DE10352361B4 - Camshaft adjuster with electric drive - Google Patents

Abstract

Device for adjusting the control times of a camshaft (3, 3 ') with respect to a crankshaft of an internal combustion engine, with an adjusting gear (1, 1') designed as a three-shaft gear, which has a drive shaft (4, 4 ') connected to the crankshaft and one to the camshaft (3, 3 ') connected output shaft (5, 5') and an adjusting shaft (6, 6 ') connected to an electric adjusting motor (2, 2'), wherein between the drive and output shaft (4, 4 '; 5, 5 ') when the adjusting shaft (6, 6') is stationary, there is a stationary gear ratio io, the level of which is determined by the type of gear (minus or plus gear) and the adjustment direction of the camshaft (3, 3 '), which has a basic or emergency running position, with a Rotor (8, 8 ') is designed as a permanent magnet, characterized in that an electric brake (11), which is designed as at least one brake winding independent of the motor phases, around a stator tooth (13, 13') and / or around a Yoke section (1 2) of the electric adjusting motor (2, 2 ') is arranged and that the stationary gear ratio io is selected such that if the electric adjusting motor (2.2') and / or its control system fails after the adjusting shaft has been braked, the base or emergency position of the Camshaft (3, 3 ') can be reached and maintained.

Description

Field of invention

The invention relates to a device for adjusting the control times of a camshaft relative to a crankshaft of an internal combustion engine, with an adjusting gear designed as a three-shaft gear, which has a drive shaft connected to the crankshaft, an output shaft connected to the camshaft and an adjusting shaft connected to an electric adjusting motor.

Background of the invention

In order to ensure a safe engine start in an internal combustion engine with hydraulic or electric camshaft adjuster, the camshaft must be in the so-called basic or emergency position. In the case of intake camshafts this is usually in the late position, in the case of exhaust camshafts in the early position. In normal operation of the engine, the camshaft is moved into the respective base position in a controlled manner when it is switched off and fixed or locked there.

Conventional, hydraulically operated rotary piston adjusters such as vane-type adjusters, pivoting or segmented blades have a locking unit. This fixes the hydraulic adjuster in its basic position until enough oil pressure has built up to adjust the camshaft.

If the engine stalls, the camshaft can be in an undefined position outside of the basic position. In order to then safely adjust the camshaft to a defined position, the camshaft with hydraulic camshaft adjusters with the basic position in the late position is automatically switched to the late basic position when the combustion engine is next started and the oil pressure is missing due to the camshaft friction torque, which acts against the direction of rotation of the camshaft adjusted. If the base position is early, the camshaft must be adjusted to the early base position against the camshaft friction torque if there is no oil pressure. This is mostly done with the help of a compensating spring, which generates a torque directed opposite to the camshaft friction torque.

These methods for reaching the base positions after the internal combustion engine has stalled, which are customary in hydraulically actuated camshaft adjusters, can only be used to a limited extent in electrically driven camshaft adjusters. The sole adjustment based on the frictional torque is possible, but does not guarantee an adjustment to the basic position in every case. One solution would be to mount a spiral spring, which, however, requires additional, axial installation space.

In the case of electric camshaft adjusters, these methods are not necessary as long as the adjusting motor system is intact and the camshaft can be adjusted to the respective basic position even when the internal combustion engine is stopped or when it is restarted. However, the adjusting motor and / or its control can fail, which means that the basic position cannot be reached.

A generic device for adjusting control times of a camshaft is based DE 698 18 946 T2 emerged.

In the DE 41 10 195 A1 describes a device for the detachable connection and adjustment of camshafts and a crankshaft of an internal combustion engine with an adjusting gear designed as a three-shaft gear, which has a drive shaft connected to the crankshaft, an output shaft connected to a camshaft and an adjusting shaft connected to an electric adjusting motor, with between drive - and output shaft when the adjusting shaft is at a standstill, the level of which is determined by the type of gear (minus or plus gear) and the direction of adjustment of the camshafts in the basic or emergency position.

A smooth and precise setting of the camshaft position is aimed for in that adjustment device. A limitation of the adjustment angle is provided so that the function of the internal combustion engine can at least barely be maintained in the event of a failure of the adjusting motor system. However, there is no indication of reaching the basic or emergency position in such a case.

Furthermore, it has been found that the adjusting shaft must be braked in order to obtain a deterministic behavior when the emergency position is reached.

Object of the invention

The invention is therefore based on the object of constructing an electric camshaft adjuster in which the camshaft can be reliably adjusted into its basic position even if the adjusting motor and / or its control system fail.

Description of the invention

According to the invention, the object is achieved by the features of claim 1. After the adjusting shaft has been braked or fixed once, the camshaft is then turned by turning the The drive shaft is adjusted to its basic or emergency position when the internal combustion engine is running at low idle or - if it has stalled - when it is restarted, even with a failed variable motor system. In this position the vehicle can be started and operated with certain restrictions so that a workshop can be reached.

