Control method, control device and computer program product for an electrohydraulic camshaft adjuster in an internal combustion engine

Abstract

The control method according to the invention and the computer program product (55) for operating an electrohydraulic camshaft adjuster (25, 35) in an internal combustion engine (1), in particular a four-stroke reciprocating internal combustion engine, are carried out by means of the electronic control device (50). According to the invention, an adaptation-relevant target adjustment process of the camshaft adjuster (25, 35) is first determined in an adjustment direction at a maximum target adjustment speed (v_soll_max) specified depending on the operating point, and an actual adjustment path curve (s_ist) of the camshaft adjuster (25, 35) is detected in said adjustment process during ongoing operation of the internal combustion engine (1). In the event of an adaptation-relevant target adjustment process, the actual adjustment path curve (s_ist) of the camshaft adjuster (25, 35) is compared with a target adjustment path curve (s_soll) of the camshaft adjuster (25, 35) specified in said adjustment process in order to determine a variable of an evaluation criterion for the control behaviour of the camshaft adjuster (25, 35). The actual adjustment speed of the camshaft adjuster (25, 35) is then reduced or increased depending on the variable of the evaluation criterion, by adapting the maximum target adjustment speed (v_soll_max) which is specified depending on the operating point, in order to optimise the control behaviour. This advantageously brings about a higher accuracy of the gas exchange process during operation of the internal combustion engine (1) at maximum adjustment speed of the camshaft adjuster (25, 35) and thus has a positive effect on the exhaust-gas emission behaviour of the internal combustion engine (1).

Description

[0001] Description

[0002] Control method, control device and computer program product for an electro-hydraulic camshaft adjuster in an internal combustion engine

[0003] The invention relates to a control method as well as an electronic control device and a computer program product for operating electro-hydraulic camshaft adjusters in a four-stroke reciprocating internal combustion engine, hereinafter referred to as an internal combustion engine or VBM for short, in particular in a four-stroke Otto internal combustion engine.

[0004] In such VBMs, combustion chambers are formed in one or more individual cylinders, in which a respective piston can move up and down. To illustrate the principle of a VBM, reference is made below to Figure 1, which shows, by way of example, a cylinder 2 of a VBM 1 (which may also have multiple cylinders) with its most important functional units.

[0005] Each piston 6 is coupled to a respective crankpin 8 of the crankshaft 9 via a connecting rod 7, the crankpin 8 being arranged eccentrically to the crankshaft's axis of rotation 9a. The up-and-down movement of the piston 6 in the cylinder 2 sets the crankshaft 9 into rotation, whereby the translational stroke movement of the piston 6 is transmitted to the crankshaft 9 via the connecting rod 7 and crankpin 8 and converted into a rotational movement of the crankshaft 9.

[0006] To enable continuous operation of the VBM 1, four strokes must be completed during a so-called working cycle of a cylinder 2. The four strokes of the VBM 1 are distributed over two revolutions (720°) of the crankshaft 9 and thus two up-and-down stroke movements of the respective piston 6 between top dead center (TDC) and bottom dead center (BDC). In the first stroke, the so-called intake stroke, the piston 6 moves from TDC to BDC. During this movement, the combustion chamber 3 in cylinder 2, enclosed by the piston 6, expands, and a fuel-air mixture 21, as well as fuel if required separately, is supplied to the combustion chamber 3 by means of an injector 5. In the second stroke, the so-called compression stroke, the piston 6 then moves from BDC to TDC, and the fuel-air mixture 21 enclosed in the combustion chamber 3 is compressed.In the third stroke, the so-called power stroke, the fuel-air mixture is ignited and burned, in the case of a gasoline engine by means of a spark plug 5, in the case of a diesel engine by compression. This increases the gas volume and pushes the piston 6 back down to bottom dead center (BDC) while delivering work. In the fourth stroke, the so-called exhaust stroke, the piston 6 moves again from BDC towards top dead center (TDC) and pushes the exhaust gas produced by the combustion out of cylinder 2 as an exhaust stream 31.

[0007] The filling of the combustion chamber 3 formed in the respective cylinder 2 with a fuel-air mixture 21 and the removal of the exhaust gas flow 31 from the combustion chamber 3 after combustion is also referred to as gas exchange. Gas exchange is effected by means of gas exchange valves, which are differentiated into intake valves 22, which can open and close the combustion chamber 3 towards the intake tract 20, and exhaust valves 32, which can open and close the combustion chamber 3 towards the exhaust tract 30. These gas exchange valves 22, 32 are actuated by means of camshafts, here an intake camshaft 23, which is assigned to the intake valves 22, and an exhaust camshaft 33, which is assigned to the exhaust valves 32. These camshafts rotate at half the crankshaft speed but in sync, i.e., in phase, with the rotating crankshaft 9 of the VBM 1.For this purpose, the camshafts23, 33 are coupled to the crankshaft 9 via mechanical transmissions and are driven by the crankshaft 9 itself.

[0008] The rotational position of the individual cams on the respective camshafts 23, 33 and the relative rotational position of the camshafts 23, 33 to the crankshaft 9 ensure that the intake valves 22 open during the intake stroke so that air or fuel-air mixture 21 can be supplied to the combustion chamber 3, and that the exhaust valves 32 open during the exhaust stroke so that the exhaust gas flow from the combustion chamber 3 can be expelled into the exhaust tract 30. During the compression stroke and the power stroke, the gas exchange valves 22, 32 remain essentially closed.

[0009] For this purpose, the intake camshaft 23 and the exhaust camshaft 33 are each coupled to the crankshaft 9 in a predetermined position relative to each other and to the crankshaft 9 via a corresponding crankshaft control adapter 10, which is designed as a gear, sprocket, or pulley, using suitable intake camshaft control adapters 24 and exhaust camshaft control adapters 34, such as gears, sprockets, or pulleys. This coupling is achieved by means of a timing drive 40, which, for example, comprises a gear drive, a timing chain, or a timing belt. The rotational position of the intake camshaft 23 and the exhaust camshaft 33 is essentially defined by this connection in relation to the rotational position of the crankshaft 9. Figure 1 shows an example of the coupling between the intake camshaft 23 and the exhaust camshaft 33 and the crankshaft 9 by means of pulleys and a timing belt.

