METHOD AND ENGINE CONTROL FOR OPERATION OF A MOTOR VEHICLE WITH AN INTERNAL COMBUSTION ENGINE AFTER A COLD START

Description

[0001] The invention relates to a method for operating a motor vehicle with an internal combustion engine comprising an internal combustion engine and an exhaust system with at least one exhaust aftertreatment device.

[0002] To achieve the lowest possible pollutant emissions from an internal combustion engine, the exhaust aftertreatment devices integrated into the exhaust system, which may include one or more catalytic converters and a particulate filter, should ideally always operate at temperatures above their respective activation temperatures (also known as "light-off" temperatures), at which point the exhaust aftertreatment system is expected to be highly effective. After a cold start of the internal combustion engine, during which the exhaust aftertreatment devices may be at temperatures below their activation temperatures, the temperatures of at least some of the aftertreatment devices should reach their activation temperatures as quickly as possible.To ensure this, it is known to actively heat exhaust aftertreatment devices, which can be achieved using dedicated heating devices, such as electric heating elements or burners. Furthermore, so-called in-engine measures can be implemented, which aim to generate relatively hot exhaust gas by operating the combustion engine at a relatively low efficiency, thus enabling relatively rapid heating of the exhaust aftertreatment devices via the exhaust gas.

[0003] Due to increasingly stringent emissions regulations, even these measures may not be sufficient, as they only accelerate the effectiveness of the exhaust aftertreatment systems, but do not guarantee it immediately upon starting the combustion engine. Thus, the problem could arise that emissions limits are not met if a vehicle transitions into driving mode immediately after a cold start of the associated internal combustion engine, a process that requires the engine to deliver a relatively high power output, which is accompanied by a correspondingly large exhaust gas mass flow.

[0004] DE 10 2014 220 442 A1 discloses a method for operating a hybrid vehicle with an internal combustion engine and an electric traction motor, wherein, in trailer operation, i.e., when a trailer is pulled by the hybrid vehicle, the internal combustion engine is automatically deactivated if the required driving power can be provided exclusively by the electric traction motor, and the internal combustion engine is automatically started if the required driving power cannot be provided exclusively by the electric traction motor.

[0005] DE 10 2021 204 100 A1 describes a method for configuring an electric vehicle in preparation for a planned journey with a trailer, whereby the trailer operation can be included in the route planning, in particular with regard to the necessary journey interruptions for charging a traction battery of the electric vehicle.

[0006] The method disclosed in US 2016 / 0129803 A1 is designed to predict the range during a journey of an electric vehicle, taking into account whether or not a trailer is being towed.

[0007] DE 10 2017 001 911 A1 discloses a method for estimating the gross mass of a motor vehicle, wherein, based on this estimation, for example, an alternative power control of an internal combustion engine can be implemented, in which the engine power corresponding to a given accelerator pedal position is controlled proportionally to the estimated gross mass.

[0008] EP 2 088 304 A2 describes a method in which a maximum torque setpoint that an internal combustion engine of a motor vehicle can generate is changed depending on the mass of the motor vehicle, whereby this is smaller the larger the dimensions of the motor vehicle.

[0009] DE 10 2021 109 520 A1 discloses a method in which the operation of a vehicle during a time interval after the cold start of the internal combustion engine is prevented.

[0010] According to EP 3 909 823 A1, a gear is only engaged in the automatic transmission of a vehicle when the catalytic converter has been sufficiently preheated.

[0011] DE 100 81 460 B4 discloses a method for adjusting a starting torque depending on the load of a vehicle or the presence of a trailer.

[0012] The invention is based on the objective of improving the pollutant emission behavior of an internal combustion engine in a motor vehicle.

[0013] This problem is solved by a method according to claim 1. A motor control system designed for an implementation of such a method is the subject of claim 15. Advantageous embodiments of the method according to the invention are the subject of further claims and will become apparent from the following description of the invention.

[0014] According to the invention, a method for operating a motor vehicle is provided, wherein the motor vehicle comprises an internal combustion engine and an exhaust system with at least one exhaust aftertreatment device. After a cold start of the internal combustion engine, during which at least the exhaust aftertreatment device has a temperature below a start-up temperature and which can correspond substantially (e.g., with a deviation of up to 10°C) to the respective ambient temperature, the operation of the internal combustion engine with respect to the torque it can deliver is limited by an engine control unit depending on the temperature of the exhaust aftertreatment device.

[0015] Limiting the operating torque of the combustion engine is intended to prevent it from operating at excessive power output during warm-up phases, which can occur particularly after a cold start and during which the at least one exhaust aftertreatment device is below its activation temperature. Such an excessive power output would result in a correspondingly high exhaust mass flow. This could lead to the at least one exhaust aftertreatment device being unable to perform sufficient exhaust aftertreatment to comply with applicable pollutant emission limits.

[0016] The limitation of the combustion engine's operating torque with respect to the available output, depending on the temperature of the at least one exhaust aftertreatment device, can advantageously be implemented until the exhaust aftertreatment device reaches its activation temperature. Furthermore, this limitation can be variable, such that it is continuously reduced as the temperature of the exhaust aftertreatment device increases. This minimizes any potential disadvantage to vehicle operation resulting from the torque limitation, as the temperature-dependent limitation is maintained only to the extent necessary to comply with pollutant emission limits.

