Electromagnetic actuation device and method for manufacturing an electromagnetic actuation device

Abstract

The invention relates to an electromagnetic actuating device having an electromagnetic coil (16) with a central recess (40) extending in the axial direction, a cylindrical pole tube (18) provided with a magnetic separation site (46) inserted into the central recess (40), an armature (20) movably arranged in the pole tube (18), wherein the armature (20) can be moved by actuating the electromagnetic coil (16), wherein the armature is supported in the pole tube (18) in a sleeve-shaped bearing film (36) inserted into the pole tube (18), wherein the bearing film (36) has an inner side (66) facing the armature (20) which serves as a sliding surface (85) and an outer side (68) facing the cylindrical pole tube (18). It is proposed that the bearing film (36) is coated at least on the inner side (66) with a first layer (87) made of a perfluoroalkoxy polymer. Furthermore, a production method for such an electromagnetic actuating device is proposed.

Description

BACKGROUND

[0001] Electromagnetic actuating devices are used, for example, in electromagnetically actuated hydraulic valves for the transmission clutch of a motor vehicle. In order to carry out these switching processes as smoothly as possible and imperceptibly for the driver, it is desirable to adjust the hydraulic pressure on the clutch with the highest pressure accuracy according to a predefined pressure ramp. The pressure required for this can be provided by means of hydraulic spool valves. These spool valves can be actuated by means of a pilot valve (pre-control) with an electromagnet or directly by means of an electromagnetic actuating device.

[0002] An electromagnetic actuating device is known, for example, from DE 10 2012 223 430 A1 and has, inter alia, an electromagnetic coil with a central recess extending in the axial direction, a cylindrical pole tube provided with a magnetic separation site inserted into the central recess, an armature movably arranged in the pole tube, and a force transmission element movably supported in the axial direction on the electromagnetic actuating device. The armature can be moved by actuating the electromagnetic coil in such a way that a force exerted by the armature can be transmitted to the force transmission element.

[0003] In electromagnetic actuating devices used in hydraulic valves, an electromagnetic force proportional to the coil current is generated with which the hydraulic valve is actuated. In order to achieve the required high pressure accuracy, the electromagnet should have a very precise force-current characteristic curve with a small variance in the force level. The scatter of the magnetic force level and the hysteresis of the force-current characteristic curve caused by friction can be limited to a minimum.

[0004] In order to achieve this, it is known to support the armature in the pole tube in a sleeve-shaped bearing film inserted into the pole tube, wherein the bearing film has an inner side facing the armature which serves as a sliding surface and an outer side facing the cylindrical pole tube, and the bearing film is at least partially made of a friction-reducing material. For example, DE 10 2006 055 796 A1 discloses an electromagnetic actuating device with a bearing film composed of a glass fiber fabric which can be impregnated with PTFE in a plurality of steps in an impregnation bath and coated on both sides with a PTFE dispersion and subsequently sintered. The use of a bearing film with a PTFE coating results in a small frictional force and thus a reproducible magnetic force for a specific armature position. Due to the small friction, a magnetic force-displacement characteristic curve is obtained on movement of the armature which has a very small hysteresis and a very small fluctuation of this hysteresis. SUMMARY

[0005] The invention relates to an electromagnetic actuating device having an electromagnetic coil with a central recess extending in axial direction, a cylindrical pole tube provided with a magnetic separation site, which is inserted into the central recess, an armature movably arranged in the pole tube, wherein the armature can be moved by actuating the electromagnetic coil, wherein the armature is supported in the pole tube in a sleeve-shaped bearing film inserted into the pole tube, wherein the bearing film has an inner side facing the armature, which serves as a sliding surface, and an outer side facing the cylindrical pole tube. According to the invention it is proposed that the bearing film is coated at least on the inner side with a first layer made of a perfluoroalkoxy polymer.

