Abstract:
The invention relates to a starter ( 10 ) for an internal combustion engine, comprising a starter motor ( 12 ) which can be coupled to the internal combustion engine by means of a pinion ( 22 ), and a device for engaging the pinion ( 22 ) in a gear rim ( 26 ) of the internal combustion engine and connecting the starter motor ( 12 ) to a DC voltage supply system ( 30, 31 ). In order to disconnect the sequence of operations, the device has separate means, in particular separate relays ( 57, 64; 60 ), for engaging the pinion ( 22 ) on one hand and turning on the starter motor on the other when the internal combustion engine is started, thus preventing reactions of the engagement dynamics on the contact system when the motor current is switched.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a starter for an internal combustion engine. By way of example, one such starter is described in the Kraftfahrtechnischen Taschenbuch (Motor vehicle manual) produced by Bosch, 25 th  edition, page 986, in the form of a pre-engaged Bendix starter, which is operated via a so-called pull-in relay. This relay carries out the pulling-in functions, that is to say engaging the pinion of the starter motor in the toothed rim on an internal combustion engine, and switching the main current of the starter motor. In this case, a distinction can be drawn between two possible processes when the pinion engages in the toothed rim: in about 20%-30% of switching operations, one tooth of the pinion engages in a gap in the toothed rim, while, in approximately 70%-80% of the switching operations, one tooth of the pinion strikes a tooth on the toothed rim during engagement, and the engagement process must be assisted by an engagement spring. This known starter design admittedly requires only a single relay and can therefore be produced at relatively low cost, but on the other hand it results in very difficult working conditions for the switching process for the high motor current on the switching contact which connects the motor windings to the voltage source. Particularly in the case of partially discharged batteries and as the mechanical wear on the engagement parts increases, the dynamic response when switching on the main starter current can decrease to such an extent that the contacts are welded by arcs which occur during the switching process. On the other hand, if the pinion engages directly in the engine toothed rim, the dynamic response of the switching process and the contact wear resulting from it may possibly be high, depending on the design of the starter, when starting from an initial tooth-in-gap position. 
     In order to improve the switching-on process, particularly in the case of high-power starters, it is also known from the abovementioned reference for the motor current to be switched on in two stages in so-called pre-engaged starters wherein, in a first stage, the pinion of the starter is moved against the toothed rim of the engine, and the armature of the starter motor is at the same time fed with a reduced current, as a result of which the armature and, with it, the pinion, rotate during the engagement process, thus simplifying the engagement process. The engagement mechanism is in this case provided with a ratchet which closes a further switching contact of the relay and, via this, the main current circuit of the motor, only at the end of the engagement process of the pinion. This allows the engagement process and the switching of the main current of the motor to be carried out in two separate processes, but the design of the pull-in relay is more complex and more susceptible to defects, from the mechanical and electrical points of view. 
     SUMMARY OF THE INVENTION 
     The starter according to the invention, has the advantage that the processes for engagement of the pinion on the one hand and the switching of the motor current on the other hand are completely decoupled by the use of separate means for this purpose, in particular by the use of separate relays, in which case, the types of relay can be optimally matched to the respective process steps. However, it is also possible to use suitable semiconductor components, preferably transistors or GTO (Gate Turn Off) thyristors, for switching relatively high currents for all of the switching means, or for individual switching means. In particular, this makes it possible to completely separate the switching function for the high main motor current during starting of the internal combustion engine from the engagement process, thus avoiding reactions from the engagement dynamics on the contact system of the relay. The speed at which the contacts close is in this case independent of the engagement situation. 
     It is particularly advantageous for the switching relay in the main circuit of the starter motor to be activated by the engagement relay itself at the end or shortly before the end of the engagement movement, and in this case for the starter motor to be connected directly to the voltage source. With little additional complexity, this results in exact interaction between the engagement movement of the pinion and the process of switching on the main starter current at the end of the engagement movement. The engagement relay is for this purpose expediently equipped with a holding winding and a separate pull-in winding, which jointly operate a switching contact for activation of the switching relay. The holding winding and the engagement winding are preferably seated on the same relay core, and are in this case selectively switched in the same sense or in opposite senses. If they are switched in the same sense, the required total flux is achieved with a smaller number of turns and/or a lower excitation current while, if the fluxes are opposite, the winding with the lesser flux can be used to damp the switching process. The numbers of turns and the excitation currents for the holding winding and the pull-in winding are in this case expediently chosen such that the holding winding produces the switching process of the engagement relay with a large number of turns and an adequate excitation current, while the pull-in winding is equipped with considerably fewer turns, but carries a considerably higher excitation current, which is sufficient to easily rotate the armature during engagement. 
