Information
-
Patent Grant
-
6766775
-
Patent Number
6,766,775
-
Date Filed
Thursday, November 1, 200123 years ago
-
Date Issued
Tuesday, July 27, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Denion; Thomas
- Corrigan; Jaime
Agents
-
CPC
-
US Classifications
Field of Search
US
- 123 9015
- 123 9016
- 123 9017
- 074 568 R
- 464 1
- 464 2
- 464 160
-
International Classifications
-
Abstract
A system and method for determining an estimation of actual cam phase angle of increased accuracy are based on an observed cam phase angle derived from a cam phase sensor and a predicted cam phase angle derived from a desired or commanded cam phase angle. The estimated cam phase angle is used in the electronic control unit in computing desired settings for engine variables which depend on cam phase angle.
Description
BACKGROUND OF INVENTION
The present invention relates generally to an improved method for estimating the camshaft phase angle in an engine with variable cam timing.
The advent of variable cam timing in internal combustion engines has complicated the engine management task. Within the engine control unit, the electronic throttle valve position (alternatively, an idle bypass valve opening if not equipped with an electronically actuated throttle valve), fuel injection pulse width, spark timing, position of the exhaust gas recirculation valve, and the cam phase angle are engine variables commanded by the engine control unit to provide the power demanded by the operator of the vehicle while also delivering high fuel efficiency, low emissions, and acceptable drivability. These engine variables are strongly coupled and have a delay time constant associated with them. Thus, the task of changing among operating conditions in a smooth manner is enabled by the engine control unit containing models of the interdependencies among the variables, dynamic models of the various actuators, accurate information from sensors about the status of the various actuators.
The inventors of the present invention have recognized that the accuracy of prior art methods for predicting the actual cam phase angle can be improved. As a result, the coupled parameters, i.e., spark timing, throttle position, etc. listed above, may be computed inaccurately due to being based on inaccurate input cam phase angle data. One prior method relies on the output of a sensor on the cam phaser. Because the signal from the sensor is noisy, the signal is filtered, thereby reducing the bandwidth of the signal and thus, causing a delay. Another prior method relies on a model within the engine control unit and bases the prediction on the commanded phase angle and the dynamic characteristics of the cam phaser. The cam phaser may fail or may change dynamic characteristics over its lifetime causing the prediction to be in error.
SUMMARY OF INVENTION
The drawbacks of prior art approaches are overcome by a method for determining an estimated camshaft phase angle of increased accuracy by determining a desired camshaft phase angle, determining an observed raw camshaft phase angle, and basing the estimated camshaft phase angle on the desired camshaft phase angle and the observed raw camshaft phase angle. The raw observed camshaft phase angle may be based on the output of a camshaft phase angle sensor located proximately to the camshaft.
A primary advantage of the invention disclosed herein is a prediction of cam angle of increased accuracy and with a lesser delay than prior art methods.
A further advantage of the present invention is that it provides an accurate prediction of cam phase angle even as the cam phaser performance changes due to wear, failure, ambient conditions, or other anomaly.
A further advantage of the present invention is that the prediction of the disclosed method provides a less noisy signal than prior art methods.
The above advantages and other advantages, objects, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
The advantages described herein will be more fully understood by reading an example of an embodiment in which the invention is used to advantage, referred to herein as the Detailed Description, with reference to the drawings wherein:
FIG. 1
is a schematic drawing of an engine indicating salient features for practicing invention;
FIG. 2
is a schematic drawing of a single cylinder of an engine showing the camshaft phasing mechanism;
FIG. 3
is a flowchart of the steps involved according to an aspect of the present invention;
FIG. 4
is schematic drawing of the calculation steps in the engine control unit according to an aspect of the present invention;
FIG. 5
is a plot of desired camshaft phase angle, raw observed camshaft phase angle, and estimated camshaft phase angle as functions of time for a disabled camshaft phaser;
FIG. 6
is a plot of desired camshaft phase angle, raw observed camshaft phase angle, estimated camshaft phase angle, and filtered observed camshaft phase angle as functions of time for an operating camshaft phaser; and
FIG. 7
displays a portion of
FIG. 6
enlarged.
