Method for carrying out a load point shift of an internal combustion engine upon activation or deactivation of an electrically heated component

A method for operating an internal combustion engine of a motor vehicle, whereby an electrically heated component of an exhaust aftertreatment system being supplied with electrical power via an electric machine driven by the internal combustion engine, a load point shift of the internal combustion engine being carried out by an activation or a deactivation of the component or by a temporary storage of the necessary electrical energy for operating the component in a battery.

This nonprovisional application claims priority under 35 U.S.C. § 119(a) to German Patent Application No. 10 2019 214 701.1, which was filed in Germany on Sep. 25, 2019, and which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for carrying out a load point shift of an internal combustion engine upon an activation or deactivation of an electrically heated component (EHC).

Description of the Background Art

Further reduced pollutant limit values will require a highly-efficient exhaust aftertreatment system (EATS) in the future. To quickly achieve a sufficiently high efficiency of the individual components, they must preferably quickly exceed their light-off temperature. One possibility is to actively heat the components with the aid of an electrically heated catalyst, a so-called EHC. For the purpose of a rapid heating, the heating power of the EHC should be greater than or equal to 2 kW, greater than or equal to 3 kW being better, preferably greater than or equal to 4 KW.

The electrical power is generally provided via an electric machine, e.g. via a belt-starter generator. The load point of the internal combustion engine is shifted thereby in the direction of a higher load. This is advantageous because a higher load point of the internal combustion engine results in higher exhaust gas temperatures and thus a faster heating of the exhaust aftertreatment system. The higher load generally results in a louder noise of the internal combustion engine, which may possibly be negatively perceived by the driver. The noise level may thus be felt to be particularly negative because the heating demand is not directly influenced or initiated by an action of the driver. EHC systems, in which the power may be only discontinuously set, are particularly critical. This occurs, among other things, when the EHC control unit is designed as a PWM/transistor switch. In the case of a discontinuous, abrupt load change, the noise of the internal combustion engine changes correspondingly abruptly. Continuously adjustable systems having a DC/DC converter also exist.

A method and a device are known from DE 10 2016 207 037 A1 (which corresponds to U.S. Ser. No. 10/654,468) and DE 10 2016 207 039 A1 (which corresponds to US 2019/0061736) for operating a hybrid vehicle, which includes an electric energy store and comprises an electric motor with a combustion unit. Defined events with masking potential, coordinated for increasing the acoustic limits for raising the load point or varying the load point, are used. A special operating strategy for an combustion unit is initiated, with the aid of which an increase of the charge state of an energy store is achievable if predefined acoustic conditions are met. The special operating strategy has a power-increasing effect, due to a load point adjustment up to variably predefined acoustic limits, which are defined as a function of the ascertained masking potential of certain acoustic events. A device for carrying out the method is proposed, which raises the acoustic limits for controlling the load point of the combustion unit at least to the level that is presently permissible, due to the masking of at least one acoustically relevant event. After commissioning a hybrid vehicle of this type, a check is made of which acoustically relevant even is currently present in each case. To coordinate the masking potential currently present in each case, the maximum of all masking potentials is ascertained in the form of a maximum sound pressure spectrum. The total sound pressure spectrum formed in this way is compared with a load-dependent sound pressure spectrum of the combustion unit, which is also stored in the control unit. The load point, whose sound pressure spectrum is below the coordinated total sound pressure spectrum in each case or is adequately masked thereby, is subsequently selected for the combustion unit. The total sound pressure spectrum is a variably predefinable acoustic limit. A load point raise may be predefined by an absolute load value as a function of the acoustically relevant masking events present in each case or as the difference from a base load value, which may also be predefined by a basic sound spectrum. A basic sound spectrum of this type may be ascertained empirically and stored in the control unit. The basic sound spectrum may be a higher engine sound accepted as the maximum if no additional masking events are present, compared to a basic state, e.g. due to speed-depending wind noise or road noise on a smooth roadway, which is always present. The basic acoustic threshold is dependent on the driving state, e.g. on the desired driving torque of the driver and on the speed. Acoustically relevant events are, in particular, events due to vehicle-internal sources of influence whose characteristic spectra are known, or whose occurrence may be controlled by vehicle-internal systems, e.g. a fan or air-conditioning unit, open windows, an open sunroof or the vehicle speed. Vehicle-external sources of influence whose occurrence is detectable by sensors, such as rain, road surfacing or travel through a tunnel, are also taken into account as events. User-induced sources of influence, in particular by operating audio systems, are furthermore taken into account. Moreover, unknown sources of influence, which are detected via at least one microphone, may be taken into account as events. The acoustic limits may be raised by the masking without sacrificing comfort.

A hybrid cold start strategy, which uses an electrically heated catalyst, is known from DE 10 2008 023 394 A1 (which corresponds to U.S. Pat. No. 8,209,970). The exhaust gas catalytic converter is assigned to a heating element, for example an electrically heated catalyst, which supplies additional heat to the exhaust gas catalytic converter. The additional heating provides for a reduced time up to the light-off of the exhaust gas catalytic converter. An internal combustion engine control module may evaluate data, including the ambient air temperature, the internal combustion engine coolant temperature, the exhaust gas flow and the power supplied to the electrically heated condenser for the purpose of estimating the time at which the electrically heated condenser is to be switched on after the internal combustion engine startup. The internal combustion engine control module may also take into account other information, including fuel/air ratios and ignition delay data, for the purpose of estimating the temperature of the catalyst in the exhaust gas condenser.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a method according to the invention, in particular in such a way that the load point shift is not perceived by the driver as bothersome.