A prerequisite for autonomous reaching of the basic position is a suitable stationary gear ratio io, which determines the desired gear type (plus or minus gear) and the adjustment direction (late or early). When selecting the variable speed gears, negative or positive gears come into question. Minus gears have a stationary gear ratio io less than 0, plus gears a gear ratio greater than 0. With a positive stationary gear ratio io, the input and output shafts have the same direction of rotation, with a negative stationary gear ratio io opposite directions of rotation, based on a stationary adjusting shaft and the components connected to it.

If the adjustment shaft is held in a minus gear and the drive shaft rotates clockwise, the output shaft and thus the camshaft rotates counterclockwise, which corresponds to a retarded adjustment.

If in a plus gear with a stationary gear ratio i0> 1, the adjustment shaft is held and the drive shaft is rotated clockwise, the output shaft rotates more slowly than the drive shaft, i.e. it is adjusted in the late direction.

If the adjusting shaft is held in a positive gear with a stationary gear ratio 0 <i0 <1 and the drive shaft rotates clockwise, the output shaft rotates faster than the drive shaft, i.e. clockwise and therefore in the direction of advance.

These ratios can be applied to all variable displacement gears in question. In summary, if the adjusting motor fails, it is necessary to fix the adjusting shaft of a minus gear with i0 <0 or a plus gear with i0> 1 to reach a late basic position and to fix the adjusting shaft of a plus gear with 0 <i0 <1 to reach an early basic position.

It is advantageous that the adjusting motor has a permanent magnet rotor with a passive self-holding torque, which increases from a central position in both directions of rotation up to a maximum and then decreases again. The self-holding torque of the adjusting motor, increased by the converted frictional torque of the adjusting gear, only needs to have 60% - 100% of the converted, maximum, dynamic camshaft torque that acts back on the adjusting shaft, since the energy content of the peaks of the camshaft torque is low and the necessary holding torque is more due to the mean camshaft torque is determined. The use of a permanent magnet rotor has the advantage over a permanent magnet stator that the current only has to be passed into the stator which is fixed to the cylinder head.

It has also been found to be advantageous that the adjustment speed of the camshaft is preferably between 30 ° and 60 ° cam angle per second due to the selected stationary gear ratio io with stationary adjustment shafts and low idling speed of the internal combustion engine. It is irrelevant here whether the adjustment motor adjusts in one or two directions of rotation when the camshaft is reset to its base position.

It is necessary that in the control position of the camshafts the drive, output and adjustment shafts of the adjustment gear rotate at the same speed. In this way there is no relative movement between the crankshaft and the camshafts.

For example, known eccentric or wave gears or wobble or double planetary gears come into consideration as adjusting gears and the adjusting motors are designed as conventional brushless permanent magnet rotor motors or externally excited DC motors equipped with brushes.

Tests have shown that the measures described so far are not sufficient to achieve an adjustment to the basic position under all operating conditions. However, it has also been found that if the adjusting motor and / or its control fail, the camshaft can be adjusted in a defined manner into the basic or emergency position by means of an electric brake.

It has proven to be particularly advantageous to use this brake as an additional brake winding in the form of a coil, which is independent of the windings of the adjusting motor phases, in order to form at least one stator tooth or the yoke. Due to its simplicity, this solution is very cost-effective and easy to implement. In principle, however, a winding of the electric adjusting motor could also be used, which is short-circuited in the event of failure. For an optimal braking effect, the brake winding should not be wound around the yoke, but around a stator tooth, since the magnetic flux and thus the braking torque is greater due to the smaller distance to the rotor.

The magnetic flux, which changes when the adjusting motor is rotating, induces a voltage in the brake winding, which in turn induces a current when the ends are closed or the ends are short-circuited. Due to the self-induction of the brake winding, a force acts back on the permanent magnet rotor, which is opposite to its direction of movement. This decelerates the permanent magnet rotor.

In order to prevent the braking torque from being generated during normal operation, the circuit of the brake winding is only closed when there is no power supply to the adjusting motor. This closing can be done either by a passive component such as a relay or by an active component such as a transistor. To prevent damage from the short circuit, the current flow can be limited using a suitable current regulator. If necessary, an active current regulator can be used to specifically influence the braking torque in order to specifically influence the short-circuit current and thus the braking process as a function of the speed.

Tests have shown that the braking torque is a function of the total resistance, the inductance and the number of turns of the brake winding. The choice of these sizes depends on the design of the electric adjusting motor.

As the total resistance increases, the maximum braking torque remains more or less constant, but it shifts to higher speeds. In addition, the braking torque is weaker in the lower speed range and stronger in the upper speed range.

The number of turns should be selected as large as possible, since the approximately constant maximum torque shifts to higher speeds with smaller numbers of turns.

