DE10257706A1 - Electrically-driven camshaft adjuster for IC engine allows adjustment of camshaft into basic advanced or retarded position by braking of adjustment shaft when setting drive rotates - Google Patents

Abstract

The camshaft adjuster has a setting drive (1) provided by a triple shaft gear unit having an input part (4) fixed to the crankshaft, an output part (5) fixed to the camshaft (3) and an adjustment shaft (6) coupled to an electric setting motor (2) having a permanent magnet rotor (8). The gear unit provides stationary gear ratios allowing the camshaft to be positioned in a basic advanced or retarded position by braking the adjustment shaft when the setting drive rotates, e.g. via short-circuit braking of the electric setting motor.

Description

Field of the Invention

The invention relates to an adjusting device for the angular position the camshaft to the crankshaft of an internal combustion engine, in particular according to the preamble of claim 1.

background the invention

To use with an internal combustion engine hydraulic or electric camshaft adjuster a safe To ensure engine start the camshaft must be in a certain basic position when starting to the crankshaft. For the intake camshaft, this is usually “late”, for the exhaust camshaft in "early".

In normal vehicle operation the camshaft is regulated in the respective when the engine is switched off Base position driven and fixed or locked there. It serves with the electric camshaft adjustment an electric adjustment motor and with hydraulic camshaft adjustment a hydraulic one Rotary piston adjuster, one as a wing cell, swivel or segment wing Has locking unit. This fixes the hydraulic adjuster in its basic position until after the restart of the internal combustion engine a sufficient high oil pressure to adjust the camshaft.

When the internal combustion engine stalls is however a regulated adjustment of the hydraulic camshaft adjuster impossible, so the camshaft is in an undefined position outside the base position.

With hydraulic camshaft adjusters with the base position in "late", the camshaft at next Start of the internal combustion engine and the lack of oil pressure due to this of the camshaft friction torque, which is opposite to the direction of rotation of the camshaft acts automatically in the late Base position adjusted. If the base position is in "early", the camshaft must in the absence of oil pressure against the camshaft friction torque in the early base position become. This is usually done with the help of a balancing spring, which is the same but opposite to the camshaft friction torque Moment created.

These are common in hydraulic camshaft adjusters Methods to reach the base position after choking the Internal combustion engines are in electrically driven camshaft adjusters not necessary because the actuator also drives the camshaft stationary internal combustion engine or when starting in the respective Can adjust base position. With electric camshaft adjusters can however, the adjusting motor and / or its control fail and thereby preventing the basic or emergency running position from being reached, the for one at least limited Operation and restart are required.

vorliegt, deren Größe die Getriebegattung (Plus- oder Minusgetriebe) und die Verstellrichtung der Nockenwelle (früh- oder spätliegende Basisposition) bestimmt. Bei dieser Verstellvorrichtung wird eine leichtgängige und genaue Einstellung der Nockenwellenlage angestrebt. Damit bei Ausfall des Verstellmotor-Systems die Funktion des Verbrennungsmotors zumindest notdürftig aufrechterhalten werden kann, ist eine Begrenzung des Verstellwinkels vorgesehen. Ein Hinweis auf das Erreichen der Basis- bzw. einer Notlaufposition in einem solchen Fall fehlt jedoch.In the DE 41 10 195 A1 describes an electrical adjusting device for the angular position of the camshaft relative to the crankshaft of an internal combustion engine, with an adjusting gear which is designed as a three-shaft gear and has a drive part fixed to the crankshaft, an output part fixed to the camshaft and an adjusting shaft. The adjusting shaft is rotatably connected to an elec tric adjusting motor, which has a permanent magnet rotor and a fixed stator, with a stationary gear ratio between the input and output parts when the adjusting shaft is stationary

is present, the size of which determines the type of transmission (plus or minus transmission) and the adjustment direction of the camshaft (early or late base position). This adjustment device strives for a smooth and precise setting of the camshaft position. A limitation of the adjustment angle is provided so that the function of the internal combustion engine can at least be maintained in the event of a failure of the adjustment motor system. However, there is no indication that the base position or an emergency running position has been reached in such a case.

The invention is based on the object to create an electric camshaft adjuster that is the camshaft even in the event of failure of the variable motor or its control or power supply simple way and without current in their emergency or basic position adjusted.

