Patent Publication Number: US-2019195365-A1

Title: Radial Shaft Seal

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a radial shaft seal with at least one sealing lip of elastomeric material that, at its inner side which is facing the shaft to be sealed, comprises a first circumferentially extending ring which is seal-tightly contacting the shaft and seals relative to the medium side; further comprises return conveying elements arranged about the circumference of the sealing lip and provided at the side of the first ring facing the air side and conveying leakage medium, independent of the rotational direction of the shaft, to the medium side; and further comprises at least one second circumferentially extending ring provided at the side of the return conveying elements that is facing the air side. 
     Radial shaft seals in the form of radial shaft seal rings are known (US 2014/0151967) and used for sealing rotating shafts. The sealing lip of the radial shaft seal ring rests under a radial force with the first circumferentially extending ring against the shaft and seals relative to the medium side. Should medium have leaked underneath the first ring, the medium is then returned by the return conveying elements back to the medium side. The return conveying elements are formed by grooves that are alternatingly oppositely slanted relative to the circumferential direction of the sealing lip and arranged at the bottom side of the sealing lip. Depending on the rotational direction of the shaft, the medium that has leaked is returned by the grooves to the first ring and conveyed underneath it. The second ring provides a sealing action against the air side. Such radial shaft seal rings are problematic when the shaft rotates at high rotational speeds. High rotational speeds are to be understood as speeds of at least 10,000 r.p.m (revolutions per minute). At such high rotational speeds, the slanted grooves are not well suited as return conveying elements for a reliable return conveyance of the medium which has leaked underneath the first ring. 
     The invention has the object to design the radial shaft seal of the aforementioned kind in such a way that it is suitable for high rotational speeds of the shaft to be sealed in both rotational directions. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, this is achieved for a radial shaft seal of the aforementioned kind in accordance with the invention in that the first circumferentially extending ring is embodied as an elevation and comprises, distributed about its circumference, depressions that are also produced by elevations and extend in the direction of the second ring and are positioned approximately between neighboring return conveying elements. 
     In the radial shaft seal according to the invention, the first circumferentially extending ring is designed as an elevation and is provided with depressions distributed about its circumference which are also embodied as elevations. They extend in the direction toward the second ring and are arranged in the region between neighboring return conveying elements. The depressions extend from the first ring in the direction toward the air side of the radial shaft seal. The depressions ensure that medium which has leaked underneath the first ring is returned in the direction toward the medium side. The first ring with the depressions reduces the disruption of the flow direction of the medium to be sealed. Also, this configuration of the first ring reduces the leakage flow. The depressions also lead to the contact surface being enlarged between the first ring and the shaft in the region of the calculated leakage flow. In this way, it is made more difficult for the medium to be sealed to move via the return conveying elements in the direction toward the air side. The radial shaft seal according to the invention is in particular suitable for such situations of use in which, even at high rotational speeds of the shaft, the medium to be sealed that possibly has leaked underneath the first ring is returned (conveyed back) to the medium side. High rotational speeds are to be understood in this context such that the shaft to be sealed has a rotational speed of at least approximately 10,000 r.p.m. With the radial shaft seal according to the invention, even shafts that operate, for example, at rotational speeds in the range of up to 50,000 r.p.m., can be reliably sealed in both rotational directions. Such specifications are in particular required in the field of electric vehicles in the automotive sector. 
     For smaller shaft diameters, smaller than approximately 30 mm, preferably smaller than approximately 20 mm, rotational speeds up to 100,000 r.p.m. may occur. Even then the radial shaft seal according to the invention reliably can reliably seal the shafts. 
     Advantageously, the return conveying elements are embodied symmetrical to their center plane which is positioned in an axial plane of the radial shaft seal. In this way, it is ensured that the medium having leaked underneath the first ring is reliably returned to the medium side in both rotational directions of the shaft. 
     Advantageously, the depressions adjoin approximately tangentially the first ring. The return conveyance of the medium is favored in an advantageously way thereby. 
     In order for the medium which has leaked underneath the first ring to be reliably returned to the medium side about the circumference of the sealing lip independent of the rotational direction of the shaft, it is advantageous when the return conveying elements extend ata slant in the circumferential direction of the sealing lip. 
