Abstract:
The invention relates to a starting method for internal combustion engines in motor vehicles, comprising a start-stop system, and to a starting device ( 10 ) for carrying out said method, said starting device comprising a starter motor ( 11 ) and an insertion device ( 12, 20 ) which axially inserts a slip-on pinion ( 13 ) into a crown gear ( 14 ) of the internal combustion engine when a stop cycle begins. In order to minimize the period until the engine can be restarted, the pinion ( 13 ) is resiliently inserted into the still rotating crown gear ( 14 ) by means of a pressure spring ( 25 ) when the stop phase begins, once the internal combustion engine ( 15 ) is switched off but before it comes to a standstill and with the starter motor ( 11 ) switched off.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a starting method for internal combustion engines in motor vehicles, with a start-stop system and to a starting device for carrying out the method. 
         [0002]    Internal combustion engines of motor vehicles are customarily turned on by means of a starter motor, wherein first of all a pinion of the starting device meshes in a ring gear of the internal combustion engine before the starter motor is switched on. In addition, with a start-stop system in motor vehicles, if the motor vehicle has stopped for a relatively long time, the internal combustion engine is automatically switched off and, at the end of the stop phase, the engine is then started again automatically in order to be able to continue the journey. 
         [0003]    It is known from EP 08 48 159 A1 to bring starter pinions into the meshed position right at the beginning of a stop state of the engine in order subsequently, at the beginning of the starting operation, to immediately switch on the starter motor at full power. This significantly reduces the time for the starting operation. However, this solution still has the disadvantage that, for the meshing of the starter pinion at the beginning of the stop phase, it is necessary to wait first until the engine is at a standstill, this meaning, if the stop phases are very short, a delay which may be critical, for example in a traffic jam because of vehicles following too closely. 
         [0004]    In order to shorten the meshing operation at the beginning of a stop phase, it has already been proposed using electronic activation of the starter motor to synchronize the rotational speed of the pinion with the rotational speed of the ring gear of the engine, in order thereby for the starter pinion to already be meshed in the still rotating ring gear of the engine. A disadvantage here is that, in order to synchronize the circumferential speed of the ring gear and of the starter pinion, a considerable electronic outlay on control has to be expended, since the circumferential speed of the ring gear changes greatly due to compressions in the engine cylinders when the switched-off internal combustion engine comes to a stop. 
       SUMMARY OF THE INVENTION 
       [0005]    It is endeavored with the present invention to ensure that, at the beginning of a stop operation, the starter pinion meshes in a simple manner in the still rotating ring gear using simple mechanical means after the internal combustion engine is switched off. 
         [0006]    In start-stop systems for an internal combustion engine for carrying out the method according to the invention and in a starting device according to the invention, a temporarily shortened starting operation is obtained using simple mechanical means by the starter pinion meshing in the engine ring gear as it comes to a stop. The electronic control of the start-stop system is substantially simplified as a result. Furthermore, this has the effect that, in comparison to an uncushioned meshing of the starter pinion in a still rotating ring gear, no damage occurs due to recoils occurring in the process at the free wheel or planetary gearing of the starter. 
         [0007]    Since, in the event of an axial pressure spring system of the starter pinion, meshing in the revolving ring gear takes place only at slow rotations of the ring gear and with the best tooth-to-gap position, in an advantageous development of the invention the effect achieved by a selected spring characteristic of the pressure spring is that the pinion is first of all engaged by a small amount in the ring gear and, in the process, is first of all carried along only via correspondingly small contact surfaces of the teeth of the pinion and ring gear. At low circumferential speeds, the pinion can be meshed completely in the ring gear by the force of the pressure spring. By contrast, the teeth of the starter pinion are pushed out of the ring gear again if the circumferential speed of the ring gear is too great. The starter pinion which now rotates slowly is then optionally repeatedly engaged again to a greater extent into the next gap until the starter pinion is finally completely meshed in the ring gear as the rotational speed increases. 
         [0008]    An advantageous development of the invention consists in that, even before the engine is at a standstill, the crankshaft can be rotated by means of the engine control unit from the starter motor into the optimum starting position in order thereby to shorten the time of the subsequent restart. 
