DE102018106780A1 - Exhaust line of an internal combustion engine and method for controlling an exhaust gas turbocharger - Google Patents

Abstract

An exhaust system for a motor vehicle with an internal combustion engine 20 includes a catalytic converter 60, which is arranged between the exhaust gas outlet 30 of the internal combustion engine 20 and an exhaust gas turbocharger 40. The exhaust gas turbocharger 40 comprises an electric drive 45 and a controller is set up to increase and reduce the rotational speed of the exhaust gas turbocharger 40 via the electric drive 45.

Description

The present invention relates to an exhaust system of an internal combustion engine and to a method for controlling an exhaust gas turbocharger.

It is known to place a catalyst in the exhaust gas flow of a motor vehicle with internal combustion engine in the exhaust gas flow direction behind the outlet from the engine and in front of an exhaust gas turbocharger. This arrangement has several advantages, in particular the higher temperature which prevails immediately after the outlet of the engine can be used for an improved catalytic purification of the exhaust gas. On the other hand, if the catalytic converter is arranged behind the exhaust-gas turbocharger, the exhaust gas is already somewhat cooled by the exhaust-gas turbocharger, which is disadvantageous in the catalytic effect.

The object of the present invention is to improve the engine management and handling, especially in vehicles, in which the catalyst is arranged between the engine and the exhaust gas turbocharger.

This object is achieved by means of the independent claims. Preferred developments are the subject of the dependent claims. In the solution of the problem was first recognized that the catalyst can act under different driving conditions as a heat sink or heat source for the exhaust stream and thus may result in the exhaust gas turbocharger. And as another result of the present invention, these effects are minimized.

An exhaust gas system for a motor vehicle with an internal combustion engine comprises a catalytic converter, which is arranged between the exhaust gas outlet of the internal combustion engine and an exhaust gas turbocharger. The exhaust gas turbocharger comprises an electric drive and a controller is set up to increase and reduce the rotational speed of the exhaust gas turbocharger via the electric drive. Increasing the speed is already known and has the advantage of increasing this directly when requesting a higher boost pressure. As a result, a turbo lag, which will be explained in more detail below, be avoided or at least reduced. It is also possible to use the electric drive as a brake, so reduce the speed, which is advantageous if a lower boost pressure is required than it would actually result from the exhaust gas (volume).

It is advantageous, in particular, if a wastegate provided with a valve is arranged parallel to the exhaust-gas turbocharger in order to permit bypassing of exhaust-gas of the exhaust-gas turbocharger, depending on the valve state. The charge air (and in particular the pressure) can also be reduced via a wastegate, so that the use in conjunction with an electric drive to reduce the exhaust-gas turbocharger speed at first glance appears to be redundant and unnecessary. But the opening of said valve is in many cases directly coupled with the pressure in the charge air region. And an electric drive, which is switched as a generator or brake, can act faster. The exhaust gas turbocharger has namely a mass inertia. With a reduction of the exhaust gas pressure in the exhaust gas turbocharger, the inertia inhibits the reduction of the rotation, which leads to a deceleration of the deceleration. About an active braking application of the electric drive, the rotational speed of the exhaust gas turbocharger can be reduced faster. Preferably, the reduction of the rotational speed of the exhaust gas turbocharger can be carried out by simultaneously opening the wastegate with an active braking of the exhaust gas turbocharger via the electric drive.

Alternatively and / or additionally, the exhaust-gas turbocharger can also be set up as a variable nozzle turbine VNT to make a change in a vane position. With the change in the blade position, in particular on the exhaust side of the stator, a desired amount of exhaust gas can be selectively supplied to the exhaust gas turbocharger. Again, the electric brake has the advantage of more immediate effect.

It is particularly advantageous if the exhaust gas turbocharger and / or a motor control is set up to recuperate energy as electrical energy for a reduction in the rotational speed of the exhaust gas turbocharger. The recuperation means a recovery, especially as electrical energy. It is known that in electric motors (in particular design-dependent) it is possible to use them as a generator without further technical changes. Constructive changes are not necessary here. It only needs to be adapted to the electrical circuit so that this energy can also be used meaningfully. This can be done by supplying it to an electrical load or by using it to charge the battery. This results in two advantageous effects, namely that the drive speed, as already described, is lowered and the energy is provided.

