outside of the pair of correspondence elements, which may circumferentially surround all of the fluid-conducting regions. In this manner, the fluid-conducting regions can be separated with only one pair of correspondence elements, optionally with only one sealing device, from the connecting parts of the connecting device and preferably also from the surroundings. The connecting parts of the connecting device can thus be easily protected from the fluid. 
         [0035]    Advantageously, at least one sealing device, in particular a sealing ring or preferably an O-ring seal or a combined seal/non-return diaphragm may be arranged between the correspondence elements of at least one pair. Thus, the fluid-conducting regions delimited with the at least one pair of correspondence elements can be better sealed off from the contact region of the connecting pieces. 
         [0036]    Advantageously, at least one fluid-conducting region of the treatment device can be sealed off from the surroundings with the at least one sealing device. Advantageously, the outer sealing ring projects upwards or downwards in the axial direction by at most 5 mm beyond the connecting device. This is advantageous with respect to the use of installation space because the sealing region uses the axial extension of the connecting device. 
         [0037]    Preferably, the at least one sealing device may surround the at least one inlet and the at least one outlet circumferentially with respect to the connecting axis. In this manner, with only one seal, it is possible to seal a plurality, in particular all of the fluid-conducting spaces off from the outside, in particular from the surroundings and/or from the connecting parts of the connecting device. 
         [0038]    Advantageously, at least one sealing device, in particular a sealing ring or a ring seal unit may be located as close as possible to the connecting axis, and thus have the smallest possible diameter. In this manner, it is possible to reduce a force which may be applied in the axial direction to the connecting device by the at least one sealing device. The connecting parts of the connecting device can thus be mechanically relieved. Endowing the at least one sealing device with the smallest possible diameter makes it possible to reduce the torque required to open or close the connecting device. Correspondingly, it is then possible to reduce the required force of opening or closing. This can have an advantageous impact on the ease of maintenance and/or the capacity of the treatment element. 
         [0039]    Advantageously, the at least one sealing device may comprise an O-ring or a molded seal. The sealing device may advantageously act so as to seal radially, in particular, outward or inward with respect to the connecting axis. Additionally or alternatively, the at least one sealing device may act so as to seal in the axial direction. 
         [0040]    The sealing groove of the sealing unit may be covered with a separate cover ring on the side thereof that faces axially away from the filter bellows. The cover ring may then be connected to the outer sealing connecting piece by means of clamping lugs. 
         [0041]    In a preferred embodiment, the sealing groove of the sealing unit is not formed by means of a separate cover ring, but rather as part of the housing cover, integrally with the housing cover. This can have an advantageous impact on the capacity of the treatment element. 
         [0042]    Advantageously, at least one sealing device may be arranged on the treatment element, in particular on the housing cover and/or optionally the end plate of the filter element. In this manner, the at least one sealing device can be replaced together with the treatment element. 
         [0043]    Advantageously, at least one spacer may be provided between the treatment element, in particular the end plate of the filter element. The spacer may be a plastic spacer. Connected to this is the advantage of a greater ease of manufacturing. 
         [0044]    Advantageously, the at least one guiding element may brush along the corresponding at least one functional surface when the treatment element is rotated. In this manner, in particular when the connecting device is opened, an axial pressing-off force on the corresponding functional surface can be generated. With the axial pressing-off force, it is possible to press against a mechanical holding force of the at least one sealing device. Thus, the at least one sealing device can be withdrawn or rotated from a corresponding sealing surface, or vice versa. 
         [0045]    In another advantageous embodiment, a material thickness of the at least one first connecting part and/or the at least one second connecting part in the circumferential direction may be respectively constant in the region of the at least one functional surface/counter functional surface. The space required for the connecting device—in particular, the axial space—can thus be reduced. 
         [0046]    In another advantageous embodiment, the at least one first connecting part and/or the at least one second connecting part may be made of sheet metal or comprise sheet metal. Sheet metal can generally be present in the initial state, as rolled metal in the shape of flat, level panels or strips. Sheet metal is easily realized with a uniform thickness. A mechanically stable connecting part can also be realized with a relatively small material thickness from sheet metal. In this manner, the required installation space, in particular in the axial direction, for the connecting device can be reduced. Sheet metal can be easily machined or processed, in particular bent, folded, punched, cut, or welded. With sheet metal, it is easy to realize connections between components, in particular crimped connections or welded connections. Advantageously, at least one of the connecting parts may be implemented as a shaped sheet metal part. 