         [0009]    In a first particularly simple and expedient embodiment for carrying out the starting method, with a starter pinion which can be displaced axially on a pinion shaft, the pressure spring in the form of a helical compression spring is clamped between a shoulder of the pinion shaft and the annular shoulder formed rear side of the pinion, wherein the pinion is accommodated as a slip-on pinion in an axially displaceable manner on the pinion shaft by means of a sliding toothing. In the event of an additional arrangement of a meshing spring which is known per se, the pressure spring advantageously has a smaller spring constant than the meshing spring. 
         [0010]    In order to facilitate the meshing of the pinion, the teeth of the pinion and/or of the ring gear are advantageously provided on the front end sides thereof with a beveled portion of the tooth flanks and with a beveled portion on the tooth tip. In this case, the beveled portions are advantageously provided in particular on those tooth flanks of the ring gear which are in front in the direction of rotation of the ring gear and on the rear tooth flanks of the pinion. In addition, the pinion shaft can advantageously be displaced axially by a drive shaft of the starting device, preferably by means of a free wheel via a sliding toothing without a quick-acting screw thread. 
         [0011]    In a further embodiment, adjacent teeth of the pinion and of the ring gear, in a development of the invention, each have an axial length which differs by the same amount in the region of the front end sides which are opposite in the demeshed state. In this embodiment, the meshing of the pinion in the ring gear can be shortened even at high rotational speeds by the protruding teeth of the pinion and ring gear now being spaced apart from one another by double the tooth pitch such that, even at high speeds of rotation of the ring gear, the pinion teeth can still penetrate to an adequate depth in the tooth gaps by means of the axial pressure spring in order to be carried along. In the simplest embodiment, every second tooth of the pinion and ring gear is shortened in relation to the pinion width and ring gear width. Expediently, the non-shortened teeth are also provided here on the front end sides thereof with a beveled portion on the tooth tip, which beveled portion is preferably shorter than the tooth projection. In order, even here, to provide the possibility of allowing the starting pinion to first of all slide off the teeth of the ring gear, it is proposed, in a refinement of the invention, to provide beveled portions on those tooth flanks of the projecting teeth of the ring gear which are in front in the direction of rotation of the ring gear and on the rear tooth flanks of the projecting teeth of the pinion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Details of the invention are explained in more detail below by way of example with reference to the figures, in which: 
           [0013]      FIG. 1  shows, in a schematic illustration, a start-stop system for motor vehicles with a starting device, 
           [0014]      FIG. 2  shows the pinion, pinion shaft and free wheeling body of the starting device as a first exemplary embodiment in a three-dimensional illustration after assembly by means of a sliding toothing, 
           [0015]      FIG. 3  shows the parts from  FIG. 2  arranged in the manner of an explosion, 
           [0016]      FIG. 4  shows an enlarged illustration of the toothing of the pinion and of the ring gear of the engine before meshing, 
           [0017]      FIG. 5  shows the pinion, pinion shaft and free wheel in longitudinal section and an enlarged illustration, and 
           [0018]      FIG. 6  shows a partial section of the ring gear and of the pinion with offset teeth in a three-dimensional, enlarged illustration as a second exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  shows, in a first exemplary embodiment, a schematic illustration of a start-stop system for internal combustion engines in motor vehicles. Said system comprises a starting device  10  with a starter motor  11 , a starter relay  12  and a pinion  13  for axial meshing in a ring gear  14  of an internal combustion engine  15 . The starter relay  12  has a relay winding  16 , a tappet  17  and a switching contact  18  for switching the main current for the starter motor  11 . The start-stop system furthermore comprises an engine control unit  19  which, like the switching contact  18  of the starter relay  12 , is connected by a positive terminal to the electrical system (not illustrated) of the motor vehicle. The engine control unit  19  is furthermore supplied via a plurality of signal inputs with various sensor signals which are used, for example, to detect clutch actuation, brake actuation, the position of a transmission selector lever, the rotational speed of the engine and of the wheels, and the like. The engine control unit  19  is furthermore connected via an output to the relay winding  16 , with which the pinion  13  meshes, via an engagement lever  20 , in the ring gear  14  of the internal combustion engine  15 , and the starter motor  11  is switched on via the switching contact  18  in order to start the internal combustion engine  15 . In this case, the starter motor  11  uses a planetary gearing  21  to drive a drive shaft  22  which, as a rule, is coupled to a free wheel  23  via a quick-acting screw thread. The free wheel  23  is connected integrally on the output side to a pinion shaft to which the pinion  13  is fastened so as to be axially displaceable, limited by stops, by means of a sliding toothing. 
