U.S. patent application number 09/681746 was filed with the patent office on 2002-12-05 for method and system for determining the variable cam timing rate-of-change in an engine.
Invention is credited to Jankovic, Mrdjan J., Magner, Stephen William.
Application Number | 20020179027 09/681746 |
Document ID | / |
Family ID | 24736604 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020179027 |
Kind Code |
A1 |
Jankovic, Mrdjan J. ; et
al. |
December 5, 2002 |
METHOD AND SYSTEM FOR DETERMINING THE VARIABLE CAM TIMING
RATE-OF-CHANGE IN AN ENGINE
Abstract
An internal combustion engine having variable camshaft timing
that incorporates a method of determining the position of the
variable cam timing phasing system for controlling the flow of
intake and exhaust gases during the combustion process. The method
includes the steps of creating a model for estimating a calculated
cam position and a calculated rate-of-change of the cam position.
The method also includes the step of measuring a measured cam
position and a measured rate-of-change of the cam position. The
calculated cam position is compared to the measured cam position
and calculated rate-of-change of the cam position and measured
rate-of-change of the cam position that are blended based upon a
comparison of the two values. The engine controller is adjusted
dependent upon the blended rate-of-change of the cam position.
Inventors: |
Jankovic, Mrdjan J.;
(Birmningham, MI) ; Magner, Stephen William;
(Lincoln Park, MI) |
Correspondence
Address: |
BROOKS & KUSHMAN P.C./FGTI
1000 TOWN CENTER
22ND FLOOR
SOUTHFIELD
MI
48075
US
|
Family ID: |
24736604 |
Appl. No.: |
09/681746 |
Filed: |
May 31, 2001 |
Current U.S.
Class: |
123/90.15 |
Current CPC
Class: |
F02D 13/0253 20130101;
F02D 41/0002 20130101; F02D 2041/001 20130101; F01L 1/34 20130101;
F02D 41/187 20130101; Y02T 10/18 20130101; F02D 41/064 20130101;
F02D 2200/0404 20130101; Y02T 10/12 20130101; F02D 2041/1432
20130101; F02D 2200/0402 20130101; Y02T 10/42 20130101; F02D
2041/1433 20130101; Y02T 10/40 20130101 |
Class at
Publication: |
123/90.15 |
International
Class: |
F01L 001/34 |
Claims
1. A method of controlling an engine having an engine controller
that controls the flow of intake and exhaust gases in a combustion
process of the engine, comprising: calculating a first cam position
and a first rate-of-change of the cam position; measuring a second
cam position and a second rate-of-change of the cam position;
comparing the first cam position to the second cam position;
blending the first rate-of-change of the cam position and the
second rate-of-change of the cam position to establish a blended
rate of change of the cam position based upon the comparison; and
adjusting the engine controller dependent upon the blended
rate-of-change of the cam position.
2. The method of claim 1 wherein the algorithm for calculating the
first cam position and the first rate-of-change of the cam position
is:
est.sub.--cam.sub.--derv(k)=Funct.sub.--sat.sub.--lim[actuator.sub.--gain-
*(cam.sub.--ph.sub.--d(k)-est.sub.--cam.sub.--pos(k-1))]est_cam.sub.--pos(-
k)=del.sub.--t*est.sub.--cam.sub.--derv(k-1)+est.sub.--cam.sub.--pos(k-1))
3. The method of claim 2 wherein an algorithm for the blending step
is:
blend(k)=funct.sub.--blend(pos.sub.--diff(k))cam.sub.--derv(k)=blend(k)*e-
st.sub.--cam.sub.--derv(k)+(1-blend(k))*cam.sub.--meas.sub.--derv(k)
4. The method of claim 1 wherein the engine controller is an
electronic throttle control.
5. The method of claim 1 wherein the engine has a dual equal cam
with equal phase intake and exhaust cams that are advanced and
retarded equally.
6. The method of claim 1 wherein when the comparison of the first
cam position to the second cam position results in a difference
below a low threshold value, the engine controller uses the first
cam position and first rate-of-change of the cam position.
