Method for operating a drive device, equipped with a lambda control system, for a motor vehicle and corresponding drive device

Abstract

A method for operating a drive device for a motor vehicle is disclosed, wherein the drive device has a drive unit which produces exhaust gas, wherein, in order to form a fuel / fresh gas mixture, fuel is introduced into a combustion chamber of the drive unit at least intermittently in accordance with at least one introduction parameter, 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 controlled to a desired combustion air ratio using closed-loop lambda control by adapting a composition of the fuel / fresh gas mixture. According to the invention, as soon as a change of the at least one introduction parameter occurs, a boost factor for at least one control element of the closed-loop lambda control is increased from a first value to a second value in order to rapidly adjust the actual combustion air ratio to the desired combustion air ratio.

Description

[0001] METHOD FOR OPERATING A DRIVE DEVICE FOR A MOTOR VEHICLE EQUIPPED WITH A LAMBDA CONTROL SYSTEM AND CORRESPONDING DRIVE DEVICE

[0002] DESCRIPTION:

[0003] The invention relates to a method for operating a drive device for a motor vehicle having an exhaust-generating drive unit, wherein fuel is introduced into a combustion chamber of the drive unit at least temporarily according to at least one introduction parameter to form a fuel-fresh gas mixture. An actual air-combustion ratio is determined based on a residual oxygen content of the exhaust gas measured by a lambda probe and regulated by adjusting the composition of the fuel-fresh gas mixture to a target air-combustion ratio using a lambda control. The invention further relates to a drive device for a motor vehicle.

[0004] For example, the prior art document DE 10 2011 085 115 A1 is known. This document describes a method for adapting a lambda control of an internal combustion engine with an exhaust gas probe arranged in an exhaust duct of the internal combustion engine as part of an exhaust gas monitoring system. The adaptation is performed based on a comparison of a modeled and a measured signal following a predetermined change in the fuel-air ratio of an air-fuel mixture supplied to the internal combustion engine. The measured signal is an actual value of an output signal of the exhaust gas probe, and the modeled signal is a model value derived from the air-fuel mixture supplied to the internal combustion engine by applying an exhaust gas model.It is intended that a step-by-step adaptation of the lambda controller parameters of a lambda control is carried out, whereby a difference between a maximum gradient of the measured air-fuel ratio and a maximum gradient of the air-fuel ratio expected from the model is used as a quality measure.

[0005] The object of the invention is to propose a method for operating a drive device for a motor vehicle, which has advantages over known methods, in particular enables rapid compensation of deviations between the actual combustion air ratio and the target combustion air ratio.

[0006] This is achieved according to the invention with a method for operating a drive device for a motor vehicle having the features of claim 1. It is provided that, upon a change in the at least one input parameter, a gain factor of at least one control element of the lambda control is increased from a first value to a second value for rapidly adjusting the actual combustion air ratio to the target combustion air ratio.

[0007] Advantageous embodiments with useful further developments of the invention are specified in the dependent claims. It should be noted that the exemplary embodiments explained in the description are not limiting; rather, any variations of the features disclosed in the description, the claims, and the figures are feasible.

[0008] The drive device serves to drive the motor vehicle, i.e. to provide a drive torque directed towards driving the motor vehicle. To provide the drive torque, the drive device has the drive unit. During operation of the drive device, fuel and fresh gas are supplied to the drive unit at least temporarily, wherein the fresh gas at least temporarily contains fresh air. In addition, the fresh gas can comprise exhaust gas, provided that exhaust gas recirculation is implemented, in which the exhaust gas generated by the drive unit is at least partially recirculated to the drive unit, namely as a component of the fresh gas. The fuel and the fresh gas supplied to the drive unit form the fuel-fresh gas mixture with a specific composition, which is reacted in the drive unit.

[0009] During operation of the drive unit, the chemical reaction between fuel and fresh gas produces exhaust gas, which is discharged to the environment outside the drive system or the motor vehicle. Since the exhaust gas generated by the drive unit contains pollutants, the exhaust gas is preferably first fed to an exhaust aftertreatment system before being released into the environment. In the exhaust aftertreatment system, the pollutants are at least partially converted into less hazardous products. Only after passing through the exhaust aftertreatment system is the exhaust gas discharged to the environment outside.

