WO2007122499A1

WO2007122499A1 - Control apparatus and control method for internal combustion engine having centrifugal compressor

Info

Publication number: WO2007122499A1
Application number: PCT/IB2007/001060
Authority: WO
Inventors: Masakazu Tabata
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2006-04-25
Filing date: 2007-04-24
Publication date: 2007-11-01
Also published as: EP2010777B1; DE602007004968D1; JP4775097B2; CN101341322A; JP2007291960A; CN101341322B; EP2010777A1

Abstract

The invention calculates a second order differential of at least one of an airflow rate of a centrifugal compressor (26a) (step S 108) and a pressure and a temperature of air in an inlet of the centrifugal compressor. Then, the invention determines whether the calculated second order differential is equal to or greater than a predetermined value (step S 110). If the number of times (counter value) the second order differential is determined to be equal to or greater than the predetermined value reaches or exceeds a threshold value (step S 116), the invention determines that a surge occurs in the centrifugal compressor (26a) (step S 118).

Description

CONTROLAPPARATUS AND CONTROL METHOD FOR INTERNAL COMBUSTION

ENGINE HAVING CENTRIFUGAL COMPRESSOR

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates to a control apparatus and a control method for

an internal combustion engine having a centrifugal compressor.

2. Description of the Related Art

[0002] As described in Japanese Patent Application Publication No. 2005-240683

(JP-A-2005-240683), in a conventional exhaust purification system for an internal

combustion engine, a turbocharger uses the exhaust energy to drive a centrifugal

compressor. The conventional system is designed to detect a surge in the centrifugal

compressor based on fluctuations in intake air volume.

[0003] If a high-boost, high-powered internal combustion engine has a centrifugal

compressor driven by an electric motor, a surge may occur during acceleration. In such an

internal combustion engine, when an incipient surge is not detected, it develops and greatly

dampens acceleration of the engine.

[0004] Thus, incipient surge detection in the centrifugal compressor is required to

avoid the occurrence of a severe surge. However, the conventional surge detection method relies on fluctuations in intake air volume or a difference between intake air volumes (first

order differential). Generally, an intake air volume sharply increases during acceleration

of the internal combustion engine, which can be improperly detected as a surge. Thus, in

the conventional method, in order to avoid such improper detection, fluctuations in intake

air volume greater than the fluctuations that generally occur during acceleration, are only

detected as a surge. Hence, the conventional method suffers from a failure to detect a

slight incipient surge.

SUMMARY OF THE INVENTION

[0005] The present invention provides a control apparatus and a control method for

an internal combustion engine having a centrifugal compressor, which allow more accurate

detection of a slight incipient surge.

[0006] A first aspect of the invention is a control appratus for an internal

combustion engine having a centrifugal compressor in an intake passage, the system

includes: differential calculating means for calculating a second order differential of at least

one of an airflow rate of the centrifugal compressor, and a pressure and a temperature of air

in an inlet of the centrifugal compressor; differential determining means for determining

whether the second order differential calculated by the differential calculating means is

equal to or greater than a predeterminedlevel; and surge determining means for determining whether a surge occurs in the centrifugal compressor if the second order differential is equal

to or greater than the predetermined level.

[0007] A second aspect of the invention is the control apparatus according to the

first aspect, in which the differential determining means determines whether the second

order differential calculated by the differential calculating means is equal to or greater than

a predetermined value, and the surge determining means determines that a surge occurs in

the centrifugal compressor if the second order differential is equal to or greater than the

predetermined value.

[0008] According to the second aspect, the control apparatus detects an inflection

point of pulsations in the airflow rate of the centrifugal compressor, the pressure or the

temperature of air in the inlet of the centrifugal compressor, and also detects large

fluctuations in the airflow rate of the centrifugal compressor, or the pressure or the

temperature of air in the inlet of the centrifugal compressor, which occur before and after

the inflection point. Accordingly, when the airflow rate of the compressor monotonously

increases, a small second order differential results. The small value is therefore not used

in determining whether a surge occurs. Thus, the determination of whether a surge occurs

is made earlier and more accurately.

