DE102017219785A1 - Method for controlling a speed of an internal combustion engine with compensation of a dead time - Google Patents

Abstract

The invention relates to a method for controlling a rotational speed (N _M ) of an internal combustion engine by means of a controller (1), wherein a system model (4) and a signal processing model (5) are provided for the compensation of at least one dead time (t _tot ).

Description

The present invention relates to a method for controlling a rotational speed of an internal combustion engine, in which at least one dead time is compensated by means of a distance model and a signal processing model. Furthermore, the invention relates to a computer program that performs each step of the method when it runs on a computing device, and a machine-readable storage medium that stores the computer program. Finally, the invention relates to an electronic control device which is set up to carry out the method according to the invention.

State of the art

Nowadays in motor vehicles regulating the speed of an internal combustion engine is common. In this controlled operation, the speed is set by means of a speed controller (hereinafter referred to as "controller") to a predetermined value. For this purpose e.g. in diesel engines, the amount of fuel injected into the internal combustion engine is adjusted accordingly. As is usual with a control, the speed is constantly detected and compared with a target speed. As a result, occurring disturbances are automatically corrected. The controller is usually designed as a modified PI (proportional-integral) controller or as a PID (proportional-integral-differential) controller. To control controller parameters are used for a nominal system, which are designed separately depending on the driving situation, environmental conditions and gear and are often stored in corresponding maps. In addition, additional measures, such. B. a setpoint tracking, provided.

In the scheme often occur dead times, ie periods between a change of an input signal and the associated signal response, i. a change of the output signal. Consequently, the dead times affect the regulation. Especially at low speeds of the internal combustion engine, the influence of dead times in the signal processing is greater. Examples of such dead times are a dead time in the signal detection of the rotational speed, at which an output signal of the signal detection is output later than the rotational speed was detected or measured, and a combustion dead time, which describes the variable duration of the combustion under changed engine conditions.

With a small number of cylinders, especially with less than four cylinders, the increasing ignition interval between the cylinders leads to correspondingly greater dead times.

In addition, dead times occur at communication interfaces where a period of time passes until the signal has been transmitted. There are efforts to centralize software functions and to implement the speed control on a central computer of the motor vehicle for this purpose. For this purpose, additional communication interfaces are necessary, which lead to further dead times.

Disclosure of the invention

A method is proposed for controlling a rotational speed of an internal combustion engine by means of a regulator, in which at least one dead time is compensated by means of a distance model and a signal processing model. The dead time describes a period of time between a change of an input signal and the associated signal response, i. a change of the output signal. This creates a time delay within the control, which reduces the quality of the control. If the dead time in the system is known, the influences from this dead time can be corrected accordingly. This makes it possible to interpret the control of the speed as if there were no dead time. It should be noted that due to the compensation, the dead times between input signal and output signal are not actually eliminated. By compensating the dead time, its negative effect on the control is reduced or even completely eliminated, whereby the performance of the control is increased.

In the following, different types of dead times are described, which can be compensated by means of the method. It should be noted that other types of dead times not described here can also be compensated. It can be a dead time, which occurs at low idle speeds in the signal detection and / or in the signal processing of a measured speed compensated. This dead time arises between the detection of the rotational speed and the outputting of an output signal. The dead time can be additionally increased by the intervening signal processing. Furthermore, a combustion dead time, which characterizes a period of time required for combustion under changed engine conditions, can be compensated. In addition, cylinders of the internal combustion engine have increased ignition intervals, leading to a greater dead time. Such increased spark gaps occur especially in internal combustion engines with a small number of cylinders, especially in internal combustion engines with three or fewer cylinders. In other words, there is a compensation of the dead time, which occurs due to the increased ignition intervals with a small number of cylinders, in particular with three or fewer cylinders. In addition, a dead time is compensated, which arises at communication points when the signal is transmitted via the communication points.

To compensate for a dead time, a system model for a controlled system and a signal processing model are provided in the control. These preferably run in succession in a software function. In the course model, a mathematical model is used with which the controlled system is described, in particular with regard to its input / output behavior. As soon as the input variable of the model, ie an indicated torque, changes, so does the output variable of the system model, ie the engine speed. By combining the system model and the signal processing model, it is possible to predict a behavior of the controlled system together with the corresponding dead time, without knowing the measured speed.