Summary the invention

The design of the adjustment gear allows the size of the stationary gear ratio i ₀ and thus the adjustment of the camshaft to be determined. The camshaft is adjusted in the direction of the early or late base or emergency running position in the event of a failure of the adjustment motor or its power supply by simply braking the adjustment shaft while the adjustment gear is rotating. This can take place during engine operation and when the internal combustion engine is running down or starting. The base position of the camshaft is optimally suitable for starting the engine and for low engine speeds, and is also possible for higher speeds, so that at least one workshop can be reached in this way.

The adjustment shaft can be braked by a mechanical or an eddy current brake. However, these brakes require electrical current to operate them. In contrast, the short-circuit brake according to the invention works with short-circuit current that is generated in the trailed servomotor and thus makes the short-circuit brake electrically self-sufficient. Since there is no mechanical friction, the short-circuit brake works without wear.

When selecting the variable speed gearboxes, minus or plus gearboxes come into question. Negative gearboxes have a stationary gear ratio i ₀ <0, plus gears have a stationary gear ratio i ₀ > 0. With positive stationary gear ratios i ₀ , the input and output shafts have the same direction of rotation, with negative stationary gear ratios i ₀ opposite directions of rotation with respect to a stationary adjusting shaft and those connected to it components.

Will the with a minus gear Adjustment shaft held and the drive shaft rotates clockwise, this is how the output shaft and thus the cam shaft turn clockwise what a late adjustment equivalent.

If the adjustment shaft is held in a positive gearbox with a stationary gear ratio i ₀ > 1 and the drive shaft is rotated clockwise, the output shaft rotates more slowly than the drive shaft, that is, counterclockwise and thus also towards the base position "late".

If the adjustment shaft is held on a positive gearbox with a stationary gear ratio 0 <i ₀ <1 and the drive shaft rotates clockwise, the output shaft rotates faster than the drive shaft, ie clockwise and thus in the direction of the base position "early". These relationships can be applied to all three-shaft transmissions in question.

It is advantageous to use an as a variable speed gear Double eccentric gear or a wobble gear and another double eccentric gear are provided. Double eccentric gears are characterized by low Friction, simple construction and vibration-free running.

An advantageous training of Invention is that the double eccentric gear is fixed to the camshaft Has lid which is fixedly connected with axial pins in the bores of two identical spur gears line contact engage and that the spur gears, that from the actuator motor over a double eccentric shaft can be driven, with a crankshaft fixed Comb ring gear.

The use of a central standard clamping screw with a screw sleeve as storage space for the roller bearing the double eccentric shaft offers cost advantages, but it does require larger axial Space. The plain bearing of the identically constructed spur gears offers across from a rolling bearing Cost and space advantages with increased friction loss.

It is also advantageous that the number of teeth Z _{NW of} each of the two identically constructed spur gears (equal to the number of output teeth) is smaller than the number of teeth Z _{KW of} the ring gear fixed to the crankshaft (equal to the number of drive teeth), which leads to a stationary gear ratio 0 <i ₀ <1. This stationary gear ratio causes a camshaft adjustment in the "early" direction in the present positive gearbox and braking of the adjusting shaft, as is common with exhaust camshafts.

An advantageous development of Invention is that another double eccentric gear has a crankshaft-proof drive wheel with axial pins is firmly connected in the bores of two structurally identical spur gears with line contact intervene and that the identically constructed spur gears that from the adjusting motor a double eccentric shaft can be driven, with a camshaft fixed Comb ring gear.

With the bearing of the double eccentric shaft the cylindrical screw head of a central special clamping screw axial installation space is gained. Both solutions for the bearing of the double eccentric shaft and the spur gears are suitable for both Double eccentric.

It is also advantageous that the number of teeth Z _{NW of} the ring gear fixed to the camshaft (equal to the number of output teeth) is greater than the number of teeth Z _KW of each of the identically constructed spur gears (equal to the number of drive teeth), which leads to a stationary gear ratio i ₀ > 1.

The three phases of the variable motor cause a fluctuation-free torque curve of the adjustment motor with low construction costs. The possibility one, two or all to short three phases, allows a fine regulation of the short-circuit braking torque.

As short-circuit switch provided are closed when the actuator is de-energized and when the actuator is energized Adjustment motor opened occur in the event of failure of the servomotor and / or its power supply immediately the fail-safe function of returning the camshaft to your Basic or emergency running position. This also applies to the case of a stalled internal combustion engine, whose camshaft position is corrected during the subsequent starting process becomes.

