Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L1/00—Valve-gear or valve arrangements, e.g. lift-valve gear
  • F01L1/02—Valve drive
  • F01L1/04—Valve drive by means of cams, camshafts, cam discs, eccentrics or the like
  • F01L1/047—Camshafts
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L1/00—Valve-gear or valve arrangements, e.g. lift-valve gear
  • F01L1/34—Valve-gear or valve arrangements, e.g. lift-valve gear characterised by the provision of means for changing the timing of the valves without changing the duration of opening and without affecting the magnitude of the valve lift
  • F01L1/344—Valve-gear or valve arrangements, e.g. lift-valve gear characterised by the provision of means for changing the timing of the valves without changing the duration of opening and without affecting the magnitude of the valve lift changing the angular relationship between crankshaft and camshaft, e.g. using helicoidal gear
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L13/00—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations
  • F01L13/0015—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for optimising engine performances by modifying valve lift according to various working parameters, e.g. rotational speed, load, torque
  • F01L13/0036—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for optimising engine performances by modifying valve lift according to various working parameters, e.g. rotational speed, load, torque the valves being driven by two or more cams with different shape, size or timing or a single cam profiled in axial and radial direction
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L1/00—Valve-gear or valve arrangements, e.g. lift-valve gear
  • F01L1/02—Valve drive
  • F01L1/04—Valve drive by means of cams, camshafts, cam discs, eccentrics or the like
  • F01L1/047—Camshafts
  • F01L2001/0471—Assembled camshafts
  • F01L2001/0473—Composite camshafts, e.g. with cams or cam sleeve being able to move relative to the inner camshaft or a cam adjusting rod

Definitions

• the invention relates to a camshaft arrangement for a drive, in particular for a motor vehicle engine.
• the camshaft arrangement comprises two shafts arranged coaxially with one another, a hollow outer shaft and an inner shaft being arranged rotatable relative to one another. Both shafts each carry a plurality of cams, wherein the outer shaft cams carried by the outer shaft are non-rotatably mounted on the outer shaft, while the inner shaft cams carried by the inner shaft are non-rotatably mounted on the inner shaft. If the inner shaft and outer shaft are rotated against each other, an adjustment of the cams to each other.
• Such adjustable camshaft arrangements are increasingly used in valve-controlled internal combustion engines for selectively influencing the control times of the valves of the engine in terms of power and torque development, fuel consumption and exhaust emission application.
• These camshaft arrangements are, for example, built-up camshaft systems with an outer shaft and an inner shaft arranged coaxially therein. The two shafts are rotatable relative to each other by means of an adjusting device. On the outer shaft alternately fixed to the outer shaft and connected to the outer shaft rotatably mounted cam elements are arranged. The rotatably mounted cam elements are fixedly attached to the inner shaft, but rotatable by a defined circumferential angle relative to the outer shaft.
• the inner shaft cam elements are connected via a connecting element fixed to the inner shaft, said connecting element projects with clearance through a recess in the outer shaft, which allows the rotation of the inner shaft and thus the inner shaft cam to the defined circumferential angle ,
• the rotation of the inner shaft to the outer shaft for example, by means of a Phaser, which allows an adjustment of the outer shaft fixedly connected to the outer shaft cam to the inner shaft fixedly connected inner shaft cam or vice versa, so as to achieve a phase shift of the valve timing.
• these cams and the inner shaft usually have bores in which corresponding connecting elements are introduced. These can be pins, bolts or screws.
• the cam elements can be designed accordingly to allow the insertion of a connecting element.
• German Patent Application DE 197 57 504 A1 discloses a camshaft with such a connecting element in the form of a cylindrical pin.
• the cylinder pin is press-fitted into a through hole in the inner shaft and with a clearance fit in the associated cam.
• the cam has for this purpose an outwardly cylindrical region in which there is a bore, in which the cylinder pin is introduced. Through the cylindrical portion, the bore should be routed away from the contact surface of the cam so as to achieve a continuous contact surface of the cam with the outer shaft.