[0009] A third aspect of the invention is the control apparatus according to the first

aspect, in which the differential determining means determines whether the second order differential calculated by the differential calculating means is equal to or greater than the

predetermined value, and the surge determining means includes storage means for storing a

number of times that the differential determining means determines that the second order

differential is equal to or greater than the predetermined value, and determines that a surge

occurs in the centrifugal compressor when the number of times that the differential

determining means determines that the second order differential is equal to or greater than

the predetermined value reaches or exceeds a threshold value.

[0010] A fourth aspect of the invention is the control apparatus according to the

third aspect, in which the surge determining means determines that a surge occurs when the

number of times that the differential determining means determines that the calculated

second order differential is equal to or greater than the predetermined value reaches or

exceeds the threshold value, the threshold value is lowered as the value of the calculated

second differential increases.

[0011] According to the fourth aspect, earlier detection of a severe surge is achieved,

thereby preventing greatly dampening of the acceleration of the internal combustion engine.

[0012] A fifth aspect of the invention is the control apparatus according to any one

of the first to fourth aspects, in which the surge determining means prohibits the

determination of whether a surge occurs when at least one of following conditions is

satisfied: an opening degree of a throttle valve changes rapidly; the opening degree of the throttle valve is equal to or lower than a predetermined opening degree; a boost pressure of

the intake air is equal to or lower than a predetermined boost pressure; the airflow rate of

the centrifugal compressor is equal to or greater than a predetermined airflow rate; or an

engine speed is equal to or greater than a predetermined engine speed.

[0013] According to the fifth aspect, the condition where there is no possibility of

occurrence of a surge is prevented from being improperly determined as a surge.

[0014] A sixth aspect of the invention is the control apparatus according to any one

of the first to fifth aspects, the control apparatus further including: a bypass passage that

communicably connects an inlet passage and an outlet passage of the centrifugal

compressor; a bypass valve that opens or closes the bypass passage; and bypass valve

control means for opening the bypass valve when the surge determining means determines

that a surge occurs. In addition, the bypass valve control means increases an opening

degree of the bypass valve as the calculated second order differential increases.

[0015] According to the sixth aspect, displacement of the bypass valve is controlled

as appropriate to the magnitude of the surge. This prevents the bypass valve from being

unnecessarily, excessively displaced in an attempt to avoid the surge, and therefore prevents

the internal combustion engine from undesirable operating conditions, which cause poor

driveability.

[0016] A seventh aspect of the invention is the control apparatus according to any one of the first to fifth aspects, the control apparatus further including: a bypass passage that

communicably connects an inlet passage and an outlet passage of the centrifugal

compressor; a bypass valve that opens and closes the bypass passage; and bypass valve

that a surge occurs, and the bypass valve control means opens the bypass valve for a longer

duration as the calculated second order differential increases.

[0017] According to the seventh aspect, the duration for which the bypass valve is

open is controlled in accordance with the magnitude of the surge. This prevents the

bypass valve from being unnecessarily, excessively displaced in an attempt to avoid the

surge, and therefore prevents the internal combustion engine from undesirable operating

conditions, which cause poor driveability.

[0018] An eighth aspect of the invention is a method for controlling an internal

combustion engine having a centrifugal compressor in an intake passage, the method

comprising the steps of: calculating a second order differential of at least one of an airflow

rate of the centrifugal compressor, and a pressure and a temperature of air in an inlet of the

centrifugal compressor; determining whether the calculated second order differential is

equal to or greater than a predetermined level; and determining that a surge occurs in the

centrifugal compressor if the second order differential is equal to or greater than the

predetermined level. BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of the invention will

become apparent from the following description of example embodiments with reference to

the accompanying drawings, wherein like numerals are used to represent like elements and

wherein:

FIG. 1 is a schematic diagram illustrating a configuration of an embodiment of the

invention;

FIG. 2 is a graph showing a relationship between a compressor outlet/inlet pressure

ratio and an airflow rate Ga of the compressor;

FIGs. 3 A and 3B are graphs for describing a method for detecting a surge according to

the embodiment of the invention;

FIG. 4 is a flowchart of a routine to be executed in the embodiment of the invention;

FIG. 5 is a conceptual graph showing the idea of how to determine if a surge occurs

according to the embodiment of the invention;

FIG. 6 is a flowchart of a routine to be executed for controlling a bypass valve in FIG.