A clocked short circuit is also suitable for limiting the temperature development of the variable motor. The short-circuit switches are opened when a certain short-circuit current is reached and then closed automatically. This process is preferably controlled and operated by the short-circuit current itself, so that the clocking works even in the event of a failure of the adjusting motor or the voltage supply to the control device. The braking current can also be taken from active components, for example from an accumulator. That automatically Closing takes place, for example, by spring force.

It is to limit the high short-circuit currents It is advantageous that there is a line resistance in the short-circuit lines is arranged.

It is also an advantage that in the Short-circuit lines an electronic operated with short-circuit current Current regulator is provided. This solution also works independently of the power supply of the adjustment motor.

Short description of the drawings

Further features of the invention result from the following description and the drawings in which a embodiment the invention is shown schematically. Show it:

1 a camshaft adjusting device with an adjusting gear designed as a three-shaft gear and an electric adjusting motor which has a stator fixed to the housing;

2 a circuit diagram of a three-phase DC variable motor with short-circuit lines and short-circuit switches;

3 a double eccentric gear with a crankshaft-fixed ring gear;

4 a double eccentric gear with a ring gear fixed to the camshaft.

Full Description of the drawings

In 1 is a camshaft adjustment device with an adjustment gear 1 and an actuator 2 schematically shown, for adjusting the angle of rotation between a crankshaft, not shown, and a camshaft 3 an internal combustion engine, not shown.

The variable speed gear 1 is designed as a three-shaft gearbox with a drive part fixed to the crankshaft 4 that a drive wheel 7 has, a camshaft-fixed drive part 5 and an adjustment shaft 6 using a permanent magnet rotor 8th of the adjustment motor 2 is rotatably connected. The adjustment motor 2 has a stator 9 on that in a casing 10 is firmly arranged.

The camshaft 3 has a basic or emergency running position, which must be achieved for a safe start and limited operation of the internal combustion engine. This works with the servomotor intact 2 even after a gagging of the internal combustion engine without difficulty, since the adjustment motor 2 the camshaft 3 with the internal combustion engine stopped or during restart restarted to the basic position. But it also has to work if the actuator fails 2 at least limited engine operation and a restart are possible in order to be able to reach at least one workshop.

The variable speed gear 1 and its stationary gear ratio i ₀ are designed so that by simply braking the adjusting shaft 6 the camshaft 3 reaches its basic position when the internal combustion engine is started and the internal combustion engine is thereby startable.

With the adjusting shaft stopped 6 and clockwise rotating drive part 4 applies to the interpretation of i ₀ :
At i ₀ <0 there is a minus gear with late adjustment; with i ₀ <1 a positive transmission with early adjustment and with i ₀ > 1 a positive transmission with late adjustment.

In 2 is a circuit diagram of the stator 9 of the adjustment motor 2 shown. The adjustment motor 2 is designed as a brushless DC motor with three phases connected in a star 11 who have favourited Stator Windings 12 have and from a control unit 13 via control lines 15 be supplied with electricity in phase.

The three phases 11 are through short-circuit lines 14 connected in a triangle. In the short-circuit lines 14 are short-circuit switches 16 provided that when the actuator is de-energized 2 closed and with the adjusting motor energized 2 are open. By closing the short circuit switch 16 a short-circuit current flows, which is used to brake the short-circuit of the servomotor operated as a generator 2 serves. Closing the short circuit switches 16 can be done individually or as a whole, whereby the braking force can be regulated.

Because the short-circuit current is too high, the servomotor 2 current limitation is required. This can be done by opening the short-circuit switch depending on the current 16 take place, which close automatically when falling below a limit value - for example by spring force.

The short-circuit current can also be controlled by power resistors 17 in the short-circuit lines 14 limit. An electric current regulator 18 that in the short-circuit lines 14 is arranged and fed by the short-circuit current, serves the same purpose.

In the 3 and 4 Adjustment gears are shown which are designed as three-shaft gears with similar, but differently arranged components.

3 shows a double eccentric gear 19 with a crankshaft-proof sprocket 21 , a camshaft-proof cover 25 and an adjustment shaft, which acts as a double eccentric shaft 29 is trained. This is via a detachable key shaft coupling 37 connected to a servomotor, not shown. Wedge, polygon, tooth, double, square, and hexagonal shaft couplings are also conceivable as releasable couplings.

