analysis of crankshaft speed fluctuations andanalysis of ...analysis of crankshaft speed...

Analysis of Crankshaft Speed Fluctuations andAnalysis of Crankshaft Speed Fluctuations and

Combustion Performance

Ramakrishna Tatavarthi

Julian VerdejoJulian Verdejo

GM Powertrain

November 10, 2008

Overview

• introduction

• definition of operating map

• d l d i t• speed-load points

• matrix of burn locations & durations

• system model of engine transmission and vehicle• system model of engine, transmission, and vehicle

• pressure based methods – discussion of LPP and LPP for MBT

• instantaneous speed based methods – LPS and LTS

• observations & conclusions

Analysis Of Speed Fluctuations 2

Overview

• introduction

Introduction

• ti ti f th t l i• motivation for the present analysis

• location of peak pressure – LPP

• can speed-based methods provide similar information?

• LPP background

• traditionally used as a simple means of tracking burn location (CA50)

• avoids complexity of performing a full heat release analysis

• requires cylinder pressure sensors

• primary strengths of LPP

• effective in tracking CA50 (burn location)

LPP f MBT i i i di i [ ]• LPP for MBT is very constant across engine operating conditions [1]

• attractive basis for closed-loop operation

[1] M t k F A M d d M f C li C b ti V i bilit SAE P 830337 1983

[1] Matekunas, F. A. Modes and Measures of Cyclic Combustion Variability. SAE Paper 830337, 1983.

Introduction

• crankshaft speed based methodsp

• examine instantaneous speed waveform over an engine cycle

• how does waveform change as combustion varies?

• subject has been explored extensively [2] – however, the present work differs significantly in 2 respects:

• combustion phasing instead of IMEP/torque – a more modest goalp g q g

• instantaneous instead of average (ie, cylinder event) speed

• LPS – location of peak speed

• potential alternative to LPP for tracking changes in combustion location

• this and other measures will be discussed

[2] Williams, J. An Overview of Misfiring Cylinder Engine Diagnostic Techniques Based on Crankshaft Angular Velocity Measurements. SAE Paper 960039. 1996.

Overview

• introduction

12 Operating Points Examined

1100 rpm 3800 rpm

260 mg

180 mg

100 mg

Matrix of Burn Locations & Durations(84 Points in Total)

burn duration (10-75%) [deg]

longer burns

burn duration (10 75%) [deg]15 20 25 30 35 40 45

-1 1 13 25 37 49 61 73

3 2 14 26 38 50 62 74

6 3 15 27 39 51 63 75

• 12 burn locations

• 8 burn durations

) [d 8 4 16 28 40 52 64 76

10 5 17 29 41 53 65 77

12 6 18 30 42 54 66 78

15 7 19 31 43 55 67 79

19 8 20 32 44 56 68 80

• 84 combinations in total

• varied duration in all 4 cyl’s

loc 19 8 20 32 44 56 68 80

24 9 21 33 45 57 69 81

30 10 22 34 46 58 70 82

37 11 23 35 47 59 71 83

45 12 24 36 48 60 72 84

• but varied location only in cyl #3

12 op pts x 84 burns = 1,008 total runs

Overview

• introduction

Description of GT-Power Model

• four cylinder engine, 2.2L, gasoline SI, port fuel injection

• l d d (i t d f d d ) i l ti• load-mode (instead of speed-mode) simulations

• each operating point set by combination of throttle angle and road inclination

• at given operating point, vehicle speed decreases as burn either advanced or retarded relative to MBT

• rigid crankshaft model – no crank twist or resonance considered

• only one torsional compliance included in the driveline – clutch spring

• strong effect on dynamic response & instantaneous speed waveform

• appropriate lumped inertias and loads represent driveline and vehicle

existing GT-Power

engine modeladditions to model to capture vehicle and driveline

d i d l di

dynamics and loading

Clutch Torsional Damping

• model had difficulty converging at first

damping

ratio = 0.5

[Nm/(rad/s)]• system underdamped

• clutch spring stiffness was provided by

12[Nm/(rad/s)]

supplier

• how to assign appropriate damping?

