WO2006108580A1

WO2006108580A1 - Method for adjusting an exhaust gas turbocharger

Info

Publication number: WO2006108580A1
Application number: PCT/EP2006/003215
Authority: WO
Inventors: Joachim Augstein; Marcus Reissing
Original assignee: Daimlerchrysler Ag
Priority date: 2005-04-09
Filing date: 2006-04-07
Publication date: 2006-10-19
Also published as: DE102005016392B3

Abstract

The invention relates to a method for adjusting an exhaust gas turbocharger (2) for a supercharged internal combustion engine (1), the method including a speed limit. The invention is characterized by setting a highest admissible speed (nATL_max_soll) of the exhaust gas turbocharger (2) for an actual operating point (BP_ist) of the compressor or the internal combustion engine (1) depending on an actual exhaust gas temperature (TAB_ist) of the internal combustion engine (1). The inventive method is mainly used in the automobile industry.

Description

Method for controlling an exhaust gas turbocharger

The invention relates to a method for regulating an exhaust gas turbocharger for an internal combustion engine charged by means of a compressor.

From the document DE 103 20 978 B3 a method for controlling an exhaust gas turbocharger for an internal combustion engine is known, which in addition to a speed monitoring over the entire operating range of the exhaust gas turbocharger and a speed monitoring to protect against excessive speeds of the exhaust gas turbocharger. An air-fuel ratio is determined by measuring an air ratio in the exhaust gas tract of the internal combustion engine. Depending on the air ratio is closed to the speed of the exhaust gas turbocharger.

A load of the exhaust gas turbocharger beyond a certain thermal and mechanical limit, can lead to the destruction of the exhaust gas turbocharger. So that the exhaust-gas turbocharger does not exceed its mechanical and thermal limit, a permissible exhaust-gas turbocharger rotational speed as a function of a maximum permissible exhaust-gas temperature is usually specified as the limit value for monitoring the exhaust-gas turbocharger. The allowed Exhaust gas turbocharger speed and the maximum permissible exhaust gas temperature apply to continuous operation of the exhaust gas turbocharger. If this maximum permissible exhaust gas temperature due to overshoots is exceeded, there is no speed protection for the turbocharger.

It is the object of the invention to provide a method for controlling an exhaust gas turbocharger for a supercharged by means of a compressor internal combustion engine, which in addition to an increase in performance brings about improved reliability of the exhaust gas turbocharger.

According to the invention, a method for controlling an exhaust-gas turbocharger for an internal combustion engine charged by means of a compressor is provided, in which a permissible maximum rotational speed of the exhaust-gas turbocharger is specified as a function of a current exhaust-gas temperature of the internal combustion engine for a current operating point of the compressor or the internal combustion engine. Maximum permissible speeds of the exhaust gas turbocharger are shown as a function of exhaust gas temperatures of a limit line. The exhaust gas turbocharger can be operated in its actual, maximum possible speed range, wherein the performance of the exhaust gas turbocharger and the internal combustion engine can be increased taking into account a thermal and a mechanical safety limit. The full load consumption and the emissions of the internal combustion engine can be reduced, since a higher exhaust gas temperature can be permitted at low and medium engine speeds, whereby a combustion air ratio λ with a value of 1 can be achieved.

In one embodiment of the method according to claim 2, depending on a speed difference of the exhaust gas turbocharger, which is determined from the maximum permissible speed and a current exhaust gas turbocharger speed, and a current operating point of the compressor or the internal combustion engine determines a correction factor. This leads to an improvement of the control quality of a control loop.

In a further embodiment of the method according to claim

3, a virtual operating point to be specified for the compressor or the internal combustion engine is preferably determined as a product of the correction factor and of a virtual, predetermined operating point of the compressor or of the internal combustion engine.

In a further embodiment of the method according to claim

4, a wastegate or a variable turbine geometry or an axial slide of a turbine of the exhaust-gas turbocharger is regulated as a function of the virtual, predetermined operating point for rapid speed control.

Further features and advantages of the invention will become apparent from the claims and the following description taken in conjunction with the drawings.

Showing:

Fig. 1 is a schematic representation of a control and

Control unit of an internal combustion engine with an exhaust gas turbocharger,

2 shows an example of a characteristic diagram of a compressor,

Fig. 3 is a schematic representation of a limit line permissible maximum speeds of an exhaust gas turbocharger in dependence on exhaust gas temperatures of a Internal combustion engine and

Fig. 4 is a schematic representation of the structure of the control of the exhaust gas turbocharger according to the invention.