[0006] Furthermore, the invention also relates to a method for manufacturing such an electromagnetic actuating device having the following steps:

[0007] - providing an electromagnetic coil with a central recess extending in axial direction,

[0008] - inserting a cylindrical pole tube provided with a magnetic separation site into the central recess,

[0009] - manufacturing a sleeve-shaped bearing film, wherein the bearing film is transformed from a flat initial shape into a sleeve shape having an outer side and an inner side serving as a sliding surface,

[0010] - inserting the sleeve-shaped bearing film into the pole tube, wherein the bearing film faces the pole tube with the outer side, and

[0011] - inserting the armature into the pole tube in such a way that the inner side of the bearing film serving as a sliding surface faces the armature.

[0012] According to the invention it is proposed that, in the manufacturing step, before the transformation into the sleeve shape, the bearing film is coated on the side provided as the inner side of the subsequent sleeve shape with a first layer made of a perfluoroalkoxy polymer.

[0013] The magnetic force that can be exerted by an electromagnet increases with a reduction of the air gap in the magnetic circuit, i.e. with a reduction of the area in which the magnetic flux is not guided in a ferromagnetic material. The reluctance decreases with a reduction of the air gap. In an electromagnetic actuating device of the type mentioned in the opening paragraph, a reduction of the air gap present advantageously leads to a greater magnetic flux and thus also to a higher axial magnetic force, which the armature can exert on the actuating element. In order to achieve that the electromagnetic actuating device can exert a large force, it is therefore advantageous on the one hand to keep the total thickness of the bearing film as small as possible in order to design the gap between the inner wall of the pole tube and the armature as small as possible.

[0014] However, due to eccentricities occurring in practice between the armature and the pole tube, in addition to the axial magnetic force, a radially acting magnetic force perpendicular thereto can also occur, which is absorbed by the bearing film. The radially acting magnetic force causes the generation of friction and an adverse effect on the hysteresis of the magnetic force-displacement characteristic. If the total thickness of the bearing film is now reduced, the radial magnetic force is increased to the same extent in addition to the axial magnetic force, so that the bearing film is subjected to a greater load. There is the danger here that the bearing film is worn out at too high a radial magnetic force.

[0015] By coating the bearing film at least on the inner side with a first layer made of a perfluoroalkoxy polymer, it is advantageously achieved that the bearing film is wear-resistant even if the total thickness of the bearing film is advantageously reduced, wherein at the same time a high axial magnetic force of the electromagnetic actuator can be achieved.

[0016] By coating the sliding surface of the bearing film on the inner side with a perfluoroalkoxy polymer (short: PFA), the surface is modified there in such a way that it can advantageously withstand a higher bearing load. Perfluoroalkoxy polymer is a perfluoroplastic, in particular a copolymer consisting of tetrafluoroethylene and perfluoroalkoxy ethylene, like for example perfluoroalkoxy propylene.

[0017] Advantageously, the perfluoroalkoxy polymer can be thermoplastically processed. Compared to PTFE, the perfluoroalkoxy polymer has better anti-adhesive properties and higher chemical resistance. Although the perfluoroalkoxy polymer has a lower scratch resistance in principle than, for example, PTFE, the perfluoroalkoxy polymer can compensate for surface unevenness on the sliding surface of the bearing film due to the lighter processability, thereby resulting in an increased bearing surface between the armature and the bearing film and a smaller surface pressure. As a result, the wear resistance is significantly improved.

[0018] Advantageous embodiments and improvements of the application are achieved by the features contained in the dependent claims.

[0019] In order to reduce costs, it is sufficient at first to apply the coating with the perfluoroalkoxy polymer (PFA layer) to the bearing film only on one side, namely on the sliding surface facing the armature. The friction coefficient of PFA is slightly higher compared to PTFE, but the small difference in the friction coefficient is not important for the electromagnetic actuator described here. In addition, the sleeve-shaped bearing film can also be additionally coated on the outer side with a second layer made of a perfluoroalkoxy polymer in order to also increase the wear resistance there.