Alternatively, it is also possible that the exhaust gas turbocharger and in particular a motor control is set up to dissipate corresponding energy for a reduction in the rotational speed of the exhaust gas turbocharger. This can happen, for example, by converting the rotational energy of the exhaust gas turbocharger into heat. This can, for example, technically by the engine control via a Resistance happen, which is connected in parallel to the electric drive of the exhaust gas turbocharger and short-circuits it via the resistor.

It is also advantageous if the load point of the internal combustion engine is used as a parameter for the deceleration of the exhaust gas turbocharger. Thus, it is possible without technical effort, for example, to reduce the load point not only the fuel supply, but also (for example, at the same time) to slow the exhaust gas turbocharger. As a result, energy is recuperated, in particular in a configuration of the exhaust system with a catalyst in front of the turbine. At the same time, the response of the engine can be accelerated. Also, via the accelerator pedal and / or the brake pedal, the driver's desire for a reduced engine performance can be detected and reduced according to the charge air pressure.

Accordingly, in a method for controlling an exhaust gas turbocharger, which comprises an electric drive for increasing the exhaust gas turbocharger speed, depending on the combustion state, in particular dependent on a boost pressure surplus, the exhaust gas turbocharger is decelerated by the electric drive. In this case, the engine exhaust gas can be passed to a catalyst and subsequently to the exhaust gas turbocharger. And the state of an accelerator pedal and / or the brake pedal is used as a parameter for the deceleration of the exhaust gas turbocharger.

Preferably, the exhaust gas turbocharger is designed as a Variable Nozzle turbine VNT and to reduce the charge air, the vane position of the VNT is brought into a flow-reduced position in which less exhaust gas flows through the exhaust gas turbocharger, and exhaust gas is passed through a high-pressure exhaust gas recirculation into the charge air line. As a result, the speed of the exhaust gas turbocharger is reduced faster and thus also faster reduces the charge air quantity than would be possible in a system without exhaust gas recirculation. The flow-reducing position of the VNT causes an increased proportion of exhaust gas to be recirculated. As a result, a faster adjustment is achieved in a load change, in particular to a lower target load. In addition, the charge air quantity can be further reduced by way of a (already described) braking effect of the electric drive. Especially through the combination of these agents, the response can be significantly improved.

In addition, it is advantageous if the catalytic converter is designed as a particulate filter and in particular as a diesel particulate filter and the vane position of the VNT is brought into a reducing position for regeneration of the particulate filter and exhaust gas is passed into the charge air line via a high-pressure exhaust gas recirculation. As a result, the catalyst can be regenerated with simple means. It acts twice, that initially the lower rotational speed of the exhaust gas turbocharger the engine less charge air is supplied and at the same time a stream of hot exhaust gas is recirculated into the engine, which naturally increases the exhaust gas temperature. By this method, the catalyst can be brought much faster to the regeneration temperature, which significantly reduces its duration and the fuel used for it. This results in a particular advantage in that electrical energy can be recuperated. It may also be the case that this reduction of the boost pressure is not sufficient, and so the charge pressure can be additionally reduced via a throttle valve. The advantage of the invention is that to reduce the boost pressure of the electric motor is used on the turbocharger, which in turn energy is recuperated.

In addition, a control over the position of a valve of a wastegate and the position of blades of a Variable Nozzle turbine VNT and a drive of the exhaust gas turbocharger can preferably control both the exhaust gas recirculation rate and the charge air quantity. In particular, the charge pressure can thus be determined independently of the exhaust backpressure. This results in advantages in the transient response and the regulation of the EGR mass flow. Thus, e.g. The exhaust gas is recirculated via an HD EGR in areas of the engine map, which have a very low driving pressure gradient between exhaust and suction side. For this purpose, the pressure gradient is artificially increased via the drive of the electric turbocharger. The drive is particularly adapted to accelerate and decelerate the exhaust gas turbocharger. In addition, these parameters can be used to regulate further parameters, such as the pressure in the charge air line and / or the exhaust line.