Figure list

• 1: eine schematische Darstellung eines Verstellgetriebes mit einem Verstellmotor, dessen Stator zylinderkopffest ist,
• 2: eine schematische Darstellung eines anderen Verstellgetriebes mit einem anderen Verstellmotor, dessen anderer Stator mit umläuft,
• 3: einen Ausschnitt des Stators, der zwei vorteilhafte Anordnungen einer als Bremswicklung ausgebildeten Bremse wiedergibt,
• 4: einen Schaltplan, aus dem die Ansteuerung eines Relais' zum Schließen eines Stromkreises, der die Bremswicklung enthält, hervorgeht.

Further features of the invention emerge from the following description and the drawing in which an embodiment of the invention is shown schematically. Show it:

• 1 : a schematic representation of a variable speed drive with a variable speed motor, the stator of which is fixed to the cylinder head,
• 2 : a schematic representation of another variable speed drive with another variable speed motor, the other stator of which also rotates,
• 3 : a section of the stator showing two advantageous arrangements of a brake designed as a brake winding,
• 4th : a circuit diagram showing the control of a relay for closing a circuit containing the brake winding.

Detailed description of the drawings

In the 1 and 2 are variable speed gears 1 , 1' with electric adjusting motors 2 , 2 ' shown, the adjustment of the angular position between the crankshaft, not shown, and the camshaft 3 , 3 ' an internal combustion engine.

The variable speed drive 1 , 1' is designed as a three-shaft transmission with a drive shaft 4th , 4 ' , an output shaft 5 , 5 ' and an adjusting shaft 6th , 6 ' .

The drive shaft 4th , 4 ' is with a drive wheel 7th , 7 ' and via this firmly connected to the crankshaft by means of a toothed wheel, not shown, or toothed belt or a toothed chain.

The output shaft 5 , 5 ' stands with the camshaft 3 , 3 ' and the adjusting shaft 6th , 6 ' with the rotor 8th , 8th' of the adjusting motor 2 , 2 ' in permanent connection.

The stator 9 of the adjusting motor 2 is with the cylinder head 10 firmly connected and stands still, the stator 9 ' of the adjusting motor 2 ' is with the drive wheel 7 ' firmly connected and rotates like the variable speed drive 1 with half the crankshaft speed. The stator 9 ' of the adjusting motor 2 ' rotates (see 2 ) with its rotor 8th' With.

The camshaft 3 , 3 ' has a basic or emergency position which must be reached for a safe start and limited operation. This succeeds with an intact adjusting motor 2 , 2 ' even after a stall of the internal combustion engine without difficulty, since the variable displacement motor 2 , 2 ' the camshaft 3 , 3 ' Adjusted to the basic position when the internal combustion engine is not running or when it is restarted. But it must also be done if the actuator motor fails 2 , 2 ' it should be possible to start again in order to reach at least one workshop.

The variable speed gear 1 , 1' and their stationary gear ratio io are designed so that by simply fixing the adjustment shafts 6th , 6 ' the camshafts 3 , 3 ' get into their base position when starting and the internal combustion engine can thus be started.

• Bei i0 < 0 liegt ein Minusgetriebe mit Spätverstellung vor; bei 0 < i0 < 1 ein PlusGetriebe mit Frühverstellung und bei i0 > 1 ein Plusgetriebe mit Spätverstellung.

With the adjusting shaft at a standstill 6th , 6 ' and clockwise drive shaft 4th , 4 ' applies to the interpretation of i0:

• If i0 <0 there is a minus gear with retarded adjustment; with 0 <i0 <1 a plus gear with advanced adjustment and with i0> 1 a plus gear with retarded adjustment.

Braking the adjusting shaft 6th , 6 ' takes place through an electrical brake designed as a brake winding 11 ( 3 ), through which an external braking torque is introduced. This has the same effect as the detent torque in both directions of rotation of the adjusting shaft 6th , 6 ' .

After a "stall" of the combustion engine or after a failure of the variable speed motor 2 , 2 ' can the camshaft 3 , 3 ' are in an undefined position. By braking the adjusting shaft 6th , 6 ' becomes the camshaft 3 , 3 ' during the subsequent start-up due to the rotary movement of the drive shaft caused by the starter motor 4th , 4 ' adjusted to its base position so that starting is possible.

3 shows a schematic diagram of a possible arrangement of the brake winding 11 . The brake winding 11 is either around the yoke 12 and / or around at least one of the stator teeth 13 , 13 ' wrapped. The number of brake windings and their number of turns depend on the conditions of the variable displacement motor 2 , 2 ' customized. Due to the rotating actuator motor 2 , 2 ' changing magnetic flux is in the brake winding 11 induces a voltage which in turn supplies a short-circuit current when the ends are closed or the ends are short-circuited. Through the self-induction of the brake winding 11 a force acts on the rotor 8th back, which is opposite to its direction of movement. This will make the rotor 8th delayed.

