U.S. patent application number 11/461928 was filed with the patent office on 2007-02-08 for mapping temperature compensation limits for pwm control of vct phasers.
This patent application is currently assigned to BorgWarner Inc.. Invention is credited to Roger T. Simpson.
Application Number | 20070028874 11/461928 |
Document ID | / |
Family ID | 37716502 |
Filed Date | 2007-02-08 |
United States Patent
Application |
20070028874 |
Kind Code |
A1 |
Simpson; Roger T. |
February 8, 2007 |
Mapping temperature compensation limits for PWM control of VCT
phasers
Abstract
A variable cam timing (VCT) phaser system including a phaser
with an actuator in which the max duty cycle is altered to maintain
a constant current in the system based on at least one engine
parameter.
Inventors: |
Simpson; Roger T.; (Ithaca,
NY) |
Correspondence
Address: |
BORGWARNER INC.
3850 HAMLIN ROAD
AUBURN HILLS
MI
48326
US
|
Assignee: |
BorgWarner Inc.
Auburn Hills
MI
|
Family ID: |
37716502 |
Appl. No.: |
11/461928 |
Filed: |
August 2, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60704714 |
Aug 2, 2005 |
|
|
|
Current U.S.
Class: |
123/90.15 ;
123/90.17 |
Current CPC
Class: |
F01L 2001/3443 20130101;
F01L 1/024 20130101; F01L 1/3442 20130101; F01L 2001/34426
20130101; F01L 1/026 20130101; F01L 2800/01 20130101; F01L 2820/01
20130101; F01L 2800/00 20130101; F01L 1/022 20130101 |
Class at
Publication: |
123/090.15 ;
123/090.17 |
International
Class: |
F01L 1/34 20060101
F01L001/34 |
Claims
1. A method of maintaining a constant actuation rate in an engine
comprising the steps of: a) setting a maximum actuation rate and
sending the rate to a controller; b) determining at least one
engine control parameter and sending the at least one engine
control parameter to the controller; c) using the at least one
engine control parameter to determine a new duty cycle in the
controller; d) comparing the new duty cycle to a current duty cycle
in the controller; and e) adjusting and outputting the new duty
cycle from the controller to an actuator.
2. The method of claim 1, wherein the at least one engine control
parameter is voltage.
3. The method of claim 1, wherein the at least one engine control
parameter is temperature.
4. The method of claim 3, wherein the temperature is from a
pressurized source of fluid, a coolant system, engine block, engine
compartment, radiator, or a cooling system.
5. The method of claim 1, wherein the at least one engine control
parameters are temperature and voltage.
6. The method of claim 1, wherein the actuator is a pulse width
modulated solenoid.
7. The method of claim 1, wherein determining the new duty cycle
comprises the steps of selecting a temperature limit curve.
8. The method of claim 1, wherein determining the new duty cycle
comprises the step of selecting a voltage curve.
9. The method of claim 1, wherein determining the new duty cycle
comprises the steps of selecting a voltage curve and selecting a
temperature limit curve.
10. The method of claim 1, wherein the new duty cycle is a maximum
duty cycle and is determined by equation: [ 1 V 0 + .DELTA. .times.
.times. V [ R 0 * .alpha. .function. ( .DELTA. .times. .times. T )
] + R 0 ] * 100 = Max .times. .times. DC , ##EQU7## where V.sub.0
is an initial voltage, R.sub.0 is an initial resistance, .DELTA.V
is a change in voltage, .DELTA.T is a change in temperature, and
.alpha. is a temperature coefficient of resistance.
11. A method of maintaining a constant actuation rate in an
internal combustion engine comprising the steps of: a) setting a
maximum actuation rate of a variable cam timing system and sending
the rate to a controller; b) determining at least one engine
control parameter and sending the at least one engine control
parameter to the controller; c) using the at least one engine
control parameter to determine a new maximum duty cycle in the
controller; d) comparing the new maximum duty cycle to a current
duty cycle in the controller; and e) adjusting and outputting the
new maximum duty cycle from the controller to an actuator, such
that the actuator positions a control valve of a variable cam
timing phaser of the variable cam timing system, altering the phase
of the variable cam timing system.
12. The method of claim 11, wherein the at least one engine control
parameter is voltage.
13. The method of claim 11, wherein the at least one engine control
parameter is temperature.
14. The method of claim 13, wherein the temperature is from a
pressurized source of fluid, a coolant system, engine block, engine
compartment, radiator, or a cooling system.
15. The method of claim 11, wherein the at least one engine control
parameters are temperature and voltage.
16. The method of claim 11, wherein the actuator is a pulse width
modulated solenoid.
17. The method of claim 11, wherein determining the new maximum
duty cycle comprises the step of selecting a temperature limit
curve.
18. The method of claim 11, wherein determining the new maximum
duty cycle comprises the step of selecting a voltage curve.
19. The method of claim 11, wherein determining the new maximum
duty cycle comprises the steps of selecting a voltage curve and
selecting a temperature limit curve.
20. The method of claim 11, wherein the new maximum duty cycle is
determined by equation: [ 1 V 0 + .DELTA. .times. .times. V [ R 0 *
.alpha. .function. ( .DELTA. .times. .times. T ) ] + R 0 ] * 100 =
Max .times. .times. DC , ##EQU8## where V.sub.0 is an initial
voltage, R.sub.0 is an initial resistance, .DELTA.V is a change in
voltage, .DELTA.T is a change in temperature, and .alpha. is a
temperature coefficient of resistance.