[0017] According to the invention, it is further provided that driving operation of the motor vehicle is prevented until a minimum limit of the deliverable torque is reached. This prevents driving operation even though, due to the limitation of the deliverable torque, it would (still) not be practically feasible, for example, because the vehicle's acceleration would be too restricted. In particular, temporarily preventing driving operation of the motor vehicle makes it possible to operate the combustion engine in a defined idle state for a period of time after a cold start, during which it generates the lowest possible exhaust mass flow, which can have a correspondingly positive effect on pollutant emissions.

[0018] A temporary prevention of a motor vehicle's operation can be perceived as an inconvenience by the driver, so this measure should be reduced to the necessary minimum. Therefore, according to the invention, the minimum limit value is varied depending on the expected driving resistance of the motor vehicle. It can be provided that the minimum limit value is chosen to be relatively small when the expected driving resistance is relatively small and relatively large when the expected driving resistance is relatively large. Consequently, at least one first minimum limit value can be provided for a first expected driving resistance and a second minimum limit value for a second expected driving resistance, wherein the first minimum limit value is smaller than the second minimum limit value and the first driving resistance is smaller than the second driving resistance.

[0019] To minimize any limitation on the operating time of the internal combustion engine with regard to the torque output, and in particular to prevent the vehicle from being driven, it is preferable to implement measures during the warm-up phase to heat the at least one exhaust aftertreatment device as quickly as possible. These measures may include, in particular, actively heating the exhaust aftertreatment device by means of, for example, an electric heating device and / or a (fuel-burning) burner. Furthermore, these measures may include operating the internal combustion engine in a way that deliberately generates relatively hot exhaust gas. This can be achieved, for example, by retarding the ignition timing for fuel combustion in the combustion chambers of the internal combustion engine.Such heating operation of the combustion engine can also be provided for, in particular, during the prevention of driving operation, because then the measures can also be carried out in such a way that the operation of the combustion engine is primarily or exclusively optimized for the generation of the hottest possible exhaust gas, without having to take into account a sufficiently good "drivability" of the internal combustion engine.

[0020] Preferably, the presence or absence of a trailer coupled to the motor vehicle can be used as a measure of the driving resistance to be overcome. Since the presence of a trailer can significantly increase the driving resistance for the motor vehicle, a sufficiently high minimum limit for the deliverable torque should be present before the motor vehicle is permitted to drive with a trailer. If such a trailer is absent, however, the motor vehicle can be permitted to drive even with a significantly lower minimum limit for the torque deliverable by the internal combustion engine, which is made possible by the variability of this minimum limit according to the invention.Consequently, it is prevented that a motor vehicle operated according to the invention, which is basically suitable for trailer operation and is equipped accordingly by the presence of a trailer coupling, is prevented from being driven for an unnecessarily long time, even if no trailer is attached to it.

[0021] A trailer is defined as any device that can be coupled to a motor vehicle's trailer hitch as intended. This includes, in particular, trailers in the classic sense, which are themselves vehicles with at least one axle with wheels, but which have no drive of their own or only an auxiliary drive. According to the invention, however, trailers are also understood to include load carriers without their own wheels, which are intended, for example, for transporting bicycles, and which are coupled to and supported by the trailer hitch.

[0022] Preferably, the presence or absence of a trailer can be automatically determined by the engine control unit. This eliminates the need for the driver to manually indicate whether a trailer is connected via a control unit. Such a "manual" selection regarding trailer operation, which can also be implemented according to the invention, might be perceived by the driver as a limitation on the vehicle's usability. Furthermore, such a manual selection could also be a source of error with potentially negative consequences regarding pollutant emissions. However, if such a manual selection is provided, a corresponding (automatically displayed) query from the engine control unit can preferably be provided at the control unit. Such a query could then, for example, be triggered every time the internal combustion engine is started.

[0023] For automatic detection of the presence or absence of a trailer, it is preferably possible to determine the status of a connector on the vehicle that is part of the trailer's electrical power supply. This electrical power supply can, in particular, provide the trailer's lighting system with electrical energy and / or control signals from the vehicle. Such a power supply can include the vehicle's connector and a mating connector on the trailer, which are detachably connected for trailer operation. If such a connector is present, the engine control unit can recognize this as the presence of the trailer and take it into account accordingly. Conversely, if such a connector is absent, the engine control unit can assume that the trailer is not connected.Such automatic detection of the presence or absence of a trailer can be implemented particularly easily and therefore cost-effectively. In particular, this requires no structural modifications to the motor vehicle and / or the trailer. Alternative options, such as sensors that detect the forces exerted on the trailer coupling by a coupled trailer, are also feasible. Furthermore, in the case of a detachable trailer coupling or a design where the trailer coupling can be moved, particularly pivoted, from an inactive position (i.e., unsuitable for coupling a trailer) to an active position (i.e., suitable for coupling a trailer), the presence or absence of the trailer can be determined based on the functional state of the trailer coupling.It can be mounted or dismounted, or in an active or inactive position.