         [0020]    During cold starting of the engine  15 , first of all the starter relay  12  is activated via the engine control unit  19  by a starting signal triggered by the motor vehicle driver, the starter motor  11  being activated and rotated slightly directly by the engine control unit  19  via a further connection. By means of the relay winding  16 , the pinion  13  is also advanced via the tappet  17  and the engagement lever  20  as far as the ring gear  14  of the engine. In a tooth-to-tooth position, an engagement spring  24  which is inserted between the free wheel  23  and engagement lever  20  is tensioned in a known manner such that, by means of slight rotation of the starter motor  11 , the teeth of the pinion  13  can engage in the next tooth gap of the ring gear  14  as far as a stop on the drive shaft  22 . 
         [0021]    The start-stop system of the motor vehicle is then activated during the driving mode, and, at the beginning of each stop phase of the vehicle, the internal combustion engine is switched off, for example, by the speed of rotation at the front wheels of the vehicle being detected. At the same time, in a first stage for preparing a subsequent restart of the engine, a meshing operation of the pinion  13  in the still moving ring gear  14  of the engine  15  is triggered by a metered excitation current being passed via the engine control unit  19  to the starter relay  12 . The pinion  13  is now advanced axially by the engagement lever  20  via the tappet  17  to mesh in the ring gear  14 . In order to make the internal combustion engine  15  ready to start again as rapidly as possible after being switched off, the pinion  13  now has to be meshed by means of an axial pressure spring  25  in the still rotating ring gear  14  even before the internal combustion engine  15  is at a standstill and with the starter motor  11  not in use. The axial pressure spring  25  is arranged and axially pretensioned here between the pinion  13  and the pinion shaft  26 . 
         [0022]      FIG. 2  shows, in a three-dimensional illustration, a constructional unit  27  consisting of the pinion  13 , the axial pressure spring  25  and the pinion shaft  26  with a free wheel basic body  23   a,  wherein the pinion  13  is designed as a slip-on pinion. 
         [0023]      FIG. 3  shows said parts in an arrangement in the manner of an explosion, specifically a stop ring  28  as an axial stop for the pinion  13 , a snap ring  29  for fixing the stop ring  28 , the pinion  13  with a splined shaft internal bore  30   a,  with a bearing bushing  31 , the axial pressure spring  25 , the pinion shaft  26  with a splined shaft toothing  30   b  and the free wheel basic body  23   a,  and finally with a further bearing bushing  31 . The pinion shaft  26 , with its splined shaft toothing  30   b  together with the splined shaft internal bore  30   a  of the pinion  13 , forms the axial sliding toothing  30  according to  FIG. 2  for installing the pinion. The two bearing bushings  31  are inserted on both sides into a central bore  26   a  of the pinion shaft, in which the drive shaft  22  is accommodated when the starting device  10  from  FIG. 1  is assembled. The axial pressure spring  25  is placed concentrically onto a thickened portion  26   b  which is arranged behind the splined shaft toothing  30   b  of the pinion shaft  26  and bears with the rear end thereof against an annular shoulder  33  of the pinion shaft  26 . The front end of the axial pressure spring  25 , which is in the form of a helical spring, bears against the rear side of the pinion. 