7. The method of claim 6 wherein when the comparison of the first
cam position to the second cam position results in a difference
above a high threshold value, the engine controller uses the second
cam position and second rate-of-change of the cam position.
8. The method of claim 7 wherein when the comparison of the first
cam position to the second cam position results in a difference
between the low threshold value and the high threshold value, the
engine controller uses the blended rate-of-change based on the
comparison and further based upon the first rate-of-change and the
second rate-of-change of the cam position.
9. In an internal combustion engine having a crankshaft and a
camshaft, the engine including a variable phase cam timing system
that alters a phase relationship between the camshaft and the
crankshaft, a method of determining a blended rate-of-change of a
cam position, the method comprising: determining a reference cam
position; utilizing a model to determine an estimated cam position
and an estimated rate-of-change of the cam position based on the
reference cam position; measuring an actual cam position;
determining a filtered rate-of-change of the actual cam position;
comparing the model estimated cam position to the measured actual
cam position; determining the blended rate-of-change of the cam
position based on the comparison, and further based on the
estimated rate-of-change of the cam position and the filtered
rate-of-change of the cam position.
10. The method of claim 9 wherein when the comparison of the model
estimated cam position to the measured actual cam position results
in a difference below a low threshold value, the engine determines
the blended rate-of-change of the cam position as the estimated
rate-of-change of the cam position.
11. The method of claim 9 wherein when the comparison of the model
estimated cam position to the measured actual cam position results
in a difference above a high threshold value, the engine determines
the blended rate-of-change of the cam position as the filtered
rate-of-change of the cam position.
12. The method of claim 11 wherein when the comparison of the model
estimated cam position to the measured actual cam position results
in a difference between the low threshold value and the high
threshold value, the engine determines the blended rate-of-change
based on the comparison as a blend of the model estimated
rate-of-change of the cam position and the filtered rate-of-change
of the cam position.
13. A system for determining the rate-of-change of a cam position
for an internal combustion engine having a crankshaft and a
camshaft, the engine including a variable phase cam timing system
that alters a phase relationship between the camshaft and the
crankshaft, the system comprising: a data processor having a model
for determining an estimated cam position relative to a reference
cam position and an estimated rate-of-change of the cam position; a
sensor for measuring an actual cam position; the data processor
having a filtering algorithm for determining a filtered
rate-of-change of the actual cam position; the data processor
comparing the estimated cam position to the measured actual cam
position; and the data processor determining a blended
rate-of-change of the cam position based upon the comparison, and
further based on the estimated rate-of-change of the cam position
and the filtered rate-of-change of the cam position.
14. The system of claim 13 wherein the engine uses the blended
rate-of-change determined to control an electronic throttle
control.
15. The system of claim 1 3 wherein the engine has a dual equal cam
with equal phase intake and exhaust cams that are advanced and
retarded equally.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to internal combustion engines using
variable camshaft timing.
[0003] 2. Background Art
[0004] In conventional engines, the timing between the crankshaft
and camshafts is rotationally fixed. Recently, engines have been
improved by including mechanisms for automatically advancing or
retarding camshaft rotation relative to the rotation of the
crankshaft. By providing automatic advance or retard, it is
possible to maximize fuel economy and minimize emissions in the
engine's exhaust. It is also possible to increase the peak torque
and improve fuel economy by optimizing the phase angle relationship
of the camshaft relative to the crankshaft.
[0005] Phase shift control is provided by a hydraulic coupler that
rotationally couples the camshaft drive sprocket to a camshaft
flange. An engine control data processor monitors continuously
varying engine operating conditions and provides a control signal
to the hydraulic coupler to set the desired relative phase angle
for the engine operating conditions. Variable camshaft timing
systems have been developed with the objective of correcting the
air charge drop during camshaft retard that may result in a dip in
torque response. One example of this approach is disclosed in U.S.
Pat. No. 5,690,071 which discloses a method for adjusting the
variable camshaft timing induced air variation that uses the air
bypass valve to compensate for induced air charge variation. The
patent also proposes the use of an electronically-controlled
throttle that compensates for induced air change variation.