[0010] The rotational angle of the crankshaft 9 traversed during a working cycle is hereinafter referred to as the working phase or simply phase. A rotational angle of the crankshaft 9 traversed within a working phase is accordingly referred to as the phase angle. The current crankshaft phase angle of the crankshaft 9 can be continuously detected by means of a position sensor 43 connected to the crankshaft 9 or the crankshaft control adapter 10 and an associated crankshaft position sensor 41. Likewise, the current phase angles of the intake camshaft 23 and the exhaust camshaft 33 can optionally also be continuously detected by means of corresponding position sensors 43 and associated camshaft position sensors 42.

[0011] For optimal operation of the VBM (with regard to emissions, fuel consumption, performance, smooth running, etc.), the so-called gas exchange, i.e., the intake of fresh gas and the expulsion of exhaust gas, should occur as precisely as possible depending on the current operating parameters of the VBM. This is largely dependent on the timing of the intake valves 22 and exhaust valves 32, i.e., the timing of the respective valve lifts in relation to the timing of the piston stroke. In other words, the gas exchange during operation depends on the phase positions of the intake and exhaust camshafts in relation to the phase position of the crankshaft and thus of the respective piston.

[0012] In modern variable valve timing (VFM) engines, additional actuators are therefore present within the mechanical linkage between crankshaft 9 and intake camshaft 23, as well as the exhaust camshaft 33. These actuators are integrated, for example, into the intake camshaft adapter 24 and the exhaust camshaft adapter 34, and can controllably adjust a desired phase position or phase offset between the intake camshaft 23, the exhaust camshaft 33, and the crankshaft 9. These are known as phase adjusters or camshaft adjusters 25, 35 in variable valve trains.

[0013] In practice, electro-hydraulic camshaft adjusters 25, 35 or electric camshaft adjusters are predominantly used. In the electro-hydraulic camshaft adjusters 25, 35 considered here, pressurized engine oil is directed into vane chambers of the camshaft adjuster by means of an electrically controlled proportional valve to adjust the phase offset. It is assumed that an electro-hydraulic camshaft adjuster is provided on both the intake and exhaust camshafts 23, 33 of the VBM under consideration.

[0014] The targeted variation of the phase position or phase offset of intake and exhaust camshafts, depending on the current operating parameters of the VBM, is therefore already an established method for optimizing the control of the gas exchange and the material composition of the air-fuel mixture in the cylinders of the VBM with the aim of controlling the engine torque, minimizing pollutant emissions, and minimizing fuel consumption and carbon dioxide emissions.

[0015] The phase shift of the intake and exhaust camshafts in relation to the crankshaft, or the travel of the camshaft adjuster, is specified as a differential rotation angle in [°CRK], assuming that the position of the camshaft adjuster in the passive stop (i.e., the stop that the camshaft adjuster moves to when the VBM is operating without control) has the value 0°CRK (differential rotation angle) and that increasing values ​​of the position of the camshaft adjuster indicate an increasing distance to the passive stop and an increasing value of the differential rotation angle.

[0016] The accuracy with which the control device, e.g., the engine control unit, determines the gas mass in the cylinder and its composition for each individual combustion process directly influences the raw emissions of the combustion engine. For each static combustion engine operating point, i.e., with constant operating parameters such as engine speed, engine temperature, intake air temperature, intake manifold pressure, exhaust manifold pressure, and the position of the actuators near the engine—especially the camshaft adjusters—the gas mass in the cylinder and its composition are measured on the engine test bench and stored as a model in the engine control unit. Therefore, in steady-state engine operation, the calculation of the gas mass in the cylinder and its composition is particularly accurate, the fuel can be metered precisely, and the engine's raw emissions are especially low.

[0017] In the dynamic operation of the VBM, however, it is necessary to dynamically adjust the phase angles of the intake and exhaust camshafts relative to the crankshaft. The transitions during rapidly changing phase angles are turbulent and, if at all possible, much less accurately modelable than with constant phase angles. This results in higher raw pollutant emissions from the VBM than in steady-state operating conditions. Therefore, to minimize raw pollutant emissions from the VBM, it is important to avoid uncontrolled adjustment movements, and especially the overshoots of the camshaft adjusters that occur primarily when the adjustment direction changes, during the dynamic adjustment of the phase angles of the intake and exhaust camshafts required for controlling the combustion engine.

[0018] This is particularly problematic with electro-hydraulic camshaft adjusters because the engine oil pressure is generated centrally in the combustion engine by a mechanically or electrically driven oil pressure pump and is often not regulated to a setpoint in a closed control loop. Furthermore, a common oil line to both camshaft adjusters is frequently used, branching off to each only as late as possible. When the camshaft adjusters are actuated by the proportional valve, oil flows out through the vane chambers, and the oil pressure drops. This, along with other negative influences such as low oil temperature, low oil pressure, high actuation speed, large actuation ranges, simultaneous actuation of both camshaft adjusters, as well as varying oil viscosity and component tolerances, can lead to significant fluctuations in oil pressure during engine operation.This promotes the formation of overshoots of the camshaft adjusters during the dynamic adjustment of the phase positions of the intake and exhaust camshafts.

[0019] Since the operating conditions of the VBM, especially when used in a motor vehicle, can change very dynamically, it is necessary that the adjustment of the phase positions of the intake and exhaust camshafts, i.e., the respective adjustment process, also takes place with high dynamics, i.e., at maximum adjustment speed. However, it has been shown that with increasing dynamics of the respective adjustment process, the tendency of the camshaft adjusters to overshoot also increases, whereas overshoots can be avoided by sufficiently reducing the adjustment speed.

