Abstract:
The invention relates to an electromagnetic switch ( 16 ) for a starting device ( 10 ), comprising two contacts ( 180 ,  181 ) that are electroconductively inter-connected by a mobile contact bridge ( 184 ). At least one of the two contacts ( 180, 181 ) preferably comprises a contact surface ( 300 ) fixed to a contact stud ( 150 ,  151 ). According to the invention, a) the contact surface ( 300 ) is at least essentially flat, and an edge ( 279 ) of the contact bridge ( 180, 181 ), is arranged in such a way that, ( 184 ), providing electrical contact between the contact bridge ( 184 ) and the contact once it has come into contact with the contact surface ( 300 ), it enables a linear contact between the contact ( 189, 181 ) and the contact bridge ( 184 ), or b) the contact surface ( 300 ) comprises bumps lying essentially in one plane, and an edge ( 279 ) of the contact bridge ( 184 ), providing electrical contact between the contact bridge ( 184 ) and the contact ( 180, 181 ), is arranged in such a way that, once it comes into contact with the contact surface ( 300 ), it enables essentially a multiple-point contact between the contact ( 180, 181 ) and the contact bridge ( 184 ), or c) a surface ( 318 ) of the contact bridge ( 184 ), oriented towards the contact ( 180, 181 ), and a longitudinal axis ( 312 ) of the contact stud ( 150, 151 ), form an angle (β) oriented towards a central axis ( 315 ) of the switch ( 16 ) and larger than 90°, or d) a surface ( 318 ) of the contact bridge ( 184 ), oriented towards the contact ( 180, 181 ), and a longitudinal axis ( 312 ) of the contact stud ( 150, 151 ), form an angle (β) which is radially outwardly oriented towards a central axis ( 315 ) of the switch ( 16 ) and is larger than  90 °. The invention also relates to a method for switching an electromagnetic switch, preferably a starting device ( 10 ), comprising two contacts ( 180, 181 ) that are connected by a mobile contact bridge ( 184 ). When the contact bridge ( 184 ) is contacted by at least one of the two contacts ( 180, 181 ), a rubbing movement is generated between the contact bridge ( 184 ) and the contact surface ( 300 ) of the contact ( 180, 181 ).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an electromagnetic switch for a starting device and to a method for operating the electromagnetic switch. 
     The German laid-open specification DE 195 49 179 A1 has disclosed an electromagnetic switch (starter relay) for a starting device. This switch has two contacts which are referred to as contact pins in said document. The two contacts are electrically conductively connected to one another by a movable contact link in order to conduct current from the contact pin, which is connected to a positive terminal or a starter battery, to a contact pin and thereby conduct electrical potential to a starter motor, which is not shown in any more detail in said document. DE 10 2004 017 160 A1 has disclosed a further relay for starting devices. This relay has a so-called self-sprung contact link, in which a transverse force is produced between the contact link or the surface thereof and the mating contacts once contact has been made between the contact link and the mating contacts owing to the elasticity of the contact link. 
     SUMMARY OF THE INVENTION 
     The intention is to improve further the contact-making between the contact link and the mating contacts in comparison with this prior art. 
     The proposed solutions attempt to produce a scraping movement between the two contact-making surfaces between the contact surface of the contacts and the surface of the contact link and thereby to remove dirt and such like by means of the switching movement. All of the first four alternatives have the common factor that the electromagnetic switch has two contacts, which are electrically conductively connected to one another by a movable contact link. Said alternatives have the further common feature that the at least one contact has a contact surface. The first alternative provides for the contact surface to be at least substantially planar and for an edge of the contact link, said edge making electrical contact between the contact link and the contact, to be arranged in such a way that, once said edge has impinged upon the contact surface, it enables substantially linear touching contact between the contact and the contact link. This has the advantage that, in comparison with the previously known solutions, a comparatively high contact pressure between the two contact-making elements can be achieved. This is a precondition for a high-quality cleaning effect between the contact faces and for a scraping effect between the contact link and the contact surface which is as good as possible. 
     The second alternative provides for at least point touching contact between the contact and the contact link to be achieved. For this purpose, provision is made for the contact surface of the contact to have elevations, the highest regions of which lie substantially on one plane. An electrical contact between the contact link and the contact-making edge of the contact link is arranged in such a way that, once said edge has impinged upon the contact surface, it enables substantially at least point touching contact between the contact and the contact link. 
     Substantially “linear touching contact” and substantially “point touching contact” means that the contact-making contact faces between the contact link and the contact are very narrow and comparatively long in the event of a substantially linear touching contact. A point touching contact means that the current passage area between the contact link and the contact is reduced to at least one, possibly a plurality of, very small area(s) which is virtually a point. 
     The third alternative provides that a face of the contact link, said face pointing towards the contact, and an axis of a contact pin enclose between them an angle which points towards a central axis of the switch and is greater than 90°. This definition applies, for example, to the rest position of the electromagnetic switch. 