[0006] While this approach improves the performance of the variable
camshaft timing system in normal circumstances, the use of a
measured cam position and cam rate-of-change values is based on a
signal that includes oscillations and a high degree of signal
filtering. Signal filtering causes delays in response to the
continuously varying engine operating conditions that may result in
a reduction in torque response or increase in emissions.
[0007] To minimize delay caused by filtering measured signals, it
has been proposed to use a model of the variable camshaft timing
rate-of-change to control engine operation. Under cold-start
conditions wherein the engine oil is cold and highly viscous, or if
inadequate oil is available to the engine, the hydraulic device
rotationally coupling the camshaft drive sprocket to the camshaft
flange may be substantially retarded relative to the model. Under
these operating conditions, the model of the variable camshaft
timing rate-of-change if used to control an engine operating system
would be less effective than the measured camshaft timing approach
proposed in U.S. Pat. No. 5,690,071.
[0008] There is a need for an internal combustion engine having a
variable camshaft timing system that minimizes delays caused by
filtering oscillations in a measured camshaft position based
system, but that includes a measured camshaft position system for
controlling the camshaft position under cold-start or when low-oil
pressure is encountered by the engine.
[0009] The present invention addresses the above problems and
fulfills the need for a system that maximizes the benefits of
variable camshaft timing as summarized below.
SUMMARY OF THE INVENTION
[0010] According to the present invention, a method of determining
the position of a variable cam timing phasing system for an engine
having an engine controller that controls the flow of intake and
exhaust gases during the combustion process is provided. The method
comprises the steps of creating a model for estimating a calculated
cam position and a calculated rate-of-change of the cam position.
The method also includes the step of measuring an actual cam
position and an actual rate-of-change of the cam position.
According to the method, the calculated cam position is compared to
the measured cam position and the calculated rate-of-change of the
cam position and measured actual rate-of-change of the cam position
are blended based upon the comparison. The engine controller is
adjusted dependent upon the blended rate-of-change of the cam
position.
[0011] According to another aspect of the invention, an algorithm
based upon test data and simulations is provided for estimating the
calculated rate-of-change of the cam position.
[0012] Based upon another aspect of the invention, an algorithm has
been developed for blending the estimated and measured actual cam
positions and measurement based rate-of-change of the cam
position.
[0013] According to yet another aspect of the invention, the engine
controller may be an electronic throttle control. The engine may
have a dual equal cam with equal phase intake and exhaust cams that
are advanced and retarded equally relative to the crankshaft.
Alternatively, the invention could be used in conjunction with an
idle speed valve system and other forms of variable cam timing
systems including exhaust only or dual independent cams.
[0014] The invention also relates to the engine controller using
the calculated cam position and calculated rate-of-change of the
cam position when the comparison of the calculated cam position to
the measured cam position is below a threshold value. The engine
controller uses the measured cam position and measured
rate-of-change of the cam position when the comparison of the
calculated cam position to the measured cam position is above a
high threshold value. When the comparison of the calculated cam
position to the measured cam position is above the low threshold
value and below the high threshold value, the engine controller
uses a blended rate-of-change based on the comparison and further
based upon the calculated rate-of-change and measured
rate-of-change of the cam position.
[0015] According to another aspect of the invention, a method of
determining a blended rate-of-change of a cam position in an
internal combustion engine having a variable phase cam timing
system is proposed that includes a first step of determining a
reference cam position. The next step of the method is to utilize a
model to determine an estimated cam position and an estimated
rate-of-change of the cam position. The system measures an actual
cam position and determines a filtered rate-of-change of the actual
cam position based upon the measurement. The model estimated cam
position is compared to the measured actual cam position. The
method further includes the step of determining the blended
rate-of-change of the cam position based on the comparison, and
further based on the estimated rate-of-change of the cam position
and the filtered rate-of-change of the cam position.
