DE102012006820B4 - Method for operating a valve train of an internal combustion engine - Google Patents

Abstract

A method for operating a valve train of an internal combustion engine having at least one base camshaft on the rotatably and axially displaceable between at least two axial positions at least one cam carrier is provided, which is assigned for axial displacement in a selected from the axial positions target position an actuator, wherein only after successful Displacing an acknowledgment signal is generated by the actuator, characterized in that for checking the actual position of the cam carrier, the actuator for relocating the cam carrier is driven to the same desired position and an error signal is generated when the confirmation signal during the checking.

Description

The invention relates to a method for operating a valve train of an internal combustion engine having at least one base camshaft, on the rotationally fixed and axially displaceable between at least two axial positions at least one cam carrier is provided, which is assigned to the axial displacement in a selected from the axial positions target position an actuator, wherein only upon successful displacement an acknowledgment signal is generated by the actuator.

The underlying this method valve trains are basically known. They are used for internal combustion engines, in which the cycle of gas exchange valves of individual cylinders of the internal combustion engine can be influenced to improve the thermodynamic properties. The at least one cam carrier, which may also be referred to as a cam piece, is arranged rotationally fixed and axially displaceable on the base camshaft. The cam carriers are usually associated with a plurality, that is to say at least two, valve actuation cams. Each of these valve actuation cams has an eccentricity, which serves to actuate one of the gas exchange valves of the internal combustion engine at a specific angle of rotation of the basic camshaft. Accordingly, the valve actuating cam run together with the base camshaft so that the respective gas exchange valve of the internal combustion engine is actuated by the associated valve actuating cam or its eccentricity at least once per revolution of the basic camshaft. The valve actuating cam cooperates preferably with a roller rocker arm of the gas exchange valve by coming into abutting contact with this.

Preferably, a plurality of valve actuation cams are provided, which may be assigned to different cam groups. The valve actuation cams of a cam group now differ, for example, with regard to the angular position of their eccentricity or the extent of the same in the radial direction (height) and / or in the circumferential direction (length). By axially displacing the cam carrier, it can be brought into at least two axial positions, for example into a first and a second axial position. In the first axial position, the gas exchange valve is actuated by a first one of the valve actuation cams and in the second axial position by a second one of the valve actuation cams associated with the same cam group. By displacing the cam carrier, it is thus possible in particular to select the opening time, the opening duration and / or the lift of the gas exchange valve, in particular as a function of an operating state of the internal combustion engine. Of course, more than two valve actuating cam per cam group and a corresponding number of axial positions may be provided.

The displacement of the cam carrier in the axial direction takes place, for example, by means of an adjusting device which comprises a shift gate on the cam carrier and a stationarily arranged actuator, usually in a cylinder head of the internal combustion engine. The actuator has, for example, an extendable driver, which can be brought into engagement with a, in particular helical or spiral, slide track or sliding groove of the shift gate. The slide track is provided on the shift gate, which is assigned to the cam carrier. For example, the shift gate is on the cam carrier or is operatively connected to it for axial displacement. The slide track is preferably formed as a radial groove, which passes through the circumference of the shift gate, so it is formed open-edge in this. The shift gate has so far at least one slide track, in which the driver of the actuator for moving the cam carrier can be introduced. The current position of the cam carrier is referred to below as the actual position and the desired position as the target position. The target position is selected from the possible axial positions of the cam carrier. Subsequently, the actuator is actuated such that the cam carrier is displaced in the direction of the desired position, so that following the displacement, the actual position coincides with the desired position. If the displacement is carried out successfully, then the confirmation signal is generated, which is provided, for example, to a control device of the valve drive or of the internal combustion engine. By evaluating the confirmation signal, the control unit thus knows the actual position of the cam carrier.

Basically, such a valve train from the EP 1 608 849 B1 The contents of which are hereby incorporated by reference. During the operation of the valve train, however, it can come to a so-called hiking cam. This is to be understood as meaning a cam or cam carrier whose actual position changes without the action of the actuator, which subsequently deviates the actual position from the setpoint position. Such displacement is effected by acting on the cam carrier axial force, which is caused for example by a misalignment of acting on the cam carrier roller cam follower. Due to the unwanted displacement of the cam carrier, there is a change in the valve lift for the gas exchange valves, which are controlled by the cam of the cam carrier. On the other hand, the control unit continues to assume that the cam carrier is in the setpoint position and a valve lift corresponding to this setpoint position is present. Accordingly, there may be noticeable or measurable influences on the exhaust gas, the consumption, the operating behavior of the internal combustion engine, the acoustics and the like. Furthermore, it is possible to influence diagnostic mechanisms that emanate from a match between the actual position and the setpoint position, which may result in faulty fault memory entries and substitute reactions being generated (subsequent error).