     A fourth alternative describes that a face of the contact link, said face pointing towards the contact, and an axis of the contact pin enclose between them an angle which points radially outwards with respect to a central axis of the switch and is greater than 90°. This definition also preferably applies to the rest position of the electromagnetic switch. 
     The central axis of the switch can be considered to be, for example, the axis around which, for example, a pull-in winding or a hold-in winding of the electromagnetic switch is wound. This axis is generally also equivalent to the central axis of a magnet core of the electromagnetic switch. 
     In accordance with the alternatives, it is possible to reduce the bounce of the contact link as it impinges on the contacts to be connected since the friction between the contact partners is produced during contact-making. This results in a reduction in the tendency to arc and therefore in a reduction in the surface temperatures of the contact and the contact link. As a result, the wear on the contact link and also the contact is reduced since there is less arc erosion. For the very rare case of cohesive connections, said alternatives enable an additional transverse force onto the respective connection, with the result that, in the end effect, the opening force or the force which acts in this connection is increased. The friction between the contact partners, namely the contact link and the contact, destroys nonconductive layers on the surfaces, with the result that cleaner contact is made because any oxide layers and/or layers of ice are broken up. In addition, the mass of the contact link can be reduced, with the result that there is a reduced tendency to bounce. 
     The invention also provides for the contact surface of the contacts to have fluting, which is preferably straight fluting or annular fluting, in order to achieve point touching contact. 
     The third alternative provides for the angle to be between 91° and 105°, preferably around 95°. The fourth alternative provides for the angle to be between 91° and 120°. 
     As regards the configuration of the edge of the contact link, provision is made for the edge to be bent or straight. The bent edge is particularly insensitive with respect to tolerances. This means that canting does not arise in practice in particularly material-saving embodiments. 
     In order to keep impact loading between the contact link and the contacts with which the contact link makes touching contact as low as possible, provision is made for, firstly, the contact link to be guided in a bearing by means of a pin and the contact link to have a region with the greatest cross section between the pin and the edge and a region with a reduced cross section between the region with the greatest cross section and the pin. This increases the bending elasticity. 
     In order to produce a transverse movement of the mutually touching contact faces on the contact link and the contact which is as effective as possible, provision is made for the contact link to comprise a central, flat section which is oriented perpendicular to the pin and which is adjoined by at least one outer flat section, pointing away from the pin. An angle which is not equal to 90° is provided between the central and the outer section. In order to achieve as good a holding capacity of the contact link as possible, provision is made for at least one of the two contacts to have a hardness which is less than a hardness of the contact link. Furthermore, provision is made for a coefficient of friction between the contact link and the at least one contact to have a value of between 0.1 and 2, preferably between 0.6 and 1. In order to achieve a particularly good scraping effect, provision is made for the edge to have a radius of less than 0.3 mm Furthermore, provision is made for the contact link to be a metal sheet which preferably has a sheet metal thickness of between 1 and 4 mm In the case of the third alternative, provision is made for that face of the contact link which points towards the contact to make contact with an edge of the contact. 
     For the case in which contact is made on the side of the contact link by means of an edge, provision is made for the contact link to have a plurality of edges which make contact with the contact. In order to optimize the contact link, provision is made for said contact link to comprise a plurality of layers. In this case, preferably one substrate layer is provided and one contact layer is provided attached to the substrate layer. Preferably, the substrate layer is intended to consist of a copper or silver alloy or steel or bronze or brass, while the contact layer is intended to consist of a copper, tin, gold or silver alloy or a metal-metal oxide composite material. 
     Provision is made for a starting device comprising an electromagnetic switch, as described. The switch is particularly advantageous insofar as it can be used very particularly in high-current applications, such as are present in starting devices, for reducing switching problems. 
     The invention also provides for either the contact link with its surface in the form of an edge to slide over the contact surface of the contact or the contact surface of the contact with its surface in the form of an edge to slide over the contact link. For the case in which a cohesive connection is produced between the contact link and a contact, provision is made for a sufficiently large shear force in the cohesive connection to detach said connection. 
