Method for operating a drive unit for a motor vehicle and corresponding drive unit

Abstract

Method for operating a drive unit (1) for a motor vehicle, which has an exhaust gas-generating drive unit (2), wherein fuel is introduced into a combustion chamber of the drive unit (2) at least temporarily according to at least one injection parameter to form a fuel-air mixture, and wherein an actual air-fuel ratio is determined on the basis of a residual oxygen content of the exhaust gas measured by means of a lambda sensor and is controlled by adjusting a composition of the fuel-air mixture to a target air-fuel ratio by means of a lambda control (3), wherein an input variable of a controller (5) of the lambda control (3) is determined from the target air-fuel ratio, the actual air-fuel ratio and an output variable of the controller (5) and the composition of the fuel-air mixture is determined from the output variable of the controller (5) and the target air-fuel ratio, characterized in thatthat the output variable is supplied to the controller (5) with a delay by means of a first delay element (13) with a first delay element parameter, and the target combustion air ratio is supplied to the controller (5) with a delay by means of a second delay element (15) with a second delay element parameter.

Description

[0001] The invention relates to a method for operating a drive unit for a motor vehicle which has an exhaust gas-generating drive unit, wherein fuel is introduced into a combustion chamber of the drive unit at least temporarily according to at least one injection parameter to form a fuel-fresh gas mixture, and wherein an actual air-fuel ratio is determined on the basis of a residual oxygen content of the exhaust gas measured by means of a lambda sensor and is controlled by adjusting a composition of the fuel-fresh gas mixture to a target air-fuel ratio by means of a lambda control, wherein an input variable of a controller of the lambda control is determined from the target air-fuel ratio, the actual air-fuel ratio and an output variable of the controller and the composition of the fuel-fresh gas mixture is determined from the output variable of the controller and the target air-fuel ratio.The invention further relates to a drive device for a motor vehicle.

[0002] For example, the prior art includes the publication DE 10 2016 203 430 A1. This describes a method for operating an internal combustion engine with a controller, wherein the controller performs lambda control, in which a manipulated variable of the controller is determined, a forward model for the control is determined, a predicted value is determined depending on the manipulated variable and the forward model, which is representative of a predicted system response, and the control of the internal combustion engine is carried out depending on the predicted value.

[0003] The publication DE 10 2011 006 787 A1 describes an air-fuel control system for an internal combustion engine with a fuel control approach that compensates for time delays in order to increase the feedback response speed of an exhaust gas sensor.

[0004] The object of the invention is to propose a method for operating a drive unit for a motor vehicle which has advantages over known methods, in particular enabling reliable and rapid control of deviations between the actual combustion air ratio and the target combustion air ratio.

[0005] According to the invention, this is achieved by a method for operating a drive unit for a motor vehicle with the features of claim 1. It is provided that the output variable is supplied to the controller with a delay by means of a first delay element with a first delay element parameter, and the target air-fuel ratio is supplied to the controller with a delay by means of a second delay element with a second delay element parameter.

[0006] Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims. It should be noted that the exemplary embodiments described in the description are not limiting; rather, any variations of the features disclosed in the description, the claims, and the figures are possible.

[0007] The drive system serves to propel the motor vehicle, thus providing the drive torque directed towards propelling the motor vehicle. To provide this drive torque, the drive system comprises the drive unit, which is preferably designed as an internal combustion engine. During operation, the drive unit is supplied with fuel and fresh gas at least intermittently, the fresh gas containing fresh air at least intermittently. Additionally, the fresh gas may contain exhaust gas if exhaust gas recirculation is implemented, in which the exhaust gas generated by the drive unit is at least partially returned to the drive unit as a component of the fresh gas. The fuel and fresh gas supplied to the drive unit form the fuel-fresh gas mixture with a specific composition, which is then reacted within the drive unit.

[0008] During operation of the drive unit, exhaust gas is produced due to the chemical reaction of fuel and fresh gas, which is discharged towards the outside environment of the drive unit or the vehicle. Since the exhaust gas produced by the drive unit contains pollutants, it is preferably first routed to an exhaust aftertreatment system before being released into the outside environment.