     It is advantageous when the return conveying elements in themselves are straight. 
     It is also possible to configure the return conveying elements in a curved shape, for example, in a sickle shape. In this context, the return conveying elements can extend in a curved shape in the direction toward the first ring and can closely contact it. The transition from the return conveying elements into the first ring is approximately tangential in this case. In case of such a configuration of the return conveying elements, a return conveyance of medium, which has leaked through the first ring, to the medium side is reliably possible at high rotational speeds of the shaft. 
     In an advantageous embodiment, return conveying elements neighboring each other in the circumferential direction of the sealing lip are arranged so as to be oppositely slanted relative to each other. In this way, about the circumference of the sealing lip a proper return conveyance of medium that has possibly leaked through underneath the first ring is achieved in both rotational directions of the shaft. 
     A return conveyance of the leaked medium to the medium side is in particular ensured when the return conveying elements adjoin the first ring and are preferably monolithically formed together with it. 
     In order for the medium to be reliably returned to the medium side by the return conveying elements and by the depressions, the return conveying elements and the depressions with their ends adjoin advantageously the first ring approximately at the same level. 
     The return conveying elements are advantageously arranged such that they are positioned at an acute angle relative to the adjacent region of the first ring. 
     In this context, the return conveying elements together with the regions of the first ring neighboring them form a pressure chamber, respectively. Upon return conveyance, the medium flows into this pressure chamber which, due to the acute angle at which the return conveying elements are positioned relative to the first ring, tapers in the flow direction of the medium to be returned. In this way, such a pressure is created in the pressure chamber that the medium to be returned flows minimally across the first ring and a return conveying mechanism at a defined location is created. 
     In an advantageous embodiment, the return conveying elements have a spacing relative to the second ring. In this way, it can be reliably prevented that medium which has leaked underneath the first ring reaches the air side. 
     A simple configuration results when the return conveying elements provided about the circumference of the sealing lip are of the same length. 
     However, it is also possible that the return conveying elements have different lengths. This may mean that all return conveying elements are of unequal length. Depending on the application, this may also mean that, for example, only one of these return conveying elements has a length different from the lengths of the other return conveying elements. 
     A safe sealing action relative to the air side is achieved in an advantageous way when at the sealing lip several second rings are provided which are coaxial to each other and to the first ring. 
     Advantageously, the second rings are identically embodied. 
     In order to keep wear minimal at high rotational speed of the shaft, the second ring in axial section has advantageously a curved outer side. 
     It is advantageous in this context that the second ring is embodied such that in axial section it has an approximately semi-circular cross section. 
     In a simple embodiment, the second rings are arranged at identical spacing one behind the other. 
     In a particularly advantageous embodiment, the second ring which is neighboring the first ring has projections which are distributed about its circumference and extend in the direction toward the first ring. Due to the projections, possible leakage flows are returned in a targeted and active way to the return conveying elements. 
     In order for this return conveying action to be ensured about the circumference of the sealing lip, the projections and the depressions are advantageously alternatingly arranged in the circumferential direction of the sealing lip. 
     The projections can be designed such that the side wall which is facing the first ring is concavely curved. Advantageously, in this context the projections are symmetrical in relation to their center plane, when projected onto the drawing plane. The medium to be returned is supplied along the curved lateral surface reliably to the return conveying elements. 
     The free ends of the return conveying elements have advantageously minimal spacing from the projections. Between the return conveying elements and the corresponding side wall of the projections, small return guiding gaps are formed in this way and the medium can be guided through them to the return conveying elements. 
     The subject matter of the invention results not only from the subject matter of the individual claims but also from all features and specifications disclosed in the drawings and the description. They are, even if they are not subject matter of the claims, considered to be important to the invention inasmuch as, individually or in combination, they are novel relative to the prior art. 
     Further features of the invention result from the additional claims, the description, and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a plan view of a radial shaft seal according to the invention. 
         FIG. 2  is a section view along the section line II-II of  FIG. 1 . 
         FIG. 3  is a detail illustration of the detail III in  FIG. 2 . 
         FIG. 4  is a detail illustration of the detail IV in  FIG. 2 . 
         FIG. 4 a    shows an enlarged illustration of the course of the return conveyance and of the leakage flow. 