• final value of 50 [Nm/(rad/s)]final pole locations

achieved with

damping of

50 [Nm/(rad/s)]

GT-Power Model of Inline 4-Cylinder Engine

Overview

• introduction

Cylinder Pressure as CA50 Varied

peak pressure

quick burn

(duration = 25o)

moves to the right as

CA50 is retarded

“good” sensitivity

CA50 locations

TDC 90o

LPP vs CA50all operating points

• location of peak pressure (LPP) vs burn location

(CA50)( 5 )

• amazingly consistent across all operating points

considered

duration = 25o

burn location (CA50)

LPP vs CA50all operating points

• location of peak pressure (LPP) vs burn location

(CA50)

slope = 43o / 46o = 0.93

duration = 25o( 5 )

• amazingly consistent across all operating points

considered TDC

• good sensitivity – a 10o change in CA50 results in

9o change in LPP P [de

lLPP loses sensitivity to

changes in

slow burn

(duration = 45o)

LPP doesn’t move to the

CA50 locations

TDC 90o

quick burn

(duration = 25o) peak pressure

h hmoves to the right as

CA50 is retarded

“good” sensitivity

CA50 locations

TDC 90o

LPP vs CA502500rpm / 180mg

• LPP vs CA50

• greater sensitivity for quicker burns (steeper

slope of blue line)

• LPP vs CA50

slope of blue line)

]• less sensitivity for longer burns (flatter slope of

black line)P

• LPP vs CA50

slope of blue line)

MBT points(for bdur=15,20,25,30)

]• less sensitivity for longer burns (flatter slope of

black line)P

• MBT operation corresponds to LPP of 10-17 deg

ATDC for range of burn durations considered

Comments on LPPLPP Sensitivity

• LPP shows strong sensitivity to changes in burn location

ti ti *across entire operating map*

• nearly 1-to-1 relation

LPP S iti it

• LPP loses sensitivity abruptly at a longer burn duration

260 0.90.98-.72

0.89.98-.70

0.88.96-.70

0.89.96-.72

0.87.96-.65

LPP Sensitivity

• LPP loses sensitivity abruptly at a longer burn duration

– on average LPP is only valid for bdurs = 15, 20, 25, 30180 0.94

.98-.870.93.98-.87

0.93.96-.87

0.92.96-.85

100 0 93 0 93 0 92

*results shown in table are based on burn durations = 15, 20, 25, 30

100 0.93.98-.85

0.93.98-.87

0.92.98-.85

1100 1800 2500 3100 3800 RPM

Comments on LPPLPP for MBT

LPP f MBT f 6o o ATDC h• LPP for MBT varies from 16o to 13o ATDC over the

entire operating range

LPP f MBT• however, at each op pt, LPP for MBT changes

appreciably with burn duration – as the burn gets longer,

LPP for MBT advances (moves to the left)

260 ~1618-13

~1517-12

~1415-11

~1314-11

~1314-10

LPP for MBT

180 ~1618-12

~1415-12

~1315-11

100 ~15 ~14 ~13100 1518-12

1417-11

1315-11

1100 1800 2500 3100 3800 RPM

Summary of LPP

• strengths of LPP

• good sensitivity to changes in burn location

(for quick to medium duration burns)

• LPP for MBT is very consistent over entire operating range

• from ~16o to ~13o across operating range

• means for closed loop control

• disadvantages

• loses sensitivity abruptly for longer burn durations

(durations > 30 deg’s)

Overview

• introduction

Speed Response

• examine instantaneous speed waveform over an engine cycle

• how does waveform change as combustion (burn location & duration) varied?

• how does it change across different operating points?

Examining the Speed Waveform

expansion

expansioncyl 2

expansion

expansioncyl 2

expansion

TDC 180o

b icombustion

peak reciprocating

mass torque

expansiontrough due to

gas compressiong p

at TDC

TDC 180o

expansion

TDC 180o

Examining the Speed WaveformDefining the Metrics

LPS – location peak speed [deg

expansion

LTS – location trough speed [deg ATDC]LTS location trough speed [deg ATDC]