Furthermore, the document is from the prior art DE 10 2009 006 632 A1 known. This describes a valve train of an internal combustion engine, with at least one camshaft on the rotatably and axially displaceable at least one cam carrier is provided, and with a displacement device for axially displacing the cam carrier on the camshaft, wherein the displacement device at least one in at least two on the cam carrier having, at least partially obliquely extending sliding grooves insertable actuator. It is provided that the sliding grooves have in the course of different Ausschieberampen for pushing out of the introduced actuator, and that the actuator has means for detecting the respective course. Further methods for operating internal combustion engines are known from the documents DE 10 2004 012 756 A1 and DE 40 28 442 A1 known.

It is therefore an object of the invention to propose a method for operating a valve train of an internal combustion engine, which does not have the aforementioned disadvantage, but in particular allows reliable detection of a deviation of the actual position of the target position, which is simple and inexpensive to implement.

This is achieved according to the invention by the method having the features of claim 1. It is provided that, for checking the (actual) actual position of the cam carrier, the actuator for relocating the cam carrier is actuated into the same desired position and an error signal is generated when the confirmation signal occurs during the checking. By checking it can be determined whether the actual actual position of the cam carrier continues to correspond to the desired position or deviates from it. The checking is carried out in such a way that displacement of the cam carrier is effected even if the nominal position and the assumed actual position coincide. This applies in particular if the (known) actual position known to the control unit coincides with the desired position. Of course, the selected procedure can also be performed if the actual actual position coincides with the target position. Even if the assumed and actual actual position matches the desired position, the actuator is thus activated in such a way that the cam carrier is displaced in the direction of the desired position, should it not already be in this position.

If the actual actual position coincides with the desired position, the actuation of the actuator does not of course cause any actual displacement of the cam carrier in the direction of the desired position. Rather, he remains in this. If, on the other hand, there is a deviation of the actual actual position from the desired position, the cam carrier is displaced in the direction of the desired position and preferably brought into this position. Because only after successful displacement, the confirmation signal is generated, this can be used to evaluate the actual actual position of the cam carrier present before checking. If the confirmation signal is present after the actuation of the actuator, then the cam carrier was displaced in the direction of the setpoint position, that is to say it was not present in this position before the activation. If, on the other hand, the confirmation signal is off, it can be assumed that the cam carrier already existed before its activation of the actuator in its setpoint position.

For example, the cam carrier is associated with at least one shift gate, which cooperates with the actuator for displacing the cam carrier, wherein the actuator has a driver, which is pushed to displace the cam carrier in the direction of a slide track of the shift gate. It is particularly provided that the shift gate is designed such that the driver can only intervene to displace the cam carrier in the slide track when the (actual) actual position is different from the desired position. In addition, the slide track may have an ejection ramp, which pushes out the driver until the conclusion of the displacement of the slide track. Likewise, it may be provided that the confirmation signal is generated only when the driver is completely forced out of the slide track.

A development of the invention provides that the checking is carried out periodically and / or after occurrence of a suspected error signal. Under the periodic check is to be understood that the actuator is driven regularly, in particular in compliance with certain time intervals, for displacing the cam carrier in the desired position, although this is unchanged. Additionally or alternatively, the checking can be carried out when the error suspected signal occurs, which is provided, for example, by the control unit. If the error suspect signal is present, it is assumed that the actual actual position may not coincide with the target position Error suspected signal may occur even when the cam carrier is actually in its desired position.

A development of the invention provides that at least one sensor and / or at least one state variable of the internal combustion engine is evaluated in order to determine the probability of a deviation of the desired position from the actual position, and that the probability of suspected error is generated when a probability threshold is exceeded by the probability. Preferably, an already existing sensor or its signal is evaluated for this purpose. If the sensor signal of the sensor or the state variable of the internal combustion engine suggests that the cam carrier is not in the desired position, then the suspected error signal is set as soon as the determined probability exceeds the probability threshold. Subsequently, as described above, the checking of the actual position is performed. Particularly preferably, a plurality of sensors and / or a plurality of state variables are evaluated. In particular, the probability is determined separately for each sensor or for each state variable. In this case, the error suspect signal is generated when at least one of the probabilities exceeds the probability threshold. Preferably, it is generated only when a plurality of probabilities, in particular all, exceed the probability threshold.

The invention provides that when the confirmation signal occurs during the checking, an error signal is generated. As already stated above, the confirmation signal occurs only when actually a displacement of the cam carrier has been performed. Thus, if the cam carrier is already in the setpoint position before the activation of the actuator, no displacement of the cam carrier is effected and the confirmation signal therefore does not occur. If, however, the confirmation signal is generated, then the cam carrier was displaced by the activation of the actuator and was therefore not in the desired position. Accordingly, the error signal is set. This is provided for example for the control unit.