Preferably, a speed difference between a speed determined from the system model and a speed determined from the signal processing model can be formed. In other words, a difference in rotational speeds is formed with and without influence of the signal processing model. Optionally, the speed difference may undergo filtering. Then a sum of this speed difference and the measured speed can be calculated. The calculated sum is hereinafter referred to as predicted speed. Finally, the controller may compare the predicted speed to a speed setpoint to perform the control.

The route model depends on physical model parameters of the controlled system, i. of the internal combustion engine and the drive train, from. These model parameters may differ from each other in two identical vehicles due to manufacturing tolerances and due to different aging. Likewise, these model parameters also depend on the driving situation.

One of the model parameters is a mass moment of inertia of the internal combustion engine and the associated components in the drive train of the vehicle. The moment of inertia indicates the inertia of the internal combustion engine and the associated components against a change in speed. Preferably, controller parameters are changed as a function of the moment of inertia so that when changing the mass moment of inertia, z. As in a gear change or actuation of the clutch, performance criteria for the scheme, such. B. do not change the overshoot and the like. For example, the controller parameters for this purpose can be multiplied by the mass moment of inertia or the controller parameters can be stored for different mass moments of inertia in a characteristic field.

Another model parameter is the load torque of the internal combustion engine and the associated components in the drive train of the vehicle. The load torque refers to the moment that counteracts the internal combustion engine during the rotational movement. As a result, the effective torque available for the acceleration of the internal combustion engine is reduced. According to one aspect, the model parameters are stored in maps as a function of a gear, a clutch signal and / or other variables. In another aspect, the model parameters may be calculated using an algorithm. The model parameters can consequently be determined as a function of the gear ratio, the clutch signal and / or other variables as well as events such. As a connection of an accessory, are calculated for the dynamic model.

Optionally, models of second order and / or higher order can also be used in the line model. As a result, the model used is more detailed and more complex component structures, such. B. a (complex structure) powertrain of a motor vehicle, are shown in detail.

Controller parameters of the controller can thus change as a function of the mass moment of inertia and / or the load torque of the internal combustion engine and the associated components in the drive train of the vehicle. This ensures that even if the moment of inertia and / or the load torque change, a constant control quality is still achieved.

In one aspect, in the signal processing model, an average engine speed may be calculated. For this purpose, signal detection and signal processing of the rotational speed measurement are preferably simulated in the signal processing model. This results in the advantage that the signal processing chain can be modeled and the dead times can be eliminated in the measurement.

The computer program is set up to perform each step of the method, in particular when it is performed on a computing device or controller. It allows the implementation of the method in a conventional electronic control unit without having to make any structural changes. For this purpose it is stored on the machine-readable storage medium.

By loading the computer program on a conventional electronic computing device, the electronic computing device is obtained, which is set to the dead time in the regulation of To compensate for the speed of the internal combustion engine. The electronic computing device can be, for example, an engine control unit or a central computer of a motor vehicle.

list of figures

• 1 zeigt ein Blockschaltbild eines Regelkreises für die Drehzahl eines Verbrennungsmotors gemäß einer Ausführungsform des erfindungsgemäßen Verfahrens.
• 2a und 2b zeigen für den Fall eines Führungsverhaltens den Verlauf der Drehzahl des Verbrennungsmotors (2a) und den Verlauf eines indizierten Drehmoments (2b) in Diagrammen über der Zeit mit einer Totzeit jeweils gemäß einer Ausführungsform der Erfindung und gemäß dem Stand der Technik.
• 3a und 3b zeigen für den Fall eines Drehzahlabfalls den Verlauf der Drehzahl des Verbrennungsmotors (3a) und den Verlauf eines indizierten Drehmoments (3b) in Diagrammen über der Zeit mit einer Totzeit jeweils gemäß einer Ausführungsform der Erfindung und gemäß dem Stand der Technik.