[0009] In the exhaust aftertreatment system, pollutants are at least partially converted into less harmful products. Only after passing through the exhaust aftertreatment system is the exhaust gas released into the environment. The exhaust aftertreatment system takes the form of a vehicle catalyst, particularly a three-way catalyst, an oxidation catalyst, or an NOₓ catalyst. x-storage catalyst or as an SCR catalyst. However, it can also be designed as a particulate filter, in particular as a gasoline particulate filter or as a diesel particulate filter, preferably with an integrated vehicle catalyst, for example with a catalytic coating.

[0010] To provide the fuel-air mixture to the combustion chamber of the engine, fuel is introduced into it, at least temporarily. This is done according to at least one injection parameter, which describes, in particular, the composition of the fuel-air mixture. The introduction of the fuel into the combustion chamber can, in principle, be carried out in any way. For example, the fuel is introduced directly into the combustion chamber, especially by injection. For this purpose, an injection valve is fluidically connected directly to the combustion chamber or even protrudes into it. In the case of such direct injection, the fuel only mixes with the air-air mixture in the combustion chamber. Additionally or alternatively, the fuel is combined with the air-air mixture outside the combustion chamber and fed into the combustion chamber together with it, i.e., already in the form of the fuel-air mixture.This can be done, for example, in the form of intake manifold injection.

[0011] The combustion chamber is located in a cylinder of the drive unit and is jointly bounded by the cylinder wall, the cylinder roof, and a piston movably arranged within the cylinder. Preferably, the drive unit has several cylinders and, accordingly, several combustion chambers. Wherever the combustion chamber is mentioned in this description, the descriptions are also applicable to configurations of the drive unit with multiple combustion chambers. In particular, they are applicable to each of the multiple combustion chambers.

[0012] The exhaust gas produced during the reaction of the fuel-air mixture in the combustion chamber is discharged. Downstream of the engine, the residual oxygen content of the exhaust gas is measured using the lambda sensor. The actual air-fuel ratio is determined from the residual oxygen content and compared with the target air-fuel ratio. If the actual air-fuel ratio deviates from the target air-fuel ratio, the composition of the fuel-air mixture is adjusted so that the actual air-fuel ratio changes towards the target air-fuel ratio, in particular until it reaches the target air-fuel ratio.

[0013] The air-fuel mixture is adjusted using lambda control. To achieve the fastest possible adjustment of the actual air-fuel ratio to the target air-fuel ratio—that is, to reduce the difference between the actual and target air-fuel ratios as quickly as possible, especially to zero or to a maximum permissible deviation—the controller is first supplied with an input variable consisting of the target air-fuel ratio, the actual air-fuel ratio, and the controller's output variable. This means that, in addition to the target air-fuel ratio and the actual air-fuel ratio, or the difference between them, feedback of the controller's output variable is provided.

[0014] Additionally, the composition of the fuel-air mixture, corresponding to a control variable of the lambda control, is to be determined both from the controller's output and directly from the target air-fuel ratio. In other words, the composition of the fuel-air mixture is determined based on the controller's output and the target air-fuel ratio, which is bypassed by the controller. This means that the target air-fuel ratio is taken into account both in the controller's input and directly in the composition of the fuel-air mixture.

[0015] For example, the composition is obtained by summing the controller's output and the target air-fuel ratio, so that the controller only compensates for any remaining difference. Preferably, an intermediate value is first determined from the output and the target air-fuel ratio, for example, by summation. This intermediate value is then converted into the composition of the fuel-air mixture, preferably using a mathematical relationship, a characteristic map, or a table. The intermediate value can have the same unit as the actual air-fuel ratio, the target air-fuel ratio, and the controller's output, whereas the unit of the composition may differ.

[0016] Directly incorporating the target air-fuel ratio, bypassed by the regulator, into the composition of the fuel-air mixture allows for particularly rapid compensation of abrupt changes in the target air-fuel ratio. Accordingly, a delay caused by the regulator in the composition rules is avoided.

[0017] The invention provides that the output variable is fed to the controller with a delay by means of a first delay element with a first delay element parameter. The controller's output variable thus only enters the controller with a time delay, or rather, only influences the controller's input variable with a time delay. The first delay element is implemented as a dead-time element, with the first delay element parameter describing the dead time of the first delay element. This implements an observer concept, and an integral element of the controller can only exert its effect with a time delay. This approach improves the control speed and stability of the lambda control.

