Abstract:
An electrical adjusting device for changing an angle of rotation of a camshaft ( 3 ) relative to a crankshaft of an internal-combustion engine is provided. The device includes an adjusting gear unit ( 1 ), which is formed as a triple-shaft gear unit, including an input part ( 4 ) that is fixed to the crankshaft, an output part ( 5 ) that is fixed to the camshaft, and an adjusting shaft ( 6 ), which is connected in a torsion-proof manner to an electric adjusting motor ( 2 ) having a permanent magnet rotor and a stator ( 8 ) fixed to the housing. A stationary gear ratio ( 10 ), the value of which defines the adjusting gear unit ( 1 ) as a positive or negative gear unit and deter-mines whether a direction of adjustment of the camshaft ( 3, 65, 69 ) is into an advanced or retarded base position, is located between the input part ( 4 ) and the output part ( 5 ) when the adjusting shaft is at rest. Due to the configuration of the adjusting gear unit ( 1 ), stationary gear ratios are provided, through which an advanced and a retarded base position of the camshaft ( 3, 65, 69 ) can be reached exclusively through braking of the adjusting shaft ( 6 ) when the adjusting gear unit ( 1 ) is rotating, and the braking of the adjusting shaft ( 6 ) is carried out through short-circuit braking of the adjusting motor ( 2 ).

Description:
BACKGROUND  
       [0001]     The invention relates to an adjusting device for changing the angle of rotation of a camshaft relative to the crankshaft of an internal-combustion engine.  
         [0002]     To guarantee reliable engine startup in an internal-combustion engine with a hydraulic or electric camshaft adjuster, the camshaft must be located in a certain base position relative to the crankshaft during startup. Typically, for an inlet camshaft, it is a “retarded” position, and for an exhaust camshaft, it is an “advanced” position.  
         [0003]     In normal vehicle operation, the camshaft is moved in a controlled way into the appropriate base position when the engine is turned off and the camshaft is fixed or locked in this position. For this purpose, the electric camshaft adjustment uses an electric adjusting motor and the hydraulic camshaft adjustment uses a hydraulic rotary piston adjuster, which has vane cells, pivoting vanes, or segmented vanes as a locking unit. This unit fixes the hydraulic adjuster in its base position until a sufficiently high oil pressure has been established for adjusting the camshaft after the restart of the internal-combustion engine.  
         [0004]     However, if the internal-combustion engine stalls, a controlled adjustment of the hydraulic camshaft adjuster is impossible, so that the camshaft can be in an undefined position outside of the base position.  
         [0005]     For hydraulic camshaft adjusters with a “retarded” base position, when the internal-combustion engine is next started and there is insufficient oil pressure due to the camshaft friction torque, which acts against the camshaft direction of rotation, the camshaft is automatically adjusted into the retarded base position. If the base position is an “advanced” position, for insufficient oil pressure the camshaft must be adjusted against the camshaft friction torque into the advanced position. This is usually performed with the help of a compensating spring, which generates a torque that is equal but opposite the camshaft friction torque.  
         [0006]     These methods typical for hydraulic camshaft adjusters for reaching the base position after the internal-combustion engine has stalled are not required for electrically driven camshaft adjusters, because the adjusting motor can adjust the camshaft into the appropriate base position even for a stopped internal-combustion engine or during startup. However, for electric camshaft adjusters, power to the adjusting motor and/or its controller can be lost and therefore the base or emergency running position cannot be reached, which is necessary for at least limited operation and restart.  
         [0007]     In DE 41 10 195 A1, an electric adjusting device that adjusts an angle of rotation of the camshaft relative to the crankshaft of an internal-combustion engine is described, with an adjusting gear unit, which is embodied as a triple-shaft gear system, and an input part that is fixed to the crankshaft, an output part that is fixed to the camshaft, as well as an adjusting shaft. Here, the adjusting shaft is connected in a torsion-proof manner to an electric adjusting motor, which has a permanent magnet motor and a stator that is fixed to the housing, wherein for a stationary adjusting shaft, between the input and output part there is a stationary gear ratio  
         i   0     =       Output   ⁢           ⁢   tooth   ⁢           ⁢   number   ⁢           ⁢     Z   NW         Input   ⁢           ⁢   tooth   ⁢           ⁢   number   ⁢           ⁢     Z   KW             
 
 whose magnitude determines the type of gear type (positive or negative gear) and the adjusting direction of the camshaft (advanced or retarded base position). This adjusting device strives for a smooth and precise setting of the camshaft position. So that the function of the internal-combustion engine can be maintained at least to some extent if the adjusting-motor system breaks down, there is a limit on the adjusting angle. However, a reference to reaching the base position or an emergency running position in such a case is lacking. 