21. The method of claim 11, wherein the variable cam timing phaser
comprises: a housing with an outer circumference for receiving
drive force; a rotor for connection to a camshaft coaxially located
within the housing having at least one vane, wherein the housing
and the rotor define at least one chambers, separated by the vane
into an advance chamber and a retard chamber, the vane being
capable of rotation to shift relative angular position of the
housing and the rotor; and a control valve coupled to the actuator
and in connection with the advance chamber and the retard chamber
for directing fluid flow to shift the relative angular position of
the rotor relative to the housing.
22. The method of claim 21, wherein the control valve allows fluid
to flow between the advance chamber and the retard chamber.
23. The method of claim 22, further comprising at least one check
valve between the advance chamber and the retard chamber and the
control valve for blocking reverse fluid flow.
24. The method of claim 21, further comprising a passage in fluid
communication with a pressurized fluid source.
25. The method of claim 24, further comprising a check valve in the
passage.
26. A variable cam timing system for an internal combustion engine
comprising: a phaser having: a housing with an outer circumference
for receiving drive force; a rotor for connection to a camshaft
coaxially located within the housing having at least one vane,
wherein the housing and the rotor define at least one chambers,
separated by the vane into an advance chamber and a retard chamber,
the vane being capable of rotation to shift relative angular
position of the housing and the rotor; and a control valve in
connection with the advance chamber and the retard chamber for
directing fluid flow to shift the relative angular position of the
rotor relative to the housing; a controller receiving input from at
least one engine parameter, and an engine control unit and
outputting a new duty cycle based on the at least one engine
parameter and the engine control unit to an actuator coupled to the
control valve for positioning the control valve, such that the
angular position of the housing relative to the rotor of variable
cam timing phaser of the variable cam timing system is altered.
27. The variable cam timing system of claim 26, wherein the control
valve allows fluid to flow between the advance chamber and the
retard chamber.
28. The variable cam timing system of claim 27, further comprising
at least one check valve between the advance chamber and the retard
chamber and the control valve for blocking reverse fluid flow.
29. The variable cam timing system of claim 26, further comprising
a passage in fluid communication with a pressurized fluid
source.
30. The variable cam timing system of claim 29, further comprising
a check valve in the passage.
31. The variable cam timing system of claim 26, wherein the engine
control unit provides the angular phase position between the
housing and the rotor.
32. The variable cam timing system of claim 26, wherein a method of
determining the new duty cycle comprises the steps of: a) setting a
maximum actuation rate of a variable cam timing system from the
engine control unit and sending the rate to a controller; b)
determining the at least one engine control parameter and sending
the at least one engine control parameter to the controller; c)
using the at least one engine control parameter to determine the
new maximum duty cycle in the controller; d) comparing the new
maximum duty cycle to a current duty cycle in the controller; and
e) adjusting and outputting the new maximum duty cycle from the
controller to an actuator, such that the actuator positions a
control valve of a variable cam timing phaser of the variable cam
timing system, altering the phase of the variable cam timing
system.
33. The variable cam timing system of claim 32, wherein the at
least one engine control parameter is voltage.
34. The variable cam timing system of claim 32, wherein the at
least one engine control parameter is temperature.
35. The variable cam timing system of claim 34, wherein the
temperature is from a pressurized source of fluid, a coolant
system, engine block, engine compartment, radiator, or a cooling
system.
36. The variable cam timing system of claim 32, wherein the at
least one engine control parameters are temperature and
voltage.
37. The variable cam timing system of claim 32, wherein the
actuator is a pulse width modulated solenoid.
38. The variable cam timing system of claim 32, wherein determining
the new maximum duty cycle comprises the step of selecting a
temperature limit curve.
39. The variable cam timing system of claim 32, wherein determining
the new maximum duty cycle comprises the step of selecting a
voltage curve.
40. The variable cam timing system of claim 32, wherein determining
the new maximum duty cycle comprises the steps of selecting a
voltage curve and selecting a temperature limit curve.
41. The variable cam timing system of claim 32, wherein the new
maximum duty cycle is determined by equation: [ 1 V 0 + .DELTA.
.times. .times. V [ R 0 * .alpha. .function. ( .DELTA. .times.
.times. T ) ] + R 0 ] * 100 = Max .times. .times. DC , ##EQU9##
where V.sub.0 is an initial voltage, R.sub.0 is an initial
resistance, .DELTA.V is a change in voltage, .DELTA.T is a change
in temperature, and a is a temperature coefficient of
resistance.
42. The variable cam timing system of claim 32, wherein the
controller is part of the engine control unit.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application claims an invention which was disclosed in
Provisional Application No. 60/704,714, filed Aug. 2, 2005,
entitled "MAPPING TEMPERATURE COMPENSATION LIMITS FOR PWM CONTROL
OF VCT PHASERS". The benefit under 35 USC .sctn.119(e) of the
United States provisional application is hereby claimed, and the
aforementioned application is hereby incorporated herein by
reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The invention pertains to the field of variable camshaft
timing systems. More particularly, the invention pertains to
methods of operating a pulse-width-modulated (PWM) variable cam
timing system at substantially the same actuation rate under
different temperature conditions by limiting the duty cycle to
different values to compensate for changes in temperature.
[0004] 2. Description of Related Art
[0005] The performance of an internal combustion engine may be
improved by the use of dual camshafts, one to operate the intake
valves of the various cylinders of the engine and the other to
operate the exhaust valves. Typically, one of such camshafts is
driven by the crankshaft of the engine, through a sprocket and
chain drive or a belt drive, and the other of such camshafts is
driven by the first, through a second sprocket and chain drive or a
second belt drive. Alternatively, both of the camshafts may be
driven by a single crankshaft powered chain drive or belt drive.
