DE102018120973A1 - Method for controlling and regulating a direct injection system of a diesel engine - Google Patents

Abstract

The invention relates to a method for controlling and regulating a direct injection system (2) of a diesel engine. Before each injection process, model values for gas state variables of a combustion gas are determined on the basis of a predetermined gas state model (5), the combustion gas being available in a cylinder of the diesel engine in the subsequent injection process. Target quantities of the direct injection system (2) are determined for the following injection process on the basis of the model values. The setpoints are set or controlled by controlling injection actuators of the direct injection system. A predetermined setpoint determination method (7) is used to determine the setpoints. The target size determination process (7) was parameterized by an optimization process.

Description

The invention relates to a method for controlling and regulating a direct injection system of a diesel engine.

The control and regulation of diesel engines is based on the target torque specified by the driver using the accelerator pedal or also via a cruise control and to be made available by the diesel engine on the transmission side. On the basis of the detected target torque, a target injection quantity or a target injection volume is usually calculated using corresponding characteristic maps, which is to be injected into the cylinders via a direct injection system such as, for example, a common rail injection system of the diesel engine, in order to be able to provide the target torque corresponding to the driver's request. On the basis of the target injection volume determined in this way and the engine speed measured by measurement, target values of the boost pressure and the required fresh air mass are also calculated using suitable target value maps. In addition, a setpoint value for the start of injection, a setpoint value for the common rail pressure and, if appropriate, a setpoint value for the position of an air movement flap in the respective intake port of the cylinders is determined using suitable characteristic maps based on the target injection volume and the engine speed. Likewise, the total target injection quantity or the total target injection volume is distributed over a number of pre-injection processes and over one main injection process.

The setpoint maps and in particular also the maps for determining the injection timing, the common rail pressure, the distribution of the injection quantity between pre-injections, main injections and post-injections and the position of the charge movement flap are usually applied to engine test benches and during test drives by experienced specialists, initially Attempts are made to find the best possible settings for stationary operation with regard to consumption, emissions and torque. Due to the many degrees of freedom and the extremely difficult physical relationships of the combustion in dynamic operation of the diesel engine, the injection parameters for dynamic operation have not been adapted accordingly or are only taken into account to a certain extent.

It is therefore considered an object of the invention to further develop the control structure known from the prior art for controlling the combustion parameters of a diesel engine in such a way that, in particular, the combustion in dynamic or transient operation of the diesel engine is improved with regard to consumption, exhaust gas emissions and the torque provided and the transient operation can easily be taken into account in the control structure.

According to the invention, this object is achieved in that model values for gas state variables of a combustion gas are determined before each injection process on the basis of a predetermined gas state model, the combustion gas being available in a cylinder of the diesel engine in the following injection process, target quantities of the direct injection system for the following injection process being determined on the basis of the model values and the setpoints are set or adjusted by controlling injection actuators of the direct injection system. The injection process may include one or more pre-injections, a main injection and one or more post-injections.

It is known from our own investigations that in dynamic operation the gas state of the combustion air in the cylinders of the diesel engine has a significant influence on the generation of emissions in the transient operation of the diesel engine. By considering the gas state of the combustion air in the control structure of the injection system, the transient operation of the diesel engine can therefore be taken into account in the control structure in a particularly simple manner.

um einen Modellwert für eine Verbrennungsgastemperatur T̂_cyl und um einen Modellwert für eine Verbrennungsgasmasse m̂_cyl handelt. Die Modellwerte werden mit Hilfe des Gaszustandsmodells berechnet. Vorteilhafterweise werden die Gaszustandsgrößen der Verbrennungsluft für den jeweiligen Zylinder bestimmt, sobald Ein- und Auslassventile der Zylinder geschlossen sind und eine Änderung der Gaszustandsgrößen und insbesondere des relativen Sauerstoffanteils des Verbrennungsgases X_cyl und der Verbrennungsgasmasse m_cyl vor dem unmittelbar bevorstehenden Einspritzvorgang nicht mehr oder nur noch insbesondere im Hinblick auf die Verbrennungsgastemperatur T_cyl in einem zu erwartenden Maße erfolgt.According to the invention, it is advantageously provided that the model values for the gas state variables are a model value for a relative oxygen portion of the combustion gas $${\widehat{X}}_{cyl}.$$