TDC 180o

expansion

TDC 180o

expansion

TDC 180o

expansion

TDC 180o

expansion

TDC 180o

expansion

TDC 180o

expansion

TDC 180o

Ability to Discern Peaks & Troughs

• there are 2 factors that reduce ability to discern peaks & troughs

• increasing engine speed – primary importance

• excessive retarding of the burn – secondary importance

How Speed Waveform Changes with RPM

1100 rpm

expansion

1800 rpm

expansion

2500 rpm

expansion

3100 rpm

expansion

3800 rpm

expansion

How Speed Waveform Changes with RPM(1100, 1800, 2500, 3100, 3800rpm)

expansion

• there are 2 factors that reduce ability to discern peaks & troughs

• increasing engine speed

• excessive retarding of the burn

• lose ability to discern as RPM increases

• lose ability to discern as spark is retarded (at some operating points)

threshold

• lose ability to discern as RPM increases

• lose ability to discern as spark is retarded (at some operating points)

• speed-based methods limited to 6 of the 12 operating points

threshold

Speed Response

• as engine speed increases• as engine speed increases …

• the ‘gas compression trough’ near TDC disappears

• the ‘hump’ due to combustion disappears

• this is because reciprocating mass effects begin to dominate speed response

• effect increases to the square of engine speed

• thus it appears that instantaneous speed methods are constrained to lower RPM

• at the 2 ‘borderline’ operating points• at the 2 borderline operating points –

ability to detect peaks/troughs disappeared as burn retarded

LTS vs CA50

expansion

LPS location peak speed [degLPS – location peak speed [deg

LTS vs CA50

LTS vs CA501800rpm / 180mg

• LTS becomes more retarded as burn (CA50) is

retarded

• LTS more ‘sensitive’ for shorter burns (steeper p

slope)

• less sensitive for longer burns (flatter slope)

• MBT operation corresponds to ~8o ATDC

retarded

slope)

retarded

slope)

retarded

LPS vs CA50

LPS – location peak speed [deg p p [ g

expansion

LPS vs CA50

LPS vs CA501100rpm / 100mg

• LPS tracks burn location (CA50)

• MBT operation corresponds to ~42o

ATDC TDC

Overview

• introduction

Observations of LTS

• useful metric at only 2 operating pointsy p g p

• surprisingly LTS not useful at 1000rpm, at any of the 3 loads – changes in burn location hardly produce any changes in LTS

• for a specific burn (say bloc=10, bdur=25) it appears that LTS is retarded (moves to the right) as RPM increases, and it advances (moves to the left) as APC inc's

• for a given burn location (say bloc=10), it appears that LTS advances (moves to the left) as burn duration increases

260 -.04 0.07 0.87.83-.91

LTS Sensitivity

180 -.04 0.87.85-.89

0.90.69-1.00

0 83100 0.05 0.83.73-.94

1100 1800 2500 3100 3800 RPM

Observations of LTS

• useful metric at only 2 operating pointsy p g p

• surprisingly LTS not useful at 1000rpm, at any of the 3 loads – changes in burn location hardly produce any changes in LTS

• for a specific burn (say bloc=10, bdur=25) it appears that LTS is retarded (moves to the right) as RPM increases, and it advances (moves to the left) as APC inc's

• for a given burn location (say bloc=10), it appears that LTS advances (moves to the left) as burn duration increases

260 -.04 0.07 0.87.83-.91

LTS SensitivityAPC

260 0.90.98-.72

0.89.98-.70

0.88.96-.70

0.89.96-.72

0.87.96-.65

LPP Sensitivity

180 -.04 0.87.85-.89

0.90.69-1.00

180 0.94.98-.87

0.93.98-.87

0.93.96-.87

0.92.96-.85

0 93 0 93 0 92 100 0.05 0.83.73-.94

1100 1800 2500 3100 3800 RPM

100 0.93.98-.85

0.93.98-.87

0.92.98-.85

1100 1800 2500 3100 3800 RPM

Observations of LTS

• at a given operating point, LTS for MBT is ~constant (more so than LPS)

• h it i l i f l t th 2 ti i t• however, it is only meaningful at the 2 operating points

260 -3 2 ~97-9

LTS for MBT

180 -2 ~76-8

~1816-19

15100 1 ~1514-16

1100 1800 2500 3100 3800 RPM

Observations of LTS

• at a given operating point, LTS for MBT is ~constant (more so than LPS)

• h it i l i f l t th 2 ti i t• however, it is only meaningful at the 2 operating points