         [0047]    Advantageously, at least one of the connecting parts may be fixedly or releasably connected to the treatment element. At least one of the connecting parts may be fixed or releasably connected to the connecting head. The at least one connecting part may be connected to the treatment element or the connecting head by means of a materially integral connection and/or a positive and/or non-positive connection, in particular by means of a crimped connection, a welded connection, a clamped connection, a latched connection, a plug connection, a threaded connection, and/or an adhesive connection. 
         [0048]    Advantageously, the housing connecting part may be connected to the housing cover and/or the housing pot, in particular by means of a crimped connection and/or a welded connection. In this manner, the housing connecting part may be stably connected to the treatment element. The housing-side connecting part may then be easily replaced together therewith. 
         [0049]    Advantageously, the housing connecting part may be held on the housing by means of a crimped connection formed between the housing cover and the housing pot. 
         [0050]    The housing connecting part may advantageously be flush in the axial direction with the axially outermost surface of the crimped connection provided between the housing cover and the housing pot. 
         [0051]    Advantageously, the housing cover may be connected in a sealed manner to the housing pot with the use of a sealing material, in particular a sealant, by means of a crimped connection 
         [0052]    Advantageously, a head-side connecting part may preferably be threaded or welded onto the connecting head. The use of a threaded connection makes it possible for the head-side connecting part to be easily released from the connecting head when necessary. 
         [0053]    Advantageously, the housing cover may be, in particular, elastically deformable. The housing cover can then be pressed against the connecting head by an overpressure, in particular, one that prevails in the housing during operation of the treatment device. The connecting head can thus support the housing cover. It is thus possible to reduce the requirements for the pressure stability of the housing cover. The housing cover can then be more easily realized, in particular from simpler materials. 
         [0054]    Advantageously, a plurality of functional surfaces of the at least one first connecting part and corresponding counter functional surfaces of the at least one second connecting part may be arranged so as to be circumferentially, in particular, uniformly distributed with respect to the connecting axis. It is thus possible to improve a circumferential, in particular uniform transmission of force. It is additionally possible to reduce overall an angle of rotation that is required to close and open the connecting device. The circumferential extension of each of the individual functional surfaces/counter functional surfaces may then be lower than with the use of only one single pair of one counter functional surface and one corresponding functional surface. Achieving a comparable uniform transmission of force requires that a single pair of one counter functional surface and one functional surface extend at least once over the entire circumference. 
         [0055]    Advantageously, the treatment device may be a filter device for filtering liquid fluids, in particular fuel, oil, or water. The filter device may advantageously be used in an internal combustion engine. 
         [0056]    Advantageously, the treatment element may be a replaceable filter, in particular a replaceable filter for oil or fuel. The housing of the treatment element may then be a filter housing. Advantageously, in the filter housing, at least one filter element may be arranged so as to be able to separate the at least one inlet from the at least one outlet. The connecting head may advantageously be a filter head, onto which the replaceable filter, in particular the filter housing can be releasably mounted by means of the connecting device. 
         [0057]    A replaceable filter is typically a filter with which the at least one filter element is replaced together with the filter housing. Generally, the at least one filter element is arranged fixedly in the filter housing. Correspondingly, the connections between the housing pot and the housing cover need not be non-destructively releasable. 
         [0058]    The invention is not limited to a treatment device of an internal combustion engine of a motor vehicle. Rather, the invention may also be used for other types of internal combustion engines, in particular industrial engines. The invention can also be used with other types of treatment devices for fluid inside or outside the field of motor vehicle technology. The invention may even be used with air de-oiling boxes or desiccant boxes. 