     Furthermore, a method is provided with which the electromagnetic switch is switched. In this case, two contacts are connected by the one movable contact link. When the contact link makes contact with at least one of the two contacts, a scraping movement takes effect between the contact link and the contact surface of the contact. A scraping movement means that a sliding movement (frictional movement) takes effect between the contact link and the contact surface of the contact. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail below by way of example with reference to the figures, in which: 
         FIG. 1  shows a starting device in a longitudinal section, 
         FIG. 2  shows a longitudinal section through the electromagnetic switch in accordance with a first exemplary embodiment, 
         FIG. 3  shows a side view of a contact link, 
         FIG. 4  shows a plan view of a contact link, 
         FIG. 5  shows three different cross sections of the contact link in accordance with the first exemplary embodiment shown in  FIGS. 3 and 4 , 
         FIG. 6  shows a plan view of the contact of a pin, 
         FIG. 7  shows a sectional illustration of a contact of a pin as shown in  FIG. 6 , 
         FIG. 8  shows a side view of a contact pin  151  and a contact link in accordance with a second exemplary embodiment, 
         FIG. 9  shows a second side view of the second exemplary embodiment shown in  FIG. 8 , 
         FIG. 10  shows a side view of a third exemplary embodiment, 
         FIG. 11  shows a fourth exemplary embodiment of a switch with a different position of the contact link, 
         FIG. 12  shows a basic illustration of a fifth exemplary embodiment as a modification of the exemplary embodiment shown in  FIG. 2 , 
         FIG. 13  shows a sixth exemplary embodiment of a pair of contact pins with a contact link, 
         FIG. 14  shows a seventh exemplary embodiment of a pair comprising a contact link and contact pins, 
         FIG. 15  shows an eighth exemplary embodiment of a pair comprising a contact link and two contact pins, 
         FIG. 16  and  FIG. 17  each show an alternative exemplary embodiment of a contact link, 
         FIG. 18  and  FIG. 19  show two further alternatives for contact links, 
         FIG. 20  shows a sectional illustration of a contact link, of which a basic illustration is shown here, 
         FIG. 21  shows a side view or sectional illustration of a further particularly advantageous combination of contact link and contact surface, 
         FIG. 22A  shows a graph illustrating the dependencies of various parameters, and 
         FIG. 22B  shows half a contact link with different dimensions of significance for  FIG. 21A . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a starting device in a longitudinal section.  FIG. 1  illustrates a starting device  10 . This starting device  10  has, for example, a starter motor  13  and an electromagnetic switch  16 , which is in the form of an engaging relay here. The starter motor  13  and the switch  16  are attached to a common input drive end plate  19 . The starter motor  13  has the functional purpose of driving a starter pinion  22  when it is engaged in the ring gear  25  of the internal combustion engine (not illustrated here). 
     The starter motor  13  has, as housing, a pole tube  28 , which bears pole shoes  31  on its inner circumference, said pole shoes each having a field winding  34  wound around them. Instead of being excited electrically, it is possible for the stator to be excited by permanent magnets. The pole shoes  31  in turn surround an armature  37 , which has an armature stack  43  comprising laminates  40  and an armature winding  49  arranged in slots  46 . The armature stack  43  is pressed onto an input drive shaft  44 . Furthermore, a commutator  52  is fitted at that end of the input drive shaft  44  which is remote from the starter pinion  22 , said commutator comprising, inter alia, individual commutator segments  55 . The commutator segments  55  are electrically connected to the armature winding  49 , in a known manner, in such a way that, when the commutator segments  55  are energized by carbon brushes  58 , a rotary movement of the armature  37  results in the pole tube  28 . A power supply line  61  arranged between the meshing relay  16  and the starter motor  13  supplies power to both the carbon brushes  58  and the field winding  34  in the switched-on state. The input drive shaft  44  is supported on the commutator side in a sliding bearing  67  with a shaft journal  64 , said sliding bearing in turn being held fixed in position in a commutator bearing cap  70 . The commutator cap  70  is in turn fixed in the input drive end plate  19  by means of tension rods  73 , which are arranged distributed over the circumference of the pole tube  28  (screws, for example 2, 3 or 4 pieces). In the process the pole tube  28  is supported on the input drive end plate  19 , and the commutator bearing cap  70  is supported on the pole tube  28 . 
