METHOD AND DEVICE FOR CONTROLLING A CAMSHAFT PHASE ADJUSTER IN AN INTERNAL COMBUSTION ENGINE

Abstract

A method for operating an internal combustion engine having a camshaft phase adjuster, including: providing a nonlinear final control element model, which indicates via a functional relationship an angular velocity of a relative adjustment of the camshaft phase adjuster as a function of an actuator correcting variable for the control of the camshaft phase adjuster; carrying out a control based on a deviation between a predefined camshaft angle adjustment setpoint value, and a camshaft angle adjustment actual value, to obtain as a control output a setpoint positioning rate of the camshaft phase adjuster; calculating the actuator correcting variable as a function of the setpoint positioning rate using an inverted final control element model; applying a predefined correction variable to the actuator correcting variable; controlling the camshaft phase adjuster using the actuator correcting variable to which the correction variable has been applied, to operate the internal combustion engine.

Claims

1. A method for operating an internal combustion engine having a camshaft phase adjuster, the method comprising the following steps: providing a nonlinear final control element model, which indicates via a functional relationship an angular velocity of a relative adjustment of the camshaft phase adjuster as a function of an actuator correcting variable for control of the camshaft phase adjuster; carrying out a control based on a deviation between a predefined camshaft angle adjustment setpoint value, which indicates a setpoint value of a relative displacement between a crankshaft position angle and a camshaft position angle, and a camshaft angle adjustment actual value, which indicates an actual relative displacement, to obtain, as a control output, a setpoint positioning rate of the camshaft phase adjuster; calculating the actuator correcting variable as a function of the setpoint positioning rate using with the aid of an inverted final control element model; applying a predefined correction variable to the actuator correcting variable; and controlling the camshaft phase adjuster using the actuator correcting variable to which the predefined correction variable has been applied to operate the internal combustion engine.

2. The method as recited in claim 1, wherein a dynamic pilot control is provided, which adds a dynamic pilot control variable to the setpoint positioning rate in order to obtain a modified setpoint positioning rate, as a function of which the actuator correcting variable is calculated using an inverted final positioning element model.

3. The method as recited in claim 1, wherein a disturbance variable monitor is used, which adds to the setpoint positioning rate a predefined monitor component of the setpoint positioning rate to compensate for disturbances at an input of a controlled system so that a modified setpoint positioning rate is obtained by which the actuator correcting variable is calculated with the aid of the inverted final control element model.

4. The method as recited in claim 1, wherein the actuator correcting variable is multiplied or divided by the correction variable.

5. The method as recited in claim 1, wherein the correction variable is determined by: determining a modeled positioning rate from the setpoint positioning rate of the controller using the final control element model, the final control element model having a model parameter which corresponds to the correction variable; ascertaining a difference between an instantaneous actual positioning rate and the modeled positioning rate; and determining the correction variable by minimizing the resulting deviation between in instantaneous actual positioning rate and the modeled positioning rate.

6. A device for operating a camshaft phase adjuster for the operation of an internal combustion engine, the device configured to: carry out a position control based on a deviation between a predefined camshaft angle adjustment setpoint value, which indicates a setpoint value of the relative displacement between a crankshaft position angle and a camshaft position angle, and a camshaft angle adjustment actual value, which indicates an actual relative displacement, in order to obtain as a control output a setpoint positioning rate of the camshaft phase adjuster; calculate an actuator correcting variable as a function of the setpoint positioning rate using an inverted final control element model, the final control element model indicating via a functional relationship an angular velocity of a relative adjustment of the camshaft phase adjuster as a function of a control of the camshaft phase adjuster; apply a predefined correction variable to the actuator correcting variable; and control the camshaft phase adjuster using the actuator correcting variable to which the predefined correction variable has been applied to operate the internal combustion engine.