[0020] It follows that, in principle, it is not possible to implement overshoot-free control of the camshaft adjusters on an engine control unit with parameters common to all individual engines of a series, using feedforward control and control based on measured actual values, which operates each individual camshaft adjuster at its maximum individual actuation speed.

[0021] A common practice to avoid the aforementioned camshaft adjuster overshoot is to select the maximum adjustment speed as high as possible, depending on the VBM operating parameters, but only so high that only acceptably small overshoots are observed in the relatively small fleet of vehicles available for engine control unit (ECU) parameterization. The ECU parameterization is thus tailored to the vehicle with the worst performance in this respect available for ECU parameterization.

[0022] It is accepted that individual vehicles in the field may exhibit larger overshoots later on due to unfavorable combinations of the aforementioned influencing parameters; and it is accepted that most vehicles do not fully exploit their potential for rapid camshaft phase adjustment. This has a negative impact on the exhaust emissions of the VBM.

[0023] The present invention is therefore based on the objective of achieving improved exhaust gas behavior, i.e., lower pollutant emissions from the VBMS in dynamic operation, by improving the actuating dynamics of each electro-hydraulic camshaft adjuster in the individual VBM while simultaneously avoiding overshoots in the actuating movement of the actuator of each individual camshaft adjuster of the VBM.

[0024] This problem is solved by an improved control method for electro-hydraulic camshaft adjusters, a corresponding electronic control device, and a computer program product for carrying out the control method, according to the independent claims. The invention advantageously results in higher accuracy of the gas exchange process during operation of the internal combustion engine while simultaneously maximizing the actuating speed of the camshaft adjuster (25, 35), thus having a positive effect on the exhaust emission behavior of the internal combustion engine (1).

[0025] Advantageous embodiments, further developments and details of the present invention will become apparent from the dependent claims, the description and the drawing.

[0026] According to the invention, a control method for operating an electro-hydraulic camshaft adjuster with camshaft position control in an internal combustion engine is provided. The method is implemented by means of an electronic control device associated with the internal combustion engine. The control method comprises at least the following process steps or the following process sequence.

[0027] In the first iteration of the control procedure, an adaptation-relevant target adjustment process of the camshaft adjuster is determined at a maximum target adjustment speed in one direction, which is predetermined based on the operating point. The target adjustment process is defined as the control-related specification for a desired adjustment of the camshaft adjuster, starting from a first adjustment range, through an adjustment range in a predetermined direction, at a maximum target adjustment speed determined based on the operating point, up to a second adjustment range. The maximum target adjustment speed of the camshaft adjuster, assigned to specific operating points of the internal combustion engine, is stored, for example, in corresponding maps in the electronic control unit and is read out during operation as a control-related specification and applied to the respective target adjustment process.

[0028] The camshaft adjuster cannot perfectly follow this control-related specification, resulting in a deviation between the actual position and the target position. Particularly during the dynamic operation of the combustion engine, camshaft adjuster adjustments in the same or different directions can occur very rapidly. This makes it difficult to reliably acquire and evaluate signals representing the actual position. Adapting the control behavior of the camshaft position control based on this is inaccurate and error-prone and should therefore be avoided. For this reason, only adjustments for which at least the target position exhibits a stable profile that meets specific criteria are used for evaluation and adaptation of the control behavior. Such an adjustment is referred to here as the adaptation-relevant target position.

[0029] During such an adaptation-relevant target adjustment process determined in the operation of the combustion engine, the corresponding actual position path of the camshaft adjuster, following the control-technical specification, is recorded by the electronic control device during the running operation of the combustion engine, for example with the help of appropriate position sensors.

[0030] If an adaptation-relevant target adjustment process is present, the actual position path of the camshaft adjuster is then compared with a target position path (s_target) of the camshaft adjuster specified in this adjustment process, and a value of an evaluation criterion for the control behavior of the camshaft adjuster is determined from this.

[0031] Depending on the magnitude of the determined evaluation criterion, the actual actuating speed of the camshaft adjuster is then lowered or raised for subsequent adjustment processes by adapting the maximum target actuating speed, which is specified depending on the operating point, in order to optimize the control behavior of the camshaft adjuster. In particular, this optimizes the actuating speed of the camshaft adjuster while avoiding excessive overshoot of the actual actuating speed above the target actuating speed.

[0032] It should be noted that the control method according to the invention is applicable both for adjustment processes in the positive adjustment direction, i.e. when increasing the adjustment path, and in the negative adjustment direction, i.e. when decreasing the adjustment path.

[0033] In an advantageous second embodiment of the control method, a maximum actual overshoot is defined as an evaluation criterion. This overshoot represents the maximum difference, normalized to the adjustment direction, between the actual position curve of the camshaft adjuster and the target position curve of the camshaft adjuster up to the end of the target adjustment process. The actual overshoot thus represents a measure of the deviation of the actual position curve from the target adjustment process or the target position curve, and therefore of the quality of the control behavior of the camshaft position control. Due to normalization to the adjustment direction, the overshoot can be used regardless of the adjustment direction, meaning it applies equally to both increases and decreases in the adjustment travel of the camshaft adjuster. The actual overshoot is significantly influenced by the achieved actual adjustment speed.Thus, the actual overshoot can be advantageously used as a basis for adapting the maximum target actuating speed specified depending on the operating point, and thus for improving the control behavior of the camshaft adjuster.