4a and 4b represent the circuit of the brake winding 11 in a circuit diagram. To prevent a braking torque of the brake winding 11 also generated during normal operation, the circuit becomes the brake winding 11 only closed when there is no power supply to the actuator 2 present. In the first illustrated case ( 4a) is a short circuit switch 14th , which is designed for example as a relay or a transistor, energized as long as the adjusting motor 2 has not failed and thus keeps the circuit open, and is otherwise de-energized. In the second case ( 4b) is the short circuit switch 14 ' de-energized and thus the circuit is closed. He assumes this position when the adjusting motor 2 or its controls fail.

The current can flow in the short-circuit lines so that no damage occurs as a result of the short circuit 16 using a suitable current regulator 15th be limited. This can be designed as a resistor, but also, for example, as an electronic current regulator operated with a short-circuit current.

In summary, the inventive design of an electric brake 11 in connection with the adjustment gear designed as a plus or minus gear 1 , 1' the camshaft 3 , 3 ' at any time, even if the electric adjusting motor fails 2 , 2 ' , safely adjusted to its base position. The solution presented is simple in structure and therefore less prone to errors; moreover, it can be implemented cost-effectively.

List of reference symbols

1, 1 '

Variable speed gear

2, 2 '

electric adjusting motor

3, 3 '

camshaft

4, 4 '

drive shaft

5, 5 '

Output shaft

6, 6 '

Adjusting shaft

7, 7 '

drive wheel

8, 8 '

rotor

9, 9 '

stator

10, 10 '

Cylinder head

11

electrical brake designed as a brake winding

12

yoke

13, 13 '

Stator teeth

14, 14 '

Short circuit switch

15th

Current regulator

16

Short circuit line

Claims (10)

Device for adjusting the control times of a camshaft (3, 3 ') with respect to a crankshaft of an internal combustion engine, with an adjusting gear (1, 1') designed as a three-shaft gear, which has a drive shaft (4, 4 ') connected to the crankshaft and one to the camshaft (3, 3 ') connected output shaft (5, 5') and an adjusting shaft (6, 6 ') connected to an electric adjusting motor (2, 2'), wherein between the drive and output shaft (4, 4 '; 5, 5 ') when the adjusting shaft (6, 6') is stationary there is a stationary gear ratio io, the level of which is determined by the type of gear (minus or plus gear) and the adjustment direction of the camshaft (3, 3 '), which has a basic or emergency running position, with a The rotor (8, 8 ') is designed as a permanent magnet, characterized in that an electric brake (11), which acts as at least one brake winding that is independent of the motor phases is designed to be arranged around a stator tooth (13, 13 ') and / or around a yoke section (12) of the electric adjusting motor (2, 2') and that the stationary gear ratio is selected such that if the electric adjusting motor (2, 2 ') and / or its control after braking the adjusting shaft, the base or emergency running position of the camshaft (3, 3') can be reached and maintained. Device according to Claim 1 , characterized in that a minus gear with io <0 or a plus gear with io> 1 is provided for a retarded adjustment of the camshaft (3, 3 ') and a plus gear with 0 <io <1 is provided for an advanced adjustment of the camshaft (3, 3') are. Device according to Claim 2 , characterized in that the electric brake (11) designed as a brake winding is automatically actuated when the electric adjusting motor (2, 2 ') is off and is automatically released when the electric adjusting motor (2, 2') is working. Device according to Claim 3 , characterized in that the adjustment speed of the device due to the selected stationary gear ratios io with a stationary adjustment shaft (6, 6 ') and low idling speed of the internal combustion engine is between 30 ° and 60 ° camshaft angle per second. Device according to Claim 4 , characterized in that in the control position of the camshaft (3, 3 ') the drive, output and adjustment shaft (4, 4'; 5, 5 '; 6, 6') of the adjustment gear (1, 1 ') at the same speed circulate. Device according to Claim 5 , characterized in that the adjusting gear (1, 1 ') is designed as an eccentric or wave gear or as a wobble or double planetary gear (minus or plus gear) and the electric adjusting motor (2, 2') as a brushless or brush-equipped DC motor. Device according to Claim 6 , characterized in that short-circuit switches (14, 14 ') are provided which are closed when the electric adjusting motor (2, 2') is de-energized and open when the electric adjusting motor (2, 2 ') is energized. Device according to Claim 7 , characterized in that a current regulator (15) operated with short-circuit current is provided in the short-circuit lines (16). Device according to Claim 8 , characterized in that the current regulator (15) is designed as a line resistor. Device according to Claim 8 , characterized in that the short-circuit switches (14, 14 ') open when a limit value of the short-circuit current is exceeded and close automatically when it falls below this limit.

Images