• German Patent Application DE 10 2005 004 976 A1 discloses a camshaft with cams rotatable relative to one another, in which a connecting element is designed in two parts.
• a first part of the connecting element is hollow and protrudes into a radial bore in the inner shaft.
• a second connecting part is inserted from the other side into the hollow first connecting part so that it widens and a tight fit is produced.
• the two connecting parts can also be designed, for example, as a screw with a complementary threaded bore.
• European Patent EP 1 362 986 B1 is the mounting of an adjustable camshaft assembly in which a hollow coupling pin with a tight fit is guided into a bore in both the inner and outer shaft and in a cam. The outer diameter of the coupling pin is then enlarged by inserting an inner pin to make a press fit.
• German patent DE 28 22 147 C3 further discloses a camshaft assembly in which the connection between the inner shaft and cam via a driver, which is fastened with a screw on the inner shaft.
• the outer shaft has a recess for the passage of the driver.
• the driver further protrudes into an inner groove, which is located at the joint diameter of the associated cam. The cam is pushed with the groove from the side on the driver and secured on the right and left with rings in its axial position.
• connection between the inner shaft cam and the inner shaft is designed as a fixed connection due to the camshaft alternating load
• a press fit of the connecting elements used in both cam and in the inner shaft is expediently used.
• This has the disadvantage, in particular in the case of the known connecting elements with a constant cross section, that the cross section of the connecting element required for achieving the interference fit must be joined over a plurality of component bores in the cam and inner shaft.
• an undefined influence on the press coverage and thus the safety of the press connection occur.
• such joint connections may not have sufficient bond strength.
• the object of the invention is therefore to provide a built camshaft assembly which is easy to add and provides a secure and sufficient strength having connection between the inner shaft and inner shaft cam.
• camshaft assembly having the features of the independent claim 1.
• Advantageous developments of the camshaft arrangement will be apparent from the subclaims 2-17.
• the camshaft assembly according to the preamble of claim 1 is characterized according to the invention in that the respective connecting element is inserted into a receptacle in the inner shaft such that a part of the connecting element protrudes from the receptacle, and that the protruding part is at least partially introduced into a recess , which is located at the joint diameter of the respective inner shaft cam.
• this recess is open towards at least one end face of the inner shaft cam, and the projecting part has at least two opposite side surfaces, which bear tightly against two corresponding inner surfaces of the recess of the respective inner shaft cam.
• the connecting element is a feather key
• the receptacle in the inner shaft is formed as a keyway recording.
• the connecting element has a shaft and a head part, wherein the shaft is introduced into a receptacle in the inner shaft, while the head part at least partially introduced into a recess which is located at the joint diameter of the respective inner shaft cam.
• this recess is open towards at least one end face of the inner-shaft cam
• the head part has at least two opposite side surfaces, which bear tightly against two corresponding inner surfaces of the recess of the respective inner shaft cam.
• the connecting element may have a shaft and a head part, wherein the shaft is introduced with a tight fit in the receptacle, while the head part is at least a part of the protruding part of the connecting element.
• the Kppfteil of the connecting element is completely outside the outer shaft.
• a can Head part only partially in the recess in the respective inner shaft cam and partially in the recess in the outer shaft.
• the head part can also be partially located in the receptacle in the inner shaft, extend through the recess in the outer shaft and then protrude into the recess in the inner shaft cam.
• the inner shaft may have as receiving a stepped bore into which the head part of the connecting element partially protrudes, while the lower portion of the bore receives the shank of the connecting element.
• This stepped bore is designed, for example, as a stepped cylindrical bore with two diameters. The larger, outer diameter accommodates a part of the head part of the connecting element.
• the section of the head part arranged in this widened part of the stepped bore is adapted to the diameter of the widened area of the stepped bore so that a cylindrical head part has a larger cross section in this area.
• a stepped bore can be provided as a receptacle in the inner shaft and a stepped recess.