     One particularly simple and cost-effective circuit design is obtained by current being passed through the starter motor in a single stage, in which case the pull-in winding of the engagement relay is connected in series with a series winding of the starter motor, as a bias resistance, and both windings of the engagement relay jointly switch a make contact, via which current is passed to the winding of the switching relay, and the starter motor is supplied with the entire motor current at the end of the pull-in movement of the engagement relay. As is known, an arrangement such as this requires an engagement spring which, in conjunction with a steep-pitched thread, in particular when the pinion and the toothed rim are in a so-called tooth-on-tooth position, assists the engagement process, before suddenly switching on the main current for the motor. 
     A particularly protective engagement process is achieved by passing current through the starter motor in two stages in a manner which is known in principle, in which case, in a first switching stage, a limited rotation current for the starter armature flows via a normally-closed contact and the pull-in winding of the engagement relay. In a second stage, current is subsequently passed through the separate switching relay via a make contact of the engagement relay at or shortly before the end of the pulling-in movement of the relay armature, and the full motor current is supplied to the starter motor. In this case, the two separate relays can be optimally designed in accordance with the different requirements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details and advantageous refinements of the invention will become evident from the dependent claims and the description of the exemplary embodiments, which will be explained in more detail in the following description and are illustrated in the drawings, in which: 
         FIG. 1  shows an outline illustration of a pre-engaged Bendix starter with a series winding, 
         FIG. 2  shows a circuit diagram of a conventional embodiment of a starter through which current is passed in a single stage, 
         FIG. 3  shows a circuit diagram of an embodiment according to the invention of a starter through which current is passed in a single stage, 
         FIG. 4  shows a first circuit diagram of an embodiment according to the invention of a starter through which current is passed in two stages, 
         FIG. 5  shows a second circuit diagram of an embodiment according to the invention of a starter through which current is passed in two stages, 
         FIG. 6  shows an outline illustration of the spatial arrangement and connection of a starter according to the invention with an engagement relay and a switching relay, and 
         FIG. 7  shows an outline illustration of the spatial arrangement and connection of a starter as shown in  FIG. 6 , with an additional pilot control relay for passing current through the engagement relay. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates the mechanical design of the starter  10  according to the invention, in the form of a pre-engaged Bendix starter for an internal combustion engine. The starter  10  has a starter motor  12  whose output drive shaft  14  has a steep-pitched thread  16  which interacts with a corresponding female thread in a driver shaft  18 . Alternatively, the output drive shaft  14  is driven via an epicyclic gearbox, which is connected in between, but is not illustrated. The driver shaft  18  is firmly connected to the outer ring of a freewheeling ring  20 , whose inner ring is fitted with a pinion  22 . The pinion  22  and the freewheeling mechanism  20  are mounted on the output drive shaft  14  such that they can move axially as far as a stop  24 . The pinion  22  in this case engages in a toothed rim  26  of an internal combustion engine, which is not illustrated. The axial movement takes place with the aid of a relay arrangement  28 , which is illustrated in detail in the following figures and acts on the freewheeling mechanism  20  via a direction-changing lever  29  and an engagement spring  32 . A battery is used as the voltage source  34  for the arrangement; the negative pole  31  of the battery is connected to ground, and its positive pole  30  is connected on the one hand directly and on the other hand via an ignition/starter switch  36  to the relay arrangement  28 . A series winding  38  is fed via the relay arrangement and is connected to ground via brushes  40 ,  42  and via the commutator  44  of the motor. The armature of the starter motor  12  is annotated  46 , and its stator is annotated  48 . 
