GB2337792A

GB2337792A - I.c. engine turbocharger with compressor by-pass

Info

Publication number: GB2337792A
Application number: GB9912198A
Authority: GB
Inventors: Rosario Pepe; Alexander Stefani; Klaus Wunderlich
Original assignee: DaimlerChrysler AG
Current assignee: Daimler AG
Priority date: 1998-05-30
Filing date: 1999-05-25
Publication date: 1999-12-01
Anticipated expiration: 2019-05-25
Also published as: ITRM990337A1; IT1306564B1; FR2779180B1; GB2337792B; DE19824476A1; FR2779180A1; ITRM990337A0; DE19824476B4; GB9912198D0

Abstract

In a spark-ignition internal combustion engine with an exhaust-gas turbocharger, in the lower part-load mode a compressor bypass 6 of the inlet line 8 is opened, the said compressor bypass 6 bypassing the compressor 4. At the same time, the compressor 4 is driven, free of load, by the charger turbine 3 driven by exhaust gas and is kept in rotation. In the event of an increase in the operating load, the compressor 4, already rotating at high speed, can generate the desired boost pressure with a short response time. There is provision for monitoring the charger speed and for opening a turbine-bypassing bypass (waste gate) of the exhaust-gas line when a predetermined limit speed is reached, and for thus counteracting a load-free increase in speed of the turbocharger 2.

Description

1 Internal combustion engine with an exhaust-gas turbocharger 2337792 The

invention relates to a supercharged internal combustion engine and to a method of operating an internal combustion engine with an exhaust-gas turbocharger.

The power output of a spark-ignition internal combustion engine is proportional to the air throughput which is proportional to the air density, so that, as is known, the power can be increased, with the same stroke volume and engine speed, by precompressing the air before it enters the cylinder or cylinders, that is to say by supercharging. Supercharging can be carried out by means of an exhaust-gas turbocharger which consists essentially of two turbo-machines connected fixedly in terms of rotation to one another. A turbine is arranged in an exhaust-gas line of the internal combustion engine and is driven by the exhaust-gas stream. The turbine, via the rotationally fixed connection of a charger shaft, drives the compressor which generates a boost pressure in the inlet line to the internal combustion engine.

When the spark-ignition internal combustion engine is in operation, the required mass flow of intake air is set for the respectively applicable operating point by means of throttle members which are provided. When the spark-ignition internal combustion engine is being supercharged in the lower part-load range, however, there is the disadvantage that the compressor has to operate against the flow resistance of the throttle member. In this case, the rotational movement of the turbine is impeded, so that the exhaust-gas stream is built up in front of the turbine. Consequently, during the outlet stroke, the pistons of the internal combustion engine, in the gas exchange process, have to push out the exhaust gases counter to the exhaust-gas counterpressure which is increased due to the build-up, so that the efficiency of the internal combustion engine is reduced. It is known, for the purpose of reducing the exhaust-gas counterpressure, to open a bypass (waste gate) of the exhaust-gas line, the said bypass extending round the turbine. When the waste gate is open, the exhaust gas flows through the exhaust-gas line, at the same time bypassing the turbine, with the result that the charger speed is rapidly reduced because the boost pressure reacts on the compressor. In the case of a load increase, the necessary boost pressure must be generated, for which purpose the turbocharger has to be accelerated again. However, 2 the response time of the turbocharger until acceleration to the necessary speeds, along with the corresponding compressor power, is very long, so that the spark-ignition internal combustion engine reacts sluggishly to a sudden load demand.

In order to improve the response behaviour of the exhaust-gas turbocharger, US 4,774,812 proposes an arrangement, in which the inlet line has a compressor bypass which bypasses the compressor and which is to be opened when the internal combustion engine is in the lower part-load mode. In the known arrangement, a throttle valve is arranged in each case both in the compressor bypass and in the inlet line branch, in which the compressor itself is arranged, the said throttle valves in each case being conn ected to a control unit via a control line for the purpose of receiving actuating corn mands. The part-streams of intake air flowing through the two parallel line branches are determined by setting the two throttle valves in coordination with one another.