1 in the embodiment of the invention; and

FIGs. 7 A and 7B are graphs for showing effects obtained by the method for detecting a

surge according to the embodiment of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] FIG. 1 is a schematic diagram illustrating a configuration of an embodiment

of the invention. As shown in FIG. 1, the system has an internal combustion engine 10.

An intake system in the internal combustion engine 10 includes an intake manifold 12 and

an intake pipe (intake passage) 14 connected to the intake manifold 12. Ambient air is

inducted into the intake pipe 14 and distributed to each cylinder through the intake manifold

12.

[0020] An air filter 16 is provided at an entrance of the intake pipe 14. An airflow

meter 18 is provided adjacent to and downstream of the air filter 16. The airflow meter 18

outputs a signal in response to a flow rate of air drawn by the intake pipe 14. A throttle

valve 20 is provided upstream of the intake manifold 12. An intercooler 22 is provided

upstream of the throttle valve 20. The intercooler 22 cools compressed air. A boost

pressure sensor 24 is located downstream of the intercooler 22. The boost pressure sensor

24 outputs a signal in response to a pressure within the intake pipe 14.

[0021] A turbocharger 26 includes a compressor (centrifugal compressor) 26a

provided in a midsection of the intake pipe 14 extending from the airflow meter 18 to the

intercooler 22. In addition to the compressor 26a, the turbocharger 26 also includes a

turbine 26b. The compressor 26a is driven and rotated by the energy of the exhaust gas flowing into the turbine 26b. The compressor 26a is not limited to being driven by the

turbine 26b using the exhaust energy, but may be driven by other assisting means, such as

an electric motor.

[0022] An intake bypass pipe 28 has a first end connected to a midsection of the

intake pipe 14 extending from the compressor 26a to the intercooler 22. The intake bypass

pipe 28 is a bypass passage that communicably connects an inlet passage and an outlet

passage of the compressor 26a. The intake bypass pipe 28 has a second end connected to

the intake pipe 14 on the upstream side of the compressor 26a. A bypass valve 30 is

located in a midsection of the intake bypass pipe 28. The bypass valve 30 controls the

flow rate of air flowing through the intake bypass pipe 28. When the inlet of the intake

bypass pipe 28 is opened by operating the bypass valve 30, part of air compressed by the

compressor 26a returns toward the inlet of the compressor 26a.

[0023] An intake pressure sensor 32 and a temperature sensor 34 are located

upstream of the compressor 26a. The intake pressure sensor 32 outputs a signal in

response to a pressure within the intake pipe 14. The temperature sensor 34 outputs a

signal in response to an air temperature of the inlet of the compressor 26a.

[0024] An exhaust system in the internal combustion engine 10 includes an exhaust

manifold 36 and an exhaust pipe 38 connected to the exhaust manifold 36. Exhaust gas

from each cylinder of the internal combustion engine 10 is collected in the exhaust manifold 36 and discharged through the exhaust manifold 36 to the exhaust pipe 38.

[0025] A control system in the internal combustion engine 10 includes an electronic

control unit (ECU) 40. The ECU 40 connected to the aforementioned plural types of

sensors. In addition, the ECU 40 is also connected to a throttle position sensor 42 and a

crank angle sensor 44. The throttle position sensor 42 outputs a signal in response to an

opening degree of the throttle valve 20. The crank angle sensor 44 detects an engine speed

NE. The ECU 40 also connects to the aforementioned plural types of actuators. Based

on the outputs from the respective sensors, the ECU 40 drives the associated actuators in

accordance with a given control program.

[0026] Now, a surge in the compressor 26a will be described. FIG. 2 is a graph

showing a relationship between a compressor 26a outlet/inlet pressure ratio and an airflow

rate Ga of the compressor 26a. A thick solid curve in FIG. 2 indicates a surging limit or a

surge line. A hatching area on the left from the surge line is equivalent to a surge area.

In other words, a surge is more likely to occur under the conditions of a higher-pressure

ratio between the inlet and outlet of the compressor 26a and a lower airflow rate Ga of the

compressor 26a. More specifically, a surge tends to occur during acceleration with the

throttle valve fully-opened.