[0024] According to a preferred embodiment of a method according to the invention, a mass of the motor vehicle and / or a mass of the trailer can be used as a measure of the driving resistance to be overcome, because these masses also significantly influence the driving resistance to be overcome and should therefore be taken into account with regard to the minimum limit of the deliverable torque. Considering the mass of the trailer can be of particular importance because it can influence the driving resistance of the motor vehicle to a considerably greater extent, since the total mass of the trailer affects the driving resistance to be overcome depending on whether the trailer is coupled or not. In contrast, with the mass of the motor vehicle, only the amount of payload varies, which can be significantly less than the total mass of the trailer.On the other hand, the mass of the motor vehicle represents a measure of the driving resistance to be overcome, which is significant in every use of the motor vehicle, whereas a trailer is not attached in the majority of motor vehicle journeys. A particularly precise variation of the minimum torque threshold above which the motor vehicle can be operated can therefore be achieved by using, firstly, the presence or absence of a trailer coupled to the motor vehicle as a measure of the driving resistance to be overcome, and secondly, the mass of the motor vehicle and / or the trailer.

[0025] The mass of the motor vehicle can, in particular, be an actual mass, which can preferably be determined automatically, i.e., by a measuring device integrated into the motor vehicle itself with automatic transmission of the measured values ​​to the engine control unit. This allows for the safest and most accurate possible variation of the minimum limit of the deliverable torque. The mass of the motor vehicle represents the sum of its unladen mass and any payload. The unladen mass of the motor vehicle can be known and essentially constant, so that determining the mass of the motor vehicle may only require determining the payload, which is then added to the unladen mass.

[0026] For the automatic determination of the mass of the motor vehicle or its payload, one or more sensors can preferably be used. This can preferably be a seat occupancy sensor, preferably one seat occupancy sensor for each available seat in the motor vehicle, thereby automatically determining whether at least one seat is occupied by a person or a relatively heavy object. Such a seat occupancy sensor can be designed to detect directly, in particular by measuring the pressure exerted on the seat by a person or an object placed on it. Such a seat occupancy sensor can also preferably be designed to quantitatively determine the mass of the person or object on the seat.A seat occupancy sensor can also be designed to detect occupancy indirectly, for example by evaluating the locked buckle of a seatbelt assigned to a seat to indicate that the seat is occupied by a person. A reference mass can then be assumed for that person.

[0027] A tire pressure sensor, preferably one for each tire of the vehicle or trailer, can also be provided as a sensor that can be used for the automatic determination of the mass of the vehicle and / or the trailer. A change in tire pressure (air pressure in the tire), particularly when the vehicle or trailer is stationary, can indicate a change in the mass of the vehicle or trailer due to an increased or decreased payload.

[0028] The varying amount of fuel stored in a vehicle's fuel tank can also significantly affect the vehicle's mass. The current fuel level can be determined using a fuel tank level sensor, which is typically installed in vehicles, and this measurement can be used to calculate the vehicle's mass.

[0029] A change in payload, and thus the mass of the vehicle, can also be detected using a tilt sensor, which, in a preferred embodiment, can detect any movement of the vehicle's body as an acceleration sensor. Due to the suspension of the wheels on the vehicle's body, a changing payload can lead to a corresponding movement of the body. This movement can be detected by the at least one tilt sensor, and the payload, and therefore the mass of the vehicle, can be determined based on this.

[0030] Furthermore, at least one displacement sensor can be used to determine the mass of the motor vehicle and / or trailer. This sensor measures the distance of a component of the motor vehicle or trailer to the ground (on which the motor vehicle or trailer is standing). Such a displacement sensor can measure the distance directly, for example, using a laser. Alternatively, a measurement based on determining the extent of compression of a sprung suspension of at least one wheel is also possible. This can be particularly advantageous on a motor vehicle's rear axle. Preferably, distance measurements can be taken at several points on the motor vehicle or trailer using suitable sensors, for example, in the area of ​​each wheel, resulting in the most accurate possible determination of the mass.

[0031] This also applies to a weighing sensor, which can likewise be used to determine the mass or payload of the motor vehicle and / or trailer and which can preferably be based on measuring deformation using, for example, a strain gauge or on the principle of electromagnetic force compensation. Such a weighing sensor can also preferably be provided in the area of ​​each wheel of the motor vehicle or trailer.

[0032] Payload and thus the mass of the motor vehicle can still be determined using one or more cameras by evaluating an image from the camera(s) with regard to the presence of persons and / or objects and a resulting (estimated) payload.

[0033] Automatically determining a vehicle's mass can involve considerable engineering effort, so it may also be possible for the driver to enter the vehicle's mass using a control unit in the vehicle. To prevent the driver from accidentally omitting this information, the engine control unit may, in particular, send a corresponding query to the control unit. If such a query is not answered, the vehicle may not be authorized to drive.The vehicle's mass can be entered or queried indirectly, meaning that the input or query does not directly relate to the mass itself, but rather to a condition of the vehicle that directly influences the mass, in particular the number of passengers being transported and / or the qualitatively or quantitatively assessed use of the vehicle's trunk. To simplify input, especially in such cases, it is preferable to have several predefined mass ranges for the vehicle (e.g., up to two passengers without luggage, up to five passengers without luggage, up to the maximum payload).