     In the input drive direction, the armature  37  is adjoined by a so-called sun gear  80 , which is part of a planetary gear mechanism  83 . The sun gear  80  is surrounded by a plurality of plant gears  86 , usually three planet gears  86 , which are supported by means of roller bearings  89  on axle journals  92 . The planet gears  86  roll in a hollow wheel  95 , which is mounted externally in the pole tube  28 . In the direction towards the output drive side, the planet gears  86  are adjoined by a planet carrier  98 , in which the axle journals  92  are accommodated. The planet carrier  98  is in turn mounted in an intermediate bearing  101  and a sliding bearing  104  arranged therein. The intermediate bearing  101  is configured in the form of a pot in such a way that both the planet carrier  98  and the planet gears  86  are accommodated in said intermediate bearing. Furthermore, the hollow wheel  95  is arranged in the pot-shaped intermediate bearing  101  and is ultimately closed by a cover  107  with respect to the armature  37 . The intermediate bearing  101  is also supported with its outer circumference on the inner side of the pole tube  28 . The armature  37  has a further shaft journal  110  on that end of the input drive shaft  44  which is remote from the commutator  52 , said shaft journal likewise being accommodated in a sliding bearing  113 . The sliding bearing  113  is in turn accommodated in a central bore in the planet carrier  98 . The planet carrier  98  is integrally connected to the output drive shaft  116 . This output drive shaft  116  is supported by its end  119  remote from the intermediate bearing  101  in a further bearing  122 , which is fixed in the input drive end plate  19 . The output drive shaft  116  is divided into various sections: a section with a so-called straight gearing  125  (inner gearing) which is part of a so-called shaft-hub connection thus follows the section arranged in the sliding bearing  104  of the intermediate bearing  101 . This shaft-hub connection  128  makes it possible in this case for a driver  131  to perform an axially linear sliding movement. This driver  131  is a sleeve-like protrusion, which is integral with a pot-shaped outer ring  132  of the freewheel  137 . This freewheel  137  (ratchet) furthermore comprises the inner ring  140 , which is arranged radially within the outer ring  132 . Clamping bodies  138  are arranged between the inner ring  140  and the outer ring  132 . These clamping bodies  138 , in interaction with the inner and the outer ring, prevent a relative rotation between the outer ring and the inner ring in a second direction. In other words: The freewheel  137  enables a relative movement between the inner ring  140  and the outer ring  132  in only one direction. In this exemplary embodiment, the inner ring  140  is integral with the starter pinion  22  and the helical gearing  143  (outer helical gearing) thereof. 
     For reasons of completeness, details are also given here on the meshing mechanism ( FIG. 1  and  FIG. 2 ). The switch  16  has a pin  150 , which bears an electrical contact  181  and is connected to the positive terminal of an electrical starter battery (not illustrated here). This pin  150  as well as a pin  151  is passed through a relay cover  153 . This relay cover  153  seals off a relay housing  156 , which is fastened to the input drive end plate  19  by means of a plurality of fastening elements  159  (screws). A pull-in winding  162  and a so-called hold-in winding  165  are furthermore arranged in the switch  16 . The pull-in winding  162  and the hold-in winding  165  both each induce an electromagnetic field in the switched-on state, said electromagnetic field flowing through both the relay housing  156  (consisting of electrically conductive material), a linearly movable armature  168  and an armature magnetic return path  171 . The armature  168  bears a push rod  174 , which is moved in the direction of a switching pin  177  during linear pull-in of the armature  168 . With this movement of the push rod  174  towards the switching pin  177 , said switching pin is moved out of its rest position in the direction towards the contact  181  and a contact  180 , with the result that a contact link  184 , which is fitted at that end of the switching pin  177  which faces the contacts  180  and  181 , electrically connects the two contacts  180  and  181  to one another. As a result, electrical power is passed from the pin  150 , beyond the contact link  184  and the pin  151 , to the power supply line  61  and therefore to the carbon brushes  58 . The starter motor  13  is energized in the process. 
     However, the switch  16  and the armature  168  furthermore also have the task of moving, with a pull element  187 , a lever which is arranged in rotationally movable fashion on the input drive end plate  19 . This lever  190 , usually in the form of a forked lever, engages with two “prongs” (not shown here) on its outer circumference around two disks  193  and  194  in order to move a driver ring  197  which is trapped between said disks towards the freewheel  137  counter to the resistance of the spring  200  and thereby to mesh the starter pinion  22  in the ring gear  25 . 
       FIG. 2  shows, furthermore, a contact release spring  220 , which pushes the contact link  184  back into its initial position with respect to the hold-in winding  165 , once the power has been disconnected. The contact release spring  220  presses for this purpose against a flange  223 , which rests on the switching pin  177 . The contact link  184  has, in its center, a hole  226 , with which the contact link  184  is supported on a sleeve section  229  of an axially movable guide collar  232 . This guide collar  232  has a substantially cylindrical cavity  235  between its outer contour and the switching pin  177 , with in turn a compression spring  238  being supported in said cavity. This compression spring  238  is supported on a snap-action sleeve  241  at that end of the switching pin  177  which faces away from the contact link  184 , said snap-action sleeve being held fixed in position with snap-action elements  244  in a slot  247 . A further compression spring  250  is effective around the snap-action sleeve  241  between the armature  168  and the armature magnetic return path  171 . 
       FIG. 3  shows a side view of the contact link  184 . This contact link  184  shows a central, flat section  270 , which has the hole  226  in its center ( FIG. 4 ). This central, flat section  270 , which is perpendicular to the switching pin  177 , is adjoined by initially an outer, flat section  273 , emerging outwards radially from the center of the hole  226  and therefore per se pointing away from the switching pin  177 . A second outer, flat section  276  is arranged diametrically opposite this first outer, flat section  273 . The two outer, flat sections  273  and  276  have an approximately circular contour. The two outer, flat sections  273  and  276  are deflected through an angle α with respect to the central, flat section  270 . This angle α preferably has a value of between 1° and 15° with 5° being preferred. The outer, flat sections  273  and  276  have an edge  279  at the point thereof which is furthest removed from the center point of the hole  226 . 