[0034] Based on the second iteration of the control procedure, a third iteration reduces the maximum target actuation speed of the camshaft adjuster for subsequent adjustment operations if the maximum actual overshoot exceeds a predetermined upper overshoot limit value, defined with respect to the adjustment direction, which characterizes the maximum permissible overshoot. For this purpose, the maximum target actuation speed, which is specified depending on the operating point, can be reduced by a predetermined increment, resulting in a reduction of the actual actuation speed. The upper overshoot limit value can be empirically determined beforehand and characterizes the maximum tolerable exceedance of the target actuation path by the actual actuation path in the respective adjustment direction.The upper overshoot limit is generally selected to allow a certain degree of overshoot between the actual position curve and the target position curve. However, the overshoot limit can also be set to zero to prevent overshoot as completely as possible. It should be noted that the target position speed, the actual position speed, and the upper overshoot limit must all be normalized to the respective adjustment direction. This reliably and quickly prevents excessive overshoot between the actual position curve and the target position curve, thus improving the exhaust emission characteristics of the combustion engine.

[0035] Building upon the second iteration of the control procedure, a fourth iteration increases the maximum target actuation speed of the camshaft adjuster for subsequent adjustment operations if the maximum actual overshoot does not reach a lower overshoot limit specified with respect to the adjustment direction. For this purpose, the operating-point-dependent maximum target actuation speed can, for example, be increased by a predetermined increment, which results in an increase in the actual actuation speed. The lower overshoot limit can be empirically determined beforehand and defines the maximum tolerable deviation of the actual actuation speed from the target position. If the lower overshoot limit is not reached, this indicates that the actual actuation speed is lower than desired and can be increased for optimization.The lower overshoot limit is generally chosen to allow a certain degree of deviation between the target and actual position profiles. This means that the lower overshoot limit can be negative for the respective adjustment direction. However, the lower overshoot limit can also be set to zero or positive, thus preventing the actual position profile from falling below the target profile as much as possible. It should be noted that the target positioning speed, the actual positioning speed, and the upper overshoot limit must also be considered normalized for the respective adjustment direction.In this way, the actual actuation speed of the camshaft adjuster is optimized to a maximum permissible level, which ensures the fastest possible adaptation of the camshaft phase position to the current operating conditions of the internal combustion engine and further improves the exhaust emission behavior of the internal combustion engine.

[0036] In another embodiment of the control method, the reduction or increase of the maximum target positioning speed is achieved by applying an adaptation factor, dependent on the magnitude of the evaluation criterion, to the maximum target positioning speed, which is predefined depending on the operating point. The maximum actual overshoot, as described in one of the previously mentioned embodiments, can be used as the evaluation criterion. In this case, the change in the target position of the camshaft adjuster is therefore not directly limited by the maximum target positioning speed originally stored in the control device's characteristic maps, depending on the operating conditions, but rather by an adapted maximum target positioning speed derived from this and the adaptation factor. The adaptation factor can be chosen to be larger or smaller depending on the value of the evaluation criterion.In the case of a desired reduction in the actual actuating speed, an adaptation factor less than "one" is chosen, whereas in the case of a desired increase in the actual actuating speed, an adaptation factor greater than "one" is chosen.

[0037] The adaptation factor can be determined for each detected target adjustment process relevant to adaptation and can preferably be stored non-volatilely in an operating data memory of the electronic control device, with the currently determined adaptation factor replacing the previously stored adaptation factor. For example, the adaptation factor is stored non-volatilely in the operating data memory at the end of each operating cycle of the combustion engine and read out again at the beginning of the next operating cycle; thus, it retains its value even after the control device is reset. For a brand-new engine, the adaptive factor can be initialized with the neutral value of 1. In this way, a gradual, continuous adaptation of the maximum adjustment speed of the camshaft adjuster is advantageously achieved.

[0038] Another implementation of the control method uses the actual overshoot as the evaluation criterion and adjusts the actual positioning speed by increasing or decreasing it depending on whether an upper overshoot limit is exceeded or a lower overshoot limit is not reached, and by means of an adaptation factor. The adaptation factor is selected based on the difference between the maximum actual overshoot and the upper overshoot limit, or the lower overshoot limit. This difference is also referred to as the "adaptation-relevant overshoot."If the actual overshoot is below the upper overshoot limit and above the lower overshoot limit, it falls within the defined tolerance band. In this case, the actual overshoot is not relevant for adaptation, and no adjustment of the maximum target actuation speed is necessary. This advantageously keeps the actual overshoot within a tolerance band between the target actuation path or the target position of the camshaft adjuster and the upper or lower overshoot limit, respectively.

[0039] Building upon the previously described implementation, a further iteration of the control procedure, after repeated detection of exceeding the upper overshoot limit or falling below the lower overshoot limit (i.e., in the case of an adaptation-relevant overshoot), reduces or increases the adaptation factor by a factor increment dependent on the difference value of the maximum overshoot. Thus, after each detected adaptation-relevant target adjustment, the overshoot or the previously described difference value (i.e., the adaptation-relevant overshoot) is checked. If the difference value is positive (i.e., if the upper overshoot limit is exceeded), the adaptation factor is reduced by a small factor increment, thereby lowering the maximum target adjustment speed.

[0040] In the case of a negative difference value, i.e., when the lower overshoot limit is undershot, the adaptation factor is increased by a small increment, thereby increasing the maximum target speed. The increment can be made dependent on the magnitude of the difference value, i.e., the overshoot relevant for adaptation.

[0041] For example, if there is a positive adaptation-relevant overshoot, i.e., if the upper overshoot limit is exceeded by, for example, 0 to 10 °CRK, the currently stored adaptation factor can be reduced and stored by a correspondingly adjusted factor increment between 0 and -0.01. Conversely, if there is a negative adaptation-relevant overshoot, i.e., if the lower overshoot limit is not reached by, for example, 0 to -10 °CRK, the currently stored adaptation factor can be increased by a factor increment between 0 and 0.01.

