DE102008010638B4 - Electromechanical camshaft adjustment system and method for adjusting a camshaft using such a camshaft adjustment system - Google Patents

Abstract

Method for adjusting a camshaft by means of an electromechanical camshaft adjustment system comprising a three-shaft gear with a first shaft connected to a camshaft chain wheel of an internal combustion engine, a second shaft connected to a camshaft and an adjustment shaft connected to a rotor shaft of an electric adjustment motor, characterized in that in operating states in which no The camshaft is to be adjusted, the speed of the adjustment shaft is varied by a constant value.

Description

field of invention

The invention relates to an adjustment of a camshaft by means of an electromechanical camshaft adjustment system according to the preamble of appended claim 1. The invention also relates to a camshaft adjustment system according to the preamble of claim 7.

Electromechanical camshaft adjustment systems consist of an electric motor, a gearbox and a control unit. Such a camshaft adjustment system is, for example, in U.S. 6,981,478 B2 described.

In electromechanical camshaft phasing systems, three-shaft transmissions are commonly used, in which a first shaft of the transmission, usually the camshaft, is connected to the camshaft sprocket of an internal combustion engine, a second shaft (crankshaft) is drivingly connected to the camshaft via the camshaft sprocket, and a third shaft, the timing shaft , is connected to the rotor shaft of an electric variable motor (electric motor). The adjustment shaft is used to adjust the relative angular position between the camshaft and crankshaft. The stator of the electric motor is preferably fixed in the cylinder head, which means that the stator does not rotate.

Examples of such three-shaft gears are swash plate gears and internal eccentric gears, which in the WO 2006/018080 A1 are described. This also includes those from the WO 2005/080757 A1 well-known strain wave gear and in the U.S. 2007/0051332 A1 and US 2003/0226534 A1 included gearbox.

If the camshaft is not to be adjusted relative to the crankshaft, it is necessary for the electric motor rotor and thus also the adjustment shaft of the three-shaft transmission to rotate synchronously with the speed of the camshaft sprocket. This means that the adjusting shaft has a relative speed of 0 rpm in relation to the camshaft sprocket. In this case, the relative speed of the outer ring of the adjusting shaft bearing used to mount the adjusting shaft is 0 rpm relative to the inner ring of the adjusting shaft bearing.

Experience has shown that the case described above can occur for around 50% of the operating time of the combustion engine. If the operating time of a motor is around 6000 hours, this means practically 3000 hours of “static” bearing operation. At the same time, however, the radial forces generated in the gear teeth must be transmitted through the bearing throughout the life of the motor.

In practice, this case, with zero relative rotation in the adjusting shaft bearing, is extremely critical for the adjusting shaft bearing, since there is a risk of corrugation.

A camshaft phaser, which is produced according to a method as in DE 102 51 347 A1 is being operated can therefore fail prematurely. The risk of failure is exacerbated if the camshaft adjuster, as in DE 22 33 151 A1 described, measures for vibration suppression take place. The static displacement of the camshaft angle according to DE 10 2006 035 384 A1 cannot prevent the formation of corrugations, nor can taking into account the combined valve spring torque of the DE 10 2004 058 930 A1 , which has no effect on the bearing of the camshaft adjuster if it is not adjusted. This in DE 10 2004 037 262 A1 The method presented for calming a traction mechanism by means of a camshaft adjuster is suitable for reducing vibrations in the traction mechanism. The problem of corrugation is not solved by the method.

The object of the present invention is therefore to provide a method for adjusting a camshaft by means of an electromechanical camshaft adjustment system, with which the operating conditions that are critical for the adjustment shaft bearing can be largely avoided and the risk of corrugation can be reduced as a result, the method only small additional costs should arise.

A method according to the appended claim 1 or a camshaft adjustment system according to the independent claim 7 serves to solve the object according to the invention.

The method according to the invention is characterized in that in operating states in which the camshaft is not to be adjusted, the speed of the adjustment shaft fluctuates by a constant value. It has proven to be particularly advantageous here if the speed of the adjustment shaft fluctuates periodically around a constant value.

A particular advantage of the solution according to the invention is that the adjustment of the adjustment shaft relative to the camshaft sprocket caused by the adjustment of the adjustment shaft according to the invention causes a continuous rotation in the adjustment shaft bearing during the critical operating states described above. Because even at these times there is relative movement between the inner ring and outer ring of the adjusting shaft bearing, these operating states, which are critical with regard to the service life of the adjusting shaft bearing and in which the relative speed of the outer ring of the adjusting shaft bearing is 0 rpm relative to the inner ring of the adjusting shaft bearing, can be avoided.

The avoidance of these critical operating conditions is very advantageous since the occurrence of corrugation in the bearing can be largely prevented. There is a significant increase in the service life of the adjustment shaft bearing and thus also of the entire adjustment system.

