Method and device for raising and/or lowering an exhaust gas temperature of a combustion engine having an exhaust gas aftertreatment device arranged in an exhaust line

A method and a control device for raising and/or lowering an exhaust gas temperature of a combustion engine having an exhaust gas aftertreatment device arranged in an exhaust line sets the exhaust gas temperature for the exhaust gas aftertreatment using an electric-motor mode and/or a generator mode of an electrified exhaust turbocharger.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for raising and/or lowering an exhaust gas temperature of a combustion engine having an exhaust gas aftertreatment device arranged in an exhaust line. The invention furthermore relates to a control device for raising and/or lowering an exhaust gas temperature of a combustion engine having an exhaust gas aftertreatment device arranged in an exhaust line.

2. Related Art

The fact that pollutant emissions from a combustion engine can be reduced in an effective manner by catalytic aftertreatment of the exhaust gas with the aid of an exhaust gas aftertreatment system, e.g., one having an exhaust gas catalyst, is known from practical experience. However, it is an important precondition for this that the catalyst has reached its light off temperature. Below this light off temperature, the exhaust gas catalyst is ineffective or not very effective, and the reaction takes place only at insufficiently low conversion rates. Particularly in systems with exhaust turbocharging, the heatsink formed by the exhaust turbine means that reaching catalyst light off in an optimum manner for emissions is extremely important in avoiding high pollutant emissions. In the case of combustion engines of this kind, it is thus necessary to take precautions to ensure that the exhaust gas catalyst reaches its light off temperature as quickly as possible.

In order to raise the exhaust gas temperature to a light off temperature, one known practice is to adjust the injection parameters of the combustion engine in such a way, for example, that the adjusted injection parameters bring about an increase in the exhaust gas temperature. This can be achieved by retarding the start of injection, for example.

Other known measures require the adjustment of a throttle valve, the activation of a burner system additionally introduced into the exhaust line or the closure of an engine braking flap. The disadvantage with the abovementioned approaches is that additional components, e.g., a burner system, an engine braking flap, etc., have to be provided and disadvantages in terms of efficiency have to be accepted.

European Patent Application EP 1 431 529 A1, for example, discloses a method and a device for raising and/or lowering an exhaust gas temperature of a combustion engine having an exhaust gas aftertreatment device arranged in an exhaust line, wherein the exhaust gas temperature is raised or lowered by gas introduced into the exhaust line. The gas introduction device used for this purpose can be an inserted nozzle configured as an injector or a shut-off nozzle inserted in the exhaust line or an ejector pump. The disadvantage of this technique is that an additional introduction device is necessary.

A combustion engine having an exhaust gas aftertreatment device in the form of a particulate filter is furthermore known from DE 43 25 004 C2. In the case of this particulate filter, raising (or lowering) the exhaust gas temperature in order to control the burn off process in the particulate filter is achieved by throttling (or de-throttling) the exhaust gas flowing through the exhaust line. This is achieved by a flap in the filter housing, which is pivoted by a thermostatically controlled linkage. In addition, an electric heater is provided for the thermostat and the particulate filter. This system is of complex construction and requires a large number of specially manufactured components. Thus, the particulate filter material must have a precisely defined contour to allow the pivoting motion of the flap. Moreover, effective control is only possible in relation to the raising of the exhaust gas temperature.

SUMMARY OF THE INVENTION

It is thus an object of the present invention to provide an improved method and an improved device for raising and/or lowering an exhaust gas temperature of a combustion engine having an exhaust gas aftertreatment device arranged in an exhaust line, by which disadvantages of conventional systems can be avoided.

These objects achieved by devices and methods explained in greater detail in the following description with reference in some cases to the figures.

According to one aspect the invention, a method for setting, in particular raising and/or lowering, an exhaust gas temperature of a combustion engine having an exhaust gas aftertreatment device arranged in an exhaust line is provided. According to general aspects of the invention, an electric-motor mode and/or a generator mode of an electrified exhaust turbocharger is used to set the exhaust gas temperature for exhaust gas aftertreatment. The combustion engine is in the fired mode during the carrying out of the method.