DETAILED DESCRIPTION
An internal combustion engine
70
is shown in FIG.
1
. Engine
70
shown is a spark-ignition engine with spark plugs
74
installed into engine
70
. The invention may also apply to a compression-ignition engine which does not rely on spark plugs for ignition. Engine
70
is supplied fuel directly into the combustion chamber through injectors
72
, as would be the case in a direct injection gasoline or diesel engine. Fuel injectors
72
could be situated, alternatively, near the intake ports to the combustion chamber. Engine
70
is provided with a cam phaser
34
, which can alter the time at which the valves open and close relative to engine crankshaft rotation. A more detailed description is provided below with reference to FIG.
2
. Engine
70
is supplied fresh air through an inlet duct containing a throttle valve
78
. The engine discharges gases into an exhaust duct
88
. A portion of the exhaust gas stream may be routed back to the intake duct through exhaust gas recirculation (EGR) valve
90
.
Continuing with
FIG. 1
, engine control unit (ECU)
18
has a microprocessor
50
, called a central processing unit (CPU), in communication with memory management unit (MMU)
60
. MMU
60
controls the movement of data among the various computer readable storage media and communicates data to and from CPU
50
. The computer readable storage media preferably include volatile and nonvolatile storage in read-only memory (ROM)
58
, random-access memory (RAM)
56
, and keep-alive memory (KAM)
54
, for example. KAM
54
may be used to store various operating variables while CPU
50
is powered down. The computer-readable storage media may be implemented using any of a number of known memory devices such as PROMs (programmable read-only memory), EPROMs (electrically PROM), EEPROMs (electrically erasable PROM), flash memory, or any other electric, magnetic, optical, or combination memory capable of storing data, some of which represent executable instructions, used by CPU
50
in controlling the engine or vehicle into which the engine is mounted. The computer-readable storage media may also include floppy disks, CD-ROMs, hard disks, and the like. CPU
50
communicates with various sensors and actuators via an input/output (I/O) interface
52
. Examples of items that are actuated under control of CPU
50
through I/O interface
52
, are fuel injection timing, fuel injection rate, fuel injection duration, EGR valve
90
position, throttle valve
78
position, and cam phaser
34
position. Sensors communicating input through I/O interface
52
may be indicating engine speed, vehicle speed, coolant temperature, manifold pressure, pedal position, camshaft phase sensor
36
, throttle valve
78
position, EGR valve
90
position, air temperature, exhaust temperature, mass air flow
82
, and others; some of which are shown explicitly in FIG.
1
and others are shown as other sensors
38
. Some ECU
18
architectures do not contain MMU
60
. If no MMU
60
is employed, CPU
50
manages data and connects directly to ROM
58
, RAM
56
, and KAM
54
. Of course, the present invention could utilize more than one CPU
50
to provide engine/vehicle control and ECU
18
may contain multiple ROM
58
, RAM
56
, and KAM
54
coupled to MMU
60
or CPU
50
depending upon the particular application.
An electronically-controlled throttle, such as throttle valve
78
shown in
FIG. 1
, provides an example of a system delay. When ECU
18
receives a signal from a pedal position sensor indicating a driver demand for additional power, ECU
18
commands throttle valve
78
to open. The additional power to the driving wheels is delayed by: ECU
18
in interpreting the signal (due to filtering) from the pedal position as a demand for power, computational delays in ECU
18
due to computational traffic, the limitations imposed by the time step at which computations are performed within ECU
18
, mechanical delay in throttle valve
78
attaining the commanded position, and inertial delay in filling the intake manifold to the new, higher manifold pressure. It is known to those skilled in the art to model the air delivered to the engine accounting for system delays. The model relies on accurate information of many system variables, including valve timing, which is related to camshaft phasing. The ability of the model to provide the desired functionality depends on the accuracy of the models in capturing the phenomena and their interactions. The subject of the present invention is increasing the accuracy of cam phase angle data within the ECU
18
.