[0018] The invention provides that the target air-fuel ratio is supplied to the controller with a delay by means of a second delay element with a second delay element parameter. This delay element, which can also be referred to as a dead-time element, delays the target air-fuel ratio supplied to the controller by a dead time defined by the second delay element parameter. In other words, the target air-fuel ratio is only fed into the controller's input variable with a delay. This takes into account a control loop encompassing the entire drive unit. This is advantageous because the target air-fuel ratio is directly incorporated into the composition of the fuel-air mixture. If the target air-fuel ratio is supplied to the controller without delay, overshooting of the lambda control can occur. This behavior is reliably avoided by the described procedure.

[0019] A further development of the invention provides that the first delay element parameter and / or the second delay element parameter are determined based on an operating point of the drive unit. The first delay element parameter or the second delay element parameter preferably describes the behavior of the controlled system, i.e., the dead time caused by the drive unit and / or the transit time of the exhaust gas to the lambda sensor. This dead time occurs primarily as a function of the exhaust gas mass flow rate, which in turn depends on the operating point. For this reason, the respective delay element parameter is to be determined using the operating point. In this way, a particularly precise tuning of the lambda control to the drive unit or drive system is achieved, resulting in a correspondingly fast control response.

[0020] A further development of the invention provides that the first delay element parameter and / or the second delay element parameter are determined from at least one of the following quantities available at the operating point: drive torque, rotational speed, exhaust gas mass flow rate, and exhaust gas temperature. These quantities each depend on the operating point of the drive unit. In particular, the operating point is characterized by the drive torque and the rotational speed of the drive unit. The exhaust gas mass flow rate and the exhaust gas temperature depend on the operating point, specifically on the drive torque and the rotational speed. Consequently, the respective delay element parameter can be determined with high accuracy from at least one of the aforementioned quantities, preferably several or even all of them. This results in extremely fast lambda control.

[0021] A further development of the invention provides that the first delay element parameter and / or the second delay element parameter is determined from the at least one quantity using a mathematical relationship, a characteristic map, or a table. In other words, the at least one quantity is an input for the mathematical relationship, the characteristic map, or the table, whereas the respective delay element parameter represents the output. For example, a separate mathematical relationship, a separate characteristic map, or a separate table is provided for each of the delay element parameters. The described procedure enables a particularly precise determination of the respective delay element parameter and thus a particularly rapid control of any deviation of the actual air-fuel ratio from the target air-fuel ratio.

[0022] A further development of the invention provides that the same delay parameter is used as both the first and second delay parameter. This means that the delay parameters always have the same value, so that both delay elements produce the same dead time. This results in particularly high stability of the lambda control.

[0023] A further development of the invention provides that a control variable for the lambda control, which influences the composition of the fuel-air mixture, is determined by adding the target air-fuel ratio to the controller's output. The control variable of the lambda control is understood to be its output, which determines the composition of the fuel-air mixture. This control variable is obtained by adding the target air-fuel ratio (bypassing the controller) to the controller's output. This means that the target air-fuel ratio is incorporated into the control variable twice: once as a component of the controller's output and again directly, bypassing the controller. As already explained, this results in a particularly rapid response of the lambda control to changes in the target air-fuel ratio.

[0024] A further development of the invention provides that the controller's input is determined from the target air-fuel ratio by subtracting the actual air-fuel ratio and adding the controller's output. To determine the input, the actual air-fuel ratio is subtracted from the target air-fuel ratio, and a control error is calculated accordingly. The controller's output is then added to this control error to implement the aforementioned observer concept. This results in high stability of the lambda control combined with a rapid response.

[0025] The invention further relates to a drive device for a motor vehicle, in particular for carrying out the method according to the embodiments within the scope of this description, wherein the drive device has an exhaust gas generating drive unit, wherein fuel is introduced into a combustion chamber of the drive unit at least temporarily according to at least one injection parameter to form a fuel-fresh gas mixture, and wherein an actual combustion air ratio is determined on the basis of a residual oxygen content of the exhaust gas measured by means of a lambda probe and is regulated by adjusting a composition of the fuel-fresh gas mixture to a target combustion air ratio by means of a lambda control.The drive unit is designed and configured to determine an input variable for a lambda control controller from the target air-fuel ratio, the actual air-fuel ratio, and an output variable of the controller, and to determine the composition of the fuel-air mixture from the controller's output variable and the target air-fuel ratio. The drive unit is further designed and configured to supply the output variable to the controller with a delay using a first delay element with a first delay element parameter, and to supply the target air-fuel ratio to the controller with a delay using a second delay element with a second delay element parameter.