In Fig. 1 is a schematic representation of a control and control unit of an internal combustion engine 1 with an exhaust gas turbocharger 2 is shown. The internal combustion engine 1, a gasoline or a diesel engine ,, is equipped with the exhaust gas turbocharger 2 and a control and control unit 3. In this control and control unit 3 operating points BP of the internal combustion engine 1 and / or a compressor, not shown, of the exhaust gas turbocharger 2 are controlled or controlled. The internal combustion engine 1 and the exhaust gas turbocharger 2 are connected to each other via pipes not shown. Although the internal combustion engine 1 and the exhaust gas turbocharger 2 are not mechanically, but thermodynamically coupled with each other.

2 shows an example of a characteristic diagram of the compressor, not shown, of the exhaust gas turbocharger 2 of the internal combustion engine 1, wherein a corrected air mass flow mL_korr and an ordinate of the characteristic field a pressure ratio πV are plotted on an abscissa of the characteristic field. The pressure ratio πV results from a division of a boost pressure at a compressor output of the compressor by a suction pressure at a compressor inlet of the compressor, wherein the pressures contain pressure losses.

The corrected air mass flow mL_korr of the map represents an air mass flow mL conveyed by the compressor, which is multiplied by a correction factor KORR__1. The correction factor KORR_1 results from the equation CORR 1 = V ¹ «- I

Pti where T _t i denotes a total temperature upstream of the compressor and P _t i a total pressure upstream of the compressor.

The usable map area is limited to the left, in the direction of small air mass flows through the so-called surge limit P. The pumping limit P of the compressor should not be exceeded during operation. Too small air mass flows, the flow of vanes of the compressor dissolves. The delivery process becomes unstable. The air flows backwards through the compressor until a stable pressure ratio is restored. The pressure builds up again. The process is repeated in quick succession. This creates a noise, the so-called pump noise. The surge limit P of the compressor is shown in dashed lines.

Solid lines provided with diamonds represent constant rotational speeds nATL_korr of the compressor or the exhaust gas turbocharger 2. The rotational speeds nATL are corrected in the same way as the air mass flows mL and are multiplied by a correction factor KORR_2. The correction factor KORR_2 results from the equation

The correction factors KORR_1 and KORR_2 reduce the values of the air mass flow and the rotational speeds to values that are independent of the intake temperature T _t i and the intake pressure p _t i at the time of the measurement. They normalize the characteristic map, as a result of which this characteristic map can also be used for other intake temperatures T _t i and intake pressures p _t i.

Efficiencies η _{v of} the compressor are represented by thin, solid lines. A dotted line represents a maximum efficiency at a corrected air mass flow mL_korr and a pressure ratio πV in the compressor map.

Furthermore, an engine intake line M is registered. This indicates, depending on an engine speed and a load, which air mass flow mL_korr is required by the internal combustion engine 1 at a specific pressure ratio πV of the compressor. In the example shown, the required air mass flow mL_korr increases with increasing

Engine speed and increasing load. The pressure ratio πV also increases with increasing engine speed and load, but decreases again at very high engine speeds and very high load.

Thus, in the case of a known map of the compressor and known engine intake line M during operation of the internal combustion engine 1, an optimum virtual operating point BP_setpoint of the compressor can be predetermined for each operating point of the internal combustion engine 1. This means that a control method of the exhaust gas turbocharger 2 as a function of operating points of the compressor further improves the control quality of the method.

3 shows a basic representation of a limit value line TAB_nATL of a permissible maximum rotational speed of the exhaust gas turbocharger 2 as a function of an exhaust gas temperature TAB of the internal combustion engine 1.

The exhaust gas turbocharger 2 has a thermal and a mechanical load limit. The thermal load limit value represents a maximum temperature TAB_max of the gas flowing through a turbine, in the case of the internal combustion engine 1 a maximum temperature TAB max of Exhaust gas that should not be exceeded. Exceeding this maximum temperature TAB_max leads to material damage to the turbine, for example to so-called "hot spots", which are punctual damage to turbine blades.

The mechanical load limit is indicated by a maximum speed nATL_max_max of the exhaust gas turbocharger 2. Exceeding this maximum speed nATL_max_max leads to a mechanical destruction of the exhaust gas turbocharger 2 due to the very high centrifugal forces.