         [0059]    The problem is furthermore solved by the treatment element in that: the treatment element comprises at least one first connecting part and/or at least one second connecting part, wherein: the at least one first one of the connecting parts has a respective functional surface on faces lying axially opposite with respect to the connecting axis, and the at least one second one of the connecting parts has at least one counter functional surface which engages behind one of the functional surfaces of the at least one first connecting part for interaction purposes; at least one guiding element is arranged on the face of the at least one second connecting part, said guiding element delimiting at least one insert gap together with the at least one counter functional surface, the axial extension of the insert gap with respect to the connecting axis being at least as large as the maximum axial distance between the two axially opposing functional surfaces of the at least one first connecting part; and the at least one first connecting part can be guided in the insert gap when the connecting device is being opened/closed, one of the functional surfaces of the at least one first connecting part being guided along the counter functional surface, and the other functional surface being guided along the at least one guiding element. 
         [0060]    The advantages and features shown in connection with the treatment device according the invention and the advantageous embodiments thereof apply correspondingly to the treatment element according to the invention and the advantageous embodiments thereof, and vice versa. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0061]    Other advantages, features, and details of the invention shall be made more apparent by the following description, which addresses embodiments of the invention in greater detail, with reference to the accompanying drawings. The features disclosed in the drawings, the description, and the claims in combination will be individually considered, as appropriate, and combined into other appropriate combinations by a person skilled in the art. In the schematic drawings, 
           [0062]      FIG. 1  illustrates a longitudinal section of a filter device for engine oil of an internal combustion engine of a motor vehicle along a cut line I-I from 
           [0063]      FIG. 3 , with a filter head and a replaceable filter that is connected to the filter head by means of a releasable bayonet-type connecting device; 
           [0064]      FIG. 2  illustrates a longitudinal section of the filter device from  FIG. 1  along a cut line II-II from  FIG. 3 ; 
           [0065]      FIG. 3  is a plan view of the filter device from  FIGS. 1 and 2 ; 
           [0066]      FIG. 4  is a detail view of the longitudinal section of the filter device from  FIG. 1 , in the region of the connecting device; 
           [0067]      FIG. 5  is an isometric depiction of the replaceable filter of the filter device from  FIGS. 1 to 4 ; 
           [0068]      FIG. 6  is an isometric depiction of the filter head of the filter device from  FIGS. 1 to 4 ; and 
           [0069]      FIG. 7  illustrates a longitudinal view of a filter device according to a second embodiment, similar to the filter device from  FIGS. 1 to 6 . 
       
    
    
       [0070]    Identical components are provided with the same reference numbers in the figures. 
       DETAILED DESCRIPTION 
       [0071]      FIGS. 1 to 6  illustrate different perspectives, sections, and detail views of a filter device  10  for engine oil of an engine oil circuit of an internal combustion engine of a motor vehicle, and components thereof. The filter device  10  serves to purify the engine oil. 
         [0072]    The filter device  10  comprises a filter head  12 , to which a replaceable filter  14  is releasably attached. The filter head  12  is fixedly connected to the internal combustion engine and serves as a connector part for the replaceable filter  14 .  FIG. 6  illustrates the filter head  12  in detail. The filter head  12  comprises a feed  16  and a discharge  18  for the engine oil. The feed  16  and the discharge  18  are connected to corresponding oil lines of the internal combustion engine, in a manner that is not of further interest here. 
         [0073]    The filter head  12  further comprises a radially inner connecting piece  22  that is coaxial with respect to a connecting axis  20 . 
         [0074]    Subsequent discussion of “axial,” “radial,” “coaxial,” “circumferential,” or the like is made with respect to the connecting axis  20 , unless otherwise indicated. In the embodiment depicted, the connecting axis  20  coincides with a filter axis of the replaceable filter  14 . 
         [0075]    The inner connecting piece  22  is approximately circularly cylindrical. The connecting piece extends on the side of the filter head  12  that faces the replaceable filter  14 . It is open on both end faces. On the side thereof that faces away from the replaceable filter  14 , the inner connecting piece  22  is connected fluidically to the discharge  18 . 
         [0076]    The inner connecting piece  22  is surrounded coaxially by a circularly cylindrical, radially outer connecting piece  24 . The inner connecting piece  22  projects beyond the outer connecting piece  24  in the axial direction on the side thereof that faces the replaceable filter  14 . 
         [0077]    The inner connecting piece  22  and the outer connecting piece  24  each circumferentially delimit a coaxial annular inlet space  26 . The annular inlet space  26  is connected to the feed  16  via a fluid connection. 