FIG. 2
shows a single piston
68
disposed in engine
70
. Camshaft
84
of engine
70
is shown in
FIG. 2
communicating with rocker arm
86
which is fixed at end
88
for actuating intake valve
64
. Exhaust valve
66
may be similarly equipped as intake valve
64
(cam phasing hardware not shown). Alternatively, camshaft
84
may be used to actuate both intake valve
64
and exhaust valve
66
, in which case a phase change in camshaft
84
affects both intake valve
64
and exhaust valve
66
timings. Camshaft
84
is directly coupled to cam phaser
34
. Cam phaser
34
forms a toothed wheel having a plurality of teeth
92
. Camshaft
84
is hydraulically coupled to an inner camshaft (not shown), which is in turn directly linked to camshaft
84
via a timing chain (not shown). Therefore, cam phaser
34
and camshaft
84
rotate at a speed substantially equivalent to the inner camshaft. The inner camshaft rotates at a constant speed ratio to crankshaft
100
. However, by manipulation of a hydraulic coupling (not shown), the relative phase of camshaft
84
to crankshaft
100
can be varied by applying a hydraulic pressure in advance chamber
96
or retard chamber
98
. By allowing high pressure hydraulic fluid to enter advance chamber
96
, intake valve
64
opens and closes at a time earlier relative to crankshaft
100
. Similarly, by allowing high pressure hydraulic fluid to enter retard chamber
98
, intake valve
64
opens and closes at a time later relative to crankshaft
100
.
Teeth
92
, being coupled to cam phaser
34
and camshaft
84
, allow for measurement of cam phase angle via cam timing sensor
92
providing a signal to ECU
18
. Four equally spaced teeth on cam phaser
34
are preferably used for measurement of cam timing for a bank of four cylinders, eg., an inline four cylinder engine or one bank of a V-8 engine. ECU
18
sends control signals to conventional solenoid valves (not shown) to control the flow of hydraulic fluid either into advance chamber
96
, retard chamber
98
, or neither.
Camshaft phase angle may be measured using the method described in U.S. Pat. No. 5,548,995, which is incorporated herein by reference. In general terms, the rotation angle between the rising edge of a signal from sensor
102
which senses a tooth (not shown) coupled to crankshaft
100
and a signal detected by camshaft phase sensor
36
from one of the plurality of teeth
92
on cam phaser
34
provides a measure of the relative cam timing. For the particular example of an inline four cylinder engine, with a four-toothed wheel on cam phaser
36
, a measure of cam timing for each bank is received four times per revolution.
Referring now to
FIG. 3
, ECU
18
schedules cam phaser
34
, in block
10
, according to models within ECU
18
, one example of which is described in U.S. Pat. No. 6,006,725, which is incorporated herein by reference. This provides the desired phase of the camshaft, which is denoted as cam_ph_d herein. Within ECU
18
is a dynamic model
16
of cam phaser
34
. The dynamic model
16
may incorporate system inertias, compliances, compressibilities, actuator delays, material characteristics, and other factors to describe the behavior of camshaft
84
in response to a command to cam phaser
34
to make an angle change. Based on dynamic model
16
, a predicted cam phase can be computed, denoted as cam_ph_pred. In block
42
, cam_ph_pred and cam_ph_obs_corr are summed to yield cam_ph_est, which is the estimated cam phase angle with increased accuracy compared to prior art methods. The observer leg of the computation begins with a measurement of the cam phase angle, cam_ph_obs_raw, which is computed in block
29
based on signals from the camshaft phase sensor
34
and the crankshaft phase sensor
102
. In block
30
, the raw signal (cam_ph_obs_raw) is compared with cam_ph_est. An error signal, cam_ph_obs_err is the output of block
30
. In block
32
, cam_ph_obs_err is integrated, which filters the signal and provides a corrected signal, called cam_ph_obs_corr herein. As discussed above, cam_ph_obs_corr is used in block
42
as one of the inputs to provide the output, cam_ph_est.