[0027] Should a surge occur during acceleration, opening the bypass valve 30 helps

prevent the surge from developing. However, if an incipient surge is not detected, it develops and greatly dampens acceleration of the internal combustion engine 10. In

contrast, in case of a slight surge, which corresponds to an area adjacent to the surge line in

FIG. 2, the relatively small displacement of the bypass valve 30 suffices for preventing such

surge from developing. This reduces an adverse effect on the acceleration.

[0028] Therefore, the compressor 26a is desirably controlled under the conditions

corresponding to the area adjacent to the surge line in FIG. 2. In order to achieve this,

incipient surge detection is required, that is, detection of a slight surge, which causes

small-amplitude pulsations in the airflow rate Ga of the compressor 26a. Thus, the system

according to the embodiment of the invention detects a surge based on a second order

differential of the airflow rate of the compressor in order to detect a relatively slight

incipient surge more accurately than conventional systems.

[0029] FIGs. 3A and 3B are graphs for describing a method for detecting a surge

according to the embodiment of the invention. More specifically, FIG. 3 A is a graph

illustrating pulsations in the airflow rate Ga of the compressor 26a, which are caused due to

the surge in the compressor 26a, in an enlarged manner. FIG. 3B is a graph for describing

a specific process for detecting a surge.

[0030] The method for detecting a surge according to the embodiment of the

invention relies on the second order differential of the airflow rate Ga of the compressor.

The method includes detecting an inflection point (circled in FIG. 3A) on the pulsation curve of the airflow rate Ga of the compressor. The method determines that a surge occurs

if large fluctuations in airflow rate Ga of the compressor are found before and after the

inflection point.

[0031] More specifically, as shown in FIG. 3B₅ the ECU 40 calculates the

difference between a current measured value (plots in FIG. 3B) and a previously measured

value of the airflow rate Ga of the compressor at predetermined sampling intervals (i.e. a

first order differential (9Ga/9t) of the airflow rate Ga of the compressor on the time series).

Then, the ECU 40 calculates the difference between the obtained current first order

differential and the previous first order differential (i.e. a second order differential

(S²GaZSt²)). If the calculated second order differential is equal to or greater than a

predetermined value, the ECU 40 determines that a surge occurs.

[0032] The first order differentials are of opposite sign before and after the

inflection point, where the airflow rate Ga of the compressor changes from increase to

decrease or from decrease to increase. Thus, the first order differentials reverse in sign,

resulting in a large second order differential, that is, a large difference between these first

order differentials. In contrast, when the airflow rate Ga of the compressor monotonously

increases or decreases, fluctuations in airflow rate Ga of the compressor are large.

Accordingly, the resultant first order differentials are large. Therefore, the second order

differential, that is a difference between these large first order differentials, is not as large as the value obtained from the first order differentials of opposite sign.

[0033] As described above, the method for detecting a surge according to the

embodiment of the invention, which uses a second order differential, allows more accurate

detection of large fluctuations in airflow rate Ga of the compressor before and after the

inflection point on the pulsation curve. This enables more accurate detection of an

incipient surge regardless of the magnitude of the surge (pulsations). In this embodiment,

the difference between adjacent measured values of the airflow rate Ga of the compressor is

calculated to obtain a second order differential. However, the invention is not limited to

this manner. Alternatively, a higher-order equation shown below as (1) may be used to

obtain a more precise second order differential.

Second order differential = (-Gal + 16Ga2 - 30Ga3 + 16Ga4 - Ga5)/12Δt²...(l),

where Gal to Ga5 represent measured values of the airflow rate Ga of the compressor,

respectively. Gal indicates the current measured value. Increases in the number after Ga

indicate older values.

[0034] FIG. 4 is a flowchart of a routine that is executed by the ECU 40 to achieve

the aforementioned functions according to the embodiment of the invention. The ECU 40

executes this routine periodically at predetermined sampling intervals. In the routine

shown in FIG. 4, first the airflow rate Ga of the compressor 26a is acquired based on a

signal output from the airflow meter 18 (step SlOO). [0035] Then, the measured airflow rate Ga of the compressor, which is acquired in

step SlOO, is set as the current value Gal. Accordingly, the prior current value Gal and

previous value Ga2 are set as the previous value Ga2 and the second previous value Ga3,

respectively (step S 102).