[0016] The invention may also be seen as a system for determining
the rate-of-change of a cam position for an internal combustion
engine having a crankshaft and a camshaft. The internal combustion
engine includes a variable phase cam timing system that alters a
phase relationship between the camshaft and the crankshaft. The
system comprises a data processor having a model for determining an
estimated cam position relative to a reference cam position and
also estimating a rate-of-change of the cam position. A sensor is
provided for measuring an actual cam position and a data processor
includes a filtering algorithm for determining the filtered
rate-of-change of the actual cam position. The data processor
compares the estimated cam position to the measured actual cam
position and determines a blended rate-of-change of the cam
position based upon the comparison, and further based on the
estimated rate-of-change of the cam position and the filtered
rate-of-change of the cam position.
[0017] These and other aspects of the present invention will be
better understood in view of the attached drawings and detailed
description of the invention.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a schematic cross-sectional view of an internal
combustion engine;
[0019] FIG. 2 is a block diagram showing the system for determining
the variable cam timing rate-of-change in an engine according to
the present invention;
[0020] FIG. 3 more specifically illustrates the cam positions and
derivatives;
[0021] FIG. 4 is a graph of the blending function;
[0022] FIG. 5 is a graph of the time responses of the cam timing
model and the actually measured cam position; and
[0023] FIG. 6 is a graph of the model-based estimate of the cam
phase rate-of-change and the combined model/measurement
estimate.
DETAILED DESCRIPTION
[0024] Referring now to FIG. 1, an internal combustion engine 10
having a dual equal variable camshaft timing (VCT) mechanism is
shown. The engine 10 includes an intake manifold 12 and an intake
port 14. The intake port opens into one of a plurality of cylinders
or combustion chambers 16. A fuel injector 18 is associated with
each intake port 14 near an intake valve 20 of each cylinder 16.
While the disclosure illustrates a port injected engine, the
invention is also applicable to direct injection engines and diesel
engines.
[0025] The intake manifold 12 is connected to an induction passage
22 that includes a throttle valve 24 and bypass passage 26. The
bypass passage 26 provides a bypass around the throttle valve 24
and includes an air bypass valve 28 that is used to control the
idle speed of the engine.
[0026] A position sensor 30 is provided to sense the angular
position of the throttle valve 24. The induction passage 22 may
include a mass flow sensor 32 and has an air cleaner system 34 at
one end. The engine 10 includes an exhaust manifold 38 that is
connected to each combustion chamber 16. Exhaust gases generated
during combustion in each cylinder 16 are released through an
exhaust valve 40. Cam shafts 42, 42 N are provided to actuate the
intake valve 20 and exhaust valve 40, respectively. The position of
the cam shafts 42, 42 N are monitored by camshaft position monitors
43, 43 N . The crankshaft 44 of the engine 10 is monitored by a
crank angle detector 46 that is used to detect the rotational
position of the crankshaft 44. An onboard computer 48 including
ROM, RAM, CPU and I/O contains engine control programs. According
to the present invention, the computer stores a cam schedule in the
form of a lookup table using throttle position entry points to
determine the camshaft timing. The ROM also may store an air bypass
valve schedule. As described below, the computer 48 is adapted to
receive input signals and provide output control signals for
controlling the process of internal combustion in the engine
10.
[0027] The method of the present invention will be described with
reference to the flow chart of FIG. 2. The method begins with the
system determining a reference or desired cam position at 50. The
reference cam position is provided to a model 52 that generates an
estimated cam rate-of-change signal that is provided to line 54 and
an estimated cam position that is provided to line 56. A suitable
model is a closed loop model based on cam position, that after the
summer, includes gain with a limiter followed by an integrator.
According to the method, the actual cam position is measured at 60
and the cam position signal is provided at line 62 to a filter at
64 that provides a filtered measured cam rate-of-change value on
line 66. A suitable filter is a second order filter followed by a
differentiator. The model estimate of the cam position is compared
to the measured cam position at 70. The comparison is then provided
to a filter at 72 that filters the comparison. A suitable filter is
a first order filter. The output of the filter is provided to the
soft switch logic at 74. The signal from soft switch logic 74 is
provided to line 76. At 80, the estimated cam rate-of-change from
line 54, filtered measured cam rate-of-change at line 66, and blend
provided by the soft switch logic 74 on line 76 are processed and
an allocation is made between the model and the measured
rate-of-change. The result of the allocation is provided at 82 to
establish a blended rate-of-change of cam position. The blended
rate-of-change of cam position is used to provide a control action
for the engine that depends on the variable cam timing phase
rate-of-change value.