is a model _value for a combustion gas temperature T̂ _cyl and a model _value for a combustion _{gas mass} m̂ _cyl . The model values are calculated using the gas state model. The gas state variables of the combustion air for the respective cylinder are advantageously determined as soon as the inlet and exhaust valves of the cylinders are closed and a change in the gas state variables and in particular the relative oxygen content of the combustion gas X _cyl and the combustion gas mass m _cyl before the imminent injection process no longer or only in particular with regard to the combustion gas temperature T _cyl to an expected extent.

The oxygen content of the combustion gas X _cyl is defined as the quotient of a fresh air mass present in the respective cylinder m _{air, cyl} and a total gas mass in the cylinder m _cyl $$X_{cyl}=\frac{m_{air.cyl}}{m_{air}}$$

In addition to the fresh air mass m _{air, cyl} advantageously the total gas mass in the cylinder m _cyl and the combustion gas temperature T _cyl determined with the help of the gas state model.

According to the invention, it is advantageously provided that the target variables are a target injection angle φ _{mi, des} to a target injection pressure p _{rail, des} and / or an air movement flap position u _{cmf, des} acts. When using a common rail injection system, the target injection pressure is advantageously the target common rail pressure. According to the invention, swirl flaps or tumble flaps can advantageously be used as the air movement flap.

In an advantageous implementation of the control structure according to the invention, it is provided that a current engine speed is used when determining the target values n _closely and a predetermined target injection quantity q _inj be taken into account.

A predetermined setpoint determination method is advantageously used to determine the setpoints. According to the invention, the setpoint determination method has a control model that starts from the gas state variables and advantageously the current engine speed n _closely and the specified target injection quantity q _inj the target values are determined.

It is advantageously provided according to the invention that at least one control map is used to determine the target values. With the control model and using the at least one control map, the setpoints are advantageously determined by interpolation of the output values of the control map corresponding to the setpoints between interpolation points from the gas state values and advantageously the engine speed n _closely and the target injection quantity q _inj corresponding input variables of the control map is determined. According to the invention, the control map has five input dimensions and three output dimensions. The input _dimensions are advantageously the model _value for the relative oxygen content of the combustion gas X̂ _cyl , the model _value for the combustion gas temperature T̂ _cyl , the model _value for the combustion _{gas mass} m̂ _cyl , and the current engine speed n _closely and the specified target injection quantity q _inj , The engine speed is advantageously recorded by measurement. The target injection quantity is advantageously determined on the basis of the driver's torque request and the current engine speed.

According to the invention, it is advantageously provided that the target size determination method has been parameterized by an optimization method. Advantageously, optimal injection parameters for predetermined gas state variables are determined in advance by measuring the respective diesel engine type. These optimal injection parameters are advantageously determined on the basis of a target function of the optimization method, with which in particular the emissions that arise during combustion, the consumption and the torque generated are evaluated. In order to shorten the optimization time, the optimization method advantageously has an online optimization algorithm, by means of which the optimization is carried out on the basis of the target function already when the diesel engine type is measured.

wobei p_cyl der Zylinderdruck in dem jeweiligen Zylinder und R_s die spezifische Gaskonstante des Verbrennungsgases ist, gelöst. Unter Verwendung von Zylinderdrucksensoren können die für das erfindungsgemäße Steuerungsverfahren vorteilhafterweise benötigten Gaszustandsgrößen T_cyl und m_cyl auf Basis der idealen Gasgleichung mit bekannten semiphysikalischen Modellgleichungen berechnet werden.To determine the gas state variables, provision is advantageously made for the model values for the gas state variables to be determined using the gas state model using cylinder pressure measured values determined with cylinder pressure sensors of the diesel engine. The ideal gas equation for the combustion gas is advantageously used to determine the gas state variables $$p_{cyl}{V}_{cyl}=m_{cyl}{R}_s{T}_{cyl}.$$

in which p _cyl the cylinder pressure in the respective cylinder and R _s the specific gas constant of the combustion gas is solved. Using cylinder pressure sensors, the gas state variables advantageously required for the control method according to the invention can be T _cyl and m _cyl can be calculated on the basis of the ideal gas equation using known semiphysical model equations.