[0036] Then, the ECU 40 determines whether the current operating conditions of the

internal combustion engine 10 are appropriate for determining whether a surge occurs (step

S104). More specifically, in step S104, if any of the following conditions is satisfied, a

determination of whether a surge occurs is prohibited. The conditions are that: the throttle

opening degree changes rapidly; the throttle opening degree is equal to or lower than a

predetermined opening degree; the boost pressure is equal to or lower than a predetermined

boost pressure; the airflow rate Ga of the compressor 26a is equal to or greater than a

predetermined airflow rate; and the engine speed NE is equal to or greater than a

predetermined engine speed.

[0037] In step S 104, if at least one of the conditions is satisfied, which indicates that

there is a possibility of improper surge determination or there is no possibility a surge

would occur, the ECU 40 determines that no surge occurs, and resets a counter value (step

S 106).

[0038] In contrast, in step S 104, if none of the aforementioned conditions are

satisfied, the ECU 40 determines that the operating conditions of the internal combustion engine 10 are appropriate to determine whether surge occurs. Then, a second order

differential of the airflow rate Ga of the compressor 26a is calculated in accordance with the

method described above (step S 108).

[0039] Then, the ECU 40 determines whether the second order differential

calculated in step S 108 is equal to or greater than a predetermined value (step SIlO). If

the determination result shows that the second order differential is equal to or greater than

the predetermined value, the counter value for determining that the surge occurs is

increased by a value corresponding to the second order differential (step S 112).

[0040] In this routine, the ECU 40 is ultimately determines whether a surge occurs

in accordance with the relationship between the value of the calculated second order

differential and the number of times that the second order differential is determined to be

equal to or greater than the predetermined value in step SIlO. FIG. 5 is a conceptual graph

showing how to determine if a surge occurs. Based on the idea shown in FIG. 5, the ECU

40 determines that the surge occurs, when the number of times the calculated second order

differential is determined to be equal to or greater than a predetermined value reaches or

exceeds a given value. The given value is reduced as a calculated second order differential

increases. This idea is embodied by the process in steps SIlO to S118.

[0041] In step S 112, as shown in FIG. 5, the calculated second order differential is

categorized into one of three levels 1 to 3. To be more specific, in step Sl 10, the ECU 40 determines whether the calculated second order differential is equal to or greater than the

level 1. Then, in step S 112, this second order differential is identified as any of the levels

1 to 3. As the level of the second order differential increases (closer to the level 3), the

counter value is increased by a larger number in step S 112. For example, in the case of the

second order differential at the level 1, the counter value is increased by 1. Likewise, in

the case of the second order differential at the level 2 and 3, the counter value is increased

by 2 and 3, respectively.

[0042] In contrast, in step S HO₅ if the second order differential is determined to be

below the predetermined value, the counter value is decreased by 1. When the current

counter value is 0, it remains unchanged (step S 114).

[0043] Then, the ECU 40 determines whether the counter value is equal to or

greater than a predetermined value (step S 116). If the determination result shows that the

counter value is below the predetermined value, the ECU determines that no surge occurs

(step S 106). In contrast, if the counter value is equal to or greater than the predetermined

value, the ECU ultimately determines that a surge occurs (step S 118).

[0044] FIG. 6 is a flowchart of a routine to be executed by the ECU 40 for

controlling the bypass valve 30 in FIG. 1. In the routine shown in FIG. 6, the ECU 40

determines whether or not a surge occurs in the compressor 26a (step S200). The surge

detection is achieved by means of the routine shown in FIG. 4. [0045] In step S200, if the ECU 40 determines that no surge occurs, the bypass

valve 30 is kept fully closed (step S202). In contrast, if the ECU 40 determines that a

surge occurs in step S200, the bypass valve 30 is opened (step S204). In step S204, as

shown in FIG. 5, as the second order differential, used when determining that a surge occurs,

increases, the bypass valve 30 is controlled such that it is opened more widely. More

specifically, as a mean value of the second order differentials, which have been obtained by

the time a surge is determined to occur (see step SIlO), increases, the bypass valve 30 is

controlled such that it is opened more widely. It is noted that the invention is not limited

to such manner. Alternatively, the bypass valve 30 may be opened to a constant degree for

a longer duration as the calculated second order differential increases.