[0020] It can be provided with advantage that the sleeve-shaped bearing film has a glass-fiber fabric impregnated with PTFE as a carrier material, which is provided on the inner side and on the outer side with a PTFE layer, respectively, wherein at least onto the PTFE layer on the inner side a first layer made of a perfluoroalkoxy polymer is applied. The coating with the perfluoroalkoxy polymer is able to compensate unevennesses in the PTFE layer, so that the sliding surface of the bearing film facing the armature becomes smoother.

[0021] The first layer and / or the second layer made of a perfluoroalkoxy polymer can advantageously have a small layer thickness of less than 5 micrometers, so that the total thickness of the bearing film remains relatively small and the magnetic force can be increased. Advantageously, the total thickness of the bearing film can be between 25 micrometers and 75 micrometers.

[0022] The bearing film can be used in combination with a one-piece pole tube, the magnetic separation site of which is configured, for example, by a slot in the pole tube, or the bearing film can also be used in combination with a multi-piece pole tube, for which the magnetic separation site is configured by a separation ring between two pole tube segments. BRIEF DESCRIPTION OF DRAWINGS

[0023] A possible embodiment of the application is explained below with reference to the drawings. In the drawings, the following is shown:

[0024] Figure 1 A schematic cross section of an electromagnetic actuating device is shown;

[0025] Figure 2 A perspective view of a bearing film is shown;

[0026] Figure 3 A partial cross section through a bearing film is shown. DETAILED DESCRIPTION

[0027] Figure 1 An electromagnetic actuating device having the reference number 10 is shown. Such an electromagnetic actuating device 10 is used, for example, in the transmission technology in motor vehicles, in particular for controlling the clutches of an automatic transmission. To this end, for example, a hydraulic valve, which is indicated only schematically in Figure 1 by a block having the reference number 12, is actuated by the electromagnetic actuating device 10.

[0028] The electromagnetic actuation device 10 includes a coil 16 arranged around a cylindrical electrode 18. The coil 16 is composed of a winding element, which, exemplarily, comprises copper wire with a specific number of turns through which current flows when energized. This is controlled or regulated by a controller (not shown in the figures). The coil 16 and the controller are electrically connected to each other via an electrical contact element 38 by means of a connecting wire (also not shown). The coil 16 has a central recess 40 that extends axially along a central axis 44 and is inserted into the electrode 18. An armature 20 is slidably supported within the cylindrical electrode 18. Figure 1 On the left-hand first axial end region 21, an annular disk-shaped flux disk 22 is mounted on or connected to the electrode tube 18. In the electrode tube... Figure 1 On the second axial end region 23 on the right side, another magnetic flux disk 24 is fixed on the pole tube 18.

[0029] Near the first axial end region 21, a groove-shaped recess 42 extending in the circumferential direction exists on the outer surface of the electrode 18 formed by the outer peripheral surface. This groove-shaped recess serves as a magnetic separation portion 46. (As in...) Figure 1 As shown, the recess 42 may have a generally trapezoidal cross-section and be filled with an annular region 52 made of a non-magnetic material, which contacts the beveled edge 48 of the recess 42. In this case, the pole tube is constructed, for example, as a three-piece unit consisting of the annular region 52, on which a pole tube segment is connected on each opposite side. However, the pole tube 18 may also be constructed integrally with the recess 42, which is only introduced into the outer peripheral surface of the pole tube. The recess 42 affects the magnetic flux passing through the pole tube 18. The pole tube 18, in principle, combines a magnetic core for radially feeding the magnetic flux into the armature 20 with a pole core, which serves as a magnetic pole complementary to the armature. The recess 42 prevents magnetic short circuits. In the case of low coil current, the thus reduced cross-section of the magnetic iron in the recess or slot becomes saturated and thus functions similarly to the air gap between the magnetic core and the pole piece.

[0030] As in Figure 1 As can also be seen, a pressling 26 is pressed into the through axial recess 32 of the armature 20. A can-shaped sleeve 28 rests against the pressling 26. A force-transmitting element 30, configured as a push rod, is pressed into the sleeve 28. A guide ring 33 for the force-transmitting element 30 is pressed into a flux disk 22. This flux disk serves as a stop for the can-shaped sleeve 28. The force-transmitting element 30 then acts on the hydraulic valve 12. Alternatively, however, the armature 20 can also act directly on the hydraulic valve 12 without a force-transmitting element.