[0010] The exhaust gas aftertreatment device is present, for example, as a vehicle catalyst, in particular as a three-way catalyst, oxidation catalyst, NOx storage catalyst, or 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. The conversion rate and thus the conversion performance of the exhaust gas aftertreatment device, with which the pollutants are converted into less hazardous products, depend in particular on the composition of the exhaust gas supplied to the exhaust gas aftertreatment device and / or on the storage charge of the exhaust gas aftertreatment device, which in turn is related to the composition of the exhaust gas.The storage loading is preferably understood to mean a loading of the exhaust gas aftertreatment device with oxygen, i.e. the amount of oxygen temporarily stored in the exhaust gas aftertreatment device.

[0011] In order to form the fuel-fresh gas mixture, namely in the combustion chamber of the drive unit, fuel is introduced into it at least temporarily. This occurs according to at least one introduction parameter. The introduction of the fuel into the combustion chamber can basically occur in any way. For example, the fuel is introduced directly into the combustion chamber, in particular injected. For this purpose, an injection valve is fluidically directly connected to the combustion chamber or even protrudes into it. In the case of such direct injection, the fuel only mixes with the fresh gas in the combustion chamber. Additionally or alternatively, the fuel is combined with the fresh gas outside the combustion chamber and fed into the combustion chamber together with the fresh gas, i.e. already in the form of the fuel-fresh gas mixture. This can be done, for example, in the form of intake manifold injection.

[0012] The combustion chamber is located in a cylinder of the drive unit and is defined jointly by a cylinder wall of the cylinder, a cylinder roof of the cylinder, and a piston movably arranged within the cylinder. The drive unit preferably has multiple cylinders and, accordingly, multiple combustion chambers. Where reference is made to the combustion chamber in this description, the explanations are also applicable to designs of the drive unit with multiple combustion chambers. In particular, they are applicable to each of the combustion chambers.

[0013] The exhaust gas produced by the reaction of the fuel-fresh gas mixture in the combustion chamber is removed from the combustion chamber. Downstream of the drive unit, the residual oxygen content of the exhaust gas is measured using the lambda sensor. The actual combustion air ratio is determined from the residual oxygen content and compared with the target combustion air ratio. If the actual combustion air ratio deviates from the target combustion air ratio, the composition of the fuel-fresh gas mixture is adjusted so that the actual combustion air ratio changes toward the target combustion air ratio, in particular up to this value.

[0014] The composition is adjusted using lambda control. The actual combustion air ratio or a difference between the target combustion air ratio and the actual combustion air ratio is used as the controlled variable of the lambda control, while the composition of the fuel / fresh gas mixture is a manipulated variable of the lambda control. Lambda control is preferably based on PID control. Short-term deviations in the composition of the fuel / fresh gas mixture, lasting only a few seconds, must be compensated for by the integral component. The controller is subject to stability criteria, so the parameterization of the integral component is always a compromise between stability and spontaneity. Since the quality of the lambda control is crucial for the conversion performance of the exhaust gas aftertreatment system, it has a significant influence on the emissions or pollutants ultimately released into the outside environment.

[0015] A change in the injection parameter according to which the fuel is introduced into the combustion chamber can result in a short-term change in the actual combustion air ratio, even if such a change is unintended. This is the case, for example, when the number of injection pulses changes, which causes a sudden change in the actual combustion air ratio, namely due to a spontaneous change in the fuel-fresh gas mixture participating in the chemical reaction in the combustion chamber. This arises from different conditions when applying the various values ​​of the injection parameter. Although the proportional component of the lambda control reacts comparatively quickly, it cannot reduce a permanent control deviation with sufficient precision. The differential component is also not capable of this, as its essentially dampening effect. Furthermore, its extent is severely limited for stability reasons.