The method is used to operate an internal combustion engine of a motor vehicle, an electrically heated component, in particular an EHC, of an exhaust aftertreatment system being supplied with electrical power via an electric machine driven by the internal combustion engine, for example a belt-starter generator. A load point shift of the internal combustion engine is carried out upon the activation or deactivation of the component or at the start of the intermediate storage of the necessary electrical energy for operating the component in a battery. According to the invention, the load point shift is carried out at one of the following points in time or in the presence of one of the following conditions:during a gear change, upon engaging a new gear;during a change in the driving mode, the vehicle being driven by the internal combustion engine in the one driving mode, the internal combustion engine being driven by the kinetic energy of the motor vehicle with the gear engaged in the other driving mode, the so-called overrun mode;by using characteristic map ranges having similar acoustics before and after the load point shift;when the gradient of the gas pedal changes;upon a change in the driving program;upon an activation or deactivation of consumers by the driver.

The load point shift, which influences the noise of the internal combustion engine, is carried out at one of the points in time when the driver expects an increase in the noise of the internal combustion engine or does not feel it to be bothersome.

Characteristic map ranges having similar acoustics may result in, for example, a sound pressure change of a few decibels as the maximum, for example less than 2 dB. A latent switching of this type preferably takes place as a function of temperature difference ΔT. The load point shift is initiated as a function of difference ΔT between the actual temperature and the setpoint temperature of the component or the exhaust gas mass flow, a low switching threshold being present for a high heating demand, and a high switching threshold being present for a low heating demand.

A load point shift is already carried out in a characteristic map range with a sound pressure change of up to 1.0 dB or 1.5 dB in the case of a first bigger difference ΔT, a load point shift being carried out in a characteristic map range with a sound pressure change of less than 0.2 dB in the case of a second smaller difference ΔT.

If a change in the driving program occurs, e.g. by actuating the sport switch, or if a consumer is activated by the driver, for example an air conditioning unit or a heater, the driver perceives a change in the noise of the internal combustion engine as not bothersome.

A DOC, an SDPF or an SCR catalyst may be considered as components. The hidden switching may be carried out, in particular, upon the activation as well as upon the deactivation of the EHC. The temperatures are detected metrologically or ascertained analytically with the aid of an equivalent diagram.

For the purpose of a rapid heating, the heating power of the EHC is greater than 2 kW, or better greater than 3 kW, preferably greater than 4 KW.

The method may be particularly preferably used in EHC systems, in which the power is only discontinuously set. This occurs, among other things, when the EHC control unit is designed as a PWM/transistor switch.

DETAILED DESCRIPTION

FIG. 1shows a highly schematic front end1of a motor vehicle, whose outer contour is indicated by a contour line. The direction of travel is indicated by an arrow. Two wheels,3,4are also shown. The wheels are driven via an internal combustion engine (ICE)5and a transmission6. An exhaust aftertreatment system (EATS) is present in exhaust tract7. The exhaust aftertreatment system or EATS comprises an EHC8, which is connected to an EHC control unit10via a cable9. EHC control unit10, in turn, is connected to a belt-starter generator12via a cable11. Belt-starter generator12is driven via a belt12aand may thus conduct current to EHC control unit10over cable11.

The exhaust aftertreatment system is illustrated schematically inFIG. 2. Exhaust gas13is first supplied from the internal combustion engine to EHC8. The EHC position is illustrated here only as an example and may also be in another location. A diesel oxidation catalyst (DOC)14is disposed downstream from EHC8. A temperature sensor15is disposed downstream from diesel oxidation catalyst (DOC)14. The exhaust gas temperature of the exhaust gas emerging from diesel oxidation catalyst14may be measured with the aid of temperature sensor15. A diesel particulate filter16, in particular having an SCR coating (SDPF), is disposed downstream from temperature sensor15.

In the method according to the invention, load point shifts, which influence the noise of internal combustion engine5, are carried out at a point in time when the driver expects an increase in the noise of internal combustion engine5or does not feel it to be bothersome. The activation, but also the deactivation, of EHC8is preferably relevant. For example, the switching may take place during a gear change upon the engagement of the new gear.

The latent switching may also take place during a change in the driving mode, the vehicle being driven by internal combustion engine (ICE)5in the one driving mode, internal combustion engine (ICE)5being driven by the kinetic energy of the motor vehicle with the gear engaged in the other driving mode, the so-called overrun mode. The latent switching may take place during a change from the one driving mode (the vehicle is driven by the ICE) to the overrun mode or from the overrun mode to the one driving mode (the vehicle is driven by the ICE).

The latent switching may furthermore take place by using characteristic map ranges having similar acoustics before and after the load point shift. The sound pressure change may be big in the case of a bigger necessary temperature change ΔT, for example 1.0 to 1.5 dB, or small in the case of a small necessary temperature change ΔT. This circumstance is shown inFIG. 3. Temperature difference ΔT, i.e. the difference between the actual temperature and the setpoint temperature, is plotted on horizontal axis18. The switching threshold is plotted on vertical axis17. Curve20now indicates that, if ΔT is big, a bigger sound pressure change is also permitted, while if delta t is small, only small sound pressure changes are desirable.

Moreover, the latent switching may take place when the gradient of the gas pedal changes. The switching threshold for a gas pedal gradient is also illustrated inFIG. 3. If ΔT is large, the switching threshold is low and is, for example, less than 50% per second. If ΔT is small, the switching threshold is high, i.e. the gas pedal gradient should be above 200% per second.

In addition, the latent switching may take place upon a change in the driving program which is possible, for example, when the driver activates a sport program.

The latent switching may also take place upon an activation or deactivation of consumers by the driver.

Moreover, a latent switching is possible by the activation of consumers by the driver. It is possible to temporarily store the necessary electrical energy for operating EHC8in a battery, the charging of the battery being switched in a latent manner via the electric machine, as described above.