[0031] As described above, the armature 20 is slidably supported in the electrode tube 18. To improve support, a bearing diaphragm 36 is provided between the armature 20 and the inner surface 34 formed by the inner circumferential surface of the electrode tube 18, as will be explained in more detail later.

[0032] The electromagnetic actuator 10 operates in such a way that it generates an electromagnetic force based on the magnitude of the current flowing through the coil 16, which acts on the armature 20 and causes the armature to... Figure 1 The initial position on the right side of the middle moves to Figure 1 In the final position on the left. In this final position, the travel of armature 20 is limited by the contact of the can-shaped sleeve 28 with the guide ring 33. If the end coil 16 is energized, then armature 20 returns to the initial position (on the right) by, for example, a spring (not shown) tensioned between pole 18 and armature 20 and / or by the hydraulic pressure acting on the force transmission element 30 via hydraulic valve 12.

[0033] The bearing membrane 38 may, for example, comprise a glass fiber fabric coated with PTFE (polytetrafluoroethylene) on both sides. The initial shape of the membrane may be formed flat. Figure 3 An exemplary cross-section through the bearing membrane 36 is shown. A glass fiber fabric 80 is used as the carrier material. This glass fiber fabric is impregnated with PTFE in a bath, wherein a first PTFE layer 81 and a second PTFE layer 82 are formed on both sides of the glass fiber fabric. This process can be repeated multiple times until the bearing membrane 36 is sintered. After sintering, the surface of the bearing membrane 36 is coated with a first layer 87 made of a perfluoroalkoxy polymer on the side 84 of the inner side 66 of the bearing membrane 36, which is configured as a subsequent sleeve shape 64. The first layer 87 made of a perfluoroalkoxy polymer is here applied, for example, directly onto the first PTFE layer 81. The thickness of the first layer 87 is preferably less than 5 micrometers. Alternatively, as... Figure 3 As shown, the bearing film 36 may have a second layer 88 made of a perfluoroalkoxy polymer coated on the opposite side 83, which is applied to the second PTFE layer 82.

[0034] Manufacturing the bearing diaphragm from a carrier material comprising a PTFE-coated glass fiber fabric is considered an advantageous embodiment of the invention. However, another carrier material may also be used, which has a first layer made of a perfluoroalkoxy polymer coated on the inner side of the subsequent sleeve shape.

[0035] Finally, the bearing film 36, if necessary, is rolled after cutting. Figure 2The sleeve shape 64 has an outer diameter 72 and an inner diameter 74 as well as an axial length 70. The total thickness 56 of the bearing film 36, i.e. half the difference between the outer diameter 72 and the inner diameter 74, can preferably be between 25 and 75 micrometers. The mutually facing ends of the bearing film 36 form a butt joint 58. The sleeve shape 64 has an open first end side 60, an open second end side 62 as well as an inner side 66 and an outer side 68. A first layer 87 made of perfluoroalkoxy polymer is located on the inner side 66 of the sleeve-shaped bearing film 36 after the manufacture of the sleeve shape 64. An optionally provided second layer 88 made of perfluoroalkoxy polymer is located on the outer side 68 of the bearing film 36.

[0036] Finally, the sleeve-shaped bearing film 36 is pushed into the pole tube 18. The axial length 70 of the bearing film 36 can be shorter than the axial length of the inner recess of the pole tube 18. After the insertion of the bearing film 36, the outer side 68 of the bearing film 36 faces and rests against the inner side 34 of the pole tube 18 or rather of the pole tube. The bearing film 36 in the sleeve shape can have a certain stress after the insertion, which presses the outer side 68 against the inner side 34 of the pole tube.

[0037] Finally, the armature 20 can be pushed into the pole tube, wherein the inner side 66 of the bearing film 36, which serves as a sliding surface 85, faces the armature 20.

