Magnetic switch for a vehicle starter

Abstract

A magnetic switch (1) for a vehicle starter comprises at least one coil (2, 3) and a channel (4) extending through the at least one coil (2, 3) in the axial direction (5). A housing (7) made of a ferromagnetic material surrounds the at least one coil (2, 3) in the radial direction, and the housing (7) comprises a first radially extending side wall (8) having an axially extending opening (9) with an inner diameter D1. A piston (10) extends through the axially extending opening (9) at least partially into the channel (4) and is arranged to be displaceable in the axial direction (5) between a first passive position, in which the switch (1) is open and the at least one coil is not energized, and a second position in which the switch (1) is closed.The piston (10) comprises a first piston section (11) and a second piston section (12) arranged axially adjacent to the first piston section (11). In the switch-closed position, the first piston section (11) extends at least partially within the axially extending opening (9) of the housing (7). In the first passive position, the second piston section (12) extends axially over the length of the axially extending opening (9) of the housing into the channel (4) in the region of the at least one coil (2, 3), and the maximum outer diameter D3 of the second piston section (12) is smaller than the maximum outer diameter D2 of the first piston section (11).

Description

TECHNICAL FIELDThis invention relates to a solenoid switch for a vehicle starter.GENERAL STATE OF THE ARTAn engine starting device is known, for example, from US20120068796A1. The starter includes a "soft start" engine-on system. The purpose of a soft start engine-on system is that the pinion of the starter engages the ring gear of the engine before full electrical power is applied to the starter motor. An electromagnet serves to axially move the pinion to engage the ring gear. When the pinion abuts the ring gear during this engagement, a small torque provided by the electric motor rotates the pinion and allows it to properly engage the ring gear before a high current is applied. A high current is applied to the electric motor only when the gears are properly meshed, so that damage to the meshed gears can be prevented.To provide the soft start, the magnet of the starter may be provided with two coils, a pull-in coil and a holding coil. In operation of a starter motor, when the ignition key is turned, the pull-in coil and the holding coil are energized. The current flowing through the pull-in coil reaches the electric motor, so that the electric motor rotates the pinion with low torque. At the same time, the energized coils exert a force on the piston of the magnet, so that the latter is moved axially. The axial movement of the magnetic piston actuates a shift lever which displaces the pinion in the direction of the ring gear. When the magnetic plunger abuts a stopper, electrical contact is made between two terminals to allow a high current to flow to the motor. By closing the connection contacts, the draw-in coil is short-circuited, so that it no longer exerts any force on the plunger and the position of the plunger is held solely by the holding coil. This is done in order to avoid excessive heat generation in the low-impedance feed coil and in order to efficiently supply the electric motor with power. Once the motor starts, the current direction in the pull-in coil reverses and the electromagnetic forces generated in the holding coil and the pull-in coil cancel each other out, so that the pinion is decoupled from the ring gear by the force of a return spring in the magnet.SUMMARY OF THE INVENTIONThe magnet according to the invention as claimed in claim 1 has the advantage that the retraction force is reduced in order to prevent component damage when the pinion engages in the ring gears, while at the same time reducing the risk of damage to the magnet.According to the invention, a magnetic switch for a vehicle starter comprises:at least one coil and a channel extending through the at least one coil in the axial direction,a housing made of a ferromagnetic material, which surrounds the at least one coil in the radial direction,wherein the housing comprises a first radially extending side wall having an axially extending opening with an inner diameter D 1,a piston which extends at least partially into the channel through the axially running opening and is arranged to be displaceable in the axial direction between a first passive position, in which the switch is open and the at least one coil is not energized, and a second position, in which the switch is closed,wherein the piston comprises a first piston portion and a second piston portion arranged axially adjacent to the first piston portion,wherein the first piston portion extends at least partially within the axially