[0034] The trailer's mass can also be advantageously an actual mass, as this allows for the most precise setting of the minimum torque threshold at which driving is permitted. However, this requires an actual, preferably automatic (i.e., by a measuring device integrated into the vehicle and / or trailer with automatic transmission of the measured values ​​to the engine control unit) measurement of the trailer's mass, which is relatively complex. Therefore, it can be advantageous to use a predefined permissible trailer mass (including load) as a measure of the driving resistance to be overcome. A permissible trailer mass need not necessarily be a limitation of the trailer itself, but can also be a permissible trailer mass, i.e.,a permissible mass that a trailer coupled to the motor vehicle may have on the part of the motor vehicle.

[0035] Since automatically determining the trailer's mass can be particularly complex, it is preferable to have the driver enter the trailer's mass using a control unit in the vehicle. To prevent the driver from inadvertently omitting this input, it is particularly preferable to have the engine control unit send a corresponding prompt to the control unit. To simplify input during such a prompt, it is preferable to have several predefined mass ranges for the trailer.

[0036] As a measure of the driving resistance to be overcome, a form factor, in particular the frontal area (A) and / or the drag coefficient (c W), especially preferably the product of the frontal area and the drag coefficient of the motor vehicle and / or the trailer, can also be used advantageously, because such a form factor can also significantly influence the driving resistance to be overcome and should therefore be taken into account with regard to the minimum limit of the deliverable torque.

[0037] The initial form factor of a vehicle (in its unladen state and otherwise unchanged from its certification) may be known, so it may be sufficient to consider only one change in this regard. Such a change can result from a vehicle payload, because this can lead to compression of the wheel suspensions and, in particular, uneven compression of these suspensions (especially more pronounced at the rear axle than at the front axle), which can negatively affect the form factor and thus the driving resistance to be overcome. Therefore, the sensors that can be used to determine a changing vehicle payload can also be used to determine a change in the vehicle's form factor.This applies in particular if they are designed and set up in such a way that an uneven distribution of the load and, consequently, an uneven compression of the wheel suspensions can be derived from their signals.

[0038] Since automatically determining the trailer's form factor can be complex, it is preferable to allow the driver to specify the trailer's form factor using a control unit in the vehicle. The engine control unit can also send a corresponding query to the control unit for this purpose. To simplify input during such a query, it is preferable to predefine several form factor ranges for the trailer.

[0039] As a measure of the driving resistance to be overcome, a type of trailer can also be advantageously used, whereby a distinction can be made in particular between load carriers that are supported exclusively on the trailer coupling of the motor vehicle and have no wheels, and trailers designed as vehicles.

[0040] As a measure of the driving resistance to be overcome, and in particular as a supplementary measure, at least one parameter of the ambient air, especially air temperature and / or air pressure and / or humidity, can be taken into account, because these can affect drag as a component of driving resistance. In particular, a higher density of the ambient air may require a higher available torque to ensure a predetermined acceleration capability of the vehicle.

[0041] When the engine control unit queries the mass of the motor vehicle and / or the type of trailer and / or the mass of the trailer and / or the form factor of the trailer, this query may, in principle, be designed in such a way that it absolutely requires an input in order to enable the motor vehicle to be driven, and possibly even a (cold) start of the internal combustion engine.

[0042] Preferably, the system can be configured to check an input at the control unit during driving. For this purpose, information regarding the vehicle's orientation to the horizontal, the engine's power output, and / or the vehicle's acceleration can be evaluated. Such information can be provided by appropriate vehicle sensors. If the test result does not match the input, the system can adjust the selected level of driving resistance to be overcome. Additionally or alternatively, the system can restrict further driving (in a manner that impairs the vehicle's handling and / or the driver's experience).It may also be possible to prevent further driving by the engine control unit, for example, by reducing the engine's power output, accompanied by warning messages, until it reaches idle and, if necessary, until the engine is switched off. Additionally or alternatively, a warning message regarding the discrepancy between the test result and the input may be displayed on a screen and / or the engine control unit may perform a new query. Furthermore, an error message regarding the discrepancy between the test result and the input may be stored in the engine control unit.

[0043] If the selected value for the driving resistance to be overcome is changed by the engine control unit as a result of the check, it may be possible to retain the changed value for a subsequent cold start or after a subsequent cold start, provided the same trailer is detected. This prevents another incorrect entry. The same can apply to any warning message that may have been displayed, which can then be shown again.

[0044] The presence of the same trailer can preferably be determined by ensuring that the occupancy state of the motor vehicle's connector, which is part of the electrical power supply for the trailer, has not been changed or has been changed twice within a period of time that is less than a limit value (e.g. three minutes).

[0045] It may also be stipulated that if a discrepancy between the test result and the input is repeatedly detected, the selection options in the query are restricted or the query is no longer performed. In particular, a measure for the driving resistance to be overcome can then always be selected that leads to a relatively large, especially a maximum, defined minimum limit.

[0046] The temperature of the exhaust aftertreatment device considered according to the invention can, in principle, be any temperature associated with the exhaust aftertreatment device. This temperature can preferably be measured, but directly measuring the (body) temperature of the exhaust aftertreatment device can involve a relatively high degree of design complexity. Therefore, it is particularly preferable that the temperature of the exhaust aftertreatment device be modeled or determined computationally using a model. This can be done, in particular, starting from the ambient temperature at the time of the cold start and the expected warming since the cold start due to the exhaust gas and any additional measures provided, such as active heating by means of an electric heating device or a burner.

[0047] A motor vehicle operated according to the invention can in particular be a wheel-based and non-rail-bound motor vehicle (preferably a passenger car or a truck).