Arranged downstream of the mouth of the compressor bypass line is a third throttle valve which determines the mass flow of combustion air ultimately entering the internal combustion engine. Together, the two throttle valves in the parallel line branches, namely the compressor bypass branch and compressor line branch, form the actuator of a boost- pressure control, the command variable of which is determined by means of a boost-pressure sensor and is entered in the control unit. The boost- pressure sensor is arranged in the inlet line downstream of the third throttle valve influencing the mass flow. The boost pressure can be varied by a variation of the intake-air part-stream led through the compressor. The flow through the compressor bypass is to be increased in the lower part-load range of the known spark-ignition internal combustion engine, whilst, in the full-load mode, the throttle valve in the compressor bypass is closed, so that the entire intake-air stream is supplied through the compressor, that is to say with a high boost pressure. The turbine is thereby driven by the exhaust-gas stream, even in the lower part-load range, and drives the compressor which operates in the idling mode due to the low air throughput. At a low boost pressure, therefore, the exhaust-gas turbocharger is operated in the idling mode, but at a higher speed. In the event of a sudden load cut-in, only slight acceleration to the speed required is thereby necessary, so that the response time of the turbocharger is reduced.

1.

3 The speed of the turbocharger is determined, during idling, by the exhaust-gas mass flow. At a high outlay in terms of construction and regulation for coordinating the settings of the two throttle valves, it is still very complicated to maintain the desired high charger speed in the lower part-load range of an internal combustion engine. Furthermore, when the known spark-ignition internal combustion engine is in operation, signs of wear of the charger running mechanism repeatedly appear very quickly, this being attributable to the frequent existence of excessive charger speeds during idling when the internal combustion engine is in specific operating states The present invention seeks to provide an internal combustion engine which makes it possible for the exhaust-gas turbocharger to operate reliably with a long life, along with a good response behaviour to load increases and optimum efficiency of the internal combustion engine, and to specify a method for operating such an internal combustion engine.

According to the present invention there is provided an internal combustion engine with an exhaust-gas turbocharger, a compressor of which is arranged in an inlet line of the internal combustion engine and is connected fixedly in terms of rotation to a turbine which is arranged in an exhaust-gas line of the internal combustion engine, a compressor bypass of the inlet line, the said compressor bypass bypassing the compressor and being capable of being opened by a shut-off member which is connected to a control unit via a control line in order to receive actuating commands as a function of the load state of the internal combustion engine, a bypass of the exhaust-gas line, the said bypass bypassing the turbine and having a waste-gate valve capable of being switched by the control unit, a device for measuring the rotational speed of the exhaust-gas turbocharger and the measurement-signal line of which is connected to the input side of the control unit, a maximum charger speed being predetermined for the control unit as a characteristic value for opening the waste-gate valve when the compressor bypass is open.

The invention also provides a method for operating an internal combustion engine with an exhaust-gas turbocharger, the compressor of which is driven 4 in an inlet passage of the internal combustion engine by a turbine which is acted upon by the exhaust-gas stream of the internal combustion engine, in a load range of the internal combustion engine between idling and part load, a compressor bypass of the inlet passage being opened as a result of the opening of a shut-off member and the fresh-air stream, bypassing the compressor, flowing through the inlet passage, wherein, in the circulating-air mode, with the compressor bypass opened, the charger speed (nATL) is monitored, and a bypass bypassing the turbine is opened when a predetermined limit speed is reached.

There is provision, according to the invention, for opening the compressor bypass in the lower part-load range, a control unit setting the shut-off member of the compressor bypass as a function of the load state of the internal combustion engine and, on detecting a higher load demand, delivering an actuating command to the shut-off member in order to close the compressor bypass. After the compressor has been bridged by the bypass in the idling mode and kept in rotation by the turbine acted upon by exhaust gas, boost pressure can instantaneously be generated in the inlet line at the speed which already prevails. In the circulating- air mode under part load, the compressor is therefore operated without any build-up of pressure, and the internal combustion engine sucks in the required fresh air through the compressor bypass. The exhaust-gas turbocharger is assigned a device for measuring the rotational speed, the measurement-signal line of which is connected to the input side of the control unit. In the circulating-air mode, the control unit monitors the speed of the charger running mechanism which, of course, in the idling mode, is determined essentially by the exhaust-gas mass flow acting on the turbine. Maximum charger speed is predetermined as a characteristic value for the control unit, and when this characteristic value is reached a bypass (waste gate) extending round the turbine and belonging to the exhaust-gas line is opened. When the charger speed increases in the circulating-air mode, with the compressor bypass opened, on account of a higher air throughput of the internal combustion engine, and therefore a higher exhaust-gas pressure, the waste-gate valve is opened when the limit speed is reached, and the exhaust gas bypasses the turbine. This counteracts any further acceleration of the charger. Signs of wear of the charger running mechanism are therefore reduced and the hitherto possible mechanical fracture of individual components of the exhaust-gas 1.

turbocharger as a result of clearly excessive charger speeds is ruled out.

