AT522942A2 - COMBUSTION ENGINE - Google Patents

Abstract

The invention relates to an internal combustion engine (1) with an exhaust gas turbocharger, which has a turbine (T) and a compressor (v) which are connected to one another via a shaft (W), the compressor (V) being connected to a shaft (W) electrical machine (E) is connected and the compressor (V) is connected to an inlet line of the internal combustion engine (1) so that the compressor (V) supplies the internal combustion engine (1) with compressed gas - in particular air -, with the connection to the inlet line a bypass line (8) is provided which connects the compressor (V) with the outlet line upstream of the turbine (T), and in which a heat exchanger (5) is provided, which is arranged in an exhaust system and through which the exhaust gas flows according to the countercurrent principle. The task is to increase the efficiency (η). This is achieved in that a valve (9) is arranged in the bypass line (8), whereby the mass flow () through the turbine (T) can be regulated or controlled by means of the valve (V).

Description

The invention relates to an internal combustion engine with an exhaust gas turbocharger, which has a turbine and a compressor which are connected to one another via a shaft, the compressor being connected to an electrical machine via the shaft and the compressor being connected to an inlet line of the internal combustion engine, so that the Compressor supplies the internal combustion engine with compressed gas, in particular air, with a bypass line being provided in the connection to the inlet line, which connects the compressor to the outlet line upstream of the turbine, and in which a heat exchanger is provided, which is arranged in an exhaust system and - especially in

Countercurrent principle - the exhaust gas flows through it.

An exhaust gas turbocharger is understood here to mean an arrangement of the turbine and compressor on a common shaft. The energy of the exhaust gas in the turbine of the exhaust gas turbocharger is used to drive the compressor.

Such an internal combustion engine is known from EP 3 078 824 A1. This internal combustion engine has a heat exchanger in the exhaust system. This heat exchanger extracts heat from the waste heat that otherwise leaves the internal combustion engine unused with the exhaust gas. The heat exchanger is flowed through on the warm side by exhaust gas and on the cold side by compressed gas from the inlet branch. The compressed gas is fed directly from the compressor to the turbine via the heat exchanger. Heat exchange takes place with the exhaust gas both downstream and upstream of the turbine with the compressed gas.

The disadvantage of this arrangement is that the exhaust gas turbocharger is designed only for one operating point at which the efficiency of the internal combustion engine is at its maximum. The optimal conditions for achieving this level of efficiency

however, are not consistently achieved.

The efficiency of the internal combustion engine is of great interest because it

Fuel consumption and pollutant emissions can be reduced.

The object of the present invention is a more efficient internal combustion engine

to specify.

This object is achieved according to the invention by the above internal combustion engine and a vehicle with such an internal combustion engine in that a valve is arranged in the bypass line, with the mass flow by means of the valve

can be regulated or controlled by the turbine.

This has the advantage that the mass flow is regulated and thus the compressor and turbine can work at the same optimum operating point. For example, in the case of transient processes, the boost pressure can be increased as quickly as possible

being constructed.

Another benefit of this arrangement arises simply from the fact that a backflow from the outlet branch can be counteracted even in particularly unfavorable operating points. This reverse current would occur if the

Pressure in the exhaust system exceeds the pressure in the inlet branch.

This object is also achieved by an associated method for operating such an internal combustion engine.

For this purpose, a map of the turbine is stored in which an optimal mass flow is assigned to each pressure ratio and the valve in the bypass line is opened when a current mass flow is less than the optimal one

Mass flow.

This measure enables turbines and compressors to be operated in a very narrow range in their respective characteristic field. This makes the question of interpretation easier. Operation at the best point is easily possible thanks to the valve, since the operating point in the map is simple due to the influence of the mass flow

can be moved along a line of constant pressure ratio.

In order to be able to react as quickly as possible to the demands on the turbine, it is advantageous if the valve in the bypass line is upstream of the

Heat exchanger is arranged.