[0028] Although a broad implementation of the present invention has
been described above, a more specific suitable implementation is
best understood with reference to FIGS. 2 and 3. Specifically,
blocks 50 and 52 of FIG. 2 utilize a model to determine an
estimated cam position 56 and an estimated rate of change of the
cam position 54, based on the reference cam position or desired cam
position.
[0029] FIG. 3 illustrates a suitable model for estimating cam
position and position rate-of-change. In FIG. 3, a desired or
reference cam position is indicated at 100. Summer 102 determines
an error signal by subtracting the predicted cam position 104 from
the referenced cam position 100. The cam position error signal from
summer 102 is fed to processor 106. Processor 106 is suitably a
straight gain function. The output of gain function processor 106
is supplied to limiter 108 so as to limit the predicted
rate-of-change of the cam position. Specifically, the estimated cam
position rate-of-change is indicated at 112. The cam position
derivative is spread to integrator 110 to determine the estimated
cam position 104 that is fed back to the summer 102. As understood
when viewing FIGS. 2 and 3, estimated cam position 104 corresponds
to line 56 of FIG. 3, and estimated cam position derivative 112
corresponds to line 54 in FIG. 2.
[0030] Further, in FIG. 2, block 60 and 64 illustrate the measuring
of the actual cam position (block 60), and the filtering of the
measured position (block 64) to filter out high frequency noise. Of
course, it is understood that there are always some delays
associated with filtering, however, embodiments of the present
invention utilize a blending function of the predicted cam position
derivative. This approach balances the advantages of the accuracy
of an actual measurement and the low delay of a model.
[0031] More specifically, FIG. 3 illustrates a suitable
implementation for filter 64 in FIG. 2. In FIG. 3, actual cam
position is measured at 120. Transfer function 122 includes a
second order filter multiplied (in frequency domain) with a
differentiator. It is appreciated that the natural frequency and
damping coefficient may vary in other suitable implementations of
the present invention and that a second order Butterworth filter is
merely exemplary. As shown in FIG. 3, line 120 is the actual
measured cam position and line 124 is the filtered derivative of
the measured cam position.
[0032] Referring back to FIG. 2, block 70 compares the measured cam
position (120, FIG. 3) and the estimated cam position (104, FIG.
3). The difference between the measured cam position and the
predicted cam position determines how the estimated derivative and
measured filter derivative will be blended together. Because the
actual cam position is a noisy signal, the absolute value of the
difference from block 70 is filtered at block 72. The filter at
block 72 may be suitably implemented as a first order filter that
averages the previous two errors. Soft logic switch 74 in FIG. 2
determines a blend value.
[0033] The determination of the blend value by soft logic switch 74
is best illustrated in FIG. 4. As shown, the blend value is lower
when the position difference (filter difference at block 72) is
greater. And, the blend value is higher when the position
difference is smaller. Although the blend value is shown as a
linear function in FIG. 4, it should be appreciated that higher
order functions may be utilized to achieve the blend value. In FIG.
2, at block 80, the blend value at line 76 is used by the logic 80
to blend the cam position rate-of-change from the model 54 with the
filtered measured cam rate-of-change 66.
[0034] With reference to FIG. 4, smaller position differences
result in a heavier weighting of the estimated cam rate-of-change
54, while larger positioned differences result in a heavier
weighting of the measured cam rate-of-change 66. In a suitable
implementation, the blend value from FIG. 4 ranges from 0 to 1.
Advantageously, embodiments of the present invention provide the
advantage of low delay by utilizing a model based cam position
while providing the accuracy of a measured cam position.