         FIG. 5  is a detail view of a section along the section line V-V in  FIG. 4 . 
         FIG. 6  is a detail view of the detail VI in  FIG. 2 . 
         FIG. 7  is a detail view of the detail VII in  FIG. 2 . 
         FIG. 8  is a section view along the section line VIII-VIII in  FIG. 7 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The radial shaft seal described in the following is embodied as a radial shaft seal ring. The radial shaft seal ring is provided in particular for shafts which in their use are subjected to extreme requirements in relation to high rotational speeds, high circumferential speeds, and changing rotational direction. Such specifications are in particular required by the automotive industry in the field of electric vehicles. In this field, electric motors are used which reach rotational speeds of at least 10,000 r.p.m. In connection with future devices, rotational speeds in the range of 20,000 to 30,000 r.p.m. are desired. When such shafts of such electric motors are drive shafts of gear boxes, the high rotational speeds are required not only in forward drive but also in reverse drive. The radial shaft seal ring described in the following fulfills these requirements. 
     The radial shaft seal ring has a ring-shaped housing  1  with L-shaped cross section; see  FIG. 2 . The housing  1  has a cylindrical wall  2  which at one end passes into a radial inwardly oriented housing bottom  3 . The housing bottom  3  is centrally provided with a through opening  4  for the shaft to be sealed. The housing  1  can be comprised of metallic material but also of hard plastic material. 
     The housing bottom  3  is provided at its outer side with a cover  5  which covers also the cylindrical wall  2  at its radial outer side. The part of the cover  5  which is covering the cylindrical wall  2  forms a static seal of the radial shaft seal ring in its installed position. Advantageously, the part of the cover  5  which covers the cylindrical wall  2  is provided with a profiling  6  which projects past the cylindrical wall  2  and upon insertion of the radial shaft seal ring into a receiving chamber is elastically compressed. In this way, a proper static sealing action is ensured. The cylindrical wall  2  of the housing  1  is seated with press fit in the installation chamber for the radial shaft seal. 
     The cover  5  surrounds also the rim  7  of the through opening  4  and extends across a portion of the inner side  8  of the housing bottom  3 . Also, the cover  5  covers advantageously the end face  9  of the cylindrical wall  2 . 
     The cover  5  is connected in a suitable way fixedly to the housing  1 , for example, with an appropriate bonding system. For example, the connection can be realized by means of an adhesive. In case of an elastomeric material, the cover  5  can be vulcanized to the housing  1 . It is advantageous when the cover  5  is connected additionally with form fit to the housing bottom  3  at the outer side of the housing bottom  3 . The housing bottom  3  comprises cutouts  10  at its outer side that are distributed about its circumference; advantageously, the cutouts  10  are distributed along a ring about the circumference of the housing bottom  3  ( FIG. 1 ). 
     The radial shaft seal ring is provided with a sealing lip  11  which in the installed position is resting with elastic deformation against the shaft to be sealed. The sealing lip  11  is advantageously monolithically formed together with the cover  5 . In principle, it is however also possible to provide the cover  5  and the sealing lip  11  as separate parts. This has the advantage that the sealing lip  11  and the cover  5  can then be produced of different materials. 
     The radial shaft seal ring can be provided with a protective lip which is also advantageously monolithically formed together with the cover  5  and thus also formed together with the sealing lip  11 . The protective lip is located at the air side  13  of the radial shaft seal ring and prevents dirt particles and the like from reaching the sealing lip  11 . 
     In the installed position, the sealing lip  11  rests with elastic deformation areally against the rotating shaft. In order to keep the friction and thus wear as minimal as possible, the surface pressure or the specific radial force at which the sealing lip  11  bears against the shaft is very minimal and is, for example, within a range of magnitude of approximately 0.01 N/mm to 0.1 N/mm. The inner side  14  of the sealing lip  11  which is facing the shaft to be sealed is provided with a structure which will be explained in detail with the aid of  FIGS. 3 to 8 . 
     A first circumferentially extending ring  15  is provided at the free rim at the inner side  14  of the sealing lip  11  and is formed by an approximately semi-circular elevation (viewed in axial section) at the inner side  14 . This first circumferential ring  15  has minimal spacing from the end face  16  of the sealing lip  11  ( FIGS. 6 and 8 ). 