[0016] For this reason, the at least one control element of the lambda control system should be adjusted such that it compensates for the change in the actual combustion air ratio caused by the change in the at least one input parameter as quickly as possible. This is achieved by increasing the gain factor of the control element from the first value to the second value. The increase in the gain factor occurs immediately during or immediately after the change in order to achieve a rapid response of the lambda control system to the change in the actual combustion air ratio.Therefore, the change is not intended to be made only when the deviation of the actual combustion air ratio from the target combustion air ratio occurs. Instead, the change is made before the actual combustion air ratio deviates from the target combustion air ratio due to the change in at least one input parameter, or before the deviation of the actual combustion air ratio from the target combustion air ratio changes, in particular increases, due to the change in at least one input parameter. The described procedure enables an extremely rapid response of the lambda control to the deviation and thus a reliable and rapid adjustment of the actual combustion air ratio to the target combustion air ratio.

[0017] A further development of the invention provides that the increase in the gain factor is carried out starting with the change in the at least one introduction parameter in a first operating mode and is omitted in a second operating mode. In other words, the increase only occurs in the first operating mode. In the second operating mode, however, the gain factor is consistently constant or is selected to be the same throughout. Preferably, the drive device is operated in the first operating mode as long as a temperature lies within a specific temperature range. If, however, the temperature lies outside the temperature range, the drive device is operated in the second operating mode.

[0018] Particularly preferably, the drive device is operated in the first operating mode as long as the temperature is lower than a temperature threshold value. If the temperature is equal to or higher than the temperature threshold value, it is operated in the second operating mode. The temperature used can be, for example, an aggregate temperature of the drive unit, also referred to as engine temperature, or a catalytic converter temperature. This allows the gain factor to be adjusted as needed. Additionally or alternatively, it is provided that the second value is selected as a function of the aforementioned temperature. In particular, the lower the temperature, the higher the gain factor is selected, and vice versa. This means that the lower the temperature, the higher the gain factor is increased more than at a higher temperature.

[0019] A further development of the invention provides that one of the following parameters is used as the at least one introduction parameter: number of introduction pulses per working cycle, introduction location, introduction speed and introduction duration. An introduction pulse is understood to mean the introduction of fuel into the combustion chamber. The working cycle comprises all working strokes of the drive unit for the combustion chamber, in particular the working cycle extends from the start of an intake stroke, through a compression stroke and a power stroke to the end of an exhaust stroke. If fuel is introduced into the combustion chamber more than once during the working cycle, i.e. the number of introduction pulses is greater than one, the fuel is introduced separately for each of the introduction pulses, i.e. separated in time from other introduction pulses.The fuel injection for one of the injection pulses is terminated before fuel is injected again during a subsequent injection pulse. For example, at least one pre-injection and one main injection are realized in this way.

[0020] The injection point refers to the location where the fuel is introduced. For example, the injection point can be the combustion chamber directly or an intake manifold arranged upstream of the combustion chamber. The injection rate describes, for example, the throughput at which the fuel is introduced, in particular the mass flow or volume flow of the fuel during injection. The injection duration, in turn, is the period of time over which fuel is introduced into the combustion chamber. These parameters cause a change in the actual combustion air ratio, since even with a constant fuel quantity per combustion cycle, the timing of the injection and thus also the course of the chemical reaction changes.

[0021] A further development of the invention provides that the amplification factor is increased, in particular only if the change in the at least one introduction parameter results in a change in the fuel proportion in the composition of the fuel-fresh gas mixture by at least 10%, at least 20% or at least 30%. A significant change in the amount of fuel introduced into the combustion chamber also causes a change in the actual combustion air ratio, which should be quickly adjusted. For this reason, the described procedure is preferably used, in particular also when the fuel proportion changes by the stated amount, for example from a previous working cycle to the current working cycle. This makes it possible to quickly adjust the actual combustion air ratio to the target combustion air ratio.

[0022] A further development of the invention provides that the second value is selected to be larger by a factor of at least 5, at least 7.5, or at least 10 relative to the first value. In order to achieve rapid adjustment of the actual combustion air ratio to the target combustion air ratio, the amplification factor is significantly increased. The second value is preferably larger than the first value by one of the aforementioned factors, with the second value being obtained by multiplying the factor by the first value. This allows rapid compensation of the deviation caused by the change in the at least one introduction parameter.