[0042] In an alternative implementation to the one described immediately preceding, after repeated detection of exceeding the upper overshoot limit or falling below the lower overshoot limit, the adaptation factor can be multiplied by a change factor dependent on the difference value of the maximum overshoot. For a positive difference value, i.e., when the upper overshoot limit is exceeded, the adaptation factor is multiplied by a change factor slightly less than one to reduce the maximum target speed. For a negative difference value, i.e., when the lower overshoot limit is not reached, the adaptation factor is increased by a change factor slightly greater than one, thus increasing the adaptive maximum target speed.The change factor can be made dependent on the magnitude of the difference value, i.e., the adaptation-relevant overshoot. For example, if the adaptation-relevant overshoot is positive (i.e., if the upper overshoot limit is exceeded by, for example, 0 to 10 °CRK), the currently stored adaptation factor can be reduced and stored accordingly with a change factor between 1 and 0.99, particularly between 1 and 0.9. Conversely, if the adaptation-relevant overshoot is negative (i.e., if the lower overshoot limit is not reached by, for example, 0 to -10 °CRK), the currently stored adaptation factor can be increased with a change factor between 1 and 1.01, particularly between 1 and 1.1.

[0043] In a further embodiment of the control method according to the invention, the adaptation-relevant target adjustment process is characterized by the following features:

[0044] - First, it is necessary that the target position of the camshaft adjuster lies at a first position level, within a defined first tolerance range, for at least a predefined first time interval;

[0045] - Furthermore, it is required that the magnitude of a control deviation of the camshaft position control during the aforementioned first time interval never exceeds a predefined first control threshold;

[0046] - Furthermore, it is required that the target position profile changes by at least one predefined minimum position immediately following the aforementioned first time interval, within a second time interval, without changing the direction of change;

[0047] Finally, it is necessary that the target position profile, following the second time interval, remains within a defined second tolerance band at a second position level for at least a predefined third time interval. These characteristics advantageously define a stable adjustment process suitable for adaptation, thereby ensuring the accuracy and stability of the adaptation of the maximum target positioning speed.

[0048] Building upon or supplementing the embodiment described immediately preceding, a further embodiment of the control method according to the invention is characterized in that the target position path of the camshaft adjuster has changed within the second time interval by at least a predefined part of a maximum position path, wherein the maximum position path characterizes the theoretical position path that could have been traveled in this time interval with the maximum target position speed specified depending on the operating point.

[0049] The electronic control device according to the invention for operating an electro-hydraulic camshaft adjuster with camshaft position control in an internal combustion engine comprises at least the following components:

[0050] - An electronic storage device in which at least one computer program product containing program instructions is provided;

[0051] - an input / output interface designed to receive and output electrical signals; as well as

[0052] - an electronic computing unit for executing program instructions, with access to at least one electronic storage device and the input / output interface.

[0053] The electronic control device is configured such that when the program instructions are executed by means of the electronic computing unit, they cause the electronic control device to execute a procedure according to one of the preceding described descriptions.

[0054] The electronic control device can be part of a central engine control unit of the internal combustion engine.

[0055] Through the automatic, continuously repeating execution of the control method according to the invention during the intended operation of the internal combustion engine, as described in one of the embodiments, the electronic control device advantageously contributes to improving exhaust emission behavior, i.e., to minimizing the pollutant emissions of the internal combustion engine during operation. The computer program product according to the invention for operating an electro-hydraulic camshaft actuator with camshaft position control in an internal combustion engine comprises program instructions for execution by the electronic processing unit of the electronic control device, as described above. When executed by the electronic processing unit, these program instructions cause the electronic control device to carry out the method according to one of the embodiments described above.Thus, the computer program product also makes a beneficial contribution to improving exhaust emission behavior, i.e., to minimizing the pollutant emissions of the combustion engine during operation.

[0056] The features and combinations of features of the embodiments of the invention described above or described below in the figure descriptions are to be applied individually, in part, or in their entirety, including in combination or complementary form, in further developments of the invention, without departing from the scope of the invention, insofar as they are not alternatively applicable or mutually exclusive. Features and details described in connection with the method naturally also apply in connection with the electronic control device and the computer program product, and vice versa, so that mutual reference can always be made to the individual aspects of the invention with regard to the disclosure of this invention.

[0057] The figures below illustrate particularly advantageous embodiments, details or further developments of the invention, although the subject matter of the invention is not limited to these examples.

[0058] The figures in this application are to be considered schematic only, and the relative sizes of the individual figures and the elements depicted within them are not to scale. Rather, individual elements may be exaggerated for clarity and / or to improve comprehensibility. Elements with identical functions, names, or similar effects are identified across all figures by the same reference symbols. In some figures, individual reference symbols may be omitted to improve clarity.

[0059] They show:

[0060] Fig. 1 is a simplified schematic representation of a reciprocating internal combustion engine with electronic control device.

[0061] Fig. 2 shows a diagram of the actuator path profiles corresponding to the control method, where the actual actuator path profile exceeds the target actuator path profile.

[0062] Fig. 3 shows a diagram like the one in Fig. 2, but the actual displacement curve does not reach the target displacement curve.

[0063] The reciprocating internal combustion engine shown schematically in Fig. 1, referred to as internal combustion engine (ICE) 1 for short, has already been described in the introduction to illustrate the functionality of the ICE and to explain the individual machine elements. In addition, an electronic control device 50 is shown schematically in simplified form in Fig. 1.

[0064] The electronic control device 50 sketched here as an example comprises an electronic computing unit 51, also referred to as a processor, an electronic storage device 52, and an input / output interface 53. In this embodiment, the electronic storage device 52 includes a program memory 52a in which a computer program product 55 according to the invention, containing program instructions, is available. Furthermore, the electronic storage device 52 includes an operating data memory 52b in which predefined operating data 56, as well as data acquired during operation, can be stored, for example, arranged in characteristic maps. A portion of this operating data memory 52b can also be used, for example, as an error memory.

[0065] The input / output interface 53 is connected to various sensor units and actuators of the VBM 1 via signal lines 54. The input / output interface 53 receives signals from the various sensor units via signal lines 54 and outputs control signals to the various actuators, such as the camshaft adjusters.