     A special exemplary embodiment for the contact link  184  provides for said contact link to consist of so-called electrical copper (E-Cu57). Furthermore, provision is made for the angle α to be equal to 5°, for the hardness of the material to be between 100 and 130 HV  10  (Vickers hardness test). 2 mm is provided for the material thickness d. The length L of the contact link  184  is selected such that contact is made between the edges  279  and the contacts  180  or  181 . The rigidity of the contact link  184  is between 150 N/mm and 250 N/mm 
       FIG. 5  shows three different cross sections of the contact link  184 . The lower part in  FIG. 5  shows the widest cross section  290  at the widest point on the outer, flat section  273 . The central part in  FIG. 5  shows the cross section  293  at the transition point between the outer, flat section  273  and the central, flat section  270 . The contact link  184  is tapered at this point. The topmost region in  FIG. 5  shows the cross section  296 , which is divided into two subareas  297 . The cross section B-B shows the cross section  296  which is at the widest point on the contact link  184  and is cut at the same time centrally through the hole  226 .  FIGS. 2 ,  3 ,  4  and  5  accordingly show that the contact link  184  is guided by means of a switching pin  177  in a bearing in the form of a guide collar  232  and the contact link  184  has a region with the greatest cross section  290  between the switching pin  177  and the edge  279  and a region with a reduced cross section  293  between the region with the greatest cross section  290  and the switching pin  177 . 
     As regards the different cross sections  290 ,  293  and  297 , provision is made in respect of the sum of the cross sections  297  for said cross sections to be greater than or equal to the cross section  293 . 
       FIG. 6  shows a plan view of the contact  180  of the pin  151 . As can be seen from said figure, the pin  151  illustrated therein is equipped with a contact  180 , the contact surface  300  of which has fluting, which is annular fluting  310 . This contact surface  300  or the fluting thereof is such that, as illustrated in  FIG. 7 , a corrugated contour results in cross-sectional view. This corrugated contour can be, for example, a sinusoidal profile or a similar profile with a corrugated configuration, i.e. one with “valleys and mountains”. The fluting illustrated here is annular fluting  310 , i.e. the corrugated contour  303  or the “mountains and valleys” thereof are oriented coaxially around the central line  306  of the pin  151  in the example. 
     In the context of the second exemplary embodiment,  FIG. 8  and the subsequent figures, a contact link  184 , as is known from  FIG. 4 , is paired with a contact pin  151 , whose contact surface  300  does not consist of annular fluting  310 , but of straight fluting  309 ,  FIG. 8 . The section line IX-IX drawn in  FIG. 8  is illustrated in  FIG. 9 . Correspondingly, the section through the contact pin  151 , the associated pin head  152  and the contact  180  are shown in said figure. As is illustrated therein in section, the straight fluting  309  on which the edge  279  of the contact link  184  is arranged is shown. 
     With reference to  FIG. 8 , it is illustrated therein how various sections are moved during switching, i.e. when contact is made between the contact link  184  and the contact  180 . Thus, the arrow at the right-hand edge of  FIG. 8  shows, denoted by V 184 , the speed, i.e. the movement of the contact link  184  so as to produce the contact between the contact  180  and the contact link  184 . Once the edge  279  has impinged upon the contact  180 , the edge  279  is caused to move by the movement of the contact link  184  and the angle of inclination α between the outer, flat section  273  and the central, flat section  270  in a short movement in the direction of the arrow denoted V 279 . With reference to  FIG. 9 , this means that the edge  279  will slide in the direction towards the observer on the straight fluting  209 . 
     The first exemplary embodiment and also the second exemplary embodiment show an electromagnetic switch  16  for a starting device  10 , wherein this electromagnetic switch  16  has two contacts  180  and  181 , which can be electrically conductively connected to one another by a movable contact link  184 . Provision is made here for at least one of the two contacts  180  and  181  to preferably have a contact surface  300  which is connected fixedly to a contact pin  151  or  150 . In this case, the contact surface  300  has elevations, which preferably lie substantially in one plane. An electrical contact between the contact link  184  and the contact-making edge  279  of the contact link  184  is arranged in such a way that, when said edge impinges on the contact surface  300 , it enables substantially multi-point touching contact between the contact  180 ,  181  and the contact link  184 . Depending on the orientation of the straight fluting  309  or the relative position of the individual elevations of the straight fluting  309  with respect to the edge  279 , initially also only single-point touching contact between the contact  180  or  181  and the contact link  184  is possible. 
     The straight fluting  309  is ideally intended to be in the form of sinusoidal longitudinal fluting. As regards the interaction between the contact  180  or  181  and the contact link  184 , the intention is for the hardness of the contact  180  or  181  to be less than or equal to the hardness of the contact link  184 . This is intended to ensure that it is not the contact link  184  but the contacts  180  and  181  which are subject to wear. 