[0026] The advantages of such a drive system design and procedure have already been mentioned. Both the drive system and the method for operating it can be further developed as described in this document, and reference is made to those details.

[0027] The features and combinations of features described in the description, in particular those described in the following figure description and / or shown in the figures, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention. Thus, embodiments that are not explicitly shown or explained in the description and / or the figures, but which emerge from or can be derived from the explained embodiments, are also to be considered as encompassed by the invention.

[0028] The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing, without limiting the invention. The drawing shows: Fig. 1 a schematic representation of a drive unit for a motor vehicle with lambda control in a first embodiment not according to the invention, and a diagram illustrating the behavior of the lambda control. Fig. 2 a schematic representation of the drive unit equipped with a second embodiment of the lambda control not according to the invention, and a diagram in which the behavior of the lambda control is shown, as well as Fig. 3 a schematic representation of the drive device with a lambda control in a third embodiment according to the invention and a diagram showing the behavior of the lambda control.

[0029] The Fig. Figure 1 shows a highly schematic representation of a drive unit 1 for a motor vehicle. The drive unit 1 has a drive assembly 2 to which a fuel-air mixture is supplied, at least intermittently. This mixture reacts in the drive assembly 2, producing exhaust gas. The composition of the fuel-air mixture is determined by a lambda control 3, which is shown here in a first embodiment. According to this embodiment, a target air-fuel ratio is supplied to the lambda control 3 at an input 4, to which an actual air-fuel ratio resulting from the reaction is to be adjusted. From the target air-fuel ratio applied to the input 4, an input variable for a controller 5 is determined by subtracting the actual air-fuel ratio from the target air-fuel ratio using a computational element 6.The result of this calculation is supplemented by an output variable of the controller 5 using a further control element 7.

[0030] The composition of the fuel-air mixture is determined from the output of controller 5 and set at the drive unit 2. In a simulation, an adder 8 (optional here) can be included, to which both the output of controller 5 and a disturbance variable, provided via input 9, are fed. In this case, the composition of the fuel-air mixture is determined from the result of the adder 8's calculation and set at the drive unit 2. The drive unit 2 can also be modeled using a dead-time element in the simulation. In this case, a dead-time parameter provided at input 10 is fed to the dead-time element.

[0031] The diagram shows a first curve 11 and a second curve 12. The first curve 11 shows the target air-fuel ratio, and the second curve 12 shows the resulting actual air-fuel ratio for the lambda control 3 in the first embodiment. It can be seen that when there are sudden changes in the target air-fuel ratio and when disturbances are applied via input 9, the actual air-fuel ratio exhibits strong fluctuations, which only subside after a considerable time.

[0032] The Fig. Figure 2 again shows a highly schematic representation of the drive unit 1, with the lambda control 3 in a second embodiment. This differs from the first embodiment of the lambda control 3 solely in the provision of a first delay element 13, to which a first delay element parameter present at an input 14 is supplied. The first delay element 13 serves to delay the output variable supplied to the input of the controller 5. One input of the first delay element 13 is connected to an output of the controller 5, and one output of the first delay element 13 is connected to the input of the controller 5, more precisely to the calculation element 7.

[0033] The effect of the first delay element 13 can be seen in the diagram, which again shows the two curves 11 and 12. It is evident that the oscillation of the lambda control 3 is reduced, so that after the jumps in the target air-fuel ratio and the disturbances, the actual air-fuel ratio is adjusted to the target air-fuel ratio more quickly than in the first embodiment.

[0034] The Fig.Figure 3 shows the drive unit 1 with a lambda control 3 in a third embodiment according to the invention, again in a very schematic representation. This differs from the second embodiment in that it includes a second delay element 15, which delays the influence of the target air-fuel ratio on the input variable of the controller 5, namely according to a second delay element parameter. This corresponds to the first delay element parameter, which is supplied via the input 14. The first delay element parameter of the first delay element 13 and the second delay element parameter of the second delay element 15 thus have the same value.