FIG. 3
is a simplified version of the invention to clearly indicate that two inputs are used to arrive at cam_ph_est.
FIG. 4
shows the method in more detail and in context within ECU
18
. ECU
18
receives input from sensors
38
and camshaft sensor
36
and crankshaft sensor
102
; from the latter two sensors, ECU
18
computes cam_ph_obs_raw in block
29
. ECU
18
computes cam_ph_d, the desired cam phase, based on a model such as taught in U.S. Pat. No. 6,006,725. Cam_ph_d and cam_ph_obs_raw are compared in operation
22
, which provides the value of cam_ph_err, that is the difference between the commanded signal and the measured signal. Cam_ph_err is used as feedback control to camshaft phaser
34
, as in prior art. Cam_ph_d, block
12
, is used in dynamic model
16
to determine cam_ph_pred. Cam_ph_pred is summed in block
42
with the output of blocks
30
and
32
, previously described in conjunction with FIG.
3
. The output of summing operation
42
yields cam_ph_est, the subject of the present invention. Cam ph_est is used within ECU
18
in relevant actuator models. These may be models which compute desired throttle valve
78
position, desired EGR valve
90
position, spark timing, fuel injection timing, and fuel injection pulse width, as examples. Output of the actuator models
60
is fed to actuators
62
.
The present invention is demonstrated in
FIGS. 5-7
, in which experimental data are used to illustrate the present invention and compare it with prior art solutions. In
FIG. 5
, an inoperable camshaft phaser
34
is commanded a camshaft position, i.e., the desired camshaft phase angle, cam_ph_d, shown as curve
110
. Because the camshaft phaser
34
is inoperable, the camshaft does not respond. Curve
112
is the cam_ph_obs_raw, i.e., the measured cam phase angle. Curve
112
does not deviate from the initial value since the camshaft phase does not change. Curve
112
, however, does indicate a typical noise level on the signal. If cam_ph_obs_raw were used as the basis to compute other engine parameters, such as throttle position, these parameters would constantly vary. Eg., throttle plate
78
would flutter in response to the noise appearing on curve
112
. The estimate of cam phase, as provided by the present invention cam_ph_est, shown in curve
114
, is based on both cam_ph_obs_raw and cam_ph_d. As such, it does deviate from a steady value in response to the command to camshaft phaser
34
. However, it readily returns to the steady value. Also, curve
114
is not a noisy signal.
In
FIG. 6
, a working camshaft phaser
34
is commanded to assume a new desired phase angle, cam_ph_d which is shown as curve
120
. Curve
122
shows the output of the measurement, cam_ph_obs_raw. Again, there is noise on the measured signal, curve
122
. Curve
124
shows the estimated camshaft phase angle, according to the present invention. Curve
126
shows a filtered version of curve
122
. As mentioned above, a problem with cam_ph_obs_raw is that due to its noise, control of other engine parameters is degraded. A common technique to remove noise from a signal is to filter the signal with the undesired consequence that the signal is time delayed. Curve
126
is a filtered version of curve
122
. It can be seen in
FIG. 6
that curve
124
, the subject of the present invention lags behind the unfiltered measured signal, curve
122
, but precedes the filtered measured signal, curve
126
.
FIG. 7
is an enlarged version of a portion of FIG.
6
. The noise of curve
122
is even more evident in FIG.
7
. The stepwise nature of curve
124
, cam_ph_est, is due to the computation time step, which is 100 msec. Similarly, the filtered version of the measured signal, curve
126
, changes on a 100 ms time scale; thus similar to curve
122
, curve
126
displays a stepwise character. Curve
126
lags curve
122
by about one computation step, or 100 msec. Thus, the present invention provides a clear advantage over filtering a measured signal.
While a preferred mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize alternative designs and embodiments for practicing the invention. The above-described embodiment is intended to be illustrative of the invention, which may be modified within the scope of the following claims.
