WO2017139822A1

WO2017139822A1 - Method for operating an internal combustion engine

Info

Publication number: WO2017139822A1
Application number: PCT/AT2017/060030
Authority: WO
Inventors: Hans Felix Seitz
Original assignee: Avl List Gmbh
Priority date: 2016-02-19
Filing date: 2017-02-15
Publication date: 2017-08-24
Also published as: AT518258B1; AT518258A4

Abstract

The invention relates to a method for operating an internal combustion engine (1) comprising an inlet system (3) and an outlet system (4), in particular for driving a motor vehicle, wherein a first compressor (10) is driven by exhaust gas via a shaft and a second compressor (13) is driven electrically, mechanically or hydraulically, wherein fresh air successively flows through the second compressor (13) and the first compressor (10) in an inlet line (11) of the inlet system (3), wherein the second compressor (13) is activated in at least one motor-braking operation of the internal combustion engine (1) and the flow cross-section is reduced in at least one exhaust gas line (7) of the outlet system (4), preferably up to a defined effective residual flow cross-section (A_eff). The braking power (P_B) can be increased if the effective residual flow cross-section (A_eff) is determined according to the following equation: formula (I) where A_eff is effective residual flow cross-section; D_Vi is the internal valve seat diameter of at least one outlet valve; N_Valve is the number of outlet valves per cylinder (2); N_Cyl is the number of cylinders (2) connected to the exhaust gas line (7) having the effective residual flow cross-section (A_eff); C is a factor in the region of 1% and 12%.

Description

Method for operating an internal combustion engine

The invention relates to a method for operating an internal combustion engine with an intake system and an exhaust system, in particular for driving a motor vehicle, wherein a first compressor via a shaft of the exhaust gas and a second compressor is electrically, mechanically or hydraulically driven, wherein the second compressor and the first Compressor are successively flowed through in an intake passage of the intake system of fresh air, wherein in at least one engine braking operation of the internal combustion engine, the second compressor is activated and the flow cross-section in at least one exhaust line of the exhaust system - preferably down to a defined effective residual flow cross section - is reduced.

Heavy-duty vehicles are typically equipped with engine braking devices to increase engine braking power when driving downhill. Such engine braking devices often have a brake flap in the exhaust system, with which the exhaust back pressure and thus the gas exchange work can be increased during engine braking operation.

From EP 2 634 405 AI an exhaust gas engine brake for an internal combustion engine is known. The braking force is increased by increasing the internal exhaust pressure. The internal combustion engine has an exhaust gas turbocharger whose compressor speed can be increased by an electric motor. Similar arrangements are also known from EP 2 634 403 A1 and EP 0 385 622 AI.

Publications JP 2009/228448 A, DE 421 0070 C1, JP H 11 324 692 A, GB 2 499 823 A and JP S 5967537 U disclose internal combustion engines each having an intake and an exhaust system, wherein an exhaust-operated first compressor and an electric, mechanically or hydraulically driven second compressor is arranged in the inlet system, wherein the second compressor and the first compressor are successively flowed through by fresh air. During engine braking operation, the second compressor is activated and the flow cross-section in the exhaust system of the exhaust system is reduced.

The object of the invention is to increase the engine braking power in an internal combustion engine.

According to the invention, this is done by determining the effective residual flow cross-section according to the following equation: With

ARMS. , , effective residual flow cross section

Dvi. , ..inner valve seat diameter of at least one exhaust valve

Nvaive -. , , Number of exhaust valves per cylinder

Ncyi. , , , Number of cylinders that are connected to the exhaust line with the effective residual flow cross-section

C ... factor in the range of 1% and 12%

A further increase in the engine braking power can be achieved if, at least during engine braking operation, the drive power for the electrically driven second compressor is provided directly by a generator, preferably the generator, of the internal combustion engine.

In the engine braking operation of the internal combustion engine, a combustion chamber decompression mode is advantageously activated, wherein the control time of at least one exhaust valve per cylinder is preferably adjusted in order to carry out the combustion chamber decompression so that the work performed by the internal combustion engine in the compression stroke is left unused for the following cycle. In this case, for example, an outlet valve or an additional valve is opened at the end of the compression stroke and thus the pressure built up in the cylinder during the compression stroke is reduced. This allows a further increase in the engine braking torque.

For carrying out the method according to the invention, an internal combustion engine of the aforementioned type is suitable, in which the second compressor can be activated in at least one engine braking mode of the internal combustion engine, which is preferably bypassable via a compressor bypass line.

In a preferred embodiment of the invention, the second compressor is disposed in the intake manifold of the intake system upstream of the first compressor. Alternatively, it is also possible to arrange the second compressor downstream of the first compressor in the inlet branch.

In order to increase the exhaust backpressure in the exhaust system in engine braking operation, it is advantageous if at least one brake valve is arranged in the exhaust system of the exhaust system, preferably downstream of the exhaust gas turbine. The brake valve can be formed in a simple manner by a brake flap. As an alternative to the brake flap, it is also possible to use a variable turbine geometry of the exhaust gas turbine for adjusting the flow cross section.