Alternatively, it is also possible for the valve to be arranged in the bypass line downstream of the heat exchanger. This can be due to the

Requirements for the packaging of the entire vehicle may be necessary.

It is advantageous if the heat exchanger is arranged downstream of the turbine in the exhaust system. This makes optimal use of the residual heat in the exhaust system.

For the most timely and automatic control or regulation of the valve, an advantageous embodiment of the invention provides a control unit in which a characteristic map of the turbine is and / or can be stored. The associated procedure provides that in a

Working step the map is stored in a control unit.

The map shows the pressure ratio over the mass flow. Lines of constant efficiency and speed characterize the operation of the

Exhaust gas turbocharger.

In order to be able to control the speed of the shaft and thus of the exhaust gas turbocharger independently of the operating state of the internal combustion engine, it is advantageous if the electrical machine is designed as a motor and / or a generator. To do this, the electric machine regulates the speed of the compressor and the turbine. In addition, the generator can be used to recuperate the excess energy and the electrical machine recuperates energy as a generator in an operating range - preferably with the valve closed.

In order to increase the overall efficiency as much as possible, it is advantageous if the compressor has at least one impeller with backswept impeller blades. Backswept is the common name for curved back

Impeller blades on compressors.

Operation can be kept in the optimum efficiency range of the characteristic diagram for as long as possible if it is provided that the valve closes when the current mass flow essentially corresponds to the amount of the optimum mass flow.

In order to facilitate the control and to counteract an overshoot process, it is advantageous if the valve is opened until the current mass flow reaches a tolerance range around the optimal mass flow and

closes in the tolerance range.

It is beneficial if the control unit determines the range in which the current mass flow is located in the characteristics map. For this purpose, the mass flow is measured or determined.

In the following, the invention will be explained with reference to the non-restrictive figures

explained in more detail. Show it:

1 shows an internal combustion engine according to the invention;

2 shows a map of a radial compressor;

3 shows a characteristic diagram of a compressor with a backswept impeller;

4 shows a first characteristic map of a compressor according to the invention

Internal combustion engine;

5 shows a first profile of two operating variables of the internal combustion engine;

6 shows a second profile of two operating variables of the internal combustion engine;

7 shows a third curve of two operating variables of the internal combustion engine;

8 shows a schematic representation of a method according to the invention in the characteristic map;

FIG. 9 shows the characteristics map from FIG. 8 with additional explanations; FIG.

10 shows the characteristics map of the compressor of a conventional internal combustion engine;

11 shows a schematic representation of the course of an operating variable of the method according to the invention in comparison with a conventional method;

and

12 shows the characteristics map of the compressor of the internal combustion engine according to the invention.

1 shows an internal combustion engine 1 according to the invention with an exhaust gas turbocharger. This has a compressor V, an electrical machine E and

a turbine T on. The compressor V, the electric machine E and the turbine T

are mechanically connected to one another via a common shaft W.

The internal combustion engine 1 shown has an inlet line which extends from an inlet 2 of the compressor V, at which fresh air is sucked in, via an intercooler 3 and an inlet manifold 4 to cylinders Z.

The air is compressed in the compressor V and heated as a result. The air is cooled again in the intercooler 3 before the air is introduced into the cylinder Z. In cylinder Z, fuel is burned together with the air and is discharged into the outlet branch by piston movement of the pistons (not shown in detail). The heated exhaust gas slides to the turbine T and is expanded there. As a result of this relaxation, kinetic energy is given off to the turbine T and with it the shaft W rotates around the axis A and drives the compressor V with it.

The compressor V can also be driven by the electrical machine E.

In certain operating points it is possible to recover excess energy through the electrical machine E by using it as a generator. That will be in the

Generally referred to as recuperation.

The exhaust gas is passed on after the turbine T into the exhaust system, not shown in detail. There the exhaust gas is cleaned of pollutants

Catalysts and particle filters and the further cooling takes place.