extending opening of the housing in the switch-closed position,wherein the second piston portion extends axially over the length of the axially extending opening of the housing into the channel in the region of the at least one coil in the first passive position,wherein the first piston portion has a maximum outer diameter D 2,wherein the second piston portion has a maximum outer diameter D 3,wherein the maximum outer diameter D3 of the second piston portion is smaller than the maximum outer diameter D2 of the first piston portion.The axial direction is the direction of movement of the piston, and the radial direction is radial to the axial direction. The region of the at least one coil is the region in the radial and axial direction within the coil or a coil holder around which the coils are wound.It would be possible to reduce the draw-in force by simply reducing the number of turns of the draw-in coil, but to do so the number of turns of the holding coil would have to be reduced, since the holding coil and the draw-in coil must be matched to one another in order to make it possible to disengage the pinion and the ring gear after starting the vehicle. However, the holding coil requires a certain number of turns in order to generate sufficient holding force. With the same number of turns of the draw-in coil, the invention achieves a reduction in the draw-in force by increasing the gap between the piston and the inner diameter of the opening in the radially extending side wall of the ferromagnetic housing when the piston is in the passive position. The passive position is the position that the piston assumes when the coils are not energized. This air gap resists magnetic flux and weakens the magnetic field, so that the force applied to the ferromagnetic piston decreases. Since the maximum diameter D 3 of the second piston section is smaller than the maximum outer diameter D 2 of the first piston section and the second piston section extends in a passive position into the channel in the region of the at least one coil, i.e. it extends axially past the radially running side wall of the ferromagnetic housing, the invention has the further advantage that, when the piston is moved from the second active position with the switch closed back into the first passive position, there is no edge on the piston which can remain hanging on the radially running side wall of the ferromagnetic housing. Therefore, no sleeve covering the inner opening in the radially extending side wall of the housing is required to prevent the piston from sticking to the side wall. Thus, in the switch closed position, the radially outer surface of the first piston portion may directly face the inner surface of the axially extending opening of the housing.The fact that the second piston section extends in a passive position into the channel in the region of the at least one coil further increases the resistance against the flow of the magnetic flux in order to reduce the draw-in force. It should be noted that with the same solenoid switch configuration, the invention allows the retraction force to be reduced by simply increasing the outer diameter D2 of the first plunger portion and correspondingly increasing the inner diameter D1 of the opening in the radially extending side wall of the housing, thereby D1>D2. The radial gap between the outer diameter D2 of the first piston portion and the inner diameter D1 of the opening in the radially extending side wall should be as small as possible to reduce the resistance to the flow of magnetic flux. This radial gap is preferably less than 1 mm. This small gap can be achieved by dispensing with a sleeve in the radial gap as described above. The transition between the first piston section and the second piston section is preferably formed as a step.In a preferred embodiment, the ratio of the maximum outer diameter D 3 of the second piston section to the maximum outer diameter D 2 of the first piston section satisfies the equation D 2 >1.1 x D 3. More preferably, D2 > 1.2 x D3. These ratios of D2 to D3 make it possible to sufficiently reduce the drawing-in force.In a preferred embodiment, the coil portion containing the at least one coil extends axially a length L1 between a first coil end proximate the radially extending side wall of the housing and a second distal coil end, and the second plunger portion extends into the coil portion a length L2 in the first passive position, where L2 > 0.1 x L1. The second piston section with the reduced diameter compared to the first piston section therefore extends substantially into the coil region. As a result, the drawing-in force is further reduced.In another embodiment, the second plunger portion extends into the coil region for a length L 3 in the second switch-closed position, where L 3>0.5 x L 1. The second piston section is cylindrical in the coil region