[0066] However, within the scope of the invention, different architectures of the electronic control device 50 are also possible, as long as the functionalities required for carrying out the method are provided. The electronic processing unit 51 is configured to carry out the method according to the invention in the embodiments described above and, if applicable, in addition thereto. For this purpose, the electronic processing unit 51 has access to, or is in a data connection (symbolized by connecting arrows) with, the input / output interface 53, the program memory 52a, and the operating data memory 52b. When executing the program instructions, the electronic processing unit 51 uses the relevant operating parameters, such as the maximum target positioning speed v_target_max and the adaptation factor, as well as various threshold values ​​for, e.g.,The electronic control device 50 is prompted to execute the control method according to the invention for operating an electro-hydraulic camshaft adjuster (25, 35) with a camshaft position control when the upper and lower overshoot limits are reached.

[0067] In accordance with the program instructions, signals representing sensor data or other operating parameters, such as the signals from the crankshaft position sensor 41 and the camshaft position sensors 42, which are used to determine the actual position profile s_actual, are received via the input / output interface 53 and, if necessary, stored as operating data 56 in the operating data memory 52b. The program then executes the calculations specified for operating the electrohydraulic camshaft actuators according to the control method of the invention. Based on this, control commands are then issued, for example, to actuate the camshaft actuators 25, 35 or the corresponding control valves.

[0068] Fig. 2 shows a diagram illustrating the relevant actuator path profiles for the control method. The actuator path s of the crankshaft adjuster is given in °CRK, as a differential rotation angle. It is assumed that the position of the camshaft adjuster in the passive stop (i.e., the stop the camshaft adjuster reaches when the VBM is operating without control) has the value 0°CRK (differential rotation angle), and that increasing values ​​of the camshaft adjuster's actuator path indicate an increasing distance from the passive stop, i.e., an increasing actuator path or differential rotation angle.

[0069] The target position curve s_target is shown as a dash-dot line, indicating the desired position curve according to the control specification. The actual position curve s_actual is also shown as a dashed line, representing the position curve detected by the respective camshaft position sensor 42 and realized in response to the control specification according to the target position curve.

[0070] According to the control method according to the invention, a target adjustment process of the camshaft adjuster 25, 35 relevant for adaptation is first determined, whereby a maximum target adjustment speed v_target_max is specified in one adjustment direction. Possible criteria that the target adjustment path s_target must fulfill in order to be determined as a target adjustment process relevant for adaptation are shown in the diagram.

[0071] One of the criteria is, for example, that the target position s_target of the camshaft adjuster 25, 35 initially lies at a first position level, within a defined first tolerance band delta_s_target_max_t1, for at least a predefined first time interval delta_t1. The specified tolerance band delta_s_target_max_t1 is shown in Fig. 2 as a hatched area extending from time t0 to time t1, i.e., over the first time interval delta_t1. The actual position s_actual fluctuates only slightly around the target position s_target within the first time interval delta_t1, so that the magnitude of a control deviation (s_target - s_actual) of the camshaft position control during this first time interval delta_t1 is never greater than a predefined first control threshold, which can be considered a further criterion for determining an adaptation-relevant adjustment process.

[0072] Another criterion is, for example, that the target position curve s_target changes by at least one predefined minimum position curve delta_s_target_min_t2 immediately following the first time interval delta_t1, within a second time interval delta_t2, without changing the direction of change. Within the second time interval delta_t2, the target position curve s_target increases continuously with a specific slope, where the slope or angle represents the maximum target position speed v_target_max, which is predetermined depending on the operating point. In the example shown, it can be seen that the maximum target position speed v_target_max is significantly reduced shortly before reaching the desired new, second position level in order to decelerate the adjustment movement of the camshaft adjuster 25, 35 to the new second position level.A further criterion for determining an adaptation-relevant target positioning process is that the target positioning path s_sol I, following the second time interval delta_t2, remains within a defined second tolerance band delta_s_soll_max_t3 at the second position level for at least a predefined third time interval delta_t3. The specified tolerance band delta_s_soll_max_t3 is also shown in Fig. 2 as a hatched area extending from time t2 to time t3, i.e., over the third time interval delta_t3.

[0073] As an additional criterion, it may be checked whether the target position path s_target of the camshaft adjuster 25, 35 has changed within the second time interval delta_t2 by at least a predefined part of a maximum position path delta_s_target_v_max_t2, for example 80%, which could have been moved in this second time interval delta_t2 with the maximum target position speed v_target_max specified depending on the operating point.

[0074] If, taking into account at least a selection of the aforementioned criteria, it has been determined that an adaptation-relevant target adjustment process is present, the control procedure can be continued by comparing the actual position profile s_actual of the camshaft adjuster 25, 35 with the target position profile s_target specified in this adjustment process in order to determine an evaluation criterion for the control behavior of the camshaft adjuster 25, 35. As shown in Fig. 2, a maximum actual overshoot delta_s_ctl_max can be used as an evaluation criterion, which represents the maximum difference, normalized with the adjustment direction, between the actual position profile s_actual of the camshaft adjuster 25, 35 and the target position profile s_target of the camshaft adjuster 25, 35 up to the end of the target adjustment process at time t3.This means that the maximum actual overshoot delta_s_ctl_max at time t3 is determined retrospectively, at least over the third time interval delta_t3, and the maximum value of the actual overshoot delta_s_ctl_max is used regardless of when it is reached. Figure 2 shows a positive change in position, i.e., an increase in the position s. However, the analysis can be performed in the same way for the opposite, negative change in position, i.e., a reduction in the position s, since normalization with the direction of travel is carried out. In other words, the evaluation criterion is the amount by which the actual position exceeds the position targeted by the desired adjustment process or the desired position in the direction of travel.In the further course of the control process, the actual actuating speed of the camshaft adjuster is then lowered or raised for subsequent adjustment operations by adapting the operating point-dependent maximum target actuating speed v_target_max as a function of the magnitude of the evaluation criterion, in this case, as a function of the maximum overshoot delta_s_ctl_max, to optimize the control behavior of the respective camshaft adjuster 25, 35. For example, the maximum target actuating speed v_target_max is lowered when the maximum overshoot delta_s_ctl_max is positive and raised when the maximum overshoot delta_s_ctl_max is negative. The greater the magnitude of the evaluation criterion, in this case, the maximum overshoot delta_s_ctl_max, the greater the reduction or increase of the maximum target actuating speed v_target_max.