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

• 1 shows a block diagram of a control circuit for the speed of an internal combustion engine according to an embodiment of the method according to the invention.
• 2a and 2 B show in the case of a leadership behavior the course of the speed of the internal combustion engine ( 2a) and the course of an indicated torque ( 2 B) in diagrams over time with a dead time each according to an embodiment of the invention and according to the prior art.
• 3a and 3b show in the case of a speed drop the course of the speed of the internal combustion engine ( 3a) and the course of an indicated torque ( 3b) in diagrams over time with a dead time each according to an embodiment of the invention and according to the prior art.

Embodiments of the invention

des Verbrennungsmotors und der damit verbundenen Komponenten im Antriebsstrang des Fahrzeugs gewählt. Zudem können weitere Parameter P, wie z. B. Federkonstanten oder Dämpfungskonstanten, in die Regelung des Reglers 1 miteinfließen. Der Regler 1 gibt ein indiziertes Drehmoment M_ind an die Regelstrecke 2 aus. Aus dem indizierten Drehmoment M_ind wird eine Kraftstoffmenge berechnet, die in den Verbrennungsmotor eingespritzt wird. Infolgedessen wird an der Regelstrecke 2 die Drehzahl N_M des Verbrennungsmotors eingestellt, wobei ein Lastmoment M_L des Verbrennungsmotors und der damit verbundenen Komponenten der Drehbewegung entgegenwirkt. Die Drehzahl N_M des Verbrennungsmotors wird gemessen und durchläuft eine Signalverarbeitung 3, die eine gemessene Drehzahl N_mess ausgibt. 1 shows a block diagram of a control circuit for a speed N _M an internal combustion engine. The control loop includes a regulator 1 , which is designed in this case as a PI controller, a controlled system 2 , which maps the internal combustion engine together with components connected thereto in the drive train of a vehicle, and signal processing 3 , With respect to a motor vehicle, the powertrain includes, for example, a clutch, a transmission, etc. The governor 1 regulates the speed N _M of the internal combustion engine to a target speed N _sp on. Controller parameters for controlling the controller 1 become dependent on an estimated moment of inertia Ĵ and an estimated load moment $\widehat{M_L}$

the internal combustion engine and the associated components in the drive train of the vehicle selected. In addition, other parameters P , such as B. spring constants or damping constants in the control of the controller 1 miteinfließen. The regulator 1 gives an indexed torque M _ind to the controlled system 2 out. From the indicated torque M _ind An amount of fuel injected into the internal combustion engine is calculated. As a result, will be at the controlled system 2 the speed N _M set of the internal combustion engine, wherein a load torque M _L counteracts the combustion engine and the associated components of the rotational movement. The speed N _M the internal combustion engine is measured and undergoes signal processing 3 that measured a speed N _mess outputs.

des Verbrennungsmotors und der damit verbundenen Komponenten im Antriebsstrang des Fahrzeugs in das Streckenmodell 4 ein. In Abhängigkeit einer Gangstufe, eines Kupplungssignals und/oder weiterer Größen sind das geschätzte Massenträgheitsmoment Ĵ und das geschätzte Lastmoment $\widehat{M_L}$

in einem Kennfeld abgelegt oder werden mittels eines Algorithmus berechnet. Die Änderung der Drehzahl N_M des Verbrennungsmotors, daher deren zeitliche Ableitung N_M , wird in diesem mathematischen Modell durch die nachfolgend dargestellte Formel 1 beschrieben: $${\dot{N}}_M=\frac{\pi }{30\ast J}\left(M_{ind}-\widehat{M_L}\right)$$

According to the invention are a route model 4 and a signal processing model 5 provided, which are arranged in series connection one behind the other. The track model 4 uses a mathematical model with which the controlled system 2 , in particular with regard to its input behavior for the indicated torque and / or its output behavior for the rotational speed N _M of the internal combustion engine is described. The model parameters are the estimated mass moment of inertia Ĵ and the estimated load torque $\widehat{M_L}$

of the internal combustion engine and the associated components in the drive train of the vehicle in the route model 4 on. Depending on a gear ratio, a clutch signal and / or other variables are the estimated moment of inertia Ĵ and the estimated load torque $\widehat{M_L}$

stored in a map or are calculated by means of an algorithm. The change of the speed N _M of the internal combustion engine, therefore their time derivative N _M , is described in this mathematical model by Formula 1 shown below: $${\dot{N}}_M=\frac{\pi }{30*J}\left(M_{ind}-\widehat{M_L}\right)$$