and the outer diameter of the second piston section is arranged to slide along a radially inwardly facing surface of the magnetic switch. The radially inwardly facing surface could be that of a spool holder that holds the at least one spool and defines the channel through which the piston travels in the axial direction. The bobbin holder may be made of a polymer material.In a particularly advantageous embodiment, the magnet comprises a ferromagnetic bypass device. The ferromagnetic bypass device is in the form of a ferromagnetic ring disposed radially between the at least one coil and the piston, whereby the radially inner surface of the ferromagnetic bypass device forms a sliding bearing surface for the piston. The outer diameter of the second piston section can be the corresponding bearing surface of the piston. The ferromagnetic bypass device provides a fixed bearing surface to maintain the concentric position of the piston in the channel. The bearing surface ensures in particular that the first piston section does not remain caught on the radially extending side wall of the housing.The first and / or the second piston section can be substantially cylindrical. The cross section of the piston in the second piston section can be solid, i.e. without hollow spaces. When the plunger is in the switch closed position and only the retaining coil is energized, the solid cross-section of the second plunger portion reduces the resistance to the flux of the magnetic flux, such that more force is applied to the plunger to retain the plunger in the switch closed position.In another embodiment, a return spring is disposed in a radial gap between the outer surface of the piston and the at least one coil. In particular, the restoring spring can be arranged to enclose the second piston section. Further, a first end of the spring may be arranged to abut a step of the piston at a transition between the first piston portion and the second piston portion, and the second end of the spring is arranged to abut a stationary part of the magnetic switch.When a ferromagnetic bypass device as described above is used, the second end of the return spring may abut an axial end surface of the ferromagnetic ring. This has the advantage that the spring abuts against a hard surface. Alternatively, the second end of the return spring may abut a step formed on the bobbin holder, and a washer may be placed between the second end of the spring and the step to provide a hard abutting surface.The at least one reel preferably comprises a feed reel and a holding reel. The feed reel can be arranged radially inside the holding reel.The magnetic switch further includes two terminals, the plunger being connected to a contact that establishes an electrical path between the two terminals when the plunger is in the switch closed position. Connecting the electrical path between the two terminals allows a high current to flow directly to the starter motor.The contact may be mounted on the plunger via a contact spring that biases the contact in the axial direction such that the contact may move axially relative to the plunger to make smooth contact with the terminals. It should be noted that, when the switch is first closed, only the holding coil is activated and the plunger moves 1-2 mm in the axial direction with respect to the terminals as a result of the contact spring being pressed together. The position with closed switch in the sense of this application is the end position that the plunger assumes when the contact connects an electrical path between the two terminals and the holding coil is energized.In another aspect, a vehicle starter is provided that includes an electric motor and a magnetic switch according to the foregoing, wherein the plunger of the magnetic switch is connected to a lever arranged to axially move a pinion connected to the electric motor.BRIEF DESCRIPTION OF THE DRAWINGSEmbodiments will now be further described by way of example only and with reference to the accompanying drawings, wherein: FIG. 1 is a side sectional view of a magnetic switch in a first passive position according to an embodiment of the invention. FIG. 2 is a side sectional view of a magnetic switch in a switch closed position according to an embodiment of the invention. FIG. 2 is a side sectional view of a magnetic switch in a switch closed position according to another embodiment of the invention. FIG. 4 is a partial sectional side view of a vehicle starter according to the invention.DETAILED DESCRIPTIONReferring now to FIGS. 1 and 2, a magnetic switch according to a first embodiment of the invention includes a pull-in coil 2 and a holding coil 3, the holding coil being shown as being disposed radially outward of the pull-in coil, but a different arrangement of the coils would be possible. A channel 4 extends through the coils 2, 3 in the axial direction 5. A