       FIG. 2  shows a circuit diagram of a conventional embodiment of a starter through which current is passed in a single stage. In this case, the positive pole  30  of the voltage source is connected to an engagement relay  49 , on the one hand via the ignition/starter switch  36  and a connection  50 , and on the other hand directly. This engagement relay  49  contains a holding winding  52  and a pull-in winding  54 , which are wound in the same sense, are wound on the same core, and are both connected at one winding end to the connection  50 . The other winding end of the holding winding  52  is connected to the negative pole  31  and to ground, and the corresponding other winding end of the holding winding  54  is connected to the negative pole  31  and to ground via the series winding  38  and the armature  46  of the starter motor  12 . The holding winding and the pull-in winding jointly operate a make contact  56  in the engagement relay  49 , via which the starter motor  12  is connected directly to the positive pole  30  as soon as the relay armature has pulled in entirely or virtually entirely, and the pinion  22  has engaged in the toothed rim  26 . 
     The holding winding  52  and the pull-in winding  54  in this known arrangement together carry out the task of engagement of the pinion  22  in the toothed rim  26  on the internal combustion engine, and at the same time the function of switching the main current for the starter motor  12 . If, during this process, a tooth of the pinion  22  meets a gap in the toothed rim  26 , then only a small amount of force is required for engagement, and the dynamic response during switching of the contact  56  is relatively high. On the other hand, the dynamic response during switching of the contact  56  is very low when, during engagement, a tooth on the pinion  22  strikes a tooth on the toothed rim  26 , as a result of which the engagement spring  32 , as shown in  FIG. 1 , must also be stressed during engagement, and only a small amount of energy is available for operation of the make contact  56 . In consequence, relatively long-lasting arcs and welding can occur, which adversely affect the operation of the starter, at least in the long term. 
       FIG. 3  shows the circuit diagram of an embodiment according to the invention of a starter through which current is passed in a single stage, and which overcomes the difficulties described above. In principle, with an engagement relay  57  and its connection to the DC voltage power supply system  30 ,  31 , the design of the circuit arrangement corresponds to that in  FIG. 2 , but in this arrangement the relay contact  56  does not carry out the switching function for the high motor current, but only for passing current through the winding  58  of a switching relay  60 , which then switches the motor current via its make contact  62 . In addition, this arrangement operates in only one stage, with the pinion  22  engaging in the toothed rim  26  in the same way as in the arrangement shown in  FIG. 2 , and with the motor current being switched on completely at the end or shortly before the end of the engagement movement of the pinion  22 . In contrast to the arrangement shown in  FIG. 2 , in addition to the engagement work for the pinion  22 , however, the engagement relay  57  only has to operate the lightly loaded contact  56 , and the actual process of switching on the motor current is carried out by the switching relay  60 , as a result of which the functions of engagement and switching are completely separate, and the engagement process does not cause any reaction on the contact system of the switching relay  60 . 
       FIG. 4  shows a circuit arrangement for passing current through a starter motor  12  in two stages. In this case, instead of the engagement relay  57  for passing current in a single stage, as shown in  FIG. 3 , there is an engagement relay  64  with a normally-closed contact  66  and a make contact  68 . The fixed connections of the contacts  66  and  68  can in this case be connected in parallel via a pilot control relay  70  to the positive pole  30 , with one end of the relay winding being connected to the negative pole  31  and to ground, and the other end being connected via the connection  50  and the ignition/starter switch  36  to the positive pole  30  of the DC voltage power supply system. The holding winding  52  of the engagement relay  64  is likewise connected via the pilot control relay  70  to the positive pole  30  and to the negative pole  31  of the DC voltage power supply system. 
     In this embodiment, the two windings  52  and  54  of the engagement relay  64  are wound in opposite senses, with the holding winding  52  having a considerably greater number of turns than the pull-in winding  54  and being excited with a sufficiently high current in order to carry out the engagement process for the pinion  22  on its own, despite the flux in the opposite direction in the pull-in winding  54 . In this case, the pull-in winding  54  advantageously damps the dynamic response of the engagement movement, and at the same time supplies a sufficiently high excitation current to the series winding  38  of the starter motor in order to rotate this slightly, and to simplify the engagement process, or to allow the engagement process. In this arrangement, an engagement spring can additionally be used in order to assist the engagement process. 