 
       SUMMARY  
       [0008]     The objective of the invention is to provide an electric camshaft adjuster, which adjusts the camshaft into its emergency running position or base position in a simple way and without power even if the adjusting motor or its controller breaks down or if the power fails.  
         [0009]     Through the structural configuration of the adjusting gear unit, the magnitude of the stationary gear ratio i 0  and thus the adjusting device of the camshaft can be defined. The camshaft is adjusted in the direction of the advanced or retarded base position or emergency running position if the adjusting motor or its power supply breaks down through simple braking of the adjusting shaft for a rotating adjusting gear unit. This can be realized during engine operation and during shutdown or startup of the internal-combustion engine. During engine startup and at low engine rotational speeds, the base position of the camshaft is optimal and operation is still possible also at higher rotational speeds, so that at least a repair shop can be reached.  
         [0010]     The braking of the adjusting shaft can be realized through a mechanical or eddy-current brake. However, these brakes require electrical current for their activation. In contrast, the short-circuit brake according to the invention operates with short-circuit current, which is generated in the dragged adjusting motor and thus makes the short-circuit brake electrically autonomous. Because no mechanical friction is present, the short-circuit brake operates free from wear and tear.  
         [0011]     For the selection of the adjusting gear unit, negative or positive gearing come into play. Negative gearing has a stationary gear ratio i 0 &lt;0. Positive gearing has a stationary gear ratio i 0 &gt;0. For a positive stationary gear ratio i 0 , the input and output shafts have the same direction of rotation. For a negative stationary gear ratio i 0 , they have opposite directions of rotation relative to a stationary adjusting shaft and the components connected to this shaft.  
         [0012]     For a negative gear unit, if the adjusting shaft is fixed and the input shaft rotates clockwise, then the output shaft and thus the camshaft rotates counterclockwise, which corresponds to a retarding adjustment.  
         [0013]     For a positive gear unit with a stationary gear ratio i 0 &gt;1, if the adjusting shaft is fixed and the input shaft rotates clockwise, then the output shaft rotates slower than the input shaft, that means counterclockwise and thus likewise in the direction of a “retarded” base position.  
         [0014]     For a positive gear unit with a stationary gear ratio 0&lt;i 0 &lt;1, if the adjusting shaft is fixed and the input shaft rotates clockwise, then the output shaft rotates faster than the input shaft, that means clockwise and thus in the direction of an “advanced” base position. These relationships can be applied to all triple-shaft gear systems in question.  
         [0015]     It is advantageous if a double eccentric gear system or a wobble gear system and another double eccentric gear system are provided as the adjusting gearing. Double eccentric gear systems are distinguished by low friction, simple construction, and vibration-free running.  
         [0016]     In one advantageous embodiment of the invention, the double eccentric gear system has a cover, which is fixed to the camshaft and which is rigidly connected to axial pins that engage in bore holes of two structurally similar spur pinions with linear contact and the spur pinions, which can be driven by the adjusting motor via a double eccentric shaft, intermesh with a ring gear that is fixed to the crankshaft.  
         [0017]     The use of a central standard tension screw with a helical sleeve as the bearing surface for the roller bearing of the double eccentric shaft offers cost advantages, but requires greater axial installation space. The sliding bearing of the structurally similar spur pinions offers cost and installation space advantages for increased friction loss relative to a roller bearing.  