housing 7 made of a ferromagnetic material surrounds the at least one coil 2, 3 in the radial direction. The housing comprises a first, radially extending side wall 8 having an axially extending circular opening 9 with an inner diameter D1. The side wall 8 is positioned on an axial side of the coils 2, 3.A piston 10 extends at least partially into the channel 4 through the axially extending opening 9 and is arranged to be displaceable in the axial direction 5 between a first passive position (shown in FIG. 1 ) in which the switch is open and the at least one coil is not energized and a second position (shown in FIG. 2 ) in which the switch is closed. The housing 7, together with the plunger 10 and a plunger stop 13, also made of ferromagnetic material, forms part of a path of the magnetic circuit.The piston 10 comprises a first piston portion 11 and a second piston portion 12 arranged axially adjacent to the first piston portion 11 As can be seen from FIGS. 2 and 3, the first axially extending piston portion 11 is at least partially positioned axially within the axially extending opening 9 of the housing side wall 8 in the closed switch position. In the first passive position shown in FIG. 1, the second piston section 12 extends axially substantially over the length of the axially extending opening 9 of the housing side wall 8 into the channel 4 in the region of the at least one coil 2, 3. The length of the axially extending opening 9 corresponds to the thickness of the housing side wall 8 in the region of the opening 9. The first piston section 11 has a maximum outer diameter D 2 and the second piston section has a maximum outer diameter D 3. According to the invention, the maximum outer diameter D3 of the second piston section 12 is smaller than the maximum outer diameter D2 of the first piston section 11 With the same number of turns of the draw-in coil, the invention achieves a reduction in the draw-in force by enlarging the gap 14 between the maximum outer diameter D3 and the inner diameter D1 of the opening 9 in the radially extending side wall 8 of the ferromagnetic housing when the piston 10 is in the passive position. This air gap 14 resists the magnetic flux and weakens the magnetic field, so that the force applied to the ferromagnetic piston 10 decreases. When the piston returns from the second position with the switch closed shown in FIG. 2 to the first switch position shown in FIG. 1, no edges are present on the piston which can remain hanging on the housing side wall 8 in the region of the opening 9. The second piston section 12 is thus free of notches or grooves. Further, no sleeve is required to cover the inner opening 9 in the radially extending side wall 8 of the housing 7 to prevent the piston 10 from sticking to the side wall 8. The radial outer surface 19 of the first piston section 11 can therefore, in the position with the switch closed from FIGS. 2 and 3, face directly the radially inwardly facing surface 20 of the axially extending opening 9 of the housing side wall 8.The first and second piston portions 11, 12 form part of the main piston body 15 that has an axial end surface 16 that abuts an opposing axial end surface 17 of the piston stop 13 when the piston 10 is in the switch closed position of FIG. 2. The piston stop 13 comprises a cylindrical portion arranged radially in the region of the at least one coil 2, 3 and a radial flange extending therefrom and forming a second side wall 18 which, together with the housing 7, surrounds the region of the at least one coil 2, 3. A coil portion 24 containing the holding coil 3 and the pull-in coil 2 extends axially a length L1 between a first coil end 22 located near the radially extending side wall 8 of the housing 7 and a second distal coil end 23.The second piston section 12 extends passively into the channel 4 in the region of the coils 2, 3. As can be seen in FIG. 1, the second piston section extends in the first passive position over a length L2 into the coil region, wherein L2>0.1 x L1. In the embodiment shown in FIGS. 1-3, in the second switch closed position, the second plunger portion 12 extends into the coil region 24 for a length L3, where L3 > 0.5 x L1. The second piston section 12 is formed cylindrically in the coil region 24, and the outer diameter surface 25 of the second piston section 12 is arranged to slide along a radially inwardly facing surface 26 of the magnetic switch 1. In the embodiment in FIG. 3, the radially inwardly facing surface 26 is formed by the coil holder 6 holding the coils 2, 3, which defines the channel through which the piston runs in the axial direction 6. The bobbin holder 6 may be made of a polymer material. In the embodiment shown in Figures 1 and 2, the magnetic switch 1 comprises a ferromagnetic bypass device 27. the ferromagnetic bypass device 27 is formed as a ferromagnetic ring arranged radially