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TRANSCRIPT
High Speed Vibrometry for
Valve Tracking + Piston Rockin
NASCAR Race Engines
Stephen JonesMenard Competition Technologies
Presentation Plan
• Introduction • NASCAR Engines• Research + Development using Lasers
(a) Valve Tracking(b) Piston Rock
• Conclusions• Questions
Leafield Technical Centre, Oxfordshire
Engine supplier for the Caparo T1
V8 90° 3.5 litre (Ex-IRL race engine) 580 BHP @10500 RPM 420 Nm @9000 RPM
Power-to-weight >1000 BHP/ton (Bugatti Veyron = 529 BHP/ton !)
Engine supplier to Superleague FormulaV12 60° 4.2 litre All-new design
750+ BHP @12000 RPM 530 Nm @9500 RPMOne-make race series due to start in Aug’08
NASCAR Engine Research + DevelopmentChevrolet V8 90° 358 cu in (5.87 litre)
775 BHP @ 9000 RPM 680 Nm @ 7250 RPMOval Speedway race series in USA
NASCAR engines• 3 Race series - CUP, Busch and Truck• 4 Base-engines - Chevrolet, Ford, Dodge, Toyota• V8 configuration (358 Cu in, 5.87 litre)• Cast iron Block • Single camshaft, Push-rod actuated valve-train• 2 valve combustion chambers• Single carburettor (No electronic fuel injection)• Fixed ignition angle + mechanical distributor• Speed limited to ≈ 9500 RPM by fixed gear ratios• Closely regulated by NASCAR officials
Paul Menard #15 Chevrolet ImpalaNASCAR NEXTEL CUP series – Rookie season 2007
Under the hood…
Engine out
Engine dressing at the circuit
Engine Testing on an MCT dynamometer.
MCT have four steady-state engine test cells.This engine is undergoing crankshaft torsional development testing.
Engine Build Shop @ MCT
Cylinder head off
Bare Crankcase – Chevrolet SB2 ‘small-block’ (circa 1955 !)
Rig Testing• MCT Test facility includes a ‘Spintron’ motoring test rig.
Used for component + system Investigation and Durability testing
• Sensors fitted for valve-tracking :-- Shaft encoder (BEI 720 pulses/rev) - Polytec twin-laser system
HSV-700 Sensor Heads (x2)HSV-800 Laser Units (x2)HSV-2002 Controller
• Standard Spintron single-laser system replaced because :-Twin-lasers cancel out rig vibrationImproved resolution (Polytec = 10.24μm ; Spintron = 20μm)
Spintron Test RigFor running steady-state or programmed test cycles.
Cylinder 5 ‘windowed’ to allow laser access
Spintron Control RoomSpintron software ; Vibsoft 4.1
(Can suffer ‘processor overload’ while simultaneously controlling the Spintron + collecting Polytec Data)
Valve Tracking Objectives
• Investigate Inlet + Exhaust Valve behaviour across the engine speedrange (3000 to 9600 RPM).
• Standard sign-off test for any new valve-train component.
• Ensure that lofting (@ peak lift) is kept below 0.040” to avoid :Valve-to-piston contact → Engine failureDeep valve pockets in piston crowns → Performance lossCamshaft damage → Engine failure
• Ensure that bounce (@ valve closing) does not occur to avoid :Valve or valve-seat damage → Engine failure
• Verify a Simpac valve-train computer model. (Interaction of Mass, Inertia, Stiffness, Natural frequency)
Valve-train Components• Valve• Springs (Inner + Outer)
• Top Retainer (Spring Top)• Collets• Shim (Lash Cap)
• Rocker• Pushrod• Tappet (Lifter, Follower)
Flat = CUP spec.Roller = Busch + Truck spec.