The camshaft-proof cover 25 is with the help of a central standard clamping screw 31 via an adapter sleeve 30 with a camshaft journal 38 a camshaft 65 braced. An opening 66 the key shaft coupling 37 enables access of a screwing tool to a screw head 36 the central standard clamping screw 31 ,

The angular position between the camshaft 65 and the camshaft-proof cover 25 is through a locating pin 39 fixed with the press fit in aligned holes of the cover 25 and the camshaft journal 38 is arranged.

The adapter sleeve 30 also serves as a storage area for a needle sleeve 32 the double eccentric shaft 29 , This has two identical, but offset by 180 ° and thus fully balanced eccentric 67 on that over plain bearings 33 two identical spur gears 28 drive. The spur gears 28 comb with internal teeth 22 a ring gear fixed to the crankshaft 20 that one piece with the sprocket 21 is trained.

The camshaft-proof cover 25 has axial holes 63 on, in the pens 26 are pressed in. These pass through axial bores 27 the identically constructed spur gears 28 and protrude through axial bores 68 of an end cover 34 , The axial bores 63 . 68 are aligned and are evenly spaced on a circle around the axis of rotation 64 of the camshaft adjuster. The axial bores 27 have a double eccentricity of the eccentric 67 larger diameter than the pins 26 that are on the inner circumference of the axial bores 27 have a line contact.

The end cover 34 serves to complete the double eccentric gear 19 and for the axial fixation of the double eccentric shaft 29 , the spur gears 28 and the ring gear 20 , It is through circlips 35 axially fixed. These sit in grooves 78 that at the from the axial holes 68 of the end cover 34 protruding ends of the pins 26 are arranged. The location of the grooves 78 determines the distance between the inner surfaces 79 . 80 of the lid 25 and the end cover 34 , The axial play required for the relative movement to the corresponding contact surfaces of the double eccentric shaft 29 , the spur gears 28 and the ring gear 20 considered.

The ring gear 20 is on the lid 25 in a plain bearing 43 stored, among other things, the forces of the sprocket 21 receives. This is with the ring gear 20 formed in one piece and is connected via a chain to the crankshaft of the internal combustion engine in a rotationally fixed connection, from which it is driven at half the crankshaft speed. The drive torque of the chain wheel 21 is about the spur gears 28 and the pens 26 on the lid 25 and the camshaft 65 transfer. The number of pens 26 depends on the amount of drive torque.

The lubrication of the double eccentric gear 19 done by engine lubricating oil. This comes from an inflow line 40 of the camshaft journal 38 into the needle sleeve 32 and from there by centrifugal force over radial lubrication oil holes 41 in plain bearings 33 , in the axial holes 27 , for internal teeth 22 , to the plain bearing 43 and through end holes 23 . 24 in the engine compartment. The double eccentric shaft 29 is through radial outflow bores 42 de-oiled. With the double eccentric gear 19 it is a plus gear, that is, the direction of rotation of the sprocket 21 and camshaft 64 are the same. Because each of the spur gears 28 a smaller number of teeth Z _NW than the number of teeth Z _{KW of} the crankshaft-fixed ring gear 20 has a stationary gear ratio:

In the present case it is the speed of the double eccentric shaft 29 for example, due to short-circuit brakes of the variable motor smaller than that of the chain wheel 21 , its speed is lower than that of the camshaft 65 , which adjusts it towards "early".

4 shows another double eccentric gear 44 , with a crankshaft-proof sprocket 46 , a camshaft-proof ring gear 51 and one as a double eccentric shaft 50 trained adjustment shaft. This is via a detachable spline coupling 62 connected to the adjusting motor, not shown. The double eccentric gear 44 is through a central special clamping screw 54 with a camshaft journal 55 a camshaft 69 braced. Again, the angular position between the camshaft 69 and the double eccentric gear 44 with a locating pin 60 fixed, the press fit in aligned holes of the ring gear 51 and the camshaft journal 55 sitting. The central special clamping screw 54 is through the spline coupling 62 tightenable through.

A cylindrical screw head 53 the special clamping screw 54 also serves as a storage area for the needle sleeve 57 the double eccentric shaft 50 , which makes it extremely short. It in turn has two identical eccentrics offset by 180 ° 70 on that about rolling bearings 56 two identical spur gears 49 drive. The roller bearings 56 can also be replaced by plain bearings, which save costs and space, but have higher friction.