The shut-off member of the inlet line is advantageously a valve capable of changing over between a position acting on the compressor and a position opening the inlet bypass in the circulating-air mode. The circulating-air valve capable of changing over between two positions ensures that, in the idling mode, the entire intakeair mass flows through the compressor bypass to the internal combustion engine. The inlet line branch having the compressor is shut off in the circulation mode, so that the compressor can rotate without any resistance and the efficiency of the exhaust-gas turbocharger and the efficiency of the spark-ignition internal combustion engine are thereby increased. The circulating-air valve is changed over as a function of the operating load of the internal combustion engine, which the control unit determines from at least one operating parameter of the internal combustion engine. Operating parameters which may be used for this purpose are the engine speed, the engine torque, the ignition timing or the setting of a throttle member acting on the fresh-air stream.

If the passage cross section of the waste-gate valve is adjustable, the charger speed can be influenced by a corresponding setting of the exhaustgas mass stream by means of the waste gate. A In a development of the invention, there is provision, in the supercharging mode, with the compressor bypass closed, and when the internal combustion engine is under higher operating loads, to regulate the boost pressure downstream of the compressor by adjusting the throughput of the waste gate. The control unit comprises a regulator for the boost pressure of the internal combustion engine, the waste-gate valve forming the actuator for boost-pressure control. A boost pressure predetermined in relation to a specific operating point is set by means of regulating control measures on the passage cross section of the waste- gate valve and the associated blow-off of a specific exhaust-gas part- stream through the waste gate.

In the dynamic mode, in the event of a load jump with an increase in the operating load of the internal combustion engine, the waste-gate valve and the circulating-air valve are transferred into the closing position, so that the necessary boost pressure can be made available. If there is a change from the circulating-air mode to the supercharging mode as a result of a load increase, the control unit first closes the circulating- air valve and immediately thereafter activates the boost-pressure control, in 6 which the waste-gate valve is activated. The boost-pressure control is activated as a function of the charger speed.

The invention is also suitable for improving the operating behaviour of those spark-ignition internal combustion engines, in which the intake-air stream, instead of being set by a throttle valve, is set by a valve mechanism of the gas exchange valves which is operable variably in terms of opening time andlor passage cross section. In the case of variable valve controls which operate, for example, on the principle of the springmass oscillator, it is therefore also possible, starting from higher speeds of the internal combustion engine, to reduce the load into the low part-load region, since an immediate drop in the boost pressure occurs as a result of the opening of the circulating-air valve. A uniform pressure level, without boost pressure, can be produced for load control in the part-load range according to the time cross section of the inlet valves which is determined by the opening duration and/or valve stroke.

An exemplary embodiment of the invention is explained in more detail below with reference to the drawing.

The single drawing figure shows a spark-ignition internal combustion engine 1 with an exhaust-gas turbocharger 2, the compressor 4 of which is arranged in an inlet line 8 of the internal combustion engine and is connected fixedly in terms of rotation to a turbine 3 by means of a charger shaft 7. The turbine 3 is arranged in an exhaust-gas line 9 of the internal combustion engine and is thus acted upon by the exhaust-gas stream when the internal combustion engine is in operation. The exhaustgas pressure acting on the turbine 3 is transmitted, via the rigid connection of the charger shaft 7, to the compressor 4 which, set in rotation by the turbine 3, compresses fresh air in the inlet line 8 and supercharges the internal combustion engine 1. The inlet line 8 has a compressor bypass 6 which bypasses the compressor 4 and which can be opened by a circulating-air valve 16. The circulating-air valve 16 can be changed over between two positions and determines whether the intake-air stream 17 is to flow through the bypass 6 in the circulating-air mode of the internal combustion engine, in the lower part-load range, or through the compressor 4 in the supercharging mode. The exhaust-gas line 9 of the internal combustion engine has a waste-gate bypass 5, through which the exhaust-gas stream, bypassing the turbine 3, can be led to the outlet. When a waste-gate valve 15, which controls the waste-gate bypass 5, is opened, the exhaust- 1 7 gas pressure on the turbine 3, and therefore the drive of the turbocharger, is reduced.