     Once again, the current flow through the starter motor  12  is provided by the switching relay  60 , independently of the operation of the engagement relay  64 . For this purpose, current is passed through the winding  58  of the switching relay  60  at the end or close to the end of the switching movement of the engagement relay  64 , by closing its make contact  68  and opening the normally-closed contact  66 , such that the switching relay  60  is supplied with its predetermined operating current via its make contact  62 , without the engagement process adversely affecting the starter motor  12 . Because the normally-closed contact  66  has been opened, there is no current through the pull-in winding  54  of the engagement relay  64 , while its holding winding  52  remains excited until the ignition/starter switch  36  opens, and thus ensures that the starting process is continued. 
     The use of a pilot control relay  70  for the operation of the circuit arrangement as shown in  FIG. 4  is not absolutely essential, and current can also be passed through the engagement relay  64  directly via the ignition/starter switch, analogously to the circuit arrangement shown in  FIG. 3 . On the other hand, in the first current-flow phase, the motor current via the pull-in winding  54  is in the order of magnitude of up to 200 A, which means that it is expedient to use a pilot control relay to bypass the ignition/starter switch  36  in the first stage of the current flow, at least for high-power starting motors. 
       FIG. 5  shows a variant of the circuit arrangement from  FIG. 4 , which differs from the previously described embodiment in that the excitation current for the winding  58  of the switching relay  60  does not flow via the pilot control relay  70 , but is tapped off directly from the supply line to the positive pole  30  of the voltage source. This admittedly has the disadvantage that an additional connection is required between the engagement relay  64  and the switching relay  60 , but on the other hand it reduces the magnitude of the current via the engagement relay  64 , and there is therefore no need for the pilot control relay  70 , at least for relatively small types of motor. All the other functions of the circuit arrangement shown in  FIG. 5  correspond to those in  FIG. 4 , and do not need to be explained again. 
     In order to explain illustrations in  FIGS. 6 and 7 ,  FIGS. 3 to 5  show additional connection points with the reference symbols  50   i ,  50   k ,  50   m  and  50   n . In this case, the connection point  50   i  is connected to the fixed connection of the relay contact of the pilot control relay  70 , the connection point  50   k  is connected to the winding connection of the switching relay  60 , the connection point  50   m  is connected to one connection, and the connection point  50   n  is connected to the other connection, of the make contact of the engagement relay  57 , or  64 . These reference symbols make it easier to interpret the illustrations in  FIGS. 6 and 7 , in which case the switching contacts which are normally in practice in the form of double contacts or have a contact plate, are likewise illustrated schematically. 
       FIG. 6  shows the design configuration of a starter according to the invention with a single-stage current flow corresponding to  FIG. 3 . In this case, the starter motor  12 , the engagement relay  57  and the switching relay  60  form one unit  72 , in which case either both relays  57  and  60  or one of them are or is integrated permanently in the housing of the starter motor  12 , or is or are detachably connected to it. The internal design of the engagement relay  57 , of the switching relay  60  and of the starter motor  12  are indicated symbolically by the respective connection points. For example, the engagement relay  57  receives its start signal via an external connection from the ignition/starter switch  36 , as a result of which the make contact  56  is closed, and the connection points  50   m  and  50   n  are connected to one another for excitation of the relay. 
     In the switching relay  60 , the positive pole  30  is connected via the make contact  62  to the connection point  45  on the relay, and this is externally connected to the starter motor  12  and, via its series winding  38 , to the negative pole  31 , and to ground. 
       FIG. 7  shows the spatial arrangement of a starter according to the invention through which current is passed in two stages, corresponding to  FIG. 4  or  5 . In this case, the pilot control relay  70 , the engagement relay  64 , the switching relay  60  and the starter motor  12  form one unit  74 . Once again, the relays  70 ,  64  and  60  are selectively integrated individually or jointly in the housing of the starter motor  12 , or are detachably connected to it. The illustration of the connection points and of the contacts corresponds to  FIGS. 4 and 5 , which differ only in the current supply to the make contact  68  in the engagement relay  64 . The connection  50   n  in the engagement relay  64  is in this case selectively connected either to the connection point  50   i  on the pilot control relay  70 , or directly to the positive pole  30  of the voltage source.