After the turbine T, the exhaust gas flows through a heat exchanger 5 for releasing part of the usable heat still present in the exhaust gas.

In the embodiment shown, a branching line 6 with a flap 7 is arranged in front of the turbine. Exhaust gas is routed past the turbine to the exhaust system via this branching line 6. This happens when the mass flow through the internal combustion engine cannot be processed at the turbine T.

A branch is also provided from the compressor V to the intercooler 3 and leads into a bypass line 8. In this bypass line, a valve 9 is arranged, which adjusts the mass flows m. In order to prevent the exhaust gas from flowing back into the inlet manifold 4 during partial load operation, the valve 9

be advantageously designed as a check valve.

The bypass line 8 leads to the heat exchanger 5. The heat exchanger 5 is traversed by the compressed air from the compressor V using the countercurrent principle. This means that the exhaust gas on the hot side of the heat exchanger 5 has its highest temperature at the first end of the heat exchanger. The air coming from the compressor V has its lowest temperature at the second end of the heat exchanger. Over the length of the heat exchanger, heat is transferred from the exhaust gas to the compressed air, thus changing the temperature level on the opposite side. The compressed air at the first end of the heat exchanger has the highest temperature and the exhaust gas has the lowest temperature at the second

End on.

In alternative implementations, other types of heat exchangers can be used

will.

From the heat exchanger 5, the compressed air is introduced into the exhaust gas upstream of the turbine T. As a result, a current mass flow is Maxtueun through the

Turbine T reached.

In the embodiment shown, the valve 9 is arranged upstream of the heat exchanger 5 and the turbine T. In other versions there is also an arrangement

of the valve 9 downstream of the heat exchanger 5 and upstream of the turbine T is possible.

The cylinders Z and the intercooler 3 are bypassed through the bypass line 8, in other words that means that the cylinder Z and the intercooler 3 are bypassed by the flow through the bypass line 8

and lead to turbine T on a different route.

In the embodiment shown, the internal combustion engine 1 has six Z cylinders. The cylinders Z are arranged on two cylinder banks of three cylinders Z each on a cylinder bank, separated by the axis A, opposite one another. The two cylinder banks share the inlet manifold 4. The arrangement shown here

corresponds in common usage to that of a V6 engine.

The branch into the bypass line 8 from the compressor V to the heat exchanger 5 is provided upstream of the intercooler 3. In alternative versions there is also a

Branch before entry into cylinder Z and after intercooler 3 is possible.

FIGS. 2 and 3 each show a characteristic map for a compressor. The two compressors are of different types. There is a mass flow in it

m a pressure ratio = plotted. The lines of constant efficiency n are 1

each labeled with the efficiency achieved within the closed line.

The inclined line shows the delimitation of the map by the surge line P. The area in which the flow occurs during operation of the is above the surge line P

Compressor breaks off because the mass flow for a certain pressure ratio 2 to

D1

is low. This can lead to a reversal of the direction of the flow, as the pressure levels cannot be maintained. Therefore, when operating the compressor, care must be taken to ensure that the surge limit P is on the right in the map

are located.

The operating range or the width of the characteristic map of the compressor depends in part on the design of the impeller of the compressor, such as the type and number of impeller blades and their twist.

If these impeller blades are designed in such a way that they have a certain proportion of what is known as a backsweep, a map is achieved which has higher peak compression efficiencies at the expense of the breadth of the map. The reduced width of the map makes it more difficult to adapt to the engine applications. Backsweep could be translated

or backswept analogously as curved back.

In contrast to normal radial impellers, backswept impellers have a blade angle that varies over the height of the impeller. By using backswept impellers, the efficiency can be reduced, especially at low

Speeds can be increased.

In Fig. 2, a compressor map for a compressor with a conventional radial impeller is shown. In comparison, FIG. 3 shows a compressor map for a compressor with a backswept impeller. This increases the achievable efficiency from 80% to 85%.