Engine performance in an engine with dual camshafts may be further
improved, in terms of idle quality, fuel economy, reduced emissions
or increased torque, by changing the positional relationship of one
of the camshafts, usually the camshaft which operates the intake
valves of the engine, relative to the other camshaft and relative
to the crankshaft, to thereby vary the timing of the engine in
terms of the operation of intake valves relative to its exhaust
valves or in terms of the operation of its valves relative to the
position of the crankshaft.
[0006] Consideration of information disclosed by the following U.S.
Patents, which are all hereby incorporated by reference, is useful
when exploring the background of the present invention.
[0007] U.S. Pat. No. 5,002,023 describes a VCT system in which the
system hydraulics include a pair of oppositely acting hydraulic
cylinders with appropriate hydraulic flow elements to selectively
transfer hydraulic fluid from one of the cylinders to the other, or
vice versa, to thereby advance or retard the circumferential
position of a driven shaft relative to a driving shaft. The control
system utilizes a control valve in which the exhaustion of
hydraulic fluid from one or another of the oppositely acting
cylinders is permitted by moving a spool away from a centered or
null position. The movement of the spool occurs in response to an
increase or decrease in control hydraulic pressure Pc on one end of
the spool, and an oppositely direct mechanical force on the other
end, from a compression spring that acts thereon.
[0008] U.S. Pat. No. 5,107,804 describes another VCT system in
which the system hydraulics includes a vane having lobes within an
enclosed housing replacing the oppositely acting cylinders
disclosed by the aforementioned U.S. Pat. No. 5,002,023. The vane
is oscillatable with respect to the housing, with appropriate
hydraulic flow elements to transfer hydraulic fluid within the
housing from one side of a lobe to the other, or vice versa, to
thereby oscillate the vane with respect to the housing in one
direction or the other. The oscillation of the vane in one
direction or the other advances or retards the position of a driven
shaft relative to a driving shaft. The control system of this VCT
system is identical to that divulged in U.S. Pat. No.
5,002,023.
[0009] U.S. Pat. Nos. 5,172,659 and 5,184,578 both address the
problems of the aforementioned types of VCT systems created by the
attempt to balance the hydraulic force exerted against one end of
the spool and the mechanical force exerted against the other end.
The improved control system disclosed in both U.S. Pat. Nos.
5,172,659 and 5,184,578 utilizes hydraulic force on both ends of
the spool. The hydraulic force on one end results from the directly
applied hydraulic fluid from the engine oil gallery at full
hydraulic pressure, P.sub.S. The hydraulic force on the other end
of the spool results from a hydraulic cylinder or other force
multiplier which acts thereon in response to system hydraulic fluid
at reduced pressure P.sub.C, supplied by a PWM solenoid. Due to the
force at each of the opposed ends of the spool being hydraulic in
origin, based on the same hydraulic fluid, changes in pressure or
viscosity of the hydraulic fluid will be self-negating, and will
not affect the centered or null position of the spool.
[0010] U.S. Pat. No. 5,289,805 discloses an improved VCT method
which utilizes a hydraulic PWM spool position control and an
advanced control algorithm that yields a prescribed set point
tracking behavior with a high degree of robustness.
[0011] U.S. Pat. No. 5,497,738 shows a control system which
eliminates the hydraulic force on one end of a spool resulting from
directly applied hydraulic fluid from the engine oil gallery at
full hydraulic pressure, P.sub.S. The force on the other end of the
vented spool results from an electromechanical actuator, preferably
of the variable force solenoid type, which acts directly upon the
vented spool in response to an electronic signal issued from an
engine control unit (ECU). The ECU receives signals from sensors
corresponding to camshaft and crankshaft positions and utilizes
this information to calculate a relative phase angle in a
closed-loop feedback system. The use of a variable force solenoid
solves the problem of sluggish dynamic response. The faster
response allows the use of increased closed-loop gain, making the
system less sensitive to component tolerances and operating
environment.
[0012] U.S. Pat. No. 5,657,725 shows a control system which
utilizes engine oil pressure for actuation. The system includes a
camshaft with a vane secured to an end thereof for non-oscillating
rotation therewith. The camshaft also carries a housing which can
rotate with the camshaft, and is also oscillatable with the
camshaft. The vane has opposed lobes which are received in opposed
recesses, of the housing. The recesses have a greater
circumferential extent than the lobes, to permit the vane and
housing to oscillate with respect to one another, and thereby
permit the camshaft to change in phase relative to a crankshaft.
The camshaft tends to change direction in reaction to camshaft
torque pulses, advancing or retarding the phaser by selectively
blocking or permitting the flow of engine oil through the return
lines from the recesses by controlling the position of a spool
within a spool valve body. The spool is moved within the spool
valve body in response to a signal indicative of an engine
operating condition from an engine control unit. The spool is
selectively positioned by controlling hydraulic loads on its
opposing end in response to a signal from an engine control unit.
The vane may be biased to an extreme position to provide a
counteractive force to a unidirectionally acting frictional torque
experienced by the camshaft during rotation.
[0013] U.S. Pat. No. 6,247,434 shows a multi-position variable
camshaft timing system actuated by engine oil. Within the system, a
hub is secured to a camshaft for rotation synchronous with the
camshaft. A housing circumscribes and is rotatable with the hub and
the camshaft and is further oscillatable with respect to the hub
and the camshaft within a predetermined angle of rotation. Vanes
extend from the hub into a chamber formed between the housing and
the hub, dividing the chamber into advance and retard chambers. A
locking device, reactive to oil pressure, prevents relative motion
between the housing and the hub. A controlling device controls the
oscillation of the housing relative to the hub.