[0035] In summary, in a suitable implementation, the method first
creates an estimate of the cam position derivative that is based on
a commanded signal and then blends this estimated derivative
together with a conventionally filtered measured cam position
signal. The system adjusts the blending by using a process term
based on the difference between the estimated and measured
position. The estimate of the cam phase derivative provides a
prompt and reasonably accurate signal under normal warm engine
operation. Engines, at times, are required to function under
non-normal conditions, such as when the engine is cold or if there
is insufficient oil or an actuator failure. Operating under
non-normal conditions may cause the estimate of the cam phase
derivative to be incorrect in its estimation of the cam actuator
position and in its estimate of the cam rate-of-change. The
variable cam timing actuator uses hydraulic pressure from the
engine oil lubrication system. Altered actuator response times may
be caused by a low oil level resulting in low pressure, a partial
blockage in an oil gallery, reduced actuator oil flow, or from the
use of oil having inappropriate viscosity. Cold weather conditions
that occur during initial engine start-up on cold days may also
impact actuator response time.
[0036] According to a method of the present invention, the measured
cam phase position signal is used to reveal non-normal behavior.
The system employs a combination of the estimated and measured cam
phase position and rate-of-change so that it automatically adjusts
to normal and non-normal conditions.
[0037] The model based cam rate-of-change at 52 then creates an
estimate of the cam position derivative using a simple model of the
actuation device. The VCT phasing actuator acts as a rate-limited,
first order, low pass filter when commanded to a VCT phase
position. The model representation below is a relatively simple
model. More or less elaborate models could also be developed that
would provide an estimate of the cam position derivative. The model
can be expressed in a computer-implemented algorithm as
follows:
est.sub.--cam.sub.--derv(k)=Funct.sub.--sat.sub.--lim[actuator.sub.--gain*-
(cam.sub.--ph.sub.--d(k)-est.sub.--cam.sub.--pos(k-1))]
est.sub.--cam.sub.--pos(k)=del.sub.--t*est.sub.--cam.sub.--derv(k-1)+est.s-
ub.--cam.sub.--pos(k-1))
[0038] where:
[0039] index k corresponds to the present computer sample;
[0040] k-1 corresponds to the computer's previous loop algorithm
sample;
[0041] est_cam_derv is an estimate of the derivative of the cam
phase position;
[0042] Funct_sat_lim is a function that limits the quantity inside
the brackets to an upper and lower set of values;
[0043] Actuator_gain is a fixed value determined through either
physical modeling of the actuator or through experiment on the
actuator;
[0044] Cam_ph_d is the commanded or desired value for the cam phase
position;
[0045] Est_cam_pos is the estimate of the cam phase position;
and
[0046] del_t is the time between processor updates of the
algorithm.
[0047] The above model could be modified by removing the rate
limiting or by the addition of higher order response terms or time
delays that may be appropriate choices, depending upon the VCT
actuator.
[0048] The measured actual cam position at 60 and estimated cam
position signal at 56 are used to reject noise having a limited
amplitude due to the limitations of the sources of the noise.
Camshaft flex, signal noise, and timing chain stretching only
introduce several degrees of cam phase error, but they are
introduced at a high rate-of-change. The rapid small fluctuations
of cam phase are considered to be noise whether they physically
occur or are the result of sensor errors. Compensation by the
control system in air flow will have a negligible response to this
type of VCT change. On the other hand, a prompt derivative of the
VCT position is required to cope with large VCT changes. It can be
promptly determined if the cam change is significant or not, and
the system can be caused to react accordingly by determining the
difference between the cam measurement base position and the
estimated position.
[0049] In addition to the model-based estimate of the cam phase
rate-of-change determined above, the method also requires a
conventionally filtered signal based on the measured sensor value
of the cam position. A second order Butterworth filter is used to
low pass filter the signal before calculating the rate-of-change.