• 1 einen beispielhaften Aufbau des Ladeluft- und Abgasstrangs eines Motors und
• 2 den Aufbau der 1 mit zwei unterschiedlichen Varianten einer Abgasrückführung.

The invention will be explained by way of example with reference to the figures. Show it:

• 1 an exemplary structure of the charge air and exhaust gas system of an engine and
• 2 the construction of the 1 with two different variants of exhaust gas recirculation.

1 schematically shows a motor 20 which may, for example, have four cylinders. The exhaust of the engine 20 is via an exhaust outlet 30 discharged and to an exhaust gas turbocharger 40 continued. There it drives a drive shaft, which in turn is used to compress via a corresponding turbine, the charge air, which is used for combustion in the engine, so that a desired volume flow of the charge air into the engine 20 is directed. In addition, the exhaust gas turbocharger includes 40 a drive 45 , which then can accelerate the exhaust gas turbocharger in addition to the exhaust gas flow, if an increased charge air pressure or quantity is needed. This can be advantageous, for example, during acceleration of the vehicle. When accelerating, the driver more strongly acts on the accelerator pedal of the vehicle and thereby causes an increased fuel supply. At this time, an increased amount of charge air is also needed to keep the combustion in the desired range. However, since the exhaust gas flow of the engine is not increased at this time, the exhaust gas turbocharger can not yet provide the required power for generating the charge air flow. The drive 45 is preferably electrical and acts to drive the exhaust gas turbocharger and thus increase its power so as to increase the charge air amount as required.

Moreover, in 1 an optional wastegate 35 shown. The wastegate 35 is a bypass, which is arranged parallel to the exhaust gas turbocharger and in particular its exhaust passage. If at a very high engine power so much exhaust gas is provided that the exhaust gas turbocharger can not process it and / or if the required charge air quantity is lower than it would result from the exhaust gas volume (or enthalpy), the engine control can Valve 36 of the wastegate 35 open, so that a portion of the exhaust gas flows parallel to the exhaust gas turbocharger 40 and thus bypasses it. In a first embodiment, a simple control may be used, which is the valve 36 gives the command of the state of being open and of being closed. In another embodiment (not shown) may be provided in the charge air line, a device for measuring the charge air pressure and a transmission of this value can for the opening of the valve 36 be used. In this case, preferably a proportional correspondence can be used and the transmission can be done, for example, with a simple mechanical coupling. In this case, for example, be integrated into the charge air flow, a pressure cell and its rash is used to control the valve 36 used.

Moreover, in 1 a catalyst 60 shown in the exhaust direction behind the combustion chamber of the engine 20 and in front of the turbocharger 40 or its bypass 35 is arranged.

If the vehicle is operated under steady driving conditions (eg constant speed), then the catalyst has 60 due to the thermal equilibrium no (significant) influence on the exhaust gas temperature, the exhaust gas turbocharger 40 arrives. However, due to its mass, the catalyst can act as a heat sink and heat source. It acts especially as a heat sink when cold starting or when accelerating. That is, at these conditions, the exhaust gas is warmer than the catalyst temperature, resulting in the catalyst 60 heats up and consequently the exhaust gas flow is cooled, leaving the catalyst 60 through the exhaust gas receives a lower Enthalpiestrom and that he can not compress the charge air as it is actually needed. Besides the influence of the catalyst 60 on the exhaust enthalpy exists in the catalyst 60 second effect of a pressure drop and a third effect of a volume reduction of the exhaust gas by the cooling in the (even colder) catalyst. Accordingly, the second and third effect to the effect that not enough charge air can be compressed.