[0014] U.S. Pat. No. 6,263,846 shows a control valve strategy for a
variable camshaft timing system. The strategy involves an internal
combustion engine that includes a camshaft and hub secured to the
camshaft for rotation therewith, where a housing circumscribes the
hub and is rotatable with the hub and the camshaft, and is further
oscillatable with respect to the hub and camshaft. Vanes extend
from the hub into a chamber formed between the housing and the hub,
dividing the chamber into advance and retard chambers. A
configuration for controlling the oscillation of the housing
relative to the hub includes an electronic engine control unit, and
an advancing control valve that is responsive to the electronic
engine control unit and that regulates engine oil pressure to and
from the advance chambers. A retarding control valve responsive to
the electronic engine control unit regulates engine oil pressure to
and from the retard chambers. An advancing passage communicates
engine oil pressure between the advancing control valve and the
advance chambers, while a retarding passage communicates engine oil
pressure between the retarding control valve and the retard
chambers.
[0015] U.S. Pat. No. 6,938,592 shows a method of adding a dither
frequency (a periodic adjustment) to the control signal to always
keep the VCT control valve moving a little in order to minimize the
effects of hysteresis with regard to valve movement. The dither
frequency is adjusted based on varying temperature conditions,
since the dither technique is less effective at higher
temperatures.
[0016] Temperature and voltage may also have an undesirable effect
on the phaser actuation rate. Therefore, it would be desirable to
have a VCT phaser which could compensate for the temperature and
voltage effects on actuation rate.
SUMMARY OF THE INVENTION
[0017] A variable cam timing (VCT) phaser system including a phaser
with an actuator in which the max duty cycle is altered to maintain
a constant current in the system based on at least one engine
parameter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1a shows a schematic of a cam torque actuated phaser of
the present invention moving in the null position.
[0019] FIG. 1b shows a schematic of a cam torque actuated phaser of
the present invention moving towards the advance position.
[0020] FIG. 1c shows a schematic of a cam torque actuated phaser of
the present invention moving towards the retard position.
[0021] FIG. 2 shows a schematic of an oil pressure actuated phaser
of the present invention in the null position.
[0022] FIG. 3 shows a schematic of a torsion assist phaser of the
present invention in the null position.
[0023] FIG. 4 shows a graph of a temperature compensation map used
for duty cycle compensation of a first embodiment.
[0024] FIG. 5 shows a method of adjusting the duty cycle for a
maximum actuation rate in view of temperature changes of a first
embodiment.
[0025] FIG. 6 shows an alternate method of adjusting the duty cycle
for a maximum actuation rate in view of temperature changes of a
first embodiment.
[0026] FIG. 7 shows a method of adjusting the duty cycle for a
maximum actuation rate in view of voltage changes in a second
embodiment.
[0027] FIG. 8 shows a graph of duty cycle versus voltage at
different constant temperatures.
[0028] FIG. 9 shows an alternate method of adjusting the duty cycle
for a maximum actuation rate in view of voltage changes in a second
embodiment.
[0029] FIG. 10 shows a method of adjusting the duty cycle for a
maximum actuation rate in view of temperature and voltage changes
in a third embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Internal combustion engines have employed various mechanisms
to vary the angle between the camshaft and the crankshaft for
improved engine performance or reduced emissions. The majority of
these variable camshaft timing (VCT) mechanism use one or more
"vane phasers" on the engine camshaft (or camshafts, in a
multiple-camshaft engine). In most cases, the phasers have a rotor
with one or more vanes, mounted to the end of the camshaft,
surrounded by a housing with the vane chambers into which the vanes
fit. It is possible to have the vanes mounted to the housing, and
the chambers in the rotor, as well. The housing's outer
circumference forms the sprocket, pulley or gear accepting drive
force through a chain, belt, or gears, usually from the crankshaft,
or possible from another camshaft in a multiple-cam engine.
[0031] The desired relative angular position between the camshaft
and the crankshaft is determined by a controller 36, which may be
further controlled by an ECU. The controller may be a
microprocessor, computer, application specific integrated circuit
(ASIC), digital electronics, analog electronics, or any combination
thereof. The controller 36 is coupled to an actuator 38 which is
capable of adjusting the spool 54 and thus the phaser to vary the
relative angular position between the camshaft and the crankshaft.
The controller 36 receives input from a temperature sensor 40, a
battery 37, and the ECU 39. Alternatively, the controller 36 may be
part of the ECU 39. The controller is preferably a Motorola Model
No. 68332 microcontroller. The temperature sensor 40 is preferably
a sensor in the main oil gallery, which supplies oil to the
actuator 38 and/or phaser. The temperature sensor may also be
present in other parts of the engine and measure an associated
temperature such as, the engine block, the engine compartment, the
radiator, and the cooling system. The battery 37 may provide
voltage to run the controller 36 and enable the controller 36 to
monitor the voltage or the controller 36 will only monitor the
voltage from the battery 37. The ECU 39 provides additional input
regarding other engine parameters to the controller 36, such as the
angular position of the camshaft relative to the crankshaft and
thus spool position.
[0032] The controller 36 is configured to adjust an actuator
control parameter, such as the duty cycle of the actuator 38, based
on input from the temperature sensor 40, the battery, and the ECU
in order to achieve a substantially constant actuation rate. The
controller may also further adjust the duty cycle based on whether
the ECU supplies input to move the phaser to a null position, a
retard position, or an advance position.