The spur gears 49 comb with internal teeth 52 of the ring gear fixed to the camshaft 51 , On the circumference is a crankshaft-proof drive wheel 45 arranged with a peripheral part 75 the one piece with the sprocket 46 and a side part 76 is trained. The latter serves, among other things, as the side end of the double eccentric gear 44 , The peripheral part 75 is on the circumference of the ring gear 51 in a plain bearing 58 stored. The side part 76 has axial holes 77 on, in the axial pins 47 are pressed in as in 3 in holes 48 the spur gears 49 intervene and the drive torque of the drive wheel 45 over the spur gears 49 on the ring gear 51 and on the camshaft 69 transfer. The crankshaft-proof drive wheel 45 and with him the spur gears 49 and the double eccentric shaft 50 are by a snap ring 59 axially fixed. This sits in a radial groove 71 of the crankshaft fixed to triebsrads 45 and lies with a flank on a face near the camshaft 72 of the ring gear 51 on. The end face remote from the camshaft 73 of the ring gear 45 lies with play on the axial inside 74 of the drive wheel 45 on. This game enables the relative movement of ring gear 51 , Drive wheel 45 , Spur gears 49 and double eccentric shaft 50 ,

The lubrication of the double eccentric gear 44 takes place as with the double eccentric gear 19 through an inflow hole 61 to the needle sleeve 57 and from there to the other components by centrifugal force.

With the double eccentric gear 44 it is also a plus gear. Since the number of teeth Z _{NW of} the ring gear fixed to the camshaft 52 larger than the number of teeth Z _{KW of} each of the identical spur gears 49 is a stationary gear ratio:

In this case, the speed of the double eccentric shaft is lower than that of the sprocket, for example due to short-circuit braking of the servomotor 46 , the camshaft turns 69 slower than this and thus adjusts to "late".

The double eccentric gear 19 serves as the adjustment gear of an exhaust camshaft with the "early" base position, the other double eccentric gear 44 as adjustment gear of an intake camshaft with base position "late".

1

variator

2

adjusting

3

camshaft

4

driving part

5

driving part

6

adjusting

7

drive wheel

8th

Permanent magnet rotor

9

stator

10

casing

11

phase

12

stator

13

control unit

14

Short-circuit line

15

control line

16

Short-circuit switch

17

power resistor

18

electronic current regulator

19

double eccentric

20

crankshaft-fixed ring gear

21

Sprocket

22

internal gearing

23

drain hole

24

drain hole

25

camshaft-fixed cover

26

pen

27

axial drilling

28

spur gear

29

double eccentric

30

clamping sleeve

31

Standard clamping screw

32

needle sleeve

33

bearings

34

End cover

35

circlip

36

Standard screw head

37

Feather shaft coupling

38

camshaft journal

39

locating pin

40

inflow line

41

Oil drilling

42

outflow bore

43

bearings

44

other double eccentric

45

crankshaft-fixed drive wheel

46

Sprocket

47

axial pen

48

drilling

49

spur gear

50

double eccentric

51

fixed to the camshaft ring gear

52

internal gearing

53

cylindrical screw head

54

Special clamping screw

55

camshaft journal

56

roller bearing

57

needle sleeve

58

bearings

59

circlip

60

locating pin

61

supply bore

62

Spline coupling

63

axial drilling

64

axis of rotation

65

camshaft

66

opening

67

eccentric

68

axial bore

69

camshaft

70

eccentric

71

radial groove

72

camshafts close front

73

camshafts distant front

74

axial inside

75

peripheral part

76

side panel

77

axial drilling

78

groove

79

inside

80

inside

Claims (15)