The maximum speed nATL_max_soll depends on the exhaust gas temperature TAB of the internal combustion engine 1. The higher this exhaust gas temperature TAB, the lower the maximum permissible speed nATL_max_soll. Usually, a limit speed nATL_max_H for the operation of the exhaust gas turbocharger 2 has previously been indicated as the maximum permissible speed nATL_max_soll, which was determined as a function of the permissible maximum temperature TAB_max. The surface hatched in Fig. 3 shows the usually unused temperature and speed range of an exhaust gas turbocharger 2. In the control of the exhaust gas turbocharger 2 by means of the limit line TAB_nATL is determined for each exhaust gas temperature TAB of the internal combustion engine 1 a maximum speed nATL_max_soll and specified for operation. This maximum speed nATL_max_max is at least as large as the limit speed nATL_max_H. At an exhaust gas temperature TAB, which is lower than the maximum temperature TAB_max, the exhaust gas turbocharger 2 can be operated at a rotational speed nATL_max_soll that is greater than the rotational speed nATL_max_H. This higher speed nATL_max_soll of the exhaust gas turbocharger 2 results in an increase in output of the exhaust gas turbocharger 2. By determining the maximum permissible speed nATL_max_soll as a function of the exhaust gas temperature TAB of the internal combustion engine 1, the thermal operating limit is also monitored. In the case of a short-term occurrence of exhaust gas temperatures TAB, which are greater than the maximum permissible maximum temperature TAB_max, the determination of the maximum permissible speed nATL_max_soll by means of the limit line TAB_nATL operates the exhaust gas turbocharger 2 in a short-term permissible operating range.

Operating the exhaust gas turbocharger 2 along the dashed line with a distance A to the illustrated limit line TAB__nATL is also possible.

The permissible maximum speeds nATL_max_soll can also be represented in the form of value pairs or in the form of a characteristic diagram or as a function of the exhaust gas temperature TAB.

4 shows a schematic representation of a structure for the inventive regulation of the exhaust gas turbocharger 2, which is embedded in the control and control unit 3.

Starting point for the control of the exhaust gas turbocharger 2 are three state variables of a current operating state of the internal combustion engine 1 and a current operating state of the exhaust gas turbocharger 2.

The first state variable is a current exhaust gas temperature TAB_act of the exhaust gas of the internal combustion engine 1. It results from the current operating state of the internal combustion engine 1. The current exhaust gas temperature TAB_act can be determined via a simulation or a measurement. The second state variable is a current pressure ratio πV_ist at the compressor in the current operating state of the exhaust gas turbocharger 2. This pressure ratio πV_ist is determined as the quotient of a current pressure p _t2 after the compressor to a current pressure p _t i before the compressor.

The third state variable required for regulation is the current air mass flow mL_act taken in by the compressor. This air mass flow mL_ist is converted by means of the explained conversion to a corrected air mass flow mL_korr_ist.

The air mass flow mL, the pressures pti and p _t 2 and the temperature T _t i are measured by means of sensors and possibly corrected with the aid of suitable models. Likewise, the air mass flow mL, the pressures p _t i and p _t 2 and the temperature T _t i could also be simulated.

The exhaust gas temperature TAB_ist is supplied to a first block 4. This block 4 stores the limit value line TAB_nATL shown in FIG. The limit value line TAB_nATL is in the form of pairs of values, one pair being formed by an exhaust gas temperature TAB and a maximum rotational speed nATL_max_soll permissible for this exhaust gas temperature. The limit line TAB_nATL could also be in the form of a function.

The exhaust gas temperature TAB_ist is compared in the block 4 shown in FIG. 4 with the stored exhaust gas temperatures TAB. From this comparison, a maximum permissible speed nATL max, which belongs to the exhaust-gas temperature TAB_act, is determined. The compressor pressure ratio πV_ist and the air mass flow mL_korr_ist are fed to a block 5. In this block 5, a map Kl is stored, which represents the map of the compressor shown in Fig. 2. The compressor pressure ratio πV_ist and the air mass flow mL_korr_ist characterize a single, specific exhaust gas turbocharger rotational speed current nATL_korr_ist, which is determined in the block 5 shown in FIG. 4 with the aid of the compressor pressure ratio πV_act and the air mass flow mL_korr_ist. The current, uncorrected speed of the exhaust gas turbocharger 2 nATL_ist is determined by multiplying the exhaust gas turbocharger speed nATL__korr_ist by the reciprocal of the correction factor KORR_2.

The output quantities nATL_max_soll and nATL_ist from block 4 and block 5 are subtracted in a block 6 and the differential rotational speed ΔnATL is fed to a block 7: ΔnATL = nATL_max_set - nATL_act.