[0033] The actuator 38 may be a flow control switch which receives
a pulse-width-modulated (PWM) signal from the controller 36 to vary
the current which allows varying amounts of pressurized hydraulic
fluid 56 to drive the spool 54 against an opposing force, here
illustrated as spring 64. The lands of the spool 54 and the
characteristics of the spring 64 may be chosen so that at some
nominal value of current, for example 0.6 amps, the spool 54 will
be in the null position, as shown in FIGS. 1a, 2, and 3, locking
the vane 46 in a position. At 1 amp, the spool will be fully moved
to an advance position, and at 0.2 amps, the spool will be moved to
a full retard position. The duty cycle that corresponds to the null
position, the full advance position, and the full retard position
will vary based on the current outputted, but ideally, based on
current, 0.2 amps corresponds to a 20% duty cycle, 0.6 amps
corresponds to 60%, and 1.0 amp corresponds to 100% duty cycle. As
explained below, if the current is greater than 1 amp, the maximum
duty cycle will be adjusted to being the maximum current back to 1
amp. It should be noted that vane 46 may be stopped at any position
and does not need to be in the position specifically shown in FIGS.
1a, 2 and 3. Since the vane 46 is not being driven in this
position, the actuation rate of the vane 46 is zero.
[0034] The controller 36 and actuator 38 may be used with any of
the following phasers: cam torque actuated, oil pressure actuated,
torsion assist, a hybrid phasers as shown in FIGS. 1a through 3 and
discussed below. For the discussion of the phasers, it is assumed
that the current outputted is equal to 1 amp and the maximum duty
cycle of 100% does not need to be altered.
[0035] Cam torque actuated (CTA) phasers use torque reversals in
the camshaft, caused by the forces of opening and closing engine
valves to move the vane. Control valves are present to allow fluid
flow from chamber to chamber causing the vane to move, or to stop
the flow of oil, locking the vane in position. The CTA phaser has
oil input to make up for losses due to leakage, but does not use
engine oil pressure to move the phaser. CTA phasers have shown that
they provide fast response and low oil usage, reducing fuel
consumption and emissions. However, in some engines, i.e.
4-cylinder engines, the torsional energy from the camshaft is not
sufficient to actuate the phaser over the entire speed range of the
engine, especially when the rpm is high and optimization of the
performance of the phaser in view of engine operating conditions
(e.g. the amount of available cam torque) is necessary.
[0036] FIGS. 1a through 1c show a cam torque actuated phaser (CTA)
of the present invention. Torque reversals in the camshaft caused
by the forces of opening and closing engine valves move the vane
46. The advance and retard chambers 50, 52 are arranged to resist
positive and negative torque pulses in the camshaft and are
alternatively pressurized by the cam torque. The control valve 51
in a CTA system allows the vane 46 in the phaser to move, by
permitting fluid flow from the advance chamber 50 to the retard
chamber 52 or vice versa, depending on the desired direction of
movement, as shown in FIGS. 1a through 1c.
[0037] When the controller 36 increases the current, from 0.6 amps
or in increases the duty cycle from 60% to 1 amp or 100%, then the
actuator 38 will increase the pressure of the oil driving the spool
54 against the spring 64, the actuator moving the spool to the left
in FIG. 1c until the force of the actuator 38 balances the force of
the spring 64, and depending on the duty cycle or current chosen, a
particular actuation rate of the phaser vane will be set in a
second direction, here illustrated as a counter-clockwise or
retarding direction, opposite the first direction.
[0038] More specifically, in moving towards the retard position of
the phaser, as shown in FIG. 1c, the spool valve 51 is internally
mounted within the rotor 42 and includes a sleeve 53 for receiving
a spool 54 with lands 54a, 54b, and a biasing spring 64. An
actuator 38, preferably a pulse width modulated (PWM) solenoid,
moves the spool 54 within the sleeve 53. In the position shown,
spool land 54b blocks line 62, and lines 60 and 58 are open.
Camshaft torque pressurizes the advance chamber 50, causing fluid
in the advance chamber 50 to move into the retard chamber 52. Fluid
exiting the advance chamber 50 moves through line 58 and the fluid
moves and into the spool valve 51 between spool lands 54a and 54b.
From the spool valve 51, fluid move back into line 60, through
check valve 51 into line 62 supplying fluid to the retard chamber
52, moving the vane 46 in the direction shown by the arrow.
[0039] Makeup oil is supplied to the phaser from supply S to make
up for leakage and enters line 55 and moves through inlet check
valve 57 to the spool valve 51. From the spool valve fluid enters
line 60 through either of the check valves 59, 61, depending on
whether fluid travels to the advance chamber 50 or the retard
chamber 52.
[0040] When the controller 36 reduces the current, from 0.6 amps or
reduces the duty cycle from 60% to 0.2 amps or 20%, respectively,
then the actuator 38 will reduce the pressure of the oil driving
the spool 54 against the spring 64 and the spring force will bias
the spool 54 to the right in FIG. 1b until the force of the
actuator 38 balances the force of the spring 64, and depending on
the duty cycle chosen, a particular actuation rate of the vane will
be set in a first direction, here illustrated as a clockwise or
advancing direction. The actuation rate of the vane is the
rotational speed at which the vane 46 is moving. Based on setting
the spool 54 for a desired actuation rate with a given duty cycle,
the vane 46 position may be carefully dialed in by allowing the
vane 46 to move for a preset time period. The actuation rate
multiplied by the time period will give a desired change in phaser
position.