In the present embodiment, it is assumed that when the indicated torque changes M _ind , the speed N _M changes accordingly and that until this movement with an opposite indicated torque M _ind counteracted. The change of the speed N _M of the internal combustion engine with changing indicated torque M _ind depends largely on the inertia J of the internal combustion engine and the associated components in the drive train of the vehicle. In addition, reduces the load torque M _L the torque available for accelerating the internal combustion engine. In embodiments of the invention, higher order models may be included in the route model. From the track model 4 will, after the change of the speed N _M was calculated, a track model speed N _st receive. By means of the route model 4 Dead times are within the controlled system 2 calculated out, so that the line model speed N _st the speed N _M of the internal combustion engine without dead times _dead equivalent.

In the signal processing model 5 become the signal acquisition and the signal processing 3 the speed N _M of the internal combustion engine. For this purpose, the speeds N _M of the internal combustion engine averaged over a previous period. The average speed becomes a signal processing model speed N _sv determined, with the measured speed N _mess can be estimated without their detection signal acquisition and signal processing 3 must be executed. Accordingly, the signal processing model speed is subject N _sv not the influences of signal acquisition and signal processing 3 and is therefore free from the dead times that occur _dead ,

It will be a speed difference .DELTA.N between the signal processing model speed N _sv and the line model speed N _st educated. The speed difference .DELTA.N goes through a filtering 51 , Following this speed difference .DELTA.N to the measured speed N _mess added up and as a sum a predicted speed N _pred receive. The predicted speed N _pred So gives the track behavior without dead times _dead on. Finally, this predicted speed N _pred to the controller 1 attributed to this predicted speed N _pred with the target speed N _sp compares and the speed N _M of the internal combustion engine based on the difference between the predicted speed N _pred and the target speed N _sp regulates.

In the present embodiment, the controller 1 , the signal processing 3 the speed N _M of the internal combustion engine and the track model 4 and the signal processing model 5 implemented in an electronic control unit. In further embodiments, said components are implemented in a central computer of a motor vehicle.

In the 2a and 2 B is in the case of a leadership behavior in which the speed N _M of the internal combustion engine is set to a predetermined desired value, an embodiment of the invention compared to the prior art shown. 2a shows in a diagram the speed N _M of the internal combustion engine over time t , It is a target course 60 which determines the given course of the speed N _M shows, in the form of a step response, a first speed value N ₁ to a second speed value N ₂ shown. There is also a course 61 the predicted speed N _pred shown at the same time as the step response of the desired course 60 increases and the second speed value N ₂ adapts. Next to it are a course 62 the speed N _M with compensation of the dead time _dead according to an embodiment of the invention (hereinafter abbreviated "speed curve 62 with compensation ") and a course 63 the speed N _M in control without compensation of the dead time _dead according to the prior art (hereinafter "speed curve 63 without compensation "). It passes the marked dead time _dead , until both speed curves 62 . 63 after the increase in the desired course 60 also increase. It turns out that the speed curve 62 with compensation directly to the second speed value N ₂ approaching, and in a form, that of the course 61 the predicted speed N _pred that have no dead time _dead includes, corresponds. The speed curve 63 without compensation has a different shape and shows an overshoot before moving to the second speed value N ₂ equalizes. This overshoot is in the speed history 62 with compensation only very weak or not available. Accordingly, the speed curve reached 62 with compensation the desired second speed value N ₂ faster than the speed curve 63 without compensation.

In 2 B is a graph of indicated torque for this case M _ind applied over time. A target course 65 , which specifies the given course of the indicated torque M _ind shows remains constant at a first torque value M ₁ because the torque should not change before and after the request. A torque curve 66 with compensation already falls off before the dead time _dead has passed while a torque curve 67 without compensation only after the dead time _dead drops. As shown here, the controller can 1 already within the dead time _dead to react to changes.