         [0024]      FIG. 4  is an enlarged illustration in three-dimensional form of a partial section of the pinion  13  of the starting device  10  from  FIGS. 1 to 3  and of the ring gear  14 , which is offset axially with respect to said pinion, of the internal combustion engine  15 . It can be seen here that, when the pinion  13  is advanced axially to the engine ring gear  14 , which is still rotating in the direction of the arrow, the pinion  13  is carried along in the direction of the arrow  34 . In order to facilitate the engagement here of the pinion  13  in the ring gear  14  of the engine, the teeth  13   a  of the pinion  13  and teeth  14   a  of the ring gear  14  on the tooth end sides, which, in the demeshed state, are opposite one another, are provided with a beveled portion  35  of the tooth flanks  13   b  and  14   b.  The beveled portion  35  is provided here on those tooth flanks  13   a,    14   a  which enter into contact with each other upon meshing of the pinion  13  in the still rotating ring gear  14 . In addition, the teeth  13   a  of the pinion  13  have a beveled end side  13   c  in the region of the tooth tip of said teeth, thus further facilitating the meshing operation. In this case, it could be sufficient, on the one hand, to provide the beveled portion  35  only on the teeth  14   b  of the ring gear  14  or on the teeth  13   a  of the pinion  13 . On the other hand, it may be expedient to provide the beveled end sides  13   c  not only on the pinion  13  but also on the ring gear  14 . The effect achieved by said measures individually or in combination is that, upon meshing in the still rotating ring gear  14  of the engine, the pinion  13  is either immediately carried along by the force of the pressure spring  25  and is then fully meshed, or the pinion  13  is first of all carried along by one of the teeth  14   a  of the ring gear  14  and that tooth  13   a  of the pinion  13  which comes into engagement with the ring gear  14  first of all once again slides off the beveled portion  35  of the tooth flanks  13   b,    14   b  in order then, with slow rotation, already to engage to a further extent in the next tooth gap of the ring gear  14 . The pinion shaft  26  is carried along in the process by the pinion  13 , and the planetary gearing  21  and the starter motor  11  are decoupled via the free wheel  23 . 
         [0025]    In a development of the invention, before the engine  15  is at a standstill, the crank shaft is now rotated by means of the engine control unit  19  from the starter motor via the ring gear  14  into an optimum starting position for the subsequent restart. 
         [0026]      FIG. 5  shows, on an enlarged scale, a longitudinal section of a modified embodiment of the invention, in which a helical spring  36  which is inserted behind the sliding toothing  30  between the pinion  13  and the pinion shaft  26  and is in the form of an axial pressure spring for the pinion  13  is partially accommodated in an annular recess  38  of the pinion shaft  26  in the region of the free wheel basic body  23   a,  and wherein the base  38   a  of the annular recess  38  forms the supporting surface for the rear end of the helical spring  36 . In the inoperative state, the helical spring  36  presses the pinion  13  against the front stop ring  28 , as a result of which y occurs in the axial spring travel between the rear side of the pinion  13  and the front end side of the free wheel basic body  23   a,  via which y the pinion  13  can be displaced axially on the sliding toothing  30  counter to the axial force of the pretensioned helical spring  26 . In this case, the axial resilience of the helical spring  36  is configured such that the resilience is softer than that of the engagement spring  24  of the starting device  10  according to  FIG. 1 . It is therefore possible for the beveled portions  35  on the front end side of the teeth  13   a  of the pinion  13  to slide off in a manner springing back resiliently with metered force during the operation to mesh the pinion in the ring gear  14  of the engine. In addition, it is provided in this embodiment to design the “quick-acting screw thread”, which is customary per se, between the free wheel and the drive shaft  22  of the starting device  10  as an axial sliding toothing  40  such that, for meshing the pinion, an undesirable rotation in the wrong direction is avoided. 
         [0027]      FIG. 6  shows a further exemplary embodiment of the invention, which relates to a particular design of the teeth of the pinion  13  and of the ring gear  14 . For this purpose,  FIG. 6  illustrates, in an enlarged, three-dimensional illustration, a partial section of the ring gear  14  of the internal combustion engine  15  from  FIG. 1  and the pinion  13  of the starting device  10 , in the demeshed state with respect to each other. The difference over the embodiment according to  FIG. 5  is that the adjacent teeth  13   a  and  14   a  of the pinion  13  and of the ring gear  14  have an axial length which differs by the same amount in the region of those end edges which lie opposite one another. In this case, every second tooth  13   a   1  of the pinion  13  and every second tooth  14   a   1  of the ring gear  14  are shortened in relation to the pinion width and the ring gear width. In the same manner as in  FIG. 4  in the first exemplary embodiment, the axially non-shortened teeth  13   a  and  14   a  of the pinion  13  and of the ring gear  14  have, on the front, opposite end sides thereof, a beveled portion  35  on the tooth flanks  13   b  and  14   b.  The beveled portion  35  is arranged on those tooth flanks  13   b  and  14   b  which are in contact with one another in the direction of rotation, which is illustrated by an arrow, of the still moving ring gear  14  upon meshing of the pinion  13 . According to  FIG. 6 , these are the front tooth flanks  14   b  of the projecting teeth  14   a  of the ring gear  14  and those tooth flanks  13   b  of the projecting teeth  13   a  of the pinion  13  which are at the rear in the direction of rotation. Furthermore, the non-shortened teeth  13   a  and  14   a  of the pinion  13  and of the ring gear  14  have beveled front end sides which lie opposite in the demeshed state. In this case, it is sufficient for the end sides to be beveled only in the region  13   c  of the tooth tips. 
