DE102015211541B4 - Energy recovery in the intake air tract of an internal combustion engine - Google Patents

Abstract

A method for operating a self-igniting internal combustion engine (2) with an intake air duct (13, 11, 19, 5, 3) which is designed to supply an intake air flow to the internal combustion engine (2) and which has a compressor (11) of an exhaust gas turbocharger (11, 12), an electric machine (8) connected to a rotor (6) arranged in the supply air flow and one located from an exhaust tract (4, 12, 20, 14, 15) of the internal combustion engine (2) to one downstream of the rotor (6). exhaust gas recirculation (16) leading to the feed point and in which the exhaust gas recirculation (16) is designed without an exhaust gas recirculation valve (17), the method having a step of setting a desired exhaust gas recirculation rate in a throttle operating mode of the internal combustion engine (2), in which the electric machine (8) is operated in a generator mode and as a function of the desired exhaust gas recirculation rate, the power thus drawn from the supply air flow being fed to an on-board electrical system (9).

Description

The invention relates to a method for operating a self-igniting internal combustion engine, a self-igniting internal combustion engine operated according to the method according to the invention, and a motor vehicle with such a self-igniting internal combustion engine.

In motor vehicle construction there is an ongoing striving for more efficient internal combustion engines in order to reduce carbon dioxide emissions. For this reason, too, there is a trend towards supercharged internal combustion engines with reduced cubic capacity, since in the case of a spark-ignited internal combustion engine, the engine is often operated unthrottled, which reduces throttle valve losses. In practice, however, in order to keep the production of nitrogen oxides within the prescribed limits, the mass flow of the intake air for the spark-ignited internal combustion engine must be controlled by a throttle valve, which increases the pumping losses of the internal combustion engine and thus impairs the efficiency of the engine. In the case of the usually lean-burn self-igniting internal combustion engines, low-load operation was traditionally set by controlling the fuel supply, while the intake air can flow unthrottled into the combustion chamber. Due to the excess oxygen, this produces a quantity of nitrogen oxides that is considered unacceptable today.

A common countermeasure is exhaust gas recirculation, in which exhaust gas from the combustion engine is returned to the intake air duct and mixed with the intake air. This avoids or dampens temperature peaks in the combustion chamber, which greatly limits the production of nitrogen oxides.

With low-pressure exhaust gas recirculation, the recirculated exhaust gas is mixed with the supply air upstream of the compressor. The problem here is the loading of the compressor by corrosive components of the exhaust gas. With high-pressure exhaust gas recirculation, the recirculated exhaust gas is mixed with the already compressed supply air downstream of the compressor. However, this can only work if the exhaust gas is recirculated at a higher pressure than that of the supply air that has already been compressed by the compressor. For this reason, an exhaust gas recirculation throttle is currently often provided in self-igniting internal combustion engines, which can throttle the supply air flow as an electronically controllable throttle valve in order to thereby increase the exhaust gas recirculation rate. The disadvantage here, however, are the throttle flap losses that occur because of the pressure drop in the compressed intake air caused by the exhaust gas recirculation throttle.

From the DE 10 2011 084 782 A1 an internal combustion engine with an exhaust pipe, an intake pipe and an exhaust gas recirculation system is known. An exhaust gas turbocharger is also provided. A throttle element, which can be bypassed by means of a bypass line, is arranged in the intake line. An expansion machine for obtaining additional energy is arranged in the bypass line.

the DE 10 2011 006 388 A1 discloses a method for operating a quantity-controlled internal combustion engine. The internal combustion engine has an intake tract and an exhaust tract, with an expansion machine being arranged in the intake tract in the flow direction of a combustion air in front of an intake valve, the output shaft of which can be coupled to an output shaft of the internal combustion engine, a heat exchanger which can be arranged on the exhaust tract being provided and with a combustion air, before it flows through the expander, is heated in the heat exchanger by an exhaust gas from the internal combustion engine.

the JP 2005 - 127 261 A describes an internal combustion engine with an exhaust gas recirculation device and an exhaust gas turbocharger. Also provided are a power generator driven by the exhaust turbine, an electric motor for driving a compressor, a battery for accumulating power generated by the generator and supplied to the electric motor, and a controller for controlling the rotational speed of the exhaust turbine. The control takes place in such a way that the amount of recirculated exhaust gas corresponds to a previously set target amount.

the DE 60 2004 001 149 T2 discloses a booster device for boosting intake air in the intake passage of an internal combustion engine based on the required intake air flow rate of the engine. The supercharger device includes a displacement supercharger, an electric motor for driving the supercharger, which can also function as a generator, a bypass passage for bypassing the supercharger, and a bypass valve in the bypass passage. In addition, there is a controller which is programmed, among other things, to adjust an opening of the bypass valve based on the discharge flow rate of the supercharger and the required intake air flow rate of the engine, so that the bypass valve opens if there is a difference between the discharge flow rate of the supercharger and the required intake air flow rate of the engine is zero.