The circulating-air valve 16 and the waste-gate valve 15 are activated by an electronic control unit 10. One or more operating parameters of the internal combustion engine are entered in the control unit 10, in order to determine the operating load of the internal combustion engine 1 from these. In the embodiment shown, when the internal combustion engine is in operation, the engine speed n, the engine torque Md, the ignition timing ZZP and the setting of a throttle member acting on the fresh-air stream 17 are detected and are entered in the control unit 10. When a throttle valve in the inlet line 8 of the internal combustion engine is used as a throttle member, the instantaneous throttle valve angle is entered in the control unit 10 as a characteristic value aD of this operating parameter. In spark-ignition internal combustion engines, the intake-air mass flow of which is set by a valve mechanism of the gas exchange valves which is capable of being set variably in terms of opening time and/or passage cross section, the instantaneous position of the valve control edges of the variable valve control is entered in the control unit 10 as the characteristic value aD. The control unit 10 has access to an engine characteristic diagram, in which characteristic values of the operating parameters and the associated operating load are stored. The engine characteristic diagram comprises further data relating to the control times of the gas exchange valves as a function of the operating point.

When the control unit 10 detects the presence of low load demands on the basis of the entered operating parameters, it generates opening actuating commands for the circulating-air valve 16 which are delivered to the latter by means of a control line 12. In the circulating-air mode, the circulating-air valve 16 is transferred via the control line 12 into the position opening the bypass 6. The waste gate 5 is kept essentially closed in the circulating-air mode, so that the turbine 3 is driven by the exhaust-gas stream. The compressor 4 co-rotates, free of load, without generating any boost pressure in the inlet line 8. When the operating load of the internal combustion engine changes within the part- load range, the circulating-air valve continues to remain in the circulating-air position. This ensures that no boost pressure is built up, that is to say atmospheric suction conditions prevail. Since the control times applied in the engine characteristic diagram for the gas exchange valves at a part-load operating point corresponds to an exact air quantity sucked in under atmospheric conditions, the air 8 density should not fluctuate. If, however, the operating load of the engine increases abruptly from part load to full load, the circulating- air valve 16 is changed over, in order to allow the build-up of boost pressure by means of the compressor. The compressor 4 is already in rotation at the changeover time, so that, in the event of a load increase, the exhaust-gas turbocharger 2 responds immediately and the necessary boost pressure is instantaneously made available. In addition to the changeover of the circulating-air valve and the associated shut-off of the compressor bypass, the waste gate 5, which may possibly be opened slightly, is also closed, in order to promote the build-up of boost pressure.

The exhaust-gas turbocharger 2 is assigned a device 11 for measuring the rotational speed. A measurement-signal line 14 of the speed counter 11 of the charger running mechanism is connected to the input side of the control unit 10. In the circuIating-air mode, with the compressor bypass 6 opened, the control unit 10 monitors the charger speed nATL, a maximum charger speed being predetermined as a characteristic value for opening the waste-gate valve 15. When the limit speed is reached, the control unit 10 causes the waste gate 5 to open and delivers the corresponding control commands to the waste-gate valve 15 by means of an actuatingsignal line 13. The exhaust gas bypasses the turbine 3 through the opened waste gate 5, so that, without any further drive, the rotational speed of the turbocharger, rotating free of any load, cannot be increased any further. The limit speed predetermined for the control unit 10 in order to open the waste gate 5 can be determined beforehand and can be optimized, taking into account the specific properties of the exhaust-gas turbocharger 2 used in each case, for example the manufacturer's speed recommendations or the specific througliflow behaviour of the turbine 3 and compressor 4.

The control unit, via the actuating-signal line, controls an actuating drive, not illustrated here, of the waste-gate valve 15, the said actuating drive accurately setting the passage cross section of the wastegate valve 15, that is to say of the bypass 5. When the internal combustion engine is in the supercharging mode, with the compressor bypass 6 closed, the boost pressure is regulated, the waste-gate valve 15 forming the actuator for boost-pressure control. The control unit 10 comprises a regulator in which the actual value of the boost pressure PL is entered. The boost pressure PL is measured by means of a corresponding pressure sensor in the inlet line 1 9 8. In the circulating-air mode, when tfie internal combustion engine is under a lower operating load, the boost-pressure control is cut out and the waste-gate valve 15 is held in a position reducing the throughflow cross section of the waste gate 5 or in the fully closed position. Insofar as the control unit 10, on the basis of the entered operating parameters n, Md, aD, M, detects when a load point provided for the supercharging mode is reached, the compressor bypass 6 is first closed, and immediately thereafter the boost-pressure control, that is to say the variable adjustability of the waste-gate valve 15, is activated for blowing off the exhaust gas via the waste-gate bypass 5. The boost- pressure control is cut in again as a function of the charger speed nATL.