         [0028]    In this exemplary embodiment, likewise at the beginning of a stop cycle of the internal combustion engine  15 , the pinion  13  is first all moved forward to the ring gear  14  by the starter relay  12  via the engagement lever  20  after the internal combustion engine is switched off and before it is at a standstill and with the starter motor  11  not in use. Upon reaching a tooth-to-gap position, the pinion  13  is first of all engaged by a small amount in the ring gear  14  by means of the pressure spring  25 . In the process, first of all two non-shortened teeth  13   a  and  14   a  of the pinion  13  and ring gear  14  come into contact by means of the beveled tooth flanks  13   b  and  14   b  thereof. The pinion is first of all carried along only via a correspondingly small contact surface of the beveled portions  35 . During slow rotation of the ring gear  14 , the pretensioning of the pressure spring  25  and the force of the engagement spring  24  of the starting device  10  are sufficient in order to carry along the low-mass pinion  13  and then to mesh the latter completely in the ring gear  14 . In the process, the starting motor  11  and the gearing  21  of the starting device  10  are decoupled by the free wheel  23 . By contrast, at a greater speed of rotation of the ring gear  14  and with pinions of larger mass, the pinion  13  is not immediately completely carried along by the ring gear  14  but rather slides in an axially resilient manner off via the beveled portion  35  of the unshortened teeth  13   a  and  14   a,  which are in contact with each other, by the pinion  13  being pressed axially out of the ring gear  14  again counter to the force of the pressure spring  25 . Since the next non-shortened tooth  14   b  of the ring gear  14  is spaced apart by twice the tooth pitch from the preceding unshortened tooth, the pinion  13  now has available twice as much distance along the teeth in order to be able to engage to a greater extent in the ring gear  14  by means of the force of the pressure spring  25 . In this position, the pinion is now completely carried along and is completely meshed in the ring gear  14  by means of the force of the engagement spring  24 . It can therefore be ensured that, even with small advancing forces on the pinion  13 , a toothing penetration depth sufficient for a long service life is achieved. When relatively low-mass slip-on pinions are used, the shortened teeth  13   a   1  and  14   a   1  and the advancing force of the engagement spring  24  cause the pinion  13  to be engaged in the ring gear  14  to a sufficient extent so as to be carried along immediately by the ring gear  14  without sliding off and springing back. Therefore, the pinion  13  slides off from and springs back axially onto the ring gear  14  only if there is a great difference in speed of rotation between the ring gear  14  and pinion  13 . 
         [0029]    The invention is not restricted to the embodiments illustrated and described but rather also comprises alternative solutions which can be adapted depending on the design of the starting device  10  from  FIG. 1 . It is thus also possible, within the context of the invention, to modify the sliding toothing between the pinion  13  and pinion shaft  26  such that the pinion  13 , as a slip-on pinion for a “pointed mouth starter” is provided at the rear end with an outer toothing and the pinion shaft with the free wheel basic body is provided with an inner toothing. Since, at greater circumferential speeds of the ring gear, contact occurs only on the end initially sides between the teeth of the ring gear and of the pinion, the impact contacts which occur in this case cause energy to be exchanged between the pinion and ring gear such that the circumferential speeds are equalized. As soon as this has taken place fully, the pinion is advanced in a tooth-gap position into the ring gear to an extent such that it is no longer pressed out therefrom. In the case of a beveled contact surface, this means that the pinion is then advanced beyond the beveled portion into the ring gear and reaches a position in which the pinion can be fully engaged.