       FIG. 10  shows a third exemplary embodiment comprising a contact link  184 , as is known from  FIG. 4 , and a contact  180 , whose contact surface  300  is at least substantially planar. The contact link  184  moves correspondingly, as in the exemplary embodiment shown in  FIG. 8 . That is to say that the edge  279  moves transversely with respect to the longitudinal axis  312  illustrated of the contact pin  151 . In this case, the edge  279  scrapes along the contact surface  300 . When considered macroscopically, a linear shape is produced for the area of touching contact between the contact link  184  and the contact surface  300 . 
     The exemplary embodiment shown in  FIG. 10  shows, correspondingly, an electromagnetic switch  16  for a starting device  10  comprising two contacts  180 ,  181 , which are electrically conductively connected to one another by a movable contact link  184 , at least one of the two contacts  180  or  181  preferably having a contact surface  300  which is fixedly connected to a contact pin  151 . In this case, provision is made for the contact surface  300  to be at least substantially planar and for an edge  279  of the contact link  184 , said edge making electrical contact between the contact link  184  and the contact  180 ,  181 , to be arranged in such a way that, once said edge has impinged upon the contact surface  300 , it enables substantially linear touching contact between the contact  180 ,  181  and the contact link  184 . 
     With reference to  FIG. 8 , a further definition for the way in which, as is the case here, the contact link  184  and the contact  180  or the contact  180  and the outer, flat section  276  are oriented relative to one another can be cited. Thus, an angle β can be specified between the outer, flat section  276  and the longitudinal axis  312  of the contact pin  151 , said angle lying in a plane, for example, which is formed by the longitudinal axis  312  and the central axis of the hole  226  ( FIG. 4 ). This central axis of the hole  226  is denoted by  315  and is covered by the movement axis of the switching pin  177  (see also  FIG. 2 ). 
     In accordance with this definition, an electromagnetic switch  16  for a starting device  10  is provided comprising two contacts  180  and  181 , which are electrically conductively connected to one another by a movable contact link  184 , at least one of the two contacts  180  or  181  preferably having a contact surface  300  which is fixedly connected to a contact pin  151 ,  150 , wherein a face  318  of the contact link  184 , said face pointing towards the contact  180 , and a longitudinal axis  312  of a contact pin  151  enclose between them an angle β which points towards a central axis  315  of the switch  16  and is greater than 90°. This definition applies to the rest position or up to the position of the switching link  184 , in which the contact link  184  is just not in touching contact with the surface  300  or is in touching contact therewith out any force. As regards the angle β, provision is made for this angle to be between 91° and 105°, preferably around 95°. 
       FIG. 11  shows a fourth exemplary embodiment of a switch  16 . Since the details of the switch shown in  FIG. 11  differ from those of the switch shown in  FIG. 2  merely in terms of a few details, only the differences will be mentioned below. 
     While the contact link  184  shown in  FIG. 2  has outer, flat sections  276  or  273 , which are inclined or bent in the direction towards the contacts  180  and  181 , the outer, flat sections  276  and  273  of the contact link  184  are not inclined with respect to the contacts  180  and  181 , but are inclined away therefrom. Correspondingly, the angle of inclination α has a different mathematical sign in comparison with the exemplary embodiment shown in  FIG. 2  and the central, flat section  270 . The angle β is in this case defined as an angle which is arranged between that face  318  of the contact link  184  which points towards the contact  180  and a longitudinal axis  312  of a contact pin  151 . The angle β is in this case oriented in such a way that it lies in a plane which is formed from the longitudinal axis  312  and the central axis  315 . In this case, the angle β points radially outwards and is greater than 90°. As regards the angle β, provision is made for said angle to be between 91° and 120°. These cited values also relate to the position of the contact link  184  in the rest position or before it touches the contact surface  180 . In the example shown in  FIG. 11 , the contacts  180  and  181  are configured, for example, in such a way that they have an edge  320  which, from the moment the contact link  184  impinges on the contact surface  300 , causes a relative movement transverse to the central axis  315  between the contact link  184  and the contact  180  or  181 . In this case, an edge  320  of the contact  180  or  181  scrapes against the contact link  184 . 
     As regards the angle α, provision is made for this angle to have a value of between −1° and −30°. The angle is in this case selected depending on the coefficient of friction between the contact partners. For the case in which there is a high coefficient of friction the angle can tend to be smaller, while the angle tends to be larger at low coefficients of friction. 
     The fifth exemplary embodiment shown in  FIG. 12  shows a basic illustration of two contact pins  150  and  151 , which are oriented with their contact surfaces  300  towards the outer, flat sections  273  and  276 . The length of the contact link  184  transverse to the central axis  315  is in this case greater than the outermost distance between the two contact pins  151  and  150 . The outer, flat sections  273  and  276  therefore do not scrape with one of their edges against the surfaces  300  of the contact pins  150  and  151 . In this case the contact link  184  switches against sharp edges  330  of the contacts  180  and  181 . 