An operating point BP_act of the compressor, which is determined from the corrected air mass flow mL_korr_act and the compressor pressure ratio πV, is determined as the second input variable to the block 7 as follows:

mL is corr

BP is = = =

^~ πV is

If the permissible maximum speed nATL_max_soll is smaller than the current exhaust-gas turbocharger speed nATL_act, the exhaust-gas turbocharger speed must be reduced in order to avoid damaging the exhaust-gas turbocharger 2. Thus, to improve the quality of control an appropriate Speed reduction of the exhaust gas turbocharger 2 can be performed, in block 7, a correction factor FAK in

Dependence of the exhaust gas turbocharger speed difference ΔnATL and the current operating point BP_ist of the compressor is determined from a characteristic map K2. The map K2 represents a dependency of the correction factor FAK on different ones

Depending on the current operating point BP_actual and differential rotational speed ΔnATL, a correction factor FAK results between 0 and 1. The greater the differential rotational speed ΔnATL, the smaller the correction factor FAK. If, for example, the correction factor FAK is determined to be 0.95, the virtual, predetermined operating point BP_setpoint must be reduced by 5%.

The correction factor FAK indicates a percentage change of a virtual, predetermined operating point BP_setpoint of the compressor. This virtual, predetermined operating point BP_soll describes a virtual operating point of the compressor, from which results, the current, real, operating point BP_act of the compressor.

In a block 8, the virtual, predetermined operating point BP_setpoint of the compressor is multiplied by the correction factor FAK. The output from block 8 is a virtual, prespecified operating point BP_reg of the compressor. Depending on the determined virtual, to be specified operating point BP_reg, a wastegate of a turbine of the exhaust gas turbocharger 2 for fast

Speed reduction can be adjusted by blowing off exhaust gas in front of the turbine. Likewise, for speed reduction, a turbine cross-sectional area of a variable turbine geometry or a cross-sectional area of a Entry diameter of the turbine can be adjusted by an axial slide.

The method is suitable both for mono-turbo engines, as well as for bi-turbo engines. For bi-turbo engines, the air mass flow mL conveyed by the compressors must be halved. The further procedure corresponds to the method described.

In this exemplary embodiment, the regulation of the exhaust-gas turbocharger 2 is carried out by means of the current operating point BP_act of the compressor, the operating point BP_reg of the compressor to be preset, and the predetermined operating point BP_setpoint of the compressor.

Likewise, an operating point of the internal combustion engine 1 could be used for control. The map of the compressor in block 1 is retained. The map K2 in block 7 would have dependencies of the differential speed ΔnATL of corresponding, used for control operating characteristics of the internal combustion engine 1. The virtual, predetermined operating point BP_soll and the virtual operating point BP_reg to be specified would be operating points of operating characteristic values of the internal combustion engine 1.

Claims

claims

A method for controlling an exhaust gas turbocharger for a supercharged by a compressor internal combustion engine ,, wherein the method comprises a speed limitation, characterized in that for a current operating point (BP_ist) of the compressor or the internal combustion engine (1) a maximum permissible speed (nATL_max_soll) of the exhaust gas turbocharger (2) depending on a current exhaust gas temperature (TAB_ist) of the internal combustion engine (1) is specified.

2. The method according to claim 1, characterized in that in dependence on a speed difference (ΔnATL), which is determined from the maximum permissible speed (nATL_max_soll) and a current exhaust gas turbocharger speed (nATL_ist), and the current operating point (BP_ist) of the compressor or the internal combustion engine ( 1) a correction factor (FAK) is determined.

3. The method according to claim 2, characterized in that a virtual, prespecified operating point (BP_reg) of the compressor or the internal combustion engine (1) as a product of the correction factor (FAK) and a virtual, predetermined operating point (BP_soll) of the compressor or the internal combustion engine ( 1) is determined.

4. The method according to claim 3, characterized in that in response to the virtual, predetermined operating point (BP_reg) a wastegate or a variable turbine geometry or an axial slide of a turbine of the exhaust gas turbocharger (2) is controlled.

5. The method according to any one of claims 1 to 4, characterized in that the current operating point (BP_ist) is determined as a quotient of a current air mass flow (mL_korr_ist) and a current pressure ratio (πV_ist).

6. The method according to any one of claims 1 to 4, characterized in that the current operating point (BP_soll) is determined as a quotient of a current air mass flow (mL_korr_soll) and a current pressure ratio (πV_soll).