[0046] In accordance with the process shown in FIG. 6, when the internal

combustion engine 10 is operating under conditions that tend to induce a surge in the

compressor 26a, part of air compressed by the compressor 26a returns toward the inlet of

the compressor 26a through the intake bypass pipe 28. This decreases the pressure ratio

between the inlet and outlet of the compressor, as well as in an increase in airflow rate Ga

of the compressor. Thereby, the surge is minimized.

[0047] FIGs. 7A and 7B are graphs for showing effects obtained by the method for

detecting a surge according to the embodiment of the invention. More specifically, FIG.

7 A shows a waveform of fluctuations in airflow rate Ga of the compressor 26a during acceleration. Also, FIG. 7B shows a waveform of fluctuations in second order differential

of the airflow rate Ga of the compressors, which is calculated in sequence.

[0048] In the aforementioned system according to the embodiment of the invention,

if a second order differential of the airflow rate Ga of the compressor 26a is equal to or

greater than a predetermined value, the ECU 40 determines that a surge occurs. In

accordance with the conventional method, whether a surge occurs is determined based on

the fluctuations in intake air volume (first order differential). Thus, a monotone increase

in intake air volume during acceleration can be improperly determined as a surge condition.

To prevent such improper determination, a larger predetermined value is necessary. This

results in a failure to detect a surge that produces relatively slight pulsations.

[0049] In contrast, as shown in FIG. 7 A, the method according to the embodiment of

the invention includes detecting the inflection points on the pulsation curve of the airflow

rate Ga of the compressor 26a. Also, the method includes detecting large fluctuations in

airflow rate Ga of the compressor, which occur before and after the respective inflection

points. Further, in accordance with this method, when the airflow rate Ga of the

compressor 26a monotonously increases, a small second order differential results. The

small value is therefore not used for determining if a surge occurs. Thus, whether or not a

surge occurs is determined earlier and more accurately.

[0050] The method according to the embodiment of the invention includes prohibiting the surge determination, if the throttle opening degree varies rapidly (see time tO

in FIGs. 7 A and 7B). Thus, even when the second order differential increases, which

results from the sharp increase in throttle opening degree, this value is prevented from being

improperly determined as a surge condition.

[0051] The method according to the embodiment of the invention further includes

prohibiting the surge determination, if the throttle opening degree is equal to or lower than a

predetermined opening degree. Thus, an improper surge determination is avoided in the

case where the volume of exhaust gas supplied to the turbine 26b is too small to raise the

boost pressure sufficiently, resulting in no possibility of occurrence of a surge. In addition,

if the boost pressure is equal to or lower than a predetermined boost pressure, the surge

determination is prohibited. Therefore, an improper surge determination is avoided in the

case where the boost pressure is so low that no surge can occur.

[0052] The method according to the embodiment of the invention prohibits the

surge determination if the airflow rate Ga of the compressor 26a and the engine speed NE

are equal to or greater than respective predetermined values. As seen from the relationship

in FIG. 2, no surge occurs when the airflow rate Ga of the compressor 26a and the engine

speed NE are equal to or greater than the respective predetermined values. Therefore, in

such a case, the surge determination is prohibited to avoid an improper determination.

[0053] In accordance with the conventional manner, whether or not a surge occurs is determined based on the difference between the intake air volumes Ga (first order

differential). Thus, in order to prevent an improper determination, once a monotonous

increase in intake air volume Ga has been detected, the measurement thereof should last for

a certain duration. In contrast, the method according to the embodiment of the invention,

in which the routine shown in FIG. 4 is executed, only requires three real-time measured

values to be stored. In turn, the alternative method, which uses the aforementioned

equation (1) to obtain a second order differential, only requires six real-time measured

values. Thus, relative to the conventional manner, the method according to the

embodiment of the invention results in a reduction in load on a memory in the ECU 40.

[0054] In the method in accordance with the routine shown in FIG. 4, the level of

the calculated second order differential is identified a required number of times for the ECU

to ultimately determine that a surge occurs. This required number of times to execute the

level identification varies depending on the level of the second order differential. This

method allows incipient detection of a severe surge, and therefore prevents greatly

dampening of the acceleration of the internal combustion engine 10.