The disadvantage, however, is that this type of construction of the impellers reduces the width of the characteristic field. In other words, the mass flow range in

which a certain efficiency n at a certain pressure ratio =

1

can be achieved becomes smaller. This makes the use of backswept

Impellers for exhaust gas turbochargers are practically impossible.

The compressor needs a linearly increasing pressure ratio> over the 1st

different mass flows m to be able to work efficiently. The compressor requires a broad map for the conditions of an internal combustion engine.

In order to be able to deliver a constant torque, the compressor must

provide a constant pressure ratio%, as when operating along a first

D1

Line a in Fig. 4 is shown. To achieve constant performance, the

Compressor a constant mass flow m for different pressure ratios%

1

as when operating along a second line b in FIG. 4.

For this reason, the efficiency n of a compressor of a full-load-optimized internal combustion engine compared to a gas turbine, which only

requires a narrow operating range, significantly lower. The line c represents the operation that reaches the maximum efficiency n.

FIGS. 5 to 7 show individual operating variables over a speed n of an exemplary internal combustion engine at full load of the internal combustion engine. 5 shows the output torque M of the internal combustion engine over speed n, FIG. 6 shows a boost pressure p of the internal combustion engine over speed n, and FIG. 7 gives a fuel mass flow mg over speed n.

However, the method according to the invention makes it possible to use this efficiency-increasing structural measure without any problems, as is clearly demonstrated on the basis of FIG. 8.

Curves k represent lines of constant compressor speed.

On the one hand, the losses are partially compensated for by heating the compressed air at the heat exchanger 5 with the exhaust gas. The greatest advantage and gain in efficiency result from the changed flow conditions at the compressor V: At lower speeds n and high boost pressures p, a higher mass flow mpypass is passed through the bypass line 8 to the turbine T.

At high speeds n and low boost pressures p, a lower mass flow Myypass is branched off. This turns the compressor V in a lot

smaller operating range in the map than with conventional internal combustion engines

operated.

The mass flows result as follows:

Mpypass 5 Moptimai 7 Mz

Moprimaı is the optimal mass flow through the compressor V and m „is the mass flow that is fed to the intercooler 3 and the cylinders Z. The optimal mass flow mMopeimaı is chosen in such a way that the highest achievable

Efficiency n is achieved.

These mass flows are not in the position of the valve 9 of the

Control unit shown in the figures regulated or controlled.

By bypassing the cylinder Z, the operating point BPv of the compressor V in the target pressure ratio DV is shifted to the right in the map. The target pressure ratio DV is the pressure ratio that is necessary to maintain efficient operation at a certain speed n. Thus, the operating point BPv is the operating point with the highest efficiency at this compressor speed.

The control unit makes estimates to regulate or control the method. A maximum efficiency n of the compressor V

can be achieved.

The mass flow rate myypass of the bypass line 8 for a specific speed n

results as the difference between the optimal mass flow rate Moprimaı UNd dem

Mass flow ıh7 of compressed air through the cylinder Z each for one

certain speed n.

To calculate the correct mass flow rate m, ypass of the bypass line, one must calculate the optimal mass flow rate moprimaı Dei for the target pressure ratio DV. For this you need the maximum efficiency of the compressor NcompressorMax. In the entire map as well as the pressure ratio DV, compressor max.) AND the mass flow mMy_ (compressor max.) DEiIM Maximum efficiency. Mass flow

Makxtueun for a certain speed n results from the following formula:

m; Moptimaı (DV) = DV En. C CompressorMax) DV,

_ (CompressorMax.)