     As a modification of the exemplary embodiment shown in  FIG. 12 , the contact link  184  shown in  FIG. 13  does not switch against the outermost edges of the contact pins  151  and  150 , but rather against bent-back edges  333 . 
       FIG. 14  shows a seventh exemplary embodiment of a pair of a contact link  184  and a contact pin  151  and  150 . This seventh exemplary embodiment is a modification of the exemplary embodiment shown in  FIG. 13  and differs from this in that: the contact link  184  no longer protrudes beyond the outermost contours of the two contact surfaces  300  and the contact pins  151  and  150 . In this case, too, the contact link  184  switches against a bent-back edge  333  of the contact pins  150  or  151 . 
       FIG. 15  shows a further, eighth exemplary embodiment of a pair comprising a contact link  184  and two contact pins  150  and  151 . The two contact pins  151  and  150  have two bevels  336  in the region of their pin heads  152 , pointing towards one another. These two bevels  336  point substantially towards one another, but are not parallel to one another. A contact link  184  is provided, whose length is shorter than the greatest distance between the bevels  336 , but greater than the smallest distance between the two bevels  336 . In this exemplary embodiment, an edge  279  of the outer, flat sections  273  and  276  scrape against the bevels  336 . 
       FIG. 16  shows a contact link  184  in a further alternative exemplary embodiment. This contact link also has a central, flat section  270  and two outer, flat sections  273  and  276 . The central, flat section  270  likewise has, in its center, a hole  226 . The edges  279 , in contrast to, for example, the exemplary embodiment shown in  FIG. 3  and  FIG. 4 , are not round but straight. The outer, flat sections  273  and  279  are likewise shown, similar to the exemplary embodiment shown in  FIG. 3  and  FIG. 10 , with an angle α with respect to the central, flat section  270 . 
     As an alternative to the embodiment shown in  FIG. 16 , as illustrated in  FIG. 17 , the contact link  184  can have two outer, flat sections  273  and  276 , which, in contrast to the exemplary embodiment shown in  FIG. 16 , are provided with slits in such a way that the respective flat sections are in the form of two lugs  340 . Instead of the term lugs, the term sheet-metal lobes would also be suitable, for example. 
       FIG. 18  shows a contact link  184 , which is substantially rectangular. In turn, said contact link has a central, flat section  270  and two outer, flat sections  276  and  273 . In turn, a hole  226  is arranged centrally in the flat section  270 . While  FIG. 18   a  shows a plan view,  FIG. 18   b  shows a sectional view of the contact link  184 . This sectional view shows the way in which the outer, flat sections  273  and  276  are bent back through the angle α. In order to influence or increase the flexibility of the outer, flat sections  273  and  276 , said sections are connected to the central, flat section  270  via notches  350 . The notches, as in the example here, can be arranged on both sides of the face of the contact link  184 , but can also alternatively be on one side. These notches  350  are in this case in the form of semicircular beads for reducing the cross section and reducing the bending strength of the contact link  184 . 
     As shown in the illustration in  FIGS. 19   a  and  19   b , a further contact link  184  is illustrated in a plan view and a sectional illustration. The constrictions for reducing the cross section or reducing the bending strength of the contact link  184  do not need to be introduced into the outer contour, as is illustrated in  FIG. 18 . It is also possible for cutouts to be introduced into the preferably rectangular contact link  184 .  FIG. 19  shows, by way of example, two circular cutouts  353 , which reduce the cross section. The cutouts can have any desired shape, for example they can be rectangular or rounded off. 
       FIG. 20  shows a contact link  184  in longitudinal section. This contact plate has, in turn, a central, flat section  270  and two outer, flat sections  273  and  276 . The central, flat section  270  has, in turn, a hole  226 , as do the preceding exemplary embodiments for contact links  184 . This contact link  184  comprises a plurality of layers. A first layer is a substrate layer  400  and a second layer attached to this substrate layer  400  is a contact layer  403 . In the case of this contact link  184 , the properties are optimized by forming the contact link  184  from a plurality of layers. Thus, the first layer, namely the substrate layer  400 , has favorable properties as a holding element imparting stability and elasticity. On the other hand, the contact layer  403  has optimized properties in terms of contact-making between the contact link  184  and the contact  180  or  181 . Provision is made for the substrate layer  400  to consist of a copper or silver alloy or steel or bronze or brass. For the contact layer  403 , provision is made for said layer to consist of a copper, tin, gold or silver alloy or a metal-metal oxide composite material. 