Since the solution according to the invention is merely a control strategy in which no additional components are required, no additional costs arise as a result. At the same time, the operating costs can be significantly reduced because the adjustment shaft bearing can be used for a longer period of time.

The adjustment of the adjusting shaft implemented according to the invention must be small enough so that the angular accuracy required by the user can be maintained. At the same time, the displacement of the adjustment shaft must be large enough that there is constant back and forth rotation in the adjustment shaft bearing in order to avoid the critical case of "static" bearing operation. The movement of the adjusting shaft has two effects. On the one hand, it causes the desired relative movement between the inner ring and the outer ring of the adjusting shaft bearing. On the other hand, it creates a slight adjustment of the camshaft. This second effect is not desired and must therefore be avoided as far as possible.

It is advantageous if the fluctuation of the adjusting shaft is generated by a control signal used to activate the adjusting motor. Here, the use of a control signal in the form of a sine wave has proven to be beneficial. In other embodiments, the control signal may be a square wave. However, there should be no restriction to the control signals mentioned. Any type of signal that produces a swaying of the adjusting shaft can be used as the control signal.

In an advantageous embodiment, the control signal is applied in the opposite direction to a movement of the camshaft caused by the camshaft changing torque. This is because the camshaft fluctuates independently of the control signal used to actuate the adjusting motor because of the camshaft alternating torque and/or the rigidity of the valve train. However, this movement of the camshaft is not desired and should therefore be avoided if possible. Due to the fact that the control signal is impressed in the opposite direction to the camshaft movement, the fluctuation of the camshaft can be completely or almost completely compensated, which in turn has a positive effect on the service life.

In an expedient embodiment, the adjustment shaft is mounted in a roller bearing. The roller bearing can be designed as a ball bearing or needle bearing. Ball bearings with different numbers of rolling elements can be used, with between 6 and 60 rolling elements usually being used. The same applies to needle bearings. Here, too, the number of rolling bodies is usually between 6 and 60. In other embodiments, the adjustment shaft bearing can also include a plurality of bearings. For example, a combination of several types of roller bearings can be used. Such storage is, for example, in WO 2006/018080 A1 described.

Furthermore, it is advantageous if the three-shaft gear is a swash plate gear, an internal eccentric gear or a strain wave gear. However, there should be no restriction to the transmissions mentioned.

All transmissions in which critical operating states similar to those described in the introduction occur can benefit from the solution according to the invention. It is irrelevant what the transmission ratio is and whether the transmission ratio is uniform or not.

The solution according to the invention can also be used in combined transmissions, such as multi-stage transmissions with series or parallel connection.

• 1 ein aus dem Stand der Technik bekanntes typisches Verhalten von Wellen eines Dreiwellengetriebes;
• 2 ein durch Anwendung eines erfindungsgemäßen Verfahrens hervorgerufene Verhalten der drei Wellen eines Dreiwellengetriebes zu einem Zeitpunkt, in dem keine Verstellung der Nockenwelle relativ zur Kurbelwelle erfolgt.

Further advantages, details and developments of the present invention result from the following description of a preferred embodiment with reference to the drawing. Show it:

• 1 a typical behavior of shafts of a three-shaft transmission known from the prior art;
• 2 a behavior of the three shafts of a three-shaft transmission caused by application of a method according to the invention at a time when the camshaft is not being adjusted relative to the crankshaft.

1 shows a typical behavior of the three shafts of a three-shaft transmission known from the prior art. A typical three-shaft transmission includes one with a camshaft chain wheel of an internal combustion engine, a first shaft connected to a camshaft, and an adjustment shaft connected to a rotor shaft of an electric adjustment motor. In the selected application, a ball bearing with 24 rolling elements is used as the adjustment shaft bearing.

In the top diagram of the 1 the speed curve is shown and in the lower diagram the adjustment angle and the differential speed between the ball bearing inner ring and the ball bearing outer ring.

In the areas where the camshaft is not to be adjusted relative to the crankshaft, i.e. in which the adjustment angle D does not change, all three shafts of the transmission must have the same speed. At a crankshaft speed A of 2000 rpm, the camshaft chain speed is 1000 rpm and thus the variable motor rotor speed B or variable shaft speed is 1000 rpm. This also results in 1000 rpm for the camshaft speed. This means that the adjusting shaft has a relative speed of 0 rpm in relation to the camshaft sprocket. The camshaft therefore does not adjust relative to the camshaft sprocket. The relative speed of the ball bearing inner ring to the ball bearing outer ring of the adjustment shaft bearing C is 0 rpm in this case. These operating states, which are critical for the adjustment shaft bearing, are labeled with S in the diagram below.