Further advantageous embodiments of the method according to the invention are explained in more detail using an exemplary embodiment.

• 1 ein schematisch dargestelltes Ablaufdiagramm einer Steuer- und Regelstruktur für einen Dieselmotor, bei dem das erfindungsgemäße Verfahren eingesetzt wird.

It shows:

• 1 a schematically illustrated flow chart of a control and regulation structure for a diesel engine, in which the inventive method is used.

In 1 is a schematic flow diagram for the control and regulation of both an air path 1 as well as a direct injection system 2 of a diesel engine, taking into account gas state _variables ζ = [m _cyl , T _cyl , X _cyl ] ^{T of} a combustion gas. In the illustrated method according to the invention, a boost pressure p _2i , a gas temperature in an inlet container of the air path 1 T _2i and a relative amount of oxygen in the inlet tank X _2i through a model-based gas condition control 3 regulated. As target values ζ _{opt, des} the model-based gas state control 3 become a target quantity X _{cyl, des} for a relative proportion of oxygen in the combustion gas, a setpoint m _{cyl, des} for the cylinder gas mass and a target size for the T _{cyl, des} Cylinder gas temperature used. These setpoints are based on a measured engine speed n _closely and a predetermined target torque M _{i, i} on the basis of predetermined setpoint maps 4 determined for the gas state variables ζ. As manipulated variables u _{ap, des} the model-based gas state control 3 serve target valve positions of an exhaust gas turbocharger with variable turbine geometry s _{vtg, des} , a high pressure exhaust gas recirculation valve s _{hpagr, des} , a low pressure exhaust gas recirculation valve s _{lpagr, des} and a throttle position s _{tv, des} ,

In the method according to the invention for controlling and regulating the direct injection system 2 of the diesel engine, based on a given gas condition model, before each injection process 5 _Model values for the gas state _variables ζ̂̂ = [m̂ _cyl , T̂ _cyl , X̂ _cyl ] ^{T of} the combustion gas were determined. Based on these model values as well as the engine speed n _closely and that in a torque conversion step 6 based on engine speed n _closely and the target torque M _{i, i} determined injection quantity q _inj are subsequently used to determine the target size 7 Target sizes u _{c, opt} of the direct injection system for the following injection process. With these target values u _{c, opt} it is an injection angle φ _{mi, des} , a common rail print p _{rail, des} and a control variable for a swirl flap system u _{vsa, des} , Actuators of the direct injection system are then based on these setpoints 2 controlled.

Claims (8)

Method for controlling and regulating a direct injection system (2) of a diesel engine, model values for gas state variables of a combustion gas being determined on the basis of a predefined gas state model (5) before each injection process, the combustion gas being available in a cylinder of the diesel engine during the following injection process, target variables of Direct injection system (2) for the following injection process can be determined on the basis of the model values and the setpoints can be set or adjusted in a controlled manner by controlling injection actuators of the direct injection system. Procedure according to Claim 1 , characterized in that the model values for the gas state _variables are a model _value for a relative oxygen _{component of} the combustion gas X̂ _cyl , a model _value for a combustion gas temperature T̂ _cyl and a model _value for a combustion _{gas mass} m̂ _cyl . Procedure according to Claim 1 or Claim 2 , characterized in that the target values are a target injection angle φ _{mi, des} , a target injection pressure p _{rail, des} and / or an air movement _{flap position} u _{cmf, des} . Method according to one of the preceding claims, characterized in that a current engine speed n _eng and a predetermined target injection quantity q _{inj are} taken into account when determining the target values. Method according to one of the preceding claims, characterized in that a predetermined target size determination method (7) is used to determine the target values. Procedure according to Claim 5 , characterized in that at least one control map is used to determine the target values. Procedure according to Claim 5 or Claim 6 , characterized in that the target size determination method (7) was parameterized by an optimization method. Method according to one of the preceding claims, characterized in that the model values for the gas state variables are determined using the gas state model (5) using cylinder pressure measured values determined with cylinder pressure sensors of the diesel engine.

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