An electrified exhaust turbocharger is known per se from the prior art and is also referred to as an exhaust turbocharger, which can be operated by electric motor or assisted by electric motor. The electrified exhaust turbocharger has an electric machine, which can be coupled or is coupled in a torque-transmitting manner to the drive shaft of the exhaust turbocharger or, in general, to the rotor. The electric machine is provided for driving or assisting the driving of the exhaust turbocharger (also referred to below as the electric-motor mode of the exhaust turbocharger) and/or can be operated as a generator by the exhaust turbocharger. The rotor of the exhaust turbocharger is formed by the exhaust turbine, the compressor and the drive shaft, wherein the exhaust turbine and the compressor are coupled by the drive shaft in terms of motion. It is already known from practical experience that the pressure-charging process of the combustion engine can be assisted temporarily by the electric motor of an electric-motor-assisted exhaust turbocharger, in particular to bridge the “turbo lag” when starting off.

Setting the exhaust gas temperature for exhaust gas aftertreatment by an electric-motor mode and/or a generator mode of an electrified exhaust turbocharger offers the advantage, in particular, that, in the case of vehicles already fitted with electrified exhaust turbochargers, further additional systems for raising the exhaust gas temperature, e.g., a burner, a throttle valve or an additional compressor, can be omitted or that, when the exhaust turbocharger is used in accordance with the invention in combination with these conventional approaches, it is possible to achieve a more rapid rise in the exhaust gas temperature.

According to a preferred illustrative embodiment of the invention, the electric-motor mode and/or the generator mode of the electrified exhaust turbocharger is started after satisfaction of at least one activation condition for activation of an exhaust gas temperature management. The term “exhaust gas temperature management” means the selective raising and/or lowering of the exhaust gas temperature. If the corresponding mode has already started at this point in time, it can be adapted, if appropriate, to ensure that the exhaust gas temperature approaches a setpoint temperature or a setpoint temperature range as quickly as possible. Here, the satisfaction of the activation condition indicates that the exhaust gas temperature should be modified in order, for example, to allow optimum operation of the exhaust gas aftertreatment device.

In an advantageous variant of this embodiment, the generator mode of the electrified exhaust turbocharger is started when the satisfaction of at least one activation condition indicates that the current exhaust gas temperature needs to be increased, e.g., if the actual exhaust gas temperature is below a light off temperature of an exhaust gas aftertreatment device. A generator mode of the exhaust turbocharger has the effect that the kinetic energy of the rotor is partially converted into electrical energy and, as a result, the rotor is braked. This reduces the boost pressure or air mass flow of the combustion engine. Owing to the reduced boost pressure, the air ratio (lambda) falls and produces hot exhaust gas. The use of the generator mode of the exhaust turbocharger to increase the exhaust gas temperature furthermore reduces the disadvantages in respect of efficiency in comparison with the approaches known from the prior art.

According to another advantageous variant of this embodiment, the electric-motor mode of the electrified exhaust turbocharger is started or adapted when the satisfaction of at least one activation condition indicates that the current exhaust gas temperature needs to be reduced. In particular, an electric-motor mode of the exhaust turbocharger comprises electric motor-assisted operation of the exhaust turbocharger, in which the electric machine additionally accelerates the rotor of the exhaust turbocharger. The exhaust turbocharger rotor accelerated to a higher speed increases the air mass flow and the air ratio (lambda) and thereby leads to a reduction in the exhaust gas temperature. This offers the advantage that the combustion engine and the exhaust gas aftertreatment device can be protected from overheating.

One possibility for implementation according to the invention furthermore envisages that at least one of the following measures is carried out when the satisfaction of at least one activation condition indicates that the current exhaust gas temperature needs to be increased: (a) adjustment of the throttle valve, (b) closure of an engine braking flap, (c) activation of an additional burner system arranged on the exhaust line, and (d) adjustment of the injection parameters of the combustion engine in such a way that the adjusted injection parameters bring about an increase in the exhaust gas temperature, wherein a retardation of the start of injection and/or an increase in the metered quantity of fuel introduced can be performed, for example, to raise the exhaust gas temperature.

In other words, the setting of the exhaust gas temperature in accordance with the invention using an electric-motor and/or motor mode of the electrified exhaust turbocharger can be combined with conventional measures and methods for adapting the exhaust gas temperature, thereby making it possible to achieve a particularly rapid increase in the exhaust gas temperature.