[0023] A further development of the invention provides for the use of an integral control element as the at least one control element. The integral control element can also be referred to as an I-control element or an I-element. It is typically very well suited for reducing a deviation between the actual combustion air ratio and the target combustion air ratio over the long term. However, an integral control element designed for permanently stable lambda control requires a relatively long period of time for this. For this reason, the gain factor is increased from the first value to the second value to accelerate the adjustment process.

[0024] The first value of the gain factor is preferably selected such that, when the drive system is operated as intended and under normal boundary conditions, the lambda control is consistently stable. The second value, however, is significantly higher. In particular, it is selected such that, when the second value of the gain factor is used continuously, the lambda control becomes unstable, i.e., no longer functions stably. To quickly correct the deviation, a short-term instability of the lambda control is accepted, thus achieving the previously described advantage.

[0025] A further development of the invention provides that gain factors of additional control elements of the lambda control are kept constant. In addition to the at least one control element, the lambda control has at least one further control element, which is also assigned a gain factor. Preferably, there are several additional control elements and correspondingly several gain factors. The gain factor of the additional control element(s) is / are kept constant, i.e., is / are not increased or otherwise changed analogously to the gain factor of the at least one control element. This ensures that the stability of the lambda control is at least temporarily and at least partially continued.

[0026] A further development of the invention provides that the increase in the gain factor is reversed after a specific period of time. With the change in the at least one introduction parameter, the gain factor is set from the first value to the second value, i.e., at the beginning of the specific period of time. At the end of the specific period of time, the gain factor is set back from the second value to the first value, and the lambda control is continuously operated with the gain factor corresponding to the first value, in particular until a change in the at least one introduction parameter occurs again. This keeps the lambda control permanently stable while still enabling the rapid correction of the deviation in the actual combustion air ratio.

[0027] A further development of the invention provides that the length of the period is determined based on at least one of the following parameters: exhaust gas transit time from the drive unit to the lambda sensor, load of the drive unit, speed of the drive unit, torque provided by the drive unit, temperature, in particular exhaust gas temperature and / or temperature of an exhaust gas aftertreatment device, and response time of the lambda sensor. The exhaust gas transit time corresponds to the time required for the exhaust gas accumulating in the combustion chamber to flow from the drive unit to the lambda sensor. Therefore, only after the exhaust gas transit time has elapsed does the change in the at least one introduction parameter become noticeable at the lambda sensor and / or in the actual combustion air ratio.

[0028] Additionally or alternatively, the load, speed and torque of the drive unit can also be used to determine the length of the period. This also applies to the temperature. The temperature used here, for example, is the exhaust gas temperature or the temperature of the exhaust gas aftertreatment system. The response time of the lambda sensor can also be referred to as the reaction time. It describes the period of time that the lambda sensor needs to react to the change in at least one introduction parameter after the exhaust gas package reaches the lambda sensor. The T90 response time, for example, is used as the response time; this is the length of time that the lambda sensor needs to reach 90% of the final value at its output, particularly in the case of a sudden change.

[0029] It may be possible to determine the length of the period based on precisely one of the parameters. Preferably, however, several or even all of the aforementioned parameters are used. For example, the length of the period corresponds at most to the exhaust gas transit time multiplied by a specific factor, which, for example, is at least 1.0 or greater than 1.0, and at most 3.0, 2.0, or 1.5. Such a selection of the length of the period enables stable implementation of the lambda control.

[0030] A further development of the invention provides that the length of the period is selected such that the increase in the amplification factor is terminated at the latest immediately after the end of a change in the residual oxygen content caused by the change in at least one introduction parameter in a direction determined by the change. The change in the introduction parameter directly causes the change in the residual oxygen content or the actual combustion air ratio, which changes in a specific direction dependent on the change in the introduction parameter.