[0055] In the method in accordance with the routine shown in FIG. 6, the bypass

valve 30 is controlled after the detection of a surge. The displacement of the bypass valve

30 varies depending on the level of the calculated second order differential. A principal

reason for detecting and avoiding a surge is to prevent the driveability from being impaired by the surge which adversely affects the operating conditions of the internal combustion

engine 10. If the bypass valve 30 is controlled such that it is opened to a constant degree

independent of the magnitude of the detected surge. Then, to avoid even a relatively slight

surge, the bypass valve 30 is unnecessarily, excessively displaced. This undesirably

results in insufficient air supply to the internal combustion engine 10, causing poor

driveability. The method according to the embodiment of the invention overcomes such

drawback.

[0056] The centrifugal compressor 26a may be incorporated in a generator operated

occasionally with a constant airflow rate Ga of the compressor 26a. In this case, the mean

value of the airflow rates Ga of the compressor, which are obtained for a certain duration,

may be calculated. Then, a difference from the mean value may be detected as pulsations,

which are taken into account to determine if a surge occurs. However, such manner may

not be suitable for a centrifugal compressor to be applied to the internal combustion engine

in which the airflow rate of the compressor continues to fluctuate depending on the engine

operating conditions. In contrast, the method for detecting a surge according to the

embodiment of the invention allows incipient and accurate surge detection in the internal

combustion engine having the above characteristics.

[0057] In the aforementioned embodiment, if the second order differential of the

airflow rate Ga of the compressor 26a is equal to or greater than a predetermined value, the ECU 40 determines if a surge occurs. However, the invention is not limited to that.

Alternatively, a second order differential of any parameters may be used as long as the

parameter varies according to the operating conditions of the centrifugal compressor, such

as pressure and temperature of the air present at the compressor inlet.

[0058] Also, in the aforementioned embodiment of the invention, the second order

differential of the airflow rate Ga of the compressor 26a is calculated at predetermined

sampling intervals to compare each calculated value with the predetermined value.

However, the invention is not limited to that. Alternatively, a difference between the

airflow rates Ga of the compressor (first order differential) may be calculated in sequence to

detect whether or not the first order differentials change sign. Then, upon detection that

the first order differentials change sign, the second order differential, calculated based on

the first order differentials before and after the inflection point, may be compared with a

predetermined value.

[0059] According to the aforementioned embodiment of the invention, the ECU 40

functions as "differential calculating means," described in the first aspect, in step S 108.

Also, the ECU 40 functions as "a differential determining means," described in the first

aspect, in step S 110. Further, the ECU 40 functions as "surge determining means,"

described in the first aspect, in steps S112 to 118. Furthermore, the ECU 40 functions as

"storage means," described in the third aspect, in steps S 112 and S 114. Still furthermore, the ECU 40 functions as "bypass valve control means," described in the sixth and seventh

aspects, in steps S202 and S204.

Claims

1. A control apparatus for an internal combustion engine (10) having a centrifugal

compressor (26a) in an intake passage (14), characterized by comprising:

differential calculating means for calculating a second order differential of at least one

of an airflow rate of the centrifugal compressor (26a), and a pressure and a temperature of

air in an inlet of the centrifugal compressor (26a);

differential determining means for determining whether the second order differential

calculated by the differential calculating means is equal to or greater than a predetermined

level; and

surge determining means for determining whether a surge occurs in the centrifugal

compressor (26a), wherein the surge determining means determines that a surge occurs in

the centrifugal compressor (26a) if the second order differential is equal to or greater than

the predetermined level.

2. The control apparatus according to claim 1, wherein the differential determining means

determines whether the second order differential calculated by the differential calculating

means is equal to or greater than a predetermined value, and

the surge determining means determines that a surge occurs in the centrifugal

compressor (26a) if the second order differential is equal to or greater than the predetermined value.

3. The control apparatus according to claim 1, wherein the differential determining means

means is equal to or greater than a predetermined value, and

the surge determining means comprises a storage means for storing a number of times

that the differential determining means determines that the second order differential is equal

to or greater than the predetermined value, and determines that a surge occurs in the

centrifugal compressor (26a) when the number of times that the differential determining

means determines that the second order differential is equal to or greater than the

predetermined value reaches or exceeds a threshold value.