[0041] In the position shown, spool land 54a blocks the exit of
fluid from line 58, and lines 60 and 62 are open. Camshaft torque
pressurizes the retard chamber 52, causing fluid in the retard
chamber 52 to move into the advance chamber 50. Fluid exiting the
retard chamber 52 moves through line 62 and into the spool valve 51
between lands 54a and 54b. From the spool valve 51, the fluid
enters line 60 and travels through open check valve 59 into line 58
and the advance chamber 50, moving the vane 46 in the direction
shown by the arrow.
[0042] Makeup oil is supplied to the phaser from supply to make up
for leakage and enters line 55 and moves through inlet check valve
57 to the spool valve 51. From the spool valve 51 fluid enters line
60 through either of the check valves 59, 61, depending on whether
fluid travels to the advance chamber 50 or the retard chamber
52.
[0043] FIG. 1a shows the phaser in null or a central position where
the spool lands 54a, 54b block lines 58 and 62, respectively and
vane 46 is locked into position. Makeup oil may be provided to the
chambers 50, 52 as necessary. In the null or central position, the
actuation rate is zero. However, the force from the actuator 38 on
the spool must balance the force of the spring 64, to maintain the
spool in a central position.
[0044] FIG. 2 shows a schematic of an oil pressure actuated phaser.
In an oil pressure actuated phaser, engine oil pressure is applied
to one side of the vane 46 or the other by a control valve 51. Oil
from the opposing chamber is exhausted back to oil sump through one
of lines 63, 65. The applied engine oil pressure alone is used to
move the vane 46.
[0045] FIG. 3 shows a schematic of a torsion assist phaser, which
may also be used with the control system of the present invention.
In torsion assist phasers, the engine oil pressure is the main
force in which moves the vane 46 in the desired direction. A check
valve 57 is added in the oil supply line 55 to block oil pressure.
The check valve blocks oil pressure pulses due to torque reversals
caused by changing load conditions from propagating back into the
oil system, prevents drainage of oil from the phaser when the
engine is stopped, and stops the vane from moving backwards due to
torque reversals. In this type of system, however, motion of the
vane due to forward torque effects is permitted. Alternatively, two
check valves may be added in the supply line to each of the
chambers. U.S. Pat. No. 6,883,481 and U.S. Pat. No. 6,763,791 also
disclose torsion assist phasers and are hereby incorporated by
reference.
[0046] The control system of the present invention described above
may also be used with a hybrid phaser, which is a CTA phaser with
proportional oil pressure as discussed in U.S. Pat. No. 6,997,150
which is hereby incorporated by reference
[0047] Ideally, the actuation rate of the vane would be constant
for a given duty cycle. Unfortunately, however, the relationship
between actuation rate and duty cycle may change under differing
temperature conditions. As the temperature increases, the actuation
rate at a given duty cycle tends to increase. An example of this
relationship is shown in FIG. 4 which graphically illustrates a
first embodiment of the present invention. The system is designed
so that at a nominal temperature 1, a first actuation rate curve 66
is present. As the temperature is increased to a temperature 2 and
to a further temperature 3, the actuation rate curves may change to
curves 68 and 70 respectively. These actuation curves 66, 68, 70
may be determined empirically during development of the VCT phaser.
Although the example actuation curves 66, 68, 70 are shown as
continuous curves, they may be discreet points in other
embodiments, and for the purposes of choosing values from such
discreet points, algorithms for rounding or interpolating may be
used. The benefit to programming, storing, or making the data
actuation rate curve data available to the controller 36 is that a
duty cycle may be set to achieve a desired actuation rate AD based
on the current temperature conditions.
[0048] When the temperature is temperature 1, actuation rate AD is
achieved by setting the duty cycle to DC1. If the temperature is
increased to temperature 2, then a duty cycle value of DC2 would
achieve the actuation rate AD. Similarly, if the temperature is
increased to temperature 3, then a duty cycle value of DC3 would
achieve the actuation rate AD. In other words, the duty cycle is
varied based on temperature to maintain a constant actuation rate.
For simplicity, duty cycles are mapped for only three temperatures
in the embodiment of FIG. 4, however, any number of temperatures
may be mapped in other applications. The temperature map values may
be stored in a non-volatile memory (NVM), read-only memory (ROM),
or populated into a volatile memory, such as a random access memory
(RAM) as needed.
[0049] FIG. 5 shows the steps for a method of adjusting the duty
cycle of the actuator 38, preferably a PWM solenoid of a phaser as
shown in FIGS. 1 through 3, based on temperature changes only,
using a temperature limit curve. In a first step 72, the maximum
actuation rate is set by the ECU 39. Then, the temperature is
determined by a sensor 40, preferably in the main oil gallery in
step 73 and sent to the controller 36. Next, a temperature limit
curve is selected in step 74 by controller 36. The temperature
limit curve may be a continuous relationship or a set of discreet
points. In step 75, a new max duty cycle is calculated and then
compared in step 76 to the current duty cycle stored in the
controller 36 and adjusted in step 77, if necessary, based on the
temperature limit curve selected in step 74. The controller 36 then
uses this duty cycle when activating the actuator 38. If the duty
cycle is the same, the method restarts at step 73.
[0050] Optional actions may be taken prior to adjusting the duty
cycle in step 77. Rather than always having to select the duty
cycle curve, particularly if the temperature was not changing or
had reached a steady state, a current duty cycle table may be
populated in step 80 with various actuation rates based on the last
changed temperature. No change would be necessary if the
temperature has not changed. Since discreet values are likely to be
used in the step 74 of selecting a temperature curve or in step 80
of populating a duty cycle table, step 82 of interpolating the
values populated into the current temperature limit curve may be
performed. Similarly, the duty cycle rate may be interpolated in
step 84 in order to determine the desired actuation rate for the
actuation rate adjustment in step 77.