between the inner coil 2 and the piston 10, the radially inner surface 28 of the ferromagnetic bypass device forming a sliding bearing surface for the piston 10. The outer diameter surface of the second piston portion 12 is the corresponding bearing surface of the piston 10. In particular, the bearing surface ensures that the first piston section 11 does not remain caught on the radially extending side wall 8 of the housing 7.The second piston section with the reduced diameter compared to the first piston section therefore extends substantially into the coil region. By the reduced diameter D 3 of the second piston portion 12 compared to the diameter D 2 of the first piston portion 11, in other words, D 3<D 2, the resistance against the flow of the magnetic flux is increased to reduce the drawing-in force. In the same magnetic switch configuration, the drawing-in force can thus be reduced simply by enlarging the outer diameter D 2 of the first piston section 11 and correspondingly enlarging the inner diameter D 1 of the opening 9 in the radially extending side wall 8 of the housing, as a result of which D 1>D 2. The ratio of the maximum outer diameter D 3 of the second piston portion to the maximum outer diameter D 2 of the first piston portion satisfies the equation D 2 >1.1 x D 3. This ratio of D2 to D3 enables a sufficient reduction in the draw-in force.A radial gap 21 between the outer diameter D 2 of the first piston section 11 and the inner diameter D 1 of the opening 9 in the radially extending side wall 8 is minimized in order to reduce the resistance to the flow of the magnetic flux when the piston is in the (retraction) position with the switch closed from FIG. 2. This radial gap 21 is preferably less than 1 mm. This small gap can be achieved by dispensing with a sleeve in the radial gap, so that the radially outward facing surface of the first piston portion 11 directly faces the radially inward facing surface of the opening 9. The first piston section 11 extends in the axial direction 5 approximately over the thickness of the side wall 8.The first piston portion 11 and the second piston portion 12 have a substantially cylindrical shape, wherein the cross section of the piston 12 in the second piston portion is solid in the embodiment shown, i.e. without hollow spaces. When the plunger is in the switch closed position and only the holding coil is energized, the solid second plunger portion 12 reduces the resistance to the magnetic flux, thereby applying more force to the plunger to hold it in the switch closed position. A return spring 29 is disposed in a radial gap 30 between the outer surface 25 of the piston 10 and the inner coil 2 such that the return spring 29 surrounds the second piston portion 12. Moreover, a first end of the spring 29 is arranged to abut a step 31 on the piston 10 at a transition between the first piston portion 11 and the second piston portion 12, and the second end of the spring 29 is arranged to abut a fixed part of the magnetic switch 1. In the embodiment of Figures 1 and 2, the ferromagnetic bypass device 27 provides a pushing surface for the second end of the return spring 29. In the embodiment of Fig. 3, the coil holder provides an axial abutment surface for the second end of the return spring 29. In an alternative embodiment (not shown), the second piston portion 12 may have a cavity for receiving at least a portion of the return spring, or the return spring may be located outside the channel 4.FIG. 4 shows a vehicle starter, wherein the piston 10 of the magnetic switch 1 is connected to a lever 37 which is arranged for axial movement of a pinion 37 connected to the electric motor 34. When an ignition key is turned, both the pull-in coil 2 and the holding coil 3 are energized, and the pinion 37 is engaged with a ring gear of an engine. When the plunger 10 reaches the switch-closed position, the draw-in coil 2 is effectively short-circuited and only the holding coil 3 is energized, maintaining the engagement position of the pinion 37 and the ring gear of the motor. The magnetic switch 1 includes two terminals 32, and the plunger 10 is connected to a contact plate 33 that establishes an electrical path between the two terminals 32 when the plunger 10 is in the switch-closed position. Connecting the electrical path between the two terminals 32 allows a high current to flow directly to the starter motor 34 so that the pinion 37 can drive the ring gear of the motor. The contact plate 33 may be mounted to the plunger 10 via a contact spring 35 that biases the contact plate 33 in the axial direction 5 such that the contact may move axially relative to the plunger 10 to make smooth contact with the terminals 32. When the switch is first closed, only the holding coil 3 is activated and the piston 10 moves by a further 1-2 mm in the axial direction 5 towards the ports 32 due