In the case of throttle-free load controls, for example due to the use of a variable valve mechanism with variable valve opening cross sections, constant pressure conditions, without the build-up of boost pressure, are achieved in the partload range, so that reproducible cylinder fillings can be obtained.

Claims

Claims

An internal combustion engine with an exhaust-gas turbocharger, a compressor of which is arranged in an inlet line of the internal combustion engine and is connected fixedly in terms of rotation to a turbine which is arranged in an exhaust-gas line of the internal combustion engine, a compressor bypass of the inlet line, the said compressor bypass bypassing the compressor and being capable of being opened by a shut-off member which is connected to a control unit via a control line in order to receive actuating commands as a function of the load state of the internal combustion engine, a bypass of the exhaust-gas line, the said bypass bypassing the turbine and having a waste-gate valve capable of being switched by the control unit, a device for measuring the rotational speed of the exhaust-gas turbocharger and the measurementsignal line of which is connected to the input side of the control unit, a maximum charger speed being predetermined for the control unit as a characteristic value for opening the waste-gate valve when the compressor bypass is open.
2. An internal combustion engine according to Claim 1, wherein the shut off member of the inlet line is a circulating-air valve capable of changing over between a position acting on the compressor and a position opening the inlet bypass in the circulation mode.
3. An internal combustion engine according to Claim 1 or 2, wherein the passage cross section of the waste-gate valve is adjustable, an actuating drive of the waste-gate valve being capable of being activated by the control unit via an actuating signal line.
4. An internal combustion engine according to Claim 3, wherein the control unit comprises a regulator for the boost pressure (PL) of the internal combustion engine, the waste-gate valve forming the actuator for boost-pressure control.

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5. An internal combustion engine according to any one of Claims 1 to 4, including a valve mechanism of the gas exchange valves which is capable of being set variably in terms of opening time and/or passage cross section.
6. An internal combustion engine according to any one of Claims 1 to 5, comprising a spark-ignition engine.
7. A method for operating an internal combustion engine with an exhaust gas turbocharger, the compressor of which is driven in an inlet passage of the internal combustion engine by a turbine which is acted upon by the exhaust-gas stream of the internal combustion engine, in a load range of the internal combustion engine between idling and part load, a compressor bypass of the inlet passage being opened as a result of the opening of a shut-off member and the fresh-air stream, bypassing the compressor, flowing through the inlet passage, wherein, in the circulating-air mode, with the compressor bypass opened, the charger speed (nATL) is monitored, and a bypass bypassing the turbine is opened when a predetermined limit speed is reached.
8. A method according to Claim 7, wherein, in the circuIating-air mode, that line branch of the inlet passage which has the compressor is shut off.
9. A method according to Claim 7 or 8, wherein a control unit changes over a circulating-air valve arranged in the inlet passage between a position acting on the compressor and a circulating-air position, with the compressor bypass opened, as a function of the operating load of the internal combustion engine.
10. A method according to Claim 9, wherein the operating load is determined from at least one operating parameter of the internal combustion engine.
11. A method according to Claim 10, wherein the operating parameter(s) comprise one or more of, the engine speed, the engine torque, the ignition timing or the setting of a throttle member acting on the fresh-air stream.

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12 12. A method according to'any one of Claims 7 to 11, wherein, in the supercharging mode, with the compressor bypass closed, the boost pressure is regulated as a result of the setting of the throughput of the waste gate by means of a waste-gate valve arranged in the waste-gate line and functioning as an actuator.
13. A method according to any one of Claims 7 to 12, wherein, in the event of a change from the circulating-air mode to the supercharging mode as a result of a load increase, the control unit first changes over the circulating-air valve and closes the compressor bypass and subsequently activates the boost-pressure control and the activation of the waste-gate valve as a function of the charger speed.
14. A method according to any one of Claims 7 to 13 wherein, in the dynamic mode, in the event of a load jump with an increase in the operating load of the internal combustion engine, the compressor bypass and the waste gate are closed.
15. An internal combustion engine with an exhaust-gas turbocharger, substantially as described herein, with reference to and as illustrated in, the accompanying drawing.