7. An engine system having an internal combustion engine, which is a reciprocating-piston internal combustion engine, the internal combustion engine having at least one camshaft), driven by the crankshaft, for operating an intake and/or exhaust valve of a cylinder of the internal combustion engine, the camshaft being coupled with a camshaft phase adjuster for a relative adjustment between the crankshaft and the camshaft, and a device for operating the camshaft phase adjuster for the operation of an internal combustion engine, the device configured to: carry out a position control based on a deviation between a predefined camshaft angle adjustment setpoint value, which indicates a setpoint value of the relative displacement between a crankshaft position angle and a camshaft position angle, and a camshaft angle adjustment actual value, which indicates an actual relative displacement, to obtain as a control output a setpoint positioning rate of the camshaft phase adjuster; calculate an actuator correcting variable as a function of the setpoint positioning rate using an inverted final control element model, the final control element model indicating via a functional relationship an angular velocity of a relative adjustment of the camshaft phase adjuster as a function of a control of the camshaft phase adjuster; apply a predefined correction variable to the actuator correcting variable; and control the camshaft phase adjuster using the actuator correcting variable to which the predefined correction variable has been applied to operate the internal combustion engine.

8. A non-transitory machine-readable memory medium on which is stored a computer program for operating an internal combustion engine having a camshaft phase adjuster, the computer program, when executed by a computer, causing the computer to perform the following steps: providing a nonlinear final control element model, which indicates via a functional relationship an angular velocity of a relative adjustment of the camshaft phase adjuster as a function of an actuator correcting variable for control of the camshaft phase adjuster; carrying out a control based on a deviation between a predefined camshaft angle adjustment setpoint value, which indicates a setpoint value of a relative displacement between a crankshaft position angle and a camshaft position angle, and a camshaft angle adjustment actual value, which indicates an actual relative displacement, to obtain, as a control output, a setpoint positioning rate of the camshaft phase adjuster; calculating the actuator correcting variable as a function of the setpoint positioning rate using with the aid of an inverted final control element model; applying a predefined correction variable to the actuator correcting variable; and controlling the camshaft phase adjuster using the actuator correcting variable to which the predefined correction variable has been applied to operate the internal combustion engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Specific embodiments are described in greater detail in the following text with the aid of the figures.

[0035] FIG. 1 shows a schematic illustration of an engine system including an internal combustion engine.

[0036] FIG. 2 shows a system having a hydraulic camshaft phase adjuster, which is able to be controlled via an electromechanical valve.

[0037] FIG. 3 shows a schematic illustration of a controller structure for a camshaft position control of the system from FIG. 2.

[0038] FIG. 4 shows a schematic illustration of an adaptation of the correction variable for adapting a camshaft position control.

[0039] FIG. 5 shows a schematic illustration of the ascertainment of the correction variable based on the modeled positioning rate.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0040] FIG. 1 shows a schematic illustration of an engine system 1 having an internal combustion engine 2, which may be developed in the form of a reciprocating-piston internal combustion engine. Internal combustion engine 2 may correspond to an air-directed (spark-ignition engine) or a fuel-directed combustion engine (Diesel engine). Internal combustion engine 2 has two pistons 3, which are able to execute a translatory movement within combustion chambers of cylinders 3 and are coupled via piston rods 4 to a crankshaft 5 in a conventional manner.

[0041] Cylinders 3 of internal combustion engine 2 are operated according to a four-stroke operation, and air is introduced into cylinders 3 in a cyclical manner via intake valves 6, and combustion exhaust gas is expelled from cylinders 3 via exhaust valves 7. The valve operations of intake and exhaust valves 6, 7 are controlled via respective camshafts, i.e. an intake camshaft 8 and an exhaust camshaft 9. Camshafts 8, 9 are mechanically connected to crankshaft 5 via a cogged belt 10, for instance, or in some other way, in a phase-locked manner.

[0042] Camshafts 8, 9 have cams 81, 91 for each cylinder 3, which operate intake valves 6 and exhaust valves 7 in order to thereby control them for the opening and closing. One of camshafts 8, 9 or both camshafts 8, 9 may be provided with a camshaft phase adjuster 82, 92, which makes it possible to adjust the position of cams 81, 91 relative to the position of crankshaft 5 of the crankshaft angle.

[0043] Since camshafts 8, 9 are driven by crankshaft 5 via a cogged belt 10, the control times are indicated as an angle of rotation in each case, which is related to the position, i.e., the angular position, of crankshaft 5.

[0044] Internal combustion engine 2 is operated via a control unit 20, which particularly also assumes the control of camshaft phase adjusters 82, 92.