[0048] A motor vehicle operated according to the invention can also have a partially electrified powertrain, such that, in addition to the internal combustion engine, at least one electric traction motor is provided, which can supply propulsion power for the motor vehicle (configuration of the motor vehicle as a hybrid vehicle). The powertrain can be designed such that the electric traction motor can only provide propulsion power as a supplement during operation of the internal combustion engine. Furthermore, the powertrain can be designed such that the electric traction motor can temporarily provide all or the entire propulsion power.

[0049] The internal combustion engine of a motor vehicle operated according to the invention can be a (self-igniting and quality-controlled) diesel engine, a (spark-ignition and quantity-controlled) gasoline engine, or a combination thereof, i.e., an internal combustion engine with homogeneous compression ignition. The internal combustion engine can be operated with either liquid fuel (i.e., diesel or gasoline) or a gaseous fuel (in particular, natural gas, LNG, or LPG).

[0050] The invention is explained in more detail below with reference to exemplary embodiments illustrated in the drawings. The drawings show, in some cases in simplified form: Fig. 1: a motor vehicle operable according to the invention with a trailer; Fig. 2: an internal combustion engine of the motor vehicle; Fig. 3: the time course of the torque available from an internal combustion engine of the internal combustion engine for operation of the motor vehicle without the trailer; Fig. 4: the time course of the torque available from an internal combustion engine of the internal combustion engine for operation of the motor vehicle with the trailer; and Fig. 5: the procedure for determining a minimum limit value MG of the available torque M as a function of the mass of the motor vehicle 1 and, based thereon, a period Δt 1 within which driving operation of the motor vehicle 1 is prevented.

[0051] The Fig. 1 Figure 1 shows a motor vehicle 1 designed for operation according to the invention, with a trailer 2. The trailer 2 is designed as a vehicle with at least one axle.

[0052] The motor vehicle includes an internal combustion engine.

[0053] According to the internal combustion engine 3, it comprises Fig. 2An internal combustion engine 4, exemplified by a reciprocating piston engine with four cylinder ports 5 arranged in a row. Each cylinder port 5, together with the pistons 6 and cylinder head (not shown) guided within it, defines a combustion chamber 7. During operation of the internal combustion engine 4, fresh gas is supplied to the combustion chambers 7 via a fresh gas line 8. The fresh gas consists at least primarily of air, which is drawn in from the environment and subsequently passed through an air filter 9 and then through a fresh gas compressor 10. This fresh gas compressor 10 is part of an exhaust gas turbocharger, which also includes an exhaust gas turbine 11 integrated into an exhaust gas line 12 of the internal combustion engine 1.Exhaust gas produced during the combustion of mixtures consisting of fresh gas and fuel injected directly into the combustion chambers 7 via fuel injectors (not shown) is discharged via the exhaust system 12 and passed through at least one exhaust aftertreatment device 13.

[0054] For maximum effectiveness of the exhaust aftertreatment in all operating states of the internal combustion engine 4, the exhaust aftertreatment device 13 must have a temperature that corresponds at least to a defined start-up temperature. If the temperature of the exhaust aftertreatment device 13 falls below the start-up temperature during a warm-up phase of the internal combustion engine 3, which may follow a cold start, the exhaust aftertreatment may be insufficient. To prevent this from resulting in non-compliance with pollutant emission limits, the operation of the internal combustion engine 3 is limited by an engine control unit 14 with respect to the torque that can be delivered by the internal combustion engine 4, depending on the temperature of the exhaust aftertreatment device 13. This procedure is described in the Figs. 3 and 4 shown.

[0055] The Figs. 3 and 4Each diagram shows the curve of the torque M (on the vertical axis) that can be delivered by the internal combustion engine 4 over time t (on the horizontal axis). The internal combustion engine 4 is off until time t0. Therefore, the torque that can be delivered by the internal combustion engine 4 is zero. At time t0, the internal combustion engine 4 is started (cold start). During a warm-up phase, which extends from time t0 to time t2, the torque M that can be delivered by the internal combustion engine 4 is limited by the engine control unit 14. The diagrams show... Figs. 3 and 4In principle – and indeed for driving operation from time t1 onwards – there is a linear decrease in the limitation or a linear increase in the deliverable torque M over time t. However, a different limitation pattern can also be provided. Time t2 is defined by the point at which the temperature of the exhaust aftertreatment device 13 has reached its activation temperature. This ends the torque output limited by the engine control unit 14, meaning that the combustion engine 4 can be operated, if required, with its design-defined maximum torque output (normal operation).

[0056] For the operation of the motor vehicle 1, a minimum limit value MG of the deliverable torque M is required to ensure adequate driving performance, particularly with regard to minimum acceleration capability. Therefore, it is provided that the operation of the motor vehicle 1 is prevented until the temperature of the exhaust aftertreatment device 13 is high enough to reach the minimum limit value MG, corresponding to the limited curve of the deliverable torque M. In the illustrated embodiment, this is achieved by the engine control unit 14 keeping the limit of the deliverable torque M at zero until the curve of the deliverable torque M, which generally increases linearly from time t 0, reaches the minimum limit value MG at time t 1.During the period Δt 1, which extends from time t 0 to t 1, the internal combustion engine 4 is therefore forcibly operated in idle mode by the engine control unit 14, and consequently independently of any other power demand that a driver of the vehicle 1 might request, for example, via an accelerator pedal. As a result, the available torque M remains zero, and the vehicle 1 cannot be driven. In particular, the engine control unit 14 can also prevent the internal combustion engine 4 from engaging in the drivetrain of the vehicle 1. Only at time t 1 does the engine control unit 1 enable the vehicle 1 to drive, because the available torque M has then reached the minimum limit value MG.In the subsequent period Δt 2, which extends from time t 1 to time t 2, it is possible to drive the motor vehicle 1, but the deliverable torque M is limited compared to the maximum possible torque output M max provided for in the design.