2 shows a behavior of the three shafts of the three-shaft transmission caused by application of the method according to the invention at a point in time when the camshaft should not be adjusted relative to the crankshaft. These so-called "static" operating states are in 1 marked with S. In order to avoid these operating states, which are critical with regard to the wear behavior of the adjustment shaft bearing, the invention provides for a very slight back and forth adjustment of the adjustment shaft by a constant value relative to the camshaft sprocket. This superimposed back and forth adjustment is preferably effected in that the adjustment motor is driven with a specific control signal. When selecting the control signal, it must only be ensured that this generates a fluctuating angle on the adjustment shaft. In the selected embodiment, the adjusting motor is driven with a control signal in the form of a sine wave.

In 2 the speed curve is again shown in the upper diagram. The lower diagram shows the adjustment angle and the position of the inner ring of the ball bearing relative to the outer ring of the ball bearing. In the selected example, the crankshaft speed A is 2000 rpm. In this case, the adjustment motor speed B or adjustment shaft speed should actually be 1000 rpm. According to the invention, however, the variable displacement motor is driven with a control signal in the form of a sine wave with a nominal value of 1000 rpm. The frequency and amplitude of the sine wave creates a wobbling motion on the adjustment shaft that has two effects. On the one hand, there is a relative movement between the inner ring and the outer ring of the adjusting shaft bearing (see lower diagram, curve E). On the other hand, this results in a slight adjustment of the camshaft (see lower diagram, curve D). While the first effect is desirable, the second effect should be avoided or minimized as much as possible. The frequency and the amplitude of the sine wave should therefore be selected in such a way that the first effect is supported and the second effect is kept low. This is possible due to the gear ratio of the gearbox.

With a gear ratio of 1:-66, the camshaft rotates once counterclockwise relative to the camshaft sprocket when the timing shaft rotates 66 times clockwise relative to the camshaft sprocket. Experience has shown that the risk of rippling increases significantly when the oscillating swivel angle between the inner and outer ring is less than twice the rolling element pitch angle. In the case of an adjusting shaft bearing in the form of a ball bearing with 24 rolling elements, the frequency and amplitude of the sine wave should therefore be selected in such a way that a pivoting angle E of around ±15° is generated at the adjusting shaft. Due to the transmission ratio of 1:-66, the adjustment angle D on the camshaft fluctuates at a significantly smaller angle. In the selected example, the adjustment angle fluctuation is ±115°/66=±0.23° camshaft=±0.46° crankshaft. This achieves the goal of supporting the positive effect of the relative movement between the inner ring and outer ring for the service life of the adjusting shaft bearing and minimizing the inevitably occurring negative side effect of the adjustment of the camshaft. This can significantly reduce the risk of corrugation. An adjusting shaft bearing operated with the method according to the invention is less susceptible to wear and can therefore be used for a significantly longer time, which not least also leads to cost savings.

Reference List

A

crankshaft speed

B

variable speed motor

C

Differential speed between ball bearing inner ring and ball bearing outer ring

D

adjustment angle

E

Position of the ball bearing inner ring relative to the ball bearing outer ring

S

“static” operating case

Claims (13)

Method for adjusting a camshaft by means of an electromechanical camshaft adjustment system comprising a three-shaft gear with a first shaft connected to a camshaft chain wheel of an internal combustion engine, a second shaft connected to a camshaft and an adjustment shaft connected to a rotor shaft of an electric adjusting motor, characterized in that in operating states in which no The camshaft is to be adjusted, the speed of the adjustment shaft is varied by a constant value. procedure after claim 1 , characterized in that the speed of the adjusting shaft is varied periodically by a constant value. procedure after claim 1 or 2 , characterized in that the changing of the speed of the adjusting shaft is effected by a control signal used to control the adjusting motor. procedure after claim 3 , characterized in that the control signal is applied in the opposite direction to a movement of the camshaft caused by a camshaft changing moment. procedure after claim 3 or 4 , characterized in that the control signal is a sine wave. procedure after claim 3 or 4 , characterized in that the control signal is a square wave. Camshaft adjustment system for adjusting a camshaft, comprising a three-shaft gear with a first shaft connected to a camshaft chain wheel of an internal combustion engine, a second shaft connected to a camshaft and an adjusting shaft connected to a rotor shaft of an electric adjusting motor, characterized in that in operating states in which the camshaft is not adjusted , the speed of the adjustment shaft fluctuates around a constant value. camshaft adjustment system claim 7 , characterized in that the fluctuation of the speed of the adjusting shaft by a control method according to one of Claims 1 until 7 is effected. camshaft adjustment system claim 7 or 8th , characterized in that the adjustment shaft is mounted in a roller bearing. procedure after claim 9 , characterized in that the roller bearing is a ball bearing or a needle bearing. Camshaft adjustment system according to one of Claims 7 until 10 , characterized in that the adjusting shaft is mounted in several roller bearings. camshaft adjustment system claim 11 , characterized in that the adjusting shaft is mounted in at least one ball bearing and at least one needle bearing. Camshaft adjustment system according to one of Claims 7 until 12 , characterized in that the three-shaft gear is a swash plate gear, an internal eccentric gear or a strain wave gear.

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