It is therefore an object of the invention to provide an operating method for a self-igniting internal combustion engine and according to the erfindungsge to introduce self-igniting internal combustion engines operated according to methods that allow a reduction in throttle valve losses.

The invention therefore introduces an improved method of operating a compression ignition internal combustion engine. The internal combustion engine is equipped with an intake air tract which is designed to supply an intake air flow to the internal combustion engine and which has a compressor of an exhaust gas turbocharger and an electrical machine connected to a rotor arranged in the intake air flow. In addition, the internal combustion engine has an exhaust gas recirculation system leading from an exhaust tract of the internal combustion engine to a feed point located downstream of the rotor. According to the invention, the exhaust gas recirculation is carried out without an exhaust gas recirculation valve and there is a step of setting a desired exhaust gas recirculation rate in a throttle operating mode of the internal combustion engine, in which the electric machine is operated in a generator mode and depending on the desired exhaust gas recirculation rate and the power drawn from the supply air flow as a result is an electrical on-board network is supplied.

The invention increases the efficiency of the self-igniting internal combustion engine by recovering power from the supply air flow when the supply air flow is throttled to increase the exhaust gas recirculation rate. Although this power is generated indirectly by the internal combustion engine and reduced by the losses in the conversion into an electrical current, the power recuperated by this type of throttling would otherwise be lost. The extraction of power from the supply air flow is particularly useful when an operating phase with relatively high engine power and correspondingly large exhaust gas volume and low exhaust gas recirculation rate is followed by one with reduced engine power. Here, in particular in the case of a supercharged self-igniting internal combustion engine with an exhaust gas turbine, power can be recovered and electrical consumers made available.

A further advantage of the invention is that the recovery is carried out on the cold air side of the self-igniting internal combustion engine, so that the load on the rotor or the electric machine for the recovery from corroding exhaust gases and soot particles is reduced or eliminated compared to an arrangement in the exhaust gas side.

In the method according to the invention, it can also be provided that the electric machine is operated in a boost operating mode of the internal combustion engine in a motor operating mode, as a result of which a boost pressure of the internal combustion engine is increased in the boost operating mode. In such a case, the electric machine is operated as an electric compressor with the rotor arranged in the supply air flow, in order to achieve a higher degree of supercharging and thus greater motor power. As a result, an internal combustion engine with a further reduced cubic capacity can be provided for a given motor vehicle mass, which is then supercharged when a higher engine output is required by using the compressor realized in this way in order to provide the required output. This offers the advantage that the electrical energy recuperated in the throttle operating mode can be used to drive the electrical compressor.

In the boost operating mode, provision can be made for the supply air flow to be routed completely via the rotor connected to the electric machine. In addition or additionally, in the throttle operating mode, a variably predeterminable part of the supply air flow can be routed past the rotor connected to the electric machine. As a result, the supplied fresh air for the intake air of the internal combustion engine can be adjusted independently of the exhaust gas recirculation rate.

In some embodiments of the method according to the invention, an electronically controlled throttle valve arranged downstream of the rotor connected to the electric machine and upstream of the feed point of the exhaust gas recirculation can be variably adjusted as an exhaust gas recirculation throttle. When controlling the throttle valve, the increase in the exhaust gas recirculation rate generated by recuperating power from the supply air flow is then taken into account. However, the exhaust gas recirculation throttle is particularly preferably omitted and the exhaust gas recirculation rate is controlled by recuperating power from the supply air flow. The elimination of the exhaust gas recirculation throttle results in cost savings.