     A wall surface  17  adjoins the first circumferential ring  15  at the side which is facing away from the end face  16  of the sealing lip  11 ; the wall surface  17  is provided with return conveying units  18  that ensure that medium (in general oil) which has leaked from the medium side  19  of the radial shaft seal ring underneath the sealing lip  11  is returned to the medium side  19 . 
     As can be seen in  FIGS. 2 and 4 , the ring  15  has sections  20  that are positioned at a spacing from each other and form sickle-shaped depressions; these depressions or sections  20  are curved in the axial direction toward the air side  13 . The sections  20  are mirror symmetrical to the corresponding axial plane, as shown in  FIG. 4 . The sections  20  are monolithically formed together with the ring  15  but have a smaller axial width than the ring  15 . In the embodiment, the sections  20  are approximate half as wide as the ring  15  (see  FIG. 4 ). 
     The sections  20  can be continuously curved across their entire circumferential length. However, it is possible that the sections  20  have at half their length a straight center section. Depending on the configuration of the curved or arched sections  20 , the return conveying quantity of the return conveying elements  18  can be influenced. 
     In the region in which the two ends of the sections  20  are passing into the ring  15 , oppositely extending return conveying elements  21 ,  22  are provided that in the circumferential direction of the sealing lip  11  are extending at an angle to each other. 
     The sections  20  and the return conveying elements  21 ,  22  form the return conveying units  18 . 
     The sections  20  and the return conveying elements  21 ,  22  like the ring  15  are formed by elevations which are projecting at the inner side  14  away from the wall surface  17 . The return conveying elements  21 ,  22  are positioned at an acute angle relative to the neighboring regions of the ring  15  with which, in plan view according to  FIG. 4 , they delimit V-shaped pressure chambers  23 ,  24 . They taper in circumferential direction in the direction toward the curved or arched section  20  extending between the two pressure chambers  23 ,  24 . The return conveying elements  21 ,  22  pass with an arc-shaped curvature into the medium-side ring  15 . 
     As shown in  FIG. 4 , the return conveying elements  21 ,  22  are connected to each other by a narrow rib  25 . The rib  25  extends in circumferential direction and parallel to the medium-side ring  15 . Advantageously, the rib  25  is formed monolithically together with the return conveying elements  21 ,  22 . 
     The curved or arched section  20  is arranged such that at half the length it has the smallest spacing from the rib  25 . 
     Distributed about the circumference of the sealing lip  11 , the arched or curved sections  20  are uniformly distributed as shown in  FIG. 2 . The sections  20  are adjoined in the described way by the return conveying elements  21 ,  22  which delimit with the neighboring regions of the medium-side ring  15  the pressure chambers  23 ,  24 . The rounded tips  26 ,  27  of the pressure chambers  23 ,  24  at both ends of the section  20  are oriented toward each other. 
     The return conveying unit  18  and the rib  25  form a return conveying device  28 . Accordingly, about the circumference of the sealing lip  11  several such return conveying devices  28  are provided at a spacing behind each other. 
     In the region between neighboring return conveying devices  28 , a raised guiding rib  29  is provided which is provided at the inner side  14  of the sealing lip  11  and advantageously has the same height as the medium-side ring  15 . The guiding rib  29  extends in circumferential direction of the sealing lip  11  and widens in a direction away from its two ends. Advantageously, the guiding rib  29  is designed mirror symmetrical relative to its transverse center plane  30  ( FIG. 7 ). 
     Across its length, the guiding rib  29  has a spacing relative to the medium-side ring  15 . In accordance with the shape of the guiding rib  29 , the spacing relative to the ring  15  at half the length is smallest while it is greatest in the region of the two ends positioned in circumferential direction. 
     The two ends  31 ,  32  are positioned approximately at the level of the free ends of the return conveying elements  21 ,  22  of the neighboring conveying units  18 . The free ends of the return conveying elements  21 ,  22  have a minimal spacing relative to the ends  31 ,  32  of the guiding rib  29 . 
     One such guiding rib  29  is arranged between two neighboring return conveying devices  28 , respectively. It is formed by a projection of a ring  33  which is provided at the inner side  14  of the sealing lip  11  and extends coaxial to the medium-side ring  15 , wherein the projection is pointing toward the ring  15 . The return conveying devices  28  are arranged between the rings  15  and  33 . 