260 -3 2 ~97-9

LTS for MBTAPC

260 ~1618-13

~1517-12

~1415-11

~1314-11

~1314-10

LPP for MBT

180 -2 ~76-8

~1816-19

180 ~1618-12

~1415-12

~1315-11

15 14 13 100 1 ~1514-16

1100 1800 2500 3100 3800 RPM

100 ~1518-12

~1417-11

~1315-11

1100 1800 2500 3100 3800 RPM

Observations of LPS

• at a given operating point, LPS tracks CA50 – as burn retarded, LPS retarded

• at a given operating point, sensitivity (slope) is ~constant for the 'nominal' burn durations (15,20,25,30), but then decreases quickly for longer burns

• there seems to be no pattern for sensitivity changing w/ either RPM or APC

• for a given burn (say bloc=10 / bdur=25), it appears LPS retards with increasing APC, and it may advance w/ increasing RPM (this is only a weak effect)

260 0.63.65-.61

0.78.76-79

0.56.71-.32

LPS Sensitivity

180 0.70.72-.67

0.72.74-.71

0 72100 0.72.74-.66

1100 1800 2500 3100 3800 RPM

Observations of LPS

• at a given operating point, LPS tracks CA50 – as burn retarded, LPS retarded

• at a given operating point, sensitivity (slope) is ~constant for the 'nominal' burn durations (15,20,25,30), but then decreases quickly for longer burns

• there seems to be no pattern for sensitivity changing w/ either RPM or APC

• for a given burn (say bloc=10 / bdur=25), it appears LPS retards with increasing APC, and it may advance w/ increasing RPM (this is only a weak effect)

260 0.63.65-.61

0.78.76-79

0.56.71-.32

LPS SensitivityAPC

260 0.90.98-.72

0.89.98-.70

0.88.96-.70

0.89.96-.72

0.87.96-.65

LPP Sensitivity

180 0.70.72-.67

0.72.74-.71

180 0.94.98-.87

0.93.98-.87

0.93.96-.87

0.92.96-.85

0 93 0 93 0 92 100 0.72.74-.66

1100 1800 2500 3100 3800 RPM

100 0.93.98-.85

0.93.98-.87

0.92.98-.85

1100 1800 2500 3100 3800 RPM

Observations of LPS

• for a given operating point LPS for MBT is constant as burn duration is varied• for a given operating point, LPS for MBT is ~constant as burn duration is varied

• it does seem to retard slightly as burn gets longer

• however LPS for MBT is not very consistent across operating points it varies from 39o to 51o• however, LPS for MBT is not very consistent across operating points – it varies from 39 to 51

• tends to retard as APC increases

• tends to advance as RPM increases

260 ~5048-52

~5149-54

~3937-44

LPS for MBT

180 ~4846-50

~4037-42

42100 ~4240-44

1100 1800 2500 3100 3800 RPM

Observations of LPS

• for a given operating point LPS for MBT is constant as burn duration is varied• for a given operating point, LPS for MBT is ~constant as burn duration is varied

• it does seem to retard slightly as burn gets longer

• however LPS for MBT is not very consistent across operating points it varies from 39o to 51o• however, LPS for MBT is not very consistent across operating points – it varies from 39 to 51

• tends to retard as APC increases

• tends to advance as RPM increases

260 ~5048-52

~5149-54

~3937-44

LPS for MBTAPC

260 ~1618-13

~1517-12

~1415-11

~1314-11

~1314-10

LPP for MBT

180 ~4846-50

~4037-42

180 ~1618-12

~1415-12

~1315-11

15 14 13 100 ~4240-44

1100 1800 2500 3100 3800 RPM

100 ~1518-12

~1417-11

~1315-11

1100 1800 2500 3100 3800 RPM

Concluding Remarks

• instantaneous speed waveform changes appreciably with combustionp g pp y

• as RPM increases, however, speed response dominated by reciprocating mass effects

• combustion information is overwhelmed

• ability to identify peaks & troughs (local max & min) limited to low RPM & high APC

• considering only a subset of engine operating points

• speed based metrics (LPS & LTS) are able to track CA50

• unfortunately, LPS (& LTS) for MBT do not remain very constant across engine operating conditions – difficult for closed-loop control

• GT-Power simulation provided means to explore best case scenario

• GT-Power outputs ‘smooth’ instantaneous speed waveforms –

very difficult to produce in the real-world

• this simulation study provides an estimate of the best we can hope to achieve

• GT P t

• GT-Power support

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