         [0078]    The inner connecting piece  22  and the outer connecting piece  24  are coaxially surrounded by a circularly cylindrical circumferential wall  28 . The free edge of the circumferential wall  28  facing the replaceable filter  14  is located approximately at the same axial height as the free edge of the outer connecting piece  24 . The circumferential wall  28  forms the radially outer delimitation of the filter head  12  on the side facing the replaceable filter  14 . The circumferential wall  28  and the outer connecting piece  24  each circumferentially delimit an annular, coaxial connection space  30 . 
         [0079]    Arranged in the connection space  30  is a head connecting part  32  of a releasable bayonet-type connecting device  34 . The replaceable filter  14  is releasably attached with the connecting device  34  to the filter head  12 . The head connecting part  32 , which overall is approximately annular in shape, is formed of sheet metal. The thickness of the sheet metal is constant, at about 2 to 3 mm. 
         [0080]    Radially inwardly, the head connecting part  32  comprises an annular head mounting section  36 . The head mounting section  36  pushes with the radially inner circumference side thereof approximately against the radially outer circumference side of the outer connecting piece  24 . The head mounting section  36  extends radially and circumferentially approximately in the same plane. The head connecting part  32  extends radially approximately as far as the middle of the connection space  30 . 
         [0081]    The head mounting section  36  passes into four head-side bayonet sections  38 . The head-side bayonet sections  38  are identical in shape and size. The head-side bayonet sections  38  are arranged so as to be distributed circumferentially uniformly. The head-side bayonet sections  38  each have a circumference section  40  that extends substantially circumferentially parallel to an imaginary circular cylinder shell about the connecting axis  20 . The circumference sections  40  each transition into a functional section  42  on the sides thereof facing away from the head mounting section  36 . The circumference sections  40  thus connect the head mounting section  36  to the respective portion sections  42 . The functional sections  42  are easily visible in particular in  FIG. 6 . The functional sections  42  each have a counter functional surface  44  on the side thereof facing away from the replaceable filter  14 . 
         [0082]    The functional sections  42 , in particular the counter functional surfaces  44 , each travel approximately helically about the connecting axis  20 . The pitch of the counter functional surfaces  44  and the functional sections  42  corresponds approximately to the pitch of a typical right-handed thread. Viewed axially out from the replaceable filter  14 , the ends of the functional sections  42  that are to the front in the clockwise direction are each closer to the replaceable filter  14  than the ends that are to the rear in the clockwise direction. Present between the front ends of the functional sections  42  and the plane of the head mounting section  36  are respective gaps through which corresponding housing-side bayonet sections  104  (described in greater detail below) can be introduced. 
         [0083]    The sheet metal of the head connecting part  32  is of equal thickness in the head mounting section  36 , in the circumference sections  40 , and in the functional sections  42 . This also signifies that the sheet metal has a uniform axial extension in the head mounting section  36  and in the functional sections  42 . 
         [0084]    The functional sections  42  each have a head-side latching projection  46 . The latching projections  46  are realized as respective bends in the counter functional surfaces  44 . The latching projections  46  rise axially on the side facing the replaceable filter  14 . 
         [0085]    Viewed out from the replaceable filter  14 , a guide peg  48  is arranged in front of each of the functional sections  42  in the clockwise direction. The guide pegs  48  are illustrated, for example, in  FIG. 6 . The guide pegs  48  are attached to the filter head  12  separately from the head connecting part  32 . The guide pegs  48  are each located at the insertion side of the head-side bayonet sections  38 . With the counter functional surfaces  44 , the guide pegs there each delimit a head-side insert gap  50 , also illustrated in  FIG. 6 . 
         [0086]    The head connecting part  32  is attached to the filter head  12  at the head mounting section  36  with four screws  52  in total, as illustrated in  FIG. 6 , from the side facing the replaceable filter  14 . The screws  52  are each located between an end of one of the head-side bayonet sections  38  to the rear in the clockwise direction and one of the guide pegs  48  in front of the end of the next head-side bayonet section  38  to the front in the clockwise direction. 
         [0087]    An annular leaf spring  54  is also arranged coaxially in the connection space  30 . A radially outer circumferential side of the leaf spring  54  extends circumferentially along the radially inner circumferential side of the circumferential wall  28 . The leaf spring  54  has four spring arms in total. The spring arms are distributed circumferentially uniformly. 