[0075] The case where the maximum overshoot Δs_ctl_max becomes negative with respect to the adjustment direction, meaning that the actual position curve s_actual does not reach the target position curve s_target, is illustrated in the diagram in Fig. 3, which otherwise corresponds to the diagram in Fig. 2. In contrast to overshoot, this case can also be referred to as undershoot, and the maximum target adjustment speed v_target_max can be increased to accelerate the adjustment process and achieve the target position curve s_target in conjunction with the actual position curve s_actual, since failing to achieve the target position curve s_target can also have negative effects on the exhaust gas behavior of the VBM.

[0076] To allow for a certain tolerance of overshoot or undershoot and avoid having to adjust the maximum target speed v_target_max for every minor deviation, an upper overshoot limit delta_s_ctl_oGw, which defines a maximum permissible positive overshoot, and a lower overshoot limit delta_s_ctl_uGw, which defines a permissible lower, and possibly negative, minimum permissible overshoot or undershoot, can be defined. The respective distance of these two limits from the target stroke profile can be selected as needed and can also be zero.

[0077] In one embodiment of the control method, it can therefore be provided that the maximum target actuating speed v_soll_max of the camshaft adjuster 25, 35 is adapted by lowering if the maximum actual overshoot delta_s_ctl_max exceeds an upper overshoot limit delta_s_ctl_oGw, which is specified with respect to the direction of adjustment and characterizes the maximum permissible overshoot.

[0078] In the embodiment shown in Fig. 2, the upper overshoot limit delta_s_ctl_oGw and the lower overshoot limit delta_s_ctl_uGw each lie on the upper and lower limits, respectively, of the defined second tolerance band delta_s_soll_max_t3 of the target position curve s_soll. As long as the actual position curve s_ist remains within the second tolerance band delta_s_soll_max_t3 during the third time interval delta_t3, no adjustment of the maximum target position speed v_soll_max will occur. However, if, as in the example shown, the actual position curve s_ist exceeds the upper overshoot limit delta_s_ctl_oGw, an adjustment will be made by reducing the maximum target position speed v_soll_max.

[0079] Furthermore, it may be provided that the maximum target actuating speed v_soll_max of the camshaft adjuster 25, 35 is adapted by raising if the maximum actual overshoot delta_s_ctl_max does not reach a lower overshoot limit delta_s_ctl_uGw specified with respect to the direction of adjustment.

[0080] In the embodiment shown in Fig. 3, the upper overshoot limit delta_s_ctl_oGw lies above the upper limit of the defined second tolerance band delta_s_soll_max_t3 of the target position curve, i.e., in the positive overshoot range. The lower overshoot limit delta_s_ctl_uGw, on the other hand, lies on the target position curve or on the target value of the position. In this case, a deviation of the target position curve s_soll is therefore not tolerated, so that the target position curve s_soll must always be reached by the actual position curve s_ist. In the illustrated case, the lower overshoot limit delta_s_ctl_uGw is not reached by the actual position curve s_ist, and the maximum target position speed v_soll_max will be adjusted by increasing it.

[0081] Lowering or raising the maximum target actuating speed v_soll_max can be achieved by applying an adaptation factor, dependent on the size of the evaluation criterion, for example the maximum actual overshoot, to the specified maximum.

[0082] The target positioning speed v_target_max is determined. The adaptation factor can be set in...

[0083] The dependency on the amount of the difference value delta_s_ctl_Dw of the maximum actual overshoot delta_s_ctl_max is chosen, by which the maximum

[0084] The actual overshoot delta_s_ctl_max exceeds the upper overshoot limit delta_s_ctl_oGw or the lower limit respectively

[0085] The overshoot limit delta_s_ctl_uGw is not exceeded. The difference value delta_s_ctl_Dw of the maximum actual overshoot delta_s_ctl_max is shown and labeled accordingly in both Fig. 2 and Fig. 3.

[0086] Reference symbol list

[0087] 1 Internal combustion engine (VBM)

[0088] 2 cylinders

[0089] 3 Combustion chamber

[0090] 4 spark plug

[0091] 5 Injector

[0092] 6 pistons

[0093] 7 Connecting rod

[0094] 8 crankpins

[0095] 9 Crankshaft

[0096] 9a Crankshaft axis

[0097] 10 Crankshaft control adapters

[0098] 20 Intake tract

[0099] 21 Fuel-air mixture

[0100] 22 inlet valves

[0101] 23 Intake camshaft

[0102] 24 Intake camshaft control adapters

[0103] 25 Camshaft adjusters (intake camshaft)

[0104] 30 Exhaust system

[0105] 31 Exhaust gas flow

[0106] 32 outlet valves

[0107] 33 Exhaust camshaft

[0108] 34 Exhaust camshaft control adapters

[0109] 35 Camshaft adjusters (exhaust camshaft)

[0110] 40 Control gear

[0111] 41 Crankshaft position sensor

[0112] 42 camshaft position sensors

[0113] 43 Position sensors 50 Electronic control device

[0114] 51 Electronic computing unit (processor)

[0115] 52 Electronic storage device

[0116] 52a Program memory

[0117] 52b Operational data storage

[0118] 53 Input / Output Interface

[0119] 54 signal lines

[0120] 55 Computer program product

[0121] 56 Operating data s Setpoint s_target Setpoint curve s_actual Setpoint curve v_target_max Maximum setpoint speed t0... ,t3 Time intervals delta t1 First time interval delta_t2 Second time interval delta t3 Third time interval delta s target max t1 First tolerance range delta s target max t3 Second tolerance range de lta_s_target I l_max i n_t2 Minimum setpoint delta_s_target_v_max_t2 Maximum setpoint at v_target_max delta_s_ctl_max Maximum actual overshoot delta_s_ctl_oGw Upper overshoot limit delta_s_ctl_uGw Lower overshoot limit delta_s_ctl_Dw Overshoot difference value