     Advantageously, several such rings  33  are provided which are coaxial to each other and advantageously have a minimal axial spacing relative to each other. Between the rings  33 , annular intermediate spaces  34  are thus formed which are coaxial to each other as well as to the medium-side ring  15  and advantageously have the same width. Of these rings  33 , only the ring  33  neighboring the medium-side ring  15  is provided with the guiding ribs  29 . 
     The rings  33  which are advantageously provided with a curved outer side  35  ensure the sealing function in the static state (when the shaft to be sealed is not rotating). 
     The rings  15  and  33 , the return conveying units  18 , and the guiding ribs  29  have preferably the same height ( FIG. 6 ). In this way, it is ensured that the medium side  19  can be sealed reliably by the ring  15 . Medium that may still have leaked through underneath the ring  15  is reliably returned by the return conveying devices  28  and the guiding ribs  29 . The rings  33  which in the installed position are resting sealingly against the shaft prevent that air is sucked in from the air side  13 . 
     In contrast to the rings  15  and  33 , the guiding rib  29  has a flat end face  36 . 
     Since the return conveying devices  28  and the guiding ribs  29 , when projected onto the drawing plane ( FIGS. 4 and 7 ), are symmetrical to the respective center plane  30 , they function optimally in both rotational directions. The medium which leaks underneath the sealing lip  11  is thus returned—independent of the rotational direction of the shaft—reliably to the medium side  19 . 
     The sections  20  to  22  as well as the rib  25  have across their length a constant axial width ( FIG. 4 ), respectively. In this way, a uniform return conveyance of the medium in both rotational directions of the shaft results. 
     The height of the sections  20  can be constant. It is moreover possible to configure these sections  20  such that their height increases continuously from both ends so that the sections  20  have their greatest height at half their length. 
     The medium-side ring  15  has a minimal spacing from the end face  16  of the sealing rib  11  (see  FIG. 8 ). In the installed position, the end face  16  is approximately positioned at a right angle to the top side of the shaft. Approximately at the level of the medium-side ring  15  at the top side of the sealing lip  11  a circumferentially extending projecting ring  37  is provided. It has advantageously a curved top side. In axial section ( FIG. 6 ), the ring  37  is configured to be approximately semi-circular. The ring  37  can contribute to a stability increase of the sealing lip  11 . 
     In the illustrated and described embodiment, the return conveying units  18  as well as the guiding rib  29  are embodied symmetrical to the transverse center plane  30 . In principle, it is however also possible to configure the return conveying devices  28 , in deviation from the illustrated preferred embodiment, to be asymmetric. Such a configuration is beneficial when the shaft to be sealed in use has a main rotational direction. In this case, the return conveying devices  28  and the guiding ribs  29  can be designed such that in this main rotational direction an optimal return conveying action is provided for the medium that has leaked through underneath the sealing lip  11 . When the shaft is then rotating in the other direction, the return conveying action of the asymmetrically configured to return conveying devices  28  and guiding ribs  29  is sufficient in this case. 
     In order to minimize possibly occurring noise, for example, in operation at very high rotational speeds, the length of the return conveying elements  21 ,  22  can also be varied. The radial shaft seal ring is therefore distinguished in use by excellent low-noise properties. The radial shaft seal ring is moreover constructively simple in its configuration and can be produced in an inexpensive way. 
     It is furthermore possible to arrange the return conveying devices  28  in circumferential direction of the sealing lip  11  such that they adjoin each other immediately and do not have, as in the illustrated embodiment, a minimal circumferential spacing from each other. 
     In use of the radial shaft seal ring, a hydrodynamic flow in the direction of the arrows indicated in  FIG. 4  is produced in the pressure chambers  23 ,  24  due to the medium to be sealed having leaked through underneath the ring  15 . Since the pressure chambers  23 ,  24  taper in flow direction, a pressure is generated in the pressure chambers  23 ,  24  that causes the ring  15  in the region of these pressure chambers  23 ,  24  to briefly lift off the shaft so that the medium to be sealed can flow from the pressure chambers  23 ,  24  across the ring  15  and back to the medium side  19 .  FIG. 4 a    shows this return conveying action of the medium side  19  in the region of the pressure chambers  23 ,  24 , illustrated by the flow arrows  38 . The flow arrows  39  indicate the leakage flow (loss flow) toward the air side  13 . 