The invention will be explained in more detail below with reference to the non-limiting embodiment illustrated in the figures. Show: 1 shows an internal combustion engine for carrying out the method according to the invention;

FIGS. 2 and 3 show a comparison of the engine braking powers for different effective residual cross sections of the brake valve when using the method according to the invention with the engine braking power according to the prior art; and

4 shows the method according to the invention in a block diagram.

1 shows an internal combustion engine 1 with, for example, six cylinders 2, an inlet system 3 for an inlet flow and an outlet system 4 for an exhaust gas flow. Downstream of an exhaust manifold 5, an exhaust gas turbine 8 of an exhaust gas turbocharger 9 is arranged, the first compressor 10 is arranged in the intake manifold 11 of the intake system 3.

Reference numeral 14 denotes an intercooler of the intake system 3 and reference numeral 15 denotes an air filter.

To increase the exhaust gas back pressure in the exhaust system 4, a control member 16 is arranged, which is formed in the embodiment shown in FIG. 1 as a downstream of the exhaust gas turbine in the exhaust line 7 arranged brake flap. Alternatively, the control member 16 may be formed by a variable turbine geometry of the exhaust gas turbine 8.

In the exemplary embodiment, the exhaust gas turbine 8 is designed with a bypass valve 6 (wastegate) arranged in a turbine bypass line 5.

Upstream of the first compressor 10, a second compressor 13, which is operated electrically via an electric motor 12, is arranged in the inlet branch 11. The second compressor 13 arranged downstream of the air filter 15 can be bypassed via a second compressor bypass line 17, in which a check valve 18 is arranged.

In the diagram shown in FIG. 2, different operating parameters such as braking power PB, medium pressure BMEP, braking torque TB and heat input Q are plotted in the cylinder head over the engine speed n for various engine braking strategies SO, SI, S2, S3, S4. FIG. 3 shows a characteristic diagram in which the pressure ratios CPR between the first compressor 10 and the second compressor 13 are plotted against the corrected air mass flow q _m . In FIG. 2 and FIG. 3, reference numeral SO designates an engine braking strategy known from the prior art, in which the pressure increase in the exhaust gas system 7 occurs only over a largely closed brake flap during engine braking operation. sl, S2, S3 and S4 designate engine braking strategies according to the invention, in which the charge pressure in the intake line is increased by means of the electrically driven second compressor 13 and the brake valve 16 is closed with differently sized remaining cross ^sections , the line S l for the largest residual cross section and S4 stands for the least residual cross section. The residual cross-section at S2 is smaller than at S l, the residual cross-section at S3 is smaller than at S2. Deut ^¬ Lich can be seen that the Bremsleistu ng PB is better, the smaller the residual cross-section of the Bremsventi ls 16 in the closed state.

In braking operation, the braking valve 16 designed as a brake flap is initially closed, with a small residual flow cross section remaining open and thus establishing a specific gas flow over the brake flap (usually brake lever position "1" in the utility vehicle).

By activating the combustion chamber decompression, the engine brake is switched on (for example, brake lever position 2). As a next step, the electrically driven second compressor 13 is switched on and it builds boost pressure in egg nlasssystem 3 of the internal combustion engine 1. The boost pressure significantly increases braking power as more air in the combustion chambers is compressed and decompressed. The boost pressure is electrically generated inde pendent ^¬ n from the engine speed and there is a high braking power PB even at low engine speed n.

Since the second compressor 13 promotes the residual flow cross section A _e ff in the brake flap, the mass flow q _m can be suitably adjusted by the engine: If the residual flow cross section A _e ff is made too small, the second compressor 13 can build up high pressure and high braking power PB is reached, but it is not enough air through the internal combustion engine 1 geför ^¬ changed. Since the braking energy is converted into heat, so not enough heat can be dissipated and the engine would thermally overloaded over ^¬ .

Is the effective Restström ungsquerschnitt A _e ff in the brake flap led to great from ^¬ or too small a brake flap integrated into the system, the second compressor 13 may n ot enough air into the system to promote or ranges due to limited electrical performance of the electrical system, the Map width of the second compressor 13 is not sufficient to cover the required area.

The effective Restström ungsquerschnitt A _e ff of the brake flap can thereby be approximately determined m it fol ^¬ gender formula: With

ARMS. , , effective residual flow cross section of the brake valve

Dvi .... inner valve seat diameter of the exhaust valves

Nvaive -. , , Number of exhaust valves per cylinder

Ncyi. , ..Number of cylinders connected to the brake valve

C ... factor in the range of 1% and 12%

The effective residual flow cross section A _e ff can be achieved by a partial targeted opening of the brake flap or by open cross sections in the closed brake flap (for example bores).