         [0088]    With respect to the connecting axis  22 , the spring arms extend approximately helically in the same direction of rotation as the functional sections  42  of the head connecting part  32 . The spring arms are resiliently flexible in the axial direction. 
         [0089]    The replaceable filter  14  is designed as a spin-on filter having a circular cross-section. The replaceable filter is substantially coaxial to the connecting axis  20 . The replaceable filter  14  comprises a filter housing  56  having a housing pot  58 , a housing cover  60  being attached to open sides thereof, at the radially outer edge, by means of a crimped connection. A radially outer diameter of the filter housing  56  in the region of the housing cover  60  is smaller than a radially inner diameter of the circumferential wall  28  of the filter head  12 . The housing pot  56  has an outwardly curved housing bottom  62 . The housing cover  60  and the housing pot  58  are made of metal. 
         [0090]    A coaxial filter element  64  is arranged in the housing pot  58 . The filter element  64  has a filter medium that is folded into a filter bellows  66  and is circumferentially closed. At end faces thereof, the filter bellows  66  is respectively connected in a sealed manner to a connecting end plate  68  (above in  FIG. 1 ) and a counter end plate  70  (below in  FIG. 1 ). The connecting end plate  68  is located on the side of the filter element  64  that faces the housing cover  60 . 
         [0091]    The filter bellows  66  surrounds an element interior space  72  of the filter element  64 . The element interior space  72  is located on a post-filtration side of the filter element  64 . 
         [0092]    The counter end plate  70  closes the element interior space  72  on the end face of the filter element  64  that faces the housing bottom  62 . Supported on the outer side of the counter end plate  70  that faces the housing bottom  62  are a plurality of spring elements  74 , which in turn are supported on the housing body  62  on the other side. 
         [0093]    A spring-loaded bypass valve  76  is arranged in the counter end plate  70 , the bypass valve allowing an oil flow of engine oil from the housing bottom  62  directly into the element interior space  72 , bypassing the filter medium, in the opened state (under conditions not of further interest here). The bypass valve  76  is depicted in the closed position in  FIG. 1 . 
         [0094]    The filter element  64  is surrounded radially outwardly by a pre-filtration-side annular space  78  that is delimited by the radially inner circumferential side of the housing pot  58 . 
         [0095]    A coaxial central tube  80  also extends in the element interior space  72 , between the counter end plate  70  and the connecting end plate  68 . A circumferential wall of the central tube  80  is permeable to the engine oil. A radially inner circumference side, namely, radially inner pleat edges of the filter bellows  66  can be supported on the radially outer circumference side of the central tube  80 . 
         [0096]    The connecting end plate  68  has a coaxial outlet opening  82  for the filtered engine oil. The connecting end plate  68  is molded on the radially inner circumferential side into a coaxial cylindrical connecting piece  83  that extends axially away from the element interior space  72 . 
         [0097]    An annular coaxial inner sealing unit  84  is attached to the side facing axially way from the element interior space  72 . The inner sealing unit  84  is composed of an elastomer. 
         [0098]    Radially outwardly, the inner sealing unit  84  has a non-return diaphragm  86 . The non-return diaphragm  86  is annular in shape and surrounds the cylindrical connecting piece  83  radially outwardly. The non-return diaphragm  86  abuts against the inner side of the housing cover  60  that faces the filter bellows  66 , under a mechanical bias. The non-return diaphragm, as illustrated in  FIGS. 1, 2, and 4 , closes off a coaxial annular inlet opening  88  of the housing cover  60  for engine oil, in the pressure-free state. As soon as engine oil is supplied to the filter device  10 , the non-return diaphragm  86  opens in the direction of passage through, due to the oil pressure. The non-return diaphragm  86  prevents the engine oil from returning through the inlet opening  88 . 
         [0099]    A radially inner ring section of the inner sealing unit  84  forms a coaxial inner sealing ring  90 . The inner sealing ring  90  abuts in a sealed manner at the radially outer circumference side thereof against the radially inner circumference side of the cylindrical connecting piece  83 . The inner sealing ring  90  abuts in a sealed manner at the radially inner circumference side thereof—when the replaceable filter  14  has been mounted—against a radial outer circumference side, designed to be a sealing surface, of the radially inner connecting piece  22 . With the inner sealing ring  90 , the post-filtration side of the replaceable filter  14  is separated from the pre-filtration side thereof in the region of the inlet opening  88 . 