A second aspect of the invention introduces an improved compression ignition internal combustion engine. The internal combustion engine has an intake air duct, which is designed to supply the internal combustion engine with an intake air flow, and which leads to a compressor of an exhaust gas turbocharger, an electric machine connected to a rotor arranged in the intake air flow, and a feed point located downstream of the rotor from an exhaust gas tract of the internal combustion engine Has exhaust gas recirculation. According to the invention, the exhaust gas recirculation is designed without an exhaust gas recirculation valve and a control unit is provided which is designed to carry out the method according to the invention, ie in particular in a throttle operating mode of the self-igniting Ver internal combustion engine to operate the electric machine in a generator mode and depending on a desired exhaust gas recirculation rate. The self-igniting internal combustion engine of the invention has the advantage that an exhaust gas recirculation throttle can be dispensed with, as a result of which the efficiency of the self-igniting internal combustion engine is increased. However, an exhaust gas recirculation throttle can still be provided in order to increase the degrees of freedom available when controlling the internal combustion engine.

The internal combustion engine preferably has a bypass valve arranged parallel to the rotor. The bypass valve makes it possible to variably specify a degree of throttling of the internal combustion engine.

The Y rotor and the electrical machine are particularly preferably parts of an electrical compressor. For example, the internal combustion engine can have a so-called supercharger, i.e. a series connection of a compressor of an exhaust gas turbocharger and an electric compressor.

A further aspect of the invention relates to a motor vehicle with a self-igniting internal combustion engine according to the preceding aspect of the invention.

The invention is explained in more detail below using an illustration of an exemplary embodiment. The only figure shows a motor vehicle 1, which has a self-igniting internal combustion engine 2, which in the present example is designed with four cylinders. Of course, other numbers of cylinders can also be provided instead. The internal combustion engine 2 has an intake air manifold 3 on the charging side and an exhaust manifold 4 on the exhaust gas side. A portion of the exhaust gas produced during operation of the internal combustion engine 2 is routed back to the intake air manifold 3 via an exhaust gas recirculation system 16, where the portion of the exhaust gas is mixed with the intake air for the internal combustion engine 2. The exhaust gas recirculation 16 can have an exhaust gas recirculation cooler 18, for example. This in 1 shown exhaust gas recirculation valve 17 is not available.

The exhaust gas that is not recirculated passes via an exhaust gas aftertreatment device 14, which can contain one or more catalytic converters, for example, to an exhaust pipe 15, which releases the exhaust gas into the environment. The exhaust after-treatment device 14 and the muffler 15 do not form an essential part of the invention and can be implemented at the discretion of the person skilled in the art in accordance with the requirements of the individual case.

The exhaust gas turbine 12 is usually connected to a compressor 11 to form a turbocharger and drives the compressor 11 . The compressor 11 draws in ambient air via an air filter 13 and compresses it, thereby increasing the charging pressure of the self-igniting internal combustion engine 2 . This compression means that a higher charge air mass can be loaded into the same working volume (turbo charging).

In embodiments of the invention with an exhaust gas turbine 12 , what is known as a wastegate 20 can be provided parallel to the exhaust gas turbine 12 , which can route a selectable quantity of exhaust gas past the exhaust gas turbine 12 . This can be done for the purpose of controlling the degree of turbocharging of the internal combustion engine 2, for example. If a larger quantity of exhaust gas is routed past the exhaust gas turbine 12 via the wastegate 20, the exhaust gas turbine 12 makes less drive power available to the compressor 11, so that the charge air supplied to the internal combustion engine 2 is compressed less and the charge pressure drops accordingly.

The supply air compressed by the compressor 11 is usually cooled by an intercooler 19 and can be supplied to the supply air manifold 3 of the internal combustion engine 2 via an exhaust gas recirculation throttle 10 designed as an electronically controlled throttle valve. According to the invention, however, the exhaust gas recirculation throttle 10 can be omitted since the exhaust gas recirculation quantity can be controlled via an electric machine 8 connected to a rotor 6 . The charge air conducted via the rotor 6 sets the rotor 6 in motion and in this way operates the electric machine 8 as a generator. The electrical power generated in this way is routed to an on-board network 9, where it is available for the operation of electrical components of the motor vehicle 1 or can be stored in a battery or a capacitor. Due to the recuperation of electrical power in the supply air flow, the air compressed by the compressor 11 is partially expanded again, so that the charging pressure decreases and a correspondingly larger exhaust gas recirculation rate is set. The control of the exhaust gas recirculation rate can thereby be performed in a fuel-saving manner.