• this stepped recess has a cylindrical portion in which the shank of the interference fit member is disposed and a non-cylindrical portion which receives the non-cylindrical head portion. Due to the non-cylindrical shape is advantageously achieved that a positionally accurate alignment of the head part is made possible relative to the longitudinal axis of the camshaft assembly, so that the inner shaft cam can be added exactly in the correct desired position.
• the shaft of the connecting element can be cylindrical and easily inserted into the cylindrical portion of the stepped recess.
• the shaft of the connecting element can extend through the body of the inner shaft through into a second recess in the outer shaft.
• An inner shaft cam can also be connected to the inner shaft by two opposing connecting elements in such a way that torque transmission is ensured.
• the shafts of two connecting elements can be introduced into a common receptacle in the inner shaft.
• the recess for the passage of the Vietnamesesele- element through the outer shaft extends over part of the circumference of the outer shaft, that a movement of the connecting element and thus the inner shaft relative to the outer shaft by an adjustment angle ⁇ is possible.
• the head part of a connecting element may be formed at right angles to the shaft part of the connecting element. Further, the two side surfaces of the head portion and the two inner surfaces of the recess may each be parallel or conical to each other to facilitate the insertion of the connecting part into the recess or the sliding of the inner shaft cam on the head part and to produce a press fit.
• the two side surfaces of the head part and / or the two inner surfaces of the recess in the inner shaft cam may also have a profiled surface.
• the recess in the inner shaft cam can be designed as a groove extending over the entire width of the inner shaft cam.
• this recess is preferably located centrally below the elevation of the inner shaft cam, and the connecting element is preferably formed as a one-piece component.
• the entire cam width, ie, the cam thickness in the axial direction, of the inner shaft cam can be utilized for the formation of the press fit between key and inner shaft cam, whereby a particularly large joint surface for the formation of the press connection between inner shaft cam and connecting element is provided becomes.
• This causes a particularly strong connection, which in turn the radial height of the inner shaft cam can be minimized, allowing a space and weight savings.
• This embodiment of the camshaft arrangement according to the invention with feather key can thus be used particularly advantageously for smaller car camshafts.
• Another advantage of the invention and in particular the second embodiment of the camshaft assembly according to the invention is that the cross section of the connecting element for the required tight fit of the connection between the connecting element and inner shaft or between the connecting element and inner shaft cam does not have to be joined over the entire connecting element. Rather, a tight fit for the connection between the connecting element and inner shaft cam is added over the cross section of the shank for the connection between the connecting element and inner shaft and separated from it via the side surfaces of the head part. This leads to an increased safety of the respective fixed seats.
• an inner shaft cam is easy to connect to the inner shaft by first the connecting element is introduced into the inner shaft and then the inner shaft cam is pushed from the side on the head part of the connecting element.
• FIG. 1 shows an embodiment of the camshaft assembly according to the invention with a connecting element
• Fig. 2 shows an embodiment of the camshaft assembly according to the invention in longitudinal section
• FIG. 3 shows a longitudinal section through a camshaft arrangement according to FIG. 2 with a mounted connecting element before the assembly of an inner shaft cam element;
• FIG. 4 shows a cross section through an embodiment of the inventive camshaft arrangement with a continuous connecting element
• FIG. 5 shows a cross section through an exemplary embodiment of the camshaft arrangement according to the invention with a short connecting element
• FIG. 6 shows a cross section through an exemplary embodiment of the camshaft arrangement according to the invention with two connecting elements
• FIG. 7 shows a cross section through an exemplary embodiment of the camshaft arrangement according to the invention, in which a rotation of the inner shaft to the outer shaft has taken place;
• FIG. 8 shows a cross section through an exemplary embodiment of the camshaft arrangement according to the invention with a region of the head part of the connecting element within the recess in the outer shaft;
• FIG. 9 shows an exemplary embodiment of the camshaft arrangement according to the invention with a feather key; and 10 shows a cross section through an exemplary embodiment of the camshaft arrangement according to the invention with feather key.
• FIG. 1 an embodiment of a generic camshaft assembly 10 is shown schematically, in which an inner shaft 30 is disposed coaxially in an outer shaft 20, wherein the shaft body are shown shortened.