According to another variant of the illustrative embodiment, in which the use of the exhaust turbocharger in accordance with the invention for the exhaust gas temperature management is combined with at least one of the conventional measures for adapting the exhaust gas temperature, an electric-motor mode of the exhaust turbocharger is started in the case of transient operating states in order to increase the exhaust gas temperature. Transient operating states are non-steady operating states, e.g., a starting process or a shifting process, in which the exhaust gas energy/quantity fed to the turbine of the exhaust turbocharger fluctuates greatly. In these transient operating states, the electric motor of the exhaust turbocharger thus compensates for the fluctuations in the exhaust gas energy/quantity by an electric-motor mode (“boost” mode). In transient operating states, the electric-motor mode compensates for the greatly fluctuating air mass flow in transient operating states, thus allowing the conventional measures to be employed more effectively.

According to another aspect of the invention, an activation condition for activating an exhaust gas temperature management, which indicates that the exhaust gas temperature needs to be increased, can be the undershooting of a lower temperature limit value by the exhaust gas temperature. The lower temperature limit value can preferably be a light off temperature of the exhaust gas aftertreatment device, e.g., of an exhaust catalyst.

According to another variant, an activation condition for activating an exhaust gas temperature management, which indicates that the exhaust gas temperature needs to be increased, can be the presence of an idling and/or part-load operating state of the combustion engine. According to this variant, a generator mode of the exhaust turbocharger to raise the exhaust gas temperature is thus employed only in idling and/or part-load operating states. In these operating states, more rapid heating of the exhaust gas is of particular significance since it otherwise generally takes an above-average time for the exhaust gas aftertreatment device to warm up to the light off temperature owing to the reduced combustion power in these operating states.

In addition to the monitoring of the exhaust gas temperature, it is possible as an alternative or in addition to use other parameters as a condition for activating the exhaust gas temperature management: for example, an activation condition for activating an exhaust gas temperature management can be determined on the basis of a particular value of at least one engine temperature sensor, wherein the at least one engine temperature sensor measures an intake air temperature, an engine cooling water temperature and/or an engine oil temperature. Low temperatures of the engine cooling water or of the engine oil indicate, for example, that the engine is in the cold-running or warmup mode, in which the temperature of the exhaust gas aftertreatment device has likewise not been warmed up sufficiently without additional measures.

Another possibility here envisages that an activation condition for activating an exhaust gas temperature management is determined on the basis of an operating phase of the combustion engine, wherein the operating phase indicates whether the engine is in cold-running mode, warm-up mode or warm mode and/or whether the combustion engine has been operated in the overrun mode for longer than a predetermined time. Such operating states correlate, in turn, with the temperature state of the exhaust gas aftertreatment device since the exhaust gas aftertreatment device generally has a temperature below the light off temperature in the cold-running mode, the warm-up mode or after a prolonged overrun mode or unfired mode.

The raising and/or lowering, described above, of the exhaust gas temperature using the electrified exhaust turbocharger is preferably carried out temporarily until the exhaust gas temperature has reached a desired setpoint value or setpoint range.

According to another aspect of the invention, a control device for setting, in particular raising and/or lowering, an exhaust gas temperature of a combustion engine having an exhaust gas aftertreatment device arranged in an exhaust line is provided. The control device is designed to check whether at least one activation condition for activating an exhaust gas temperature management has been satisfied and, if yes, to activate an electrified exhaust turbocharger of the combustion engine to establish an electric-motor and/or a generator mode of the electrified exhaust turbocharger in order to set the exhaust gas temperature.

In particular, the control device can be embodied to carry out the method as disclosed herein. To avoid repetition, features which are disclosed purely in the context of the method shall also be deemed to be applicable and claimable in the context of the device.