First, the conditions for accelerating the engine are discussed in more detail, where the problem of the "turbo lag" is known. As a turbo lag is called an effect that occurs only in turbocharged engines. In the lower load range, the engine operates only as a naturally aspirated engine, since the amount of exhaust gas is insufficient and / or not needed to keep the exhaust gas turbocharger at high speed. Because of the low speed, the compressor can not compress the air strong enough; he reached its control boost pressure only above a certain speed. The driver notices the turbo lag by initially only modest acceleration of the car, even if he presses the accelerator pedal fully, because a dependent of the boost pressure control ensures that the maximum possible injection quantity (despite "full throttle") is increased only by the degree the boost pressure rises. During the initially tough acceleration, the speed of the supercharger increases only slowly and thus also the boost pressure; However, from a characteristic engine speed (depending on the engine between 1600 and 2500 rpm), it reaches its maximum relatively quickly, because the shaft of the turbocharger rotates fast enough because of the now sufficient exhaust gas flow and therefore can build up the supercharging boost pressure. This delay is felt in older engines as this "hole".

It has been recognized as an essential aspect of the invention that a reverse effect can occur just when the catalyst is arranged in front of the exhaust gas turbocharger and the driver takes his foot off the gas pedal. Since then the exhaust gas flow from the engine is less hot, the catalyst acts as a heat source and heats it up (enthalpy increase), so that consequently the exhaust gas turbocharger would promote more charge air than is necessary or desired. And to remedy this problem, the motor drive can be controlled by the motor control as a brake and / or as a generator. By both ways, a resistance to the exhaust gas turbocharger is effected, which directly reduces its rotational speed and thus reduces the charge air quantity as desired. As the direct result, a charge air surplus can be prevented. If, for example, the pressure in the charge air region of the engine intake area becomes too great, it can be reduced by this means. The braking of the rotation of the exhaust gas turbocharger 40 has a much more immediate time than, for example, opening the bypass 35 or adjusting blades of a suitably adjustable VNT turbocharger. Thus, an undesired charge air / fuel ratio is avoided or at least reduced with a reduction in the passage of the accelerator pedal and / or an actuation of the brake pedal.

In addition to and / or in addition to the advantage of the improved driving conditions, electrical energy can also be recuperated by the motor drive 45 of the exhaust gas turbocharger 40 is used as a generator and the electrical energy thus generated is fed into the electrical system and / or so that a battery is charged.

Alternatively and / or in addition to the wastegate 35 can the exhaust gas turbocharger 40 be designed as a variable Nozzle turbine VNT, where the vanes of the exhaust gas inlet of the exhaust gas turbocharger 40 are adjustable so that it is more or less accelerated depending on their position. Even with a VNT system, the charge air delivery can be reduced in the described operating conditions. The (in particular supplementary) braking by the electric drive 45 has the advantage that the response speed is significantly improved.

The in 2 shown construction of the engine is largely identical to the structure of 1 , so that the above explanations and operations are analogously applicable. In addition, an exhaust gas recirculation 70 drawn from the exhaust line behind the catalyst 60 derived and into the charge air line 15 after the exhaust gas turbocharger 40 is initiated. In a dashed line is an alternative exhaust gas recirculation 70a shown immediately after the exhaust from the engine and before the catalyst 60 a part of the exhaust stream branches off and into the charge air line 15 initiates. The exhaust gas recirculations are preferred 70 and 70a alternatively, so that only one of these variants is used. The variant 70a has the advantage of hotter exhaust gas in the charge air line 15 is supplied, which is for the below-explained regeneration of the catalyst 60 is advantageous. The variant 70 has the alternative advantage that already purified exhaust gas in the charge air line 15 which significantly reduces sooting of the EGR cooler,

The turbocharger 40 is preferably designed as a variable Nozzle turbine VNT, can be adjusted at the blades, in particular at the exhaust gas inlet. Depending on the position of the blades more or less exhaust gas passes into the exhaust gas turbocharger 40 , which causes the rotational speed of the exhaust gas turbocharger is higher or lower and thus the charge air quantity is higher or lower. In addition, the exhaust gas pressure in the exhaust system is higher or lower and so is more or less exhaust gas through the exhaust gas recirculation 70 . 70a recycled. By a higher return rate, for example, the nitrogen oxide reduction is improved.