• the two shafts are rotatably supported by bearings, also not shown to each other.
• the adjustment of the two shafts to each other by a twist angle ⁇ can be done for example by an adjusting device, also not shown in the form of a phase adjuster.
• the inner shaft can be designed as a solid or hollow shaft, wherein in the embodiment of Figures 1-8, a solid shaft has been selected.
• outer shaft cam 21 On the outer surface of the outer shaft 20 a plurality of outer shaft cam 21 are non-rotatably mounted.
• the attachment of these external shaft cam elements can be done in a known manner, for example by shrinking, wherein a press fit is generated.
• the joint diameter of the cam is selected such that it is smaller than the outer diameter of the outer shaft at ambient temperature by a certain "overlap.”
• the cam element When the cam element is heated, the inner diameter widens and the cam element can be threaded onto the outer shaft and positioned
• the surface of the outer shaft in the area of the cam is previously processed or treated, for example, a profiling can be provided, and the outer shaft can additionally be cooled so as to reduce the diameter of the outer shaft
• Intermediate elements such as bushes may optionally be provided between the outer shaft and the respective cam element When the cam element cools, the cam is shrunk onto the shaft, the overlap preventing the cam from moving on the outer shaft.
• any suitable method can be used for the rotationally fixed attachment of the cam 21 on the outer shaft 20.
• the outer shaft cams on the outer shaft to be welded, or in the areas in which the cams are to be attached, are created by rolling tools tools produced by material displacement beads or webs.
• the cams are provided for example with a chamfered inner recess and are pushed with this recess over the beads. These are thereby deformed in the outer region and thus squeezed into the recess, whereby the cam is positively and non-positively held on the outer shaft.
• the outer shaft 20 also carries a plurality of inner shaft cam 31, which are rotatably mounted on the outer shaft, but rotatably connected to the inner shaft 30. Between the inner diameter of the inner shaft cam members 31 and the outer diameter of the outer shaft 20 thus a clearance is provided to allow rotation of the inner shaft cam 31 about the longitudinal axis of the camshaft assembly.
• the inner shaft cams 31 are fixedly connected via a pin-shaped connecting element with the inner shaft 30, as shown schematically in Fig. 1.
• the connecting element preferably comprises a shaft 41 and a head part 42.
• the shaft 41 of the connecting element is press-fitted into a bore in the inner shaft 30, while the head part is press-fitted into a groove in the inner shaft cam element 31.
• Between the bore and the shaft 41, or between the groove and the head part 42 is a corresponding dimensional overlap in order to ensure a tight fit.
• the shape of the head part 42 is adapted to the shape of the groove 32 and vice versa. Both fixed seats are independent of each other.
• Fig. 2 shows a longitudinal section through an embodiment of the camshaft assembly according to the invention with a continuous connecting element 40.
• the connecting element of the shaft 41 and the head part 42 is preferably formed in one piece.
• a shaft part 41 and a head part 42 can also be joined together to form a two-piece connecting element.
• This connection can be made for example via a screw or pin connection.
• the shaft 41 may be a circular, rectangular or other geometric shaft have cross-section, which is adapted to the cross section of the associated receptacle in the inner shaft 30.
• a round shaft cross-section for example, has the advantage that the shaft 41 and the associated bore 37 in the inner shaft 30 can be made simpler than with other shaft cross-sections.
• the head part 42 is preferably formed at right angles to the shaft 41 and may for example be cuboid.
• the connecting element 40 is thus preferably enlarged by the head part upwards.
• the head part is smaller than the shaft and, for example, mounted as a cuboid on the upper surface of a pin.
• the head part 42 always has at least two side surfaces 43 and 44 (see Fig. 5), which run parallel or conical to each other. These side surfaces 43 and 44 of the head part 42 may have a profiling.
• the side surfaces 43 and 44 of the head portion 42 of the connecting member 40 are tightly engaged with the inner surfaces 34 and 35 of the groove 32 so as to make a firm connection (see Fig. 5).