     For the contacts  180  and  183  of the contact pins  151  and  150 , respectively, it is generally intended for said contacts to likewise consist of electrical copper and to have a hardness of between 100 and 130 HV10. 
     By virtue of the shape of the contact link  184 , for example as shown in  FIG. 4  (“constriction”),  FIG. 16 ,  FIG. 17 ,  FIG. 18  and  FIG. 19 , the spring stiffness is reduced with respect to previously known contact links. This results in increased elastic deformation when the contacts  180  and  181  are connected with the above-described advantages of increased damping and the destruction of an oxide layer which has been produced. 
     As regards the edges  279  and  320 , provision is made for said edges to have a radius of &lt;0.3 mm This results in a “chisel effect”, so that the edges  279  and  320  remove disruptive layers during respectively opposite contact. Contact-making properties are thus considerably improved. In the region of the edges  279  and  320 , in this case an areally or linearly very small cohesive connection is preferably produced owing to switch-on arcs. By virtue of these cohesive connections being ripped open, the respective edge  279  or  320  is resharpened repeatedly, as a result of which characteristics or point contact between the edge and the mating contact remain even after repeated switching. The edges  279  and  320  also have the advantage that layers of ice which are formed on the contacts  180  and  181  in the switch as a result of any moisture in the air are broken through. 
     As regards the material thickness of the contact link  184 , provision is generally made for the corresponding metal sheet to preferably have a thickness of between 1 and 4 mm 
     Furthermore, a method for switching an electromagnetic switch  16  is provided, wherein said electromagnetic switch has two contacts  180  and  181 , which are connected by a movable contact link  184 . When contact is made between the contact link  184  and at least one of the two contacts  180  and  181 , a scraping movement takes effect between the contact link  184  and the contact surface  300  of the contact  181  or  180 . Either the contact link slides with its surface in the form of an edge  279  over the contact surface  300  of the contact  180  or  181  or the contact surface  300  of the contact  180  or  181  slides with its surface shape of an edge  320  over the contact link  184 . Any cohesive connection between the contact link  184  and the contacts  180  and  181  is intended to be detached in the release case by shear force loading in the cohesive connection (welding). 
     The edge  279  serves the purpose of scraping or chafing on the surface of the contacts  180  and  181 , thereby producing friction and ultimately converting energy. The energy to be converted is the energy from the movement of the contact link  184  and the parts which are moved during the switching operation, for example the switching pin  177 , the snap-action sleeve  241 , the compression spring  238 , the guide collar  232 , the flange  223 . This movement energy will be dissipated by the friction of the contact link  184  on the contacts  180  and  181  to such an extent that the contact link  184  substantially no longer bounces back and thus the tendency to form arcs between the contacts  180  and  181  and the contact link  184  is at least considerably reduced. 
       FIG. 21  shows a side and a sectional view of the contact link  184 , which produces an electrical connection with the contact  180  of the pin  151 . As can be seen from said figure, the contact  180  or the contact surface  300  thereof has fluting, which is annular fluting  310 . This contact surface  300  or the fluting thereof is such that, in the cross-sectional view, a corrugated contour is produced. This corrugated contour can, for example, be a sinusoidal profile or a similar profile with a corrugated shape, i.e. one with “valleys and mountains” (see also  FIG. 6 ). The fluting illustrated here is annular fluting  310 , i.e. the corrugated contour  303  or the “mountains and valleys” thereof are oriented coaxially around the central line  306  of the pin  151  in the example. Provision is made for the contact link  184  to slide or rub with its outer, flat section  276  along a flank  420  of the corrugated contour  303  when switching or when contact is made. 
       FIG. 22A  shows a graph, which illustrates the bending stress in the constricted region depending on a constriction ratio and a lever arm ratio. The constricted region is in this case the region of the contact link  184  which corresponds to the tapered cross section  293  illustrated in  FIG. 5 . In principle, this applies to all of the contact links  184  with a reduced cross section, as is also illustrated in  FIGS. 16 to 19 , for example. The three curves K 25 , K 50  and K 75  illustrated there represent different parameters. Curve K 25  represents a lever arm ratio of 25%, K 50  represents a lever arm ratio of 50%, K 75  represents a lever arm ratio of 75%. “Lever arm ratio” means that, with reference to  FIG. 22B , a ratio of LH/L=1/4=25%. The greater the lever arm ratio, the greater the stress S in cross section  293  is given the same force loading. Furthermore, the constriction ratio V is taken into consideration. V is the quotient of the width BE with respect to the width B  184 . In order to avoid or prevent contact bounce and to convert this into a frictional or sliding movement, provision is made for the bending stress S in cross section  293  to be greater than 20 N/mm 2  Furthermore, the bending stress S should be less than 100 N/mm 2  For the constriction ratio V, it is desirable for this ratio to be less than or equal to 75%, preferably greater than 25%. A ratio of between 70% and 35% has proven to be particularly favorable.