to the compression of the spring 35.LIST OF REFERENCE CHARACTERS1 Magnetic switch 2 draw-in coil 3 holding coil 4 channel 5 axial direction 6 coil holder 7 housing 8 housing side wall 9 opening 10 piston 11 first piston section 12 second piston section 13 piston stop 14 gap 15 piston body 16 axial end face 17 axial end face 18 side wall 19 radial outer face 20 radially inwardly facing surface 21 radial gap 22 first coil end 23 second coil end 24 coil region 25 piston surface 26 radially inwardly facing surface 27 ferromagnetic bypass device 28 radially inwardly facing surface 29 spring 30 radial gap 31 step 32 connection 33 contact plate 34 motor 35 spring 36 lever 37 pinion D 1 inner diameter of the opening D 2 maximum outer diameter of the first piston section D 3 maximum outer diameter of the second piston sectionReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedUS20120068796A1

[0002]

Claims

A magnetic switch (1) for a vehicle starter, the magnetic switch (1) comprising: at least one coil (2, 3) and a channel (4) extending through the at least one coil (2, 3) in the axial direction (5), a housing (7) made of a ferromagnetic material surrounding the at least one coil (2, 3) in the radial direction, wherein the housing (7) comprises a first radially extending side wall (8) having an axially extending opening (9) with an inner diameter D1, a piston (10) extending through the axially extending opening (9) at least partially into the channel (4) and arranged to be interposed in the axial direction (5) between a first passive position, in which the switch (1) is open and the at least one coil is not energized, and a second position, in which the switch (1) is closed, A sliding device, wherein the piston (10) comprises a first piston section (11) and a second piston section (12) arranged axially adjacent to the first piston section (11), wherein the first piston section (11), in the position with closed switch, extends at least partially into the axially extending opening (9) of the housing (7), wherein the second piston section (12), in the first passive position, extends axially over the length of the axially extending opening (9) into the channel (4) in the region of the at least one coil (2, 3), wherein the first piston section (11) has a maximum outer diameter D2, wherein the second piston section (12) has a maximum outer diameter D3, wherein the maximum outer diameter D3 of the second piston section (12) is smaller than the maximum outer diameter D2 of the first piston section (11).Magnetic switch (1) according to claim 1, characterised in that the ratio of the maximum outer diameter D3 of the second piston section (12) to the maximum outer diameter D2 of the first piston section (11) satisfies the equation D2 > 1.1 x D3.Magnetic switch (1) according to claim 1, characterised in that the ratio of the maximum outer diameter D3 of the second piston section (12) to the maximum outer diameter D2 of the first piston section (11) satisfies the equation D2 > 1.2 x D3.Magnetic switch (1) according to one of the preceding claims, characterized in that a coil region (24) containing the at least one coil (2, 3) extends axially over a length L1 between a first coil end (22) close to the radially extending side wall (8) of the housing (7) and a second distal coil end (23), and the second piston section (12) extends in the first passive position over a length L2 into the coil region (24), wherein L2 > 0.1 x L1.Magnetic switch (1) according to one of the preceding claims, characterized in that the first and / or the second piston section (11, 12) are of cylindrical design.Magnetic switch (1) according to one of the preceding claims, characterized in that the piston (10) is solid in the second piston section (12).Magnetic switch (1) according to one of the preceding claims, characterized in that a piston return spring (29) radially surrounds the piston (10) and is arranged in a radial gap (30) between the second piston section (12) and the at least one coil (2, 3).Magnetic switch (1) according to one of Claims 1 to 5, characterized in that a piston return spring (29) is arranged in a cavity of the piston radially inside the radial outer surface (25) of the piston (10).Magnetic switch (1) according to one of the preceding claims, characterized in that, in the position with the switch closed, the radially outer surface (19) of the first piston section faces directly the inner surface of the axially running opening of the housing (7).The magnetic switch (1) according to any one of the preceding claims, characterized in that the magnetic switch (1) further comprises two terminals (32), wherein the plunger (10) is connected to a contact plate (33) that connects an electrical path between the two terminals (32) when the plunger (10) is in the switch closed position.

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