• the shank 41 has a round cross section, while the head part 42 formed at right angles to this pin is cuboid and sits on the shank end.
• the shaft 41 of the connecting element 40 is inserted in the assembled state of the assembled camshaft assembly 10 in a preferably radial receptacle 37 in the inner shaft 30.
• This receptacle 37 is, for example, a round bore, which is introduced radially into the material of the inner shaft 30.
• the round shaft 41 of the connecting element 40 is preferably inserted into this bore 37 with an interference fit.
• a recess 50 is provided in the outer shaft 20 in order to prevent a protrusion of the connecting element 40 from the inner shaft 30 to the inner shaft 30.
• the connecting element 40 is guided through the recess 50 and the head part 42 of the connecting element is introduced into a recess 32 at the joint diameter of the inner-two-cam 31.
• the recess 32 is preferably a groove which extends in the direction of the axis of the camshaft assembly 10 and is open towards at least one end face of the inner shaft cam 31.
• a through-groove 32 which is easier to manufacture and has two parallel or conically tapering inner surfaces 34 and 35 is provided. These inner surfaces, like the side surfaces of the head part 42 of the connecting element 40, can be profiled.
• FIGS. 4-8 show that the groove 32 is preferably located centrally below the elevation 36 of the cam 31. However, it can also be arranged offset to this, if the material thickness of the cocoon allows it.
• the shaft 41 is inserted in each case a connecting element 40 with tight fit in the associated bore 37 in the inner shaft.
• the associated head part 42 is aligned in the direction of the camshaft axis in such a way that an inner shaft cam 31 is threaded onto the outer shaft 20 and pushed with its groove 32 from the side to the protruding over the outer shaft 20 head portion 42 and press fit into the groove 32nd can be joined.
• This is shown in Fig. 3, wherein the mechanical joining operation can be supplemented by conventional joining methods such as shrinking. If the side surfaces 43 and 44 of the head part 42 and the inner surfaces 34 and 35 of the groove 32 taper conically, the inner shaft cam 31 is pushed over the head part so that the shape of the head part 40 is congruent with the shape of the groove 32.
• the connecting element 40 is a continuous component which protrudes through a through-bore in the inner shaft 30 and into a second recess 50 'in the outer shaft.
• the two recesses 50 and 50 'in the outer shaft 20 a rotation of the inner shaft 30 within the Enable external shaft.
• the recesses 50 and 50 ' limit a maximum possible angle of rotation ⁇ of the inner shaft 30 to the outer shaft 20 and vice versa.
• the connecting element 40 does not protrude through a through hole in the inner shaft 30 through into a recess 50 in the outer shaft 20, but it is a shorter connecting pin which is inserted into a blind hole. In this case, only one recess 50 in the outer shaft 20 is required for a rotation of the inner shaft 30 to the outer shaft 20.
• the connecting element 40 can have any length and in a further exemplary embodiment, for example, also completely extend through the inner shaft 30, but not into the outer shaft 20.
• FIG. 6 another embodiment of the invention is shown, in which two connecting elements 40 and 40 'are used, which are inserted from opposite sides into a through hole 37 in the inner shaft 30.
• the inner shaft cam member 31 has two likewise opposite grooves 32 and 33, in which the head parts of the two connecting elements are pushed.
• two recesses 50 and 50 'are provided in which the two connecting elements can be moved with rotation of the inner shaft to the outer shaft with play.
• an inner shaft cam element has a sufficient hub wall thickness in the base circle region.
• the head part of the connecting element protrudes below the cam lobe 36 further into the material of the inner shaft cam 31 as the head part of the opposite connecting element.
• FIG. 7 shows a camshaft arrangement in which a rotation of the inner shaft 30 relative to the outer shaft 20 has taken place.
• the connecting members 40 and 40 'of the associated inner shaft cam 31 is taken so that it rotates about the outer shaft 20 on which it is mounted with play.
• the underside of the head part can be adapted to the outer contour of the outer shaft 20 and, for example, slightly curved concave executed.