A development of the invention provides that when the error signal occurs a countermeasure initiated, in particular a cylinder deactivation of the internal combustion engine is prevented. The error signal occurs only if a deviation of the actual actual position from the target position has been detected. Accordingly, at least one suitable countermeasure must be taken in the presence of the error signal. One such example is the prevention of cylinder deactivation. Additionally or alternatively, the error signal can also be entered into a fault memory, which can be evaluated, for example, subsequently during maintenance of the internal combustion engine.

• Figur ein Ablaufdiagramm eines Verfahrens zum Betreiben eines Ventiltriebs einer Brennkraftmaschine.

The invention will be explained in more detail with reference to the embodiments illustrated in the drawings, without any limitation of the invention. The only one shows

• FIG. 1 shows a flow chart of a method for operating a valve train of an internal combustion engine.

The figure shows a flow chart, with which a method for operating a valve train of an internal combustion engine is illustrated. The valve drive has at least one base camshaft, on the rotationally fixed and at least one cam carrier is provided axially displaceable between at least two axial positions. The cam carrier is associated with an actuator by means of which it can be displaced into a desired position, which corresponds to one of the axial positions. The actuator generates a confirmation signal only after successful displacement of the cam carrier. During operation of the valve train or the internal combustion engine, however, it may happen that the cam carrier is displaced without the actuator being actuated, so that the actual actual position deviates from the setpoint position.

It can be provided to evaluate an existing sensor of the valve train or of the internal combustion engine and / or a state variable of the internal combustion engine in order to determine a probability with which such a deviation of the actual actual position from the desired position exists. If this probability exceeds a certain probability threshold, a suspected error signal is generated. However, this does not mean that there is actually a deviation of the actual position from the target position. Rather, there is only the possibility or a certain probability for this. The method described below with reference to the flowchart serves, in particular, to check the actual actual position of the cam carrier. It starts at a starting point 1 from which to a diversion 2 is advanced. In this there is a query whether the error suspected signal is present. If this is not the case, it immediately becomes an endpoint 3 branches of the process.

If, on the other hand, the error suspected signal is present, then in one step 4 the actuator of the valve drive for renewed displacement of the cam carrier in the same, that is already set previously setpoint position. This means that although there is no change in the target position and possibly the actual actual position coincides with the target position, the actuator for displacing the cam carrier is to be actuated. As already stated above, the confirmation signal is generated only after successful displacement of the cam carrier. This will be in a turnoff 5 which on the step 4 follows, queried. If the confirmation signal does not occur, then it can be assumed that the actuation of the actuator did not cause a displacement of the cam carrier and that therefore already existed in the setpoint position. Accordingly, there is no fault of the valve train, so that in the absence of the confirmation signal to the end point 3 is branched.

On the other hand, if the confirmation signal occurs, the cam carrier was not in the setpoint position before the actuator was actuated, but had shifted out of it without activation of the actuator. Accordingly becomes a step 6 Branches, in which appropriate countermeasures are taken. At the same time an error signal is set. For example, in the step 6 only the error signal entered in a fault memory. Additionally or alternatively, however, it may be provided that a suitable countermeasure is carried out until the error signal is reset. One such countermeasure is, for example, preventing cylinder deactivation of the internal combustion engine. The error signal which is generated when the acknowledgment signal appears during the checking of the actual position of the cam carrier is preferably persistent, ie it is retained even when the internal combustion engine is switched off.

LIST OF REFERENCE NUMBERS

1

starting point

2

diversion

3

endpoint

4

step

5

diversion

6

step

Claims (4)

A method for operating a valve train of an internal combustion engine having at least one base camshaft on the rotatably and axially displaceable between at least two axial positions at least one cam carrier is provided, which is assigned for axial displacement in a selected from the axial positions target position an actuator, wherein only after successful Displacing an acknowledgment signal is generated by the actuator, characterized in that for checking the actual position of the cam carrier, the actuator for relocating the cam carrier is driven to the same desired position and an error signal is generated when the confirmation signal during the checking. Method according to Claim 1 , characterized in that the checking is performed periodically and / or after occurrence of a suspected error signal. Method according to Claim 2 , characterized in that at least one sensor and / or at least one state variable of the internal combustion engine is evaluated to determine the probability of deviation of the desired position of the actual position, and that the probability of failure is generated when a probability threshold is exceeded by the probability. Method according to one of the preceding claims, characterized in that a countermeasure is initiated when the error signal occurs.

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