In the 3a and 3b is in the case where the speed N _M from a higher third speed value N ₃ to a lower fourth speed value N ₄ drops, an embodiment of the invention compared to the prior art shown. 3a shows in a diagram the speed N _M of the internal combustion engine over time t , Here is a target history 90 the speed N _M shown, the predetermined course of the speed N _M shows and therefore constant on the fourth speed value N ₄ lies. There is also a course 71 the predicted speed N _M shown below the third speed value N ₃ starts and then drops off at a constant slope until it reaches the fourth speed value N ₄ has reached, and then adapted to this. A speed curve 72 with compensation and a speed curve 73 without compensation, both initially fall from the third speed value N ₃ with a constant slope, that of the slope of the course 71 the predicted speed N _pred equivalent. In the compensation of the dead time _dead is already before reaching the fourth speed value N ₄ an oppositely indicated torque M _ind built up to the load moment M _L counteract. This is also on 3b directed. As soon as the fourth speed value N ₄ is reached, the speed curve swings 72 with compensation quickly to the specified fourth speed value N ₄ on. Accordingly, the speed curve corresponds 72 with compensation the course 71 the predicted speed N _pred with a shift that is essentially just the dead time _dead equivalent. By contrast, the speed curve falls 92 without feedforward, first below the fourth speed value N ₄ and swings to the fourth speed value N ₄ on.

In 3b is a graph of indicated torque for this case M _ind applied over time. A target course 75 , which indicated the specified course torque M _ind shows, also remains constant at a second torque value M ₂ , As already mentioned, in the compensation of the dead time _dead , according to the route model 4 an opposite indexed torque M _ind built up to the load moment M _L counteract (see also formula 1). A torque curve 76 Compensation therefore increases well in time before the corresponding speed curve 72 with compensation, the fourth speed value N ₄ has reached continuously. In contrast, a torque curve increases 97 without compensation, since the controller in this case without compensation only to a deviation between the current torque curve 97 and the desired course 75 can react later than the torque history 76 with compensation, then exceeds the second torque value M ₂ and swings to the second torque value M ₂ on. The undershoot of the speed N _M and the associated overshoot of the torque M _ind have a negative effect on the running characteristics of the internal combustion engine and also influence driving comfort.

Claims (12)

Method for controlling a rotational speed (N _M ) of an internal combustion engine by means of a controller (1), characterized in that a system model (4) and a signal processing model (5) are provided for the compensation of at least one dead time (t _tot ) in the control. Method according to Claim 1 , characterized in that a speed difference (ΔN) is formed between a rotational speed (N _st ) determined from the track model (4) and a rotational speed (N _sv ) determined from the signal processing model (5), a predicted rotational speed (N _pred ) is calculated as the sum of this speed difference (ΔN) and a measured speed (N _mess ), and the controller (1) compares the predicted speed (N _pred ) with a speed set point (N _sp ) to execute the control. Method according to Claim 2 , characterized in that the speed difference (ΔN) passes through a filtering (51) before the sum of the speed difference (ΔN) and the measured speed (N _mess ) is calculated. Method according to one of the preceding claims, characterized in that a mass moment of inertia (Ĵ) of the internal combustion engine and the components associated therewith is included in the system model (4). Method according to one of the preceding claims, characterized in that a load torque $\left(\widehat{M_L}\right)$

of the internal combustion engine and the components associated therewith flow into the system model (4). Method according to one of Claims 4 or 5 , characterized in that the mass moment of inertia (Ĵ) and / or the load torque $\left(\widehat{M_L}\right)$

are stored in maps. Method according to one of Claims 4 or 5 , characterized in that the mass moment of inertia (Ĵ) and / or the load torque $\left(\widehat{M_L}\right)$

is calculated by means of an algorithm. Method according to one of the preceding claims, characterized in that the second-order and / or higher-order models are also included in the route model (4). Method according to one of the preceding claims, characterized in that the signal processing model (5) calculates an average speed of the internal combustion engine by a signal detection and a signal processing (3) of the measured speed (N _mess ) are modeled. Computer program, which is set up, each step of the procedure according to one of Claims 1 to 9 perform. Machine-readable storage medium on which a computer program is based Claim 10 is stored. Electronic control unit, which is adapted to operate by means of a method according to one of Claims 1 to 9 to compensate at least one dead time (t _tot ) in the control of a speed (N _M ) of an internal combustion engine.

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