[0051] Alternative to using a temperature limit curve is to
determine the maximum duty cycle by equation (1.1), calculated in
controller 36 at a constant voltage. [ 1 V 0 [ R 0 * .alpha.
.function. ( .DELTA. .times. .times. T ) ] + R 0 ] * 100 = Max
.times. .times. DC ( 1.1 ) ##EQU1## Where: [0052] R.sub.0 is the
Initial Resistance at starting temperature; [0053] .DELTA.T is the
change in temperature from a starting temperature to a final
temperature; [0054] .alpha. is the Temperature coefficient of
resistance; and [0055] V.sub.0 is the initial voltage
[0056] For example, if the starting temperature of the main oil
gallery is 20.degree. C., the initial resistance is 6 ohms, the
temperature coefficient of resistance is for copper, due to the
windings in the controller, the voltage is 14 volts, and the
temperature increases to 135.degree. C., the maximum duty cycle
(MaxDC) would be calculated as follows: [ 1 14 [ 6 * .0039 .times.
( 115 ) ] + 6 ] * 100 = Max .times. .times. DC ( 1.1 ) ##EQU2##
62.08%=MaxDC at 135.degree. C. Therefore, the maximum duty cycle
would be set at 62.08% in order to receive the maximum current
output of 1.0 amp.
[0057] FIG. 6 shows the steps for a method of adjusting the duty
cycle of a PWM solenoid of a phaser as shown in FIGS. 1 through 3
based on temperature changes only, using equation (1.1) calculated
in controller 36. In a first step 72, the maximum actuation rate is
set by the ECU 37. Then, the temperature is determined by a sensor
40, preferably in the main oil gallery in step 173 and the initial
resistance is at the initial starting temperature is determined and
sent to the controller 36. The temperature and the initial
resistance at the initial starting temperature is inputted into
step 175 and a new duty cycle is determined, preferably using
equation (1.1) in the controller 36. In step 176, the new max duty
cycle is compared to the current duty cycle stored in the
controller 36 and adjusted if necessary in step 177. The controller
36 then uses this duty cycle when activating the actuator 38. If
the duty cycle is the same, the method restarts at step 173.
[0058] In a second embodiment, the controller varies the duty cycle
sent to the actuator 38, preferably a PWM solenoid is varied based
on voltage only in the phasers shown in FIGS. 1 through 3. The
voltage is preferably from a battery in the engine. Based on the
system designed, the current outputted as a result of the voltage
is reduced (if necessary) to a maximum current that is
non-detrimental to the both the system as a whole and the solenoid
valve through the duty cycle of the PWM solenoid or actuator 38.
For the examples in this application, the maximum amount of current
used with the system is 1 amp. One amp of current corresponds to
full movement of the spool in a direction from a null position of
the spool. While 1 amp was chosen as the maximum current of the
system, other values may be chosen. Table 1 shows a range of
voltages at a constant temperature and the current originally
outputted from the system and the max percent duty cycle used to
maintain the one amp maximum set. TABLE-US-00001 TABLE 1 Initial
New Max Voltage Temperature Current Max Duty Cycle Current Output 9
V 40.degree. C. 1.36 amps 73.3% 1.0 amp 12 V 40.degree. C. 1.82
amps 55.0% 1.0 amp 15 V 40.degree. C. 2.27 amps 44.0% 1.0 amp 18 V
40.degree. C. 2.73 amps 36.7% 1.0 amp (Assuming an initial
resistance of 6.6 ohms).
The maximum duty cycle for a change in voltage may be calculated
using equation (2.1). [ 1 V 0 + .DELTA. .times. .times. V R 0 ] *
100 = Max .times. .times. DC ( 2.1 ) ##EQU3## Where: [0059] V.sub.0
is the Voltage initial; [0060] R.sub.0 is the Resistance initial;
and [0061] .DELTA.V=is the change in voltage.
[0062] For example, if the voltage changes from outputting 9 volts
to 12 volts with an initial resistance of 6.6 ohms at a constant
temperature of 40.degree. C., the maximum duty cycle (MaxDC) would
be calculated as follows: [ 1 V 0 .times. + .times. .DELTA. .times.
.times. V R 0 ] * 100 = Max .times. .times. DC .times. [ 1 9 + 3
6.6 ] * 100 = Max .times. .times. DC ( 2.1 ) ##EQU4## 55%=MaxDC at
12V and a constant temperature of 40.degree. C.
[0063] The max duty cycle at 12 volts and a constant temperature
40.degree. C. is 55% to insure that only 1 amp of current is
received by the actuator 38. The max duty cycle for other voltages
are listed in Table 1.
[0064] FIG. 7 shows steps for a method of a method of adjusting the
duty cycle of a PWM solenoid of a phaser as shown in FIGS. 1
through 3 based on voltage changes only, using equation (2.1) which
is calculated in controller 36. In a first step 72, the maximum
actuation rate is set by the ECU 37. Then, the voltage outputted by
the battery is determined and the initial resistance at the
constant temperature is determined in step 273. Next, in step 275,
the new maximum duty cycle is determined in the controller 36,
preferably using equation (2.1). In step 276, the new max duty
cycle is compared to the current duty cycle stored in the
controller 36 and adjusted if different in step 277. The controller
36 then uses the new adjusted duty cycle from step 277 when
actuating actuator 38. If the duty cycle is the same, the method
restarts at step 273.