In words, this means that the optimum mass flow Mopeimaı (DV) increases linearly with the pressure ratio at a specific target pressure ratio DV, corrected with the mass flow ratio at maximum efficiency

My _compressor max.) TO pressure ratio at maximum efficiency DV, compressor max.) *

The mass flow 17 through the cylinder Z at the speed n results in

the following product:

m (n) _ PvorCompressor * DV (n) * TEintass (n) * n (n) x n + * 2

Dyor compressor is the pressure upstream of the compressor V, DV (n) is the target pressure ratio at speed n. 7ginass (N) is the inlet temperature at speed n. N.gxu (nm) stands for the volumetric efficiency of the

Internal combustion engine 1, Vz for the cylinder volume and h for the engine stroke.

In a comparison between the conventional method and the method according to the invention in FIGS. 10 to 12, the lines d and e show the operation of the compressor V at different speeds n. In FIG. 11, the line f for a conventional method is shown in solid lines and the line g for the method according to the invention is shown. FIG. 11 shows the mass flow my through the compressor V over the speed n. It can be seen from FIG. 12 that the operating points

of the compressor V move along the straight line of the highest efficiency n.

Claims (1)

PATENT CLAIMS Internal combustion engine (1) with an exhaust gas turbocharger, which has a turbine (T) and a compressor (V) which are connected to one another via a shaft (W), the compressor (V) being connected to an electrical machine (W) via the shaft (W). E) is connected and the compressor (V) is connected to an inlet line of the internal combustion engine (1), so that the compressor (V) supplies the internal combustion engine (1) with compressed gas, in particular air, with a bypass line ( 8) is provided, which connects the compressor (V) with the outlet line upstream of the turbine (T), and in which a heat exchanger (5) is provided, which is arranged in an exhaust system and through which the exhaust gas flows according to the countercurrent principle, characterized in that, that a valve (9) is arranged in the bypass line (8), the mass flow (Maxtueu) through the turbine (T) being adjustable or controllable by means of the valve (V). Internal combustion engine (1) according to claim 1, characterized in that the valve (9) is arranged in the bypass line (8) upstream of the heat exchanger (5). Internal combustion engine (1) according to claim 1, characterized in that the valve (9) is arranged in the bypass line (8) downstream of the heat exchanger (5). Internal combustion engine (1) according to one of claims 1 to 3, characterized in that the heat exchanger (5) downstream of the turbine (T) is arranged in the exhaust system. Internal combustion engine (1) according to one of Claims 1 to 4, characterized in that a control unit is provided in which a characteristic diagram of the turbine (T) is and / or can be stored. Internal combustion engine (1) according to one of Claims 1 to 5, characterized in that the electrical machine (E) is designed as a motor and / or as a generator. 7. Internal combustion engine (1) according to one of claims 1 to 6, characterized in that the compressor (V) has at least one impeller with backswept impeller blades. 8. Vehicle with an internal combustion engine (1) according to one of claims 1 to 7. 9. The method for operating an internal combustion engine (1) according to one of claims 1 to 8, characterized in that a map of the turbine (T) is stored in which each pressure ratio (3) an optimal Mass flow (Moprimaı) is assigned and that the valve (9) in the bypass line (8) is opened when a current mass flow (Makxtuein) is smaller than the optimal mass flow (Moptimal) - 10. The method according to claim 9, characterized in that the valve (9) closes when the current mass flow (Maxeueun) is essentially the Amount of the optimal mass flow (Mopgimaı) corresponds to. 11. The method according to claim 9 or 10, characterized in that the valve (9) is opened until the current mass flow (Maxtueu) reaches a tolerance range around the optimal mass flow (Mopeimaı) and in Tolerance range closes. 12. The method according to any one of claims 9 to 11, characterized in that the electrical machine (E) has a speed (n) of the compressor (V) and the turbine (T) regulates. 13. The method according to any one of claims 9 to 12, characterized in that the electrical machine (E) in an operating range - preferably with the valve (9) closed - recuperates energy as a generator. 14. The method according to claim 9 to 13, characterized in that the map is stored in a control unit. 15. The method according to claim 14, that the control unit determines in which Range is the current mass flow (Maxtueu) in the map. 2019 12 16