Browse Publications Technical Papers 2004-01-1389
2004-03-08

Characterization of Engine Variable Cam Phaser Fluid Dynamics and Phaser's Ability to Reject System Disturbances 2004-01-1389

Vane type cam phasers have been widely used in internal combustion engines to vary valve timing to achieve purposes such as low emissions, greater torque, and higher horsepower. One of the primary concerns in using a vane phaser is its position holding ability when disturbances are present. Disturbances include cam torque oscillation, cam pulley speed fluctuation, oil pressure fluctuation, and engine acceleration or deceleration. Cam torque disturbance is the biggest contributor to phaser position error. This paper will first present the generic schematic of a variable cam phasing system and its challenges, followed by the characterization of the fluid dynamics of the vane phaser, with an emphasis on the effects of pressure, leakage, and oil aeration on the vane phaser fluid dynamics and its ability to reject cam torque disturbance. Finally, numerical evaluations of the vane phaser's ability to reject cam torque disturbance and sensitivity to various system parameters will be presented.

NOTATIONS

ϕ
Fractional air content by volume
χ
Fractional air by volume that is undissolved
γ
Polytropic index
β
Effective oil bulk modulus
β0
A reference oil bulk modulus
θ
Rotor angular displacement relative to its equilibrium position
θ0
Bias spring pre-compressed angle
θd
Desired cam position relative to cam pulley
θS
Phaser moving authority or stroke
ωh
Hydraulic natural frequency
ζ
Damping ratio
A
Effective pressure area
I
Cam load inertia
L
Leakage coefficient
L1
Flow coefficient in flow path from advancing chamber to vent via OCV
L2
Flow coefficient in flow path from supply to advancing chamber via OCV
L3
Flow coefficient in flow path from supply to retarding chamber via OCV
L4
Flow coefficient in flow path from retarding chamber to vent via OCV
L5
Leakage coefficient in leak path from supply to advancing chamber
L6
Leakage coefficient in leak path from supply to retarding chamber
L7
Leakage coefficient in leak path from advancing chamber to vent
L8
Leakage coefficient in leak path from advancing chamber to retarding chamber
L9
Leakage coefficient in leak path from retarding chamber to vent
K
Phaser bias spring rate
N
Number of oil chambers of same type
P
Oil pressure
Pa0
Static oil pressure in advancing chamber
Pa
Oil pressure change from Pa0 in advancing chamber
Pabs
Absolute oil pressure
Patmos
Absolute atmosphere pressure
Pm0
Differential oil pressure across the load at equilibrium condition
Pm
Oil pressure change from Pm0
Pr0
Static oil pressure in retarding chamber
Pr
Oil pressure change from Pr0 in retarding chamber
Ps
Supply oil pressure
Psat
Air saturate pressure
ql
Oil leakage
r0
Force to torque gain, or distance from force centroid to centerline
s
Laplace transform operator
t
Time
T
Temperature
Tabs
Absolute temperature
Tf
Friction torque
Vt
Total volume of oil chambers
x
Oil control valve spool displacement
xS
Oil Control Valve (OCV) spool stroke
x1
OCV spool displacement to shut off flow from retarding chamber to vent
x2
OCV spool displacement to shut off flow from supply to advancing chamber
x3
OCV spool displacement to open flow from supply to retarding chamber
x4
OCV spool displacement to open flow from advancing chamber to vent
dB
Decibel
FTP
Federal test procedure
lpm
Liter per minute
OCV
Oil control valve
PCM
Powertrain control module
PD
Proportional and derivative
PI
Proportional and integral
PID
Proportional, integral and derivative
PWM
Pulse width modulated
VCP
Variable cam phasing

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