         [0100]    The housing cover  60  comprises a stepped coaxial outer sealing connecting piece  92  in the region of the inlet opening  88 . A narrowing of the outer sealing connecting piece  92  at the end thereof that faces axially away from the filter bellows  66  forms an outer sealing groove  94  for an outer sealing ring  96 . The outer sealing ring  96  is designed as an O-ring. 
         [0101]    A radially outer diameter of the outer sealing connecting piece  92  outside of the region of the sealing groove  94  corresponds approximately to the radially inner diameter of the outer connecting piece  24  of the filter head  12 . When the replaceable filter  14  is mounted, the sealing connecting piece  92  is inserted into the outer connecting piece  24 . The radially outer circumference side of the outer sealing connecting piece  92  abuts then against the radially inner circumference side of the radially outer connecting piece  24 . 
         [0102]    The outer sealing groove  94  is covered with a cover ring  98  on the side thereof that faces axially away from the filter bellows  66 . The cover ring  98  is connected to the outer sealing connecting piece  92  by means of four clamping lugs. 
         [0103]    When the replaceable filter  14  is mounted, the outer sealing ring  96  abuts against the radial inner circumference side, designed as a sealing surface, of the radially outer connecting piece  24  in a sealed manner. The outer sealing ring  96  thus separates the oil-conducting region of the filter device  10  from the connection space  30  and from the surroundings. 
         [0104]    An annular coaxial housing connecting part  100  of the connecting device  34  is molded out of sheet metal. A thickness of the sheet metal of the housing connecting part  100  corresponds approximately to the thickness of the sheet metal of the head connecting part  31 . 
         [0105]    The housing connecting part  100  extends radially from the radially outer circumference side of the housing cover  60  to over the radial center of the connection space  30 . The housing connecting part  100  overlaps with the head connecting part  32 . 
         [0106]    The housing connecting part  100  comprises a housing mounting section  102  that extends radially and circumferentially approximately in the same plane. The housing mounting section  102  is fixed radially outwardly between the housing cover  60  and the crimped connections of the housing pot  58  to the housing cover  60 . The housing mounting section rests on one side flat against the housing cover  60 . 
         [0107]    The housing mounting section  102  transitions on the radially inner side thereof into four identical housing-side bayonet sections  104 . The housing-side bayonet sections  104  are arranged so as to be distributed circumferentially uniformly. The housing-side bayonet sections have approximately the same shape and size as the head-side bayonet sections  38 . 
         [0108]    The housing-side bayonet sections  104  have, on axially opposite sides, an inner functional surface  106  and an outer functional surface  108 . The functional surfaces  106  and  108  extend opposite to the counter functional surfaces  44 , each approximately helically about the connecting axis  20 , with the same pitch as the counter functional surfaces  44 . 
         [0109]    The inner functional surfaces  106  are located on the side of the respective housing-side bayonet section  104  that faces the housing cover  60 . The outer functional surfaces  108  are correspondingly located on the axially opposite side. In the closed state of the connecting device  34 , the outer functional surfaces  108  each are engaged from behind by one of the counter functional surfaces  44  of one of the head-side bayonet sections  38 , for the purpose of interaction. Then, the outer functional surfaces  108  each abut flat against the corresponding counter functional surfaces  44 . 
         [0110]    The housing-side bayonet sections  104  each comprise a housing-side latching projection  110 . The latching projections  110  rise axially away from the housing cover  60 . When the replaceable filter  14  is mounted, the housing-side latching projections  110  lock behind the corresponding head-side latching projections  46 . 
         [0111]    For the purpose of installation, the replaceable filter  14  is inserted with the housing cover  60  forward, coaxially onto the connection side of the filter head  12 . 
         [0112]    At the latest when the cover ring  98  arrives at the end face of the radially outer connecting piece  24  of the filter head  12  and/or the housing connecting part  100  arrives at the head connecting part  32 , the replaceable filter  14  is additionally rotated about the connecting axis  20  in the right-handed direction of rotation, which is the direction of rotation for closing the connecting device  34 . 