Claims
- 1. A computer readable storage medium having stored data representing instructions executable by a computer to control an internal combustion engine and a camshaft phaser coupled to a camshaft of the engine, comprising:instructions to determine a predicted camshaft phase angle based on the desired camshaft phase angle and a model of dynamic characteristics of the camshaft phaser; and instructions to compute an estimated camshaft phase angle based on an observed raw camshaft phase angle and said predicted camshaft phase angle.
- 2. The computer readable storage medium according to claim 1 wherein said observed raw camshaft phase angle is based on a signal from a camshaft phase angle sensor proximate to the camshaft phaser.
- 3. The computer readable storage medium according to claim 1 further comprising:instructions to compute a desired position of a throttle valve disposed in an intake duct of the engine, said desired position being based on said estimated camshaft phase angle; and instructions to actuate said throttle valve to attain said desired position.
- 4. The computer readable storage medium according to claim 1 further comprising:instructions to compute a desired state of an engine actuator coupled to the engine, said desired state being based on said estimated camshaft phase angle; and instructions to actuate said engine actuator to attain said desired state.
- 5. The computer readable storage medium according to claim 4 wherein said engine actuator may comprise a second camshaft phaser, a fuel injector, an exhaust gas recirculation valve, a throttle valve, or a spark plug.
- 6. The computer readable storage medium according to claim 1 wherein said medium comprises a computer chip.
- 7. A method for determining an estimated camshaft phase angle relative to a default phase angle, the method comprising the steps of:determining a desired camshaft phase angle; determining an observed raw camshaft phase angle; determining the estimated camshaft phase angle based on said desired camshaft phase angle and said observed raw camshaft phase angle; and determining a predicted camshaft phase angle based on said desired camshaft phase angle and a model of dynamic characteristics of a camshaft phaser coupled to the camshaft, wherein said camshaft phaser causes the phase angle shift of the camshaft.
- 8. The method according to claim 7 comprising the further step of determining an observed camshaft phase angle error based on a difference of said observed raw camshaft phase angle and the estimated camshaft phase angle.
- 9. The method according to claim 8 comprising the further step of determining a corrected observed camshaft phase angle based on the integration of said observed camshaft phase angle error.
- 10. The method according to claim 7 wherein said observed raw camshaft phase angle is based on a signal from a camshaft phase angle sensor proximate to said camshaft.
- 11. The method of claim 7, further comprising the step of: determining the estimated camshaft phase angle based on the sum of said predicted camshaft phase angle and said corrected observed camshaft phase angle.
- 12. The method of claim 7, wherein the camshaft is coupled to an internal combustion engine.
- 13. The method according to claim 12 wherein a desired value of an engine parameter of said engine is based on said estimated camshaft phase angle.
- 14. The method according to claim 13 wherein said engine parameter may comprise a throttle valve position, an exhaust gas recirculation valve position, an idie air bypass valve position, a spark timing, a fuel pulse width, or a fuel injection timing.
- 15. A system for determining an estimated camshaft phase angle, comprising:a camshaft; a camshaft phaser coupled to said camshaft to shift phase angle of said camshaft relative to a default phase angle; a camshaft phase angle sensor proximate to said camshaft which yields a signal based on said phase angle shift; and an electronic control unit operably connected to said camshaft phaser and said camshaft phase angle sensor, said electronic control unit actuates said camshaft phaser to achieve a desired camshaft phase angle and determines an estimated camshaft phase angle based on said desired camshaft phase angle and said camshaft phase angle sensor signal wherein said estimated camshaft phase angle is based on a sum of a predicted camshaft phase angle and a corrected observed camshaft phase angle.
- 16. The system according to claim 15 wherein said predicted camshaft phase angle is based on said desired camshaft phase angle and a model of dynamic characteristics of said camshaft, said model being disposed in said electronic control unit.
- 17. The system according to claim 16 wherein said corrected observed camshaft phase angle is based on integrating an observed camshaft phase angle error.
- 18. The system accozding to claim 17 wherein said camshaft phase angle error is based on a difference of said observed raw camshaft phase angle and the estimated camshaft phase angle.
US Referenced Citations (17)