The invention furthermore relates to a motor vehicle, in particular a commercial vehicle, having a combustion engine pressure-charged by an electrified exhaust turbocharger, having a control device as disclosed in this document.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1schematically shows a pressure-charged combustion engine2of a commercial vehicle, typically a diesel engine, and an electrified exhaust turbocharger10associated therewith, also referred to below as ETC, in the form of a highly schematized block diagram. The ETC10comprises a turbine12, which is driven by the exhaust gas from the combustion engine2, which is fed to the turbine12via the exhaust line5b. After this, the exhaust gas mixture flows via the turbine outlet through an exhaust line6, in which an exhaust gas aftertreatment device3known per se, e.g., in the form of an exhaust catalyst, is arranged. After passing through the exhaust gas aftertreatment device3, the exhaust gas flows via another exhaust line7to the exhaust.

The turbine12is connected to a compressor11by a shaft13. Fresh air is fed to the compressor11via the compressor inlet line4. The compressor11compresses the charge air to be fed to the combustion engine2and thus boosts the power of the combustion engine2in normally fired operation. The charge air compressed by the compressor11is fed via a charge air line to a charge air cooler8and is then fed into the combustion engine2via line5a.

The ETC10is embodied as an electrified exhaust turbocharger, that is to say an electric-motor-assisted exhaust turbocharger. For this purpose, the ETC10is provided with an electric machine14, which can be operated as a motor and, as a generator, can be coupled or is coupled in a torque-transmitting manner to the drive shaft13and is provided for the purpose of driving or assisting with the driving of the rotor, comprising the compressor11, the turbine12and the shaft13, of the exhaust turbocharger.

The motor mode and the generator mode of the electric machine14, e.g., an electric motor, are controlled by a control device1, which is connected for this purpose, via electric lines, to the electric machine14and to an energy storage device15for electrical energy, e.g., a starter battery or a high-voltage battery of a hybridized drive train, the electric line between the control device1and the electric machine14being indicated schematically by the dotted line9and the electric connection between the control device1and the energy storage device15being indicated schematically by the dotted line17. For the motor mode of the electric machine14, this energy is supplied by the energy storage device15. The power generated in the generator mode of the electric machine14can be fed to the energy storage device15via the control device1.

In the illustrative embodiment under consideration, the control device1is furthermore embodied as a controller which can actively perform exhaust gas temperature management in order to raise and/or lower an exhaust gas temperature. Here, the controller, which is configured to comprise a microprocessor for example, is connected to the combustion engine2via the control line18in order to supply the engine2with modified injection parameters, e.g., retardation of the starter injection, in order to raise the exhaust gas temperature.

The control device1is furthermore configured to control the operation of the exhaust gas aftertreatment device3, this being indicated by the electric line16. Line16connects the sensors of the drive train and/or of the exhaust gas aftertreatment system to the control device1. By the sensors, it is possible in a manner known per se to measure the exhaust gas temperature after the turbine12, the temperature ahead of and/or after a catalytic converter or particulate filter, a differential temperature, a pressure ahead of and/or after a catalytic converter or particulate filter or the differential pressure, for example.

The control device1is configured to control the exhaust gas temperature and to continuously receive data from various engine temperature sensors. For example, there is a temperature sensor20arranged in the compressor inlet line4, the sensor measuring the temperature of the intake air and transmitting the measured values to the control device1via the signal line19. The control device1receives measured values from further temperature sensors (not shown inFIG. 1), which measure the exhaust gas temperature and the temperature of the engine cooling water and of the engine oil in a known manner.

One special feature is that the control device1is preferably configured to activate the ETC10as part of the exhaust gas temperature management, in particular to raise the exhaust gas temperature through a generator mode of the ETC10or, if appropriate, to lower the exhaust gas temperature through an electric-motor mode of the ETC10.

The corresponding mode and the corresponding method are illustrated, by way of example, in the flow diagram inFIG. 2.