         [0018]     It is also advantageous that the tooth number Z NW  of each of the two structurally similar spur pinions (equal to output tooth number) is smaller than the tooth number Z KW  of the ring gear fixed to the crankshaft (equal to input tooth number), which leads to a stationary gear ratio 0&lt;i 0 &lt;1. For the present positive gear unit and braking of the adjusting shaft, this stationary gear ratio has the effect of camshaft adjustment in the direction towards an “advanced” position, as is typical for exhaust camshafts.  
         [0019]     One advantageous improvement of the invention is that another double eccentric gear unit has a drive wheel, which is fixed to the crankshaft and which is connected rigidly to axial pins that engage in bore holes of two structurally similar spur pinions with linear contact, and the structurally similar spur pinions, which can be driven by the adjusting motor via a double eccentric shaft, intermesh with a ring gear fixed to the camshaft.  
         [0020]     The bearing of the double eccentric shaft on the cylindrical screw head of a central special tension screw produces axial installation space. Both solutions for the bearing of the double eccentric shaft and the spur pinions are suitable for both double eccentric gear units.  
         [0021]     It is also advantageous that the tooth number Z NW  of the ring gear fixed to the camshaft (equal to output tooth number) is greater than the tooth number Z KW  of one of the structurally similar spur pinion (equal to input tooth number), which leads to a stationary gear ratio i 0 &gt;1.  
         [0022]     The three phases of the adjusting motor have the effect of a low-vibration torque profile of the adjusting motor with simultaneously low installation expense. The possibility of short-circuiting one, two, or all three phases enables a fine control of the short circuit braking torque.  
         [0023]     Because short-circuit switches are provided, which are closed when the adjusting motor is not powered and which are opened when the adjusting motor is powered, the fail-safe function of returning the camshaft into its base position or emergency running position is initiated immediately if the adjusting motor and/or its power supply breaks down. This also applies for the case of a stalled internal-combustion engine, whose camshaft position is corrected during the subsequent startup process.  
         [0024]     For limiting the temperature build-up of the adjusting motor, clocked short-circuiting is also suitable. Here, the short-circuit switches are opened when a certain short-circuit current has been reached and then automatically closed. This process is preferably controlled and operated by the short-circuit current itself, so that the clocking is functional even if the adjusting motor or the voltage supply of the controller breaks down. The braking current can also be taken from active components, for example, from a storage battery. The automatic closing is realized, for example, through spring force.  
         [0025]     For limiting the high short-circuit currents, it is advantageous to arrange a power resistor in the short-circuit lines.  
         [0026]     It is also advantageous to provide an electronic current regulator operated with short-circuit current in the short-circuit lines. This solution also functions independent of the power supply of the adjusting motor. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     Additional features of the invention can be taken from the following description and the drawings, in which a preferred embodiment of the invention is shown schematically. In the drawings:  
         [0028]      FIG. 1  is a view of a camshaft adjusting device, with adjusting gearing formed as a triple-shaft gear unit and an electric adjusting motor, which has a stator fixed to the housing;  
         [0029]      FIG. 2  is a circuit schematic of a three-phase DC adjusting motor with short-circuit lines and short-circuit switches;  
         [0030]      FIG. 3  is a cross-sectional view of a double eccentric gear unit with a ring gear fixed to the crankshaft;  
         [0031]      FIG. 4  is a cross-sectional view of a double eccentric gear unit with a ring gear fixed to the camshaft. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     In  FIG. 1 , a camshaft adjusting device with an adjusting gear unit  1  and an adjusting motor  2  is shown schematically. This device is used for adjusting the position of the angle of rotation between a crankshaft (not shown) and a camshaft  3  of an internal-combustion engine (not shown).  
         [0033]     The adjusting gear unit  1  is formed as a triple-shaft gear unit with an input part  4 , which is fixed to the crankshaft and which has a drive wheel  7 , an output part  5  that is fixed to the camshaft, and an adjusting shaft  6 , which is connected in a torsion-proof manner to a permanent magnet rotor  8  of the adjusting motor  2 . The adjusting motor  2  has a stator  9 , which is arranged fixed in a housing  10 .  