Camshaft Lift eg. Peak = 11.7 mm (0.461”)Valve Lift eg. Peak = 20.4 mm (0.803”) Rocker-ratio = 1.75Valve speed eg. Peak = 12.0 m/s @ 9600 RPM engine speed
0
5
10
15
20
25
-100
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100
Camshaft Degrees
Lift
(mm
)
-15
-10
-5
0
5
10
15
Velo
city
(m
/s)
Twin-Lasers directed at inlet valve head and cylinder head.Retro-reflective tape used for best signal strength.
Baseline valve lift trace @ 3000 RPMA-B displacement signal displayed by Spintron software
Overlaid Valve lift trace @ 9000 RPM
Look for :- ‘Late Opening’, ‘Lofting’, ‘Harmonics’, ‘Early Closing’, ‘Valve Bounce’
Zone definitions for valve control assessment
Comparison spreadsheetDatafiles post-processed using an Excel Macro.
Deviations integrated for each of the 5 zones at 35 test speeds.
Piston Rock Objectives• Rock is significant in NASCAR race engines because :
- Large piston-to-bore clearance due to radiator blanking practice.
- Large bore diameter (4.185” = 106.3 mm)- High piston mass (NASCAR rule = 400g)
• Characterise the rock around the gudgeon pin• Determine which areas of the skirt do the most work• Use the findings to improve the skirt design
(Piston design + manufacture is part of MCT’s core business)• Investigate the effect of crankcase depression on rock
Piston-rock laser set-up(Oil contamination affected signal strength; Airlines + extraction helped)
Laser B
Laser A
Retro-reflective Tape
Extraction forOil mist (Blowby)TOP
BOTTOM
CYLS 2,4,6,8R/H BANK
CYLS 1,3,5,7L/H BANK
VIEWFROMFRONT
BB
AA
Schematic of ‘Positive-Rock’. (A-B = +ve)
NASCAR engines run a ‘large’ piston-to-bore clearance ≈ 0.010”
Piston ‘skirt’ supports the piston-rock
•FRONT
CYL 8
REACTION FORCE (BOTTOM OF SKIRT)
+VE ROCKDIRECTION
REACTION FORCE (TOP OF SKIRT)
Piston Displacement + Velocity v. Crank AngleOver one engine revolution
(Engine Speed = 9000 RPM ; Stroke = 82.55 mm ; Conn-rod length = 152.4 mm)Concern that piston speeds > ±30 m/s outside capability of HSV-2002 controller
0
10
20
30
40
50
60
70
80
90
100
0 30 60 90 120 150 180 210 240 270 300 330 360
Crank degrees
Dis
plac
emen
t (m
m)
[
Dow
n bo
re is
+ve
dire
ctio
n]
-50
-40
-30
-20
-10
0
10
20
30
40
50
Velo
city
(m/s
)
Trigger signal (From shaft encoder once per engine rev).Rock trace suffered from :
Drift and discontinuities.Blow-by oil contamination robbed signal strength± 8V signal voltage resets
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3 0.35 0.4 0.45 0.5 0.55 0.6
Time
Dis
plac
emen
t
2
2.5
3
3.5
4
4.5
Volta
ge A - B
Trigger
( Sample Frequency = 25.6 kHz ; Sample Time = 1.28 s ; No Filters )
Raw Vibsoft Data Trace
Vibsoft datafiles were exported as ASCII files and analysed in Excel.1. Cut out a ‘good’ trace between two triggers.2. Convert x-axis from time-base to crankangle-base.3. Correct the trace for drift.
Typical piston rock trace. (8500 RPM Cylinder 8)
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
0 60 120 180 240 300 360
Crank Angle (Degrees)
Roc
k (m
m)
VaccNo Vacc
110°71.0 HP- 70 mBarNo Vacc
50.4 HP- 640 mBarVacc
Power-to-drive SpintronCrankcase Depression
Conclusions• Accurate valve tracking allows us to develop a more durable valve-
train and to improve engine performance.
• Piston rock measurement allowed us to better understand piston dynamics and helped with piston skirt design.
• Results compromised by non-firing engine, ie.No combustion pressureNo combustion temperature No thermal growth
Any Questions ?