[0035] Furthermore, the target air-fuel ratio and the output of the controller 5 are fed to the adder 8, which adds these values ​​together. During the simulation, the disturbance variable can also be fed to the adder 8. From the result of the calculation by the adder 8, i.e., at least from the sum of the target air-fuel ratio and the output of the controller 5, the composition of the fuel-air mixture is determined and set at the drive unit 2.

[0036] The advantages of directly considering the target air-fuel ratio and the presence of the second delay element 15 are shown in the diagram, which again plots curves 11 and 12 over time. It is evident that, compared to the second embodiment, the lambda control 3 reacts significantly faster to changes in the target air-fuel ratio, meaning the actual air-fuel ratio rapidly approaches the target air-fuel ratio. This results in a responsive lambda control that is also extremely stable. REFERENCE MARK LIST: 1 Drive unit 2 Drive unit 3 Lambda control 4 Entrance 5 regulators 6 Calculation element 7 Calculation element 8 Adders 9 Entrance 10 Entrance 11 Course 12 Course 13 1. Delay element 14 Entrance 15 2. Delay element

Claims

[1] Method for operating a drive unit (1) for a motor vehicle which has an exhaust gas-generating drive unit (2), wherein fuel is introduced into a combustion chamber of the drive unit (2) at least temporarily according to at least one injection parameter to form a fuel-air mixture, and wherein an actual air-fuel ratio is determined on the basis of a residual oxygen content of the exhaust gas measured by means of a lambda sensor and is controlled by adjusting a composition of the fuel-air mixture to a target air-fuel ratio by means of a lambda control (3), wherein an input variable of a controller (5) of the lambda control (3) is determined from the target air-fuel ratio, the actual air-fuel ratio and an output variable of the controller (5) and the composition of the fuel-air mixture is determined from the output variable of the controller (5) and the target air-fuel ratio, characterized by, that the output variable is supplied to the controller (5) with a delay by means of a first delay element (13) with a first delay element parameter and the target combustion air ratio is supplied to the controller (5) with a delay by means of a second delay element (15) with a second delay element parameter. [2] Method according to claim 1, characterized by , that the first delay element parameter and / or the second delay element parameter are determined based on an operating point of the drive unit (2). [3] Method according to any one of the preceding claims, characterized by , that the first delay element parameter and / or the second delay element parameter are determined from at least one of the following quantities available at the operating point: drive torque, speed, exhaust mass flow and exhaust temperature. [4] Method according to any one of the preceding claims, characterized by, that the first delay element parameter and / or the second delay element parameter are determined from at least one quantity using a mathematical relationship, a characteristic map or a table. [5] Method according to any one of the preceding claims, characterized by , that the same delay parameter is used as both the first and second delay parameter. [6] Method according to any one of the preceding claims, characterized by , that a control variable of the lambda control (3) influencing the composition of the fuel-fresh gas mixture is determined by adding the target combustion air ratio with the output variable of the controller (5). [7] Method according to any one of the preceding claims, characterized by, that the input variable of the controller (5) is determined from the target combustion air ratio by subtracting the actual combustion air ratio and adding the output variable of the controller (5). [8] Drive unit (1) for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, wherein the drive unit (1) has an exhaust gas generating drive unit (2), wherein fuel is introduced into a combustion chamber of the drive unit (2) at least temporarily according to at least one injection parameter to form a fuel-fresh gas mixture, and wherein an actual air-fuel ratio is determined on the basis of a residual oxygen content of the exhaust gas measured by means of a lambda sensor and is controlled by adjusting a composition of the fuel-fresh gas mixture to a target air-fuel ratio by means of a lambda control (3), wherein the drive unit (1) is provided and configured to derive an input variable of a controller (5) of the lambda control (3) from the target air-fuel ratio,to determine the actual combustion air ratio and an output variable of the controller (5) and the composition of the fuel-fresh gas mixture from the output variable of the controller (5) and the target combustion air ratio, characterized by , that the drive device (1) is further designed and configured to supply the output variable to the controller (5) with a delay by means of a first delay element (13) with a first delay element parameter and to supply the target combustion air ratio to the controller (5) with a delay by means of a second delay element (15) with a second delay element parameter.

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