         [0034]     The camshaft  3  has a base position or emergency running position, which must be reached for reliable startup and limited operation of the internal-combustion engine. This is successful for an intact adjusting motor  2  even after the internal-combustion engine stalls without any difficulty, because the adjusting motor  2  adjusts the camshaft  3  into the base position for a stopped internal-combustion engine or during restart. However, at least a limited motor operation and restart must also be possible if the adjusting motor  2  breaks down in order to be able to reach at least a repair shop.  
         [0035]     The adjusting gear unit  1  and its stationary gear ratio i 0  are designed so that the camshaft  3  is brought into its base position during startup of the internal-combustion engine through simple braking of the adjusting shaft  6 , and the internal-combustion engine thus becomes ready to start.  
         [0036]     For a stationary adjusting shaft  6  and input part  4  turning to the right, the following applies for the setting of i 0 :  
         [0037]     For i 0 &lt;0, a negative gear unit with retard adjustment is provided; for i 0 &lt;1, a positive gear unit with advance adjustment is provided; and for i 0 &gt;1, a positive gear unit with retard adjustment is provided.  
         [0038]     In  FIG. 2 , a circuit diagram for the stator  9  of the adjusting motor  2  is shown. The adjusting motor  2  is formed as a brushless DC motor with three phases  11  connected in a star, which have stator windings  12  and are powered by a controller  13  via phase-corrected control lines  15 .  
         [0039]     The three phases  11  are connected in a triangle by short-circuit lines  14 . In the short-circuit lines  14 , short-circuit switches  16  are provided, which are closed when the adjusting motor  2  is not powered and which are opened when the adjusting motor  2  is powered. Closing the short-circuit switches  16  makes a short-circuit current flow, which is used for short-circuit braking of the adjusting motor  2  operated as a generator. The closing of the short-circuit switches  16  can be realized individually or as a whole, which allows the braking force to be controlled.  
         [0040]     Because a short-circuit current that is too high endangers the adjusting motor  2 , a current limiter is necessary. This can be realized through current-dependent opening of the short-circuit switches  16 , which automatically close, for example, through spring force, when the current falls below a limiting value.  
         [0041]     The short-circuit current can also be limited by power resistors  17  in the short-circuit lines  14 . An electric current regulator  18 , which is arranged in the short-circuit lines  14  and which is powered by the short-circuit current, is used for the same purpose.  
         [0042]     In  FIGS. 3 and 4 , adjusting gear units are shown, which are formed as triple-shaft gear units, with similar components that are arranged differently, however.  
         [0043]      FIG. 3  shows a double eccentric gear unit  19  with a chain wheel  21  fixed to the crankshaft, a cover  25  fixed to the camshaft, and an adjusting shaft, which is formed as a double eccentric shaft  29 . This is connected to a not-shown adjusting motor via a suitable detachable keyed shaft coupling  37 . The detachable couplings can also be, among other things, splined, polygon, toothed, two-edged, square, and hexagonal shaft couplings.  
         [0044]     The cover  25  that is fixed to the camshaft is attached with the help of a central standard tension screw  31  via an adapter sleeve  30  with a camshaft pin  38  of a camshaft  65 . An opening  66  of the shaft coupling  37  enables the access of a drive tool to a head  36  of the central standard tension screw  31 .  
         [0045]     The position of the angle of rotation between the camshaft  65  and the cover  25  fixed to the camshaft is set by a positioning pin  39 , which is arranged with a force fit in aligned bore holes of the cover  25  and the camshaft pin  38 .  
         [0046]     The adapter sleeve  30  is used simultaneously as a bearing surface for a needle bushing  32  of the double eccentric shaft  29 . This has two equal, but offset by 180° and thus completely balanced eccentrics  67 , which drive two structurally similar spur pinions  28  via sliding bearing  33 . The spur pinions  28  intermesh with internal teeth  22  of a ring gear  20 , which is fixed to the crankshaft and which is formed integrally with the chain wheel  21 .  