Claims

1. Electromagnetic actuating device having an electromagnetic coil (16) with a central recess (40) extending in axial direction, a cylindrical pole tube (18) provided with a magnetic separation site (46) inserted into the central recess (40), an armature (20) movably arranged in the pole tube (18), wherein the armature (20) can be moved by actuating the electromagnetic coil (16), wherein the armature is supported in the pole tube (18) in a sleeve-shaped bearing film (36) inserted into the pole tube (18), wherein the bearing film (36) has an inner side (66) facing the armature (20) which serves as a sliding surface (85) and an outer side (68) facing the cylindrical pole tube (18), characterized in that, The bearing film (36) is coated on at least the inner side (66) with a first layer (87) made of perfluoroalkoxy polymer, wherein the sleeve-shaped bearing film (36) has a glass-fiber fabric (80) impregnated with PTFE as a carrier material, which is provided on the inner side (66) and the outer side (68) with a PTFE layer (81, 82), respectively, wherein at least to the PTFE layer (81) on the inner side (66) a first layer (87) made of perfluoroalkoxy polymer is applied, wherein the first layer (87) made of perfluoroalkoxy polymer has a layer thickness of less than 5 micrometers.

2. The electromagnetic actuation device of claim 1, wherein, The sleeve-shaped bearing film (36) is additionally coated on the outer side (68) with a second layer (88) made of perfluoroalkoxy polymer.

3. The electromagnetic actuation device of claim 2, wherein, The second layer (88) made of perfluoroalkoxy polymer has a layer thickness of less than 5 micrometers.

4. Electromagnetic actuation device according to any of the preceding claims, characterized in that The pole tube (18) is configured in one piece or in multiple pieces.

5. Electromagnetic actuation device according to any of the preceding claims, characterized in that The total thickness (56) of the bearing film (36) is between 25 micrometers and 75 micrometers.

6. Electromagnetic actuation device according to any of the preceding claims, characterized in that The electromagnetic actuating device (1) has a force transmission element (30) which is movable along an axial direction, wherein a force applied by the armature (20) can be transmitted to the force transmission element (30).

7. A method for manufacturing an electromagnetic actuating device according to any one of claims 1 to 6, having the following steps: - providing an electromagnetic coil (16) having a central recess (40) extending along an axial direction, - inserting a cylindrical pole tube (18) provided with a magnetic separation site (46) into the central recess (40), - manufacturing a sleeve-shaped bearing film (36), wherein - transforming the bearing film (36) from a flat initial shape into a sleeve shape (64) having an outer side (68) and an inner side (66) serving as a sliding surface (85), - inserting a sleeve-shaped bearing film (36) into the pole tube (18), wherein the bearing film (36) faces with the outer side (68) towards the pole tube (18), - inserting the armature (20) into the pole tube (18) in such a way that the inner side (66) of the bearing film (36) serving as a sliding surface (85) faces towards the armature (20), characterized in that, in the manufacturing step, before the transformation into the sleeve shape (64), the bearing film (36) is coated on a side (84) provided as the inner side (66) of the subsequent sleeve shape (64) with a first layer (87) made of perfluoroalkoxy polymer.

8. The method of claim 7, wherein, The bearing film (36) is additionally coated on a side (83) provided as the outer side (68) of the subsequent sleeve shape (64) with a second layer (88) made of perfluoroalkoxy polymer.

9. The method of any one of claims 7-8, wherein, The bearing film (36) has a glass-fiber fabric (80) impregnated with PTFE as a carrier material, which has a PTFE layer (81) on each of two mutually facing sides (83, 84), wherein at least the PTFE layer (81) is coated on the side (84) arranged as an inner side (66) of the subsequent sleeve shape (64) with a first layer (87) made of perfluoroalkoxy polymer.

10. The method according to any one of claims 7 to 9, characterized in that, The PTFE layer (82) is coated on the side (83) arranged as an outer side (68) of the subsequent sleeve shape (64) with a second layer (88) made of perfluoroalkoxy polymer.

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