It is also advantageous if, in a preferred embodiment of the invention, an exhaust gas recirculation 70 or 70a and also a wastegate 35 is used, since so the volume of the recirculated exhaust gas can be controlled or regulated independently of the charge air volume. This happens in particular via the electric drive 45 or its braking of the exhaust gas turbocharger 40 in combination with the position of the corresponding valve 36 ,

For the regeneration of a catalyst 60 , which includes a particulate filter, the VNT can also be brought into the reducing position. This means that due to the reduced charge air quantity and additionally due to the hot recirculated exhaust gas, the engine temperature rises and so the soot in the particulate filter can be burned off.

LIST OF REFERENCE NUMBERS

15

Charge air train

20

Engine, internal combustion engine

30

exhaust outlet

35

wastegate

36

Valve (wastegate valve)

40

turbocharger

45

(electric) drive

60

catalyst

70, 70a

two different options for exhaust gas recirculation

Claims (10)

Exhaust line for a motor vehicle with an internal combustion engine (20); wherein a catalytic converter (60) is arranged between the exhaust gas outlet (30) of the internal combustion engine (20) and an exhaust gas turbocharger (40) and the exhaust gas turbocharger (40) comprises an electric drive (45) and a control is set up via the electric drive (45 ) to increase and reduce the rotational speed of the exhaust gas turbocharger (40). Exhaust line according to Claim 1 in which a wastegate (35) provided with a valve (36) is arranged parallel to the exhaust-gas turbocharger (40) in order to permit bypassing of exhaust-gas of the exhaust-gas turbocharger (40) depending on the valve state. Exhaust line according to Claim 1 or 2 wherein the exhaust gas turbocharger (40) is configured as a Variable Nozzle Turbine (VNT) to make a change in a vane position. Exhaust line according to one of the preceding claims, wherein the exhaust gas turbocharger (40) and in particular a motor control is arranged to recuperate energy as electrical energy for reducing the rotational speed of the exhaust gas turbocharger (40). Exhaust line according to one of Claims 1 to 3 wherein the exhaust gas turbocharger (40) and in particular a motor control is arranged to dissipate corresponding energy for reducing the rotational speed of the exhaust gas turbocharger (40) via the electric drive (45). Exhaust tract according to one of the preceding claims, wherein the controller is adapted to use as a parameter for the deceleration of the exhaust gas turbocharger, the load point or the deviation between the target and Istladedruck. Method for controlling an exhaust gas turbocharger (40) comprising an electric drive (45) for increasing the exhaust gas turbocharger speed, wherein the exhaust gas turbocharger (40) is braked by the electric drive (45) depending on the combustion pressure, in particular the engine exhaust gas a catalyst (60) and subsequently to the exhaust gas turbocharger (40) is passed and particularly is used as a parameter for the deceleration of the turbocharger, the load point or the deviation between the setpoint and Istladedruck. Method according to Claim 7 wherein the exhaust gas turbocharger (40) is designed as a Variable Nozzle turbine VNT and the vane position of the VNT (40) and the electric machine of the turbocharger are used for the simultaneous control of the boost pressure and the recirculated exhaust gas mass. Method according to one of Claims 7 or 8th wherein the catalyst (60) is designed as a particulate filter and in particular as a diesel particulate filter and is brought to regenerate the particulate filter, the vane position of a VNT in a reducing position and exhaust gas is passed via a high-pressure exhaust gas recirculation into the charge air line. Method according to one of the one of Claims 7 to 9 wherein a control over the position of a valve (36) of a Wastegates (35) and the position of blades of a variable Nozzle turbine VNT and a drive (45) of the exhaust gas turbocharger (40), which is in particular adapted to accelerate the exhaust gas turbocharger (40) and decelerate, both the exhaust gas recirculation rate and the charge air quantity controls.

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