The result of the measured/processed cam derivative is referred to
as cam_meas_derv. The discrete time equations for the second order
filter are as follows: 1 CD_NF _DT = del_t * CD_nat _freq CD_X1 ( k
) = CD_X1 ( k - 1 ) + CD_NF _DT * CD_X2 ( k - 1 ) CD_X2 ( k ) = ( 1
- 2 * CD_damping * CD_NF _DT ) * CD_X2 ( k - 1 ) + CD_NF _DT * (
cam_actual - CD_X1 ( k - 1 ) ) cam_meas _derv = CD_nat _freq * C D
( X2 ( k - 1 )
[0050] where CD_nat_freq is adjustable for the cutoff frequency of
the low pass filter and the CD_damping adjusts the second order
damping. The k or k-1 indices refer to current and past values of
the states of variables of the filter that result when a continuous
frequency domain filter is transformed into a discrete(for
microprocessor implementation)approximati- on.
[0051] The difference between the two types of cam positions are
calculated and a term is calculated that will govern the blending
of the measurement based and estimated cam derivative. An
approximate first order filter is used to process the difference in
measured versus estimated positions to further suppress noise that
is outside the bandwidth of the intake manifold of the engine. The
formula is as follows: 2 fk ( k ) = del_t del_t + TC_est _cam
abs.sub.--diff(k)=.vertline.est.sub.--cam.sub.--pos(k)-cam.sub.--meas(k).v-
ertline.
pos.sub.--diff(k)=fk(k)*abs.sub.--diff(k)+(1-fk(k))*pos.sub.--diff(k-1)
[0052] where:
[0053] fk is the filter constant based on the update rate del_t and
the time constant determined from the engine models; and
[0054] Pos_diff is the result of filtering the absolute difference,
which will determine the blending of the estimated versus the
measured based derivative.
[0055] For small amplitude differences, less than 2 degrees, the
system relies on the estimated cam derivative because the
derivative based on measurements will contain noise at this
amplitude. For large amplitude differences, of about 12 or more
degrees, the measured value captures real and unexpected
(un-modeled) cam behavior which should be responded to by the
control system. For values that fall between 2 and 12 degrees, the
system blends the estimated and measured cam derivatives. The exact
range of cam position differences is system-dependent.
[0056] The blending function can be expressed as follows:
blend(k)=funct.sub.--blend(pos.sub.--diff(k))
cam.sub.--derv(k)=blend(k)*est.sub.--cam.sub.--derv(k)+(1-blend(k))*cam.su-
b.--meas.sub.--derv(k)
[0057] The function funct_blend graphed in FIG. 4, maps values of
position difference to a percent of the blending between the two
types of derivative values. The line plot 90 is the function of the
estimated cam derivative that will be used in the final output of
the cam derivative.
[0058] The potential improvement of the model may be seen with
reference to FIG. 5 wherein the model-based estimate of position is
shown in a solid line 92 with the measured position being presented
in the dotted line 94. The plot is of cam phase response versus
time for the model and the actual measured cam phase. The large
motion responses of the two are very similar. However, the model
has the advantage of providing between 50-100 milliseconds lead
time. The presence of high frequency oscillations in the measured
cam phase would require additional filtering of this signal before
its derivative could be used that would further increase the phase
lag.
[0059] The use of a model-based estimate is justified if the model
response remains close to the actual measured cam phase
rate-of-change. If the actual cam timing does not follow the
desired cam reference, a significant difference between the model
and the actual response is indicated. In this case, the performance
of the method described in the invention can be judged by how fast
the system determines the discrepancy and starts using the measured
signal. FIG. 6 illustrates this aspect of the algorithm performance
in the case when the cam phase remains at zero degrees while the
cam reference is based on actual vehicle operation. The dotted
curve 96 corresponds to the model-based estimate of the cam phase
rate-of-change est_cam_derv, while the solid curve 98 is the
cam_derv signal that combines the model- and measurement-based
estimates.
[0060] Referring to FIG. 6, after about 0.6 seconds, the system
recognizes that the model-based derivative estimate is incorrect
and switches to the measurement-based one, which in this case is
equal to zero. During the 0.6 seconds, the cam_derv signal is much
smaller (much closer to the measured) than the est_cam_derv signal
because of the soft switch capabilities of the algorithm.
[0061] While the best mode for carrying out the invention has been
described in detail, those familiar with the art to which this
invention relates will recognize various alternative designs and
embodiments for practicing the invention as defined by the
following claims.
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