[0031] In other words, the actual combustion air ratio is changed in a specific direction by changing the feed parameter, for example towards smaller values ​​or towards larger values. The end of this change occurs when the residual oxygen content or the actual combustion air ratio begins to change in the other direction again due to the lambda control. In relation to the control deviation between the target combustion air ratio and the actual combustion air ratio, this means that the end of the change occurs at the maximum control deviation, i.e. at a point in the control deviation from which the previously continuously increasing change becomes smaller again. It is intended that the period ends at the latest with the end of this change, preferably even earlier.This means that the increase in the gain factor is withdrawn or reversed at the latest when the change in the residual oxygen content ends. This ensures the stability of the lambda control. The invention further relates to a drive device for a motor vehicle, in particular for carrying out the method according to the explanations in the context of this description, wherein the drive device has a drive unit generating exhaust gas and fuel is introduced into a combustion chamber of the drive unit at least temporarily according to at least one introduction parameter to form a fuel-fresh gas mixture, and wherein an actual air-combustion ratio is determined based on a residual oxygen content of the exhaust gas measured by means of a lambda probe and is controlled by adapting a composition of the fuel-fresh gas mixture to a target air-combustion ratio by means of a lambda control.The drive direction is provided and designed to increase a gain factor of at least one control element of the lambda control from a first value to a second value for quickly adjusting the actual combustion air ratio to the target combustion air ratio, starting from a change in the at least one introduction parameter.

[0032] The advantages of such a drive device design or such a procedure have already been pointed out. Both the drive device and the method for its operation can be further developed according to the explanations in this description, so reference is made to these in this regard.

[0033] The features and combinations of features described in the description, in particular the features and combinations of features described in the following description of the figures and / or shown in the figures, can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from the scope of the invention. Thus, embodiments are also to be considered as encompassed by the invention that are not explicitly shown or explained in the description and / or the figures, but which emerge from the explained embodiments or can be derived from them. The invention is explained in more detail below with reference to the exemplary embodiments illustrated in the drawings, without any limitation of the invention. The only

[0034] Figure 1 shows several diagrams in which the course of different variables relating to an operating method for a drive device of a motor vehicle is plotted over time.

[0035] A method for operating a drive device for a motor vehicle is explained with reference to Figure 1. The drive device has a drive unit to which, at least temporarily during its operation, a fuel-air mixture is supplied, which chemically reacts or burns in a combustion chamber of the drive unit to form exhaust gas. The fuel-fresh gas mixture is formed by introducing fuel into the combustion chamber, wherein the introduction takes place according to an introduction parameter. As an introduction parameter, for example, a number of introduction pulses for the combustion chamber per working cycle of the drive unit is used. The number describes how often fuel is introduced into the combustion chamber at discrete times per working cycle, for example by means of an injection valve.

[0036] The composition of the fuel-fresh gas mixture used in the drive unit is adjusted by means of a lambda control system. For this purpose, a lambda probe measures the residual oxygen content of the exhaust gas downstream of the drive unit, preferably upstream of an exhaust aftertreatment device of the drive unit, which may be a vehicle catalytic converter, for example. With the help of the lambda control system, the actual air-combustion ratio is adjusted or regulated to a target air-combustion ratio, namely by adjusting the composition of the fuel-fresh gas mixture.

[0037] The lambda control preferably comprises several control elements, for example a proportional control element (P element), an integral control element (I element), and a differential control element (D element). The lambda control therefore uses a PID controller. The gain factors of the control elements are selected such that, when the drive device is operated as intended, stable control of the actual combustion air ratio is achieved over a long period of time. This can result in a significant control deviation, i.e. a difference between the target combustion air ratio and the actual combustion air ratio, being able to be corrected only over a comparatively long period of time. Such a significant control deviation is caused, for example, by a change in the introduction parameter. For this reason, it is intended to increase the gain factor from a first value to a second value upon change in the introduction parameter.This can result in a rapid reduction in the control deviation.