Electrical adjustment device for the angular position of the camshaft ( 3 . 65 . 69 ) to the crank shaft of an internal combustion engine, with an adjusting gear ( 1 ), which is designed as a three-shaft transmission and a crankshaft-fixed drive part ( 4 ), a camshaft-fixed output part ( 5 ) and an adjustment shaft ( 6 ) which is non-rotatable with an electric adjustment motor ( 2 ) connected to a permanent magnet rotor ( 7 ) and a housing-fixed stator ( 8th ), whereby between the drive part ( 4 ) and stripping section ( 5 ) with the adjusting shaft stopped ( 6 ) a stationary gear ratio

is present, the size of which is the type of the adjustment gear ( 1 ) as plus or minus gear and the adjustment direction of the camshaft ( 3 . 65 . 69 ) determined in an early or late base position, characterized in that due to a suitable constructive design of the adjustment gear ( 1 ) Stationary gear ratios i ₀ can be implemented, by means of which an early and a late base position of the camshaft ( 3 . 65 . 69 ) simply by braking the adjustment shaft ( 6 ) with rotating adjustment gear ( 1 ) can be reached and that the braking of the adjustment shaft ( 6 ) preferably by short-circuit braking of the adjustment motor ( 2 ) he follows. Adjusting device according to claim 1, characterized in that with a stationary gear ratio 0 <i ₀ <1 a positive gear for a camshaft adjustment in the "early" direction and with a stationary gear ratio i ₀ > 1 a positive gear for a camshaft adjustment in the "late" direction can be realized. Adjusting device according to claim 2, characterized in that as the adjusting gear ( 1 ) a double eccentric gear ( 19 ) or a wobble gear and another double eccentric gear ( 44 ) are provided. Adjusting device according to claim 3, characterized in that the double eccentric gear ( 19 ) a camshaft-proof cover ( 25 ) with axial pins ( 26 ) is firmly connected in the holes ( 27 ) two identical spur gears ( 28 ) with line contact and that the spur gears ( 28 ) by the adjustment motor ( 2 ) via a double eccentric shaft ( 29 ) can be driven with a ring gear fixed ring gear ( 20 ) comb. Adjusting device according to claim 4, characterized in that the double eccentric shaft ( 29 ) on a screw sleeve ( 30 ) a central standard clamping screw ( 31 ) with a needle sleeve ( 32 ) with roller bearings and the identically constructed spur gears ( 28 ) on the double eccentric shaft ( 29 ) in plain bearings ( 33 ) are stored. Adjusting device according to claim 5, characterized in that the number of teeth Z _{NW of} each of the two identical spur gears ( 28 ) (equal to the number of driven teeth) less than the number of teeth Z _{KW of} the crankshaft-fixed ring gear ( 20 ) (equal to the number of drive teeth), which leads to a stationary gear ratio 0 <i ₀ <1. Adjusting device according to claim 3, characterized in that another double eccentric gear ( 44 ) a crankshaft-proof drive wheel ( 45 ) has that with axial pins ( 47 ) is firmly connected in the holes ( 48 ) two identical spur gears ( 49 ) with line contact and that the identically constructed spur gears ( 49 ) by the adjustment motor ( 2 ) via a double eccentric shaft ( 50 ) can be driven with a camshaft-fixed ring gear ( 51 ) comb. Adjusting device according to claim 7, characterized in that the double eccentric shaft ( 50 ) on a cylindrical screw head ( 53 ) a central special clamping screw ( 54 ) and the identically constructed spur gears ( 49 ) on the double eccentric shaft ( 50 ) preferred in rolling bearings ( 56 ) are stored. Adjusting device according to claim 8, characterized in that the number of output teeth Z _{NW of} the camshaft-fixed ring gear ( 51 ) greater than the number of drive teeth Z _KW of each of the identical spur gears ( 49 ) is what leads to a stationary gear ratio i ₀ > 1. Adjusting device according to claim 1, characterized in that the stator ( 8th ) of the adjustment motor ( 2 ) preferably three phases ( 10 ), which individually and as a whole for short-circuit braking of the adjustment motor ( 2 ) can be short-circuited. Adjusting device according to claim 10, characterized in that short-circuit switch ( 15 ) are provided, which are used with a de-energized servomotor ( 2 ) closed and with powered actuator ( 2 ) are open. Adjusting device according to claim 11, characterized in that measures are provided to limit the short-circuit current. Adjusting device according to claim 12, characterized in that the short-circuit switches ( 15 ) If a limit value of the short-circuit current is exceeded, preferably open with the help of the same and close automatically when the same is signed. Adjusting device according to claim 12, characterized in that in the short-circuit line tungen ( 13 ) a line resistance ( 16 ) is arranged. Adjusting device according to claim 12, characterized in that in the short-circuit lines ( 13 ) an electronic current regulator operated with short-circuit current ( 17 ) is provided.