[0057] According to the invention, the minimum limit value MG is varied depending on the driving resistance that the motor vehicle 1 potentially or expected to have to overcome by the drive power generated by the internal combustion engine 4.

[0058] For this purpose, the presence or absence of the trailer 2 coupled to the motor vehicle 1, as well as, if the trailer 2 is present, the type of trailer 2 and, if applicable, a specific mass range of the trailer 2, can be taken into account as a measure of the driving resistance to be overcome. Fig. 3This then shows the limitation regarding the deliverable torque M for operation of the motor vehicle 1 without the trailer 2 or with the trailer 2, provided that this - unlike in the Fig. 1 shown - only a load carrier supported by a trailer coupling 18, such as a bicycle carrier, is shown. Since the driving resistance to be overcome will be relatively low in these cases, the minimum limit value M G1 for the deliverable torque M, from which driving operation of the motor vehicle 1 is permitted, is relatively low. Fig. 4 In contrast, it shows exemplary limitations regarding the deliverable torque M for the operation of the motor vehicle 1 with the or, in principle, with a trailer 2, which is designed as a vehicle with at least one axle (cf. Fig. 1), where, by way of example, three different minimum limit values ​​M G2, M G3, M G4 are defined for the deliverable torque M, from which driving operation of the motor vehicle 1 is permitted. These minimum limit values ​​M G2, M G3, M G4 differ from that according to the Fig. 3, i.e., from the minimum limit value M G1, which is intended for the operation of the motor vehicle 1 without trailer 2 or with trailer 2 configured as a load carrier. The minimum limits M G2, M G3, and M G4 are each higher than the minimum limit value M G1. The selection of one of the three minimum limits M G2, M G3, or M G4, which is to apply to the operation of the motor vehicle 1 with a specific trailer 2, depends on the maximum permissible mass of the trailer 2. The selected minimum limit value M G2, M G3, or M G4 is lower the smaller the mass of the trailer 2. The smallest minimum limit M G2 can be provided, for example, for a mass of the trailer 2 up to 200 kg, the medium minimum limit M G3 for a mass of the trailer 2 up to 1000 kg and the largest minimum limit M G4 for a mass of the trailer 2 which corresponds at most to the maximum trailer load permitted for the motor vehicle 1 (e.g. 1800 kg).The smaller the minimum limit value M G2 , M G3 , M G4 is, the shorter the period Δt 1 within which driving operation of the motor vehicle 1 is prevented by means of the engine control 14 (Δt 12 , Δt 13 , Δt 14 ).

[0059] While the presence or absence of the trailer 2 is automatically determined by the motor control unit 14 by checking the occupancy status of a connector 15 of the motor vehicle 1, which is part of an electrical power supply for the trailer 2 and to which a mating connector 16 of the trailer 2 can be connected, the type of trailer 2 (load carrier or vehicle-style trailer 2) and, in the case of a vehicle-style trailer 2, the specific mass range of the trailer 2 can preferably be selected by the driver of the motor vehicle 1, for which purpose a corresponding query can appear on a control unit 17, for example a touch-sensitive display, in the interior of the motor vehicle 1.The vehicle identification number (VIN) of trailer 2 can also be queried, and any input can be supplemented with information from a database containing the corresponding mass range. Such a database can be stored locally in the engine control unit or externally. If stored externally, a query via telecommunications data (online query) is preferred.

[0060] The query can be performed even before the combustion engine 4 is started. The combustion engine 4 can be started by the driver, for example, by pressing a start button (not shown). The engine control unit 14 can assume that the combustion engine 4 will start soon, for example, if a driver's door of the vehicle 1 has been opened and then closed. The presence of a driver in the vehicle 1's seat can also be taken into account. A query regarding the mass of the trailer 2 can also be performed after the engine has started, during the period Δt 1.This has the advantage that, by the time the driver has made the appropriate selection regarding the mass range of the trailer 2, the period Δt 1, during which the operation of the motor vehicle 1 is prevented by the engine control unit 14, may already have at least partially elapsed. This minimizes any impairment to the driver with regard to the operation of the motor vehicle 1.

[0061] It can be provided that the engine control unit 14 verifies a driver input, which is a response to a query, during the operation of the vehicle 1. For this purpose, a signal from a tilt sensor 24 of the vehicle 1 and / or the acceleration of the vehicle 1 and the drive power required to achieve this acceleration can be used, for example. This verification can take place, for example, within the first two or three seconds of operation. If such a verification reveals a discrepancy between the test result and the input, the engine control unit 14 can prevent further operation. Furthermore, a new query can be performed as a prerequisite for resuming operation after a temporary interruption involving the shutdown of the internal combustion engine.Alternatively, the motor control unit 14 can automatically set a different response to the original query.