[0038] Figure 1 shows four diagrams, with the lowest diagram showing curve 1 of the injection parameter. In the second diagram, viewed from below, curves 2 and 3 show gain factors, namely curve 2 for a conventional operating method and curve 3 for the operating method described here. In the third diagram, viewed from below, curves 4, 5, 6, 7, 8, and 9 illustrate the operating mode of the lambda control. In the top and fourth diagrams, respectively, curves 10 and 11 show the control deviation, namely curve 10 for the conventional operating method and curve 11 for the operating method described here.

[0039] It can be seen that at a time t0 the injection parameter is changed. For example, the number of injection pulses per working cycle is reduced, for example from three to two. In the conventional operating mode, the gain factor is kept constant according to curve 2. Curve 3, on the other hand, shows that the gain factor is increased from time t0 to a time t1, namely from the first value to the second value. Curves 4, 6 and 8 show the share of the P element (curve 4), the share of the I element (curve 6) and curve 8 a sum of the shares of the control elements for the conventional operating mode. Curves 5, 7 and 9, on the other hand, show the share of the P element (curve s), the share of the I element (curve 7) and the sum of the shares of the lambda control (curve 9) for the operating mode described here.It is clearly visible that due to the larger amplification factor of the I element, its contribution is significantly increased, resulting in a larger sum. Overall, this leads to the control deviations recorded in curves 10 and 11. It is clear that the conventional operating method according to curve 10 requires significantly longer to compensate for the change caused by the change in the injection parameter than the operating method described here according to curve 11. Overall, the new operating method allows for significantly faster correction of the control deviation.

[0040] LIST OF REFERENCE SYMBOLS:

[0041] 1 History

[0042] 2 History 3 History

[0043] 4 History

[0044] 5 History

[0045] 6 History

[0046] 7 History 8 History

[0047] 9 History

[0048] 10 History

[0049] 11 History

Claims

PATENT CLAIMS:

1. A method for operating a drive device for a motor vehicle having a drive unit generating exhaust gas, wherein fuel is introduced into a combustion chamber of the drive unit at least temporarily in accordance with at least one introduction 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 controlled by adapting a composition of the fuel-fresh gas mixture to a target combustion air ratio by means of a lambda control, characterized in that as soon as there is a change in the at least one introduction parameter, a gain factor of at least one control element of the lambda control is increased from a first value to a second value for quickly adjusting the actual combustion air ratio to the target combustion air ratio.

2. Method according to claim 1, characterized in that one of the following parameters is used as the at least one introduction parameter: number of introduction pulses per working cycle, introduction location, introduction speed and introduction duration.

3. Method according to one of the preceding claims, characterized in that the amplification factor is increased if the change in the at least one introduction parameter results in a change in a fuel proportion in the composition of the fuel-fresh gas mixture by at least 10%, at least 20% or at least 30%.

4. Method according to one of the preceding claims, characterized in that the second value is selected to be greater by a factor of at least 5, at least 7.5 or at least 10 relative to the first value.

5. Method according to one of the preceding claims, characterized in that an integral control element is used as the at least one control element.

6. Method according to one of the preceding claims, characterized in that gain factors of further control elements of the lambda control are kept constant.

7. Method according to one of the preceding claims, characterized in that the increase in the gain factor is reversed after a certain period of time.

8. Method according to one of the preceding claims, characterized in that a length of the period is determined based on at least one of the following parameters: exhaust gas transit time from the drive unit to the lambda probe, load of the drive unit, speed of the drive unit, torque provided by the drive unit and temperature.

9. Method according to one of the preceding claims, characterized in that the length of the period is selected such that the increase in the amplification factor is terminated at the latest immediately after the end of a change in the residual oxygen content caused by the change in the at least one introduction parameter in a direction determined by the change.

10. Drive device for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, wherein the drive device has a drive unit generating exhaust gas and fuel is introduced into a combustion chamber of the drive unit to form a fuel-fresh gas mixture at least temporarily according to at least one introduction parameter, 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 by adjusting a composition of the fuel-fresh gas mixture to a target combustion air ratio by means of a lambda control, characterized in that the drive device is provided and designed to increase a gain factor of at least one control element of the lambda control from a first value to a second value for quickly adjusting the actual combustion air ratio to the target combustion air ratio as of a change in the at least one introduction parameter.

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