In a first step S1, the control device1monitors, in the fired mode of the combustion engine2, whether a predetermined activation condition for an exhaust gas temperature management in which the exhaust gas temperature will be increased or reduced selectively has been satisfied. Here, the satisfaction of the activation condition indicates that the exhaust gas temperature should be actively modified, e.g., to allow optimum operation of the exhaust gas aftertreatment device3. The activation condition is satisfied and indicates that the exhaust gas temperature should be raised, for example, when the actual exhaust gas temperature in the exhaust line5bis below the light off temperature of the exhaust gas aftertreatment device3. To monitor this activation condition, the control device1can continuously monitor the measured values from the exhaust gas temperature sensor20′. As a further activation condition, the control device can check whether the combustion engine2is in a cold-running or warm-up mode since, in these operating states, the exhaust gas aftertreatment device3has generally likewise not yet warmed up sufficiently. When the current exhaust gas temperature needs to be increased, at least one of the following measures is carried out when the satisfaction of at least one activation condition indicates that: (a) adjustment of the throttle valve30, (b) closure of an engine braking flap35, (c) activation of an additional burner system arranged on the exhaust line40, and (d) adjustment of the injection parameters of the combustion engine in such a way that the adjusted injection parameters bring about an increase in the exhaust gas temperature.

As an alternative, the control device1can monitor the activation condition using engine temperature sensors, which measure the temperature of the intake air, of the engine water or of the engine oil. If the measured temperature values are each below a predetermined temperature threshold, the control device3can infer from this that the activation temperature of the exhaust gas aftertreatment device3has not been reached. Such temperature thresholds can be determined experimentally on a test rig, for example.

According to the illustrative embodiment under consideration, the system checks, as a further activation condition for the generator mode of the ETC10whether an idling or part-load operating state is present. In other words, an exhaust gas temperature that is too low is only raised actively by a generator mode of the ETC10when an idling or part-load operating state is present.

FIG. 3shows an engine operating map to illustrate operating states of this kind. The curve denoted by the reference sign41represents the full-load limit curve of the engine operating map. The region of operating points, which are surrounded by the line denoted by40, represent operating points, in the part-load mode of an illustrative commercial vehicle engine for which exhaust gas temperature management is carried out. For an illustrative commercial vehicle combustion engine, the part-load operating states are those operating points at which the engine speed is in a speed range of from 600 to 1600 revolutions per minute and in a torque range of from 0 to 700 Nm.

Returning to step S2, of the flow chart ofFIG. 2, the control device1thus checks whether the activation condition has been satisfied. If this is the case and the activation condition furthermore indicates that the exhaust gas temperature should be actively raised, step S3is then carried out, in which the control device1starts a generator mode of the electric machine14of the ETC10.

In the generator mode, the electric machine14coupled to the drive shaft13of the rotor in terms of motion is accelerated by the rotor (11,12,13) supplied with exhaust gas energy from the combustion engine, with the result that the kinetic energy of the rotor (11,12,13) is partially converted into electrical energy and, as a result, the rotor is braked. Consequently, a generator mode of the exhaust turbocharger has the result that the boost pressure or air mass flow of the combustion engine is reduced. Owing to the reduced boost pressure, the air ratio (lambda) falls and produces hotter exhaust gas during combustion.

The temporary generator mode of the ETC10is ended when the temperature of the exhaust gas has exceeded the light off temperature of the exhaust gas aftertreatment device. The method is then continued again with step S1.

As already mentioned above, one particular advantage of the invention consists furthermore in that the method can be used analogously to lower the exhaust gas temperature in order to protect the combustion engine2and the exhaust gas aftertreatment device3if the exhaust gas temperature is too high. For this purpose, there is furthermore monitoring, in step S1, of activation conditions that indicate an exhaust gas temperature which is too high. Consequently, the system furthermore checks in step S2whether there is a case of an exhaust gas temperature which is too high. This would be the case, for example, if the exhaust gas temperature exceeded a predetermined upper limit value for the exhaust gas temperature. In this case, step S4is then carried out.

In step S4, the ETC10is driven by the electric motor, i.e., the rotor (11,12,13) of the ETC10is additionally accelerated by the electric-motor mode of the ETC10.

Owing to the acceleration of the rotor to a higher speed, the air mass flow increases and leads to a lowering of the exhaust gas temperature. The temporary electric-motor-assisted mode of the ETC10is ended if the exhaust gas temperature value has fallen below the upper limit value. The method is then continued again with step S1.

The invention is not restricted to the preferred illustrative embodiments described above. On the contrary, a large number of variants and modifications which likewise make use of the inventive concept and therefore fall within the scope of protection is possible. In particular, the invention also claims protection for the subject matter and the features of the dependent claims independently of the claims to which they refer.