Claims

Patent claims 1. Control method for operating an electro-hydraulic camshaft adjuster (25, 35) with a camshaft position control in an internal combustion engine (1), wherein the method is carried out by means of an electronic control device (7) associated with the internal combustion engine (1) and comprises the following method steps: - Determining an adaptation-relevant target adjustment process of the camshaft adjuster (25, 35) at an operating point-dependent specified maximum target adjustment speed (v_target_max) in one adjustment direction and recording an actual adjustment path (s_actual) of the camshaft adjuster (25, 35) during this adjustment process in the running operation of the internal combustion engine (1 ); - If an adaptation-relevant target adjustment process is present, compare the actual position curve (s_actual) of the camshaft adjuster (25, 35) with a target position curve (s_target) specified in this adjustment process, to determine an evaluation criterion for the control behavior of the camshaft adjuster (25, 35); - Lowering or raising the actual actuating speed of the camshaft adjuster for the following adjustment processes, by adapting the operating point-dependent specified maximum target actuating speed (v_target_max) depending on the size of the evaluation criterion, to optimize the control behavior of the camshaft adjuster (25, 35).

2. Control method according to claim 1, wherein a maximum actual overshoot (delta_s_ctl_max) is defined as the evaluation criterion, which represents the maximum difference normalized with the adjustment direction between the actual position path (s_actual) of the camshaft adjuster (25, 35) and the target position path (s_target) of the camshaft adjuster (25, 35) until the end of the target adjustment process.

3. Control method according to claim 2, wherein the maximum target actuating speed (v_target-max) of the camshaft adjuster (25, 35) is reduced when the maximum actual overshoot (delta_s_ctl_max) exceeds an upper overshoot limit value (delta_s_ctl_oGw) specified with respect to the direction of actuation, which characterizes the maximum permissible overshoot.

4. Control method according to claim 2, wherein the maximum target actuation speed (v_soll_max) of the camshaft adjuster (25, 35) is increased when the maximum actual overshoot (delta_s_ctl_max) does not reach a lower overshoot limit value (delta_s_ctl_uGw) specified with respect to the direction of adjustment.

5. Control method according to one of the preceding claims, wherein the lowering or raising of the maximum target actuating speed (v_soll_max) is carried out by applying an adaptation factor dependent on the size of the evaluation criterion to the specified maximum target actuating speed (v_soll_max).

6. Control method according to one of claims 3 or 4 and 5, wherein the adaptation factor is selected depending on a difference value (delta_s_ctl_Dw) of the maximum actual overshoot (delta_s_ctl_max) by which the maximum actual overshoot (delta_s_ctl_max) exceeds the upper overshoot limit (delta_s_ctl_oGw) respectively falls below the lower overshoot limit (delta_s_ctl_uGw).

7. Control method according to claim 6, wherein, after a repeated detection of exceeding the upper overshoot limit (delta_s_ctl_oGw) or falling below the lower overshoot limit (delta_s_ctl_uGw), the adaptation factor is decreased or increased by a factor increment that depends on the amount of the difference value (delta_s_ctl_Dw) of the maximum overshoot (delta_s_ctl_max).

8. Control method according to claim 6, wherein, after a repeated detection of exceeding the upper overshoot limit (delta_s_ctl_oGw) or falling below the lower overshoot limit (delta_s_ctl_uGw), the adaptation factor is multiplied by a change factor dependent on the difference value (delta_s_ctl_Dw) of the maximum overshoot (delta_s_ctl_max).

9. Control method according to claim 1, wherein the adaptation-relevant target adjustment process is characterized in that the target position path (s_target) of the camshaft adjuster (25, 35) is initially determined for at least one predefined first time interval (delta_t1 ) at a first position level, within a defined first tolerance bandwidth (delta_s_soll_max_t1 ), - where the magnitude of a control deviation of the camshaft position control during this first time interval (delta_t1) is never greater than a predefined first control threshold and - wherein the target position profile (s_target) changes immediately following the first time interval (delta_t1) within a second time interval (delta_t2) by at least one predefined minimum position (delta_s_target_min_t2) without changing the direction of change and - wherein the target position path (s_sol I) , following the second time interval (delta_t2), lies at least for a predefined third time interval (delta_t3) at a second position level, within a defined second tolerance bandwidth (delta_s_soll_max_t3).

10. Control method according to claim 8, wherein the target position path (s_target) of the camshaft adjuster (25, 35) has changed within the second time interval (delta_t2) by at least a predefined part of a maximum position path (delta_s_target_v_max_t2) which could have been traversed at maximum speed in this time interval (delta_t2) with the maximum target position speed (v_target_max) specified depending on the operating point.

11. Electronic control device (50) for operating an electro-hydraulic camshaft adjuster (25, 35) with camshaft position control in an internal combustion engine (1), with at least - an electronic storage device (52) in which at least one computer program product (55) containing program instructions is provided and - an input / output interface (53) designed to receive and output electrical signals, as well as - an electronic computing unit (51 ) for executing the program instructions, with access to the at least one electronic storage device (52) and the input / output interface (53); wherein the program instructions, when executed by means of the electronic computing unit (51 ), cause the electronic control device (50) to execute the method according to one of the preceding claims. Computer program product (55) for operating an electro-hydraulic camshaft adjuster (25, 35) with camshaft position control in an internal combustion engine (1), comprising program instructions for execution by the electronic computing unit (51) of the electronic control device (50) according to claim 11, wherein the program instructions, when executed by the electronic computing unit (51), cause the electronic control device (50) to carry out the method according to any one of claims 1 to 10.

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