[0065] Alternatively, as shown in FIGS. 8 and 9, a voltage curve
may also be used to determine the maximum duty cycle. In a first
step 72, of a method of adjusting the duty cycle of a PWM solenoid
of a phaser as shown in FIGS. 1 through 3, the maximum actuation
rate is set by the ECU 37. Then, the voltage outputted by the
battery is determined and the constant temperature is determined in
step 373. Next, in step 374, a voltage curve, as shown in FIG. 8 is
selected by controller 36 and is used to determine a new duty
cycle. The voltage curve may be a continuous relationship or a set
of discreet points. In step 375, the new max duty cycle is compared
to the current duty cycle stored in the controller 36 and adjusted
if different in step 377. The controller 36 then uses the new
adjusted duty cycle from step 377 when actuating actuator 38. If
the duty cycle is the same, the method restarts at step 373. The
duty cycle rate may be interpolated in step 384 in order to
determine the desired actuation rate for the actuation rate
adjustment in step 377.
[0066] In a third embodiment, the duty cycle of the actuator 38,
preferably a PWM solenoid of a phaser as shown in FIGS. 1 through 3
is varied based on voltage and temperature. The voltage is
preferably from a battery in the engine. Based on the system
designed, the current outputted as a result of the voltage and
temperature is altered to a maximum current that is non-detrimental
to the both the system as a whole and the solenoid valve through
the duty cycle of the PWM solenoid or actuator 38. For the examples
in this application, the maximum amount of current used with the
system is 1 amp. One amp of current corresponds to movement of the
spool in a first direction from null and may be the advancing
direction. As the temperature changes, the voltage from the battery
changes, thus the amps outputted also changes due to resistance. In
order to maintain the maximum actuation rate of the phaser, the
current outputted from the varying voltage and temperature is
altered back to 1 amp by varying the duty cycle as in previous
embodiments.
[0067] The initial current as the voltage and temperature change
may be calculated using equation (3.1). [ 1 V 0 + .DELTA. .times.
.times. V [ R 0 * .alpha. .function. ( .DELTA. .times. .times. T )
] + R 0 ] * 100 = Max .times. .times. DC ( 3.1 ) ##EQU5## Where:
[0068] V.sub.0 is the Initial Voltage; [0069] R.sub.0 is the
Initial Resistance; [0070] .DELTA.V is the Change in Voltage;
[0071] .DELTA.T is the Change in Temperature; and [0072] .alpha. is
the Temperature coefficient of resistance.
[0073] For example, if the initial temperature and voltage of the
system were -40.degree. C. and 10 volts respectively, with the
initial resistance determined to be 5 ohms for the system, the
actuator has copper windings, and the system changed to 20.degree.
C. and 12 volts, the max duty cycle based on the initial current
and the current maximum of 1 amp would be calculated as follows
using equation (3.1). [ 1 V 0 .times. + .times. .DELTA. .times.
.times. V [ R 0 * .alpha. .function. ( .DELTA. .times. .times. T )
] .times. + .times. R 0 ] * 100 = Max .times. .times. DC .times. [
1 10 + 2 [ 5 * .0039 .times. ( 60 ) ] + 5 ] * 100 = Max .times.
.times. DC ( 3.1 ) ##EQU6## 51.4%=MaxDC at 12V and 20.degree.
C.
[0074] While not shown in the above example, the duty cycle may
also be calculated for other positions of the spool, such as null
position and for other temperatures and voltages.
[0075] FIG. 10 shows the steps for a method of adjusting the duty
cycle of a PWM solenoid of a phaser as shown in FIGS. 1 through 3
based on temperature and voltage changes. In a first step 72, the
maximum actuation rate is set by the ECU. Then, the temperature,
the voltage, and the initial resistance at the temperature measured
is determined in step 473. The temperature may be measured by a
sensor 40, which is preferably in the main oil gallery. Next, in
step 474a, a temperature limit curve and a voltage curve are
selected by the controller 36. The temperature limit curve and the
voltage curve may be continuous relationships or sets of discreet
points. In step 475, a new max duty cycle is determined and then
compared in step 476 to the current duty cycle stored in the
controller 36. If the new duty cycle is the same as the current
duty cycle, the method is repeated starting at step 473. If the new
duty cycle differs from the current duty cycle, the duty cycle is
adjusted in step 477, and the new duty cycle is used when
activating actuator 38.
[0076] Step 474 may be removed from the method, and in step 475,
the new max duty cycle may be determined by using equation (3.1)
calculated in the controller 36. In another alternative, the max
duty cycle for a system with both voltage and temperature changes
may be determined using the temperature limit curve or the voltage
curve and equations (2.1) and (1.1) for the other.
[0077] Optional actions may be taken prior to adjusting the duty
cycle in step 477. Rather than always having to select the duty
cycle curve, particularly if the temperature and/or voltage was not
changing or had reached a steady state, a current duty cycle table
may be populated in step 480 with various actuation rates based on
the last changed temperature or voltage. No change would be
necessary if the temperature and voltage have not changed. Since
discreet values are likely to be used in the step 474 of selecting
a temperature curve or a voltage curve or in step 480 of populating
a duty cycle table, step 482 of interpolating the values populated
into the current temperature limit curve or voltage curve may be
performed. Similarly, the duty cycle rate may be interpolated in
step 484 in order to determine the desired actuation rate for the
actuation rate adjustment in step 477.
[0078] Accordingly, it is to be understood that the embodiments of
the invention herein described are merely illustrative of the
application of the principles of the invention. Reference herein to
details of the illustrated embodiments is not intended to limit the
scope of the claims, which themselves recite those features
regarded as essential to the invention.
* * * * *