         [0047]     The cover  25  that is fixed to the camshaft has axial bore holes  63 , in which pins  26  are pressed. These penetrate through axial bore holes  27  of the structurally similar spur pinions  28  and project through axial bore holes  68  of a cover plate  34 . The axial bore holes  63 ,  68  are aligned and lie at a uniform distance on a circle about the rotational axis  64  of the camshaft adjuster. The axial bore holes  27  have a diameter that is greater by twice the eccentricity of the eccentric  67  than the pins  26 , which have linear contact on the inner periphery of the axial bore holes  27 .  
         [0048]     The cover plate  34  is used for closing the double eccentric gear unit  19  and for axial positioning of the double eccentric shaft  29 , the spur pinions  28 , and the ring gear  20 . It is fixed in the axial direction by securing rings  35 . These sit in grooves  78 , which are arranged on the ends of the pins  26  projecting from the axial bore holes  68  of the cover plate  34 . The position of the grooves  78  determines the distance of the inner surfaces  79 ,  80  of the cover  25  and the cover plate  34 . Here, the axial play necessary for the relative motion relative to the corresponding contact surfaces of the double eccentric shaft  29 , the spur pinions  28 , and the ring gear  20  is taken into account.  
         [0049]     The ring gear  20  is supported on the cover  25  by a sliding bearing  43 , which receives, among other things, the forces of the chain wheel  21 . This is formed integrally with the ring gear  20  and is in torsion-proof connection to the crankshaft of the internal-combustion engine via a chain, by which it is driven at half the crankshaft rotational speed. The driving torque of the chain wheel  21  is transferred via the spur pinions  28  and the pins  26  to the cover  25  and the camshaft  65 . The number of pins  26  depends on the magnitude of the driving torque.  
         [0050]     The double eccentric gear unit  19  is lubricated by lubricating motor oil. This is led from an inflow line  40  of the camshaft pin  38  into the needle bushing  32  and from there through centrifugal force via radial lubricating oil bore holes  41  in the sliding bearing  33 , in the axial bore holes  27 , to the internal teeth  22 , to the sliding bearing  43  and via closing bore holes  23 ,  24  into the engine chamber. Oil is removed from the double eccentric shaft  29  through radial discharge bore holes  42 . The double eccentric gear unit  19  is a positive gear unit, that means the direction of rotation of the chain wheel  21  and the camshaft  64  are the same. Because each of the spur pinions  28  has a smaller tooth number Z NW  than the tooth number Z KW  of the ring gear  20  that is fixed to the crankshaft, this produces a stationary gear ratio:  
         i   0     =           Z   NW       Z   KW       ⁢   0     &lt;     i   1     &lt;   1.         
 
         [0051]     In the present case, if the rotational speed of the double eccentric shaft  29 , for example, through short-circuit braking of the adjusting motor, is smaller than that of the chain wheel  21 , then its rotational speed is lower than that of the camshaft  65 , wherein this is adjusted in the direction towards an “advanced” position.  
         [0052]      FIG. 4  shows another double eccentric gear unit  44 , with a chain wheel  46  that is fixed to the crankshaft, a ring gear  51  that is fixed to the camshaft, and an adjusting shaft formed as a double eccentric shaft  50 . This is connected to the adjusting motor (not shown) via a detachable splined shaft coupling  62 . The double eccentric gear unit  44  is tensioned by a special central tension screw  54  with a camshaft pin  55  of a camshaft  69 . Here, the position of the angle of rotation between the camshaft  69  and the double eccentric gear unit  44  is also set by a positioning pin  60 , which sits in a force fit in aligned bore holes of the ring gear  51  and the camshaft pin  55 . The central special tension screw  54  can be tightened through the splined shaft coupling  62 .  
         [0053]     A cylindrical head  53  of the special tension screw  54  is used simultaneously as the support surface for the needle bushing  57  of the double eccentric shaft  50 , which is therefore built extremely short. In turn, it has two equal eccentrics  70 , which are offset by 180° and which drive two structurally similar spur pinions  49  via the roller bearings  56 . The roller bearings  56  can also be replaced by sliding bearings, which produce savings in terms of cost and installation space but exhibit higher friction.  