[0045] FIG. 2 schematically shows a hydraulic camshaft phase adjuster 82, 92 and a control unit 15 intended for it. Camshaft phase adjuster 82, 92 has a housing G and a final control element S, which are rotationally adjustable relative to each other. Housing G and final control element S have teeth that point toward each other in order to define hydraulic chambers. Hydraulic chambers situated opposite in relation to a tooth of final control element S act against each other so that final control element S is retained in its position when equal pressures are present in the hydraulic chambers and the final control element is moved in the direction of the chamber having the lower pressure when unequal pressures are present in the hydraulic chambers. When final control element S is spring-loaded, a certain pressure differential between the hydraulic chambers is required in order to retain final control element S. Any deviation from this pressure differential leads to a positioning movement of camshaft phase adjuster 82, 92. The hydraulic chambers are connected to a pump which supplies the required hydraulic pressure.

[0046] Control unit 15 has an electromechanical control valve 16, which is controllable by a positioning actuator 17 based on an actuator correcting variable x in order to provide a certain valve setting. The valve setting causes oil to be applied to the hydraulic chambers at a pressure that is predefined by the valve setting. For this purpose, hydraulic oil is supplied from a hydraulic accumulator 18 and an oil pressure pump 19. This is an integral controlled system in which the camshaft position angle is adjusted by an adjustment of final control element S until a mechanical stop is reached or until this movement is counteracted by an opposite pulse duty factor or a corresponding load.

[0047] The relationship between the angular velocity {dot over ()} of camshaft phase adjuster 82, 92 and actuator correcting variable x is nonlinear and is described via a corresponding nonlinear final control element model that indicates this functional relationship. In particular, the transformation ratio between actuator correcting variable x and resulting positioning rate {dot over ()} may vary as a result of constructive measures. The characteristic curve of the final control element model thus describes the resulting positioning rate as a function of the used actuator correcting variable x. The characteristic curve of the final control element model in particular makes it possible to describe the varying transformation ratio via the nonlinear relationship. It was found that aging and wear effects as well as component tolerances predominantly manifest themselves in scaling of the final control element characteristic curve.

[0048] If the holding pulse duty factor U.sub.fwd,steady is not seen as part of the final control element characteristic curve, then it, too, (or the correction value from the disturbance variable monitor, which is not described here) has a considerable dependence on these influences. This is an additional degree of freedom for the application. During the initial operation, it may perhaps not be possible to express all influences in velocity coordinates.

[0049] In FIG. 3, the structure of the camshaft position control, which is carried out in control unit 20, is schematically illustrated. Toward this end, a camshaft angle adjustment setpoint value .sub.sp, which is specified by an engine control algorithm and indicates a setpoint value of the relative displacement between the crankshaft position angle and the camshaft position angle, and a camshaft angle adjustment actual value .sub.actual, which indicates an actual relative displacement and which is able to be measured by a position sensor, is forwarded to a difference block 21 so that a position deviation may be ascertained as a control difference e.

[0050] Control difference e is forwarded to a control unit 22, which is preferably developed as a PD controller. The PD controller is developed so that the control output as the correctional variable corresponds to a setpoint value {dot over ()}.sub.ctrl for a positioning rate (setpoint positioning rate) of camshaft phase adjuster 82, 92.

[0051] In order to reduce the loading of the control during a transient operation, a dynamic pilot control, for example, is able to be used, which adds a predefined dynamic pilot control variable {dot over ()}.sub.fwd,dyn to the setpoint positioning rate {dot over ()}.sub.ctrl from the control in a first summation block 23. Dynamic pilot control variable {dot over ()}.sub.fwd,dyn may be developed to estimate on the basis of the mathematical position encoder model the required characteristic of a pilot control rate from the time characteristic of the predefined camshaft angle adjustment setpoint value .sub.sp. Camshaft angle adjustment setpoint value .sub.sp is used as output information for a trajectory calculated in reverse by the position encoder model, which is then to be realized by the pilot control. The trajectory may also correspond to the characteristic of camshaft angle adjustment setpoint value .sub.sp. This trajectory may also include time filtering of camshaft angle adjustment setpoint value .sub.sp.