     Due to the depression  20  the return conveyance of the medium (flow arrow  38 ) is not deflected or only deflected to a much lesser degree than the leakage flow (flow arrows  39 ). In comparison to conventional radial shaft seal rings, the leakage flow (arrows  39 ) can be significantly reduced as a result of the depression  20 . The medium which is exiting from the medium chamber  19  passes due to the shaft rotation into the pressure chambers  23 ,  24  and is conveyed by means of the described return conveying devices  28  back to the medium side  19 . The possibly occurring leakage flow  39  is kept at a minimum because the return conveyance (arrows  38 ) of the medium to the medium side  19  experiences no or only a very minimal flow change that is significantly smaller in comparison to that of the leakage flow (arrows  39 ). 
     Also, by widening the region  40  in comparison to the region  41  ( FIG. 4 a   ), it is possible to counteract the typical compression force distribution of concentric gaskets. This has the result that the leakage or loss flow (arrow  39 ) experiences a greater resistance than the return conveyance (flow arrow  38 ). 
     The widened portion  40  is provided at the transition from the return conveying elements  21 ,  22  into the depression  20 . The widened portion  41  is located at the transition from the ring  15  into the depression  20 . In regard to these two widened portions  40 ,  41 , reference is expressly being had to  FIG. 4 a    where these conditions are schematically illustrated. 
     The described radial shaft seal ring is characterized in that the sealing lip  11  at the medium-side rim is provided with a circumferentially extending ring  15  that comprises the sections  20  distributed uniformly about the circumference. They form so-called recesses oriented toward the air side  13 . Similar to alternating-rotation elements, the return conveying elements, in the form of the sections  21 ,  22  are centrally arranged relative to these recesses (sections  20 ). The sections  20  open approximately tangentially into the ring  15 . 
     The rear regions facing the air side  13  are provided with the rings  33  that serve for securing the static sealing action. At the ring  33  which is neighboring an d facing the medium-side ring  15 , the guiding ribs  29  are provided which form the projections arranged in distribution about the circumference. The number of these projections  29  corresponds to the number of depressions  20 . The depressions  20  and the projections  29  are provided alternatingly in the circumferential direction. 
     The projections  29  in the form of the guiding ribs ensure that the medium volume in the form of leakage flow (arrow  39 ), which has not been returned by the return conveying elements  21 ,  22 , is actively guided to the neighboring return conveying element. Due to this additional active conveying action of the medium volume to the return conveying elements, the return conveyance into the medium chamber is improved. 
     The medium-side ring  15  with the depressions  20  reduces the disruption of the flow direction of the medium to be sealed. Due to the inertia of the medium, the leakage (loss) flow is reduced. This is achieved inter alia in that the most narrow gap of the dual-convergent gap that is formed by the pressure chambers  23 ,  24 , viewed in radial direction, is positioned at the medium side  19 . 
     Moreover, the contact surface in the region of the calculated leakage (loss) flow is enlarged. In this way, it is made more difficult for a possibly present leaked medium to move across the return conveying elements in the direction toward the air side  13 . 
     The projections in the form of the guiding ribs  29 , provided at the ring  33  neighboring and facing the ring  15 , guide possible leakage or loss flows in a targeted and active way back to the return conveying elements  21 ,  22 . 
     The radial shaft sealing ring can be used in all fast rotating applications and alternating rotational directions of a shaft. The shaft to be sealed can have high rotational speeds as well as corresponding high circumferential speeds. Alternating rotational directions between the medium side  19  and the air side  13  are reliably sealed. A main field of application can be, for example, in electric vehicles for sealing a gear box input shaft. 
     In deviation from the illustrated embodiment, the radial shaft seal can also be configured such that it is integrated into a sealing flange, for example. In this case, the radial shaft seal requires no housing. For example, the sealing lip can be glued to the sealing flange, vulcanized thereto or connected in any other suitable way. 
     The specification incorporates by reference the entire disclosure of German priority document  10   2017   012   166 . 4  having a filing date of Dec. 22, 2017. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.