[0062] Alternatively or additionally, it may be provided that, after the end of driving operation and during subsequent use of the motor vehicle 1 with the same trailer 2, which includes a cold start of the internal combustion engine, a warning message regarding the discrepancy between the test result and the input is displayed on a screen, which may in particular be part of the control unit 17. In addition, the engine control unit 14 may automatically set or maintain a predefined response to the original query.

[0063] Additionally or alternatively, the mass of the motor vehicle 1 can be taken into account as a measure of the driving resistance to be overcome. Fig. 3The figure then shows the limitation regarding the deliverable torque M for operation of the motor vehicle 1 with only one occupant. Since the driving resistance to be overcome is relatively low in this case, the minimum limit M G1 for the deliverable torque M, from which operation of the motor vehicle 1 is permitted, is correspondingly low. Fig. 4 In contrast, it shows exemplary limitations regarding the deliverable torque M for the operation of the motor vehicle 1 at higher masses, whereby three different minimum limit values ​​M G2, M G3, M G4 for the deliverable torque M, above which driving operation of the motor vehicle 1 is permitted, are shown as examples. These minimum limit values ​​M G2, M G3, M G4 differ from that according to the Fig. 3, i.e., from the minimum limit value M G1, which is intended for operation of the motor vehicle 1 occupied by only one person. The minimum limits M G2, M G3, M G4 are each greater than the minimum limit value M G1, and the minimum limit value M G2, M G3, M G4 automatically selected by the engine control unit 14 is lower the smaller the mass of the motor vehicle 1. The highest minimum limit value M G4, for example, may be intended for a mass of the motor vehicle 1 that it has when all seats are occupied and the cargo space of the motor vehicle 1 is fully loaded. The next lower minimum limit value M G3, for example, applies when only all seats of the motor vehicle 1 are occupied, while the cargo space is empty. The minimum limit value M G2, on the other hand, results, for example, from a mass of the motor vehicle 1 that it has when the motor vehicle 1 is occupied by only two people and the cargo space is empty.The smaller the minimum limit value M G2 , M G3 , M G4 is, the shorter the period Δt 1 within which driving operation of the motor vehicle 1 is prevented by means of the engine control 14 (Δt 12 , Δt 13 , Δt 14 ).

[0064] The mass of the motor vehicle 1 is preferably determined automatically by evaluating signals from several sensors of the motor vehicle. According to one embodiment, the signals from the following sensors are used to determine the mass of the motor vehicle 1: seat occupancy sensors 19, fuel level sensor 21 of a fuel tank 20 of the motor vehicle 1, tire pressure sensors 22, displacement sensors 23 on a rear axle of the motor vehicle, and the tilt sensor 24 for determining the tilt of the body of the motor vehicle 1.

[0065] Since the determined mass of motor vehicle 1 is fundamentally continuously variable, it is also provided that the engine control unit continuously adjusts the derived minimum limit value MG. The in the Figs. 3 and 4 The minimum limit values ​​M G1 , M G2 , M G3 , M G4 shown are merely discrete example values ​​in this respect.

[0066] The Fig. 5The diagram further illustrates the basic process of determining a minimum limit value MG of the deliverable torque M as a function of the mass of the vehicle 1 and, based on this, a time period Δt 1 during which the vehicle 1 is prevented from being driven. This determination begins, according to step S1, with the start-up of the internal combustion engine 4, whereupon the determination is initialized according to step S2. Step S3 involves querying measured values ​​from the seat occupancy sensors 19, the fluid level sensor 21, the tire pressure sensors 22, the displacement sensors 23 on the rear axle of the vehicle 1, and the tilt sensor 24. Based on these measured values, the mass of the vehicle 1 is determined in step S4. Additionally, environmental data, such as the ambient air temperature, air pressure, and humidity, are determined in step S5.From the determined mass and the determined environmental data, the minimum limit value MG of the deliverable torque M is determined in step S6. Based on this minimum limit value MG of the deliverable torque M, the period Δt 1, during which driving of the vehicle 1 is prevented, is determined in step S7. Once this period Δt 1 has expired, driving is enabled in step S8. REFERENCE MARK LIST

[0067] 1 Motor vehicle 2 Trailer 3 Internal combustion engine 4 Internal combustion engine 5 Cylinder opening 6 Reciprocating piston 7 Combustion chamber 8 Fresh air system 9 Air filter 10 Fresh air compressor 11 Exhaust turbine 12 Exhaust system 13 Exhaust aftertreatment device 14 Engine control unit 15 Connector 16 Mating connector 17 Control unit 18 Trailer coupling 19 Seat occupancy sensor 20 Fuel tank 21 Fuel tank level sensor 22 Tire pressure sensor 23 Travel sensor 24 Tilt sensor Maximum deliverable torque of the internal combustion engine Mmax Maximum deliverable torque MG Minimum limit of the deliverable torque for authorization to drive MG1 Minimum limit for authorization to drive without a trailer / with only one person in the vehicle MG2 Minimum limit for authorization to drive with a trailer with a mass of up to 200 kg / with only two persons in the vehicle MG3 Minimum limit for authorization to drive with a trailer with a mass of up to 1000 kg / with a fully occupied vehicle and empty cargo space MG4 Minimum limit for authorization to drive with a trailer with a mass up to the maximum trailer load / with a fully occupied vehicle ttime t0 Time of start-up of the internal combustion engine t1 Time of authorization to drive the vehicle without a trailer t12 Time of authorization to drive the vehicle with a trailer with aMass up to a maximum of 200 kg t 13 Time of release for the motor vehicle to drive with a trailer with a mass up to a maximum of 1000 kg t 14 Time of release for the motor vehicle to drive with a trailer with a mass up to the maximum trailer load t 2 Time of release for normal operation Δt 1 Period from t 0 to t 1 Δt 12 , Period from t 0 to t 12 Δt 13 , Period from t 0 to t 13 Δt 14 Period from t 0 to t 14 Δt 2 Period from t 1 to t 2 Δt 22 , Period from t 12 to t 2 Δt 23 , Period from t 13 to t 2 Δt 24 Period from t 14 to t 2