         [0054]     The spur pinions  49  intermesh with internal teeth  52  of the ring gear  51  that is fixed to the camshaft. On its periphery, there is a drive wheel  45  that is fixed to the crankshaft with a peripheral part  75  that is formed integrally with the chain wheel  46  and a side part  76 . The latter is used, among other things, for closing the side of the double eccentric gear unit  44 . The peripheral part  75  is supported on the periphery of the ring gear  51  in a sliding bearing  58 . The side part  76  has axial bore holes  77 , in which axial pins  47  are pressed, which engage in bore holes  48  of the spur pinions  49  as in  FIG. 3  and transfer the driving torque of the drive wheel  45  via the spur pinions  49  to the ring gear  51  and to the camshaft  69 . The drive wheel  45  that is fixed to the crankshaft and with it the spur pinions  49  and the double eccentric shaft  50  are fixed in the axial direction by a retaining ring  59 . This sits in a radial groove  71  of the drive wheel  45  that is fixed to the crankshaft and contacts with one edge an end  72  of the ring gear  51  near the camshaft. The end  73  of the ring gear  45  far from the camshaft contacts the axial inner side  74  of the drive wheel  45  with play. This play enables the relative motion of the ring gear  51 , drive wheel  45 , spur pinions  49 , and double eccentric shaft  50 .  
         [0055]     The double eccentric gear unit  44  is lubricated as in the double eccentric gear unit  19  through an inflow bore hole  61  to the needle bushing  57  and from there through centrifugal force to the other components.  
         [0056]     The double eccentric gear unit  44  likewise concerns a positive gear unit. Because the tooth number Z NW  of the ring gear  52  that is fixed to the camshaft is greater than the tooth number Z KW  of each of the structurally similar spur pinions  49 , this produces a stationary gear ratio:  
         i   0     =         Z   NW       Z   KW       &gt;   1         
 
         [0057]     In this case, if the rotational speed of the double eccentric shaft, for example, through short-circuit braking of the adjusting motor, is smaller than that of the chain wheel  46 , then the camshaft  69  turns slower than this and adjusts towards a “retarded” position.  
         [0058]     The double eccentric gear unit  19  is used as the adjusting gear unit of an exhaust camshaft with “advanced” base position. The other double eccentric gear unit  44  is used as an adjusting gear unit of an inlet camshaft with “retarded” base position.  
                                         List of reference symbols                                1   Adjusting gear unit       2   Adjusting motor       3   Camshaft       4   Input part       5   Output part       6   Adjusting shaft       7   Drive wheel       8   Permanent magnet rotor       9   Stator       10   Housing       11   Phase       12   Stator winding       13   Controller       14   Short-circuit line       15   Control line       16   Short-circuit switch       17   Power resistor       18   Electronic current regulator       19   Double eccentric gear unit       20   Ring gear fixed to crankshaft       21   Chain wheel       22   Internal teeth       23   Discharge bore hole       24   Discharge bore hole       25   Cover fixed to the camshaft       26   Pin       27   Axial bore hole       28   Spur pinion       29   Double eccentric shaft       30   Adapter sleeve       31   Standard tension screw       32   Needle bushing       33   Sliding bearing       34   Seal cover       35   Securing ring       36   Standard head       37   Keyed shaft coupling       38   Camshaft pin       39   Positioning pin       40   Inflow line       41   Lubricating oil bore hole       42   Discharge bore hole       43   Slide bearing       44   Other double eccentric gear unit       45   Drive wheel fixed to the crankshaft       46   Chain wheel       47   Axial pin       48   Bore hole       49   Spur pinion       50   Double eccentric shaft       51   Ring gear fixed to camshaft       52   Internal teeth       53   Cylindrical head       54   Special tension screw       55   Camshaft pin       56   Roller bearing       57   Needle bushing       58   Slide bearing       59   Securing ring       60   Positioning pin       61   Inflow bore hole       62   Splined shaft coupling       63   Axial bore hole       64   Rotational axis       65   Camshaft       66   Opening       67   Eccentric       68   Axial bore hole       69   Camshaft       70   Eccentric       71   Radial groove       72   End near camshaft       73   End far from camshaft       74   Axial inner side       75   Peripheral part       76   Side part       77   Axial bore hole       78   Groove       79   Inner side       80   Inner side