         [0113]    As soon as the free ends of the housing-side bayonet sections  104  are positioned in the region of the corresponding head-side insert gaps  50 , the respective outer functional surfaces  108  begin to be guided from the outside along the corresponding counter functional surfaces  44  on the respective guide pegs  48  and the inner functional surfaces  106 . The spring arms of the leaf springs  54  are supported with the free ends thereof on the housing connecting part  100  in the axial direction. The tension achieved by the helical pitch of the counter functional surface  44  and the inner functional surface  106  in the axial direction between the bayonet sections  38  and  104  draws the inner sealing ring  90  onto the radially inner connecting piece  22  and the outer sealing ring  96  into the radially outer connecting piece  24 . 
         [0114]    As soon as the housing-side latching projections  110  abut against the corresponding head-side latching projections  46 , a corresponding locking force must be overcome in order to continue turning. The locking force is realized through the restoring force of the spring arms of the leaf spring  54 . 
         [0115]    After the locking force is overcome, the housing-side latching projections  110  lock behind the housing-side latching projections  46 , and thus ensure against an unintentional opening of the connecting device  34 . 
         [0116]    In order to separate the replaceable filter  14  from the filter head  12 , the replaceable filter  14  is rotated to the left, i.e., the direction of opening rotation, about the connecting axis  20 . This requires first overcoming the locking force of the housing-side latching projections  110  with the head-side latching projections  46 . 
         [0117]    Under the spring biasing of the leaf spring  54 , the inner functional surfaces  106  are guided along the corresponding counter functional surfaces  44 . In addition, the outer functional surfaces  108  are guided along the respective guide pegs  48 . Then, with the guide pegs  48 , a respective axial pressing-off force onto the outer functional surfaces  108  is generated, and acts against a respective holding force of the inner sealing ring  90  and the outer sealing ring  96 . The holding forces are realized through the respective friction between the inner sealing ring  90  and the inner connecting piece  22 , and between the outer sealing ring  96  and the outer connecting piece  24 . The pressing-off force draws the inner sealing ring  90  off in the axial direction from the inner connecting piece  22 , and draws the outer sealing ring  96  out from the outer connecting piece  24 . 
         [0118]    As soon as the housing-side bayonet sections  104  leave the corresponding head-side insert gaps  50  after further rotational movement, the replaceable filter  14  is drawn away from the filter head  12  with an axial movement. 
         [0119]    When the filter device  10  is operating, i.e., when the internal combustion engine is operating, engine oil to be purified flows through the feed  16 , indicated by an arrow  112 , into the annular inlet space  26 . The engine oil flows out from there through the inlet opening  88 , and is released by the non-return diaphragm  86  into the pre-filtration-side annular space  78  of the filter housing  56 . The engine oil to be purified flows through the filter bellows  66  from radially outward to radially inward, and passes through the openings of the central tube  88  into the element interior space  72 . From the element interior space  72 , the purified engine oil passes through the outlet opening  82  and the radially inner connecting piece  22  of the filter head  12  to the discharge  18 . The purified engine oil leaves the filter head  12  and therewith leaves the filter device  10 , through the discharge  18 . 
         [0120]      FIG. 7  illustrates a second embodiment of a filter device  10 . Those elements that are similar to those of the first embodiment from  FIGS. 1 to 6  are provided with the same reference signs. The second embodiment differs from the first embodiment in that an inner seal  190  of the inner sealing unit  84  is arranged in an axially sealing manner between the radially inner connecting piece  22  of the filter head  12  and the cylindrical connecting piece  83  of the replaceable filter  14 . The connecting piece  22  and the cylindrical connecting piece  83  have the same diameter. The connecting piece and the cylindrical connecting piece abut against one another in the axial direction of the interposition of the inner seal  190 . 
         [0121]    An outer sealing ring  196  is located radially outward between a radially inner circumference side of a coaxial cylindrical section of the housing cover  60  and a radially outer circumference side of the circumferential wall  28  of the filter head  12 . The outer sealing ring  196  seals the connection space  30  off from the surroundings. The connection space  30  itself is fluidically connected to the annular inlet space  26 . 
         [0122]    The second embodiment also omits a bypass valve.