Abstract:
A parallel starter system for starting an internal combustion engine has at least two parallel-connected starters and a thermal switch associated with each of the starters, which thermal switch interrupts operation of the respective starter in the event of a response. The thermal switches are connected in series so that in the event of tripping of one of these thermal switches, the operation of all starters is interrupted.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a parallel starter system for starting an internal combustion engine having at least two starters connected in parallel. Such parallel starter systems are used with engines having a larger displacement, in order to be able to supply the required high starter power. 
     2. Description of Related Art 
     Published German patent application document DE 39 22 492 A1 describes a starter protection circuit for starting an internal combustion engine of a motor vehicle. A thermal switch, which operates a starter operation-interrupting relay in the event of a response, is assigned to the starter. After resuming the cold-switching state of the thermal switch, renewed starter operation may be achieved via a relay operation button. 
     Published German patent application document DE 10 2005 006 248 A1 describes a parallel starter system having a low wiring complexity. It includes multiple starters connected in parallel, each having a starter motor and an engagement relay. This parallel starter system may be implemented in a particularly simple and inexpensive manner if at least one of the switches includes a power relay, which switches the main current path to the respective starter motor, and the engagement relay, the power relay and the starter motor are implemented as a structural unit. 
     BRIEF SUMMARY OF THE INVENTION 
     A parallel starter system of the present invention has the advantage over the related art that terminal  50  (shown in  FIG. 1 ) of both or all starters of the parallel starter system is reliably isolated in the event the thermal switch of one of the starters is tripped. This increases the reliability of a parallel starter system in the event of a thermal overload of one of the starters. 
     The design and internal wiring of the connecting line ensures that both or all starters may have the same design. The wiring is determined only via the wiring in the connecting line. Each starter receives a plug contact having 8 pins. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows a wiring diagram of a parallel starter system according to one exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a parallel starter system having two starters S 1  and S 2  connected in parallel. Starter S 1  includes a starter relay  13   a , an engagement relay  4   a  having a hold-in winding HW and a pull-in winding EW, a power relay  17   a , a starter motor  2   a , a winding  3   a , a thermal switch TS 1  and switches  14   a ,  15   a ,  16   a  and  18   a . Starter S 2  includes a starter relay  13   b , an engagement relay  4   b  having a hold-in winding HW and a pull-in winding EW, a power relay  17   b , a starter motor  2   b , a winding  3   b , a thermal switch TS 2  and switches  14   b ,  15   b ,  16   b  and  18   b.    
     The main current of starter motor  2   a  of first starter S 1  is switched by power relay  17   a . The main current of starter motor  2   b  of second starter S 2  is switched by power relay  17   b . Engagement relay  4   a  serves to engage a pinion (not shown) into the appropriate gear rim of starter S 1  and to provide the current for turning over starter S 1 . Engagement relay  4   b  engages a pinion (not shown) in the appropriate gear rim of starter S 2  and provides the current for turning over starter S 2 . 
     In addition, the parallel starter system shown in  FIG. 1  contains a system cable implemented in the form of a plug ST within which the connecting lines run between two starters S 1  and S 2 . Each of the starters has a plug contact, each having 8 pins via which the respective starter S 1  and S 2  is connected to the plug, i.e., the system cable. The aforementioned 8 pins are labeled as TS87, TS87a, TS87b, 50, 50n, 50m, 30 and 50k. 
     Plug ST has a terminal in its upper area corresponding to terminal  50 . This is connected by a switch SW to positive pole+of a battery B. In addition, a line leads from the positive pole of battery B through plug ST to terminal  30  of first starter S 1 . A line also leads from the positive pole of battery B through plug ST to terminal  30  of second starter S 1 . A connecting line leads from terminal  50  in the upper area of plug ST to pin  50  of starter S 1 . Another connecting line leads from terminal  50  in the upper area of plug ST to pin  50  of starter S 2 . 
     The negative pole of battery B is connected to pin  31  of first starter S 1 , to pin  31  of second starter S 2 , and to thermal switch TS 2  of starter S 2  via pin TS 87  of starter S 2 . 
     Pin  31  of first starter S 1  is connected to starter motor  2   a  of first starter S 1  via winding  3   a . Pin  31  of second starter S 2  is connected to starter motor  2   b  of second starter S 2  via winding  3   b.    
     Thermal switches TS 1  of first starter S 1  and TS 2  of second starter S 2  are connected in series. Terminal  50  in the upper area of plug ST is thus connected to thermal switch TS 2  of second starter S 2  via pin  50  of first starter S 1 , starter relay  13   a  of first starter S 1 , pin TS 87   b  of first starter S 1 , pin TS 87   a  of first starter S 1 , thermal switch TS 1  of first starter S 1 , pin TS 87  of first starter S 1 , and pin TS 87  of second starter S 2 . The other terminal of thermal switch TS 2  is connected to the negative pole—of battery B via pin TS 87   a  of second starter S 2 . 
     In a starting operation, initiated by closing of switch SW, starter relays  13   a  and  13   b , which are connected in parallel, start at the same time and close corresponding switches  14   a  and  14   b . Therefore, within the particular starter, the connection between pin  30  and point  50   i  is closed, and the control terminals of engagement relays  4   a  and  4   b  receive power. 
     The pinion of starters S 1  and S 2  is moved forward into the gear rim by both engagement relays  4   a  and  4   b  being pulled in. A limited current then flows into starters S 1  and S 2  via the pull-in winding of engagement relays  4   a  and  4   b , thus causing the pinion to turn slightly. This slight turning simplifies the engagement procedure because tooth-on-tooth positions of the pinion on the gear rim may be eliminated in this way. 
     Switch  16   a  of engagement relay  4   a  and switch  16   b  of engagement relay  4   b  are able to close only when both pinions have been engaged. After both switches have closed, power relays  17   a  and  17   b  receive power, and therefore switch  18   a  of relay  17   a  and switch  18   b  of relay  17   b  are closed. After both switches are closed, starters S 1  and S 2  receive power directly and are able to start the engine. 
     The advantage of this circuit is that starting is possible only when both pinions have been engaged. This ensures that a uniform load on the starters is achieved. 
     If there is a thermal overload on one of the starters, then the particular thermal switch is tripped and interrupts operation of the particular starter. Since the two thermal switches are connected in series, tripping of one of the thermal switches also results in the current flow through the other thermal switch being interrupted. Therefore, operation of both starters is interrupted because they are no longer triggered via pin  50 . This has the advantage that in the event of a thermal overload on one of the starters, operation of not only the overloaded starter but also the other starter of the parallel starter system is interrupted, thus preventing a thermal overload of the additional starter(s) of the parallel starter systems. 
     In contrast, in known parallel starter systems, the starter relay of the particular starter is interrupted by the tripping of a thermal switch, resulting in a drop in both power relays. However, this causes only a drop in the engagement relay of the particular starter. The second engagement relay remains pulled in, which may result in a thermal overload on the relay and additional subsequent damages. These disadvantages do not occur with a parallel starter system according to the present invention.