[0052] In addition, it is alternatively or additionally possible to use a disturbance variable monitor 25, which adds a predefined monitor component {dot over ()}.sub.distobs of the setpoint positioning rate from control unit 22 to setpoint positioning rate {dot over ()}.sub.ctrl in a second summation block 24. Disturbance variable monitor 25 may include a model block for calculating an inverse position encoder model and a filter. Disturbance variable monitor 25 is used to compensate for position deviations that may occur due to an input disturbance in the position encoder system, and in particular, also to compensate for unknown disturbances at the input of the controlled system. If there is a change in position on account of a disturbance, e.g., a spring torque of a restoring spring, a moment of friction, leakage of the hydraulic system or disturbance moments of external consumers, then disturbance variable monitor 25 is able to compensate for the disturbance. Disturbance variable monitor 25 is able to calculate the disturbance from the instantaneous correcting variable and actual position .

[0053] From the result of the application of pilot control variable {dot over ()}.sub.fwd,dyn and monitor component {dot over ()}.sub.distobs to setpoint positioning rate {dot over ()}.sub.ctrl a modified setpoint positioning rate {dot over ()}.sub.sp is obtained, which is supplied to a characteristic curve block 26 as an input variable for a predefined inverted final control element model. Because of the inverted final control element model, modified setpoint positioning rate {dot over ()}.sub.sp is allocated to a preliminary actuator controlled variable x, which may be developed as a pulse duty ratio for a pulse-width modulated control of positioning actuator 17 or the like, for instance.

[0054] To adapt this control, a correction variable K is able to be applied to the preliminary actuator correcting variable x.sub.raw ascertained in this way, in particular in a division block 27 as a quotient.

[0055] In addition, a holding correcting variable x.sub.steady may be added to corrected actuator correcting variable x.sub.corr in a summing block 28 in order to obtain actuator correcting variable x for the control of positioning actuator 17.

[0056] The actuator characteristic curve is able to be ascertained on a test stand, in particular in a manner known per se, in the process of which predefined actuator correcting variables are applied to camshaft phase adjuster 82, 92 in order to be able to detect a corresponding positioning rate.

[0057] FIG. 4 schematically illustrates a function model for providing correction variable K; camshaft angle adjustment actual value .sub.actual of the final control element of camshaft phase adjuster 82, 92 is derived in terms of time according to a high-pass filter 31 in order to obtain an instantaneous actual positioning rate {dot over ()}.sub.actual. In addition, model positioning rate {dot over ()}.sub.mod,flt is determined from setpoint positioning rate {dot over ()}.sub.sp via the non-inverted final control element model. The non-inverted final control element model has a model parameter that corresponds to correction variable K.

[0058] In a difference block 33, a difference is ascertained between the instantaneous actual positioning rate {dot over ()}.sub.actual and modeled positioning rate {dot over ()}.sub.mod,flt.

[0059] The resulting deviation err (positioning rate difference) of the positioning rate (positioning rate difference) is forwarded to an ascertainment block 34 in which correction variable K is optimized, for instance with the aid of a gradient descent method.

[0060] FIG. 5 schematically illustrates ascertainment block 34 in greater detail. Resulting positioning rate difference err is multiplied by a scaling factor in a first multiplication block 41. Scaling factor specifies the measure of a convergence rate.

[0061] Moreover, modeled positioning rate {dot over ()}.sub.mod,flt is partially derived in a derivation block 44 at a predefined time constant and also multiplied by positioning rate difference err in a second multiplication block 42.

[0062] The result is integrated in an integrator block 43 in order to obtain correction variable K.

[0063] On the whole, correction variable K is calculated in that positioning rate difference err from instantaneous actual positioning rate {dot over ()}.sub.actual and modeled positioning rate {dot over ()}.sub.mod,flt is multiplied by a constant and/or variable scaling factor and subsequently integrated.

[0064] The above approach allows for a particularly reliable control of a camshaft phase adjuster 82, 92, which is easily adaptable, in particular. By separating the nonlinear response of the control system into the final control element model and the recognition that aging and wear tolerances are able to be represented in the final control element model via a multiplicative correction factor , the above control system may be used in a particularly flexible manner for different camshaft phase adjusters 82, 92. In addition, because of the automatic adjustment of correction variable K through an optimization method, an automatic adaptation to the conditions of the control system is able to take place.