• the head part 42 of a connecting element 40 is not completely outside the outer shaft, but is partially disposed in the recess 50 or 50 'within the outer shaft.
• This embodiment has, for example, the advantage that no defined clearance between the underside of the head part and the outer surface of the outer shaft has to be set.
• the connecting element 40 (and / or 40 ') only has to be introduced into the inner shaft so far that the groove 32 of an inner shaft cam element 31 can be joined over the region of the head part which protrudes from the outer shaft.
• This embodiment can be chosen for any forms of connecting elements and is not limited to the embodiment shown in Fig. 8 with two opposing connecting elements.
• the bore 37 shown in Fig. 8 can also be designed as a single-sided or double stepped bore, and the head part can partially protrude into the stepped bore. However, this embodiment is not shown in FIG. 8.
• a connecting element can also be formed by a continuous connecting pin with a quadrangular cross-section, the cross-sectional shape of which does not change over the length.
• the pin has a lower shaft region, which is introduced into a recess in the inner shaft 30.
• the dimensions of the upper head area are chosen so that the groove 32 of an inner shaft cam 31 can be pushed from the side over the head area.
• Between two opposite inner surfaces of the groove and the corresponding side surfaces of the head Rich of the connecting pin is also set a tight fit, which can be ensured by a suitable dimensional overlap between the groove of the inner shaft cam and the head area.
• the side surfaces of the connecting element in the head region can be provided with a profiling in order to improve the tight fit with the inner shaft cam element 31.
• a connecting element of a shaft and a rectangularly shaped head portion may be more advantageous, since the shape and dimensions of the shaft can be chosen so that it can be easily introduced into a recess in the inner shaft, while the shape and the dimensions of the head part can be adapted to the requirements for receiving in the groove of an inner shaft cam.
• another shape may be advantageous for the shaft than for the head part of a connecting element.
• FIGS. 9 and 10 A further embodiment of the invention is shown in FIGS. 9 and 10, in which a connecting element is designed as a feather key 60, which is introduced into a keyway in the inner shaft 30.
• the side surfaces of the key 60 are also tight against the lateral inner surfaces of the groove 32 in the inner shaft cam 31 at.
• the key 60 extends at least over the entire length of the groove 32.
• the side surfaces of the key can be parallel or conical to each other. Furthermore, these side surfaces of the key 60 can be made profiled.
• a further key 61 may be provided, which is introduced into a second keyway 37 'in the inner shaft, as shown in Fig. 10.
• both feather keys are designed differently, so that the feather key 60 below the elevation 36 of the inner shaft cam 31 is higher than the opposite feather key 61.
• the groove 37 ' is made flatter on the opposite side and the feather key 61 projects to a lesser extent into the material of the inner shaft cam 31.
• the recess 32 in the inner shaft cam 31 may be provided with Abstützsteüen, which limit a radial movement of the respective connecting element, if such a radial movement occurs undesirable.
• Abstützsteüen which limit a radial movement of the respective connecting element, if such a radial movement occurs undesirable.
• these support points can also be located on the upper side of the respective connecting element

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Valve-Gear Or Valve Arrangements (AREA)
• Valve Device For Special Equipments (AREA)
• Gears, Cams (AREA)

Applications Claiming Priority (2)

Publications (2)

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Family Applications (1)

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Cited By (1)

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• 2008
  • 2008-05-29 DE DE102008025781A patent/DE102008025781A1/de not_active Withdrawn
• 2009
  • 2009-05-04 WO PCT/EP2009/003173 patent/WO2009143950A1/fr active Application Filing
  • 2009-05-04 CN CN200980119728.3A patent/CN102046930B/zh active Active
  • 2009-05-04 EP EP09753605A patent/EP2286067B1/fr active Active
  • 2009-05-04 AT AT09753605T patent/ATE528486T1/de active
  • 2009-05-04 US US12/994,651 patent/US8495980B2/en not_active Expired - Fee Related

Non-Patent Citations (1)

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