A bypass valve 7 can be arranged parallel to the rotor 6 in order to control the proportion of the supply air flow routed via the rotor 6 . The rotor 6 and the bypass valve 7 here represent a typical so-called booster 5, the bypass valve 7 being closed and closed in a boost operating mode according to the prior art the rotor 6 is electrically driven for additional compression.

The invention enables the exhaust gas recirculation rate to be increased in a throttle operating mode with the recovery of part of the engine power, which increases the efficiency of the overall device. In this case, the power is also advantageously not taken from the exhaust gas side of the internal combustion engine 2, for example by an exhaust gas turbine connected to an electric generator, but rather on the intake air side. This offers the advantage that the rotor 6 is not exposed to the increased temperatures and aggressive chemical substances that are typical on the exhaust gas side, which increases the service life of the device.

According to the invention, the rotor 6 and the electric machine 8 can also be used as a compressor in a boost operating mode of the internal combustion engine 2 . In this case, the electric machine 8 drives the rotor 6 and thus increases the degree of compression of the intake air for the self-igniting internal combustion engine 2. This increases the charging of the internal combustion engine 2, so that its drive power also increases. The boost operating mode allows the use of combustion engines with reduced displacement, which brings about the efficiency gains typical of this "downsizing".

The invention was explained in more detail with reference to exemplary embodiments, but is not restricted by the examples disclosed. Variations of the invention can be derived by a person skilled in the art from the exemplary embodiments without departing from the protective scope of the invention as defined in the claims.

Reference List

1

motor vehicle

2

combustion engine

3

inlet manifold

4

exhaust manifold

5

booster

6

rotor

7

bypass valve

8th

electric machine

9

electrical system

10

exhaust gas recirculation throttle

11

compressor

12

exhaust turbine

13

air filter

14

exhaust aftertreatment device

15

Exhaust

16

exhaust gas recirculation

17

exhaust gas recirculation valve

18

exhaust gas recirculation cooler

19

intercooler

20

wastegate

Claims (8)

A method for operating a self-igniting internal combustion engine (2) with an intake air section (13, 11, 19, 5, 3) which is designed to supply an intake air flow to the internal combustion engine (2) and which has a compressor (11) of an exhaust gas turbocharger (11, 12), an electric machine (8) connected to a rotor (6) arranged in the supply air flow and one located from an exhaust tract (4, 12, 20, 14, 15) of the internal combustion engine (2) to one downstream of the rotor (6). exhaust gas recirculation (16) leading to the feed point and in which the exhaust gas recirculation (16) is designed without an exhaust gas recirculation valve (17), the method having a step of setting a desired exhaust gas recirculation rate in a throttle operating mode of the internal combustion engine (2), in which the electric machine (8) is operated in a generator mode and depending on the desired exhaust gas recirculation rate, the power thus drawn from the supply air flow being fed to an on-board electrical system (9). The method of the preceding claim, in which the electric machine (8) is operated in a boost operating mode of the internal combustion engine (2) in a motor operating mode and a boost pressure of the internal combustion engine (2) is thereby increased. The method of the preceding claim, in which, in the boost operating mode, the supply air flow is routed completely over the rotor (6) connected to the electric machine (8). The method of one of the preceding claims, in which, in the throttle operating mode, a variably predeterminable part of the supply air flow is routed past the rotor (6) connected to the electric machine (8). A self-igniting internal combustion engine (2) with an intake air tract (13, 11, 19, 5, 3), which is designed to supply the internal combustion engine (2) with an intake air flow, and a compressor (11) of an exhaust gas turbocharger (11, 12), a with a inside the rotor (6) arranged in the intake air flow and has an exhaust gas recirculation system (16) leading from an exhaust tract of the internal combustion engine (2) to a feed point located downstream of the rotor (6), characterized by a control unit which is designed to Method of carrying out one of the preceding claims and characterized in that the exhaust gas recirculation (16) is designed without an exhaust gas recirculation valve (17). The internal combustion engine (2) of the preceding claim, with a bypass valve (7) arranged in parallel with the rotor (6). The internal combustion engine (2) of one of the Claims 5 or 6 , in which the rotor (6) and the electric machine (8) are parts of an electric compressor. A motor vehicle (1) with an internal combustion engine (2) according to one of Claims 5 until 7 .

Images