In Fig. 4, the inventive method for achieving the desired high braking performance in a variant by the example of a control over gas temperature T _A (for example, the fresh air downstream of the second compressor 13 in the intake system 3 or the exhaust gas in the exhaust system 4) is shown, but it is also the regulation of other limiting parameters such as speed of the electric second compressor 13 or gas pressure in the intake system 3 or exhaust system 4 vorschellbar. The control can be done via sensors and maps in a control loop on the running internal combustion engine 1. Alternatively, a suitable selection of the design parameters such as compressor drive power and opening degree of the brake flap during the design and testing phase of the internal combustion engine 1 can take place and incorporated as a fixed geometry in the engine concept or be stored as maps in the engine control.

Depending on the desired braking power is in in Fig. 4 illustrated embodiment, the first brake stage BS l, the second brake stage BS2 or the third brake stage BS3 switched. In the first braking stage BS1, the brake valve 16 is closed except for a defined effective residual flow cross-section A _e ff. In the second brake stage BS2, a combustion chamber decompression mode is activated, wherein, for example, at least one exhaust valve per cylinder is opened constantly or cyclically close to the top dead center of the ignition. In the third braking position BS3, the second compressor 13 is additionally driven via the electric motor 12.

In step BS4, it is checked whether the gas temperature T _G exceeds a maximum value T _G max. If this is the case ("y"), the effective residual flow area Aeff is increased by opening the brake valve 16. If the gas temperature TA is not greater than the defined maximum value TGmax, it is checked in step BS5 whether the desired braking power PB _{s is} reached. If this is not the case ("n"), the drive power of the second compressor 13 is increased. The drive power for the electrically driven second compressor 13 can be generated directly from the alternator of the internal combustion engine 1 during braking operation - the required drive power of the generator increases the braking power of the internal combustion engine 11.

Claims

P A T E N T A N S P R E C H E

Method for operating an internal combustion engine (1) with an intake system (3) and an exhaust system (4), in particular for driving a motor vehicle, wherein a first compressor (10) via a shaft of the exhaust gas and a second compressor (13) electrically, mechanically or is driven hydraulically, wherein the second compressor (13) and the first compressor (10) successively in an intake passage (11) of the intake system (3) are flowed through by fresh air, wherein in at least one engine braking operation of the internal combustion engine (1) of the second compressor (13 ) is activated and the flow cross section in at least one exhaust line (7) of the exhaust system (4) - preferably down to a defined effective residual flow cross-section (Aeff) - is reduced, characterized in that the effective residual flow cross-section (A _e ff) is determined according to the following equation :

With

Aeff ... effective residual flow cross section

Dvi .. ..inner valve seat diameter of at least one exhaust valve

Nvaive. , , Number of exhaust valves per cylinder (2)

Ncyi. , .. Number of cylinders (2), which are connected to the effective residual flow cross-section (Aeff) having exhaust line (7)

C ... factor in the range of 1% and 12%

A method according to claim 1, characterized in that at least in the engine braking operation, the drive power for the electrically driven second compressor (13) directly from a generator, preferably the alternator, the internal combustion engine (1) is provided.

A method according to claim 1 or 2, characterized in that engine braking operation of the internal combustion engine (1) a Brennraumdekompressions- mode is activated, preferably for performing the combustion chamber decompression, the control time of at least one exhaust valve per cylinder (2) is adjusted.

Internal combustion engine (1) having an intake system (3) and an exhaust system (4), in particular for driving a motor vehicle, with at least one of them - preferably via a turbine bypass line (5). walkable - exhaust gas turbine (8) and one of these via a shaft driven first compressor (10) having exhaust gas turbocharger (9), and an electrically, mechanically or hydraulically driven second compressor (13), wherein the second compressor (13) and the first compressor (10) are arranged successively in an intake branch (11) of the intake system (3), wherein in at least one engine braking operation of the internal combustion engine (1) - preferably via a compressor bypass line (17) bypassable - second compressor (13) can be activated to perform the Method according to one of claims 1 to 3, characterized in that the brake valve (16) in the closed state has an effective residual flow cross-section (Aeff) wherein preferably the effective residual flow cross-section (Aeff) is dimensioned according to the following equation:

With

ARMS. , , effective residual flow cross section of the brake valve (16)

Dvi. , ..inner valve seat diameter of at least one exhaust valve

Nvaive -. , , Number of exhaust valves per cylinder (2)

Ncyi. , ..Number of cylinders (2) connected to the brake valve (16) C ... Factor in the range of 1% to 12%

Internal combustion engine (1) according to claim 4, characterized in that the second compressor (13) in the inlet branch (11) of the inlet system (3) upstream of the first compressor (10) is arranged.

Internal combustion engine (1) according to claim 4 or 5, characterized in that in the exhaust line (7) of the exhaust system (4) - preferably downstream of the exhaust gas turbine (8), at least one brake valve (16) is arranged.

Internal combustion engine (1) according to claim 6, characterized in that the brake valve (16) is formed by a brake flap.

2017 02 15

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