Claims

1. Method for operating a motor vehicle (1) having an internal combustion engine (2) which comprises a combustion motor (4) and an exhaust gas system (12) having at least one exhaust gas aftertreatment device (13), operation of the combustion motor (4) being limited, after a cold start of the internal combustion engine (2) where the exhaust gas aftertreatment device (13) has a temperature below a light-off temperature, by means of an engine control unit (14) on the basis of a temperature of the exhaust gas aftertreatment device (13) with regard to the torque (M) which can be delivered by the combustion motor (4), driving operation of the motor vehicle (1) being prevented until a minimum limit value (MG) of the deliverable torque (M) is reached, characterized in that the minimum limit value (MG) is varied on the basis of a driving resistance of the motor vehicle (1) to be overcome.

2. Method according to claim 1, characterized in that the presence or absence of a trailer (2) coupled to the motor vehicle (1) is used as a measure of the driving resistance to be overcome.

3. Method according to claim 2, characterized in that the presence or absence of the trailer (2) is automatically determined by the engine control unit (14).

4. Method according to claim 3, characterized in that the presence or absence of the trailer (2) is determined by an occupancy state of a plug connector (15) of the motor vehicle (1), which plug connector is part of an electrical power supply for the trailer (2).

5. Method according to any of the preceding claims, characterized in that a mass and / or a form factor of the motor vehicle (1) and / or a type and / or a mass and / or a form factor of the trailer (2) and / or at least one parameter relating to the ambient air is used as a measure of the driving resistance to be overcome.

6. Method according to claim 4 or 5, characterized in that the mass of the motor vehicle (1) and / or the mass of the trailer (2) is automatically determined by the engine control unit (14).

7. Method according to claim 5 or 6, characterized in that to determine the mass of the motor vehicle (1) and / or the mass of the trailer (2), a signal from one or more of the following sensors is evaluated: a seat occupancy sensor (19) of the motor vehicle (1), a tire pressure sensor (22) of the motor vehicle (1) and / or the trailer (2), a fill level sensor (21) of a fuel tank (20) of the motor vehicle (1), an inclination sensor of the motor vehicle (1), a distance sensor of the motor vehicle (1) and / or the trailer (2) which measures a distance to a ground, and a weighing sensor of the motor vehicle (1) and / or the trailer (2).

8. Method according to any of claims 4 to 7, characterized in that - the presence or absence of the trailer (2) and / or - the mass of the motor vehicle (1) and / or - the type and / or the mass and / or the form factor of the trailer (2) is queried by the engine control unit (14) at an operating unit (17) of the motor vehicle (1).

9. Method according to claim 8, characterized in that an input at the operating unit (17) is checked by the engine control unit (14) during driving operation, and if the test result does not match the input, - the selected measure of the driving resistance to be overcome is changed by the engine control unit (14) and / or - further driving operation is hindered by the engine control unit (14) and / or - a warning message regarding the test result not matching the input is displayed on a display and / or - a new query operation is carried out and / or - an error entry regarding the test result not matching the input is stored in the engine control unit (14).

10. Method according to claim 9, characterized in that for or after a subsequent cold start, the changed measure of the driving resistance to be overcome is maintained and / or the warning message is displayed again if the presence of the same trailer (2) is detected.

11. Method according to claim 4 and claim 10, characterized in that the presence of the same trailer (2) is detected by the fact that the occupancy state of the plug connector (15) has not been changed or has been changed twice within a period of time which is less than a defined limit value.

12. Method according to any of claims 5 to 10, characterized in that a plurality of mass ranges are defined for the mass of the motor vehicle (1) and / or for the mass of the trailer (2) and / or a plurality of form factor ranges are defined for the form factor of the trailer (2).

13. Method according to any of the preceding claims, characterized in that operation of the combustion motor (4) is limited until the light-off temperature of the exhaust gas aftertreatment device (13) is reached.

14. Method according to any of the preceding claims, characterized in that the limitation with regard to the deliverable torque is continuously reduced as the temperature of the exhaust gas aftertreatment device (13) increases.

15. Engine control unit (14) for a motor vehicle (1) having an internal combustion engine (2) which comprises a combustion motor (4) and an exhaust gas system (12) having at least one exhaust gas aftertreatment device (13), having a memory, wherein a computer program is stored in the memory, which computer program is designed to carry out a method according to any of the preceding claims.