4. The control apparatus according to claim 3, wherein the surge determining means

determines that a surge occurs when the number of times that the differential determining

means determines that the calculated second order differential is equal to or greater than the

predetermined value reaches or exceeds the threshold value, the threshold value is lowered

as the value of the calculated second order differential increases.

5. The control apparatus according to any one of claim 1 to 4, wherein the surge determining means prohibits the determination of whether a surge occurs when at least one

of following conditions is satisfied: an opening degree of a throttle valve (20) changes

rapidly; the opening degree of the throttle valve (20) is equal to or lower than a

predetermined opening degree; a boost pressure of the intake air is equal to or lower than a

predetermined boost pressure; the airflow rate of the centrifugal compressor (26a) is equal

to or greater than a predetermined airflow rate; and an engine speed is equal to or greater

than a predetermined engine speed.

6. The control apparatus according to any one of claims 1 to 5, further comprising:

a bypass passage (28) that communicably connects an inlet passage and an outlet

passage of the centrifugal compressor (26a);

a bypass valve (30) that opens and closes the bypass passage (28); and

bypass valve control means for opening the bypass valve (30) when the surge

determining means determines that a surge occurs, and the bypass valve control means

increases an opening degree of the bypass valve (30) as the calculated second order

differential increases.

7. The control apparatus according to any one of claims 1 to 5, further comprising:

a bypass passage (28) that communicably connects an inlet passage and an outlet passage of the centrifugal compressor (26a);

a bypass valve (30) that opens and closes the bypass passage (28); and

bypass valve control means for opening the bypass valve (30) when the surge

opens the bypass valve (30) for a longer duration as the calculated second order differential

increases.

8. A method for controlling an internal combustion engine (10) having a centrifugal

compressor (26a) in an intake passage (14), comprising the steps of:

calculating a second order differential of at least one of an airflow rate of the

centrifugal compressor (26a), and a pressure and a temperature of air in an inlet of the

centrifugal compressor (26a);

determining whether the calculated second order differential is equal to or greater than

a predetermined level; and

determining that a surge occurs in the centrifugal compressor (26a) if the second order

differential is equal to or greater than the predetermined level.

9. The method according to claim 8, wherein whether the calculated second order

differential is equal to or greater than a predetermined value is determined, and it is determined that a surge occurs in the centrifugal compressor (26a) if the second order

differential is equal to or greater than the predetermined value.

10. The method according to claim 8, wherein a number of times that the calculated

second order differential is determined to be equal to or greater than the predetermined

value is stored, and it is determined that a surge occurs in the centrifugal compressor (26a)

if the number of times that the calculated second order differential is determined to be equal

to or greater than the predetermined value reaches or exceeds a threshold value.

11. The method according to claim 10, whereinit is determined that a surge occurs when

the number of times that the calculated second order differential is equal to or greater than

the predetermined value reaches or exceeds the threshold value, the threshold value is

lowered as the value of the calculated second order differential increases.

12. The method according to any one of claim 8 to 11, wherein the determination of

whether a surge occurs is prohibited when at least one of following conditions is satisfied:

an opening degree of a throttle valve (20) changes rapidly; the opening degree of the

throttle valve (20) is equal to or lower than a predetermined opening degree; a boost

pressure of the intake air is equal to or lower than a predetermined boost pressure; the airflow rate of the centrifugal compressor (26a) is equal to or greater than a predetermined

airflow rate; and an engine speed is equal to or greater than a predetermined engine speed.

13. The method for controlling an internal combustion engine (10) having a centrifugal

compressor (26a), a bypass passage (28) that communicably connects an inlet passage and

an outlet passage of the centrifugal compressor (26a), and a bypass valve (30) that opens

and closes the bypass passage (28) according to any one of claim 8 to 12, further

comprising the step of:

increasing an opening degree of the bypass valve (30) as the calculated second order

differential increases, when it is determined that a surge occurs.

14. The method for controlling an internal combustion engine (10) having a centrifugal

comprising the step of:

opening a bypass valve (30) for a longer duration as the calculated second order

differential increases, when it is determined that a surge occurs.